EFFECT OF PROPRANOLOL ON THE VENTRICULAR ARRHYTHMIAS INDUCED BY HYPERCARBIA DURING HALOTHANE ANAESTHESIA IN MAN

The effects of propranolol on arterial blood pressure, heartrate, and cardiac rhythm during ventricular arrhythmias initiatedby hypercarbia were investigated in thirteen subjects during1 per cent halothane anaesthesia. Propranolol was consistentlyeffective in the treatment of ventricular arrhythmia inducedby hypercarbia in all subjects. The successful use of propranololsuggests that the mechanism for ventricular arrhythmia producedby respiratory acidosis during halothane anaesthesia was relatedto beta adrenergic receptors. Blockade of these receptors bybeta adrenergic agents decreased markedly the sensitizationof myocardium to sympathetic stimulation.     

Renin-angiotensin-aldosterone system and plasma vasopressin in surgical patients anaesthetized with halothane or isoflurane

The effects of halothane and isoflurane anaesthesia on plasma renin activity and plasma concentrations of aldosterone and vasopressin were investigated in 20 cholecystectomy patients. Plasma renin activity rose significantly during both halothane and isoflurane anaesthesia without surgery, and increased further after the commencement of operation. Plasma aldosterone increased slightly during halothane and isoflurane anaesthesia, but the highest concentrations, three times the control values, were measured during surgery in both groups. Plasma vasopressin decreased during halothane and isoflurane anaesthesia to half of the control values, but rose significantly during cholecystectomy. During anaesthesia and surgery there were no significant differences in the mean arterial pressures of the groups. The results demonstrate that isoflurane stimulates the renin-angiotensin system to a similar extent as halothane, although it causes hypotension by a different mechanism. The activation of the renin-angiotensin-aldosterone system may be an essential compensatory mechanism, which antagonizes the decrease of blood pressure. Plasma vasopressin probably has no role in regulating blood pressure during anaesthesia.     

Anaesthesia and the QT intervalEffects of isoflurane and halothane in unpremedicated children

The effects of isoflurane and halothane on the QT interval were investigated during induction of anaesthesia. Fifty-one unpremedicated, ASA grade 1 children were studied. Anaesthesia was induced with either isoflurane ( n  = 25) or halothane ( n  = 26) and was maintained to the end of the study with end-tidal concentrations of between 2.5% and 3%. Recordings of the electrocardiograph, heart rate and systolic arterial pressure were obtained at the following times: before induction of anaesthesia; 1 min and 3 min after stable end-tidal concentrations of anaesthetic agent had been reached; 1 min and 3 min following vecuronium administration; at the time of tracheal intubation and 1 min and 3 min later. Isoflurane significantly prolonged the QT interval (p < 0.001), in contrast to halothane which shortened it (p < 0.01). Heart rate remained largely unchanged during isoflurane anaesthesia but it decreased in the presence of halothane (p < 0.001). In both groups, systolic arterial pressure decreased significantly after induction of anaesthesia (p < 0.001) and remained so to the end of the study. In the isoflurane group, 12 children developed ECG repolarisation abnormalities and in one child an arrhythmia was noticed. In the halothane group, one child developed repolarisation changes while arrhythmias were observed in 10 children. There were no adverse sequelae. It is concluded that halothane may be a better anaesthetic agent than isoflurane for use in children with a prolonged QT interval.     

Cardiac Arrhythmias in Non-intubated Children during Adenoidectomy. A Comparison between Enflurane and Halothane Anaesthesia

The incidence of cardiac arrhythmias, heart rate, blood pressure, capillary perfusion and end-tidal CO2 tension were studied in 167 healthy children 1-12 years of age undergoing adenoidectomy (n = 82) and myringotomy (n = 85) during enflurane and halothane anaesthesia. The incidence of cardiac arrhythmias was significantly lower during myringotomy than during adenoidectomy. In children undergoing adenoidectomy the incidence of arrhythmias was 38.9% during enflurane anaesthesia and 86.6% during halothane anaesthesia (P less than 0.001). In the halothane group ventricular arrhythmias were observed in 19 patients (41.3%) but only in one child (2.8%) in the enflurane group. The ventricular arrhythmias seen during halothane anaesthesia were unifocal in six patients and multifocal in five and classified as ventricular tachycardia in eight children. Heart rate was increased by about 40% at the onset of ventricular arrhythmias. The heart rate remained unchanged with enflurane anaesthesia during surgery, which may reflect a decreased sympathomimetic activity. It is suggested that the low incidence of ventricular arrhythmias during enflurane anaesthesia may be explained by the combination of a reduced sympathomimetic activity and a lowered susceptibility of the myocardium to the actions of endogenous catecholamines.     

