Long‐Term Treatment of Two Patients with Respiratory Insufficiency with IPPV/PEEP and HFPPV/PEEP

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Abstract
The respiratory centre is a multi‐input system and positive‐pressure ventilation is known to interfere with respiratory control mechanisms. Further, in intermittent positive‐pressure ventilation (IPPV) the ventilatory pattern produced by the ventilator and the lung systems is known to influence pulmonary and cardiovascular functions. High‐frequency positive‐pressure ventilation (HFPPV) has been shown to eliminate respiration‐synchronous variations in blood pressure and blood flow, and at frequencies of 60 per min or more spontaneous breathing ceases almost instantaneously if adequate alveolar ventilation and arterial oxygenation are achieved. However, activation of other inputs to the respiratory centre, e.g. chemo‐receptor inputs, can induce spontaneous respiration during HFPPV. Consequently the balance between excitatory and inhibitory afferents is decisive for the patient's spontaneous respiratory efforts (discoordination) during artificial ventilation.The balance between excitatory and inhibitory mechanisms during artificial ventilation is illustrated in two patients with pulmonary insufficiency. Both patients exhibited spontaneous respiratory efforts (discoordination) during ventilation with a “conventional” type of respirator (ventilatory frequency 20 per min) despite adequate alveolar ventilation, adequate arterial oxygenation and administration of sedatives and respiratory depressants. During HFPPV, at ventilatory frequencies of 60 per min or more, there was an inhibitory effect on spontaneous respiration, and with adequate alveolar ventilation and adequate arterial oxygenation (obtained at lower inspiratory airway pressures than with a “conventional” type of ventilation) it was possible to discontinue sedatives and respiratory depressants without discoordination occurring between the patient and the ventilator. However, in one of the patients, with decreasing pulmonary compliance and diminishing arterial oxygenation (due to increasing intrapulmonary shunting and cardiac decompensation), spontaneous respiratory efforts were present despite high ventilatory frequencies and administration of sedatives and respiratory depressants.From experimental investigations reported elsewhere, this study in two patients and similar experience in other patients, it seems that it is easier to adapt a patient to a ventilator which has a negligible compression volume and which is set at a high frequency.

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