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

Study design: A pilot case control study of the acid-base and electrolyte s tatus in 30 long-term ventilator-dependent (LTVD) and 30 self ventilating p ersons with tetraplegia. Objectives: To assess the extent of respiratory alkalosis and screen for as sociated hypokalaemia, hypomagnesaemia and/or hypophosphataemia. Setting: Medically stable persons with tetraplegia under the long-term care of the Southport Spinal Injuries Centre, England. Methods: Blood gases and electrolytes were sampled from 30 control patients with tetraplegia and from 30 patients having been LTVD for more than 12 mo nths. Results: All the blood gas measurements in the LTVD group lay outside both the reference range and the 95% confidence intervals (CI) of the control gr oup: pH 7.46 (0.06); PCO2 3.46 (1.1) kPa: bicarbonate 18.3 (3.8) and base e xcess -3.2 (2.8) mmol/l; PO2 13.8 (2.8) kPa (means and standard deviations) . The serum potassium, magnesium, phosphate, and sodium means lay within th e reference ranges but the potassium, phosphate and calcium were at or belo w the 95% Cl of the control values. One patient on part-time ventilatory su pport having less bicarbonate compensation had low serum electrolytes durin g ventilation. Conclusion: There was no evidence of biochemical jeopardy from long-term me chanical hyperventilation although acutely administered hyperventilation ha s the potential to cause falls in serum potassium, magnesium and phosphate and so caution should be exercised in part-time ventilated persons. The ful l range of electrolytes should be assayed during stabilisation in LTVD and periodically thereafter. Hyperventilation helps to maintain good oxygenatio n in LTVD persons with paralysis and normal lungs. Sponsorship: None.