Influence of desflurane,isoflurane and halothane on regional tissue perfusion in dogs

The actions of desflurane, isoflurane and halothane on regional tissue perfusion were studied using radioactive microspheres in dogs chronically instrumented for measurement of arterial and left ventricular pressure, global (left ventricular dP/dtmax) and regional (percent segment shortening) contractile function, and diastolic coronary blood flow velocity. Systemic and coronary haemodynamics and regional tissue perfusion were measured in the conscious state and during anaesthesia with equihypotensive concentrations of desflurane, isoflurane, and halothane. All three volatile anaesthetics (P < 0.05) increased heart rate and decreased mean arterial pressure, left ventricular systolic pressure, and left ventricular dP/dtmax Myocardial perfusion was unchanged in subendocardial midmyocardial, and subepicardial regions by the administration of either dose of desflurane. No redistribution of intramyocardial blood flow (endo/epi ratio) was observed during desflurane anaesthesia. Although regional myocardial perfusion was reduced (P < 0.05) in a dose-related fashion by halothane and by isoflurane at high concentrations, redistribution of intramyocardial blood flow was not observed during halothane or isoflurane anaesthesia. All three volatile anaesthetics reduced blood flow to the renal cortex, but only desflurane produced a decrease in renal cortical vascular resistance. Hepatic blood flow decreased in response to halothane but not desflurane or isoflurane. Concomitant decreases in hepatic resistance were observed during administration of desflurane and isoflurane. Dose-related decreases in intestinal and skeletal muscle blood flow were observed during halothane and isoflurane but not desflurane anaesthesia. The results suggest that desflurane maintains myocardial, hepatic, intestinal, and skeletal muscle blood flow while halothane and isoflurane decrease regional tissue perfusion in these vascular beds to varying degrees during systemic hypotension in the chronically instrumented dog.     

Halothane, enflurane and isoflurane anaesthesia for adenoidectomy in children, using two different premedications

In 48 children subjected to adenoidectomy, comparisons of airway problems, heart rates, cardiac arrhythmias, ventilation and stress hormone reactions were studied during halothane, enflurane and isoflurane anaesthesia. Sixteen children were anaesthetized with either of the three agents and eight patients in each group received diazepam 0.25 mg kg-1 and atropine 0.015 mg kg-1 rectally (DA) as premedication and the remainder diazepam 0.5 mg kg-1, morphine 0.15 mg kg-1 and scopolamine 0.01 mg kg-1 (DMS) rectally. All children were intubated and breathing spontaneously. Equianaesthetic inspired concentrations of halothane, enflurane and isoflurane were used. Airway problems were of the same magnitude during halothane and isoflurane anaesthesia but were less frequent with both agents compared with enflurane anaesthesia. DMS reduced the number of airway reactions in all groups. Respiratory rates were uninfluenced by anaesthesia, intubation and surgery during enflurane anaesthesia. Cardiac arrhythmias were less frequent with enflurane and isoflurane than with halothane. Plasma ACTH and cortisol were similar with all three agents. During induction of anaesthesia in the DA-premedicated halothane group, however, plasma catecholamines were higher than in the group which received DMS, in contrast to the findings during enflurane and isoflurane anaesthesia. The DMS premedication decreased the response of plasma ACTH, cortisol and plasma catecholamines to surgery.     

