A Real-Time Method for Estimating the Concentrations of Isoflurane in Mixed Venous Blood by a Derived Fick???s Equation
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We propose an equation derived from Fick's laws and Lin's concept of effective blood concentration to calculate the blood concentration of inhaled anesthetics in mixed venous blood (MVBC) without direct blood sampling. We investigated the relationship between the calculated concentrations and the actual blood sample concentrations in mixed venous blood of patients undergoing cardiac surgery during isoflurane anesthesia in this study. Sixteen patients were recruited for Experiment 1. At different time points, pulmonary arterial blood samples were collected for gas chromatography/mass spectrometric determination via the pulmonary artery catheter: these samples represented the actual concentrations. The inspired and expired concentrations of isoflurane measured by a gas monitor were used for the MVBC calculations. Lin's effective blood concentration method was also used, and the obtained results were then compared with MVBC. Studies were conducted on 11 additional patients (Experiment 2) to confirm the results obtained from Experiment 1. The MVBC and the actual blood concentrations showed a similar kinetic pattern and level during anesthesia and had high correlation coefficients within subjects. We have demonstrated that MVBC could represent the actual pulmonary blood concentrations of isoflurane during cardiac surgery. The results suggest that MVBC could be a useful method of estimating the real-time pulmonary blood concentration of isoflurane. The clinical significance and importance of the method merit further investigation.Keywords:
Venous blood
Desflurane is a new inhalation anaesthetic with a low blood/gas solubility which should allow a fast emergence from anaesthesia. In a prospective open randomized study, desflurane was compared with isoflurane paying special attention to recovery and the quality of the post-operative period. The occurrence of pain and post-operative nausea and vomiting (PONV) was recorded during the first 20 post-operative hours. Seventy women ASA Grade I-II scheduled for elective gynaecological laparoscopic procedures were studied. Patients receiving desflurane were extubated earlier than patients receiving isoflurane, 5 +/- 1 and 9 +/- 1 min respectively (P < 0.05) and the patients anaesthetized with desflurane were able to tell their name and date on average 5 min earlier than those who had received isoflurane; however, time in the recovery room was the same for both groups of patients. Twenty-two of 35 patients receiving desflurane, and 18 of 35 receiving isoflurane required analgesia. PONV was recorded in 18 patients anaesthetized with desflurane and 12 patients anaesthetized with isoflurane. In both groups PONV was more frequently observed in patients after leaving the recovery room. PONV in the recovery room was associated with a delayed discharge, 139 vs. 114 min respectively. Desflurane seems to be an useful alternative to isoflurane for laparoscopic procedures.
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A randomized, single-blind study design was used to compare desflurane with isoflurane in 31 adults undergoing intraocular surgery to determine whether the lower blood:gas partition coefficient of desflurane would result in a more rapid emergence after endotracheal extubation of deeply anesthetized patients. A standardized general anesthetic technique was used, consisting of sufentanil, 0.25 μg/kg, and propofol, 1.5 mg/kg, followed by either isoflurane (n = 15) or desflurane (n = 16) in an air/oxygen mixture. After the operation and reversal of residual neuromuscular block, spontaneous ventilation was reestablished and the patients' tracheas were extubated at equianesthetic concentrations of desflurane and isoflurane (i.e., approximately 1.4 times the minimum alveolar anesthetic concentration [MAC]). Spontaneous movements occurred 5.7 (22.4) and 8.7 min (23, l; P = 0.005) after extubation in the desflurane and isoflurane groups, respectively. Eye opening and orientation also occurred significantly earlier after desflurane compared to isoflurane. Patients receiving desflurane (versus isoflurane) were also able to be transferred from the operating room significantly earlier (10.4 ± 3.7 vs 14.5 ± 4.3 min, P = 0.01). Use of desflurane (versus isoflurane) was not associated with an increased incidence of coughing or airway irritation during the emergence period. However, use of desflurane did not significantly reduce the duration of the postanesthesia care unit (PACU) stay or alter later recovery events compared to isoflurane. In conclusion, the more rapid emergence would favor the use of desflurane when tracheal extubation during deep anesthesia is required.
