Bedside blood glucose determinations in critical care medicine: a comparative analysis of two techniques

Bedside capillary blood glucose measurements in critically ill patients: influence of catecholamine therapy

OBJECTIVE

To evaluate the effects of catecholamine therapy on the accuracy of capillary glucose measurements in hyperglycemic patients.

PARTICIPANTS

43 hyperglycemic patients older than 18 years admitted to the intensive care unit of a tertiary medical center were included from December 2005 to March 2006.

MEASUREMENTS

This prospective study compares fingerstick and earlobe measurements simultaneously to sampled laboratory venous glucose in patients treated without (group 1) or with (group 2) catecholamine. Three venous samples for serum glucose analysis at three fixed hours and simultaneously two capillary glucose determinations were performed during the two first successive days after inclusion. A difference between the methods of glucose measurements greater than 2.3 mmol/l was considered significant.

RESULTS

The mean difference between the two methods was -0.05 mmol/l in group 1 and +0.29 mmol/l in group 2, while the limits of agreement were +4.03 and -4.13 mmol/l and +5.63 and -5.05 mmol/l in groups 1 and 2, respectively. A difference between paired measurements greater than 2.3 mmol/l was observed in 29% in group 1 and in 40% in group 2 (p=0.038). The alternative site did not improve the accuracy.

CONCLUSIONS

In critically ill patients treated with catecholamine capillary fingerstick blood glucose measurement seems inaccurate. Earlobe sampling does not improve accuracy.

Comparative evaluation of ultramicro-and macro-chemo enzyme based assays of glucose, cholesterol and triglycerides

A comparison of the absorbance, enzyme/substrate concentration, reaction efficiency and sensitivity has been made for enzyme-based clinical chemistry assays, using a conventional colorimeter versus a strip-microwell reader, in order to establish the value of ultra-microchemical procedure, with reaction volume 87 μl (light path length=0.25 cm). By utilizing commercial kits available for the quantitation of serum glucose, cholesterol and triglycerides, it has been established that the micro method is highly cost effective (9-30 fold), reproducible and sensitive. Comparison of blood drawn by a finger prick (capillary) and venipuncture for normal and pathological specimens show reproducibility between different laboratory technologists and in reference with the values reported by an accredited reference laboratory. Since the micro method uses very little serum, it is most suitable for analyses of small smaples, from large population-based field trials. However, the assay range has to be titrated for each commercial kit to establish the enzyme/substrate equivalence.

Evaluation of a real-time blood glucose monitor in children with diabetic ketoacidosis

Use of a real-time bedside glucose monitor was analyzed during the course of management of diabetic ketoacidosis (DKA) in children. Simultaneous determinations of blood glucose were obtained, using three methods: bedside glucose meter (One Touch II), laboratory glucose analyzer (YSI 2300 STAT), and a real-time bedside glucose monitor (VIA 1-01G Blood Chemistry monitor). Study patients included seventeen patients < 18 years of age admitted to a Pediatric Intensive Care Unit, with blood samples obtained during treatment of DKA by continuous insulin infusion. Four patients did not complete the study. Three experienced temporary technical problems with the monitor, and four required repeat IV placement. Duration of monitor use ranged between 6 and 47 h (mean 24 +/- 4 h). Blood glucose values ranged between 2.6 and 22.5 mmol/l. Overall correlation of blood glucose values were as follows: 0.965, 0.965, 0.973, VIA 1-01G vs. One Touch II, VIA 1-01G vs. YSI 2300 STAT, and One Touch II vs. YSI 2300 STAT, respectively (all P-values < 0.0001). This real-time bedside glucose monitor is accurate at glucose values < 13.8 mmol/l, and reliable for rapid, repetitive analyses. Results indicate that blood glucose values obtained using this real-time monitor are comparable to those using standard methods of measurement, and that this device is clinically applicable for use in management of children with DKA.

Accuracy of reagent strips in detecting hypoglycemia in the emergency department

STUDY OBJECTIVE

Although reagent strips are commonly used, their reliability to estimate blood glucose concentration and guide administration of dextrose solutions in the emergency department environment has not been proved. We determined the accuracy of visually interpreted reagent strips (Chemstrip bG, Boehringer Mannheim Corp, Indianapolis, IN) and their ability to identify hypoglycemic patients in the ED.

METHODS

We conducted a prospective, nonrandomized blinded clinical study of the visual estimation of blood glucose values by ED personnel using Chemstrip bG reagent strips during a 4-month period. Simultaneously obtained blood samples sent for laboratory glucose determination served as controls. The study was conducted at a large university hospital ED with an urban patient population. A convenience sample of 215 adult ED patients underwent serum glucose determination with data form completion. No study intervention was tested, although timing of administration of dextrose solutions, if given, was recorded.

RESULTS

Hypoglycemia was defined as a glucose concentration less than 60 mg/dL on standard laboratory analysis. Reagent strips identified 28 of 29 of these patients (sensitivity=97%), and 171 of 182 patients without hypoglycemia (specificity=94%, negative predictive value=99%) compared with control samples. The 1 false-negative reagent strip reading of 80 mg/dL was obtained from blood stored in a serum separator tube and had a laboratory glucose value of 39 mg/dL. Eighty-seven percent of the reagent strips were within +/-60 mg/dL of the control value for the laboratory glucose reference range less than 350 mg/dL.

CONCLUSION

Visually interpreted Chemstrip bG reagent strips provide an acceptable estimation of blood glucose concentration in the ED and are highly sensitive in detecting hypoglycemia.

