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Literature Review

Evaluation of Outcomes and Complications in Patients Who Experience Hypoglycemia After Cardiac Surgery

Lowden E, Schmidt K, Mulla I, et al. Endocr Pract. 2017;23(1):46-55.

Reviewers: Talia K. Ben-Jacob, MD1; Ahmed Awad, MD2

  1. Cooper University Hospital, Department of Anesthesiology, Division of Critical Care, Camden, NJ
  2. Cooper University Hospital, Department of Anesthesiology, Camden, NJ
Background

The risks, characteristics, and detrimental effects of worsening hypoglycemia in postoperative cardiac surgery patients has been inconsistent, yet the newest recommendations have shifted from intensive glycemic control to an increased target range of 140–180 mg/dL. Recent studies have shown that a more stringent blood glucose level is effective and safe. The purpose of this study was to elucidate short-term (30 days) and long-term detrimental effects in patients experiencing postoperative hypoglycemia after cardiac surgery. Another objective was to compare postoperative morbidity and mortality in patients who experience hypoglycemia in the immediate postoperative periods and those who did not. This study was conducted to solidify recommendations on glycemic control in postoperative cardiac patients.

Methods

A retrospective chart review over a 3.5-year period was performed on patients who underwent cardiac surgery and had postoperative glucose management. This was a subgroup analysis of a previously published trial. A total of 1325 patients between the ages of 18 and 90 who survived more than 24 hours after cardiac surgery were included. The daily highest and lowest glucose levels of each patient were extracted from the medical record. Patients were divided into 2 groups based on whether or not they had a hypoglycemic episode. Severe hypoglycemia was defined as blood glucose <40 and moderate hypoglycemia was definite as <70. Statistical analysis was then performed. Primary endpoints compared postoperative surgical complications, hospital readmission, morbidity, and mortality.

Results

Of the 1325 patients, 215 experienced a hypoglycemia episode. Patients who had an episode of low blood glucose were more likely to be female, be normal weight, have a diagnosis of diabetes preoperatively, and have a history of cerebrovascular disease. The preoperative sugars were not significantly different between those with hypoglycemic episodes and those without. The 30-day outcome in patients who developed hypoglycemia showed that they were more likely to become septic, develop ventilator-dependent respiratory failure, have renal failure, require renal replacement therapy, and have cardiac arrest. There was no difference in 30-day mortality between the patients with hypoglycemia and those without; however, long-term mortality was higher in the patients who experienced hypoglycemia. It also was noted that the patients with multiple hypoglycemic episodes had increased rates for a number of complications.

Conclusions

Hypoglycemia from intensive postoperative glucose control is common in postoperative cardiac surgery patients. Though single episodes of hypoglycemia in the postoperative period do not seem to injure patients, there is a significant increased risk of long-term mortality and complications in patients who experience more than one episode. 

Discussion

This study showed that hypoglycemia is likely more common than what has been previously reported. In addition, the study found that an increasing number of hypoglycemic events increased the likelihood that a patient would develop an adverse outcome. These hypoglycemic episodes also led to an increased risk for mortality in the long term. These results are supported by various other studies. Limitations of this study include that it is a single-center retrospective study. Because the institution that produced this research has its own glucose management service, it is extremely proficient in management of postoperative glucose control, and therefore the results may not be applicable to other institutions. In addition, because the study is a chart review, the other mitigating factors determining long-term mortality outside of the hospital admission cannot be determined. This study only shows a linkage of hypoglycemic episodes to increased morbidity and mortality in postoperative cardiac surgery patients. The underlying mechanism of this association still needs to be investigated and elucidated.