The pulmonary physician in critical care. 8: Ventilatory management of ALI/ARDS.

Current data relating to ventilation in ARDS are reviewed. Recent studies suggest that reduced mortality may be achieved by using a strategy which aims at preventing overdistension of lungs.

High molecular weight kininogen deficiency: a patient who underwent cardiac surgery.

A 66 year old male, referred for cardiac surgery, was found to have high molecular weight kininogen deficiency (activity <1%). Apart from activated partial thromboplastin time (APTT) >300 s, tests of haemostasis were otherwise normal (factors VIII, IX, XI, XII and prekallikrein). No inhibitor of coagulation was found. The activated coagulation time (ACT) was 800 s pre-operatively and >1000 s after heparin. Heparin levels were measured directly by an anti-Xa chromogenic assay, with values of between 2.9 and 3.2 u/ml during cardiopulmonary bypass. Thrombin-antithrombin levels rose from 2.3*g/l before surgery to a peak of 83.5*g/l at the end of cardiopulmonary bypass. Cross linked fibrin d-dimers (XDP) levels rose from 100 ng/ml before operation to 600 ng/ml after protamine administration. The patient had no excess bleeding and no thrombotic complications from surgery. This patient shows that high molecular weight kininogen is not required for thrombin formation or fibrinolysis during cardiac surgery and illustrates the need to measure heparin directly in patients with such contact factor deficiencies.

Lung volume reduction surgery in a ventilated patient with severe pulmonary emphysema.

There are a limited number of reports in the literature cocerning lung volume reduction surgery in patients receiving mechanical ventilation. We present a case in which a ventilator-dependent patient with apparent endstage pulmonary emphysema underwent lung volume reduction with a successful outcome. Although the role of this procedure for selected nonventilated patients has been widely discussed its use in ventilated patients is still not clearly defined. We show that lung volume reduction surgery may facilitate ventilatory weaning in such cases and improve functional status.

Intravascular gas exchange.

Intravascular gas exchange, in which miniaturized hollow fibre oxygenators are inserted into the caval veins, has been proposed as a simpler and safer alternative to extracorporeal support in severe respiratory failure. One such device, the IVOX (intravascular oxygenator), has undergone clinical trials (160 implants) and, despite individual benefits, was found to be limited in its gas exchanging capacity. The peculiarities of oxygen physiology render pre-pulmonary oxygenation inefficient and variable, whereas carbon dioxide clearance is much more predictable. Several devices are currently undergoing development and may offer substantially enhanced gas exchange. The new devices, which may be several years from widespread clinical assessment, offer exciting therapeutic options in severe respiratory failure but are unlikely to completely replace extracorporeal techniques in the most severe forms of respiratory failure.

Ventilatory support in the acute respiratory distress syndrome.

Ventilatory support in the acute respiratory distress syndrome (ARDS) has undergone considerable transformation in the 1990s. Current approaches include lung protective techniques which, while attempting to recruit and maintain lung volume, limit the shear stresses associated with ventilation by avoiding both alveolar overdistension and cyclical end-expiratory collapse. In addition, gas exchange targets have been liberalized and ventilatory conduct is much more tailored to individual pulmonary mechanics. Assessment of the inspiratory volume-pressure (V-P) curve provides information which can direct ventilator settings. Recent information from clinical trials has provided new insights into appropriate ventilatory modification and set the foundation for future clinical investigations.

Reduced mortality in association with the acute respiratory distress syndrome (ARDS).

