Uptake of halothane and isoflurane by mother and baby during Caesarean section

Twenty-three patients undergoing Caesarean section receivedeither 0.5% halothane or 0.8% isoflurane to supplement nitrousoxide-oxygen anaesthesia. We studied the rate of uptake of theagents by the mother and fetus by measuring partial pressuresin maternal arterial (Pa) and fetal umbilical venous (Puv) blood.Mean induction-delivery interval did not differ between thehalothane (10.8 mm) and isoflurane (11.7 mm) groups. There wereno differences in maternal heart rate, arterial pressure, pHand blood-gas tensions and fetal pH, blood-gas tensions or Apgarscores between the two groups. Isoflurane uptake by the motherwas more rapid than halothane; at delivery, mean Pa of isofluraneas a fraction of the inspired partial pressure (P1) was 0.44compared with 0.35 for halothane (P < 0.05). Mean Puv asa fraction of maternal Pa at delivery was 0.71 for both agents;thus placental transfer was the same for both agents. Consequentlymean Puv/P1 was greater for isoflurane (0.32) than halothane(0.26) (P < 0.05). We conclude that both halothane and isofluraneare suitable agents for general anaesthesia for Caesarean section.The rate of uptake of isoflurane by the mother during Caesareansection was more rapid than halothane. The rate of uptake bythe fetus from the mother was the same for halothane and isoflurane,so that fetal partial pressure as a fraction of the inspiredpartial pressure was greater for isoflurane than halothane.      

Hepatic circulation during surgical stress and anesthesia with halothane, isoflurane, or fentanyl

Hepatic blood flow and the oxygen supply/uptake relation were studied in 19 miniature pigs using labeled microspheres. Changes in hepatic arterial blood flow and portal blood flow, as well as total hepatic blood flow during halothane anesthesia were more closely associated with changes in mean arterial pressure (MAP) and cardiac output than during anesthesia with isoflurane or fentanyl. Halothane or isoflurane administered in concentrations that decreased MAP by approximately 30% were accompanied by decreases in hepatic oxygen delivery (DO2th) averaging 46% during halothane and 31% during isoflurane anesthesia and parallel decreases in hepatic blood flow. In concentrations that decreased MAP by 50%, halothane and isoflurane decreased DO2th 61 and 37%, respectively. DO2th was maintained (statistically insignificant, 23% increase) during both doses of fentanyl administered (20 micrograms/kg followed by 0.17 microgram . kg-1 . min-1, and 50 micrograms/kg followed by 0.42 microgram . kg-1 . min-1). Hepatic oxygen uptake increased 50% during fentanyl and was maintained at baseline levels during both doses of halothane and isoflurane anesthesia. Oxygen content in hepatic venous blood was maintained at baseline levels during fentanyl and isoflurane administration and was decreased by both concentrations of halothane anesthesia. The hepatic oxygen supply demand ratio was maintained at baseline levels after both doses of fentanyl and during isoflurane administered in a concentration that decreased blood pressure 30%; the ratio decreased during isoflurane administered in a concentration decreasing blood pressure by 50% and during both doses of halothane anesthesia.(ABSTRACT TRUNCATED AT 250 WORDS)     

Hepatic oxygen supply during halothane or isoflurane anesthesia in guinea pigs

The present study was designed to determine changes in hepatic oxygen supply in guinea pigs during halothane or isoflurane anesthesia. Twenty-seven guinea pigs were randomly divided into three equal groups: control (no anesthesia) group, and animals anesthetized with halothane or isoflurane to decrease mean arterial pressure (MAP) by 50%. Hepatic arterial blood flow (HABF) and portal blood flow (PBF), as well as arterial and portal venous blood oxygen content, were determined in awake animals (stage I, baseline values), and during anesthesia (stage II). HABF was found to be extremely low (0.04 ml.min-1.g-1) during both stages of observation in the control (no anesthesia) group, as well as during stage I (awake) in animals treated with halothane or isoflurane. Equal degrees of arterial hypotension during halothane and isoflurane anesthesia were accompanied by decreased HABF during halothane (37%), but no significant change in HABF during isoflurane anesthesia. PBF decreased significantly in both experimental groups; however, the decrease was more prominent during halothane than during isoflurane anesthesia (57% vs. 23%). The observed hepatic circulatory changes led to a 65% decrease in hepatic oxygen delivery during halothane, but only a 34% decrease during isoflurane anesthesia. The present study does not exclude the possibility that liver damage in the guinea pig model is related to the reductive metabolism of halothane or any other mechanism. However, the extremely low HABF and a prominent reduction in both HABF and PBF during halothane anesthesia may be responsible for hepatic damage observed in the guinea pig model.     

