Respiratory alkalosis and associated electrolytes in long-term ventilator dependent persons with tetraplegia

A pilot case control study of the acid-base and electrolyte status in 30 long-term ventilator-dependent (LTVD) and 30 self ventilating persons with tetraplegia.

To assess the extent of respiratory alkalosis and screen for associated hypokalaemia, hypomagnesaemia and/or hypophosphataemia.

Medically stable persons with tetraplegia under the long-term care of the Southport Spinal Injuries Centre, England.

Blood gases and electrolytes were sampled from 30 control patients with tetraplegia and from 30 patients having been LTVD for more than 12 months.

All the blood gas measurements in the LTVD group lay outside both the reference range and the 95% confidence intervals (CI) of the control group: pH 7.46 (0.06); PCO(2) 3.46 (1.1) kPa; bicarbonate 18.3 (3.8) and base excess -3.2 (2.8) mmol/l; PO(2) 13.8 (2.8) kPa (means and standard deviations). The serum potassium, magnesium, phosphate, and sodium means lay within the reference ranges but the potassium, phosphate and calcium were at or below the 95% CI of the control values. One patient on part-time ventilatory support having less bicarbonate compensation had low serum electrolytes during ventilation.

There was no evidence of biochemical jeopardy from long-term mechanical hyperventilation although acutely administered hyperventilation has the potential to cause falls in serum potassium, magnesium and phosphate and so caution should be exercised in part-time ventilated persons. The full range of electrolytes should be assayed during stabilisation in LTVD and periodically thereafter. Hyperventilation helps to maintain good oxygenation in LTVD persons with paralysis and normal lungs.

None.