Inspiratory Muscle Dysfunction after Prolonged Periods of Mechanical Ventilation: Two case studies

Abstract

Background and purpose Mechanical ventilation necessitates periods of bed rest and relative immobility that, combined with other factors, lead to skeletal muscle atrophy. As the respiratory muscles are skeletal muscles, they are theoretically prone to disuse atrophy. Sustained maximal inspiratory pressure (SMIP) measures are a new form of assessment of inspiratory muscle function that may reflect inspiratory work capacity. The aim of this study was to establish whether inspiratory or peripheral muscle function is abnormal after a period of prolonged mechanical ventilation, and whether any changes in function occur during a prolonged weaning programme. Methods Two adult patients who had required mechanical ventilation on a general intensive care unit for more than 14 days consented to take part in the study. Baseline SMIP, standard maximal inspiratory pressure (MIP) and handgrip strength measures were performed when weaning began. Repeated SMIP, MIP and grip measures were taken twice a week during the weaning programme until each patient was able to breathe without support for 48 hours. Findings Baseline SMIP and handgrip measures were found to be abnormally low in both subjects. SMIP measures increased over a series of measurement sessions, in parallel with increases in measures of handgrip and diminishing levels of respiratory support. Standard MIP measures started from a level that would generally indicate ability to breathe without support and showed little change over time. Conclusions If SMIP is accepted as a reliable measure of inspiratory muscle function, then these findings support the hypothesis that periods of mechanical ventilation have a detrimental effect on respiratory muscle function. These findings also suggest that SMIP is responsive to changing inspiratory muscle function, but as they are from uncontrolled studies, no firm conclusions can be drawn. Mechanical ventilation necessitates periods of bed rest and relative immobility that, combined with other factors, lead to skeletal muscle atrophy. As the respiratory muscles are skeletal muscles, they are theoretically prone to disuse atrophy. Sustained maximal inspiratory pressure (SMIP) measures are a new form of assessment of inspiratory muscle function that may reflect inspiratory work capacity. The aim of this study was to establish whether inspiratory or peripheral muscle function is abnormal after a period of prolonged mechanical ventilation, and whether any changes in function occur during a prolonged weaning programme. Two adult patients who had required mechanical ventilation on a general intensive care unit for more than 14 days consented to take part in the study. Baseline SMIP, standard maximal inspiratory pressure (MIP) and handgrip strength measures were performed when weaning began. Repeated SMIP, MIP and grip measures were taken twice a week during the weaning programme until each patient was able to breathe without support for 48 hours. Baseline SMIP and handgrip measures were found to be abnormally low in both subjects. SMIP measures increased over a series of measurement sessions, in parallel with increases in measures of handgrip and diminishing levels of respiratory support. Standard MIP measures started from a level that would generally indicate ability to breathe without support and showed little change over time. If SMIP is accepted as a reliable measure of inspiratory muscle function, then these findings support the hypothesis that periods of mechanical ventilation have a detrimental effect on respiratory muscle function. These findings also suggest that SMIP is responsive to changing inspiratory muscle function, but as they are from uncontrolled studies, no firm conclusions can be drawn.