Accuracy of Bioimpedance Spectroscopy in the Detection of Hydration Changes in Patients on Hemodialysis

OBJECTIVES

The body composition monitor (BCM) is a bioimpedance spectroscopy device, specifically developed for patients on hemodialysis (HD) to improve ultrafiltration (UF) programming, based on an objective assessment of the degree of overhydration (OH) at the start of HD. However, its acceptance in clinical practice remains limited because of concerns about the accuracy at the individual level. The aim of this study is to examine the performance of the BCM and to identify means of improvement.

METHODS

Precision of the OH estimate was assessed by 6 consecutive measurements in 24 patients on HD. Accuracy was examined in 45 patients, by comparing the change in OH (ΔOH) during HD with UF volume. Accuracy was considered acceptable if the volume error in individual patients was ≤0.5 L.

RESULTS

The OH estimate had an analytical precision of 1.0 ± 0.4%. The correlation between UF volume and ΔOH was moderate (Slope = 0.66, R² = 0.44, P < .001) and indicated underestimation of UF volume, in particular for high UF volumes. Accuracy at individual level was highly variable. A volume error >0.5 L occurred in 44% of patients. Accuracy improved over the course of HD, with a decrease in total error range from 2.3 L in the first hour to 1.1 L in the final hour of HD.

CONCLUSIONS

The accuracy of BCM volume change estimates is highly variable and below requirements of daily practice. Improvement may be achieved by a switch to an end-of-HD measurement.

Impact of diffusion, ultrafiltration, and posture on total body electrical resistance in patients on hemodialysis

Monitoring of hydration in patients on hemodialysis (HD) by currently available bioelectrical impedance analysis (BIA) methods is hampered by limited accuracy. This may be caused by changes in total body electrical resistance (TBER) that are induced by processes other than ultrafiltration (UF). To identify these sources of error, we examined the impact of UF, diffusion, and postural change (PC), separately. Extracellular TBER (TBER_e) was measured by bioimpedance spectroscopy every 30 min in 23 patients on HD, for 2 h during diffusion-only (DO), followed by 2-h UF-only (UFO). The impact of PC from upright to semi-recumbent position was assessed by a 2-h TBER_e measurement on the day after HD. TBER_e increased by 23.5 ± 12.4 Ω (P < 0.001) during DO and by 40.0 ± 16.2 Ω (P < 0.001) during UFO. PC, evaluated on a separate day, was associated with an increase in TBER_e of 27.6 ± 26.0 Ω (P < 0.001). TBER_e changes during DO were mainly attributed to PC and to a lesser extent to electrolyte exchange. Extrapolation of the data to a conventional 4-h HD session indicates that about 32% of the total increase in TBER_e is not related to UF. In conclusion, a significant part of the increase in TBER during HD is not related to UF but can be attributed to other processes such as the effects of PC and diffusion-related electrolyte exchange. These factors have to be taken into account when TBER-guided UF is considered.NEW & NOTEWORTHY Current BIA methods have limited accuracy in patients on HD. This may be related to the incorrect assumption that all changes in total body electrical resistance (TBER) are caused by changes in body water volumes. The present study indicates that two-thirds of the change in TBER during a conventional 4-h HD session can be attributed to fluid extraction, and that the remaining part is caused by other processes such as postural change and electrolyte exchange. This may cause volume prediction errors when not recognized.

Treatment of Severe Protein Malnutrition After Bariatric Surgery

BACKGROUND

Severe protein malnutrition, with a serum albumin < 25 g/L, is one of the complications that may develop after bariatric surgery. It is associated with increased morbidity and mortality and requires timely diagnosis and appropriate treatment to prevent rapid clinical deterioration. However, evidence-based recommendations for a specific treatment approach are currently not available. The present study describes the efficacy of a newly developed treatment regimen for post-bariatric patients presenting with severe hypoalbuminemia.

METHODS

A single-centre, retrospective analysis of eleven post-bariatric patients presenting with severe hypoalbuminemia, treated with continuous 24 h nasal-jejunal tube feeding of a medium chain triglyceride (MCT) formulation in combination with pancreatic enzyme supplementation every 3 h.

RESULTS

Duration of tube feeding ranged from 25 to 156 days (median 64 days) and pancreatic enzyme was supplemented for 22-195 days (median 75 days). An increase in serum albumin levels of 5 g/L and 10 g/L was achieved after a median period of 20 (range 6-26 days) and 36 days (range 21-57 days), respectively. Albumin levels were > 35 g/L after a median period of 58 days (range 44-171 days).

