Anaesthetic induction with alfentanil: comparison with thiopental, midazolam, and etomidate

The speed, side effects and cardiovascular changes associated with anaesthetic induction and endotracheal intubation following alfentanil (20 micrograms/kg/min, IV), thiopental (84 micrograms/kg/min, IV), etomidate (5 micrograms/kg/min, IV) and midazolam (20 micrograms/kg/min, IV) prior to halothane-nitrous oxide general anaesthesia were evaluated and compared in 80 patients undergoing elective general surgical operations. Anaesthetic induction was fastest with etomidate and thiopental (approximately one minute) and slowest with midazolam (about two minutes). Systolic arterial blood pressure (SBP) was decreased at the moment of unconsciousness with thiopental but unchanged with the other compounds. Heart rate (HR) was increased at unconsciousness with midazolam and thiopental but unchanged with etomidate and alfentanil. After intubation HR was increased in all groups except those induced with alfentanil. Arrhythmias were infrequent (5 per cent or less in all groups). Rigidity during induction only occurred with alfentanil (55 per cent) and pain on injection only with etomidate (35 per cent) and alfentanil (5 per cent). Postoperative vomiting was infrequent in all groups (15 per cent) except etomidate (55 per cent). No patient remembered any aspect of laryngoscopy or the operation and all rapidly regained consciousness at the end of operation. The results of this study demonstrate that with the exception of rigidity (which is easily overcome with succinylcholine) and a slightly slower onset of action, alfentanil compares favourably as an induction agent with thiopental and is better than midazolam and etomidate. Alfentanil is superior to all three other induction agents with respect to cardiovascular stability during induction and intubation.     

Hemodynamic action profile of propofol in comparison with midazolam. A study in coronary surgical patients

Propofol, a rapid and short-acting i.v. anesthetic, was associated with the risk of anaphylactic reactions in its original cremophor-EL formulation. It has been reformulated in a soybean emulsion with satisfactory anesthetic properties. A former study of hemodynamic changes after i.v. induction with propofol, thiopental, methohexital, etomidate, and midazolam in patients with coronary artery disease demonstrated that in comparison to other induction agents propofol depressed systolic and diastolic arterial pressures more severely, compromising coronary perfusion. In the present investigation left ventricular parameters as well as hemodynamic effects during extracorporeal circulation (ECC) were studied in comparison to midazolam during opiate analgesia. Methods. Hemodynamic effects of 2 mg/kg body weight propofol as compared to 0.15 mg/kg midazolam were studied in 34 patients during coronary artery surgery before cannulation of the large vessels (measurement of left ventricular parameters) or during ECC (measurement of arterial perfusion pressure and oxygenator volume). Results (see Table 1, Figs. 1 and 2). Propofol decreased systolic and diastolic pressures (-27%, -22%) more than midazolam (-10%, -9%). Cardiac index and stroke volume index were diminished following both drugs (propofol: -14%, -9%; midazolam: -15%, -11%); total systemic resistance was reduced significantly by propofol (-22%). Dp/dtmax was compromised more markedly by propofol (-24%) than by midazolam (-18%), but there was no significant difference.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of midazolam and thiopental for rapid sequence anesthetic induction for elective cesarean section

Sixty healthy mothers undergoing elective cesarean section received at random either midazolam 0.2 mg/kg or thiopental 3.5 mg/kg with succinylcholine 1 mg/kg for rapid sequence intravenous anesthetic induction. Maintenance of anesthesia was identical in all patients: 50:50 N2O in oxygen, halothane 0.5% and pancuronium 0.05 mg/kg. Hemodynamic responses were similar, as were the biochemical status of mothers and infants, and maternal to fetal blood gas/acid base gradients. Correlation between maternal arterial and fetal (umbilical venous/arterial) pH, PCO2 and base excess values were statistically better with midazolam. However, 1-min Apgar minus color (A-C) scores less than 5/8 (representing "severe" neonatal depression) were recorded in five infants after midazolam, three of whom required tracheal intubation, and one whose mother was given thiopental. This difference reached statistical significance (P less than 0.05). It is concluded that midazolam is less suitable than thiopental for anesthetic induction in patients undergoing cesarean section.     

