Effects of patient-triggered automatic switching between mandatory and supported ventilation in the postoperative weaning period

Abstract

Objective: To compare two ventilator settings in the postoperative weaning period. Patient-triggered automatic switching between controlled ventilation and supported spontaneous breathing (Automode, AM) was compared to synchronised intermittent mandatory ventilation (SIMV) with stepwise manual adjustment of mandatory frequency according to the breathing activity.

Design: Prospective clinical investigation.

Setting: Eighteen-bed intensive care unit in a university hospital.

Patients: Forty postoperative patients with healthy lungs who had undergone brain tumour surgery.

Interventions: Randomisation either to the AM or SIMV weaning procedure after entering the ICU.

Measurements and results: Total weaning time and number of manipulations on the ventilator were observed. Cardiocirculatory and respiratory parameters were measured consecutively at five points during the weaning period. No significant differences were seen for cardiocirculatory parameters, airway pressures and oxygenation between the two groups. There was a trend to shorter weaning times with AM (136 +/- 46 min vs 169 +/- 68 min, n.s.), the average number of manipulations on the ventilator was lower (0.55 +/- 0.69 vs 5.05 +/- 1.19,p < 0.001) and arterial partial pressure of carbon dioxide (PaCO2) levels showed fewer variations in the late phase of the weaning period (39.5 +/- 3.1 vs 38.3 +/- 7.2, p < 0.001 for differences in variance).

Conclusions: Automatic, patient-triggered switching between controlled and supported mode of ventilation can be used for postoperative weaning of neurosurgical patients with healthy lungs. Compared to a SIMV weaning procedure, fewer manipulations on the ventilator are necessary and individual adaptation of ventilation seems to be more accurate.