Microcirculatory imaging in cardiac anesthesia: ketanserin reduces blood pressure but not perfused capillary density.

OBJECTIVES

It has become possible to image the human microcirculation at the bedside using sidestream dark field (SDF) imaging. This may help the clinician when correlation between global and microvascular hemodynamics may not be straightforward. Ketanserin, a serotonin and alpha-1 adrenoceptor antagonist, is used in some countries to treat elevated blood pressure after extracorporeal circulation. This might hamper microcirculatory perfusion. Conversely, it is also conceivable that microcirculatory flow is maintained or improved as a result of flow redistribution. In order to introduce SDF imaging in cardiac anesthesia, the authors set out to directly observe the sublingual microcirculation in this setting.

DESIGN

An observational study.

SETTING

A large teaching hospital.

PARTICIPANTS

Mechanically ventilated patients with elevated arterial blood pressure immediately after extracorporeal circulation (ECC).

INTERVENTION

An intravenous bolus of ketanserin, 0.15 mg/kg.

MEASUREMENTS AND MAIN RESULTS

Five minutes before and 10 minutes after ketanserin administration, global hemodynamic variables were recorded. In addition, the authors used SDF imaging to record video clips of the microcirculation. Analysis of these allowed for quantification of microvascular hemodynamics including determination of perfused vessel density (PVD) and microcirculatory flow index (MFI). After ketanserin administration, there was a significant reduction in systolic arterial blood pressure (129 +/- 9 to 100 +/- 15 mmHg, p = 0.0001). At the level of the microcirculation, the mean MFI did not change significantly for small (diameter <20 microm, 2.79 [interquartile range, 1.38-3] to 2.38 [1.88-2.75], p = 0.62) or large (diameter >20 microm, 2.83 [1.4-3] to 2.67 [0.35-2.84] p = 1.0) vessels. There was a significant increase in mean PVD for large vessels (1.23 +/- 0.63 to 1.70 +/- 79 mm(-1), p = 0.017) but not for small vessels (5.59 +/- 2.60 to 5.87 +/- 1.22 mm(-1), p = 0.72) where red blood cell flow was maintained.

CONCLUSIONS

SDF imaging clearly showed a discrepancy between global and microvascular hemodynamics after the administration of ketanserin for elevated blood pressure after ECC. Ketanserin effectively lowers arterial blood pressure. However, capillary perfusion is maintained at a steady value. Both effects may be explained by an increase in shunting in the larger vessels of the microcirculation.