Br.J. Anaesth. (1975), 47, 1339 CORRESPONDENCE OXYGEN THERAPY
retained inside the swivel connector, making reconnection of the two impossible (fig. 1). This is particularly likely to occur if any lateral force is used to separate the tube and connector.
FIG. 1. The tube on the left has lost its sealing ring, which can be seen inside the swivel connector. A normal tube and connector are shown on the right for comparison. I understand that Portex Ltd are changing the construction of their tubes to obviate this problem, but until new tubes are introduced, I would suggest that both a spare tracheostomy tube and connector be present at the bedside of patients who are ventilated artificially. R.
J.
WARE
London BLIND NASAL INTUBATION
Sir,—I have read with interest the article on bund nasal intubation by Oyegunle (1975) in a recent issue of your Journal. It is to be hoped that further interest has been G. B. DRUMMOND aroused in this much neglected but valuable technique, Edinburgh and that more anaesthetists will be encouraged to acquire the necessary skill. REFERENCES There are several passages in the text of this article which Bake, B., Wood, L., Murphy, B., Macklem, P. T., and are so strikingly similar to passages in two articles on the Milic-Emili, J. (1974). Effect of inspiratory flowrate on same subject written by myself that I formed a strong regional distribution of inspired gas. J. Appl. Physiol., impression that I was reading my own words (Davies, 37,8. 1968, 1972). Dr Oyegunle was generous enough to Grant, B. J. B., Jones, H. A., and Hughes, J. M. B. (1974). acknowledge one of these publications but not the more Sequence of regional filling during a tidal breath in man. recent one concerned with a technique almost identical to J. Appl. Physiol., 37, 158. his own. The results achieved were also very similar. With Leigh, J. M. (1974). Oxygen therapy at ambient pressure; a single dose of propanidid he performed endotracheal in Scientific Foundations of Anaesthesia (eds. C. F. Scurr intubation in 33% of his patients at the first attempt, and S. A. Feldman), 2nd edn., p. 253. London: compared with 43% in my series. With up to three attempts Heinemann. he intubated 68%, compared with 75% in my series. (1975). Postoperative oxygen administration. Br. J. These small differences are probably of no significance, Anaesth., 47, 108. although it is possible that the slightly larger dose of propanidid (6-7 mg/kg body weight) given in my series A HAZARD OF PORTEX SOFT SEAL TRACHEOSTOMY TUBES produced greater hyperventilation which might account WITH SWIVEL CONNECTORS for the difference. Although propanidid has much to commend it, its use Sir,—Portex soft seal cuffed tracheostomy tubes are being used increasingly for ventilation of the patient with a carries with it certain dangers which should be balanced tracheostomy. I would like to draw attention to a problem against its advantages. Notice must be taken of the reports I have encountered several times when these tubes were of serious adverse reactions which have appeared in the used in combination with Portex swivel connectors. The literature (Manz and Fank, 1969; Bradburn, 1970; Larard, sealing ring on the p.v.c. tube became detached and was 1970; Johns, 1970; Stovner and Endresen, 1971; Dundee
Downloaded from http://bja.oxfordjournals.org/ at University of Iowa Libraries/Serials Acquisitions on June 28, 2015
Sir,—I would like to comment on the paper of Dr J. M. Leigh on postoperative oxygen therapy (Leigh, 1975) regarding the possibility of oxygen toxicity if oxygen therapy is administered after operation using a variable performance device such as the MC mask. Using an oxygen flow rate of 10 litre/min Leigh (1974) described peaks of oxygen concentration of up to 95% shortly after the start of inspiration. It is, however, unlikely that this small fraction of the tidal volume will consistently ventilate the same regions of the lung. Grant, Jones and Hughes (1974) showed that at inspiratory flow rates of 0.4 litre/sec, gas inspired from the mouth shows only a small tendency to ventilate preferentially the dependent portions of the lung. Average ventilation per unit of lung volume at the base was about 1.2, and at the apex about 0.9. Bake and others (1974) reported similar findings, with a ratio of apex : base ventilation of 0.76 : 1, at an inspiratory flow rate of 0.51 litre/sec. Flow rates of this magnitude correspond to the phase of inspiration at which Leigh demonstrated peaks of inspired oxygen concentration. As these peak oxygen concentrations are attained well before the peak of inspiratory flow, the total volume of high concentration oxygen inspired will be low. Consequently the majority of the inspired gas will dilute this initial portion as at peak inspiratory flow the distribution of ventilation becomes more uniform, with all lung regions filling and emptying synchronously. I would certainly agree that it is rational that predictable concentrations of oxygen should be administered to any patient in need of oxygen therapy, but it is unlikely that oxygen toxicity will be a consequence of the use of a variable performance device.
