Microcirculatory hemodynamic alterations during cardiac luxation in off-pump coronary artery bypass grafting surgery

Introduction

During luxation of the beating heart in off-pump coronary artery bypass grafting surgery the cardiac output drops and causes hypotension (<60 mmHg). It is expected that this state of obstructive shock is detrimental for adequate perfusion and oxygenation of organ tissue. However, it is unknown whether these luxations cause microcirculatory dysfunction. In this study we have explored the hemodynamics of the sublingual microcirculation during mechanical manipulations of the beating heart.

Methods

During cardiac luxations, in 12 patients reflectance spectrophotometry (O₂C^®; Lea Medizintechnik, Germany) was used to measure oxygen availability and in 12 other patients sidestream dark field imaging (MicroScan^®; MicroVision Medical, The Netherlands) was used to directly visualize the sublingual microcirculatory hemodynamics in a single network of micro-vessels. Microvascular analysis software (MAS^®; MicroVision Medical) was used to analyze the vessel density and blood flow. Synchronously, systemic hemodynamics were recorded and the cardiac output was calculated by pulse contour analysis of arterial pressure (PulseCO^®; LiDCO, UK) in all patients.

Results

During cardiac luxations, the oxygen availability in the sublingual microcirculation decreased (μHbO₂ 64.2 ± 9.1 to 48.6 ± 8.7%; P < 0.01) while the functional capillary density did not change (15.9 ± 1.1 to 15.6 ± 1.3 mm/mm²; P = 0.65). Although the small vessels (0–20 μm) did not fall out they did show hypoperfusion (V_max 895 ± 209 to 396 ± 178 μm/s; P < 0.01), whereas in the medium vessels (20–50 μm) there was no significant change in blood velocity (V_max 751 ± 239 to 596 ± 192 μm/s; P = 0.18) as observed with sidestream dark field imaging and calculated with microvascular analysis software.

Conclusion

Alterations in sublingual microcirculation hemo-dynamics reflect the direct effects of obstructive shock and elucidate the microcirculatory autoregulation.