Yung J. Sohn

Monitoring with two-dimensional transesophageal echocardiography. Comparison of myocardial function in patients undergoing supraceliac, suprarenal-infraceliac, or infrarenal aortic occlusion.

When the aorta must be temporarily occluded at the suprarenal or supraceliac levels during surgery, the resulting large increase in afterload may make the myocardium ischemic, even though systemic and pulmonary artery pressures and cardiac output are maintained at normal levels. These traditional indices of myocardial well-being do not appear to be sufficiently sensitive, since cardiac complications are still the most frequent cause of perioperative death and morbidity after aortic reconstruction. To evaluate two-dimensional transesophageal echocardiography as a monitor of myocardial well-being, we studied 24 American Society of Anesthesiologists physical status class III or IV adult patients who were undergoing aortic reconstruction and occlusion at the supraceliac (n = 12), suprarenal-infraceliac (n = 6), or infrarenal (n = 6) level. In addition to traditional monitors, we used a gastroscope tipped with a special 3.5 MHz two-dimensional echocardiographic transducer (Diasonics) that was placed in the esophagus to give a cross-sectional view of the left ventricle through the base of the papillary muscles. The hemodynamic effects of clamping the aorta were managed by administration of vasodilating drugs, anesthetics, and fluids to keep systemic and pulmonary arterial pressures normal. Occlusion at the supraceliac level caused major increases in left ventricular end-systolic and end-diastolic areas, decreases in ejection fraction, and frequent wall motion abnormalities; these changes were not detected by conventional monitoring devices. Occlusion at the suprarenal-infraceliac level caused similar but smaller changes, and occlusion at the infrarenal level caused only minimal cardiovascular effects. We conclude that the two-dimensional transesophageal echocardiogram offers promise as an intraoperative monitoring device.

Clinical Pharmacology of ORG NC45 (NorcuronTM)A New Nondepolarizing Muscle Relaxant

To determine the neuromuscular effects of a new muscle relaxant, ORG NC45 (NorcuronTM), a monoquaternary homologue of pancuronium, 84 ASA Class I or II patients were studied under halothane and nitrous oxideanesthesia. The ED50 (dose of muscle relaxant causing a 50 per cent depression of twitch tension) of pancuronium and ORG NC45 was 0.022 mg/kg (r = 0.90) and 0.015 mg/kg (r = 0.80), respectively, for a potency ratio of 1.5 (0.022/0.015). The duration of action (time from injection to 90 per cent recovery of control twitch tension) was 27 ± 5 min with ORG NC45, 0.02 mg/kg, and 65 ± 16 min with pancuronium in an equivalent dose of 0.03 mg/kg. The increase in duration of neuromuscular blockade from repetitive doses was greater with pancuronium than with ORG NC45. Reversal of an ORG NC45 neuromuscular blockade was accomplished with doses of neostigmine slightly less than those required for pancuronium. Under thiopental-nitrous oxide anesthesia, endotracheal intubation was easily performed using ORG NC45, 0.07–0.14 mg/kg. The duration of action of ORG NC45, 0.07 mg/kg, was about one-third that of pancuronium (0.1 mg/kg). It was concluded that ORG NC45 is more potent and has a shorter duration of action with both initial and repetitive doses than does pancuronium. With these characteristics and the reported lack of cardiovascular effects, the authors believe further clinical trials are warranted.

Does anesthetic technique make a difference? Augmentation of systolic blood pressure during carotid endarterectomy: effects of phenylephrine versus light anesthesia and of isoflurane versus halothane on the incidence of myocardial ischemia

Whether anesthetic technique affected the incidence of myocardial ischemia in 60 patients undergoing carotid endarterectomy was investigated. The patients were randomly assigned to receive halothane or isoflurnne (with nitrous oxide) either nt a low concentration alone or at a higher concentration with phenylephrine added to support blood pressure. Blood pressure wns maintained within 20% of each patients average ward systolic pressure. Seven leads of electrocardiograms (ECC) and echocardiograms were analyzed for segmental wall motion. The echocardiograms were analyzed using standard formulae for end-systolic meridional wall stress (SWS) and rntecorrected velocity of fiber shortening (Vcfc). Because of the nature of these calculations, only echocardiograms with normal regional wall motion could be accurately analyzed. The patients had postoperative ECG and creatinine phosphokinase (CPK)isoenzyme determinations and regularly scheduled clinical examinations to detect perioperntive myocardial infarction and neurologic deficits. Although blood pressures were similar, the patients who received a higher concentration of anesthetic plus phenylephrine had a higher wall stress, regardless of the choice of anesthetic agent. All four techniques allowed provision of the same stump pressures (the marker surgeons used for adequacy of collateral carotid flow). No difference could be found in wall stress or incidence of myocardial ischemia between isoflurane and halothane. The patients who received phenylephrine had a threefold greater incidence of myocardial ischemia than did the patients who had light anesthesia to maintain similar systolic blood pressures and stump pressures. The groups were demographically and hemodynamicnlly similar; in particular, the heart rates were not different. Increased wall stress in anesthetized patients is associated with an increased incidence of myocardial ischemia as evidenced by new segmental wall motion and wall thickening abnormalities (SWMA).

