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.