| The first study compared the cardiovascular responses of ephedrine at 0.2 mg/kg, IV (repeated if inadequate response) and dopamine infusion at 5 mug/kg/min, IV (doubled to 10 mug/kg/min, IV, if inadequate response) to manage hypotension in clinical canine cases during routine anesthetic management. Treatments were randomly assigned to treat hypotension (mean arterial pressure, MAP < 60 mm Hg) in 12 cases. When MAP remained lower than 70 mm Hg at 10 minutes post treatment, the ephedrine bolus was repeated or the dopamine infusion was doubled. The pressure-elevating effect of ephedrine was found to last less than 5 minutes, with improvement in cardiac index (CI), stroke volume index (SVI) and oxygen delivery index (DO2I), but a decrease in systemic vascular resistance (SVR) at 10 minutes. Repeating the ephedrine did not produce further improvement. The infusion of dopamine at 5 mug/kg/min did not improve blood pressure (BP), CI, DO2I or SVI within 10 minutes. Increasing the infusion to 10 mug/kg/min improved BP within 5 minutes, and increased CI, DO2I and SVI by 10 minutes. The ephedrine boluses were less effective than the dopamine infusions to augment BP, but the improvement in Cl, DO2I and SVI by the end of the 20-minute study period was not different between treatments.; The second study validated the use of a commercial system (PulseCO(TM)) that estimates cardiac output (CO) based on arterial pressure waveform analysis (PCO) in anesthetized dogs, and assessed the agreement between PCO and lithium dilution CO (LiD) during variable hemodynamic situations induced by changes in anesthetic depth and administration of inotropes (dopamine and dobutamine). Pressure waveform from the dorsal pedal artery was used to track the CO changes by the PCO monitor following a one-point calibration with LiD. Analysis based on 48 pairs of CO measurements found that PCO always produced higher readings than LiD during deep anesthesia but lower than LiD during dopamine infusions. Differences were not detected during light anesthesia or dobutamine infusions. The coefficient of correlation (r) was 0.6289. Tolerance limits varied according to treatment. Power to detect 30% or more difference between PCO and LiD was 92.5%. It was concluded that PCO can be used to monitor CO when conditions are similar to those during calibration with LiD. Recalibration is recommended for accurate estimation of CO when hemodynamic conditions or pressure waveform change significantly. |
