Increasing cardiac output by fluid loading: effects on indocyanine green plasma disappearance rate and splanchnic microcirculation

BACKGROUND: Sufficient cardiac pre-load for maintaining adequate cardiac output is a major goal in the treatment of critically ill patients. We studied the effects of increasing cardiac output by fluid loading on the indocyanine green plasma disappearance rate (ICG-PDR) and gastric mucosal regional CO2 tension (PRco2) as an indicator of splanchnic microcirculation. METHODS: With approval by our ethics committee and written consent, we studied post-operatively 12 patients (1 female, 11 males; 66 +/- 13 years) with elective coronary artery bypass grafting (n = 10) or aortic valve replacement (n = 2). All patients had received pulmonary artery and left atrial catheterization previously for clinical indications. Cardiac output and filling pressures were measured immediately after intensive care unit (ICU) admission and 1 h after the beginning of fluid loading. RESULTS: Overall, 630 +/- 130 ml of 6% hydroxyethylstarch (130 kDa) was infused with the splanchnic perfusion pressure remaining constant. Norepinephrine and epinephrine dosages were unchanged. The cardiac index increased significantly from 2.8 +/- 0.7 to 3.5 +/- 0.6 l/min/m2 and the stroke volume index from 30 +/- 7 to 38 +/- 8 ml/m2. ICG-PDR showed no significant change, i.e. from 21.2 +/- 6.5 to 21.6 +/- 6.5%/min. Gastric mucosal PRco2 and the Pco2 gap (difference between regional and end-tidal CO2 tension) were constant, i.e. changed from 5.1 +/- 0.8 to 5.5 +/- 1.1 kPa and from 0.9 +/- 0.5 to 1.0 +/- 0.7 kPa, respectively. CONCLUSION: Increasing cardiac output to supranormal values by fluid loading is not associated with a significant change in ICG-PDR or gastric mucosal PRco2.