Association of Hypophosphatemia with Failure-to-Wean from Mechanical Ventilation
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Available online at www.annclinlabsci.org 144 Annals of Clinical & Laboratory Science, vol. 40, no. 2, 2010 Association of Hypophosphatemia with Failure-to-Wean from Mechanical Ventilation Mohammad H. Alsumrain,1 Sami Abdul Jawad,2 Nashat B. Imran,3 Sandeep Riar,1 Vincent A. DeBari,2 and Marc Adelman1 Departments of 1Critical Care Medicine and 2Internal Medicine, Saint Michael’s Medical Center, Newark, New Jersey, 3Department of Internal Medicine, Trinitas Regional Medical Center, Elizabeth, New Jersey, and Seton Hall University School of Health and Medical Sciences, South Orange, New Jersey Abstract. Severe hypophosphatemia is known to be associated with respiratory failure, but there are few studies that specifically examine the relationship between serum phosphorus concentration and failure to wean patients from mechanical ventilation. This study investigated the association between hypophos- phatemia and weaning failure in patients in two medical intensive care units (ICU). The study was conducted in a prospectively developed cohort of 66 patients being treated with ventilatory support and in whom 193 weaning trials were attempted. Ultimately, all 66 subjects were successfully weaned. A cross- sectional analysis was conducted on serum phosphorus levels and success or failure to wean the patients from ventilators. At the time of the successful weaning attempts (n = 66), the subjects’ serum phosphorus concentrations (mean ± SD) were 1.18 ± 0.27 mmol/L, whereas at all failed weaning attempts (n = 127) serum phosphorus concentrations averaged 1.06 ± 0.31 mmol/L (p = 0.008). Subjects with phosphorus concentrations below the reference interval (RI) in our laboratory (
Hypophosphatemia and ventilator weaning failure 145
affiliates of the School of Health and Medical Sciences of Prism v.5 software (GraphPad, San Diego, CA) on a personal
Seton Hall University. The protocol was approved by the computer. Cuzick’s test results were computed manually.
Institutional Review Boards (IRB) of St. Michael’s Medical
Center (Newark, NJ) and Trinitas Regional Medical Center
Results
(Elizabeth, NJ). For medically related protocols at its affiliated
healthcare institutions, Seton Hall University’s IRB delegates
the approval process to the individual facilities at which the A total of 66 patients were enrolled in this study
studies are performed. (35 male and 31 female). Of those, 14 patients
(21.2%) developed hypophosphatemia (defined as a
Protocol and patients. This study examined a prospective
cohort of 66 consecutive patients on mechanical ventilation
value below the lower limit of the RI) during at
admitted to a medical ICU during the 8-mo period from least one of their weaning trials; the other 52
December 2008 to July 2009, inclusive. The inclusion criteria subjects had either normal or slightly elevated
were: patients on ventilatory support above the age of 21 yr
who met the criteria for weaning, which includes patients able
Table 1. Baseline characteristics of subjects in the study. The
to breath spontaneously, who have an adequate cough reflex,
two groups are based on serum phosphorus levels at the time
respiratory rate146 Annals of Clinical & Laboratory Science, vol. 40, no. 2, 2010
serum phosphorus concentrations for all weaning 0.61 suggests that the association of phosphorus
attempts. The baseline characteristics for both of levels with weaning success, though statistically
these groups are shown in Table 1. significant (p = 0.012), is not particularly strong.
A total of 193 weaning trials were conducted The cut-off determined from the ROC curve was
on these patients. Ultimately, all 66 subjects were 1.05 mmol/L, roughly in the middle of the
successfully weaned. Overall, at the time of laboratory RI. We examined the issue of weaning
successful weaning, the subjects’ mean serum failure and found that at the time of successful
phosphorus concentration was 1.18 ± 0.27 mmol/L, weaning (extubation), 48 of 66 (72.7%) subjects
whereas at the time of failed weaning attempts (n = had serum phosphorus levels above the cut-off,
127) serum phosphorus concentrations averaged while for failed weaning trials, ie, extubation not
1.06 ± 0.31 mmol/L (p = 0.008). Total serum accomplished, 70 of 127 (55%) trials were associated
calcium concentrations, obtained simultaneously with serum phosphorus levels below 1.05 mmol/L
with phosphorus, were nearly identical for the two (RR = 1.62; 95% CI: 1.27 to 2.07; p = 0.0002).
