Low Tidal Volume Ventilation

1. Low Tidal Volume Ventilation Brad Winters, Ph.D., M.D. Armstrong Institute for Patient Safety and Quality

2. Purpose of Low Tidal Volume Strategies • Lung Protection • “Volutrauma” • Barotrauma • Ameliorate activation of chemical inflammatory mediators • Prevent development of ARDS • Improve oxygenation • Improve outcomes (ARDS mortality is as high as 60%)

3. Traditional Ventilation • Large tidal volume (Vt) ventilation; > 10cc/kg • Became common after Bendexin published in 1963 a study showing the development of atelectasis in patients on lower tidal volumes • Since atelectasis is viewed as undesirable (shunt, hypoxia) this large tidal volume approach became the norm. • However, this approach has been shown to increase morbidity and mortality in critically ill patients, esp. those with ARDS

4. The Problem with Large Vt • In acute lung injury there is a breakdown in lung architecture • This leads to stiff lungs with areas of over-inflation and under-inflation • Large Vt results in over-distension of some areas • This leads to inflammatory responses that damage the lung

5. The Problem with Large Vt • This can also lead to barotrauma (rupture of alveoli, pneumothorax etc.) • Additionally, some airspaces collapse but then re-open cyclically causing “volutrauma” due to shear stresses from the “popping open and closed” • Much of the problem is related to the pressure effects of the large volumes

6. Low Vt: the new way • Based on animal studies and some small clinical studies, the “ARDSNET” Trial compared outcomes using traditional tidal volumes (>10 cc/kg) to lower volumes (4-6cc/kg) finding significant benefit. • Several more studies and a meta-analysis led to the conclusion that large Vt and the high pressures it generates were harmful.

7. Low Vt: the new way • Based on this body of literature: • For ARDS, • It is recommended that patients should be ventilated with Vt of 6-8 cc/kg • And that plateau pressures should be measured, documented and targeted to be no more then 30 cm H20.

8. Role of PEEP • Use of Positive end-expiratory pressures (PEEP) of ≥ 5 cm H20 is recommended along with the low Vt • PEEP helps to prevent alveolar collapse at these low Vt, preventing atelectasis and “volutrauma” • How much PEEP is required is unclear, there are several published Vt:PEEP protocols (ARDSNET) • What is clear is that zero PEEP (“ZEEP”) is to be avoided.

9. Who should get Low Tidal Volume? • The evidence strongly shows that anybody who meets criteria for Acute Respiratory Distress Syndrome (ARDS) or Acute Lung Injury (ALI) should receive this therapy. • Criteria • Lung injury of acute onset (not a chronic process) • Bilateral CXR opacities not explained by cardiac causes (CHF) • Resp failure not explained by heart failure or volume overload • PAO2/FIO2 ratio < 200 (ALI) or 150 (ARDS) OR • Alternatively, • mild ARDS: ratio is 201 - 300 mmHg (≤ 39.9 kPa) • moderate ARDS: 101 - 200 mmHg (≤ 26.6 kPa) • severe ARDS: ≤ 100 mmHg (≤ 13.3 kPa)

10. Other Options for ARDS? • For ARDS, there are other popular strategies instead of Low Vt • Airway Pressure Release Ventilation (APRV) or Bi-Level Ventilation • Certain centers prefer these modes for ARDS and they have potential advantages • For right now, the jury is out in terms of direct comparisons of the two strategies (limited data) • The consensus is clear that until there is more data, Low Vt strategy should be used in patients with ARDS/ALI

11. What about non-ARDS patients on mechanical ventilation? • There is emerging evidence that pre-emptive Low Vt strategy is good for a wider range of mechanically ventilated patients. • The basis for this “pre-emptive” approach is that the initial injury may be subtle and not obvious and data suggests the diagnosis is often delayed • Once ARDS/ALI criteria are met • the “cat is out of the bag” • only a few hours of mechanical ventilation with large Vt may start the cascade

12. Pre-emptive Low Vt • The deleterious effects of conventional large Vt ventilation just amplifies the injury: • “multi-hit theory of ARDS” • In this way some progression to ARDS is “iatrogenic” • Most patients admitted to an ICU will have at least one risk factor for this

13. Acute Lung Injury Risk Factors • Sepsis, Severe Sepsis, Septic Shock (from non-lung source) • Pneumonia (with or without sepsis) • Aspiration and Toxic Inhalation • Severe Burns • Trauma • Pancreatitis • Cardio-pulmonary Bypass • Massive Transfusions (Transfusion Associated ALI)

