Effect of changes in inspired oxygen fraction on oxygen delivery during cardiac surgery: a substudy of the CARROT trial

Effects of intraoperative inspired oxygen fraction (FiO2 0.3 vs 0.8) on patients undergoing off-pump coronary artery bypass grafting: the CARROT multicenter, cluster-randomized trial

BACKGROUND

To maintain adequate oxygenation is of utmost importance in intraoperative care. However, clinical evidence supporting specific oxygen levels in distinct surgical settings is lacking. This study aimed to compare the effects of 30% and 80% oxygen in off-pump coronary artery bypass grafting (OPCAB).

METHODS

This multicenter trial was conducted in three tertiary hospitals from August 2019 to August 2021. Patients undergoing OPCAB were cluster-randomized to receive either 30% or 80% oxygen intraoperatively, based on the month when the surgery was performed. The primary endpoint was the length of hospital stay. Intraoperative hemodynamic data were also compared.

RESULTS

A total of 414 patients were cluster-randomized. Length of hospital stay was not different in the 30% oxygen group compared to the 80% oxygen group (median, 7.0 days vs 7.0 days; the sub-distribution hazard ratio, 0.98; 95% confidence interval [CI] 0.83-1.16; P = 0.808). The incidence of postoperative acute kidney injury was significantly higher in the 30% oxygen group than in the 80% oxygen group (30.7% vs 19.4%; odds ratio, 1.94; 95% CI 1.18-3.17; P = 0.036). Intraoperative time-weighted average mixed venous oxygen saturation was significantly higher in the 80% oxygen group (74% vs 64%; P < 0.001). The 80% oxygen group also had a significantly greater intraoperative time-weighted average cerebral regional oxygen saturation than the 30% oxygen group (56% vs 52%; P = 0.002).

CONCLUSIONS

In patients undergoing OPCAB, intraoperative administration of 80% oxygen did not decrease the length of hospital stay, compared to 30% oxygen, but may reduce postoperative acute kidney injury. Moreover, compared to 30% oxygen, intraoperative use of 80% oxygen improved oxygen delivery in patients undergoing OPCAB. Trial registration ClinicalTrials.gov (NCT03945565; April 8, 2019).

Effect of the Fraction of Inspired Oxygen on Intermittent Central Venous Oxygen Saturation Measurements

Background:

Central venous oxygen saturation (ScvO2) is an essential test readily performed both by medical and nursing personnel in a critical care setting. It gives information on the patient‘s oxygen supply, oxygen consumption, and cardiac output. It plays an important role in early goal-directed treatment.

Objectives:

This study was planned to assess the effect of different fractions of inspired oxygen (FiO2) levels on central venous oxygen saturation for consideration during the evaluation of central venous oxygen saturation.

Methods:

This interventional cross-over study enrolled 60 critically ill, nonmechanically ventilated patients. Blood samples were repeatedly drawn from the distal end of the central venous catheter for blood gas analysis after administration of 30%, 40%, and 50% FIO2 respectively.

Results:

The results showed that increasing FiO2 from 30% to 40% resulted in a mean increase in ScvO2 of 6.2%. While increasing FiO2 from 40% to 50% resulted in a mean increase in ScvO2 of 3.2%. A significant increase in ScvO2 with changes in FiO2 level was recorded among patients in shock or patients with pneumonia (from 30% to 50%, p=0.002 in shock patients and from 30% to 40%, p=0.02 in patients with pneumonia).

Conclusion:

Increasing FiO2 resulted in a substantial rise in ScvO2. ScvO2 changes in response to a therapeutic challenge should be interpreted at constant FiO2 level, especially in patients with pneumonia.