A technique for continuous bedside monitoring of global cerebral energy state

Abstract

Background: Cerebral cytoplasmatic redox state is a sensitive indicator of cerebral oxidative metabolism and is conventionally evaluated from the extracellular lactate/pyruvate (LP) ratio. In the present experimental study of global cerebral ischemia induced by hemorrhagic shock, we investigate whether the LP ratio obtained from microdialysis of cerebral venous blood may be used as a surrogate marker of global cerebral energy state.

Methods: Six female pigs were anesthetized and vital parameters were recorded. Microdialysis catheters were placed in the left parietal lobe, the superior sagittal sinus, and the femoral artery. Hemorrhagic shock was achieved by bleeding the animals to a mean arterial pressure (MAP) of approximately 40 mmHg and kept at a MAP of about 30-40 mmHg for 90 min. The animals were resuscitated with autologous whole blood followed by 3 h of observation.

Results: The LP ratio obtained from the intracerebral and intravenous catheters immediately increased during the period of hemorrhagic shock while the LP ratio in the arterial blood remained close to normal levels. At the end of the experiment, median LP ratio (interquartile range) obtained from the intracerebral, intravenous, and intra-arterial microdialysis catheters were 846 (243-1990), 309 (103-488), and 27 (21-31), respectively. There was a significant difference in the LP ratio obtained from the intravenous location and the intra-arterial location (P < 0.001).

Conclusions: During cerebral ischemia induced by severe hemorrhagic shock, intravascular microdialysis of the draining venous blood will exhibit changes of the LP ratio revealing the deterioration of global cerebral oxidative energy metabolism. In neurocritical care, this technique might be used to give information regarding global cerebral energy metabolism in addition to the regional information obtained from intracerebral microdialysis catheters. The technique might also be used to evaluate cerebral energy state in various critical care conditions when insertion of an intracerebral microdialysis catheter may be contraindicated, e.g., resuscitation after cardiac standstill, open-heart surgery, and multi-trauma.

Keywords: Cerebral energy state; Hemorrhagic shock; Ischemia; Microdialysis.

Fig. 1

Median (interquartile range) arterial pressure (MAP) and brain tissue oxygen tension (PbtO₂) in pigs with induced hemorrhagic shock. Note that during the period of hemorrhagic shock, the declining MAP was accompanied by a decrease in PbtO₂ to a very low level (<5 mmHg). After re-infusion of autologous blood, MAP increased to close to baseline level whereas PbtO₂ remained very low. S indicates the start of bleeding to achieve a MAP of 40 mmHg. The black bar on the x-axis from 0 to 90 min indicates the shock period before resuscitation was started

Fig. 2

Logarithmic illustration of the LP ratios (median (interquartile range)) in the sagittal sinus and femoral artery during hemorrhagic shock in pigs. The increase in the LP ratio in the sagittal sinus was significantly higher (p < 0.001) than in the arterial blood. S indicates the start of bleeding to achieve a MAP of 40 mmHg. The black bar on the x-axis from 0 to 90 min indicates the shock period before resuscitation was started

Fig. 3

Microdialysis levels of lactate (median (interquartile range)) in the sagittal sinus and femoral artery doing hemorrhagic shock in pigs. Note that lactate levels increases in both compartments during shock. After re-infusion of blood, lactate levels in the sagittal sinus remain at a high level throughout the monitoring period. In contrast, the lactate levels in the femoral artery decline to a near-normal level. S indicates the start of bleeding to achieve a MAP of 40 mmHg