The authors' objectives were as follows: 1) to characterize for the first time the relationship between whole body O2 delivery (Ḋ(O2)) and O2 consumption (V̇(O2)) in adult conscious dogs; and 2) to assess the effects of the inhalational anesthetic, halothane, on that relationship. Ḋ(O2) 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. V̇(O2) was measured at different values of Ḋ(O2) in dogs in the fully conscious state and again during halothane anesthesia. A 'binning' technique indicated that halothane decreased V̇(O2) (P < 0.01) at any given value of Ḋ(O2) over a broad range of V̇(O2). 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·kg-1·min-1 and increased (P < 0.01) O2 extraction at COD from 31 ± 3 to 40 ± 2%. However, the Ḋ(O2)-V̇(O2) plots measured in both conscious and halothane-anesthetized dogs did not exhibit a discrete discontinuity but rather were closely fit (correlation coefficient = 0.98) by an exponential equation of the following form: O2 extraction = B1·(1 - exp (-Ḋ(O2)/B2))/Ḋ(O2), where B1 is the delivery-independent estimate of V̇(O2) and B2 is the 'delivery constant', i.e., the Ḋ(O2) associated with a V̇(O2) equal to 63% of B1. Halothane decreased B1 (P < 0.01) from 5.3 ± 0.1 to 3.9 ± 0.1 ml·kg-1·min-1 and decreased B2 (P < 0.01) from 5.6 ± 0.3 to 3.6 ± 0.3 ml·kg-1·min-1 compared with that measured in conscious dogs. Thus, compared with the conscious state, halothane anesthesia alters the fundamental relationship between Ḋ(O2) and V̇(O2) and may have a beneficial effect on tissue oxygenation at low values of Ḋ(O2).
All Science Journal Classification (ASJC) codes
- Anesthesiology and Pain Medicine