Abdominal compliance: A bench-to-bedside review

Abdominal compliance is an important determinant and predictor of available workspace during laparoscopic surgery. Furthermore, critically ill patients with a reduced abdominal compliance are at an increased risk of developing intra-abdominal hypertension and abdominal compartment syndrome both of which are associated with high morbidity and mortality. Despite of this, abdominal compliance is a concept, which has been neglected in the past. Abdominal compliance is defined as a measure of the ease of abdominal expansion, expressed as a change in intra-abdominal volume per change in intra-abdominal pressure: abdominal compliance = delta intra-abdominal volume / delta intra-abdominal pressure. AC is a dynamic variable, dependent on base-line IAV and IAP as well as reshaping and stretching capacity. Whereas abdominal compliance itself can only rarely be measured, it always needs to be considered an important component of intra-abdominal pressure. Patients with decreased abdominal compliance are prone to fulminant development of abdominal compartment syndrome when concomitant risk factors for intra-abdominal hypertension are present. This review aims to clarify the pressure-volume relationship within the abdominal cavity. It highlights how different conditions and pathologies can affect abdominal compliance and which management strategies could be applied to avoid serious consequences of decreased abdominal compliance. We have pooled all available human data to calculate abdominal compliance values in patients acutely and chronically exposed to intra-abdominal hypertension and demonstrated an exponential abdominal pressure-volume relationship. Most importantly, patients with high level of intra-abdominal pressure have a reduced abdominal compliance. In these patients, only small reduction in intra-abdominal volume can significantly increase abdominal compliance and reduce intra-abdominal pressures. A greater knowledge on abdominal compliance may help in selecting a better surgical approach as well as reducing complications related to intra-abdominal hypertension

The respiratory pressure-abdominal volume curve in a porcine model

Background: Increasing intra-abdominal volume (IAV) can lead to intra-abdominal hypertension (IAH) or abdominal compartment syndrome. Both are associated with raised morbidity and mortality. IAH can increase airway pressures and impair ventilation. The relationship between increasing IAV and airway pressures is not known. We therefore assessed the effect of increasing IAV on airway and intra-abdominal pressures (IAP). Methods: Seven pigs (41.4 +/−8.5 kg) received standardized anesthesia and mechanical ventilation. A latex balloon inserted in the peritoneal cavity was inflated in 1-L increments until IAP exceeded 40 cmH2O. Peak airway pressure (pPAW), respiratory compliance, and IAP (bladder pressure) were measured. Abdominal compliance was calculated. Different equations were tested that best described the measured pressure-volume curves. Results: An exponential equation best described the measured pressure-volume curves. Raising IAV increased pPAW and IAP in an exponential manner. Increases in IAP were associated with parallel increases in pPAW with an approximate 40% transmission of IAP to pPAW. The higher the IAP, the greater IAV effected pPAW and IAP. Conclusions: The exponential nature of the effect of IAV on pPAW and IAP implies that, in the presence of high grades of IAH, small reductions in IAV can lead to significant reductions in airway and abdominal pressures. Conversely, in the presence of normal IAP levels, large increases in IAV may not affect airway and abdominal pressures

Incidence, Risk Factors, and Outcomes of Intra-Abdominal Hypertension in Critically Ill Patients-A Prospective Multicenter Study (IROI Study)

To identify the prevalence, risk factors, and outcomes of intra-abdominal hypertension in a mixed multicenter ICU population. Prospective observational study. Fifteen ICUs worldwide. Consecutive adult ICU patients with a bladder catheter. None. Four hundred ninety-one patients were included. Intra-abdominal pressure was measured a minimum of every 8 hours. Subjects with a mean intra-abdominal pressure equal to or greater than 12 mm Hg were defined as having intra-abdominal hypertension. Intra-abdominal hypertension was present in 34.0% of the patients on the day of ICU admission (159/467) and in 48.9% of the patients (240/491) during the observation period. The severity of intra-abdominal hypertension was as follows: grade I, 47.5%; grade II, 36.6%; grade III, 11.7%; and grade IV, 4.2%. The severity of intra-abdominal hypertension during the first 2 weeks of the ICU stay was identified as an independent predictor of 28-and 90-day mortality, whereas the presence of intra-abdominal hypertension on the day of ICU admission did not predict mortality. Body mass index, Acute Physiology and Chronic Health Evaluation II score greater than or equal to 18, presence of abdominal distension, absence of bowel sounds, and positive end-expiratory pressure greater than or equal to 7 cm H2O were independently associated with the development of intra-abdominal hypertension at any time during the observation period. In subjects without intra-abdominal hypertension on day 1, body mass index combined with daily positive fluid balance and positive end-expiratory pressure greater than or equal to 7 cm H2O (as documented on the day before intra-abdominal hypertension occurred) were-associated with the development of intraabdominal hypertension during the first week in the ICU. In our mixed ICU patient cohort, intra-abdominal hypertension occurred in almost half of all subjects and was twice as prevalent in mechanically ventilated patients as in spontaneously breathing patients. Presence and severity of intra-abdominal hypertension during the observation period significantly and independently increased 28-and 90-day mortality. Five admission day variables were independently associated with the presence or development of intra-abdominal hypertension. Positive fluid balance was associated with the development of intra-abdominal hypertension after day 1474535542NIGMS NIH HHSUnited States Department of Health & Human ServicesNational Institutes of Health (NIH) - USANIH National Institute of General Medical Sciences (NIGMS) [U54 GM104940

