Patricia A. Kapur

Propofol for maintenance of general anesthesia: a technique to limit blood loss during endoscopic sinus surgery

PURPOSE Most cases of endoscopic sinus surgery are amenable to techniques using local anesthesia with monitored sedation. However, it is frequently the preference of the patient to have surgery under general anesthesia. One major drawback of general anesthesia is the increased bleeding encountered which can interfere with optimal visualization of the intranasal anatomy. In this study, an analysis was made to see if technique of general anesthesia has an impact on estimated blood loss in patients undergoing endoscopic sinus surgery. METHODS Twenty-five patients undergoing outpatient endoscopic sinus surgery under general anesthesia over a 1-year period were reviewed retrospectively to determine if anesthetic technique had an impact on estimated blood loss. Twelve patients were identified who received a continuous intravenous infusion of the nonbarbituate hypnotic agent propofol as the primary anesthetic agent, and 13 patients were identified who received anesthesia based on inhalational isoflurane. RESULTS There was no difference between the duration of surgery or the intraoperative mean arterial blood pressure when comparing the two groups. The average estimated blood loss in the propofol group was 101 mL compared with an average estimated blood loss of 251 mL in the isoflurane group (P < .01). CONCLUSIONS General anesthesia based on propofol infusion may have the advantage of decreased bleeding compared with conventional inhalation agents, making endoscopic sinus surgery technically easier and safer by improving endoscopic visualization of the surgical field. This anesthetic technique may have other applications in otolaryngology, where bleeding within a confined space frequently can interfere with visibility.

Patient simulator competency testing: ready for takeoff?

T he number of whole-body computerized patient simulators in use worldwide continues to grow. More than 70 such simulators are now active for training purposes, compared with less than 20 simulators 2 yr ago. Approximately one third of the currently available simulators are in United States academic anesthesiology training programs. The remainder are in allied health programs, such as respiratory therapy, paramedic, or nursing programs, in the United States, or are located at international sites, primarily anesthesiology programs, such as the site of the study conducted by Devitt et al. (l), published in this issue of Anesthesia b Analgesia. Two commercially distributed simulator models make up the majority in use, but several venues, primarily in Europe, have developed their own units on site. The rapidly growing interest in potential applications of patient simulator technology in the field of anesthesiology is also evidenced by the recent appointment of an ad hoc committee on simulators to investigate the current state of the art for the American Society of Anesthesiologists. Obvious potential applications include training, research, and competency testing. (2-4) It is the latter that undoubtedly raises the most anxiety among practitioners, as questions of consistency, reproducibility, validity, and relevance of responses in the simulator environment to true performance in the clinical arena all have yet to be answered. Which testing methodology will best predict clinical performance versus simply representing understanding of the limitations and familiarity with the simulator milieu? Will patient simulator testing (real-time coordination of knowledge with eye-hand responses) evolve into a third component, along with written (fundamental body of factual knowledge) and oral (integrative application of knowledge) competency testing methods? These and other questions are far from being answered. Certainly, simulators have a wide range of teaching applications. In our institution, under the direction of

Comparison of Cardiovascular Responses to Verapamil during Enflurane, Isoflurane, or Halothane Anesthesia in the Dog

The cardiovascular responses to increasing infusion rates of the slow calcium channel inhibitor, verapamil, were studied in three groups of dogs during either enflurane, isoflurane, or halothane anesthesia. Control hemodynamic values and plasma samples were taken after 2 h of anesthesia with the given agent. Increasing infusion rates of verapamil were given to achieve a range of plasma verapamil levels up to approximately 500 ng · ml−1. Each infusion rate was administered for 30 min, at which time repeat measurements and plasma samples for verapamil were taken. Mean arterial blood pressure, cardiac index, and left ventricular dP/dt decreased with increasing plasma verapamil levels in the enflurane and isoflurane groups compared with the control values. The values for the enflurane-verapamil combination were significantly lower than those for the other anesthetics at comparable verapamil levels. Compared with enflurane, higher verapamil levels were required with isoflurane to achieve the equivalent degree of hemodynamic depression. A higher incidence of conduction abnormalities also was noted in the enflurane group. In the halothane group, the only significant change observed at these verapamil levels, achieved by continuous infusion, was a prolongation of the PR interval of the ECG. In this animal model, verapamil was least well tolerated by the cardiovascular system during enflurane anesthesia.

The development of ambulatory anesthesia and future challenges.

It is difficult to predict the future but foolish to ignore the past. The history of ambulatory anesthesia is one of many trends and societal or economic forces that have provided the impetus for the growth of the specialty. By understanding the events of the past one can have a greater understanding of the present and some insight into the possible trends of the future. Financial and societal forces will continue to drive the growth of ambulatory anesthesia. New technology, surgical techniques, and progress in anesthesiology will be financed and supported by society so long as ambulatory surgery continues to decrease the costs of health care. Although new technology may increase the direct costs of providing care in the operating room, the overall costs to society should be reduced by a decrease in lost productivity and individual suffering on the part of the patients. Regardless of future changes, the anesthesiologist must remain dedicated to the safety and comfort of the patient first and foremost. If that happens, then the future of ambulatory anesthesiology and surgery will continue to be bright.

