Ventilation in ARDS
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This document discusses various topics related to ARDS including definitions, causes, ventilator strategies, and treatments. It provides the American-European Consensus definition of ARDS which requires bilateral infiltrates, hypoxemia, and no evidence of cardiogenic pulmonary edema. Common causes of ARDS are also mentioned. Regarding ventilator management, low tidal volumes, appropriate PEEP levels based on oxygen needs, and maintaining low plateau pressures are emphasized. Additional strategies discussed include prone positioning, recruitment maneuvers, and neuromuscular blockade. While high frequency oscillatory ventilation and inhaled treatments were investigated, they did not show clear benefits.
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Ventilation in ARDS
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- 4. cardiogenic vs noncardiogenic
- 5. American-European Consensus ARDSDefination • An acute condition characterized by bilateral pulmonary infiltrates and severe hypoxemia in the absence of evidence for cardiogenic pulmonary edema. • PaO2/FiO2 <300 = ALI PaO2/FiO2 <200 = ARDS • Cardiogenic pulmonary edema must be excluded either by clinical criteria or by a pulmonary capillary wedge pressure (PCWP) lower than 18 mm Hg
- 6. WHAT IS P/FRATIO… • PAO2/ FIO2 •Fio2 is 0.5, 0.6, 0.7 etc. •If pao2 140, fio2 0.7 •p/f ratio will b •140/ 0.7 = 200
- 7. Limitations of ConsensusDefinitions •The chest radiograph is subject to variability in interpretation,,, & acute is ill defined •PaO2/FiO2 may vary according to ventilator parameters, e.g., PEEP, and at extremes of FiO2 •Accuracy in excluding the presence of heart failure may be influenced by measurement methodology and timing •PACs are rarely used •PCWP may oscillate above and below the cut-off and may be elevated for reasons other than heart failure
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- 10. Maintaining a lowtidal volume Monitoring plateau pressure Setting PEEP based on the FiO2 requirement
- 14. TARGETS OF VENTILAIONSTRATEGY • Avoid overdistending lung units by limiting the inflation volume and pressure • Avoid repetitive opening and collapse by applying adequate PEEP • Ideally, ventilation would take place in a “zone of safety”on the deflation limb of the PV curve
- 16. The “Baby lung” ARDSLung has alveoli “normal” alveoli partially aerated alveoli unaerated alveoli “Normal” segments inflate easily Unaerated segments distend poorly High pressure Slow response Normal lung segments may be over-inflated when ventilated with traditional tidal volumes
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- 24. FACE MASK VSHELMET NIV MASK • In a single-center trial, 83 patients with ARDS who required NIV using full face mask for at least eight hours were randomly assigned to continue face mask NIV or switch to helmet- delivered NIV . • Helmet-delivered NIV involves the administration of positive pressure and oxygen through a transparent hood that covers the entire head and face and is sealed with a rubber collar at the neck. • Helmet-delivered NIV reduced the need for intubation (18 versus 62 percent) in ARDS patients, most of whom had mild or moderate disease. In addition, • it was also associated with a higher rate of ventilator-free days, shorter ICU stay, and lower 90-day mortality without an increase in adverse effects
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- 29. Available evidence isinsufficient to confirm whether PCV offers any advantage over VCV in improving outcomes for people with ALI on ventilator
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- 33. RCT,USA,821 pts 6 vs12ml/kg
- 34. • In 2000,the NIH ARDS Network published the findings of their first randomized, controlled, multi-center clinical trial in 861 patients. • The trial was designed to compare a lower-tidal-volume ventilatory strategy (6 mL/kg predicted body weight, plateau pressure < 30 cm H2O) with a higher tidal volume (12 mL/kg predicted body weight, plateau pressure <50 cm H2O). • In this trial, the in-hospital mortality rate was 40% in the 12 mL/kg group and 31% in the 6 mL/kg • Ventilator-free days and organ failure–free days were also significantly improved in the low-tidal-volume group. These findings were truly remarkable, since no prior large randomized clinical trial of any specific therapy for ALI/ARDS has ever demonstrated a mortality benefit.
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- 36. EVIDENCE FOR HIGHPEEP VS
- 38. PEEP / FIO2TABLE…
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- 41. OPEN LUNG VENTILATION •Open lung ventilation (OLV) is a strategy that combines low tidal volume ventilation (LTVV) with a recruitment maneuver and subsequent titration of applied PEEP to maximize alveolar recruitment. • The LTVV and set limits on plateau pressure aim to mitigate alveolar overdistension, while the applied PEEP seeks to minimize cyclic atelectasis. Together, these effects are expected to decrease the risk of ventilator- associated lung injury.
- 42. RECRUITMENT MANEUVERS • asupplement to high peep vent mgt. • Periodically bt briefly raises the transpulmonary pressures to higher levels than used for tidal inflation. • 3 RCTs have tested RMs in ARDS. • Transient improvement in gas exchange but no apparent sustained benefit. • Risks –pulmonary / hemodynamic • 3 negative trials of PEEP has prompted investigators to explore alternative strategies to guide PEEP titration. • CT imaging to titrate PEEP risk of pt transfer, cost, radiation exposure • Electrical impedance tomography(ETT) • Lung ultrasound • Pressure-volume relationship analysis—LIP as well as STRESS INDEX. • Targeted transpulmonary pressure(airway pressure-pleural pressure).
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- 49. 466 ARDS patients–PaO2/FiO2 < 150 cmH20 28 day mortality Prone: 16% vs Control 32.8% Unadjusted 90-day mortality Prone: 23.6% vs supine 41.0%
- 50. 4 RCTS ---1,573 patients In the most hypoxaemic 486 patients PaO2/FiO2 < 100 mmHg •absolute mortality reduction 10% (6% to 21%)
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- 60. 548 ARDS patients PaO2/FiO2< 200 cmH20 , Fi02 > 0.5 In-hospital mortality HFOV 47% vs Control 35% (RR 1.33; 95% CI 1.09 to 1.64; P = 0.005)
- 61. 548 ARDS patients –PaO2/FiO2< 200 cmH20 –PEEP > 5 cmH20 30 day mortality •HFOV 41.7% vs Control 41.1% •Difference 0.6%, 95% CI −6.1 to 7.5
- 64. 340 ARDS patients PaO2/FiO2< 150 mmHg Adjusted Mortality at Day 90 NMB: 31.6% vs placebo: 40.7% (95% CI 0.48 to 0.98; P = 0.04)
- 66. 282 patients withALI Aerosolized albuterol vs saline Ventilator-free days •albuterol 14.4 vs control 16.6 d (95% CI difference –4.7 to 0.3 d: P = 0.087) Hospital death albuterol 23.0% vs control 17.7% (95% CI difference –4.0 to 14.7%,P=0.30)
- 67. INVERSE RATIO VENTILATION •PCIRV increases mean airway pressures and improves oxygenaion • Little benefit • Auto PEEP • Haemodynamic instability
- 68. PARTIAL LIQUID VENTILATION •Nobenefit in mortality
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