BRITISH JOURNAL OF ANAESTHESIA
1340
J. A. H. DAVIES
Birmingham
regained during the period of the operation and the patient remained paralysed for 2 hr 40 min. Artificial ventilation with nitrous oxide and oxygen was therefore continued for this period of time, and when the patient regained sufficient muscle power to ventilate adequately, the trachea was extubated. No nerve stimulation tests were performed at this time; edrophonium and neostigmine were not administered. Subsequently, she made an uneventful recovery. Questioning revealed that she had been anaesthetized only for dental extractions in the past and she knew of no resulting complications. Biochemical investigations revealed the following results, compatible with abnormal pseudocholinesterase activity: Dibucaine no. 30 Fluoride no. 5 Chloride no. 70 Following this experience, I would be reluctant to follow Dr Baraka's advice. In future I shall refrain from administering a non-depolarizing muscle relaxant after suxamethonium, until signs of returning muscle tone have become apparent, regardless of the presence or absence of muscle fasciculations. JENNIFER M. HUNTER
Liverpool REFERENCES
Atkinson, R. S. (1971). Propanidid and blind nasal intubation. Anaesthesia, 26, 510. Bradburn, C. C. (1970). Severe hypotension following induction with propanidid. Br. J. Anaesth., 42, 362. Davies, J. A. H. (1968). Blind nasal intubation using doxapram hydrochloride. Br. J. Anaesth., 40, 361. (1972). Blind nasal intubation with propanidid. Br. J. Anaesth., 44, 528. Dundee, J. W., Assem, E. S. K., Gaston, J. M., Keilty, S. R., Sutton, J. A., Clarke, R. S. J., and Grainger, D. (1974). Sensitivity to intravenous anaesthetics: a report of three cases. Br. Med. J., 1, 63. Johns, G. (1970). Cardiac arrest following induction with propanidid. Br. J. Anaesth., 42, 74. Larard, D. G. (1970). Cardiac arrest following induction with propanidid. Br. J. Anaesth., 42, 652. Manz, R., and Fank, G. (1969). Zur Frage allergischer Reaktionen nach Epontol. Anaesthesist, 18, 223. Oyegunle, A. O. (1975). The use of propanidid for blind nasotracheal intubation. Br. J. Anaesth., 47, 379. Stovner, J., and Endresen, R. (1971). Repeated propanidid in cancer. Br. J. Anaesth., 43, 207. ABSENCE OF SUXAMETHONIUM FASCICULATIONS IN PATIENTS WITH ATYPICAL PSEUDOCHOLINESTERASE
Sir,—I would like to sound a note of caution after reading with interest Dr Baraka's letter regarding the absence of fasciculations in patients with abnormal pseudocholinesterase (Baraka, 1975). Recently, I anaesthetized a healthy, 32-year-old female for elective Caesarean section. Following pre-oxygenation, anaesthesia was induced with atropine 0.6 mg, methohexitone 100 mg and suxamethonium 100 mg i.v. Such marked, generalized fasciculations occurred that I commented to the theatre technician on the classic display! Tracheal intubation was performed without difficulty and the patient was ventilated artificially. Muscle tone was not
REFERENCE
Baraka, A. (1975). Absence of suxamethonium fasciculations in patients with atypical plasma cholinesterase. Br.J. Anaesth., 47, 419. Sir,—I read with interest the report of Dr Hunter on the generalized marked fasciculations which followed induction of anaesthesia with methohexitone and suxamethonium in a patient with atypical plasma cholinesterase activity. Such marked fasciculations can be attributed to the depolarizing activity of suxamethonium. However, this observation differs from our previous findings in five patients who were atypical homozygotes, and who did not show any fasciculations following the injection of suxamethonium (Baraka, 1975). Muscular excitatory phenomena following the induction of anaesthesia with an hypnotic-suxamethonium sequence may result from the central excitatory effect of the hypnotic or the peripheral depolarizing activity of the suxamethonium, or both. Induction of anaesthesia with methylated barbiturates, particularly in non-premedicated patients, can be associated with tremor, spontaneous involuntary muscle movements or hypertonus (Dundee, 1965). The patient reported by Dr Hunter was given methohexitone, and the marked excitatory phenomena observed may be related to this anaesthetic induction agent. ANIS BARAKA
Beirut, Lebanon REFERENCES
Baraka, A. (1975). Absence of suxamethonium fasciculations in patients with atypical plasma cholinesterase. Br.J. Anaesth., 47, 419. Dundee, J. W. (1965). Some effects of premedication on the induction characteristics of intravenous anaesthetics. Anaesthesia, 20, 299.