Prospective,randomized trial comparing general with spinal anesthesia for cesarean delivery in preeclamptic patients with a nonreassuring fetal heart trace

BACKGROUND: There are no randomized studies on neonatal outcome after spinal versus general anesthesia for cesarean delivery in preeclamptic patients with a nonreassuring fetal heart trace. This study examined both markers of neonatal hypoxia and maternal hemodynamics. METHODS: Seventy patients were randomized to general (n = 35) or spinal anesthesia (n = 35). The general anesthesia group received thiopentone, magnesium sulfate, and suxamethonium intravenously before intubation, followed by 50% nitrous oxide in oxygen, 0.75-1.5% isoflurane, and morphine after delivery. The target end-tidal partial pressure of carbon dioxide (Pco2) was 30-34 mmHg. The spinal anesthesia group received 1.8 ml hyperbaric bupivacaine plus 10 microg fentanyl at the L3-L4 interspace. Heart rate and blood pressure were measured at specific time points. Hypotension was treated with ephedrine. Maternal arterial and neonatal umbilical arterial blood gas samples were taken at delivery. Resuscitation requirements were recorded. RESULTS: In both groups, hemodynamic measures remained within acceptable limits. Spinal anesthesia patients required more ephedrine (13.7 vs. 2.7 mg). Maternal Paco2 was lower in the spinal group (28.9 vs. 32.4 mmHg). One-minute Apgar scores were lower after general anesthesia. Base deficit was greater (7.13 vs. 4.68 mEq/l) and neonatal umbilical arterial pH was lower (7.20 vs. 7.23) after spinal anesthesia. Post hoc analysis showed that if maternal diastolic blood pressure on admission was greater than 110 mmHg, neonatal umbilical arterial base deficit was greater after spinal anesthesia. There was no difference in the number of patients with Apgar scores less than 7 at 1 or 5 min or umbilical arterial pH less than 7.2 or in the requirements for resuscitation. CONCLUSIONS: In preeclamptic patients with a nonreassuring fetal heart trace, spinal anesthesia for cesarean delivery was associated with a greater mean neonatal umbilical arterial base deficit and a lower median umbilical arterial pH. The clinical significance remains to be established. Maternal hemodynamics were similar and acceptable with either anesthetic technique.     

Hemodynamic alterations and regional myocardial blood flow during supraceliac aortic occlusion in dogs with a critical coronary stenosis

The hemodynamic consequences and myocardial blood flow alterations associated with cross-clamping of the thoracic aorta were studied during pentobarbital (control), halothane (1 MAC), and isoflurane (1 MAC) anesthesia in dogs with a critical stenosis of the left circumflex coronary artery. Aortic clamping at the level of the diaphragm resulted in significant and equivalent increases in mean aortic pressure and left atrial pressure during the control clamp, halothane clamp, and isoflurane clamp periods. Likewise, aortic clamping resulted in a significant and equivalent decrease in cardiac output during control-clamp, halothane clamp, and isoflurane clamp. Myocardial contractility as assessed by dP/dt was depressed during halothane and isoflurane anesthesia when compared with control, but no further change in contractility was associated with aortic clamping. No significant alterations in regional or transmural myocardial blood flow were found with halothane or isoflurane anesthesia, or with aortic clamping during halothane or isoflurane anesthesia. It is concluded that there are significant hemodynamic consequences associated with aortic clamping, that neither halothane nor isoflurane anesthesia alters these consequences when compared with pentobarbital anesthesia alone, and that the deterioration in myocardial function observed during aortic clamping with halothane and isoflurane anesthesia cannot be attributed to any maldistribution of myocardial blood flow.     

