Effect of Anesthesia Type on Airway Assessment Tests in Cesarean Delivery Operations: A Prospective Comparative Study

Introductıon

Ventilation and oxygenation management in anesthesia practice is considered one of the most basic skills that anesthesiologists should have. If the patient’s airway is not suitable for mask ventilation or intubation during anesthesia, it can create a challenging situation for the anesthesiologist, and this situation is defined as “difficult airway” [1]. Various predictive methods, such as the modified Mallampati score, upper lip bite test, thyromental distance, sternomental distance, height-to-thyromental distance ratio, and neck circumference, have been developed and are widely used as bedside predictors of difficult airway. The modified Mallampati score evaluates oropharyngeal visibility to estimate intubation difficulty. The upper lip bite test assesses mandibular mobility based on the patient’s ability to bite the upper lip with the lower incisors. The thyromental distance and sternomental distance measure anatomical spaces that reflect mandibular space and neck extension, respectively. The height-to-thyromental distance ratio is a proportion derived from body height and thyromental distance, proposed to enhance predictive accuracy. Neck circumference, typically measured at the level of the thyroid cartilage, is considered a risk factor when increased [2]. The clinical utility of these assessments in anticipating difficult airway scenarios has been supported both by expert consensus and by studies evaluating their individual diagnostic accuracy [2–4].

Airway evaluation tests are applied in the same way in obstetric cases. Anatomic and physiologic changes during pregnancy are among the factors that increase the risk of a difficult airway [5,6]. In addition, it is not clear when pregnancy-related airway changes will return to normal. In obstetric anesthesia, airway management holds particular clinical importance due to the combination of physiological changes during pregnancy and the potential for emergent interventions in the postpartum period. The altered anatomy, fluid shifts, and increased vascularity of airway tissues can render intubation more challenging, especially when rapid decision-making is required. These factors, alongside the observed frequency of airway interventions in obstetric intensive care admissions [7,8], underscore the relevance of anticipating and addressing airway risks. Therefore, a deeper understanding of how different anesthesia techniques affect airway evaluation scores can contribute meaningfully to improving safety in cesarean deliveries.

A study by Boutonnet et al reported that modified Mallampati scores after cesarean delivery did not completely return to normal levels even 48 h after delivery [9]. Therefore, it is very important to repeat the airway evaluation before anesthesia each time for cases that can require reoperation, such as postpartum hemorrhage, and to have the necessary equipment and personnel ready for difficult airway management. Systemic complications that develop in the postpartum period can lead not only to reoperation but also to the need for intensive care. A retrospective evaluation of obstetric cases by Alay et al reported that intubation and mechanical ventilation rates during the intensive care period were at a remarkable level and were closely related to mortality [7]. In a study by Korkmaz et al focusing on the peripartum period, hypertensive diseases and postpartum hemorrhage were determined as the most common reasons for intensive care unit hospitalization, and the need for mechanical ventilation was found to be 25% in these cases [8]. These findings reveal that physiologic stress responses that can develop in the early postpartum period can turn into conditions requiring urgent intervention, such as respiratory failure and the need for intubation, and that determining risk in advance in terms of difficult airway management can directly affect clinical outcomes.

This study aimed to compare the effects of general and spinal anesthesia on postoperative airway assessment parameters in women undergoing cesarean delivery. It was hypothesized that general anesthesia, due to its association with endotracheal intubation, would lead to more pronounced airway changes.

Material and Methods

STUDY DESIGN AND PATIENT SELECTION:

This study was conducted as a prospective cross-sectional observational study between May 20, 2021, and November 30, 2021, following the principles of the Declaration of Helsinki. The approval for the study was granted by the Clinical Research Ethics Committee of Bursa Yüksek İhtisas Training and Research Hospital on 05.05.2021 (approval number 2011-KAEK-25/2021-05.11). Written informed consent was obtained from all participants. Pregnant women scheduled for elective cesarean delivery were included in the study and the patients were divided into 2 groups according to the method of anesthesia: those who underwent spinal anesthesia were defined as group 1, and those who underwent general anesthesia were defined as group 2. This study employed a convenience sampling method, as participants were included consecutively based on eligibility and willingness to participate, with anesthesia type determined by clinical need and patient preference.