Downloaded from http://bja.oxfordjournals.org/ at University of Iowa Libraries/Serials Acquisitions on June 28, 2015
et al.j 1974). Nor would I care to recommend its use in all circumstances. For example, in certain cases of ankylosing spondylitis, trismus and carcinoma of the tongue the airway may be lost, never to be regained once general anaesthesia is induced. In such situations I would prefer to perform endotracheal intubation with the patient awake, and if unsuccessful proceed with an inhalation agent to induce the very lightest plane of anaesthesia before further attempts at blind nasal intubation. A surgeon, prepared to perform a tracheostomy if necessary, should be present during the induction of anaesthesia. In drawing attention to these considerations, my aim is not to discourage anaesthetists from practising this technique. Indeed, it is only familiarity with the technique of blind nasal intubation which enables the anaesthetist to confront difficult cases with confidence. This familiarity must come from constant practice with straightforward cases using well-established techniques or modifications such as that employing propanidid described by Dr Oyegunle and previously by both Atkinson (1971) and myself.
retained inside the swivel connector, making reconnection of the two impossible (fig. 1). This is particularly likely to occur if any lateral force is used to separate the tube and connector.
FIG. 1. The tube on the left has lost its sealing ring, which can be seen inside the swivel connector. A normal tube and connector are shown on the right for comparison. I understand that Portex Ltd are changing the construction of their tubes to obviate this problem, but until new tubes are introduced, I would suggest that both a spare tracheostomy tube and connector be present at the bedside of patients who are ventilated artificially. R.
J.
WARE
London BLIND NASAL INTUBATION
Sir,—I have read with interest the article on bund nasal intubation by Oyegunle (1975) in a recent issue of your Journal. It is to be hoped that further interest has been G. B. DRUMMOND aroused in this much neglected but valuable technique, Edinburgh and that more anaesthetists will be encouraged to acquire the necessary skill. REFERENCES There are several passages in the text of this article which Bake, B., Wood, L., Murphy, B., Macklem, P. T., and are so strikingly similar to passages in two articles on the Milic-Emili, J. (1974). Effect of inspiratory flowrate on same subject written by myself that I formed a strong regional distribution of inspired gas. J. Appl. Physiol., impression that I was reading my own words (Davies, 37,8. 1968, 1972). Dr Oyegunle was generous enough to Grant, B. J. B., Jones, H. A., and Hughes, J. M. B. (1974). acknowledge one of these publications but not the more Sequence of regional filling during a tidal breath in man. recent one concerned with a technique almost identical to J. Appl. Physiol., 37, 158. his own. The results achieved were also very similar. With Leigh, J. M. (1974). Oxygen therapy at ambient pressure; a single dose of propanidid he performed endotracheal in Scientific Foundations of Anaesthesia (eds. C. F. Scurr intubation in 33% of his patients at the first attempt, and S. A. Feldman), 2nd edn., p. 253. London: compared with 43% in my series. With up to three attempts Heinemann. he intubated 68%, compared with 75% in my series. (1975). Postoperative oxygen administration. Br. J. These small differences are probably of no significance, Anaesth., 47, 108. although it is possible that the slightly larger dose of propanidid (6-7 mg/kg body weight) given in my series A HAZARD OF PORTEX SOFT SEAL TRACHEOSTOMY TUBES produced greater hyperventilation which might account WITH SWIVEL CONNECTORS for the difference. Although propanidid has much to commend it, its use Sir,—Portex soft seal cuffed tracheostomy tubes are being used increasingly for ventilation of the patient with a carries with it certain dangers which should be balanced tracheostomy. I would like to draw attention to a problem against its advantages. Notice must be taken of the reports I have encountered several times when these tubes were of serious adverse reactions which have appeared in the used in combination with Portex swivel connectors. The literature (Manz and Fank, 1969; Bradburn, 1970; Larard, sealing ring on the p.v.c. tube became detached and was 1970; Johns, 1970; Stovner and Endresen, 1971; Dundee
