COMPLICATIONS ASSOCIATED WITH THE ADULT RESPIRATORY DISTRESS SYNDROME

Thrombocytopenia in the intensive care unit

STUDY OBJECTIVE

To determine the prevalence of thrombocytopenia in an ICU and assess which factors were associated with thrombocytopenia.

DESIGN

A review of the medical records of patients admitted during 3 separate months during 1 academic year. Patients must have survived at least 12 h in the ICU.

SETTING

A medical ICU at a university hospital.

PATIENTS

General medicine patients admitted to the ICU.

INTERVENTIONS

All medical records were reviewed. During the ICU stay, daily medications, events, and platelet count were noted. All patients were followed up until death or hospital discharge. In 22 patients, including 18 who had thrombocytopenia, bone marrow aspirates were performed.

MEASUREMENTS AND RESULTS

One hundred sixty-two admissions were evaluated. Thirty-eight (23 percent) had platelet counts less than 100,000/mm3 at least once, and 17 (10 percent) patients had platelet counts less than 50,000/mm3. Several factors were associated with thrombocytopenia; however, only sepsis, use of antineoplastic chemotherapy, elevated creatinine level, or elevated bilirubin value were independent risk factors for severe thrombocytopenia. In only one patient were the bone marrow findings different from those expected by the clinical presentation. Thrombocytopenia was associated with longer hospital stay (p < 0.001) and higher mortality (p < 0.001).

CONCLUSION

Thrombocytopenia is a common occurrence in the ICU, usually due to the underlying disease, and is associated with an increased mortality.

Elevated urinary leukotriene E4 excretion in patients with ARDS and severe burns

Increased synthesis of peptidoleukotrienes may occur in a variety of inflammatory diseases. To test this theory, hospitalized patients with a variety of diseases were studied and urine LTE4 quantitated as an index of total body peptidoleukotriene synthesis. 10 patients with ARDS, 7 of which had additional organ involvement, and 5 patients suffering from severe burn injuries were studied. Patients with uncomplicated ARDS excreted approximately 6-fold higher amounts of LTE4 in urine compared to healthy subjects. When ARDS was complicated by multiple organ failure (MOF), urine LTE4 levels were 2- to 150-fold higher than in healthy volunteers. Patients with severe burn injuries had peak urine LTE4 levels which were approximately 20-fold higher than in healthy volunteers. As additional controls, patients with cardiac arrhythmias (absence of inflammatory disease) and patients with uncomplicated pneumonia (localized inflammation) showed normal or mildly elevated urinary LTE4 levels. The urinary LTE4 levels in ARDS patients did not correlate with serum creatinine, bilirubin, or LDH levels, or with the WBC, nor did renal or liver failure by itself predict extremely elevated urinary LTE4 levels. In conclusion, patients with ARDS or ARDS/MOF and patients with severe injuries and sepsis syndrome excrete higher levels of urinary LTE4 than patients healthy volunteers or patients with limited inflammatory disease. In certain situations, urinary LTE4 levels may be useful as a marker of the degree of inflammation.

Risk factors for nosocomial pneumonia after coronary artery bypass graft operations

We attempted to determine risk factors for nosocomial pneumonia in patients undergoing a coronary artery bypass graft operation. We reviewed the microbiology and medical records for any patient with a sputum culture who had undergone a coronary artery bypass graft operation in 1988 to identify patients with pneumonia according to a standard clinical definition. We found 19 cases of pneumonia through our initial review; complete medical records were found on 15 cases. Gram-negative bacilli predominated as the most common etiologic agent causing pneumonia in this cohort. There were no clusters noted. Mortality was 26.6%. Pneumonia occurred approximately 4 days after the operation. Thirty-six controls were randomly selected from patients undergoing coronary artery bypass graft operations in 1988. Logistic regression analysis revealed that a history of chronic obstructive lung disease, duration of more than 2 days of mechanical ventilation after operation but before diagnosis of pneumonia, and receipt of gastric acid inhibitors (antacids or H2-blockers) were independent risk factors for nosocomial pneumonia. Only the last risk factor was amenable to intervention at the time of operation.

The adult respiratory distress syndrome

The adult respiratory distress syndrome is a condition of life-threatening organ failure triggered by blood-borne factors and challenges which arrive via the airways. Vascular damage is a necessary, but often not sufficient criterion for ARDS, which is observed in an acute and chronic form. There is a consensus that neutrophils and their products contribute to the pathogenesis of the syndrome, and that lung vascular tone regulation and endothelial and epithelial cell permeability are affected in ARDS. Whereas the precise roles of individual mediators for the development of ARDS are still ill-defined, a synergism between lipid mediators and other injurious principles is recognized. Chronic ARDS is a proliferative disorder which may require different treatment strategies than acute ARDS. Specific treatment modalities which inhibit the interaction between activated neutrophils and the lung endothelium, and surfactant replacement might have a future as early therapy approaches.

