Andersson, S., A. Kronstrom, et al. (1989). "Viscoelastic properties of the normal human bladder." Scand J Urol Nephrol 23(2): 115-20.

Continuous and stepwise cystometry were performed through suprapubic catheters in 12 healthy young subjects in order to assess passive viscoelastic variables of the normal human bladder during the collection phase. Elastic contants increased non-linearly with bladder distension. Relative elastic modulus and relaxation time of the bladder wall increased or tended to increase with bladder distension and infusion rate. There was considerable interindividual variation in all variables suggesting that discrimination between normal and abnormal bladder wall viscoelasticity may be difficult in routine clinical practice.

Intra-abdominal fluid volume and hydrostatic pressure were elevated by positive pressure infusion of Tyrode solution into the peritoneal cavity of anesthetized dogs. The compliance of the peritoneal cavity fell from 10.8 to 0.56 ml X mmHg-1 X kg-1 of body wt as intra-abdominal pressure increased from 0 to 40 mmHg. Intrathoracic pressure also increased as elevated peritoneal pressure caused diaphragmatic bulging. Cardiac output and stroke volume were reduced by 36% after an intra-abdominal pressure rise of 40 mmHg; in contrast, heart rate did not change. Flow in the celiac, superior mesenteric, and renal arteries was reduced by 42, 61, and 70%, respectively. Pressure in the femoral vein increased to 46 mmHg, while flow in the femoral artery decreased by 65%. Whole-body O2 consumption, pH, and arterial PO2 decreased as intra-abdominal pressure rose. The peritoneal cavity, with its high initial compliance, affords the body an ideal location for the temporary accumulation of small to moderate volumes of fluid during episodes of increased vascular pressure or permeability. The marked alterations in the hemodynamic properties of the cardiovascular system are indicative of the physiological changes that occur when intra-abdominal fluid accumulation becomes excessive and peritoneal pressure rises to high levels.

In clinical measurement comparison of a new measurement technique with an established one is often needed to see whether they agree sufficiently for the new to replace the old. Such investigations are often analysed inappropriately, notably by using correlation coefficients. The use of correlation is misleading. An alternative approach, based on graphical techniques and simple calculations, is described, together with the relation between this analysis and the assessment of repeatability.

Positive pressure ventilation with PEEP may be required in patients with increased IAP. Separately, PEEP and increase IAP have been shown in both man and animals to have significant hemodynamic effects. The results of this study demonstrated that, in dogs, the combination of PEEP with elevated IAP results in markedly increased CVP, PCWP, mean PAP and PVR. CO is depressed but to no greater degree than with the combination of IAP and positive pressure ventilation without PEEP. Interestingly, serum lactate levels markedly increase when both PEEP and IAP are applied, a finding not explained by the fall in CO. Possibly, the combination of PEEP with elevated IAP inhibits hepatic metabolism of lactate. Measures taken to reduce IAP and PEEP may not only improve hemodynamics but may result in reduced serum lactate levels.

Elevated intraabdominal pressure (IAP) occurs with intraabdominal bleeding, with tense ascites, or after application of military anti-shock trousers to trauma patients. While changes in renal perfusion with elevated IAP have been documented, there are no data available on blood flow to other viscera. Under pentobarbital anesthesia an inflatable bag was placed intraabdominally to create graded increases in IAP in 9 adult mongrel dogs (20 kg). Hemodynamic parameters and organ blood flow (OBF) using radioactive microspheres were measured at baseline and after increasing the IAP to 20 and 40 mm Hg. The organ blood flow index (OBFI = OBF/cardiac output) was determined for each organ (stomach, duodenum, jejunum, ileum, colon, pancreas, liver, spleen, kidney, and adrenal gland). Elevated IAP caused a decrease in OBF for all organs measured except the adrenal glands where the OBF was increased. The OBFI was decreased significantly for all intraabdominal viscera except the renal cortex and the adrenal gland. These changes in OBF are more marked than can be accounted for by changes in cardiac output alone, suggesting that local control mechanisms may be responsible for changes in OBF. Our data raise the possibility that elevation in IAP may result in visceral ischemia and organ dysfunction.

