Patient Preparation

Patient Preparation

• Informed Anesthesia Consent: Ensure the patient understands the anesthesia process and risks.
• Fasting Order Pre-Anesthesia: To reduce the risk of aspiration.
• Blood Request: Based on the type of surgery.
• Postoperative Care Location: Day case, admission, ICU.
• Perioperative Fluid Management.

Total Body Water (TBW)

• Body water compartments and electrolyte contents.
• Primary ECF cation is Na, with a very small contribution from K, Ca, Mg.
• Primary ICF cation is K, with smaller contributions from Mg, Na.

Fluid & Electrolyte Regulation

• Volume regulation:
  • Antidiuretic hormone.
  • Renin/angiotensin/aldosterone system.
  • Baroreceptors in carotid arteries and aorta.
  • Stretch receptors in atrium and juxtaglomerular apparatus.
  • Cortisol.

Importance of Adequate Oxygen Delivery

The final goal is the delivery of adequate oxygen to the tissues. Factors affecting oxygen delivery include:

• Cardiac output (stroke volume x heart rate).
• Hemoglobin concentration.
• Oxygen saturation.

ASA Fasting Guidelines

• Clear liquid and water: 2 hours
• Breast milk: 4 hours
• Formula milk: 6 hours
• Light meal: 6 hours
• Heavy meal: 8 hours

Perioperative Fluid Requirements

• Maintenance fluid requirements.
• Fluid deficits.
• Third space losses.
• Replacing third space losses.
• Blood loss.
• Special additional losses.

Example Calculation

62-year-old gentleman, 70 kg, going for open hemicolectomy at 08:00 am.

• NPO after 22:00, received bowel prep.
• Expected procedure duration is 3 hours.
• Expected blood loss is 500 ml.

Estimated Intraoperative Fluid Requirements:

• Maintenance: Use rule 4-2-1.
  • 10 kg x 4 = 40 ml
  • 10 kg x 2 = 20 ml
  • 50 kg x 1 = 50 ml
  • Total: 40 + 20 + 50 = 110 ml x 3 hours = 330 ml.
• Fluid Deficit: Maintenance x NPO hours.
  • NPO (110 ml x 10 hours = 1100 ml).
  • Bowel prep (1000 ml).
  • Total deficit = 2100 ml.
• Third Space Losses: Surgical trauma type x weight x surgery duration.
  • 8 ml/kg/hr (8 x 70 x 3) = 1680 ml.
• Blood Loss: 1:3 rule.
  • 500 ml x 3 = 1500 ml.
• Total: 330 + 2100 + 1680 + 1500 = 5610 ml.

Intravenous Fluids

• Crystalloids: Combination of water and electrolytes.
  • Isotonic salt solution.
  • Hypotonic salt solution.
  • Hypertonic salt solution.

Blood Transfusion

Why?

• Improvement of oxygen transport.
• Restoration of red cell mass.
• Correction of bleeding caused by platelet dysfunction.
• Correction of bleeding caused by factor deficiencies.

When is Transfusion Necessary?

• “Transfusion Trigger”: Hgb level at which transfusion should be given.
• Varies with patients and procedures.

Oxygen Delivery

Oxygen Delivery (DO2) is the oxygen that is delivered to the tissues.

• DO2 = COP x CaO2
• Cardiac Output (CO) = HR x SV
• Oxygen Content (CaO2):
  • (Hgb x 1.39) O2 saturation + PaO2(0.003).
• Hgb is the main determinant of oxygen content in the blood.

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