Prospective, Randomized Trial Comparing General with Spinal Anesthesia for Cesarean Delivery in Preeclamptic Patients with a Nonreassuring Fetal Heart Trace

Background: There are no randomized studies on neonatal outcome after spinal versus general anesthesia for cesarean delivery in preeclamptic patients with a nonreassuring fetal heart trace. This study examined both markers of neonatal hypoxia and maternal hemodynamics.

Methods: Seventy patients were randomized to general (n = 35) or spinal anesthesia (n = 35). The general anesthesia group received thiopentone, magnesium sulfate, and suxamethonium intravenously before intubation, followed by 50% nitrous oxide in oxygen, 0.75-1.5% isoflurane, and morphine after delivery. The target end-tidal partial pressure of carbon dioxide (Pco2) was 30-34 mmHg. The spinal anesthesia group received 1.8 ml hyperbaric bupivacaine plus 10 [mu]g fentanyl at the L3-L4 interspace. Heart rate and blood pressure were measured at specific time points. Hypotension was treated with ephedrine. Maternal arterial and neonatal umbilical arterial blood gas samples were taken at delivery. Resuscitation requirements were recorded.

Results: In both groups, hemodynamic measures remained within acceptable limits. Spinal anesthesia patients required more ephedrine (13.7 vs. 2.7 mg). Maternal Paco2 was lower in the spinal group (28.9 vs. 32.4 mmHg). One-minute Apgar scores were lower after general anesthesia. Base deficit was greater (7.13 vs. 4.68 mEq/l) and neonatal umbilical arterial pH was lower (7.20 vs. 7.23) after spinal anesthesia. Post hoc analysis showed that if maternal diastolic blood pressure on admission was greater than 110 mmHg, neonatal umbilical arterial base deficit was greater after spinal anesthesia. There was no difference in the number of patients with Apgar scores less than 7 at 1 or 5 min or umbilical arterial pH less than 7.2 or in the requirements for resuscitation.     

Simultaneous evaluation of left ventricular end-systolic pressure-volume ratio and time constant of isovolumic pressure decline in dogs exposed to equivalent MAC halothane and isoflurane

The effects of 1.5, 2.0, and 2.5 MAC halothane (N = 8) and isoflurane (N = 6) upon systolic performance and isovolumic relaxation were evaluated in open chest dogs. Left ventricular internal volume was determined using piezoelectric crystals. Left ventricular end-systolic pressure-volume points were determined for a series of normal sinus beats during transient venae caval occlusions. The slope of the line formed by those points is a load-independent inotropic index (EES). Left ventricular pressure points during isovolumic relaxation were plotted for computing the time constant of isovolumic pressure decline (T). Both drugs dose-dependently decreased mean arterial blood pressure with no change in heart rate, end-diastolic pressure, or end-diastolic volume. Increasing halothane concentration decreased the values of EES, the maximum rate of rise of left ventricular pressure (dP/dtMAX), and systolic ejection fraction (SEF). Total systemic resistance was unchanged by halothane. Increasing isoflurane concentration decreased EES and dP/dtMAX. The EES was significantly larger (P less than 0.05) with 2.5 MAC isoflurane than 2.5 MAC halothane. The SEF was unchanged by increasing isoflurane. Total systemic vascular resistance was decreased by increasing isoflurane. Isovolumic relaxation was prolonged and became more load-dependent with increasing halothane concentration. Isoflurane did not alter T, but the load-dependency of T was increased by 2.5 MAC isoflurane. There were no differences in T or its load-dependency between drug groups. These results indicate that both anesthetics evoke load-independent negative inotropic effects. Systolic ejection fraction is maintained during isoflurane anesthesia by decreased systemic vascular resistance and less pronounced negative inotropic effects than equivalent MAC halothane.(ABSTRACT TRUNCATED AT 250 WORDS)     