Oliguria in association with elevated intra-abdominal pressure developed in a patient with an ovarian mass. Operative decompression of the abdomen reversed the oliguric state. Clinically, laparotomy may be indicated in the presence of decreasing urinary output and elevated intra-abdominal pressure.

Massive elevation of intra-abdominal pressure (IAP) causes cardiovascular, respiratory, and renal dysfunction. We managed eight patients with high IAP (mean 51 +/- 7 cm H2O), six of whom had hemodynamic measurements; a clinical syndrome, characterized by hemodynamic, respiratory, and renal dysfunction, then became apparent. We report a) a baseline cardiopulmonary profile and response to an acute vascular volume challenge in six patients and b) surgical decompression of the abdomen in four patients. The clinical impression of hypovolemia was confused by small to normal left ventricular end-diastolic volume (64 +/- 14 ml) and normal ejection fraction (55 +/- 6%) despite very high right and left atrial filling pressures. Complete ventilatory support was necessary to maintain oxygenation and ventilation; oliguria (urine output less than 10 ml/h) was present. Pericardial effusion was absent. After fluid challenge (10 ml/kg of colloid or crystalloid infused iv over 10 min), filling pressures, cardiac output, and stroke volume all increased significantly (p less than .025) while heart rate decreased. Surgical decompression of the abdomen improved oxygenation, ventilation, cardiac output, atrial filling pressures, and urine output within 15 min. The cardiovascular effects of massively elevated IAP compounded by the requisite supportive care may require surgical relief.

The hemodynamic interaction of acute hypovolemia and halothane anesthesia in dogs with increased intra-abdominal pressure caused by intraperitoneal instillation of N2, N2O and CO2 was studied. During normovolemia and just basal pentobarbital anesthesia, the response to increase of intra-abdominal pressure to 40 torr consisted of a 35 per cent decrease in cardiac output, which was equal to the decrease in magnitude of inferior vena caval blood flow. During basal pentobarbital anesthesia, the addition of halothane anesthesia (1 MAC) in combination with hypovolemia (15 per cent blood volume loss) depressed the pre-inflation cardiac output more than addition of halothane anesthesia alone or induction of hypovolemia alone. During each of these conditions, superimposition of increased intra-abdominal pressure to 40 torr caused a further 26-43 per cent decrease in cardiac output compared with the pre-inflation value. Therefore, the greatest cardiovascular depression occurred when the animals were both hypovolemic and anesthetized with halothane. There was no difference in the responses to increased intra-abdominal pressure with the different inflating gases at any time. These findings indicate that in the presence of halothane anesthesia or hypovolemia, induction of pneumoperitoneum may cause severe cardiovascular depression.

We studied 17 victims of multiple trauma and found that right ventricular function can be reliably monitored at the bedside using the thermodilution method. In addition, we noted that right ventricular dysfunction occurred early in victims of major trauma without affecting the left ventricular function. If right ventricular function does not improve, the patient is likely to die. Further studies are needed to determine if early intervention aimed at improving right ventricular function can improve survival.

A deviation in an indirect measurement of intramural pH below the limits of normality (6.86) was used as a diagnostic test for sigmoid ischemia in 25 high-risk patients undergoing abdominal aortic operations. The clinical diagnosis of ischemic colitis was made by the attending physicians in only two of the 25, on the day after operation in one and three months after operation in another. In neither was the ischemic colitis considered to have been a causative factor in their subsequent deaths. In contrast, six patients developed pH evidence of ischemia on the day of operation. All six subsequently developed a transient episode of guaiac-positive diarrhea, four developed physical signs consistent with ischemic colitis, and four died. Of 19 who did not develop pH evidence of ischemia, none developed guaiac-positive diarrhea, none developed any signs of ischemic colitis, and none died. Stepwise logistic regression showed the duration of pH evidence of ischemia on the day of operation to be the best predictor for the symptoms and signs of ischemic colitis and for death after operation.

