Shock/Sepsis/Trauma/Critical careChanges in blood lactate levels after major elective abdominal surgery and the association with outcomes: a prospective observational study
Introduction
Despite considerable advances in surgical techniques and perioperative care, significant morbidity and mortality still remains after major abdominal surgery, particularly in patients with advanced age and poor physiological reserve and patients undergoing emergency surgery [1]. The etiology of postoperative complications is complex, but poor tissue perfusion and oxygenation caused by impaired microvascular flow, which can contribute to organ system dysfunction development, remains a major cause [2], [3], [4], [5], [6]. Clinical and hemodynamic parameters, such as blood pressure, urine output, and central venous pressure are unreliable or late signs of inadequate tissue perfusion and, hence, have limited value in risk-stratifying patients and guiding timely therapy [7]. Theoretically, an important mechanism of adaptation to marginal tissue perfusion and oxygen delivery is an increased oxygen extraction ratio from arterial blood, which would inevitably result in decreased venous oxygen saturation [6]. Clinically, mixed venous oxygen saturation (SvO2) or its surrogate, central venous oxygen saturation (ScvO2), has been proposed to be indicators of balance between tissue oxygen delivery and consumption, and low ScvO2/SvO2 have been associated independently with an increased risk of complications in high-risk surgical patients [6], [8], [9]. However, ScvO2/SvO2 monitoring is an invasive measurement and requires time, expertise, and specialized equipment, all of which collectively limit their wide use in clinical practice [10], [11].
Another important adaptive mechanism to survive tissue hypoxia caused by hypoperfusion is increased production of lactate by anaerobic glycolysis [12]. The subsequent elevation of blood lactate is easy to measure. There was a strong correlation between the severity of microvascular alterations and blood lactate levels [2], [5], and blood lactate clearance was shown to be significantly associated with improved microcirculatory flow [13]. These results indicated that blood lactate can reliably reflect the adequacy of tissue perfusion and oxygenation [7], [14]. Many studies have confirmed that increased blood lactate levels at admission were independently associated with morbidity and mortality in critically ill patients, irrespective of arterial hypotension and that, over time, early changes in these levels can predict patient outcomes [14], [15], [16], [17], [18], [19], [20], [21]. Consistent with those observations, previous observational studies (including ours) have suggested that the initial lactate level [15], [16], [18] and lactate clearance time (time to the normalization of blood lactate) [18], [19] may be useful in predicting outcomes after major abdominal surgery. Furthermore, one interventional study has suggested that interventions that attempt to keep serum lactate levels <1.7 mmol/L by adjusting intravenous fluid administration intraoperatively and up to 72 h postoperatively may be associated with reduced morbidity rates after major elective abdominal surgery [22]. However, most of the above-mentioned observational studies in abdominal surgery included a variable mix of both elective and emergency procedures. Given that in the critically ill the prognostic performance of lactate is dependent upon both time [23] and the admitting diagnosis [24], the prognostic values of lactate have yet to be determined in a homogeneous group of patients undergoing elective abdominal surgery. In addition, microcirculatory alteration in patients undergoing major elective surgery is most obvious within the first 24 h postoperatively, and its severity is significantly associated with outcomes [2], [3], [4], [5]. However, the association between changes in blood lactate concentration during the first 24 postoperative h and postoperative morbidity after major abdominal surgery has not yet been investigated. We hypothesized that the dynamic postoperative changes in blood lactate levels during the first 24 h were significantly associated with postoperative morbidity and mortality in patients undergoing elective major abdominal surgery.
The purpose of this paper was to study the relationship between the dynamic changes in blood lactate concentration during the first 24 h postoperatively and the postoperative complications in patients undergoing major elective abdominal surgery. Several indices of lactate homeostasis in the first 24 postoperative h (i.e., peak lactate, lactime [the time during which hyperlactatemia is present], time-weighted average lactate [LACTW], and lactate clearance at different time intervals), in addition to lactate levels at specified time points, were examined to determine their ability to predict postoperative complications.
Section snippets
Study design and patients
This study was approved by the human studies ethics committee at the Affiliated Hospital of Jianghan University, and written informed consent was obtained from the patients or their next of kin. In this single-center prospective observational study, which was conducted at the Affiliated Hospital of Jianghan University from September 2009 to December 2010, we enrolled all consecutive adult patients (aged >18 years) who were scheduled for major elective abdominal surgery. Major abdominal surgery
Results
During the study period, 174 patients underwent 177 major elective abdominal procedures. Only the primary surgery was registered in this study, and re-operations after the index surgery (n = 3) were excluded. A further 60 were excluded: refusal of admission to the SICU (n = 49), liver insufficiency (n = 6), chronic renal insufficiency (n = 2), and surgery (n = 2) or ICU admission (n = 1) within the mo prior to the operation. Data were collected from 114 patients. Two (1.7%) patients were
Discussion
Elevated blood lactate levels commonly result from acute tissue hypoperfusion and anaerobic metabolism and has been shown to be a surrogate for oxygen debt or oxygen deficit accumulated over time [7], [12], [14], [28], [29]. Our previous retrospective study showed that the initial blood lactate level was significantly associated with postoperative complications and could independently predict in-hospital morbidity after major abdominal surgery [15]. However, this finding was not the case in our
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