Second dose thiopentone attenuates the haemodynamic response to laryngoscopy and intubation

The study was undertaken to evaluate the effectiveness of large (divided) thiopentone dosage on the peripheral haemodynamic response to laryngoscopy and intubation. Seventy-six (76) patient aged 18 to 67 years were sequentially assigned to either the second dose thiopentone group (n = 36) or the control group (n = 40). The first group had 4 mg.kg-1 thiopentone for induction of anaesthesia, then 1.5 mg.kg-1 suxamethonium chloride for muscle relaxation and a second dose of thiropentone (4 mg.kg-1) just before laryngoscopy and intubation. The control group had thiopentone 4 mg.kg-1 for induction of anaesthesia, suxamethonium 1.5 mg.kg-1 for muscle relaxation and then laryngoscopy and intubation. The heart rate (HR), systolic arterial pressure (SAP), diastolic arterial pressure (DAP), mean arterial pressure (MAP), and rate pressure product (RPP) were measured before induction of anaesthesia and after laryngoscopy and intubation. The difference in the values represented the haemodynamic response to laryngoscopy and intubation. The second dose thiopentone technique compared with the control group, significantly attenuated the post-intubation rise in HR (19.7 vs. 30.9), SAP (18.0 vs. 37.5) and RPP (4795.4 vs. 8440.0). The post intubation rise in DAP (33.9 vs. 42.5) and MAP (31.9 vs. 42.0) didn't show significant difference between the two groups.     

Hemodynamic effects of the induction of general anesthesia after low thoracic epidural anesthesia

Sixteen ASA 1 or 2 patients scheduled for abdominal surgery were included in the study after they had given their informed consent. Thirty minutes after starting a low-thoracic epidural anaesthesia (median level of sensitivity loss: T5), the patients were randomly given an intravenous bolus injection of either thiopentone (4 mg.kg-1, n = 8) or etomidate (0.5 mg.-1, n = 8), associated with succinylcholine 1 mg.kg-1. One minute after induction of general anaesthesia, the patients were intubated and mechanically ventilated (V(T) 8 ml.kg-1, rate 12 c.min-1). Mean arterial blood pressure (MAP) (oscillometric method), cardiac output (CO) (transthoracic bioimpedance) and heart rate were recorded semi-continuously. Total peripheral resistances (TPR) were calculated using the formula TPR = (MA/CO)*80. There were no differences between the groups in patient age, height, weight, and cardiovascular consequences of epidural anaesthesia. After anaesthetic induction and before endotracheal intubation, there was a slight decrease in CO in both groups, without any change in MAP. After intubation, MAP increased in both groups through peripheral vasoconstriction, whereas CO did not increase further. A significant tachycardia was occurred only seen in the thiopentone group, before and after tracheal intubation. This study showed that thiopentone and etomidate were suitable drugs for anaesthetic induction in a patient under epidural blockade. However, the absence of tachycardia following etomidate may be beneficial in cardiac patients. The monitoring of cardiac output determinants during thiopentone and etomidate anaesthesia require further invasive investigations.     

Comparison of the effects of topical lignocaine spray applied before or after induction of anaesthesia on the pressor response to direct laryngoscopy and intubation

In an attempt to attenuate the cardiovascular pressor response to laryngoscopy and intubation, 30 patients presenting for routine ophthalmic surgery were studied and were randomly allocated into two groups: group A (n = 15) received direct laryngeal/tracheal lignocaine spray immediately before intubation; and group B (n = 15) received orolaryngeal lignocaine spray before the induction of anaesthesia. In both groups, general anaesthesia was induced with thiopentone 3-5 mg kg-1, followed by atracurium 0.6 mg kg-1 to facilitate tracheal intubation. Laryngoscopy and endotracheal intubation caused a significant increase in heart rate, by 28% in group A and 23% in group B (P < 0.05 in both), and in diastolic blood pressure, by 28% in group A and 24% in group B (P < 0.05 in both). In group A, the systolic blood pressure also increased significantly (by 18%) after intubation, but there was no significant change in group B. In addition, the plasma lignocaine concentrations remained well below the toxic range in both groups. It was concluded that topical lignocaine administration as an orolaryngeal spray before the induction of anaesthesia is effective in reducing but not abolishing the pressor response to laryngoscopy and endotracheal intubation.     

