Normal Intraabdominal Pressure in Healthy Adults

Journal of Surgical Research 129, 231–235 (2005) doi:10.1016/j.jss.2005.06.015 Normal Intraabdominal Pressure in Healthy Adults William S. Cobb, M.D.,1 Justin M. Burns, M.D., Kent W. Kercher, M.D., Brent D. Matthews, M.D., H. James Norton, Ph.D., and B. Todd Heniford, M.D. Carolinas Laparoscopic and Advanced Surgery Program, Carolinas Medical Center, Charlotte, North Carolina Submitted for publication February 18, 2005 Background. Intraabdominal pressure (IAP) has been considered responsible for adverse effects in trauma and other abdominal catastrophes as well as in formation and recurrence of hernias. To date, little information is available concerning IAP in normal persons. Our purpose in this study was to measure the normal range of IAP in healthy, nonobese adults and correlate these measurements with sex and body mass index (BMI). Methods. After Institutional Review Board approval, 20 healthy young adults (<30 years old) with no prior history of abdominal surgery were enrolled. Pressure readings were obtained through a transurethral bladder (Foley) catheter. Each subject performed 13 different tasks including standing, sitting, bending at the waist, bending at the knees, performing abdominal crunches, jumping, climbing stairs, bench-pressing 25 pounds, arm curling 10 pounds, and performing a Valsalva and coughing while sitting and also while standing. Data were analyzed by Student’s t-test and Pearson’s correlation coefficients Results. Intraabdominal pressure was measured in 10 male and 10 female subjects. The mean age of the study group was 22.7 years (range, 18 –30 years), and BMI averaged 24.6 kg/m2 (range, 18.4 –31.9 kg/m2). Mean IAP for sitting and standing were 16.7 and 20 mm Hg. Coughing and jumping generated the highest IAP (107.6 and 171 mm Hg, respectively). Lifting 10pound weights and bending at the knees did not generate excessive levels of pressure with the maximum average of 25.5 mm Hg. The mean pressures were not different when comparing males and females during 1 To whom correspondence and reprint requests should be addressed at Division of Gastrointestinal and Minimally Invasive Surgery, Carolinas Laparoscopic and Advanced Surgery Program, Carolinas Medical Center, 1000 Blythe Blvd., MEB #601, Charlotte, NC 28203. E-mail: [email protected]. each maneuver. There was a significant correlation between higher BMI and increased IAP in 5 of 13 exercises. Conclusion. Normal IAP correlates with BMI but does not vary based on sex. The highest intraabdominal pressures in healthy patients are generated during coughing and jumping. Based on our observations, patients with higher BMI and chronic cough appear to generate significant elevation in IAP. Thus, this group of patients may potentially be at increased risk for abdominal wall hernia formation following surgery. © 2005 Elsevier Inc. All rights reserved. Key Words: pressure; abdomen; hernia; urinary catheterization; valsalva maneuver. INTRODUCTION The importance of elevated intraabdominal pressure (IAP) has been recognized in the trauma and critical care literature for its potential detrimental effects [1, 2]. Elevations in IAP can have several adverse effects such as decreased cardiac output due to reduced venous return, reduced splanchnic and hepatic perfusion, and decreased renal blood flow and glomerular filtration rate [3]. With improvements in the management of the multiorgan dysfunction patient and a better understanding of volume resuscitation and the effects of ischemia-reperfusion injury, the calculation of IAP has become an important adjunct in the care of the critically injured patient. Recently, the role of IAP as it pertains to hernia repair has been investigated. Junge and colleagues have attempted to study the elasticity and tensile strength of the abdominal wall [4]. Calculations based on Pascal’s principle of hydrostatics have predicted the maximum tensile strength of the abdominal wall to be 16 N/cm [5]. Polypropylene mesh has been shown to have a bursting strength that is more than 10 times this calculated force. Based on their mathematical 231 0022-4804/05 $30.00 © 2005 Elsevier Inc. All rights reserved. 232 JOURNAL OF SURGICAL RESEARCH: VOL. 129, NO. 2, DECEMBER 2005 models and stereotaxy of human abdominal walls, it is hypothesized that the currently available prosthetics may in fact be overengineered, or more dense and less compliant than needed for an optimal hernia repair [5]. However, the abdominal wall pressures are calculated and not a direct measure. Due to the invasiveness of direct IAP measurement, the measurement of urinary bladder pressure via a bladder catheter has been used as an indirect method of determining IAP [6, 7]. The majority of intensive care patients have a bladder catheter in place, making bladder pressure measurement a readily accessible option for patients at risk for abdominal compartment syndrome. To date, little information is available regarding IAP measurements in noncritically ill patients. Fusco and colleagues evaluated bladder pressure during laparoscopy and showed a close approximation between IAP and bladder pressure [8]. In an attempt to determine a normal range for IAP, Sanchez and coworkers measured IAP in hospitalized patients with bladder catheters