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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