The effect of intranasally administered nitroglycerin on the blood pressure response laryngoscopy and intubation in patients undergoing coronary artery by-pass surgery

The effect of intranasally administered nitroglycerin (NTG) on the cardiovascular response to laryngoscopy and intubation was studied. Thirty patients scheduled to undergo coronary artery by-pass surgery under thiopentone, enflurane and pancuronium anaesthesia were randomly divided into three groups. Group I received lignocaine 1.5 mg/kg i. v. prior to laryngoscopy and intubation (control group). Group II received lignocaine 1.5 mg/kg i. v. and in addition 2 mg nitroglycerin (NTG) was given intranasally. Group III received only 2 mg NTG intranasally. In Group I laryngoscopy and intubation caused a significant increase in mean arterial pressure (MAP) ( P <0.01), heart rate (HR) ( P <0.01) and rate pressure product (RPP) ( P <0.01) compared to preoxygenation values. In Group II and III MAP and RPP remained unchanged, whereas HR increased ( P <0.01 and P <0.01 respectively). It can be concluded that intranasally administered NTG effectively attenuates the pressor response to laryngoscopy and intubation in patients presenting for coronary artery by-pass surgery and that it is a more effective and convenient method than intravenous lignocaine.     

Influence of anaesthesia and muscle relaxation on intubating conditions and sympathoadrenal response to tracheal intubation

Background : The study aimed to assess the relative influence of anaesthesia and muscle relaxation on intubating conditions and the haemodynamic and catecholamine responses to tracheal intubation.
Methods : Sixty ASA 1 or 2 patients were randomly assigned to one of four groups (15 patients each) that differed in the depth of anaesthesia (thiopentone plus fentanyl 2.5 μg kg^-1 or thiopentone alone) and the degree of vecuronium–induced neuromuscular block (100% or _>: 65%) at intubation. Muscle relaxation was measured at 0.1 Hz by means of mechanomyography. Heart rate (HR) and mean arterial blood pressure (MAP) were measured before and after induction of anaesthesia, and 1 min and 5 min following intubation, while adrenaline (A) and noradrenaline concentrations (NA) were determined from arterial blood samples.
Results : Intubating conditions were improved primarily by providing complete muscle relaxation at the adductor pollicis muscle (P<0.001) and to a lesser extent by adding fentanyl to thiopentone (P=0.04). The response of HR and MAP to tracheal intubation was attenuated mainly by fentanyl (P<0.001). Complete muscle relaxation further diminished the response of MAP to intubation (P=0.03). Changes in A and NA were dependent on the depth of anaesthesia only (P =>0.01).
Conclusion : The results of the study demonstrate that the sympathoadrenal response to intubation is attenuated by adding fentanyl (2.5 kg^-1) to an induction regimen with thiopentone, whereas provision of complete muscle relaxation at the adductor pollicis muscle is necessary to attain smooth intubating conditions.     

喉罩与气管插管在全麻或复合硬膜外阻滞时的心率和血压改变

目的比较喉罩与气管插管用于全麻或全麻复合硬膜外阻滞患者的HR和BP变化.方法妇科手术80例,随机分为全麻气管插管(T)组、全麻喉罩(L)组、硬膜外阻滞 全麻气管插管(ET)组、硬膜外阻滞 全麻喉罩(EL)组,每组20例.硬膜外阻滞用1%利多卡因 0.15%丁卡因.全麻诱导咪唑安定2 mg、芬太尼0.2 mg、丙泊酚1.5 mg/kg、琥珀胆碱1.5 mg/kg后插气管导管或喉罩.全麻维持50%N2O O2 异氟醚,静注阿曲库铵、芬太尼.于麻醉前(基础,入室静卧10 min后)、插管后1 min、切皮、进腹探查后5 min、拔管后1 min记录MAP、SpO2、HR、PETCO2.结果插管时HR和MAP均低于基础值,而两组喉罩HR低于插气管导管者,硬膜外复合全麻喉罩组MAP低于气管插管组.切皮时两组全麻MAP高于复合硬膜外组.探查时两组复合硬膜外者HR和MAP均低于基础值,且MAP低于单纯全麻者(P＜0.05).拔管时各组HR均显著高于基础值,MAP未复合硬膜外者显著高于基础值.结论(1)插喉罩对BP和HR的影响不如气管导管剧烈;(2)复合硬膜外阻滞时气管插管或喉罩置入应激反应轻,也可减轻探查时的BP波动.     