In four patients with ruptured abdominal aortic aneurysms increased intra-abdominal pressure developed after repair. It was manifested by increased ventilatory pressure, increased central venous pressure, and decreased urinary output associated with massive abdominal distension not due to bleeding. This set of findings constitutes an intra- abdominal compartment syndrome caused by massive interstitial and retroperitoneal swelling. The purpose of this report is to establish criteria for this syndrome and suggest a method of treatment. The syndrome developed within 24 hours; in one patient within 5 hours postoperatively. All four patients received more than 25 liters of fluid resuscitation (electrolyte and blood) during and within 16 hours after operation and had massive abdominal distension. Decompressive laparotomies were performed in the Intensive Care Unit with placement of Marlex (Bard Corp., Billerica, MA) mesh. In two additional patients, at the completion of the aneurysmectomy the abdominal incision was left open with interposition Marlex mesh. Opening the abdominal incision was associated with dramatic improvements in central venous pressure, urinary output, ventilatory pressure, arterial carbon dioxide tension, and oxygenation. The authors conclude that some patients with ruptured abdominal aortic aneurysm do not tolerate the closure of the abdominal wall, as manifested by increased ventilatory pressures, decreased oxygenation, and decreased urinary output. Opening the abdominal wound or delayed closure may reverse the oliguria and improve oxygenation. Recognition and treatment of this condition by opening the abdominal wound or delayed closure may affect outcome in some cases.

Right and left ventricular function was evaluated in 21 men with cirrhosis and tense ascites during staged removal of ascitic fluid. During paracentesis it was observed (1) that there was a significant increase in cardiac output, stroke volume, right and left ventricular stroke work and mean rate of systolic ejection; (2) that up to a certain stage of drainage (about 5,000 ml), there was a relationship between the amount of fluid removed and the intraabdominal and right atrial pressures and (3) that there was a direct relationship between improvement of cardiac function and normalization of right atrial pressure. It is believed that the increased intra-abdominal hydrostatic pressure acting upon the diaphragm affects the intrathoracic pressure to such an extent that the transmural filling pressure of the heart is reduced, and the mean pressure and respiratory pulsations of the right atrium increased, all of which impede venous return. Improved cardiac function during paracentesis appears to be due to an augmented filling of the heart and to a larger venous return.

The effect of increased intra-abdominal pressure on cardiac output and renal function was investigated using anesthetized dogs into whom inflatable intraperitoneal bags were placed. Hemodynamic and renal function measurements were made at intra-abdominal pressures of 0, 20, and 40 mmHg. Renal blood flo and glomerular filtration rate decreased to les than 25% of normal when the intra-abdominal pressure was elevated to 20 mmHg. At 40 mmHg intra-abdominal pressure, three dogs became anuric, and the renal blood flow and glomerular filtration rate of the remaining dogs was 7% of normal, while cardiac output was reduced to 37% of normal. Expansion of the blood volume using Dextran-40 easily corrected the deficit in cardiac output, but renal blood flow and glomerular filtration rate remained less than 25% of normal. Renal vascular resistance increased 555% when the intra-abdominal pressure was elevated from 0 to 20 mmHg, an increase fifteen-fold that of systemic vascular resistance. This suggests that the impairment in renal function produced by increased intra-abdominal pressure is a local phenomenon caused by direct renal compression and is not related to cardiac output.

The determination of intra-abdominal pressure (IAP) may be useful in a variety of clinical situations. Despite this, invasive IAP monitoring is seldom performed due to the risks involved. Using a standard canine model of increased IAP, we evaluated the accuracy of transurethral bladder catheter pressure in reflecting IAP. Throughout the range of IAP studied (10 +/- 5 to 70 +/- 10 mm Hg), bladder pressure did not differ significantly from the direct measurement of IAP. We conclude that the measurement of bladder pressure using a standard transurethral bladder catheter provides an accurate determination of IAP.