INCLUSION CRITERIA:

Patients aged between 18 and 45 years, classified as ASA I–II, scheduled for elective cesarean delivery under spinal or general anesthesia, and capable of providing informed consent were eligible for inclusion.

EXCLUSION CRITERIA:

The exclusion criteria were refusal to participate, conversion from spinal to general anesthesia due to failed block, inability to complete airway assessments at the designated postoperative time points, intraoperative complications that interfered with standard clinical monitoring (eg, severe bleeding resulting in failure to extubate, hemodynamic instability requiring protocol deviation, or need for postoperative ICU admission), known difficult airway, craniofacial anomalies, history of head and neck surgery or radiotherapy, emergency surgical indications (eg, fetal distress, cord prolapse, and placental abruption), edentulism, restricted neck mobility, presence of laryngeal masses, and inability to tolerate the supine position.

ANESTHESIA PROCEDURE:

Pregnant women who agreed to participate in the study and signed the informed consent form were evaluated before anesthesia, and demographic data and comorbidities were recorded. In the preoperative period, all patients underwent standard monitoring, including noninvasive arterial blood pressure, electrocardiography, and pulse oximetry (SpO₂). Intravenous access was established using a 20 G cannula.

For spinal anesthesia, patients without contraindications who opted for this method received a single intrathecal injection of 10 to 12 mg of 0.5% hyperbaric bupivacaine (Buvasin Vem Pharmaceuticals, Turkey) using a 25G Quincke needle at the L3–L4 or L4–L5 interspace in the sitting position. After confirming free cerebrospinal fluid flow, the drug was injected over 10 to 15 s. Patients were then placed in the supine position with a left uterine tilt, and oxygen was administered via nasal cannula at 3 to 4 L/min. Hypotension (defined as a >20% decrease from baseline systolic pressure) was treated with 5 to 10 mg intravenous ephedrine boluses.

For general anesthesia, patients received 2 to 2.5 mg/kg propofol (propofol Fresenius vial, Germany) and 1 to 2 μg/kg fentanyl (Talinat, Vem Pharmaceuticals, Turkey) for induction, followed by 0.6 mg/kg rocuronium (Myokron, Vem Pharmaceuticals, Turkey) to facilitate intubation. After achieving adequate muscle relaxation, endotracheal intubation was performed with cuff pressure maintained between 20 to 30 cmH₂O. Anesthesia was maintained with sevoflurane in a 50% oxygen-air mixture. All patients were ventilated with volume-controlled ventilation to maintain normocapnia. Postoperatively, patients were transferred to the recovery room after extubation and monitored until full recovery.

AIRWAY ASSESSMENT METHODS:

Airway assessments were performed by experienced anesthesiologists according to a standardized protocol, and all measurements were performed by the same observers at the bedside. To minimize interobserver variability, all airway assessments throughout the study were performed by the same anesthesiologist, who was trained and experienced in applying the standardized protocol. Five different airway assessment tests were performed at 4 time points for each patient (T1: before cesarean delivery, T2: 1 h after cesarean delivery, T3: 6 h after cesarean delivery, and T4: 24 h after cesarean delivery) and recorded [10]. In addition, the ratio of height and thyromental distance was calculated for each individual and used in the analyses.

