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Decrease in minimum alveolar concentration of sevoflurane during anaesthesia and arthroscopy
1Self Defense Force Hanshin Hospital, Department of Anaesthesia, 4-1-50 Kushiro, Kawanishi, Hyogo 666-0024, Japan. higu-chi@ka2.so-net.ne.jp
Background And Objective:
Although the MACtetanus (minimum alveolar concentration that prevents movement in response to electrical tetanus stimulation in 50% of patients) of isoflurane decreases during anaesthesia and surgery, it is not known whether this occurs to the same extent with other inhalational anaesthetics. We determined the MACtetanus of sevoflurane before and after surgery.
Methods:
Eleven patients who underwent arthroscopy of the shoulder underwent inhalational induction of anaesthesia with sevoflurane and tracheal intubation by succinylcholine. MACtetanus was determined in each patient by testing the response to a 10 s, 50 Hz, 80 mA transcutaneous tetanic electrical stimulus to the ulnar nerve at varying concentrations of sevoflurane. The end-tidal concentration of sevoflurane was kept constant for 15 min before each stimulus and the concentration of sevoflurane varied in increments of 0.1% until a sequence of three alternate responses (move, not move, move) or (not move, move, not move) was obtained. After arthroscopy of the shoulder, individual MACtetanus were measured as described above.
Results:
The mean MACtetanus decreased from 2.22 +/- 0.29% before arthroscopy to 1.82 +/- 0.26% after arthroscopy (P < 0.01).
Conclusions:
It is concluded that the MACtetanus of sevoflurane decreases during anaesthesia and surgery.
Insights
The minimum alveolar concentration (MAC) of sevoflurane that prevents movement during surgery decreased significantly in patients undergoing shoulder arthroscopy. This finding indicates sevoflurane
Area of Science:
- Anesthesiology
- Pharmacology
Background:
- The minimum alveolar concentration (MAC) of isoflurane decreases during anesthesia and surgery.
- It is unknown if other inhalational anesthetics exhibit similar MAC reduction.
Purpose of the Study:
- To determine the MACtetanus of sevoflurane before and after surgery.
- To investigate the effect of surgery on sevoflurane's anesthetic potency.
Main Methods:
- Eleven patients undergoing shoulder arthroscopy received sevoflurane anesthesia.
- MACtetanus was determined using transcutaneous electrical tetanic stimulation before and after surgery.
- Sevoflurane concentration was adjusted until a specific motor response pattern was achieved.
Main Results:
- The mean MACtetanus of sevoflurane decreased from 2.22% before surgery to 1.82% after surgery (P < 0.01).
- This reduction was statistically significant.
Conclusions:
- The MACtetanus of sevoflurane decreases during anesthesia and surgery.
- Sevoflurane's potency is reduced by surgical procedures.