Interesting Case

Anesthetic Considerations for Patients with Duchenne Muscular Dystrophy and Becker Muscular Dystrophy: Management of a 15-year-old Male with Muscular Dystrophy for a Cystourethroscopy, Laser Lithotripsy and Stent Placement – A Case Study

By Elyse Parchmont, DNP, CRNA
Department of Anesthesiology
Presbyterian Hospital, Anesthesia Associates of New Mexico

Sally Vender, MD
Department of Anesthesiology 
Presbyterian Hospital, Anesthesia Associates of New Mexico

Abstract

Anesthetic management of patients with Duchenne Muscular Dystrophy (DMD) and Becker Muscular Dystrophy (BMD) can be challenging and involves multifactorial considerations and interventions.  When patients with DMD and BMD present for elective surgery, time is more readily afforded to fully assess critical patient issues, such as pulmonary function and cardiac status, and to optimize the patient holistically.  When patients present emergently, however, time may be of the essence and, therefore, desired testing and optimization may not be logistically possible.  

Patients with DMD and BMD are living longer due to continued advancements in medicine, research, and knowledge.  As such, these patients may increasingly present to the operating room for surgeries and procedures that are more commonly thought of for the adult population, such as laser lithotripsy for nephrolithiasis.  In some situations, such as the community hospital, pediatric anesthesia providers may not be readily available, and providers may not have been exposed to patients with DMD and BMD.  Consideration must be given toward safe anesthetic management and the multifaceted clinical scenario of these special patients.  The aim of this clinical case study is to review DMD and BMD and to help prepare providers for such clinical situations.

Clinical Case Scenario 

We present a 15-year-old male with new onset flank pain and dark colored urine who is diagnosed with nephrolithiasis, dehydration and rhabdomyolysis.  He presents to the general operating room from the emergency department (ED) urgently on the weekend for a cystourethroscopy, laser lithotripsy and stent placement.  The patient has a medical history of muscular dystrophy (unclear diagnosis of Duchenne vs. Becker), baseline tachycardia, hypertension, chest pain, restrictive lung disease, obstructive sleep apnea with home BiPAP use, osteoporosis, mild gastrointestinal reflux, and obesity.  The patient is taking atenolol and has taken the am dose.  Labs were reviewed. 

Among abnormal lab findings, his WBC and liver enzymes are elevated, BUN and creatinine are decreased, and the creatinine kinase was noted to be elevated at > 4000 U/L.  An electrocardiogram was obtained demonstrating sinus tachycardia with a ventricular rate of 117, a nonspecific T wave abnormality, and being read as a borderline ECG.  Other ECG values were: PR interval 127 ms, QRS duration 77 ms, and QT/QTc 300/450 ms.  A transthoracic echocardiogram was noted in the chart and demonstrated mild left ventricular dilation, normal biventricular systolic function, no evidence of left ventricular diastolic dysfunction, normal wall thicknesses, and no indirect evidence of significant pulmonary hypertension.

The patient’s vital signs in the preoperative area indicated a heart rate of 96, a non-invasive blood pressure of 124/78, an oxygen saturation of 94% on room air, a respiratory rate of 16, and a skin temperature of 36.6oC.   His height and weight were 135 cm and 59 kg, respectively. 

Perioperative course
The patient presented from the ED with an in situ peripheral intravenous line.  He did not receive premedication with midazolam due to possible negative respiratory side effects and instead verbal reassurance was used to calm the patient during separation from his mother in holding and while in the operating room (OR).  This was successful even though the patient had slight anxiety, which was managed by distractions and calming verbalizations.  The patient was able to slowly move to the OR table with assistance. 

Standard American Society of Anesthesiologists (ASA) monitors were placed and all vital signs were stable.  He was preoxygenated with 1.0 FiO2 via face mask.  The anesthesia machine had been prepared with activated charcoal filters, flushed with 100% oxygen, and the circuit and absorbent had been changed for malignant hyperthermia (MH) precautions.  The patient was cautiously induced with lidocaine (60 mg), fentanyl (25 mcg), and propofol (150 mg total in boluses of 100 mg and 50 mg).  After the patient was anesthetized, a #3 LMA was easily placed and the patient was placed on pressure support ventilation with a propofol infusion that was titrated between 200-250 mcg/kg/min.  No inhalational agents were utilized for this anesthetic. 

