To Sum Up...

Over the past four weeks we have covered a lot of information on the use of NMES. So to re-cap, NMES is a form of electrical stimulation where by a high intensity short duration electrical stimulation is applied to a normally innervated but weakened muscle in order to elicit a contraction. The premise being that by forcing the 

muscle to contract, the muscle will strengthen allowing the child to function normally.

There are no recommended ‘safe’ parameters for NMES use on children; however it is common practice to start with low settings and gradually increase until the desired effect is attained without causing pain or distress. This threshold will vary between clients. The parameters must be gradually increased at the start of each application. 

When using NMES in children it is important to remember that, depending on the age of the child and the degree of disability, they may not understand what you are asking of them. NMES must be introduced slowly so that the child adjusts to the therapy in order for it to be successful. It is a good idea to apply the treatment to the parent first to eliminate any worries that they may inadvertently pass onto the child. 

There are many contraindications and precautions that you must screen for before beginning NMES treatment on any client but extra attention must be paid if treating a child. I believe that the precautions most likely to affect CP children are skin conditions, infection and, especially in this day and age, obesity.  However, the other precautions should not be disregarded.

There are contraindications regarding the placement of electrodes as well and these should be strictly adhered to. It is also important to choose the correct size electrode for the muscle being stimulated and have a reasonable distance between the electrodes (i.e. neither too far apart nor too close).

There is quite a lot of research out there on NMES and other electrotherapy modalities for treating CP children. These studies show a positive result after NMES treatment however, there seems to be a lack of control groups in these studies, so we don’t know how much of the improvement is due to the NMES or natural improvement. There is definitely a need for more study in this area however based on the current research I would not hesitate to prescribe NMES treatment to a CP child with a muscle weakness as anything we can do to improve these children’s quality of life is definitely worthwhile.  

The Evidence...

After researching the use of NMES in children with CP, it became evident to us that there is a multitude of evidence and research for its use. In this post, we aim to provide you with an overview of the current literature available at the present time. Firstly, we will give you an overview of the use of NMES for the upper limb.

A study completed by Kamper, Yasukawa [1] looked at the effects of NMES on upper limb impairment in children with CP, specifically spasticity, coactivation, weakness and heightened passive resistance to wrist rotation. The subjects included nine children with CP from aged five to 15 years all with spastic hemiparesis and impaired voluntary wrist movement with curled fingers.

Subjects were enrolled in a three month NMES program, consisting of two 6-week phases. The first six weeks included stimulation of both wrist flexors and extensors using a pulse duration of 280us, frequency of 35Hz and a pattern of 5s extensors on / 5s extensors off / 5s flexors on / 5s flexors off etc, for 15 minutes. Magnitude was set to maximise muscle contraction at a comfortable level for the subject. Ramp up time was set to 0.5s and ramp down time was zero. This protocol was completed six days per week and subjects were instructed to flex or extend with the corresponding stimulation.

The second six weeks consisted of stimulation of the wrist extensors only with a pattern of 10s on/10s off for 30 minutes. When the subject was able to perform full wrist extension, they were instructed to resist the extension. All other treatment parameters were kept the same.

Outcome measures of voluntary wrist extension, spasticity, passive resistance, strength and co-activation were used to measure results. There were statistically significant increases in voluntary wrist extension (Figure 1) and strength (Figure 4) and also found a significant decrease in co-activation (Figure 5). There were no statistically significant results for spasticity or passive resistance.

Positive results from this study support that NMES can indeed be used for improvement of strength, range of motion and co-activation, however it is important to note that these can be achieved without changes in level of spasticity (which is often a primary treatment goal). It was suggested by Kamper, Yasukawa [1] that increase its effectiveness on spasticity, NMES could be combined with a stretching program which has previously been shown to decrease spasticity in children with CP [2]. A clear limitation of this study is the absence of a control group, so it is difficult to differentiate improvements due to NMES from improvements due to active wrist flexion and extension.

Another interesting study completed by Carmick [3] presented two case studies on the effect of NMES on the upper limb as an adjunct to a dynamic-systems, task-oriented physical therapy program. The first case study included a 19 month old male, diagnosed with left hemiplegia secondary to CP. He began physical therapy at 7 months of age, consisting of task-oriented motor learning activities and various neurodevelopmental techniques to increase sensory awareness. However, by 19 months he was unable to use the left upper limb and therefore had corresponding difficulties when learning to creep and prop on extended elbows. A vibrator was first used on the triceps muscle to elicit a contraction in the left arm, however when removed the arm would collapse.

He was then placed on a NMES program for the triceps. Amplitude was always kept within the child’s comfort, frequency of 30-35Hz, ramp up time of 0.5s on a pattern of 15s on / 25s off for 15-20 minutes, one session per week.