Comparison of isoflurane and halothane when used to control intraoperative hypertension in patients undergoing coronary artery bypass surgery

The hemodynamic effects of isoflurane and halothane when used to control intraoperative hypertension were evaluated in 20 patients undergoing coronary artery bypass grafting. The patients were anesthetized with flunitrazepam, fentanyl, pancuronium, and N2O-O2. Control measurements were made after skin incision. When mean arterial pressure increased to 110 mm Hg due to sternal spread or surgical manipulation of the aorta, isoflurane or halothane were used to return arterial pressure to control levels. Using a non-rebreathing system, inspired isoflurane concentrations of 1.5-2.0 vol% or halothane concentrations of 1.0-1.5 vol% were necessary. Measurements were repeated during the hypertensive episode and after treatment with isoflurane or halothane while surgical stimulation continued. Both inhalation anesthetics decreased arterial pressure to baseline values within 5-10 min. The lowering of arterial pressure with halothane was not accompanied by significant decreases in the elevated systemic vascular resistance and pulmonary capillary wedge pressure. Cardiac index and stroke volume index decreased markedly when halothane was used (18% and 25%, respectively). In contrast, isoflurane significantly decreased systemic vascular resistance (42%). This reduction of left ventricular afterload was associated with an increase in cardiac index (22%) and a decrease in left ventricular filling pressure. Heart rate did not change significantly. These findings indicate that isoflurane is superior to halothane for controlling intraoperative hypertension during coronary artery bypass surgery.     

Doses of epinephrine causing arrhythmia during enflurane, methoxyflurane and halothane anaesthesia in dogs.

The arrhythmogenic dosage of epinephrine, administered by constant intravenous infusion, was measured in five dogs during enflurane, methoxyflurane and halothane anaesthesia. While premature ventricular contractions were observed in only one of five dogs with enflurane and methoxyflurane, epinephrine-induced arrhythmias were seen in all animals during halothane anaesthesia. Epinephrine dosage and the resultant increase in mean arterial blood pressure at which arrhythmias occurred during halothane anaesthesia were significantly less (p less than 0.05) than with the other anaesthetics. These observations indicate that enflurane and methoxyflurane, as compared to halothane, possess relatively less arrhythmogenic potential as sensitizing agents in the presence of increased circulating catecholamines.     

The effects of halothane and isoflurane on cardiovascular function in laterally recumbent horses

Background. Experimental studies in adult horses have shownthat general anaesthesia maintained with isoflurane is associatedwith less depression of cardiovascular function compared withhalothane anaesthesia. Adverse effects of intermittent positive-pressureventilation (IPPV) have also been demonstrated. Nevertheless,the haemodynamic effects of these agents and the effects ofdiffering modes of ventilation have not been assessed duringclinical anaesthesia in horses undergoing surgery. Methods. The haemodynamic effects of isoflurane or halothaneanaesthesia during spontaneous or IPPV were studied non-invasivelyin 32 laterally recumbent horses undergoing elective surgery.Indices of cardiac function and measurements of femoral arterialblood flow and resistance were recorded using transoesophagealand transcutaneous Doppler echocardiography, respectively. Arterialpressure was measured directly using a facial artery catheter. Results. Cardiac index (CI) was significantly higher duringisoflurane anaesthesia than during halothane anaesthesia andwas also higher during spontaneous ventilation with isoflurane.CI decreased significantly over time and an inverse relationshipwas observed between CI and mean arterial pressure (MAP). Horseswith higher MAP had a significantly lower CI. During isofluraneanaesthesia, femoral arterial blood flow was significantly higherin both pelvic limbs compared with halothane anaesthesia, andflow in the lower limb was significantly higher during spontaneousventilation than during IPPV. No significant change in femoralblood flow was observed over time. Conclusion. The effects of anaesthetics and mode of ventilationon cardiovascular function recorded under surgical conditionsin horses are similar to those reported under experimental conditions.However, in contrast with previous experimental studies, CIprogressively decreased over time regardless of agent used ormode of ventilation employed.     

A comparison of isoflurane and halothane in anaesthesia for intra-ocular surgery

Isoflurane 0.75% was compared with halothane 0.5% as the volatile supplement in a normocapnic technique for intra-ocular surgery. Both agents gave satisfactory conditions for operation with a comparable reduction in intra-ocular pressure during the procedure. Systolic arterial pressure, however, was significantly lower in the isoflurane group at the end of surgery and after tracheal extubation than in the halothane group. Isoflurane provides a useful alternative to halothane in anaesthesia for intraocular surgery.     

