S2E6 - Maintenance

Airwayve

Two overarching goals for the maintenance phase of an anesthetic:

• Maintain appropriate depth of anesthetic
• Maintain patient’s stability

Inhalational Anesthetics

• Volatile agents: sevoflurane and desflurane (most common), isoflurane (less common)
• Nitrous oxide: low potency, can be used in MH, flammable
• Minimum alveolar concentration (MAC): alveolar concentration of a specific inhaled agent that inhibits motor response to a painful stimulus in 50% of patients

IV infusion

• TIVA: total intravenous anesthetic
• Infusion of a sedative agent (most commonly propofol) +/- other agents (such as opioids or benzodiazepines)
• Advantages: can be used in MH cases, less postoperative nausea and vomiting, can avoid airway instrumentation and aerosolization

Intraoperative monitoring

• For each physiologic system, consider:
  • What parameters should I be concerned with?
  • How can I measure or monitor them?
  • What actions can I take to correct an imbalance?

Temperature

• Monitor: temperature probe
• Adjust: air warming device or IV fluid warmer

Neuromuscular

• Monitor: observe patient movement, check Train-of-Four on peripheral nerve stimulator
• Adjust: give neuromuscular blocker if needed, or reversal if appropriate

Ventilation

• Monitor: observe chest rise, auscultate lungs, end-tidal CO2 tracing, flow-volume loop (this goes in the opposite direction with positive pressure ventilation vs. spontaneous breathing!)
• Adjust: ventilator settings such as PEEP, inspiratory pressure, tidal volume, respiratory rate

Oxygenation

• Monitor: observe lips for cyanosis, pulse oximetry on the monitor
• Adjust: FiO2

Hemodynamics

• Monitor: blood pressure, heart rate, ECG tracing
• Adjust: sedative drugs, analgesics, IV fluids; if necessary, consider rescue drugs such as phenylephrine, ephedrine, and atropine

Volume status

• Monitor: blood pressure, intraoperative blood loss, urine output
• Adjust: IV crystalloid fluids, blood products if needed

Practical things to do during the maintenance phase:

• Come to the OR with some questions in mind; the maintenance phase can be a good time to discuss physiology and other concepts with your staff
• Read up on your patient and try to anticipate any specific issues that could arise
• Catch up on charting, if this is done by hand
• Draw up medications for the next case, and ensure that your syringes are organized and labelled
• Go see your next patient and do a preoperative assessment
• Ask your staff, “How can I help?”

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