Clinical Pharmacology of Vecuronium and Atracurium

Vecuronium and atracurium provide addition flexibility to the clinician using neuromuscular blocking drugs. The shorter duration of action, lack of significant cardiovascular effects, and the lack of dependence on the kidney for elimination provide clinical advantages over, or alternatives to, currently available nondepolarizing neuromuscular blocking drugs.

Renal function and the pharmacokinetics of neostigmine in anesthetized man.

The pharmacokinetics of neostigmine in patients with normal renal function (n = 8) were determined and compared with those of patients undergoing renal transplantation (n = 6) or bilateral nephrectomy (n = 4). All patients were anesthetized with nitrous oxide and halothane. d-Tubocurarine was infused at a rate sufficient to maintain 90 per cent depression of twitch tension. Ten to 15 minutes prior to the end of operation and anesthesia, the d-tubocurarine infusion was terminated and neostigmine, 0.07 mg/kg, and atropine, 0.03 mg/kg, were given by infusion over a 2-min period. Concentrations of neostigmine in blood drawn periodically during the following four hours were determined by gas-liquid chromatography and the data fitted to a two-compartment pharmacokinetic model. In anephric patients elimination half-life (181 ± 54 min, mean ± SD) was significantly prolonged when compared with comparable values for patients with normal renal function (80 ± 48 min). Total serum clearance was significantly decreased from 16.7 ± 5.4 ml/kg/min in patients with normal renal function to 7.8 ± 2.6 ml/kg/min in anephric patients. Neostigmine pharmacokinetics following renal transplantation were not different from those in patients with normal renal function. It is concluded that renal excretion accounts for 50 per cent of neostigmine clearance and, in the absence of renal function, the serum half-life of neostigmine is prolonged, similar to that of d-tubocurarine.

Cardiovascular and neuromuscular effects of Org NC 45, pancuronium, metocurine, and d-tubocurarine in dogs.

We compared the cardiovascular and neuromuscular effects of Org NC 45 with those of pancuronium, metocurine, and d-tubocurarine in six dogs anesthetized with halothane. The ED90 (dose of drug which produced a 90% depression of twitch tension) of Org NC 45, pancuronium, metocurine, and d-tubocurarine was 14 ± 3, 22 ± 3, 63 ± 19, and 130 ± 19 μg/kg, respectively. All subsequent neuromuscular and cardiovascular effects were determined from a dose equal to 3 times the ED90 of muscle relaxant. Org NC 45, pancuronium, metocurine, and d-tubocurarine produced a neuromuscular blockade with a duration (time from relaxant administration until recovery of 50% of the original twitch tension) of 42 ± 2, 108 ± 10, 109 ± 21, and 100 ± 19 minutes, respectively. Org NC 45 caused no significant cardiovascular changes. Pancuronium increased heart rate, mean arterial blood pressure, cardiac output, and pulmonary wedge pressure, and it decreased systemic vascular resistance (p < 0.05). Although metocurine also increased heart rate and cardiac output (p < 0.05), mean arterial blood pressure and pulmonary wedge pressure did not change. d-Tubocurarine decreased all cardiovascular parameters except heart rate which increased significantly (p < 0.05). We conclude that Org NC 45 produces a neuromuscular blockade of shorter duration with fewer cardiovascular changes than that of pancuronium, metocurine, or d-tubocurarine.

Operating Room Temperature Prior to Surgical Draping: Effect on Patient Temperature in Recovery Room

Assessment was made of whether a cold-room environment prior to surgical draping affected patient temperature or the incidence of shivering in the recovery room in patients undergoing major vascular surgery when warming blankets and warmed fluids were used to maintain intraoperative temperature. Forty-two patients scheduled to undergo major vascular surgery were randomly assigned in equal numbers to a “cold” or “warm” room. Temperatures in the “warm” rooms were 22.2 C or above (range 22.8–25.6 C) until draping, and in “cold” rooms, 18.9 C or below (range 13.9–17.8 C). Once surgical drapes were placed, the room temperature control was set at its minimum, 17 C. All intravenous fluids and blood were warmed to 37.5 C, and a heating blanket was maintained at 37.8 C before and during the operative procedure. Patient temperatures initially did not differ between groups. Despite significantly greater heat loss prior to draping in the cold-room group (0.63 ± 0.14 C) than in the warm-room group (0.32 ± 0.10 C)(p < 0.01), there were no differences in temperature in the recovery room, shivering, myocardial, renal, CNS, pulmonary, or graft morbidity in the two groups. In major intra-abdominal vascular operations the use of warming blankets and the practice of warming all fluids for infusion allow a comfortable room temperature without detriment to patient care.