Does alfentanil preserve left ventricular pump function during rapid sequence induction of anaesthesia?

A double-blind, randomised trial was conducted in 24 patients without cardiopulmonary disorders (20-43 years), to assess the effect of an intravenous bolus of alfentanil on the circulatory and catecholamine responses to rapid sequence induction of general anaesthesia. Induction included injection of thiopentone 5 mg/kg and suxamethonium 1.5 mg/kg in rapid succession, followed by laryngoscopy and intubation. Half of the patients received alfentanil 100 micrograms/kg immediately before thiopentone. The other half received saline. Blood pressure, heart rate, and plasma catecholamine concentrations were measured repeatedly, together with left ventricular ejection fraction assessed by radionuclide angiocardiography. The responses following laryngoscopy and intubation were completely different in the saline vs. the alfentanil group: rate pressure product +76% vs. -32%, mean arterial blood pressure +46% vs. -25%, heart +46% vs. no change, noradrenaline +117% vs. -25%, adrenaline +50% vs. -53%, and left ventricular ejection fraction -32% vs. no change. In conclusion, during rapid sequence induction of anaesthesia with thiopentone and suxamethonium, an intravenous bolus of alfentanil 100 micrograms/kg 1 min before laryngoscopy and intubation completely prevents hypertension, tachycardia, decrease in left ventricular ejection fraction, and activation of plasma catecholamines, though at the expense of moderate hypotension.     

Increased haemodilution in hypotension induced by epidural anaesthesia

This study examined whether the increased haemodilution from fluid loading in patients who develop hypotension at the onset of epidural anaesthesia (EDA) can be explained by high-level blockade or by stressinduced elevation of the blood glucose concentration. In 20 men aged between 53 and 87, crystalloid volume loading was carried out with 10 ml-kg^-1 b.w. and EDA was induced with mepivacaine 2% and adrenaline 1:200 000. Irrespective of the blood pressure reaction to the blockade, there was no change in blood glucose level. A strong linear correlation between haemodilution and arterial pressure was found, in spite of unchanged blood glucose levels, in 10 patients in whom EDA was induced with bupivacaine 0.5%, and in 10 patients who received spinal anaesthesia with tetracaine 1 %. There was no correlation between the haemodilution and the extent of sensory analgesia. These results support the view that low arterial pressure alone triggers the increased haemodilution observed during EDA-induced hypotension.     

Haemodynamic effects of ketamine and thiopentone during anaesthetic induction for caesarean section

Ketamine (1 mg . kg-1) or thiopentone (4 mg . kg-1) was used to induce anaesthesia for Caesarean section in 62 normotensive patients. During induction of anaesthesia and before laryngoscopy, blood pressure did not change in either group (preinduction systolic blood pressure, 131 mmHg, and diastolic blood pressure, 75 mmHg). When laryngoscopy and intubation were performed, mean blood pressures of both patient groups increased 20-30 per cent. With ketamine (n = 30) heart rate was unchanged from the preinduction rate of 85 beats/min before laryngoscopy and increased significantly by 15 per cent during laryngoscopy and intubation. With thiopentone (n = 32), heart rate increased significantly to 20 per cent above the preinduction rate of 87 beats/min during induction and increased further (to 35 per cent above the preinduction rate) during laryngoscopy and intubation. The average maximal rate-pressure product calculated for the thiopentone group was over 18,000, which was significantly higher than the 15,000 calculated for the ketamine group. Neonatal outcome as assessed by Apgar score and umbilical blood gas analysis was good and did not differ significantly between groups.     

Effects of beta-adrenoceptor antagonism on the cardiovascular and catecholamine responses to tracheal intubation

The catecholamine and cardiovascular responses to laryngoscopy and tracheal intubation were studied in 20 patients who underwent elective gynaecological surgery and who were allocated randomly to receive either practolol 10 mg or saline intravenously prior to induction of anaesthesia. Anaesthesia was induced with fentanyl and thiopentone; atracurium was administered and the lungs were ventilated artificially with 67% nitrous oxide in oxygen. Tracheal intubation was performed when muscle relaxation was adequate. Arterial pressure, heart rate, plasma noradrenaline and adrenaline concentrations were measured before and after tracheal intubation. A significant increase in catecholamine concentrations occurred in both groups in response to tracheal intubation but the magnitude of the increase in adrenaline was greater in the practolol group. There were no significant differences in arterial pressure or heart rate changes between the groups. We conclude that pretreatment with practolol is of no value in the attenuation of the hypertensive response to direct laryngoscopy and tracheal intubation in previously normotensive patients.     

