What Is Emergence?
What Is Emergence?
Emergence is the period of recovery from anesthesia which occurs from the termination of the anesthetic until the patient is able to respond to verbal stimuli. At the end of anesthesia and surgery the patient should be awake or easily arousal, protecting their airway, maintaining adequate ventilation and with their pain under control. Time to emerge from anesthesia is very variable and depends on many factors related to the patient, the type of anesthetic given and the length of surgery.
Recovery from general or regional anesthesia is a time of great physiological stress for many patients. Emergence from general anesthesia should ideally be a smooth and gradual awakening in a controlled environment. Unfortunately, it often begins in the operating room or during transport to the recovery room and is frequently characterized by airway obstruction, shivering, agitation, delirium, pain, nausea and vomiting, hypothermia, and tachycardia. Even patients receiving spinal or epidural anesthesia can experience marked decreases in blood pressure during transport or recovery; the sympatholytic effects of regional blocks prevent compensatory reflex vasoconstriction when patients are moved or when they sit up.
Emergence Following an Inhalational-Based Anesthetic
The speed of emergence is directly proportionate to alveolar ventilation but inversely proportionate to the agent's blood solubility.
As the duration of anesthesia increases, emergence also becomes increasingly dependent on total tissue uptake, which is a function of agent solubility, the average concentration used, and the duration of exposure to the anesthetic. Recovery is therefore fastest with desflurane slowest from prolonged deep anesthesia with halothane and enflurane. Hypoventilation delays emergence from inhalational anesthesia.
Emergence From an Intravenous Anesthetic
Is a function of its pharmacokinetics (the way in which a drug interacts with the body). Recovery from most intravenous anesthetic agents is dependent primarily on redistribution rather than on elimination half-life (the time required for a quantity to fall to half its value as measured at the beginning of the time period). As the total administered dose increases, however, cumulative effects become apparent in the form of prolonged emergence; the termination of action becomes increasingly dependent on the elimination or metabolic half-life. Under these conditions, advanced age or renal or hepatic disease can prolong emergence. Use of short and ultra- short-acting anesthetic agents such as propofol significantly shortens emergence, time to awakening, and discharge.