Hemodynamic and Renal Effects of Dopexamine and Dobutamine in Patients With Reduced Cardiac Output Following Coronary Artery Bypass Grafting: Statistical Methods

Four of the five patients in the dopexamine group and three of the five in the dobutamine group had been receiving digoxin preoperatively; this was restarted after the surgical procedure. No other inotropic medications were given to the patients during the study period.
Hemodynamic data and renal function are reported as mean ± SEM. Significant differences in hemodynamic data were sought using repeated measures analysis of variance. Demographic factors were initially added to the repeated measures analysis as covariates; however, none of these demographic covariates showed any significance as main effects or time interactions (all with p>0.2) on PCWP, Cl, or HR. Thus, these demographic covariates were removed as effects in the repeated measures analyses to conserve error degrees of freedom. For MAP, however, the weight-time interaction and the creatinine clearance-time interactions were significant (p=0.005 and p=0.013, respectively) when both were included in the statistical model; thus, weight and creatinine clearance were retained as covariates only in the repeated measures analysis of MAP. Flovent inhaler flovent inhaler Individual contrasts for time and drug effects were made using Holm’s sequentially rejective Bonferroni correction for multiple comparisons.

Independent analyses were performed for data obtained during the OR loading phase (initial 30 min after drug administration) and for the ICU maintenance phase of the study. Possible drug effects on urinary volumes and sodium excretion were determined using analysis of variance with preoperative creatinine clearance as a covariate. Power analyses were performed to determine theoretical sample sizes needed to show that dopexamine significantly (a=0.05) increases 24-h urine output and sodium excretion. These power analyses were based on the one-sided t test with the urine output and sodium excretion data regression-adjusted for creatinine clearance. The power analyses were performed post hoc with SDs estimated from the experimental data. Results are tabulated in Tables 1 and 2. Estimated SDs of the regression-adjusted data were 925 ml/24 h for urine output and 346 mEq/24 h for sodium excretion. Statistical significance is set at an a level of 0.05 with adjustments for multiple comparisons when appropriate.

Table 1—Power Analysis of Urine Volume

Increase in Urine Output, ml/24 h Power
50% 80% 90%
250 74 170 235
500 18 42 59
750 8 19 27
1,000 5 11 15
1,500 2 5 7

Table 2—Power Analysis of Sodium Excretion

Increase in Sodium Excretion, mEq/24 h Power
50% 80% 90%
10 6,475 14,800 20,500
50 260 600 820
75 115 265 365
100 65 148 205
150 29 66 91
This entry was posted in Pulmonary Function and tagged Cardiac surgery (CABG), dobutamine, dopexamine, inotropic support (inotropy).