[Yao's Anesthesiology] Anesthesia management of myasthenia gravis (2)

A patient with myasthenia gravis, female, 25 years old, G3P2, 24 weeks of gestation, intrauterine death, planned to undergo cervical dilation and uterine evacuation, has progressively worsening diplopia and dysphagia symptoms
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Suffering from myasthenia gravis (MG) for 10 years, she underwent thymectomy for thymoma in the early stage of her second pregnancy 2 years ago, and the symptoms disappeared after surgery, and she stopped taking medicine
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The vital signs were as follows: pulse 60 beats/min, blood pressure 150/80 mmHg, respiratory rate 20 beats/min
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Arterial oxygen saturation was 98% on inhalation
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Height 155cm, weight 65kg
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C.
Intraoperative management 1.
How to monitor this patient intraoperatively? 2.
What anesthesia options are available for this patient? 3.
Can myasthenia gravis patients use muscle relaxants? D.
Postoperative Management 1.
Does the patient require prolonged ventilation support postoperatively? 2.
How to provide postoperative analgesia for this patient? 3.
The patient was successfully removed from the tracheal tube in the operating room.
After 40 minutes, she felt weak and could not breathe.
Why? C Intraoperative management 01 How to perform intraoperative monitoring on this patient? In such patients, ECG, blood pressure, pulse oxygen saturation, and end-tidal carbon dioxide partial pressure should be monitored during surgery
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Depending on the nature of the procedure and the severity of the patient's muscle weakness, arterial puncture may facilitate weaning from mechanical ventilation and monitoring of arterial blood gases during tracheal tube removal
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Nerve stimulators should be used to monitor muscle strength even if muscle relaxants are not used intraoperatively
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Inhalational anesthetics can suppress muscle twitch responses in MG patients even without muscle relaxants, and they are particularly sensitive to the neuromuscular junction (NMJ)—the inhibitory characteristic of volatile anesthetics
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 02Which anesthesia options are available for this patient? The patient's anesthesia can be selected from tracheal intubation general anesthesia, double-tube laryngeal mask, regional anesthesia and even monitoring anesthesia
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Determining which anesthesia is the most appropriate method of anesthesia for this patient depends on balancing the risk of pregnancy-induced vomiting against the risk of anesthesia in MG itself, especially in the postoperative period
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The most conservative anesthesiologists believe that the risk of aspiration is greater than the risk of MG and choose general endotracheal anesthesia
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Other anesthesiologists will choose regional or monitored anesthesia by weighing the risk of aspiration against the risk of difficult airway in pregnant women or postoperative complications of MG
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There is no single correct answer, and regardless of the method of anesthesia chosen, the patient's anesthesia regimen should be one with minimal and brief interference with ventilation and neuromuscular function
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  During general anesthesia, adequate oxygenation should be performed prior to induction with thiopental, propofol, or etomidate
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Opioids should be used with caution because these patients are quite sensitive to their respiratory depressant effects
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Assist breathing with 100% oxygen and control breathing if necessary
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Once the airway is safely established, the volatile anesthetic can be inhaled
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Laryngoscopy and endotracheal intubation with muscle relaxants are rarely required if the depth of anesthesia is adequate
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Lidocaine can be sprayed on the vocal cords before intubation
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Ventilation should be controlled to ensure gas exchange, and anesthesia should be maintained with oxygen, nitrous oxide, and volatile anesthetics, or concurrently with a continuous infusion of short-acting intravenous anesthetics
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There are reports that desflurane and moderate-acting muscle relaxants are an effective combination
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Dexmedetomidine or propofol may be considered if total intravenous anesthesia is used
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Remifentanil may be an appropriate opioid for such patients due to its short duration of action
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With the end of the operation, the anesthesia should be gradually reduced to allow the patient to wake up in time
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Extubation should be performed when the patient is awake, responsive, has strong muscle strength, and is able to generate at least a negative inspiratory pressure of 30 cm H2O
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In addition, patients should be able to maintain normal oxygenation and normal carbon dioxide partial pressure before extubation
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If regional anesthesia is chosen, either epidural or spinal, depending on the level of skin block, ensuring that the chest muscles are not blocked maximizes ventilation
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 03Can myasthenia gravis patients use muscle relaxants? Responses to muscle relaxants in patients with myasthenia are altered due to the effects of the MG disease itself and the anticholinesterase drugs used for treatment
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The depolarizing muscle relaxant succinylcholine has long been used for endotracheal intubation; however, patients with MG have variable responses to succinylcholine depending on the treatment regimen
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In MG patients without anticholinesterase drugs, due to the reduction of functional receptors, the endplate is "resistant" to succinylcholine, so the dosage of succinylcholine needs to be increased to ensure smooth intubation
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In patients treated with anticholinesterase drugs, plasma cholinesterase activity is reduced, so more succinylcholine can reach the motor endplate
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Because of the slowed metabolism of succinylcholine in these patients, the muscle relaxant effect was extended from 4 minutes to 87 minutes
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Phase II block has been reported following a single intubation dose of 0.