The hemodynamic and cardiovascular effects of isoflurane and halothane anesthesia in children

The hemodynamic and cardiovascular effects of isoflurane and halothane anesthesia were studied in 15 unpremedicated ASA I children using measurements of heart rate, blood pressure and M-mode echocardiography (echo). The children (ages 2 to 7.3 yr) were randomly assigned to receive either isoflurane (N = 8) or halothane (N = 7) with oxygen. End-tidal carbon dioxide concentrations (range 30-44 mmHg) were monitored throughout the study in each child. The experimental protocol was completed prior to intubation and the initiation of surgery. Within each anesthetic group, preinduction (control) hemodynamic and echo measurements were compared with measurements obtained at two sequential equipotent end-tidal anesthetic concentrations (0.74% and 2.22% isoflurane; or 0.5% and 1.5% halothane). We also compared the data of the isoflurane group with that of the halothane group at each equipotent end-tidal anesthetic concentration. Preinduction hemodynamic (heart rate, blood pressure) and echo measurements (left ventricular dimensions and function) were similar between the two anesthetic groups. With isoflurane or halothane administration, blood pressure decreased significantly, while heart rate remained essentially unchanged. The observed alterations in heart rate and blood pressure were similar in both study groups at each equipotent end-tidal anesthetic concentration. In contrast, there were marked differences in the echo measurements of the two anesthetic groups. Halothane was associated with a significant dose-dependent decrease in echo-measured left-ventricular shortening fraction and mean velocity of circumferential fiber shortening. These echo measurements were not significantly altered by isoflurane at either end-tidal anesthetic concentration. These alterations suggest halothane is associated with significant myocardial depression in normal children, while myocardial function is well preserved during isoflurane anesthesia.     

Hemodynamic responses to nitrous oxide during inhalation anesthesia in pediatric patients

STUDY OBJECTIVE: To measure the hemodynamic changes produced by nitrous oxide (N2O) during halothane and isoflurane anesthesia in infants and children. DESIGN: A repeated measures design in two groups of infants and small children. SETTING: Operating rooms at a university hospital. PATIENTS: Nineteen healthy unmedicated infants and small children (mean age 12 months) who required elective surgery. INTERVENTIONS: Prior to anesthesia induction, cardiovascular measurements were recorded using pulsed Doppler and two-dimensional echocardiography. Following anesthesia induction with halothane (n = 10) or isoflurane (n = 9) in oxygen (O2) and air, anesthetic measures were stabilized at 1.0 minimum alveolar concentration (MAC) and cardiovascular measures were repeated. After 30% N2O was added to the 1.0 MAC anesthetic concentration, a third set of cardiovascular measurements was recorded. A final cardiovascular data set was measured 5 minutes following an increase in N2O concentration to 60%. MEASUREMENTS AND MAIN RESULTS: Mean arterial pressure (MAP), cardiac index (CI), stroke volume (SV), and ejection fraction (EF) decreased similarly and significantly at 1.0 MAC halothane and isoflurane. Heart rate (HR) increased during isoflurane anesthesia but decreased during halothane anesthesia. The addition of N2O resulted in a decrease in HR, CI, and MAP when compared to 1.0 MAC levels of halothane or isoflurane; however, SV and EF were not significantly changed from levels measured during 1.0 MAC halothane or isoflurane. CONCLUSIONS: The addition of N2O to halothane and isoflurane anesthesia in infants and children decreased HR. This decrease led to a decrease in cardiac output (CO). Unlike with adults, N2O did not produce cardiovascular signs of sympathetic stimulation in infants and children.     

