Adult respiratory distress syndrome in association with acute pancreatitis. Evaluation of positive end expiratory pressure ventilation and pharmacologic doses of steroids

Adult respiratory distress syndrome: a systemic overview of incidence and risk factors

OBJECTIVE

To determine the published incidence of adult respiratory distress syndrome (ARDS) as well as the clinical evidence supporting a casual association between ARDS and its major risk factors.

DATA SOURCES

The National Library of Medicine MEDLINE database and the bibliographies of selected articles.

STUDY SELECTION

Clinical studies were selected from the English literature, if they pertained to either the incidence of ARDS or its association with one or more commonly identified risk factors.

DATA EXTRACTION

All relevant studies identified by the search were evaluated for strength of design, and risk factors were scored according to established criteria for the strength of causation.

DATA SYNTHESIS

A total of 83 articles were considered relevant: six of incidence and 77 on risk factors. Only 49% of the 83 articles provided a definition of ARDS; a definition of risk factors was given in 64%, and 23% had no definition for either ARDS or risk factors. The published, population-based incidence of ARDS ranges from 1.5 to 5.3/10(5) population/yr. The strongest clinical evidence supporting a cause-effect relationship was identified for sepsis, aspiration, trauma, and multiple transfusions. The weakest clinical evidence was identified for disseminated intravascular coagulation. The following study types were represented by the 77 articles on risk factors: observational case-series (56%); cohorts (23%); case-controls (12%); nonrandomized clinical trials (5%); and randomized clinical trials (3%). Only a single study reported an odds ratio.

CONCLUSIONS

The significant variation in the incidence of ARDS is attributed to differences in the type and strength of study designs, as well as definitions or ARDS. While a substantial body of evidence exists concerning a casual role of ARDS risk factors, such as sepsis, aspiration, and trauma, > 60% of clinical studies employed weak designs. The lack of reproducible definitions for ARDS or its potential risk factors in 49% of studies raises concerns about the validity of the conclusions of these studies regarding the association between ARDS and the supposed risk factors.

Pulmonary microvasculature in experimental acute haemorrhagic and oedematous pancreatitis

The pulmonary microvasculature was examined in two experimental models of acute pancreatitis by scanning electron microscopy of microvascular corrosion casts. Haemorrhagic pancreatitis was induced in eight male Sprague-Dawley rats using an intraductal injection of 5 per cent sodium taurocholate. Oedematous pancreatitis was induced in seven male Sprague-Dawley rats using an intravenous infusion of supramaximal doses of caerulein (5 micrograms/kg per hour). The pulmonary vessels were cast using a polymer resin and the cast studied by scanning electron microscopy at 3 and 12 h in those with haemorrhagic and at 1 and 4 h in those with oedematous pancreatitis. Vascular abnormalities were present in both models at the initial study time with abruptly terminating vessels being more prominent in the caerulein model. At the later times, however, the abnormalities in the sodium taurocholate model were much more severe, with a substantial loss of vascular density, tortuosity and abrupt terminations of those vessels present. Microvascular abnormalities may be responsible for some of the pulmonary changes seen in oedematous and haemorrhagic pancreatitis.

The effect of caerulein induced pancreatitis on the hepatic microvasculature

A three-dimensional morphological study of the hepatic microvasculature in caerulein induced oedematous pancreatitis was performed using scanning electron microscopy (SEM) vascular casts and transmission electron microscopy (TEM) of hepatocytes and hepatic sinusoids. TEM studies provided ultrastructural evidence of hepatocellular damage while SEM views demonstrated gross irregularity of the sinusoidal outline with abruptly terminating sinusoidal buds and extravasation of cast material, findings which were similar to those previously reported in the pancreas itself using the same model and which were supported by TEM cross-sectional views of the hepatic sinusoids. The results suggest that caerulein induced pancreatitis is associated with extrapancreatic microvascular damage which may be an important factor in the pathogenesis of extrapancreatic organ impairment associated with acute pancreatitis.