Comparison of etomidate, ketamine, midazolam, propofol, and thiopental on function and metabolism of isolated hearts.

The authors examined direct myocardial and coronary vascular responses to the anesthetic induction agents etomidate, ketamine, midazolam, propofol, and thiopental and compared their effects on attenuating autoregulation of coronary flow as assessed by changes in oxygen supply/demand relationships. Spontaneous heart rate, atrioventricular conduction time during atrial pacing, left ventricular pressure (LVP), coronary flow (CF), percent oxygen extraction, oxygen delivery, and myocardial oxygen consumption (MVo2) were examined in 55 isolated guinea pig hearts divided into five groups of 11 each. Hearts were perfused at constant pressure with one of the drugs administered at steady-state concentrations increasing from 0.5 microM to 1 mM. Adenosine was given to test maximal CF. At concentrations below 10 microM no significant changes were observed; beyond 50 microM for midazolam, etomidate, and propofol, and 100 microM for thiopental and ketamine, each agent caused progressive but differential decreases in heart rate, atrioventricular conduction time (leading to atrioventricular dissociation), LVP, +dLVP/dtmax, percent oxygen extraction, and MVo2. The concentrations (microM) at which +dLVP/dtmax was reduced by 50% were as follows: etomidate, 82 +/- 2 (mean +/- SEM); propofol, 91 +/- 4; midazolam, 105 +/- 8; thiopental, 156 +/- 11; and ketamine, 323 +/- 7; the rank order of potency was etomidate = propofol = midazolam greater than thiopental greater than ketamine; results were similar for LVP. At the 100 microM concentration, CF was decreased 11% +/- 2% by ketamine and 5% +/- 3% by thiopental but was increased 17% +/- 6% by etomidate, 21% +/- 5% by midazolam, and near maximally to 57% +/- 10% by propofol; MVo2 was decreased 8% +/- 4% by thiopental, 10% +/- 5% by ketamine, 19% +/- 5% by midazolam, 29% +/- 7% by etomidate, and 37% +/- 5% by propofol; oxygen delivery/MVo2 was unchanged by thiopental and ketamine but was increased 62% +/- 7% by midazolam, 71% +/- 9% by etomidate, and 150% +/- 15% by propofol. Between 100 microM and 1 mM, thiopental and ketamine did not increase CF but decreased MVo2 and percent oxygen extraction, whereas propofol maximally increased CF and decreased MVo2 and midazolam and etomidate had intermediate effects. These results indicate that on a molar basis, propofol, and less so midazolam and etomidate, depress cardiac function moderately more than thiopental and ketamine, and that propofol markedly attenuates autoregulation by causing coronary vasodilation. With doses used to induce anesthesia, propofol and thiopental appear to depress cardiac function more than ketamine or etomidate.     

四种常用静脉麻醉药对老年病人血液动力学影响的比较

目的 探讨脑电双频指数(BIS)为50时，硫喷妥钠、丙泊酚、咪唑安定、依托咪酯用于老年病人全麻诱导的剂量及其对血液动力学的影响。方法 65岁以上的老年病人48例，随机分为四组：硫喷妥钠组，丙泊酚组，咪唑安定组，依托咪酯组。四组均缓慢静注，并且用HXD-1型脑电监测仪测量每例病人的BIS。当BIS逐渐下降至50时停止静注，分别于注药前、注药后1、3、5、10min用Rheo Cardio Monitor连续非创伤性血液动力监测仪记录和计算出血液动力学有关参数。结果 BP下降以丙泊酚组为显著。丙泊酚组和硫喷妥钠组的PEP/LVEF比值明显增加，但丙泊酚组＞硫喷妥钠组。除依托咪酯组以外其他各组的每搏指数(SD、心脏指数(CI)、射血速率(EV)和每搏功(LVP)均有不同程度的降低，但以丙泊酚组为显著。依托咪酯组体循环血管阻力(SVR)无明显变化，硫喷妥钠组和咪唑安定组均有不同程度的升高，以咪唑安定组为显著，丙泊酚组明显下降。舒张末容量(EDV)咪唑安定组明显下降，其他各组无明显变化。结论 四种静脉麻醉药对老年病人血液动力学的影响由大到小依次为丙泊酚＞咪唑安定＞硫喷妥钠＞依托咪酯。BIS为50时，老年病人各静脉麻醉药的等效剂量为硫喷妥钠4mg／kg、丙泊酚1．2mg／kg、咪唑安定0．16mg／kg、依托咪酯0．34mg／kg。对于心功能较差和血容量不足的老年病人全麻诱导，依托咪酯是首选的静脉麻醉诱导药。     

