Matrix effects and the performance and selection of quality-control procedures to monitor PO2 measurements.

We have assessed how variation in the matrix of control materials would affect error detection and false-rejection characteristics of quality-control (QC) procedures used to monitor PO2 in blood gas measurements. To determine the expected QC performance, we generated power curves for S(mat)/S(meas) ratios of 0.0-4.0. These curves were used to estimate the probabilities of rejecting analytical runs having medically important errors, calculated from the quality required by the CLIA '88 proficiency testing criterion and the precision and accuracy expected for a typical analytical system. When S(mat)/S(meas) ratios are low, the effects of matrix on QC performance are not serious, permitting selections of QC procedures based on simple power curves for a single component of variation. As S(mat)/S(meas) ratios increase, single-rule procedures generally show a loss in error detection, whereas multirule procedures, including the 3(1)s control rule, show an increase in false rejections. An optimized QC design is presented.

Sweating, hemodynamic responses, and thermal equilibration during hyperthermia in humans.

Hyperthermia, to 42 degrees C, for treatment of cancer, was induced 23 times in 13 anesthetized patients utilizing an extracorporeal heat-exchange circuit. Sweating rate over the chest, abdomen, arm and forearm ranged from 0.2 to 0.9 mg sweat X min-1 X cm-2. Cardiac index (CI), stroke volume index (SVI), left ventricular stroke work index, and right ventricular stroke work index initially increased to 221 +/- 12.5, 162 +/- 9.6, 142 +/- 11, and 203 +/- 29% but later fell to 169-173, 113-120, 69, and 148-117% of control, respectively. Heart rate initially rose to 145 +/- 5.9% and then stabilized at 160-162% of control. Pulmonary arterial occlusion pressure and central venous pressure initially fell to 82 +/- 8 and 93 +/- 9% but later rose to 87-102 and 105-120% of control levels, respectively. The hemodynamic response to severe heat stress in anesthetized humans was characterized by peripheral vasodilation accompanied by compensatory increases in heart rate and CI. Ventricular function, as reflected by SVI and CI, declined with continued heat stress, despite reduced afterload and stable or increased filling pressures. Pulmonary arterial temperature rose fastest, followed by the esophageal, rectal, and bladder temperatures, respectively. Jugular bulb temperature also rose rapidly.

Lung lymph flow during volume infusions.

We investigated the effect of intravenous isotonic crystalloid solution infusion on lung lymph flow. Tracheobronchial lung lymph vessels were cannulated in 13 anesthetized dogs. The lymph flow rate was measured 1) with the lymph flowing against atmospheric pressure (QL), and 2) with the pressure at the outflow end of the lymph cannula equal to systemic venous pressure (QLV). QL and QLV were measured alternately in each lymph vessel. In one group of nine dogs, the base-line QL and QLV were 18 +/- 9 and 13 +/- 6 (SD) microliter/min, respectively (P less than 0.05). QL increased by 4.8 +/- 1.4-fold, and QLV increased by 3.5 +/- 2.1-fold during a 4-h infusion of 25 ml X kg-1 X h-1 of Ringer solution. QLV was significantly less than QL at all times. The increases in lymph flow were caused primarily by a reduction in the effective resistance of the lymph vessels with little rise in the pressure driving lymph from the lungs. Because QLV flowed against systemic venous pressure, the increase in QLV was blunted by a 3.1 +/- 2.3 cmH2O rise in venous pressure during the infusions. In the remaining four dogs, we infused Ringer solution rapidly in order to raise venous pressure to greater than 15 cmH2O. This caused QL to increase by 25 +/- 7-fold; however, QLV decreased to zero. We conclude that elevations in venous pressure which occur during volume infusions oppose lung lymph flow and lead to accumulation of excess fluid in the lungs.

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.