Cardiac Arrhythmias in Intubated Children During Adenoidectomy. A Comparison Between Enflurane and Halothane Anaesthesia

In 75 children undergoing adenoidectomy, occurrence of cardiac, arrhythmias and influence of anaesthesia on respiration were studied during halothane and enflurane anaesthesia. All the children were intubated orally. In 25 children halothane, and in another 25 children enflurane was used during spontaneous ventilation. Twenty-five children were also followed during halothane anaesthesia with manually controlled ventilation. The overall incidence of cardiac arrhythmias was higher during halothane anaesthesia (72% at spontaneous breathing and 68% with controlled ventilation) than during enflurane anaesthesia (32%, P <0.05). Ventricular arrhythmias were noted in 20% of the spontaneously breathing children and in 12% of those with controlled ventilation during halothane anaesthesia. Three children breathing spontaneously during halothane anaesthesia developed ventricular tachycardia. During enflurane anaesthesia the incidence of ventricular arrhythmias was lower (8 %) in spite of higher end-tidal CO₂ tensions and an anaesthetic depth that was only just the level needed to allow intubation. The incidence of ventricular arrhythmias during halothane anaesthesia was shown to be influenced by the anaesthetic technique used, which was not found with enflurane anaesthesia. The greater stability in cardiac rhythm with enflurane indicates a more favourable effect of this agent on the myocardium as well as a decreased sympathetic response to anaesthesia and surgery as compared with halothane anaesthesia.     

Early and late post-ischaemic recovery of contractile function is affected to different degrees by isoflurane and halothane in the anaesthetized rabbit model

The protective efficacy of halogenated anaesthetics on myocardial injury has never been compared during early reperfusion and late reperfusion in an in vivo animal model. We compared recovery of left ventricular function under isoflurane (0.5 MAC) and halothane (0.5 MAC) anaesthesia after a brief period of regional ischaemia (15 min) in acutely instrumented rabbits. Rabbits were instrumented for the measurement of regional segment length and left ventricular pressure. Rabbits receiving isoflurane showed greater recovery of systolic shortening fraction (%SS) both during early and late reperfusion compared with halothane anaesthesia. Isoflurane protected the post- ischaemic myocardium to a greater extent than halothane anaesthesia. Early recovery of contractile function may be a predictor of contractile recovery during the later stages of reperfusion.      

The stress response to induced hypotension for cerebral aneurysm surgery: a comparison of two hypotensive techniques

Plasma epinephrine (PE), plasma norepinephrine (PNEj, plasma renin activity (PRA), mean arterial pressure (MAP) and heart rate (HR) were measured before, during and after induced hypotension in two groups of patients undergoing cerebral aneurysm surgery, in Group I isoflurane was used to maintain anaesthesia and induce hypotension. Mean PE fell significantly during hypotension and remained reduced after hypotension, mean PNE remained unchanged, while mean PRA rose slightly but not significantly during hypotension, falling again after hypotension. In Group II halothane was used to maintain anaesthesia and sodium nitroprusside to induce hypotension, During anaesthesia and surgical stimulation PNE and PRA were significantly greater compared to Group I. Mean PE, PNE and PRA all rose during hypotension and remained elevated after hypotension. The rise in PNE and PRA was statistically significant. After hypotension the MAP in Group II was significantly higher when compared to Group I. There was no significant change in HR during the study in either group, in conclusion, isoflurane-induced hypotension with isoflurane anaesthesia unlike sodium nitroprusside-induced hypotension with halothane anaesthesia attenuated the stress response.     

Cardiovascular effects of 50% nitrous oxide in older adult patients anaesthetized with isoflurane or halothane

We have studied the cardiovascular effects of equipotent concentrations of halothane or isoflurane, with or without 50% nitrous oxide in oxygen, in 80 patients, aged 60 yr or more, during 20 min of stable equipotent anaesthesia. Non-invasive measurement techniques were used, with suprasternal Doppler ultrasonography for estimating cardiac output. Both isoflurane and halothane reduced heart rate and systemic arterial pressure. With isoflurane, mean rate decreased from 72 (SD 9.7) to 67 (10.4) beat min-1 and with halothane from 76 (10.1) to 65 (9.1) beat min-1 (P < 0.05). Mean diastolic arterial pressure decreased from 81 (11.3) to 58 (17.0) mm Hg with isoflurane and from 86 (14.7) to 70 (13.3) mm Hg with halothane (P < 0.05). Cardiac index decreased from 3.1 (1.03) to 2.7 (0.71) litre min-1 m-2 with isoflurane and from 3.1 (0.98) to 2.5 (0.57) litre min-1 m-2 with halothane (P < 0.05). Systemic vascular resistance decreased significantly in all groups except those receiving halothane with nitrous oxide. Nitrous oxide resulted in significantly less depression of cardiac index when given with isoflurane than when given with halothane. The mean percentage change in cardiac index during isoflurane anaesthesia without nitrous oxide was 16.7%; with nitrous oxide there was a 0.5% increase. Halothane, in combination with nitrous oxide, resulted in greater depression of cardiac index than isoflurane with nitrous oxide. The mean percentage change with halothane was 20.4% (22.2%); with isoflurane there was a 0.5% (27.1%) increase (P < 0.05). Hypotension was more pronounced in patients anaesthetized with isoflurane (n = 40) than those anaesthetized with halothane (n = 40), irrespective of the presence of nitrous oxide. The mean percentage decrease with isoflurane was 29.7% (21.10%) compared with 16.8% (16.78%) with halothane (P < 0.05).      

