Original Research

Point-of-Care versus Central Laboratory Glucose Testing in Postoperative Cardiac Surgery Patients

Journal of Clinical Outcomes Management. 2019 March;26(2):69-76

References

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Methods

Setting

Maine Medical Center is a 600-bed tertiary care teaching hospital. It is a level 1 trauma center where 1000 cardiac surgical operations are performed annually. POCT glucose monitoring is relied upon to monitor blood glucose and adjust the CII accordingly. This project, which did not require any additional procedures outside of the standard of care for this population of patients, was reviewed by the Institutional Review Board, who determined that this activity does not meet either the definition of research as specified under 45 CFR 46.102 (d) or the definition of clinical investigation as specified in 21 CFR 56.102 (c).

Patients

Using central laboratory glucose values drawn from the radial artery as the gold standard, we created a registry of consecutive postoperative cardiac surgery patients who had undergone CABG surgery and had blood glucose determinations from both POCT (fingerstick and radial artery samples) and central laboratory testing (radial artery sample) during a 7-month period (May 2016 through February 2017). To be included in the registry, patients had to (1) be postoperative following isolated CABG or CABG plus Maze procedure; (2) have been on cardiopulmonary bypass (CPB); (3) have radial arterial lines; and (4) be on a CII. A total of 116 patients qualified according to the inclusion criteria. Patients missing glucose results in 1 or more of the variables were excluded from data analysis.

Measurements and Variables

Using a POCT glucometer (FreeStyle Precision Pro, Abbott Laboratories, Abbott Park, IL), blood glucose conentrations were measured on samples obtained from both fingerstick and radial artery. Concurrently, radial arterial blood was sent to the central laboratory for glucose measurement. Blood glucose values were compared in CABG patients on CII upon arrival to the cardiothoracic surgery intensive care unit (CTICU) from the operating room and CABG patients on CII 6 hours after arrival in the CTICU. During the 6-hour interval, blood glucose levels were tested hourly or more frequently, allowing nurses to identify trends in blood glucose changes in order to keep blood glucose in the prescribed goal range of 110 to 150 mg/dL. At each of these 2 time points, on arrival to CTICU and 6 hours later, blood glucose values obtained with radial artery POCT and fingerstick POCT were compared with values obtained with central laboratory testing of radial artery samples. The amount of blood required was 1 drop each for POCT fingerstick and POCT radial artery and 2 mL for central lab testing.

Patient characteristics were identified from the electronic medical record. The variables recorded were type of operation, time on CPB, time of CTICU arrival, temperature, vasoconstrictor infusions (norepinephrine, vasopressin, phenylephrine), preoperative diagnosis of diabetes mellitus, preoperative HbA1c, and hemoglobin/hematocrit. Hemoglobin/hematocrit was only available at the time of the patient’s arrival to CTICU. The study was completed within the confines of our center’s standard of care protocol for postoperative cardiac surgical patients.

Analysis

We used standard statistical techniques to describe the study population, including proportions for categorical variables and means (standard deviations) for continuous variables. Correlation and regression techniques were used to describe the relationship between POCT and laboratory (gold standard) tests, both measured as continuous variables, and paired t-tests with Bonferroni correction were used to compare the central tendency and range of these comparisons. We calculated the differences between the gold standard measure and the POCT measure as an indication of outliers (ie, cases in which the 2 tests gave markedly different results). We examined plots to ascertain at which levels of the gold standard test these outliers occurred. An interim analysis was done at the halfway point and submitted to the Institutional Review Board, but no correction to the P value was done based on this analysis, which was largely qualitative. We used Bonferroni correction to declare a P value of 0.025 statistically significant with the 2-way comparisons of both fingerstick and radial artery values to central laboratory values. When the data was stratified by a clinical characteristic creating a 4-way comparison, we used Bonferroni correction to declare a P value of 0.0125 to be statistically significant when comparing both fingerstick and radial artery values to central laboratory values.