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In this randomized, double-blind, controlled study, we tested the hypothesis that nitrous oxide (N2O) affects bispectral index (BIS) and 95% spectral edge frequency (SEF95) in response to tracheal intubation during anesthesia with isoflurane and sevoflurane. In protocol 1, we randomly allocated 90 ASA physical status I patients to 6 groups (n = 15 each). Anesthesia was induced with isoflurane or sevoflurane with 0%, 33%, or 66% N2O. The concentration of isoflurane and sevoflurane was gradually increased and end-tidal concentrations were maintained at 1.1% and 1.7%, respectively. Tracheal intubation was performed 12 min after induction of anesthesia. BIS was significantly increased 1 min after tracheal intubation compared before laryngoscopy in patients receiving only isoflurane or sevoflurane (P = 0.001 and 0.007, respectively). In patients receiving 66% N2O-isoflurane or 66% N2O-sevoflurane, both BIS and SEF95 were significantly decreased after tracheal intubation and significantly lower than in those patients receiving only isoflurane or sevoflurane, respectively (P < 0.01 for both). In protocol 2, 3 microg/kg of IV fentanyl completely abolished the decrease of BIS and SEF95 after tracheal intubation during anesthesia with 66% N2O-isoflurane and 66% N2O-sevoflurane (n = 10). We conclude that 66% N2O induced a paradoxical decrease of BIS in response to tracheal intubation during anesthesia with isoflurane and sevoflurane.
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The aim of this study is to control the depth, the quality of recovery of total inhalation isoflurane anesthesia with or without nitrous oxide.Controlled comparative study was carried out on 51 patients, aged 40-54 yr, ASA 1, undergoing saphenectomy, in an University Clinic.Induction: thiopental (3.5 mg kg), atracurium (0.6 mg kg) i.v. Patients were randomly assigned to: group 1 (26 patients), 5% isoflurane in air, by mask; group 2 (25 patients), 3% isoflurane and 60% N2O, by mask. Maintenance: group 1, 2% isoflurane in air; group 2, 1.2% isoflurane and 60% N2O. During anesthesia, consciousness and analgesia level were monitored by EEG Compressed Spectral Array, and clinical signs of pain by Evans' test; arousal time evaluation by "Time to correct response test". The subjective impressions, eventual dreams and recalls were collected using a standard set of questions one hour after the end of anesthesia and 24 hours later. One hour before anesthesia and two hours after the end of surgical procedures, a psychomotor performance recovery evaluation was performed using Zazzo's "deux barrages" test.Student's "t" test.Adequate anesthetic depth was documented in all patients. Recovery time was statistically longer in isoflurane group (group 1 16.7 sd 2.2 minutes vs 10.3 sd 1.9 minutes group 2, p < 0.01). No patient reported recalls relative to anesthetic period. Two hours after recovery no significant differences in psychomotor performance tests were recorded.Isoflurane anesthesia in air, in adequate concentrations, provides a sufficient level of analgesia, hypnosis, amnesia, without clinical side effects.
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Fifty unpremedicated patients scheduled for outpatient restorative dentistry and/or oral surgery lasting 2 to 4 h were anaesthetized with either propofol infusion or isoflurane inhalation. Before induction of anaesthesia with propofol (2.5 mg.kg-1), all patients were given 75 mg of diclofenac and 0.01 mg.kg-1 vecuronium intravenously. Intubation was facilitated with suxamethonium (1.5 mg.kg-1) and anaesthesia was maintained in random order either with propofol infusion (12 mg.kg-1.h-1 for the first 20 min, 9 mg.kg-1.h-1 for the next 20 min, and 6 mg.kg-1.h-1 for the rest of the anaesthesia) or with isoflurane (inspired concentration 1-2.5%), both with nitrous oxide and oxygen (30%). The patients breathed spontaneously using a non-rebreathing circuit. Patients given propofol infusion became re-orientated faster (11.0 +/- 5.5 min vs. 16.5 +/- 7.5 min; P less than 0.01) and at 30 min walked along a straight line better (P less than 0.01). At 60 min, none of the propofol patients displayed an unsteady gait, whereas 11 of the 25 isoflurane patients did (P less than 0.001). None of the patients receiving propofol had emesis at the clinic, compared with 10 of the 25 patients receiving isoflurane (P less than 0.001). The overall incidence of emesis was 2 of 25 and 14 of 25 in the propofol and isoflurane groups, respectively (P less than 0.01). Patients receiving propofol were discharged home earlier than patients receiving isoflurane (80 +/- 14 min and 102 +/- 32 min, respectively; P less than 0.01). It is concluded that propofol allows early discharge of patients, even after long anaesthesias.
