Continuous total intravenous anesthesia, using propofol and fentanyl in an open-thorax rabbit model: evaluation of cardiac contractile function and biochemical assessment.

Effects are reported of an anesthetic protocol involving use of predetermined intravenous (i.v.)-administered drug doses during acute experimental procedures in vagotomized, New Zealand White rabbits with open thorax (n = 20) in a nonsurvival study. After induction of anesthesia by intramuscular (i.m.) administration of ketamine hydrochloride (25 mg/kg of body weight) and xylazine hydrochloride (15 mg/kg), continuous total intravenous anesthesia (TIVA) with propofol (0.6 mg.kg-1.min-1), fentanyl (0.48 micrograms.kg-1.min-1) and the neuromuscular agent vecuronium bromide (0.003 mg.kg-1.min-1) was maintained. Oxygenation conditions, acid-base balance, biochemical and hemodynamic variables, and cardiac contractile function were assessed. Measurements were made and blood analysis was done at the moment of ear vein catheterization (P1); before (P2) and after (P3) sternotomy; after complete instrumentation (P4); and at the beginning (T1), in the middle (T2), and at the end (T3) of the experimental protocol. From T1 to T3, heart rate was kept constant by use of atrial pacing at a rate of 235 +/- 15 beats/min. During surgical preparation and instrumentation, hemoglobin (Hb) concentration decreased from 12.5 +/- 0.9 g/dl (mean +/- SEM) to 7.7 +/- 0.7 g/dl and remained stable thereafter. Blood gas analysis (PO2, PCO2, pH, HCO3-, base excess, measured SaO2) and measurement of plasma lactate concentration revealed constant, adequate oxygenation. Plasma electrolyte values (Na+, Cl-, K+, Ca2+) remained within physiologic ranges throughout. Blood glucose concentration increased from 229 +/- 30 mg/dl at P1 to 382 +/- 34 mg/dl at P3. At T1, glycemia had returned to normal values and remained stable. Heart rate, blood pressure, ventricular elastance (Ees), and diastolic stiffness constant (Kc) remained stable throughout. Other indices of ventricular function (dP/dtmax, thickening, ejection duration, and maximal left ventricular pressure) remained unaltered as well. Left ventricular relaxation (dP/dtmin, tau) did not change. After anesthesia induction by i.m. administration of ketamine and xylazine, TIVA with predetermined drug dosages of propofol and fentanyl provided stable cardiovascular function for open-thorax long-term experimental observations in a nonsurvival setting.