General Anesthesia Using Supraglottic Airway Device in a Myasthenic Patient Undergoing Reverse Shoulder Arthroplasty.

Myasthenia gravis (MG) is a neuromuscular disorder characterized by weakness and fatigability of skeletal muscles. The decrease in the number of acetylcholine receptors results in decreased efficiency of neuromuscular transmission. Although acetylcholine is released normally, it produces small end-plate potentials that fail to trigger muscle action potentials. Failure of transmission at many neuromuscular junctions results in weakness of muscle contraction. This also makes them susceptible to neuromuscular blocking agents which pose a challenge to the anesthesiologist. Here, we report a case of a patient who was a known case of MG posted for reverse shoulder arthroplasty, who was managed using a supraglottic airway device and spontaneous respiration.

INTRODUCTION

Myasthenia gravis (MG) is an autoimmune neuromuscular disease wherein the patient complains of weakness and fatigability after exercise which recovers after a period of rest or medications. The disease is characterized by autoantibody attack of acetylcholine receptors (AChRs) at the motor end plate of skeletal muscles, decreasing the capacity of the neuromuscular end plate to transmit the nerve signal which results in variable muscle weakness made worse by exercise.[1] The incidence of MG is 3–7 people per 100,000.

In 1958, Osserman classified the patients depending on their symptoms: (i) localized (ocular), (ii) generalized (mild or moderate), (iii) acute fulminating, (iv) late severe, and (v) muscle atrophy. Later, Osserman divided group II into the subclassification: A (mild) and B (moderate). This classification allows one to grade the disease and assess the perioperative risk and possible complications.[2]

Death and severe complications are commonly seen during surgery and anesthesia in myasthenic gravis patients. The risk is mainly related to a markedly higher sensitivity to muscle relaxants observed in this group of patients, even in periods of complete remission.[3] Myasthenia patients often require prolonged ventilation in the Intensive Care Unit (ICU) setting.[245] A significant, though less common, perioperative risk in myasthenic patients is cholinergic crisis.

The most proper approach during anesthesia in patients with MG is to apply deep inhalational anesthesia without muscle relaxing agents.

In this case report, we describe how anesthesia for a reverse shoulder arthroplasty was given successfully using general anesthesia (GA) with a supraglottic airway device SGA device-supraglottic airway (SGA) devicewith the patient in beach chair position.

CASE REPORT

We are reporting a 49-year-old male patient weighing 54 kg, a known case of MG, posted for a right shoulder reverse arthroplasty.

Preoperatively, the patient was diagnosed to be a known case of MG Grade I (localized to ocular muscles) as per Osserman classification[2] on steroid therapy following thymectomy surgery in the year 1994. He was also diagnosed to be a type II diabetic since the past 26 years on regular medications.

On general physical examination, the patient had a good effort tolerance with stable vitals. He had accessible veins for cannulation and no external skin lesions. All system examinations were within normal limits.

Airway was adequate with normal dentition and no missing or loose teeth, adequate mouth opening with Mallampati class 2 grading, and no restriction in the temporomandibular joint or neck mobility.

On the previous day of surgery, a written informed consent was taken and was asked to continue his steroid therapy (tablet Wysolone 10 mg) the night before surgery and to skip his morning antidiabetic medications. He was kept nil per oral for solids 8 h before the scheduled time of surgery but was allowed sips of water till 2 h before surgery. The patient received no premedication due to existing contraindications to benzodiazepines. The patient was in the optimum condition for surgery, with no absolute neurological contraindications to the operation and no abnormalities identified in laboratory tests.

On the day of surgery, patients' sugar levels and serum electrolytes were within normal range. He was shifted to the preoperative holding room where his vitals were checked again. Two cannulas, an 18G in the left upper limb and a 16G in the left lower limb, were secured and intravenous (i.v.) fluid was connected. He was then shifted to the operation theater (OT).

The OT was kept ready with ambient temperature, anesthesia workstation, all monitors and drugs checked before patient arrival.

On arrival, i.v. fluid was on flow. All monitors such as electrocardiography, noninvasive blood pressure, and SpO2 were connected and vitals noted. Preoxygenated with 100% oxygen at the rate of 8 L/min. Premedication with0.02mg/kg injection of midazolam and 2 μg/kg injection fentanyl. Induction of GA was obtained with propofol in titrated doses until the loss of verbal response. Size 4 I-Gel™ was inserted, and the patient was put on assisted ventilation. The I-gel™ demonstrated oropharyngeal leak pressures and maximum minute ventilation above the thresholds of 25 cm H2O and 10 L/min, respectively, considered to reflect adequate clinical efficacy. Maintained with propofol continuous i.v. infusion at 10 mg/kg/min and sevoflurane at minimum alveolar concentration 1 in a nitrous oxide/oxygen mixture with low gas flow. Doses of anesthetic agents were modified according to the clinical assessment of the depth of anesthesia. The patient was placed in beach chair position for the procedure and was put back in supine position at the end of the surgery.

