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Fluid Management

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1. Give reasons for establishing central venous access.

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  • Sits in subclavian or internal jugular with tip directed towards SVC.
  • Measures RAP RVEDP = RV preload and thought to parallel LAP and thus LV preload.
  • Inaccurate in patients with pulmonary HTN, Right heart disease, valvular pathologies, pulmonary edema, PEEP (↑ intrathoracic pressure during expiration ↑ CVP)
  • Also used to infuse inotropes or vasopressors

2. Describe some causes of preoperative hypovolemia.

  • NPO Status
  • Vomiting
  • Diarrhea
  • Bowel Prep
  • Fever
  • Sepsis
  • Trauma
  • Fluid shifts (e.g. burns, ascites, pleural effusion)

3. How is intravascular fluid volume evaluated?

Not very reliable:

  • HR and BP (control for PPV and anesthetics may cause relative hypovolemia)
  • Pulse Oximetry (waveform wanders from baseline)
  • Urine Output (stress response from surgery increases ADH so not reliable measure).
  • Serial ABGs to check lactate.

Reliable in the absence of heart pathology

  • Central Venous Catheter (for CVP).

Very reliable:

  • Pulmonary artery catheter: Most commonly used for in RV dysfunction, pulmonary hypertension, valvular pathology (AS, MR), LV dysfunction.
  • Transesophageal Echocardiogram: Commonly used in major cardiac surgeries and liver transplants.

4. Calculate the maintenance fluid requirements for a 70 kg man.

Maintenance: Generally 4-2-1 rule is used. 4ml/hr/kg for first 10 kg, 2 ml/hr/kg for next 10 kg, 1 ml/hr/kg for each additional kg.

For a 70 kg man, the total fluid requirements are 4 x 10 kg + 2 x 10 kg + 1 x 50 kg = 110 ml/hr.

5. This man has been NPO for 8 hrs. How do these affect intraoperative fluid maintenance requirements?

Compensation for pre-existing fluid deficits: Multiply maintenance requirements by the number of hours NPO. Give 1/2 of additional fluids in the first hour, 1/4 in the 2nd hour, and 1/4 in the 3rd hour.

If the man in the example above has been NPO for 8 hours, he needs an additional 880 ml (for a total of 990 ml). 440 ml (on top of the maintenance 110 ml) will be given in the first hour of the surgery. 220 ml (+110 ml maintenance) will be given in each of the next two hours).

6. What complications are associated with the use of colloids?

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7. What are the ASA guidelines for blood transfusion?

  • Hg < 6 in young, healthy patients. (Patient and practitioner variability)

  • At Hgb 6-10 g/dl, the decision to transfuse is based on:

    • Ongoing signs of organ ischemia
    • Potential or ongoing blood loss
    • Volume status
    • Risk factors for vulnerability to low O2.

8. What fluid is given with blood transfusions?

Normal Saline is used because:

  • LR: Theoretical clot formation due to calcium.
  • D5W: hypotonic solutions (less than 0.9% saline → hemolysis).

  • What are the guidelines for FFP transfusion?

  • Urgent reversal of Coumadin

  • Correction of known factor deficiency
  • Correction of 1) microvascular bleeding with INR > 1.5, 2) INR > 2, or 3) PTT > 2x normal
  • During massive transfusion (before lab results available)
  • Heparin resistance (i.e. antithrombin III deficiency) in patients requiring heparinization