PBLD- Table #12. What a Shock: A Young Man with Duchenne Muscular Dystrophy Presents for Lithotripsy at Your Outpatient Surgery Center!

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1 PBLD- Table #12 What a Shock: A Young Man with Duchenne Muscular Dystrophy Presents for Lithotripsy at Your Outpatient Surgery Center! Moderators: Bridget L. Muldowney MD, and Lana M. Volz MD Institution: University of Wisconsin School of Medicine and Public Health American Family Children s Hospital, Madison, WI Learning Objectives 1. Describe the pathophysiology and presentation of Duchenne muscular dystrophy 2. Evaluate the disease progression in Duchenne muscular dystrophy with emphasis on respiratory and cardiac involvement 3. Assess preoperative evaluation of patients with Duchenne muscular dystrophy 4. Identify the anesthetic implications of Duchenne muscular dystrophy 5. Analyze the risks associated with lithotripsy and relate them to a patient with Duchenne muscular dystrophy Stem Case and Key Question Content A 22 year-old, 41kg male with symptomatic nephrolithiasis presents for extracorporeal shock wave lithotripsy. Past medical history is significant for Duchenne muscular dystrophy (DMD). Past surgical history includes muscle biopsy as a young child, posterior spinal fusion 10 years ago. He is wheelchair bound and uses nocturnal noninvasive ventilation. He was admitted to the hospital 2 years ago with a congestive heart failure (CHF) exacerbation. Current medications include omeprazole, ipratropium, lorazepam, aspirin, furosemide, and lisinopril. What is the pathophysiology of muscular dystrophy? Specifically, what is unique to Duchenne muscular dystrophy? What preoperative information and testing should be obtained prior to surgery? Would you proceed ahead if the patient did not have recent PFT s? Is this case appropriate for an outpatient surgery center? Would that be different if the patient is dependent on ventilation through a tracheostomy? The patient s mother states that during her son s spinal surgery there was difficulty securing his airway and he nearly died. What is the likely mechanism of a difficult airway in a patient with Duchenne muscular dystrophy? What are options to safely secure the airway in these patients? The patient is very anxious and says that he is a very hard IV stick and would prefer to be asleep prior to having his IV placed. Is an inhalational induction safe for patients with DMD? Is he at increased risk of malignant hyperthermia? Is there a safe alternative to IV induction in this patient? Could a regional or neuraxial anesthetic be considered for the procedure? 1

2 The patient s mother states that her son has been stable since his CHF exacerbation 2 years ago, however she is concerned that the lithotripsy and anesthesia might set him back. An echocardiogram obtained 6 months ago shows moderate left ventricular dilation and dysfunction, fractional shortening of 11.4%, LV EDV Z-score of 4.66, and ejection fraction of 43%. The patient also had a Holter monitor placed 6 months ago that captured frequent PVC s. What is the natural progression of cardiac involvement in DMD? What are the anesthetic concerns for a patient with known CHF? Is invasive monitoring warranted for this procedure? If the patient had a pacemaker and/or AICD is it safe to proceed with lithotripsy? The mother recalls her son having significant blood loss requiring transfusion during his spinal fusion. She is concerned he will bleed again. Does this procedure put him at risk of bleeding? Should the patient have coagulation studies prior to proceeding to the OR? The patient proceeds to the OR and, with assistance, positions himself comfortably. He is sedated with 70% nitrous oxide in 30% oxygen via facemask and a 24G PIV is placed in the only vein found in the foot. You proceed to give the patient 2mg of Midazolam. What is your plan for induction and maintenance of anesthesia? Is a LMA sufficient for airway management? If not how do you plan to manage the patient s airway? You place an LMA to provide pressure support ventilation. The patient is relaxed but still making occasional movements, and the urologist asks that the patient be more immobile. What are options to deepen the plane of anesthesia? Is propofol safe in the setting of cardiomyopathy? What are alternatives? Is it safe to give a patient with DMD a non-depolarizing neuromuscular blocking drug? Do patients with DMD have an altered response to non-depolarizing neuromuscular blockers compared to unaffected patients? The patient receives a small dose of fentanyl follow by a sedative infusion. The patient is now immobile making very brief utterances from time to time. As the urologist begins the shock wave lithotripsy the monitor is alarming and the oxygen saturation tone is lost. The monitor shows ventricular tachycardia. Does the patient s disease put him at higher risk of arrhythmias? Could the procedure be causing the arrhythmia? How can one distinguish between a true arrhythmia and artifact? What is the treatment for sustained ventricular tachycardia? The patient tolerates the procedure well and awakens shortly after discontinuation of the anesthetic. 2

