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ATRACURIUM AND DOUBLE BURST STIMULATION
Br. J. Anaesth. (1989), 63, 637-640
CORRESPONDENCE times (approximately 9 min for both agents) or in psychometric recovery, attributing this to the intermittent bolus method of administration where we were allowing the effects of one bolus to wear off before giving the next. In a subsequent study using continuous infusions of propofol or methohexitone we found a mean rate of 10.8 mg kg"1 h"1 for propofol and 7.8 mg kg"1 h"1 for methohexitone was required to provide general anaesthesia without an accompanying regional block—results again very similar to Schwilden's with a relative potency of 0.72. In this study significant differences were seen in respect of recovery times—19 and 25 min from stopping infusion to opening eyes, and 21 and 31 min to repeating date of birth for propofol and methohexitone, respectively. N. MACKENZIE I. S. GRANT
Dundee J. H. MCCLURE G. JONES
Edinburgh REFERENCE 1. Jones G, Paul DL, Elton RA, McClure JH. Comparison of bupivacaine and bupivacaine with fentanyl in continuous extradural analgesia during labour. British Journal of Anaesthesia 1989; 63: 254-259.
REFERENCES 1. Schwilden H, Stoeckel H, Schiittler J. Closed-loop feedback control of propofol anaesthesia by quantitative EEG analysis in humans. British Journal of Anaesthesia 1989; 62: 290-296. 2. Mackenzie N, Grant IS. Comparison of propofol with methohexitone in the provision of anaesthesia for surgery under regional blockade. British Journal of Anaesthesia 1985; 57: 1167-1172. 3. Mackenzie N, Grant IS. Propofol for continuous intravenous anaesthesia. A comparison with methohexitone. Postgraduate Medical Journal 1985; 61: 70-75.
RELATIVE POTENCIES OF PROPOFOL AND METHOHEXITONE INFUSIONS Sir,—We were interested to read the recent paper by Schwilden and colleagues on closed-loop feedback control of Sir,—Thank you very much for giving me the opportunity to propofol anaesthesia using quantitative EEG analysis and reply to the correspondence from Drs Mackenzie and Grant. Unfortunately, in thefinalproofs I overlooked the mistyping comparing this with methohexitone [1]. It is gratifying to find that the required rates of infusion for the two agents, as or error of the language revision. My original manuscript delivered by closed-loop EEG computer control to volunteers, stated in the discussion ' This study gave, however, no evidence were similar to our findings in the clinical setting [2]. We used for different recovery times for propofol and methohexitone'. In the printed article, this sentence was modified, omitting intermittent bolus administration of propofol and methohexitone to provide light general anaesthesia for surgery under the word 'different'. I regret that I overlooked this omission in the final proofs. regional block, and found a mean administration rate of 7.8 mg I am grateful to Drs Mackenzie and Grant for drawing kg"1 h"1 for propofol and 5.4 mg kg"1 h"1 for methohexitone, giving a relative potency of 0.68. Schwilden's volunteers attention to this error. required propofol 1452 mg over 2 h (approximately 10 mg H. SCHWILDEN kg"1 h"1 for a 70-kg subject) and they demonstrated a relative Bonn potency of propofol to methohexitone of 0.72. In their discussion, however, referring to our paper they state that we gave no data on recovery times. However, we did state that "a particular objective of this study was to assess ATRACURIUM AND DOUBLE BURST STIMULATION recovery. Because no other drugs were required this facilitated direct comparison of propofol with methohexitone". We Sir,—We read with interest the article by Engbaek and examined both early indices of recovery (eye-opening and colleagues [1] on the use of Double Burst Stimulation (DBS) repeating date of birth), as did Schwilden, and we included for the assessment of pancuronium- induced neuromuscular more detailed psychometric assessment involving choice block. Our preliminary observations using DBS to assess reaction time and critical flicker fusion threshold. Unlike spontaneous recovery of neuromuscular function following Schwilden, we found no significant differences in recovery administration of atracurium have been less encouraging.
