Thank you for your inquiry. Some health care facilities continue to follow a monitoring period of 4-5 hours for the MH susceptible or those with established diagnoses. There are a few hospitals however that have adopted a shorter required monitoring period of 2-3 hours, as the first hour post-anesthesia is key.
I contacted MHAUS, and will have posted their reply below.
Thank you for contacting OPANA.

Post-operative Procedure
If the anesthetic course has been uneventful:
Continue to monitor vital signs for one to two hours. Perioperative dantrolene is not necessary if there has been no evidence of hypermetabolism.

The patient susceptible to MH undergoing outpatient surgery may be discharged on the day of surgery if the anesthetic has been uneventful. A minimum period of 1.0 hour in PACU monitoring vital signs at least every 15 minutes and 1.5 hours in phase 2 PACU/step down is recommended