The effect of various administration routes of lidocaine on hemodynamics and ECG rhythm during endotracheal intubation

Observations of arterial blood pressure, heart rate and cardiac rhythm during endotracheal intubation and within a five minute period thereafter were made in 80 patients randomly assigned into four groups. The aim was to study the cardiovascular changes following endotracheal intubation using a standard anesthesia technique and to compare the efficacy of lidocaine in controlling cardiovascular changes using different administration techniques. Anesthesia was induced with thiopentone and succinylcholine followed by endotracheal intubation. In group A, the control group, no lidocaine was given. In groups B, C, and D, lidocaine as laryngotracheal spray, transtracheal injection or intravenous injection in a dosage of 1 mg/kg BW was administered prior to endotracheal intubation. In the control group, laryngoscopy and endotracheal intubation caused a significant rise in blood pressure and heart rate with a high percentage (60%) of cardiac dysrhythmias including serious types. In the lidocaine groups, we observed significantly lower values of blood pressure and cardiac dysrhythmias as compared to the control group. Only 20-25% of the cases showed sinus tachycardia. No significant differences were noticed between the lidocaine groups. We conclude from our study that those patients who had received lidocaine prior to endotracheal intubation showed minimal cardiovascular changes. Lidocaine should therefore routinely be used prior to endotracheal intubation.     

Circulatory effects of short-term hypercapnia during thoracolumbar epidural anaesthesia

In ten elderly patients subjected to extensive thoracolumbar epidural anaesthesia, circulatory changes were studied before and during sympathetic stimulation. Induced hypercapnia was used as a sympathetic stimulus. After establishment of the epidural anaesthesia, which extended from T1 to L2, there were decreases in heart rate, mean arterial blood pressure, cardiac output and systemic vascular resistance. Hypercapnia before the epidural block increased heart rate, arterial blood pressure and cardiac output, while hypercapnia after established epidural block induced only a slight increase in arterial blood pressure. The results indicate that in spite of an extensive epidural block, there are some "escaped" sympathetic nerve fibres that can be mobilized during sympathetic stimulation.     

Tracheal intubation after induction of anaesthesia with thiopentone or propofol without muscle relaxants

This study was designed to compare the ease of performing laryngoscopy and endotracheal intubation without muscle relaxants after the induction of anaesthesia with either thiopentone or propofol in 106 patients scheduled for elective surgery. Thiopentone (5 mg/kg) or propofol (2.5 mg/kg), supplemented with lidocaine (1.5 mg/kg) and alfentanil (30 micrograms/kg), were used in random order for the induction of anaesthesia. Jaw tone, visualisation of the larynx, position of vocal cords, ease of intubation and tolerance of the tracheal tube were assessed. The jaw was relaxed and the vocal cords were immobile/open in most patients in both groups. Visualisation of the larynx was good in 60 and 46% and intubation was easy in 48 and 22% of the patients given thiopentone and propofol, respectively (P less than 0.05 between groups for intubation). After induction of anaesthesia with thiopentone or propofol, endotracheal intubation is not recommended without the use of muscle relaxants.     

Intravenous lidocaine does not attenuate the haemodynamic response of children to laryngoscopy and tracheal intubation

The haemodynamic responses to laryngoscopy and intubation after induction of anaesthesia with thiopentone alone or in combination with 1.5 mg · kg^?1 IV lidocaine were measured in 125 children age 2 to 12 yr to determine whether lidocaine administered one, two, three or four minutes before tracheal intubation attenuated the pressor response. Lidocaine did not attenuate the increases in heart rate and arterial blood pressure. The pressor response was significantly affected by baseline haemodynamic values, P < 0.05. The increases in systolic and mean blood pressure were significantly affected by the age of the patient, P < 0.05. Lidocaine is not a beneficial adjunct to induction of anaesthesia with thiopentone in healthy children for the purpose of attenuating the pressor response to intubation.     