Extravascular lung water as an indicator of pulmonary dysfunction in acute hemorrhagic pancreatitis

This study quantifies lung water in acute hemorrhagic pancreatitis to determine the degree to which pulmonary dysfunction occurs subclinically, before alterations in the arterial blood gases can be measured. Pancreatitis was induced in ten dogs by injecting 0.5 ml/kg of bile into the pancreatic ducts, which had been surgically cannulated. Pulmonary and systemic blood gases and blood pressures, heart rate, extravascular lung water, and lung blood flows were studied over 5 hours while cardiac output and mean arterial pressure were maintained at control values by Ringer's lactate infusion. The percentage of water in lung tissue was determined at the time of sacrifice using gravimetric measurements. Mean arterial pressure, cardiac output, and pulmonary capillary wedge pressure, reflecting intravascular volume status, did not change through at the experiment. By contrast, major disturbances were measured in the pulmonary bed with pulmonary artery pressures rising from 15.6 +/- 1.8/8.1 +/- 1.3 mmHg to 22.0 +/- 1.2/15.6 +/- 1.7 mmHg over 5 hours (p less than 0.01). Peripheral vascular resistance rose from 3.6 +/- 0.6 units to 6.6 +/- 0.4 units (p less than 0.05), whereas bronchial blood flow to the lung fell significantly. These changes in pulmonary hemodynamics were not reflected by changes in the arterial blood gases. Arterial oxygenation was maintained during 5 hours of pancreatitis. The partial pressure of carbon dioxide and the serum pH did not change significantly. There was, however, a progressive rise in extravascular lung water measured by the double-dilution technique from 10.2 +/- 0.8 ml/kg at control to 18.1 +/- 2.8 ml/kg (p less than 0.01) at 5 hours. This was confirmed by direct gravimetric measurements, which revealed an increase in the water content of the lung from 78.1 +/- 0.3% to 86.4 +/- 2.4% over the course of the experiment. Arterial blood gases, therefore, do not necessarily reflect the pulmonary deterioration in acute pancreatitis. These data supported a mechanism of lung dysfunction independent of the circulatory compromise, which often accompanies the disease in the clinical setting.

Death due to acute pancreatitis. A retrospective analysis of 405 autopsy cases

A large retrospective autopsy study of patients was analyzed to evaluate the major etiologic and pathologic factors contributing to fatal acute pancreatitis (AP). From an autopsy population of 50,227 patients, 405 cases were identified where AP was defined as the official primary cause of death. AP was classified according to morphological and histological, but not biochemical, criteria. Patients with AP died significantly earlier than a control autopsy population of 38,259 patients. Sixty percent of the AP patients died within 7 days of admission. Pulmonary edema and congestion were significantly more prevalent in this group, as was the presence of hemorrhagic pancreatitis. In the remaining 40% of patients surviving longer than 7 days, infection was the major factor contributing to death. Major etiologic groups in AP were chronic alcoholism; postabdominal surgery; common duct stones; a small miscellaneous group including viral hepatitis, drug, and postpartum cases; and a large idiopathic group comprising patients with cholelithiasis, diabetes mellitus, and ischemia. The prevalence of established diabetes mellitus in the AP group was significantly higher than that observed in the autopsy control series, suggesting that this disease should be considered as an additional risk factor influencing survival in AP. Pulmonary complications, including pulmonary edema and congestion, appeared to be the most significant factor contributing to death and occurred even in those cases where the pancreatic damage appeared to be only moderate in extent. Emphasis placed on the early recognition and treatment of pulmonary edema in all cases of moderate and severe AP should contribute significantly to an increase in survival in this disease.

Acute and chronic pancreatitis. An update on management

Therapeutic measures for acute pancreatitis depend on the severity of the disease and its complications. Since complications of acute pancreatitis may develop at any time, patients should be admitted to an intensive care unit for assessment (and frequent reassessment) of the severity of the disease and the development of complications. Basic therapy should include relief of pain, total fasting, nasogastric suction, parenteral replacement of fluids, electrolytes, albumin and blood, and antibiotics. Hyperglycaemia should be corrected and heparin should be given in cases of disseminated intravascular coagulation. In renal insufficiency, peritoneal dialysis is important, and in respiratory complications, humidified oxygen or artificial ventilation including positive and expiratory pressure therapy should be applied. Although the effect of peritoneal dialysis has been proven only in animal experiments and in retrospective studies in man, it is recommended in severe cases for shock therapy and for correction of electrolyte imbalance when ascites is present, even before anuria occurs. Conservative treatment measures in chronic pancreatitis are limited to the management of pain and of exocrine and endocrine pancreatic insufficiency.

