Mechanical power and opening pressure. Fellowship training program Intensive Care Radboudumc, Nijmegen

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1 Mechanical power and opening pressure Fellowship training program Intensive Care Radboudumc, Nijmegen

2 Mechanical power Energy applied to the lung: Ptp * V (Joule) Power = Energy per minute (J/min) Power = Ptp * V * RR (J/min)

3 Mechanical power

4 An example RR = 3 RR = 6 RR = 9 RR = 12 RR = 15 P Flow (L/s) <.1 Mechanical power (J/min) <.1 TV 38 ml/kg Cressoni M. Anesthesiology 216;124:11-118

5 When is mechanical power harmful? Whole lung edema A TV 38 ml/kg, Pplat 27 RR 3,6,9,12,15/min B TV 11 or 22mL/kg RR 35 One-field edema Isolated densities Baseline Transpulmonary Mechanical Power (J/min) Cressoni M. Anesthesiology 216;124:11-118

6 A Lung weight (g) Transpulmonary Mechanical Power (J/min) B 15 PaO 2 /FiO Transpulmonary Mechanical Power (J/min) C Lung elastance (cmh 2 O/l) Transpulmonary Mechanical Power (J/min) g. 2. Cressoni M. Anesthesiology 216;124:11-118

7 esents the total volume (i.e. TV + PEEP volume), us represents the plateau pressure. The slope resents the compliance of the system, (in mh2o = 4 ml/cmh2o). The area of this large stic energy present at plateau pressure and cmh2o)/2.98 = 1764 J. This total components: the smaller triangle (Elastic presents the energy delivered just once when he larger rectangle trapezoid (Elastic Dynamic, present the elastic energy delivered at each the rectangle trapezoid results from the sum of rs h azure): a rectangle, whose area is TV PEEP he power equation), and a triangle, whose area ual to ELrs TV 1/2 (first component of the third component of the power equation is the Resistive parallelogram (yellow), whose area at) TV. b Dynamic pressure volume loop O PEEP, with the following measured parameters: 29.2 cmh2o, TV 33 ml. The measured energy, ezoid described by the inspiratory blue line, the ajor base), the PEEP line (minor base) and the TV J, computed was.8 J. With the RR = 18 bpm, was then 13.9 J/min and the computed power It follows that: Tinsp = Ttot (I:E/(1 + I:E)) Thus, substituting Tinsp in the Eq. (4): Mechanical power! Ebreath =!V 2 ELrs 1 (1 + I : E) + RR Raw 2 6 I : E Based on the Equation of Motion +!V PEEP " (5) 1569 If we express the volumes in liters and the pressures in cmh2o, their aw product multiplied by.98 will be expressed in Joules. 1 P = EL V + R F + PEEP Ebreath =!V!V ELrs 2 +!V Raw F +!V PEEP. (2) The first term of the Eq. (2), which is equal to V P, has been divided by 2 (area of a triangle) in order to approximate the integral of their product (see Fig. 1a), while the second and the third terms do not require any correction, as they represent a parallel translation along the axis. From Eq. (2): Mechanical power According = to Eq. (5), the mechanical power expressed in J/min will be:! " # + I : E) 1 (1 E ELrs (3) Raw Powerrsbreath=.98 RR!V + RR 2 6 I : E $ Therefore: "! +!V PEEP 1. 1 (6) 2 R +!V PEEP. E =!V EL +! " 1!V =!V ELrs +!V Raw 2 +!V PEEP. 2 Tinsp 2 breath rs 2 Tinsp aw (4) In order to express the Tinsp as a function of respiratory rate (RR) and inspiratory-to-expiratory ratio (I:E), both readily available in every ventilator s settings, the following derivation may be applied: Premises: Gattinoni Tinsp/Texp = I/E, L. Intensive Care Med 216;42:

8 Fig. 2 a c Gattinoni L. Intensive Care Med 216;42:

9 Gattinoni L. Intensive Care Med 216;42:

10 Effect of ventilator components on mechanical power Mechanical power Change in ventilator parameter Fig. 4 The percent increase of mechanical power as a function of Gattinoni L. Intensive Care Med 216;42:

11 Opening pressures Lung protective ventilation LTV Sufficient evidence Recruitment PEEP No evidence Minimal evidence } Current practice uses insufficient opening pressures and/or PEEP? Cressoni M. Intensive Care Med 217;43:63-611

