Evaluation of a modified piezoresistive technique and a water-capsule technique for direct and continuous measurement of intra-abdominal pressure in a porcine model

Measurement of intra-abdominal pressure in large incisional hernia repair to prevent abdominal compartmental syndrome

INTRODUCTION

The repair of large incisional hernias may occasionally lead to a substantial increase in intra-abdominal pressure (IAP), and rarely to abdominal compartmental syndrome (ACS) with subsequent respiratory, vascular, and visceral complications. Measurement of the IAP has recently become a common practice in monitoring critical patients, even though such measurements were obtained in the early 1900s.

PATIENTS AND METHODS

A prospective study involving 54 patients undergoing elective abdominal wall gap repair (mean length, 17.4 cm) with a tension-free technique after incisional hernia was conducted. The purpose of the study was to determine whether or not urinary pressure for indirect IAP measurement is a reliable method for the early identification of patients with a higher risk of developing ACS. IAP measurements were performed using a Foley catheter connected to a HOLTECH® medical manometer. IAP values were determined preoperatively, after anesthetic induction, upon patient awakening, upon patient arrival in the ward after surgery, and 24 h after surgery before removing the catheter. All patients were treated by the same surgical team using a prosthetic composite mesh (PARIETEX®).

RESULTS

Incisional hernia repair caused an increase in the mean IAP score of 2.68 mmHg in 47 of 54 patients (87.04%); the IAP was decreased in two patients (3.7%) and remained equal in five patients before and 24 h after surgery (9.26%). FEV-1, measured 24 h after surgery, increased in 50 patients (92.6%), remained stable in two patients (3.7%), and decreased in two patients (3.7%). The mean increase in FEV-1 was 0.0676 L (maximum increase = 0.42 L and minimum increase = 0.01 L) in any patient who developed ACS.

CONCLUSIONS

Measurement of urinary bladder pressure has been shown to be easy to perform and free of complications. Measurement of urinary bladder pressure can also be a useful tool to identify patients with a higher risk of developing ACS.

What is the best animal model for acs?

INTRODUCTION

Current treatment of the abdominal compartment syndrome (ACS) is based on consensus definitions but several questions regarding fluid regime or critical level of intra-abdominal hypertension (IAH)) remain unsolved. It is questionable whether these issues can be addressed in prospective randomized trials in the near future. This review aimed to summarize current animal models and to outline requirements for the best model.

METHODS

PubMed® data base was searched for articles describing animal models of ACS.

RESULTS

25 articles were found. ACS in animals has not been defined yet. Investigations varied considerably regarding the experimental design. Animals were rats, rabbits, dogs and pigs with a bodyweight from 200g to 70 kg. IAP increase varied from 20 to 50 mmHg. The time period of IAH ranged between 30 min and 24h. The time between the IAH insult and organ dysfunction varied between 15 min and 18h. Investigations demonstrated that IAH is able to induce loss of intravascular volume, organ hypoperfusion, ischemic organ damage and multiple organ failure within 4 to 6h.

CONCLUSION

In contrast to IAH or pneumoperitoneum for surgical exposure, ACS in an animal may be stated if an artificially increased IAP leads to circulatory, respiratory and renal insufficiency. A next step in animal research would be the development of a "pathological" model in which haemorrhage or systemic inflammation together with resuscitation lead to abdominal fluid accumulation and increased intra-abdominal pressure.

Continuous intra-abdominal pressure monitoring

BACKGROUND

Intra-abdominal hypertension (IAH) and abdominal compartment syndrome (ACS) can develop within 12 hours of ICU admission in high-risk patients. Until recently the intermittent intra-abdominal pressure (IAP) measurement via the urinary catheter was the clinical standard. This is a relatively labour intensive technique and its intermittent nature could prevent timely recognition of significant changes in IAP. The historical continuous IAP (CIAP) measurements were poorly reproducible (gastric route) or invasive/impractical (direct measurement). The aim of this paper is to review the current evidence on CIAP monitoring.

METHODS

A broad Medline search of the English literature was performed using the terms of "intra abdominal pressure" and "continuous". This result was analysed based on the title and abstract. Only original clinical studies with continuous IAP measurement were considered in this review. New techniques of CIAP monitoring evaluated in large animal models are discussed as potential future directions.

