Results
Glucose POCT evaluations were carried out on 116 consecutive patients who underwent CABG surgery with or without a Maze procedure on CPB with a CII and an arterial line. Due to missing glucose results in 1 or more of the variables, 10 patients were excluded from data analysis for the time point of arrival in the CTICU and 14 patients were excluded from data analysis for the time point of 6 hours post CTICU arrival. This gave a final count of 106 CABG patients for CTICU arrival data analysis and 102 CABG patients for the 6 hours after CTICU arrival data analysis.
Patients ranged in age from 43 to 85 years, with a mean of age of 66 years, 22% were were women, 41% were diabetic, and 18% had peripheral vascular disease (Table 1). The average preoperative HbA1c was 6.4% ± 1.3% (range, 4.6% to 11.1%). Mean time on CBP for the group was 101 ± 31 minutes (range, 43 to 233 minutes). Postoperative mean hematocrit and hemoglobin were 32.5% and 11.4 g/dL, respectively. The average core temperature of patients on arrival was 36.0°C, which rose to an average of 36.6°C 6 hours later. A vasoconstrictor drip was infusing on 52% of patients upon CTICU arrival; 65% had a vasoconstrictor drip infusing 6 hours after arrival to the CTICU. Hemoglobin results were available only upon CTICU arrival as they are not routinely checked at 6 hours; 74 (64%) patients had a hemoglobin < 12 g/dL.
Compared to central laboratory testing, which we are defining as the gold standard, fingerstick POCT performed better on arrival, while radial artery POCT performed better at 6 hours (Table 2). At CTICU arrival, the mean blood glucose value for fingerstick POCT was 121 ± 24.1 mg/dL, 116 ± 27.2 mg/dL for radial artery POCT, and 128 ± 23.5 mg/dL for central lab testing. The difference in mean blood glucose between the fingerstick POCT and central lab testing was not statistically significant (P = 0.032), while the difference in mean blood glucose between radial artery POCT and central lab testing was statistically significant (P = 0.001). At 6 hours post arrival to the CTICU, the mean fingerstick POCT blood glucose value was 130 ± 23.9 mg/dL, compared to the mean central lab testing value of 137 ± 22.4 mg/dL; this difference was statistically significant (P = 0.019), while the radial artery POCT blood glucose value (133 ± 24.6 mg/dL) was not significantly different from the central lab testing value.
Blood glucose values from fingerstick POCT and central laboratory testing correlated well (r = 0.83 for admission and 0.86 for 6-hour values), as did radial artery POCT and central lab values (r = 0.87 for admission and 0.90 for 6-hour values) (Figures 1, 2, 3, and 4). Comparing individual values for fingerstick POCT and central lab testing, within-person differences between the 2 values ranged from –45 to 25 mg/dL, with 21% of pairs discrepant by 20 mg/dL or more (Figure 1); results were similar at 6 hours (Figure 2), with slightly less discrepancy.
The differences between radial artery POCT and central lab testing values at CTICU arrival ranged from –43 to 80 mg/dL, with 24% of pairs discrepant by 20 mg/dL or more (Figure 3). At 6 hours post CTICU arrival, the difference between radial artery POCT and central lab testing values ranged from –130 to 27 mg/dL, with 11% of pairs discrepant by 20 mg/dL or more (Figure 4). Ninety-two percent of central laboratory values were either close to (± 20) or within the moderate glycemic control target range (110–150 mg/dL).
When the patient cohort was stratified by anemia, diabetes, body temperature, and receipt of vasoconstrictor, there were no significant differences between mean fingerstick POCT and central lab testing values for any strata on CTICU arrival, while there were significant differences between radial artery POCT and central lab testing means for both vasoconstrictor strata as well as for patients with core temperature > 36.1°C (Table 2). At 6 hours, there were no statistically significant differences when stratified for receipt of vasoconstrictor or presence of diabetes. Stratification for anemia or core body temperature was not done for patients at the 6-hour post CTICU arrival time because no hemoglobin value was available and all patients except 1 reached a core temperature of 36.1°C.
Although we measured POCT values obtained using 2 different blood sample sources, fingerstick POCT performed better than radial artery POCT testing with regard to the mean values when compared with the central lab. However, radial artery POCT performed better with regard to correlation with the central lab value. In other words, fingerstick POCT values were less significantly different than radial artery POCT values when compared with the central lab, while radial artery POCT values correlated better with values from the central lab. In spite of this unexplained variability in differences and correlation, the blood glucose values stayed in the target goal range (Figures 1-4).