Improvements were seen immediately, with creeping elicited in the first session. Improvements continued even with the NMES removed (Refer to figures below), with the child being able to creep 0.3-0.6m at home each day.

The second case consisted of a 6.7 year old, who had an inability to extend the left wrist, as well as poor functionality of the left hand. He was given NMES treatments using the same parameters in case one to the elbow, wrist and thumb extensors as well as thumb abductors and finger flexors. It took four sessions of NMES before a muscle contraction could be elicited in the wrist extensors. After 10 sessions, the child was able to spontaneously use the hand, and occasionally use the hand to hold objects.

Although this study is limited by a small number of subjects and the lack of a control group, both of the cases provide positive results for the use of NMES in the upper limb to stimulate movement, and increase function, particularly when used as an adjunct to task-oriented physical therapy.

Further research is certainly warranted in this area as the current literature lacks a randomised-controlled trial comparing NMES treatments to a control group. It is therefore difficult to make inferences about the effect of NMES on children with CP, despite the seemingly positive results of the current studies.

The available literature on the use of NMES in the lower limb is also extensive, but not conclusive, and suggests that more research and investigating needs to be done. So really it’s effectiveness in children with CP is still unknown, although it doesn’t take a genius to realise that all treatment should be individualized and therefore all results and affects are also individualized. Common sense and good clinical reasoning should be used when prescribing NMES.

Kerr, McDowell [4] conducted a randomized placebo-controlled trial which investigated the efficacy of NMES and threshold electrical stimulation (TES) in strengthening quadriceps in both legs in children with CP. Sixty children with the mean age of 11yrs were randomly placed into three groups. Of the three groups there was a statistically significant difference between NMES and TES vs. the placebo group for impact of disability at the end of treatment, although only the TES group maintained this difference at the 6 week follow up this can be seen in the table below.

Stackhouse, Binder-Macleod [5] was the first to investigate the use of NMES to increase muscle force production in kids with CP using high force and low repetitions. This preliminary study did find some clinically significant results that included an increase in maximal cross sectional area of the muscle in the children receiving NMES. They also achieved a greater normalized force production as well as an increase in walking speed.

The percentage gains in force production are comparable to that of healthy pre-pubescent children. Stackhouse may have found greater force production in the NMES group due to a more consistent training force; each contraction was not susceptible to voluntary activation. Although voluntary muscle activation was found to be the primary factor that accounts for changes in force production in children with CP after 12 weeks of training.

The use of percutaneous electrodes meant treatment was more tolerable for the children, partly because the implanted electrodes avoided the sensory receptors in the skin and subcutaneous tissue. None of the children experienced any negative responses other than short term muscular soreness after the initial onset of training and after the load was increased.

Over all by ensuring that the contraction was not causing joint pain and through the use of good technique, while being supervised a reasonable level of safety was reached throughout this training protocol. Keeping this in mind it should be noted that in chronic conditions such as CP a little benefit may go a long way for the appropriate patient.

The appropriate application of NMES has been shown to provide some benefits for children with Cerebral Palsy and there is great potential for NMES to be used in conjunction with other forms of Physiotherapy and varying treatment modalities. More research particularly randomized controlled trials need to be conducted before anything definite can be said about NMES as a single modality of treatment. This is the one thing that all the literature has agreed on in regards to the use of NMES in the lower and upper limbs.

 References:

1.            Kamper, D.G., et al., Effects of neuromuscular electrical stimulation treatment of cerebral palsy on potential impairment mechanisms: a pilot study. Pediatr Phys Ther, 2006. 18(1): p. 31-8.

2.            Zhang, L.Q., et al., Intelligent stretching of ankle joints with contracture/spasticity. IEEE Trans Neural Syst Rehabil Eng, 2002. 10(3): p. 149-57.

3.            Carmick, J., Clinical use of neuromuscular electrical stimulation for children with cerebral palsy, Part 2: Upper extremity. Phys Ther, 1993. 73(8): p. 514-22; discussion 523-7.

4.            Kerr, C., et al., Electrical stimulation in cerebral palsy: a randomized controlled trial. Dev Med Child Neurol, 2006. 48(11): p. 870-6.

5.            Stackhouse, S.K., et al., Neuromuscular electrical stimulation versus volitional isometric strength training in children with spastic diplegic cerebral palsy: a preliminary study. Neurorehabil Neural Repair, 2007. 21(6): p. 475-85.

Precautions & Contraindications

Now that you know what NMES is and the recommended parameters for its use, let’s talk about why we may not want to use NMES as a treatment modality. The list of contraindications and precautions (see Table below) for the use of NMES is extensive and covers a range of conditions, all of which could apply to any child presenting at your clinic.

