Advanced Ventilatory Strategies in ARDS

1. Advanced Ventilatory Strategies in ARDS Alex Yartsev, Dec 2010

2. Whats the problem in ARDS Thickened diffusion membrane Inflamed exudate-filled alveoli Collapsed bronchioles Lost elasticity of parenchyma Massive shunt Thus, severe hypoxia

3. Challenge to ventilation in ARDS Lung is inelastic: compliance is poor Poor cokpliance = small tidal volume = poor ventilation Poor ventilation = hypercapnoea, acidosis Normal ventilation requires larger volumes� Small changes in volume = large changes in pressure Large changes in pressure = barotrauma Severe hypoxia = high FiO2 requirements High FiO2 for long periods = O2 toxicity

4. The gospel of ARDS net Massive protocol derived from multiple trials �lung protective ventilation� with low tidal volume Aim PaO2 55-80 Tidal volume of ONLY 6ml/kg Pplat to be kept under 30 pH to be kept over 7.30 - ANY ventilator mode

5. What can you do with a Drager Evita XL? Quite a lot SIMV PCV (pressure control ventilation) APRV (airway pressure-release ventilation)

6. Pressure control ventilation The target pressure is set, and never exceeded by the machine Tidal volume and minute volume may vary depending on lung compliance and resistance Does not guarantee minute ventilation; guarantees pressure instead

7. Evidence for pressure control ventilation Any better than standard volume control? According to Esteban and co (2000, 79 pts), there was lower mortality in the PCV group� but not because of ventilation (!) Refractory hypoxia was the same, VCV or PCV; but VCV patients died more frequently, � of non-respiratory organ failures. Other trials: Lessard et al. (9 pts, no difference) Rappaport et al (27 patients, fewer ventilated days on PCV) General consensus: studies are underpowered, but trend favours PCV

8. Airway Pressure Release Ventilation Similar to inverse ratio ventilation Patient breathes spontaneously at high pressure support, with short breaks of low support

9. APRV vs standard modes Is it any better than SIMV+PSV? Varpula and c o. (2004) � 58 pts randomised APRV or SIMV; NO DIFFERENCE in ventilated days, gas exchange, cardiac output or mortality (18% vs 19%) Liu et al (2009) � also 58 pts � APRV vs SIMV PaO2/FiO2 ratios were better, APRV mortality 31% vs SIMV mortality 59% Kyle et al (2010) � trial in progress Alex couldn�t afford the journal access, findings were presented at the annual meeting in 2010 Is it any better than PCV? Putensen�s 30 pt prospective trial (2001) � 15 to PCV, 15 to APRV PCV stayed ventilated for longer (21 vs 15) mortality essentially the same (12 vs 11)

10. High Frequency Oscillatory Ventilation Tiny volumes, high frequency. Generally, generates tidal volumes less than the dead space of the lung Pressure oscillates around the mean airway pressure There are several theories as to how gas mixing leads to oxygenation in the alveoli with a tidal volume this low Higher pressure, lower peak pressure, thus better oxygenation with less barotrauma, �theoretically

11. HFOV vs standard modes in ARDS RCTs:

12. HFOV vs standard modes in ARDS Also lots of prospective and retrospective studies Consensus: Looks like mortality is lower in HFO group However, trials are old New, good outcomes being published with standard modes; is HFOV any better? No trials to compare.

13. Extra-Corporal Membrane Oxygenation Veno-venous or veno-arterial (VA also provides pump support a�la cardiopulmonary bypass) Patients blood is sucked through a membrane which acts as a gas exchange surface; blood is returned to the lung or to the tissues

14. ECMO in ARDS Early trials: Zapol, 1979: 90 pts, 10% survival on ECMO(VA)- no difference Morris, 1994 34% survival on ECMO (VV) � no difference

15. ECMO in ARDS More recently: 2009 CESAR trial: 180 pts Survival: 63% (VV ECMO) vs 47% (standard)

16. Experimental strategies

17. Total Liquid Ventilation Ventilator pushes fluid through a gas-exchange membrane into the lungs Liquid is a perfluorocarbon Used with variable success in preterm neomates No adult human trials Numerours sheep have died

18. Partial Liquid Ventilation Unlike TLV, does not require a whole new ventilator Only the functional residual capacity is full of liquid A conventional ventilator delivers breaths on top of it No mortality benefoit according to Cochrane

19. DOUBLE ECMO! Single case report from a month ago 49 yo M with severe HSV pneumonia � AND a fall from significant height, ? aortic dissection Had a veno-venous ECMO circuit AS WELL as a veno-arterial ECMO circuit Survived, somehow.

20. No further questions, please.

21. References Esteban et.al, 2000 Prospective Randomized Trial Comparing Pressure-Controlled Ventilation and Volume-Controlled Ventilation in ARDS CHEST June 2000 vol. 117 no. 6 1690-1696 Kenneth et. al. 2007 High-Frequency Oscillatory Ventilation for Adult Patients With ARDS CHEST June 2007 vol. 131 no. 6 1907-1916 Krishnan et al 2000 High-frequency ventilation for acute lung injury and ARDS. Chest 2000;118,795-807 Varpula et al, Airway pressure release ventilation as a primary ventilatory mode in acute respiratory distress syndrome Acta Anaesthesiol Scand 2004; 48: 722�731 Liu et al, Practical use of airway pressure release ventilation for severe ARDS--a preliminary report in comparison with a conventional ventilatory support. Hiroshima J Med Sci. 2009 Dec;58(4):83-8. Petrucci et al, 2007 Lung protective ventilation strategy for the acute respiratory distress syndrome, Cochrane Database of Systematic Reviews 2007, Issue 3. Art. No.: CD003844. Kyle et al 2010, APRV Vs. ARDSnet Protocol Ventilation For ARDS/ALI m. J. Respir. Crit. Care Med..2010; 181: A1691 Putensen et al. Long term effects of APRV. AJRCCM 2001;164:43. Kenneth et al, High-Frequency Oscillatory Ventilation for Adult Patients With ARDS CHEST June 2007 vol. 131 no. 6 1907-1916 Lewandowski K, Extracorporeal membrane oxygenation for severe acute respiratory failure Critical Care 2000, 4:156-168