Isoflurane and total oxygen consumption in spontaneously breathing dogs in basal metabolic conditions

To study the metabolic effects of isoflurane, whole body oxygen consumption (VO2) was measured on 7 occasions in 7 dogs under standard conditions. The dogs were trained to lie unrestrained in the lateral position for the measurement of VO2 (STPD) in the unanaesthetized state. Blood gas tensions and pH of arterial blood, heart and respiratory rates, blood pressure, rectal temperature and CO2 production (VCO2) also were determined. The maximum VO2 (ml X kg-1 X min-1) of the alert and the minimum of the drowsy resting states averaged (+/- SE) 6.9 +/- 0.5 and 3.6 +/- 0.3 respectively. The calculated mean basal rate was 4.4 +/- 0.1 and VO2 during natural delta-sleep 2.8 +/- 0.3. With isoflurane and spontaneous ventilation VO2 averaged 4.1 +/- 0.2, 4.0 +/- 0.3 and 3.6 +/- 0.3 at 1, 1.5 and 2 Vol-% (inspired) respectively. During anaesthesia with isoflurane VO2 fluctuates between the calculated basal rate and that of natural sleep.     

Carbon dioxide elimination in anaesthetized children

Carbon dioxide elimination (VCO2) was measured in 186 anaesthetized, spontaneously breathing infants and children with body weights ranging from 2.8 to 26.5 kg. They all underwent minor paediatric surgical procedures. The influence on VCO2 of age, operation, premedication, caudal anaesthesia, and different volatile anaesthetic agents was investigated. The volume of exhaled gas, during three- to five-minute collection periods, was measured and the fraction of exhaled CO2 was determined by a CO2 meter. Under basal anaesthetic conditions, the average output before operation followed the equation: VCO2 (ml.min-1) = -1.25X + 13.0X2, in which X = lne (body weight, kg). Expressed on a weight basis, the youngest infants (weighing less than 5 kg) had the lowest VCO2. Higher values were measured up to a body weight of 10 kg above which a negative correlation occurred between VCO2 (ml.min-1.kg-1) and body weight. The use of premedication resulted in a more variable VCO2 during operations than when opioid premedication was not used. The combination of a general anaesthetic and caudal anaesthesia stabilized VCO2. Also, children anaesthetized with halothane had a higher VCO2 than those who were anaesthetized with enflurane or isoflurane (P less than 0.05). The variable VCO2 emphasizes the need for increased monitoring of VCO2 during routine anaesthesia and operation in infants and children.     

Oxygen consumption after flumazenil reversal

The effect of flumazenil reversal of midazolam-induced anesthesia on whole body oxygen uptake (VO2) was investigated in a double-blind trial in 48 patients (ASA, 1 or 2) undergoing elective surgery under general anesthesia. VO2 was measured in spontaneously breathing patients during recovery from anaesthesia induced with midazolam 0.25 mg.kg-1 and maintained with nitrous oxide 60% in oxygen and halothane. The level of sedation was evaluated by a subjective score. To reverse midazolam-induced anesthesia, patients were randomly allocated to receive placebo or flumazenil (6 micrograms.kg-1). No significant changes in VO2 (160 +/- 53 vs 150 +/- 39 ml.min-1.m-2 or sedation score (2.5 +/- 1.0 vs 2.1 +/- 0.9) were observed in the placebo group. After flumazenil administration, the sedation score significantly (P less than 0.05) improved (2.9 +/- 1.0 vs 1.3 +/- 0.8) whereas no significant change in VO2 was observed (158 +/- 67 vs 157 +/- 61 ml O2.min-1.m-2). These data show that reversal of benzodiazepine effects with flumazenil resulted in no significant change in oxygen uptake.     

The Magill-Venturi attachment: studies in volunteers and patients

Including a venturi injector in a Magill breathing attachment reduces the requirement of compressed gases to 40% of that normally used: 100-120 ml x kg-1 x min-1. The entrainment of ambient air through the venturi injector enables the supply of an adequate flow of gas mixture to the patient. In 10 awake volunteers and 12 patients under N2O/halothane anaesthesia, it was demonstrated that a fresh gas flow from the anesthetic machine of 40 ml x kg-1 x min-1 is sufficient to prevent rebreathing during spontaneous respiration, when the venturi injector is included in the Magill attachment.     

