Haemodynamic responses to sevoflurane compared with halothane during inhalational induction in children

We studied the haemodynamic changes during induction of anaesthesia in 50 ASA I and II children (1–12 yrs) undergoing minor elective surgery. The patients were randomly divided into two groups to receive either halothane (n=25) or sevoflurane (n=25) in a mixture of O₂ and N₂O (40:60) for mask induction of anaesthesia. Induction of anaesthesia was performed with an overpressure technique by administering rapid increases of gas concentrations, in increments of 1% up to 7% for sevoflurane and of 0.5% up to 3% for halothane. Induction was smooth and rapid in both groups but characterized by increases in heart rate and systolic blood pressure up to 20% especially in the sevoflurane group (P<0.05); these increases in the latter group were significant compared with baseline and the halothane group (P<0.05). No serious complications were observed. The authors conclude that more children experienced heart rate and blood pressure increases during the early stage of inhalational induction with sevoflurane compared with halothane.     

General anaesthesia for surgery can influence circulating melatonin during daylight hours

Background: Both melatonin and anaesthetics have been shown to affect sleep and behaviour. The effect of general anaesthesia on circulatory melatonin has not been reported, but anaesthetic-related alterations in hormone profiles are known. We hypothesize that differences in recovery from anaesthesia may be associated with differences in circulatory melatonin levels because of melatonin's sedative effect in humans. Methods: The influences of general anaesthesia and surgery on circulating melatonin, prolactin, and Cortisol concentration were investigated in 32 female patients scheduled for elective gynaecological surgery to study differences in hormone profiles and responses during anaesthesia and the recovery period. Patients were randomly assigned to one of two groups. General anaesthesia was induced with either thiopentone/fentanyl (Group 1: n=16) or propofol/fentanyl (Group 2: n=16). Maintenance of anaesthesia was achieved with either isoflurane (0.8–1.0 vol%)/fentanyl (Group 1) or propofol (6 mg · kg^?1· h^?1)/fentanyl (Group 2) with a N₂O/O₂ flow ratio of 2:1 in both groups. During anaesthesia, patients' eyes were carefully taped shut to prevent light effects. Blood samples were taken before and after premedication, immediately before induction of anaesthesia, every 15 min during anaesthesia, and hourly in the recovery room for 8 h. The control group consisted of 6 healthy women who were not subjected to surgery, but who were in a similar environment, including light conditions, as the study groups. Results: Isoflurane and propofol anaesthesia as well as darkness elicited elevated plasma melatonin levels that persisted in the recovery period in patients anaesthetized with isoflurane, but gradually decreased during the recovery of patients anaesthetized with propofol. Circulating prolactin and Cortisol values were also elevated during anaesthesia and had similar decreases during the recovery period. Conclusion: Higher plasma levels of melatonin during the recovery period following isoflurane anaesthesia may, in part, explain increased sedation in these patients compared with patients who received propofol anaesthesia. However, the relationship between recovery from anaesthesia and plasma melatonin levels may not be simple and straightforward.     

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.      

Continuous measurement of oxygen consumption using the reversed fick method

We developed a continuous oxygen consumption (Vo₂) measurement system employed the reversed Fick method, in which Vo₂ in computed from continuously measured sured arterial and mixed venous oxygen saturation assed by pulse oximetry and mixed venous oximetry, respectively, and cardiac output by the heat deprivation technique. This system was compared with the conventional intermittent reversed fick method in 7 patients during surgery and with indirect calorimetry in 4 intensive care unit (ICU) patients. The Vo₂ measured by the continuous reversed Fick method showed a high correlation with those simultaneously measured by the intermittent Fick method (r=0.97,P<0.01) and by indirect calorimetry (r=0.74,P<0.01). The 95% confidence limits (bias±2 SD) of the continuous reversed Fick method were −0.6±45 ml·min⁻¹ with the intermittent Fick method and −31±56 ml·min⁻¹ with indirect calorimetry. The continuous Fick method is in satisfactory agreement with the conventional methods for the measured of Vo₂ and potentially allows for convenient assessment of Vo₂ in critically ill patients. This study was supported in part by Grants-in-Aid for the Encouragement of Young Scientists 01771185 and 04857171 from the Ministry of Education, Science and Culture of Japan     

