VENTILATION IN ARDS AND ASTHMA - THE OPTIMAL BLOOD-GAS VALUES

Artificial ventilation of patients with acute respiratory diseases, i. e. ARDS and severe asthma, may involve the risk of pulmonary oxygen to xicity as well as volutrauma. The relationship between ventilator trea tment and volutrauma suggests that only in patients with normal lungs the aim of ventilator treatment should be an arterial carbon dioxide t ension and pH within the normal ranges. In patients suffering from a l ung disease the clinical target must be based not only upon the arteri al blood gases but also upon airway pressure and respiratory tidal vol ume. Thus during artificial ventilation of a patient with an acute pul monary disease the following arterial pH and pCO2 optima are proposed: pH 7.35, with a range from 7.1 to 7.4; pCO2 is related to pH but an a cceptable range is 5-12 kPa. The lowest acceptable fraction of inspire d oxygen and thereby the safe lower level of arterial pO2 for an indiv idual patient depends on many factors. The lower limit may be about 3 kPa, but the arterial pO2 should not be evaluated as an isolated param eter. It is related to the general oxygen transport capability of arte rial blood, extractable oxygen, cardiac output and the microcirculatio n.