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Anaesthetic management of a patient with amyotrophic lateral sclerosis undergoing laparoscopic diaphragmatic pacing

Sir, 
 
Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterised by progressive asymmetric limb weakness, bulbar symptoms such as dysarthria, dysphagia and respiratory muscle weakness.[1,2] The diaphragmatic pacing system (DPS) is used to stimulate the diaphragmatic muscle to prevent atrophy and prolong life by preventing pulmonary complications.[3,4] 
 
A 68-year-old, 74 kg, female, diagnosed as ALS since 4 years, was admitted for laparoscopic insertion of DPS and percutaneous endoscopic gastrostomy (PEG). Her disease had progressed to involve all four limbs and developed dysphagia and dysarthria without involving diaphragm. She was on bi-level positive airway pressure (BiPAP) for 6 h each night for obstructive sleep apnoea. She had history of bronchial asthma and was on salbutamol nebulisation and also history of painful muscle spasms. Her speech was difficult to comprehend. She was non-hypertensive and non-diabetic. Airway assessment revealed Mallampati Grade III. Routine biochemistry was normal and pulmonary function tests showed a forced vital capacity of 45%. Arterial blood gas (ABG) analysis showed partial pressure of carbon dioxide (CO2) of 41.2 mmHg and oxygen saturation of 94% on room air. 
 
Nebulisation with ipratropium and budesonide was started 48 h before surgery. The patient was asked to take her routine medications, which included clonazepam, glycopyrrolate, fluvoxamine, and antibiotics. On the morning of surgery, nebulisation with 4% lignocaine, ipratropium, and budesonide was administered and glycopyrrolate 0.2 mg was given intravenously. Difficult intubation cart, along with fibreoptic laryngoscope was kept ready. Monitoring included five lead electrocardiogram with ST segment analysis, pulse oximetry, end-tidal CO2, non-invasive blood pressure, and Bi-spectral index (BIS®) monitoring. 
 
She was sedated with 60 μg fentanyl and 0.6 mg midazolam. Injection propofol 70 mg was given till loss of eyelid reflex. The possibility of mask ventilation was confirmed and intermittent positive pressure ventilation with 100% oxygen and sevoflurane, (gradually increased to a dial concentration of 3%) was administered. The patient was ventilated for 3 min. At laryngoscopy, the cords were easily visualised, and sprayed with 2% lignocaine. Endotracheal intubation was accomplished with a 7.5 mm tube and 14 gauge nasogastric tube was inserted. 
 
The patient was mechanically ventilated with tidal volume of 500 ml and respiratory rate of 12/min. Airway pressures ranged from 0 to 15 cm H2O. The patient was ventilated with oxygen:nitrous oxide (50:50); inhalational agent was changed to desflurane. The fresh gas flow (FGF) was 1.2 L and the desflurane dial settings were adjusted to ensure end-tidal levels around 4.5%. Fentanyl (40 μg) and midazolam (0.4 mg) were repeated. 
 
Intraabdominal pressure with CO2 pneumoperitoneum was maintained at 12 mmHg. Diaphragm was stimulated at multiple points to identify optimum electrode placements sites. After the DPS was in place, PEG was performed. Desflurane was reduced gradually; FGF was increased to 5 L/min, and the patient was ventilated with 100% oxygen. When the patient was awake and spontaneous respiration was adequate, she was extubated after obtaining ABG analysis, which was normal. Throughout surgery, her vital parameters remained steady, and BIS® remained at 40. In the recovery room, chest X-ray revealed left sided capnothorax, which resolved spontaneously without intervention. The patient was monitored for 48 h in the intensive care unit, which was uneventful, with DPS working normally and the patient not requiring the BiPAP support. 
 
ALS has no direct effect on the lungs but severely affects the mechanical function of the respiratory system. Progressive inspiratory muscle weakness leads to an inability to clear secretions and CO2 retention and hypercapnoeic respiratory failure are the major cause of death in ALS.[2] 
 
DPS was developed initially to provide natural negative pressure ventilation in patients with spinal cord injury. It was observed that 98% of them could be weaned off the ventilator.[3,5] Our case was a patient of ALS in which DPS was being performed, which is rare in India. Anaesthesia needed to be modified to avoid muscle relaxants, prevent an unpredictable response to reversal agents and the need to stimulate the diaphragm to identify implantation points. Short-acting agents such as desflurane and fentanyl were used to ensure quick reversal. Desflurane as the inhalational agent was selected as it is least soluble of available volatile anaesthetics which leads to early and predictable recovery of patients from general anaesthesia including early recovery of airway functions.[6] We also utilised the property of desflurane which, when used above one minimum alveolar concentration causes good muscle relaxantion in dose-dependent fashion. This was important as adequate muscle relaxation was required.[7] 
 
Thus, in a patient of ALS, we should avoid skeletal muscle relaxants, use shorter-acting agents and should be prepared for continuous positive airway pressure/BiPAP ventilatory support in the post-operative period if the need arises.