Evidence-based Mechanical Ventilation

 

What do we actually know? Which ventilation strategies are supported by evidence?

There really are only a few studies which have changed the practice of ventilation over the years.

Low tidal volume ventilation (6ml/kg) improves survival in ARDS.
      • Limiting tidal volume to 6-7 mL per kg predicted body weight reduces the probability of ventilator-associated lung injury and improves the survival of patients with ALI. This was confirmed by the ARDS Network people in their landmark study (NEJM, 2000). They were comparing low volumes with "conventional" tidal volumes of 10-15ml/kg. There is no long term data (the study looked at 28 day outcomes) nor was there any attempt to investigate what happens with "middle" volumes (8 ml/kg? 9ml/kg?)
NIV improves survival in COPD patients.
      • A Cochrane review of NIV in the COPD patient group has demonstrated that in comparison to the invasively ventilated group, patients treated with NIV have greatly reduced mortality (by half), reduced hospital stay, and reduced risk of pneumonia.
NIV improves survival in acute pulmonary oedema patients.
      • A Cochrane review of NIV in acute pulmonary oedema found that it dramatically improves survival (RR = 0.6) and decreases the rate of intubation and the length of ICU stay.
Early extubation onto NIV improves survival in COPD patients.
      • As soon as they can breathe spontaneously, they should be extubated and supported with NIV. This Cochrane review suggests this strategy can halve mortality and reduce the rate of VAP to one third. Conversely, this suggests that staying intubated is a significant mortality risk for COPD patients (i.e. invasive ventilation DOUBLES their mortality and triples the risk of pneumonia); this is another good argument againt intubation.
NIV improves survival in immunocompromised patients with hypoxic respiratory failure.
      • Noninvasive mechanical ventilation enhances the survival of immunocompromised patients: this small trial among 52 patients demonstrated that you should avoid intubation if you can help it.
Prophylactic antibiotics in intubated patients decrease the risk of pneumonia.
      • Its the selective digestive tract decontamination thing again. The published evidence seems to suggest that SDD is helpful. Worse yet, it seems systemic antibiotics are more helpful than topical ones (purely oral regimens reduced the rates of respiratory tract infections but did nothing to improve mortality, whereas systemic antibiotics actually improved survival).
        However of all the trials reviewed only one study reported on the most important thing: the development of drug resistance. Most people, in spite of this evidence of benefit, would still withhold antibiotics.
Steroids decrease the rate of post-extubation stridor in adults at risk of post-extubation stridor.
      • This Cochrane review suggests that steroids are helpful in patients who were at high risk of post-extubation stridor; at least in the adult group. These were patients with low cuff leak volumes. they all received multiple doses of dexamethasone for 24 hours.

What we have no strong evidence for

HFOV in ARDS: is it really better than conventional ventilation?...
      • The widely held belief among intesivists is that in ARDS early HFOV is better by sparing lung parenchyma the VILI insult of conventional ventilation. This Cochrane review from 2008 was unable to demonstrate whether this translates into a mortality benefit. At 30 days, mortality and ventilated days were similar for both groups. In the pediatric population, there seemed to be some benefit (at the 30th day fewer children required supplemental oxygen in the HFOV group)
Recruitment manoeuvres in ARDS: is there any point to them?...
      • There is a perception that recruitment manoeuvres in ARDS improve oxygenation, and indeed most people will find that the gases improve in ARDS patients who are recruited (by whichever strategy). However, does this process improve survival? This Cochrane review was unable to demonstrate any survival benefit. They do mention that oxygenation improved markedly, and that there was no increase in the risk of barotrauma.
Early tracheostomy: is it really better than late tracheostomy?...
      • There is a widely held belief that early (i.e. before day 10) tracheostomy in patients who will have a slow ventilator wean is somehow better than a tracheostomy later, mainly by virtue of decreasing the length of hospital stay. This Cochrane review was inconclusive owing to trial heterogeneity. They quote a reduction in ICU stay as being the most notable improvement in outcome (but there was no mortality benefit demonstrated).
Heated humidifers: are they really better than heat and moisture exchangers?...
      • Most people would say yes. But, this Cochrane review didn't find any hard outcome difference. The only positive findings were that hydrophobic HMEs may reduce the risk of pneumonia.
Inhaled nitric oxide in ARDS: does it really improve outcomes?...
      • It was a beautiful dream. The idea is certainly good. Vasodilate the pulmonary arteries, improve oxygenation, and thus increase survival. But, this Cochrane review didn't find any survival benefit. There was a transient improvement in oxygenation in the first 24 hours; after that, nitric oxide made no difference.