3 Should the patient go through PACU and be discharged home? If kept overnight what is the appropriate location for the patient? On a post-op visit the following day in the ICU the patient is packed up and ready to leave. He is grateful and says, That wasn t bad at all. I won t mind if I have to come back for this again. Thanks! 3

4 Discussion Pathophysiology and Presentation of Duchenne Muscular Dystrophy (DMD) Muscular dystrophy is a group of inherited disorders causing progressive muscle weakness and loss of muscle tissue. Muscular dystrophies result from the dissociation of contractile force from the muscle and the surrounding connective tissue. Although the actin-myosin filaments contract, the electrical signal from the muscle cell is not translated into an effective force. Duchenne muscular dystrophy, the most common and severe form of muscular dystrophy, occurs in 1/3,500 live male births. It is an X-linked recessive disorder characterized by the lack of dystrophin. Mutations occur in the dystrophin gene located on the short arm of the X chromosome (Xp21 position). Mutations, the majority of which are deletions but can also be duplications, result in a complete lack of dystrophin in skeletal muscles. Dystrophin is a large protein that anchors the actin-myosin filaments to the cell membrane and surrounding cellular matrix. The absence of dystrophin results in instability and increased permeability of the sarcolemma and increased intracellular calcium levels. Postsynaptic acetylcholine receptors are also dependent on dystrophin. Abnormalities occur in the type, number, and location of receptors. In the absence of dystrophin there is an increase in the expression of acetylcholine receptor subunits as well as changes in interacting proteins. 1 Duchenne muscular dystrophy typically presents in early childhood with motor delays and weakness. Delayed walking is often an initial sign. Affected young boys present with progressive weakness of the proximal muscles that is most prominent in the lower extremities. They will have compensatory pseudohypertrophy of the calves. They often use their hands and arms to walk up the body when rising from the floor known as Gower s sign. Disease Progression in Duchenne Muscular Dystrophy Duchenne muscular dystrophy is a progressive disease. Nearly all patients are symptomatic by school age, and struggle to run or jump and walk with a waddling gate. By the preteen and early teen years most patients progress to wheelchair dependency. Many develop severe contractures due to muscle weakness. Steroids have become the primary treatment for the skeletal muscle disease. 2 The disease affects not only skeletal muscle, but also cardiac muscle and smooth muscle. Weakness combined with restrictive lung physiology due to neurogenic scoliosis often impairs adequate ventilation. Patients are more susceptible to pulmonary infections and aspiration. Cardiac muscle is also involved in the disease. Patients develop a progressive dilated cardiomyopathy. As the treatment and care for the pulmonary and skeletal muscle symptoms of patients with DMD has advanced, cardiomyopathy has emerged as a significant cause of morbidity and mortality. 3 Many patients are now surviving into the third and even forth decade of life, and will present with significant cardiomyopathy and heart failure needing sedation and anesthesia for unrelated procedures. Preoperative Assessment of Patients with Duchenne Muscular Dystrophy Preoperative assessment should focus on respiratory and cardiac status. 4