RESULTS

There is a growing evidence of measuring (monitoring) CIAP using several techniques (gastric, direct abdominal, inferior vena cava, and urinary bladder. The strongest evidence supports the direct abdominal, the gastric and the bladder route. From these three techniques the CIAP monitoring via the bladder has excellent agreement with the current standard of intermittent bladder pressure measurement. While the direct measurement could be very accurate it is an invasive method and feasible in patient who underwent laparotomy or laparoscopy.

CONCLUSIONS

Until a better technique is available the CIAP monitoring via the bladder or stomach should be considered as the standard for continuous monitoring of the IAP. It is a less labour intensive, safe, less invasive and reliable method.

Noosa, 2 years later… a critical analysis of recent literature

INTRODUCTION

Since the second World Congress on the Abdominal Compartment Syndrome (WCACS) in Noosa 2 years ago, interest and publications on intra-abdominal hypertension (IAH) and ACS have increased exponentially. This paper aimed to critically review recent publications and put this new data into the context of already acquired knowledge concerning IAH/ACS.

METHODS

A Medline and PubMed search was performed from January 2005 up to now using "intra-abdominal pressure (IAP)", "intra-abdominal hypertension (IAH)", "abdominal compartment syndrome (ACS)" and "decompressive laparotomy" as search items.

RESULTS

Although consensus definitions of IAH/ACS have been formulated recently, data on awareness are still disconcerting. Several groups refined current IAP measurement techniques and tested new direct IAP measurement devices for use in selected subpopulations. A series of recent publications identified specific patient subpopulations in IAH/ACS, like patients with burns or severe acute pancreatitis, with their specific pathophysiology and therapy. Although many studies already assessed the effect of elevated IAP on regional and micro-circulatory organ perfusion, a number of new publications attempted to unravel the link between elevated IAP and more "downstream" organ function or histology. Finally, therapy for IAH/ACS still reveals more questions than it answers. Global resuscitation does not necessarily equate with organ resuscitation. In fact, fluid-resuscitation may even induce IAH/ACS.

CONCLUSIONS

After publication of consensus guidelines on IAH/ACS, there is an urgent need for human intervention studies and, in parallel, clinically relevant animal models. Given moderately low incidence of ACS and the complex and interrelated pathologies of the critically ill patient with IAH/ACS, large animal models of pathology-induced IAH/ACS might create the opportunity to gain clinically relevant knowledge on the treatment of IAH/ACS.

Rational intraabdominal pressure monitoring: how to do it?

INTRODUCTION

Intraabdominal hypertension (IAH) is increasingly appreciated by intensivists as an important cause of organ dysfunction, even at pressure levels which were previously thought to be harmless. Therefore, the goal of this review is to describe the different methods commonly used in clinical practice for intraabdominal pressure (IAP) measurement, the advised methodology for each measurement method, and finally to give a rational approach for IAP monitoring in daily clinical practice.

METHODS

A Medline search of the English literature was performed using the term "intra abdominal pressure" and "measurement". This resulted in 194 studies, which were then analysed based on the title and abstract. Only clinical studies in human subjects with IAP measurement or related issues as the subject of the study, were considered for inclusion in the study. Reviews, animal experiments and case reports were excluded, while one specific review on IAP measurement and 3 large animal studies (domestic swine > 40 kg) were included in the analysis. This left us with 19 studies, published between 1984 and 2006: 1 specific review, 2 studies in children, 13 in adults and 3 in domestic swine. The references from these studies were searched for relevant articles that may have been missed in the primary search. These articles served as the basis for the recommendations below.

RESULTS

Clinical data regarding the validation of new IAP measurement methods or the reliability of established measurement techniques are scarce. The transvesical route, which has been studied most extensively, can be used as reliable route for intermittent IAP measurement, as long as instillation volumes below 25mL are used. Continuous IAP and APP monitoring can be done via a balloon-tipped catheter placed in the stomach or directly intraperitoneal.

CONCLUSIONS

Rational IAP monitoring should be based on a site specific protocol, based on known risk factors, the monitoring equipment available and nursing staff experience, and should be linked directly to a local treatment protocol.

Consensus conference definitions and recommendations on intra-abdominal hypertension (iah) and the abdominal compartment syndrome (acs) - the long road to the final publications, how did we get there?