In addition to the propofol infusion, additional doses of medication were administered to keep the patient anesthetized and hemodynamically stable.  Additional medications were two more fentanyl boluses of 25 mcg each, one propofol bolus of 50 mg, and 16 mcg dexmedetomidine (in 4 mcg increments).  A 4 mg dose of ondansetron was given for antiemetic prophylaxis.  Mild tachycardia and hypertension were noted perioperatively; however, the patient was overall very stable intraoperatively.  At the end of the case, the patient was successfully extubated awake and taken to the PACU on 100% O2 simple face mask with spontaneous ventilations and maintaining his airway well with the head of the stretcher raised 30 degrees.  He was conversing and doing very well shortly thereafter. 

Discussion

What is Duchenne Muscular Dystrophy and Becker Muscular Dystrophy?  What are the genetic implications?
For the purposes of this case study, the focus will be on two myopathies: Duchenne Muscular Dystrophy (DMD) and Becker Muscular Dystrophy (BMD).  DMD is a more common occurring genetic disease, which occurs in approximately 1:3,000 males.  While BMD is less common with approximately 1:30,000 males being affected.  Both DMD and BMD are X-linked and arise from a mutation in the gene located at Xp21.  This gene encodes dystrophin, which is a sarcolemmal protein that is found copiously in cardiac and smooth muscle cells.  Dystrophin is generally lacking in DMD and can be diminished in size or amount in BMD.1,2

Duchenne Muscular Dystrophy is most often diagnosed early in childhood, primarily between the ages of three and seven years.1 Proximal muscle weakness is a classic presentation.3 Respiratory distress and cardiomyopathy appear as the disease process advances.3 Progressive skeletal muscle weakness generally occurs and eventual loss of ambulation is likely around seven to thirteen years of age.  BMD may present and, therefore be diagnosed later in childhood and into the teenage years.1 Patients suffering from DMD usually succumb secondary to cardiac or respiratory failure in the second or third decade of life.  While patients with BMD may live well into the fourth or fifth decade prior to likely succumbing to cardiorespiratory sequelae.

What are cardiac manifestations associated with DMD and BMD?
Both DMD and BMD may manifest cardiac disease as a generally progressive dilated cardiomyopathy.1,4 A large percentage of patients with DMD may develop a cardiomyopathy involving the inferobasal and lateral left ventricle.2 In the presentation and progression of BMD, cardiac disease may be more evident than skeletal muscle weakness.2 It should be noted that end-stage cardiac disease is identified with interspersed areas of myocyte atrophy, hypertrophy, and fibrosis.1  The incidence of cardiomyopathy in patients with DMD is approximately 25% by six years of age and up to 59% by ten years of age. 

If a patient with DMD reaches 30 years of age, they have a remarkable 90% risk of having cardiac involvement.5 BMD has a distinctively elevated rate of heart transplantation within the year after diagnosis of cardiomyopathy.2 An implantable cardioverter-defibrillator (ICD) may be considered and warranted in these patients and placement may be based on patient status as well as patient and family desires.2   Interestingly, female carriers of DMD and BMD may also develop symptomatic sequelae.  While female carriers of the diseases are not generally found to have significant cardiomyopathy during childhood, it has been noted to present later in life.2

Patients with DMD and BMD are also at risk for development of brady- and tachydysrhythmias and may even experience sudden cardiac death, which may be a more likely occurrence in patients with end-stage muscular disease.2  The cause of sudden death is relatively unclear, although a correlation has been found between sudden death and the presence of complex ventricular dysrhythmias.2  Furthermore, ventricular dysrhythmias were found to correlate to the progression and state of the anatomical cardiomyopathy.2  It is estimated that up to 50% of patients with BMD progressively acquire cardiac sequelae and eventual death from congestive heart failure related dysrhythmias.

Sinus tachycardia is the most common dysrhythmia identified in the presence of DMD and can be steadfast or may fluctuate.2  Distal conduction system disruptions with complete heart block and bundle branch reentry ventricular tachycardia have been noted.2  Atrial dysrhythmias including atrial fibrillation and atrial flutter may develop in patients with dilated cardiomyopathy and frequently materialize in the setting of respiratory dysfunction with cor pulmonale.2 Atrioventricular conduction disturbances have been recognized with either a short or prolonged PR interval presentation. 

