Neuromuscular Blockade Masks Anesthetic Awareness

A new study reports that while one in 20,000 patients accidentally wakes up during general anesthesia (GA), neuromuscular paralysis prevents them from alerting medical staff.

Researchers at Oxford University Hospitals NHS Trust (United Kingdom), St. James Hospital (Dublin, Ireland), and other institutions participating in the 5th National Audit Project (NAP5) conducted a study to estimate incidences of accidental awareness during GA. The results showed that the incidence of certain, probable, and possible accidental awareness cases was about 1:19,600 anesthetics. The incidence of accidental awareness during GA reported to NAP5 were overwhelmingly during neuromuscular blockade (1:8,200), while without it the incidence was only 1:135,900.

The results also showed a considerable variation across subtypes of techniques or subspecialties, with the highest incidence of accidental awareness being during caesarean section delivery (1:670). The results also showed that two-thirds of cases of accidental awareness experiences arose in the dynamic induction and emergence phases of anesthesia. During induction, factors included use of thiopental, rapid sequence induction, obesity, difficult airway management, neuromuscular blockade, and interruptions of anesthetic delivery during movement from anesthetic room to theatre.

During emergence from anesthesia, residual paralysis was perceived by patients as accidental awareness, and commonly related to a failure to ensure full return of motor capacity. The one third of accidental awareness events that arose during the maintenance phase of anesthesia were mostly due to problems at induction or towards the end of anesthesia. Risk factors of accidental awareness included female sex, age, obesity; anesthetist seniority, previous awareness, out-of-hours operating, emergencies, type of surgery, and use of neuromuscular blockade. The study was published in the October 2014 issue of Anaesthesia.

“Patients described a range of sensations, including choking, paralysis, pain, hallucinations, and near-death experiences. Most episodes were short-lived, with 75% of them lasting under five minutes,” said lead author consult anesthetist Prof. Jaideep Pandit, of Oxford University Hospitals. “Among the symptoms experienced during the event, paralysis was the most distressing to patients, more so than pain. Paralysis is terrifying and has never been experienced by most people.”

GA involves a drug concoction that often includes a paralytic to ease the insertion of a breathing tube, prevent patients from moving, and allow surgeons to operate in areas that are inaccessible when muscles are tense. Anesthetic awareness occurs when the amount of anesthesia is sufficient to cause paralysis, but is not enough to suppress human consciousness. Certain surgeries, where lower doses of anesthesia are required, carry a higher risk. Emergency C-sections, for instance, necessitate lower doses of anesthetic to prevent harm to the baby. Lower doses are also required during cardiac and emergency trauma surgeries, since large doses could harm the patient.

Related Links:
Oxford University Hospitals NHS Trust
St. James Hospital