Effect of Permissive Mild Hypercapnia on Cerebral Vasoreactivity in Infants: A Randomized Controlled Crossover Trial.
PaCO2 is a major regulator of cerebral vascular tone. Hypocapnia can result in poor neonatal neurological outcomes, presumably through decreased cerebral blood flow. The clinical effect of mild hypercapnia is less well known.
- This study investigates whether mild hypercapnia increases cerebral blood flow by calculating Tissue Oxygenation Index (TOI) and Tissue Haemoglobin Index (THI) using NIRS monitoring.
- 19 infants aged < 1 year were recruited into a randomised crossover study.
- Infants randomised to Group N(ormal) were ventilated to an EtCO2 of 5.5kPa, then 6.5kPa, then back to 5.5kPa.
- Infants randomised to Group H(ypercapnia) were ventilated to an EtCO2 of 6.5kPa, then 5.5kPa, then back to 6.5kPa.
- The primary outcome of this study found no evidence that mild hypercapnia affected TOI and THI. There was a large scatter in all NIRS parameters.
- Ancillary analysis found that mean arterial pressure (MAP) did correlate with TOI and THI.
- Overall, this study suggests that mild hypercapnia is not a strategy for increasing cerebral blood flow.
- The scatter of NIRS parameters shows its limitations as a single monitor of cerebral perfusion.
- Controlling MAP could be more important than PaCO2 for cerebral blood flow but the study was not designed to examine this specifically.
- Further studies are required to investigate whether more hypercapnia increases cerebral blood flow.
Reviewed by M. Tan