Joseph C. Gabel

Effect of Cardiac Output on Extravascular Lung Water Estimates Made with the Edwards® Lung Water Computer

The Edwards lung water computer system uses the thermal-dye indicator technique to estimate the lung extravascular fluid volume (EVLW). The authors tested the effect of changes in cardiac output (CO) on EVLW estimates made with the lung water computer in six dogs anesthetized with halothane. Baseline CO was 2.5 +/- 1.3 l/min (mean +/- SD); CO subsequently was increased either by 220% or decreased by 70% by either giving 0.5 mg/kg of isoproterenol or increasing the inspired halothane (1-4%), respectively. There was a significant correlation between the estimated EVLW and CO in each animal (P less than 0.05) such that a 50% decrease in CO from baseline caused an approximately 40% increase in estimated EVLW. Postmortem examination showed that the lungs were not edematous, even though the lung water computer data indicated that severe pulmonary edema had developed at reduced COs. At increased COs, estimated EVLW decreased. The authors conclude that the Edwards lung water computer overestimates lung water, possibly because the thermal indicator diffuses into nonpulmonary as well as pulmonary tissue. The overestimate is greatest at low cardiac outputs.

Pulmonary capillary pressure and permeability.

An appreciation of the “state of the art” of pulmonary capillary pressure and permeability must necessarily form an important part of the basis of a rational choice of fluid therapy. The present state of the understanding of pulmonary transcapillary fluid exchange is developed. Laboratory data are used in conjunction with clinical evidence to construct and support the physiological concepts set forth.

Relation between lowered colloid osmotic pressure, respiratory failure, and death.

Plasma colloid osmotic pressure was measured each day in 84 intensive care unit patients. Probit analysis demonstrated a direct relationship between colloid osmotic pressure (COP) and survival. The COP associated with a 50% survival rate was 15.0 torr. COP was higher in survivors than in nonsurvivors without respiratory failure and in patients who recovered from respiratory failure. We conclude that lowered COP is associated with an elevated mortality rate. However, the relationship to death is not explained by the relationship to respiratory failure.

Comparison of techniques to measure pulmonary capillary filtration coefficients in dogs

The pulmonary capillary filtration coefficient (Kf) was estimated with two different techniques in the same preparation. The lower left lobes of nine halothane-anesthetized dogs were continuously weighed while the perfusion pressures were controlled. In one technique (weight transient technique) we increased the arterial (Pa) and venous (Pv) pressures in previously isogravimetric lobes and estimated the initial rate of capillary filtration from the rate of weight gain. The initial rate of weight gain was then divided by the calculated change in capillary pressure (Pc = (Pa + Pv)2) to calculate Kf. For the second Kf determination, Pa and Pv were increased to edema-producing levels and the rate of weight gain was determined at two or three elevated pressures (constant weight gain technique). Kf was calculated as the change in the rate of weight gain divided by the change in Pc. Although the weight transient Kf (0.047 ± 0.005 g/min · mm Hg) was significantly higher than the continuous weight gain Kf of 0.038 ± 0.004 (P < 0.05, paired data), the two Kfs were close. These data indicate that in experiments performed in this way, these two independent techniques yield similar values of Kf.