Dye circulation times during cardiac arrest

Dye dilution curves have been used to calculate cardiac output under conditions of normal circulation. Unfortunately, these curves cannot be integrated easily to determine cardiac output under the low flow states of CPR. The time to initial dye appearance (circulation time), may be useful in judging relative changes in flow when studying experimental resuscitation techniques. The purpose of this study was to investigate the relationship between dye circulation times and other hemodynamic measures during CPR. Repeated measurements of coronary perfusion pressure, dye circulation times, blood gases, and end-tidal CO2 (ETCO2) were made in dogs undergoing CPR. Dye circulation time was significantly associated with the systolic, diastolic, and coronary perfusion pressures. The correlation between circulation time and ETCO2 was -0.70 (P less than 0.0001). There was no correlation with the arterial-venous PO2 gradient. There were significant correlations between the circulation time and both the A-V PCO2 and the A-V pH gradients. We conclude that dye circulation times may be used to gauge relative changes in blood flow during CPR, particularly in laboratory investigations involving repeated measurements.