Saline-induced hyperchloraemic metabolic acidosis: an unrecognised phenomenon among medical staff?

Introduction

Hyperchloraemic acidosis is well recognised within critical care, is implicated in the development of organ dysfunction and is an important consequence of administration of large volumes of chloride-containing intravenous (i.v.) fluid, such as normal (0.9%) saline [1, 2]. Within most hospitals, junior medical staff with differing levels of experience prescribe the majority of i.v. fluid therapy.

Aims and methods

A clinical scenario was used to assess current knowledge among medical staff regarding i.v. fluid therapy. 'An 85-year-old lady is brought into A&E semiconscious. Temperature 32°C, blood pressure 90/50 mmHg and BM 6.5 mmol/l. Arterial blood gases (ABG) on room air: pH 7.12 pO₂ 10.8 kPa, pCO₂ 2.6 kPa, HCO₃^- 12 mmol/l, O₂ saturation 94% and base excess -19'. Medical staff were asked to complete a questionnaire relating to the case under supervised conditions.

Results

Eighty-seven questionnaires were completed by seven SpR/consultants, 48 F2/senior house officers, 13 F1 and 19 final-year medical students. ABG interpretation was correct in 80/87 (92%). Only 52/87 (59.8%) could calculate the anion gap and only 1/87 listed fluid as a cause of a metabolic acidosis. Eighty-three staff (93.4%) knew that a metabolic acidosis caused an increased respiratory rate. Normal saline was the first-choice fluid for resuscitation in almost 60% (52/87) cases. The chloride concentration of normal saline was known by 12/87 staff (13.8%). The serum chloride concentration was known by 28/87 staff (32%).

Conclusion

The majority of medical staff prescribe normal saline as their first-choice intravenous fluid. Many medical staff are unaware of the electrolyte composition of normal saline, the phenomenon of hyperchloraemic metabolic acidosis, or how to differentiate hyperchloraemic metabolic acidosis from lactic acidosis by calculating the anion gap. A good understanding of fluid therapy is important for all medical staff.