Читать книгу Respiratory Medicine - Stephen J. Bourke - Страница 97

The primary disturbance is generally an increase in acid. This has an effect on the equation

Figure 3.10 Acid/base disturbances. The oval indicates the normal position, the shaded areas indicate the directions of observed ‘pure’ or uncomplicated disturbances of acid/base balance. Bicarbonate levels are omitted for clarity. Letters (a)–(d) are referred to in the section on mixed disturbances.

H⁺ + HCO₃ ⁻ ⇌ H₂O + CO₂, pushing it to the right. The CO₂ produced is removed by increased ventilation and the net result is a lowering of plasma bicarbonate. In practice, the fall in pH causes further respiratory stimulation, so that CO₂ is promptly blown off, and the pH changes are therefore much less dramatic than they would have been. The arterial point moves in the direction indicated in Fig. 3.10. This respiratory compensation is an inevitable accompaniment of metabolic acidosis – acute and chronic – unless there is some other factor limiting ventilatory function or responsiveness.

This pattern is seen in diabetic ketoacidosis, renal tubular acidosis, acute circulatory failure, sepsis and other forms of lactic acidosis.