Direct effect of anesthetic inducers on the electromyographic signals of the adductor pollicis

OBJECTIVES: To analyze the effect of thiopental, propofol, etomidate and midazolam on electromyographic study of the adductor pollicis before muscle relaxation. PATIENTS AND METHOD: Prospective study of 96 adults ASA I-II patients (gynecologic surgery) by electromyographic (Reflexograph Datex) recording of the adductor pollicis every 20 seconds with train-of-four (TOF) stimuli. After giving informed consent, the patients were randomized for type of induction agent. We studied changes in T1 (amplitude of the first response to TOF) and the TOF-ratio (T4/T1). The induction agent (thiopental 5 mg/kg), propofol 3 mg/kg, midazolam 0.2 mg/kg or etomidate 0.3 mg/kg) was given by slow 30 s injection 100 s after calibration of the Relaxograph. Changes in T1 and the TOF-ratio were recorded until 240 s. RESULTS: The groups were statistically homogeneous. In the thiopental group, T1 readings at 20, 40, 60 and 80 s (control times) were statistically different from the readings at 180, 220 and 240 s (after administering thiopental). T1 was significantly different at 120 and 200 s in the etomidate group. CONCLUSIONS: Thiopental and etomidate induce slight muscle relaxation at the expense of a reduction in T1 without changing the TOF-ratio, an effect that might be useful for rapid induction. Propofol and midazolam do not affect the electromyogram of the adductor pollicis. Thus, propofol is the anesthetic induction agent of choice for clinical studies on non-depolarizing muscle relaxants given that it changes neither T1 nor the TOF-ratio.     

Anesthesia for elective cardioversion: a comparison of four anesthetic agents.

Elective cardioversion is a short procedure performed under general anesthesia for the treatment of cardiac dysrhythmias. Selection of the anesthetic agent is important, because a short duration of action and hemodynamic stability are required. Forty-four patients scheduled for elective cardioversion in the coronary care unit were studied prospectively. All patients were randomly assigned, according to the last digit of their clinical record number, to receive one of the four anesthetic agents studied: group 1, 12 patients who received 3 mg/kg of sodium thiopental; group 2, 10 patients who received 0.15 mg/kg of etomidate; group 3, 12 patients who received 1.5 mg/kg of propofol; and group 4, 10 patients who received 0.15 mg/kg of midazolam. All patients also received 1.5 micrograms/kg of fentanyl 3 minutes before induction. All four drugs provided satisfactory anesthesia for cardioversion and there were no major complications. Midazolam produced a more prolonged duration of effect and more interindividual variability. Propofol was associated with hypotension and a higher incidence of apnea, and its duration of action was similar to that of etomidate or thiopental. Etomidate produced myoclonus and pain on injection; however, it was the only agent that did not decrease arterial blood pressure. Thiopental reduced blood pressure but otherwise seemed an appropriate anesthetic for this procedure. In conclusion, all four anesthetic agents were acceptable for cardioversion, although their pharmacological differences suggest specific indications for individual patients.     

Comparative study of propofol with thiopental and etomidate in anesthetic induction]

Anesthetic characteristics were studied in three homogeneous groups of twenty patients ASA I who underwent intravenous anesthetic induction with propofol 2 mg/kg; thiopental 5 mg/kg; or etomidate 0.3 mg/kg. The unconsciousness time was similar in the three groups, whereas awaking time and time of response and orientation were longer after thiopental and etomidate than after propofol. Intravenous injection of the three anesthetic agents was followed by a decrease in systolic and diastolic arterial pressure. Heart rate increased after thiopental and etomidate and had only slight fluctuations after propofol. After tracheal intubation there was a significant increase in systolic and diastolic arterial pressure and heart rate in thiopental and etomidate group. These changes were minimal after propofol. The highest number of complications occurred after etomidate.     

