The Carrico index is the parameter that guides the requirement of oxygen in the postoperative period in patients undergoing head and neck surgery under general anaesthesia: a cross-sectional study.

Background & aims: Altered lung function and consequent decrease in oxygenation has been linked to the duration of anaesthesia. This necessitates oxygen monitoring and supplementation in the perioperative period. But, evidence is lacking regarding the parameter that guides best the oxygen supplementation in the postoperative period and the parameter that correlates best with the duration of anaesthesia.

Methods: Adult patients scheduled for head & neck surgery under general anaesthesia were recruited. Two radial arterial blood samples one at pre-induction and the other at one hour after extubation were obtained. Primary outcome measures were partial pressure of oxygen (PaO₂), saturation (SpO₂), arterial oxygen content (CaO₂) and Carrico index (PaO₂/FiO₂) and their relation with duration of anaesthesia.

Results: Data from 112 patients showed a hypoxaemia incidence of 11.6%. We observed a drop in the mean CaO₂ and haemoglobin concentration but a rise in the mean PaO₂ at recovery. The mean PaO₂/FiO₂ deteriorated by 225.65 ± 72.46 (95% CI 367.66, 83.64, p = 0.000) at recovery and there was a significant correlation (r = 0.2, p = 0.03) between duration of anaesthesia and decrease in PaO₂/FiO₂ at recovery with a regression coefficient of 0.27 (95% CI 0.02, 0.50).

Conclusions: The Carrico index was proven to be the best parameter which needs to be monitored perioperatively to detect the alteration in the gaseous exchange in patients undergoing general anaesthesia for head and neck surgery. There is a positive correlation between the decrease in the Carrico index and the duration of anaesthesia especially when it is prolonged beyond 150 minutes.