These patients may present with a pacemaker device; however, this may not prevent sudden death due to the chance of ventricular dysthymias.2 The most common ventricular dysrhythmia appears as premature ventricular beats. Ventricular dysrhythmias may occur in up to 30% of this population, and complex ventricular dysrhythmias are found to be more common in patients with severe musculoskeletal disease per Rajev and Groh.  These authors also found that the presence of systolic dysfunction was a compelling predictor of mortality; however, they did not find a correlation between ECG abnormalities, late potentials, or ventricular dysrhythmias and mortality.2

What are the echocardiographic findings most often associated with dilated cardiomyopathy (DCM)?
Echocardiography is central in the diagnosis of dilated cardiomyopathy (DCM). Echocardiographic features of DCM are: left ventricular (LV) dilation, systolic dysfunction, impaired global contractility, normal LV wall thickness, and LV diastolic dysfunction with elevation in LV filling pressure. Other frequently occurring findings include: LV dyssynchrony, right ventricular (RV) dysfunction, atrial dilation, functional mitral and tricuspid regurgitation, and secondary pulmonary hypertension. Newer echocardiographic technologies can be utilized, such as three-dimensional (3D) echocardiography, for greater accuracy in assessing LV volumes and ejection fraction (EF).  Speckle tracking can be particularly helpful in the analysis and early diagnosis of strain per Pinamonti et al.6

What are the electrocardiograph (ECG) findings associated with DMD and BMD?
Patients with DMD are likely to have an abnormal electrocardiograph (ECG) tracing with the typical electrocardiographic pattern of: characteristic tall R waves and heightened R/S amplitude in V13 with noted deep and narrow Q waves which occur in the left precordial leads and may be related to the association of the posterolateral left ventricle.2 A short PR interval and right ventricular hypertrophy may also be common electrocardiographic findings. Per Rajdev and Groh, there has yet to be a conclusive association between the presence of dilated cardiomyopathy and electrocardiographic disturbances; however, they do state that a bundle branch block may be seen in patients presenting with dilated cardiomyopathy.2

What are other co-morbidities associated with DMD and BMD? 
In addition to cardiomyopathy, cardiac dysrhythmias, and respiratory compromise in patients with DMD and BMD, patients may present with a variety of other comorbidities that can affect their perioperative course.  Therefore, a thorough history and physical should be assessed in order to tailor an appropriate anesthetic plan. 

Muscle degeneration can predispose patients with DMD and BMD to thromboembolic events due to prothrombotic sequelae.  Though there is minimal evidence of evidence-based benefit, they may present on preventative anticoagulation therapy.1 Patients may also develop contractures which could affect positioning and intravenous access.  Patients with DMD and BMD can have scoliosis which may further impact respiratory function. Scoliosis can affect echocardiographic imaging, often limiting diagnostic capabilities for diagnosing cardiomyopathy due to poor echocardiographic acoustic windows.1 Patients may also develop lordosis or kyphosis, which can add to perioperative concerns.

Glucocorticoids are in the treatment regimen for patients with DMD and BMD because they have been shown to slow the decline of muscle strength.7 Patients, therefore, can have typical sequelae of long-term glucocorticoid use such as obesity, osteoporosis/bone fractures, glucose intolerance, left ventricular hypertrophy, and elevated systemic blood pressure.1 Due to chronic glucocorticoid therapy, stress-dose steroids may be indicated intraoperatively.8

Patients with DMD and BMD may also have cognitive dysfunction as dystrophin helps stabilize neural tissue.7 Children with DMD and BMD can have difficulties in focusing attention, verbal learning, memory, and emotional interactions.  Behavioral conditions including autism, attention deficit/hyperactivity disorder, obsessive–compulsive disorder, and anxiety are common in this patient population.  Due to cognitive dysfunction, behavioral difficulty may ensue with induction and emergence from anesthesia.

What should be included in a pre-operative assessment for patients with DMD and BMD?
Due to the cardiorespiratory involvement of DMD and BMD, a thorough pre-operative assessment is crucial.  ECG, echocardiography, and stress tests are warranted.9   Physical assessment and obtaining past medical history are also key in determining perioperative risk.  Sedentary lifestyle and wheelchair bound status creates a situation of little cardiac strain; therefore, those patients with existing dilated cardiomyopathy may present asymptomatically.5 Patients with DMD and BMD should be optimized whenever possible prior to surgical procedures.4

Non-cardiac associated abnormalities that should be assessed include macroglossia, limited mandibular and cervical spine mobility with subsequent possibility of a difficult airway.3

The patient’s pre-operative baseline room air oxygen saturation should be noted. Pulmonary function testing pre-operatively is prudent.10 Unbalanced calcium regulation is a possibility in patients with muscular dystrophies along with findings of altered membrane permeability with notable elevated serum levels of muscle-specific cytoplasmic proteins such as creatine kinase.4   Creatinine kinase (CK) is a known biomarker for muscle damage. CK activity levels, and also elevated protein levels of the muscle form of CK, demonstrate that muscle disturbance is continuing.11

