Effects of Trunk Inclination on Respiratory Mechanics in Patients with COVID-19–associated Acute Respiratory Distress Syndrome: Let’s Always Report the Angle!

Abstract

The role of trunk inclination on respiratory function has been explored in patients with "typical" Acute Respiratory Distress Syndrome (ARDS) (1-3). Data regarding patients with COVID-19-associated ARDS (C-ARDS) are currently lacking.Aim of our study was to assess the effects of changes in trunk inclination on lung mechanics and gas exchange in mechanically ventilated patients with C-ARDS. MethodsThis single-center physiological cross-over study (ethical committee approval #70-11022021) was conducted on adult patients admitted to our COVID-ICU between March 3 and May 4, 2021. Diagnosis of C-ARDS, deep sedation, paralysis, and volume-controlled mechanical ventilation, were the inclusion criteria. Contraindications to mobilization (e.g., intracranial hypertension, spinal cord injury, tracheal lesions) and pregnancy constituted exclusion criteria. Patients were enrolled according to study personnel availability. A 5-Fr esophageal balloon (CooperSurgical, Trumbull, Connecticut) was inserted. The balloon was inflated with 1 ml of air and the correct position/function was verified before each measurement (4).Mechanical ventilation parameters, kept constant throughout the study, were set by the attending physician. Usually, PEEP is set according to the best respiratory system compliance (C RS ) assessed with a recruitment maneuver followed by a decremental PEEP trial. Of note, trunk inclination during PEEP selection is not standardized.Patients underwent three 15-minute steps in which trunk inclination was changed from 40° (semi-recumbent, baseline) to 0° (supine-flat), and back to 40° during the last step.At the end of each step, partitioned respiratory mechanics, arterial/central venous blood gas analysis and basic hemodynamics were recorded. Ventilatory ratio was calculated.

External chest-wall compression in prolonged COVID-19 ARDS with low-compliance: a physiological study

“…During all steps, the patients were placed in supine flat position (0° trunk inclination) to standardize every measurement [ 16 ] and the ventilator settings were unchanged (except for PEEP in step 4). No recruitment maneuvers were performed.…”

Trendelenburg in Acute Respiratory Distress Syndrome: Should We Do More than Proning?

“…The decrease in lung overdistension was seen mainly in the nondependent lung areas. A recent observational study by Marrazzo et al 6 noted similar improvement in the lung compliance in 20 patients with COVID-19-related ARDS when the head position was lowered from 40° head up to flat-supine position. Based on these observations, the “rigid chest wall” theory suggested by Kodamanchili et al may have some merit, although the amount of lung recruitment might vary between dependent and nondependent lung zones.…”

Paradoxical response to chest wall loading predicts a favorable mechanical response to reduction in tidal volume or PEEP

“…In our study, not only was mechanical paradox encountered in all but two of the nineteen patients with ARDS who met our inclusion criteria, but also it was present in spite of consistent adherence to ventilator settings widely regarded as lung-protective; it was frequently encountered early in the course of invasive mechanical ventilation; and the mechanics of all patients with paradox responded favorably to even small reductions in V T and PEEP. The use of manual compression to detect paradox may thus serve as a valuable tool for revealing otherwise undetected excessive tidal strain, and its presence should prompt re-evaluation of modifiable determinants of end-tidal overdistension, including PEEP, V T , and positioning [ 18 , 19 ]. In some patients with severe and unresolving ARDS, however, protection of the entire lung may simply be impossible without extracorporeal gas exchange as excessive end-tidal strain may be the unavoidable consequence of adequate ventilation.…”