Table 3: Contraindications and Precautions

Pacemakers/Inbuilt simulators

Peripheral Vascular Disease

Hypertension/Hypotension

Areas of excess adipose tissue

Neoplastic Tissue

Areas of Active tissue infection

Exacerbation of Existing Conditions

Sensory loss

Unable to communicate or co-operate

Unable to understand or provide feedback

NMES is contraindicated in patients with pacemakers and other inbuilt stimulators because there is a risk that the electrical stimulation coming from the NMES treatment could cause overstimulation of the heart (or other organ) or cause the pacemaker to switch off. This becomes very dangerous if the patient requires constant stimulation from the pacemaker. However, depending on how the pacemaker is utilised, this can be overridden with the consent of the relevant physician (Robertson, Chipchase, Laasko, Whelan, McKenna, 2001). 

NMES can cause movement of a thrombus in patients with peripheral vascular disease and can affect the autonomic responses of people with hyper- or hypo-tension (Kitchen & Bazin, 1998, Roberston et al, 2001). Obese subjects may require high levels of stimulation in order for the treatment to reach the target muscle. This high level of stimulus can cause autonomic changes (Kitchen & Bazin, 1998).

When neoplastic tissue or areas of active tissue infection are involved, there is the potential for NMES to cause dissemination of the neoplastic/infected tissue. This is considered a precaution only as when the neoplastic/infected tissue is in an area well outside the treatment area, electrical stimulation can be used safely (Kitchen & Bazin, 1998, Robertson et al, 2001). Electrotherapy can also be used safely in palliative care.

NMES and electrotherapy can cause exacerbation of existing conditions such as skin conditions, areas of increased fluid tension, areas recently treated with radiotherapy, haemorrhagic conditions and severe organ states (Robertson et al, 2001).

Sensory loss is a very important precaution (Robertson et al, 2001). The patient must be able distinguish hot from cold or sharp from blunt to know if the treatment is going well or causing them harm. However, if the patient does have some sensory loss, treatment can still be administered as long as the treatment area includes an area of normal sensation.

Even though the cohort we are talking about treating are children with CP or ABI’s and it would be unlikely that a child with these conditions would also have one of the contraindicated conditions above, it is possible. Therefore we must always take a detailed history to ensure NMES is a safe option for our clients, even more so because they are children.

The interesting thing about the use of NMES in children with CP is that it is contraindicated in patients who are unable to understand the nature of the intervention or provide feedback about the treatment (Kitchen & Bazin, 1998, Watson, 2008). Patients unable to comprehend instructions, cooperate or communicate are contraindicated for general electrotherapy treatment (Robertson et al, 2001, Watson, 2008). Both of these guidelines generally preclude children from benefiting from NMES and all other electrotherapy modalities. Studies have shown that with careful consideration, patience and the support of proactive carers, NMES can be used safely and effectively in children as young as 16 months old (Carmick, 1993, Carmick, 1997). NMES can be safely used on children with CP and other motor deficits caused by neurological disorders. It has been shown that if the child is given some level of control over the device, they are more cooperative and the treatment can then progress as normal (Carmick, 1993, Carmick, 1997).

Once we have ascertained that it is safe to use NMES on our client, we need to consider electrode placement. Electrodes should never be placed trans-abdominally or trans-thoracicly as well as over the carotid sinus and the phrenic nerve (Kitchen & Bazin, 1998, Robertson et al, 2001, Watson, 2008). This is because the electrical current used for the therapy has the potential to interfere with the normal rhythm of the heart, damage the viscera, and affect nerve conduction and the baroreceptors found in the carotid sinus. Electrodes should not be placed too far apart and they should be an appropriate size so the target muscle is isolated and there is minimal outflow to surrounding muscles.

By Sara Gibbs

References:

Kitchen, S., Bazin, S. (1998). Clayton's Electrotherapy (10 ed.). London, England: WB Saunders Company Ltd.

Watson, T. (2008). Physiotherapy Essentials : Electrotherapy : evidence-based practice (12 ed.). St Louis, MO, USA: Churchill Livingstone.

Carmick, J. (1997). Guidelines for the Clinical Application of Neuromuscular Electrical Stimulation (NMES) for Children with Cerebral Palsy. Pediatric Physical Therapy 128-136

Carmick, J. (1993). Clinical Use of Neuromuscular Electrical Stimulation for Children with Cerebral Palsy, Part 1: Lower Extremity. Phys Ther 73 505-513

Roberston, V. J., Chipchase, L. S., Laasko, E. L., Whelan, K. M., McKenna, L. J. (2001) Guidelines for the Clinical Use of Electrophysical Agents. Australian Physiotherapy Association

So How Do We Apply NMES?

