A Review of Non-Cardiac Complications of General Anesthesia: The Current State of Knowledge

Introduction

Despite the development of minimally invasive surgery techniques and regional anesthesia, many surgical procedures still require general anesthesia (GA). An example is laparoscopic surgery, which is the most common surgical technique [1]. Due to the continuous development of medical science, including anesthesiology, the use of GA, which has an increasingly lower risk and mortality, has decreased significantly over the past 5 decades [2]. Nonetheless, it is impossible to completely eliminate the complications of this type of anesthesia. Complicatios range from mild postoperative discomfort such as a sore throat or hoarseness to intraoperative, potentially fatal emergencies or severe illnesses that develop long after the procedure. The most common perioperative complications are cardiovascular and respiratory disorders [2]. However, due to the wide range of cardiovascular and hemodynamic complications, an exhaustive description of them would go beyond the scope of this article, making it too elaborate. Therefore, we decided to include respiratory complications in this review, covering intraoperative emergencies, pathological conditions that develop postoperatively, and situations induced by complications in instrumental airway management. In addition, we have included the most specific and relevant complications of GA, which are separate disease entities and are well documented in the literature, the non-inclusion of which would make this review incomplete. Although complications of GA are well described in the literature, this review comprehensively summarizes non-cardiovascular and hemodynamic complications, taking into account their etiology as well as their diagnosis and interventions, so that it becomes a valuable introduction to further development for anesthesiology personnel. Our intention was not to subsume the characteristic complications for a particular GA technique and type of surgery, but to describe selected complications in the non-pediatric population in a cross-sectional manner, so that the clinicians can effectively identify the described pathological states and select the appropriate type of management. It takes into account the impact of medications, procedures, and intraoperative management of patients regarding anesthesiology, while taking into account the specifics of selected surgical procedures and patient-related conditions, in case of significant impact on the type a particular complication. An undoubted advantage of this article is the inclusion of new directions of monitoring, diagnosis, prevention, and treatment, taking into account the latest analyses and studies, including those in the preclinical stage, which can unquestionably contribute to safer anesthesia. It represents a systematization of the described theoretical knowledge combined with new reports, so it can prove to be a valuable resource for both beginning and experienced clinicians. The condition for inclusion in the review was the subject of the article focusing on the topic of a particular complication or a description of research on the latest findings in methods of prevention, diagnosis, or intraoperative monitoring of the included complication. For the development of the review, the most recent articles available on the Internet were used, which are both research papers, review papers, and case reports published between 2006 and 2024.

Complications from the Respiratory System

Respiratory complications constitute a broad group of complications of general anesthesia, to which much of this article is devoted. They include emergencies occurring intraoperatively, and conditions developing over a long period of time after surgery, having their origin in improper perioperative management. Their causes can be traced to any stage of anesthesia, from improper patient qualification for surgery, incorrect selection of the type of anesthesia, inappropriate selection or dosage of drugs used in induction, complications during airway management, ventilation mode settings and equipment failures, to improperly managed awakening and neglected postoperative care [3,4].

Bronchospasm

The incidence of perioperative bronchospasm in patients undergoing general anesthesia is estimated at 0.2–3% [5,6] and account for as much as 7% of deaths in patients undergoing anesthesia (in France) [5]. It can be induced at any stage of anesthesia, but most often occurs during the induction period, which is mainly related to irritation of the airway by the intubation procedure, suctioning, and aspiration into the airway of gastric contents, blood, sputum, and other foreign bodies. The pharmacological mechanism is also important, through drugs that stimulate the ejection of histmin stimulating bronchoconstriction, to which we can include atracurium, mivacurium, morphine, or meperidine [5–7]. Exposed to bronchospasm, especially induced by the above factors, are patients with hyper-responsive airways, which include a large number of asthmatic patients, with 9% of asthmatics undergoing general anesthesia developing perioperative bronchospasm appearing as an exacerbation. According to the recommendations of The National Asthma Education and Prevention Program Expert Panel Report, 3 proper asthma management conditioning adequate asthma control and preoperative examination are crucial in this population to ensure safety during anesthesia. In addition, patients at risk include smokers, those with gastroesophageal reflux disease (GERD), other pulmonary and respiratory diseases, allergies or atopy, a history of respiratory complications after anesthesia, and those undergoing surgery in the chest or upper abdomen [5]. An important point to note is that bronchospasm can occur on the basis of an IgE-mediated (immunoglobulin E) anaphylactic reaction and be a component of its spectrum of symptoms, as described in more detail later in this article. More often in that case, it is accompanied by hemodynamic (hypotension and tachycardia) or skin symptoms and its occurrence under anesthesia is mainly associated with the perioperative drugs used [5–7]. Differentiating isolated bronchospasm from that on the ground of anaphylaxis is necessary for resuming appropriate rescue interventions and further management of the patient. In situations where it is difficult to do so on the basis of the clinical picture alone, additional tests for anaphylaxis, including serum tryptase and possible further tests like specific IgE levels and skin tests with suspected triggers, may be helpful, especially in further diagnostic and treatment proceedings [5,7]. Bronchospasm is manifested by wheezing (mainly expiratory) with prolonged expiratory phase, and drops in saturation, often sudden, leading in many cases to respiratory failure. Hemodynamic symptoms are accompanied less frequently and occur mostly after the onset of wheezing compared to anaphylactic reaction [5–7]. Auscultation is manifested by diffuse wheezes over the lung fields of varying severity up to and including the absence of auscultatory artifacts, depending on the degree of bronchial tree obstruction. Capnogram diagrams show a characteristic shape with an elongated expiratory peak resembling “shark fins”. In addition, a decrease in minute ventilation (MV) and tidal volume (TV) can be observed with an increase in mean airway pressure (Pmean), which indicates a decrease in lung compliance. This causes difficulties in mechanical ventilation, especially during bag ventilation [5,7]. Before appropriate emergency measures are taken, other possibilities causing the above clinical picture must first be ruled out. The differential diagnosis should consider a kinked or obstructed endotracheal tube, insertion into the bronchus or esophagus, laryngospasm, and aspiration of secretions or foreign bodies into the airway. In addition, too shallow anesthesia should be ruled out first. Inhaled anesthetics such as sevoflurane and isoflurane as well as propofol are effective in both preventing and relieving bronchospasm. In contrast, desflurane irritates the airways and can promote bronchospasm. Conditions not amenable to bronchodilator treatment should be considered in the context of pneumothorax or pulmonary edema [5–7]. In the case of isolated bronchospasm, the first emergency measures, after ruling out anesthesia that is too shallow and other causes that mimic bronchospasm, should be to start ventilating with 100% oxygen. Initially, it is recommended to conduct it with a bag, which can allow preliminary differentiation of the causes of increased airway resistance. Avoid causing increased intrathoracic pressure, as this reduces venous return and further CO (cardiac output). The first-choice drug to abolish obstruction is short-acting, selective β2-agonists administered by inhalation (mainly salbutamol). If ineffective, other airway muscle relaxants should be added, such as inhaled, fast-acting anticholinergics (such as ipratropium), followed by magnesium sulfate (inhaled or intravenous). Ketamine infusion may be considered, as it has bronchodilator properties due to stimulation of catecholamine release, and has been described mainly in patients with asthmatic conditions. The addition of systemic steroids (eg, methylprednisolone, hydrocortisone) is recommended, especially in cases of inflammatory obstruction, due to the abolition of inflammatory edema. Epinephrine should be administered immediately in cases of established anaphylaxis and should be considered if cardiovascular collapse not caused by anaphylaxis develops. An anaphylactic reaction, in addition to the inclusion of epinephrine, requires specific treatment, as described in more detail elsewhere [5–7]. Extubation under deep anesthesia should also be considered to prevent reflex bronchoconstriction [6,7]. In addition, postoperative allergologic and immunologic diagnostics are indicated to diagnose the potential cause and provide safer anesthetia care in the future [5,7].