What are anesthetic considerations for patients with DMD and BMD?
It is well documented that patients with DMD and BMD are at an increased risk of experiencing extreme hyperthermia, rhabdomyolysis, and hyperkalemic arrest if depolarizing muscle relaxants such as succinylcholine are administered.3,4,12  Therefore, the administration of depolarizing muscle relaxants is contraindicated.4,5,12 Gurnaney et al. found that there was not a notable increase in risk of malignant hyperthermia (MH) susceptibility in patients with DMD or BMD when compared to the general population.4  However, there have been reports of disease related cardiac complications and a malignant hyperthermia-like syndrome, which is characterized in part by rhabdomyolysis.4,12

Though the reaction is not MH, which usually presents with hypermetabolism - such as respiratory acidosis, metabolic acidosis, and excessive heat production - the MH-like reaction can be equally as lethal.5,12  Not only has rhabdomyolysis been documented but also hyperthermia and hyperkalemic arrest have been reported following administration of halogenated inhalational anesthetic agents such as sevoflurane and isoflurane.3 

This reaction has been termed Anesthesia Induced Rhabdomyolysis (AIR) and/or Adverse Muscular or Metabolic Reaction to Anesthesia (AMRA).5 This reaction can occur not only at induction of anesthesia and intraoperatively but also may be delayed in presentation and occur in the post-operative period.4  The pathophysiology and mechanism of the development of AIR/AMRA is not completely understood.  One hypothesis is that in dystrophic patients, inhaled anesthetic agents exacerbate breakdown of the existing fragile and sensitive membranes of the muscle that are then further disturbed by patient movement or administration of reversal agents. 

Though only a small percentage of patients experience rhabdomyolysis after inhalational anesthetics, a total intravenous anesthetic is considered the safest anesthetic.3,12 Providers should realize, however, that the use of intravenous anesthesia alone has been implicated in the development of heart failure related to preexisting disease in patients with DMD.12  Per Litman et al., cardiac and respiratory dysfunction as well as other comorbidities in this patient population must be considered in anesthetic choice and planning.12 

Though published studies have documented and described the idea that utilization of volatile agents to patients with DMD and BMD can be safe, other authors and patient safety organizations have strongly encouraged the strict avoidance of volatile anesthetics in this patient population.12  Nitrous oxide induction has been documented to be safe;3 however, it is suggested that precautions be taken to ensure these patients are not exposed to inhalational agents by preparing the anesthesia machine with activated charcoal filters, flushing the machine, and exchanging the circuit and absorbent.3,9  Planning preparation to treat acute rhabdomyolysis or hyperkalemia with sodium bicarbonate, insulin, calcium chloride, and mannitol may be beneficial.10

What are the airway considerations for patients with DMD and BMD?
Patients with DMD and BMD may experience respiratory compromise as well as possess the potential for a difficult airway situation.  They may have a myriad of airway concerns such as: macroglossia, weak upper airway dilator muscles, and/or limited mobility of the mandible and cervical spine.  These factors can contribute to upper airway obstruction, make performing a jaw thrust maneuver challenging, and contribute to the difficulty of rapidly securing the airway.  Restrictive lung disease, inadequate secretion management, and ineffective ability to effectively cough all contribute to the increased risk during extubation at case completion.  Therefore, highlighting the perioperative nature of anesthetic concerns and patient management.13

What are the hemodynamic goals for induction and maintenance during anesthesia for patients with dilated cardiomyopathy? 
Dilated cardiomyopathy can occur idiopathically or can be associated with a number of genetic conditions including DMD and BMD.  Regardless of etiology, key findings include impaired systolic function in either the right or left ventricle, or in both ventricles, resulting in diminished stroke volume.  Patients with dilated cardiomyopathy will likely present on a medical therapy regimen which may include medications such as angiotensin converting enzyme (ACE) inhibitors, diuretics, beta blockers, and/or inotropes.  

These medications with the exception of ACE inhibitors should be continued in the perioperative period and the patient should be closely monitored for possible additional medication therapy and intervention.  Due to the fact that dysrhythmias are common in patients with dilated cardiomyopathy, it is prudent to have emergency medications and equipment - such as epinephrine, vasopressors, and an external defibrillator with pads present and ready.  Hemodynamic goals for anesthetic management of patients with DMD and BMD include: maintaining myocardial oxygenation, maintaining adequate preload, and avoidance of increases in afterload.  Decreasing myocardial demand is key as acute tachycardia and hypotension are poorly tolerated.  

