Difficulties with protocol compliance in both arms. Will simplify protocol.

Surgery for scoliosis correction, the abnormal curvature of the spine, is a major procedure often undertaken in adolescents. In adult anesthesia, there is a large volume of literature debating how to optimize fluids administered during surgery, as both too much fluid and too little fluid are associated with worse outcomes. The investigators will compare fluid administration based on the measured amount of blood pumped by the heart during each heart beat (goal-directed therapy), against standard anesthetic management. The main outcomes are a) post-surgical kidney dysfunction, b) prevalence of intraoperative hypotension, c) volumes of administered fluids, and d) length of hospitalization.

1. Written informed consent from parent/guardian and assent from the patient will be obtained.

2. Each patient will be randomized into either the control arm or Cardio Q directed fluid therapy arm.

3. The following standard monitors will be placed before induction of anesthesia: electrocardiography, non-invasive blood pressure and pulse oximetry. The patient is anesthetized in the supine position using a standardized anesthetic technique. All attempts will be made to maintain normothermia

4. Following induction of anesthesia, the following will be placed: invasive arterial cannula, large bore intravenous cannula, Bispectral index monitor, temperature probe and central venous cannula (if needed).

5. Cardiac output monitor: Following induction of anesthesia and after placement of appropriate lines and monitors, a transoesophageal doppler (TED) probe will be inserted through the mouth into the esophagus and positioned correctly. A normal saline infusion will be started once the patient is anesthetized at 0.5 ml/kg/hour in the line where the drugs will be infused.

   1. Control Group: In this group, fluid administration, using boluses of 5ml/kg of plasmalyte at the anesthesiologist's discretion will be used. Anesthesiologists will be blinded to the cardio-Q numerics on the monitor. The flow waveform and sound will be available to optimize probe position.
   2. Intervention groups: Boluses of 5ml/kg plasmalyte will be given when: either MAP drops 20% from baseline or stroke volume drops 15% from baseline. If the patient is fluid responsive, a further 5ml/kg of fluid will be given.
   3. Vasopressor use: MAP (and stroke volume) becomes unresponsive to a fluid bolus then a bolus of phenylephrine or ephedrine may be given at the anesthesiologist's discretion.

Inclusion Criteria:

• Patients undergoing scoliosis repair
• ASA physical status classification system (ASA) I-III

Exclusion Criteria:

• Pre-existing chronic kidney disease
• Oropharyngeal disease, e.g. pharyngitis
• Esophageal disease, e.g. heartburn, esophageal varices or hiatus hernia.
• Coagulopathy
• Scheduled for two stage procedures