Case History

Case 1

A 39-year-old male weighing 63 kg, was diagnosed to have myasthenia gravis Osserman class IIB. He had clinically well preserved respiratory function with pyridostigmine (60 mg, 6 hourly), and prednisolone (20 mg once a day). Patient had received anti tuberculosis therapy in the past. His routine investigations including haematological and ECG were within normal limits. The patient was posted for VATS thymectomy. The morning dose of pyridostigmine was omitted. Two peripheral intravenous cannulae (16G) were placed in the arm and leg. ECG, intra-arterial blood pressure, and central venous pressure (CVP) monitoring were set in. General anaesthesia for this patient was given with midazolam (1.5 mg), fentanyl (100 mcg), and propofol (200 mg). Anaesthesia was maintained with propofol infusion (50-80 mg/hr) and isoflurane (0.6-1.0%).

Neuromuscular junction monitoring was also started by stimulating ulnar nerve at wrist using surface electrodes. Adductor pollicis response was recorded using accelograph (Biometer Ltd, Denmark). After stabilising the adductor pollicis response at the titrated supramaximal stimuli (1 Hz for 5 minutes), train-of-four (4 stimuli at 2 Hz) stimuli were given at 15s interval. Atracurium (5 mg) was given intravenously and we noted for its onset times to ‘0’-response (90s). After confirming ‘0’ response at adductor pollicis, Carlens double lumen tube (6 Fr) was passed orally and left ponchial intubation was confirmed clinically. Atracurium (0.5 mg/ml) by infusion was titrated to maintain T(1) around >10% of its control height. Rate of atracurium infusion varied from 10-25 ml/hour and 78 mg total atracurium was given during 10 hours surgery.

Surgery was performed in left decubitus position. When one lung ventilation (OLV) was started, the right lung failed to collapse completely, due to pleural adhesions from childhood tuberculosis. Adenolysis was done but as it did not help much, a fourth port was added to put retractor on right lung for better surgical exposure.

During OLV, initially oxygen saturation dropped from 100% to 96% and it continued around that for next 90 minutes at FiO(2) (1.00). It gradually improved to 98% after 2 hours when FiO(2)­ was reduced to 80%. Total duration of OLV was 10 hours 30 minutes. At the end of surgery two-lung ventilation was resumed by replacing double lumen tube [DLT] with single lumen endotracheal (ET) tube. At this point, 10 ml of fresh frothy blood was aspirated. In view of the patient developing pulmonary oedema, and prolonged surgery, patient was put on positive pressure ventilation at peak end expiratory pressure (PEEP) of 10 cm H(2)O post-operatively. Pulmonary oedema subsided in due course of time of ventilation in intensive care unit (ICU) and the patient was extubated after 6 hours. Effect of atracurium was not reversed and pyridostigmine was restarted next morning through nasogastric tube.

Case 2

A 38-year-old female (weighing 53kg) patient was having features of myasthenia gravis (Ossermann class IIB) for past two years was planned for VATS thymectomy. She was getting oral pyridostigmine 60 mg 6 hourly. Pulmonary function test was suggestive of mild obstructive airway disease. Morning dose of pyridostigmine was omitted on the day of surgery. Two peripheral intravenous cannulae (16G) were put in the arm and the leg. General anaesthesia was induced with fentanyl (150mcg), propofol (100 mg) and atracurium (5 mg) intravenously. Her anaesthesia was maintained using isoflurane (0.6% to 1.2%), propofol infusion (50-80 mg/hr) and atracurium infusion (5-7.5 mg/hr) to maintain T(1) around 10% of its control response at adductor pollicis as in first patient. Onset time to ‘0’ response was after 3 minutes and recovery time to T(1) after first dose was 27 minutes. For analgesia total of 15 mg morphine was given. Intra-operative monitoring included ECG, intra-arterial pressure, CVP, pulse oximetry and temperature. OLV was executed using Carlens DLT (5.0F) and surgery was performed in left lateral decubitus position. Her arterial blood gases and haemodynamic parameters were well maintained throughout surgery. OLV lasted for 6 hours 30 minutes in this patient. At the end, DLT was changed with single lumen tube and the patient was shifted to ICU for mechanical ventilation and extubated 2 hours later.

Case 3

A 30-year-old female (weighing 40kg) was diagnosed for myasthenia gravis one year prior to surgery. She was controlled by pyridostigmine orally (90 mg, 8 hourly) and developed sudden exacerbation four days prior to surgery. To protect her lungs from aspiration and support her respiration, orotracheal intubation and pressure support ventilation was started in ICU. All her medications (pyridostigmine 90 mg 6 hourly and neostigmine 15 mg 8 hourly) were stopped to re-establish neuromuscular junction physiology. She was classified as Osserman class III.