Common complications in critically ill patients

Patients in intensive care units (ICUs) are subject to many complications connected with the advanced therapy required for their serious illnesses. Complications of ventilatory support include problems associated with short-term and long-term intubation, barotrauma, gastrointestinal tract bleeding, and weaning errors. Cardiac tachyarrhythmias can arise from a patient's intrinsic cardiac disease, as well as from drug therapy itself. Hemodynamic monitoring is crucial to careful patient management, but it is associated with technical complications during insertion such as pneumothorax, as well as interpretive errors such as those caused by positive end-inspiratory pressure. Acute renal failure can develop as a result both of therapy with drugs such as aminoglycosides and hypotension of many etiologies, as well as the use of contrast media. Nosocomial infection, which is a dreaded complication in ICU patients, usually arises from sources in the urinary tract, bloodstream, or lung. Complications frequently can arise if the interactions of drugs commonly used in the ICU are not recognized. Further, the ICU patient is subject to nutritional complications, acid base problems, and psychological disturbances. This monograph deals with the frequency, etiology, and prevention of these common ICU complications.

Adult respiratory distress syndrome in pediatric patients. II. Management

Adult respiratory distress syndrome, a clinical syndrome of respiratory failure that follows many kinds of insults, often in patients with no previous pulmonary disease, occurs in pediatric patients. This group of disorders has a typical clinical, pathologic, and pathophysiologic course, the hallmark of which is injury to the alveolar-capillary membrane with increased permeability of the pulmonary vasculature and pulmonary edema. Resolution may occur at any stage, but most patients die and many develop chronic lung disease requiring respiratory support for weeks or months. Multiple organ system failure, secondary infection, and irreversible respiratory dysfunction are responsible for the poor outcome. The underlying mechanisms that relate injury to the development of pulmonary disease are unclear. In some cases there may be direct injury to the lung, but in others, such as septic shock, there are mediators that link the initial insult to the subsequent lung injury. The leukocyte may have a central role in this process, although this is uncertain. Therapeutic measures needed to support the patient, especially increased inspired oxygen, are additional factors in the progression of lung disease. Current therapy, as summarized in Table II, is primarily supportive. Efforts to treat ARDS after it is clinically apparent have been disappointing. The pathogenic mechanisms that lead to ARDS are probably well advanced by the time the syndrome is diagnosed on the basis of the usual clinical signs. Therefore an emphasis on understanding the mechanisms of lung injury so that specific markers can be used to predict which patients will develop ARDS, allowing intervention in the early stages of the process, may prove rewarding.

Complications of acute respiratory failure

Many complications can occur during the management of acute respiratory failure and may involve multiple organs. Some of these complications can be avoided by preventive measures. We find evaluation of serial chest roentgenograms extremely useful for the early detection of several complications (figure 4). In addition, prophylactic use of heparin to prevent pulmonary emboli, prophylactic antacid or cimetidine therapy to prevent gastric bleeding, careful monitoring of renal function, appropriate measures to reduce the incidence of colonization and nosocomial infection, and early recognition of nosocomial infections are some of the measures essential to increased survival of patients with acute respiratory failure.

Acute respiratory failure. Pathophysiology, causes, and clinical manifestations

Acute respiratory failure is a common life-threatening process with myriad causes. It is characterized by a failure of oxygenation or ventilation, or both. Hypoxemia is common to all causes of respiratory failure, whereas PaCO2 may be normal, decreased, or elevated. These abnormalities result from several pathophysiologic processes, including intrapulmonary venoarterial shunt, alveolar hypoventilation, diffusion impairment, and ventilation-perfusion mismatch. Type I failure results from processes that lead to hypocapnia or normocapnia; type II failure is distinguished by the presence of hypercapnia. The clinical manifestations of acute respiratory failure are nonspecific; for this reason, a high index of suspicion and early examination of arterial blood gases are essential to successful management.

Continuous positive airway pressure by face mask in acute cardiogenic pulmonary edema

The therapeutic efficacy of continuous positive airway pressure (CPAP) administered by face mask was studied in 40 patients with acute cardiogenic pulmonary edema and respiratory failure. Arterial blood gas values and pH, systemic arterial pressure, heart rate and respiratory rate were measured during administration of 30% oxygen with a high-flow face mask apparatus at ambient airway pressure. Twenty patients were then randomly chosen to continue ambient airway pressure breathing and 20 received 10 cm H2O of CPAP. The measurements were repeated 10, 60 and 180 minutes after therapy was initiated. During the first 10 minutes of CPAP treatment, arterial blood oxygen partial pressure increased 8 +/- 9 mm Hg (mean +/- 1 standard deviation), (p less than 0.01) and respiratory rate decreased 5 +/- 5 breaths/min (p less than 0.001). Systolic arterial pressure decreased 12 +/- 21 mm Hg (p less than 0.05), and heart rate by 10 +/- 11 beats/min (p less than 0.001). A decrease in respiratory rate by 2 +/- 5 breaths/min (p less than 0.05) was the only change that occurred in the control group. The improvement in arterial blood oxygenation persisted throughout the investigation period (p less than 0.05). Thirteen patients (65%) in the control group and 7 patients (35%) in the CPAP group met our criteria for treatment failure during the study (p = 0.068). Thus, CPAP administered by face mask improves gas exchange, decreases respiratory work, unloads circulatory stress, and may reduce the need for ventilator treatment in acute cardiogenic pulmonary edema.

Classification of acute respiratory failure

Acute respiratory failure can result from a wide variety of etiologies. Hypoxemia is the hallmark of this condition and is responsible for the major clinical signs and symptoms. The use of arterial blood gas analysis is the cornerstone of diagnosis and is also critical in the subsequent evaluation of the effectiveness of therapy. Treatment must be individualized and coordinated in the setting of an intensive care unit.