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Clinical Review ABC of intensive care

Respiratory support

BMJ 1999; 318 doi: (Published 19 June 1999) Cite this as: BMJ 1999;318:1674
  1. Maire P Shelly,
  2. Peter Nightingale

    Most patients admitted to intensive care require some form of respiratory support. This is usually because of hypoxaemia or ventilatory failure, or both. The support offered ranges from oxygen therapy by face mask, through non-invasive techniques such as continuous positive airways pressure, to full ventilatory support with endotracheal intubation.

    Oxygen masks and nasal cannula

    Oxygen therapy

    Oxygen is given to treat hypoxaemia. Patients should initially be given a high concentration. The amount can then be adjusted according to the results of pulse oximetry and arterial blood gas analysis. The dangers of reducing hypoxic drive have been overemphasised; hypoxaemia is more dangerous than hypercapnia. The theoretical dangers of oxygen toxicity are unimportant if the patient ishypoxaemic.

    Continuous positive airways pressure requires a tight fitting mask and appropriate valve and breathing system

    Oxygen is usually given by face mask, although nasal prongs or cannulas may be better tolerated. A fixed performance, high flow, air entrainment mask can provide a known fractional inspired oxygen concentration (FiO2) within the range 0.24-0.60. The fractional inspired oxygen concentration is not known with the more common variable performance masks. The maximum concentration is 0.6 unless a reservoir bag is added to the mask.

    Non-invasive respiratory support

    If the patient remains hypoxaemic on high flow oxygen (15 l/min) continuous positive airways pressure (CPAP) may be used. The technique improves oxygenation by recruiting underventilated alveoli and so is most successful in clinical situations where alveoli are readily recruited, such as acute pulmonary oedema and postoperative atelectasis. It is also helpful in immunocompromised patients with pneumonia. As intubation is avoided the risks of nosocomial pneumonia are reduced. The continuous positive airways pressure mask often becomes uncomfortable and gastric distension may occur. Patients must therefore be cooperative, able to protect their airway, and have the strength to breathe spontaneously and cough effectively.

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