Hepatolobectomy-induced depression of hepatic circulation and metabolism in the dog is counteracted by isoflurane, but not by halothane

BACKGROUND: The effects of isoflurane and halothane anesthesia on hepatic circulation and oxygen metabolism during hepatolobectomy were investigated in the dog, in an attempt to assess which of the anesthetics was the better one for hepatic resection. METHODS: Mongrel dogs (n=24) were divided into two groups and accordingly anesthetized with isoflurane (n=12) or halothane (n = 12). Each test anesthetic was administered in air. Electromagnetic flowmeters were used to measure hepatic arterial and portal venous blood flows 1) before the inhalation of each anesthetic (baseline); 2) 1 h inhalation of 1.5 MAC (minimum alveolar concentration) of each anesthetic; and 3) 1 h after hepatolobectomy with each anesthesia. Measurements of systemic hemodynamics, blood gas tensions, and the arterial ketone body ratio were made at the same time. RESULTS: Isoflurane maintained portal venous, hepatic arterial and total hepatic blood flows better than halothane anesthesia before and after hepatolobectomy. With halothane anesthesia, hepatolobectomy decreased prominently hepatic arterial blood flow. Hepatic arterial and mesenteric vascular resistance increased in the halothane group, but remained constant in the isoflurane group after hepatolobectomy. Hepatic oxygen delivery was significantly suppressed in the halothane group, but did not change in the isoflurane group. No significant difference was found in hepatic oxygen consumption between the two groups, but the arterial ketone body ratio decreased significantly only in the halothane group before and after hepatolobectomy. CONCLUSION: The present data indicate that isoflurane has less adverse effect than halothane anesthesia on hepatic circulation, oxygen delivery and energy charge in hepatolobectomy cases.     

The stress reaction in the recovery phase from halothane and isoflurane anesthesia

This study was undertaken to investigate the influences of halothane and isoflurane as well as different extubation techniques on the endocrine stress response during recovery from general anesthesia. Forty patients scheduled for herniorrhaphy and cholecystectomy were randomly allocated to 4 groups: 20 received halothane and 20 received isoflurane anesthesia. Within the halothane and isoflurane groups, 10 patients each were extubated during anesthesia (1/2 MAC) and a further 10 had awake extubation. Premedication, induction of anesthesia, and intraoperative anesthetic management were standardized in all groups. Plasma levels of endocrine stress parameters as well as mean arterial pressure (MAP), heart rate (HR), and arterial oxygen saturation (SaO2) were measured at nine time points up to 60 min after extubation. Biometric data and duration of operation and anesthesia were comparable in all groups. In the recovery period, epinephrine levels were higher in the isoflurane groups than in the halothane groups (P = 0.02). With respect to time course, earlier and more marked increases of epinephrine, norepinephrine, and antidiuretic hormone (ADH) levels were observed in the isoflurane groups compared to the halothane groups (P less than 0.01), representing the more rapid elimination of isoflurane. The sympathoadrenergic stress response was more pronounced in patients with extubation during anesthesia than in those with awake extubation: epinephrine levels were slightly higher and group levels of norepinephrine were significantly increased (P = 0.02). No influence of the extubation techniques was observed on ADH, ACTH, and cortisol levels or on MAP, HR, or SaO2. In summary, extubation during anesthesia did not reduce the endocrine stress response. It is concluded that awake extubation should be preferred unless the operation or the patient's condition requires extubation during anesthesia.     

Intraoperative fetal heart rate monitoring during emergency neurosurgery in a parturient

Malignant brain tumors during pregnancy are rare, and these patients seldom require immediate surgical intervention. A 27-year-old pregnant woman underwent emergency craniotomy. Anesthesia was induced with intravenous thiopental-fentanyl; it was maintained with isoflurane in oxygen and continuous intravenous remifentanil infusion. We used full stomach precautions but omitted succinylcholine for fear of increasing the intracranial pressure during induction of anesthesia. To detect fetal hypoxia and the effects of anesthesia on fetal hemodynamics, the fetal heart rate (FHR) was monitored using a fetal Doppler ultrasonography unit fixed to the mother's abdominal wall. Intraoperative and recovery periods were uneventful. Use of an isoflurane and remifentanil combination provided stable hemodynamics with adequate arterial blood pressure to avoid uterine hypoperfusion and fetal hypoxia. In this case, using FHR monitoring we found that craniotomy can be performed safely under isoflurane/remifentanil based-general anesthesia during the second trimester of pregnancy.     

