49

8 Cardiorespiratory Monitoring

Rebecca J. Fay

Cardiac Monitoring

A. Purpose

1. To provide reliable and accurate monitoring of neonatal cardiac activity

a. Provide trends of heart rate over time

b. Monitor beat-to-beat heart rate variability (1,2)

2. To allow assessment and surveillance of critically ill

neonates

3. To provide early warning of potentially significant

changes in heart rate by identification of heart rates

above or below preset alarm limits

4. To identify bradycardia (with or without associated

apnea) in at-risk infants

B. Background

1. Electrical activity of the heart is detected using

impedance technology through skin surface electrodes

(3).

2. The low-level electrical signal is amplified and filtered

to eliminate interference and artifacts.

3. The electrical signal, defined in millivolts, is displayed

as an electrocardiogram (ECG) tracing.

4. R-wave detection from the QRS complex is used to calculate heart rate.

5. The typical three-lead configuration (i.e., leads I, II,

III) provides alternative vectors for ECG analysis.

C. Contraindications

None

D. Limitations

1. The three-lead ECG is most useful for long-term continuous cardiac monitoring; more detailed cardiac evaluation (i.e., assessment of hypertrophy or axis) or the

identification of abnormal cardiac rhythms may require

complete 12-lead ECG with rhythm strip.

2. Close proximity of electrodes in extremely small infants

may cause difficulty with signal detection.

E. Equipment

Hardware—Specifications

1. The monitoring system should have the appropriate frequency response and sensitivity to track the fast and

narrow QRS complex of the neonate accurately.

2. Heart rate is processed on a beat-to-beat basis with a

short updating interval.

3. Default heart rate alarm limits should be tailored to the

neonatal population.

a. Low heart rate (bradycardia) limit of 100 beats/min

(Note: Some term infants may have resting heart

rates of 80 to 100 beats/min, requiring lower bradycardia alarm settings.)

b. High heart rate (tachycardia) limit of 175 to

200 beats/min

4. Monitor displays

a. Cathode-ray tube (CRT)

(1) Has highest resolution and best definition

(2) Display can be either color or monochrome

b. Liquid-crystal display (LCD)

(1) Flat, thin display monitor

(2) Resolution may be suboptimal for fast and narrow QRS complex of neonate

(3) Back-lighting is necessary for viewing in lowlight environments

(4) Unlike CRT, viewing angle is critical

5. Heart rate displayed as alphanumeric part of waveform

display or in a separate numerical display window

6. Recorder (optional)

a. Electronic memory

(1) Real-time ECG

(2) Delayed ECG—stored retrospective display

used primarily for review of a short time interval

prior to the occurrence of an alarm

b. Printed record of ECG trend information

(1) Typically used to document selected segments

of ECG tracings such as periods associated with

alarms or abnormal rhythms

(2) Monitors may have dedicated printers (often

integrated into monitor cases)

50 Section II ■ Physiologic Monitoring

(3) Central monitoring stations can provide remote

access to information from all networked monitor units with printing capabilities.

7. Units available for both bedside and transport monitoring (Figs. 8.1 and 8.2)

a. Transport monitors typically smaller and batterypowered

b. Similar capabilities regarding parameter availability,

but monitor-specific

Consumables—Specifications

1. Disposable neonatal ECG electrodes

a. Silver–silver chloride electrodes are available in a

variety of forms designed specifically for the neonatal population.

(1) Patient contact surfaces of electrodes are coated

in adhesive electrolyte gel, which acts as conductive medium between the patient and the

metal lead while preventing direct patient contact with the metal.

(2) Typical commercially available neonatal leads

incorporate silver–silver chloride electrodes

directly onto paper, foam, or fabric bodies with

integrated lead wires.

(3) Less commonly, adhesive electrode pads are

separate from lead wires, which connect to the

electrodes via clips.

(4) ECG limb plate electrodes may be used rarely,

when the application of chest leads would interfere with resuscitation or the performance of

other procedures. Use of electrode gel as a conductor at the skin interface (rather than alcohol

pads) is imperative in such cases.

b. Characteristics to consider in electrode selection:

(1) Adherence to skin of an active infant

(2) Quality of signal attained

(3) Minimal skin irritation

(4) Ease of removal using water or adhesive remover

without damage to or removal of skin

(5) Performance in the warm, moist environment of

an infant incubator

(6) Adhesive–skin interaction under overhead infant

warmers

2. Lead wires and patient cable

a. All cables should be clean and the insulation should

be free of nicks or cuts.

b. Lead wires should lock or snap into the patient

cable, preventing easy disconnections.

c. If using electrodes that attach via clips, use infant/

pediatric lead wires with small electrode clips—

standard adult-size clips will place too much torsion

on the infant electrode, tugging on the skin and possibly peeling off the electrode.

F. Precautions

1. Do not leave alcohol wipes under electrodes as

conductors.

2. Do not apply electrodes to broken or bruised skin.

3. Avoid placing electrodes directly on the nipples.

4. Select the smallest appropriate/effective electrode for

patient monitoring to minimize skin exposure and limit

potential complications from irritation/adhesives.

5. Do not apply electrodes to clear film plastic dressings—

dressing will act as an insulator between the skin and

the electrode.

Fig. 8.1. Typical multiparameter neonatal bedside monitor.

(Courtesy of Philips Medical Systems.)

Fig. 8.2. Typical multiparameter neonatal transport monitor

with integrated printer. (Courtesy of Philips Medical Systems.)