Slow controlled titration of induction agents is crucial; keeping in mind that circulation times may be decreased.14 There are pros and cons with induction agent choices; however, etomidate has been noted to cause the least amount of hemodynamic change. It should be noted that etomidate may lead to increased systemic vascular resistance (SVR) as it does not blunt the hemodynamic effects of laryngoscopy.  Propofol is a negative inotropic agent but does decrease SVR, which could be useful on induction if administered with caution.  Opioids are helpful in diminishing the requirement of anesthetic agents, have minimal cardiovascular effect, and can aid in blunting the hemodynamic effects of laryngoscopy.  Ketamine can cause elevations in heart rate, increased myocardial oxygen requirement, and raise SVR and, therefore, it may be prudent to avoid this medication in patients with cardiomyopathy.

Maintenance of anesthesia in patients with dilated cardiomyopathy can be managed multimodally. It is well documented that volatile anesthetics cause myocardial depression in high concentration.  In patients with DMD or BMD, after taking into consideration the entire clinical scenario, a total intravenous anesthetic (TIVA) may be the optimal maintenance anesthetic of choice as volatile anesthetics could possibly cause life-threatening Anesthesia Induced Rhabdomyolysis (AIR) and/or Adverse Muscular or Metabolic Reaction to Anesthesia (AMRA).5  In other populations of patients with dilated cardiomyopathy, a maintenance with low dose volatile anesthetic, opioid, and propofol infusion may help to maintain optimal hemodynamic goals while providing adequate anesthesia.

Often, patients with DCM require cardiovascular support in the perioperative period.  With swift decreases in blood pressure, there are considerations with the use of pure alpha agonist vasopressors such as phenylephrine.  It should be noted that acute increases in venous constriction may transiently lead to increased venous return in hearts that are preload dependent resulting in improved cardiac output.  In failing hearts, however, increased inferior vena cava (IVC) flow from a bolus of a medication, such as phenylephrine, may result in decreased stroke volume, increased left ventricular afterload, and increased myocardial oxygen demand.15

Positive inotropic agents such as milrinone, dobutamine, levosimendan, and low dose dopamine may more optimally support the failing ventricle by increasing contractility, decreasing systemic vascular resistance and promoting forward flow of blood.14 In combination with inodilators, pure alpha agonists such as phenylephrine may help counteract the extreme vasodilation that occurs with these agents.16 In patients with severe systolic dysfunction, biventricular pacing, intra-aortic balloon pump, or left ventricular assist device (LVAD) placement may be considered.  Placement of a central venous line and an arterial line should be considered in the full clinical scenario and patient presentation and may be prudent adjuncts to assist with anesthetic management.14

What are postoperative management considerations in patients with DMD and BMD? 
Postoperative mechanical ventilation may be necessary if the vital capacity (VC) is less than 50% predicted.  A VC of less than 30% predicted may be a significant precursor for serious postoperative complications even in the setting of mechanical ventilation.10  Patients with DMD have a decreased ability to cough and clear secretions and are, therefore, at increased risk for postoperative pneumonia.10   Hypomotility in conjunction with weak laryngeal reflexes may also put these patients at an increased risk of aspiration in the perioperative period.10  Securing the airway postoperatively should be considered based on the entire clinical picture including vital sign stability, degree of chest muscle weakness, quality of cough, and secretion management. 

As stated earlier, if volatile anesthetic agents are utilized intraoperatively, then the presentation of AIR/AMRA can occur not only at induction of anesthesia and intraoperatively, but also may be delayed in presentation and occur in the post-operative period.4,5   Therefore, providers should be on the lookout for signs and symptoms of these reactions and communication with the perioperative team is vital. 

Conclusion

The anesthetic management of patients with DMD and BMD requires thoughtful consideration and planning.  Evaluation of the patient history and clinical presentation including respiratory and cardiac status as well as existing comorbidities is crucial for optimal planning and optimization.  Induction of anesthesia, maintenance, emergence, and the post-operative course can all be challenging periods.  

It is for these reasons that adequate planning for any and all scenarios is of the utmost importance.  Dilated cardiomyopathy is common in patients with DMD and BMD; therefore, the possibility of hemodynamic compromise must be considered during all stages of anesthesia from induction to emergence and well into the postoperative period.  Total intravenous anesthetic is recommended when possible secondary to the high risk of AIR/AMRA from exposure to volatile anesthetics, and the use succinylcholine is absolutely contraindicated.  It is clear that patients with DMD and BMD require thorough investigation, planning, and communication with the perioperative team for optimal patient safety and clinical outcomes. 

