Case Study
A 24-year-old morbidly obese nulliparous parturient with an unremarkable medical and obstetric history presented at 39 weeks’ gestation in active labor. On examination, her cervix was dilated 4 cm, and she was having regular uterine contractions. As per her plan of care, a combined spinal-epidural (CSE) technique was initiated for labor analgesia. Within 1 hour of initiation of the CSE, the patient was rushed to the OR because cardiotocography (CTG) showed persistent fetal bradycardia of 75 beats/min. During the transfer, the trainee anesthetist began topping up the epidural catheter using 20 ml 2% lidocaine with 100 µg epinephrine and 100 µg fentanyl. The repeat CTG in the OR showed persistent fetal bradycardia requiring immediate delivery of the fetus. Because the epidural block was found to be inadequate on testing, a decision was made to proceed with general anesthesia (GA). After preoxygenation using four vital capacity breaths, induction of GA was started using a standard rapid-sequence induction (RSI) technique with thiopental 375 mg and suxamethonium 100 mg. The first attempt at intubation with direct laryngoscopy using a Macintosh No. 3 blade revealed a Cormack Lehane view of Grade IIIb, leading to an unsuccessful intubation attempt. After face mask ventilation with 100% oxygen for 30 seconds while maintaining cricoid pressure, a second attempt at intubation was made with a Macintosh No. 4 blade using a conventional malleable stylet which was also not successful. Continuous face mask ventilation with 100% oxygen was maintained while a senior anesthetist from another OR attended the call for urgent help and successfully performed endotracheal intubation using a gum elastic bougie. The patient maintained her oxygen saturation levels above 95% at all times, but her heart rate and blood pressure showed higher than baseline readings. Surgery proceeded immediately after confirmation of the endotracheal tube position, and anesthesia was maintained with an end-tidal minimal alveolar concentration (MAC) of 0.7 using sevoflurane with a mixture of 50% oxygen in nitrous oxide (N2O). The surgery and anesthesia remained otherwise uncomplicated.
The next day, the anesthetist responsible for her original management was called by the ward nurse to assess the patient, who appeared to be in distress and claimed to remember events that took place during surgery. She looked terrified while recollecting her memory of “painful pressure on her throat” and a “feeling of suffocation.” A Brice-modified questionnaire (Table 29.1) was used to make a diagnosis of intraoperative awareness. Using the Michigan classification of awareness instrument (Table 29.2), the intraoperative event was graded as Class 4D. The patient was counseled and had a detailed explanation about the series of events that could have been responsible for her postoperative distress. The anesthetist apologized for the unfortunate occurrence and offered reassurance with expert help. The patient eventually developed posttraumatic stress disorder (PTSD), which was managed by a psychotherapist using cognitive-behavioral therapy (CBT). She made a complete recovery within 3 years and went on to have another child by cesarean delivery under regional anesthesia.
| 1. What was the last thing you remember before going to sleep? |
| 2. What is the first thing you remember after waking up? |
| 3. Do you remember anything between going to sleep and waking up? |
| 4. Did you dream during your procedure? |
| 5. What was the worst thing about your operation? |
Table 29.2 Michigan Awareness Classification Instrument
| Class 0: No awareness |
| Class 1: Isolated auditory perceptions |
| Class 2: Tactile perceptions (e.g., surgical manipulation or endotracheal tube) |
| Class 3: Pain |
| Class 4: Paralysis (e.g., feeling one cannot move, speak, or breathe) |
| Class 5: Paralysis and pain. An additional designation of “D” for distress is included for patient reports of fear, anxiety, suffocation, sense of doom, sense of impending death. |
| D: Modifier that is added to signify emotional distress |
Key Points
Patients may experience accidental awareness during general anesthesia (AAGA) due to insufficient anesthesia.
Multiple factors causing AAGA include inadequate doses of induction anesthetic agent and the absence of anesthesia maintenance during difficult airway management.
Some patients may develop PTSD, which ideally should be managed with psychotherapy.
Discussion
Accidental awareness during general anesthesia (AAGA) is an infrequent but serious complication of general anesthesia occurring due to the inability to achieve the intended level of unconsciousness throughout the whole procedure. It is believed to occur as a result of an imbalance between the depth of anesthesia and the stimulus to which a patient is exposed.
AAGA is classified based on the patient’s ability to recall any intraoperative event. Explicit awareness refers to the conscious recollection of events, either spontaneously or on direct questioning. Implicit awareness, by contrast, refers to changes in performance or behavior that are produced by previous experiences but without any conscious recollection of those experiences.1
Owing to rarity and underreporting, the true incidence of AAGA remains unknown. Several multicenter studies using the Brice questionnaire consistently quote the incidence to be 0.1–0.2 percent2–4 in the general population. It is three times more likely to occur in females than in males. A high incidence is observed in the obstetric population with a range varying between 0.4 and 1.3 percent.5–7 According to the National Audit Project 5 (NAP5) activity survey (http://www.nationalauditprojects.org.uk/NAP5report), which relied only on the self-reporting of awareness, cases from the obstetric population comprised of 0.8 percent of all general anesthesias (GAs) but accounted for 10 percent of all cases of AAGA.