Laryngospasm

Analogous factors to bronchospasm due to shallow anesthesia, desflurane, airway irritation, history of asthma, respiratory tract infections, and smoking are predisposing factors for laryngeal spasm. In addition, patients are at risk who are obese, have airway anomalies, and undergo surgery in the oral region, airway, and during which the superior laryngeal nerve or hypoxesophageal nerve is stimulated. The pediatric population is particularly vulnerable. Besides hypoxemia and hypercarbia, laryngospasm can induce further bronchospasm and hemodynamic instability. The mainstay of treatment, with airway patency assured, is to remove any triggers and clear the pharynx, ventilate with 100% oxygen, and deepen anesthesia. After extubation, it sometimes becomes necessary to manage the airway intermittently by needle cricothyrotomy [8].

Postoperative Pulmonary Complications (PPC)

As a preliminary comment, it is important to explain why postoperative pulmonary complications (PPC), which are not intraoperative emergencies, are above the paragraph focused on hypoxemia, which belongs to such conditions. The reason is the common denominator of hypoxemia and PPC, the phenomenon of atelectasis, which is the cause of both intraoperative blood gas abnormalities and one of the more important causes of subsequent pathological conditions (and a separate complication at the same time) of the respiratory system developing after surgical procedures. This paragraph covers the pathophysiology of atelectasis and protective ventilation strategies in the context of preventing further conditions. In contrast, the section on hypoxemia focuses on the problem of intraoperative atelectasis as a cause of blood gas imbalances. Thus, the phenomenon of atelectasis should be treated holistically. Intraoperatively, it leads to dangerous hypoxemia, which if it persists after the end of anesthesia is one of the trigger points of many diseases of the respiratory system [3,4].

Postoperative pulmonary complications (PPC), which are a collection of diseases to which patients undergoing general anesthesia are more vulnerable, can include almost any complication from the respiratory spectrum, resulting in a non-uniform definition. The most important incidents belonging to PPC (according to European Perioperative Clinical Outcomes – EPCO) seem to include respiratory infection, pneumonia, including that caused by aspiration, atelectasis, pleural effusion, pneumothorax, bronchospasm, acute respiratory distress syndrome (ARDS), tracheobronchitis, pulmonary embolism, exacerbation of the primary disease, or respiratory failure, which is considered the most common of those listed. For major surgeries, the incidence of PPC can reach as high as 23%, and the 30-day mortality rate ranges from 14% to 30%. In view of the multitude of symptoms comprising PPC, the pathophysiology of this group of complications is immediately complex and, for the purposes of this review, requires simplification and presentation of major processes only. Due to altered thoracic mechanics and geometry caused by, among other things, specific positioning, the nature of the operation or drugs used in the induction of GA, the functional residual capacity (FRC) is reduced in favor of the formation of the atelectatic areas. The development of atelectasis is also largely favored by the use of neuromuscular conduction blocking agents (NMBAs), as well as the perioperative use of 100% oxygen. Disturbed lung ventilation combined with a decrease in CO results in disturbed ventilation/perfusion ratio (V̇/Q̇) having a reflection in the form of hypercapnia and hypoxemia; anesthetic drugs further impair the body’s compensatory responses to the above blood gas imbalance. Moreover, the residual block associated with NMBA use impairs postoperative respiratory function by impairing physiological defense reflexes and increasing the risk of aspiration [3]. The POPULAR multicenter observational study [9] confirmed that the use of NMBA during general anesthesia is associated with an increased incidence of PPC. Of the 21 694 patients who received the muscle relaxant during anesthesia, as many as 7.6% developed a condition belonging to the spectrum of pulmonary complications within 28 days after the surgery. Interestingly, the results were not improved by the use of reversal agents in the form of neostigmine and sugammadex and or by extubation at a TOF of at least 0.9. However, the exact effect of individual blockade reversal drugs on the incidence of PCC needs further research [9]. In addition, monitoring of the degree of relaxation is recommended [3]. There are many more causes of pulmonary complications, and further sections of the article expand on these issues, such as some adverse events of instrumented airway management. It is important that factors promoting the development of PPC are taken into account when qualifying patients for surgery and selecting the appropriate type of anesthesia. The most significant modifiable ones, in addition to the aforementioned GA and the use of NMBA (especially long-acting) during it, include smoking, inappropriate mechanical ventilation strategy, or existing comorbidities, especially cardiorespiratory diseases such as COPD (chronic obstructive pulmonary disease), asthma, CHF (congestive heart failure), OSA (obstructive sleep apnea), and preoperative parameters like hypoxemia (SpO2 <96%), anemia (Hb <100 g/dl), and other laboratory abnormalities. It is essential that appropriate interventions be implemented early in the preoperative preparation to compensate for the severity of existing conditions or smoking cessation. The most significant non-modifiable risk factors include advanced age and frailty syndrome, ASA (American Society of Anesthesiologists) status ≥II, urgency, duration and type of surgery; thoracic, neurosurgical, vascular or surgeries involving the head, neck and upper abdominal region are particularly high risk [3].

