Maintenance of Anesthesia

Techniques
1. Inhalational anesthetics, supplemented with IV analgesics and antiemetics have been the mainstay of anesthesia, but TIVA has recently emerged as a reasonable alternative.
  1. One key advantage that distinguishes inhalational anesthetics from IV anesthesia is the ability to continuously measure the end-tidal (alveolar) anesthetic concentrations of inhaled agents. This measurement provides invaluable information regarding the accuracy of our delivery system and the anesthetic partial pressures in the vessel-rich group of tissues.
  2. Currently, isoflurane, sevoflurane, and desflurane are used to maintain anesthesia in children.
2. TIVA (propofol, ketamine, remifentanil) has become the primary anesthetic technique for children with malignant hyperthermia, for those undergoing spine surgery who also require motor evoked potential monitoring, and for those with a history of severe perioperative nausea and vomiting. In some institutions, it is the standard anesthetic for most surgeries.
Fluid Management
1. General Principles. For young children, a 500-mL bag of lactated Ringer's solution with a graduated Buretrol is appropriate; for infants (<1 year), a 250-mL bag with a Buretrol is preferable. Infants and children <2 years of age who may be hypovolemic should be assessed preoperatively to determine the magnitude of their fluid deficit (mild, moderate, or severe).
2. Elective Surgery
  1. The traditional calculation for the hourly fluid infusion rate has been based on replacing the triad of fluid deficit during fasting, ongoing maintenance, and blood and third-space losses (4 mL/kg is for the first 10 kg, 2 mL/kg is for the second 10 kg, and 1 mL/kg is for the third 10 kg and any additional body weight thereafter).
  2. A reappraisal of the traditional approach recommends establishing euvolemia as quickly as possible with 10 to 40 mL/kg of isotonic solution (with adjustment for those with cardiac and renal diseases) infused during the perioperative period and for children who require IV fluids beyond 6 hours postoperatively, continuing a maintenance solution of isotonic fluid at half their original fluid rate or 2–1–0.5 mL/kg.
Blood Transfusion Therapy
1. Initial blood loss may be replaced with balanced salt solution at a rate of 3 mL of solution for every 1 mL of blood loss.
2. For third-space losses, the replacement volume is based on the severity of the losses (1–2 mL/kg/hr for minor surgery, 2–5 mL/kg/hr for moderate surgery, and 6–10 mL/kg/hr for major surgery and large third-space losses).
3. The threshold for initiating packed red blood cell transfusions in children has undergone a renaissance in the past decade as evidence that the outcome and complications associated with a transfusion threshold of 7 g/100 mL hemoglobin is similar to that of 9 g/100 mL.
  1. The estimated blood volume in children decreases with increasing age from 95 to 100 mL/kg in premature infants to 70 mL/kg in adults.
  2. Maximum allowable blood loss = (starting Hct – target Hct)/(starting Hct).
Prophylaxis for Postoperative Vomiting (Table 42-12: Risk Factors for Postoperative Nausea and Vomiting in Children)
1. To reduce POV after elective surgery, children should be fasted for brief periods and not forced to drink oral fluids postoperatively until they request them (to reduce the risk of vomiting).
2. The optimal prophylactic antiemetic strategy to administer to children during anesthesia is dexamethasone and a 5-HT₃ receptor antagonist, such as ondansetron.
3. Pain is another factor in the genesis of PONV. It can be mitigated with regional anesthesia and NSAIDs instead of opioids.
Regional Anesthesia and Pain Management. There has been a shift from neuraxial (spinal, epidural, caudal) to peripheral nerve blocks, both single-dose and continuous local anesthetic administration for perioperative pain management facilitated by the introduction of ultrasound guidance.
1. Caudal blockade is useful for both lower abdominal and lower extremity surgery in infants and children who are undergoing ambulatory surgery.
  1. For all surgical procedures, a single-shot caudal block can be achieved with 1 mL/kg of bupivacaine 0.175% with epinephrine (1:250,000).
  2. If a continuous caudal block is planned for a child remaining in the hospital for a period, then an 18-gauge IV catheter should be inserted to accept a 21-gauge epidural catheter (0.2 mg/kg/hr of bupivacaine).
  3. Fentanyl (1–2 µg/mL) is often added to the caudal/epidural solution.
2. Epidural anesthesia is performed in the same manner as in adults except that a shorter 5-cm Tuohy 18-gauge needle is more manageable.

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