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Background: Serum lactate is a biomarker that predicts mortality in patients with non-cardiogenic circulatory shock like sepsis or severe trauma. Some reports suggest using the serum lactate to predict the prognosis in patients with acute abdomen, but this is not well understood. We hypothesized that the preoperative serum lactate level can help to predict the postoperative outcome in patients undergoing exploratory laparotomy for acute abdomen.
Methods: Medical records of 293 consecutive patients who underwent emergent exploratory laparotomy for acute abdomen from 2007 through 2010 were reviewed. Patients' demographics, preoperative laboratory tests including white blood cell counts (WBC), serum lactate, postoperative diagnosis, Systemic Inflammatory Response Syndrome (SIRS) Score, the American Society of Anesthesiologists (ASA) physical status classification, postoperative in-hospital mortality were reviewed. These factors were compared between patient who died in hospital after the exploration and who survived, as well as between patients with bowel ischemia and without bowel ischemia. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for the mortality and bowel ischemia were analyzed. PASW Statistics 18 was utilized for statistical analysis.
Results: Two hundred and two patients who had recorded preoperative serum lactate(s) were included in the study. The preoperative serum lactate was checked only once in 130 patients and more than once in 72 patients. For patients with serial lactates, the trend over time was recorded. Postoperative diagnoses were small bowel obstruction (n=67, 33%), large bowel obstruction (n=44, 22%), bowel ischemia (n=38, 19%), perforated gastric or duodenal ulcers (n=31, 15%), colonic perforation (n=13, 6%), acute diverticulitis (n=19, 9%), others (n=21, 10%), and negative exploration (n=3, 1%). There were 34 (17%) postoperative in-hospital mortalities (The median time between surgery to death: 6.5 days [Range: 0 - 102]). All 3 patients who underwent negative laparotomy had a normal serum lactate(s) preoperatively. As shown on Table 1, the persistent abnormal or up-trending serum lactate was seen more frequently in patients in who died in hospital after exploration (53% vs 26%, p= 0.002); as well as, in patients with bowel ischemia (46% vs 28%, p=0.090) . The serum lactate had the similar specificity and NPV to SIRS score, ASA class and WBC; however, had the lower sensitivities than other factors.
Conclusion: Normal or down-trending serum lactate strongly predicts postoperative survival in patients who undergo emergent exploratory laparotomy for acute abdomen, although persistently elevated serum lactate does not necessarily predict mortality. It may be useful prognostic information for patients and families if combined with other factors.
Table 1

		SIRS score ≥2		ASA class 4 or 5		WBC (cells/µL) >12,000 or <4,000		Lactate persistent abnormal or trend up
		No	Yes	No	Yes	No	Yes	No	Yes
Mortality	Survived	96	9	127	5	100	11	124	18
	Died	69	24	36	28	64	22	44	16
	P value	0.001		<0.0001		0.003		0.002
	Sensitivity, Specificity, PPV, NPV	73%, 58%, 26%, 91%		85%, 78%, 44%, 96%		67%, 61%, 26%, 90%		53%, 74%, 29%, 89%
Bowel Ischemia	No	86	19	116	16	95	16	118	22
	Yes	74	19	43	21	64	22	46	16
	P value	0.677		0.001		0.049		0.09
	Sensitivity, Specificity, PPV, NPV	50%, 54%, 20%, 82%		57%, 73%, 33%, 88%		58%, 60%, 26%, 86%		42%, 72%, 26%, 84%