Downloaded from http://bja.oxfordjournals.org/ at University of Manitoba on June 6, 2015
COMPARISON OF BUPIVACAINE AND BUPIVACAINE WITH FENTANYL IN CONTINUOUS EXTRADURAL ANALGESIA DURING LABOUR Sir,—Following the recent publication of our study on extradural analgesia during labour [1], we would wish to notify a case of profound respiratory depression 100 min after the use of bupivacaine and fentanyl in extradural analgesia for Caesarean section. The dose of fentanyl (100 ug) was similar to that used as a loading dose in our study. A detailed case report will follow. We would therefore strongly advise that patients are observed continuously for a period of 2-3 h following the use of extradural bupivacaine and fentanyl, particularly if there has been evidence of an initial high level of local anaesthetic block.
638
BRITISH JOURNAL OF ANAESTHESIA
N. BRAUDE S. GHOSH London
REFERENCES 1. Engbaek J, 0stergaard D, Viby-Mogensen J. Double Burst Stimulation (DBS): A new pattern of nerve
stimulation to identify residual neuromuscular block. British Journal of Anaesthesia 1989; 62: 274-278. 2. Carter JA, Arnold R, Yate PM, Flynn PJ. Assessment of the Datex Relaxograph during anaesthesia and atracurium-induced neuromuscular block. British Journal of Anaesthesia 1986; 58: 1447-1452. 3. Williams NE, Webb SN, Calvey TN. Differential effects of myoneural blocking agents on neuromuscular transmission. British Journal of Anaesthesia 1980; 52: 1111— 1115. 4. Bowman WC. Prejunctional and postjunctional cholinoceptors at the neuromuscular junction. Anesthesia and Analgesia 1980; 59: 935-943. THE OHMEDA OAV 7710 VENTILATOR Sir,—Ohmeda have recently introduced into clinical practice a microprocessor-controlled, electro-pneumatically driven patient ventilator, the OAV 7710. This ventilator was designed to operate in either a rebreathing (circle) or non-rebreathing mode, the choice being dictated by the selection of the appropriate patient circuit cassette. In the Primary controlled mode the respiratory variables, expired tidal/minute volumes and rate are monitored by a flow transducer which may be placed at any suitable point in the expiratory circuit. The manufacturer recommends that the respirometer unit is placed at the patient end of the breathing circuit. This necessitates the inconvenience of a cable passing from the transducer to the ventilator, and places the transducer in a vulnerable position. Therefore, in clinical practice, the majority of users have placed the transducer unit as shown in the photograph (fig. 1). In this position, used in conjunction with an Ohmeda Boyle Mk III absorber (which
FIG. 1. Unusual placement of transducer in relation to ventilator.
Downloaded from http://bja.oxfordjournals.org/ at University of Manitoba on June 6, 2015
After opioid premedication, anaesthesia was induced in eight ASA I, adult patients with i.v. thiopentone 5mgkg~'. Nitrous oxide and 0.8% enflurane in oxygen were used to maintain anaesthesia, and neuromuscular block was achieved with a bolus dose of atracurium 0.5 mg kg"'. The lungs were ventilated to maintain PE'COI at 4.5-5.5 kPa. Before administration of atracurium the ulnar nerve at one wrist was stimulated and baseline compound electromyographic potentials from the thenar eminence were recorded using a Datex Relaxograph [2]. The opposite ulnar nerve was stimulated supramaximally using DBS at 5-min intervals. The pattern of stimulation was identical to that used by Engbaek and colleagues [1], comprising two bursts of three stimuli; the response was evaluated manually at the thenar eminence. Absence of DBS fade with atracurium was noted first when the mean of the TOF ratio was 29 % (95 % confidence limits 20-37%). This contrasts with the findings of Engbaek and colleagues [1] who demonstrated DBS fade in all patients following pancuronium at this TOF ratio. This apparent discrepancy may result from differences in presynaptic effect between the two agents [3]; fade during rapid stimulation probably results from prejunctional receptor binding impairing transmitter release [4]. It is therefore unlikely that all neuromuscular blocking agents have similar DBS characteristics.