To achieve the lowest possible rate of pulmonary complications after anesthesia, it is crucial to properly manage anesthesia, which mainly consists of choosing the appropriate mechanical ventilation technique as well as the anesthesia procedure itself.

Mechanical Ventilation Strategy

An essential issue in preventing the development of complications belonging to the PPC spectrum is the use of an appropriate intraoperative mechanical ventilation strategy. It has been proven that the use of the protective ventilation technique, which belongs to the algorithms for the management of patients with ARDS, reduces the incidence of complications. Among the main tenets are the use of low tidal volumes (VT), the use of appropriate recruitment maneuvers (RM) and adequate selection of PEEP (positive end-expiratory pressure). The appropriate TV in both obese and non-obese patients is 6–8 ml/kg of predicted body weight (PBW), as high values have been shown to promote the development of inflammation and acute lung injury. On the other hand, the selection of appropriate PEEP values is a further issue of research and should be selected individually. Undoubtedly, the use of PEEP prevents the development of atelectasis and alveolar damage, improving blood oxygenation, while the harmful effects of its high values (>10 cmH2O) such as impaired hemodynamic performance are proven. In the strategy of protective ventilation to reverse atelectasis, the use of appropriate RM is also important, but due to the multiplicity of techniques for its performance, their description is beyond the extent of this article [3]. However, the essence of this procedure is short-term increase in airway pressure using a ventilator, resulting in high trans-lung pressure to aerate collapsed regions of the lungs [4]. In summary, non-obese patients with normal lungs and unaffected baseline blood gas parameters should receive low VT (6–8 ml/kg of PBW), an FIO2 (Fraction of Inspired Oxygen) of 0.4 [3], andPEEP of 2–5 cmH2O [4].

Adequate Selection of General Anesthesia Technique

In addition to proper ventilation of the patient, choosing the optimal GA technique may result in fewer pulmonary complications. Analyzing groups of patients with tumors of the head and neck region undergoing microvascular reconstruction [10] or free flap surgery [11] anesthetized using the total intravenous anesthesia technique (TIVA) with propofol had a lower incidence of PPC than patients undergoing inhalational anesthesia (sevoflurane or desflurane). TIVA anesthesia results in greater hemodynamic stability than inhalational anesthesia, requiring less intraoperative fluid administration. Hypervolemia leads to loss of capillary endothelial integrity and fluid escape and, in the case of the pulmonary capillary bed, these processes induce inflammation, leading to the development of further pulmonary pathologies. In addition, the properties of propofol that maintain endothelial integrity and suppress systemic inflammatory reactions that are induced by surgical interference are important. On the other hand, the type of surgical procedure should be taken into account, as the superiority, equivalence, and inferiority of inhaled anesthetics over intravenous anesthetics in cardiothoracic surgery have been demonstrated in the context of further development of pulmonary complications [4]. In selected cases, the addition of epidural anesthesia to GA is worth considering, by improving anesthesia and possibly reducing the opioid burden, which can also induce postoperative respiratory disorders, mainly due to causing respiratory depression and inhibiting the cough reflex [3,4]. The addition of regional anelgesia can reduce the incidence of pneumonia and the need for re-intubation and mechanical ventilation [3].

Intraoperative Hypoxaemia

In considering intraoperative blood gas abnormalities, we should consider hypoxemia above all, as this is a condition that can rapidly lead to irreversible complications. Hypoxemia is a symptom secondary to numerous pathologies or complications of anesthesia, and is defined as a decrease in arterial blood oxygen saturation below 90%. However, it does not always correlate with hypoxia, defined as insufficient oxygen delivery to tissues [12]. Hypoxemia is a common problem in patients undergoing general anesthesia, with drops in peripheral saturation below 90% estimated to occur in 6.8% of those under general anesthesia, and decreases below 85% lasting at least 2 minutes in 3.5%. Most cases of intraoperative hypoxemia occur at the beginning of surgery, as this is when airway manipulations are performed [13]. Specific events are airway management complications described in the following paragraph, such as prolonged intubation [3,14,15], aspiration of digestive contents [16], unrecognized misplacement of the endotracheal tube [17,18] or irritation-induced airway spasm [5–8]. If sudden hypoxemia occurs, the other conditions belonging to the acronym DOPES described elsewhere [19,20,21] (Table 1), as well as further complications described in this article, should also be excluded. It is important to consider that other conditions, primarily unrelated to the respiratory system, may also be the source of the drop in saturation. A comprehensive group are hemodynamic complications leading to a decrease in cardiac output and hemodynamic failure, resulting in impaired pulmonary perfusion and subsequent disruption of the ventilation/perfusion ratio (V̇/Q) [3,4]. Among the factors conducive to the occurrence of intraoperative hypoxemia we can include the age of the patient, as older people have lower arterial blood oxygen saturation. In addition, a high ASA status, smoking, COPD, or asthma indicate a worse condition of the patient and can affect respiratory capacity, increasing the risk of hypoxemia. High body mass index (BMI) correlates with a higher risk of severe or prolonged hypoxemia lasting more than 5 minutes, due to reduced lung and chest wall compliance, increased airway resistance, and reduced residual capacity, among other factors. The type or length of surgery is important, as the longer the procedure, the greater the risk of hypoxemia. Procedures such as bronchoscopy, video-assisted thoracoscopic surgery, and thoracotomy are more likely to lead to hypoxemia due to direct manipulation in the vicinity of the respiratory system [22]. Also, laparoscopic, thoracic surgeries, especially requiring ventilation of 1 lung, and Trendelenburg position procedures can cause hypoxemia due to alveolar collapse and restriction of diaphragm mobility, favoring areas of atelectasis, which obese patients are particularly predisposed to develop. This complication requires more extensive commentary, to which a separate paragraph has been devoted [4,22]. An essential tool to ensure intraoperative safety is continuous monitoring of blood saturation with a pulseoximetry and using the SpO2/FiO2 (Oxygen Saturation to Fraction of Inspired Oxygen) ratio might help in early diagnosis of impaired blood oxygenation [4]. It is also important to continuously monitor hemodynamic parameters for pulmonary perfusion abnormalities [4] and selected ventilation parameters to assess the risk of hypoxemia or observe developing pathologies [7,23]. However, these commonly used methods are imperfect, as they inform us of already developed complications or help estimate the risk, but with significant inaccuracy. Treatment of intraoperative hypoxemia consists primarily of correcting the underlying disorder that subsequently caused the desaturation, so intraoperative monitoring of respiratory and hemodynamic parameters is important. The use of higher values of inspired oxygen is rational before intubation, in situations of decreased saturation, and before extubation. Maintaining hyperoxia, especially intraoperatively, should be considered only in reasonable cases, being aware of its adverse effects. In addition to causing athelectasis, as elaborated below [4,24], hyperoxia during ventilation can cause coronary vasoconstriction, but at the same time reduces oxygen consumption by the myocardium. Moreover, experimental studies have shown that the increase in reactive oxygen species production induced by hyperoxia has a degrading effect on cellular structures, which can lead to acute lung damage [24].

