Optimizing ventilatory settings using pulse oximetry in the transition between life and death

Abstract

In the patient with catastrophic lung disease intra- and extrapulmonary factors interact to determine the O₂-delivery to the peripheral lifethreathened organs. The therapeutic strategy will take into account both settings on the ventilator that are not harmful to the patient i.e. avoiding high peak airway pressures and high inspired oxygen fractions and circulatory support keeping the cardiac output adequate. Usually the arterial blood gases are frequently monitored as parameters determining optimal therapy. Recently pulse oximetry has been suggested as a noninvasive continuous monitoring method. It could be looked upon as an indicator and monitor of both ventilatory and circulatory optimality, because the parameter tells what “the sensor sees.” This might not be identical to the “true arterial saturation”, but it can be argued that this does not matter as long as the trend observed is useful in therapeutic decision making.

In this study 25 patients with catastrophic lung disease i.e. a) panlobar alveolar infiltrates, b) a PaO₂ >7.00 kPa with an FIO₂ > 0.8 with 15 cm H₂O PEEP and a cardiac index above 3.5 L/min/m² and c) an effective compliance below 25 ml/cm H₂O were studied and ventilatory and circulatory adjustments were made in order to reduce peak airway pressure to below 50 cm H₂O and the FIO₂ to below 0.6. Fourteen patients were randomised to monitoring with pulse oximetry and eleven to conventional arterial blood gas analysis. Using pulse oximetry the median time for optimization was 45 min with a range of 20–120, without pulse oximetry the median time was 95 min with range 60–240, p <0.05.

It is concluded that pulse oximetry is a fast, reliable index of peripheral O₂-delivery and can be regarded a “new parameter” in optimizing ventilatory strategy.

Key-words:

• Acute respiratory failure
• mechanical ventilation
• ARDS