Online Supplemental material to
Variable ventilation versus stepwise lung recruitment manoeuvre for lung recruitment: A comparative study in an experimental model of atelectasis
Luigi Vivona1,2*, Robert Huhle1*, Anja Braune1,3,Martin Scharffenberg1, Jakob Wittenstein1, Thomas Kiss1,4, Michael Kircher5,6, Paul Herzog1, Moritz Herzog1, Marco Millone1,7, Marcelo Gama
de Abreu1,8 and Thomas Bluth1
Study protocol
Figure e1 - Time course of interventions and measurements with PEEP, positive end-expiratory pressure; RM, recruitment manoeuvres; VCV, volume-controlled ventilation; VV, variable volume controlled ventilation; CT, computed tomography, EIT, electrical impedance tomography.
Determination of E
1and E
2and %E
2In order to calculate respiratory system mechanics, first, airway flow ( V˙ ) and pressure (Paw) were low-pass filtered (cut-off 30 Hz) prior to offline processing. From these signals, respiratory cycles were detected and identified semi-automatically, based on flow and volume thresholds followed by manual correction, as described previously.(1) Then, VT as well as mean (meanPaw) and peak airway pressure (peakPaw) were calculated. Airway driving pressure (∆Paw) was calculated as difference between airway plateau pressure and PEEP. Respiratory system mechanics
were derived by fitting the equation of motion (Eq. 1) to the sampled flow V˙ , volume V and pressure Paw signals for each respiratory cycle using non-linear reflective trust-region algorithm.
Respiratory resistance (R), volume-independent elastance (E1), volume-dependent elastance (E2), total elastance (E) of the respiratory system, and the end-expiratory pressure (PEEP) were calculated according to Eq. 1 (2–4):
Paw(t)=R❑V˙ (t)+E1∙V(t)+E2∙V2(t)+PEEP . Eq. 1
%E2 was calculated as
%E2= E2∙VT E1+
|
E2|
∙VTEq. 2 According to Eq. 2, E2 represents the deviation from a linear relationship between volume and airway pressure, which can be due to an increase (overdistension) or decrease (recruitment) of elastance with a given volume, as described previously.(1) Negative values of %E2 point towards concavity of the elastic airway pressure versus volume (Pel·V) curve, thus, decreasing lung stiffness during inflation and intratidal recruitment.(2,3,5,6) In contrast, positive %E2 values point towards convex Pel·V curve, thus, indicate alveolar overdistension. In contrast, higher positive %E2 values indicate a convex Pel·V curve, thus alveolar overdistension. Since respiratory signals were not measured consistently at the Y-piece (Supplemental Digital Content 1), analysis of %E2 in relation to previously published threshold values was omitted.(5,7)
Airway pressure and flow tracings during variable ventilation and conventional volume controlled ventilation
Figure e2 - Inspired volume and airway pressure during variable ventilation (VV, left column) and corresponding tidal volume and plateau pressure (right column); coefficient of variation of VT for the displayed values was CV=28.8%.
References
1. D’Antini D, Huhle R, Herrmann J, Sulemanji DS, Oto J, Raimondo P, et al. Respiratory System Mechanics During Low Versus High Positive End-Expiratory Pressure in Open Abdominal Surgery: A Substudy of PROVHILO Randomized Controlled Trial. Anesth Analg.
2018 Jan;126(1):143–9.
2. Kano S, Lanteri CJ, Duncan AW, Sly PD. Influence of nonlinearities on estimates of respiratory mechanics using multilinear regression analysis. J Appl Physiol Bethesda Md 1985. 1994 Sep;77(3):1185–97.
3. Jandre FC, Modesto FC, Carvalho ARS, Giannella-Neto A. The endotracheal tube biases the estimates of pulmonary recruitment and overdistension. Med Biol Eng Comput. 2008
Jan;46(1):69–73.
4. Rohrer F. Der Strömungswiderstand in den menschlichen Atemwegen und der Einfluss der unregelmässigen Verzweigung des Bronchialsystems auf den Atmungsverlauf in
verschiedenen Lungenbezirken. Pflüg Arch Für Gesamte Physiol Menschen Tiere. 1915 Oct 1;162(5):225–99.
5. Carvalho AR, Spieth PM, Pelosi P, Vidal Melo MF, Koch T, Jandre FC, et al. Ability of dynamic airway pressure curve profile and elastance for positive end-expiratory pressure titration. Intensive Care Med. 2008 Dec;34(12):2291–9.
6. Carvalho AR, Pacheco SA, de Souza Rocha PV, Bergamini BC, Paula LF, Jandre FC, et al.
Detection of tidal recruitment/overdistension in lung-healthy mechanically ventilated patients under general anesthesia. Anesth Analg. 2013 Mar;116(3):677–84.
7. Soares JHN, Carvalho AR, Bergamini BC, Gress MAK, Jandre FC, Zin WA, et al. Alveolar Tidal recruitment/derecruitment and Overdistension During Four Levels of End-Expiratory Pressure with Protective Tidal Volume During Anesthesia in a Murine Lung-Healthy Model.
Lung. 2018 Jun 1;196(3):335–42.
