Ventilatory management pf acute lung injury & acute respiratory distress syndrome

1. Ventilatory management pf acute lung injury & acute respiratory distress syndrome By Sherif G. Anis M.D.

2. Ventilatory management of ALI & ARDS Acute respiratory distress syndrome • Acute onset of hypoxemia • Bilateral Lung infiltrates • Absence of left atrial hypertension • Risk factors: Pulmonary e.g. Pneumonia Non pulmonary e.g. Pancreatitis

3. Ventilatory management of ALI & ARDS Diagnostic Criteria for ARDS

4. Ventilatory management of ALI & ARDS Diagnostic Criteria for ARDS

5. Ventilatory management of ALI & ARDS American European consensus conference (AECC) 1994 • Acute lung injury (ALI) [PaO2/FIO2] ratio<300) • Acute Respiratory distress syndrome (ARDS): (PaO2/FIO2 ratio <200)

6. Ventilatory management of ALI & ARDS Mechanical Ventilation in ARDS Injurious ventilator associated lung injury Necessary to reverse Hypoxaemia

7. Ventilatory management of ALI & ARDS • The lung with ALI or ARDS are particularly prone to ventilator associated lung injury: (Baby lung) • Collapsed, consolidated, less compliant areas (Dependant) • Normal areas (non dependant)

8. Ventilatory management of ALI & ARDS

9. Ventilatory management of ALI & ARDS • Ventilator associated lung injury: • High inflation pressure Barotrauma • Over distension Volutrauma • Repetitive opening & closing of alveoli Atelect-trauma • SIRS & cytokines release Biotrauma.

10. Ventilatory management of ALI & ARDS • Lung protective ventilation in comparison with conventional approaches Evidence Synthesis

12. Ventilatory management of ALI & ARDS • 3 Meta analysis of these 5 clinical trials have been performed: • One analysis shows that there is no reflection of the standard of care, in addition low tidal volumes may be harmful, in the intervention group of the 2 trials showing survival advantage. (Eichacker PQ et al, 2002) • 2 subsequent meta analyses suggested that volume limited ventilation, particularly in the setting if elevated plateau pressure > 30 cmH2O, has a short term survival benefit. (Petruccin et al, 2004) (Moran Jl et al, 2005)

13. Ventilatory management of ALI & ARDS • One meta analysis also concluded that decreased tidal volume may be advantageous below a threshold level (<7.7 ml/Kg BW) (Moran Jl et al, 2005)

14. Ventilatory management of ALI & ARDS Lung protective ventilation strategy • Pressure & volume limitation • Higher PEEP • Recruitment maneuvers (Dynamic process of reopening collapsed alveoli through increase in trans pulmonary pressure)

15. Ventilatory management of ALI & ARDS Lung protective ventilationn etiology • Which method of recruitment maneuvers should be Used ? • The most well Known method of recruitment maneuver is sustained application of CPAP of 30- 50 Cm H2O for 30 seconds • Periodic recruitment with a series of traditional sigh breaths • Intermittently raising PEEP over several breaths • Extended sigh maneuver with step wise increase in PEEP while Vt is decreased • Intermittent application of pressure controlled ventilation with incremental high PEEP

16. Ventilatory management of ALI & ARDS Consequences of lung protective ventilation • Permissive hypercapnea (acute respiratory acidosis) TTT: increase respiratory rate in a stepwise up to 35 Bicarbonate infusion increase Vt • Worsened oxygenation & transient desaturation • Increased sedation or analgesia • Hypotension & arrhythmias • Barotraumas (Pneumothorax) • Bacterial translocation

17. Ventilatory management of ALI & ARDS • Further studies are needed to: • Inform on a clinically relevant threshold if hypercapnea, & acidosis both require intervention • Increased sedation & analgesic effects (Kahn JM & colleagues, 2005 show no increase in sedation use in low tidal volume ventilation) • Safety of recruitment maneuvers

18. Ventilatory management of ALI & ARDS Alternative Ventilatory Approaches to Lung Protection • High-frequency ventilation (jet, oscillation, and percussive ventilation) HFOV allows for higher mean airway pressures & markedly reduced tidal volumes (1-3 ml/kg) Lung recruitment & reduce lung injury.

19. Ventilatory management of ALI & ARDS Alternative Ventilatory Approaches to Lung Protection • Airway pressure release ventilation (APRV) It provides two levels of airway pressure (P high & P low) during two time periods (T high & T low) , usually a long Thigh & short Tlow with spontaneous breathing during both. Advantages: Decrease barotrauma, provide better V/P matching, cardiac filling & patient comfort.

20. Ventilatory management of ALI & ARDS Adjunctive therapies to lung-protective Ventilation • Prone positioning: recruitment of dorsal (nondependent) atelectatic lung units, improved respiratory mechanics, decreased ventilation- perfusion mismatch, increased secretion drainage, reduced and improved distribution of injurious mechanical forces (Pelozi P et al, 2002)

21. Ventilatory management of ALI & ARDS Adjunctive therapies to lung-protective Ventilation • inhaled nitric oxide : Selective VD in ventilated lung units improving V/Q mismatch, decrease PaO2 & pulmonary hypertension ( no sustained clinical benefit) (Tayler RW et al, 2004)

22. Ventilatory management of ALI & ARDS • Irrespective of this controversy as to whether the exact ARDSNet protocol should be adopted, the existing evidence supports that clinicians should change their practice and adopt volume and pressure limited ventilation for patients with ALI or ARDS. As additional evidence emerges, ongoing reassessment and evolution of these protocols will be necessary.

23. Ventilatory management of ALI & ARDS Conclusions and Future Considerations • mechanical ventilation, although life saving, can contribute to patient morbidity and mortality • Volume and pressure limited ventilation clearly leads to improved patient survival • The role of re­cruitment maneuvers, higher levels of PEEP, or both remain controversial • At this time, use of alternative modes of ventilation (e.g., HFOV) and adjunctive therapies (e.g., inhaled nitric oxide and prone positioning) should be limited to future clinical trials and rescue therapy for patients with ALI or ARDS with life threatening hypoxemia failing maximal conventional lung protective ventilation.

24. Thank you