The role of abdominal compliance, the neglected parameter in critically ill patients — a consensus review of 16. Part 1: definitions and pathophysiology

Abstract

Over the last few decades, increasing attention has been paid to understanding the pathophysiology, aetiology, prognosis, and treatment of elevated intra-abdominal pressure (IAP) in trauma, surgical, and medical patients. However, there is presently a relatively poor understanding of intra-abdominal volume (IAV) and the relationship between IAV and IAP (i.e. abdominal compliance). Consensus definitions on Cab were discussed during the 5th World Congress on Abdominal Compartment Syndrome and a writing committee was formed to develop this article. During the writing process, a systematic and structured Medline and PubMed search was conducted to identify relevant studies relating to the topic. According to the recently updated consensus definitions of the World Society on Abdominal Compartment Syndrome (WSACS), abdominal compliance (Cab) is defined as a measure of the ease of abdominal expansion, which is determined by the elasticity of the abdominal wall and diaphragm. It should be expressed as the change in IAV per change in IAP (mL [mm Hg]⁻¹). Importantly, Cab is measured differently than IAP and the abdominal wall (and its compliance) is only a part of the total abdominal pressure-volume (PV) relationship. During an increase in IAV, different phases are encountered: the reshaping, stretching, and pressurisation phases. The first part of this review article starts with a comprehensive list of the different definitions related to IAP (at baseline, during respiratory variations, at maximal IAV), IAV (at baseline, additional volume, abdominal workspace, maximal and unadapted volume), and abdominal compliance and elastance (i.e. the relationship between IAV and IAP). An historical background on the pathophysiology related to IAP, IAV and Cab follows this. Measurement of Cab is difficult at the bedside and can only be done in a case of change (removal or addition) in IAV. The Cab is one of the most neglected parameters in critically ill patients, although it plays a key role in understanding the deleterious effects of unadapted IAV on IAP and end-organ perfusion. The definitions presented herein will help to understand the key mechanisms in relation to Cab and clinical conditions and should be used for future clinical and basic science research. Specific measurement methods, guidelines and recommendations for clinical management of patients with low Cab are published in a separate review.

Abdominal pressure and gastrointestinal function: an inseparable couple?

“…Signs of organ dysfunction, duration of mechanical ventilation, ICU length of stay and ICU mortality are increased in most studies [10,11,25]. whether a patient develops IAH or abdominal compartment syndrome (ACS) [9,[26][27][28][29].…”

“…The effect of increasing intra-abdominal volume on the development of IAH. [26][27][28][29]. Abdominal compliance -a measure of the ease of abdominal expansion -differs between individuals (e.g.…”

The Neglected Role of Abdominal Compliance in Organ-Organ Interactions

“…In the patient with poor compliance, the reshaping phase went from an IAV of 0 to 2.8 l (vs 0 to 3.8 l when compliance was normal), the stretching phase from IAV of 2.8 to 5.6 l (vs 3.8 to 7.2 l) and the pressurization phase from > 5.6 l vs 7.2 l in the patient with normal compliance. Adapted from [2] with permission indices and imaging techniques. Anthropomorphicbased indices for estimation of IAV have been described in obesity [17].…”

“…Patients with android obesity do not have this reshaping and stretching capability. Adapted from [2] with permission dialysis or by drainage of intra-abdominal fluid (ascites in liver cirrhosis, peripancreatic fluid or pseudocyst, serous fluid collections in trauma or burns) [2][3][4].…”

“…C ab should be expressed as the change in IAV per change in IAP (expressed in ml/mmHg). C ab is one of the most neglected parameters in critically ill patients, despite playing a key-role in understanding the deleterious effects of unadapted IAV on IAP, organ-organ interactions and end-organ perfusion [2,3]. Although there are some papers related to C ab in surgical patients, only a few papers have been published addressing this issue in critically ill patients [2][3][4].…”