Trial Information

Incidence of Postoperative Ketosis and Metabolic Acidosis

Metabolic acidosis is a frequent occurrence following major surgery. Monitoring acid base
disturbances and in particular diagnosing the aetiology of the acidosis are important parts
of assessing a patient's cardiovascular status following surgery. The presence of a
metabolic acidosis is frequently attributed to anaerobic metabolism leading to the
generation of lactic acid due to hypovolaemia and poor tissue perfusion. This commonly
results in clinicians treating postoperative patients with a metabolic acidosis by
administering intravenous fluids containing 0.9% saline or Hartmann's solution (compound
sodium lactate). If the cause of the metabolic acidosis is not hypovolaemia, treatment with
intravenous fluids may actually exacerbate the acidosis by causing hyperchloraemia. An often
overlooked cause of metabolic acidosis after surgery is starvation leading to ketoacidosis.
All patients are starved for a minimum of six hours prior to general anaesthesia due to the
potential risk of aspiration of gastric contents into the bronchial tree. Many patients are
in fact fasted for much longer periods than this. There is, however, little data describing
the incidence of ketoacidosis following surgery. In addition, there may be other causes of
acidosis after surgery which often overlooked but can be determined using equations and
mathematical models. The aim of this study is to define the incidence and nature of acidosis
after major cancer surgery using using equations to directly determine acids. This study
will also aim to compare the ability of commonly used indirect measures (base deficit, anion
gap, corrected anion gap and lactate) to identify the presence of tissue acids in this
population. The incidence of postoperative ketoacidosis as a contributor to tissue acidosis
will be assessed through the use of point of care urinalysis.