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PEDIATRIC ANESTHESIA

The Cerebrovascular Response to Hypocapnia in Children Receiving Propofol

From the Department of Anesthesia, The Hospital for Sick Children and the University of Toronto, Toronto, Ontario, Canada.

Address correspondence and reprint requests to C. Karsli, MD, Department of Anesthesia, The Hospital for Sick Children, 555, University Avenue, Toronto, ON. M5G 1X8, Canada. Address email to cengiz.karsli{at}sickkids.ca

Hypocapnia is used to treat acute increases in intracranial pressure during neurosurgery. Cerebrovascular reactivity to carbon dioxide (CCO₂R) is preserved above 35 mm Hg ETCO₂ in children during propofol anesthesia; however, a plateau effect has been suggested below 35 mm Hg. To further delineate this phenomenon, we measured CCO₂R by transcranial Doppler (TCD) sonography over small increments in ETCO₂ in 27 healthy children. Anesthesia comprised a standardized propofol infusion and a caudal epidural block. A TCD probe was placed to measure middle cerebral artery blood flow velocity (V_mca). ETCO₂ was adjusted between 24 and 40 mm Hg at 1–2 mm Hg increments using an exogenous source of CO₂. There was an exponential relationship between ETCO₂ and V_mca above an ETCO₂ value of 30 mm Hg (r = 0.82). However, V_mca did not change with ETCO₂ less than 30 mm Hg (r = 0.06). There were no significant changes in heart rate or arterial blood pressure. We conclude that when contemplating methods to decrease brain volume and intracranial pressure, hyperventilation to ETCO₂ values less than 30 mm Hg may not be necessary in children receiving propofol, as no further reduction in cerebral blood flow velocity will be achieved.

IMPLICATIONS: Cerebrovascular reactivity to CO₂ is preserved above 30 mm Hg ETCO₂ in children during propofol anesthesia but lost below 30 mm Hg. Reducing ETCO₂ values to less than 30 mm Hg in children receiving propofol anesthesia may not result in any further reduction in cerebral blood flow velocity.

This article has been cited by other articles:

				T. Engelhardt, M. K. Chan, A. J. McCheyne, C. Karsli, I. Luginbuehl, and B. Bissonnette The Effect of Varying Continuous Propofol Infusions on Plasma Cyclic Guanosine 3',5'-Monophosphate Concentrations in Anesthetized Children Anesth. Analg., September 1, 2007; 105(3): 616 - 619. [Abstract] [Full Text] [PDF]

Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999