Influence of diltiazem on cardiovascular function and coronary hemodynamics during isoflurane anesthesia in the dog: correlation with plasma diltiazem levels.

Diltiazem was administered to dogs by intravenous infusion to achieve plasma levels of 47 ± 3 (n = 7), 148 ± 12 (n = 8), 263 ± 10 (n = 8), and 379 ± 43 (n = 8) ng·ml−1, to evaluate the effects of diltiazem on cardiovascular function and coronary hemodynamics, when given in the presence of anesthetic concentrations of isoflurane. Plasma level related prolongation of the PR interval of the electrocardiogram was the most prominent effect observed, with development of 2° heart block or functional rhythms in several of the animals at the two higher plasma levels. Mean arterial pressure, transiently decreased after the loading dose in all groups, was no different from control values after 30 min of infusion. Left ventricular dP/dt was mildly decreased at the three highest plasma levels, whereas right and left heart filling pressures were increased at the two highest plasma levels. Cardiac index and systemic vascular resistance were unchanged. No changes were observed in coronary sinus blood flow, coronary vascular resistance, myocardial oxygen uptake, myocardial lactate extraction, or circulating epinephrine or norepinephrine levels in any of the groups. In the presence of anesthetic concentrations of isoflurane, over the range of plasma levels investigated in this study, the vasodilating properties of diltiazem were not abserved, yet conduction effects were prominent and decreases in left ventricular performance occurred. No untoward effects on global myocardial metabolism were detected under these conditions.

The Cardiovascular and Adrenergic Actions of Verapamil or Diltiazem in Combination with Propranolol during Halothane Anesthesia in the Dog

Continuous infusions of verapamil and diltiazem were established in halothane-anesthetized dogs (1.15–1.35% end tidal concentration) with or without a concomitant propranolol infusion to investigate changes: in cardiovascular function, in reflex activation as reflected in circulating catecholamine levels, and in the chronotropic response to the exogenously administered beta agonist, isoproterenol. Verapamil plasma levels of approximately 100 and 250 ng · ml-1, diltiazem plasma levels of approximately 140 and 325 ng · ml-1, and propranolol levels of approximately 70 ng · ml-1 were tolerated individually in the presence of halothane, although atrioventricular conduction was prolonged in the verapamil and diltiazem groups. Catecholamine levels were increased in the high verapamil group. However, when propranolol was combined with the lower levels of verapamil or diltiazem, the result was decreased heart rate, blood pressure, left ventricular maximum rate of tension development (dP/dt), and cardiac index with increased systemic vascular resistance. When the attempt was made to proceed to the increased plasma levels of verapamil or diltiazem in the presence of propranolol, 6/6 animals in the verapamil-propranolol group and 4/6 animals in the diltiazem-propranolol group were unable to maintain a mean arterial blood pressure of greater than 50 mmHg, and many developed 2° or higher heart block. Analysis of the plots of the logarithms of the doses of isoproterenol versus changes in heart rate revealed that larger amounts of isoproterenol were required to achieve the same increase in heart rate as with halothane alone if these plasma levels of propranolol, verapamil, or diltiazem individually were present, and that very much larger doses of isoproterenol were required to increase heart rate to the same level as with halothane alone when a combined block with verapamil or diltiazem plus propranolol was present.

Effects of Verapamil on Uterine Blood Flow and Maternal Cardiovascular Function in the Awake Pregnant Ewe

Calcium entry blocking drugs may have a role in the treatment of manternal and fetal tachyarrhythmias, as well as for treatment of premature labor. This study was undertaken to mess the hemodynamic effects of verapamil in the awake pregnant ewe. Verapamil, 0.2 mg/kg administered intravenously over 3 min, resulted in the following maternal cardiovascular changes: transient (2 min) hut significant decreases in systolic, diastolic, and mean blood pressures, arid significant but equally transient increases in central venous pressure arid mean pulmonary arterial pressure. Pulmonary capillary wedge pressure increased for 5 min. These results are consistent with the negative inotropic and peripheral vasodilating effects of verapamil. Cardiac output, systemic vascular resistance, and pulmonary vascular resistance were unaffected. Uterine blood flow decreased 25% at 2 min and remained significantly (7–18%;) below control levels for 30 min after drug injection. The effects of verapamil on uterine blood flow suggest that it should be used with caution in cases where uteroplacental perfusion is compromised.

Cardiovascular interactions of lidocaine with verapamil or diltiazem in the dog.