Effect of angiotensin-converting enzyme inhibitor and angiotensin receptor blocker initiation on organ support-free days in patients hospitalized with COVID-19

IMPORTANCE Overactivation of the renin-angiotensin system (RAS) may contribute to poor clinical outcomes in patients with COVID-19. Objective To determine whether angiotensin-converting enzyme (ACE) inhibitor or angiotensin receptor blocker (ARB) initiation improves outcomes in patients hospitalized for COVID-19. DESIGN, SETTING, AND PARTICIPANTS In an ongoing, adaptive platform randomized clinical trial, 721 critically ill and 58 non–critically ill hospitalized adults were randomized to receive an RAS inhibitor or control between March 16, 2021, and February 25, 2022, at 69 sites in 7 countries (final follow-up on June 1, 2022). INTERVENTIONS Patients were randomized to receive open-label initiation of an ACE inhibitor (n = 257), ARB (n = 248), ARB in combination with DMX-200 (a chemokine receptor-2 inhibitor; n = 10), or no RAS inhibitor (control; n = 264) for up to 10 days. MAIN OUTCOMES AND MEASURES The primary outcome was organ support–free days, a composite of hospital survival and days alive without cardiovascular or respiratory organ support through 21 days. The primary analysis was a bayesian cumulative logistic model. Odds ratios (ORs) greater than 1 represent improved outcomes. RESULTS On February 25, 2022, enrollment was discontinued due to safety concerns. Among 679 critically ill patients with available primary outcome data, the median age was 56 years and 239 participants (35.2%) were women. Median (IQR) organ support–free days among critically ill patients was 10 (–1 to 16) in the ACE inhibitor group (n = 231), 8 (–1 to 17) in the ARB group (n = 217), and 12 (0 to 17) in the control group (n = 231) (median adjusted odds ratios of 0.77 [95% bayesian credible interval, 0.58-1.06] for improvement for ACE inhibitor and 0.76 [95% credible interval, 0.56-1.05] for ARB compared with control). The posterior probabilities that ACE inhibitors and ARBs worsened organ support–free days compared with control were 94.9% and 95.4%, respectively. Hospital survival occurred in 166 of 231 critically ill participants (71.9%) in the ACE inhibitor group, 152 of 217 (70.0%) in the ARB group, and 182 of 231 (78.8%) in the control group (posterior probabilities that ACE inhibitor and ARB worsened hospital survival compared with control were 95.3% and 98.1%, respectively). CONCLUSIONS AND RELEVANCE In this trial, among critically ill adults with COVID-19, initiation of an ACE inhibitor or ARB did not improve, and likely worsened, clinical outcomes. TRIAL REGISTRATION ClinicalTrials.gov Identifier: NCT0273570

Are we neglecting extra-vascular pressures?

To the editor: We read with great interest Groombridge and colleagues’ article comparing central venous pressure at the superior vena cava and femoral vein sites.1 We completely agree with the conclusions drawn by the authors that superior vena cava pressure (SVCP) and femoral venous pressure (FVP) are two different pressure entities altogether. Unfortunately, despite examining the influence of positive end-expiratory pressures (PEEP) and intra-abdominal pressures on SVCP and FVP, the authors did not point out how important it is to assess potential extra-vascular pressures when interpreting SVCP or FVP correctly when caring for critically ill patients

Intra-abdominal measurement techniques: Is there anything new?

Intra-abdominal pressure (IAP) measurements are essential to the diagnosis and management of intra-abdominal hypertension (IAH) and abdominal compartment syndrome. A variety of IAP measurement techniques have been described. The intravesicular or bladder technique remains the gold standard. This commentary reviews each of the different techniques for IAP measurement and discusses their clinical application. It also explores how IAP is affected by changes in body position, body mass index, and positive end-expiratory pressure (PEEP). IAP should be measured every 4 to 6 hours in patients with risk factors for IAH. Putting patients in the semi-recumbent position changes the IAP measurement significantly. The role of prone positioning in unstable patients with IAH remains unclear. PEEP has a small effect on IAP

What’s new in medical management strategies for raised intra-abdominal pressure: evacuating intra-abdominal contents, improving abdominal wall compliance, pharmacotherapy, and continuous negative extra-abdominal pressure

