Commentary: Using central mechanical support devices: When in doubt, remember central cannulation.

Alexander Schutz, MD, and Subhasis Chatterjee, MD, FACS, FACC, FCCP

Extracorporeal membrane oxygenation using central cannulation is a useful strategy for select patients. Minimally invasive techniques can make ambulatory central cannulation a viable option.

See Article page 22.

In the review by Salna and Naka, the authors provide insight into when central cannulation for extracorporeal membrane oxygenation (ECMO) may be the preferred method of cannulation. They offer surgeons practical tips with an easy-to-follow decision scheme and creative strategies to facilitate minimally invasive central cannulation.

Several options are available for percutaneous mechanical circulatory support (MCS); however, its utilization is influenced by the expertise and familiarity of proceduralists, local practice patterns, and occasionally, cost considerations. Ultimately, individualizing device selection to benefit the patient requires understanding each device's capabilities, capacity for ventricular support, and risks. The role of ECMO in these patients can vary depending on the center; it may be an option early on, or it may become an option later after alternative percutaneous MCS options have been considered or exhausted. This influences outcomes in patients who ultimately require ECMO.

To establish the role and benefit of central cannulation, the authors discuss relative contraindications to peripheral cannulation. These include circumstances that may result in technically difficult peripheral cannulation (eg, extreme obesity or severe peripheral vascular disease), complications of peripheral ECMO that cannot be rectified (eg, differential hypoxemia), or insufficient hemodynamic support. On the other hand, the benefits of central cannulation are that it provides full biventricular support, avoids differential hypoxemia, and has greater potential for mobilization than does bifemoral peripheral cannulation.

Understanding the physiology of ECMO in patients who are in cardiogenic shock can help determine the optimal therapeutic modality and cannulation configuration. Ideally, the 2 goals of MCS in cardiogenic shock are to provide circulatory support that prevents end-organ malperfusion and to promote ventricular rest that allows for myocardial recovery. Although peripheral ECMO can often prevent end-organ malperfusion, the increase in left ventricular (LV) afterload makes it theoretically less effective at allowing myocardial recovery. Central cannulation avoids increased LV afterload, theoretically promoting myocardial recovery.

For cardiothoracic surgeons, the most common indication for ECMO is postcardiotomy shock (PCS), which is required in 1% to 2% of adult cardiac surgical cases. The use of PCS-ECMO has exponentially increased, despite decreasing survival rates over the past 2 decades. It remains unclear whether this phenomenon reflects the increased confidence in ECMO, resulting in the offering of surgery to higher-risk patients who may have been denied surgery previously, or the increased utilization of ECMO in surgical patients in extremis (postsurgical cardiac arrest). The peripheral approach is the most common cannulation strategy for PCS-ECMO. Recently, a systematic review and meta-analyses of 31 studies and 2986 patients in whom ECMO was used for PCS showed that peripheral ECMO was used in 79% of cases. However, the cannulation strategy varied widely within the PC-ECMO registry of 781 postcardiotomy ECMO patients from 19 European and Middle Eastern centers, demonstrating that the center-specific use of peripheral ECMO ranges from 25% to 94% and of central ECMO from 5% to 69%.

Regardless of cannulation strategy, the survival rate for PCS-ECMO patients is about 35%. Because conducting randomized trials is difficult in this field, data from high-quality registries, systematic reviews, and meta-analyses form the high-quality evidence that guides our understanding. A recent meta-analysis cited by Salna and Naka showed comparable in-hospital survival rates when peripheral or central strategies were utilized in both PCS and non-PCS patients, although a lower risk of bleeding, transfusion, and renal replacement therapy was observed when peripheral strategies were utilized. Unexpectedly, no significant difference was observed in limb complications between the 2 strategies. Salna and Naka state that peripheral cannulation remains their preferred strategy in PCS patients and that central cannulation is reserved for PCS patients with the chest left open for bleeding, severe biventricular failure, or poor upper body oxygenation. It would be interesting to know how often the authors actually utilize central cannulation, including the use of the minimally invasive method.

Although alternative minimally invasive central cannulation strategies may be advantageous in mitigating the known risks of bleeding and transfusion associated with central cannulation or sternotomy, others have found that bleeding can be better managed with a closed sternum and peripheral cannulation. Salna and Naka cite central cannulation as an improved technique for treating severe biventricular failure due to afterload-induced LV dysfunction in patients with peripheral support, which was mostly likely related to the need for LV venting. One advantage of central cannulation is that it facilitates LV venting, but this has not always been the case. In an ECMO patient cohort (19 centers; 781 patients), an LV vent was used in only 8% of cases, despite central cannulation being used in 85% of cases. Although most meetings about ECMO are characterized by a robust debate on routine versus selective venting, the authors do appropriately caution that so-called overventing could result in stasis and thrombus formation without adequate LV ejection. This underscores the need to examine pulsatility on the arterial line and assess for aortic valve opening on echocardiography during daily ECMO rounds. Nonetheless, it does appear that early LV venting (within 12 hours of ECMO initiation) has a demonstrable survival advantage, as shown in a systematic review and meta-analysis of 7995 patients and 62 observational studies. Although the authors describe the use of the Impella (Abiomed, Danvers, Mass) device as an LV vent instead of as a first-line tool for hemodynamic support, this is highly center and proceduralist specific. More centers are increasingly using the Impella 5.0 as a bridge to transplantation or ventricular assist device as an alternative to longer-term ECMO.

The highly valuable review by Salna and Naka demonstrates their thoughtful understanding of physiology and creative surgical ingenuity in approaching these high-risk patients.