12 Figure 1 shows a representative example of subsequent CT scans during inspiration in a patient with severe ARDS. As shown, recruitment and inhomogeneities occur along the whole pressure volume curve. Figure 2 reports the average recruitment pressure curves obtained in patients with mild, moderate, and severe ARDS (with and without ECMO). From this figure it is evident that (a) the total amount of recruitable tissue increases with ARDS severity and is largely different between mild, moderate, and severe ARDS at each applied inspiratory pressure; (b) the amount of recruitatissue between 3 and 45 cmh2o (set on the ventilascanble tor) was negligible in mild ARDS (1 ± 29 g, 8 ± 21%), modest in moderate ARDS (54 ± 86 g, 17 ± 27%), and much greater in severe ARDS, both without ECMO (162 ± 92 g, 43 ± 21%, p =.2 vs mild ARDS and p <.1 vs moderate ARDS) and with ECMO is modest and not significant in mild ARDS (56 ± 5 increases significantly in moderate ARDS (116 ± 71 and amounted to 236 ± 22 g in severe ARDS witho ECMO and to 231 ± 177 g in severe ARDS with ECMO The lower panel of Table 2 reports the amount of t sue which tidally opened and collapsed approximat 15 times per minute at PEEP 5 and 15 cmh2o in mi moderate, and severe ARDS ventilated with similar ti volumes (6 8 ml/kg IBW). As shown, the amount collapsing and decollapsing tissue increased from m to moderate, to severe ARDS and, within the differe severity classes, was not significantly different betwe CT PEEPscan 5 and 15 cmh2o. The changes in gas exchange a in respiratory mechanics when increasing PEEP from to 15 cmh2o (according to the PEEP test performed the ICU before the CT scan) are reported in the ESM. Early ARDS (< 5 D) CT Mild N=5 7 4 cmh2o Moderate N = ± 2 28 ± Severe N=9 Recruited lung tissue (g) cmh2o 4 2 cmh2o 3 2 PEEP 5 cmh2o 4 ± 2 1 cm H Airway Pressure (cmh2o) Severe ECMO N= Lung inhomogeneities Table 3 reports the extent of lung inhomogeneities es mated in mild, moderate, and severe ARDS at the d ferent end-inspiratory and end-expiratory pressur 6-8 (a) the extent of inhomogeneities increas As Tv shown, (butml/kg not significantly) from mild to moderate and seve IBW ARDS, at each tested pressure; (b) within the same cl of severity, the decrease of lung inhomogeneity, incre 5 ingpeep the plateau pressure, reached statistical significan in patients with moderate ARDS and in patients w PEEPARDS 15 with ECMO; (c) within the same class severe severity, increasing PEEP from 5 to 15 cmh2o reduc (Pplat: the lung inhomogeneities in mild and mo significantly erate19±2 ARDS, while it did not change in the severe AR and groups. The variability and the extent of the inhomogen 27±3) with PEEP are evident in Fig. 3, where t ity variation changes of inhomogeneity in the single patients are re resented. As shown, in some patients with moderate severe ARDS, the increase of PEEP was associated w an increase in lung inhomogeneity. Fig. 1 A representative CT scan pressure curve in a patient with severe ARDS. The shown CT scans are taken at hilum at 5 cmh2o PEEP and at measured plateau pressures of 19.5, 3, and 45 cmh2o plateau pressure set on the ventilator. The measured pressures may slightly differ from the set ones. Uninflated tissue is represented in light blue, inhomogeneous lung tissue in red. In this patient the uninflated tissue of the whole lung amounted to 191 g at 5 cmh2o Additional results Recruitment?and 812, 747, and 477 g at the indicated plateau pressures. Lung recruitment IntratidalInspiratory opening lung & closure inhomogeneities were 2% at PEEP 5 cmh2o and 2, 22, and 21% at and opening/closing pr

13 Recruitability is higher in severe ARDS 5 Recruitable tissue (%) Mild Moderate Severe Severe - ECMO Cressoni M. Intensive Care Med 217;43:63-611

14 Recruitability is higher in severe ARDS Substantial recruitment in severe ARDS > 3 cm inspiratory pressure 6 Recruited lung tissue (g) Airway Pressure (cmh 2 O) Cressoni M. Intensive Care Med 217;43:63-611

15 Higher PEEP levels also recruit lung tissue with severe ARDS Amount of recruited lung tissue (gr) Mild Moderate Severe Severe - ECMO Cressoni M. Intensive Care Med 217;43:63-611

16 More collaps/reinflation with severe ARDS independent of PEEP 25 Amount of collaps/reinflation (gr) Mild Moderate Severe Severe - ECMO Mild Moderate Severe Severe - ECMO PEEP 5 PEEP 15 Cressoni M. Intensive Care Med 217;43:63-611

17 Amount of inhomogeneities Severe ARDS (with and without ECMO) 4 Amount of inhomogeneities (%) *** *** PEEP 5 Pplat 19 Pplat 28 Pplat 4 PEEP 15 Pplat 27 PEEP 5 Pplat 19 Pplat 28 Pplat 4 PEEP 15 Pplat 27 Severe Severe + ECMO Cressoni M. Intensive Care Med 217;43:63-611

18 Main consequences Compressive forces due to lung weight Usually 1-15 cm H2O Surface tension Usually 15-2 cm H2O Pressure to lift the chest wall Usually 5-1 cm H2O Opening pressure 3-45 cm H2O The main counterforces that must be overcome PEEP of 15 cm H2O may be insufficient to keep a lung fully open during low tidal volume ventilation