Changes in expression of lymphocyte surface markers following administration of etomidate, midazolam or methohexital

Stress alters cellular immunity, affecting lymphocyte function, total lymphocyte count, and the frequency distribution of the lymphocyte subpopulations. Cortisol may mediate these stress-related changes, and drugs affecting cortisol levels might therefore alter lymphocyte patterns. Etomidate and midazolam both prevent the normal perioperative cortisol increase in minor surgery, but the mechanisms by which they do this are not identical: etomidate inhibits steroid synthesis in the adrenal cortex, leading to low cortisol and high ACTH levels, whereas midazolam primarily prevents ACTH increases. Methohexital has little or no influence on cortisol levels. By comparing the effects of these three drugs on the expression of lymphocyte surface markers and the interleukin-2 (Il-2) receptor, we hoped to gain further information on the effects of perioperative cortisol changes on cellular immunity. METHODS. Healthy, young male patients scheduled for routine body surface operations were premedicated with 2 mg flunitrazepam the evening before surgery and 50 mg promethazine and 15 mg piritramide i.m. 1 h before arrival in the operating room. Anaesthesia was induced with 0.2-0.3 mg fentanyl, 2 mg pancuronium, and either etomidate (0.3 mg/kg body wt.), midazolam (0.2 mg/kg body wt.), or methohexital (1.5 mg/kg body wt.). The induction bolus was followed by an infusion at the rate of 0.36 mg/kg/h for etomidate, 0.09 mg/kg/h for midazolam, and no infusion for methohexital. Intubation was facilitated with 100 mg succinylcholine. The patients were ventilated to normocapnia with 66% nitrous oxide in oxygen. Fentanyl was given as 0.1 mg bolus injections whenever necessary.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of sedative infusions during regional anesthesia--methohexital, etomidate, and midazolam

Using a randomized, double-blind study design, the intra- and postoperative sedative effects of three intravenous central nervous system depressants were compared in 64 patients during regional anesthesia. After establishing regional anesthesia, methohexital 59 +/- 29 mg IV, etomidate 12.6 +/- 8 mg IV, or midazolam 3.7 +/- 1.5 mg IV (mean dose +/- SD) were infused in a titrated fashion over 5-15 minutes to achieve similar end points of sedation. This level of sedation was then maintained with a variable-rate infusion of either methohexital 180 +/- 65 mg/hr, etomidate 32 +/- 12 mg/hr, or midazolam 7.5 +/- 4 mg/hr (mean dose +/- SD) To maintain a stable level of sedation, changes in the maintenance infusion rate were required more frequently with methohexital (4.6 +/- 3 times) than with etomidate (2.6 +/- 2 times) or midazolam (2.7 +/- 3 times). Decreases in oxygen saturation below 95% were more frequent with midazolam than with methohexital and etomidate, while recall of intraoperative events was less frequent after midazolam. Observer evaluations found less sedation in the methohexital and etomidate groups than in the midazolam group during the early postoperative period. However, the patients' evaluation of residual sedative effects (e.g., postoperative sedation visual analogue scores) and discharge times from the recovery room were similar in all three groups. Nevertheless, patients given midazolam had significantly greater impairment of performance on the digit-symbol substitution test in the early postoperative period than did patients given either methohexital or etomidate.     

