Electric Stim to Prevent DVTs After Total Hip Replacement

Haemodynamic performance of neuromuscular electrical stimulation (NMES) during recovery from total hip arthroplasty. Broderick BJ, Breathnach O, Condon F, Masterson E, Ólaighin G. J Orthop Surg Res. 2013 Mar 5;8:3.

Abstract
BACKGROUND:
Patients post total hip arthroplasty (THA) remain at high risk of developing Deep Vein Thrombosis (DVT) during the recovery period following surgery despite the availability of effective pharmacological and mechanical prophylactic methods. The use of calf muscle neuromuscular electrical stimulation (NMES) during the hospitalised recovery period on this patient group may be effective at preventing DVT. However, the haemodynamic effectiveness and comfort characteristics of NMES in post-THA patients immediately following surgery have yet to be established.

METHODS:
The popliteal veins of 11 patients, who had undergone unilateral total hip replacement surgery on the day previous to the study, were measured using Doppler ultrasound during a 4 hour neuromuscular electrical stimulation (NMES) session of the calf muscles. The effect of calf muscle NMES on peak venous velocity, mean venous velocity and volume flow were compared to resting values. Comfort was assessed using a 100mm non-hatched visual analogue scale taken before application of NMES, once NMES was initiated and before NMES was withdrawn.

RESULTS:
In the operated limb NMES produced increases in peak venous velocity of 99% compared to resting. Mean velocity increased by 178% compared to resting and volume flow increased by 159% compared to resting. In the un-operated limb, peak venous velocity increased by 288%, mean velocity increased by 354% and volume flow increased by 614% compared to basal flow (p<0.05 in all cases). There were no significant differences observed between the VAS scores taken before the application of NMES, once NMES was initiated and before NMES was withdrawn (p=.211).

CONCLUSIONS:
NMES produces a beneficial hemodynamic response in patients in the early post-operative period following orthopaedic surgery. This patient group found extended periods of calf-muscle NMES tolerable.

My comments:
I get a lot of total hip arthroplasty (THA) and total knee arthroplasty (TKA) and blood clots/deep vein thrombosis (DVT) are a real problem, usually soon after the procedure and before I get them for physical therapy. Often they are treated with anti-coagulants and if high enough risk with intermittent pneumatic compression (IPC). I don’t at all consider myself an expert regarding DVT or the various prophylactic drugs or compression devices, but my electrical stimulation knowledge is right up there and I’m always interested in new applications.  So it was interesting to read what they found in this study, how they found it, and I had some ideas that I thought would make EMS both more effective and easier to apply. According to the paper DVT are caused by 3 factors, 1) altered blood constitution or hypercoagulability, 2) alterations blood flow, or venous stasis, and 3) vascular endothelial damage. They reported 1 and 2 were closely linked, saying that when venous stasis is present hypercoagulability follows.

They used 2 channel bi-phasic square wave stimulator with a 350 uS pulse width, which is pretty stout, going at 36 hz that sounds like it alternated between 30 second contraction between the right and left leg, thus 30 seconds on and 30 seconds off for 4 hours. Volume of venous blood flow increased 159% in the operated limb and 614% in the unoperated limb. So it obviously worked but I will have to read up on the IPC devices to see how they compare. While it more than doubled blood flow to the operated limb, the unoperated limb increased blood flow over 6 times so there were apparently some restrictions on the side due to the surgery. According the the paper DVT also in the unoperated limb due to similar inactivity after surgery.

The researchers reported they had some difficulty properly locating the motor points to put the electrodes in the right position and it was hard on the patients, due to post-op pain to position themselves to get the electrodes right. However I think a problem was they were using 5 cm square electrodes, which are usually the cheapest, smallest, sticky electrodes that come with the machines. If however they used 10 cm circular rubber carbon electrodes, which are more comfortable and last longer, make it so you don’t have to be so particular about locating motor points.  The larger electrodes you can just stick them over the muscle and you are good to go. With the larger surface area, but big electrodes generally cover several motor points, if you are into that.  Also I wouldn’t expect the 30 second on, 30 second off duty cycle to be ideal for increasing blood flow. Most of the research coming out on cardiovascular conditioning are using constant 4-6 Hz frequency to mimic shivering and I expect similar parameters would improve lower extremity blood flow more effective than the parameters given here, such that the 4 hour treatment time could be shortened. Also in my own subjective experience with EMS to increase a pumping action of the calves, having one large electrode of the gastrocnemius and another over the tibialis anterior sure feels like it is not only inducing muscle contractions but feels like it is mechanically squeezing the muscles against the tibia and fibula bones so it would be interesting to see if that has any additional improvement on blood flow and venous return. Having one electrode over the tibialis anterior should also at least partially offset the forceful plantar flexion contractions experienced by a minority of subjects in the study. I would think larger pads and a 4 channel device, so that you could add a pad to the quadriceps and hamstrings, as well as the calves would significantly improve blood flow as compared to just doing so on the calf musculature in this study. All in all it has me thinking about getting my own ultrasound doppler device to test these variables out on my own.

Also if the machines are programmable they would be able to change the settings to prevent post-op muscle atrophy and decrease pain as well, which is not bad for a machines that only cost a couple hundred dollars. I imagine that compares favorably in the cost benefit ratio over the IPC machines. Though this paper was done on total hip replacements, my assumption would be that the EMS would also work for other procedures where DVT are a problem to include total knee replacements.

As always, if you have any further questions or need for clarifications, please don’t hesitate to ask. Being aware that some of my blog ideas are contentious and occasionally a bit out of the field of my expertise, I encourage my readers to come forth with any questions/comments that are of interest or concern. Your comments are valued and welcomed.

Chad Reilly is a licensed physical therapist, located in North Phoenix, practicing science based medicine with treatment protocols unique and effective enough to proudly serve patients from Phoenix, Scottsdale, Mesa, Chandler, Tempe, Peoria, and Glendale.

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