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Desflurane is a new inhalation anaesthetic with a low blood/gas solubility which should allow a fast emergence from anaesthesia. In a prospective open randomized study, desflurane was compared with isoflurane paying special attention to recovery and the quality of the post-operative period. The occurrence of pain and post-operative nausea and vomiting (PONV) was recorded during the first 20 post-operative hours. Seventy women ASA Grade I-II scheduled for elective gynaecological laparoscopic procedures were studied. Patients receiving desflurane were extubated earlier than patients receiving isoflurane, 5 ± 1 and 9 ± 1 min respectively (P<0.05) and the patients anaesthetized with desflurane were able to tell their name and date on average 5 min earlier than those who had received isoflurane; however, time in the recovery room was the same for both groups of patients. Twenty-two of 35 patients receiving desflurane, and 18 of 35 receiving isoflurane required analgesia. PONV was recorded in 18 patients anaesthetized with desflurane and 12 patients anaesthetized with isoflurane. In both groups PONV was more frequently observed in patients after leaving the recovery room. PONV in the recovery room was associated with a delayed discharge, 139 vs. 114 min respectively. Desflurane seems to be an useful alternative to isoflurane for laparoscopic procedures.
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A randomized, prospective study was performed to evaluate the hemodynamic changes and recovery characteristics in 60 ASA physical status class I-II unpremedicated patients undergoing gynecological laparotomies with either isoflurane anesthesia only (ISO group) or isoflurane anesthesia followed by propofol infusion (ISO-PRO group). All patients received isoflurane 0.5-1.5% and nitrous oxide (N2O) 66% in oxygen after tracheal intubation. ISO-PRO group (n = 30) received 6 mg kg-1 hr-1 propofol infusion in substitution for isoflurane 25 minutes before the end of surgery. Propofol in ISO-PRO group and isoflurane in ISO group (n = 30) were discontinued 5 minutes before the end of surgery. In both groups, N2O was administered throughout the operation until skin was closed. Hemodynamic measurements were similar between the two groups except at extubation when heart rate and blood pressure were lower in ISO-PRO group. The maximal blood pressure was also lower in ISO-PRO group. In ISO-PRO group, the time required to responsiveness to verbal commands and to orientation were significantly shorter. ISO-PRO group had better Steward's score on arrival at the recovery room and was earlier to get a full score of six. The two groups experienced similar rates of emesis and excitement either two hours or 24 hours postoperatively. We conclude that in relatively long intra-abdominal operations, replacement of isoflurane by propofol infusion 25 minutes before the end of surgery may provide stable maintenance of anesthesia and a faster recovery.
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Desflurane
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Objective To investigate the neuromuscular effect of rocuronium under propofol target controlled infusion (TCI) anesthesia or isoflurane anesthesia. Methods Forty-eight ASA class Ⅰ or Ⅱ patients undergoing selective operations were randomly divided into propofol TCI group (group P, n=24) and isoflurane inhalation group (group I, n=24). All patients were induced with propofol TCI, fentanil and rocuronium 0.6 mg/kg. Patients in group P were maintained with propofol TCI and remifentanil, and those in group I with 1MAC isoflurane and remifentanil. The TOF mode of stimulation was used to monitor neuromuscular blocking variables of onset time, no-response time, the time to recovery of T1 to 25% of control, recovery index and the TOF ratio (TOFr) to 0.25.Results TOFr to 0.25 and recovery index were greater under isoflurane anesthesia than those under propofol-remifentanil anesthesia (P0.05). But there were no significant differences in the onset time, no-response time, and T1 25% recovery time between two groups. Conclusion Propofol TCI-remifentanil anesthesia has little effect on rocuronium but 1MAC isoflurane inhalation potentiates the neuromuscular effect of rocuronium.
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