Zinc supplementation in intensive care: Results of a UK survey☆
Introduction
Zinc plays a crucial role in many metabolic processes, and because of its involvement in the immune response and wound healing, it is considered to be of importance in critically ill patients. Such patients have an increased metabolic rate [1], often against a background of recent inadequate dietary intake and ongoing feeding difficulties. The low plasma concentrations of zinc that are often found might seem to reflect poor nutrition. However, this does not necessarily indicate deficiency because plasma zinc concentrations fall as part of the systemic inflammatory response [2]. This decrease in plasma zinc is partially caused by redistribution of carrier proteins because of increased vascular permeability; sequestration into tissues [3]; and losses in urine, drains [4], and mucosal secretions [5]. Plasma zinc is predominantly bound to albumin, and so, the low concentrations of albumin found during the systemic inflammatory response also partially explain low plasma zinc concentrations. Consequently, plasma zinc measurement during the systemic inflammatory response and, therefore, in critically ill patients is uninformative and may be misleading.
A recent Scottish survey demonstrated that during routine clinical care of patients on total parenteral nutrition, the existence of an acute inflammatory response is often not considered when interpreting plasma trace element concentrations (personal findings). This laboratory receives significant numbers of plasma zinc requests from intensive care units (ICUs) throughout Scotland, suggesting that this is also the case in this setting. This prompted the current survey, by questionnaire and telephone inquiry, of UK ICUs to investigate whether zinc was measured routinely, if low results were inappropriately considered to indicate deficiency, if this prompted zinc supplementation, and if so, the doses used.
Section snippets
Methods
A list of adult ICUs in the UK was compiled from the ICU directory. A questionnaire (see Supplemental Material) was addressed to the first named consultant in the units and sent to all 263 ICUs throughout the UK. Nonresponders were contacted by telephone, and responses to the questionnaire were recorded.
Intensive care units were asked if zinc supplementation was administered in addition to Additrace (Fresenius Kabi, Bad Homburg, Germany) or any of the standard proprietary enteral or parenteral
Results
A total of 92 (35%) of 263 questionnaires were returned by post. The response rate increased to 259 (99%) by contacting nonresponders by telephone and recording questionnaire details. Two questionnaires, which were completed irrationally, were discarded.
Plasma zinc was routinely measured in 40 (18%) of 227 ICUs (36 ICUs did not reply to this question). When plasma zinc is measured, the frequency was daily in 6 ICUs (2.6%), twice-weekly in 10 (4.4%), weekly in 18 (7.9%), and fortnightly in 6
Discussion
Zinc is an essential trace element having important structural roles and as a cofactor in many enzyme reactions. It is required in the immune system for normal T-cell function [6], [7]; for pancreatic synthesis, storage, and secretion of insulin [8]; as an antioxidant in superoxide dismutase [9]; and in wound healing by stimulation of keratinocytes, fibroblasts, and collagen synthesis [10]. As a result of its wide-ranging biologic effects, the rationale for its replacement in zinc deficiency is
Conclusions
In ICU patients, zinc deficiency cannot be diagnosed based on a low plasma zinc concentration, and resultant supplementation with zinc is inappropriate. Plasma zinc is effectively uninterpretable in the presence of a significant inflammatory response, making its routine measurement in ICU patients irrelevant. The practice of supplementation of pharmacologic doses of zinc, in excess of 90 mg/d, that we found in a significant minority of ICUs is not evidence based. Therefore, it would be unwise
Acknowledgments
We would like to acknowledge the secretarial support of Sadie Murray for the preparation of questionnaires and letters and for entering results onto a database.
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There are no conflicts of interest to declare.