Blood gases and acid-base values of unanesthetized rats exposed to hypoxia

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Abstract
Rats were exposed to O2 concentrations reduced gradually to and maintained for 20 min. at 10.4, 8.3, 6.6, and 4.9%. Arterial O2 saturation of unanesthetized rats averaged 91.3% in controls and, after the above graded hypoxia, fell to 65, 61, 50, and 38%, respectively. At 6.6 and 4.8% O2 the rat values were about 15% higher than existing data on dogs at comparable hypoxic levels at altitude. Arterial acid-base changes at 10.4 and 8.3% O2 were minimal except for increased pH; CO2 content, plasma bicarbonate, lactic acid, and pyruvic acid were not significantly altered. At 6.6% O2 the CO2 content and bicarbonate declined, pH remained elevated, and five of nine rats showed "excess lactate." At 4.9% O2 the CO2 content and bicarbonate were low, pH varied, excess lactafe was high, and mortality was 13%. The critical O2 concentration for the appearance of significant excess lactate was approximately 6.6% with O2 saturation about 50%.