OBJECTIVE

There has been an exponentially increasing interest in intraabdominal hypertension (IAH) and the abdominal compartment syndrome (ACS) over the last decade, and different definitions have been suggested. Nevertheless, there has been an impetus from experts in the field to modify these definitions to reflect our current understanding of the pathophysiology of these syndromes. An international multidisciplinary group of interested doctors met with the goal of agreeing on a set of definitions that could be applied to patients with IAH and ACS. The goal of this consensus group was to provide a conceptual and practical framework to further define ACS, a progressive injurious process that falls under the generalized term 'IAH' and that includes IAH-associated organ dysfunction.

DESIGN

In total, 21 North American, Australasian and European surgical, trauma and critical care specialists agreed to standardize the current definitions for IAH, ACS and related conditions in preparation for the second World Congress on Abdominal Compartment Syndrome (WCACS). The WCACS-meeting was endorsed by the European Society of Intensive Care Medicine (ESICM) and the World Society on Abdominal Compartment Syndrome (WSACS).

METHODS

The consensus conference (Noosa, Australia; December 7, 2004) was attended by 21 specialists from Europe, Australasia and North America and approximately 70 other congress participants. In advance of the conference, a blueprint for the various definitions was suggested. After the conference the participants corresponded electronically with feedback. A writing committee was formed at the conference and developed the final manuscript based on executive summary documents generated by each participant. The final report of the 2004 International ACS Consensus Definitions Conference has recently been published. This article will describe the long road towards this final publication with the evolution of the different definitions and recommendations from the initial suggestions in 2004 to the further refinement and final publications in 2006 and 2007. It will try to explain how we got there and will also give the percentage of agreement with each proposed definition by the participants.

RESULTS

New definitions were offered for some terms, while others were discarded and not kept in the final manuscript. Different cut-offs for defining IAH and ACS were given, as well as broad definitions of primary, secondary and recurrent IAH/ACS. A classification system was introduced taking into account the duration, origin, and etiology of IAH. The use of an organ severity scoring method, by means of the Sequential Organ Failure Assessment (SOFA) score when dealing with ACS patients was not recommended as an adjunctive tool to assess morbidity in the final publication.

CONCLUSION

This document reflects a process whereby a group of experts and opinion leaders suggested definitions for IAH and ACS. This document should be used as a reference for the next consensus definitions conference in March 2007.

Measurement of intra-abdominal pressure in dogs and cats

OBJECTIVE

To review and summarize the human and veterinary literature on intra-abdominal pressure measurement techniques.

DATA SOURCES

Human and veterinary clinical studies, research articles, reviews, and textbooks with no date restrictions with a focus on techniques for intra-abdominal pressure (IAP) measurement and their limitations.

HUMAN DATA SYNTHESIS

Human literature has established the intravesicular method as the gold standard for indirect measurement of IAP. However, current research has explored the intragastric method as a valid alternative. Recently, debate has focused on the shortcomings of the various measurement methods.

VETERINARY DATA SYNTHESIS

Early human literature using dogs as models contributed to the original data for IAP measurements in small animals. Since that time, a number of clinical studies and 1 case report have contributed to that original information. A reference interval for IAP measured by the intravesicular method has recently been determined in healthy cats.

CONCLUSIONS

Further studies investigating IAP in critically ill veterinary patients are required to establish the optimal technique for this measurement in veterinary medicine.

Identifying the association among risk factors and mortality in trauma patients with intra-abdominal hypertension and abdominal compartment syndrome

Intra-abdominal hypertension and abdominal compartment syndrome (ACS) have become key players in increasing mortality among critically ill trauma patients. Many risk factors place the trauma patient at risk for developing ACS. Very few studies exist to establish a predictive relationship between any one risk factor and mortality among these patients. A retrospective, nonexperimental, descriptive project considering preidentified risk factors and their direct association with mortality in patients exhibiting intra-abdominal hypertension and ACS was carried out in an urban level 1 trauma center. Polytransfusion was strongly predicted among those with ACS for mortality (P < .001). Mortality was strongly associated with a reported history of diabetes (P < .05). The total amount of blood products showed a perfect correlation with death as well (r = 1.0, P < .001).

The effect of body position on compartmental intra-abdominal pressure following liver transplantation

BACKGROUND

Current assumptions rely on intra-abdominal pressure (IAP) being uniform across the abdominal cavity. The abdominal contents are, however, a heterogeneous mix of solid, liquid and gas, and pressure transmission may not be uniform. The current study examines the upper and lower IAP following liver transplantation.

