Brain glucose and lactate levels during ventilator-induced hypo- and hypercapnia*

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Abstract

Objective

Levels of glucose and lactate were measured in the brain by means of microdialysis in order to evaluate the effects of ventilator-induced hypocapnia and hypercapnia on brain metabolism in healthy non-brain-traumatized animals.

Design and setting

Prospective animal study in a university laboratory.

Subjects

Eight adult Landrace/Yorkshire pigs.

Interventions

The microdialysis probe was inserted in the brain along with a multiparameter sensor and intracranial pressure (ICP) probe. The animals were ventilated in a pressure-controlled mode according to the open lung concept with an inspired oxygen fraction of 0·4/1·0. Starting at normoventilation (PaCO2 ±40 mmHg) two steps of both hypercapnia (PCO2 ± 70 and 100 mmHg) and hypocapnia (PaCO2 ± 20 and 30 mmHg) were performed. Under these conditions, brain glucose and lactate levels as well as brain oxygen (PbrO2), brain carbon dioxide (PbrCO2), brain pH (brpH), brain temperature and ICP were measured.

Results

At hypercapnia (PaCO2 = 102·7 mmHg) there were no significant changes in brain glucose and lactate but there was a significant increase in PbrCO2, PbrO2 and ICP. In contrast, at hypocapnia (PCO2 = 19·8 mmHg) there was a significant increase in brain lactate and a significant decrease in both brain glucose and PbrCO2.

Conclusions

Hypocapnia decreases brain glucose and increases brain lactate concentration, indicating anaerobic metabolism, whereas hypercapnia has no influence on levels of brain glucose and brain lactate.

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