Determination of prehospital blood glucose: a prospective, controlled study

STUDY OBJECTIVE

To determine if emergency medical personnel can effectively rule out hypoglycemia in the prehospital setting.

DESIGN

During a 10-week period, emergency medical personnel determined the fingerstick glucose on all prehospital patients with altered mental status using the Chemstrip bG. Statistical comparisons were made to serum glucose levels performed by hospital laboratory personnel on blood samples obtained prior to glucose administration. A serum glucose level less than 60 mg/dL was considered a positive test for hypoglycemia.

PARTICIPANTS

170 consecutive patients with altered mental status (AMS) ranging in age from 13 to 90 years were enrolled.

MEASUREMENTS AND MAIN RESULTS

Of these patients, 158 were normal or hyperglycemic, 12 were hypoglycemic, and one patient was hypoglycemic but had only a borderline negative fingerstick test. Thus, a sensitivity of 91.7% and a negative predictive value of 99.3% were obtained. The specificity was 92.4%, and positive predictive value was 47.8%.

CONCLUSION

The Chemstrip bG may be used safely in the prehospital setting to rule out hypoglycemia.

The empiric use of hypertonic dextrose in patients with altered mental status: a reappraisal

STUDY HYPOTHESIS

Neither response to hypertonic glucose (D50W) nor presence of hypoglycemia can be reliably predicted by "typical" clinical findings (tachycardia, diaphoresis, and/or an available history of diabetes mellitus) in prehospital patients with altered mental status (AMS).

POPULATION

Three hundred forty consecutive patients who received D50W for prehospital AMS as ordered by a university hospital paramedic base.

METHODS

Review of prehospital records and tape recordings for all subjects to determine presence or absence of tachycardia, diaphoresis, and/or available history of diabetes mellitus at the time of field presentation, as well as response to D50W; final diagnosis was determined from emergency department charts in the 301 patients for whom they were available.

RESULTS

Twenty-five patients (7.4%) had a complete response to D50W: 20 had hypoglycemia, diagnosis for one patient was unknown, and four had other causes of AMS. Three patients with an ED diagnosis of hypoglycemia had partial or equivocal responses to D50W, and five had no response. Complete responders were more likely than other patients to have diaphoresis (40% vs 13%, P less than .001) and available history of diabetes (52% vs 12.1%, P less than .001) but not tachycardia (36% vs 35.2%, P = NS). Nine complete responders, including five with hypoglycemia, had none of the three clinical signs.

CONCLUSION

Although patients with hypoglycemia who respond to D50W are diaphoretic and have an available history of diabetes more often than other patients with prehospital AMS, 25% of complete responders who are hypoglycemic would not receive D50W if it were used only in patients with "typical" clinical findings. Selective use of D50W for AMS is desirable because very few patients respond, but it is only feasible with concomitant field use of a rapid test of serum glucose.

A prospective evaluation of glucose reagent teststrips in the prehospital setting

Reagent teststrip determination of blood glucose has been shown to be accurate for hospital and home testing and is commonly used in prehospital care despite the lack of studies in this arena. This prospective, multicenter study examines the ability of glucose reagent teststrips to detect hypoglycemia when used under field conditions compared with simultaneously drawn control samples for laboratory glucose determination. Also examined was the accuracy of the teststrips in the laboratory glucose range less than or equal to 200 mg/dL. One hundred eighty-one pairs of data were analyzed. Hypoglycemia was defined as laboratory glucose less than or equal to 60 mg/dL. The teststrips correctly identified 31 of 33 patients in this range (sensitivity = 94%), and 125 of 148 patients without hypoglycemia (specificity = 85%). The two false negative readings were 70 and 90 mg/dL. Reagent teststrips were within +/- 40 mg/dL of the laboratory value in 70% of cases. The correlation coefficient (Spearman r) between teststrip and laboratory glucose in the range less than or equal to 200 mg/dL was .80. Using teststrip readings of 90 mg/dL or less as a measure of hypoglycemia yields 100% sensitivity with a specificity of 57%. We conclude glucose reagent teststrips are a useful adjunct for use in the prehospital setting and may be valuable for the detection of hypoglycemia.

Evaluation of bedside testing options for the critical care unit

Bedside testing offers a unique opportunity for earlier and more specific diagnosis, faster and more frequent monitoring, and the opportunity to improve patient care and reduce hospital costs. However, if abused it may not improve patient care and may increase hospital costs. In the future, more clinical studies will need to be performed to determine which tests are cost-effective.

Bedside analysis of arterial blood gases and electrolytes during and after cardiac surgery

Intraoperative changes in arterial blood gas tensions and serum electrolyte concentrations may contribute to the development of arrhythmias and cardiovascular insufficiency. Rapid intraoperative assessment of these parameters may improve patient care by permitting earlier treatment of abnormalities. We evaluated a portable blood gas and electrolyte analyzer in six patients undergoing coronary artery bypass surgery. Evaluation by anesthesia personnel took place in the operating room. The analyzer produced rapid, accurate, and reliable data that were comparable to clinical laboratory data. Correlation coefficients between the analyzer and laboratory determinations for PaO2, PaCO2, pH, K+, Ca++, and hematocrit were all greater than 0.92. Large changes in circulating ionized calcium (18%) and potassium (38%) concentrations were noted during cardiac surgery. Bedside blood gas and electrolyte analyzers represent a new technology worthy of further evaluation.