METHODS

IAP was measured directly via intra-peritoneal catheters placed at the liver and outside the bladder. Compartmental pressure data were recorded at 10-min intervals for up to 72 h following surgery, and the effect of intermittent posture change on compartmental pressures was also studied. Pelvic intra-peritoneal pressure was compared to intra-bladder pressure measured via a FoleyManometer.

RESULTS

A significant variation in upper and lower IAP of 18% was observed with a range of differences of 0 to 16 mmHg. A sustained difference in inter-compartmental pressure of 4 mmHg or more was present for 23% of the study time. Head-up positioning at 30° provided a protective effect on upper intra-abdominal pressure, resulting in a significant reduction in all patients. There was excellent agreement between intra-bladder and pelvic pressure.

CONCLUSIONS

A clinically significant variation in inter-compartmental pressure exists following liver transplantation, which can be manipulated by changes to body position. The existence of regional pressure differences suggests that IAP monitoring at the bladder alone may under-diagnose intra-abdominal hypertension and abdominal compartment syndrome in these patients. The upper and lower abdomen may need to be considered as separate entities in certain conditions.

Evaluating intra-abdominal pressures in a porcine model of acute lung injury by using a wireless motility capsule

BACKGROUND

Intra-vesical pressure measurement as the reference standard for assessing intra-abdominal pressures is mainly indirect and discontinuous. We therefore evaluated a motility capsule for continuous intra-abdominal pressure measurement in an animal model with a high probability for capillary leakage and intestinal edema.

MATERIAL/METHODS

Motility capsules were inserted into the stomachs of 8 anesthetized and ventilated pigs. Stomach pH, pressure, and temperature data were wirelessly transmitted to a recorder attached to each animal's abdomen. Intra-gastric pressures measured by the capsule were compared to intra-vesical pressures measured by a pressure transducer system.

RESULTS

The intra-abdominal pressures ranged from 3 to 15 mmHg (7.8 ± 2.4 mmHg [mean ± SD]) measured via the bladder. The capsule pressure recordings ranged from 1 to 3 mmHg (1.7 ± 0.5 mmHg [mean ± SD]). Bland-Altman analysis revealed an unacceptable bias between the 2 methods. The test bias was 6.2 (± 1.4) mmHg and the limits of agreement were from 3.3 to 8.9 mmHg.

CONCLUSIONS

Pressures in the stomach as measured by motility capsule underestimated the intra-vesical pressures. Discrepancies between gastric and intra-vesical pressures could be caused by gastric dilatation or different position of the 2 devices to the zero reference point.

A Novel Method (CiMON) for Continuous Intra-Abdominal Pressure Monitoring: Pilot Test in a Pig Model

Background. Intravesical pressure (IAP(ivp)) measurement is considered to be the gold standard for assessment of intra-abdominal pressure (IAP). This study evaluated a new minimally invasive IAP monitoring device (CiMON) against three other devices in a wide range of clinically relevant IAP and in different body positions in healthy pigs. Methods. The CiMON catheter (IAP(CiM)) and another balloon-tipped catheter (IAP(spie)) were positioned into the stomach. Fluid-filled catheters were used for direct intraperitoneal (IAP(dir)) and IAP(ivp) measurement. Both in supine and 25° head-of-bed positions, IAP was increased from baseline to 30 mmHg. At every IAP level, 4 IAP measurements were recorded simultaneously. Mean differences and the limits of agreement were calculated. Results. Bias between IAP(CiM) and IAP(spie) was nearly zero with very good agreement, both in supine and 25° position. In supine position, IAP(CiM) slightly overestimated IAP(ivp) and IAP(dir) by 1.5 and 2.1 mmHg with reasonable agreement. In 25° position, IAP(CiM) underestimated IAP(ivp) and IAP(dir) by 1.0 and 0.5 mmHg, again with reasonable agreement. Conclusions. Agreement between IAP(CiM) and IAP(spie) was very good, while good-to-moderate agreement exists between IAP(CiM) and IAP(dir) or IAP(ivp). Simplicity, continuous monitoring, and the combination with a feeding tube should lead to further clinical studies, evaluating this new CiMON device.

