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21 July 2021: Clinical Research  

Comparison of Intra-Abdominal Pressure Measurements in Critically Ill Patients Using Intravesical Normal Saline at 15°C, 25°C, and 35°C

Jianfeng Zou1ABD*, Lili Zheng2EG, Weizheng Shuai1DE, Qi Li1CD, Qian Wang1BE, Zhicheng Zhang1DE, Dawei Li1BD

DOI: 10.12659/MSM.932804

Med Sci Monit 2021; 27:e932804



BACKGROUND: The incidence of intra-abdominal hypertension (IAH) and abdominal compartment syndrome (ACS) in intensive care units is high. Dynamic monitoring of intra-abdominal pressure (IAP) is important to treat patients with these conditions. The World Society of Abdominal Compartment Syndrome revised IAP measurement and treatment guidelines in 2013. IAP is measured by instilling ≤25 mL of sterile saline into the bladder, but there is no requirement for the saline to be at a specific temperature. Many doctors presume that using cold saline will trigger bladder muscle spasms, resulting in measurement error. In the present study, we investigated the effect of body-temperature saline on IAP measurements.

MATERIAL AND METHODS: A single-center study was conducted in 12 patients with IAH over a 2-year period. IAP was measured via the bladder with instillation of sterile saline at temperatures of 35°C, 25°C, and 15°C. We analyzed the data using R software, version 4.1.0. Paired t tests were used for comparisons between groups. A Spearman rank correlation analysis was performed to compare groups. Analysis results were plotted using the R packages ggplot2, ggpubr, and BlandAltmanLeh. P<0.05 was considered statistically significant.

RESULTS: There was a significant difference in IAP measurement between the 15°C and 35°C groups (t=-2.55, P=0.027). There was no significant difference between the 25°C and 35°C groups (t=0.73, P=0.48). Bland-Altman analysis showed that IAP was consistent in the 25°C and 35°C groups.

CONCLUSIONS: Although it is preferable to measure IAP with saline at body temperature (35°C), a temperature >25°C is associated with accurate results. Using saline at <15°C should be avoided.

Keywords: Compartment Syndromes, intra-abdominal hypertension, Muscular Diseases, Body Temperature, Critical Care, Critical Illness, saline solution, Temperature


Intra-abdominal pressure (IAP) is approximately 5 to 7 mmHg in critically ill adults. A persistent increase in IAP in critically ill patients in the Intensive Care Unit (ICU) – resulting from acute respiratory failure, gastrointestinal dysfunction, abdominal and pelvic hemorrhage, effusion, intensive fluid resuscitation, and/or septic shock – can lead to intra-abdominal hypertension (IAH) or abdominal compartment syndrome (ACS) [1]. IAH is defined as a sustained or repeated pathological increase in IAP to ≥12 mmHg. ACS is defined as a sustained IAP >20 mmHg (with or without an abdominal perfusion pressure <60 mmHg) that is associated with new organ dysfunction/failure. IAH severity is defined as follows: grade I, 12 to 15 mmHg; grade II, 16 to 20 mmHg; grade III, 21 to 25 mmHg; and grade IV, >25 mmHg [2].

Attention increasingly is being paid to the incidence of IAH [3]. It reportedly occurs in 30% to 50% of critically ill patients and 8% to 15% subsequently develop ACS [4,5]. IAH can cause dysfunction in pulmonary, cardiovascular, renal, and gastrointestinal systems, which leads to a vicious cycle. If not effectively treated in a timely manner, IAH can cause multiple-organ dysfunction or death; diagnosing it is heavily dependent upon dynamic measurement of IAP. Early treatment can prevent deterioration, improve patient outcomes, and reduce mortality.

IAP monitoring has received increasing attention in patients who are at high risk and critically ill [5]. The World Society of the Abdominal Compartment Syndrome (WSACS) is dedicated to research about ACS. The organization revised its guidelines for ACS measurement and treatment in 2013, based on published clinical studies [6]. The current guidelines recommend placing the patient in the supine position, inserting a urethral catheter and emptying the bladder, connecting the catheter to the piezometer, injecting ≤25 mL of sterile saline into the urethral catheter, and setting the 0 point at the midaxillary line. IAP is the pressure measured at the end of expiration. The standard unit of measure is mmHg. However, there is no specific requirement for saline temperature. A common current practice is to measure bladder pressure using ≤25 mL of saline. In this context, we presumed that sufficient accuracy could be achieved using room-temperature saline. Measurement of IAP is fundamental to the diagnosis and treatment of IAH and ACS; therefore, we evaluated the effects of saline temperature on IAP measurement.

