The duration of mechanical ventilation and its outcomes in patients requiring extracorporeal membrane oxygenation (ECMO) has been known for some time.1,2 At our institution, our criteria for extracorporeallife support, both for respiratory and cardiac failure, include a list of 22 absolute and relative contraindications. Duration of mechanical ventilation greater than 7–10 is one of only five absolute contraindications, with the remaining being nonphysiologic parameters such as inability to anticoagulate, refusal of blood products, or do-not-resuscitate/do-no-intubate status. In their manuscript, Wu et l. 3 confirmed the association between a longer duration of mechanical ventilation before ECMO and increased mortality and recommend a cutoff of 7 days.
There are often patients with severe acute respiratory failure in extremis that clearly meet criteria for ECMO and would not survive much longer without it. In these patients, the decision to cannulate for ECMO is usually clear and easy. On the other hand, the patients for whom more evidence and guidance are needed are those patient who are within the first 5 to 6 days of their disease process and meet criteria for ECMO but are not in extremis and could potentially improve with time or optimized therapy. As part of a consulting team seeing patients with severe adult (or acute) respiratory distress syndrome (ARDS), we are often torn with this subset of patients and debate waiting another day for optimal management and avoid the risk of ECMO or cannulating early and avoid the risk of additional mechanical ventilation. Wu et al. 3 interestingly found no difference in morality in those mechanically ventilated for less than 3 days or 3–7 days. This would support that the additional day of ventilator induced lung injury in the early days of ARDS may outweigh the risk of ECMO. This is not entirely surprising, as ventilation practices have changed since the landmark ARDSnet trial4 with decreased volutrauma.
The other area where additional research is needed is guidance for once ECMO is placed. In 50 years of research and improved understanding of ARDS, the mortality rate surrounding ARDS is between 35% and 50%,5 and ECMO is not a life-sustaining strategy that is without risk. In their population of 151 patients, 30 patients died while on ECMO and 13 because of hemorrhagic complications. Which patients benefit from ECMO is becoming more objective with scores like the RESP score used by Wu et al. 3 at their institution. However, there is little evidence to guide clinicians when to terminate ECMO. As with each day of mechanical ventilation carrying an additional risk of ventilator induced lung injury, each additional day of ECMO carries risks associated with anticoagulation and mechanical problems. Wu et al. 3 mention the trend of PaO2/FiO2 ratios as they hoped to identify contributing factors to prolonged ventilation before ECMO. Examining similar parameters after the placement may shed some light on the point of declining benefits of additional days of ECMO support and identify an appropriate time for decannulation. Having this additional objective data will also help guide clinicians in the more difficult decision when additional time of ECMO support would not be beneficial and comfort care measures should be instituted. As we have identified pre-ECMO predictors of mortality, we need to determine objective data to identify when additional days of ECMO will not improve mortality.
1. Pranikof T, Hirschl RB, Steimle CN, Anderson HL 3rd, Bartlett RH. Mortality is directly related to the duration of mechanical ventilation before the initiation of extracorporeal life support for severe respiratory failure. Crit Care Med 1997.25(1): 28–32.
2. Hemmila SR, Rowe SA, Boules TN, et al. Extracorporeal life support for sever acute respiratory distress syndrome in adults. Ann Surg. 2004.240(4): 595–605.
3. Wu MY, Huang CC, Wu TI, et al. Is there a reasonable limit on mechanical ventilation time before institution of adult respiratory exctracorporeal membrane oxygenation. ASAIO 2017.63:650–658.
4. Brower RG, Matthay MA, Morris A, Schoenfeld D, Thompson BT, Wheeler A; 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. NEJM 2000.342: 1301.
5. Pham T, Rubenfeld GD. Fifty years of research in ARDS. The epidemiology of acute respiratory distress syndrome. A 50th birthday review. Am J Respir Crit Care Med 2017.195: 860–870.