Systematic review and meta-analyses of the effect of lipid emulsion on microbial growth in parenteral nutrition

BACKGROUND

As lipid in parenteral nutrition (PN) purportedly enhances microbial growth, recommendations limit infusion of lipid PN (or lipid emulsion) from a single container to 24h (48h for lipid-free PN). However, the associated evidence base is ambiguous.

AIM

To examine factors affecting microbial growth in PN.

METHODS

A systematic review with meta-analyses examined effects of nutrients on microbial growth in PN infusates over a 48-h period using the growth ratio {GR=log₁₀[colony-forming units (cfu)/mL at 48h/cfu/mL at time zero]}.

FINDINGS

Factors influencing GR in PN included glucose, microbial species, temperature, osmolarity, presence of vitamins, trace elements and lipid, and amino acid profile. Using unmatched datasets (N=306), a general linear model found that lipid inclusion in PN represented 3.3% of the variability, which was less than that due to glucose concentration (5.8%), microbial species (35.3%) and microbe-infusate interaction (4.4%). Using matched datasets (N=38 pairs), lipid inclusion in PN represented 5.4% of the variability (P=0.076), which was less than that due to glucose concentration (8.5%; P=0.025), microbial species (75.5%; P<0.001) and microbe-infusate interaction (13.3%; P=0.382). Using meta-analyses of matched datasets, the presence of lipid in PN at fixed glucose concentrations did not significantly increase GR of Candida albicans, Escherichia coli or Staphylococcus epidermidis (P=0.352, P=0.025 and P=0.494, respectively; overall P=0.175).

CONCLUSION

Lipid inclusion in PN is only one of several factors that may influence microbial growth in PN. Any recommendations about the duration of PN infusion from a single container should account for all these factors, and should be weighted according to microbial species likely to contaminate PN.

Nutritional support in critical care patients

Malnutrition in the form of insufficient nutrient intake to support tissue metabolism undermines appropriate medical or surgical therapeutic management of a case. The major consequences of malnutrition in all patients are decreased immunocompetence, decreased tissue synthesis and repair, and altered intermediary drug metabolism. A practical goal is to begin nutritional support within 24 hours of the injury, illness, or presentation. There are only two methods by which nutrients can be supplied to the body: enteral and parenteral. General guidelines are presented to help establish a foundation.

Use of endotoxin retentive intravenous filters with paediatric total parenteral nutrition solutions

We studied the retention of endotoxin released in a clinically relevant form by senescent bacteria during filtration of amino acid-based total parenteral nutrition (TPN) solutions by the PALL Intravenous Set Saver Filter (ELD96). The ELD96 was shown to be capable of providing an effluent free of detectable endotoxin (less than 0.125 endotoxin unit-equivalents/ml) when challenged with 10(6) total cells of Pseudomonas aeruginosa during simulated clinical TPN infusion. Parallel control experiments showed that endotoxin was released from the test organism and penetrated through conventional intravenous (i.v.) solution filters.

Growth of microorganisms in total nutrient admixtures

It has been reported that intravenous fat emulsions, because of their isotonicity and neutral pH, support microbial growth, but traditional parenteral nutrition solutions, being hypertonic and more acidic, are not as supportive. To date, few studies have documented microbial growth in total nutrient admixtures (TNA) containing dextrose, amino acids, fat, electrolytes, vitamins, and trace elements. This study was undertaken to analyze the growth of Staphylococcus aureus, Candida albicans and four gram-negative enteric bacilli in three different nutrient admixtures, with and without the inclusion of 5% fat emulsion. The composition of the admixtures was either 5, 10, or 25% dextrose; either 0 or 5% fat; and 3% amino acids, electrolytes, vitamins, and trace elements. All admixtures were innoculated with 100 colony-forming units per milliliter, incubated at room (25 degrees C) or refrigerated (4 degrees C) temperature, with samples withdrawn at 0, 3, 6, 12, 24, and 48 hours and plated in triplicate. Only C. albicans demonstrated any significant growth regardless of fat content. The pH of the admixtures was similar (acidic), and all solutions were hypertonic and found to inhibit bacterial growth. Conclusions suggest that TNA, when formulated with normal concentrations of additives, is no more likely to support growth of contaminant organisms than the traditional solutions. This contradicts the notion that the addition of fat to total parenteral nutrition will enhance the ability of these admixtures to support microbial growth.

