The investigators will determine the feasibility, safety and efficacy of intravenous sodium bicarbonate in reducing progression to overt acute renal failure in patients with the systemic inflammatory response syndrome, and low urine output or early acute renal impairment as defined by serum neutrophil gelatinase-associated lipocalin (NGAL).

The investigators hypothesise:

1. In patients with SIRS and oliguria the early administration of sodium bicarbonate or sodium chloride (control) triggered by an abnormally high NGAL level is feasible.
2. In patients with SIRS and oliguria the early administration of sodium bicarbonate or sodium chloride (control) triggered by an abnormally high NGAL level is safe.
3. In patients with SIRS and oliguria the early administration of sodium bicarbonate or sodium chloride (control) triggered by an abnormally high NGAL level leads to signs or trends of efficacy as measured by serum creatinine derived indices.

Inclusion Criteria:

• Consent obtained
• Diagnosis of SIRS. Requires any TWO of:

temperature > 38°C or < 36°C OR heart rate > 90 beats/min OR respiratory rate > 20 breaths/min. PaCO2 < 32 mm Hg OR alteration of white blood cell count > 12,000 cells/mm3, < 4,000 cells/mm3, or the presence of > 10% immature neutrophils

• elevated lipocalin level
• Arterial line already in place
• Central venous catheter already in place
• Age ≥ 18 years
• Within 24 hours of admission to the ICU

Exclusion Criteria:

• Unlikely to remain in ICU for >72 hours
• Moribund patient
• Pre-existing CKD, transplant or ESRD
• Receiving (or about to receive) continuous renal replacement therapy for acute renal failure at time of enrolment
• Diagnosis of acute GN, AIN, vasculitis or post-renal aetiology
• Known/suspected study allergy to sodium bicarbonate
• Enrolling physician concern about patient enrolment