Hypophosphatemia in Critically Ill Adults in a Tertiary Hospital in South India: Prevalence and its Relationship to Outcome

INTRODUCTION: Phosphorus is a vital element in body functions like energy transfer, genetic information storage, intracellular signalling and maintenance of membrane integrity. Critically ill patients may have depleted phosphate stores due to reasons like malnutrition, diuretic use or internal redistribution(1). Recent large studies from western critically ill population have shown a high incidence of hypophosphatemia ranging from 15% to 34%(2,3). There is some evidence for association of hypophosphatemia and adverse outcomes in critically ill(4). Admission day hypophosphatemia was associated with increased intensive care unit (ICU) length of stay and duration of mechanical ventilation(5). However, data on epidemiology of hypophosphatemia in the Indian setting is limited. Our study aims at investigating the burden of hypophosphatemia and the significance of monitoring phosphate levels in critically ill patients. OBJECTIVES: To study the prevalence of hypophosphatemia in adult critically ill population in a tertiary hospital in South India and its relationship to clinical outcomes. MATERIALS AND METHODS: All consecutive patients admitted to the adult ICU were enrolled in the study and admission day clinical details and serum phosphorus levels were noted. Serum phosphorus levels < 2.5 mg/dL was defined as Hypophosphatemia. Patients were assessed for length of stay, need and days of invasive mechanical ventilation, ICU readmission and 28-day mortality. RESULTS: Among 200 adult critically ill patients included in the study, 46 patients (23%) had admission-day hypophosphatemia. The prevalence of mild, moderate and severe hypophosphatemia were 16%, 5.5% and 1.5% respectively. ICU length of stay was longer in patients with hypophosphatemia (Mean 5.7 ± 5.9 days vs 4.63 ± 5.05 days. p = 0.106). Prevalence of hypophosphatemia was greater among females (29% vs 19.8%). However, these differences were not statistically significant. There was a statistically significant difference in prevalence of hypophosphatemia with estimated glomerular filtration rate(eGFR) (36.1% in patients with eGFR ≥ 90 vs 15.6% in patients with eGFR <90; p = 0.003). Hypophosphatemic patients had a higher requirement for need of invasive mechanical ventilation, albeit without statistical significance. (34.8% vs 23.4%; p = 0.122). Other parameters like APACHE II score, SOFA score, NUTRIC score, mortality rates, length of invasive mechanical ventilation, ICU readmission rates were comparable between the two groups. Among patients with normal eGFR (n = 72), the ICU length of stay was longer (p= 0.067) and median SOFA score was higher in patients with hypophosphatemia and this was statistically significant, yet may be clinically insignificant. (p = 0.067). CONCLUSION: This study shows prevalence of admission day hypophosphatemia of around 23%. This first data in Indian adult critically ill is consistent with earlier studies(2,3). However, this study was not powered to explore the association of hypophosphatemia with clinical outcomes. The presence of renal dysfunction in around 64% of patients in study population may have been a confounder between serum phosphorus levels and mortality. This finding suggests that serum phosphorus levels alone may have limited prognostic value(6). This study highlights need of further research on phosphate homeostasis in critically ill.