Novel Methods in Predicting Intraoperative Hypoxemia

A breakthrough in predicting intraoperative hypoxemia may be the Prescience system based on machine learning, which can predict in real time the risk of significant drops in blood saturation over the next 5 minutes. By analyzing numerous data related to the patient’s static and dynamic parameters, as well as the procedure and specific drugs used, it allows anesthesiologists to predict the risk of hypoxemia 2 times more often before desaturation occurs. Although machine learning models are not yet widely used during surgery and Prescience’s effectiveness would be greater if enriched with other relevant patient-related data, algorithms using the above technique are a promising direction in predicting adverse intraoperative events and enable timely incorporation of adequate corrective actions [23]. Bedside lung ultrasound is increasingly used to detect disorders that can result in both intraoperative hypoxemia and increase the risk of developing postoperative PPC. In the preoperative period, USG allows early detection of acute interstitial pulmonary edema, pleural effusion, lung consolidation, and their causes, such as pneumonia and atelectasis. Lung ultrasound has a sensitivity of more than 90% in detecting the B-line pattern, which is much more sensitive than its traditional counterpart, lung crackle, and is highly likely to suggest the presence of interstitial pulmonary edema. In addition, inhomogeneous B-lines combined with irregular pleural lines, decreased lung sliding, and subpleural consolidations may suggest ARDS and are more conclusive in determining its severity than lung compliance or oxygenation index testing. If the described pathologies are found preoperatively, one should be prepared for the possibility of difficulty in maintaining intraoperative and postoperative adequate blood saturation. On the other hand, lung ultrasound performed intraoperatively allows diagnosis of some of the causes of desaturation by assessing the position of the endotracheal tube, diagnosing pneumothorax, and monitoring the development of atelectasis and its impact on oxygenation [25].

Atelectasis and the Occurrence of Intraoperative Hypoxemia

Intraoperative pulmonary atelectasis requires special clarification, as it is a condition leading to intraoperative disruption of gas exchange, resulting in hypoxemia, as well as causing further development of pathologies collectively defined as PPC. In addition to individual factors and the peculiarities of the surgery, it is necessary to mention the most important risk factors associated with general anesthesia, which are related to the special risk of intraoperative atelectasis. Both intravenous and inhaled anesthetics carry the possibility for intraoperative collapse of part of the pulmonary parenchyma. The use of NMBA, in addition to postoperative residual effects, also attenuates the risk intraoperatively by altering the geometry of the chest wall. It is also important to maintain negative pleural pressure through adequate diaphragmatic tension. Its impaired function, in addition to the muscle relaxation used, may result from too deep anesthesia, or paralysis of the phrenic nerve if additional regional anesthesia is used in the cervical area, especially performed without USG control. As FiO2 level increases, the risk and extent of atelectasis, arising from alveolar oxygen absorption, increases, so normoxic conditions should be maintained during surgery. High oxygen content is recommended only before intubation and extubation, and in combating intraoperative hypoxemia. However, alveolar hyperoxemia causing atelectasis will not be reflected in the intraoperative drop in saturation. Low TV without PEEP is also dangerous. Important in terms of preventing safety-threatening intraoperative desaturation and the subsequent development of complications is the appropriate early recognition of atelectasis during the course of the procedure and the implementation of appropriate interventions. In case of a decrease in saturation or an increase in driving pressure (reflecting a decrease in lung compliance), other causes such as secretion obstruction or airway spasm should be eliminated first and inspiratory oxygen content should be increased. If atelectasis is suspected, higher PEEP values (4–12 cmH2O) preceded by RM are set. In situations of further respiratory dysfunction and high risk of atelectasis, PEEP should be titrated based on standard monitored driving pressure. More advanced and increasingly used techniques such as esophageal pressure monitoring (imaging transpulmonary pressure), electrical impedance tomography (EIT), or USG can also be used. To reduce atelectasis in patients with persistent hypoxemia after cardiothoracic and abdominal surgery, the ESA/ESICM (European Society of Anesthesiology/European Society for Intensive Care) suggest immediate use of NIV (non-invasive ventilation) or CPAP (continuous positive airway pressure) [4]. The most important conditions associated with general anesthesia leading to intraoperative hypoxemia are summarized in Table 2.

Complications Associated with Instrumented Airway Management – Endotracheal Intubation

Instrumental airway management is an indispensable part of completing the induction of any general anesthesia. The most common method of choice is endotracheal intubation [26], which is considered a relatively safe method, but carries a spectrum of complications well documented in the literature [27]. Before anesthesia, the patient should be carefully evaluated for “difficult airway,” paying special attention to comorbidities and airway injuries, since difficult intubation promotes the occurrence of complications, especially in the form of mechanical injuries [26,27]. Intubations of patients undergoing emergency surgery can also be conducive to these [27]. Obese patients are especially prone to difficult intubation, especially as a result of anatomical distinctiveness and comorbidities [27,28], but there is insufficient evidence that obesity promotes higher rates of injury related to the procedure itself [27].

Mechanical Damage and Complications

The rate of mechanical complications associated with orotracheal intubation is 0.5–7% and the most common site of injury is the larynx [27]. A remarkably wide spectrum of symptoms has been documented, especially in the larynx, pharynx, oral cavity, and trachea. Among the most common are transient postoperative hoarseness, dysphonia, sore throat, dysphagia, shortness of breath [26,27] or cough [29,30]. When their occurrence is a reaction of the body to the pain stimulus of chronic tissue irritation with the endotracheal tube, they can be prevented by applying a superficial mucosal anesthesia to the pharynx and larynx. Analysis of patients undergoing general anesthesia lasting less than 120 minutes showed the effectiveness of 2% lignocaine injected into the larynx before endotracheal intubation, especially in preventing postoperative cough and sore throat, which may be a useful routine procedure [29]. Pre- and intraoperative administration of lignocaine by intravenous infusion has a similar effect [30]. Other important causes of these symptoms is damage to the vocal cords, the laryngeal cartilaginous apparatus, or the laryngeal walls during intubation tube insertion or due to prolonged compression of the inflated tube cuff causing prolonged ischemia of the compressed structures or nerve damage, especially to the recurrent laryngeal nerve. Prolonged cuff compression can also cause late complications in the form of laryngotracheal stenosis or formation of tracheal fistulas. However, complications caused by compression, especially late ones, are characteristic of prevalently intubated patients, which is not the case in the operating theater setting, so developing this issue is beyond the context of this review.