CORRESPONDENCE times (approximately 9 min for both agents) or in psychometric recovery, attributing this to the intermittent bolus method of administration where we were allowing the effects of one bolus to wear off before giving the next. In a subsequent study using continuous infusions of propofol or methohexitone we found a mean rate of 10.8 mg kg"1 h"1 for propofol and 7.8 mg kg"1 h"1 for methohexitone was required to provide general anaesthesia without an accompanying regional block—results again very similar to Schwilden's with a relative potency of 0.72. In this study significant differences were seen in respect of recovery times—19 and 25 min from stopping infusion to opening eyes, and 21 and 31 min to repeating date of birth for propofol and methohexitone, respectively. N. MACKENZIE I. S. GRANT
Dundee J. H. MCCLURE G. JONES
Edinburgh REFERENCE 1. Jones G, Paul DL, Elton RA, McClure JH. Comparison of bupivacaine and bupivacaine with fentanyl in continuous extradural analgesia during labour. British Journal of Anaesthesia 1989; 63: 254-259.
REFERENCES 1. Schwilden H, Stoeckel H, Schiittler J. Closed-loop feedback control of propofol anaesthesia by quantitative EEG analysis in humans. British Journal of Anaesthesia 1989; 62: 290-296. 2. Mackenzie N, Grant IS. Comparison of propofol with methohexitone in the provision of anaesthesia for surgery under regional blockade. British Journal of Anaesthesia 1985; 57: 1167-1172. 3. Mackenzie N, Grant IS. Propofol for continuous intravenous anaesthesia. A comparison with methohexitone. Postgraduate Medical Journal 1985; 61: 70-75.
RELATIVE POTENCIES OF PROPOFOL AND METHOHEXITONE INFUSIONS Sir,—We were interested to read the recent paper by Schwilden and colleagues on closed-loop feedback control of Sir,—Thank you very much for giving me the opportunity to propofol anaesthesia using quantitative EEG analysis and reply to the correspondence from Drs Mackenzie and Grant. Unfortunately, in thefinalproofs I overlooked the mistyping comparing this with methohexitone [1]. It is gratifying to find that the required rates of infusion for the two agents, as or error of the language revision. My original manuscript delivered by closed-loop EEG computer control to volunteers, stated in the discussion ' This study gave, however, no evidence were similar to our findings in the clinical setting [2]. We used for different recovery times for propofol and methohexitone'. In the printed article, this sentence was modified, omitting intermittent bolus administration of propofol and methohexitone to provide light general anaesthesia for surgery under the word 'different'. I regret that I overlooked this omission in the final proofs. regional block, and found a mean administration rate of 7.8 mg I am grateful to Drs Mackenzie and Grant for drawing kg"1 h"1 for propofol and 5.4 mg kg"1 h"1 for methohexitone, giving a relative potency of 0.68. Schwilden's volunteers attention to this error. required propofol 1452 mg over 2 h (approximately 10 mg H. SCHWILDEN kg"1 h"1 for a 70-kg subject) and they demonstrated a relative Bonn potency of propofol to methohexitone of 0.72. In their discussion, however, referring to our paper they state that we gave no data on recovery times. However, we did state that "a particular objective of this study was to assess ATRACURIUM AND DOUBLE BURST STIMULATION recovery. Because no other drugs were required this facilitated direct comparison of propofol with methohexitone". We Sir,—We read with interest the article by Engbaek and examined both early indices of recovery (eye-opening and colleagues [1] on the use of Double Burst Stimulation (DBS) repeating date of birth), as did Schwilden, and we included for the assessment of pancuronium- induced neuromuscular more detailed psychometric assessment involving choice block. Our preliminary observations using DBS to assess reaction time and critical flicker fusion threshold. Unlike spontaneous recovery of neuromuscular function following Schwilden, we found no significant differences in recovery administration of atracurium have been less encouraging.
