Incidence and Clinical Effects of Intra-abdominal Hypertension in Critically Ill Patients

Abstract & Commentary

By Richard J. Wall, MD, MPH, Pulmonary Critical Care & Sleep Disorders Medicine, Southlake Clinic, Valley Medical Center, Renton, WA. Dr. Wall reports no financial relationship to this field of study. This article originally appeared in the October 2008 issue of Critical Care Alert. It was edited by David J. Pierson, MD, and peer reviewed by William Thompson, MD. Dr. Pierson is Professor, Pulmonary and Critical Care Medicine, Harborview Medical Center, University of Washington, and Dr. Thompson is Staff Pulmonologist, VA Medical Center; Associate Professor of Medicine, University of Washington. Drs. Pierson and Thompson report no financial relationships relevant to this field of study.

Synopsis: This study showed that intra-abdominal hypertension is associated with increased organ dysfunction and higher ICU mortality, and two commonly used methods for measuring intra-abdominal pressure have equivalent predictive capabilities.

Source: Vidal MG, et al. Incidence and clinical effects of intra-abdominal hypertension in critically ill patients. Crit Care Med. 2008;36:1823-1831.

This prospective cohort study examined the epidemiology and outcomes of patients with intra-abdominal hypertension (IAH). The study was conducted in a mixed medical-surgical ICU at a university hospital in Argentina. Patients were eligible for inclusion if they had an indwelling bladder catheter and an expected ICU stay > 24 hours. The main study goals were to describe the incidence of IAH and to examine the relationship of various patient outcomes to IAH. In addition, Vidal et al compared two different methods that are commonly used to measure intra-abdominal pressure (IAP): IAPmax and IAPmean. Although most studies have traditionally used IAPmax, recent international guidelines suggest the latter may be more appropriate.1,2

IAP was measured using a Foley bladder catheter in the supine position. After injecting 50 mL of saline into the bladder, a pressure transducer provided measurements at end expiration. IAP was measured every six hours for seven days (or until death or ICU discharge). IAH was defined as at least three consecutive IAP values ≥ 12 mmHg. Vidal et al compared the predictive capabilities of IAPmax (the highest daily value) with IAPmean (the average of the four daily values).

During a nine-month study period, data were obtained from 83 patients. Using IAPmax, 31% had IAH upon ICU admission and 33% developed new IAH, yielding a prevalence of 64%. Patients with IAH had higher hospital mortality (53% vs 27%, p = 0.02), longer ICU stays (10 vs 3 days, p = 0.001), and more organ dysfunction (especially respiratory and renal). Risk factors for developing IAH included acute respiratory distress syndrome, mechanical ventilation, fluid resuscitation, ileus, and various other signs of septic shock. Although only 10 patients (12%) developed full-blown abdominal compartment syndrome, their mortality was 80%. Receiver operator curves for IAPmax and IAPmean showed similar predictive capabilities for survival, with areas under the curves of 0.70 and 0.71, respectively.

Commentary

Although IAH was originally thought to be a condition of trauma patients, it is now recognized that this condition is also common among general ICU patients. With growing awareness of this entity, there has been renewed interest in developing standardized definitions and methods for measuring IAP. Recently, a detailed two-part report from an international conference was published on the subject.1,2

The current study contributes to the field in several ways. First, the study confirms the high incidence (33%) of IAH in a mixed medical-surgical ICU population. In fact, only 27% of the subjects in the current study were trauma patients. Second, the study demonstrates that IAH is independently associated with longer ICU stay, worsening organ failure, and higher mortality. Third, the study shows that two common methods for measuring IAP have equivalent abilities for predicting survival. Thus, both techniques are probably comparable for the purpose of making the diagnosis. Regardless of the chosen method, however, clinicians should familiarize themselves with the numerous potential sources of error when measuring IAP.1 Unlike the situation with blood pressure, a difference of 10 mmHg here can have enormous clinical implications.

Other studies have also shown a relationship between high-volume fluid resuscitation and IAH. The thought is that excessive fluids lead to bowel edema and impaired gut perfusion. However, such a relationship does not prove causality. For example, IAH may simply be seen in the sickest patients, and these are the individuals who require the highest fluid volumes. Any proposed relationship between IAH and mortality must also be viewed with similar caution.

Although the two measurement methods (IAPmax and IAPmean) had "similar" abilities to predict survival, neither performed well in this regard. In fact, the proposed values only correctly identified the patient's outcome 65% of the time. Given the many other tools available for predicting survival in ICU patients, I do not recommend using Vidal et al's cutoff values for this purpose. Monitoring IAP as a routine "vital sign," as proposed by Vidal et al, seems a bit more plausible. However, this approach will need to be validated before it is ready for widespread use.

Perhaps the most striking finding is that 31% of patients had IAH at ICU admission. This suggests that IAH may develop quickly and even prior to fluid resuscitation. For this reason, many experts recommend that all ICU patients be screened for IAH upon ICU admission and whenever there is new or progressive organ failure.2 Although reasonable, I wonder how many clinicians routinely follow this advice. In general, any management decisions should be based upon serial IAP measurements and finding sustained (or rising) values over time.

References

1. Malbrain ML, et al. Results from the International Conference of Experts on Intra-abdominal Hypertension and Abdominal Compartment Syndrome. I. Definitions. Intensive Care Med. 2006;32:1722-1732.

2. Cheatham ML, et al. Results from the International Conference of Experts on Intra-abdominal Hypertension and Abdominal Compartment Syndrome. II. Recommen-dations. Intensive Care Med. 2007;33:951-962.