Learning from Experience – 11 and 12

Chapter 11

Myasthenia Gravis-Nightmare to the Anaesthesiologist

Dr. Vasanthi Vidyasagaran*

Department of Anaesthesiology, Kauvery Hospital, Chennai, Tamilnadu, India

*Correspondence: [email protected]

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Anaemia-or-Hydrocele

 

Case 1

A 28-year-old primigravida, known case of Myasthenia Gravis was posted for an elective LSCS. She was on tablet Pyridostigmine 60 mg twice daily. She had grade 2a disease, well controlled under medications. All other routine preoperative investigations were within normal limits. She was asked to continue Pyridostigmine up to the morning of surgery. It was decided to proceed with spinal anaesthesia. She was administered a stress dose of hydrocortisone. Spinal was given with a 25G needle, and 1.8 ml of 0.5% Bupivacaine heavy was administered. After ensuring adequate level of block the surgery was allowed to proceed. It was completed successfully in 40 minutes and the patient had an uneventful recovery

Case 2

A 58-year-old woman, was admitted to the ward waiting to be investigated to undergo a hysterectomy. One day prior to surgery she had a fall in the bathroom and was unable to get up. On being helped onto her feet, she was found to limp. She developed difficulty in breathing and became semi-conscious. She was brought into emergency room. Her vitals were deteriorating and she was quickly shifted to the ICU. She required mechanical ventilation to stabilize. Haemodynamics were maintained well.

The attending physicians began investigating and suspected pulmonary embolism due to the fracture that she sustained during her fall. All her investigations were normal. Other differential diagnosis included hypoglycaemia, or hypothyroidism. There was no associated head injury. One of the anaesthetists suggested a diagnosis of myasthenia gravis. Subsequent electromyography testing confirmed the diagnosis.

This was a scenario, where the presentation for the first time of the pathology was myasthenic crisis. Fortunately for the entire team, especially the anaesthesiologist, this happened one day prior to surgery and not on the operating table! And the patient was also lucky since this incident took place in a hospital and she could be attended to, without any delay.

Discussion

Myasthenia gravis is a disease of great significance to the anaesthesiologist because it affects the neuromuscular junction. Many patients with this condition are treated by surgical thymectomy. Implications under anaesthesia:

  1. Patients are very sensitive to non-depolarizing NMBAs and are resistant to depolarising agents like suxamethonium. Hence doses must be titrated very carefully. While reversing NMBAs, the reversal agents should be titrated to effect, guided by the use of an objective twitch monitor.
  2. Peri-operative care plan has to be well defined
  3. Close watch in high dependency unit will be needed

‘Red flags’ in the history to raise concerns are:

  1. Bulbar symptoms (e.g. dysphagia, dysarthria, nasal speech, or low-intensity speech) which may predispose to aspiration
  2. History of myasthenic crisis and need for endotracheal intubation
  3. Respiratory muscle weakness, shortness of breath, and dyspnoea
  4. Associated diseases, including other autoimmune diseases (e.g. thyroiditis, rheumatoid arthritis, systemic lupus erythematosus)
  5. Four risk factors, score >= 10 points suggest need for postoperative ventilation
    1. Duration of disease longer than 6 years (12 points)
    2. COPD independent of respiratory dysfunction (10 points)
    3. Pyridostigmine greater than 750 mg/day (8 points)
    4. Preoperative vital capacity less than 2.9 L (4 points)

Medications commonly taken by these patients are;

  1. Prednisolone
  2. Azathioprine
  3. Cyclosporine
  4. Pyridostigmine

Medications that may exacerbate Myasthenia Gravis include:

  1. Antibiotics like Macrolides, Gentamicin
  2. Antiepileptic like Phenytoin
  3. Antiarrhythmic agents like beta-blockers, Quinidine, calcium channel blockers, Lignocaine
  4. Paradoxically steroids may exacerbate symptoms. However, they may be indicated when there is a crisis.

Pregnancy and Myasthenia

Patients must have an antenatal plan regarding management of labour and delivery. Anaesthesia concerns specific to obstetrics include:

  1. Effective labour analgesia must be in place to prevent vicious cycle of pain triggering crisis
  2. Neuraxial analgesia can be provided for assisted vaginal delivery
  3. Caesarean section under spinal/epidural anaesthesia can be done safely, care to be taken regarding level of block. High motor block can trigger respiratory difficulty.
  4. Postoperative high dependency unit and pain management essential.

