Effect of hyperventilation on cerebral oxygen supply-demand balance in patients with traumatic brain injury

Minghua CHENG; Yingna XU

ABSTRACT

BACKGROUND:

Inadequate hyperventilation may trigger cerebrovascular contraction and lead to lowered cerebral perfusion and oxygen supply-demand imbalance.

OBJECTIVE:

To investigate the influence of hyperventilation on oxygen saturation in the internal jugular vein, difference in oxygen and lactic acid contents between the cerebral arteries and veins in patients with serious traumatic brain injury.

DESIGN:

Case analysis.

SETTING:

Department of Anesthesiology, First Hospital Affiliated to Shantou University.

PARTICIPANTS:

Sixteen patients who received emergency operations in the First Hospital Affiliated to Shantou University between January and July 2002.

METHODS:

Patients with traumatic brain injury underwent operation under general anesthesia, and the PaCO2 was maintained at 30 mm Hg for 15 minutes by regulating the respiration rate, followed by decrease to 25 mm Hg, maintained for 15 minutes before restoration to 30 mm Hg for 15 minutes. The fractional concentration of inspired oxygen was adjusted to maintain blood PaO2 at around 100-150 mm Hg, and the blood sample was collected from the artery and internal jugular vein 15 minutes after adjustment of PaCO2 for blood gas analysis. The PaO2 was then increased to 200-250 mm Hg by increasing the fractional concentration of inspired oxygen, and the PaCO2 was adjusted from 30 to 25 and then back to 30 mm Hg in the described manner, and the oxygen saturation in the internal jugular vein, difference in oxygen and lactic acid contents between the arteries and the veins were measured.MAIN OUTCOME

MEASURES:

Influence of blood PaO2 and PaCO2 on oxygen saturation in the internal jugular vein, difference in oxygen and lactic acid contents between the arteries and the veins.

RESULTS:

Sixteen patients met the diagnostic criteria and completed data collection. The arterial PaCO2 decreased from 30 to 25 mm Hg when arterial blood oxygen pressure increased from 100-150 to 200-250 mm Hg, which leads to obvious decrease of oxygen saturation in the internal jugular vein and obvious increased difference in oxygen content between the cerebral artery and vein. However the absolute value of oxygen saturation in the internal jugular vein was obviously higher at PaO2 of 200-250 mm Hg than that at PaO2 of 100-150 mm Hg, while the absolute value of cerebral arteriovenous difference of brain oxygen content was obviously lower. Compared to the basal level, the arteriovenous lactic acid difference was obviously increased at PaO2 of 100-150 mm Hg,PaCO2 of 30 and 25 mm Hg, and at PaO2 of 200-250 mm Hg and PaCO2 of 25 mm Hg.

CONCLUSION:

Relatively higher PaO2 (200-250 mm Hg) and mild hyperventilation (PaCO2 of 30 mm Hg) has no obvious effect on brain oxygen supply-demand balance.