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Delayed Awakening / Recovery / Emergence from Anaesthesia
Vandana Lahiri
Often we here from people saying that so
and so did not come out of (awaken from) anaesthesia or that a person was given excessive dose of an anaesthetic and hence went into coma. Is this possible? Well, one must remember that time to emerge from anaesthesia is very variable and depends on many factors which may be related to the patient, the type of anaesthetic given and the length of surgery. Let us review those factors as well as the causes.
As the patient begins to awaken from general anaesthesia, he/she may experience some confusion, disorientation, difficulty in moving limbs or difficulty thinking clearly. This is normal. It may take some time before the effects of the anaesthesia are completely gone. At the end of anaesthesia and surgery the patient should be awake or at least easily arousable, protecting his / her airway and maintaining adequate ventilation.
Anaesthesiologists give combination of various drugs including anaesthetic agents, hypnotics, sedatives, narcotics / analgesics, muscle relaxants etc.
In this modern era, anaesthetic drugs and narcotic drugs with short duration of action are available, also ample of monitoring facilities and equipment having precise controll on delivery of the anaesthetic agents are available which help the anaesthesiologists titrate their dosages of drugs and achieve their most important goal of bringing the patient back to his preoperative status as early as possible after having anaesthetised him. Despite all of these, patients may have delayed recovery from anaesthesia due to the following factors.
A. Drug Related factors / causes
Duration and type of anaesthetic given: When the duration of surgery and therefore inhalational anaesthetic agent (halothane, isoflurane, sevoflurane, desflurane etc.) is longer, emergence is prolonged / delayed as it depends on the total tissue uptake of the inhalational agent.
For most of the intravenous anaesthetic drugs the termination of drug action depends on the time required to metabolise or excrete the drug (elimination or metabolic half life) and in this situation, advanced age or renal or hepatic disease can prolong drug action. For intravenous anaesthetic agents like thiopentone and propofol, immediate recovery depends mainly on redistribution from blood and brain into muscle and fat. Patients given propofol for induction and/or maintenance recover faster than those receiving other agents because propofol is rapidly metabolised by the liver and possibly also at other extrahepatic sites.
Potentiation by other drugs: Prior ingestion of sedative premedication, such as benzodiazepines or alcohol, will potentiate the central nervous system depressant effects of anaesthetic and analgesic drugs, and may delay emergence from anaesthesia. Patients may be given narcotics (pethidine, morphine, norphine, fentanyl, sufentanil. alfentanil) to relieve their pain and these agents may delay recovery.
Prolonged neuromuscular blockade: Prolonged apnoea following suxamethonium “scoline apnoea” is due to an abnormal or absent plasma cholinesterase enzyme. In pregnancy and liver disease, levels of this enzyme are lower and repeated doses of suxamethonium) may produce a “dual block” which is prolonged and slow to recover. The newer muscle relaxant mivacurium is also metabolised by plasma cholinesterase and ‘mivacurium apnoea’ may occur.
In renal failure there is reduced elimination of non depolarizing muscle relaxants such as pancuronium and vecuronium. Large doses of aminoglycoside antibiotics (gentamicin etc) can prolong muscle relaxant action. Acidosis can also have this effect.
Patients with myasthenia gravis are very sensitive to non-depolarising muscle relaxants. In the muscular dystrophies there is also increased sensitivity to muscle relaxants and to all respiratory depressant drugs.
Residual neuromuscular blockade results in paralysis which may be perceived as unresponsiveness though the patient may be fully conscious and awake. This may occur secondary to overdose (relative overdose or inadvertent overdose) or incomplete reversal of non-depolarising muscle relaxants or in a patient with suxamethonium apnoea. A nerve stimulator will assist the diagnosis.
Hepatic and / or Renal diseases: Almost all the anaesthetic drugs are dependent for their metabolism and excretion on these two organ systems, hence diseases of any one of them will have effect on recovery from anaesthesia if the dosages of the anaesthetic drugs are not given keeping derangement of these two organ systems in mind.
Overdose: Frail, small or elderly patients generally require lower doses than fit, normal sized adults just like smaller doses are required in patients with renal or hepatic failure. If regular doses are given in these patients then recovery may be delayed due to delayed drug metabolism and or excretion.
B. Metabolic factors / causes
An underlying metabolic derangement or disorder may be responsible for delayed recovery after anaesthesia. Conditions include:
Hypoglycaemia can occur in small children having been advised preoperative starvation and those who have been given insulin or oral hypoglycaemic drugs. It may also occur in liver failure, in the presence of alcohol excess and in septicaemia and malaria.
Hyperglycaemia may occur in decompensated diabetics i.e.: hyperosmotic hyper-glycaemic diabetic coma, or diabetic ketoacidosis.
Electrolyte imbalance: Most important causes are hyponatraemia, hypokalaemia and hypocalcaemia. This may be secondary to the underlying illness or as a consequence of the surgical procedure e.g. hyponatraemia occurring with trans-urethral resection of prostate (where glycine or other hypotonic fluid is used for irrigation).
Hypothermia: It can easily occur in extremes of age with modern operation theaters having temperatures in the range of 20 – 22 degree Celsius. Severe hypothermia may lead to reduce conscious level. A core temperature of less than 33oC has a marked anaesthetic effect itself and will potentiate the CNS depressant effects of anaesthetic drugs. In addition hypothermia reduces the MAC value of inhalational agents, antagonises muscle relaxant reversal and limits drug metabolism.
