IPPVadjusting the ventilator

Ventilator adjustments are usually made in response to blood gases, pulse oximetry or capnography, patient agitation or discomfort, or during weaning. 'Migration' of the endotracheal tube, either distally to the carina or beyond, or proximally such that the cuff is at vocal cord level, may result in agitation, excess coughing and a deterioration in blood gases. This, and tube obstruction, should be considered and rectified before changing ventilator or sedation dose settings.

The choice of ventilator mode depends upon the level of consciousness, the number of spontaneous breaths being taken, and the blood gas values. The spontaneously breathing patient can usually cope adequately with pressure support ventilation alone. However, on occasion, a few intermittent mandatory breaths (SIMV) may be necessary to assist gas exchange or slow an excessive spontaneous rate. The paralysed or heavily sedated patient will require mandatory breaths, either volume- or pressure-controlled.

The order of change will be dictated by the severity of respiratory failure and individual operator preference. Earlier use of increased PEEP is advocated to recruit collapsed alveoli and thus improve oxygenation in severe respiratory failure.

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