Accuracy of a novel noninvasive transdermal continuous glucose monitor in critically ill patients.

Stress hyperglycemia and hypoglycemia are associated with increased morbidity and mortality in the critically ill. Intermittent, random blood glucose (BG) measurements can miss episodes of hyper- and hypoglycemia. The purpose of this study was to determine the accuracy of the Symphony® continuous glucose monitor (CGM) in critically ill cardiac surgery patients. Fifteen adult cardiac surgery patients were evaluated immediately postoperatively in the intensive care unit. Prelude® SkinPrep prepared the skin and a sensor was applied to 2 test sites on each subject to monitor interstitial fluid glucose. Reference BG was sampled at 30- to 60-minute intervals. The skin at the test sites was inspected for adverse effects. Accuracy of the retrospectively analyzed CGM data relative to reference BG values was determined using continuous glucose-error grid analysis (CG-EGA) and mean absolute relative difference (MARD). Using 570 Symphony CGM glucose readings paired with reference BG measurements, CG-EGA showed that 99.6% of the readings were within zones A and B. BG measurements ranged from 73 to 251 mg/dL. The MARD was 12.3%. No adverse device effects were reported. The Symphony CGM system is able to safely, continuously, and noninvasively monitor glucose in the transdermal interstitial fluid of cardiac surgery intensive care unit patients with accuracy similar to that reported with other CGM systems. Future versions of the system will need real-time data analysis, fast warm-up, and less frequent calibrations to be used in the clinical setting.

L-[1-(13)C] phenylalanine breath test for monitoring hepatic function after living donor liver transplant surgery.

Although metabolic response after partial hepatectomy has been well studied in animal models, there are few studies examining restoration of metabolic capacity after right hepatectomy in humans. The L-[1-(13)C]-phenylalanine breath test (PBT) is a simple non-invasive diagnostic tool which allows measurement of liver functional reserve. We investigated the PBT for monitoring hepatic function in living liver donors by measuring the metabolism of L-[1-(13)C]-phenylalanine ((13)C-Phe). We used (13)C-Phe administered orally and iv to adult living liver donor patients and measured exhaled (13)CO(2) to determine the extent of metabolic impairment and time course of its return. Patients given oral (13)C-Phe had approximately 70-90% reduction in (13)CO(2) production compared with baseline 2-3 days after surgery. Patients given iv (13)C-Phe had only 40-50% reduction in (13)CO(2) production and recovered their baseline (13)C-Phe metabolism much sooner than their oral (13)C-Phe metabolic capacity (P < 0.05). In some cases oral (13)C-Phe did not recover to baseline for as long as 56 days after surgery. Patients recovering (13)C-Phe metabolism had significantly higher (13)CO(2) recovery 60 min after ingestion by day 4 (0.97 versus 3.06, P = 0.033) and day 7 (1.50 versus 5.02, P = 0.031). We conclude that orally administered amino acids may not be well absorbed and/or metabolized in some subjects for weeks after partial hepatectomy whereas intravenously delivered substrates are much better oxidized by the regenerating liver. These findings may be due to impaired gut motility due to trauma to the gastrointestinal tract or portal venous flow that reduces delivery of oral agents after liver surgery. In early recovery phase for living liver donor patients, the iv PBT would be a better predictor of functional hepatic reserve.