Therapeutic strategies used in critical care for the management of patients with sepsis and patients undergoing high-risk major surgery are often based on macrovascular parameters. Blood pressure, heart rate and stroke volume are used to guide fluid and medication administration. Another approach would be to consider blood flow through the capillary bed, microvascular blood flow. Microvascular blood flow can be measured at the bedside with side-stream dark field imaging (SDF). On systematic review, pharmacological agents were found to affect microvascular flow in septic patients. The ino-dilator levosimendan, variable dosing of the vasodilator GTN and steroids were all found to improve microvascular flow, in contrast to vasoconstrictors which demonstrated no improvement in flow. I found acceptable reproducibility on Bland-Altman analysis of SDF imaging and automated analysis of measurements taken in healthy volunteers. In a prospective study of 55 patients undergoing liver resection surgery, I found divergence of the macrocirculation and microcirculation. There was no correlation between MAP and microvascular measurements (MFI, sPPV or PVD) at any time point (Pearson and Spearman correlation co-efficients). Microvascular flow was impaired post-operatively and was not restored on completion of goal-directed fluid therapy. There was evidence of endothelial glycocalyx disruption with shedding of syndecan-1. A fall in circulating antithrombin was found in the post-operative period, which may be related to increased infiltration of the glycocalyx and binding to the endothelium during hypoperfusion.