Laryngoscopy is also associated with risk of damage to the oral cavity, most often with damage or breakout of teeth, as well as injury to the soft tissues of the labia, soft palate, buccal area, bottom of the mouth, and tongue [27]. Extremely rare, although the most traumatic complications of intubation, are perforations of the upper and lower airways [27,31], most often involving the trachea (less than 0.37% of the general population) [31]. They can lead to inflammation [27] and mediastinal emphysema, pneumothorax, or subcutaneous emphysema, even reaching the extremities [31,32].

When nasotracheal intubation is required, the most frequent complication, occurring in as many as 29–96% of cases, is bleeding of varying severity due to damage to the structures of the nasal cavity [27].

Video laryngoscopy also carries some risk of mechanical injury, but in contrast to traditional laryngoscopy, it most often involves the soft palate, caused by the endotracheal tube, which is initially inserted “blindly” before being visualized on the monitor [27].

Non-Injury Complications

In additional to mechanical complications, unintentional misplacement of the endotracheal tube can also occur. This complication is most common in urgent cases where emergency induction of anesthesia and intubation is indicated, occurring in up to 17% of patients [33]. In contrast, it occurs in 1 in 30 patients undergoing elective surgery [18]. Unrecognized esophageal intubation can be fatal, leading to rapid hypoxia including CNS (central nervous system) damage and death, so early recognition of such a situation is crucial. Due to the unreliability of methods that focus on observing chest movements and auscultatory methods, the 2022 Project for Universal Management of Airway and international airway societies guidelines emphasize the importance of monitoring capnography and saturation, and promote use of videolaryngoscopy to reduce the incidence of incorrect intubation [18]. In addition, a promising method has been proposed that, using a thin catheter inserted into the endotracheal tube connected to a pressure transducer, allowed the tracheal or esophageal position of the endotracheal tube to be differentiated in a few seconds based on ventilation pressure patterns during manual ventilation [33]. Misplacement of the endotracheal tube is another possibility, as the tube is inadvertently placed in the main bronchus, most often the right bronchus, by being pushed too deep. Reports have shown that this complication is the most common incident associated with endotracheal intubation, occurring in 3.7% of 2947 patients studied. The sequelae of endotracheal intubation are selective ventilation of 1 lung, resulting in hypoxemia, and also pneumothorax due to excessive distension of the ventilated lung, and postoperative atelectasis or pneumonia [17]. Due to numerous anatomical distinctions, a predisposition to tube migration with neck movements, and the unreliability of methods focusing on auscultation of the lung fields and monitoring of capnometry and saturation, a new method of identifying tube position may be remarkably useful. Using the AnapnoGuard system (successfully used in practice to detect air leakage around the cuff) that continuously analyzes the CO2 concentration above the tube cuff, coming only from the unventilated lung while ensuring optimal cuff tightness. Thus, there is potential utility of this method in early detection of bronchial misintubation [17].

Mechanical irritation through a laryngoscope, endotracheal tube, or other airway instrumentation can cause the previously described bronchospasm or laryngospasm. This mainly affects patients who are in the described risk groups and, in the case of bronchospasm, also have hyperreactive airways. Improper endotracheal tube placement can lead to rapid hypoxemia and CO2 retention [5–8].

Aspiration of gastric contents into the lungs is another complication of general anesthesia, of which instrumented airway instrumentation is an important cause [16,34,35], as then physiological mechanisms like lower esophageal sphincter (LES) tension and airway reflexes are suppressed by the drugs used in induction of anesthesia [35]. Gastric secretions irritating the airways can lead to their contraction and progressive desaturation [16]. In addition, by inducing pneumonia, it is thought to cause acute respiratory distress syndrome (ARDS) developing postoperatively, which can even lead to death [16,34]. Patients with full gastric contents are particularly vulnerable, which often include those undergoing emergency, unplanned surgeries [16,34,35]. Compression of the annular cartilage during intubation can protect against aspiration [16]. Despite widespread recommendations, inserting a gastric probe for decompression can stimulate the emesis reflex [35]. In patients with a suspected full stomach, intubation should be performed under the RSI (rapid sequence intubation) protocol. In addition to the hypnotic drug, it takes into account the use of succinylcholine, or large doses of rocuronium, as they provide convenient conditions for intubation in less than 90 seconds. Despite adverse effects in the form anaphylaxis, prolonged neuromuscular block, or postoperative respiratory distress, the beneficial effect of remifentanil replacing the above muscle relaxants in reducing pointubation complications has not been demonstrated [34]. To rule out a full stomach and choose the optimal intubation technique, a gastric USG analyzing selected antral parameters may be useful, as has been confirmed in the context of intubation in emergency departments [35].

In addition to the aforementioned events leading to hypoxemia associated with intubation and prolonged airway instrumentation, it is important to note that populations particularly vulnerable to rapid desaturation have been described. These include, among others, obese patients due to anatomical and physiological peculiarities [28] and critically ill patients, mainly due to alveolar collapse and inefficient gas exchange [14,15]. Depending on the clinical situation, some modifications to preoxygenation techniques in the form of specific positioning, high-flow intranasal oxygen [14,28] or apneic oxygenation (Ap-Ox) [15] techniques can be used before intubation to reduce the risk of hypoxemia.

Laryngoscopy and irritation of the larynx and trachea with an endotracheal tube are also painful stimuli that can lead to adrenergic stimulation in addition to airway contraction. It manifests clinically as an increase in blood pressure (BP) and heart rate (HR), and their uncontrolled increase can result, sometimes even in lethal cardiovascular complications, especially in patients with cardiovascular problems. Premedication with the α2 agonist dexmedetomidine can provide lower BP and HR during intubation and extubation than in patients who were not given dexmedetomidine. Its effect may be particularly beneficial in patients with cardiovascular risk [36].

