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HYPERVENTILATION, BRAIN DAMAGE AND FLICKER
'448
BRITISH JOURNAL OF ANAESTHESIA Labelling. The metal cylinder is painted blue and carries a label stating the name of the gas. In addition, the name of the gas or the symbol "N.O' is stencilled in paint on the shoulder of the cylinder. Action and Use. General anaesthetic. EDITOR'S NOTE. The British Pharmacopoeia edition of 1958 differs from the above only in the omission of the last Use.
Footnote. Appendix III is published with the kind permission of the General Medical CounciL The British Pnarmacopoeial Commission is at present actively engaged in improving the present specification. One of the improvements likely to be introduced is a Saltzmantype method for control of combined nitric oxide and nitrogen dioxide content The level at which these contaminants will be controlled has yet to be confirmed but a suggestion that the value be 10 v.pjn. is bting considered.
CORRESPONDENCE A NEONATAL VENTILATOR
HYPERVENTILATION, BRATN DAMAGE AND FUCKER
Sir,—Increased interest in mechanical ventilation in the neonatal period has led to the appearance of several new ventilators, but as yet there is no ideal solution to the requirements of this age group. The Adelaide ventilator (Kenny and Lewis, 1960) has been redesigned to meet the requirements for neonatal use. The bellows are powered from a constant-speed electric motor by means of a cam-andlcver system. A range of easily selected cams is provided to allow choice of respiratory pattern according to patients' requirements. The speed from the "flameproof" motor is modified by a variable-speed gearbox to give a respiratory rate from 12 to 70 b.pjn. Bellows travel controls the tidal volume (providing a range of 10 to 300 ml with standard children's bellows and other ranges available as required). Pressures from —5 to +80 cm H,O are available and there is a positive pressure release valve which may be set as required. A hot water humidifier (within the cabinet) is provided with duplicate thermostats and a warning light to protect against overheating if the control thermostat should fail. A mechanically operated valve is used with the non-rebreathing circuit. This electrically powered ventilator offers intermittent positive, or positive-negative ventilation on closed or non-rebreathing circuits. (A second bellows is used for negative phase on the non-rebreathing circuit) Anaesthetic gases or room air, with or without added oxygen, may be used and with air the machine is independent of any compressed gas source. A bacterial filter may be fitted to the inspiratory valve if required. M.
A.
LEWIS
Belfast REFERENCE
Kenny, S. H., and Lewis, M. A. (1960). The Adelaide respirator. Brit. J. Anaesth., 32, 444.
Sir,—Despite the three-month delay in arrival of the November 1966 journal, we cannot ignore the aspersions cast by Whitwam and colleagues (Brit. J. Anaesth., 38, 846) and are most intrigued by the emotional way in which they have tried to "cast doubt on the validity of (our) findings"—and this without supporting data from comparable studies. It is not possible to compare young and fit conscious volunteers observed only during the period of hyperventilation with our group of patients requiring operation under general anaesthesia studied for several days postopera lively. It appears to us that Whitwam and his colleagues did not fully understand flicker fusion and Berg's test (as their criticism of our control data indicates). A more diligent search of the literature would have revealed that three of Berg's controls showed a 2-3-day depression (Berg, 1958). If we were now to criticize our own paper it would be to express regret that arterial blood gases could not be readily obtained by a direct method at that time. The degree of hyperventilation obtained and the presence or absence of atelectasis or shunting would then be documented. Observed effects (no matter how interpreted) which last for 1 to 3 days postoperatively are not insignificant findings. GERALD D. ALLEN LUCIEN E. MOBKIS
Seattle, Washington REFERENCES
Allen, G. D., and Morris, L. E. (1962). Central nervous system effects of hyperventilation during anaesthesia. Brit. J. Anaesth., 34, 296. Berg, O. (1958). Flicker fusion in cerebral hypoxia. Acta psychial. scand., 33, 21.
Printed in Great Britain by John Sherratt A S o n Ltd.. Park Road. Altrlnchara
Downloaded from http://bja.oxfordjournals.org/ at University of Michigan on June 26, 2015
phosphorus pmtoxide; then pass it through a tube containing iodine pentoxide (previously dried at 200") maintained at a temperature of 120°, absorbing the liberated iodine in potassium iodide solution. Sweep out the apparatus by passing through it 5000 ml. of air free from carbon monoxide. Titrate the iodine with N/500 sodium thiosulphate, and from the amount used subtract the amount required in a similar experiment, in which 5000 mL of air free from carbon monoxide is used. Each mL of N/SOO sodium thiosulphate is equivalent to 0.112 ml. of CO at normal temperature and pressure. Water vapour and carbon dioxide. Pass a measured quantity successively through absorption tubes containing (a) phosphorus pentoxide and (b) soda lime. The increase in weight of the tube (a) does not exceed the equivalent of 2 mg. per 1000 ml. of gas at normal temperature and pressure, and the increase in weight of tube (b) does not exceed the equivalent of 0.5 mg. per 1000 mL of gas at normal temperature and pressure, both the initial and final weighings of the absorption tubes being made when the air in them has been displaced by nitrous oxide. Assay. Cool a measured volume in liquid oxygen in a suitable apparatus. Not less than 99.0 per cent v/v is condensed.
