Читать книгу Respiratory Medicine - Stephen J. Bourke - Страница 99

Mixed respiratory and metabolic disturbances are common. There are usually a number of possible explanations, so it is essential to consider all the clinical details before interpreting the acid/base data. Fig. 3.10 shows the situations that may arise in complex acid/base disturbances.

 Fig. 3.10a (low pH, normal PCO2, low bicarbonate) indicates a mixed metabolic and respiratory acidosis. The metabolic disturbance is perhaps obvious and the respiratory component can be deduced, as the PCO2 is higher than might have been suspected had this been a pure metabolic problem. This pattern could arise in a number of different clinical scenarios, such as a patient with acute severe pulmonary oedema with low cardiac output and ventilatory compromise or a patient in renal failure given a narcotic sedative suppressing ventilatory response to acidosis. Blood gas results should be interpreted in light of clinical data.

 Fig. 3.10b could represent the situation soon after a cardiac arrest, where severe lactic acidosis exists and ventilation has been insufficient.

 Fig. 3.10c could represent the situation in severe aspirin poisoning, where aspirin‐induced hyperventilation has been complicated by aspirin‐induced metabolic acidosis.

 Fig. 3.10d could represent the situation in an individual with chronic ventilatory failure as a result of COPD who is stimulated to increase ventilation by a pulmonary embolism.