Study objectives: To assess the safety of frequent pressure-volume (PV) curve measurement in patients with acute lung injury (ALI)/ARDS.
Design: Prospective observational study.
Setting: Academic medical-surgical critical care unit.
Patients: Consecutive patients with ALI or ARDS.
Interventions: Static inspiratory PV curves of the respiratory system were determined twice on day 1, then once daily for up to 6 days using a syringe. At each time point, three separate measurements of the PV curve were made. A 100-mL graduated syringe was used to inflate patients’ lungs with 50- to 100-mL increments up to an airway pressure of 45 cm H2O or a total volume of 2 L; each volume step was maintained for 2 to 3 s until a plateau airway pressure was recorded. Outcome measures were mean arterial BP, heart rate (HR), and oxyhemoglobin saturation (Spo2) prior to and immediately after PV curve measurement. There were a priori criteria for procedure discontinuation if poorly tolerated.
Measurements and results: Eleven patients were enrolled with a total of 134 PV curves generated. Spo2 was 93 ± 4% (mean ± SD) before and fell to a nadir of 89 ± 5% during PV curve measurement (p < 0.001), but increased to 97 ± 4% immediately afterwards (p < 0.001, before vs after). HR rose from 106 ± 22 to 108 ± 22 beats/min immediately after the maneuver (p < 0.001). Mean arterial BP was 93 ± 15 mm Hg before and 100 ± 17 mm Hg immediately afterwards (p < 0.001). During PV curve measurement, systolic BP in one patient fell to 64 mm Hg from 113 mm Hg; in another patient, Spo2 dropped to 79% from 89%. Both changes were transient. The study was discontinued in one patient because of inability to tolerate zero positive end-expiratory pressure; in another patient, the study was discontinued because of the development of subcutaneous emphysema.
Conclusions: PV curve measurement by syringe technique is well tolerated in most patients. Nonetheless, the maneuver may cause significant changes in oxygenation and/or hemodynamics, necessitating close monitoring.