in place. They found a mean value of 6.2 mm Hg and a significant relationship between body mass index (BMI), recent abdominal surgery, and IAP [9]. Investigators are currently using indirect pressure measurements for clinical applications. Shafik et al. recorded IAP with an anal manometric catheter during straining and evaluated the effects of increased abdominal pressure on the function of the perineal musculature [10]. The IAP generated during typical daily activities cannot be adequately evaluated in critically ill patients on mechanical ventilation or in patients hospitalized after recent surgery; therefore, a study in healthy subjects was undertaken. The goal of this study was to evaluate multiple healthy subjects to determine a normal range of IAP during typical activities of daily living. This would provide information to establish a baseline force that abdominal closure and hernia repair techniques, including prosthetic biomaterials, must withstand to be considered adequate. We anticipated that there would be a wide range of forces depending on the type of activity performed. The information generated may allow for subsequent comparison studies using variables such as gender or body mass index (BMI). METHODS This study was designed to measure urinary bladder pressure in healthy subjects performing a variety of actions common in daily living. Approval for the study design was granted by the Institutional Board Review at the Carolinas Medical Center. Informed consent was obtained from each patient before enrollment. Healthy subjects without significant medical problems between 18 and 30 years of age were eligible. Patients were excluded if they had any known physical limitations that would prevent physical activities including sit-ups, jumping, bench-pressing 25 pounds, or lifting 10 pounds. Additionally, pregnancy, the prestudy diagnosis of a urinary tract infection, previous abdominal surgery, heart disease, lung disease, degenerative joint disease, neurological disorders, seizure disorders, or the use of prescribed or illicit drugs that may affect balance were reasons for exclusion. For this study, nonmorbidly obese subjects with a body mass index ⬍30 kg/m2 were selected for enrollment. Ten male and 10 female adults were enrolled in the study. Prior to participation, a medical history was obtained, and a physical examination was performed on each subject by a physician. A baseline urinary analysis was performed on all subjects to evaluate for an underlying urinary tract infection which would exclude the person from participating. A Foley catheter was inserted into the urinary bladder using standard sterile techniques by a licensed healthcare professional (R.N. or M.D.). The bladder was filled with 50 mL of sterile saline using a previously described closed-system technique [11]. The hydrostatic pressure in the bladder was obtained by connecting the catheter to a pressure transducer with sterile tubing [6]. The line was cleared of air bubbles, and the transducer was zeroed while the patient was supine. The pressure transducer was clipped to the patients’ waist to place it at the level of the symphysis pubis for an accurate reading. Pressure measurements were made in mm Hg. Three separate measurements were recorded with the patient relaxed in both the supine and the standing position. The patients then performed routine bodily functions including coughing and straining against a closed epiglottis (Valsalva maneuver) while sitting and again while standing. Measurements were then recorded during simple tasks such as sitting in a chair, rising from a chair, jumping in place, bending at the waist, genuflecting, and walking up a flight of stairs. Study subjects performed more strenuous exercises, such as abdominal crunches, bench-pressing 25 pounds, and armcurling a 10-pound weight. For each activity, the peak pressure obtained was recorded, the activity repeated, and a total of three separate measurements recorded. Once the battery of 13 maneuvers was complete, the bladder was emptied, refilled with 50 mL of saline, and rezeroed in the supine position. Measurements were then repeated three times for the 13 different maneuvers. A total of nine measurements were obtained for each subject during each of the 13 exercises. Data were analyzed using standard statistical methods. Descriptive statistics including means, ranges, and standard deviations were used to describe the maximum IAP measurement for each subject, each activity, and by gender for each activity. A Shapiro– Wilk test was performed for each maneuver to determine if the data were equally distributed. Comparisons between male and female participants were made using a Student’s t-test. Pearson’s correlation coefficients were used to determine the relationship of BMI and IAP for each of the 13 maneuvers. A P value of ⬍0.05 was considered significant for all tests. The SAS® System, version 8.02 (SAS Institute, Inc., Cary, NC) was used to complete all statistical analyses. RESULTS Twenty subjects were enrolled, 10 male and 10 female. The mean age of the study group was 22.7 years (range, 18 –30 years), and BMI averaged 24.6 kg/m2 (range, 18.4 –31.9 kg/m2). The range of the maximum pressures for each of the 13 maneuvers is demonstrated in Table 1. The mean pressure while supine was 1.8 mm Hg with a standard deviation of 2.2. The maximum pressures for coughing and jumping were the highest obtained. Bending at the knees and lifting light amounts of weight did not generate excessive levels of IAP. The mean pressures were not different when comparing males and females during each maneuver. 