Evaluation of the Humphrey A.D.E. breathing system

A new breathing circuit (the Humphrey A.D.E., double lever model) was evaluated in adults to determine (1) the fresh gas flow (FGF) needed to achieve normocapnia during controlled ventilation and to just induce rebreathing during spontaneous ventilation, (2) end-expired CO2 (PECO2) at those FGF values, (3) the standard deviation of FGF requirements for controlled and spontaneous breathing (reliability of recommended FGF settings) and (4) the magnitude of change in PECO2 produced by varying FGF from the recommended values (sensitivity of the system). The FGFs that provided normocapnia with controlled ventilation and just induced rebreathing with spontaneous ventilation were 67 +/- 10 and 52 +/- 7 ml . kg-1 . min-1 (mean +/- SD), respectively. PECO2 values were 36.0 +/- 0.3 and 41.6 +/- 3.9 mmHg respectively. During controlled ventilation low reliability was offset by low sensitivity so that PECO2 changed little when FGF was raised or lowered from recommended values (0.2 mmHg/ml . kg-1 . min-1). In contrast, during spontaneous ventilation low reliability was additive with high sensitivity when using FGFs lower than the mean value that just induced rebreathing. A threshold was reached where lowering FGF from recommended values caused large changes in PECO2 (1.1 mmHg/ml . kg-1 . min-1). It is concluded that the FGF recommended by Humphrey for controlled ventilation is satisfactory. However, the FGF recommended by Humphrey for spontaneous ventilation may result in hypercapnia in some patients. This can be prevented either by using a higher FGF of 66 ml . kg-1 . min-1 routinely in all patients or by using lower flows with CO2 monitoring.     

Metabolic regulation of cardiac output during inhalation anaesthesia in dogs

BACKGROUND: The metabolic regulation of tissue blood flow manifests itself in a linear relation between blood flow and oxygen consumption, the latter being the independent variable. It is unknown, however, if this fundamental physiological principle operates also during inhalation anaesthesia known to be associated with decreases in both cardiac output (Q) and oxygen consumption (VO2). METHODS: Seven dogs (23-32 kg) with chronically implanted flow probes around the pulmonary artery were repeatedly anaesthetized with halothane, enflurane, isoflurane, sevoflurane, and desflurane at increasing minimum alveolar concentrations (1-3 MAC). Cardiac output (ultrasound transit-time flowmeter) and VO2 (indirect calorimetry) were measured continuously. We also imposed selective changes in Q, and thus of O2 supply, to see if and to what extent this would alter VO2 during anaesthesia (1.5 MAC). RESULTS: In awake dogs under basal metabolic conditions, VO2 was 4.6 +/- 0.1 ml.kg-1.min-1 and Q 105 +/- 3 ml.kg-1.min-1 (mean +/- SEM). During inhalation anaesthesia, VO2 and Q decreased by approximately 30% and 60%, respectively. The concentration-effect relations of both variables did not differ between anaesthetics, yielding a uniform Q/VO2 relation, which was nearly linear in the range (0-2 MAC) with an average slope of 39 +/- 1 (range 30-55). Above 2 MAC, Q decreased more for a given change in VO2, and O2 extraction increased by 50%, indicating compromised oxygen delivery (DO2). Imposed changes in Q, both in awake and anaesthetized dogs, yielded Q/VO2 relations which were notably steeper (slopes 114 to 187) than those observed during inhalation anaesthesia. More important, imposed increases in Q and thus DO2 during anaesthesia (1.5 MAC) to rates comparable to that in the awake state produced a much less than proportional increase in VO2 without restoring it to baseline. CONCLUSIONS: Inhalation anaesthesia is characterized by a uniform Q/VO2 relation with an almost linear course at an anaesthetic concentration up to 2 MAC, regardless of the anaesthetic. Metabolic regulation of blood flow apparently operates also during inhalation anaesthesia up to 2 MAC so that the decrease in VO2 determines Q. This implies that cardiac output alone provides little information on the function of the circulation during inhalation anaesthesia unless related to metabolic demands, i.e. to VO2.     

