A preliminary evaluation of a prospective study of pulmonary function studies and symptoms of hypoventilation in ALS/MND patients
Introduction
Although the benefits of non-invasive positive pressure ventilation (NPPV) in patients with amyotrophic lateral sclerosis (ALS) are apparent in several studies [1], [2], [3], there is still no clear consensus as to which physiologic marker and/or clinical symptom(s) should be used to initiate NPPV. In addition, at the present time, there is no single test that has been shown to reliably detect early respiratory insufficiency. A recent evidence-based review of the subject pointed out that most patients with ALS are symptomatic of hypoventilation by the time the vital capacity (FVC) falls below 50% of predicted [4]. The authors provided a management algorithm that suggests that NPPV should be instituted when patients are symptomatic and when FVC reaches 50% of the predicted value based on age, sex and height.
The Health Care Financing Administration (HCFA) has recently established criteria [5] for initial coverage of respiratory assist devices which also serves to establish a “standard of care”. In order for NPPV to be covered by Medicare, the patient must have documentation of symptoms characteristic of sleep-associated hypoventilation, such as hypersomnolence, excessive fatigue, morning headache, cognitive dysfunction, or dyspnea. In addition, a patient must demonstrate one of the following: an arterial blood gas PaCO2 which is >45 mm Hg while awake, have nocturnal oximetry data demonstrating oxygen desaturation <88% for at least five continuous minutes, have FVC <50% of predicted or a maximum inspiratory pressure <60 cm H2O. Most of these HCFA criteria are based on measurements corresponding with relatively severe respiratory insufficiency.
Our hypothesis was that initiation of NPPV at a time point earlier than our current “standard of care” may provide additional benefits in terms of respiratory function and quality of life. The aims of this study were to determine which pulmonary measurement best correlates with symptoms of early nocturnal hypoventilation and to compare the quality of life and functional status before and 3 months after early initiation of NPPV.
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Materials and methods
A prospective randomized single blind study was performed. Patients were recruited from the ALS Centers at the University of Texas Health Science Center at San Antonio, the University of Texas Southwestern Medical Center and the Carolinas Neuromuscular/ALS-MDA Center. The protocol was accepted by the Institutional Review Board at each institution and all patients signed an informed consent prior to participation. Inclusion criteria included the diagnosis of probable or definite ALS based on new
Results
Twenty patients were enrolled and to date, 13 have met randomization criteria with seven patients randomized to our “early intervention” group (Group 1) and six patients randomized to our “standard of care” group (Group 2) (Table 2). Five patients continued to be followed with monthly nocturnal oximetry studies and have not yet reached randomization criteria. Two patients who were enrolled elected to withdraw prior to randomization. Seven patients were randomized immediately following
Discussion
Although current practice parameters [4] recommend that the decision to initiate NPPV be based upon FVC%, our preliminary data suggest that FVC% correlates poorly with early respiratory symptoms and with other measurements of pulmonary function including MIP, MEP, PCEF, and duration of nocturnal desaturation <90%.
The identification of nocturnal oxygen desaturation <90% for at least one cumulative minute appears to be the most sensitive indicator for detecting early respiratory insufficiency in
Acknowledgements
We wish to thank the National Amyotrophic Lateral Sclerosis Association for their funding of this pilot study. We also wish to acknowledge Respironics for their provision of equipment to conduct the study as well as their extensive technical and educational support.
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