During a routine cesarean section under general anesthesia in a 28-year-old primigravida, the anesthesiologist notices that the patient moves in response to surgical incision despite an end-tidal sevoflurane concentration of 1.2%. The patient's heart rate and blood pressure are stable. What is the most appropriate immediate next step?

Explanation

## Clinical Context The patient is demonstrating inadequate anesthetic depth (movement to surgical stimulus) despite receiving sevoflurane. The end-tidal concentration of 1.2% is below the MAC of sevoflurane (2.0%), explaining the inadequate anesthesia. Hemodynamic stability indicates that increasing the volatile agent concentration is safe. ## Understanding MAC and Anesthetic Depth **Key Point:** MAC (minimum alveolar concentration) is the steady-state end-tidal concentration of an inhalational agent at which 50% of patients do not respond to a standard surgical stimulus (incision). To ensure reliable anesthesia in 95% of patients, a concentration of 1.3× MAC is recommended. **Mnemonic:** MAC = **M**inimum **A**lveolar **C**oncentration — the dose-response threshold for inhalational anesthetics. **High-Yield:** Sevoflurane MAC = 2.0%. To ensure adequate anesthesia in most patients, target 1.3 × 2.0% = 2.6% end-tidal concentration. At 1.2%, the patient is at only 60% of MAC—inadequate for surgery. ## MAC Values of Common Volatile Agents | Agent | MAC (%) | Clinical Notes | | --- | --- | --- | | Nitrous oxide | 104 | Cannot be used as sole anesthetic; adjuvant only | | Desflurane | 6.0 | Rapid emergence; airway irritant | | Isoflurane | 1.15 | Slower emergence than sevoflurane | | Sevoflurane | 2.0 | Rapid emergence; popular for induction | | Halothane | 0.75 | Rarely used (hepatotoxicity risk) | ## Management Algorithm for Inadequate Anesthetic Depth ```mermaid flowchart TD A[Patient moves to surgical stimulus]:::outcome --> B{Hemodynamically stable?}:::decision B -->|Yes| C[Increase volatile agent concentration<br/>to 1.3× MAC]:::action B -->|No| D[Investigate cause:<br/>Hypovolemia, sepsis, etc.]:::action C --> E[Reassess depth after 2-3 minutes]:::action E --> F{Adequate anesthesia?}:::decision F -->|Yes| G[Maintain current concentration]:::action F -->|No| H[Consider IV opioid adjunct<br/>or deepen further]:::action ``` **Clinical Pearl:** In obstetrics, volatile agents are often used at lower concentrations to minimize fetal exposure. However, inadequate anesthesia is dangerous for both mother and fetus. If movement occurs, increase the volatile agent concentration first before resorting to IV agents, as this is the most direct and predictable approach. ## Why This Answer is Correct The patient is at 1.2% sevoflurane, which is below MAC (2.0%). The hemodynamic stability permits safe increase to 1.8–2.0% (approaching 1.3× MAC). This will reliably deepen anesthesia and prevent intraoperative awareness and movement. Reassessment after 2–3 minutes allows the anesthetic to reach steady state at the new concentration.