Phosphate Urine Excretion in Critically Ill Patients

Data collection We will document the following data for each patient, for maximum of five days from admission: * Demographic data, including age; sex, height, weight, admission reason to ICU. * Acute Physiology And Chronic Health Evaluation II (APACHE II) Score (24 hours after ICU admission) * Daily Sequential Organ Failure Assessment (SOFA) Score and SOFA components. * Daily Ventilation status * Daily vasopressor requirement * Daily Renal replacement therapy (if any) * Daily urine volume * Daily fluid balance - including daily fluid input and output * Daily 6 hours urine collection, with documentation of collection volume, urine creatinine, and urine electrolytes. Specimens from the first two days of admission will be sent to laboratory analysis only after the patient is admitted for more than 48 hours. * Calculation of glomerular filtration rate (GFR) based on urine collection findings. * Calculation of phosphate excretion amount based on urine collection findings - both maximal phosphate tubular reabsorption rate (TmP) and Fractional Excretion of phosphate (FePi). * Daily serum phosphate and calcium levels * Daily phosphate intake - from enteral nutrition, parenteral nutrition, and supplemental (enteral and parenteral). * For the last 60 patients - a single measurement of PTH and vitamin D. * Patient outcomes: ICU length of stay; Hospital length of stay; Length of ventilation; Ventilator free days at 28 days; Mortality - at ICU, during hospital admission, and at 28 \& 90 days.