Halothane Alters the Oxygen Consumption-Oxygen Delivery Relationship Compared with Conscious State

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Abstract
The authors'' objectives were as follows: 1) to characterize for the first time the relationship between whole body O2 delivery (.ovrhdot.DO2) and O2 consumption (.ovrhdot.VO2) in adult conscious dogs; and 2) to assess the effects of the inhalational anesthetic, halothane, on that relationship. .ovrhdot.DO2 was varied over a wide range in chronically instrumented dogs by gradual inflation and deflation of a hydraulic occluder implanted around the thoracic inferior vena cava to alter venous return and cardiac output. .ovrhdot.VO2 was measured at different values of .ovrhdot.DO2 in dogs in the fully conscious state and again during halothane anesthesia. A "binning" technique indicated that halothane decreased .ovrhdot.VO2 (P < 0.01) at any given value of .ovrhdot.DO2 over a broad range of .ovrhdot.VO2. A two-line piecewise linear regression analysis technique indicated that halothane decreased (P < 0.01) the critical O2 delivery (COD) from 20 .+-. 3 to 10 .+-. 1 ml .cntdot. kg-1 .cntdot. min-1 and increased (P < 0.01) O2 extraction at COD from 31 .+-. 3 to 40 .+-. 2%. However, the .ovrhdot.DO2-.ovrhdot.VO2 plots measured in both conscious and halothane-anesthesized dogs did not exhibit a discrete discontinuity but rather were closely fit (correlation coefficient = 0.98) by an exponential of the following form: O2 extraction = B1 .cntdot. (1-exp(-.ovrhdot.DO2/B2))/.ovrhdot.DO2, where B1 is the delivery-independent estimate of .ovrhdot.VO2 and B2 is the "delivery constant," i.e., the .ovrhdot.DO2 associated with a .ovrhdot.VO2 equal to 63% of B1. Halothane decreased B1 (P < 0.01) from 5.3 .+-. 0.1 to 3.9 .+-. 0.1 ml .cntdot. kg-1 .cntdot. min-1 and decreased B2 (P < 0.01) from 5.6 .+-. 0.3 to 3.6 .+-. 0.3 ml .cntdot. kg-1 .cntdot. min-1 compared with that measured in conscious dogs. Thus, compared with the conscious state, halothane anesthesia alters the fundamental relationship between .ovrhdot.DO2 and .ovrhdot.VO2 and may have a beneficial effect on tissue oxygenation at low values of .ovrhdot.DO2.