The determination of intra-abdominal pressures (IAP) may be useful in many clinical situations. The authors recently demonstrated in the canine model a close correlation between actual IAP and the bladder pressure measurements obtained from a transurethral catheter. The purpose of this study was to clinically validate this technique. The authors studied 16 patients, and compared IAP in three positions (supine, with compressions, and semi-erect) utilizing both direct intraperitoneal pressure monitoring and the pressure obtained with a transurethral bladder catheter. Their results demonstrated a linear relationship between the two methods described, with a mean r value of 0.95 in the supine and semi-erect positions, and 0.99 with abdominal compressions (P less than 0.0001). The authors conclude that transurethral monitoring of bladder pressure offers a safe, simple, and highly accurate method for evaluating IAP at the bedside. Studies evaluating the indication for its use in the operating room and intensive care settings appear warranted.

Acute elevation of intra-abdominal pressure above 30 mmHg caused oliguria in 11 postoperative patients. Operative re-exploration and decompression in seven patients resulted in immediate diuresis. Four patients who were not re-explored developed renal failure and died. If intra-abdominal pressure rises above 25 mmHg in the early postoperative period and is associated with oliguria and normal blood pressure and cardiac index, the patient should undergo re-exploration and decompression of the abdomen.

The stroke volume and cardiac output changes in twenty-four patients undergoing laparoscopy were measured using the non-invasive technique of impedance cardiography. There was a moderate fall of stroke volume and cardiac output during intraperitoneal insufflation of carbon dioxide which was directly related to the volume of gas used. The need for caution during laparoscopy particularly in ill patients is emphasised.

Intra-abdominal pressures were measured simultaneously with a wireless radio pill and two wire-connected pressure transducers introduced orally and rectally respectively. Measurements were made on 8 men during common postures, simple activities and static and dynamic lifting. An acceptable correspondence was found in wave forms of the generated pressure curves in time and shape. The three systems showed, however, a less good agreement in recorded peak differences, i.e. highest and lowest pressure responses to each task. The radio pill is simple to use, but more difficult to calibrate and expensive, compared to the wire-connected methods, which however are less attractive for use in the work environment.

Anuric renal failure developed in four patients in association with increased intra-abdominal pressure from postoperative hemorrhage. Polyuria and resolution of the renal failure occurred in each patient in response to operative decompression of the abdomen. Renal failure secondary to increased intra-abdominal pressure has been previously produced experimentally in dogs by the intraperitoneal installation of graded amounts of saline. This is the first report of this type of renal failure in clinical practice.

Direct measurement of blood pressure with a fluid-filled catheter and transducer is widely accepted in clinical practice. However, errors associated with the measurements are often not appreciated. The system frequently is unable to reproduce rapidly changing waveforms and overshoots to produce higher peak pressures. The most common causes of this phenomenon are trapped small air bubbles and long connecting tubing. To assess the inaccuracy in pressure measurements, we calculated the weighted sum of the percentage difference between reference and recorded amplitudes of sinusoidal waveforms for several catheters and connecting tubings. We found that when the connecting tubing was shorter than 3 feet long and no air bubbles were trapped readings were accurate. On the contrary, connecting tubings 7 feet long or longer, and/or air bubbles, were frequently associated with inaccurate results. For example, minimal air bubbles (0.25 ml) in a system exaggerated the systolic pressure measurement by 41 torr when simulated blood pressure was 150/50 torr.

Postoperative oliguria or anuria can rarely be attributed to an increase in intra-abdominal pressure. In this documented case, postoperative anuria responded to reduction in abdominal pressure by celiotomy. Actual abdominal pressure measurements are not available but probably would not be useful. However, hemodynamic measurements that were not consistent with diminished renal blood flow in a middle-aged patient were nevertheless associated with anuria, which responded to release of the abdominal pressure. Because of the association of regional pressure and acute renal decompensation, release of abdominal tension should be considered as a therapeutic option when hemodynamic measurements cannot explain a rapid decline in urine production.