BRITISH JOURNAL OF ANAESTHESIA Labelling. The metal cylinder is painted blue and carries a label stating the name of the gas. In addition, the name of the gas or the symbol "N.O' is stencilled in paint on the shoulder of the cylinder. Action and Use. General anaesthetic. EDITOR'S NOTE. The British Pharmacopoeia edition of 1958 differs from the above only in the omission of the last Use.
Footnote. Appendix III is published with the kind permission of the General Medical CounciL The British Pnarmacopoeial Commission is at present actively engaged in improving the present specification. One of the improvements likely to be introduced is a Saltzmantype method for control of combined nitric oxide and nitrogen dioxide content The level at which these contaminants will be controlled has yet to be confirmed but a suggestion that the value be 10 v.pjn. is bting considered.
CORRESPONDENCE A NEONATAL VENTILATOR
HYPERVENTILATION, BRATN DAMAGE AND FUCKER
Sir,—Increased interest in mechanical ventilation in the neonatal period has led to the appearance of several new ventilators, but as yet there is no ideal solution to the requirements of this age group. The Adelaide ventilator (Kenny and Lewis, 1960) has been redesigned to meet the requirements for neonatal use. The bellows are powered from a constant-speed electric motor by means of a cam-andlcver system. A range of easily selected cams is provided to allow choice of respiratory pattern according to patients' requirements. The speed from the "flameproof" motor is modified by a variable-speed gearbox to give a respiratory rate from 12 to 70 b.pjn. Bellows travel controls the tidal volume (providing a range of 10 to 300 ml with standard children's bellows and other ranges available as required). Pressures from —5 to +80 cm H,O are available and there is a positive pressure release valve which may be set as required. A hot water humidifier (within the cabinet) is provided with duplicate thermostats and a warning light to protect against overheating if the control thermostat should fail. A mechanically operated valve is used with the non-rebreathing circuit. This electrically powered ventilator offers intermittent positive, or positive-negative ventilation on closed or non-rebreathing circuits. (A second bellows is used for negative phase on the non-rebreathing circuit) Anaesthetic gases or room air, with or without added oxygen, may be used and with air the machine is independent of any compressed gas source. A bacterial filter may be fitted to the inspiratory valve if required. M.
A.
LEWIS
Belfast REFERENCE
Kenny, S. H., and Lewis, M. A. (1960). The Adelaide respirator. Brit. J. Anaesth., 32, 444.
Sir,—Despite the three-month delay in arrival of the November 1966 journal, we cannot ignore the aspersions cast by Whitwam and colleagues (Brit. J. Anaesth., 38, 846) and are most intrigued by the emotional way in which they have tried to "cast doubt on the validity of (our) findings"—and this without supporting data from comparable studies. It is not possible to compare young and fit conscious volunteers observed only during the period of hyperventilation with our group of patients requiring operation under general anaesthesia studied for several days postopera lively. It appears to us that Whitwam and his colleagues did not fully understand flicker fusion and Berg's test (as their criticism of our control data indicates). A more diligent search of the literature would have revealed that three of Berg's controls showed a 2-3-day depression (Berg, 1958). If we were now to criticize our own paper it would be to express regret that arterial blood gases could not be readily obtained by a direct method at that time. The degree of hyperventilation obtained and the presence or absence of atelectasis or shunting would then be documented. Observed effects (no matter how interpreted) which last for 1 to 3 days postoperatively are not insignificant findings. GERALD D. ALLEN LUCIEN E. MOBKIS
Seattle, Washington REFERENCES
Allen, G. D., and Morris, L. E. (1962). Central nervous system effects of hyperventilation during anaesthesia. Brit. J. Anaesth., 34, 296. Berg, O. (1958). Flicker fusion in cerebral hypoxia. Acta psychial. scand., 33, 21.
Printed in Great Britain by John Sherratt A S o n Ltd.. Park Road. Altrlnchara
Downloaded from http://bja.oxfordjournals.org/ at University of Michigan on June 26, 2015
phosphorus pmtoxide; then pass it through a tube containing iodine pentoxide (previously dried at 200") maintained at a temperature of 120°, absorbing the liberated iodine in potassium iodide solution. Sweep out the apparatus by passing through it 5000 ml. of air free from carbon monoxide. Titrate the iodine with N/500 sodium thiosulphate, and from the amount used subtract the amount required in a similar experiment, in which 5000 mL of air free from carbon monoxide is used. Each mL of N/SOO sodium thiosulphate is equivalent to 0.112 ml. of CO at normal temperature and pressure. Water vapour and carbon dioxide. Pass a measured quantity successively through absorption tubes containing (a) phosphorus pentoxide and (b) soda lime. The increase in weight of the tube (a) does not exceed the equivalent of 2 mg. per 1000 ml. of gas at normal temperature and pressure, and the increase in weight of tube (b) does not exceed the equivalent of 0.5 mg. per 1000 mL of gas at normal temperature and pressure, both the initial and final weighings of the absorption tubes being made when the air in them has been displaced by nitrous oxide. Assay. Cool a measured volume in liquid oxygen in a suitable apparatus. Not less than 99.0 per cent v/v is condensed.