不同全麻诱导药对循环及内分泌功能的影响

目的 评价三种静脉药在全麻诱导时对循环、垂体－肾上腺皮、髓抽内分泌功能的影响。方法 将择期全麻手术病人43例,随机分为三组：Ⅰ（组（异丙酚2.5mg/kg）;Ⅱ组（硫喷妥钠5mg/kg）和Ⅲ组（依托咪酯03mg/kg）各14例。行桡动脉直接测压,同时边疆监测ECG、SpO2。快速静注琥珀碱1.5-2.0mg/kg行气管插管。插管2min后静注维库溴铵4mg,5min后各组吸入安氟醚维持1.3MAC,15min后复合吸入N2O。在诱导前（T0）,窥喉插管即刻（T1）,插管后2min（T2）,5min(T3),15min(T4)取外周静脉血测定血浆去甲肾上腺素（NE）、肾上腺素（E）、皮质醇（cort）、泌乳素（PRL）、生长素（GH）、β－内啡肽（β－EP）、胰岛素和血糖的水平。结果 异丙酚诱导气管插管能抑制高血压反应,不增加心肌耗氧量,明显优于友喷妥钠和依插咪酯;三药诱导气管插管均不能抑制E和NE升高;均使腺垂体分泌PRL增加,而H、β-EP无变化;插管后15min依托咪酯使肾上腺皮质分泌cort减少;使血糖升高,胰岛素降低;说明对糖耐量呈现抑制作用。结论 异丙酚对循环和内分泌影响较小,是目前首选的全麻诱导药。     

Comparison of psychomotor skills and amnesia after induction of anesthesia with midazolam or thiopental

In two groups of 31 healthy patients undergoing minor elective surgery, anesthesia was induced intravenously with either midazolam maleate, 0.2 mg/kg, or thiopental, 3.5 mg/kg. All subjects received 2 micrograms/kg fentanyl 5 min before the induction agents. Induction time with midazolam was significantly longer than with thiopental (97.1 +/- 10.9 sec vs 59.4 +/- 5.0 sec) and time to orientation postoperatively was significantly longer after midazolam (31.7 +/- 4.2 min vs 11.0 +/- 1.1 min). Continued recovery after orientation, measured by a series of psychomotor tests, was also significantly longer with midazolam than with thiopental. Anterograde amnesia was evident in 84.8% of the midazolam treated patients and in only 31.4% of the thiopental group. This degree of absence of recall was acknowledged positively by the affected patients. The protracted recovery period may limit the use of midazolam in short surgical procedures.     

Inotropic and anesthetic potencies of etomidate and thiopental in dogs

The effects of etomidate and thiopental on myocardial contractility were compared in 10 experiments on isolated papillary muscle preparation perfused by a conscious donor dog. Equianesthetic doses of etomidate (1.4 mg/kg) and thiopental (15.5 mg/kg) were determined separately in conscious dogs. Tension developed by the papillary muscle decreased significantly less after etomidate (17 +/- 2%) than after thiopental (33 +/- 3%) (P less than 0.002) when injected intravenously in equianesthetic doses in donor dogs. When added to arterial blood perfusing the papillary muscle, etomidate had 4-5 times more negative inotropic effect than thiopental. At the same time, the anesthetic potency of etomidate was approximately 11 times greater than that of thiopental. We conclude that both etomidate and thiopental produce a dose-dependent direct negative inotropic effect but that in equianesthetic doses, etomidate causes less pronounced depression of myocardial contractility than thiopental.     

A comparison of etomidate and thiopental anesthesia for cardioversion

Sixteen ASA class II or III male patients (aged, 52 to 66 years) undergoing elective cardioversion were randomly assigned to receive either thiopental or etomidate according to an observer-blinded, parallel study design. The appropriate drug was administered in 2-mL aliquots every 15 seconds until the patient no longer responded to verbal commands, at which time cardioversion was attempted. The total dose for induction was 0.22 +/- 0.2 mg/kg and 3.2 +/- 0.4 mg/kg for etomidate and thiopental, respectively. The cardiorespiratory data after induction were evaluated for maximal percent change from baseline. The baseline heart rate was 106 +/- 6 beats/min and 98 +/- 8 beats/min for the etomidate and thiopental groups, respectively (mean +/- SEM). The heart rate decreased 5% after induction with etomidate and increased 7% with thiopental (P less than 0.05). The baseline mean arterial pressure (MAP) was 96 +/- 3 mm Hg and 105 +/- 11 mm Hg for the etomidate and thiopental groups, respectively (mean +/- SEM). The MAP decreased 4% with etomidate and 3% with thiopental. Respiratory rate was significantly increased by 22% after etomidate compared with a 22% decrease in respiratory rate with thiopental (P less than 0.05). Seven of eight patients in the thiopental group required only one countershock, whereas four of eight patients in the etomidate group required only one shock. One patient in each group could not be successfully cardioverted. Recovery time and clinical side effects were similar between groups except for mild myoclonus in the etomidate group. Titration to effect of either etomidate or thiopental provided satisfactory anesthesia for elective cardioversion in hemodynamically stable patients.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of general anesthesia on the human blink reflex

