A prospective randomised study on clinical and economical aspects of closed loop control and common weaning protocols after cardiac surgery

Introduction

Adaptive support ventilation (ASV) is a microprocessor-controlled ventilatory mode allowing automated weaning. Under controlled ventilation a preset minimum minute ventilation is guaranteed and, based on a breath-to-breath-analysis, ventilatory support is withdrawn gradually with recovering spontaneous breathing. The self-controlled weaning process includes both reduction of mandatory breaths and reduction of pressure support. Respiratory rate and tidal volume are calculated using Otis' formula for optimal breathing pattern [1].

We asked whether there are differences between weaning protocols based on ASV or on common ventilatory modes after cardiac surgery regarding clinical and economical aspects.

Methods

After IRB approval and informed consent we studied 2 × 28 patients for hemodynamic and 2 × 10 patients for ventilatory parameters admitted to the ICU after aortocoronary bypass surgery. They were randomly assigned to the ASV group (GALILEO^®; Hamilton Medical, Rhäzüns, Switzerland) or to the standard group (EVITA 4^®; Dräger Medical, Lübeck, Germany). ICU staff was not involved in the study except in the instruction to use ASV in the ASV group until extubation, and no interventions were planned. The standard group was ventilated in the routine way using CPPV, SIMV and PS. Switches in the ventilatory mode (standard group) and ventilator adjustments according to blood gas analyses (both groups) were carried out by the nursing staff in consultation with the physician. All patients were sedated with propofol during the rewarming phase until the rectal temperature reached 36°C. Extubation was possible at normothermia, hemodynamic stability, sufficient spontaneous ventilation and without signs of imminent organ failure or major complications. We documented ventilatory and hemodynamic parameters every 60 min from admission to the ICU until transfer to the peripheral ward. For statistical analyses we built up matched pairs by age, gender and pre-existing diseases. Patient groups were equal regarding anaesthesia, postoperative sedation, kind and duration of operation and body temperature.

Results

There were no significant differences between both groups, neither in hemodynamic parameters nor in breathing parameters or blood gas analyses. Length of ICU stay was 1.7 ± 2.5 days (standard group) and 1.5 ± 1.4 days (ASV group), and time until extubation totalled 7.2 ± 3.4 h (standard group) and 7.8 ± 4.5 h (ASV group). Reintubation was not necessary in both groups. No patient failed ASV, so there was no need to change the ventilatory mode in this group. Using the ASV ventilator, adjustments were necessary 0.5 times at median (range 0–3), adapting the guaranteed minimal ventilation ('%MinVol') to blood gas analyses. In the standard group, the ventilatory mode was switched once at median (range 1–3), plus adaption of respiratory frequency or pressure support until extubation. The procedures to reduce FiO₂ were equal in both groups and PEEP remained constant.

Conclusion

In this study no differences in clinical parameters could be found between closed loop control and standard weaning protocol using the fast track concept after cardiac surgery. Considering economical aspects, adaptive support ventilation was superior to standard weaning since the nursing staff spent significantly less workload on ventilatory adjustments.