Abstract â–¡ 65

Additional inspired oxygen is given to patients with hypoxaemia to minimise its adverse effects, including (i) breathlessness; (ii) increased airway resistance and bronchoconstriction; (iii) pulmonary hypertension and right heart failure; (iv) cyanotic-apnoeic episodes; (v) poor weight gain. Oxygen therapy may reduce the risks both sudden, severe hypoxaemia and, of sudden death in chronic respiratory conditions. The decision to commence additional inspired oxygen has significant care and resource implications, and is in part dependent upon how oxygenation is assessed, and what SpO2 levels are considered important to treat.

Assessment of oxygenation is best made using pulse oximetry, but this technique is subject to errors. For example, averaging varies between pulse oximeters and can result in normal episodic desaturations (to 80%) that occur in periodic breathing giving falsely low baseline values. Similarly, it will underestimate the degree of desaturation in major hypoxaemic episodes. When clinical observations record borderline levels of SpO2 (93-96%), an 8-12 hour recording of Sp02, pulse waveform (to confirm adequate pulse detection) and breathing movements (to relate desaturations to apnoeic pauses) helps guide decisions on starting long term oxygen therapy. Interpretation of such recordings requires knowledge of normal values for baseline and episodic desaturation for the particular recording system used.

Oxygen therapy is adjusted to ensure normal baseline levels of SpO2 (*95%). Current pulse oximetry does not provide adequate measurements during periods when hypoxaemia is likely to occur: eg during crying, nappy changes and with vigorous body movements. Transcutaneous pO2 provides lower false alarms and more stable measurements for home use, but may be superseded by improvements in oximetry technology. Home monitoring of oxygenation should but undertaken to detect early the increased oxygen requirement with respiratory infections, the accidental discontinuation of the oxygen, or sudden, major disaturations.