Effect of end-inspiratory pause duration on plateau pressure in mechanically ventilated patients.
OBJECTIVE
To compare the values of plateau pressure (Pplat) recorded at different times after end-inspiratory occlusion and those of static elastance (Est,rs) and total resistance (Rrs) of the respiratory system.


METHODS
Physiological study.


METHODS
Medical intensive care unit of a university hospital.


METHODS
Eleven patients with ARDS and ten patients with COPD requiring tracheal intubation and mechanical ventilation were investigated. COPD patients were investigated on zero end-expiratory pressure (ZEEP) and ARDS patients on both ZEEP and positive end-expiratory pressure (PEEP).


RESULTS
Respiratory mechanics were assessed using the rapid airway occlusion technique. Tracheal pressure (Ptr) was measured downstream the endotracheal tube. Ptr was recorded 0.5 s, 1 s, 2 s, 3 s, and 5 s after a 5-s end-inspiratory occlusion. Est,rs and Rrs were computed at the same times using standard formula. In ARDS patients on ZEEP, Pplat amounted to 20+/-5, 20+/-5, 19+/-5, 19+/-5, and 18+/-5 cmH(2)O at 0.5, 1, 2, 3 and 5 s, respectively (P <0.001). In COPD patients, these values were 18+/-4 cmH(2)O, 17+/-4 cmH(2)O, 17+/-4 cmH(2)O, 16+/-4 cmH(2)O, and 16+/-4 cmH(2)O (P <0.001). Except for one ARDS patient on PEEP, Pplat was always less than 35 cmH(2)O, regardless of the time of measurement. As compared to 5 s, measurements at 0.5 s resulted in overestimation of Est,rs by 14% and 29% and in underestimation of Rrs by 34% and 24%, in ARDS and COPD patients, respectively.


CONCLUSIONS
Very early post-occlusion values of Pplat were statistically greater than at 3 s or 5 s. This probably has no major impact on the occurrence of volutrauma. Clinicians must be aware, however, that Est,rs and Rrs are greatly modified by the time of recording of Pplat.
Barberis
Luigi
L
Department of Anaesthesiology and Intensive Care Unit, Ospedale Maria Vittoria, Turin, Italy.
Manno
Emmanuello
E
Guérin
Claude
C
D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011175:Positive-Pressure Respiration / Q000379:methods*; D029424:Pulmonary Disease, Chronic Obstructive / Q000628:therapy; D012128:Respiratory Distress Syndrome / Q000628:therapy; D015656:Respiratory Mechanics