Most cases of AAGA are inconsequential, but some patients experience unwanted psychological sequelae, particularly if it is accompanied by a painful memory of the surgery. These can range from short-term insomnia, anxiety disorders, and distressing flashbacks to irreversible fear of future surgery, depression, and posttraumatic stress disorder.8–10 It may also have serious medicolegal implications for the anesthetist. A recent analysis by the American Society of Anesthesiologists’ (ASA) Closed Claim Project revealed that 1.9 percent of all claims were for awareness under general anesthesia.8
Risk Factors
Intraoperative awareness is a multifactorial event. Available epidemiologic studies classify the risk factors into three main categories.
1. Patient Related
Young Age.
The obstetric population represents a younger age group, and a higher incidence is described in young patients undergoing GA.2, 11 Resistance to anesthetic agents and the higher level of anxiety observed in this age group could be contributing factors.
Difficult Airway.
The incidence of difficult airway in the pregnant population is eight times higher than in their nonpregnant counterparts.12–14 Prolonged instrumentation due to a difficult airway remains one of the major predisposing factors of AAGA today.
Obesity.
Obesity is frequently encountered during pregnancy, which, in turn, puts parturients at high risk of having a difficult airway and underdosing of anesthetic agents.
Fear and Anxiety.
Most GAs are administered for emergency cesarean deliveries, which consequently elevates patients’ anxiety levels.
Factors Associated with Resistance to Anesthetic Agents.
Pyrexia, previous frequent exposure to anesthetics, hyperthyroidism, tobacco smoking, alcohol consumption, and chronic use of drugs (e.g., opioids, amphetamines, cocaine, and benzodiazepines) are all established causes of resistance to anesthetics.
Avoidance of Premedication.
Obstetric patients are not prescribed sedative or analgesic premedication because of the concern of causing unwanted side effects to the unborn baby.
Physiologic Changes of Pregnancy.
The tachycardia in pregnancy may mask the clinical signs of inadequate anesthesia. At the same time, increased cardiac output not only decreases the duration of action of IV anesthetics but also prolongs the time to establish effective partial pressure of volatile agents, leading to a potential period of “light” or inadequate anesthesia and AAGA.
2. Anesthesia Related
Rapid-Sequence Induction (RSI).
The tradition of using a RSI technique for induction of GA in the obstetric population remains unchanged. Frequently, due to the nature of the emergency, adequate time is not allowed for the anesthetic drugs to take full effect before airway manipulation or surgery is undertaken. Moreover, routine ventilation with volatile anesthetics is often avoided by some anesthetists before endotracheal intubation.
Choice of Induction Agents.
The choice of propofol versus thiopental for induction of GA is still a subject of controversy in obstetrics. Some anesthetists favor the use of thiopental because it has a faster onset, has an easily detectable definitive endpoint indicating the onset of unconsciousness, and provides better hemodynamic stability than propofol. However, the optimal dose of thiopental is still controversial, and it has been suggested that the recommended maximum dose in adults may not be sufficient for the obstetric population.15, 16 More recently, propofol has been gaining popularity in obstetrics despite some earlier concerns about its slower onset and the effect on the compromised mother and fetus, the last being rare in clinical practice. Another reason for favoring the use of propofol is the well-known risk of thiopental–antibiotic syringe swap increasing the risk of AAGA (http://www.nationalauditprojects.org.uk/NAP5report).
Inappropriate Use of Volatile Agents and Nitrous Oxide.
Previous practice advocated the use of a lower end-tidal MAC of volatile anesthetic agents in an attempt to minimize the occurrence of neonatal sedation and blood loss secondary to uterine atony. Moreover, a recurring theme called “mind the gap” has been emerging in the induction section of obstetric anesthesia. This gap is the period between rapid redistribution of the IV induction agent and slowly increasing partial pressure of the volatile anesthetic (Figure 29.1). Difficult airway management, delay in turning on the agent, and a slow increase in the ratio of inhaled anesthetic fraction due to low anesthesia gas-flow techniques are attributable factors causing a delay in achieving an effective partial pressure of a volatile agent such as sevoflurane. Furthermore, the practice of using a high concentration of oxygen until delivery of the fetus prevents the use of N2O.
Figure 29.1 Mind the gap: diagrammatic representation of a gap that corresponds to the period between the rapid redistribution of the IV induction agent and the slowly increasing partial pressure of the volatile anesthetic.
Avoidance of Opioids.
Opioids are not routinely administered as a part of standard RSI because they readily cross the placenta and may cause neonatal respiratory depression. Their use also may delay the return of spontaneous ventilation in the mother in case of a failed intubation. However, these concerns lack scientific evidence, and opioids are increasingly being used as part of a balanced anesthetic technique for obstetric GA in the same manner as for nonobstetric procedures.
Difficulty in Monitoring the Depth of Anesthesia (DOA).
Despite substantial advancements in anesthesia over several decades, unfortunately there is no single foolproof method of monitoring the DOA. Several studies4 demonstrated that absolute reliance on either bispectral index (BIS) or end-tidal anesthetic concentration (ETAC) to be questionable. Over and above this, the physiologic signs of pregnancy, as mentioned earlier, add more uncertainty.
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