233 COBB ET AL.: NORMAL INTRAABDOMINAL PRESSURE TABLE 1 Range of Maximum Pressures Generated for Each Maneuver among the 20 Subjects Maneuver Minimum (mm Hg) Maximum (mm Hg) Mean (mm Hg) SD Supine Standing Sitting Stairs Abdominal crunch Bend at waist Bend at knees Cough Standing cough Valsalva Standing Valsalva Jumping Bench press Arm curl ⫺1 15 10 40 7 6 14 40 64 20 32 43 2 17 6 27 21 110 47 30 30 127 141 64 116 252 34 37 1.8 20.0 16.7 68.9 26.7 14.4 20.6 81.4 107.6 39.7 64.9 171 7.4 25.5 2.2 3.8 2.9 17.4 10.7 5.3 4.4 25.6 23.0 11.0 22.0 48.4 7.3 6.0 SD ⫽ standard deviation. There was a significant correlation between higher BMI and increased IAP in 5 of 13 exercises (Table 2). DISCUSSION There is considerable literature on the abdominal compartment syndrome and the different techniques for measuring bladder pressure. Relatively few attempts to quantify IAP in healthy patient populations have been made. Normal IAP was determined to be zero or slightly less than zero based on several studies performed from 1910 to 1940 [12, 13]. Kron and associates randomly measured transurethral bladder pressures in 10 supine patients within the first 24 h following elective surgical procedures. The mean IAP was 7.4 mm Hg (range, 3–13 mm Hg) [6]. A prospective study evaluating IAP in 77 hospitalized patients was performed by Sanchez et al. in 2001. The authors found that mean IAP was increased in patients with higher BMI and with prior abdominal surgery. Based on their calculations, an equation was derived to measure mean “resting” IAP in hospitalized patients [9]. To date, no study evaluating IAP in healthy subjects at rest and during normal activities of daily living has been performed. Historically, IAP has been measured directly via a cannula inserted into the abdominal cavity [13] or by an intraperitoneal catheter connected to a pressure transducer [7, 14]. Measurement of intravesicular or bladder pressure is an effective and convenient “noninvasive” technique to quantify IAP. The wall of the urinary bladder behaves as a passive diaphragm when the bladder is instilled with 50 –100 ml of saline. The accuracy of bladder pressure as a measure of IAP was verified by Iberti and colleagues [15]. In a canine model, the investigators compared bladder pressure measurements with IAP at different pressures generated by instilling saline in the abdomen. Over a range of 10 to 70 mm Hg, bladder pressures did not differ significantly from the direct IAP measurements [15]. Clinically, the validity of bladder pressures was proven by Fusco et al. [8] Thirty-seven patients undergoing laparoscopy had intravesicular pressures measured at IAPs of 0, 5, 10, 15, 20, and 25 mm Hg. Different volumes of saline were instilled into the bladder, and measurements were compared over the range of pressures. The authors found that bladder pressure readings differed only by an average of 0.79 mm Hg for all pressures when the bladder was empty. For the highest IAP (25 mm Hg), a bladder volume of 50 ml had the lowest bias; the bladder pressure was 1 to 3 mm Hg higher than the measured IAP [8]. Additionally, Yol and colleagues compared bladder pressure with insufflator pressure during laparoscopic cholecystectomy in healthy adults with no prior history of surgery. The two measurements of IAP correlated well with one another (r ⫽ 0.973, P ⬍ 0.0001) [16]. Given this information, the most accurate, noninvasive technique for estimating IAP is the transurethral measure of bladder pressure. The importance of quantifying IAP has been well recognized in the management of critically injured or multiorgan dysfunction patients. The diagnosis and management of intraabdominal hypertension and the abdominal compartment syndrome are largely influenced by the estimation of IAP via bladder pressures. In a survey of trauma surgeons, 71% of those responding said that bladder pressure measurements were largely responsible for the decision to perform abdominal decompression [17]. Intraabdominal pressure also plays a significant role in abdominal wall hernia forTABLE 2 Relationship of Body Mass Index and Intraabdominal Pressure Maneuver Correlation coefficient P value Supine Standing Sitting Stairs Abdominal crunch Bend at waist Bend at knees Cough Standing cough Valsalva Standing Valsalva Jumping Bench press Arm curl 0.41 0.63 0.43 0.28 ⫺0.11 0.41 0.65 0.75 0.84 0.40 0.53 0.33 0.14 0.30 0.07 0.003* 0.06 0.23 0.65 0.07 0.002* 0.0001* ⬍0.0001* 0.08 0.02* 0.16 0.56 0.20 * Statistically significant correlation between body mass index and intraabdominal pressure. 