Early and late recovery after major abdominal surgery. Comparison between propofol anaesthesia with and without nitrous oxide and isoflurane anaesthesia

A comparison was made between early and late recovery after major abdominal surgery under intravenous anaesthesia with propofol (with and without nitrous oxide) or inhalational anaesthesia with isoflurane. Sixty patients were randomly allocated to one of three forms of anaesthesia: propofol, propofol/nitrous oxide, or isoflurane/nitrous oxide anaesthesia. All received fentanyl and vecuronium. Recovery was monitored during the first 2 h after extubation and on days 1, 2, 3, 7 and 30 after surgery. Every 30 min during the first 2 postoperative hours, the Steward recovery scale, sedation, orientation, collaboration, and comprehension were assessed by a blinded observer. Psychomotor function was evaluated by computerised simple reaction time and finger tapping speed in 32 patients. A scale of symptoms and mood check list were filled in by 35 patients on days 1, 2, 3, 7 and 30. The preoperative values for all tests were collected 1–4 days before surgery. The time between end of surgery and extubation was longer in the propofol group, but early and late recovery of psychomotor function were similar in the three groups. Patients anaethetised with isoflurane reported more vegetative symptoms than those who received propofol (P < 0.03). The addition of nitrous oxide to propofol did not change the reported degree of symptoms. The difference in vegetative symptoms between groups was most obvious on day 7. Patients anaesthetised with propofol reported better subjective control (P < 0.02) and were more socially oriented (P < 0.05) than patients anaesthetised with isoflurane. We conclude that early recovery was similar in the three groups. Patients anaesthetised with propofol reported fewer late symptoms and better mood after operation than those anaesthetised with isoflurane. The addition of nitrous oxide did not affect the results.     

Differential effects of halothane and isoflurane on lumbar dorsal horn neuronal windup and excitability

Background. Windup of spinal nociceptive neurones may underlietemporal summation of pain, influencing the minimum alveolarconcentration (MAC) of anaesthetics required to prevent movementto supramaximal stimuli. We hypothesized that halothane andisoflurane would differentially affect windup of dorsal hornneurones. Methods. We recorded 18 nociceptive dorsal horn neurones exhibitingwindup to 1 Hz electrical hindpaw stimuli in rats. Effects of0.8 and 1.2 MAC isoflurane and halothane were recorded in thesame neurones (counterbalanced, crossover design). Windup wascalculated as the total number of C-fibre (100–400 mslatency) plus afterdischarge (400–1000 ms latency) spikes/20stimuli (area under curve, AUC) or absolute windup (C-fibreplus afterdischarge–20xinitial response). Results. Increasing isoflurane from 0.8 to1.2 MAC did not affectAUC, but increased absolute windup from 429 (62) to 618 (84)impulses/20 stimuli (P<0.05) and depressed the initial C-fibreresponse from 14 (3) to 8 (2) impulses (P<0.05). Increasinghalothane from 0.8 to1.2 MAC depressed AUC from 690 (79) to537 (65) impulses/20 stimuli (P<0.05) and the initial responsefrom 18 (2) to 13 (2) impulses (P<0.05), but absolute windupwas not affected. Absolute windup was 117% greater during 1.2MAC isoflurane compared with 1.2 MAC halothane. Conclusions. Windup was significantly greater under isofluranethan halothane anaesthesia at 1.2 MAC, whereas the initial C-fibreresponse was suppressed more by isoflurane. These findings suggestthat these two anaesthetics have mechanistically distinct effectson neuronal windup and excitability.     

