occurring in 1 out of 240 parenteral sedation cases and 1 out of 521 general anesthetic cases [1]. It is usually related to patient's anxiety in the preoperative setting and is most frequently observed upon venipuncture for placement of an IV line [16]. Syncope responds well to placing the patient in the Trendelenburg position, as this places the patient's head lower than the thoracic cavity and speeds blood return to the brain. Supplemental oxygen is beneficial and should always be given; it is also useful in cases of near‐syncope. Ammonia smelling salts may also be helpful and are usually applied in situations where Trendelenburg positioning and supplemental oxygen do not result in a rapid return to consciousness.
In the postoperative period, patients may experience syncope due to vasovagal response or transient orthostatic hypotension when rising too quickly from a seated or supine position. This complication may be prevented by assisting all patients when they stand or begin walking, since syncope under these circumstances carries the additional risk of injury from falling. Management consists of patient positioning, supplemental oxygen, and ammonia salts if needed.
Any period of unexpected patient unconsciousness that lasts for several minutes is not considered true syncope. If a loss of consciousness episode lasts more than a few minutes, other causes should be investigated without delay, including the possibility of hypoglycemia, hypotension, dehydration, partial seizure, oversedation, or cerebrovascular accident.
Algorithm 1.1: Loss of Consciousness with Vasovagal Prodrome
Algorithm 1.2: Loss of Consciousness without Vasovagal Prodrome
Oversedation
Oversedation is a relatively common event observed during ambulatory anesthesia that can rapidly develop in severity. It initially manifests as lack of adequate patient response to appropriate stimuli. For example, a patient who previously responded to loud verbal or forceful physical stimuli may suddenly fail to respond. In cases of profound oversedation, a patient may fail to respond to increasingly painful stimuli, and when the plane of general anesthesia is reached, the patient will have lost protective airway responses. If allowed to progress without intervention, oversedation can rapidly advance to airway obstruction, hypopnea, or apnea leading to hypoxemia. In severe cases, respiratory depression can lead to respiratory arrest and depression of cardiac output will be observed.
Oversedation in ambulatory anesthesia takes two forms: unintended deep sedation or general anesthesia during the procedure, or prolonged or delayed awakening in the postoperative period. Intraoperatively, oversedation is produced by too high a dose of an anesthetic drug or a dose of anesthetic that is administered too quickly. Patient factors often figure prominently in cases of oversedation, as patients who are very sensitive to the effects of an anesthetic or who have greatly decreased elimination kinetics will have a narrowed therapeutic range compared to an “average” patient. It can be quite difficult to titrate anesthetic drugs in such a patient, with the result that oversedation is more likely to occur.
Age is an important factor in a patient's response to anesthesia. Sensitivity to anesthetic drugs and alterations in the dosages required to achieve specified levels of sedation are seen with extremes of age. While this may seem self‐evident in the elderly, research shows that the reduction in required anesthetic dose begins as early as age 40–45 [17]. For each decade past the age of 40, there is an observed 10% reduction in the dose of fentanyl required, while for propofol the dose reduction is about 8% [17]. The pediatric population in particular has a markedly idiopathic response to anesthetic drugs, and titration of sedation can be more challenging in this age group. Ironically, patients with very high anxiety levels may be prone to oversedation because they typically require a high initial dose of anesthetic to achieve sedation, but often markedly less medication to maintain a given level of anesthesia. Failure to reduce the dosage of anesthesia adequately after the initial induction bolus in these patients can result in oversedation.
Oversedation may be caused when boluses of a drug are given too quickly or too close together. This typically occurs during an anesthetic procedure when a patient begins to awaken or becomes agitated and additional medications are administered to rapidly deepen the anesthesia. Since all anesthetic drugs take some period of time to exert their effect, failure to wait for the drug to take effect can result in the observation that the dose was insufficient and the administration of an additional bolus. Subsequently, when the additional boluses have had time to take effect, the patient may be in a deeper plane of anesthesia than was intended. This can be partially prevented by the spacing of additional drug boluses and knowing the time to effective onset of the anesthetic drugs utilized. Not all pharmacological agents demonstrate first‐order kinetics, however, and rate of drug onset can be increased or decreased depending on the patient's plasma drug level.
Oversedation can sometimes result when the level of surgical stimulation is rapidly or dramatically decreased. Since surgical stimulation tends to counteract the sedative effects of anesthetic drugs, a higher dose of anesthesia is typically required for more stimulating surgical procedures. A patient who is at an appropriate level of anesthesia may quickly become oversedated if stimulation is decreased or discontinued. In situations where changes in the level of surgical stimulation can be predicted, allowing time for the anesthetic drug to wear off or decreasing the rate of infusion can effectively prevent most oversedation in these cases.
Management of mild oversedation may consist of briefly interrupting the administration of anesthetic drugs and observing the patient for a return to the desired level of anesthesia. If any degree of respiratory obstruction or depression is noted, maneuvers aimed at opening the airway such as a chin lift or jaw thrust should be performed as well. Given the rapid redistribution and short duration of effect of many anesthetic drugs, mild oversedation is self‐correcting with supportive measures within a matter of a few minutes.
Although not a mainstay of treatment, administration of reversal agents may be considered as an adjunctive therapy for oversedation. Few drugs used in ambulatory anesthesia have a reversal agent, but naloxone is able to reverse the effects of opioid agonist drugs and flumazenil is an effective antagonist of the benzodiazepine class of drugs. These reversal agents can be effective in reversing the effects of oversedation due to drug overdosage, but they reverse all actions of a drug including desirable effects such as analgesia, hypnosis, and anxiolysis. They may be considered for the treatment of oversedation and prolonged awakening in the postoperative period and are generally well tolerated. Research has not supported the routine use of reversal agents to speed recovery from ambulatory anesthesia procedures.
Seizures
Seizure activity, both partial type and tonic–clonic seizures, represents abnormal CNS excitation. Because anesthetic drugs act by causing depression of the CNS, seizure activity during an anesthetic procedure is unlikely to occur. In patients with seizure disorders, however, seizures may occur in the preoperative and postoperative periods. Management of seizures involves positioning the patient to avoid injury and loosening tight or restrictive clothing as much as possible. Most seizures will terminate after a few minutes and require no other treatment, though benzodiazepines such as midazolam, lorazepam, or diazepam may be given intravenously or intramuscularly to terminate seizure activity. Since patients will typically become hypoxic during the clonic phase of a tonic–clonic seizure, supplemental oxygen may be beneficial in the immediate postictal period.
CARDIOPULMONARY