The methods used for airway assessment were conducted through 5 basic tests in the study. First, the modified Mallampati test was evaluated by placing the patient’s head in a neutral sitting position, opening the mouth maximally, and protruding the tongue. This test is divided into 4 classes: class 1 shows soft palate, uvula, pharynx, and anteroposterior pleats; class 2 shows soft palate, uvula, and pharynx; class 3 shows soft palate and base of uvula; and class 4 shows hard palate only. Classes 3 and 4 are associated with difficult airway [11]. The second method, thyromental distance measurement, was performed by measuring the distance in centimeters between the thyroid cartilage protrusion and the midpoint of the jaw tip, with the patient’s head in full extension and mouth closed. A measurement result of less than 6 cm was accepted as an indicator of a difficult airway [12]. The third measurement was the sternomental distance, the distance between the upper border of the sternum of the manubrium and the lower tip of the jaw, which was measured with the patient’s head in full extension and mouth closed; a distance of ≤13.5 cm was considered as the possibility of a difficult airway [13]. The fourth assessment was neck circumference measurement. This measurement was performed at the level of the thyroid cartilage, and values above 43 cm were considered to be associated with a difficult airway [14]. Finally, the upper lip bite test was performed. In this test, the patient was asked to bite the upper lip mucosa with the lower incisors, and classification was made according to the findings obtained. In class 1, the lower incisors can completely cover the upper lip mucosa, while in class 2, contact with the upper lip is achieved but the mucosa cannot be covered. In class 3, the lower incisors cannot bite the upper lip. In this test, class 3 was accepted as a difficult airway indicator [15].

STATISTICAL ANALYSIS:

All statistical analyses were performed using IBM SPSS Statistics 28.0 software. Quantitative data are presented as mean, standard deviation, median, minimum, and maximum; categorical data are reported as frequency and percentage. The distribution of continuous variables was assessed using the Shapiro-Wilk test.

A post hoc power analysis was conducted using G*Power 3.1.9.7 software. Given the final sample sizes (n=64 in the spinal anesthesia group and n=36 in the general anesthesia group), the assumed effect size was Cohen’s d=0.45 (95% CI: 0.037–0.863), and the significance level was set at α=0.05. Based on these parameters, the estimated statistical power of the study was approximately 57%.

Comparisons between 2 independent groups were made using the independent samples t test or Mann-Whitney U test, depending on the distribution of the data. Time-dependent changes within groups were analyzed with the Friedman test. When significant results were observed, post hoc pairwise comparisons were performed using the Bonferroni-corrected Wilcoxon signed-rank test. Categorical data were analyzed using the Pearson chi-squared test, Yates corrected chi-square test, Fisher exact test, or Fisher-Freeman-Halton test, as appropriate. A P value <0.05 was considered statistically significant.

Results

A total of 134 pregnant women scheduled to undergo elective cesarean delivery were assessed for eligibility. Of these, 11 patients declined to participate in the study. Nine patients who initially received spinal anesthesia were excluded due to conversion to general anesthesia following inadequate anesthesia. Ten patients who underwent general anesthesia were excluded due to intraoperative complications. These complications included severe intraoperative bleeding resulting in failure to extubate (thus preventing T3 and T4 assessments), hemodynamic instability requiring deviation from standard anesthetic protocols, and the need for postoperative intensive care admission, which precluded timely evaluation. Four patients were excluded because airway assessment could not be completed at the T3 and T4 time points. As a result, 100 patients were included in the final analysis (Figure 1).

Demographic and preoperative characteristics of the groups are summarized in Table 1. There was no statistically significant difference between the 2 groups in terms of age, body weights before pregnancy and at delivery, gestational week, parity distribution, gestational pathologies, and ASA score (P>0.05).

Intraoperative and postoperative findings are presented in Table 2. Systolic and diastolic blood pressures measured at the 2nd and 5th minutes after anesthesia induction were significantly lower in group 1, spinal anesthesia, than in group 2, general anesthesia (P<0.001). No significant difference was observed between the groups in terms of other intraoperative parameters. The frequency of postoperative nausea and vomiting was significantly higher in group 2, the group under general anesthesia (P=0.016). There was no statistical difference between the groups in terms of other postoperative maternal complications (P>0.05).

As shown in Table 3, no statistically significant changes were observed over time in any of the airway assessment parameters – including the modified Mallampati score, thyromental distance, sternomental distance, neck circumference, upper lip bite test, and the height-to-thyromental distance ratio – in the spinal anesthesia group.

In contrast, Table 4 demonstrates that, in the general anesthesia group, only the modified Mallampati score exhibited a significant postoperative increase over time (P<0.001). Specifically, the score at time point T1 was significantly lower than at T2, T3, and T4, while there were no significant differences among T2, T3, and T4. All other airway parameters remained stable over the 24-h postoperative follow-up.