Flow requirements for the Bain breathing circuit during anaesthesia for caesarean section

We studied the relationship between arterial carbon dioxide tension (PaCO2) and fresh gas flow (FGF) during use of the Bain breathing circuit for Caesarean section anaesthesia. Thirty-one patients undergoing Caesarean section were anaesthetised using the Bain circuit with intermittent positive pressure ventilation. The PaCO2 were measured at FGF of 70 ml X kg-1 X min-1, 80 ml X kg-1 X min-1, and 100 ml X kg-1 X min-1. The FGF requirement to maintain a given PaCO2 during Caesarean section anaesthesia is the same as the requirements for nonpregnant subjects, despite the increase in carbon dioxide production associated with pregnancy. This is probably because the total FGF determined by body weight and given during Caesarean section anaesthesia is 15-20 per cent higher than nonpregnant levels, due to the weight gain associated with pregnancy. A FGF of 100 ml X kg-1 of pregnant weight/min maintains PaCO2 of 4.44 kPa predelivery, which is in the desirable range of PaCO2 during Caesarean section.     

Fresh gas flow in coaxial Mapleson A and D circuits during spontaneous breathing

In a lung model simulating spontaneously breathing halothane anaesthesia, the rebreathing characteristics of the coaxial Mapleson A (Lack circuit) and D (Bain circuit) systems were tested. Using decreasing fresh gas flows (VF), the end-tidal carbon dioxide fraction (FACO2) was monitored and the point of rebreathing (R.P.) detected. The effects of changes in minute volume (VE), dead-space to tidal volume ratio (VD/VT) and carbon dioxide elimination (VCO2) were studied. The effect of increased tidal volumes (VT) on FACO2 was investigated for some different fresh gas flows (VF). The VF/VE ratio for R.P. in the Bain circuit was approximately 2 and in the Lack circuit 0.88. In both circuits an increase in VE and a decrease in the VD/VT ratio resulted in higher demands on VF if rebreathing was to be avoided. The latter effect was much more pronounced in the Lack circuit. In neither system did any changes in VCO2 affect the rebreathing characteristics. The conclusion was drawn that the Lack system is a much better choice concerning the fresh gas flows for anaesthesia with spontaneous breathing than the Bain system. It was also concluded that the fresh gas flows recommended by Humphrey for the Lack system (i.e. 51 ml X min-1 X kg b.w.-1) and by the manufacturers for the Bain system (i.e. 100 ml X min-1 X kg b.w.-1) are inadequate and should be increased if a considerable degree of rebreathing is to be avoided.     

Flow Pattern and Respiratory Characteristics during Halothane Anaesthesia

Using pneumotachography, the flow pattern was analysed in detail and tidal volume, respiratory rate, dead-space to tidal volume ratio (VD/VT) and carbon dioxide output were measured in adults (Group A, n = 12) and 3-8-year-old children (Group B, n = 10) during spontaneous breathing anaesthesia with halothane and surgery. The respiratory cycle was divided by equidistant points into 40 parts and the flow at each point related to peak inspiratory and expiratory flow. Thus a relative flow pattern was derived. This relative flow pattern was almost identical in both groups. Characteristically, the flow curve showed rapid turns from high expiratory to high inspiratory flow rates without any end-expiratory flow pause (except in one adult). The minute ventilation was 6.6 +/- 2.0 1 X min-1 in Group A and 3.4 +/- 0.6 1 X min-1 in Group B, being correlated both to body weight and body surface area in Group A but not in Group B. The tidal volume was 210 +/- 60 ml in Group A and 78 +/- 13 ml in Group B, respiratory rate 31 +/- 4 X min-1 and 44 +/- 10 X min-1, respectively, and the VD/VT ratio 0.40 +/- 0.10 and 0.55 +/- 0.12, respectively. Carbon dioxide output was 173 ml X min-1 (STPD) in the adults and 82 +/- 13 ml X min-1 (STPD) in the children. It was correlated to both body weight and body surface area in the adults but not in the children.     