Myasthenia gravis (MG) is an autoimmune disorder characterized by fatigable weakness of skeletal muscles. This is due to antibody-mediated immunological reaction in acetylcholine receptors in the postsynaptic membrane of the neuromuscular junction. This leads to decreased receptors, decreased nerve signal transmission and henceforth decreased muscular activity.

Osserman classification of Myasthenia Gravis:

Grade 1 – Only eyes affected

Grade 2a – Mild generalised myasthenia gravis, responding well to drugs Grade 2b – Moderate myasthenia gravis, responding less well to medication Grade 3 – Severe generalised disease

Grade 4 – myasthenic crisis requiring mechanical ventilation

It is important to differentiate between myasthenic crisis and cholinergic crisis Myasthenic crisis:

  1. Criteria: Severe respiratory muscle and/or bulbar muscle weakness necessitating intubation and delayed extubation after surgery. This may occur spontaneously due to the stress of surgery or due to precipitating factors like infection, residual anaesthetics, withholding or tapering of MG medications.
  1. In awake patients, impending crisis may be identified by watching for signs such as dysphagia, change in phonation, obstruction, weak cough, and difficulty handling secretions. Increased respiratory rate may be the first sign.
  1. Treatment must be discussed with neurologist. Urgent rapid therapy with plasma exchange or intravenous immunoglobulin therapy may be required.

Cholinergic crisis :

  1. Criteria: Anticholinesterase drug therapy puts patients at risk for cholinergic crisis.
  1. Signs of cholinergic excess includes weakness, salivation, lacrimation, urination, defecation, gastrointestinal distress and emesis. It is rare and usually occurs in patients outside the operating room, but may occur after administration of an anticholinesterase for reversal of neuromuscular blockade in patients with MG, in the theatre. In such cases, the recovery is delayed, and prolonged paralysis often results.
  1. Treatment includes Atropine or Glycopyrrolate for symptom control of muscarinic effects and further anticholinesterase must be withheld.

References

  1. Abel M, et al. Anaesthetic implications of myasthenia gravis. Mt Sinai J Med. 2002
  2. Jamal BT, Herb K. Perioperative management of patients with myasthenia gravis: prevention, recognition, and treatment. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2009;107:612.
  3. Blobner M, Mann R. Anesthesia in patients with myasthenia gravis. Anaesthesist. 2001;50:484-93.
  4. Viby-Mogensen J. Postoperative residual curarization and evidence-based anaesthesia. Br  J Anaesth. 2000;84:301-3.

Knowledge without application at the right time does not serve any purpose.

Chapter 12

Preoperative Hyponatremia

A ninety-year-old lady was hospitalised for fracture neck of femur following a fall. Hemiarthroplasty was planned. Physician had seen the patient and given clearance for surgery on admission. The anaesthetist was informed only the day before the surgery which was four days from the date of admission. On examination, the anaesthetist found her to be drowsy and lethargic. On asking her relatives about her daily activities, they mentioned that she was quite active till the day before her fall and was not on any medications except vitamin supplements.

Pulse – 100/min. BP – 90/50. Lungs were clear, heart sounds were normal, but of lower intensity. Blood investigations including blood glucose were normal except for a slightly raised urea and creatinine which was 55mgs and 1.9 mgs respectively.

Not being satisfied with the available investigation, serum electrolytes and ABG was asked for, and these were the values.

Sodium: 122 meq/L, Potassium: 4 meq/L, Chloride: 90 meq/L, Bicarbonate: 25 meq/L, ABG did not show any gross hypoxia or hypercarbia

Hyponatremia was gradually corrected, and the patient became fully conscious and cheerful and she had an uneventful surgery under spinal, after three days.

Discussion

Electrolyte disorders especially Hyponatremia is common in the geriatric population, and accounts for several signs and symptoms occurring in old age and should be corrected appropriately. SIADH is more frequently encountered than what is believed, but difficult to diagnose as there is no reliable biomarker for the volume status in old people. Whether it is hypovolemic or euvolemic hyponatremia, needs to be established before commencing treatment with diuretics, or replacement of sodium, or use of vasopressin receptor antagonist. This is a common problem in geriatric population and deserves more attention.

References

1. Hyponatremia: Practice Essentials, Pathophysiology, Epidemiology https://emedicine.medscape.com/article/242166-overview

2. Hyponatremia: A practical approach – NCBI – National Institutes of Health

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4192979/

In elective cases, be sure to optimize the medical conditions before taking up the patient.

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