Isocapnic hyperventilation provides early extubation after sevoflurane anaesthesia for major ENT surgery: a clinical feasibility study  

BACKGROUND
Isocapnic hyperventilation (IHV) is a method that shortens time to extubation after inhalation anaesthesia by increasing airway CO2 during hyperventilation (HV).(1,2) In a pilot study on patients undergoing long-duration sevoflurane anaesthesia for major ear-nose-throat (ENT) surgery, we evaluated the feasibility of an alternative technique of IHV. (3,4)

METHODS
Fifteen adult patients weighing 76±12 kg were included. After end of surgery mechanical HV was started and CO2 delivered (DCO2) to the inspiratory limb of a closed standard breathing circuit. (Figure 1) DCO2 was dosed according to gender and weight, based on previous experimental studies.(3,4) Time to extubation and eye-opening was recorded. Inspired (FICO2) and expired (FETCO2) CO2 and arterial CO2 levels were monitored during IHV. (Figure 2) Cognition was tested preoperatively and at 20, 40 and 60 min after arrival in the PACU.

RESULTS
A DCO2 of 285±45 ml/min was necessary to achieve isocapnia during HV. The corresponding FICO2-level was 3.0±0.3%. Time from turning off the vaporizer (1.3±0.1 MAC) to extubation (0.2±0.1 MAC) was 11.3±1.8 min (range 8-14 min) after 342±131 min (range 206-676 min) of anaesthesia. PaCO2 and FETCO2, remained at normal levels during and after IHV. In 85% of patients postoperative cognition returned to preoperative values within 60 minutes. (Table 1, 2)

CONCLUSION
The patients were safely extubated shortly after discontinuing long-term sevoflurane anaesthesia. 
Perioperatively, we did not find any adverse effects on arterial blood gases or postoperative cognition. 
Use of standard anaesthesia monitoring is sufficient for easy administration of CO2 during hyperventilation and
FICO2 and FETCO2  values can be used to fine tune DCO2 during isocapnic hyperventilation 
This alternative method for IHV can potentially be used to decrease emergence time from inhalation anaesthesia.

References: (1) Sasano et al A Simple Apparatus for Accelerating Recovery from Inhaled Volatile Anesthetics Anesth Analg 2001; 93:1188-91. (2) Katznelson et al Isocapnic Hyperpnoea Shortens Postanestetic Care Unit Stay After Isoflurane Anesthesia Anesth Analg 2010; 111:403-8. (3) Hallen K et al. A simple method for isocapnic hyperventilation evaluated in a lung model. Acta anaesthesiologica Scandinavica 2016; 60: 597-606.(4) Hallen K et al Isocapnic hyperventilation shortens washout time for sevoflurane - an experimental in vivo study. Acta anaesthesiologica Scandinavica 2016; 60: 1261-9. (4)

Isocapnic hyperventilation provides early extubation after sevoflurane anaesthesia for major ENT surgery: a pilot study