Canadian Journal of Anesthesia, Vol 25, 474-478, Copyright © 1978 by Canadian Anesthesiologists' Society

The Linear Relation of Cerebral Blood Flow to Arterial Oxygen Saturation in Hypoxic Hypoxia Induced with Nitrous Oxide or Nitrogen

¹ Department of Anaesthesia, St. Michael's Hospital, and University of Toronto
² Department of Anaesthesia, Univ. of Toronto

This study has demonstrated a linear relationship between cerebral blood flow and arterial oxygen saturation (Sa_OO2) in the cerebral blood flow response in the hypoxic range of PaO_OO2 values, which we believe is documented for the first time. The cerebral blood flow increased 1.02 per cent for each percentage decrease in Sa_OO2 in hypoxia induced with nitrogen. Hypoxia induced with nitrous oxide increased cerebral blood flow at the rate of 2.09 per cent for each one per cent decrease in Sa_OO2 which was dramatically more than the increase associated with hypoxia induced with nitrogen. Increased survival rates at lower Sa_OO2 levels suggested that nitrous oxide also exerts a protective effect on dog myocardium.

The mechanism by which hypoxia increases cerebral blood flow is unclear but the prevalent theory is one of neurogenic control which causes cerebral blood flow to increase as the intracellular hydrogen ion ([H⁺]I) increases in the progressive lactacidosis of hypoxia. The demonstration of a linear relationship between cerebral blood flow and Sa_OO2 will provide the statistician, the researcher and the clinician with a useful tool for the neurophysiological assessment of cerebralblood flow.