New thresholds for noninvasive ventilation predicted by respiratory assessments improve care for adult spinal muscular atrophy patients.
A recent study reveals innovative respiratory function assessments may optimize noninvasive ventilation strategies for adults with spinal muscular atrophy.
The management of spinal muscular atrophy (SMA) has primarily focused on the pediatric population, but as treatment outcomes improve, adults now represent nearly one-third of patients. This shift necessitates updated practices to address the unique respiratory challenges faced by adults with SMA, the most significant of which is the decline of respiratory function—a primary cause of morbidity and mortality.
A recent study conducted by researchers at the University of Palermo aimed to understand the feasibility and effectiveness of various inspiratory muscle strength tests, particularly maximal inspiratory pressure (MIP) and sniff nasal inspiratory pressure (SNIP), as well as their predictive capability for the need for noninvasive ventilation (NIV) treatment. The study encompassed a retrospective analysis of 20 adult patients diagnosed with SMA types 2 or 3, examining data collected between January 2022 and December 2023.
Respiratory function deterioration can lead to nocturnal hypoventilation requiring NIV, often initiated once specific threshold values from respiratory and muscular function tests indicate danger. Traditionally, forced vitality capacity (FVC) has served as the standard metric, with values below 50% of the predicted normal indicating the need for NIV. Yet the study emphasized the necessity of refining predictive thresholds, particularly as compromises may occur due to the respiratory characteristics of adults with SMA.
Key findings revealed both MIP and SNIP tests were feasible for all participants; SNIP yielded significantly higher values than MIP. Most critically, ROC analysis indicated MIP was only a weak predictor for NIV initiation, whereas SNIP offered more accurate predictive value, achieving area under the curve (AUC) values of 0.84 compared to MIP’s AUC of only 0.57. The optimal cut-off for SNIP was determined to be less than 61 cmH2O, demonstrating superior sensitivity, and yielding remarkable precision for identifying those who would benefit from NIV.
Meanwhile, the FVC remained accurate as well, with the cut-off threshold for FVC effective at less than 20% of the predicted value. This adaptability marks the search for personalized treatment pathways for adult SMA patients, considering the disproportionate relationship between respiratory muscle strength and lung volume loss as seen across different SMA types.
The authors highlighted: "SNIP shows higher values than MIP and may be more appropriate than MIP to estimate the ability of the patients to ventilate." They conclude, "The accuracy of FVC and SNIP was higher than accuracy of MIP, but the traditional predictive threshold values did not fit well." Consequently, they conclude SNIP and FVC can considerably improve decision-making processes when initiating NIV therapy.
Another aspect explored was respiratory oscillometry—a relatively newer method for assessing mechanical lung properties by measuring airway resistance. The results indicated some abnormal readings among patients but correlated strongly with SNIP and FVC scores. Importantly, oscillometric measurements could support respiratory assessments for patients who might struggle with more traditional testing methods, after noting, "Oscillometry can be useful to estimate lung mechanics and respiratory muscle strength, especially for patients unable to cooperate with standard tests." This presents exciting potentials for tailoring assessments to meet the capabilities of patients.
This study opens the door to enhanced respiratory monitoring methodologies for adult SMA patients, potentially shaping future clinical guidelines. Anticipated multicenter studies may validate the findings and expand upon the innovative assessment techniques identified. By refining prediction thresholds and embracing diverse testing methods, clinicians can promote optimal care strategies, reducing the burden of respiratory decline among this patient population.