Poor correlation between diaphragm ultrasound and invasive gold standard technique derived respiratory muscle strength assessment in patients after hospitalization for COVID-19.

Introduction: Individuals who survive acute coronavirus disease 2019 (COVID-19) might experience diaphragm muscle weakness. Diaphragm ultrasound may be an easy-to-obtain bedside tool for determining diaphragm function. However, twitch transdiaphragmatic pressure (twPdi) following magnetic stimulation (MS) of the phrenic nerves is the gold standard for non-volitional assessment of diaphragm strength. This study investigated whether diaphragm thickening ratio (DTR) measured on diaphragm ultrasound reflects diaphragm strength as measured by twPdi following MS of the phrenic nerves or other (volitional) invasively obtained pressure values and could therefore be used to accurately diagnose diaphragm weakness.

Methods: One year after discharge, 50 individuals (14 female, age 58±12 years) who had been hospitalised and treated for moderate-severe COVID-19 underwent standard spirometry and diaphragm ultrasound. TwPdi following cervical MS of the phrenic nerve and volitional inspiratory manoeuvres (Sniff and Mueller manoeuvre) were measured using oesophageal and gastric balloon catheters after transnasal placement.

Results: At follow-up, no clinically meaningful restrictive lung function impairment was evident on spirometry. On diaphragm ultrasound, diaphragm dysfunction, i. e. an impaired diaphragm thickening ratio was detected in 24% (12/50) of participants. An objective diagnosis of diaphragm dysfunction, defined as twPdi <16 cmH2O, was made in 60% (30/50) of participants. The measurement results of the two methods did not agree, given that there were many false negative, but also false positive results, so diaphragm ultrasound diagnosed in parts other patients with diaphragm dysfunction than TwPdi. Diaphragm ultrasound had a sensitivity of 26.67% and a specificity of 80.0% in the detection of diaphragm dysfunction (Positive predictive value 66.67%, negative predictive value 42.10%).

Conclusion: Diagnosis of diaphragm weakness in individuals who have recovered from COVID-19 cannot be made accurately on diaphragm ultrasound (via DTR), but requires twPdi as the gold standard for assessment of diaphragm strength.