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)     

Increased lung clearance of isoflurane shortens emergence in obesity: a prospective randomized‐controlled trial

Background: There is a concern that obesity may play a role in prolonging emergence from fat‐soluble inhalational anaesthetics. We hypothesized that increased pulmonary clearance of isoflurane will shorten immediate recovery from anaesthesia and post‐anaesthesia care unit (PACU) stay in obese patients. Methods: After Ethics Review Board approval, 44 ASA I–III patients with BMI>30 kg/m² undergoing elective gynaecological or urological surgery were randomized after completion of surgery to either an isocapnic hyperpnoea (IH) or a conventional recovery (C) group. The anaesthesia protocol included propofol, fentanyl, morphine, rocuronium and isoflurane in air/O₂. Groups were compared using unpaired t‐test and ANOVA. Results: Minute ventilation in the IH group before extubation was 22.6±2.7 vs. 6.3±1.8 l/min in the C group. Compared with C, the IH group had a shorter time to extubation (5.4±2.7 vs. 15.8±2.7 min, P<0.01), initiation of spontaneous ventilation (2.7±2.3 vs. 6.5±4.5 min, P<0.01), BIS recovery >75 (3.2±2.3 vs. 8.9±5.8 min, P<0.01), eye opening (4.6±2.9 vs. 13.6±7.1 min, P<0.01) and eligibility for leaving the operating room (7.1±2.9 vs. 19.9±11.9 min, P<0.01). There was no difference in time for eligibility for PACU discharge. Conclusion: Increasing alveolar ventilation enhances anaesthetic elimination and accelerates short‐term recovery in obese patients.     

Hepatic Effects of Halothane,Isoflurane or Sevoflurane Anaesthesia in Dogs

The effects of halothane, isoflurane and sevoflurane anaesthesia on hepatic function and hepatocellular damage were investigated in dogs, comparing the activity of hepatic enzymes and bilirubin concentration in serum. An experimental study was designed. Twenty‐one clinically normal mongrel dogs were divided into three groups and accordingly anaesthetized with halothane (n = 7), isoflurane (n = 7) and sevoflurane (n = 7). The dogs were 1–4 years old, and weighed between 13.5 and 27 kg (18.4 ± 3.9). Xylazine HCI (1–2 mg/kg) i.m. was used as pre‐anaesthetic medication. Anaesthesia was induced with propofol 2 mg/kg i.v. The trachea was intubated and anaesthesia maintained with halothane, isoflurane or sevoflurane in oxygen at concentrations of 1.35, 2 and 3%, respectively. Intermittent positive pressure ventilation (tidal volume, 15 ml/kg; respiration rate, 12–14/min) was started immediately after intubation and the anaesthesia lasted for 60 min. Venous blood samples were collected before pre‐medication, 24 and 48 h, and 7 and 14 days after anaesthesia. Serum level of aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP) and gamma‐glutamyltransferase (GGT), lactate dehydrogenase (LDH GGT) activities and bilirubin concentration were measured. Serum AST, ALT and GGT activities increased after anaesthesia in all groups. In the halothane group, serum AST and ALT activities significantly increased all the time after anaesthesia compared with baseline activities. But in the isoflurane group AST and ALT activities increased only between 2 and 7 days, and in the sevoflurane group 7 days after anaesthesia. GGT activity was increased in the halothane group between 2 and 7 days, and in the isoflurane and sevoflurane groups 7 days after anaesthesia. All dogs recovered from anaesthesia without complications and none developed clinical signs of hepatic damage within 14 days. The results suggest that the use of halothane anaesthesia induces an elevation of serum activities of liver enzymes more frequently than isoflurane or sevoflurane from 2 to 14 days after anaesthesia in dogs. The effects of isoflurane or sevoflurane anaesthesia on the liver in dogs is safer than halothane anaesthesia in dogs.     

