X-linked myotubular myopathy (XLMTM) is a severe congenital centronuclear myopathy that is typically limited to skeletal muscle and spares cardiac muscles. Patients demonstrate early hypotonia and develop musculoskeletal abnormalities such as scoliosis. There have been minimal case reports of anesthetizing patients with XLMTM and none have described prone positioning.1 This report documents hemodynamic collapse with prone positioning and imaging revealing caval and cardiac compression.
The patient’s family has provided written consent to publish this case report.
A 40-kg, 15-year-old boy with a history of XLMTM presented with severe progressive scoliosis requiring T2 to sacrum posterior spinal fusion. Previous full-length seated upright radiographs demonstrated left thoracolumbar scoliosis with a 109° Cobb angle. His myopathy was associated with pectus excavatum, severe hypotonia, and chronic respiratory failure requiring tracheostomy and chronic 24-hour mechanical ventilatory support. Home medications included montelukast 5 mg oral daily and levalbuterol 1.25 mg nebulized as needed. Before presenting to our institution, the patient had 2 aborted attempts at posterior spinal fusion. During each previous attempt, the patient had experienced cardiac arrest while being positioned prone after induction of general anesthesia. In both instances, the patient was hemodynamically stable until the time of repositioning. The second anesthetic attempt utilized an identical approach to the first.
After the second failed attempt at positioning, the patient underwent a computed topography (CT) angiogram in the prone position without general anesthesia. The imaging revealed normal vasculature anatomy and patency in the supine position but severe compression and obstruction of the inferior vena cava and right ventricular outflow tract when prone (Figure).
A multidisciplinary team consisting of anesthesiologists, surgeons, pediatric intensivists, and pediatric cardiologists was involved with a decision to proceed with surgery in a staged fashion. The patient underwent an anterior spinal T10-L4 fusion performed via anterolateral approach in the supine position without significant events. Two years postoperatively, the patient continued to have worsening disease with severe adding-on, long sweeping thoracolumbar scoliosis, severe pelvic obliquity, and difficulties with sitting and comfort. The decision was made to proceed with posterior fusion.
Before surgery, the patient was admitted to an academic center capable of providing intraoperative pediatric transesophageal echocardiography, extracorporeal mechanical circulatory support, and postoperative intensive care. Maintenance fluids were administered during preoperative fasting. On the day of surgery, full malignant hyperthermia precautions were observed. General anesthesia was induced with propofol 2.5 mg/kg intravenously (IV). The patient’s in situ tracheostomy was replaced with an endotracheal tube. Halogenated volatile agents and depolarizing neuromuscular blocking agents were avoided for the entirety of the surgery. Maintenance anesthesia consisted of the following IV infusions: propofol 100 µg/kg/min; ketamine 10 mg/kg/h; dexmedetomidine 0.2 µg/kg/h; and fentanyl 1.5 μg/kg/h. An arterial line was inserted after induction. Two peripheral IV catheters (18 and 16 gauge) were also placed, followed by a 7F right internal jugular central venous triple lumen catheter for central venous pressure monitoring and administration of vasoactive substances. Defibrillation pads were placed before positioning. A stretcher bed was kept in the room during the surgery in case of emergent need for repositioning. Before positioning, the patient was prehydrated with a 10 mL/kg bolus of Plasmalyte-A in anticipation of decreased preload from caval obstruction. Central venous and arterial pressures were monitored and maintained by use of norepinephrine (started at 30 ng/kg/min increased to a sustained maximum of 75 ng/kg/min) and IV fluid administration. As the patient was flipped prone, he was positioned in an oblique manner with the left hemithorax elevated approximately 30° above the bed to reduce pressure on the precordium and left chest. In addition, a recessed cushion was placed under the chest to further disperse pressure. The patient was able to tolerate prone positioning with minimal increases in vasopressor support, <20% deviation in mean arterial pressure, and no observed alterations in arterial or central venous pressure waveforms. No intraoperative transesophageal echocardiography was performed.
The posterior fusion was performed in a caudal to cephalad direction with a plan to stop the procedure if surgical manipulation and pressure imparted severe hemodynamic consequences at higher vertebral levels. The patient was able to tolerate fusion from T2 to sacrum without any hemodynamically significant events. After surgery, the endotracheal tube was replaced with a cuffed tracheostomy tube and the patient was transferred to the pediatric intensive care unit. He was returned to his home ventilator settings on postoperative day 1. He was discharged on postoperative day 7 after routine intensive care unit care without any cardiovascular events.