groups (successfully weaned: 2.34 ± 0.15 mmol/L; There were 16 subjects who required 4 weaning
failed: 2.34 ± 0.16; p = 0.86). When the patients trials prior to finally being weaned. We examined
were hypophosphatemic, the number of failed phosphorus concentrations during each of these
weaning trials was 26 and the number of successful trials to determine if successive approaches toward
weaning trials was 4. When the patients had a presumably adequate phosphorus level would be
normal or high serum phosphorus levels, based on observed in these subjects. These data are shown in
the RI, the number of failed weaning trials was 101 Fig. 2. As the subjects proceeded toward a successful
and the number of successful trials was 62. (RR = outcome, the median values of serum phosphorus
1.18; 95% CI: 1.06 to 1.32; p = 0.011). demonstrated significant (pHypophosphatemia and ventilator weaning failure 147
Discussion levels increased until they were adequate to effect a
successful outcome. It is important to recognize
Weaning from mechanical ventilation includes the that this effect does not appear related to secondary
entire process of withdrawing ventilator support alterations in serum calcium; indeed, the serum
and removal of the endotracheal tube. Only after calcium concentrations were remarkably similar.
the underlying pathophysiology necessitating In a study such as this, even though
mechanical ventilation is resolved, can the weaning prospectively conducted, there are many factors
process be initiated [13]. associated with weaning failure that are impossible
Hypophosphatemia and other electrolyte to control. We caution strongly against inferring a
abnormalities can cause respiratory failure, but causal role for hypophosphatemia in situations
there are few studies that specifically evaluate the where patients are unable to be weaned from
relative contribution of each of these metabolic ventilator support. However, Aubier et al [4]
derangements to weaning failure [14]. Respiratory performed a quasi-experimental (non-randomized)
insufficiency and failure-to-wean may well be due study of 8 subjects with hypophosphatemia that
to inadequate 2,3-diphosphoglycerate production documented changes in physiologic parameters
causing a shift in the hemoglobin dissociation (eg, diaphragmatic contractility) associated with
curve to the left. Additionally, the respiratory hypophosphatemia. Their data suggest a physiologic
muscles may be weakened by inadequate production mechanism that might explain the weaning failure
of phosphorylated intermediates such as ATP or we observed.
creatine phosphate [15] and diaphragmatic In conclusion, this study supports the import-
contractility may be impaired during the ance of adequate serum phosphorus levels in
hypophosphatemic state [4]. maintaining the strength of the musculature
Gravelyn and colleagues [16] studied 23 responsible for ventilation and it addresses the
hospitalized patients with low serum phosphate specific issue of weaning patients from mechanical
level (148 Annals of Clinical & Laboratory Science, vol. 40, no. 2, 2010
7. Varsano S, Shapiro M, Taragan R, Bruderman I. Hypo- 12. Cuzick J. A Wilcoxon-type test for trend. Stat Med
phosphatemia as a reversible cause of refractory ventil- 1985;4:87-90.
atory failure. Crit Care Med 1983;11:908-909. 13. Alía I, Esteban A, Weaning from mechanical ventilation.
8. Oud L. Transient hypoxic respiratory failure in a patient Crit Care 2000:4:72-80.
with severe hypophosphatemia. Med Sci Monit 2009;15: 14. Boles JM, Bion J, Connors A, Herridge M, Marsh B,
CS49-53. Melot C, Pearl R, Silverman H, Stanchina M, Vieillard-
9. Liu PY, Jeng CY. Severe hypophosphatemia in a patient Baron A, Welte T. Weaning from mechanical ventilation.
with diabetic ketoacidosis and acute respiratory failure. J Eur Respir J 2007;29:1033-1056.
Chin Med Assoc 2004;67:355-359. 15. Dooley J, Fegley A. Laboratory monitoring of mechanical
10. Hasselstrøm L, Wimberley PD, Nielsen VG. Hypophos- ventilation. Crit Care Clin 2007;23:135-148.
phatemia and acute respiratory failure in a diabetic 16. Gravelyn TR, Brophy N, Siegert C, Peters-Golden M.
patient. Intensive Care Med 1986;12:429-431. Hypophosphatemia-associated respiratory muscle weak-
11. Brown EL, Jenkins BA. A case of respiratory failure ness in a general inpatient population. Am J Med 1988;
complicated by acute hypophosphataemia. Anaesthesia 84:870-876.
1980;35:42-45.You can also read