Comparative study in pediatric inhalation anesthesia. Clinical characteristics and anesthetic complications with halothane and isoflurane]

OBJECTIVES. Comparative study of clinical characteristics and complications during induction, maintenance, and recovery in pediatric inhalational anesthesia between two commonly used fluoride agents (halothane and isoflurane). MATERIAL AND METHODS. We studied 66 children aged 1 month to 13 years undergoing general anesthesia for short lasting surgery who were divided into two groups of 33 patients each one: Isoflurane group and halothane group. Induction and maintenance anesthesia was performed with the corresponding inhalant agent. Parameters measured were duration of unconsciousness, time elapsed for intubation and recovery, heart rate, arterial blood pressure, and incidence of complications. RESULTS. Children anesthetized with isoflurane showed a shorter period of unconsciousness (1.55 +/- 0.11 min) than those anesthetized with halothane (1.91 +/- 0.12 min); whereas that the time required for intubation was significantly more prolonged (8.94 +/- 0.51 and 6.57 +/- 0.32 min, respectively). The incidence of complications was higher in the isoflurane group, mainly expressed as laryngeal spasm during the induction period. Both groups of patients showed a similar hemodynamic behaviour, although diastolic arterial pressure during maintenance anesthesia was significantly lower with isoflurane. Anesthesia recovery was faster and more predictable with isoflurane than with halothane. CONCLUSIONS. Anesthetic agent isoflurane is less appropriate than halothane for induction in pediatric anesthesia due to a high incidence of complications, specially laryngeal spasm.     

The comparative cardiovascular effects of sevoflurane with halothane and isoflurane

Using closed chest dogs, the cardiovascular effects of sevoflurane were compared with those of halothane and isoflurane in equipotent doses of 1.0, 1.5, 2.0, 2.5 and 3.0 MAC. They were evaluated by the changes of arterial blood pressure, central venous pressure, pulmonary artery pressure, maximum rate of left ventricular pressure rise (LV dp/dt), cardiac output and coronary sinus blood flow. The suppression of left cardiac function by sevoflurane was less than that of halothane, but was greater than that of isoflurane. Heart rate, systemic vascular resistance with sevoflurane were slightly lower than that of isoflurance. The coronary sinus blood flows with sevoflurane and isoflurane were significantly (P < 0.05 at 1.0 MAC, P < 0.005 at 2.0 MAC) higher than halothane. There was no significant difference on coronary sinus flow between sevoflurane and isoflurane. The depth of anesthesia could be quickly changed by adjustment of inspired sevoflurane concentration in comparison with the other two anesthetics.(Kazama T, Ikeda K: The comparative cardiovascular effects of sevoflurane with halothane and isoflurane. J Anesth 2: 63–68, 1988)     

Effects of halothane and isoflurane on transient renal dysfunction associated with infrarenal aortic cross-clamping.

Aortic cross-clamping for reconstructive aortic surgery is associated with impairment of renal function. Halothane or isoflurane was used to assess the influence of volatile anesthesia on renal hemodynamics during aortic surgery. Nineteen patients with normal preoperative creatinine clearances who were scheduled for reconstructive aortic surgery were randomly divided into two groups: halothane group (n = 9) and isoflurane group (n = 10). Induction of anesthesia consisted of midazolam, fentanyl, and pancuronium. Anesthesia was maintained with fentanyl and halothane or isoflurane in nitrous oxide and oxygen (50/50). Systemic hemodynamics were similar in both groups throughout surgery. Before aortic cross-clamping, effective renal plasma flow (ERPF) (131I-hippuran clearance) and glomerular filtration rate (GFR) (99Tc-DTPA clearance) were significantly lower in the halothane group (118.4 +/- 25.6 and 19.7 +/- 5.2 mL/min, respectively) than in the isoflurane group (253.4 +/- 51.5 and 44.9 +/- 8.4 mL/min) (P less than 0.05 for both). During cross-clamping, the renal variables were not markedly affected in either group and remained higher in the isoflurane-anesthetized patients (232.9 +/- 47.1 and 49.5 +/- 1.2 mL/min for ERPF and GFR, respectively) than in the halothane-anesthetized patients (132.4 +/- 31.6 and 14.8 +/- 3.7 mL/min, respectively) (P less than 0.05). After aortic unclamping, ERPF increased markedly in both groups (467.8 +/- 122 and 362.5 +/- 57.7 mL/min in the halothane and isoflurane groups, respectively), as did GFR (74.8 +/- 22 and 71.8 +/- 13.1 mL/min, respectively). These results suggest that anesthesia with halothane is associated with transient renal vasoconstriction during abdominal surgery. In contrast, aortic cross-clamping during isoflurane anesthesia was not associated with renal hemodynamic impairment.     