Lidocaine in low and high doses was given by sequential infusions to isoflurane-anesthetized dogs (1.75 0.03% end-tidal concentration) with or without concurrent infusions of diltiazem or verapamil, to assess changes in cardiovascular function. When lidocaine was administered alone, the low plasma levels (∼2 μg/ml) caused only a modest reduction in left ventricular dP/dt. The higher plasma lidocaine levels (~6 μg/ml) reduced both left ventricular dP/dt and cardiac index, and increased pulmonary capillary wedge pressure and systemic vascular resistance. Diltiazem or verapamil, when administered alone at plasma concentrations of approximately 150–200 ng/ml, prolonged atrioventricular conduction, decreased heart rate and cardiac index, and, in the case of verapamil, also decreased left ventricular dP/dt and mean arterial pressure. When lidocaine was added to diltiazem or verapamil, the low plasma levels of lidocaine depressed cardiac function in the presence of either calcium channel blocking drug. In the presence of these levels of verapamil or diltiazem, only one of six verapamil-treated animals and three of six diltiazem-treated animals were able to maintain a mean arterial pressure greater than 50 mmHg with the higher dose of lidocaine. Caution may be advised if the addition of lidocaine, by whatever route, is indicated in subjects who have recently received intravenous verapamil or diltiazem.

Amrinone and Verapamil-propranolol Induced Cardiac Depression during Isoflurane Anesthesia in Dogs

This study was designed to investigate the possibility of whether verapamil diminishes the effects of amrinone, whether amrinone can reverse verapamil-propranolol depression, and also to evaluate whether the order of administering the drugs would have any effect during 1.7–1.8% end-tidal isoflurane anesthesia in dogs. At 3–4-week intervals, each of six conditioned mongrel dogs (23 ± 1 kg) received amrinone (A) (4 mg/kg plus 100 μg ± kg−1 ± min−1), verapamil (V) (200 μg/kg plus 7.5 μg ± kg−1 ± min−1) and propranolol (P) (150 μg/kg plus 0.8 μg ± kg−1 ± min−1) in four different orders of administration: VAP, AVP, VPA, and PVA. Plasma levels achieved were 15 ± 1 to 24 ± 2 μg/ml for amrinone, 24 ± 2 to 59 ± 10 ng/ml for propranolol, and 81 ± 10 to 163 ± 17 ng/ml for verapamil, equivalent to high therapeutic (amrinone) and therapeutic (propranolol, verapamil) levels in humans. The results of this study show that amrinone is able to reverse many of the effects of verapamil (group VAP) and also many of the effects of verapamil-propranolol or propranolol-verapamil (groups VPA, PVA) combinations. Amrinone improved cardiac index, left ventricular dP/dtmax, pulmonary capillary wedge pressure, and central venous pressure without increasing catecholamines. However, mean arterial pressure remained decreased with decreased systemic vascular resistance, which necessitates careful consideration depending upon patient circumstances. The results also show that verapamil-propranolol can reverse the positive inotropic effects of amrinone (group AVP). The authors conclude that amrinone is of therapeutic value for the reversal of untoward effects of potent cardiodepressant drugs, such as verapamil and propranolol, even in the presence of inhalation anesthetics.

Plasma diltiazem levels, cardiovascular function, and coronary hemodynamics during enflurane anesthesia in the dog.

Diltiazem was administered to dogs by an intravenous infusion protocol, which resulted in plasma levels of 71 ± 6 (n = 7), 139 ± 9 (n = 7), 353 ± 33 (n = 10), and 1064 ± 143 (n = 6) ng/ml, to evaluate the effects of diltiazem on cardiovascular function and coronary hemodynamics in the presence of anesthetic concentrations of enflurane. An additional group of six dogs received enflurane only. The only changes observed with enflurane alone were a decrease in left ventricular (LV) dP/dt, cardiac index (CD, and coronary blood flow 60 min after the baseline measurements were made. In all of the diltiazem groups, plasma level-related prolongation of the PR interval of the electrocardiogram was observed, with development of second degree heart block and functional rhythms in animals at the two higher plasma levels. Mean arterial pressure and LV dP/dt decreased at the two higher diltiazem plasma levels after 30 min of infusion, and three of six dogs in the highest group had to be dropped from the study because of severe hypotension. The cardiac index was no different from enflurane alone with the three lower plasma diltiazem levels. No changes were observed in coronary sinus blood flow, coronary vascular resistance, myocardial oxygen uptake, or myocardial lactate extraction. Circulating norepinephrine levels were elevated in the two higher diltiazem groups. In the presence of anesthetic concentrations of enflurane, over the range of plasma diltiazem levels investigated in this study, conduction effects were prominent and decreases in left ventricular performance and blood pressure occurred as plasma diltiazem levels increased. No untoward effects on global myocardial metabolism were detected at plasma levels less than 500 ng/ ml. However, the occurrence of circulatory collapse in half of the animals at the highest plasma levels prevented evaluation of metabolic effects of high levels of diltiazem during enflurane anesthesia.