A comparison of sevoflurane to halothane in paediatric surgical patients: results of a multicentre international study

Induction, emergence and recovery characteristics were compared during sevoflurane or halothane anaesthetic in a large (428) multicentre, international study of children undergoing elective inpatient surgical procedures. Two hundred and fourteen children in each group underwent inhalation induction with nitrous oxide/oxygen and sevoflurane or halothane. Incremental doses of either study drug were added until loss of eyelash reflex was achieved. Steady state concentrations of anaesthesia were maintained until the end of surgery when anaesthetic agents were terminated simultaneously. Time variables were recorded for induction, emergence and the first need for analgesia in the recovery room. In addition, in 86 of the children in both groups, venous blood samples were drawn for plasma fluoride levels during and after surgery. There was a trend toward smoother induction (induction of anaesthesia without coughing, breath holding, excitement laryngospasm, bronchospasm, increased secretion, and vomiting) in the sevoflurane group with faster induction (2.1 min vs 2.9 min, P= 0.037) and rapid emergence times (10.3 min vs 13.9 min, P= 0.003). Among the children given sevoflurane, 2% developed bradycardia compared with 11% in the halothane group. Postoperatively, 46% of the children in the halothane group developed nausea and or vomiting versus 31% in the sevoflurane group (P= 0.002). Two children in the halothane group developed cardiac dysrhythmia and were dropped from the study. In addition, a child in the halothane group developed malignant hyperthermia, received dantrolene, and had an uneventful recovery. Mean maximum inorganic fluoride concentration was 18.3 μM˙l^?1. The fluoride concentrations peaked within one h of termination of sevoflurane anaesthetic and returned rapidly to baseline within 48 h. This study suggests that sevoflurane may be the drug of choice for the anaesthetic management of children.     

Ventilatory compensation for inspiratory resistive loads during anaesthesia with halothane or isoflurane

We have analysed the ventilatory response to sustained inspiratory resistive loads in 14 patients, while awake and during halothane (n = 7) or isoflurane (n = 7) anaesthesia. Patients breathed halothane or isoflurane in oxygen at 1.2 minimum alveolar concentration (MAC). Inspiratory resistances of 0, 12 and 37 cm H2O litre-1 s were applied. Tidal volume (VT) was maintained with the greater loads. At the greatest resistance, a significant reduction in minute ventilation occurred in both awake (-18.9%) and anaesthetized states, with both halothane (-10.4%) and isoflurane (-14.5%). Ventilatory frequency decreased significantly from mean 14.6 (SD 4.7) to 12.5 (4.3) bpm in the awake state and during anaesthesia, with increasing inspiratory resistance (29.5 (3.6) to 23.7 (7.2) bpm and 25.8 (3.3) to 23.4 (4.0) bpm, respectively, for halothane and isoflurane) because inspiratory time (TI) was significantly longer (P < 0.01). End-tidal PCO2 increased by 0.3 kPa, on average, from baseline to the highest level of resistance (P < 0.01). Inspiratory occlusion pressure at 100 ms increased significantly with increased loading in all situations (P < 0.001). We found a similar pattern of ventilatory adaptation to sustained inspiratory flow resistive loads both in awake and anaesthetized states. VT was maintained at increased loads because of an increase in inspiratory neuromuscular output and inspiratory duration.      

Recall of music: a comparison between anaesthesia with propofol and isoflurane

Sixty patients undergoing laparoscopy were randomly assigned to receive total intravenous anaesthesia with propofol or inhalation anaesthesia with isoflurane. Patients in these two groups were also randomly assigned to three subgroups listening to soft music, hard rock music or no music at all. Twenty-four hours after surgery all patients were interviewed and asked if they had heard music during the operation. A tape with seven different pieces of music was also played for the patients. The music they heard during surgery was one of these. No patient had any memories or experiences from the operation. Four patients had dreams, three from the total intravenous anaesthesia group and one from the inhalation anaesthesia group. Twelve patients believed they had heard music, ten from the total intravenous anaesthesia group and two from the inhalation anaesthesia group (P<0.05). Two patients, one from each group, picked the right melody. In conclusion, there was no difference between the two groups with respect to recall during anaesthesia. Patients in the TIVA group were significantly more inclined to state that they had been exposed to music.     

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).      