In the future, medical management may play an increasingly important role in the prevention and management of intra-abdominal hypertension (IAH). A review of different databases was used (PubMed, MEDLINE and EMBASE) with the search terms ‘Intra-abdominal Pressure’ (IAP), ‘IAH’, ‘ Abdominal Compartment Syndrome’ (ACS), ‘medical management’ and ‘non-surgical management’. We also reviewed all papers with the search terms ‘IAH’, ‘IAP’ and ‘ACS’ over the last three years, only extracting those papers which showed a novel approach in the non-surgical management of IAH and ACS.IAH and ACS are associated with increased morbidity and mortality. Non-surgical management is an important treatment option in critically ill patients with raised IAP. There are five medical treatment options to be considered to reduce IAP: 1) improvement of abdominal wall compliance; 2) evacuation of intra-luminal contents; 3) evacuation of abdominal fluid collections; 4) optimisation of fluid administration; and 5) optimisation of systemic and regional perfusion.This paper will review the first three treatment arms of the WSACS algorithm: abdominal wall compliance; evacuation of intra-luminal contents and evacuation of abdominal fluid collections. Emerging medical treatments will be analysed and finally some alternative specific treatments will be assessed. Other treatment options with regard to optimising fluid administration and systemic and regional perfusion will be described elsewhere, and are beyond the scope of this review.Medical management of critically ill patients with raised IAP should be instigated early to prevent further organ dysfunction and to avoid progression to ACS. Many treatment options are available and are often part of routine daily management in the ICU (nasogastric, rectal tube, prokinetics, enema, sedation, body position). Some of the newertreatments are very promising options in specific patient populations with raised IAP. Future studies are warranted to confirm some of these findings

Fluid therapy and perfusional considerations during resuscitation in critically ill patients with intra-abdominal hypertension

Intra-abdominal hypertension (IAH) and abdominal compartment syndrome (ACS) are consistently associated with morbidity and mortality among the critically ill or injured. Thus, avoiding or potentially treating these conditions may improve patient outcomes.With the aim of improving the outcomes for patients with IAH/ACS, the World Society of the Abdominal Compartment Syndrome recently updated its clinical practice guidelines. In this article, we review the association between a positive fluid balance and outcomes among patients with IAH/ACS and how optimisation of fluid administration and systemic/regional perfusion may potentially lead to improved outcomes among this patient population.Evidence consistently associates secondary IAH with a positive fluid balance. However, despite increased research in the area of non-surgical management of patients with IAH and ACS, evidence supporting this approach is limited. Some evidence exists to support implementing goal-directed resuscitation protocols and restrictive fluid therapy protocols in shocked and recovering critically ill patients with IAH. Data from animal experiments and clinical trials has shown that the early use of vasopressors and inotropic agents is likely to be safe and may help reduce excessivefluid administration, especially in patients with IAH. Studies using furosemide and/or renal replacement therapy to achieve a negative fluid balance in patients with IAH are encouraging. The type of fluid to be administered in patients with IAH remains far from resolved. There is currently insufficient evidence to recommend the use of abdominalperfusion pressure as a resuscitation endpoint in patients with IAH. However, it is important to recognise that IAH either abolishes or increases threshold values for pulse pressure variation and stroke volume variation to predict fluid responsiveness, while the presence of IAH may also result in a false negative passive leg raising test.Correct fluid therapy and perfusional support during resuscitation form the cornerstone of medical management in patients with abdominal hypertension. Controlled studies determining whether the above medical interventions may improve outcomes among those with IAH/ACS are urgently required

The effect of non-invasive ventilation on intra-abdominal pressure

BackgroundNon-invasive ventilation is a well-established treatment modality in patients with respiratory failure of different aetiologies. A previous case report described how non-invasive ventilation caused gastric distension and intra-abdominal hypertension with subsequent cardio-respiratory arrest and clinical recovery following resuscitative efforts including gastric decompression with a nasogastric tube.MethodsThe aim of this prospective multicentre observational study was to assess the effect of non-invasive ventilation on intra-abdominal pressure. Following informed consent, intra-abdominal pressure and PaCO2 were measured before and after the application of non-invasive ventilation for up to three days in critically ill patients requiring non-invasive ventilation.ResultsThirty-five patients were enrolled; mean (±SD) age of 67.8 (±12.5) years, median (interquartile range) body mass index of 27.9 (24.5–30.0) kg m–2, Acute Physiology and Chronic Health Evaluation II score of 15.8 (±6.4). On admission and after 24 hours of non-invasive ventilation, intra-abdominal pressure was 11.0 (7.5–15.0) mm Hg and 11.0 (8.5–14.5) mm Hg (P = 0.82) and PaCO2 was 44.4 (±11.4) mm Hg and 51.3 (±14.3) mm Hg (P = 0.19), respectively.ConclusionsThe application of non-invasive ventilation was not associated with an increase in intra-abdominal pressure over 72 hours in this small observational study. Thus, it appears that intra-abdominal pressure does not frequently increase when applying non-invasive ventilation in critically ill patients with respiratory failure