Blood gases and acute pancreatitis

Acute pancreatitis, i.e. acute inflammation of the pancreas, causes sudden onset of severe upper abdominal pain often radiating to the back. Other symptoms include vomiting, constipation and pyrexia. Two main causes - alcohol abuse and gall stone disease – account for the majority (~80 %) of cases. The condition has a variable course. 

In many cases inflammation resolves with little or no intervention over a period of a few days to a week, with no long-term consequences, but in others the condition can be severe, progressing rapidly to systemic inflammation, sepsis and multiple organ failure. Severe acute pancreatitis is thus a potentially fatal condition that warrants immediate admission to intensive care. 

A major problem for initial emergency room management of patients presenting with acute pancreatitis is to distinguish those whose course is likely to be benign from those who are likely to suffer severe disease and therefore require admission to intensive care. There is currently no single reliable prognostic test and clinicians must depend on rather cumbersome clinical scoring systems to predict outcome. 

The authors of a recently published study sought to examine the value of admission acid-base parameters (pH, bicarbonate and base excess) in predicting outcome among patients with acute pancreatitis.

The notion that these might be useful prognostic markers is based partially on the observation that metabolic acidosis (characterized by reduced pH, bicarbonate and base excess) is a frequent complication of severe acute pancreatitis and other acute conditions that require admission to intensive care.

The studied population comprised all patients presenting to a tertiary care hospital in India with a diagnosis of acute pancreatitis over a 23-month period. After exclusion, 205 patients remained in the study. At the time of admission arterial blood was sampled from all 205 patients for determination of pH, bicarbonate and base excess. 

Patients were prospectively followed to either clinical recovery or death; details of complications (organ failure, shock), and major interventions required (e.g. surgery) during the course of the illness were recorded for the study and used as outcome measures.

To assess the prognostic value of admission blood gas results, patients were categorized to sub-groups based upon pH (<7.35 or ≥7.35), bicarbonate (<22 mmol/L or ≥22 mmol/L) and base excess (<–4 mmol/L or ≥–4 mmol/L). An association between outcome measures and all three acid-base parameters was evident. 

For example, 91.4 % of 35 patients with pH <7.35 suffered organ failure, whereas just 67 % of those with pH >7.35 did so. Clinical shock developed during the course of illness in 34 % of study patients whose admission pH was <7.35, but in only 8 % of those whose pH was >7.35. Mortality was higher (54.3 %) among those with pH <7.35 than among those whose admission pH was >7.35 (just 6.5 %).

A very similar association between admission bicarbonate and outcome measures was also found, with those 119 patients whose bicarbonate was <22 mmol/L more likely to fare worse than those whose admission bicarbonate was >22 mmol/L. 

And again, when base excess was examined, there was a clear distinction in outcome measures between the two groups. Those whose base excess was <–4 mmol/L were more likely to fare worse than those whose base excess was >–4 mmol/L.

The authors conclude that among patients with acute pancreatitis reduced pH, bicarbonate and base excess at presentation predict an adverse outcome with higher frequency of organ failure, need for intervention and mortality. They suggest that it is prognostically useful to perform blood gases on patients with acute pancreatitis at the time of admission.