5 Prior to surgery or sedation a patient should see the pulmonologist and have pulmonary function testing to include forced vital capacity (FVC), maximum inspiratory pressure (MIP), maximum expiratory pressure (MEP), peak cough flow (PCF), and oxyhemoglobin saturation measured by pulse oximetry on room air. If oxyhemoglobin saturation is less that 95% on room air then blood or end tidal carbon dioxide level should be measured to assess the degree of hypoventilation. Patients are at increased risk of respiratory complications with a FVC <50% of predicted, and are at high risk of complications if FVC is <30% of predicted. High-risk patients can be trained in noninvasive positive pressure ventilation (NPPV) prior to surgery. Patients at high risk of ineffective cough (PCF <270L/min or MEP <60cm H20) can be trained in using manual and mechanical cough assists. 4 In any patient who is not yet ventilator dependent it is prudent to discuss the possible need for post-operative ventilatory support and discuss the patient s wishes should he be unable to wean from mechanical ventilation. Patients should also have cardiology consultation prior to anesthesia. Although all patients will develop dilated cardiomyopathy, less that half of patients over the age of 18 show classic symptoms of heart failure due to their inability to ambulate. Symptoms of progressive heart failure are often vague and include sleep disturbance, loss of appetite, nausea, abdominal pain or fullness, increased cough or secretions, and weight loss. More classic symptoms including chest pain, palpitations, dizziness, or syncope may indicate arrhythmias rather than the progression of heart failure. An EKG should be preformed and noted for any recent changes. EKG changes are often present before patients have echocardiographic findings of cardiomyopathy. At baseline many patients with DMD have sinus tachycardia with a shortened PR interval and prolonged QTc interval. Premature atrial and ventricular complexes are common. An echocardiogram is the gold standard for evaluation of cardiac function in DMD patients. It can be technically challenging to obtain good echocardiographic views due to scoliosis and contractures often present in these patients. Echo should evaluate both the ejection fraction and the shortening fraction. Even in the setting of a normal ejection fraction strain is often seen on the myocardium. Many centers are also using cardiac MRI to monitor patients, especially when echo images are not optimal. 5,6 B-type natriuretic peptide, often used to assess for degree of heart failure, is not a useful indicator of heart failure in DMD patients. 6 Therapy for cardiomyopathy often includes steroids, ACE inhibitors, and betablockers. Anesthetic Implications of Duchenne Muscular Dystrophy Patients with DMD can be safely anesthetized when appropriate precautions are taken. The use of inhalational anesthetics should be avoided when possible. Previous belief was patient s with DMD are at increased risk of malignant hyperthermia. Review of case reports suggests that this is not the case. Also, most patients with DMD have negative caffeine-halothane contracture testing, and such testing is unreliable in the diseased muscle of DMD patients. More recent evidence suggests that the reaction that DMD patients have to inhalational anesthetics is more consistent with rhabdomyolysis rather than malignant hyperthermia. 7,8 When the sarcolemma is exposed to an inhalational anesthetic, or a depolarizing neuromuscular blocker, the muscle membrane is stressed and further increases its permeability and instability. Intracellular calcium levels increase and potassium and creatine kinase leak from cells causing the symptoms of rhabdomyolysis. A retrospective review of 59 volatile anesthetic exposures in patients with DMD showed no anesthetic related complications. All patients were older than 8 5

6 years of age and this safety may not be generalized to younger dystrophin-deficient children. 9 Even though only a small minority of patients with DMD will experience rhabdomyolysis in response to inhalational anesthetics, it is prudent to avoid them. One should consider the risk and benefit of using a neuromuscular blocker. DMD patients have upregulation of extrajunctional acetylcholine receptors, and administration of depolarizing neuromuscular blockers can cause massive potassium release and hyperkalemic cardiac arrest. Succinylcholine should also be avoided due to the predisposition to anesthesia induced rhabdomyolysis, as discussed above. Nondepolarizing neuromuscular blocking drugs are safe to use but caution should be used with dosing. Patients with DMD have an increase in the time to onset and a prolonged response to nondepolarizing neuromuscular blockers when compared to unaffected individuals. 10,11,12 Care should be taken when dosing muscle relaxants, recognizing the impact that residual weakness will have on a patient with baseline compromised respiratory function. Patients with DMD can present challenges in airway management. The presence of obesity as well as hypertrophy of the tongue can make intubation difficult. 13 Scoliosis and contractures can also contribute to a challenging airway. Video laryngoscopy and/or fiberoptic bronchoscopy should be readily available, as well as LMA in case of difficulty with both mask ventilation and intubation. The choice of anesthetic technique should be based on the aforementioned concerns as well as the patient s cardiac function. Patients with cardiomyopathy, even in the setting of a preserved ejection fraction, are at risk of intraoperative hypotension requiring inotropic support. 14 As cardiomyopathy progresses it is prudent to avoid drugs that act as myocardial depressants. This is often difficult to balance with the need to avoid inhalational anesthetics. Inotropic support should be readily available. Regional anesthesia may be a useful technique for some surgical procedures. Most patients having undergone posterior spinal fusion and instrumentation are not good candidates for neuraxial anesthesia. Risks of Lithotripsy and Implication for Patients with Duchenne Muscular Dystrophy Extracorporeal shock wave lithotripsy is a noninvasive treatment for nephrolithiasis. It involves the application of focused high intensity acoustic pulses externally to break up stones in the kidney. Lithotripsy is painful and therefore anesthesia or sedation is required. The shock waves produce sharp and stinging pain at the entry site on the flank. Patients are often placed in semi lateral or lateral positions, which must be done with caution in patients with DMD due to contractures. Skin bruising and flank ecchymosis are common at the shock wave site. The shock waves can also cause renal parenchymal and subcapsular hemorrhage, and hematuria is common post procedure. It is reasonable to check coagulation status (PT/INR, PTT, and platelets) prior to the procedure. Lung tissue can be damaged by shock waves, leading to hemoptysis that can be massive and life threatening. This is more common in children due to the shorter distance from the lung base to the kidney. Arrhythmias during lithotripsy, although previously reported, are now extremely rare. Mechanical stress on the conduction system caused by the shock waves was believed to be the cause. Premature atrial and ventricular complexes, atrial fibrillation, 6

