Comparison of the lower inflection point on the static total respiratory compliance curve with outcomes in postoperative cardiothoracic patients

BACKGROUND: Routine use of positive end-expiratory pressure (based on the pressure at the lower inflection point on the static total respiratory compliance curve) along with a maneuver to recruit atelectatic lung has been advocated after cardiothoracic surgery. OBJECTIVES: To determine if the lower inflection point is related to outcomes in patients after sternotomy and cardiopulmonary bypass. METHOD: A prospective observational study involving estimation of the lower inflection point on the inflation pressure-volume plot obtained with a low-flow technique. Duration of intubation, length of stay, respiratory complications, and results of spirometry were compared between patients with a "high " inflection point (> or =10 cm H2O) and patients with a "low" inflection point (< or =5 cm H2O). RESULTS: Ninety-five patients were enrolled. After exclusion for incomplete data, 65 patients (49 men, 16 women; mean age, 66.1 years; SD, 9.5 years) were included. The mean lower inflection point was 6.33 cm H2O (SD, 3.4 cm H2O). A second lower inflection point was observed on 5 plots (mean, 21 cm H2O; SD, 1.4 cm H2O). Nine patients had high inflection points (mean, 13.1 cm H2O; SD, 3.0 cm H2O), and 33 had low inflection points (mean, 3.9 cm H2O; SD, 0.98 cm H2O). No outcome measures differed between groups. CONCLUSIONS: In patients with short intubation times and predictable postoperative course, general use of a lung recruitment strategy involving sustained inflations and adjustment of positive end-expiratory pressure based on the lower inflection point is difficult to justify.