Emergence from anesthesia was initiated after closure of the surgical wound. On emergence from anesthesia and removal of I-Gel™, the patient was transferred to the recovery room. There was no compromise in the patient's respiratory function and circulatory status. Postoperative analgesia was provided with injection paracetamol 1 g slow i.v. TID and injection diclofenac aqueous solution 75 mg BD. He was kept in the postoperative room for 24 h monitoring. The patient was discharged on the 7th postoperative day.

DISCUSSION

The underlying defect in myasthenic patients is a decrease in the number of available AChRs at the neuromuscular junction due to antibody-mediated autoimmune attack. As an anesthesiologist, special management in preparation for surgery is essential in MG patients, particularly those undergoing major surgery and/or suffering from comorbid disorders.[3] Special considerations in myasthenic patients are their sensitivity to nondepolarizing neuromuscular blocking drugs. During GA, neuromuscular monitoring is essential to avoid problems of prolonged neuromuscular block in myasthenic patients. To avoid such a complication, here, we managed this case under GA using SGA device with patient on spontaneous respiration without muscle relaxation.

In this case report, we used a SGA device, i.e. the I-gel™, to manage the airway. This novel second generation SGA device I-gel™ (Intersurgical, Wokingham, UK) was designed by UK anesthetist, Muhammed Nasir. I-gel™ is commonly used for securing and maintaining a patent airway in routine and emergency anesthetics of fasted patients, during spontaneous or intermittent positive pressure ventilation and as a conduit for intubation under fiberoptic guidance in a known or unexpectedly difficult intubation, by personnel who are suitably trained and experienced in the use of airway management techniques and devices.[6]

Propofol infusion along with volatile anesthetics was used for the maintenance of anesthesia in this patient. Across all clinical studies, the mean infusion maintenance rate for all patients was 27 ± 21 μg/kg/min. The maintenance infusion rates required to maintain adequate sedation ranged from 2.8 to 130 μg/kg/min.[7] The infusion rate was lower in patients over 55 years of age (approximately 20 μg/kg/min) compared to patients under 55 years of age (approximately 38 μg/kg/min). Although there are reports of reduced analgesic requirements, most patients received opioids for analgesia during maintenance of ICU sedation. In these studies, morphine or fentanyl was used as needed for analgesia. Some patients also received benzodiazepines and/or neuromuscular blocking agents.[7]

Although currently used neuromuscular transmission blockers are considered safe, the time of administration of these agents is of major importance since if administered prematurely, they can paradoxically result in neuromuscular block reversal. As many as 60% of patients undergoing surgery under GA are believed to be likely to experience problems with residual activity of skeletal muscle relaxants.[8910] Hence, wherever possible, avoidance of muscle relaxation is advised and if used should be in smaller doses with neuromuscular transmission monitoring.[11]

Patients in the beach chair position are at risk for an intraoperative stroke; hence, cerebral perfusion pressure and blood flow have to be borne in mind when the patient is placed in this position. A thorough understanding of the physiologic changes associated with the upright position and the physical effects of gravity on blood pressure in the brain is crucial to prevent catastrophic neurologic outcome during shoulder surgery in the sitting position.[12] Deliberate hypotension has to be avoided and BP values <80% of preoperative resting values should be treated aggressively to enhance the margin of safety.[12] Head positioning is also important because of the degree of head manipulation that is required when positioning the patient in beach chair position.[13] Finally, hypotension and generalized circulatory instability can result from gas embolism. This rare complication has been reported with both air and carbon dioxide distension of the joint capsule followed by pressurized injection of irrigation fluid. Thus, anesthesiologists should keep the possibility of venous gas embolism in mind during shoulder arthroscopy in the sitting position if sudden cardiovascular collapse occurs.[14] Potential complications that can occur are excessive head flexion that can cause arterial and venous obstruction leading to upper airway edema and potential airway compromise following extubation. Endotracheal tube obstruction can lead to poor and difficult ventilation. The endotracheal tube can also compress the tongue if the head is not positioned correctly, leading to macroglossia and postextubation airway obstruction.

A similar case report was published by Lee et al. where they presented a case of failed intubation in a patient with subglottic stenosis successfully managed with an I-gel™ supraglottic airway device. They concluded that the device provided a good seal and allowed for controlled mechanical ventilation with acceptable peak pressures while the patient was in the beach-chair position.[15] A similar case was published by Tan et al. where a laryngeal mask airway (LMA) Protector™ was used for shoulder surgeries in beach-chair position.[16] They reported their initial experience and satisfactory performance of the LMA Protector™ in three patients scheduled for elective shoulder surgeries performed in beach-chair positions. The LMA Protector™ is similar to the I-gel™ supraglottic airway device and was recently introduced in 2016. LMA Protector™ is a single-use second-generation supraglottic airway device complete with a pharyngeal chamber and dual gastric access ports.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.