DEPRESSION OF HYPOXIC VENTILATORY RESPONSE BY HALOTHANE, ENFLURANE AND ISOFLURANE IN DOGS

The ventilatory responses to isocapnic hypoxia and hypercapniawere studied in six dogs each with a tracheostomy, awake andduring anaesthesia with halothane, enflurane and isoflurane(1–2.5 MAC). Isocapnic hypoxic ventilatory response (HVR)was expressed as the parameter A, such that the greater thevalue of A, the greater the hypoxic response. In the anaesthetizeddogs HVR (A) was reduced significantly from the awake valueof 2010±172 (mean+SEM) to 630±173 by 1 MAC halothane,495± 105 by 1 MAC enflurane and 952±157 by 1 MACisoflurane (P<0.05). All three anaesthetic agents producedsignificant depression of HVR at 1 MAC, but enflurane was moredepressant than isoflurane. At 1.5 MAC all three anaestheticsproduced equal and significant depression of HVR at equianalgesicconcentrations. Further increases in anaesthetic concentrationcaused no increase in depression. Hypercapnic drive, as measuredby the slope of the VE/PA_co2 response curve, was reduced significantlyfrom 9.75 litre min^–1 kPa^–1 ± 2.4 in awakedogs to 0.83 ± 0.56 after 1 MAC halothane, 0.68 ±0.53after 1 MAC enflurane and 1.58 ±0.75 after 1 MAC isoflurane.In addition, hypercapnia-induced augmentation of the hypoxicdrive was abolished by 1 MAC halothane or enflurane and diminishedmarkedly by 1 MAC isoflurane. It may be clinically significantthat hypoxia and hypercapnia during anaesthesia with these agentsdid not produce optimal stimulation of ventilation.     

Effect of epidural dexmedetomidine on intraoperative awareness and post‐operative pain after one‐lung ventilation

Background: During combined general and regional anaesthesia, it is difficult to use autonomic signs to assess whether wakefulness is suppressed adequately. We compared the effects of a dexmedetomidine–bupivacaine mixture with plain bupivacaine for thoracic epidural anaesthesia on intraoperative awareness and analgesic benefits, when combined with superficial isoflurane anaesthesia (<0.05 maximum alveolar concentration) in patients undergoing thoracic surgery with one‐lung ventilation (OLV). Methods: Fifty adult male patients were randomly assigned to receive either epidural dexmedetomidine 1 μg/kg with bupivacaine 0.5% (group D) or bupivacaine 0.5% alone (group B) after induction of general anaesthesia. Gasometric, haemodynamic and bispectral index values were recorded. Post‐operative verbal rating score for pain and observer's assessment of alertness/sedation scale were determined by a blinded observer. Results: Dexmedetomidine reduced the use of supplementary fentanyl during surgery. Patients in group B consumed more analgesics and had higher pain scores after operation than patients of group D. The level of sedation was similar between the two groups in the ICU. Two patients (8%) in group B reported possible intraoperative awareness. There was a limited decrease in PaO₂ at OLV in group D compared with group B (P<0.05). Conclusion: In thoracic surgery with OLV, the use of epidural dexmedetomidine decreases the anaesthetic requirements significantly, prevents awareness during anaesthesia and improves intraoperative oxygenation and post‐operative analgesia.     

Anesthesia with sevoflurane, but not isoflurane, prolongs bleeding time in humans

Purpose. Halothane has been shown to suppress platelet aggregation in vitro and ex vivo and to prolong bleeding time. In a previous in vitro study, we demonstrated that sevoflurane had a stronger suppressive effect on platelet aggregation than halothane. The present study investigated whether clinical use of sevoflurane affects bleeding time in vivo. Methods. Thirty-four patients undergoing minor elective surgery were randomly assigned to sevoflurane or isoflurane. Anesthesia was induced with intravenous thiopental and maintained with sevoflurane or isoflurane with nitrous oxide. Bleeding time was measured by the Duke method. An initial (control) measurement was obtained in the operating room before the induction of anesthesia, and a second was obtained 5–10 min after endotracheal intubation but before starting the operation, when the end-expiratory concentration of sevoflurane or isoflurane had been stabilized at 1–1.5 times the minimum alveolar concentration (MAC), and the mean arterial pressures were between 80% and 120% of the preanesthetic values. Results. Bleeding time was increased from the preanesthetic value of 2.07 ± 0.82 min to 2.83 ± 0.93 min (n = 15) in the sevoflurane group (P < 0.01) but was not significantly altered in the isoflurane group. Conclusion. Sevoflurane alters bleeding time in the clinical situation. Received for publication on May 28, 1998; accepted on June 8, 1999     