The blink reflex was studied in 10 patients undergoing elective procedures under general anesthesia. Anesthetic agents were isoflurane, halothane, nitrous oxide, methohexital, and thiopental in various combinations. At induction, blink reflexes were diminished by low-dose thiopental (1-1.5 mg/kg) and abolished by high-dose thiopental (4-8 mg/kg) and methohexital (1.5 mg/kg). Blink reflexes were absent during halogenated volitile inhalational anesthesia and did not return until patients were in the recovery room, well after end-tidal anesthetic levels were zero by mass spectroscopy. Recovery of consciousness and the ability to blink on command often preceded return of any blink reflex activity, indicating that the blink reflex is not useful as a postoperative test of facial nerve function in the operating room after anesthesia. In six patients, blink reflexes were still diminished 2-3 hours after cessation of anesthesia, at a time when patients were fully oriented and corneal and eyelid reflexes were clinically normal. This finding suggests that the blink reflex might be a sensitive test of subtle CNS dysfunction after inhalational anesthesia and potentially could serve as a useful objective indicator of recovery from anesthesia for outpatient surgery.     

Comparison of the Effects of Etomidate, Propofol, and Thiopental on Respiratory Resistance after Tracheal Intubation

Background: Tracheal intubation frequently results in reversible bronchoconstriction. Propofol has been reported to minimize this response in healthy patients and in asthma patients, but may be unsuitable for hemodynamically unstable patients for whom etomidate may be preferable. The current study examined respiratory resistance after tracheal intubation after induction with either thiopental, etomidate, or propofol. A supratherapeutic dose of etomidate was used to test the hypothesis that the bronchoconstrictive response could be minimized by deep intravenous anesthesia.

Methods: Seventy-seven studies were conducted in 75 patients. Anesthesia was induced with either 2.5 mg/kg propofol, 0.4 mg/kg etomidate, or 5 mg/kg thiopental. Respiratory resistance was measured at 2 min after induction.

Results: Respiratory resistance at 2 min was 8.1+/-3.4 cmH sub 2 O *symbol* l sup -1 *symbol* s (mean+/-SD) for patients receiving propofol versus 11.3+/-5.3 for patients receiving etomidate and 12.3+/-7.9 for patients receiving thiopental (P less than or equal to 0.05 for propofol vs. either etomidate or thiopental).     

Endocrinological changes following etomidate, midazolam, or methohexital for minor surgery

Etomidate is known to inhibit adrenocorticosteroid synthesis. The extent and duration of the effects of etomidate (63 +/- 6.4 mg) on spontaneous and stimulated corticosteroid levels, as well as on plasma concentrations of ACTH, beta-endorphin, and catecholamines were examined and compared to those following administration of the new benzodiazepine, midazolam, or of methohexital. Twenty-nine healthy, young, male orthopedic patients were randomized into three groups receiving either etomidate/fentanyl (n = 12), midazolam/fentanyl (n = 8), or methohexital/fentanyl (n = 9). Etomidate caused cortisol levels to decrease from 12.5 +/- 1.2 micrograms/dl preoperatively to 5.9 +/- 0.8 micrograms/dl after operation (P less than 0.001), compared to an increase from 12.0 +/- 1.9 micrograms/dl to 18.5 +/- 2.9 micrograms/dl in the group receiving methohexital. At 6 and 20 h postoperatively, all cortisol levels were normal. The cortisol decrease from 12.5 +/- 1.7 to 7.6 +/- 1.5 caused by midazolam was similar to that following etomidate, but the response to exogenous ACTH was significantly impaired in patients receiving etomidate as compared to those receiving midazolam. ACTH and beta-endorphin levels increased in patients receiving etomidate, presumably as a result of the interruption of negative feedback due to cortisol synthesis inhibition. Midazolam on the other hand prevented the increase of ACTH and beta-endorphin levels. Etomidate completely suppressed spontaneous aldosterone levels (from 33 +/- 6.7 to 7 +/- 2.1 pg/ml), as well as the response to stimulation with exogenous ACTH without affecting serum electrolytes. Etomidate had no influence on plasma catecholamines, but midazolam attenuated the stress-related epinephrine increase.     