XLMTM is the most severe centronuclear myopathy and is often fatal at an early age, with a reported life expectancy of 29 months.2,3 XLMTM is caused by a mutation in the MTM1 gene leading to dysfunction of the enzyme myotubularin.4 Patients present with perinatal hypotonia and musculoskeletal abnormalities. Chronic respiratory failure occurs early in the disease course, requiring tracheostomy and mechanical ventilation.5 Patients who survive into childhood commonly present for orthopedic procedures related to scoliosis, hip dislocations, club foot, or temporomandibular joint disease.6 Recent studies have suggested that long-term survival is higher than previously reported, prompting support for palliative and preventative surgeries in this population.7 Of note, patients with XLMTM have a skeletal muscle–specific phenotype and it is rare to develop involvement of cardiac muscle fibers during their life span.
There are numerous anesthetic considerations for patients with XLMTM. Airway manipulation may be complicated by temporomandibular joint disease, spinal disease, high arched palates, poor upper airway tone, avoidance of succinylcholine, and previous surgical alteration of the airway.8 However, these patients often do not require neuromuscular blockade for intubation or optimization of surgical conditions given their innate hypotonia.1 To the best of our knowledge, there has never been a documented case of exaggerated hyperkalemia or malignant hyperthermia after administration of succinylcholine to a patient with XLMTM. However, it is generally avoided given the association between other myopathies and these events. Chronic respiratory failure often necessitates postoperative mechanical ventilation and an appropriate monitored setting. Patients often have difficulties with feeding and may present volume depleted or with nutritional deficiencies.
Obstructive hypotension has been documented with prone positioning of healthy patients.9 Thoracolumbosacral orthosis braces have been used to prevent hemodynamic instability with prone positioning of unstable spine fractures, but may not fit patients with advanced scoliosis.10 Our approach focused on avoiding direct pressure on the precordium by using a recessed cushion and oblique positioning. This positioning redirected body weight and surgical pressure from the mediastinum.
We believe that previous hypotension and cardiac arrests in this patient were related to vascular compression secondary to hypotonia and neuromuscular scoliosis. Both of these conditions share XLMTM as a proximate cause. High chest wall compliance was suggested by physical examination, low airway pressures, and CT scan with significant anteroposterior shortening in the prone position. Preoperative imaging suggests that his skeletal deformities held internal structures in an orientation that allowed compression of major cardiovascular structures with precordial pressure. XLMTM is not associated with cardiac disorders so it is unlikely that hemodynamic instability was related to intrinsic heart disease, but rather noncardiac mechanisms.11
When not anesthetized, this patient tolerated prone positioning to undergo a CT scan. Without sedation, he was able to position himself on a flat-padded bed, and was on minimal pressure-support mechanical ventilation. These conditions are different compared to those experienced when positioned prone for surgery. Exposures to anesthetics such as volatile agents cause myocardial depression, vasodilation, and changes in central venous pressure. Chest wall mechanics can also be altered by medications such as neuromuscular blocking agents. Increases in ventilator requirements associated with prone positioning and surgical pressure may further decrease preload and increase afterload of the right ventricle, worsening right-sided cardiac output. In addition, bolstered surgical beds apply pressure over a focused region of the chest.
In summary, XLMTM is a rare congenital centronuclear myopathy that is often fatal at birth and is associated with an array of conditions such as hypotonia, chronic respiratory failure, and neuromuscular scoliosis. These patients are living later in life than previously demonstrated and will present more frequently for prone-positioned spinal fixation to improve quality of life and prevent worsening of deformities.6,7 Our case presentation highlights the possibility of hypotension related to caval and cardiac compression in the prone position. This case also shows that this pathology may be demonstrated in a preoperative CT angiogram. We provide an example of care that was able to avoid previously encountered physiologic disasters by minimizing direct pressure on the precordium, utilizing oblique prone positioning, early use of fluids, vasopressors, and interdisciplinary teamwork.
Name: Devon C. Flaherty, MD.
Contribution: This author helped compose the article.
Name: Baron Lonner, MD.
Contribution: This author helped care for the patient, and review the manuscript.
Name: Jonathan S. Gal, MD.
Contribution: This author helped care for the patient, and review the manuscript.
This manuscript was handled by: Raymond C. Roy, MD.
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