Awareness under general anesthesia is a unique process that could be happen when there is a recall of surrounding events by surgical patients like pain when they were given the general anesthesia.

The main objective of general anesthesia in surgical operations is to abolish the consciousness and pain and to prevent motor, autonomic, and cardiovascular reflex responses. In some of the cases awareness may develop due to overly light anesthesia. Awareness may occur during the operation with or without memory of events. The former is known as “recall” and is an explicit achievement in memory that can be directly asked about.

Improper depression of consciousness leads to clear cut awareness and memories of the events during general anesthesia by blocking cognitive signal processing, it seems convincing that when consciousness is incompletely depressed, acoustic signal transductions may reach the brain.

Causes of awareness during anesthesia:


Awareness usually is associated with one of these situations

  • Light anesthesia. 
  • For some operations, like Cesarean section, or in hypovolemic patients or patients with minimal cardiac reserve, the anesthesiologist may aim to provide light anesthesia. During such circumstances, consciousness and recall is not surprising because judgments of depth of anesthesia are not precise. Muscle relaxants also lead to the problem of the unintentionally “too light” anesthesia in the motionless patient. This is probably the most common cause of awareness, and represents, in a sense, an iatrogenic mishap. Because anesthetic concentrations that block awareness are less than those that prevent motor responses to pain,  inadequately anesthetized, but nonparalyzed, patient usually communicates awakeness by movement.


  • Increased anesthetic requirement of some patients:
  • Some patients are more “resistant” to the results of anesthetics than others. Younger age, tobacco smoking, long-term use of certain drugs can cause an extension in the anesthetic dose needed to produce unconsciousness.
  • Machine malfunction or misuse resulting in an inadequate delivery of anesthetic:
  • This can be caused by an empty vaporizer or a malfunctioning intravenous pump or disconnection of its delivery tubing.


Management during awareness during anesthesia:


There have been cases of fraudulent claims and mistaken recall of events during emergence from anesthesia, however most claims are genuine and credibility can be established easily.

The patient should be assured that the anesthesiologist believes their account and sympathizes with their suffering. Denial of the authenticity of the patient’s experience may adversely influence the patient’s psychologic recovery and may turn the patient toward litigation.

Some explanation of what happened and its reasons should be given;e.g.  , necessity to administer light anesthesia in the presence of significant cardiovascular instability.

The patient should be offered psychologic or psychiatric support. The details of the interview should be recorded in the patient’s chart, and the surgeon, the patient’s nurse, and the hospital lawyer or the physician’s insurer should be notified. [5]


Incidence of awareness of anesthesia:

Awareness experiences range from isolated auditory perceptions to reports of a patient being fully awake, immobilized, and in pain. Awareness during anaesthesia may be experi­enced by 1 or 2 cases out of every 1000 patients who receive general anaesthesia (0.1-0.2%). The overall incidence is higher among obstetric and cardiac cases where it has been quoted at 0.4% and 1.1-1.5% respectively. In children, the incidence is once again higher at 0.8-1.2%.

Most of the patients have a vague auditory recall or a sense of dreaming and may not be unduly disturbed by this experience. In fact, dreams may be recalled more often than actual events and occasion­ally these are very distressing to the patient.

Incidence of AWR varies widely due to methodological differences in postoperative assessment of awareness and differences in anesthetic practice. Although the most common outcome measured is postoperative recall for the awareness event, intraoperative consciousness and explicit recall of intraoperative events may be dissociated from each other. In one study, only one in four patients with evidence of intraoperative awareness had explicit postoperative recall of the event. [6]




Case reports suggest that certain patient characteristics may be associated with intraoperative awareness including age, sex, ASA physi­cal status and drug resistance or tolerance.

Patients at increased risk for intraoperative awareness include those with a history of substance use or abuse (eg opioids, benzodiazepines, cocaine) and chronic pain patients using high doses of opioids. A past history of aware­ness, difficult intubation, ASA physical status of IV/V and a limited haemodynamic reserve are also risk factors. Procedures which are associated with a higher risk include cardiac surgery, caesarean delivery, trauma and emergency surgery.

The use of reduced an­aesthetic doses in the presence of paralysis, rapid se­quence induction and total intravenous anaesthesia have also been implicated.

Awareness of conversations during surgery may be distressing for a patient, but awareness of total paralysis or the excruciating pain of surgical incision may alter a patient’s life permanently.

A careful preoperative evaluation is therefore rec­ommended by the Practice Advisory for identifying patients at risk and a thorough review of the patient’s medical records, a detailed physical examination and a patient or patient family interview may help identify a vulnerable patient.
The causes of intraoperative awareness are as yet not fully established and may be multifactorial. Four categories of causes have been postulated which are as follows:

Unexpected patient specific variability in the dose requirements of anaesthetic drugs:

Cer­tain group of patients have been documented to be more ‘resistant’ to effects of anaesthetics as compared to the others. A younger age group, smoking, long term use of drugs like opiates and alcohol consumption may in­crease the individual requirement for an anaesthetic drug.