Storage of mixtures for total parenteral nutrition. II. Microbiological control of large volume TPN mixtures

Microbiological control of TPN mixtures can be performed either by controlling the aseptic filling procedure using culture medium instead of intravenous solutions, or by an end-product sterility test. A microbiological process control of the filling procedure is described, and it is shown that a hospital pharmacy can prepare 3-litre bags without contamination. The number of 3-litre bags necessary in the process control is discussed, as well as the frequency with which a control should be performed. A possible non-destructive system for testing each 3-litre bag microbiologically is outlined and discussed. This system may be used when TPN mixtures without lipid emulsion are stored for longer periods.

Home parenteral nutrition programs

The technique of home parenteral nutrition (HPN) is becoming a more widely used method to treat patients who cannot eat for prolonged periods; to date, more than 500 patients have been trained nationwide. Training has been limited for the most part to larger centers which have more experience in providing this complex patient education. As this technique becomes more widely accepted, however, other less experienced health care professionals will be called upon to develop HPN training programs. For this reason, it is important to simplify these training programs, with initial attention directed toward the procedures used to prepare the total parenteral nutrition solution. The chance of potential errors can be reduced by using amino acid solutions with electrolytes included in the formulation. When possible, complexity can be reduced by administering vitamins and extra electrolytes orally. The teaching program can be simplified by developing or using existing training manuals, which standardize procedures so that consistent methods are taught and performed. The manual can serve as a reference for patient and teacher alike. Distribution of supplies can be simplified by employing commercially available shipment programs; but, while these are very convenient for the patient and pharmacy, the costs of such programs could be a limitation. Finally, the extensive work required to arrange reimbursement for services and supplies also can be simplified. Often a social worker can facilitate this process because of experience and training in dealing with payment problems. In addition, training fees should be negotiated with third party payors early in the development of HPN programs. By simplifying these basic elements in an HPN, the task of training patients is less imposing and can be made more widely available to those who need this treatment modality.

Potential hazards associated with microbial contamination of in-line filters during intravenous therapy

The survival and multiplication of Enterobacter agglomerans, Klebsiella pneumoniae, Serratia marcescens, and Pseudomonas aeruginosa in 0.45- and 0.22-micrometer in-line filter sets during simulated infusions were studied to evaluate the ability of each filter type to prevent infusions of these bacteria into patients. Bacteria were found to proliferate in the upstream compartment of sets housing both filter porosities. None of the 0.22-micrometer in-line filters were penetrated by the test bacteria. In contrast, P. aeruginosa was observed to penetrate each 0.45-micrometer in-line filter examined within 12 h of continuous infusion. Tribe Klebsielleae organisms penetrated a proportion of the 0.45-micrometer filters usually between 48 and 72 h of infusion. In addition, the elution of endotoxin from gram-negative bacteria trapped in the filter set during infusion is reported. Collected infusion filtrate exhibited a trend of increasing endotoxin-like activity with an increasing duration of infusion. In the case of E. agglomerans, mean peak levels of approximately 65 pg of Escherichia coli endotoxin per ml were attained after 72 h. Other bacteria produced similar results, except mean peak levels ranged from 5 to 30 pg/ml. It was noted that endotoxin-like activity was not detected in filtrate eluted from contaminated filter sets during the initial 24 h of infusion. We conclude that to avoid potential hazards of bacterial penetration and endotoxin production during continuous use of in-line filter sets, the 0.22-micrometer filter type must be employed and replaced every 24 h.