Effects of zero reference position on bladder pressure measurements: an observational study

Area of Science:

• Critical Care Medicine
• Surgical Physiology
• Measurement Science

Background:

• Current guidelines recommend the midaxillary line (MAL) for intra-abdominal pressure (IAP) measurement standardization.
• Evidence supporting the MAL as the optimal zero reference level is limited.

Purpose of the Study:

• To investigate the influence of zero reference position on bladder pressure measurements as an estimate of IAP.
• To compare IAP measurements using MAL versus symphysis pubis (SP) as zero reference levels.

Main Methods:

• Intra-abdominal pressure (IAP) was measured in 100 surgical patients within 24 hours post-laparotomy.
• Transurethral technique with 25 ml priming volume was used, with measurements taken at MAL (IAPMAL) and SP (IAPSP) zero reference levels.
• Correlations with body mass index (BMI), surgery type, gender, and age were analyzed.

Main Results:

• Mean IAPMAL (8.5 ± 2.8 mmHg) was significantly higher than IAPSP (6.5 ± 2.8 mmHg) (p < 0.0001).
• A bias of 2.0 ± 1.5 mmHg with a 35.1% percentage error was observed between the two reference levels.
• Body mass index (BMI) correlated with IAP values irrespective of the zero reference used.

Conclusions:

• The choice of zero reference level critically affects IAP measurements in post-laparotomy patients, potentially causing over or underestimation.
• Further anthropometric studies are required to determine the ideal reference level.
• MAL remains the recommended reference due to its anatomical location at the iliac crest in the absence of superior evidence.