Complications of Supraglottic Methods

In the operating room, supraglottic devices are increasingly being used for airway clearance, with laryngeal masks (LMAs) being the most popular choice. They are considered a less invasive and safer option, but complications associated with their use have been described. Some of the non-traumatic as well as traumatic complications (mainly involving the oral cavity) are analogous to endotracheal intubation and relate to events during their insertion. In addition, ischemia of the tongue and both unilateral and bilateral paralysis of the lingual, sublingual and recurrent laryngeal nerves have been proven. These dysfunctions are most often transient and are related to prolonged pressure of the mask cuff on the soft tissues, impairing microcirculation. For this reason, it is crucial to properly select the mask size and intracuff pressure, and it is additionally recommended to check the pressure every 30 minutes when using nitrous oxide in anesthesia, as it is postulated to diffuse into the cuff [27]. In elderly patients (≥70 years) undergoing general anesthesia for planned surgery, the possibility of reducing incident postoperative pulmonary complications (mainly coughing) when endotracheal intubation is replaced by a supraglottic device has been demonstrated [37].

The Acronym DOPES as a Useful Tool in Daily Practice

Intubation-related complications can also occur later, despite intubation performed without complications or awareness of them. The condition of an intubated patient undergoing mechanical ventilation can deteriorate at any time. In the search for the cause of decompensation in daily clinical practice, especially in inexperienced anesthesia personnel, the acronym DOPES (displacement, obstruction, patient, equipment, stomach) can be extremely useful. Although there are many more causes of respiratory decompensation, including hypoxemia, the acronym takes into account events that should be excluded as soon as deterioration is observed. It summarizes the most common sources of deterioration of the condition of patient associated with intubation and artificial airways [19–21]. The events included in the acronym DOPES are summarized in Table 1.

Other Complications Related to Anesthesia

In addition to hemodynamic and respiratory complications, and instrumented airway management complications, other complications associated with general anesthesia should also be mentioned. Although they usually do not occur often or do not have the proper attention of staff, they can be fatal, so anesthesia personnel must be aware of their potential occurrence and be prepared to implement appropriate interventions.

Anaphylactic Reaction

Anaphylactic reaction, due to its hemodynamic impairment, is often treated as a cardiovascular complication. However, in view of the often accompanying respiratory, gastrointestinal, or skin symptoms, we decided to include this complication in this article and describe it comprehensively, taking into account the hemodynamic and non-hemodynamic component.

It is necessary to mention the anaphylactic reaction, which is most often traced back to intraoperatively administered drugs, with antibiotics (especially beta-lactams) and NMBAs (administered only under general anesthesia) most often responsible for causing it [38,39]. The reaction they cause will typically develop rapidly, within the first 30 minutes of anesthesia. Considerably less common causes are antiseptics, colloids and blood products, latex, dyes, sugammadex, and other intraoperatively administered agents [39]. The incidence of anaphylaxis estimated at 1: 10000 and the mortality is less than 0.001% [40]. Symptoms can range from mild skin lesions to cardiovascular collapse and may be initially unnoticeable due to the patient’s sedation, skin covering, or similar effects on the hemodynamics of the drugs used in anesthesia [39]. Typical manifestations include features of developing shock expressed by hypotension and tachycardia, as well as respiratory distress due to obstruction of the lower and/or upper airways, skin lesions such as rash, erythema, or edema, gastrointestinal symptoms, and even respiratory or cardiac arrest. The symptoms below are caused by the release of mediators, primarily histamine from basophils and tissue mast cells, mediated or not by the action of IgE. [40,41]. It should be borne in mind that symptoms may manifest atypically. A case of anaphylaxis occurring under the mask of isolated hypotension refractory to fluid therapy and vasopressors has been described [38]. When it is difficult to diagnose anaphylaxis based on the clinical picture alone, measuring plasma levels of tryptase, its laboratory marker, can be helpful. It should be remembered, however, that it reaches its peak level only 15 minutes after the onset of anaphylaxis, so it absolutely cannot be taken as a marker for introducing appropriate treatment. After surgery, skin tests and sometimes blood-specific IgE testing may prove beneficial in investigating the cause of anaphylactic reactions. These will help guide the prevention of further episodes and the introduction of possible treatment [39].

The primary intervention, in addition to immediate termination of exposure to the causative agent, is administration of epinephrine (i.v., doses up to 0.5 mg, depending on clinical condition) together with ensuring airway patency along with 100% oxygen therapy and fluid resuscitation (2–4 L of crystalloids). In addition, depending on the clinical situation, inhaled, fast-acting bronchodilators such as salbutamol (selective β2-agonist) or ipratropium (M3 muscarinic receptor antagonist) or intravenous steroids (mainly hydrocortisone) can be used as adjuncts. Antihistamines, blocking H1 receptors, are also being used at times [39–41]. Furthermore, the unconventional attachment of ketamine, which is used to reverse asthmatic airway spasm in patients unresponsive to standard treatment, can reverse bronchospasm in patients with anaphylaxis [41].

Neurological Complications

A comprehensive group of complications in patients undergoing general anesthesia, developing mainly in the postoperative period, are neurological disorders. They are most often related to the drugs used perioperatively and their improper dosage, residual effects, or interactions. Groups of drugs like anesthetics, opioids, benzodiazepines, a number of agents with anticholinergic effects, and numerous drugs taken by the patient in the perioperative period, interacting with the previously mentioned ones, can cause delayed awakening after general anesthesia. In addition to residual effects and interactions of the drugs used, this complication is influenced by the co-morbidity of the patient undergoing surgery, as well as intraoperative metabolic disorders [42,43]. Worthy of special attention is residual neuromuscular block (RNMB), which is the unwanted presence of signs and symptoms of muscle weakness after the patient regains consciousness. Despite extensive information on the subject, it often remains unrecognized, leading to numerous complications, especially respiratory ones, that can be fatal [44]. Further development of previously mentioned PPC should also be remembered. It is caused by prolonged effects of non-depolarizing muscle relaxants and is diagnosed when TOFR (train-of-four ratio) is <0.9 [44,45]. To prevent its occurrence, a muscle relaxant that is as short-acting as possible should be selected and dosed according to the clinical situation. According to the ASA’s (American Society of Anesthesiologists) 2023 guideline, quantitative methods (which can include acceleromiography – AMG, or electromyography – EMG) are recommended for monitoring RNMB, which have advantages over qualitative methods in this case. In addition, studies show the superiority of sugammadex over neostigmine in preventing RNMB. It should be kept in mind that patients with liver, kidney, neuromuscular diseases, geriatric, pediatric, morbidly obese or those undergoing cardiac and thoracic surgery are particularly susceptible to the occurrence of this complication [44].