Studies of midazolam, diazepam and thiopentone on respiratory and cardiovascular function during induction anesthesia

In this study, the effects of midazolam (M), diazepam (D) and thiopentone (T) on respiratory and cardiovascular systems were compared. The patients were randomly divided into 6 groups, besides minute ventilatory volume (MV), onset of induction and cardiovascular changes were also observed. Induction was performed by a bolus injection of one of the following: midazolam (0.3 mg/kg), diazepam (0.3 mg/kg) or thiopentone (5 mg/kg). Five minutes later, 5 micrograms/kg fentanyl and 1.5-2.0 mg/kg succinylcholine were administered. The results showed that: (1) Inhibitory effect on MV was not prominent and similar after use of midazolam and diazepam but was remarkable after thiopental; (2) As for the onset, midazolam was faster than diazepam but slower than thiopentone; (3) Hemodynamic changes of midazolam, diazepam and thiopentone were similar, however during intubation, cardiovascular response was the least in midazolam, diazepam the intermediate and thiopentone the most significant. We conclude that midazolam is a water-soluble, safe and effective inductive anesthetic with its short eliminated half-life period, and much lesser venous irritation, and it is certainly superior to both diazepam and thiopentone.     

Inotropic Effects of Propofol, Thiopental, Midazolam, Etomidate, and Ketamine on Isolated Human Atrial Muscle

Background: Cardiovascular instability after intravenous induction of anesthesia may be explained partly by direct negative inotropic effects. The direct inotropic influence of etomidate, ketamine, midazolam, propofol, and thiopental on the contractility of isolated human atrial tissue was determined. Effective concentrations were compared with those reported clinically.

Methods: Atrial tissue was obtained from 16 patients undergoing coronary bypass surgery. Each fragment was divided into three strips, and one anesthetic was tested per strip in increasing concentrations (10 sup -6 to 10 sup -2 M). Strips were stimulated at 0.5 Hz, and maximum isometric force was measured. Induction agents were studied in two groups, group 1 (n = 7) containing thiopental, midazolam, and propofol, and group 2 (n = 9) consisting of etomidate, ketamine, and propofol.

Results: The tested anesthetics caused a concentration-dependent depression of contractility resulting in complete cessation of contractions at the highest concentrations. The IC50 S (mean +/-SEM; micro Meter) for inhibition of the contractility were: thiopental 43+/-7.6, propofol 235+/-48 (group 1), and 246+/-42 (group 2), midazolam 145+/-54, etomidate 133 +/-13, and ketamine 303+/-54.     

Comparison of anesthesia with thiopental or etomidate in short duration operations

Forty ASA I-II women who were scheduled for uterine curettage were randomly allotted to two groups of 20 patients each. Both groups were age- and weight- matched. They were pre-treated with atropine (0.01 mg/kg) and diazepam (0.1 mg/kg). Anesthesia was induced with 2.5% thiopental (5 mg/kg) or 0.1% etomidate (0.3 mg/kg) and was maintained with N2/O2 at 50% and isoflurane at 1% adding supplementation doses of inducer (20% of initial dose) when required. Quality of induction and maintenance of anesthesia, cardiovascular effects, secondary effects and quality and rapidity of awakening were evaluated. Etomidate patients presented a higher number of secondary effects and pain on injection of the drug (p less than 0.05) and occurrence of excitatory motions (p less than 0.01) attained statistical significance. Evaluation of anesthesia quality was significantly higher with thiopental (p less than 0.05). There were no differences with respect to the remaining studied variables. We conclude that etomidate when used as unique agent in anesthesia induction has no advantages over thiopental in healthy patients undergoing short duration operations.