Downloaded from http://bja.oxfordjournals.org/ at University of Manitoba on June 6, 2015
COMPARISON OF BUPIVACAINE AND BUPIVACAINE WITH FENTANYL IN CONTINUOUS EXTRADURAL ANALGESIA DURING LABOUR Sir,—Following the recent publication of our study on extradural analgesia during labour [1], we would wish to notify a case of profound respiratory depression 100 min after the use of bupivacaine and fentanyl in extradural analgesia for Caesarean section. The dose of fentanyl (100 ug) was similar to that used as a loading dose in our study. A detailed case report will follow. We would therefore strongly advise that patients are observed continuously for a period of 2-3 h following the use of extradural bupivacaine and fentanyl, particularly if there has been evidence of an initial high level of local anaesthetic block.
638
BRITISH JOURNAL OF ANAESTHESIA
N. BRAUDE S. GHOSH London
REFERENCES 1. Engbaek J, 0stergaard D, Viby-Mogensen J. Double Burst Stimulation (DBS): A new pattern of nerve
stimulation to identify residual neuromuscular block. British Journal of Anaesthesia 1989; 62: 274-278. 2. Carter JA, Arnold R, Yate PM, Flynn PJ. Assessment of the Datex Relaxograph during anaesthesia and atracurium-induced neuromuscular block. British Journal of Anaesthesia 1986; 58: 1447-1452. 3. Williams NE, Webb SN, Calvey TN. Differential effects of myoneural blocking agents on neuromuscular transmission. British Journal of Anaesthesia 1980; 52: 1111— 1115. 4. Bowman WC. Prejunctional and postjunctional cholinoceptors at the neuromuscular junction. Anesthesia and Analgesia 1980; 59: 935-943. THE OHMEDA OAV 7710 VENTILATOR Sir,—Ohmeda have recently introduced into clinical practice a microprocessor-controlled, electro-pneumatically driven patient ventilator, the OAV 7710. This ventilator was designed to operate in either a rebreathing (circle) or non-rebreathing mode, the choice being dictated by the selection of the appropriate patient circuit cassette. In the Primary controlled mode the respiratory variables, expired tidal/minute volumes and rate are monitored by a flow transducer which may be placed at any suitable point in the expiratory circuit. The manufacturer recommends that the respirometer unit is placed at the patient end of the breathing circuit. This necessitates the inconvenience of a cable passing from the transducer to the ventilator, and places the transducer in a vulnerable position. Therefore, in clinical practice, the majority of users have placed the transducer unit as shown in the photograph (fig. 1). In this position, used in conjunction with an Ohmeda Boyle Mk III absorber (which
FIG. 1. Unusual placement of transducer in relation to ventilator.
Downloaded from http://bja.oxfordjournals.org/ at University of Manitoba on June 6, 2015
After opioid premedication, anaesthesia was induced in eight ASA I, adult patients with i.v. thiopentone 5mgkg~'. Nitrous oxide and 0.8% enflurane in oxygen were used to maintain anaesthesia, and neuromuscular block was achieved with a bolus dose of atracurium 0.5 mg kg"'. The lungs were ventilated to maintain PE'COI at 4.5-5.5 kPa. Before administration of atracurium the ulnar nerve at one wrist was stimulated and baseline compound electromyographic potentials from the thenar eminence were recorded using a Datex Relaxograph [2]. The opposite ulnar nerve was stimulated supramaximally using DBS at 5-min intervals. The pattern of stimulation was identical to that used by Engbaek and colleagues [1], comprising two bursts of three stimuli; the response was evaluated manually at the thenar eminence. Absence of DBS fade with atracurium was noted first when the mean of the TOF ratio was 29 % (95 % confidence limits 20-37%). This contrasts with the findings of Engbaek and colleagues [1] who demonstrated DBS fade in all patients following pancuronium at this TOF ratio. This apparent discrepancy may result from differences in presynaptic effect between the two agents [3]; fade during rapid stimulation probably results from prejunctional receptor binding impairing transmitter release [4]. It is therefore unlikely that all neuromuscular blocking agents have similar DBS characteristics.