Abdominal compartment syndrome - Intra-abdominal hypertension: Defining, diagnosing, and managing

Abdominal compartment syndrome (ACS) and intra-abdominal hypertension (IAH) are increasingly recognized as potential complications in intensive care unit (ICU) patients. ACS and IAH affect all body systems, most notably the cardiac, respiratory, renal, and neurologic systems. ACS/IAH affects blood flow to various organs and plays a significant role in the prognosis of the patients. Recognition of ACS/IAH, its risk factors and clinical signs can reduce the morbidity and mortality associated. Moreover, knowledge of the pathophysiology may help rationalize the therapeutic approach. We start this article with a brief historic review on ACS/IAH. Then, we present the definitions concerning parameters necessary in understanding ACS/IAH. Finally, pathophysiology aspects of both phenomena are presented, prior to exploring the various facets of ACS/IAH management.

[Intraabdominal hypertension and abdominal compartment syndrome]

Although intraabdominal pressure (IAP) has been studied for more than 100 years, the concepts of intraabdominal hypertension (IAH) and abdominal compartmental syndrome (ACS) have only been developed as clinical entities of interest in intensive care in the last 5 years. At the first Congress on Abdominal Compartment Syndrome in December 2004, a series of definitions were established, which were published in 2006. IAH is defined as IAP ≥ 12 mmHg and is classified in four severity grades, the maximum grade being ACS, with the development of multiorgan failure. The incidence of IAH in patients in intensive care units is high, around 30% at admission and 64% in those with a length of stay of 7 days. The increase in IAP leads to reduced vascular flow to the splenic organs, increased intrathoracic pressure and decreased venous return, with a substantial reduction in cardiac output. If IAH persists, these physiopathologic episodes are followed by the development of multiorgan failure with renal, cardiocirculatory and respiratory failure and intestinal ischemia. Mortality from untreated ACS is higher than 60%. The only treatment for ACS is surgical decompression. In patients with moderate IAH, medical treatment should be optimized, based on the following measures: a) serial IAP monitoring; b) optimization of systemic perfusion and the function of the distinct systems in patients with high IAP; c) instauration of specific measures to decrease IAP; and d) early surgical decompression for refractory IAH. The application of the medical measures that can reduce IAP and early abdominal decompression in ACS improve survival in critically ill patients with IAH.

Intra-abdominal hypertension: evolving concepts

This article focuses primarily on the recent literature on abdominal compartment syndrome (ACS) and the definitions and recommendations published by the World Society for the Abdominal Compartment Syndrome. The definitions regarding increased intra-abdominal pressure (IAP) are listed and are followed by an overview of the different mechanisms of organ dysfunction associated with intra-abdominal hypertension (IAH). Measurement techniques for IAP are discussed, as are recommendations for organ function support and options for treatment in patients who have IAH. ACS was first described in surgical patients who had abdominal trauma, bleeding, or infection; but recently, ACS has been described in patients who have other pathologies. This article intends to provide critical care physicians with a clear insight into the current state of knowledge regarding IAH and ACS.

Abdominal compartment syndrome — the new killer

Abdominal compartment syndrome (ACS) results from an increase in intra-abdominal pressure (IAP) within the relatively fixed confines of the abdominal cavity. This increase in abdominal pressure can have deleterious consequences on multiple organ systems and amongst the intensive care population is associated with increased morbidity and mortality. Trauma victims commonly have multiple risk factors for the development of ACS, yet in the past routine measurement of IAP in intensive care patients in the UK has been variable. Recent consensus guidelines have helped to clarify the identification, diagnosis and management of patients at risk of ACS.

Gastrointestinal microcirculation and cardiopulmonary function during experimentally increased intra-abdominal pressure

OBJECTIVES

The aim of this study was to assess gastric, intestinal, and renal cortex microcirculation parallel with central hemodynamics and respiratory function during stepwise increase of intra-abdominal pressure (IAP).

DESIGN

Prospective, controlled animal study.

SETTING

Research laboratory, University Hospital.

SUBJECTS

Twenty-six anesthetized and mechanically ventilated pigs.

INTERVENTIONS

Following baseline registrations, CO2 peritoneum was inflated (n = 20) and IAP increased stepwise by 10 mm Hg at 10 mins intervals up to 50 mm Hg and subsequently exsufflated. Control animals (n = 6) were not insufflated with CO2.