BACKGROUND: A study was undertaken to investigate possible reductions in mortality and/or changes in outcome predictive factors in patients with the acute respiratory distress syndrome (ARDS) managed in a single centre. METHODS: The study was a prospective observational cohort study of two patient populations with ARDS. Group 1 comprised 41 patients enrolled between May 1990 and April 1993, and group 2 consisted of 78 patients enrolled between June 1993 and March 1997. The end points of the study were mortality and various factors predictive of death. RESULTS: There was a marked reduction in mortality between groups 1 and 2 (66% versus 34%; relative risk 1.77; CI 1.23 to 2.55). There were no significant differences between the groups in terms of age (40.6 (3.3) versus 45.5 (2.2) years), APACHE score (14.5 (0.72) versus 13.6 (0.1)), lung injury score (2.95 (0.07) versus 2.8 (0.1)), incidence of multi-organ failure (29% versus 32%), incidence of sepsis (31% versus 39%), or PaO2/FIO2 (kPa) ratio (11.8 (0.67) versus 12.0 (0.6)). There was a significantly lower proportion of men in group 1 (51% versus 74%). The case mix of the two groups was closely matched: following elective surgery 48% versus 48%, trauma 17% versus 16%, primary lung injury 12% versus 24%. Patients in group 1 were supported using several ventilatory and other modes (volume preset, non-inverse ratio ventilation, n = 15; pressure controlled inverse ratio ventilation (PC-IRV), n = 11; ultra high frequency jet ventilation (UHFJV), n = 13; an intravascular oxygenation device (IVOX) and extracorporeal gas exchange (ECGE), n = 2). Within group 1 no significant difference in mortality was observed between the patients on volume controlled ventilation and the remainder. In group 2 all patients received PC-IRV (n = 78) but, in addition, some received other support techniques (UHFJV n = 4, ECGE n = 2). In group 1 only sepsis on admission (21% (survivors) versus 56% (non-survivors)) predicted death. In group 2 age of survivors and non-survivors (41.2 (2.6) versus 52.6 (3.5)), APACHE score (12.2 (0.6) versus 15.8 (0.9)), and PaO2/FIO2 (12.8 (0.86) versus 10.5 (0.72)) predicted survival, but not the incidence of sepsis or multi-organ failure. CONCLUSIONS: In recent years a highly significant reduction in mortality associated with ARDS has been observed between two groups of patients well matched for disease severity and case mix. Changes in ICU organisation rather than specific interventions may account for this reduction, although different ventilatory and other management strategies used in the two groups may also be relevant.

Clinical strategies in intravascular gas exchange.

Specific therapies in the management of acute pulmonary failure remain elusive, with attention being focused instead on novel supportive measures. The benefits of extracorporeal gas exchange support remain uncertain, and the perceived simplicity of intravascular gas exchange has, therefore, attracted much interest. Initial clinical experience with the intravascular oxygenator (IVOX) device confirms its safety and simplicity, but estimated mean gas-transfer values represent only 25% of basal gas-exchange requirements. The inherent limitations of IVOX as an oxygenator are discussed, providing a rationale for considering IVOX as primarily a CO2 removal device. Reappraisal of the clinical place of intravascular gas exchange and the identification of specific applications most likely to yield benefit to patients are suggested. Design modifications enhancing efficacy are anticipated, further strengthening the potential of intravascular gas-exchange devices in selected patients with pulmonary failure.

Pseudomembranous necrotising bronchial aspergillosis complicating chronic airways limitation.

Pseudomembranous necrotising bronchial aspergillosis is a variety of invasive aspergillosis found in immunosuppressed patients. A case is presented of a 66 year old woman whose only underlying disease was chronic airways limitation. The pathological findings and clinical implications are discussed.

Computed tomography in established adult respiratory distress syndrome. Correlation with lung injury score.

STUDY OBJECTIVES: To identify serial changes in the appearances of the lungs on computed tomography (CT) in patients with established adult respiratory distress syndrome (ARDS). Second, to evaluate any relationship between the extent of morphologic abnormalities on CT anatomic and physiologic derangement using a numeric score of the severity of lung injury. DESIGN: Retrospective, descriptive. SETTING: Adult intensive care unit, Department of Radiology, and outpatient department of a national tertiary referral center. PATIENTS: Eight patients meeting diagnostic criteria for ARDS able to tolerate CT scanning during the acute phase of their illness and who survived to be reevaluated during convalescence. INTERVENTIONS: Mechanical ventilatory support. Conventional intensive care support of other failed systems a appropriate. MEASUREMENTS AND RESULTS: Thin-section CT scans of the lungs categorized as to extent (calculated percent volume of abnormal lung), distribution, and dominant disease pattern. Concurrent lung injury score (LIS) was recorded at the time of the CT during the acute phase of illness (mean, 26 days; range, 3 to 48 days after precipitating event) and at follow-up (96; 17 to 187 days). On initial CT scans, disease patterns included ground-glass opacification (8/8), parenchymal distortion (8/8), multifocal areas of consolidation (6/8), reticular opacities (6/8), and linear opacities (5/8). On follow-up scans, there was clearing of consolidation in all patients, but ground-glass opacification persisted in four of eight patients. The reticular pattern persisted unchanged in five of eight patients, became more extensive in two of eight, and developed in one. A reticular pattern was most pronounced in areas that had been densely consolidated previously. Evidence of parenchymal distortion, present on the initial scan in all patients, persisted in six of eight patients. Computed tomographic features suggestive of emphysema developed in one patient. The LIS revealed moderate to severe ARDS in all patients initially; this decreased to a mild or zero LIS at follow-up. Overall, there was 76.9% +/- 5.3% abnormal lung on the initial CT scan and 34.5 +/- 9.3% on the follow-up CT scan. There was a significant correlation between the extent of abnormalities on CT and LIS (r = 0.75, p < 0.01). CONCLUSIONS: The CT appearances of patients with ARDS who survive are variable and relate to the pattern of disease in the acute phase. Furthermore, the extent of CT abnormalities correlates strongly with LIS in both the acute phase and at follow-up.

