Increased intrathoracic pressure affects cerebral oxygenation following cardiac surgery

Summary

Background

Cerebral oximetry reflects circulatory stability during surgery. We evaluated whether frontal lobe oxygenation is influenced by a transient increase in intrathoracic pressure as induced by a lung recruitment manoeuvre.

Methods

Intrathoracic pressure was increased to 40 cm H₂O for 20 s immediately after cardiac surgery in ten patients (age 64 ± 10 year, mean ± SD) with frontal lobe oxygenation assessed by near-infrared spectroscopy and cardiac output by thermodilution.

Results

The lung recruitment manoeuvre increased arterial O₂ pressure (from 29 ± 15 to 40 ± 12 kPa) with a decrease in mean arterial pressure (MAP) (from 69 ± 7 to 55 ± 11 mmHg), cardiac output (from 5·4 ± 0·6 to 5·0 ± 0·7 l min⁻¹) and frontal lobe oxygenation (from 68 ± 9 to 60 ± 13%; all P<0·05). A reduction in MAP by more than 15 mmHg caused cerebral desaturation by 10%, the lowest cerebral oxygenation (44%) was with a reduction in MAP by 24 mmHg, and according to multiple linear regression, only MAP predicted cerebral deoxygenation (P = 0·03). Following the lung recruitment manoeuvre, hemodynamic variables and frontal lobe oxygenation were restored.

Conclusions

A lung recruitment manoeuvre decreases frontal lobe oxygenation when MAP is low suggesting that with increased intrathoracic pressure, arterial pressure should be kept within the limits of cerebral autoregulation.