MEASUREMENTS AND MAIN RESULTS

The microcirculation of gastric mucosa, small bowel mucosa, small bowel seromuscular layer, colon mucosa, colon seromuscular layer, and renal cortex were selectively studied at all pressure levels and after exsufflation using a four-channel laser Doppler flowmeter (Periflex 5000, Perimed). Central hemodynamic and respiratory function data were registered at each level and after exsufflation. Cardiac output decreased significantly at IAP levels above 10 mm Hg. The microcirculation of gastric mucosa, renal cortex and the seromuscular layer of small bowel and colon was significantly reduced with each increase of IAP. The microcirculation of the small bowel mucosa and colon mucosa was significantly less affected compared with the serosa (p < 0.01).

CONCLUSIONS

Our animal model of low and high IAP by intraperitoneal CO2-insufflation worked well for studies of microcirculation, hemodynamics, and pulmonary function. During stepwise increases of pressure there were marked effects on global hemodynamics, respiratory function, and microcirculation. The results indicate that intestinal mucosal flow, especially small bowel mucosal flow, although reduced, seems better preserved in response to intra-abdominal hypertension caused by CO2-insufflation than other intra-abdominal microvascular beds.

Abdominal compartment syndrome: A review

OBJECTIVES

The aims of this review were to summarize a) the consensus definitions of normal and pathologic intra-abdominal pressure (IAP); b) the techniques to measure IAP; c) the risk factors for intra-abdominal hypertension (IAH) and abdominal compartment syndrome (ACS); d) the pathophysiology of ACS; and e) the current recommendations for management and prevention of ACS.

DATA SOURCES

PubMed was searched using the following terms: ACS, IAH, IAP, and abdominal decompression.

DATA SYNTHESIS

ACS represents the natural progression of end-organ dysfunction caused by increased IAP and develops if IAH is not recognized and treated appropriately. Although the reported incidence of ACS is relatively low in critically ill children (0.6%-4.7%) it may be under-recognized and under-reported. The diagnosis of IAH/ACS depends on a high index of suspicion and the accurate and frequent measurement of IAP in patients at risk. Mortality from ACS remains high (50%-60%) even when decompression of the abdomen is performed early, which highlights the importance of detection and treatment of elevated IAP before end-organ damage occurs.

CONCLUSIONS

A widespread awareness of the recognition and current approach to management and prevention of IAH and ACS is needed among pediatric intensivists, so outcome of these life-threatening disease processes might be improved.

Incidence and clinical effects of intra-abdominal hypertension in critically ill patients

OBJECTIVE

The objective of this study was to determine the epidemiology and outcomes of intra-abdominal hypertension in a heterogeneous intensive care unit population.

DESIGN

This was a prospective cohort study.

SETTING

This study was conducted at a medical-surgical intensive care unit in a university hospital.

PATIENTS

Study patients included all those consecutively admitted during 9 months, staying > 24 hrs, and requiring bladder catheterization.

MEASUREMENTS AND MAIN RESULTS

On admission, epidemiologic data and risk factors for intra-abdominal hypertension were studied; then, daily maximal and mean intra-abdominal pressures (IAP(max) and IAP(mean)), abdominal perfusion pressure, fluid balances, filtration gradient, and sequential organ failure assessment score, were registered. IAPs were recorded through a bladder catheter every 6 hrs until death, discharge, or along 7 days. Intra-abdominal hypertension was defined as IAP > or = 12 mm Hg. Abdominal compartment syndrome was defined as IAP > or = 20 mm Hg plus > or = 1 new organ failure. Main outcome measure was hospital mortality. Of 83 patients, considering IAP(max), 31% had intra-abdominal hypertension on admission and another 33% developed it after (23% and 31% with IAP(mean)). Main risk factors were mechanical ventilation, acute respiratory distress syndrome, and fluid resuscitation (relative risk, 5.26, 3.19, and 2.50, respectively). Patients with intra-abdominal hypertension were sicker, had higher mortality (53% vs. 27%, p = .02), and consistently showed higher total and renal sequential organ failure assessment score, daily and cumulative fluid balances, and lower filtration gradient. Nonsurvivors had higher IAP(max), IAP(mean), and fluid balances and lower abdominal perfusion pressure. Abdominal compartment syndrome developed in 12%; 20% survived. Logistic regression identified IAP(max) as an independent predictor of mortality (odds ratio, 1.17; 95% confidence interval, 1.05-1.30; p = .003) after adjusting with Acute Physiology and Chronic Health Evaluation II and comorbidities (odds ratio, 1.15; 95% confidence interval, 1.06-1.25; p = .001; and odds ratio, 2.68; 95% confidence interval, 1.27-5.67; p = .013, respectively). Models with IAP(mean) and abdominal perfusion pressure also performed well. Areas under receiver operating characteristic curves were .81 and .83.