Adult respiratory distress syndrome: has there been a change in outcome predictive measures?

BACKGROUND: Studies suggest that the mortality in adults with acute respiratory distress (ARDS) has not changed over the past two decades, despite the introduction of new therapeutic techniques and sophisticated ventilatory support devices. Mortality and physiological variables that might predict outcome in patients with ARDS were therefore assessed. METHODS: A retrospective survey was undertaken in 41 patients with ARDS. RESULTS: Mortality was 66%. Only the presence of sepsis predicted death. CONCLUSION: Mortality from ARDS is unchanged. Currently available severity scoring systems are not helpful in predicting outcome.

Continuous veno-venous haemofiltration following cardio-pulmonary bypass. Indications and outcome in 35 patients.

OBJECTIVE: To study the impact of continuous veno-venous haemofiltration on survival in patients with acute renal failure (ARF) following cardio-pulmonary bypass (CPB) surgery. DESIGN: A retrospective study of all patients requiring haemofiltration after CPB over a 2 year period. SETTING: A 20 bedded, adult cardothoracic intensive care unit in a postgraduate teaching hospital. PATIENTS: 35 patients (26 male, age range 24-74 years) required haemofiltration (2.7% of the total number of patients undergoing CPB). MAIN RESULTS: Cardiovascular failure post CPB was the commonest causes of ARF (n = 16). Indications for haemofiltration were uremia (21), oligo-anuria (11), volume overload (2) and hyperkalaemia (1). Mean time from CPB to the initiation of haemofiltration was 8 days (range 0-15 days). Mean urea was 30 mmol/l and creatinine 362 mumol/l immediately prior to treatment. Urea was well-controlled in all patients, although 2 needed haemodiafiltration. Twenty-six patients died during their admission to the ICU (74% mortality). A further 3 patients died during their hospital admission, following discharge from ICU. Outcome was particularly poor in patients with cardiovascular failure following CPB (16 cases, 0 survivors). Survivors tended to commence filtration earlier (mean of 4 vs 7 days for non-survivors) and required treatment for a mean period of 8 days (range 1-26 days). Survival was determined by the number of failed organ systems at the start of haemofiltration. Thus, 100% of patients with single system failure survived, compared to only 10% with 3 or more system failure. CONCLUSIONS: Despite the theoretical advantages of haemofiltration and the effective control of uraemia the mortality associated with ARF following CPB remains high and is probably determined by the number of failed organs systems.

The pulmonary physician and critical care. 2. The injured lung: conventional and novel respiratory therapy.

Several alternatives to conventional ventilation in acute lung injury are now available and have been investigated to a varying degree. The assessment of all such techniques is limited by difficulties in designing proper comparative studies and by the time needed to recruit a large number of appropriate patients with acute lung injury. A common theme of lung volume maintenance combined with strategies designed to limit the extent of ventilator induced lung damage has emerged and should encourage reassessment of the conventional approach. The results of several large prospective comparative studies are eagerly awaited. Meanwhile we may reasonably suggest that improvements in respiratory support, together with advances in microbiological and pharmacological treatment, have the potential for improving the persistently disappointing survival rate in acute lung injury.

Adult respiratory distress syndrome following cardiopulmonary bypass: incidence and prediction.

The outcome of adult respiratory distress syndrome complicating cardiopulmonary bypass has changed little in recent years. A retrospective, case-controlled study was designed to assess the incidence of the adult respiratory distress syndrome in these circumstances and the extent to which it could be linked with pre and peri-operative predictive factors. Eleven patients who developed the syndrome out of 840 who underwent cardiopulmonary bypass over a 9 month period were compared with 53 controls matched for sex, operation and surgeon. The incidence of adult respiratory distress syndrome and its mortality were 1.3% and 53% respectively. Significant predictors were a high intra and postoperative intervention score, the total volume of blood pumped during bypass (greater than 300 l) and age (greater than 60 years). These risk factors should alert the clinician to the possibility of severe postoperative pulmonary complications.