Am. J. Respir. Crit. Care Med.,
Volume 156, Number 4, October 1997, 1210-1216
End-Inspiratory Airway Occlusion
A Method To Assess the Pressure Developed by Inspiratory Muscles in
Patients with Acute Lung Injury Undergoing Pressure Support
GIUSEPPE
FOTI,
MAURIZIO
CEREDA,
GIULIANA
BANFI,
PAOLO
PELOSI,
ROBERTO
FUMAGALLI,
and
ANTONIO
PESENTI
Department of Anesthesia and Intensive Care, Ospedale S. Gerardo, Monza; Ospedale Maggiore, IRCCS, Milan;
and University of Milan, Milan, Italy
We evaluated the end-inspiratory occlusion maneuver as a means to estimate the inspiratory effort
during pressure support ventilation (PS). In nine nonobstructed acute lung injury (ALI) patients, we
applied four levels of PS (0, 5, 10, 15 cm H2O) to modify the inspiratory effort. End inspiratory occlusions (2 to 3 s) were performed at the end of each experimental period by pushing the inspiratory
hold button of the ventilator (Servo 900 C; Siemens, Berlin, Germany). We took the difference between the end-inspiratory occlusion plateau pressure and the airway pressure before the occlusion
(PEEP + PS) as an estimate of the inspiratory effort and called it PMI (Pmusc,index). From the esophageal pressure tracing we obtained a reference measurement of the pressure developed by the inspiratory muscles at end inspiration (Pmusc,ei) and of the pressure-time product per breath (PTP/b)
and per minute (PTP/min). In each patient, PMI was correlated with Pmusc,ei (p < 0.01) and PTP/b
(p < 0.01). A PMI threshold of 6 cm H2O detected PTP/min < 125 cm H2O s/min with a sensitivity of
0.89 and a specificity of 0.89. We conclude that PMI is a good estimate of the pressure developed
by the inspiratory muscles in ALI patients and may be used to titrate PS level. The major advantage
of PMI is that it can be obtained from the ventilator display without any additional equipment.