7 supraventricular tachycardia, and ventricular tachycardia have all been reported. Artifact on EKG is far more common. These artifacts can resemble ventricular tachycardia, and it is prudent to differentiate between artifact and actual arrhythmia, especially in the patient with DMD who is prone to arrhythmias. Both the artifacts and arrhythmias typically stop with the cessation of treatment, but occasionally persist and require treatment. 15 Patients with pacemakers can be treated successfully with lithotripsy. The pacer should be programmed to a nondemand mode to ensure pacing in the case of interference by the shock waves. Occasionally the pacemaker is damaged in the path of the shock wave. Backup modes of pacing should always be available. Although an AICD is generally considered a contraindication to lithotripsy, patients with AICD s have been successfully treated. The AICD should be turned off prior to the procedure and immediately turned on after the procedure. Backup defibrillation equipment must be available during the procedure. The location of newer transvenous AICD s is more favorable than the older abdominally implanted devices. 15 References: 1. Morgan, P. Muscular Dystrophy Syllabus. Refresher Course 2011 SPA meeting. 2. Ames, WA, et al. The role of corticosteroids in Duchenne muscular dystrophy: a review for the anesthetist. Pediatric Anesthesia 2005; 15: Bushby, k, et al. The Multidisciplinary management of Duchenne Muscular Dystrophy. Current Paediatrics 2005; 15: Birnkrant, DJ, 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: Klitzner, TS, et al. Cardiovascular Health Supervision for Individuals Affected by Duchenne or Becker Muscular Dystrophy. Pediatrics 2005: 116: Spurney, CF. Cardiomyopathy of Duchenne Muscular Dystrophy: Current Understanding and Future Directions. Muscle Nerve 2011; 44: Hayes, J, et al. Duchenne muscular dystrophy: an old anesthesia problem revisited. Pediatric Anesthesia 2008; 18: Gurnaney, H, et al. Malignant Hyperthermia and Muscular Dystrophies. Anesth Analg 2009 Oct: 109: Segura, LG, et al. Anesthetis and Duchenne or Becker muscular dystrophy: A review of 117 anesthetic exposures. Pediatric Anesthesia 2013; 23: Ihmsen, H, et al. Influence of Disease Progression on the Neuromuscular Blocking Effect of Mivacurium in Children and Adolescents with Duchenne Muscular Dystrophy. Anesthesiology 2009; 110: Muenster, T, et al. Rocuronium 0.3mg/kg (ED95) induced a normal peak effect but an altered time course of neuromuscular block in patients with Duchenne muscular dystrophy. Pediatric Anesthesia 2006; 16: Wick, S, et al. Onset and Duration of Rocuronium-induced Neuromuscular Blockade in Patients with Duchenne Muscular Dystrophy. Anesthesiology 2005; 102: Morris, P. Duchenne muscular dystrophy: a challenge for the anaesthetist. Paediatric Anaesthesia 1997; 7: Kipps, AK, et al. Children with cardiomyopathy: complications after noncardiac procedures with general anesthesia. Pediatric Anesthesia 2007; 17: Malhotra, V, et al. Anesthesia and the Renal and Genitourinary Systems. Miller s Anesthesia. 7 th ed. 2009: