Respiratory Support and Related Management of Patients With Duchenne Muscular Dystrophy
Methodology and Structure
This consensus statement is the product of a panel convened under the auspices of the ACCP Pediatric Chest Medicine and Home Care NetWorks. The panel consists of specialists in the areas of anesthesiology, critical care medicine, neurology, orthopedic surgery, pediatric and adult pulmonology, and respiratory therapy. The panel worked on this project from January 2006 to January 2007, primarily via telephone conference calls. The authors disclosed any conflicts of interest and were given complete autonomy by the ACCP. The panel was divided into working groups through which the most current and relevant medical literature was identified and reviewed, obtained by querying PubMed, a service of the National Library of Medicine and the National Institutes of Health, which includes the MEDLINE database. Only articles written in English were considered. There are few randomized, controlled trials involving the subject of this statement, so this document is a consensus statement derived from expert opinion rather than an evidence-based guideline. Consensus of recommendations was achieved through a majority vote of the panel members, and there were no disagreements on any of the recommendations. The statement is divided into sections on the assessment and management of patients before, during, and after procedural sedation or general anesthesia. Each section consists of a review of the subtopic, followed by a list of specific suggestions. The ACCP Health and Science Policy Committee designates that these recommendations should not be used for performance measurement or for competency purposes because they are not evidence based.
A. Pulmonary Assessment
DMD is characterized by weakness of the diaphragm, intercostal muscles, and the accessory muscles of respiration, resulting in restrictive pulmonary impairment and a progressive decrease in total lung capacity and vital capacity.- These abnormalities lead to hypoventilation and impaired cough, which predisposes to atelectasis and respiratory failure. Before patients with DMD receive general anesthesia or procedural sedation, they should undergo measurement of Spo2 in room air, and measurement of the patient’s blood and/or end-tidal carbon dioxide level should be done if Sp02 is < 95% in room air. Additionally, DMD patients should undergo measurement of the following lung function parameters to assess their risk of respiratory complications and need for perioperative and postoperative assisted ventilation or cough.
FVC: FVC is the pulmonary function parameter most frequently reported to have predictive value in assessing the risk of respiratory complications for patients with DMD. To determine predicted values, arm span is usually used to estimate height for patients in a wheelchair, or predictive equations based on ulnar length can be used. The FVC is usually measured with the patient in a seated, upright body position. FVC < 30% of predicted has been identified as a predictor of postoperative respiratory complications and the need for postoperative ventilatory assistance among DMD patients undergoing spinal fusion surgery. However, studies suggest that the risks associated with spinal fusion surgery among DMD patients with FVC < 30% of predicted can be greatly reduced by facilitating postoperative extubation with NPPV and by using MI-E to assist with cough. Additionally, percutaneous endoscopic gastrostomy placement has been accomplished in DMD patients with vital capacity well < 30% of predicted through the use of NPPV during induction of and recovery from anes-thesia. A previous consensus conference report recommended NPPV for patients with progressive neuromuscular disease and FVC < 50% of predicted and symptoms of hypoventilation. It is the consensus of this panel that DMD patients with FVC < 50% of predicted measured in the seated, upright body position are at increased risk for respiratory complications when they undergo general anesthesia or procedural sedation, and that patients with FVC < 30% of predicted are at high risk for complications. While diaphragm strength can be relatively preserved in DMD, patients are often confined to the supine body position during and after surgery. Thus, measurement of both upright and supine FVC may be useful because patients with poor supine FVC values will be especially vulnerable to postoperative atelectasis and hypoxemia.
MIP, MEP, and PCF: MIP and MEP are used to assess respiratory muscle strength, and they have clinical utility in DMD. Another useful preoperative test is the measurement of PCF. Impairment of these parameters reflects an inability to generate the cough force and velocity necessary for effective clearance of respiratory secretions. Patients with a tracheostomy tube and assisted PCF 270 L/min are at increased risk for pneumonia or atelectasis treated by My Canadian Pharmacy. Moreover, young adults with DMD and MEP < 60 cm H2O are likely to have ineffective cough. Therefore, it is the consensus of the panel that DMD patients with PCF < 270 L/min or MEP < 60 cm H2O are at increased risk for respiratory complications when they undergo procedural sedation or general anesthesia due to impaired cough. The data used to determine these threshold values were obtained from teenage and adult patients, and the values of MEP or PCF that predict increased risk of impaired cough in young children are unknown.