Material and Methods


The present study was conducted in the Critical Care Medicine Department of the Sixth Medical Center, a tertiary hospital in Beijing, China. Our ICU has 14 beds and approximately 300 hospitalizations per year. Patients treated in the ICU in the past 2 years who were at high risk of IAH because of factors such as major abdominal surgery, severe trauma, and acute severe pancreatitis were included in the study. Patients were excluded if they had bladder lesions, contracture, trauma, neurogenic bladder, and other bladder-related issues. All patients enrolled in the study provided written informed consent. The protocol was approved by our institution’s Ethics Committee before the start of the study (approval number: HZKY-PJ-2021-16).


Sterile normal saline was prepared and kept at constant temperatures of 35°C, 25°C, and 15°C using a heating bath (Model DK-8D, Qianjun, Shanghai, China). IAP was measured using the intravesical pressure method, as described by the WSACS [6]. First, the patient’s bladder was emptied. IAP measurements were recorded after installation of 25 mL of sterile saline into the bladder and with the patient in the supine position at end expiration and the transducer zeroed at the level of the midaxillary line. First, 35°C was used, then 25°C, and finally 15°C. It took about 10 s to infuse 25 mL of saline into the bladder and close the catheter. The IAP was read 10 s after the instillation. After each measurement, the patient’s bladder was emptied again [7]. Two colleagues read the IAP measurements independently and their readings were averaged and recorded as the final value. Before the study, these clinicians were well trained by the author in how to measure IAP.


All analyses were conducted with R software, version 4.1.0 (R Foundation for Statistical Computing, Vienna, Austria). Paired t tests were used for comparison between groups. Analysis results were plotted using the R packages ggplot2, ggpubr, and BlandAltmanLeh. P<0.05 was considered statistically significant. A Spearman rank correlation was performed to compare groups.



Twelve patients at high risk of IAH (8 men and 4 women; median age 66.4±18.9 years) who were admitted to our department from June 2017 to September 2019 were included in the present study. Their baseline clinical characteristics are shown in Table 1. Of the patients, 2 had severe pancreatitis, 4 had septic shock, 2 had postoperative abdominal infections, 1 had a metastatic tumor in the gastrointestinal tract, 1 had thrombotic intestinal necrosis, 1 had obstetric pathology, and 1 had trauma and multiple injuries with gastrointestinal perforation.


The results of the Spearman correlation analysis for IAP measurement with saline infusion between 15°C and 35°C were P<2.2e-16 and rho=0.958042. For the measurements made with the 25°C and 35°C infusions, the results were P<2.2e-16 and rho=0.986014. Both analyses showed a positive correlation between the saline temperatures and the IAP measurements (Figure 1A, 1B).

Figure 2A shows IAP measurements using saline at 35°C, 25°C, and 15°C. There was a significant difference between measurements using the 15°C and 35°C infusions (t=−2.55, P=0.027). Figure 2B shows that there was no significant difference between the 25°C and 35°C infusions (t=0.73, P=0.48).

Bland-Altman analysis showed a considerable difference between the groups with the 15°C and 35°C infusions (mean difference±SD, 0.625±1.661; Figure 3A). In contrast, there was a minimal difference between the 25°C and 35°C groups (mean difference±SD, 0.067±0.622; Figure 3B). These findings indicate that IAP measurements using saline at 25°C and 35°C are consistent, which suggests that either temperature is acceptable for clinical IAP measurement. However, the results differed when using saline at 15°C, which suggests that lower temperatures should be avoided.



In the present study, modifying saline temperature by 10°C was too large an increment and smaller ranges may lead to more accurate IAP measurements. In a future study, we plan to assess IAP measurement using saline at 20°C and 30°C, and to include a larger group of patients, if possible.


Timely trans-bladder measurement of IAP is important for critically ill patients. Our study revealed that room-temperature saline (>25°C) can be used directly to measure IAP, without heating it to body temperature. Use of saline at temperatures <15°C should be avoid and it should be heated to 25°C to 35°C before infusion into the bladder.


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