Downloaded from http://bja.oxfordjournals.org/ at University of Iowa Libraries/Serials Acquisitions on June 28, 2015
Sir,—I would like to comment on the paper of Dr J. M. Leigh on postoperative oxygen therapy (Leigh, 1975) regarding the possibility of oxygen toxicity if oxygen therapy is administered after operation using a variable performance device such as the MC mask. Using an oxygen flow rate of 10 litre/min Leigh (1974) described peaks of oxygen concentration of up to 95% shortly after the start of inspiration. It is, however, unlikely that this small fraction of the tidal volume will consistently ventilate the same regions of the lung. Grant, Jones and Hughes (1974) showed that at inspiratory flow rates of 0.4 litre/sec, gas inspired from the mouth shows only a small tendency to ventilate preferentially the dependent portions of the lung. Average ventilation per unit of lung volume at the base was about 1.2, and at the apex about 0.9. Bake and others (1974) reported similar findings, with a ratio of apex : base ventilation of 0.76 : 1, at an inspiratory flow rate of 0.51 litre/sec. Flow rates of this magnitude correspond to the phase of inspiration at which Leigh demonstrated peaks of inspired oxygen concentration. As these peak oxygen concentrations are attained well before the peak of inspiratory flow, the total volume of high concentration oxygen inspired will be low. Consequently the majority of the inspired gas will dilute this initial portion as at peak inspiratory flow the distribution of ventilation becomes more uniform, with all lung regions filling and emptying synchronously. I would certainly agree that it is rational that predictable concentrations of oxygen should be administered to any patient in need of oxygen therapy, but it is unlikely that oxygen toxicity will be a consequence of the use of a variable performance device.
BRITISH JOURNAL OF ANAESTHESIA
1340
J. A. H. DAVIES
Birmingham
regained during the period of the operation and the patient remained paralysed for 2 hr 40 min. Artificial ventilation with nitrous oxide and oxygen was therefore continued for this period of time, and when the patient regained sufficient muscle power to ventilate adequately, the trachea was extubated. No nerve stimulation tests were performed at this time; edrophonium and neostigmine were not administered. Subsequently, she made an uneventful recovery. Questioning revealed that she had been anaesthetized only for dental extractions in the past and she knew of no resulting complications. Biochemical investigations revealed the following results, compatible with abnormal pseudocholinesterase activity: Dibucaine no. 30 Fluoride no. 5 Chloride no. 70 Following this experience, I would be reluctant to follow Dr Baraka's advice. In future I shall refrain from administering a non-depolarizing muscle relaxant after suxamethonium, until signs of returning muscle tone have become apparent, regardless of the presence or absence of muscle fasciculations. JENNIFER M. HUNTER
Liverpool REFERENCES
