Gagan D. Kamal

Inconsistent esophageal doppler cardiac output during acute blood loss

Application of the Doppler principle can provide relatively noninvasive and continuous measurement of cardiac output. However, it is based on certain assumptions that may introduce error. Esophageal Doppler cardiac output was compared with Fick cardiac output during acute blood loss (35-45% estimated blood volume) in eight anesthetized pigs. Mean Fick cardiac output decreased from 4.8 to 1.9 l/min, mean Doppler cardiac output from 4.9 to 2.9 l/min. This was accompanied by a decrease in mean arterial pressure from 119 to 55 mmHg and increase in heart rate from a mean of 115 to 156 beats/min. There was an inconsistent association between the two methods both within and between individual animals. Cubic polynomial regression equations of cardiac output with time indicated small measurement error in Fick (R2: mean 0.93, range 0.99-0.75) as opposed to Doppler (R2: mean 0.67, range 0.93-0.16) cardiac output. In one animal Doppler cardiac output showed an increase with time and in one the Doppler cardiac output measurements were unrelated to time. There was highly variable association comparing Fick versus Doppler cardiac output with correlations ranging from -0.76 to 0.98. A sign test for mean differences indicated that Doppler derived cardiac output was higher than Fick cardiac output, and the chance of this occurring if the true difference was zero was less than 1 in 1,000. A test for homogeneity of correlations was also rejected. Inaccuracies in individual assumptions in the computation of esophageal Doppler cardiac output, especially unaccounted changes in aortic diameter, are responsible for the inconsistent and unpredictable values of Doppler cardiac output obtained in this experimental model of hemorrhage.

Reduced Intravascular Catheter-related Infection by Routine Use of Antibiotic-bonded Catheters in a Surgical Intensive Care Unit

We report a comparative analysis of intravascular catheter-related infection before and after routine use of antibiotic-bonded catheters in an intensive care unit. Cefazolin-bonded catheters were placed in patients requiring catheterization for at least 3 days, or with remote infection, standard catheters at other times. One thousand forty-five catheters (259 patients) over 6 months were compared with 801 (236 antibiotic-bonded, 565 standard) catheters (239 patients) the next 6 months. After use of antibiotic-bonded catheters, we found: 1.7% catheters infected versus 3.7% (p = 0.01); catheter-associated bacteremia 0.1% versus 1.3% (p < 0.005); catheter-related infection rate 4.39 versus 10.73 per 1000 patient days (p < 0.005), and 5.06 versus 11.47 per 1000 catheter days (p < 0.01); and cumulative risk of infection decreased (p < 0.005). Antibiotic-bonded catheters were used with more remote infections (52% versus 27%, p < 0.001), had longer indwelling time (4.4 versus 3.1 days, p = 0.0001), and more were inserted over a guide wire (66% vs. 28%, p < 0.001). In conclusion routine use of antibiotic-bonded catheters was associated with a significant reduction in infectious complications.

Stable and reproducible porcine model of acute lung injury induced by oleic acid

Background and Methods.Previous studies on acute lung injury induced with oleic acid did not attempt to limit the influence of secondary changes on pulmonary circulation, and cardiopulmonary variable data were only collected and processed intermittently. Our study was designed to continuously monitor the following variables in five swine: systemic and pulmonary pressure; mixed venous oxygen saturation (Sao2) and arterial oxygen saturation (Sao2); minute oxygen consumption and CO2 production before, during, and for 4 hr after the infusion of oleic acid. A personal computer was programmed to produce 20-sec updates of deadspace ratio (VD/VT), venous admixture (Qsp/Qt), pulmonary (PVR) and systemic vascular resistance (SVR), and cardiac output (Qt) from these data. Results.During the oleic acid infusion, there were increases in PVR, SVR, heart rate (HR), mean pulmonary arterial pressure (MPAP), Qsp/Qt, and VD/VT, and a decrease in Qt, Sao2, and Svo2. Thirty minutes after the oleic acid infusion, there was a further increase in HR, Qsp/Qt, and VD/VT, while MPAP, PVR, and SVR gradually decreased to pre-oleic acid infusion levels. No further decrease in Sao2, Svo2, and Qt was observed during that time. After the 30-min period, there was no further change in the cardiopulmonary variables.Conclusion: Our method of continuous monitoring was able to demonstrate in swine both the dynamic changes during, and stability after, the oleic acid infusion. (Crit Care Med 1991; 19:405)

Continuous, in vivo pulmonary venous admixture from fiberoptically measured hemoglobin saturations.

In six anesthetized swine, pulmonary venous admixture (Qsp/Qt) was calculated by four methods: a) Qsp/Qt 1, fiberoptically measured arterial and mixed venous Hgb saturation (SaO2 and SvO2), PaO2 and PvO2 derived from saturations; b) Qsp/Qt 2, fiberoptically measured SaO2 and SvO2, PaO2 and PvO2 measured by blood gas analysis; c) Qsp/Qt 3, PaO2 and PvO2 measured by blood gas analysis, SaO2 and SvO2 derived from tensions; d) Qsp/Qt 4, SaO2 and SvO2 measured by bench oximetry, PaO2 and PvO2 derived from saturations. Input from the fiberoptic catheters was fed into a computer programmed to calculate Qsp/Qt 1 every 20 sec. Fifty-eight of these values were compared with simultaneously calculated Qsp/Qt 2, 3, and 4. There was no difference between fiberoptic and derived SaO2 or fiberoptic and cooximetric SvO2. Correlations and slopes for Qsp/Qt 1 with Qsp/Qt 2, 3, and 4 were significant (p less than .05). Comparing mean differences, Qsp/Qt 1 was significantly different only from Qsp/Qt 3 (p less than .01). We conclude that dual oximetry reliably tracks Qsp/Qt.

Reduced venous admixture in hemorrhagic hypovolemia: maintenance of arterial oxygenation by selective pulmonary vascular collapse

In nine anesthetized and ventilated swine, a microcomputer calculated cardiac output, venous admixture (Qsp/Qt) and physiologic deadspace (VD/VT) every 20 sec, utilizing dual oximetry and a gas exchange analyzer. After lung injury with ethchlorvynol (ECV), animals were bled 40% blood volume over 40 min. Mean cardiac output decreased 7.0 to 2.2 L/min (p < .05) accompanied by a decrease in mean Qsp/Qt from 0.28 to 0.14 (p < .05) and an increase in mean VD/VT from 0.39 to 0.54 (p < .05). Arterial Hgb saturation (Sao2) increased from 88 ± 7% to 90 ± 6%. On regression of all data points for each variable, Qsp/Qt had a positive correlation with cardiac output (r = .90), mean arterial pressure (MAP, r = .87), mean pulmonary artery pressure (MPAP, r = .86), and mixed venous Hgb saturation (Svo2, r = .89, p < .001). VD/VT had an inverse correlation with cardiac output (r = −.90), MAP (r = −.82), Qsp/Qt (r = −.83), MPAP (r = −.77), and Svo2 (r = −.92, p < .001). The decreasing Qsp/Qt and increasing VD/VT, with decreasing pulmonary perfusion pressures, were attributed to selective loss of perfusion to alveoli with low ventilation/perfusion ratios. (Crit Care Med 1990; 18:208)