A number of drugs with anticholinergic effects can cause anticholinergic syndrome, which includes central anticholinergic syndrome (CAS) manifested mainly by central nervous system (CNS) excitation or a peripheral form that is a spectrum of symptoms of parasympathetic nervous system (PNS) blockage. When this syndrome occurs, the administration of physostigmine (1 mg i.v.) is indicated [46]. Among the neurological complications of general anesthesia, we can also include postoperative delirium, postoperative cognitive dysfunction (POCD), or significantly rarer focal neurological disorders like perioperative stroke (POS), spinal cord ischemia (SCI), or postoperative visual loss (POVL). These are complications that are often difficult to identify and differentiate, so anesthesiologists should know the baseline neurological status of patients before they undergo general anesthesia [47].

Postoperative Nausea and Vomiting (PONV)

Postoperative nausea and vomiting (PONV), occurring within 24 hours after surgery, is another postoperative complication that patients undergoing general anesthesia are at greater risk of. Their incidence ranges from 30% to as high as 80% in high-risk patients. On the anesthetic side, risk factors for PONV, in addition to the type of anesthesia, include its duration and the use of volatile anesthetics, N2O, and opioids, especially those used postoperatively. In addition, a number of patient-related factors can increase the risk of this complication. Among the most important are female sex, younger age (<50 years), non-smokers, and those with a history of PONV and/or motion sickness. The type of surgery itself and its extent and duration are also important. A reduction in the incidence of nausea and vomiting can be achieved by using regional anesthesia; if general anesthesia is required, the lowest risk is TIVA (total intravenous anesthesia) using continuous infusion of propofol and non-use of N2O in the breathing compound. In addition, replacing opioids with non-opioid analgesics and alternative methods of pain management yielded better results [48]. Moreover, pharmacological prevention of PONV is used, standardized by 2 antiemetic drugs, like a combination of a 5-HT3 (5-hydroxytryptamine or serotonin) receptor antagonist (the “gold standard” is ondansetron [48]) with dexamethasone. Patients at higher risk should receive 1–2 medications with separate points of entry. It has been shown that aprepitant, a NK1 (neurokinin 1) receptor antagonist, had the highest efficacy in preventing PONV [49]. Drugs from the butyrophenone group (haloperidol, droperidol), phenothiazines (metoclopramide, perphenazine), antihistamines (dimenhydrinate, meclizine), and anesthetics such as propofol and dexmedetomidine, or midazolam have antiemetic effects and in addition to the previously mentioned agents are also listed by the Society for Ambulatory Anesthesia [48]. Combinations of different antiemetic drugs are more effective than monotherapy [49].

Accidental Awareness During General Anesthesia (AAGA)

A complication that is particularly feared by patients undergoing general anesthesia and also by the anesthesia team is accidental awareness during general anesthesia (AAGA), occurring in 0.1–0.2% of patients undergoing this anesthesia, although some are higher [50]. This complication is more common in obstetric (0.47%) and pediatric patients (up to 1.2%) [51]. It is an unexpected awakening by the patient during surgery, often with inability to move due to neuromuscular blockade. This is caused by too shallow anesthesia caused by the low anesthetic concentration in the body, which does not allow adequate suppression of external stimuli during surgery. This complication carries serious consequences, as memories of the awakening can cause psycho-emotional disorders in patients. One of these consequences is post-traumatic stress disorder (PTSD) and is estimated to occur in up to more than 70% who have experienced AAGA. The best form of prevention is to monitor the depth of anesthesia using bispectral index (BIS), patient state index (PSI), entropy using EEG (electroencephalogram) recording, or measuring the expiratory concentrations of anesthetic gases. However, these techniques are still not fully reliable and able to prevent AAGA [50]. A promising new method has been proposed that could more effectively alert to the occurrence of AAGA and allow the anesthesiologist to react more quickly to deepen anesthesia. A brain-computer interface (BCI) that reads specific signals from the motor cortex as intention to move induced by stimulation of the median nerve has been suggested as a possible tool to demonstrate that a muscle-relaxed patient, as a result of perceived pain stimuli on intention to move, could serve as a predictor of accidental awareness [50]. There are reports that rapid administration of midazolam for suspected AAGA can cause memory consolidation impairment and retrograde amnesia in patients with accidental intraoperative awareness [52].

Hypothermia

An intra- and postoperative complication that patients undergoing long procedures under general anesthesia are particularly vulnerable to is hypothermia, which is a core body temperature of <36°C [53–55]. Despite its occurrence postoperatively in 26–90% of patients, it is still a complication that many clinicians do not pay due attention to [54]. It is caused by a change in functioning of the hypothalamic thermoregulatory center after induction of general anesthesia and redistribution of central-circulatory temperature due to vasodilation and heat exchange with the environment [53,54]. Impaired thermoregulatory control has been attributed to anesthetic gases, propofol, or opioids commonly used in general anesthesia [55]. The most important risk factors include age (>60 years and children), malnutrition and cachexia, current diseases impairing thermoregulation, long (>2 h) and extensive surgical procedures, as well as intraoperative infusions of large volumes of unheated irrigation fluid solutions or cold blood products, general anesthesia combined with regional anesthesia near the spinal cord, and low temperature in the operating room [54]. The importance of hypothermia should not be underestimated, as it can contribute to a number of serious consequences. Cardiac complications (myocardial infarction, arthymias), coagulopathies leading to excessive bleeding and necessitating the use of transfusions, impaired wound healing and infection, prolonged effects of anesthetic drugs, and prolonged awakening through impaired pharmacokinetics, and a number of others, resulting in worse postoperative outcomes and prolonged hospitalization [53,54]. Because of this, it is recommended to monitor deep temperature in the surgical patient. The reference site is the pulmonary artery using a Swan-Ganz catheter, but non-invasive measurement locations are commonly used, such as the nose, throat, esophagus, bladder, or tympanic membrane. All the listed measurement areas are in recommendation class A according to the Oxford Centre for Evidence Based Medicine [54]. Documented intraoperative interventions to prevent hypothermia include active warming with a special heating blanket, warming infusion and irrigation fluids as well as blood products with dedicated warmers, passive thermal isolation of the patient, or keeping the operating room temperature above 21°C (for adults) [54]. In contrast, the effectiveness of active warming during the induction of anesthesia in preventing further hypothermia has not been clearly confirmed. There are reports both supporting [53] and challenging [55] the effectiveness of preoperative rewarming in reducing the incidence and severity of perioperative hypothermia, so that this method is still not widely accepted in clinical practice.

