Oxygen Fraction Adjustment According to Body Surface Area during Extracorporeal Circulation

Abstract

Background: The inspiratory oxygen fraction (FiO₂) is usually set between 60% and 100% during conventional extracorporeal circulation (ECC). However, this strategy causes partial oxygen pressure (PaO₂) to reach hyperoxemic levels (>180 mmHg). During anesthetic management of cardiothoracic surgery it is important to keep PaO₂ levels between 80-180 mmHg. The aim of this study was to assess whether adjusting FiO₂ levels in accordance with body temperature and body surface area (BSA) during ECC is an effective method for maintaining normoxemic PaO₂ during cardiac surgery.

Methods: After approval from the Ethics Committee of the University of Acıbadem, informed consent was given from 60 patients. FiO₂ adjustment strategies applied to the patients in the groups were as follows: FiO₂ levels were set as 0.21 × BSA during hypothermia and 0.21 × BSA + 10 during rewarming in Group I; 0.18 × BSA during hypothermia and 0.18 × BSA + 15 during rewarming in Group II; and 0.18 × BSA during hypothermia and variable with body temperature during rewarming in Group III. Arterial blood gas values and hemodynamic parameters were recorded before ECC (T1); at the 10th minute of cross clamp (T2); when the esophageal temperature (OT) reached 34°C (T3); when OT reached 36°C (T4); and just before the cessation of ECC (T5).

Results: Mean PaO₂ was significantly higher in Group I than in Group II at T2 and T3 (P = .0001 and P = .0001, respectively); in Group I than in Group III at T1 (P = .02); and in Group II than in Group III at T2, T3, and T4
(P = .0001 for all). 

Conclusion: Adjustment of FiO₂ according to BSA rather than keeping it at a constant level is more appropriate for keeping PaO₂ between safe level limits. However, since oxygen consumption of cells vary with body temperature, it would be appropriate to set FiO₂ levels in concordance with the body temperature in the
rewarming period.