Effects of optimizing cardiac output by fluid loading on the indocyanine green plasma disappearance rate and splanchnic microcirculation
© BioMed Central Ltd 2005
Published: 7 March 2005
Hypovolemia may be associated with splanchnic hypoperfusion and reduced in liver blood flow and function. In general, optimizing the cardiac preload to increase the cardiac output – a major determinant of systemic oxygen delivery – is a primary clinical goal. In this study, we tested the hypothesis that increasing the cardiac output by optimizing the intravascular fluid status leads to an improved regional (i.e. hepato-splanchnic) blood flow and function as assessed by the indocyanine green plasma disappearance rate (ICG-PDR), which has been shown to be of major prognostic relevance .
With approval by our ethics committee and written patient consent we prospectively studied 12 postoperative cardiac surgical patients (mean age 66 ± 13 years) who underwent elective coronary artery bypass grafting. All patients underwent extended hemodynamic monitoring by a pulmonary artery and left atrial catheter for clinical indication. Microcirculation within the splanchnic area was assessed by gastric tonometry, and liver blood flow and function were determined non-invasively by transcutaneous measurement of ICG-PDR. All these patients who were considered hypovolemic underwent hemodynamic optimization by infusion of hydroxyethylstarch (130 kDa). Global and regional parameters were measured at baseline and 1 hour after fluid challenge. All patients received pressure-controlled mechanical ventilation and respirator settings remained unchanged throughout the study. Data are expressed as mean ± standard deviation. For statistical analysis, a paired t test was used and P < 0.05 was considered significant.
Overall, 630 ± 130 ml hydroxyethylstarch were administered. In all patients, the cardiac index significantly increased following fluid administration, on average from 2.8 ± 0.7 to 3.6 ± 0.6 l/min/m2 and the stroke volume index from 30 ± 7 to 38 ± 8 ml/m2, respectively. With respect to cardiac preload, the central venous pressure significantly increased from 6 ± 2 to 12 ± 2 mmHg and the left atrial pressure from 5 ± 3 to 11 ± 3 mmHg, respectively. However, the ICG-PDR and PCO2 gap (difference between gastric mucosal and end-tidal CO2 tension) did not change significantly (i.e. from 21.2 ± 6.5 to 21.6 ± 6.5%/min and from 0.9 ± 0.5 to 1.0 ± 0.7 kPa).
Optimizing cardiac output by fluid loading per se is not associated with a significant change in ICG-PDR or gastric mucosal PCO2. However, since ICG-PDR in all patients with a value <18%min increased, we hypothesize that particularly patients with an a priori low ICG-PDR may benefit from optimizing cardiac index by fluid loading. Further studies are needed to test this hypothesis.