Capnographic detection of anaesthesia circle valve malfunctions

To determine whether capnographic waveforms can characterize valve malfunction of the anaesthesia circle, which would enable such problems to be identified and rectified immediately, we monitored capnographic respiratory waveforms during anaesthesia with simulated circle valve malfunctions. Ten mongrel dogs were anaesthetized with pentobarbitone, 25 mg.kg-1 IV, and halothane, 0.5 to 1 per cent. Respiratory gas was sampled from the elbow of the circle system for capnographic monitoring. At fresh gas flow rates of 2.5 or 5 L.min-1 during consecutive periods of controlled and spontaneous ventilation, the inspiratory valve, the expiratory valve, or both valves of the circle system were opened for 15 min. Inspired CO2 concentration increased significantly every time a valve was opened, except during spontaneous breathing at 5 L.min-1. At 2.5 L.min-1, inspired CO2 increased from baseline to 0.41 +/- 0.28 per cent with the inspiratory valve opened and to 2.22 +/- 1.72 per cent with the expiratory valve opened during controlled ventilation and to 0.43 +/- 0.20 per cent and 2.02 +/- 1.28 per cent, respectively, during spontaneous ventilation. Inspired CO2 increased to almost 1 per cent when the inspiratory valve was open and to greater than or equal to 1.89 per cent when the expiratory valve was open. The effects with the expiratory valve open and with both valves open were similar. Capnograms were affected in characteristic ways by the valve malfunctions.     

Halothane alters the oxygen consumption-oxygen delivery relationship compared with conscious state

The authors' objectives were as follows: 1) to characterize for the first time the relationship between whole body O2 delivery (DO2) and O2 consumption (VO2) in adult conscious dogs; and 2) to asses the effects of the inhalational anesthetic, halothane, on that relationship. DO2 was varied over a wide range in chronically instrumented dogs by gradual inflation and deflation of a hydraulic occluder implanted around the thoracic inferior vena cava to alter venous return and cardiac output. VO2 was measured at different values of DO2 in dogs in the fully conscious state and again during halothane anesthesia. A "binning" technique indicated that halothane decreased VO2 (P less than 0.01) at any given value of DO2 over a broad range of VO2. A two-line piecewise linear regression analysis technique indicated that halothane decreased (P less than 0.01) the critical O2 delivery (COD) from 20 +/- 3 to 10 +/- 1 ml.kg-1.min-1 and increased (P less than 0.01) O2 extraction at COD from 31 +/- 3 to 40 +/- 2%. However, the DO2-VO2 plots measured in both conscious and halothane-anesthetized dogs did not exhibit a discrete discontinuity but rather were closely fit (correlation coefficient = 0.98) by an exponential equation of the following form: O2 extraction = B1.(1 - exp (-DO2/B2))/DO2, where B1 is the delivery-independent estimate of VO2 and B2 is the "delivery constant," i.e., the DO2 associated with a VO2 equal to 63% of B1. Halothane decreased B1 (P less than 0.01) from 5.3 +/- 0.1 to 3.9 +/- 0.1 ml.kg-1.min-1 and decreased B2 (P less than 0.01) from 5.6 +/- 0.3 to 3.6 +/- 0.3 ml.kg-1.min-1 compared with that measured in conscious dogs. Thus, compared with the conscious state, halothane anesthesia alters the fundamental relationship between DO2 and VO2 and may have a beneficial effect on tissue oxygenation at low values of DO2.     

The effects of shivering on oxygen consumption and carbon dioxide production in patients rewarming from hypothermic cardiopulmonary bypass