Q & A

1) What is the MOST PREVALENT echocardiographic abnormality found in pediatric patients with Duchenne and Becker Muscular Dystrophy?

A. Left ventricular hypertrophy
B. Dynamic left ventricular outflow tract obstruction
C. Left ventricular dilation
D. Thickened interventricular septum

2) What medications should be avoided for patients with BMD?

A. Opioids
B. Depolarizing muscle relaxants
C. 5-HT3 antagonist
D. Epinephrine

3) What is the most common dysrhythmia identified in the presence of DMD?

A. Bundle branch block
B. Q-T prolongation
C. Atrioventricular nodal reentrant tachycardias
D. Sinus tachycardia

4) Female carriers of DMD and BMD can exhibit symptomatic cardiac sequelae of the disease processes.

A. True
B. False

Answers

1) C. Left ventricular dilation
2) B. Depolarizing muscle relaxants
3) D. Sinus tachycardia
4) A. True

References

1. Colgrove L. Cardiovascular health supervision for individuals affected by Duchenne or Becker muscular dystrophy. American Academy of Pediatrics clinical report: Organizational principles to guide and define the child health care system and/or improve the health of all children section on cardiology and cardiac surgery. Pediatrics. 2005; 116(6): 1569-1573.
2. Rajdev A, Groh W. Arrhythmias in the muscular dystrophies. Card Electrophysiol Clin. 2015; 7(2): 303–308.
3. Bhutia M, Pandia M, Rai A. Anaesthetic management of a case of Duchenne muscle dystrophy with Moymoya disease. Indian J Anaesth. 2014; 58(2): 219-221.
4. Gurnaney H, Brown A, Litman R. Malignant hyperthermia and muscular dystrophies. Anesthesia and Analgesia. 2009; 109: 1043-1048.
5. Sinton J. Muscular dystrophy. Editors. Adler A, Chandrakantan A, Litman R. In: Case Studies in Pediatric Anesthesia. Cambridge, United Kingdom: Cambridge University Press; 2019: 64-67.
6. Pinamonti B, Abate E, De Luca A, Finocchiaro G, Korcova R. Genetics to Clinical Management: Role of cardiac imaging. Retrieved 1/6/21
7. Crean P, Peake D. Essentials of neurology and neuromuscular disorders. Editors. Cote C Lerman J, Anderson B. In A Practice of Anesthesia for Infants and Children. 5th Ed. Philadelphia, PA: Elsevier Saunders; 2013: 488-490.
8. Serfass E. Muscular dystrophy. Editors. Chu L, Traynor A, Kurup V. In Manual of Clinical Anesthesiology. 2nd Ed. Philadelphia, PA: Lippincott Williams and Wilkins; 2021: 696-700.
9. Lerman J, Sampathi V, Watt S. Induction, maintenance, and emergence from anesthesia. Editors. Gregory G, Andropoulos A. In: Gregory’s Pediatric Anesthesia. 5th ed. West Sussex, UK: Blackwell Publishing; 2012: 330-360.
10. Ko, R. Muscular Dystrophy. Editors. Houck P, Haché M, Sun L. In: Handbook of Pediatric Anesthesia. New York, NY: McGraw-Hill Education; 2015: 132-135.
11. Szigyarto C, Spitali P. Biomarkers of Duchenne muscular dystrophy: current findings. Degener Neurol Neuromuscul Dis. 2018; 8: 1–13.
12. Litman R, Griggs S, Dowling J, Raizi S. Malignant hyperthermia susceptibility and related diseases. Anesthesiology. 2018; 128: 159–167.
13. Birnkrant D, Panitch H, Benditt J, et al. American College of Chest Physicians consensus statement on the respiratory and related management of patients with Duchenne Muscular Dystrophy undergoing anesthesia or sedation. Chest. 2007; 132: 1977-1986.
14. Ibrahim I, Sharma V. Cardiomyopathy and anaesthesia. BJA Education. 2017; 11: 363-369.
15. Canneson M, Jian Z, Chen G, Vu T, Hatib F. Effects of phenylephrine on cardiac output and venous return depend on the position of the heart on the Frank-Starling curve. J. Appl Physiol 2012; 113: 281-289.
16. Juneja R, Nambiar P. Cardiomyopathies and anaesthesia. Indian J Anaesth. 2017; 61(9): 728-735.