234 JOURNAL OF SURGICAL RESEARCH: VOL. 129, NO. 2, DECEMBER 2005 mation. Prior calculations using Pascal’s principle of hydrostatics have estimated that the maximum tensile strength of cadaveric abdominal walls is 16 N/cm [4]. Prosthetic materials for hernia repair, fixation devices to secure the mesh, and the subsequent fixation strength at the mesh–tissue interface after collagenous ingrowth must withstand this force. Prosthetic biomaterials are frequently used to buttress hernia repairs, and decreased recurrence rates have been documented with their use [18 –20]. However, the forces acting on the abdominal wall that these materials must resist has not been accurately measured. In fact, until recently, they had been poorly studied. It has been suggested by several investigators that many of the current mesh materials used for hernia repair restrict normal abdominal wall mobility because they are actually much stronger and stiffer than needed for an adequate repair [21]. Second- and thirdgeneration prosthetic biomaterials have been developed, which are intentionally less dense (g/cm2) with less tensile strength (N/cm) than standard, nonabsorbable mesh, and which are more compliant with abdominal wall motion and more resistant to contraction due to reduced inflammation and good tissue ingrowth [5, 22]. These novel biomaterials may provide adequate strength and improved postoperative function; however, little information is available regarding long-term outcomes after implantation. Determining IAP during typical daily activities of healthy subjects provides quantitative benchmarks to evaluate the strength of new mesh products, as well as the adequacy of hernia repair techniques and materials currently in use. In addition, a better grasp of this topic may allow surgeons to understand and explain postoperative “do’s and don’t’s” to our patients to prevent hernia formation after laparotomy or reherniation after repair. Postoperatively, patients who have undergone an abdominal operation are typically instructed not to strain or lift objects weighing more than 10 or 15 pounds. It seems intuitive that, following a fascial incision, a patient should avoid strenuous activity and lifting; however, there is little scientific basis for this assumption. Greater IAPs are generated following coughing and jumping. Patients with chronic obstructive pulmonary disease are likely at greater risk of developing incisional hernias not only due to the poor quality of their fascia but also to the repetitive strain on their wound during coughing episodes. Based on our data, it is plausible that, following abdominal operations, patients may be better served by a cough suppressant or expectorant to reduce their risk of wound dehiscence or herniation. More studies are needed to determine IAP while lifting heavier objects and performing more strenuous activities. In our study, the maximum IAP generated by healthy, nonobese individuals occurred during cough- ing and jumping. While coughing, the maximum IAP was 127 mm Hg while sitting and 141 mm Hg while standing. A pressure as high as 252 mm Hg was obtained while a test subject jumped in place. For Valsalva in this healthy adult population, the maximum pressures were 64 mm Hg while sitting and 116 mm Hg while standing. Considering the abdominal cavity as a cylinder and using Pascal’s principle of hydrostatics, the maximum tensile strengths would range from 11 to 27 N/cm for these exercises. Biomaterials and their fixation devices should tolerate these pressures to minimize the risk of hernia recurrence. Obesity has been shown to increase IAP. It has been determined that severe obesity (BMI ⱖ 35 kg/m2) is a greater risk factor for incisional hernia formation than chronic steroid use [23]. The proposed mechanism for this increased risk is the higher IAP present in the obese patient, especially those with central obesity. In a clinical trial, Sugerman and colleagues measured bladder pressures in their population undergoing gastric bypass and compared them to a “normal” group undergoing colectomy. The mean resting IAP correlated with the sagittal diameter of the abdominal wall [24]. In a series of hospitalized patients, bladder pressures in the supine position were directly related to BMI [9]. Obesity has also been established as a risk factor for recurrence after incisional hernia repair. This patient population often presents with larger defects, requires longer operative times, has more complications, and develops more recurrences [18]. This study demonstrates the direct relationship between increased BMI and elevated IAP. Of the 13 maneuvers performed, 5 demonstrated significant correlation between BMI and IAP. For the abdominal crunch, there was a negative correlation between BMI and IAP. One hypothesis to explain this finding is that the patients with a lower BMI may have more abdominal wall muscle and less fat. More abdominal wall muscle would produce more strain or compression on the abdominal wall during an abdominal crunch, resulting in an increased IAP. This would result in someone with a lower BMI generating a higher pressure during contraction of the abdominal wall. The participants in this study were selected to represent healthy, nonobese individuals, so the range of BMI in this population is limited. Further studies of this type are needed to evaluate morbidly obese individuals and IAP. CONCLUSION Transurethral bladder pressure measurements are an accurate assessment of IAP. Intraabdominal pressure increases as BMI increases but does not vary based on sex. The highest IAPs in healthy, nonobese patients are generated during coughing and jumping. 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