Anaesthesia was induced with propofol (100 mg), fentanyl (100 mcg), and atracurium (3 mg). She was maintained on propofol infusion (50-80 mg/hour) and isoflurane (0.6%-1.0%) titrated on the basis of haemodynamics. After atracurium the onset time to ‘0’-twitch response to supramaximal train-of-four stimuli was 70s and recovery time to one response after first dose was 30 minutes. Since pyridostigmine was stopped from last five days after cholinergic crisis, patient showed extreme sensitivity towards atracurium first dose and to atracurium (0.5 mg/ml) infusion (3 ml/hour to 5 ml/hour) to maintain T(1) around 10% of control in train-of-four monitoring and the total atracurium (9 mg) in 4 hours 30 minutes. At the end of surgery, DLT was replaced with single lumen endotracheal tube. Considering the past crisis, reversal of atracurium effect was differed again and patient was shifted to ICU and was gradually weaned off ventilation in next 7days.

Discussion

Thymectomy to start was reserved for patients with serious disability, because the operation had a high mortality. However with the advances in surgery and anaesthesia, the peri-operative mortality is now negligible.(1) Thymectomy is now recommended for most patients with generalised myasthenia gravis. Trans-sternal approach is the most frequently used approach for thymectomy.(2) Recently VATS is becoming popular for thymectomy.(3,4) Here, three or four incisions (10 mm) are performed at different intercostal spaces to accommodate ports for video camera, and dissecting forceps. The advantages being cosmetically acceptable incisions within inconspicuous areas of the anatomy, its less invasive nature and blood loss, better surgical dissection, relatively short surgical and anaesthesia time, minimal pain medication postoperatively, and quick discharge from the hospital.(5)

The anaesthetic challenges during surgery are the execution of adequate oxygenation during OLV, the lateral positioning, haemodynamic stability and separate venous accesses to superior and inferior vena cava system. We also need to deal with myasthenia related problems viz. hypersensitivity to non-depolarisers, poor upper airway protection, and respiratory depression.

Left-sided DLT is routinely preferred for OLV, due to its ease of placement, no matter which side is being approached for surgery,(5) and so we did. Patients were positioned supine, with a small roll placed under the ipsilateral axilla, to elevate thorax by 20(0) to 30(0) on the operative side of the patients. It allows placement of trocar posterior to the midaxillary line.(6) Ventilation of the lung opposite to the side of surgery was continued using same tidal volume (8-10 ml/kg) and respiratory rate adjusted to optimise ETCO(2) (35-40mmHg). Ipsilateral lung was vented out and allowed to get collapsed, to create space for surgery. After initial drop in oxygen saturation, the oxygen saturation improved with the setting in of hypoxic pulmonary vasoconstriction in the collapsed lung and then FiO(2) was reduced. We used propofol infusion and isoflurane for maintenance of anaesthesia as both the agents have least effect on normal hypoxic pulmonary vasoconstriction in the non-ventilated lung.(7,8)

Atracurium by infusion has been the recommended muscle relaxant in myasthenia gravis patients for prolonged use.(9,10) Our plan to omit morning dose of pyridostigmine and use of isoflurane(11) increased patient’s sensitivity for atracurium and helped to manage with smaller doses of atracurium (one sixth of usual intubation dose). Since in VATS, thoracic bony rigid wall do not collapse and deflated lung on the side of surgery provides enough room for surgery, we were able to maintain desired muscle relaxation with smaller doses of atracurium.

Contrary to claimed advantages viz. quick surgical and anaesthesia time, we faced prolonged surgical operation, and OLV lasting from 3 hours 45 minutes to as long as 10 hours 30min. None of our patient could be extubated quickly. In first patient, it was due to pleural adhesions preventing lung collapse during OLV and required constant retraction from an extra port. This forceful retraction resulted in re-expansion pulmonary oedema and prolonged mechanical ventilation with PEEP postoperatively. The third patient developed cholinergic crisis while waiting for surgery in ward and required mechanical ventilation in ICU prior to surgery and thus could not be extubated in immediate post-operative period. Only second patient was quickly extubated two hours later in ICU. Blood loss was significantly less in later two patients (150 ml and 100 ml); however it exceeded (800 ml) in the first patient and required blood products.

In summary, whenever a new surgical procedure is started, we must have the preparedness for prolonged duration of surgery. We could manage well OLV, as long as 10 hours without significant problem, as we opted elective ventilation in intensive care to optimise cardiovascular and respiratory functions of the patient. Our experience suggested that the optimisation of the medical condition with the pyridostigmine and omission of its morning dose on day of surgery followed by routine balanced anaesthesia with one-sixth the standard dose of atracurium and its monitored infusion worked well for VATS thymectomy. We allowed spontaneous recovery from relaxation effect of atracurium postoperatively and was probably a better approach considering the prolonged duration of surgery.

Table 1

References

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