416

Correspondence

case and the photographic departments of Queen Mary’s Hospital for Children and Mount Vernon Hospital and to Mr R. Hook for drawing Fig. 3.

Mount Vernon Hospital

I. MCLELLAN

Northwood, Middlesex HA6 2RN References 1. ROLLASON, W.N. (1956) Asphyxia due to faulty apparatus. British Medical Journal, 2,658. 2. FORRESTER, A. (1959) Mishaps in anaesthesia. Anaesthesia, 14, 388. 3. OSTERUD, A. (1974) Dangerous fault in disposable connector for orotracheal tube. BritishJournalof Anaesthesia, 46, 952. 4. MACINTRYRE, I.M. (1968) An unexpected source of respiratory obstruction during general anaesthesia. Anaesthesia, 23,657. 5. Ross, E.D.T. (1974) Misuse of the plug of Cobb’s suction union. Anaesthesia, 29,66. 6. SHAW, E.A. (1971) Airway obstruction. Anaesthesia, 26,368.

CPAP after open heart surgery The system described by Crew, Wall & Varkonyi (Anaesthesia, 1975, 30, 67) for applying continuous positive airway pressure (CPAP)’ is in many respects an attractive one. My intention in writing is to point out, for those who have not yet had occasion to use CPAP after open heart surgery, certain aspects which warrent consideration CPAP systems which develop the desired airway pressure by having the gas outlet submerged under a height of water are inherently noisy, and in my experience are not well tolerated by older children (from say 9 months onwards). Possible solutions are to use a larger reservoir bag and a constant, though adjustable, resistance instead of the bubbler, or to more heavily sedate the child, which unfortunately negates one of the advantages of CPAP. Effective auscultation of the lungs is also impossible with a bubble system since the breath sounds are obscured by loud transmitted bubbling noises. It should be appreciated that in the management of many patients on CPAP, the distribution and the quality of vesicular breath sounds and the presence or absence of crepitations and various noises from the airways, are of considerable clinical value. CPAP is used in infants and children after open heart surgery for a variety of reasons.z Often, especially in the younger age groups, it provides a safe controlled transition from an ‘artificially ventilated-intubated’ state to a ‘spontaneously breathing-xtubated’ state. Sometimes, its use enables a patient who could not otherwise be taken off artificial ventilation, to resume spontaneous respiration. The choice of the optimal CPAP pressure for patients in this category, and their subsequent management, is not as simple as is often suggested. Assessment of the apparent work involved in breathing, the close monitoring of the necessary cardiovascular parameters, and the measurement of arterial oxygen and carbon dioxide tensions (PO, andPco,) especially when the patient is first put on CPAP, are all important. Auscultation of the lungs, at the CPAP pressure being used, and when a change in pressure is being made, provides further- and very relevant-information. An alternative method of applying CPAP has been described by myself and my colleague^,^ and has been in effective use for over 2 years. It is virtually silent and was designed to simplify medical and nursing care. Properly managed it is as safe as any non-bubbling system: the high and low pressure warning alarms are not essential but serve as an additional safety factor. Anaesthetic Department, Brompton Hospital, London S. W.3

J. PFITZNER

Correspondence

417

References 1. GREGORY, G.A., KITTERMAN, J.A., PHIBBS,R.H., TOOLEY, W.H. & HAMILTON, W.K. (1971) Treatment of the idiopathic respiratory-distresssyndrome with continuous positive airway pressure. New England Journal of Medicine, 284, 1333. 2. STEWART, S., EDMUNDS, L.H., KIRKLIN, J.W. & ALLARDE, R.R. (1973) Spontaneousbreathing with continuous positive airway pressure after open intra cardiac operations in infants. Journal of Thoracic and Cardiovascular Surgery, 65, 37. 3. PFITZNER, J., BRANTHWAITE, M.A., ENGLISH, I.C.W. & SHINEBOURNE, E.A. (1974) Continuous positive airway pressure: A new system. Anaesthesia, 29, 326,

.4 reply Thank you for the opportunity to add to the discussion of our paper. It is necessary to briefly discontinue the underwater blow-off while the lung fields are being auscultated. We have not found this to be a practical disadvantage and consider that the changes in breath sounds on altering the airway pressure are too indeterminate to be of practical value. The clinical advantages of CPAP develop over minutes or hours rather than seconds, and, although the regression occurs more rapidly when the airway pressure is reduced, immediate auscultation at ambient pressure has proved to be satisfactory. We have no evidence that the sound of the underwater blow-off has been in any way considered significant by any age group of patient up to adult. With a mechanical expiratory resistor, the fresh gas flow should be large compared to the peak inspiratory flow of the patient, otherwise a significant fall in airway pressure occurs with a theoretical increase in the work of breathing. We have noted that a fluctuating airway pressure is not tolerated so well as a continuous airway pressure in the post cardiac surgery patient. A large elastic reservoir bag will help sustain the airway pressures during peak inspiration as Dr Pfitzner suggests. In adults peak inspiratory flows in excess of 30 litreslminute are common, and even in small children 10-1 5 litres/minute are frequently noted. With an underwater blow-off it is necessary to equal these flows in order to sustain a constant airway pressure, with a mechanical resistor these flows must be appreciably exceeded. I n practice we have found such large fresh gas flows to be unmanagable as these are beyond the range of most available hospital flow meters. At such high flows, should condensed water in the circuit reach the resistor, a marked increase in airway pressure will occur. Leeds Regional Thoracic Surgical Centre, Killingbeck Hospital, York Road, Leeds LS14 6UQ

A. D. CREW

Letter: CPAP after open heart surgery.

416 Correspondence case and the photographic departments of Queen Mary’s Hospital for Children and Mount Vernon Hospital and to Mr R. Hook for drawi...
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