Oxygen consumption (VO2), carbon dioxide production (VCO2), end-tidal carbon dioxide partial pressure (PETCO2), mixed venous oxygen saturation (SvO2) and haemodynamic variables were recorded every 30 min for four hours in 15 patients recovering from hypothermic cardiopulmonary bypass (CPB). All patients had been anaesthetised with fentanyl 40 micrograms.kg-1, supplemented with isoflurane, and pancuronium 0.15 mg.kg-1 for muscle relaxation. Three of the 15 patients (20 per cent) shivered, defined as intermittent or continuous, vigorous movements of chest or limb muscles. Patients who shivered had a VO2 of 159 +/- 16.4 ml.min-1.m-2 on arrival in the ICU which rose to a maximum value of 254 +/- 28.3 ml.min-1.m-2 by 150 min post-CPB. In contrast, patients who did not shiver had a significantly lower VO2 of 93.1 +/- 6.9 ml.min-1.m-2 on arrival in the ICU which rose to a maximal value of only 168 +/- 11.5 ml.min-1.m-2 by 180 min post-CPB. Maximal VO2 in both groups was reached when the nasopharyngeal temperature (NPT) was approaching normal. VCO2 paralleled the increase in VO2 in both groups. By four hours there was no significant difference between the two groups; however, the VO2 in both groups (160.5 +/- 21.3 ml.min-1.m-2 and 173.9 +/- 12.3 ml.min-1.m-2 respectively) was approximately twice values commonly measured in anaesthetized patients. Patients who shivered had a significantly higher heart rate and cardiac index and significantly lower SvO2. We conclude that the high VO2 and VCO2 associated with shivering causing increased myocardial work may be detrimental to patients who have impaired cardiac function post-coronary artery surgery (CAS).     

Cerebral blood flow and metabolism in patients undergoing anesthesia for carotid endarterectomy. A comparison of isoflurane, halothane, and fentanyl

The effects of isoflurane, halothane, and fentanyl on cerebral blood flow (CBF) and cerebral metabolic rate for oxygen (CMRO2) during anesthesia prior to carotid endarterectomy were compared using the intravenous method of 133-Xenon CBF determination. Patients, mean (+/- SE) age 68 +/- 2, received either isoflurane (N = 16), 0.75% in O2 and N2O, 50:50; halothane (N = 11), 0.5% in O2 and N2O, 50:50; or fentanyl (N = 10), 5-6 micrograms/kg bolus and then 1-2 micrograms.kg-1.h-1 infusion in addition to O2 and N2O, 40:60. Measurements were made immediately before carotid occlusion. Mean (+/- SE) CBF (ml.100 g-1.min-1) was 23.9 +/- 2.1 for isoflurane, 33.8 +/- 4.8 for halothane, and 19.3 +/- 2.4 for fentanyl. CMRO2 (ml.100 g-1.min-1) was available from 22 patients and was 1.51 +/- 0.28 for isoflurane (N = 7), 1.45 +/- 0.24 for halothane (N = 6), and 1.49 +/- 0.21 for fentanyl (N = 9). Although CBF was greater during halothane than during isoflurane or fentanyl anesthesia (p less than 0.05), there were no demonstrable differences in CMRO2 among the 3 agents. We conclude that choice of anesthetic agent for cerebrovascular surgery with comparable anesthetic regimens should not be made on the basis of "metabolic suppression." During relatively light levels of anesthesia, vasoactive properties of anesthetics are more important than cerebral metabolic depression with respect to effects on the cerebral circulation.     

Esmolol prevents and suppresses arrhythmias during halothane anaesthesia in dogs

The antiarrhythmic effect of esmolol, a selective beta 1 adrenoreceptor blocker, was evaluated in the presence of epinephrine induced arrhythmias in dogs (n = 6). The arrhythmogenic dose of epinephrine (ADE) during 1.2 MAC halothane in dogs was increased from 3.23 +/- 0.25 (mean +/- SD) to 30.90 +/- 3.56 micrograms.kg-1.min-1 (P less than 0.001) by the prior administration of esmolol 0.5 microgram.kg-1 bolus followed by an infusion at the rate of 150 micrograms.kg-1.min-1. Higher esmolol infusion doses of 200 micrograms.kg-1.min-1 further increased ADE to 99.0 +/- 2.92 micrograms.kg-1.min-1 (P less than 0.001). After discontinuation of esmolol and during continued halothane anaesthesia, ventricular tachycardia was induced by increasing the infusion rate of the 100 micrograms.ml-1 solution of epinephrine. In all dogs ventricular tachycardia was restored to sinus rhythm by a bolus dose of esmolol (1 microgram.kg-1). We conclude that esmolol pretreatment increases the ADE during halothane anaesthesia in dogs. Our data suggest that esmolol may be useful as an antiarrhythmic agent in the management of epinephrine-related ventricular arrhythmias during anaesthesia in man.     

