Canadian Journal of Anesthesia, Vol 13, 476-494, Copyright © 1966 by Canadian Anesthesiologists' Society

Respiratory Distress Syndrome of the Newborn: A Critique of Current Management of the Vetilation-Oxygenation Problem

¹ Department of Anaesthesia, The Children's Hospital, Winnipeg, Manitoba, and University of Manitoba

The anaesthetist is usually a consultant in the management of the respiratory distress syndrome of the newborn (R.D.S.). Although he may not tell the paediatrician how to manage the whole condition, some criticisms of present practices in respiratory care are in order.

Anaesthetic literature is currently dealing in detail with problems relating to alveolar-arterial oxygen differences, and paediatrician and anaesthetist are losing an opportunity to learn from one another.

Some of the pertinent literature and original observations by the authors are described, relevant to changes in normal arterial blood gases in the first few days of life. Most marked changes occur in the first 24 hours, mainly a sharp rise in oxygen tensions and a fall in carbon dioxide tensions. True right-to-left shunting at 24 hours of life in the normal infant is around 20 to 25 per cent, compared with less than 5 per cent in the adult. The authors' findings suggest values at three days of life which are not significantly different from those in healthy older children. Apart from increased alveolar-arterial oxygen difference the lung of the newborn compares more favourably than was previously believed with that of the adult. Details of a preferred technique of arterial puncture are given.

It is easy to diagnose R.D.S. but usually impossible to give a prognosis from clinical observation alone. It is useful to have a classification of degrees of severity. This has been done by measurement of shunting, or more simply by arterial oxygen tensions reached with 100 per cent inspired oxygen. Both of these methods facilitate the assessment of various regimes of management against expected mortality.

The criticisms by anaesthetists of current treatment fall into three groups:

1. The accepted criteria for the use of artificial ventilation are extreme, and can only be explained, if not justified, by the severe complications described as following endotracheal intubation and ventilator care.

2. The requirements of a ventilator in these circumstances, viz. high pressures, constant flow, rapid cycling, and low, controllable tidal volumes, are only approached by the Engstrom; but even the Bird and Bennett tend to be used below their capabilities. Thus one finds them frequently out of phase with spontaneous respiration. There is a dominant fear in the minds of some paediatricians of using too much pressure and of hyperventilation. This often results in totally inadequate function. High pressures, often 40 cm. H₂O or more, and ideally constant high flows during inspiration, are needed to ventilate through infant-size endotracheal tubes. Wide variations in arterial carbon dioxide tensions are tolerable provided that good oxygenation is achieved.

3. It is fundamentally a better approach to look for a unified concept of pathology and management than to treat fully developed respiratory and metabolic acidosis. The answer may lie in promoting better pulmonary blood flow early in the disease. The hope that drugs might be found to do this has not yet been fulfilled; oxygen is a potent pulmonary vasodilator.

If R.D.S. is merely one sign of reaction of an immature vascular bed, then some thought might be given to improving tissue blood flow and oxygenation by drugs such as hydrocortisone, which have been extremely effective on the peripheral circulation of shocked animals and of man.

There is some suggestion that negative pressure respirators of the tank type may give better oxygenation than intermittent positive pressure in R.D.S., even when ventilation is not as good. Some of the success may be due to simpler operation, but there is also the possibility, still unsupported by concrete evidence, that negative pressure results in better matching of ventilation to perfusion.

It is suggested that specifically designed miniature monitors may be more useful for the nurses than cumbersome electrocardioscopes.

The anaesthetist's main problems as a consultant are to establish the best possible respirator care in an atmosphere where ventilators are usually reserved for the moribund; to exchange ideas with the neonatologists, to educate nurses in premature units in respiratory care with ventilators, and to co-ordinate the premature intensive care unit with the general intensive care unit in the hospital.

Note:

Supported in part by Dominion-Provincial Grant No. 606-7-92.