Atkinson, R. S. (1971). Propanidid and blind nasal intubation. Anaesthesia, 26, 510. Bradburn, C. C. (1970). Severe hypotension following induction with propanidid. Br. J. Anaesth., 42, 362. Davies, J. A. H. (1968). Blind nasal intubation using doxapram hydrochloride. Br. J. Anaesth., 40, 361. (1972). Blind nasal intubation with propanidid. Br. J. Anaesth., 44, 528. Dundee, J. W., Assem, E. S. K., Gaston, J. M., Keilty, S. R., Sutton, J. A., Clarke, R. S. J., and Grainger, D. (1974). Sensitivity to intravenous anaesthetics: a report of three cases. Br. Med. J., 1, 63. Johns, G. (1970). Cardiac arrest following induction with propanidid. Br. J. Anaesth., 42, 74. Larard, D. G. (1970). Cardiac arrest following induction with propanidid. Br. J. Anaesth., 42, 652. Manz, R., and Fank, G. (1969). Zur Frage allergischer Reaktionen nach Epontol. Anaesthesist, 18, 223. Oyegunle, A. O. (1975). The use of propanidid for blind nasotracheal intubation. Br. J. Anaesth., 47, 379. Stovner, J., and Endresen, R. (1971). Repeated propanidid in cancer. Br. J. Anaesth., 43, 207. ABSENCE OF SUXAMETHONIUM FASCICULATIONS IN PATIENTS WITH ATYPICAL PSEUDOCHOLINESTERASE
Sir,—I would like to sound a note of caution after reading with interest Dr Baraka's letter regarding the absence of fasciculations in patients with abnormal pseudocholinesterase (Baraka, 1975). Recently, I anaesthetized a healthy, 32-year-old female for elective Caesarean section. Following pre-oxygenation, anaesthesia was induced with atropine 0.6 mg, methohexitone 100 mg and suxamethonium 100 mg i.v. Such marked, generalized fasciculations occurred that I commented to the theatre technician on the classic display! Tracheal intubation was performed without difficulty and the patient was ventilated artificially. Muscle tone was not
REFERENCE
Baraka, A. (1975). Absence of suxamethonium fasciculations in patients with atypical plasma cholinesterase. Br.J. Anaesth., 47, 419. Sir,—I read with interest the report of Dr Hunter on the generalized marked fasciculations which followed induction of anaesthesia with methohexitone and suxamethonium in a patient with atypical plasma cholinesterase activity. Such marked fasciculations can be attributed to the depolarizing activity of suxamethonium. However, this observation differs from our previous findings in five patients who were atypical homozygotes, and who did not show any fasciculations following the injection of suxamethonium (Baraka, 1975). Muscular excitatory phenomena following the induction of anaesthesia with an hypnotic-suxamethonium sequence may result from the central excitatory effect of the hypnotic or the peripheral depolarizing activity of the suxamethonium, or both. Induction of anaesthesia with methylated barbiturates, particularly in non-premedicated patients, can be associated with tremor, spontaneous involuntary muscle movements or hypertonus (Dundee, 1965). The patient reported by Dr Hunter was given methohexitone, and the marked excitatory phenomena observed may be related to this anaesthetic induction agent. ANIS BARAKA
Beirut, Lebanon REFERENCES
Baraka, A. (1975). Absence of suxamethonium fasciculations in patients with atypical plasma cholinesterase. Br.J. Anaesth., 47, 419. Dundee, J. W. (1965). Some effects of premedication on the induction characteristics of intravenous anaesthetics. Anaesthesia, 20, 299.
Downloaded from http://bja.oxfordjournals.org/ at University of Iowa Libraries/Serials Acquisitions on June 28, 2015
et al.j 1974). Nor would I care to recommend its use in all circumstances. For example, in certain cases of ankylosing spondylitis, trismus and carcinoma of the tongue the airway may be lost, never to be regained once general anaesthesia is induced. In such situations I would prefer to perform endotracheal intubation with the patient awake, and if unsuccessful proceed with an inhalation agent to induce the very lightest plane of anaesthesia before further attempts at blind nasal intubation. A surgeon, prepared to perform a tracheostomy if necessary, should be present during the induction of anaesthesia. In drawing attention to these considerations, my aim is not to discourage anaesthetists from practising this technique. Indeed, it is only familiarity with the technique of blind nasal intubation which enables the anaesthetist to confront difficult cases with confidence. This familiarity must come from constant practice with straightforward cases using well-established techniques or modifications such as that employing propanidid described by Dr Oyegunle and previously by both Atkinson (1971) and myself.
