Elsevier

Journal of Critical Care

Volume 28, Issue 5, October 2013, Pages 838-843
Journal of Critical Care

Clinical Potpourri
Hypophosphatemia on the intensive care unit: Individualized phosphate replacement based on serum levels and distribution volume,☆☆,

https://doi.org/10.1016/j.jcrc.2013.03.002Get rights and content

Abstract

Background

Hypophosphatemia occurs in about 25% of patients admitted to the intensive care unit. To date, a safe and validated phosphate replacement protocol is not available.

Objective

To evaluate an individualized phosphate replacement regimen.

Design

Fifty consecutive intensive care unit patients with a serum phosphate level < 0.6 mmol/L were treated with sodium-potassium-phosphate intravenously at a rate of 10 mmol/h. The dose was calculated according to the following equation: Phosphate dose in mmol = 0.5 × Body Weight × (1.25 – [serum Phosphate]). Phosphate levels were measured immediately upon completion of the infusion, as well as the next morning at 8 am.

Results

Post-infusion phosphate levels were > 0.6 mmol/L in 98% of the patients. Hyperphosphatemia, hyperkalemia or a decrease in serum calcium were not observed. In about a third of patients serum phosphate decreased to < 0.6 mmol/L within the next 24 hours after infusion. The phosphate distribution volume calculated from the results of infusion and corrected for renal phosphate loss during the infusion period was 0.51 L/kg (95% CI 0.42–0.61 L/kg).

Conclusion

This study shows that phosphate replacement with dose calculation based on serum phosphate levels and a Vd of 0.5 L/kg is effective and safe.

Introduction

Hypophosphatemia, defined as a serum phosphate level < 0.6 mmol/L, is a frequent finding in intensive care unit (ICU) patients. It may be caused by redistribution, gastro-intestinal loss, or renal phosphate loss. The reported prevalence of ICU hypophosphatemia ranges from 10–80%, with a mean of about 25% [1]. Severe hypophosphatemia, defined as a level < 0.3 mmol/L, can lead to respiratory insufficiency, heart failure, arythmias, rhabdomyolysis, neuropathy, and thrombocytopenia [2], [3]. The clinical significance of moderate hypophosphatemia (serum phosphate 0.3-0.6 mmol/L) is currently not exactly known. However, it is common practice to correct phosphate levels < 0.6 mmol/L in patients on the ICU because there is evidence to suggest that moderate hypophosphatemia may impair diaphragmatic contractility, reduce left ventricular stroke work and can lead to insulin resistance [4], [5], [6], [7].

Several phosphate replacement schedules have been proposed [1], [2], [8], [9], [10], [11], [12]. Most are based on the use of fixed doses without adjustment for the degree of hypophosphatemia or body weight, and most studies included only small numbers of patients. To date, no uniform policy or protocol has emerged from these data. There is no international guideline for phosphate replacement on the ICU, and thus, much variability exists between countries and individual hospitals. Based on a pilot-study in 7 subjects, French et al have proposed a protocol with individualized dose-calculation derived from the actual serum phosphate level and an apparent phosphate distribution volume [13]. This approach is attractive because physiologically it is the most rational approach of all previously proposed regimens. We therefore decided to implement this protocol as standard practice in our ICU, to assess its effects on serum phosphate levels, and to evaluate its safety. The present report describes the results of this analysis.

Section snippets

Patients and methods

This study was performed in a 15 bed ICU of a large teaching hospital in the Netherlands. The ICU population mainly consisted of general medical and surgical patients. It did not include post-CABG (coronary artery bypass graft) or severe trauma patients. All patients admitted to this ICU are routinely screened for hypophosphatemia on day 1, 3, 5, and 7. The present study includes the first 50 patients who were found to have a serum phosphate level < 0.60 mmol/L during their stay. Exclusion

Results

Baseline characteristics such as age, gender, weight, APACHE score, and ICU admission diagnosis are summarized in Table 1.

Pre-infusion phosphate levels ranged from 0.18–0.58 mmol/L, with a mean of 0.46 ± 0.01 mmol/L. Two out of 50 patients had a serum P < .30 mmol/L. The mean phosphate replacement dose was 28 ± 1 mmol (range, 16-52 mmol). This was associated with a mean potassium infusion of 23 ± 1 mmol (range, 13–46 mmol). The mean infusion time was 2 hours and 45 minutes (range, 1.5-5.5

Discussion

This study demonstrates the effect and safety of a calculated phosphate loading dose based on a distribution volume of 0.50 L/kg body weight and a target serum phosphate of 1.25 mmol/L. Ninety-eight percent of the patients achieved a serum phosphate ≥ 0.6 mmol/L, and none of the patients developed clinically relevant hyperphosphatemia or hyperkalemia. In addition, the Ca × P product never exceeded the upper normal limit, and serum calcium did not change significantly. Thus, intravascular or

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Conception and design: AB, MB, DT, MR, HdB.

☆☆

Analysis and interpretation: AB, MR, MB, CM, HdB.

Important intellectual content: AB, MB, HdB.

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