Validation the use of refractometer and mathematic equations to measure dietary formula contents for clinical application

Serial Measurements of Refractive Index, Glucose and Protein to Assess Gastric Liquid Nutrient Transport—A Proof-of-Principal Study

Delayed gastric emptying contributes to complications as aspiration or malnutrition. Among patients suffering from acute neurological diseases, motility disorders are prevalent but poorly understood. Thus, methods to measure gastric emptying are required to allow for appropriate adaptions of individual enteral nutrition algorithms. For enterally fed patients repetitive concentration measurements of gastric content have been proposed to assess gastric emptying. This approach can be used to calculate the gastric residual volume (GRV) and transport of nutrition formula (NF), but it has not yet been implemented in clinical routine. The aim of this study was to investigate whether refractometry or other likewise straightforward analytical approaches produce the best results under in vitro conditions mimicking the gastric milieu. We measured NF in different known concentrations, either diluted in water or in simulated gastric fluid (SGF), with each of the following methods: refractometer, handheld glucose meter, and Bradford protein assay. Then, in enterally fed patients suffering from acute neurological disease, we calculated GRVs and nutrition transport and tested possible associations with clinical parameters. In water dilution experiments, NF concentrations could be assessed with the readout parameters of all three methods. Refractometry yielded the most precise results over the broadest range of concentrations and was biased least by the presence of SGF (detection range for Fresubin original fibre, given as volume concentration/normalized error of regression slope after incubation with water or SGF: 0–100 vs. 0–100%/0.5 vs. 3.9%; glucose-measurement: 5–100 vs. 25–100%/7.9 vs. 6.1%; Bradford-assay: 0–100 vs. 0–100%/7.8 vs. 15.7%). Out of 28 enterally fed patients, we calculated significant slower nutrition transport in patients with higher blood glucose (Rho −0.391; p = 0.039) and in patients who received high-dose sufentanil (Rho −0.514; p = 0.005). Also, the calculated nutrition transport could distinguish patients with and without feeding intolerance (Median 6 vs. 17 ml/h; Mann-Whitney test: p = 0.002). The results of our study prove that serial refractometry is a suitable and cost-effective method to assess gastric emptying and to enhance research on gastrointestinal complications of stroke.

Peptide-based enteral formula improves tolerance and clinical outcomes in abdominal surgery patients relative to a whole protein enteral formula

AIM

To compare a dipeptide- and tripeptide-based enteral formula with a standard enteral formula for tolerance and nutritional outcomes in abdominal surgery patients.

METHODS

A retrospective study was performed to assess the differences between a whole-protein formula (WPF) and a dipeptide- and tripeptide-based formula (PEF) in clinical outcomes. Seventy-two adult intensive care unit (ICU) patients with serum albumin concentrations less than 3.0 g/dL were enrolled in this study. Patients were divided into two groups (WPF group = 40 patients, PEF group = 32 patients). The study patients were fed for at least 7 d, with ≥ 1000 mL of enteral formula infused on at least 3 of the days.

RESULTS

The mean serum albumin level on postoperative day (POD) 10, prealbumin levels on POD-5 and POD-10, and total lymphocyte count on POD-5 were significantly higher in the PEF group compared to those in the WPF group (P < 0.05). The average maximum gastric residual volume of the PEF patients during their ICU stays was significantly lower than that for WPF patients.

CONCLUSION

Dipeptide- and tripeptide-based enteral formulas are more efficacious and better tolerated than whole-protein formulas.

Applicability of refractometry for fast routine checking of hospital preparations

Quality control of hospital pharmacy formulations is of the utmost importance to ensure constant quality and to avoid potential mistakes before administration to the patient. In this study we investigated the applicability of refractometry as a fast, inexpensive and easy-to-use quality control measurement. Refractive indices (RI) of a multitude of different hospital formulations with varying concentrations of active compound were measured. The samples consisted of a number of binary aqueous solutions (one compound in water), complex aqueous solutions (multiple compounds in water or in a constant matrix), two suspensions and one emulsion. For all these formulations, linear regression analysis was performed, quality control limits determined and accuracy and repeatability were checked. Subsequently, actual hospital pharmacy samples were analyzed to check whether they were within the specified limits. For both binary and complex aqueous formulations, repeatability was good and a linear correlation for all samples could be observed on condition that the concentration of the active compound was sufficiently high. The refractometer was not sensitive enough for solutions of folic acid and levothyroxine, which had too low a concentration of active compound. Due to lack of homogeneity and light scattering, emulsions and suspensions do not seem suitable for quality control by refractometry. A mathematical equation was generated to predict the refractive index of an aqueous solution containing clonidine HCl as active compound. Values calculated from the equation were compared with measured values and deviations of all samples were found to be lower than 1.3%. In order to use refractometry in a hospital pharmacy for quality control of multicomponent samples, additional intermediate measurements would be required, to overcome the fact that refractometry is not compound specific. In conclusion, we found that refractometry could potentially be useful for daily, fast quality measurements of relatively concentrated binary and more complex aqueous solutions in the hospital pharmacy.

Enteral nutrition: better navigation, yet unknown destination?

The nutrition dose truly absorbed by a patient is crucial information in the management or the investigation of nutrition during critical illness. In the present issue of Critical Care, assessment of nutritional losses in stools was studied. These losses together with enteral nutrition lost in gastric fluids and enteral nutrition prescribed but never infused make up the difference between the dose supposedly given to a patient and the amount effectively taken up. Additionally, the optimal dosing and timing of nutrition during critical illness are still debated. When enteral nutrition is insufficient, the options are limited.