Sizing the lung of mechanically ventilated patients.

INTRODUCTION: This small observational study was motivated by our belief that scaling the tidal volume in mechanically ventilated patients to the size of the injured lung is safer and more 'physiologic' than scaling it to predicted body weight, i.e. its size before it was injured. We defined Total Lung Capacity (TLC) as the thoracic gas volume at an airway pressure of 40 cm H2O and tested if TLC could be inferred from the volume of gas that enters the lungs during a brief 'recruitment' maneuver. METHODS: Lung volume at relaxed end expiration (Vrel) as well as inspiratory capacity (IC), defined as the volume of gas that enters the lung during a 5 second inflation to 40 cm H2O, were measured in 14 patients with respiratory failure. TLC was defined as the sum of IC and Vrel. The dependence of IC and Vrel on body mass index (BMI), respiratory system elastance and plateau airway pressure was assessed. RESULTS: TLC was reduced to 59 ± 23% of that predicted. Vrel/TLC, which averaged 0.45 ± 0.11, was no different than the 0.47 ± 0.04 predicted during health in the supine posture. The greater than expected variability in observed Vrel/TLC was largely accounted for by BMI. Vrel and IC were correlated (r = 0.76). Taking BMI into account strengthened the correlation (r = 0.92). CONCLUSIONS: We conclude that body mass is a powerful determinant of lung volume and plateau airway pressure. Effective lung size can be easily estimated from a recruitment maneuver derived inspiratory capacity measurement and body mass index.

Toward the prevention of acute lung injury: protocol-guided limitation of large tidal volume ventilation and inappropriate transfusion.

OBJECTIVE: We evaluated the effect of two quality improvement interventions (low tidal volume ventilation and restrictive transfusion) on the development of acute lung injury in mechanically ventilated patients. DESIGN: Observational cohort study. SETTING: Three intensive care units in a tertiary academic center. PATIENTS: We included patients who were mechanically ventilated for > or =48 hrs excluding those who refused research authorization or had preexisting acute lung injury or pneumonectomy. INTERVENTIONS: Multifaceted interdisciplinary intervention consisting of Web-based teaching, respiratory therapy protocol, and decision support within computerized order entry. MEASUREMENTS AND MAIN RESULTS: Of 375 patients who met the inclusion and exclusion criteria, 212 were ventilated before and 163 after the interventions. Baseline characteristics were similar between the two groups except for a lower frequency of sepsis (27% vs. 17%, p = .030), trend toward lower median glucose level (140 mg/dL, interquartile range 118-168 vs. 132 mg/dL, interquartile range 113-156, p = .096), and lower frequency of pneumonia (27% vs. 20%, p = .130) during the second period. We observed a large decrease in tidal volume (10.6-7.7 mL/kg predicted body weight, p < .001), in peak airway pressure (31-25 cm H2O, p < .001), and in the percentage of transfused patients (63% to 38%, p < .001) after the intervention. The frequency of acute lung injury decreased from 28% to 10% (p < .001). The duration of mechanical ventilation decreased from a median of 5 (interquartile range 4-9) to 4 (interquartile range 4-8) days (p = .030). When adjusted for baseline characteristics in a multivariate logistic regression analysis, protocol intervention was associated with a reduction in the frequency of new acute lung injury (odds ratio 0.21, 95% confidence interval 0.10-0.40). CONCLUSIONS: Interdisciplinary intervention effectively decreased large tidal volumes and unnecessary transfusion in mechanically ventilated patients and was associated with a decreased frequency of new acute lung injury.

Failure of non-invasive ventilation in patients with acute lung injury: observational cohort study.

INTRODUCTION: The role of non-invasive positive pressure ventilation (NIPPV) in the treatment of acute lung injury (ALI) is controversial. We sought to assess the outcome of ALI that was initially treated with NIPPV and to identify specific risk factors for NIPPV failure. METHODS: In this observational cohort study at the two intensive care units of a tertiary center, we identified consecutive patients with ALI who were initially treated with NIPPV. Data on demographics, APACHE III scores, degree of hypoxemia, ALI risk factors and NIPPV respiratory parameters were recorded. Univariate and multivariate regression analyses were performed to identify risk factors for NIPPV failure. RESULTS: Of 79 consecutive patients who met the inclusion criteria, 23 were excluded because of a do not resuscitate order and two did not give research authorization. Of the remaining 54 patients, 38 (70.3%) failed NIPPV, among them all 19 patients with shock. In a stepwise logistic regression restricted to patients without shock, metabolic acidosis (odds ratio 1.27, 95% confidence interval (CI) 1.03 to 0.07 per unit of base deficit) and severe hypoxemia (odds ratio 1.03, 95%CI 1.01 to 1.05 per unit decrease in ratio of arterial partial pressure of O2 and inspired O2 concentration--PaO2/FiO2) predicted NIPPV failure. In patients who failed NIPPV, the observed mortality was higher than APACHE predicted mortality (68% versus 39%, p < 0.01). CONCLUSION: NIPPV should be tried very cautiously or not at all in patients with ALI who have shock, metabolic acidosis or profound hypoxemia.