Effects of propofol vs isoflurane on respiratory gas exchange during laparoscopic cholecystectomy

Background : Respiratory function and pulmonary gas exchange are affected in laparoscopic procedures where a pneumoperitoneum is introduced using CO₂. Previous studies have shown differing results concerning pulmonary gas exchange during laparoscopic procedures: Whereas in patients undergoing isoflurane anaesthesia decreases in PaO₂ are demonstrated, this factor remains unchanged in patients undergoing propofol anaesthesia. In the present study, the effects of propofol on pulmonary gas exchange were compared with those of isoflurane in patients undergoing elective laparoscopic cholecystectomy in a prospective randomised manner. Methods : Twenty ASA patients with physical status I and II were divided randomly between isoflurane (IG) and propofol groups (PG). After induction of anaesthesia patients were moderately hyperventilated. Respirator settings remained unchanged during pneumoperitoneum (PP) until 10 min after deflation of the peritoneal cavity. Blood gas analyses were performed at 5 time points: 15 min after induction of anaesthesia (giving pre-PP values), immediately before carbon dioxide insufflation (0 min PP), after both 30 and 60 min of PP and 10 min post PP. Inspiration plateau pressure (P_plat), compliance of the respiratory system, and both ins- and expiratory gas concentrations were continuously recorded by an Ultima V® monitor (Datex Corp., Helsinki, Finland). The difference between arterial and end-tidal CO₂ partial pressure (P(a-et)CO₂) was calculated so as to allow assessment of physiological dead space by the modified Bohr equation. Results : Pulmonary gas exchange differed significantly after 30 min of PP between the IG and the PG. At this time, PaO₂ was 19.5 ± 2.9 kPa (mean ± SD) in the IG and 23.1 ± 1.8 kPa in the PG (P<0.01), whereas PaCO₂ was 5.5 ± 0.37 kPa in the IG and 4.9 ± 0.27 kPa in the PG (P<0.01). These discrepancies remained until after carbon dioxide desufflation. At 10 min post PP, PaO₂ was 18.3 ± 2.6 kPa in the isoflurane group and 21.9 ± 2.2 kPa in the propofol group (P<0.01), whereas PaCO₂ was 5.4 ± 0.46 kPa in the IG and 4.8 ± 0.22 kPa in the PG (P<0.01). During carbon dioxide insufflation the P(a-et)CO₂ increased significantly in the IG from 0.47 ± 0.13 kPa to 0.76 ± 0.37 kPa (P<0.05), while the values in the PG remained constant. Conclusion : This study demonstrates that pulmonary gas exchange in patients with laparoscopic cholecystectomy is affected by the choice of anaesthetic procedure. During and after laparoscopic cholecystectomy using isoflurane as the anaesthetic, the PaCO₂ is significantly higher and the PaO₂ significantly lower than they are with propofol.     

END-TIDAL CONCENTRATIONS OF HALOTHANE AND ISOFLURANE DURING INDUCTION OF ANAESTHESIA IN YOUNG AND ELDERLY PATIENTS

Twenty-two young (18–32 yr) and 22 healthy elderly (60–80yr) patients received either halothane or isoflurane for maintenanceof anaesthesia during controlled ventilation. Endtidal fractionalconcentrations (FE) of the agents were measured for 20 min aftertheir introduction into inspired gas and the increase in end-tidalconcentrations of the two agents was compared during inductionof anaesthesia using the ratios of FE to the inspired fraction(F1). FE: F1 ratios for isoflurane were higher than those forhalothane in both young and elderly patients, confirming thatequilibration of end-tidal with inspired concentration occursmore rapidly with isoflurane than with halothane in both agegroups. FE: F1 ratios for isoflurane became significantly lowerin the elderly than in the young after 15 min administrationof isoflurane. This suggests slower induction of anaesthesiain the elderly if equipotent concentrations of isoflurane areused; the clinical significance of this difference is probablysmall. Mean FE: F1 ratios for halothane in elderly patientswere similar to those in the young throughout induction of anaesthesia.     

