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

Objective: To compare two ventilator settings in the postoperative weaning period. Patient-triggered automatic switching between controlled ventilatio n and supported spontaneous breathing (Automode, AM) was compared to synchr onised intermittent mandatory ventilation (SIMV) with stepwise manual adjus tment 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 aft er 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 s ignificant differences were seen for cardiocirculatory parameters, airway p ressures and oxygenation between the two groups. There was a trend to short er weaning times with AM (136 +/- 46 min vs 169 +/- 68 min, n.s.), the aver age 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 (Pa CO2) 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 neur osurgical patients with healthy lungs. Compared to a SIMV weaning procedure , fewer manipulations on the ventilator are necessary and individual adapta tion of ventilation seems to be more accurate.