Possible pitfalls in the interpretation of microcirculatory measurements. A comparative study using intravital
1Department of Surgery, Charité University Medical Center, Campus Benjamin Franklin, Humboldt and Freie Universitat Berlin, Germany.
Background:
Microcirculation and tissue oxygenation play key roles in many diseases and have been studied in various settings. Comparison and interpretation of measurements at the capillary level, however, is difficult when different techniques are employed and when data on systemic parameters are missing.
Aim:
To investigate (a) how changes in systemic parameters influence microcirculation and tissue oxygenation; (b) if these changes are detectable at the capillary level, and (c) which systemic parameters must be monitored for reliable interpretation of microcirculatory parameters.
Methods:
Assessment of capillary blood flow (CBF) and mucosal oxygen supply (Hb(Sat)O(2), p(muc)O(2)) of the colon in rats by (i) intravital microscopy (IVM), (ii) micro-light guide spectroscopy (EMPHO), and (iii) polarographic micro-catheter probe (LICOX) under (a) physiological conditions, (b) hypovolaemia, and (c) hypoxia.
Results:
CBF (IVM), Hb(Sat)O(2) (EMPHO) and p(muc)O(2) (LICOX) changed significantly under hypovolaemia, but with different extents. Under hypoxia, CBF did not change, whereas Hb(Sat)O(2) and p(muc)O(2) decreased significantly to 52 and 67% of baseline. Correlation of IVM/EMPHO and IVM/LICOX was poor (r = 0.12; r = 0.03).
Conclusion:
Changes of systemic parameters have significant effects on peripheral tissue oxygenation but may not always be detected at the capillary level. MAP, blood gases and haematocrit must be analysed to correctly interpret microcirculatory parameters.
