End-inspiratory pause prolongation in acute respiratory distress syndrome patients: effects on gas exchange and mechanics

Abstract

BackgroundEnd-inspiratory pause (EIP) prolongation decreases dead space-to-tidal volume ratio (Vd/Vt) and PaCO2. We do not know the physiological benefits of this approach to improve respiratory system mechanics in acute respiratory distress syndrome (ARDS) patients when mild hypercapnia is of no concern.MethodsThe investigation was conducted in an intensive care unit of a university hospital, and 13 ARDS patients were included. The study was designed in three phases. First phase, baseline measurements were taken. Second phase, the EIP was prolonged until one of the following was achieved: (1) EIP of 0.7 s; (2) intrinsic positive end-expiratory pressure ≥1 cmH2O; or (3) inspiratory–expiratory ratio 1:1. Third phase, the Vt was decreased (30 mL every 30 min) until PaCO2 equal to baseline was reached. FiO2, PEEP, airflow and respiratory rate were kept constant.ResultsEIP was prolonged from 0.12 ± 0.04 to 0.7 s in all patients. This decreased the Vd/Vt and PaCO2 (0.70 ± 0.07 to 0.64 ± 0.08, p < 0.001 and 54 ± 9 to 50 ± 8 mmHg, p = 0.001, respectively). In the third phase, the decrease in Vt (from 6.3 ± 0.8 to 5.6 ± 0.8 mL/Kg PBW, p < 0.001) allowed to decrease plateau pressure and driving pressure (24 ± 3 to 22 ± 3 cmH2O, p < 0.001 and 13.4 ± 3.6 to 10.9 ± 3.1 cmH2O, p < 0.001, respectively) and increased respiratory system compliance from 29 ± 9 to 32 ± 11 mL/cmH2O (p = 0.001). PaO2 did not significantly change.ConclusionsProlonging EIP allowed a significant decrease in Vt without changes in PaCO2 in passively ventilated ARDS patients. This produced a significant decrease in plateau pressure and driving pressure and significantly increased respiratory system compliance, which suggests less overdistension and less dynamic strain.

Fifty Years of Research in ARDS.Vt Selection in Acute Respiratory Distress Syndrome

“…Prone positioning may lead to substantial recruitment in many patients with ARDS, which may also reduce dead space and respiratory acidosis. In addition, increasing the duration of inspiration, as with an endinspiratory pause, can decrease Pa CO 2 in small amounts to decrease acidosis from smaller VTs (45,46).…”

Hypercapnia during acute respiratory distress syndrome: the tree that hides the forest!

“…Aguirre- (37). They showed that this decrease in PaCO 2 was correlated with the drop in physiological dead space (37). However, it has also been reported that ventilation with inverted I/E ratio could have deleterious hemodynamic effects (38).…”

“…To avoid such a side effect of too high a RR, Prin et al reported that the use of heated humidifiers significantly decreased the level of PaCO 2 in moderate or severe ARDS, as compared with the use of heat and moisture exchangers (36). Aguirre- (37). They showed that this decrease in PaCO 2 was correlated with the drop in physiological dead space (37).…”

Individualized mechanical ventilation in a shared ventilator setting: limits, safety and technical details.

“…In ARDS, this could result in higher levels of intrinsic PEEP, and dynamic airway obstruction and expiratory flow limitation frequently result in air trapping. [15] Our bench setup was designed to see whether we could demonstrate the presence of intrinsic PEEP in the individual patient in a dynamic situation.…”