Oxygen Consumption Changes in the Septic Pony

SUMMARY Oxygen consumption was studied in 5 awake septic ponies after iv injection of live Escherichia coli . Cardiac output, rectal temperature, pcv , heart rate, arterial and pulmonary arterial blood gas, pH, and hemoglobin (Hb) determinations were performed before (base line) and after injection of E coli . After injection of E coli , the cardiac index decreased from a base line mean of 4.45 ± 0.15 L/min/m 2 to 2.83 ± 0.21 L/min/m 2 ( P < 0.05). Mean arterial oxygen content increased from a base line mean of 15.19 ± 0.67 ml of O 2 /dl of blood to 20.73 ± 0.07 ml of O 2 /dl ( P < 0.05). Mean mixed venous content increased from a mean base-line value of 10.65 ± 0.74 ml of O 2 /dl to 16.65 ± 1.14 ml of O 2 /dl at postinfusion hour ( pih ) 1 ( P < 0.05). There were no significant changes in the difference between mean arterial and mean mixed venous oxygen content. Arterial pcv increased from a mean base line of 28.91 ± 0.31% to 39.44 ± 0.54% ( P < 0.05). Although pcv was increased, there were no significant changes in total protein until pih 5. Arterial Hb increased from a base-line mean of 11.18 ± 1.71 g/dl to 14.73 ± 1.0 g/dl ( P < 0.05). Oxygen delivery index was maintained near a base-line mean of 587.2 ± 29.0 ml of O 2 /min/m 2 . Significant decreases in oxygen delivery were seen only at pih 5. Oxygen consumption index decreased from a mean base-line value of 181.7 ± 2.8 ml of O 2 /min/m 2 to mean value of 122.8 ± 7.8 ml of O 2 /min/m 2 at pih 2 ( P < 0.05). Significant decreases were also seen in the oxygen diffusion capacity to 2.42 ± 0.49 ml of O 2 /min/m 2 /mm of Hg from a base-line mean of 5.05 ± 0.49 ml of O 2 /min/m 2 /mm of Hg. The septic pony develops pronounced changes in total body oxygen consumption. Although cardiac depression was severe, oxygen delivery was maintained due to an increased arterial Hb concentration. The oxygen consumption decreased as oxygen diffusion capacity decreased. Early decreases in oxygen consumption may have been due to the decreased area for oxygen diffusion that resulted from an increased peripheral resistance, whereas later decreases in oxygen consumption may have been due to increased amounts of interstitial fluid.