Gastric Mucosal Perfusion in Dogs: Effects of Halogenated Anesthetics and of Hemorrhage

The gastrointestinal tract is one of the first organs affected by hypoperfusion during hemorrhagic shock. The hemodynamics and oxygen transport variables during hemorrhagic shock and resuscitation can be affected by the anesthetics used. In a model of pressure-guided hemorrhagic shock in dogs, we studied the effects of three halogenated anesthetics—halothane, sevoflurane, and isoflurane—at equipotent concentrations on gastric oxygenation. Thirty dogs were anesthetized with 1.0 minimum alveolar anesthetic concentration (MAC) of either halothane, sevoflurane, or isoflurane. A gastric tonometer was placed in the stomach to determine mucosal gastric CO₂ (PgCO₂) and for the calculation of gastric-arterial PCO₂ gradient (PCO₂ gap). The dogs were splenectomized and hemorrhaged to hold mean arterial pressure at 40–50 mm Hg over 45 min and then resuscitated with the shed blood volume. Hemodynamics, systemic oxygenation, and PCO₂ gap were measured at baseline, after 45 min of hemorrhage, and at 15 and 60 min after blood resuscitation. Hemorrhage induced reductions of mean arterial pressure and cardiac index, while systemic oxygen extraction increased (p <. 05), without significant differences among groups (p >. 05). Halothane group showed significant lower PCO₂ gap values than the other groups (p <. 05). After 60 min of shed blood replacement, all groups restored hemodynamics, systemic oxygenation, and PCO₂ gap to the prehemorrhage levels (p >. 05), without significant differences among groups (p >. 05). We conclude that halothane is superior to preserve the gastric mucosal perfusion in comparison to isoflurane and sevoflurane, in dogs submitted to pressure-guided hemorrhagic shock at equipotent doses of halogenated anesthetics.     

Effects of halothane and isoflurane anaesthesia on microcirculatory blood flow in musculocutaneous flaps

Hypoperfusion and necrosis in musculocutaneous flaps used forreconstruction of tissue defects is still a significant clinicalproblem. Although the causes of hypoperfusion are frequentlysurgical in nature, little is known about the effects of anaestheticmanagement on blood flow in flaps or the outcome of flap surgery.We compared in minipigs the effects of halothane and isofluraneanaesthesia in equipotent doses on microcirculatory blood flow(MBF) in the skin and muscle part of musculocutaneous flapsand also in intact (control) skin and muscle. Measurements weremade during stable normovolaemic conditions and during mildto moderate hypovolaemia (withdrawal of 5%, 10% and 15% of totalblood volume). Multi-channel laser Doppler flowmetry (LDF) wasused to measure MBF and electromagnetic flowmetry (EMF) fortotal flap blood flow. During normovolaemic conditions therewas no significant difference between the two groups in centralhaemodynamic or respiratory data. After 15% blood loss, however,there was a significant decrease in mean arterial pressure andcardiac output in the halothane group while there was no significantchange in the isoflurane group (P < 0.05). MBF in controlskin, control muscle and flap muscle remained approximately10–15% higher in the isoflurane than in the halothanegroup throughout the study. In the isoflurane group, MBF inflap skin was unchanged during normovolaemia and there was lessthan 10% decrease during hypovolaemia. In the halothane grouphypovolaemia caused a significant decrease in MBF in flap skin:27% decrease after 5% blood loss, 45% decrease after 10% bloodloss and 49% decrease after 15% blood loss compared with 5%,20% and 21%, respectively, in intact skin. We conclude thatduring normovolaemic conditions MBF was well maintained in musculocutaneousflaps in minipigs both with halothane and isoflurane anaesthesia;however, during mild to moderate hypovolemia MBF decreased markedlyin flap skin with halothane anaesthesia while it remained unchangedwith isoflurane.