Hypothyroidism : Because of decreased drug metabolism, regular doses may become relative overdoses of medications (e.g., morphine, hypnotics, anaesthetic agents, sedatives) and may lead to delayed recovery or can even precipitate myxoedema crisis.
Central anticholinergic syndrome may rarely follow the use of anticholinergic drugs especially hyoscine, but also antihistamines, antidepressants, phenothiazines and pethidine. It has also been reported after volatile anaesthetic agents, ketamine and benzodiazepines. It may manifest as confusion, restlessness, hallucinations, convulsions and coma, and therefore as delayed awakening from anaesthesia. Peripheral anti-cholinergic effects; dry mouth, tachycardia, blurred vision etc may also be present. Treatment is with physostigmine .
C. Respiratory system related factors / causes
Patients with chronic obstructive pulmonary disease who do not breathe effectively during or after anaesthesia may become hypercarbic (raised CO2) to a level that may produce sedation or even unconsciousness. Risk factors in addition to underlying respiratory disease, particularly those with CO2 retention preoperatively, include high dose opioids, obstructed airway and poor relaxant reversal. The diagnosis is usually suspected clinically and may be confirmed by arterial blood gas analysis or measurement of the end tidal CO2. Note that patients receiving oxygen may have normal SpO2 readings even with significantly raised CO2 readings. They will require ventilatory support for some time.
D. Neurological Complications
Cerebral hypoxia due to any reason may result in reduced conscious level, which may first present as delayed awakening from anaesthesia, especially if the hypoxic insult has occurred during anaesthesia e.g., severe bronchospasm, severe hypotension, cardiac arrest etc. Even obstructed breathing during induction of anaesthesia in patients who have abnormal anatomy of airway giving rise to difficulty in passing an endotracheal tube or maintenance of patent airway once they lose consciousness may give rise to cerebral hypoxia. Anaesthetic accidents like disconnection of circuit, inadvertent hypoxic mixture due to faulty anaesthesia machine, hypoventilation during anaesthesia etc. can give rise to cerebral hypoxia, but these things can be diagnosed before cerebral hypoxia can occur by various monitoring parameters used during the course of anaesthesia and hence are rare causes of cerebral hypoxia with modern technology.
Intracerebral event such as haemorrhage, embolism or thrombosis, though very rare except in neurosurgery, cardiac surgery, cerebrovascular and carotid surgery, may give rise to delayed recovery or even coma. When patient does not regain consciousness the anaesthesiologists may be blamed for giving excess anaesthetic agents unless proved by detailed investigations.
Coma during the course of anaesthesia is impossible to diagnose. Even if it occurs due to any reason that is not related to anaesthesia, at the end of an anaesthetic procedure it will lead to a condition called “patient not waking from anaesthesia”. The reasons can be multiple and should be sought for and ruled out, especially patients not having revealed their suffering from diseases like diabetes, endocrine disorders, neurological disorders, hepatic and renal problems.
Evaluation, Management and Immediate Care
Airway - maintain a clear airway and give oxygen. Reintubate if indicated.
Breathing - ensure adequate respiration. If indicated ventilate the patient effectively via an endotracheal tube. Monitor SpO2.
Circulation - assess blood pressure, heart rate, ECG, peripheral perfusion, consciousness level and urine output. Inotropes may be needed.
Review the history, investigations, and perioperative management, including the anaesthetic chart and the timings of drug administration, looking for a possible cause of the delay in recovery.
Assess for persisting neuromuscular blockade, using a nerve stimulator if available.
Look for signs of opioid narcosis - pin point pupils and slow respiratory rate. In this situation a test dose of naloxone may be given: The duration of action of naloxone is approximately 20 minutes and this may be shorter than the effect of the opioid. Subsequent doses of naloxone may therefore be required.
Where it is suspected that the delayed recovery is due to an excess of benzodiazepine (diazepam or midazolam) or other drugs, management is supportive, with maintenance of airway and ventilation until the drug has been metabolised. Where the specific benzodiazepine antagonist flumazenil is available it can be tried. However, Flumazenil is expensive, and may cause arrhythmias, hypertension and convulsions. Its use is generally not indicated.
Measure the patient’s temperature, and warm if necessary. Forced air warming device is the most effective method. However wrapping in blankets, and / or tin foil sheets, ensuring the room is kept warm, and giving warmed iv fluids, will also help.
Check blood glucose - and correct with iv dextrose if it is less than 3 mmol/l. Hyperglycaemia should be managed by sliding scale of insulin.
Measure and correct plasma electrolytes – If no other cause can be found for delayed emergence from anaesthesia, an intracerebral event may be suspected and a full neurological examination should be performed, looking particularly for localising signs. However radiological imaging (CT or MRI scan) is often required to confirm the diagnosis.
Summary
Recovery from anaesthesia occurs as the effects of the anaesthetic medications wear off. How quickly the patient recovers from anaesthesia depends on the type of anaesthesia received, duration of surgical procedure and therefore anaesthesia time, individual patient’s response to the anaesthetic drugs, and whether the patient received other medications which may sedate the patients and apparently it looks as if the patient is still under the effects of an anaesthetic drug or he has delayed recovery.
Patient’s age and general health also affect how quickly he/she recovers. Patients with certain medical conditions may have difficulty clearing anaesthetics from their body, which can delay recovery.
Delayed awakening of varying degrees is not uncommon after anaesthesia, and may have a number of different causes, individual or combined, which may be both drug or non - drug related. The primary management is always support of airway, breathing and circulation, whilst the cause is sought and treated as outlined above. |
