The Challenges Faced With Early Mobilization of Patients on Extracorporeal Membrane Oxygenation*
Over the past few years, this practice has gained popularity, with several institutions sharing their early experiences (7, 8). In this issue of Critical Care Medicine, Wells et al (9), at the University of Maryland, share their institution’s experience with early initiation of PT—including standing and ambulation—in patients on both venovenous and venoarterial ECMO and examine the feasibility and safety of such practices.
Their retrospective review analyzes 2 years of patient data at a high-volume ECMO center, with a particular focus on femoral cannulation, 80% of the study population had at least one femoral cannula. The 254 ECMO patients were divided into two arms: PT (n =167) versus non-PT (n = 87) and then stratified by venovenous versus venoarterial ECMO and cannulation strategy. The groups had comparable demographics, with the exception of fewer venoarterial ECMO patients in the PT group (41% vs 57% in the non-PT group). ECMO outcomes and survival data, as well as discharge status, were consistent with the literature. The PT group had higher survival to discharge, with 60% of the venoarterial and 70% of the venovenous ECMO patients discharged, versus 30% of the venoarterial and 57% of the venovenous in the non-PT cohort.
Wells et al (9) obtained PT consultations in 67% of their 254 ECMO patients. Through well-established PT protocols and a careful patient selection, the authors were able to provide 2.75 PT sessions per patient on ECMO without any major adverse events. The staff was experienced with screening patients to ensure not only medical stability and cannula security prior to mobilization, but also that ECMO flows did not change with hip flexion.
In broad terms, ECMO patients can be stratified based on their cannulation strategy—venoarterial versus venovenous—and the specific vessels being cannulated. There are numerous operator-dependent cannulation techniques and a variety of vessels accessed (10–13). The ECMO teams at the author’s institution had a clear preference and comfort with femoral ECMO cannulation and were able to modify their technique with mobilization in mind. The cannulae were anchored to the skin with suture and adhesives, and all patients with a femoral arterial cannula had a distal perfusion catheter.
Mobilization of ECMO patients should be factored into all aspects of the cannulation strategy. The risk of cannula kinking and dislodgement needs to be considered in patients that will be mobilized. Traditionally, totally, upper body cannulation is considered easier and safer to ambulate with (14, 15). This can include a dual lumen cannula for venovenous ECMO or an upper body artery and internal jugular vein for venoarterial ECMO (11, 12).
A challenge of mobilizing femoral ECMO patients is the turbulent interface of a static tapered cannula and the dynamic distance between the femoral vessels and the skin. This distance between the femoral vessels and the overlying skin can vary with hip flexion or ambulation. To facilitate placement, ECMO cannulae tend to be tapered at the point in which they enter the vessel. Suturing of the cannula to the skin prevents catastrophic dislodgement, but does little to prevent the subtle cannula migrations associated with hip flexion. A tapered, migrating cannula in a femoral artery with a fixed opening can cause significant blood loss. This can be mitigated in part with purse-string sutures at time of cannulation, but obligates two open procedures, just like an upper body cannulation.