Once a patient has a temporary pacemaker inserted, checking its
threshold parameters and assuring proper functioning is the nurse's
responsibility. To do this you need to understand the concepts and principles
of cardiac pacing and how to adjust the settings on the pulse generator.
Let's start with cardiac pacing. A temporary pacemaker is typically
indicated for patients with symptomatic bradycardias, such as slow escape
rhythms, conduction defects, and heart blocks. The tip of the pacing catheter,
or lead wire, sits against the inner wall of the right atrium, right
ventricle, or both, depending upon the type of pacemaker placed—atrial,
ventricular, or AV sequential, for example. The proximal end of the catheter is
attached to the pulse generator.
The pulse generator houses the pacemaker's controls and energy source.
Electricity is delivered to the myocardium via the lead wire at a prescribed
rate. Always check to see that the rate prescribed matches the rate set on the
pulse generator.
The mode of pacing can be set on either demand or asynchronous. When it is
set on demand, the pacemaker senses the heart's impulses, and paces only when
the patient needs it. When it's in the asynchronous mode, the pacemaker fires
at a fixed rate regardless of the heart's ability to generate
impulses.
Achieving capture
The ability of the myocardium to contract when stimulated by the pacemaker
is called capture. It's determined by the amount of voltage delivered to the
muscle measured in milliamps (mA). The stimulation threshold is the lowest
amount of mA needed for capture.
Successful capture will show up on an EKG or telemetry as a spike—a
perfectly vertical line—followed by a P wave if the atrium is paced; or by
an R wave if the ventricle is paced. (See the image below).
Before determining the stimulation threshold, make sure the pacemaker is in
the demand mode. Then, set the pacemaker rate 10 beats above the patient's own heart
rate, or as high as needed to see 100% capture—a pacer spike with every beat.
Next, slowly turn down the mA until 1:1 capture is lost. The EKG or telemetry
strip will show spikes without complexes following them. Slowly turn up the mA
until capture is regained. This is the stimulation threshold. The mA should be
set two to three times higher than the stimulation threshold.
Delivering the beats
Sensing refers to the ability of the pacemaker to detect the heart's own
electrical activity and deliver paced beats only when needed.
To determine if the pacemaker is sensing properly, set the rate 10 beats
below the patient's inherent rate. (Note: This step is contraindicated if a
patient has no intrinsic rate, or has symptomatic bradycardia.)
Reduce the mA to its lowest level (threshold). Then, turn the sensitivity
dial counterclockwise toward a higher numerical setting. (The sensing light,
which flashes when sensing, will stop.) The pacemaker is now less sensitive to
the patient's heartbeat.
Now, turn the sensitivity dial clockwise (down) until the sensing light
starts flashing again. This is the sensitivity threshold. Set the sensitivity,
measured in millivolts (mV), at half the sensitivity threshold value obtained.
Thus, if the sensitivity threshold is 4, you'll set the dial on 2 mV. Restore
the mA and rate to their proper settings.
It's important to note that an atrioventricular (AV sequential) pulse
generator may have dials for atrial settings on the left, and ventricular
settings on the right. Although it operates like any other pacemaker, you won't
need to determine the atrial sensitivity threshold, so there is no dial for
this function.
How to troubleshoot
Checking the stimulation and sensitivity thresholds should be done at least
daily if the pacemaker is in demand mode. It's unnecessary with the
asynchronous mode, though, because this mode is usually reserved for those
whose underlying rhythm is asystole.
Troubleshooting, however, applies to both the demand mode and the
asynchronous mode and includes the following:
Failure to pace is confirmed when there's no pacer spikes shown on your EKG or telemetry
strip.
Always check the batteries and replace them if necessary. (A good rule of
thumb is to replace them every two to three days.) Then, check to make sure all
connections are tight.
If you're still not seeing pacer spikes it may mean the pacemaker is
oversensing. A pacemaker will sense, or pick up and interpret, muscle movement
and artifact as heart beats if the sensitivity threshold is set too high, or
there are items in the vicinity of the pacemaker that interfere with its
signals, or the lead wire is fractured.
If oversensing is the likely cause of the failure to pace, lower the mV on
the sensitivity dial, as it raises the sensitivity of the pacemaker, and remove
items that could cause electromechanical interference such as electric razors,
radios, or cautery devices. You'll need a chest X-ray to rule out a fractured
lead wire.
However, not seeing pacer spikes can be normal, such as when the patient's
heart is beating faster than the rate set on the pacemaker.
Failure to capture is confirmed when pacer spikes are seen on EKG and telemetry, but the
spikes aren't followed by a ventricular or atrial complex. Again, always check
the batteries and make sure all connections are tight. Then, try repositioning
the patient onto his left side to regain capture, as the lead wire may be
dislodged.
If you still don't see capture, the electrical output may be too low. In
this case, increase the mA until you regain capture.
Another problem can occur when the pacemaker fails to sense the patient's
intrinsic beats. Undersensing can be dangerous: Pacer spikes that fire indiscriminately
throughout the cardiac cycle can trigger a lethal dysrhythmia if a spike falls
on a T wave. In this case, lower the pacemaker's sensitivity to the heart by
turning up the dial to a higher mV.
SOURCES
1. Diepenbrock, N. H. (2004). Quick reference to critical care (2nd
ed.), (pp. 119 – 125). Philadelphia: Lippincott Williams & Wilkins.
2. Breuninger, C., Follin, S., et al. (Eds.). (2001). Handbook of
nursing procedures (pp. 603 – 604). Springhouse, PA: Springhouse
Corporation.
Seemoreat:http://www.modernmedicine.com/modern-medicine/news/temporary
pacemakers#sthash.vJit4rJo.dpuf
0 komentar:
Posting Komentar