Goal Directed Fluid Therapy in Free Flap Patients
Condition: Free Flap Post Mastectomy
Study type: Interventional

Summary: 
      Fluid management of surgical patients has changed dramatically in recent years. Recent
      studies have shown that so called 'restrictive' fluid strategies can improve outcomes such as
      length of stay and time to fitness for discharge. Furthermore, new monitoring technologies
      have been developed that allow the clinician to better monitor the effects of intravenous
      fluid therapy.

      The fluid management of free flap reconstruction surgery is controversial. As vasoactive
      agent use during the anesthetic is not the preferred intervention for the treatment of
      hypotension, fluid therapy is often administered to correct hemodynamic instability. A
      liberal fluid strategy may predispose the flap to edema, venous congestion and ultimately
      flap failure. A restrictive fluid strategy however has (at this institution) anecdotally been
      reported to lead to a higher incidence of deep venous thrombosis (DVT) and pulmonary embolus
      (PE). Thus, there is clinical equipoise as to the optimal fluid management for these
      patients.

      Non-invasive cardiac output (CO) monitoring based on the arterial pulse contour is a nascent
      technological advance that has been widely validated in the operating theatre. The
      calculation of CO is based on the assumption that stroke volume is proportional to the
      integral of the area under the arterial pressure versus time curve. With these monitors, the
      variation in stroke volume during mechanical ventilation is also calculated and this can be
      utilized as an estimate of the patient's volume status. A stroke volume variation (SVV) of
      less than 15% has been shown to be indicative that a patient is no longer volume responsive.

      In our study, we plan to recruit patients undergoing microvascular free flap reconstruction.
      Patients will be randomized to either standard care, or goal directed fluid therapy.

      All patients will receive a pre-operative 5 ml kg-1 bolus of normal saline. Subsequently, all
      patients will then receive lactated ringers at a rate of 5 ml kg-1 hr-1. Patients in the
      intervention group will have their CO and SVV monitored by a Flo-Trac pulse contour monitor
      (Edwards Life Sciences, Irvine, CA). Patients in the intervention group will receive 6%
      tetrastarch boluses (Voluven, Fresenius Kabi, Hamburg, Germany) if their SVV exceeds 15%.
      Patients in the control arm will receive fluid at a rate and type at the discretion of the
      attending anesthesiologist to maintain hemodynamic stability and a urine output of 0.5 ml
      kg-1 hr-1.

      Intra-operative variables studied will include total fluid administered (colloid and
      crystalloid), urine output, SVV and CO (both at the start and end of surgery). Postoperative
      variables examined will be urine output, daily fluid balance (days 0-3), incidence of DVT,
      PE, pulmonary edema, rate of re-operation, daily serum creatinine, chloride and bicarbonate
      concentration, and incidence of flap failure.

      Measurements of flap oxygenation and water content will be made with near infrared
      spectroscopy at baseline, and during the immediate post-operative period (days 1-7).

      We hypothesize that the goal directed group would have more intra-operative colloid given
      with a reduced incidence of adverse outcomes.
    


Intervention name(s): Goal Directed Fluid Administration; Control
Intervention type(s): Other; Other
Intervention description(s): Intravenous Fluid will be given if SVV exceeds 13%; Fluids titrated at discretion of anesthesiologist.
Allocation: Randomized
Intervention model: Single Group Assignment
Masking: Single
Primary purpose: Treatment