Ventilation-perfusion inhomogeneity increases gas uptake in anesthesia: computer modeling of gas exchange.
Ventilation-perfusion (VA/Q) inhomogeneity was modeled to measure its effect on overall gas exchange during maintenance-phase N(2)O anesthesia with an inspired O(2) concentration of 30%. A multialveolar compartment computer model was used based on physiological log normal distributions of VA/Q inhomogeneity. Increasing the log standard deviation of the distribution of perfusion from 0 to 1.75 paradoxically increased O(2) uptake (VO(2)) where a low mixed venous partial pressure of N(2)O [high N(2)O uptake (VN(2)O)] was specified. With rising mixed venous partial pressure of N(2)O, a threshold was observed where VO(2) began to fall, whereas VN(2)O began to rise with increasing VA/Q inhomogeneity. This phenomenon is a magnification of the concentrating effects that VO(2) and VN(2)O have on each other in low VA/Q compartments. During "steady-state" N(2)O anesthesia, VN(2)O is predicted to paradoxically increase in the presence of worsening VA/Q inhomogeneity.
Peyton
P J
PJ
Department of Anaesthesia, Austin and Repatriation Medical Centre, Heidelberg 3084, Australia. phil@austin.unimelb.edu.au
Robinson
G J
GJ
Thompson
B
B
D000758:Anesthesia; D005740:Gases / Q000493:pharmacokinetics*; D006706:Homeostasis; D008954:Models, Biological; D010101:Oxygen Consumption; D011659:Pulmonary Gas Exchange; D012016:Reference Values; D014692:Ventilation-Perfusion Ratio
D005740:Gases