Comparative effect of halothane and isoflurane on peroperative cardiac arrhythmias

Cardiac arrhythmias were studied in twenty ASA class 1 patients under general anesthesia using halothane or isoflurane to supplement nitrous oxide in oxygen. The study began during the maintenance period, once the expiratory MAC value had reached a stable level of 1, and stopped one hour later. Both intubation and recovery periods were excluded. The end-tidal gas concentration was measured for carbon monoxide and vapours. The ECG was recorded on a magnetic tape. The incidence of arrhythmias was higher in the halothane group when compared to the isoflurane group (p less than 0.05). The main types of arrhythmias observed were supraventricular and ventricular ectopic beats. None of the arrhythmias observed were serious; in particular the ventricular beats were all unifocal and occasional. Heart rate measured at 10 min intervals tended to be more rapid in the isoflurane group.     

Circulatory effects of isoflurane in patients with ischemic heart disease: a comparison with halothane

The circulatory effects of isoflurane (I) were compared with those of halothane (H) in two groups of patients premedicated with morphine and scopolamine and scheduled for coronary artery bypass surgery. Both groups were similar with respect to age, weight, sex distribution, body surface area, left ventricular function, and preoperative dose of propranolol. While the patients were awake and breathing 100% oxygen, cardiac output and related hemodynamics were measured. The patients were then anesthetized by the same anesthesiologist with either isoflurane or halothane plus 50% N2O in O2. Ventilation was controlled to keep PaCO2 within the normal range. Hemodynamic measurements were repeated 10 min after intubation and during surgery 10 min after sternotomy. Heart rate did not change significantly in either group. Arterial blood pressure fell equally during anesthesia and returned toward baseline values during surgical stimulation in both groups. Cardiac output decreased in both groups during anesthesia and surgery. Cardiac output decreased significantly (P less than 0.05) more in the H group during surgery than in the I group. Systemic vascular resistance was significantly (P less than 0.05) lower in the I group during anesthesia and surgery. The manner and degree of maximum increases in arterial pressure and heart rate after intubation and the onset of surgical stimulation were similar in both groups.     

Effects of surgical stress and volatile anesthetics on left ventricular global and regional function in patients with coronary artery disease. Evaluation by computer-assisted two-dimensional quantitative transesophageal echocardiography.

We investigated the effects of halothane, enflurane, and isoflurane on central hemodynamics and left ventricular global and regional function when used to control intraoperative hypertension in 39 patients with coronary artery disease. Left ventricular short-axis, midpapillary images were obtained by transesophageal echocardiography. Using a centerline algorithm, we analyzed left ventricular images for global area ejection fraction (GAEF) and segmental area ejection fraction (SAEF). The SAEF/GAEF ratio was calculated for each of eight segments. Measurements were performed after induction of anesthesia but before skin incision; 1 min after sternotomy; and during administration of the inhaled anesthetic. The increase in arterial blood pressure during sternotomy was due to an increase in vascular resistance accompanied by increases in heart rate and filling pressures while GAEF decreased. No changes in the SAEF/GAEF ratio appeared during sternotomy. The inhaled anesthetics restored arterial blood pressure by a similar decrease in vascular resistance. Isoflurane caused an increase in cardiac index that was not seen with halothane or enflurane (halothane vs isoflurane, P < 0.05). The GAEF was decreased by halothane but unaffected by isoflurane and enflurane (halothane vs enflurane; P < 0.05). Isoflurane induced a decrease in the SAEF/GAEF ratios of two segments corresponding to the inferolateral wall of the left ventricle that was, in one of these segments, significantly more pronounced compared with both halothane and enflurane. Halothane or enflurane did not cause any change in regional wall motion. We conclude that isoflurane is more likely to cause regional wall motion changes than halothane or enflurane in patients with coronary artery disease.     

