Randomised controlled trial to investigate the relationship between mild hypercapnia and cerebral oxygen saturation in patients undergoing major surgery

Objectives The effects of hypercapnia on regional cerebral oxygen saturation (rSO2) during surgery are unclear. We conducted a randomised controlled trial to investigate the relationship between mild hypercapnia and rSO2. We hypothesised that, compared with targeted normocapnia (TN), targeted mild hypercapnia (TMH) during major surgery would increase rSO2. Design A prospective, randomised, controlled trial in adult participants undergoing elective major surgery. Setting A single tertiary centre in Heidelberg, Victoria, Australia. Participants 40 participants were randomised to either a TMH or TN group (20 to each). Interventions TMH (partial pressure of carbon dioxide in arterial blood, PaCO2, 45–55 mm Hg) or TN (PaCO2 35–40 mm Hg) was delivered via controlled ventilation throughout surgery. Primary and secondary outcome measures The primary endpoint was the absolute difference between the two groups in percentage change in rSO2 from baseline to completion of surgery. Secondary endpoints included intraoperative pH, bicarbonate concentration, base excess, serum potassium concentration, incidence of postoperative delirium and length of stay (LOS) in hospital. Results The absolute difference between the two groups in percentage change in rSO2 from the baseline to the completion of surgery was 19.0% higher in both hemispheres with TMH (p Conclusion TMH was associated with a stable increase in rSO2 from the baseline, while TN was associated with a decrease in rSO2 in both hemispheres in patients undergoing major surgery. This resulted in a clear separation of percentage change in rSO2 from the baseline between TMH and TN over time. Our findings provide the rationale for larger studies on TMH during surgery. Trial registration number The Australian New Zealand Clinical Trials Registry (ACTRN12616000320459).