Increasing cardiac output by epinephrine after cardiac surgery: effects on indocyanine green plasma disappearance rate and splanchnic microcirculation

Introduction

Most clinical studies have so far focused on the regional effects of epinephrine (i.e. hepato-splanchnic blood flow) in septic patients. In cardiac surgical patients, however, inotropic (i.e. epinephrine) support is often necessary for optimizing cardiac output postoperatively. We tested whether increasing cardiac output by epinephrine leads to an improved regional (i.e. hepato-splanchnic) blood flow and function.

Methods

After approval by our ethics committee and written consent, we postoperatively studied 12 patients (mean age 71 ± 8 years) with elective coronary artery bypass grafting (n = 2) or aortic valve replacement (n = 10). All patients had a reduced left ventricular function and underwent extended hemodynamic monitoring by a pulmonary artery (CCO-PAC) for clinical indication. Microcirculation within the splanchnic area was assessed by gastric tonometry, liver blood flow and function non-invasively by transcutaneous measurement of the ICG-PDR. Since fluid loading led to no increase in cardiac output, patients were considered nonfluid responsive. Measurements were made on ICU admission and after 1 hour of epinephrine treatment. The mean epinephrine dosage was changed from 0.02 to 0.08 μg/kg/min. All patients were on pressure-controlled mechanical ventilation and respirator settings remained unchanged throughout the study period. Data are the mean ± SD. P < 0.05 was considered statistically significant.

Results

The heart rate significantly increased from 97 ± 11 to 106 ± 12/min. Central venous (10 ± 3 vs 10 ± 4 mmHg) and left atrial (10 ± 5 vs 11 ± 5 mmHg) pressures were unchanged. The cardiac index and stroke volume index significantly increased from 2.7 ± 0.5 to 3.2 ± 0.5 l/min/m² and from 28 ± 6 to 31 ± 5 ml/m². Although systemic O₂ delivery and O₂ consumption significantly increased, the ICG-PDR did not change significantly (i.e. from 18.0 ± 5.6 to 19.5 ± 6.4%/min). The gastric mucosal PCO₂ and the PCO₂ gap (difference between regional and end-tidal PCO₂) significantly increased from 5.4 ± 1.0 to 5.9 ± 1.1 kPa and from 1.2 ± 0.8 to 1.5 ± 0.7 kPa, respectively.

Conclusion

Increasing cardiac output by epinephrine was associated with no change in the ICG-PDR but with a significant deterioration in gastric mucosal blood flow in patients after cardiac surgery.