Comparison between lithium dilution and pulse contour analysis techniques for cardiac output measurement in isoflurane anaesthetized ponies: influence of different inotropic drugs.

To compare cardiac output () measurements using lithium dilution (LiDCO) and pulse contour analysis (PulseCO) techniques in isoflurane-anaesthetized ponies before and during the administration of different inotropic/vasoactive drugs. Prospective randomized experimental cross-over trial. Six ponies aged 5.0 +/- 1.6 (4-6.5) years and weighing 286 +/- 53 (212-368) kg. After sedation (romifidine) and induction (midazolam + ketamine), anaesthesia was maintained with isoflurane in oxygen. After 90 minutes (= T0), one of four treatments was administered: saline 0.1 mL kg(-1) (S), enoximone 0.5 mg kg(-1) IV (E), enoximone followed by dobutamine (0.5 microg kg(-1) minute(-1) for 120 minutes) (ED) or enoximone followed by a calcium chloride infusion (0.5 mg kg(-1) minute(-1) for 10 minutes) (EC). Data were recorded for 120 minutes after T0. The PulseCO (recorded from carotid artery) was calibrated before T0, no further recalibrations were performed. was determined with LiDCO ((LiDCO)) and PulseCO ((PulseCO)) simultaneously at T5, T10, T20, T40, T60, T80, T100 and T120. Systemic vascular resistances (SVR(LiDCO) and SVR(PulseCO)) were calculated. In the saline group, (PulseCO) was 4.9 +/- 12.3% lower than LiDCO (p < 0.01), whereas SVR(PulseCO) was 6.9 +/- 14.4% higher than SVR(LiDCO) (p < 0.01). These differences increased over time (mean +/- SEM), by 0.06 +/- 0.03% minute(-1) (p = 0.042) and SVR by 0.08 +/- 0.03% minute(-1) (p = 0.018). (PulseCO) was higher than (LiDCO) in the EC group (1.8 +/- 23.3%), but lower than (LiDCO) in groups E (-11.7 +/- 20.4%) and ED (-10.0 +/- 25.9%) (significant difference between treatments, p < 0.01). The differences in SVR in groups E (20.4 +/- 32.0%) and ED (20.7 +/- 35.3%) were significantly higher than in groups S (6.9 +/- 14.4%) and EC (3.1 +/- 22.2%) (p < 0.01). Pulse contour analysis values deviated significantly from LiDCO measurements in isoflurane-anaesthetized ponies. This difference was influenced by inotropic/vasoactive drugs.