Effect of i.v. Atropine on Cardiac Rhythm, Heart Rate, Blood Pressure and Airway Secretion during Isoflurane Anaesthesia

Atropine, 0.01 mg kg-^-1, was given i.v. to 30 patients before mask anaesthesia with isoflurane. Controls (n = 28) received a placebo. ECG was recorded on tape throughout anaesthesia and analysed later. There were no ventricular arrhythmias, but six patients in the atropine group and two patients in the placebo group had supraventricular arrhythmias of very short duration. Most cases occurred shortly after atropine, i.e. before anaesthesia. Heart rate increased significantly in both groups, more so after atropine (up to 60%), and remained elevated. In both groups blood pressure fell after the induction of anaesthesia but was close to control during surgery. Suction of airway secretions was necessary in three placebo patients, but excessive secretions were not met. The frequency of airway reflexes was similar in the two groups. It is concluded that due to the pronounced tachycardia the routine use of i.v. atropine can hardly be recommended before mask anaesthesia with isoflurane.     

Epinephrine-induced premature ventricular contractions and changes in arterial blood pressure and heart rate during I-653, isoflurane, and halothane anesthesia in swine

I653 is a new inhalation anesthetic having especially desirable recovery characteristics because of its very low blood and tissue solubility. Investigations of its cardiovascular and electroencephalographic effects have revealed actions similar to those of isoflurane. However, these studies did not evaluate the potential of I653 to predispose the heart to epinephrine-induced arrhythmias. In this investigation, we studied eight domestic swine to compare the effects of I653 with those of other anesthetics on the cardiac arrhythmogenic actions of intravenously infused epinephrine. I653, isoflurane, and halothane each were given, on separate days, at 0.7-0.8 and at 1.1-1.2 MAC. The rate of infusion of epinephrine needed to produce premature ventricular contractions (PVCs) when the animals were anesthetized with I653 (6.9 +/- 0.7 and 6.6 +/- 0.9 micrograms.kg-1.min-1 at 0.8 and 1.2 MAC) did not differ from that during isoflurane anesthesia (5.7 +/- 1.1 and 6.0 +/- 1.0 micrograms.kg-1.min-1 at 0.7 and 1.1 MAC), but was greater than that required during halothane anesthesia (1.3 +/- 0.2 and 1.1 +/- 0.3 micrograms.kg-1.min-1 at 0.7 and 1.1 MAC). Similar mean arterial blood pressures and heart rates resulted from like infusions of epinephrine during I653 and isoflurane anesthesia. PVCs occurred at lesser infusion rates of epinephrine and at lower mean arterial blood pressures and heart rates with halothane than with I653 or isoflurane. Anesthetic concentration, over the range studied, did not alter the infusion rate of epinephrine required to produce arrhythmias with any anesthetic. The authors conclude that I-653 and isoflurane have similar properties with respect to epinephrine-induced arrhythmias and increases in heart rate and arterial blood pressure.     

Comparison of sevoflurane and halothane for outpatient dental anaesthesia in children

In a prospective, randomized, double-blind clinical study, we have studied 100 children, aged 2-12 yr, to compare halothane and sevoflurane in outpatient dental anaesthesia. All patients were unpremedicated and received inhalation induction using nitrous oxide in oxygen supplemented with either halothane (maximum inspired concentration 5%) or sevoflurane (maximum inspired concentration 8%). Time to loss of the eyelash reflex was more rapid using sevoflurane although time to adequate anaesthesia (to allow insertion of a mouth prop) was slower in the sevoflurane group. The incidence of cardiac arrhythmia was higher during halothane (62%) than during sevoflurane anaesthesia (28%) (P < 0.005) and the arrhythmias were more often ventricular in origin. The two agents were comparable in terms of ease of use and quality of anaesthesia, and times to eye opening and satisfying discharge criteria were similar. We conclude that sevoflurane has qualities that have made halothane the most used inhalation agent for children, and that it is superior to halothane in dental outpatients where cardiac arrhythmias are a particular problem.