Catecholamine response to laryngoscopy and intubation

The haemodynamic response and changes in plasma catecholamine concentrations associated with laryngoscopy and tracheal intubation were compared during anaesthesia employing three strictly standardised techniques with commonly used drug combinations. Thirty-six patients were investigated consecutively resulting in 12 patients in each of three study groups. Anaesthesia was induced with thiopentone 5 mg.kg-1 (group 1), fentanyl 6 micrograms.kg-1 with thiopentone 5 mg.kg-1 (group 2), or midazolam 0.2 mg.kg-1 with fentanyl 6 micrograms.kg-1 (group 3). Undesirable changes in haemodynamic effects and an elevation of plasma catecholamine concentrations during laryngoscopy and intubation occurred in group 1. Heart rate and mean arterial pressure increased significantly (34% and 23% respectively). Noradrenaline concentration increased by a maximum of 147%. The addition of fentanyl (groups 2 and 3) attenuated the adverse haemodynamic response and elevation of plasma catecholamine concentrations; heart rate and mean arterial pressure did not differ from pre-intubation values and plasma catecholamine concentrations decreased steadily. Substitution of thiopentone by midazolam in combination with fentanyl abolished the adverse haemodynamic response and modified the increase in plasma catecholamine concentrations. 'High-dose' opioid anaesthesia is not necessary to produce optimal conditions during laryngoscopy and intubation.     

Effect of oral gabapentin on the intraocular pressure and haemodynamic responses induced by tracheal intubation

Background: Laryngoscopy and tracheal intubation may cause undesirable increases in blood pressure, heart rate (HR) and intraocular pressure (IOP). Gabapentin has been used effectively to attenuate the pressor response to laryngoscopy and tracheal intubation. We investigated whether the pre-treatment with gabapentin attenuates the IOP in addition to a haemodynamic response to tracheal intubation.
Methods: Sixty ASA I–II patients were randomly allocated into two groups who received either gabapentin (800 mg) or placebo 2 h before surgery. IOP, mean arterial pressure (MAP) and HR were measured before and after the induction of anaesthesia as well as at 0, 1, 3, 5, 10 and 15 min following intubation.
Results: IOP and MAP increased from baseline immediately after intubation in the placebo group ( P =0.001 and 0.002, respectively). When compared with the placebo group, IOP values of the gabapentin group were significantly lower for the first 15 min after tracheal intubation ( P =0.002 at 0 min, P =0.006 at 1 min, P <0.001 at 3 min, P <0.001 at 5 min, P <0.001 at 10 min and P =0.003 at 15 min) while MAP was lower in the first 10 min ( P =0.001 at 0 min, P =0.002 at 1 min, P <0.001 at 3 min, P <0.001 at 5 min and P =0.028 at 10 min). These results showed that gabapentin effectively suppresses the increase in IOP secondary to endotracheal intubation and attenuates the increases in MAP.
Conclusion: It is suggested that gabapentin is a useful adjuvant in order to prevent an increase in the IOP in response to laryngoscopy and tracheal intubation.     

Narcotic reversal in hypercapnic dogs: comparison of naloxone and nalbuphine

Reversal of opioid effects by naloxone (NX) can lead to significant cardiovascular problems. We have reported previously that hypercapnic dogs develop greater increases in blood pressure and plasma catecholamine (CA) levels than hypocapnic ones when reversed with naloxone. We have also demonstrated differences between NX and nalbuphine (NBPH) in producing excitatory adrenergic responses when administered during normocapnia. The present study was designed to investigate possible dissimilarities in cardiovascular and sympathetic events after administration of either NX or NBPH in dogs made hypercapnic following fentanyl administration. After induction of anaesthesia with thiopentone and intubation, two groups of dogs were maintained with controlled ventilation on enflurane in oxygen anaesthesia and given 50 micrograms.kg-1 fentanyl IV. This caused a significant decrease in heart rate (HR) (P less than 0.001), mean arterial blood pressure (MAP) (P less than 0.001), and plasma concentrations of norepinephrine (NE) (P less than 0.002). Then, ventilation was decreased to produce a PaCO2 of 60 mmHg; this was accompanied by a significant elevation in plasma level of both epinephrine (EPI) (P less than 0.02) and NE (P less than 0.001). Administration of 20 micrograms.kg-1 NX to six dogs resulted in immediate increases in HR (P less than 0.01) and MAP (P less than 0.01), and a further rise in CA levels to greater than pre-fentanyl baseline values. In six other dogs, NBPH (0.3 mg.kg-1) caused increases in HR (P less than 0.001) and MAP (P less than 0.001) only, and the MAP rise was significantly less than that seen in the NX group (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of nicardipine, diltiazem and verapamil for controlling the cardiovascular responses to tracheal intubation

