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Chapter 8 ■ Cardiorespiratory Monitoring 53

(1) Typically utilizes the same electrodes as are

used for cardiac monitoring

(2) Signal path usually from right arm (white) to left

arm (black) electrodes, although some monitors

may use right arm (white) to left leg (red or

green) (Fig. 8.7)

b. Impedance to the high-frequency signal is measured.

(1) Impedance is the electrical resistance to the signal.

(2) Changes in lung inflation cause an alteration in

the density of the chest cavity, which is detected

as a change in impedance.

(3) Changes in impedance modulate a proportional

change in the amplitude of the high-frequency

signal.

c. The change in impedance, as seen by the modulation of the high-frequency signal, is detected and

quantified by the monitor and recorded as breaths

per minute.

d. The monitor has an impedance threshold limit below

which changes in impedance are not counted as valid

respiratory activity—cardiac pumping with associated

changes in pulmonary blood flow will also cause

Fig. 8.6. Normal P-, QRS-, and T-wave detection. Top: Lead II

tracing with electrodes properly placed. Note normal P-, QRS-, and

T-wave detection. Middle: Lead II tracing with electrodes close

together on anterior chest wall. Note altered QRS- and decreased

T-wave amplitude. Bottom: Lead II tracing with electrodes placed

lateral on the abdomen. Note decreased wave amplitude and flattened P wave.

Fig. 8.7. Transthoracic impedance pneumography: Diagrammatic

representation of the path of the high-frequency signal between

chest wall electrodes. Most monitors transmit signal right arm

(white) → left arm (black), less commonly right arm (white) → left

leg (red).

changes in thoracic impedance (usually much smaller

changes than those associated with respiration).

C. Contraindications

None

D. Equipment

Hardware—Specifications

1. Equipment is the same as that for cardiac monitoring;

multiparameter monitors incorporate both cardiac and

respiratory monitoring into single units.

2. Respiratory monitoring parameters

a. Low-level threshold (for impedance) for breath validation should not be below 0.2 to minimize cardiogenic artifact.

b. Coincidence alarm with rejection applies when

respiratory rate being detected is equal to the heart

rate activity being detected by the cardiac portion of

the system.

c. Default limits should be tailored to the neonatal

population.

54 Section II ■ Physiologic Monitoring

(1) Adjustable apnea time-delay setting (length of

apnea in seconds before alarming)

(2) Typical apnea time delay is 15 to 20 seconds.

Consumables—Specifications

Same as for cardiac monitor

E. Precautions

1. Include previously discussed precautions for cardiac

monitoring

2. Muscular activity may be interpreted as respiration,

resulting in failure to alarm during an apneic episode

(see G3a following).

F. Technique

1. Same as for cardiac monitor

2. Ensure that the respiratory waveform correlates to the

true initiation of inspiration.

3. Move right and left arm electrodes up toward the axillary area if detection of respiration is poor due to shallow breathing.

4. Set desired low and high respiratory rate and apnea

delay alarm limits.

G. Complications

1. Skin lesions (see H1 under Cardiac Monitoring)

2. Monitor or cable failure

a. Hardware or software failure

b. Cable disconnection

3. Alarm failure

a. False-positive “respiratory” signal in the absence of

effective ventilation

(1) Chest wall movement with airway obstruction

(obstructive apnea)

(2) Nonrespiratory muscular action (i.e., stretching,

seizure, or hiccups) producing motion artifact

(Fig. 8.8)

b. False apnea alarm despite normal respiratory activity

(1) Improper sensitivity not detecting present respiratory activity

(2) Incorrect electrode placement

(3) Loose electrodes

c. Inappropriate alarm parameters for patient

4. Accurate assessment of respiratory rate not practical

when using high-frequency ventilatory modes

Cardiorespirograph Monitoring

A. Definition

1. Graphical representation of heart rate and respiratory

rate over time

B. Purpose

1. Monitoring of infants for identification and quantification of heart rate and respiratory activity, with detection

of apnea, periodic breathing, and bradycardia

2. Identification of chronologic relationships between

bradycardia and apnea

3. Many systems also provide continuous SaO2 information to allow correlation with desaturation events.

C. Background

1. Heart rate is plotted graphically as beats per minute

(y-axis) versus time (x-axis).

2. Respiratory waveform is compressed to allow display of

time range.

3. Short-term trending allows constant updating as the

oldest information is displaced (typically based on a

2-minute window of time).

4. Time relationship between heart rate and respiratory

activity is maintained.

a. Allows for visualization of entire apneic episodes

and identification of precipitating factors (e.g., a

drop in respiratory rate may precede bradycardia)

5. Inclusion of SaO2 allows identification of temporal relationship for desaturation events (SaO2 is plotted in the

same fashion as the heart rate on a second y axis)

D. Contraindications

None

Fig. 8.8. Tracings of artifacts affecting ECG/respiratory tracings. Top: Loose electrode affected by motion. Bottom: Motion

artifact caused by patient’s moving arm coming in contact with

chest electrodes (note change in respiratory frequency signal).