Alcohol and the respiratory tract

Possible mechanisms by which alcohol may adversely affect the respiratory system are considered. Alcohol ingestion impairs glottic reflexes, and alcoholics are predisposed to pneumonias and lung abscesses from aspiration of oropharyngeal bacteria. Alcohol intoxication also increases the frequency of sleep apnea and may result in respiratory failure from oversedation.

Pulmonary complications in fatal acute hemorrhagic pancreatitis

Morphological changes of the lung occur frequently in fatal acute hemorrhagic pancreatitis. The pulmonary alterations are independent of mechanical ventilation and therefore not due to iatrogenic damage caused by high inspired oxygen concentrations. The histological findings are similar to those seen in the so-called shock lung syndrome. The pulmonary lesion develops progressively and three stages can be separated: early, late, and final phase. The pulmonary complications in acute hemorrhagic pancreatitis may be explained by the release of mediators such as pancreatic enzymes or free fatty acids into the blood stream. In acute hemorrhagic pancreatitis a close monitoring for shock parameters is necessary. A fall in arterial PO2 is an early indication for mechanical ventilation, including positive end-expiratory pressure.

Acute pancreatitis following renal allotransplantation. A lethal complication

Since first described by Starzl in 1964 (1), acute pancreatitis following renal homotransplantation has been the subject of sporadic reports and reviews (2-5). The generally reported incidence has been around 2%, with a mortality rate of 50-60%. A recent experience with such a patient caused us to retrospectively analyze our own series of renal transplant recipients. In an eight-year period, there were six patients who had documented pancreatitis out of a total 120 renal homograft recipients, an incidence of 5%. The mortality was distressingly high; five out of the six succumbed directly to this complication, a rate of 83%. The purpose of this paper is to review these six patients in detail, with special attention to the protean etiologies and manifestations of this lethal complication.

New approaches to the management of severe acute pancreatitis

A recent experience with seventy-seven patients admitted to Boston City Hospital for acute pancreatitis permitted us to identify thirteen patients (17 per cent) whom we diagnosed as having severe protracted acute pancreatitis. These alcoholic patients obviously had fulminant pancreatitis similar to that reported by others in two instances and pancreatic abscesses in two additional instances, but nine of the patients did not fulfill the criteria usually used by others as a basic for surgical intervention. Specific preoperative diagnosis was obtained in these patients by the aggressive use of endoscopic cannulation of the pancreatic ducts, which documented the presence of surgically correctable lesions. These patients had sustained significant malnutrition, which was corrected only by protracted therapy extending an average of two months and involving all modalities currently available for nutritional support of the severely ill patient. After proper preoperative identification of a specific lesion and correction of the malnutrition, the eleven patients without fulminant disease were operated on with no deaths or significant complication. Nine of the patients had elective procedures, which included six distal pancreatectomies and one total pancreatectomy. Thus, severe protracted acute pancreatitis can be identified, and once categrorized, it can have therapeutic implications.

The pathogenesis of pulmonary edema in acute pancreatitis

Acute pulmonary edema appeared 3 or more days after the onset of acute pancreatitis in 7 patients, an approximate incidence of 8%. The severity of pancreatitis in these patients was characterized by massive requirements for intravenous colloid and by marked hypocalcemia. In addition, at least 5 of the 7 patients had very high serum levels of triglycerides at the time of hospital admission. Hemodynamic studies during pulmonary edema showed normal central venous pressure, pulmonary artery pressure, pulmonary capillary wedge pressure, and pulmonary vascular resistance. Cardiac index was appropriately elevated. Respiratory treatment, consisting of endotracheal intubation and controlled ventilation with PEEP, was successful in allowing reversal of the pulmonary injury and recovery of respiratory function within 1-2 weeks in all cases. Two patients died later from pancreatic abscesses. The findings indicate that a distinct form of pulmonary injury may occur in acute pancreatitis, characterized by loss of integrity of the alveolar-capilllary membrane, leading to pulmonary edema. The mechanism of injury is not known but may be caused by circulating free fatty acids, phospholipase A, or vasoactive substances. The pulmonary membrane lesion appears to heal during the period of intensive respiratory support.

Acute respiratory failure in acute pancreatitis

The respiratory complications of acute pancreatitis are discussed, with particular reference to the incidence, pathophysiology and management of acute respiratory distress.