Jugular bulb desaturation during rewarming from cardiopulmonary bypass is influenced by isoflurane

Introduction

Jugular bulb oxyhaemoglobin desaturation (SjO₂≤ 50%) during the rewarming phase of cardiopulmonary bypass (CPB) is associated with postoperative cognitive deficits [1]. Isoflurane effects cerebral blood flow and cerebral metabolic rate, both of which affect SjO₂ [2]. We report the effect of isoflurane on the incidence of desaturation during rewarming from CPB for coronary artery surgery.

Materials and methods

One hundred and nine men and 16 women of mean age 60 years (standard deviation 9 years) were studied. Isoflurane 1% was used on CPB for hypnosis in 61 patients and 64 received either propofol or a combination of morphine and midazolam. A catheter was positioned in the right jugular bulb. At 36°C, during rewarming, paired jugular bulb and arterial samples were taken for blood gas and SjO₂ measurements. Nasopharyngeal temperature was measured throughout. SjO₂ values were analyzed as measured and also after correction to an arterial carbon dioxide tension of 5.3 kPa. The number of patients who desaturated in each group was analyzed by χ²test and the mean differences in the variables by Student's t-test.

Results

Blood gas and blood pressure results are summarised in Table 1. Correcting for carbon dioxide significantly reduced the number of patients who desaturated in the morphine and midazolam group (25–4.7%, χ² = 10.4; P < 0.01) but not the isoflurane group (4.9–1.6%; P > 0.2).

Table 1 Blood gas and blood pressure results

Conclusion

The incidence of desaturation during rewarming was significantly reduced by isoflurane. This suggests the balance between cerebral blood flow and cerebral metabolic rate during the rewarming phase of CPB is better preserved in the presence of isoflurane. Different arterial carbon dioxide tension levels cannot explain this effect, but the rate of rewarming may be one factor. Whether prevention of desaturation by isoflurane improves cognitive outcome is yet to be determined.

Acknowledgement

Funded by Wellcome Trust grant 050190.