Systolic time intervals by intratracheal pneumocardiogram and the effects of inhalation anesthetics on cardiac function using this technic

Intratracheal pressure change due to cardiogenic oscillation was obtained by a high gain pressure transducer attached to the endotracheal tube while the patient was apneic during the operation. Such pressure change has been called as intratracheal pneumocardiogram (ITCG), which consists of wide waves and some spikes. Systolic time interval (STI) was obtained by measuring the intervals between certain spikes. The STIs measured by ITCG were compared with those by echocardiogram and by the conventional method. Also the effects of halothane, enflurane and isoflurane on cardiac performance were evaluated using the STI by ITCG. The STI measured by ITCG correlated well with that by echocardiogram, which indicated that the STI by ITCG was a useful noninvasive method to monitor the cardiac performance during general anesthesia. The STI by ITCG showed that the left ventricular ejection time (LVET) decreased in halothane and enflurane anesthesia. The pre-ejection period (PEP) and the PEP/LVET ratio increased in all three types of anesthesia. Especially the PEPs during halothane and enflurane at 1.8 MAC (minimum alveolar concentration) were greater than that of isoflurane. The results suggest that isoflurane has less cardiac depressive action than halothane and enflurane.     

The effects of volatile anesthetics on the Q-Tc interval

OBJECTIVE: To examine the effects of halothane, isoflurane, and sevoflurane on Q-Tc interval (corrected for heart rate) during inhalation induction of anesthesia. DESIGN: Prospective, double-blind, randomized study. SETTING: Departments of Cardiology and Anesthesiology in a university hospital. PARTICIPANTS: Patients undergoing noncardiac surgery. INTERVENTIONS: A total of 65 American Society of Anesthesiologists physical status I-II patients, aged 16 to 50 years, undergoing general anesthesia, were randomly allocated to receive halothane, isoflurane, or sevoflurane. MEASUREMENTS AND MAIN RESULTS: The time to reach the predetermined end-tidal concentrations of 3 minimum alveolar concentration was 6 to 10 minutes. When compared with preinduction values, heart rate decreased after halothane (p < 0.01) and sevoflurane (p < 0.05) administration; in contrast, heart rate increased after induction of anesthesia with isoflurane (p < 0.05). The mean QRS intervals were not significantly changed after halothane, isoflurane, or sevoflurane. The Q-Tc interval was increased with isoflurane compared with baseline (465 +/- 23 v 441 +/- 18 msec, p < 0.01), not changed with sevoflurane (441 +/- 17 v 434 +/- 19 ms, p > 0.05), and shortened with halothane (426 +/- 23 v 445 +/- 21 msec, p < 0.01). CONCLUSION: Sevoflurane or halothane may be preferred to isoflurane in patients with conditions that are known to induce a prolonged Q-Tc interval. The effects of Q-Tc interval changes resulting from different anesthetic agents on morbidity and the incidence of arrhythmias during anesthesia warrant further investigation.     

DETERMINATION OF THE PARTIAL PRESSURE OF HALOTHANE (OR ISOFLURANE) IN BLOOD

A gas chromatographic method is described for the direct quantitativedetermination of the partial pressure of halothane {or isoflurane)in blood as well as the blood-gas partition coefficient. A headspace technique and a flame ionization detector were used. Standardblood was obtained by equilibrating patients' blood with knowngas concentrations in a tonometer. Using an infra-red analyserto measure the halothane gas concentration in the tonometerand within the anaesthetic system allowed for the direct comparisonof the partial pressure in blood to the partial pressure inthe inspired gas. Technical problems associated with this procedure,and with comparable methods, are discussed.     