Ventilatory response during halothane and enflurane anaesthesia

In six children with body weights between 11.4-18.7 kg, minute ventilation, tidal volume, respiratory rate, end-tidal CO2 concentration and CO2 elimination were measured during both CO2 free breathing and CO2 breathing due to low fresh gas flows (maximal inspired CO2 about 2%) or the addition of CO2 from Rotameters (mean inspired CO2 about 1.5%) during both halothane and enflurane anaesthesia. All patients were undergoing hypospadias repair, received caudal analgesia prior to surgery and were intubated and allowed to breathe halothane/enflurane in O2/N2O (FIO2 0.5) spontaneously through a modified T-piece system (Mapleson F). End-tidal CO2 concentrations were similar with both agents during CO2-free breathing and did not increase during CO2 breathing because of increased minute ventilation, of the same magnitude with both agents, which was achieved by larger tidal volumes. Respiratory rates were unchanged. No differences were found between halothane and enflurane at the light levels of general anaesthesia made possible by combination with caudal block.     

The effect of paralysis on oxygen consumption in normoxic children after cardiac surgery

To determine whether paralysis reduces oxygen consumption (V02) after cardiac surgery in infants, the authors measured V02 before and after paralysis in 17 sedated infants who were ventilated mechanically after cardiac surgery. Oxygen consumption was determined as being the difference between oxygen content of inspired and expired gases. The absence or presence of "movement" (breathing or repeated movement of the extremities) before paralysis was noted. For eight infants who did not "move" before paralysis, VO2 was similar before (9.1 +/- 1.2 ml . kg-1 . min-1, mean +/- SD) and after (9.0 +/- 1.5 ml . kg-1 . min-1) paralysis (P = 0.81). However, for nine infants who did "move" before paralysis, VO2 decreased from 9.2 +/- 1.4 ml . kg-1 . min-1 before paralysis to 8.0 +/- 1.4 ml . kg-1 . min-1 after paralysis (P less than 0.05). One infant in each group had an increase in VO2 greater than 10% of the baseline value (i.e., 12% and 14%). In conclusion, if breathing or repeated movement is present before paralysis, paralysis decreases VO2 by 13% in sedated infants after cardiac surgery. If repeated or regular movement is not present before paralysis, paralysis does not decrease VO2. These data suggest that in normoxic patients, muscle paralysis does not significantly alter V02 and therefore should not be used for this purpose.     

Cerebral blood flow, cerebral metabolic rate of oxygen and relative CO2-reactivity during craniotomy for supratentorial cerebral tumours in halothane anaesthesia. A dose-response study

Fourteen patients were studied during craniotomy for small supratentorial cerebral tumours. Cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO2) were measured twice by a modification of the Kety-Schmidt technique using 133Xe intravenously. Anaesthesia was induced with thiopental 4-6 mg kg-1, fentanyl and pancuronium, and maintained with an inspiratory halothane concentration of 0.45% in nitrous oxide 67% at a moderate hypocapnic level. In one group of patients (n = 7) the inspiratory halothane concentration was maintained at 0.45% throughout anaesthesia. About 1 h after induction of anaesthesia CBF and CMRO2 averaged 35 +/- 2 ml 100 g-1 min-1 and 2.7 +/- 0.3 ml O2 100 g-1 min-1 (mean +/- s.c. mean), respectively. During repeat studies 1 h later CBF and CMRO2 did not change. In another group of patients (n = 7) an increase in halothane concentration from 0.45% to 0.90% was associated with a significant decrease in CMRO2 from 2.3 +/- 0.1 to 2.0 +/- 0.1 ml O2 100 g-1 min-1. The CO2-reactivity measured after the second flow measurement was preserved. It is concluded that halothane in this study induces a dose-dependent decrease in cerebral metabolism, an increase in CBF while CO2-reactivity is maintained.     