References

Wunsch H, Mapstone J. High-frequency ventilation versus conventional ventilation for treatment of acute lung injury and acute respiratory distress syndrome. Cochrane Database of Systematic Reviews 2004, Issue 1. Art. No.: CD004085. DOI: 10.1002/14651858.CD004085.pub2.

Burns KEA, Adhikari NKJ, Keenan SP, Meade MO. Noninvasive positive pressure ventilation as a weaning strategy for intubated adults with respiratory failure. Cochrane Database of Systematic Reviews 2010, Issue 8. Art. No.: CD004127. DOI: 10.1002/14651858.CD004127.pub2.

The acute respiratory distress syndrome network. Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome. New England Journal of Medicine 2000;342:1301-8.

Hodgson C, Keating JL, Holland AE, Davies AR, Smirneos L, Bradley SJ, Tuxen D. Recruitment manoeuvres for adults with acute lung injury receiving mechanical ventilation. Cochrane Database of Systematic Reviews 2009, Issue 2. Art. No.: CD006667. DOI: 10.1002/14651858.CD006667.pub2.

Ram FSF, Picot J, Lightowler J, Wedzicha JA. Non-invasive positive pressure ventilation for treatment of respiratory failure due to exacerbations of chronic obstructive pulmonary disease. Cochrane Database of Systematic Reviews 2004, Issue 3. Art. No.: CD004104. DOI: 10.1002/14651858.CD004104.pub3.

Gomes Silva BN, Andriolo RB, Saconato H, Atallah ÁN, Valente O. Early versus late tracheostomy for critically ill patients. Cochrane Database of Systematic Reviews 2012, Issue 3. Art. No.: CD007271. DOI: 10.1002/14651858.CD007271.pub2.

Vital FMR, Saconato H, Ladeira MT, Sen A, Hawkes CA, Soares B, Burns KEA, Atallah ÁN. Non-invasive positive pressure ventilation (CPAP or bilevel NPPV) for cardiogenic pulmonary edema. Cochrane Database of Systematic Reviews 2008, Issue 3. Art. No.: CD005351. DOI: 10.1002/14651858.CD005351.pub2.

Kelly M, Gillies D, Todd DA, Lockwood C. Heated humidification versus heat and moisture exchangers for ventilated adults and children. Cochrane Database of Systematic Reviews 2010, Issue 4. Art. No.: CD004711. DOI: 10.1002/14651858.CD004711.pub2.

D'Amico R, Pifferi S, Torri V, Brazzi L, Parmelli E, Liberati A. Antibiotic prophylaxis to reduce respiratory tract infections and mortality in adults receiving intensive care. Cochrane Database of Systematic Reviews 2009, Issue 4. Art. No.: CD000022. DOI: 10.1002/14651858.CD000022.pub3.

Khemani RG, Randolph A, Markovitz B. Corticosteroids for the prevention and treatment of post-extubation stridor in neonates, children and adults. Cochrane Database of Systematic Reviews 2009, Issue 3. Art. No.: CD001000. DOI: 10.1002/14651858.CD001000.pub3.

Afshari A, Brok J, Møller AM, Wetterslev J. Inhaled nitric oxide for acute respiratory distress syndrome (ARDS) and acute lung injury in children and adults. Cochrane Database of Systematic Reviews 2010, Issue 7. Art. No.: CD002787. DOI: 10.1002/14651858.CD002787.pub2.

Gilles Hilbert, M.D., Didier Gruson, M.D., Fréderic Vargas, M.D., Ruddy Valentino, M.D., Georges Gbikpi-Benissan, M.D., Michel Dupon, M.D., Josy Reiffers, M.D., and Jean P. Cardinaud, M.D. Noninvasive Ventilation in Immunosuppressed Patients with Pulmonary Infiltrates, Fever, and Acute Respiratory FailureN Engl J Med 2001; 344:481-487

Most of this information comes from only two textbooks. With "Basic Assessment and Support in Intensive Care" by Gomersall et al (was well as whatever I picked up during the BASIC course) as a foundation, I built using the humongous and canonical "Principles and Practice of Mechanical Ventilation" by Tobins et al – the 1442 page 2nd edition.