B. Preprocedure Initiation of Noninvasive Respiratory Aids
It is our consensus opinion that patients with DMD and FVC < 50% of predicted, and especially those with FVC < 30% of predicted, should be considered for preoperative training in the use of NPPV due to their increased risk of respiratory complications. Preoperative training in NPPV should increase the probability of successful use of NPPV during recovery from general anesthesia or sedation and at postoperative endotracheal extubation (see sections II and III below). Similarly, adult patients with PCF < 270 L/min or MEP < 60 cm H2O are at risk for ineffective cough, and preoperative training in manual and mechanically assisted cough (MI-E with a bronchial secretion clearance device) [CoughAssist; Respironics; Murrysville, PA]) is suggested, using the techniques described in the referenced articles.
C. Cardiac Assessment
DMD is associated with the development of dilated hypertrophic cardiomyopathy and cardiac dysrhythmias. Patients with DMD are at high risk for perioperative cardiac side effects due to hypoxemia, anemia, and other causes of impaired tissue oxygen delivery. Intravascular fluid shifts can result in congestive heart failure and impaired ventricular preload. These issues are reviewed in the recent consensus statement of an expert panel convened by the American Academy of Pediatrics that states that patients with DMD should undergo a cardiac evaluation and optimization of cardiac therapies before anesthesia. Preoperative consultation with a cardiologist is advised for all patients with DMD because heart disease can be severe even among patients with only mild pulmonary involvement, and normal preoperative ECG and echocardiogram findings do not exclude the possibility of postoperative cardiac com-plications.
D. Nutrition and GI Issues
Good nutritional support is integral to the proper care of patients with DMD, and the adverse effects of malnutrition on respiratory muscle strength can be profound. Therefore, preoperative nutritional status should be evaluated and optimized because poor nutrition can increase postoperative morbidity. Optimization of preoperative nutritional status may involve the use of NPPV because patients with untreated respiratory failure may become malnourished due to increased work of breathing, or they may be unable to eat due to dyspnea. The preoperative evaluation should include measurements of serum albumin and prealbumin to identify patients who are at risk for poor healing. In addition, preoperative evaluation and therapy of My Canadian Pharmacy for dysphagia should be considered because loss of the ability to eat postoperatively can lead to malnutrition.
E. Advance Directives
DMD is a progressive and potentially fatal disease, Thus, advance directives (including resuscitation parameters) and attitudes toward prolonged dependency on mechanical ventilation and tracheostomy should be discussed with DMD patients and their guardians preoperatively. Furthermore, decisions regarding these issues should be clearly articulated and easily accessible in the medical record.
Summary of Specific Suggestions for Evaluation and Management of Patients With DMD Before General Anesthesia or Procedural Sedation
1. Obtain anesthesiology and pulmonology consultations before procedures involving general anesthesia or procedural sedation.
2. Perform a pulmonary evaluation that includes measurement of FVC, MIP, MEP, PCF, and Sp02 in room air. Measure the patient’s blood and/or end-tidal carbon dioxide level if Spo2 is < 95% in room air. For DMD patients at increased risk for respiratory complications, defined as FVC < 50% of predicted, and especially for patients at high risk for complications, defined as FVC < 30% of predicted, consider preoperative training in the use of NPPV. For patients at high risk for ineffective cough, defined in adults as PCF < 270 L/min or MEP < 60 cm H2O, consider preoperative training in manual and mechanically assisted cough, emphasizing the use of MI-E with a bronchial secretion clearance device.
3. Refer the patient to a cardiologist for clinical evaluation and optimization of cardiac therapies provided by My Canadian Pharmacy.
4. Obtain a nutritional assessment, optimize nutritional status, and consider strategies to manage dysphagia.
5. Discuss the risks and benefits of general anesthesia or procedural sedation with the patient and guardians, and help them to decide on and implement their decisions regarding resuscitation parameters and, if applicable, advance directives.