We have compared the efficacy of three calcium channel blockers, nicardipine, diltiazem and verapamil, in attenuating the cardiovascular responses to laryngoscopy and intubation in 60 normotensive patients (ASA I) undergoing rapid sequence induction of anaesthesia with thiopentone and fentanyl. We also examined whether or not these blockers inhibited catecholamine release induced by intubation. The patients were allocated to one of four groups (n = 15 for each): saline (control), nicardipine 30 micrograms kg-1, diltiazem 0.2 mg kg-1 or verapamil 0.1 mg kg-1. Verapamil and the three other drugs were administered 45 s and 60 s before the start of direct laryngoscopy, respectively, in a double-dummy design. Anaesthesia was induced with thiopentone 4 mg kg-1 i.v. and fentanyl 2 micrograms kg-1 i.v. Tracheal intubation was facilitated with vecuronium 0.2 mg kg-1. During anaesthesia, ventilation was assisted or controlled with 1% isoflurane and 50% nitrous oxide in oxygen. Laryngoscopy lasting 30 s was attempted 2 min after administration of thiopentone and vecuronium. Patients receiving saline exhibited significant increases in systolic and diastolic arterial pressures (AP), heart rate (HR) and plasma concentrations of catecholamines associated with tracheal intubation. The increase in AP was attenuated in patients treated with any calcium channel blocker. The greatest effect was elicited by verapamil, which attenuated the increase in HR, although nicardipine seemed to enhance tachycardia. All three drugs failed to suppress the increase in plasma catecholamine concentrations in response to tracheal intubation. These findings suggest that bolus injection of verapamil 0.1 mg kg-1 was a more effective method of controlling hypertension and tachycardia associated with intubation than diltiazem 0.2 mg kg-1 or nicardipine 30 micrograms kg-1, and that these prophylactic effects were not caused by inhibition of the catecholamine response.      

Evaluation of i.v. verapamil effects on cardiovascular responses in normotensive patients during laryngoscopy

Laryngoscopy and intubation are known to increase systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), and heart rate (HR). In this study, we demonstrated that the injection of intravenous verapamil (0.1 mg/kg) prior to laryngoscopy can blunt the cardiovascular responses to laryngoscopy and intubation and result in stable hemodynamic profile in normotensive patients.     

Haemodynamic and catecholamine changes after induction of anaesthesia with either thiopentone or propofol with suxamethonium

We have compared the haemodynamic and cate-cholamine responsesto laryngoscopy and tracheal intubation in 43 patients afterinduction of anaesthesia with either thiopentone 5.1 (SD 0.9)mg kg^–1 or propofol 2.2 (0.1) mg kg^–1, each withsuxamethonium and without opioid pretreatment. Heart rate increasedsignificantly above baseline after induction and intubationin both groups, but there were no differences between groups.Arterial pressure increased significantly at 7 min after intubationin both groups and at 2 min in the thiopentone group only. Plasmaconcentrations of adrenaline increased significantly comparedwith concentrations before induction, 1 min after intubationin both groups and at 2 min in the thiopentone group only. Plasmaconcentrations of adrenaline were significantly greater in thethiopentone group than in the propofol group at both 1 and 2min after intubation. Plasma concentrations of noradrenalineshowed no significant time-based within-group changes, but weresignificantly greater in the thiopentone group at 1 and 2 minafter intubation. We conclude that doses of either thiopentoneor propofol sufficient to obtund the eyelash reflex with suxamethonium1 mg kg^–1 alone do not adequately block the catecholamineand hypertensive responses to laryngoscopy and intubation innormal patients and although propofol suppressed increases incatecholamines to a greater extent than thiopentone, there wereno clinical advantages. (Br. J. Anaesth. 1994; 72: 596–598)