Comparison of enflurane, halothane, and isoflurane for diagnostic and therapeutic procedures in children with malignancies

The authors performed a randomized, prospective trial comparing enflurane, halothane, and isoflurane (each administered with nitrous oxide) to establish which inhaled anesthetic produced the fewest complications and the most rapid induction of anesthesia for children undergoing general anesthesia for diagnostic procedures as oncology outpatients. Sixty-six children, ranging from 8 months to 18 years, underwent a total of 124 anesthetics. Induction of anesthesia (time from placement of facemask to beginning of skin preparation) was faster with halothane (2.7 +/- 1.0 min, mean +/- SD, n = 46) than with enflurane (3.2 +/- 0.8 min, n = 43) or isoflurane (3.3 +/- 1.2 min, n = 35). Emergence from anesthesia (time from completion of the procedure to spontaneous eye opening) was more rapid with enflurane (4.7 +/- 4.4 min) than with halothane (6.2 +/- 4.5 min) or isoflurane (6.2 +/- 3.9 min). Total time from the start of procedure until discharge was longer with isoflurane (25.1 +/- 6.8 min) than with enflurane (21.5 +/- 8.6 min) or halothane (22.3 +/- 7.6 min). During induction, the incidence of laryngospasm was greatest with isoflurane (23%) and the incidence of excitement least with halothane (13%). During the maintenance of, emergence from, and recovery from anesthesia, coughing occurred most frequently with isoflurane. During the recovery period, headache occurred most frequently with halothane (9%); there were no significant differences in the incidence of nausea, vomiting, hunger, or depressed effect. The authors conclude that the rapid induction and minimal airway-related complications associated with halothane anesthesia make it an excellent anesthetic agent for pediatric patients undergoing short diagnostic procedures.     

Comparative coronary vascular reactivity and hemodynamics during halothane and isoflurane anesthesia in swine

To assess the dose-response effects of isoflurane and halothane anesthesia on hemodynamics and coronary artery reactivity, the authors studied myocardial hyperemic responses following brief single artery flow arrests in 21 open chest, isocapnic swine in which arterial blood pressures and cardiac outputs were recorded. A specially designed Doppler probe was used to measure the peak and time course of coronary blood flow velocity in the left anterior descending coronary artery (LAD) after 15-s LAD occlusions. The ratio of peak velocity of blood flow to resting velocity (coronary reserve), relative repayment of flow debt, and duration of hyperemic responses were studied. Surgery was performed at MAC end-tidal concentrations ([Et]isoflurane = 1.45%. [Et]halothane = 1.25%) of isoflurane (n = 7) or halothane (n = 7), and recordings were made after 15-min steady state [Et]agent at 0.5, 1, 1.25, 1.5, 1.75, 2 MAC, and further 0.5 MAC increments until the demise of each animal. To compare coronary reactivity at similar coronary pressures, an aortic snare was used to elevate arterial pressures in a third group of halothane anesthesized pigs (n = 7) to those in the previously studied isoflurane group at each MAC level. There were three major differences between halothane and isoflurane. First, cardiac depression (reduction in arterial pressure, cardiac output, and stroke volume) was less with isoflurane compared with halothane anesthesia. Second, with halothane anesthesia, there was a marked decrease in coronary reactivity independent of coronary perfusion pressures with marked, dose-dependent reductions in both coronary reserve and relative flow repayment. During isoflurane anesthesia, coronary reactivity and coronary reserve was well preserved within physiologic limits up to 1.75 MAC [Et]. Third, halothane anesthesized pigs died in cardiac collapse at much lower agent concentrations than with isoflurane (no animals survived 1.75 MAC halothane, whereas all animals survived 2.5 MAC isoflurane). Therefore, pigs anesthesized with isoflurane had greater coronary reserve, better preserved cardiac function, and greater tolerance to increasing agent concentration than pigs anesthesized with halothane.