Malignant Hyperthermia (MH)

An extremely rare complication of general anesthesia in which volatile anesthetics (sevoflurane, desflurane, isoflurane) and/or succinylcholine are used is malignant hyperthermia (MH) [56,57]. It is a pharmacodynamic disorder with an estimated incidence of 0.0004–0.01% of procedures using the above-mentioned agents, which are known to be specific triggers. It is inherited in an autosomal dominant manner, associated with a number of gene mutations, and, simplifying, involves malfunction of the ryanodine receptor, which, under the influence of specific triggers, causes uncontrolled release of Ca2+ ions from the sarcoplasmic reticulum of skeletal muscle. This causes abnormally increased contractile activity and metabolism of muscle tissue, leading to rhabdomyolysis [57]. The onset of MH manifests as an unexplained and unexpected increase in ETCO2 (end-tidal carbon dioxide), oxygen consumption, HR, or temperature increase, as well as muscle rigidity, acidosis, hyperkalemia, and other markers of ongoing rhabdomyolysis and its complications [56,57]. The criterion standard for diagnosis is the test of contraction of a biopsy of muscle tissue under halothane, or caffeine; in addition, methods based on analysis of relevant DNA sequences are being introduced [57]. According to the Association of Anesthesiologists’ 2020 guidelines, management of MH, in addition to cessation of exposure to the inducing agent, is the administration of dantrolene (at an initial dose of 2–3 mg/kg, followed by continuation of administration as needed) and specific symptomatic treatment such as recommended active body cooling. Without intervention, it leads to death in most cases [56].

Conclusions

The article comprehensively describes respiratory complications, which, along with cardiac complications, are the most common complications of general anesthesia. It is important to be aware that factors leading to acute states of intraoperative respiratory decompensation, especially when inadequately diagnosed and treated, can cause postoperative pulmonary complications, which are a variety of pathological conditions of the respiratory system. A perfect example combining the 2 conditions is athelectasis. Intraoperatively, it can result in respiratory failure, while in the case of unsuccessful recruitment of collapsed parenchyma, after surgery it is included in late pulmonary complications and is also the starting point for development of other pathologies. In addition, the article takes into account a number of GA-specific complications that are not directly cardiovascular and respiratory pathologies, but which can manifest symptoms of cardiopulmonary failure at times, such as anaphylaxis or selected complications of intubation and laryngoscopy.

In the context of complications related to general anesthesia, additional mention should be made of renal complications, estimated to occur in 1–5% of patients. Particularly at risk are patients with preexisting preoperative conditions such as kidney disorders. The main pathophysiological mechanism is pre-renal insufficiency, primarily caused by hypoperfusion. On the anesthetic side, it occurs on the basis of hypotension induced by anesthetics, positive-pressure ventilation or preoperative fluid restriction; also important are intraoperatively administered drugs that have nephrotoxic effects or impair renal autoregulation of perfusion. These mainly include non-steroidal anti-inflammatory drugs (NSAIDs), aminoglycoside antibiotics, or inhibitors of the RAA (renin-angiotensin-aldosterone) pathway [2]. We have not focused more attention on this complication, as it is mainly secondary to hypotension, a component of hemodynamic complications not included in the review.

It should be noted that some are interrelated, constituting a cause-and-effect sequence, so their issues should be considered comprehensively. Adverse effects can occur at any stage of anesthesia, but msny occur during induction, or shortly thereafter, which is primarily related to the drugs used or instrumental airway clearance. It is extremely important to properly qualify patients for anesthesia and choose the most appropriate anesthesia technique. The usefulness of this review is due to the careful annotation of each complication with risk factors related to the patient’s initial condition and predisposing types of surgery, if there is such a relationship. Continuous intraoperative monitoring of vital signs and adherence to the “5N rule” – keeping the surgical patient in a state of normovolemia, normotension, normoglycemia, normocapnia, and normotermia – is crucial [47]. Also not without significance is the awakening of a properly prepared patient (bearing in mind the residual effects of drugs, especially NMBA) and appropriate postoperative care, as many complications from the spectrum of pulmonary complications stem from an inadequately conducted post-anesthesia period.

Future Directions

The unquestionable value of this review is to summarize the latest research, especially on the diagnosis and prevention of induced general anesthesia, with the well-studied and reported facts about them. The article reveals a number of potential directions on which further clinical research should be conducted or more widely implemented in daily clinical practice.

Ultrasound should be an increasingly common diagnostic tool used perioperatively to diagnose and predict the development of further PPCs. This would have implications for the selection of patients at particular risk of developing specific pulmonary complications and appropriate intraoperative measures, as well as intraoperative diagnosis of certain causes of respiratory decompensation. In addition, an interesting option is the use of USG in the exclusion of a full stomach before intubation, which is currently applicable in emergency medicine. For these reasons, additional training of anesthesia personnel with the development of rapid diagnostic protocols should be introduced. To improve intubation safety, it would be beneficial to conduct clinical trials on larger groups of patients to confirm the effectiveness and implement into clinical daily life the use of AnapnoGuard and pressure transducer-based systems for rapid diagnosis of endotracheal tube malposition. These are promising and relatively inexpensive methods with greater specificity than conventional methods based on auscultation and monitoring of changes in capnography and saturation, and they may soon be permanently part of the standard intubation procedure. In addition, anesthesia teams should be encouraged to routinely use distinct preoxygenation techniques in obese patients or those in critical conditions, because of the documented reduction in the risk of hypoxemia.

Moreover, in the context of PPC development, it is still unclear which type of general anesthesia (comparing inhaled anesthesia and TIVA) is more beneficial in the context of selected surgical procedures, so further research, especially multicenter studies, should be conducted to establish guidelines for safer anesthesia. Efforts are also required to determine the indications for the choice of sugammadex, or neostigmine, to effectively and safely reverse relaxation in individual patients undergoing different types of surgery while possibly reducing the incidence of pulmonary complications.

Another promising direction is the use of computer systems to predict the risk of intraoperative adverse events. The article considers a brain-computer interface (BCI) to predict AAGA, and Prescience, which is a machine learning model to predict the 5-minute risk of intraoperative hypoxemia. These are extremely innovative directions that have the potential to revolutionize modern anesthesiology. They certainly require further research and improvement, taking as an example the Prescience system, whose algorithms need to be enhanced with further variables related to the patient’s condition.

Further studies are also needed to definitively clarify the efficacy and validity of preoperative rewarming in the context of preventing intraoperative hypothermia. In addition, more widespread use of dexmedetomidine as pre-intubation premedication may provide better hemodynamic stability after intubation and administration of aprepitant to reduce the incidence of PONV. Also, the validity of the bronchodilatory effect of ketamine in situations other than the asthmatic state should be confirmed.