There is a high prevalence of vitamin D deficiency in the critically ill patient population, with approximately 60% of patients found to be vitamin D deficient, (25(OH)D concentrations <20 ng/mL) and an additional 30% of patients being vitamin D insufficient, (25(OH)D = 20-30 ng/mL).Approximately 80% of sepsis/septic shock patients experience respiratory failure and require mechanical ventilation. Furthermore, several studies document that vitamin D deficiency could be associated with poor outcomes in critically ill patient.

Inclusion Criteria:

• Diagnosed with sepsis and required mechanical ventilation (MV) within 24 hours from ICU admission.
• Expected to require mechanical ventilation for at least 72 hours after study entry.

Exclusion Criteria:

• Age <18 years.
• inability to obtain informed consent from the patient and/or legally authorized representative.
• BMI> 40.
• Pregnant or breastfeeding.
• Chronic kidney diseases
• Pancreatitis.
• Hepatic insufficiency
• Cases with coagulopathy
• Moribund and not expected to survive 96 hours.
• Ongoing shock
• History of therapy with high dose vitamin D3 within previous 6 months.
• History of disorders associated with hypercalcemia
• Cancer as the cause of sepsis.
• Subjects undergoing chemotherapy.
• Immune compromised patients.
• Pneumonia developed < 48 hours following intubation.
• Patients with history of aspiration before intubation.
• known allergy to vitamin D.