When comparing both groups, no statistically significant between-group differences were detected in the time-dependent trends of thyromental distance, sternomental distance, neck circumference, upper lip bite test, or height-to-thyromental distance ratio.

Discussion

LIMITATIONS:

This study was conducted as a single-center, cross-sectional prospective observational investigation and had a limited sample size. The inclusion of only pregnant women who met specific clinical criteria and underwent elective cesarean delivery restricts the generalizability of the findings to the broader obstetric population. Although all airway assessments were performed by the same trained anesthesiologist, to ensure consistency, the inherently subjective nature of some evaluation methods can still limit the objectivity and reproducibility of the results. Nonetheless, the findings can offer valuable contributions to airway management practices in similar clinical settings, in which cesarean deliveries are performed under general or spinal anesthesia. Caution should be exercised when extrapolating these results to populations with different demographic or clinical characteristics, emergency cesarean deliveries, or other healthcare systems.

The absence of radiologic or biochemical methods to objectively evaluate post-intubation edema represents a key limitation of this study. Consequently, the observed increase in the modified Mallampati score during the postoperative period was based solely on clinical assessment, which can introduce subjectivity. The follow-up period was confined to 24 h, which limited our ability to assess the persistence or resolution of airway changes beyond the early postoperative phase.

Another limitation is the non-randomized allocation of patients into anesthesia groups, which may have introduced selection bias. However, baseline demographic and clinical characteristics were comparable between the 2 groups. Additionally, perioperative management protocols were standardized across all patients, to reduce variability in clinical practice. The observed group imbalance was due to the more frequent preference for spinal anesthesia in our clinical practice, and this is consistent with the observational nature of the study.

Moreover, a post hoc power analysis revealed that with the present sample size (64 patients in the spinal group and 36 in the general anesthesia group), and an assumed effect size of Cohen’s d=0.45 at α=0.05, the achieved statistical power was approximately 57%. The 95% confidence interval for this effect size ranged from 0.037 to 0.863, indicating a wide range of potential effect magnitudes, from minimal to moderate. Although this value is below the commonly accepted threshold of 80%, we believe it still offers a meaningful analytical context that supports the interpretability of our results and highlights trends worthy of further investigation.

Furthermore, we acknowledge that the inclusion of additional statistical measures, such as effect sizes and confidence intervals, as well as further methodological clarity, would enhance the robustness and interpretability of the findings. Nevertheless, this study addresses a clinically relevant and under-investigated topic and presents preliminary data that can contribute to future research in the field.

It is recommended that these findings be confirmed in future studies with larger sample groups, multicenter data, and longer follow-up periods.

Conclusions

This study is among the first to comparatively assess the effect of anesthesia type on postoperative upper airway evaluations in cesarean delivery cases. While no significant time-dependent changes were observed in airway assessment parameters under spinal anesthesia, a statistically significant increase in modified Mallampati scores was found in the early postoperative period among patients who received general anesthesia. This change is likely related to inflammatory and edematous responses induced by endotracheal intubation.

The clinical relevance of this finding is underscored by the fact that the Mallampati score is a widely used, practical bedside tool in airway assessment. Therefore, increased postoperative scores, particularly among patients receiving general anesthesia, can indicate a higher risk of difficult airway, underscoring the need for heightened vigilance during early postpartum airway management.

In addition, the higher frequency of postoperative nausea and vomiting observed in the general anesthesia group supports the physiological effect of volatile agents and intraoperative opioids. These findings highlight the need to optimize anesthetic techniques, pharmacological choices, and airway protection strategies in obstetric patients, especially those with predisposing risk factors.

In clinical practice, this calls for careful perioperative planning in high-risk subgroups, such as those with elevated ASA scores, obesity, or preeclampsia. Our findings provide evidence to support more personalized airway management strategies and can serve as a foundation for future multicenter trials aimed at improving maternal safety in cesarean anesthesia.