5 mg/kg of succinylcholine
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Although succinylcholine is not contraindicated in patients with MG, some clinicians prefer not to use it because of the risk of prolonged neuromuscular blockade
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Patients with MG are extremely sensitive to non-depolarizing muscle relaxants and often experience significant muscle weakness after only precurare doses
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This high sensitivity is due to the fact that the number of AchRs in such patients can be reduced by as much as 70%, the number of receptors available is only sufficient to generate end-plate potentials just above the thresholds for neuromuscular conduction and muscle contraction, and the reduced receptor density decreases Dosage of muscle relaxants that relax muscles
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Although MG patients have increased sensitivity to non-depolarizing muscle relaxants, non-depolarizing muscle relaxants can be safely used in MG patients, but their doses should be significantly reduced
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It has been reported that 1/4 of the usual dose of pancuronium bromide is sufficient to cause 95% neuromuscular blockade
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Moderate-acting muscle relaxants are more suitable for MG patients due to their shorter duration of action.
The dosage is 10% to 50% of the dosage of non-MG patients.
After spontaneous recovery of neuromuscular blockade or residual neuromuscular blockade can be antagonized in time.
Dial the tube
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Since micuronium is metabolized by plasma cholinesterase, it may be less suitable for patients with MG
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 D.
Postoperative Management 01 Does the patient require prolonged ventilation support after surgery? A number of predictive criteria have been proposed for the need for prolonged postoperative ventilatory support
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Leventhal, Orkin, and Hirsch developed the following 4-factor scoring system: disease duration over 6 years: 12 points History of COPD: 10 points pyridostigmine bromide, >750 mg/d: 8 points Vital capacity <2.
9L: 4 points Patients with a score lower than 10 can be extubated immediately after surgery; patients with a score greater than 12 need postoperative ventilation support
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This criterion is not widely applicable for predicting whether a patient will require prolonged endotracheal intubation and ventilatory support
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Transthymectomy patients more often require postoperative ventilatory support than do cervical thymectomy patients, likely because the less invasive procedure is less disruptive to respiratory function
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Similarly, patients with myasthenia who underwent upper abdominal surgery were more likely to require postoperative ventilatory support than patients who underwent peripheral surgery
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Obviously, the need for postoperative ventilatory support should be assessed on an individual basis for each patient
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 02How to provide postoperative analgesia for this patient? Postoperative analgesia regimens for patients should avoid aggravating respiratory impairment
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Because such patients are extremely sensitive to the respiratory depressive effects of parenteral narcotic analgesics, they should be used sparingly
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Epidural opioids are an alternative to parenteral administration, which can provide better analgesia in smaller doses and cause less respiratory depression
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 03 The patient was successfully removed from the tracheal tube in the operating room.
After 40 minutes, she felt weak and could not breathe.
Why? The anesthesiologist needs to distinguish whether the exacerbation of myasthenic symptoms is due to a cholinergic crisis or a myasthenic crisis
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During myasthenic crisis, the patient's response to anticholinesterase drugs is enhanced
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Cholinergic crisis is caused by an overdose of anticholinesterase drugs
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Both are possible in the immediate postoperative period, when myasthenic symptoms may be exacerbated due to surgical stress, and the amount of anticholinergic medication may be changed
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In either case, exacerbation of myasthenic symptoms may require ventilatory support
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Muscle weakness, salivation, and sweating occur in either myasthenic crisis or cholinergic crisis
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It has been suggested to differentiate between the two crises based on the patient's response to 10 mg of intravenous epoxidil chloride, with improvement in muscle strength in patients with myasthenic crisis and no improvement in muscle weakness or respiratory distress in patients with cholinergic crisis aggravated
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Notes/Chen Lingjun Typesetting/Dingdang Maruko Ma END