As mentioned before, we intend to discuss some of the important clinical parameters in the use of NMES for kids with CP. Another important component of applying NMES is how to get children to tolerate it. The current literature describes multiple parameters for the application of NMES we will discuss their approaches to introducing and applying NMES to children with CP as there are no current recommended guidelines.

Familiarizing children with the application of NMES is important for compliance and the addition of educating the parents can be equally as important. Initially Carmick [1] introduced NMES to children by demonstrations first on the therapists arm and then on the parent’s arm. The children who hadn’t experienced EMG before were introduced to a hand-held vibrator. They were then informed that they would feel a tapping sensation similar to the vibrator. After the skin was prepared, the electrode was placed on the limb and the amplitude was slowly increased to a threshold that could either be seen as a trace contraction or was felt by the child.

The dose/effect relationship of NMES has not been explored to any great extent and so there is no way of confidently prescribing a ‘safe’ range or set of parameters when applying NMES. The common protocol is to begin with minimal parameters i.e. intensity, frequency and pulse duration, and then slowly increase these parameters until the desired result is reached in each individual. This has to be repeated on every application as patient tolerance will vary and so will equipment performance and environmental variables can alter the overall treatment effect.

Ozer, Chesher [2] used a constant current output that ranged from 0 to 100mA and used a stimulus waveform that consisted of biphasic symmetric rectangular pulses 200ms in duration. They had a pulse rate which ranged between 40 and 60 pulses/second and had an adjustable stimulus amplitude (30-40mA) which was used to produce tolerable muscle contractions. After going through the process of demonstrating the NMES on the physicians then parents arms, a 5sec on ramp, 2sec off ramp, 10sec on duty, and 7sec off duty cycle was selected to produce rhythmical muscle contraction. Ozer, Chesher [2] did not justify these parameters but mentioned that the that “the stimulus amplitude threshold was determined by increasing the stimulus until the muscle started to contract, then gradually reduced it until no contractions were apparent. This amplitude was then doubled and used routinely.” The amplitude was only altered after that to make contractions tolerable.

Cauraugh [3] conducted a meta-analysis on gait and electrical stimulation in children with cerebral palsy. Of the 40 cerebral palsy and electrical stimulation studies, the studies using NMES as their treatment protocol have been listed in Table II to provide a comparison of the parameters, duration, frequency and intensity used.

Study	E-Stim Parameters	Tx Sessions	Duration (total min)
Comeaux et.al 1997	32Hz stimulation ,0.5 onset amplitude turned up slowly until visible contraction observed, in comfort range for 15min.	Daily for 4 weeks.	840
Kerr et.al 2006	35Hz stimulation, pulse duration 300ms, on:off time 7:12s, ramp up 2s ramp down 1s, 60min at highest intensity tolerated.	5 days/week for 16 weeks.	4800
Maenpaa et.al 2006	10-20 Hz stimulation at sensory threshold, pulse duration 300ms, intensity ranged 4-20mA, on:off time 1:1s	8 times	256
Nunes et.al	50Hz stimulation, pulse width 250us, current intensity 28-44mA, on:off time 5:10s	Group 1: 14 sessions Group 2: 7 sessions	420 210
Stackhouse et.al 2007 (percutaneous NMES)	50Hz stimulation, pulse duration 5-200us, intensity 20mA, 3s ramp up time, on:off time 15:45s	3 days/week for 8 weeks.	1080

Table II; customized from Cauraugh, Naik [3].

Considerations that need to be taken into account when determining neuromuscular electrical stimulation effects on children with cerebral palsy include; age, location on body for stimulation, stimulus parameters (intensity, duration, frequency and number ofsessions) and physiological responses. A better understanding of these effects will allow for more controlled studies as well as help clinicians make decisions about parameter values for individual children [3]. The parameters and dose ranges required for a safe application of NMES must be individualised to the child.

By Ailsa Walker

References:

1.            Carmick, J., Clinical use of neuromuscular electrical stimulation for children with cerebral palsy, Part 2: Upper extremity. Phys Ther, 1993. 73(8): p. 514-22; discussion 523-7.

2.            Ozer, K., S.P. Chesher, and L.R. Scheker, Neuromuscular electrical stimulation and dynamic bracing for the management of upper-extremity spasticity in children with cerebral palsy. Dev Med Child Neurol, 2006. 48(7): p. 559-63.

3.            Cauraugh, J.H., et al., Children with cerebral palsy: a systematic review and meta-analysis on gait and electrical stimulation. Clin Rehabil, 2010. 24(11): p. 963-78.