Atrotech Atrostim PNS Anwenderhandbuch Seite 9

Atrostim PNS
3 MEASUREMENT OF PHRENIC NERVE LATENCY
A standard will be created for measuring phrenic nerve latency before long-term
phrenic nerve stimulation (diaphragm pacing) is initiated for treatment of central
apnea. A common standard would help to compare results during follow-up, but
would be especially helpful for comparing results of different patients.
Any modern EMG-apparatus is valid for these studies, but the type should be
mentioned when results are published.
1. Pick-up: Surface electrodes are used. The active electrode is placed
in the eighth intercostal space in the anterior axillary line.
2. Reference: The reference electrode is placed on the xiphoid (which
is, however, negative in relation to the "active" electrode).
3. Ground: The ground may be placed half way between xiphoid and
manubrium.
4. Stimulation: A surface electrode may be used, if supramaximal
response is obtained easily and without activating the brachial plexus.
However, in most cases a conventional monopolar needle electrode is
recommended. The anode may be a surface electrode placed on the
manubrium.
The stimulating needle cathode is inserted near the posterior margin
of the sternocleidomastoid muscle at the level of the cricoid cartilage.
The needle is advanced forward toward the midline so that the tip
comes to lie within a few millimetres of the phrenic nerve in front of
the scalene muscle (McLean & Mattioni 1981). The intensity of the
stimulation is increased until a supramaximal M-wave is achieved.
5. Electromyograph setting: Frequency 10 Hz - 5 kHz, sweep speed
5 ms/div, gain 200 uV.
6. Reference values: For adults, mean onset latency is 7.5 ms
(SD 0.6 ms), upper limit 9.0 ms (age range 18 - 74 years).
Amplitude range 0.2 - 1.5 mV from baseline to peak (the amplitude
is, however, of less value than latency).
In children latencies decrease from birth (2.5 ms, SD 0.4) to the age
of 6 months (2.2 ms, SD 0.4), when the phrenic nerve is fully
myelinated, and then increase with growing length of the nerve
(4.2 ms, SD 0.7) between 5 and 11 years; between 18 and 75 years
there are normally only small changes of latency (Moosa 1981,
Brouillette et al. 1983).
April 2002
3
Presurgical procedure