CONCLUSIONS

Intra-abdominal hypertension, diagnosed either with IAP(max) or IAP(mean), was frequent and showed an independent association with mortality. Intra-abdominal hypertension was significantly associated with more severe organ failures, particularly renal and respiratory, and a prolonged intensive care unit stay.

Validation and experience with a simple continuous intra-abdominal pressure measurement technique in a multidisciplinary medical/surgical critical care unit

BACKGROUND

Raised intra-abdominal pressure (IAP) or intra-abdominal hypertension (IAH) may induce many adverse effects including the abdominal compartment syndrome. We evaluated a new technique for continuous monitoring of intra-abdominal pressure (CIAP) using a standard three-way bladder catheter in a diverse group of intensive care unit patients.

METHODS

CIAP measured using a standard three-way bladder catheter was compared with five standard intermittent IAP (IIAP) measurements in 79 patients.

RESULTS

Mean (standard deviation) CIAP was identical (15.4 mm Hg [5.8]) for CIAP and IIAP one minute after saline injection. Mean differences between methods were less than 1 mm Hg, and similar whether IIAP was measured at 1 minute, 2 minutes, 3 minutes, 4 minutes, or 5 minutes. Bland-Altman analysis comparing CIAP and IIAP (1 minute) revealed a mean difference (95% confidence interval) of -0.06 mm Hg (-0.51, 0.39). Limits of agreement were -4.12 mm Hg to 4.00 mm Hg. Considering gradations of IAH defined by the World Society of the Abdominal Compartment Syndrome, CIAP was sensitive for detecting slightly elevated IAP (>11 mm Hg) but is less sensitive for distinguishing between higher grades of IAH (e.g., pressures >20 mm Hg or 25 mm Hg). Limits of agreement were best for patients with IAP less than 20 mm Hg, surgical or traumatic diagnoses and for patients with BMI less than 26.

CONCLUSIONS

Overall, CIAP is an accurate and simple means of measuring IAP when compared with the current standardized method. Elevated CIAP measurements should be confirmed with IIAP measurements if accurate grading is required until further validation and experience is obtained.

Abdominal compartment syndrome: clinical aspects and monitoring

Markedly elevated intra-abdominal pressures will result in predictable hemodynamic consequences related to compromised venous return. When the hemodynamic abnormalities are associated with organ dysfunction of failure, patients suffer from the abdominal compartment syndrome. At-risk patients should be routinely monitored for intra-abdominal hypertension, and a multidisciplinary care paradigm should be established. Vigorous resuscitation of both surgical and medical patients highly correlates with IAH and ACS risk. Vigilance, prompt diagnosis, and intervention for abdominal compartment syndrome will reduce the morbidity and mortality in critically ill. Future challenges include altering resuscitation strategies to reduce ascites formation, earlier diagnosis of organ dysfunction, and intra-organ monitoring techniques.

Abdominal compartment syndrome

Compartment syndrome is a pathophysiological term, comprising a variety of tissues and organ alterations, due to a higher than normal pressure in an anatomically detached space (compartment). In the human body, areas denoted as compartments include the orbital globe, the sub and epidural space, the abdomen, pleura, pericardium, and others. Compartment syndrome was described initially in limbs. Abdominal compartment syndrome is defined as an intra-abdominal pressure above 20 mmHg with evidence of organ failure. Abdominal compartment syndrome develops when the intra-abdominal pressure rapidly reaches certain pathological values, within several hours (intra-abdominal hypertension is observed), and lasts for 6 or more hours. The key to recognizing abdominal compartment syndrome is the demonstration of elevated intra-abdominal pressure which is performed most often via the urinary bladder, and it is considered to be the "gold standard." Multiorgan failure includes damage to the cardiac, pulmonary, renal, neurological, gastrointestinal, abdominal wall, and ophthalmic systems. The gut is the most sensitive to intra-abdominal hypertension, and it develops evidence of end-organ damage before alterations are observed in other systems. The surgical decompression of the abdomen remains the treatment of choice of abdominal compartment syndrome; this usually improves the organ changes, and is followed by one of the temporary abdominal closure techniques in order to prevent secondary intra-abdominal hypertension.

