• Institution of renal replacement therapy [ Time Frame: 28 days ] [ Designated as safety issue: No ]
• Duration of ICU stay [ Time Frame: 28 days ] [ Designated as safety issue: No ]
• Duration of hospital stay [ Time Frame: 28 days ] [ Designated as safety issue: No ]
• Hospital mortality [ Time Frame: 28 days ] [ Designated as safety issue: No ]
• Hospital discharge with the ongoing requirement for renal replacement therapy [ Time Frame: 28 days ] [ Designated as safety issue: No ]
• Peak serum NGAL and cystatin C. [ Time Frame: 28 days ] [ Designated as safety issue: No ]
• Peak urine NGAL, IL-18 and cystatin C [ Time Frame: 28 days ] [ Designated as safety issue: No ]

• Institution of renal replacement therapy [ Designated as safety issue: No ]
• Duration of ICU stay [ Designated as safety issue: No ]
• Duration of hospital stay [ Designated as safety issue: No ]
• Hospital mortality [ Designated as safety issue: No ]
• Hospital discharge with the ongoing requirement for renal replacement therapy [ Designated as safety issue: No ]
• Peak serum NGAL and cystatin C. [ Designated as safety issue: No ]
• Peak urine NGAL, IL-18 and cystatin C [ Designated as safety issue: No ]

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

The investigators hypothesise:

1. In patients with SIRS (including the subsets of patients with greater illness severity, such as severe sepsis and septic shock), sodium bicarbonate will delay or avert the development of acute renal failure (RIFLE class I, F, L or E).
2. In patients with SIRS (including the subsets of patients with greater illness severity, such as severe sepsis and septic shock), serum NGAL is a sensitive and specific predictor of the subsequent development of acute renal failure (RIFLE class I, F, L or E).
3. Serum NGAL can accurately identify patients with SIRS who will gain the greatest benefit from an intervention capable of delaying or averting the progression of early renal impairment to acute renal failure.
4. Changes in serum NGAL with and without treatment with sodium bicarbonate are more predictive of subsequent clinical course at an earlier time point than are conventionally measured markers of renal function (serum creatinine, serum urea, calculated glomerular filtration rate) and other experimental markers of renal function (urine IL-18 and NGAL, serum or urine cystatin C).

To test these hypotheses the investigators have designed a protocol that simultaneously tests both NGAL as a diagnostic strategy and sodium bicarbonate as a therapeutic intervention.

• Systemic Inflammatory Response Syndrome
• Oliguria
• Renal Impairment

• Drug: Sodium bicarbonate
• Drug: Placebo

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

• 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