14. Pre-emptive Low Vt • Several studies have shown that employing a low Vt, high PEEP strategy vs. a large Vt, low PEEP strategy • Reduces inflammatory biomarkers • Improves Oxygenation • Improves Clinical Outcomes • Those who seem to benefit most are critically ill patients and patients intra-operatively undergoing high risk procedure (CABG, TAA etc) • Large RCTs are ongoing

15. Pre-emptive Low Vt • One recent multi-center RCT (Futier et al. NEJM, Vol. 369 Aug. 2013 pp 428-37) of intra-op patients who were intermediate to high risk for pulmonary complications undergoing major abdominal surgery found that a Low Vt lung protective statistically reduced pulmonary complications, need for intubation or non-invasive ventilation (BiPAP) and length of stay.

16. Pre-emptive Low Vt • The clinical evidence is quickly mounting that most if not all patients on mechanical ventilation, whether in the ICU or the operating room, would benefit from a Low Vt strategy.

17. Low Vt in practice • Identification of patients who meet criteria: ARDS, ALI, at risk for ARDS • Need a strategy for this • Stakeholders (Resp therapy, Nursing etc) • Consistent practice: Make sure every patient is assessed every day, Daily Goals? • If your approach will be to employ Pre-emptive Low Vt, how do you make sure it gets applied immediately after intubation? • Create a process to implement: order sets • RT initiated • Physician initiated • Part of mechanical ventilation orders for at risk patients

18. Low Vt in practice • Early on establish controlled ventilation so Vt can be controlled • Unclear when to allow assisted ventilation as patient improves though early return (as soon as possible) to spontaneous ventilation is considered desirable • Problem with assisted ventilation is that Vt is harder to control • Clinician judgment is necessary

19. Setting the Vt • For ARDS/ALI • 6-8 cc/kg predicted body weight (PBW) • For pre-emptive Low Vt • Absolutely use <10 cc/kg PBW • 6-8 cc/kg is is likely best (NEJM article used this) • PBW uses height and a standardized calculation commonly used in the ICU for medication dosing • Your pharmacists can share this if you are not already using it • Do not use actual body weight as this will over estimate the Vt especially for patients with BMI>25 • Of note over the years that these trials have been done the incidence of BMI>30 has gone from 10% (1980s) to 40% now.

20. Setting the PEEP • Low Vt does cause atelectasis (Bendixen was right in that regard) • PEEP counteracts this tendency • 8-12 cm H2O is recommended by many especially if ARDS is diagnosed but anywhere between 5-15 is probably fine. • Many studies of pre-emptive Low Vt use 5-8 cm H2O. • Don’t use ZEEP • Associated with hypoxia, VAP and increase mortality

21. Setting FIO2 • Usually start at 100% • Need to reduce ASAP with target below 60% • This reduces denitrificationatelectasis • Reduce oxygen toxicity • In ARDs patients it is recommended to target Oxygen Sat= 88-92% • Do the same if using a pre-emptive Low Vt approach though if oxygenation is good, may start at 60%. • One possible exception is the use of hyperoxia in abdominal surgery to reduce SSI. Will need to reconcile this for these patients.

22. Respiratory Rate • Using Low Vt requires increased respiratory rates to prevent hypercarbia (elevated carbon dioxide) • Maintain minute ventilation as best possible • Minute ventilation = VtxResp Rate/min • Often start at about 20 bpm but may need to increase to 30 or more. • This may be difficult especially if the patient had a high minute ventilation before going on the ventilator • Downsides with these high rates include • Breath-stacking and high auto-PEEP • This can drop BP by dropping preload and decreasing cardiac performance

23. Respiratory Rate • If Resp Rate is kept below 30 these problems are less likely to occur • However, minute ventilation may then be too low to control CO2 • Therefore, CO2 is usually allowed to rise moderately (into the 50’s mmHg) causing a respiratory acidosis • This is referred to as Permissive Hypercapnia • Usually tolerated well unless there is also a severe metabolic acidosis • Dialysis may be necessary under some circumstance to control pH

24. Plateau Pressure • Need to keep <30 cm H2O • To achieve this, Vt may need to be dropped further • Bronchodilators, sedation or rarely paralysis may be necessary. • Sedation and paralysis should be used very sparingly, especially paralytics • The Respiratroy Therapist may also be able to adjust the inspiratory waveform or gas flow or other vent parameters to meet this target

25. Translation into Practice • Closing the Quality Gap • It is estimated that less then half of ARDS patient get low Vt applied in their care • A much smaller fraction of “at-risk” patients likely receive this therapy • Focusing on adaptive change, that is how we do our work, is essential to closing this gap

26. Discussion