Concurrent medications can also af­fect the metabolism and distribution of anaesthetic agents adversely. Pharmacogenetics may therefore be an important factor contributing to intraoperative awareness.

Requirement for light anaesthesia:

Certain operations like caesarean section may require the anaesthesiologist to aim for lighter anaesthesia. In other cases, patients may often be unable to tolerate a suffi­cient dose of anaesthetic because of low physiologic reserves related to factors such as poor cardiac func­tion or severe hypovolemia. Judgement about the ad­equate depth of anaesthesia can thus be imprecise in such patients.

Pharmacological masking of signs of inad­equate depth of anaesthesia:

Anaesthetic concen­trations that block awareness are less than those that prevent motor responses to pain.  Anonparalyzed but inadequately anaesthetized patient usually commu­nicates by movement.

The use of muscle relaxants ren­der such a patient motionless and can lull the anaesthesiologist into a false sense of security. Also the use of drugs like beta blockers or vasodilator agents which have to be given preoperatively for disorders like hypertension may affect intraoperative haemodynamics.

Sometimes the anaesthesiologist may use these drugs to tackle intraoperative tachycardia and hypertension without addressing the underlying cause like inadequate depth of anaesthesia.

Machine malfunction or misuse resulting in an inadequate delivery of anaesthesia:

This can be caused by an empty vaporizer, a malfunctioning intrave­nous pump or a disconnection of its delivery tubing.  Breathing system malfunctions and disconnections have been associated with awareness. Vaporizers may malfunction in a number of ways, each having the potential to deliver an inadequate dose of anaesthetic. These include: an empty vaporizer, miscalibration, impurities in the volatile agent (reducing its saturated vapour pressure) and disconnection from the anaesthetic machine. Blockage of an i.v. infusion pump or catheter, disconnection from the cannula or extravascular location of the cannula may risk awareness during TIVA.

Selection of inadequate anaesthetic dose

Awareness is frequently associated with poor anaesthetic technique. Errors include the omission or late commencement of a volatile agent, inadequate dosing or failure to recognize the signs of awareness.

The selection of anaesthetic dose is based upon the patient’s expected requirement. Patients vary significantly.

Resistance to anaesthetic agents

Factors associated with a degree of resistance to anaesthetic agents include: pyrexia; hyperthyroidism; obesity; anxiety; young age; tobacco smoking; regular, heavy alcohol use; use of recreational drugs (e.g. opioids, amphetamines, cocaine); chronic use of sedatives (e.g. temazepam); and previous and repeated exposure to anaesthetic agents. [7]


Risk factors of awareness under anesthesia:

Risk Factors Episodes of unintended awareness may occur as a result of an inadequate level of anesthesia, equipment malfunction, or patient-related factors, such as alcohol use, substance use disorder, or hemodynamic instability. Unintended awareness may also be related to specific procedures, including trauma surgery, cardiac surgery, cesarean-section, and craniotomy. [8]


Types of awareness

Awareness of conversations during surgery may be distressing for a patient, but awareness of total paralysis or the excruciating pain of surgical incision may alter a patient’s life permanently. The formation of explicit and implicit memories during anaesthesia and surgery is considered potentially damaging to the human psyche. Explicit memory may be recalled spontaneously, or may be provoked by postoperative events or questioning.


Recognizing awareness

The signs of awareness are generated through sympathetic activation. These signs include: sweating, tachycardia, hypertension, tear formation, pupil dilatation and pupil reactivity to light.

Awareness during anaesthesia may also be recognized through the use of a monitor of depth of anaesthesia.


Postoperative management

If a patient complains in the postoperative period of intraoperative awareness, the anaesthetist should visit the patient and obtain a detailed account of the patient’s experience. The anaesthetist should establish the perioperative timing of the episode and distinguish between dreaming and awareness. The details of recalled should be noted in the patient’s records. This information may be of great importance should medico-legal issues arise.

While there have been fraudulent claims and confusion by patients between awareness and memories of events at induction or emergence, the vast majority of claims of awareness are genuine.

It is important that the patient’s experience is taken seriously and that sympathy is expressed. Denial of the veracity of the patient’s claim is very likely to worsen psychological outcome after awareness.


Avoiding awareness

We spoke with the Anaesthesiologists at an Australian Anaesthetic billing company, Fast Tracking Anaesthetic Billing Services. The following recommendations were provided to reduce the risk of awareness.

Premedication with benzodiazepines, or administration of benzodiazepines during induction, reduces the incidence of awareness, particularly in the high-risk period a few minutes after induction. Adequate doses of anaesthetic agents should be given. If cardiovascular or respiratory depression occurs then these systems may require support (e.g. mechanical ventilation, inotropes). Titration of anaesthetic agents to arterial pressure risks intraoperative awareness.

In high-risk situations, the use of a monitor of depth of anaesthesia (e.g. BIS) is probably justified. Such situations include Caesarean section, emergency surgery, surgery associated with large blood loss and patients with a history of previous intraoperative awareness. The use of such monitoring may also be advisable in patients in whom clinical signs of light anaesthesia may be masked (e.g. concurrent β-blockers, diabetes). [9]