The aim of PLUS is to conduct a multi-centre, blinded, randomised, controlled trial (RCT) to determine whether fluid resuscitation and therapy with a "balanced" crystalloid solution (Plasma-Lyte 148®) decreases 90-day mortality in critically ill patients requiring fluid resuscitation when compared with the same treatment using 0.9% sodium chloride (saline)

Fluid resuscitation is a fundamental component of the management of acutely and critically ill patients and the choice of fluid is a longstanding issue of debate.

Worldwide, 0.9% saline has traditionally been the most widely used resuscitation fluid, however its use is increasingly challenged by emerging evidence that suggests its high chloride content may have clinically important adverse effects and that resuscitation with so-called "balanced" or "buffered" crystalloids (such as Plasma-Lyte 148®) offer patients better outcomes.

Given the limitations of current evidence, there is now a scientific, ethical and health economic imperative to provide an accurate and reliable estimate of the comparative risks versus benefit of Plasma-Lyte 148® versus 0.9% saline.

The PLUS study is a prospective, multi-centre, parallel group, concealed, blinded, randomised, controlled trial.

The study will test the hypothesis that in a heterogeneous population of critically ill adults, random assignment to Plasma-Lyte 148® for intravascular volume resuscitation and crystalloid fluid therapy in the Intensive Care Unit (ICU) results in different 90-day all-cause mortality when compared with random assignment to 0.9% sodium chloride (saline) for the same treatment.

Each patient who meets all inclusion criteria and no exclusion criteria will be randomised to receive either Plasma-Lyte 148® or 0.9% saline for all resuscitation episodes and for all compatible crystalloid therapy while in ICU for up to 90 days after randomisation. Other crystalloid fluids may be used as carrier fluids for the infusion of any drug for which either Plasma-Lyte 148® or 0.9% saline is considered incompatible.The study treatments will be supplied in identical 1000 ml bags and treatment assignment will be concealed.

The volume of study fluid being administered will be titrated against clinical endpoints determined by the treating clinicians and reviewed as clinically appropriate during the period of resuscitation and ICU treatment.

Inclusion Criteria:

• The patient will receive fluid resuscitation defined as a bolus of fluid, prescribed to be administered over one hour or less to increase or maintain intravascular volume that is in addition to maintenance fluids, or specific fluids used to replace non-physiological fluid losses
• The patient is expected to be in the ICU the day after tomorrow
• The patient is not expected to be well enough to be eating tomorrow
• An arterial or central venous catheter is in situ, or placement is imminent as part of routine management
• Both Plasma-Lyte 148® and 0.9% saline are considered equally appropriate for the patient
• The requirement for fluid resuscitation is supported by at least one of seven pre-specified clinical signs: heart rate > 90 beats per minute; systolic blood pressure < 100 mmHg or mean arterial pressure < 75 mmHg; central venous pressure < 10 mmHg; pulmonary artery wedge pressure < 12 mmHg; capillary refill time > 1 second; OR urine output < 0.5 ml/kg for at least one hour

Exclusion Criteria:

• Age less than 18 years
• Patients who have received more than 500mls of fluid resuscitation (as defined above) prescribed in the ICU during this current ICU admission
• Patients transferred directly from another ICU who have received more than 500mls of fluid resuscitation (as defined above) during that ICU admission
• Contraindication to either study fluid e.g. previous allergic reaction to Plasma-Lyte 148®
• Patients admitted to the ICU with specific fluid requirements: the treatment of burns; following liver transplantation surgery; for correction of specific electrolyte abnormalities
• Patients with traumatic brain injury or those considered at risk of developing cerebral oedema
• Patients in whom death is deemed imminent and inevitable
• Patients with an underlying disease process with a life expectancy of <90 days
• Patients in whom it is unlikely the primary outcome can be ascertained
• Patients who have previously been enrolled in PLUS
• Known or suspected pregnancy