Summary
The cerebral blood flow response to hypocapnia was quantitated utilizing two methods of ventilation. Increased volume hyperventilation produced hypocapnia and decreased CBF but was associated with cardiopulmonary changes which raised mean intrathoracic pressure, decreased venous return and decreased cardiac output. This resulted in increased CSFP, decreased cerebral perfusion pressure and decreased CMRO2 at PaCO2 values below 20 mm Hg which was indicative of hypoxia. Constant volume hyperventilation with incremental removal of mechanical dead space was considered as hypocapnia where PaCO2 was the singular variable because associated cardiopulmonary changes were minimized. This resulted in no CSFP changes and no changes in CMRO2 even at low PaCO2 values below 20 mm Hg.
It is concluded that hypocapnia per se does not produce brain tissue hypoxia in normal or brain injured dogs. Hypoxia secondary to hypocapnia is the result of the associated cardiopulmonary and cerebrovascular changes associated with mechanical hyperventilation.
Résumé
La réponse vasculaire cérébrale à 1’hypocapnée fut investiguée par deux techniques de ventilation. D’une part, l’hyperventilation à grand volume produit une hypocapnée, diminue le flot vasculaire cérébral, mais s’accompagne d’une augmentation de la pression intra-thoracique moyenne, d’une diminution du retour veineux et du débit cardiaque. Ceci se solde par une augmentation de la pression du L.C.R., par une diminution de la pression de perfusion cérébrale et du C.M.R. O2 à une PaCO2 inférieure à 20 mm Hg qui signale une hypoxie.
D’autre part, une hyperventilation à volume constant avec diminution marquée de l’espace mort fut considérée comme hypocapnée où la PaCO2 se présente comme la seule variable puisque les changements cardio-pulmonaires furent minimes. Nous retrouvons aucune variation de la pression du L.C.R., de la C.M.R. O2 à une PaCO2 inférieure à 20 mm Hg.
L’hypocapnée per se n’apporte done aucune hypoxie tissulaire cérébrale chez le chien normal ou lésé au point de vue cérébral. L’hypoxie secondaire à l’hypocapnée est le résultat de changements cario-pulmonaires ou cérébro-vasculaires associés à l’hyperventilation mécanique.
Article PDF
Similar content being viewed by others
Avoid common mistakes on your manuscript.
References
Reivich, M. Arterial PCO2 and cerebral hemodynamics. Amer. J. Physiol.206: 25–35 (1964).
Raichle, M.E., Posner, J.B., &Plum, F. Cerebral blood flow during and after hyper-ventilation. Arch. Neurol.33: 394–403 (1970).
Cournand, A., Motley, H.L., Werko, C., &Richards, D.W., Jr. Physiological studies of the effects of intermittent positive pressure breathing on cardiac output in man. Am. J. Physiol.152: 162 (1948).
Morgan, B.C., Crawford, E.W., Hornbein, T.F., Martin, W.E., &Guntheroth, W.G. Hemodynamic effects of changes in arterial carbon dioxide tension during intermittent positive pressure ventilation. Anesthesiol.28: 866 (1967).
Morgan, B.C., Martin, W.E., Hornbein, T.F., Crawford, E.W., &Guntheroth, W.G. Hemodynamic effects of intermittent positive pressure respiration. Anesthesiology27: 584–590 (1966).
Dawson, B., Michenfelder, J.D., &Theye, R.A. Effects of ketamine on canine cerebral blood flow and metabolism: modification by prior administration of thiopental. Anesth. &Analg.50: 443–447 (1971).
Rapela, C.E. &Green, H.D. Autoregulation of canine cerebral blood flow. Suppl. I. Circ. Res. Vol. XIV and SV. 205–41 (1964).
Bruce D., Schutz, H., &Langfitt, T. 1972 (personal communication).
Tababaddor, K., Bhushan, C, PevsneR, P.A., &Walker, A.E. Prognostic value of CBF and CMRO2 in acute head trauma. J. of Trauma:12: No. 12, 1053–1055 (1972).
Yamaguchi, T., Regli, F., &Waltz, A.C. Effect of PaCO2 on hyperemia and Ischemia in experimental cerebral infarction. Stroke:2: 139–147 (1971).
Harp, J.R. &Wollman, H. Cerebral metabolic effects of hyperventilation and deliberate hypotension. Brit. J. Anaesth.45: 256–262 (1973).
Fink, B.R. &Haschke, R.H. Anaesthetic effects on cerebral metabolism. Anesthesiology39: 199–215 (1973).
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Stoyka, W.W., Schutz, H. Cerebral response to hypocapnia in normal and brain-injured dogs. Canad. Anaesth. Soc. J. 21, 205–214 (1974). https://doi.org/10.1007/BF03013113
Issue Date:
DOI: https://doi.org/10.1007/BF03013113