CONCLUSION

In this case series, a continuous 24-h nasal-jejunal MCT tube feed combined with frequent pancreatic enzyme supplementation was effective in all patients presenting with severe post-bariatric hypoalbuminemia and was not associated with adverse effects.

Pharmacokinetics of Glucocorticoid Replacement Before and After Bariatric Surgery in Patients With Adrenal Insufficiency

Adequate glucocorticoid replacement in patients with primary or secondary adrenal insufficiency is essential to maintain general well-being. Little is known about the effects of bariatric surgery on glucocorticoid absorption. This study evaluates glucocorticoid absorption before and after bariatric surgery, with assessment of plasma cortisol profiles in five patients receiving glucocorticoid replacement therapy for primary (n = 1) or secondary (n = 4) adrenal insufficiency. One patient underwent sleeve gastrectomy (SG), one a one-anastomosis gastric bypass (mini-GB), and three a Roux-en-Y gastric bypass (RYGB). Pharmacokinetic calculations were based on plasma cortisol measurements performed during the first 6 hours after ingestion of the morning dose. Plasma cortisol profiles were very similar before and after surgery; only minor differences were observed. After SG, plasma peak cortisol concentration and cortisol area under the curve (AUC) were higher by 23% and 24%, respectively, and time to peak cortisol was 10 minutes shorter. The mini-GB had no marked effect on pharmacokinetic parameters. In the three patients who underwent RYGB, AUC changes ranged from -12% to 20%. In conclusion, in this small number of patients with adrenal insufficiency, plasma cortisol profiles were similar before and after bariatric surgery. However, in view of individual differences in response to different types of surgery, we recommend postoperative cortisol profiling to guide appropriate glucocorticoid dose adjustment.

Continuation of Liraglutide during Fasting is not Associated with Hypoglycaemia

Liraglutide, a glucagon-like peptide-1 (GLP-1) analog, is increasingly used in obese patients with type 2 diabetes mellitus (T2DM) in doses of up to 3.0 mg/day because of its attractive pharmacological profile. It is currently not known how to proceed with this medication during fasting for surgery. Discontinuation is likely to result in hyperglycaemia, while continuation might lead to hypoglycaemia, but, in view of its mode of action, continuation of GLP-1 analogs is likely to be safe. However, as evidence-based guidelines on GLP-1 management during perioperative fasting are not available, the safety of either policy needs to be confirmed on an individual basis. We therefore decided to perform a preoperative assessment of the glucose response to fasting during continuation of GLP-1 before giving a recommendation in individual cases. So far, 12 severely obese T2DM patients scheduled for bariatric surgery have been evaluated preoperatively by measuring glucose and insulin levels during a 32-hour fast with continuation of liraglutide. Hypoglycaemia was not observed. This suggests that liraglutide in doses of up to 3.0 mg can be safely continued during surgery without risking hypoglycaemia.

Rapidly rule out acute myocardial infarction by combining copeptin and heart-type fatty acid-binding protein with cardiac troponin

Background

The rapid exclusion of acute myocardial infarction in patients with chest pain can reduce the length of hospital admission, prevent unnecessary diagnostic work-up and reduce the burden on our health-care systems. The combined use of biomarkers that are associated with different pathophysiological aspects of acute myocardial infarction could improve the early diagnostic assessment of patients presenting with chest pain.

Methods

We measured cardiac troponin I, copeptin and heart-type fatty acid-binding protein concentrations in 584 patients who presented to the emergency department with acute chest pain. The diagnostic performances for the diagnosis of acute myocardial infarction and NSTEMI were calculated for the individual markers and their combinations. Separate calculations were made for patients presenting to the emergency department <3 h, 3–6 h and 6–12 h after chest pain onset.

Results

For ruling out acute myocardial infarction, the net predictive values (95% CI) of cardiac troponin I, copeptin and heart-type fatty acid-binding protein were 90.4% (87.3–92.9), 84% (79.8–87.6) and 87% (83.5–90), respectively. Combining the three biomarkers resulted in a net predictive value of 95.8% (92.8–97.8). The improvement was most pronounced in the early presenters (<3 h) where the combined net predictive value was 92.9% (87.3–96.5) compared to 84.6% (79.4–88.9) for cardiac troponin I alone. The area under the receiver operating characteristic for the triple biomarker combination increased significantly ( P < 0.05) compared to that of cardiac troponin I alone (0.880 [0.833–0.928] vs. 0.840 [0.781–0.898], respectively).

Conclusions

Combining copeptin, heart-type fatty acid-binding protein and cardiac troponin I measurements improves the diagnostic performance in patients presenting with chest pain. Importantly, in patients who present early (<3 h) after chest pain onset, the combination improves the diagnostic performance compared to the standard cardiac troponin I measurement alone.