Changes in ventilation, oxygen uptake, and carbon dioxide output during recovery from isoflurane anesthesia

Recovery from inhalation anesthesia is often marked by the occurrence of postoperative tremor that resembles shivering, which is known to be associated with an increase in oxygen uptake (VO2), CO2 output (VCO2), and minute ventilation (VE). This study determined the time course of the ventilatory changes observed during the first hour of recovery from isoflurane anesthesia. Ten patients (ASA PS 1) scheduled for minor orthopedic surgery (knee arthroscopy) were included in this study. Anesthesia was induced with thiopental (5 mg/kg) and maintained with 70% N2O and isoflurane (1-2%) in oxygen, allowing spontaneous ventilation. In the recovery room, after N2O had been discontinued, patients were connected to a Beckman Metabolic measurement cart, which allowed a continuous monitoring of VE, VO2, VCO2, and PETCO2. Postoperative tremor was observed in all patients within 7.1 +/- 1.2 min (mean +/- SEM) after isoflurane discontinuation and was associated with a marked increase in the following: VO2, from 173 +/- 26 ml/min at the end of anesthesia to 457 +/- 88 ml/min; VCO2, from 149 +/- 18 ml/min at the end of anesthesia to 573 +/- 98 ml/min; and VE, from 6.8 +/- 0.7 l/min at the end of anesthesia to 16.6 +/- 2.8 l/min (values obtained 20 min after isoflurane discontinuation). In three patients during intense shivering, VO2, VCO2, and VE reached peak values higher than 800 ml/min, 1,300 ml/min and 30 l/min, respectively. This study shows that postoperative tremor following isoflurane anesthesia may be associated with prolonged and large increases in oxygen uptake, CO2 output, and minute ventilation.     

Use of isoflurane in a closed-circuit. Economic advantages

The present study was designed to assess whether isoflurane requirement was significantly affected by fresh gas flow in a closed-circuit system. Sixty patients scheduled for orthopaedic procedures were randomly assigned into three groups. In group A (n = 20), anaesthesia was conducted with a fresh gas flow of 482.5 +/- 186.6 ml X min-1, corresponding to the patient's metabolic demand. In group B (n = 20), the fresh gas flow was 2000 ml X min-1. In group C (n = 20), it was adjusted to the ventilation minute, i.e. 7145 +/- 986 ml X min-1. Artificial ventilation was conducted using a tidal volume of 10 ml X kg-1 and a rate of 10 to 12 c X min-1. Anaesthesia was induced after 10 min denitrogenation with fentanyl (4 micrograms X kg-1), thiopentone (4 mg X kg-1) and vecuronium (0.1 mg X kg-1). FIO2 was then brought to 0.5 in nitrous oxide and was monitored continuously using a polarographic oxymeter. Liquid isoflurane was injected in the expiratory limb of the circuit using an electrical syringe driver. Alveolar concentration of isoflurane was set at 0.92 vol. % according to Lowe and Ernst. Statistical analysis was carried out using Student's test for means. Anaesthesia lasted 138 +/- 88.3 min in group A, 125.5 +/- 45.1 min in group B and 146.5 +/- 50 min in group C, no difference being significant.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ventilation and ventilatory CO2 response in children during halothane anaesthesia after nonopioid (midazolam) and opioid (papaveretum) premedication

The influence of non-opioid (NO) and opioid (O) premedication on ventilation and ventilatory CO2 response was studied in 18 spontaneously breathing children during halothane anaesthesia. Eight patients in Group NO and 10 in Group O were comparable in age, body weight and type of surgery performed. The sedative effect was evaluated and measurements by pneumotachography and in-line capnography were made immediately after induction of sleep, just before the start of surgery, during surgery and after surgery both before and after 3 min of about 2% CO2 inhalation. Immediately after induction the mean value (+/- s.e. mean) of end-tidal CO2 concentration (ETCO2) was 4.86 +/- 0.21% in Group NO and 5.28 +/- 0.22% in Group O. Before and during surgery, minute ventilation (VE) was higher in Group NO (P less than 0.05) mainly due to higher respiratory rates. ETCO2 was similar in the two groups before, during and after surgery. The ratio of VE to CO2 elimination (VCO2) and of dead space (VD) to tidal volume (VT) was higher in Group NO, but ventilatory response to CO2 inhalation immediately before the postoperative period was similar in both groups. It was concluded that opioid premedication resulted in more efficient ventilation during anaesthesia and surgery, and that CO2 response at the end of surgery was maintained in both groups.