In vitro validation of a novel method for continuous intra-abdominal pressure monitoring

OBJECTIVE

Intra-abdominal pressure (IAP) measurement is important in daily clinical practice. Most measurement techniques vary in automaticity and reproducibility. This study tested a new fully automated continuous technique for IAP measurement, the CiMON.

METHODS

Three IAP measurement catheters (a Foley manometer and two balloon-tipped catheters) contained in a 50-ml infusion bag were placed on the bottom of a half open 3-l container. To simulate IAH the container was filled with water using 5 cmH2O increments (0-30 cmH2O). Pressure was estimated by observers using the Foley manometer (IAP(FM)) and simultaneously recorded using two IAP monitors: IAP(spie) with Spiegelberg and IAP(CiM) with CiMON. Observers were blinded to the reference levels. Fifteen observers (three intensivists, four residents, two medical students, and six nurses) conducted three pressure readings at each of the seven pressure levels with the FM technique, giving 315 readings. These were paired with the automated IAP(spie) and IAP(CiM) readings and the height of the H2O column.

RESULTS

The intra- and interobserver coefficients of variation (COVA) were low for all methods. There was no difference in the results between specialists, physicians in training, andnurses. Spearman's correlation coefficient (R2) values for all paired measurements were greater than 0.9, and Bland-Altman analysis comparing the reference H2O column, IAP(FM), and IAP(spie) to IAP(CiM) showed a very good agreement at all pressure levels (bias -0.1+/-0.6 cmH2O, 95%CI -0.2 to 0). There was a consistent, low underestimation of the reference H2O pressure by the Spiegelberg technique and a low overestimation at pressures below 20 cmH2O by both other techniques.

CONCLUSIONS

All three measurement techniques, IAP(FM), IAP(spie), and IAP(CiM) have good agreement with the applied hydrostatic pressure in this in vitro model of IAP measurement.

Abdominal compartment syndrome

The term abdominal compartment syndrome (ACS) describes the clinical manifestations of the pathologic elevation of the intra-abdominal pressure (IAP). When the IAP exceeds 12 mm Hg it is referred to as intra-abdominal hypertension (IAH) while ACS generally sets in at an IAP in excess of 20 mm Hg. This syndrome is most commonly observed in the setting of severe abdominal trauma and in the aftermath of major abdominal operations. ACS affects mainly the respiratory, cardiovascular, renal, gastrointestinal and the central nervous systems. Fundamental to the development of ACS are the obstruction of venous return to the heart via the inferior vena cava and the splinting of the diaphragm due to elevated IAP. Preventing ACS by the identification of patients at risk and early diagnosis is paramount to its successful management. To this end a high index of suspicion is sine qua non. The management of established ACS requires clinical astuteness and decisiveness with a readily available and generous team support. The purpose of this review is to enhance awareness among clinicians about a subtle condition with a devastating impact on morbidity and mortality if undiagnosed.

Results from the International Conference of Experts on Intra-abdominal Hypertension and Abdominal Compartment Syndrome. I. Definitions

OBJECTIVE

Intra-abdominal hypertension (IAH) and abdominal compartment syndrome (ACS) have been increasingly recognized in the critically ill over the past decade. The variety of definitions proposed has led to confusion and difficulty in comparing one study to another.

DESIGN

An international consensus group of critical care specialists convened at the second World Congress on Abdominal Compartment Syndrome to standardize definitions for IAH and ACS based upon the current understanding of the pathophysiology surrounding these two syndromes.

METHODS

Prior to the conference the authors developed a blueprint for the various definitions, which was further refined both during and after the conference. The present article serves as the final report of the 2004 International ACS Consensus Definitions Conference and is endorsed by the World Society of Abdominal Compartment Syndrome (WSACS).

RESULTS

IAH is redefined as an intra-abdominal pressure (IAP) at or above 12 mmHg. ACS is redefined as an IAP above 20 mmHg with evidence of organ dysfunction/failure. ACS is further classified as either primary, secondary, or recurrent based upon the duration and cause of the IAH-induced organ failure. Standards for IAP monitoring are set forth to facilitate accuracy of IAP measurements from patient to patient.

CONCLUSIONS

State-of-the-art definitions for IAH and ACS are proposed based upon current medical evidence as well as expert opinion. The WSACS recommends that these definitions be used for future clinical and basic science research. Specific guidelines and recommendations for clinical management of patients with IAH/ACS are published in a separate review.