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The Pediatric Pneumogram: A New Method for Detecting and Quantitating Apnea in Infants

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The

Pediatric

Pneumogram:

A New

Method

for Detecting

and Quantitating

Apnea

in Infants

Israel M. Stein, M.D., and Daniel C. Shannon, M.D.

From Clinical Data, Inc., and the Pediatric Intensive Care Unit, Children s Service, Massachusetts General

Hospital, and the Department of Pediatrics, Harvard Medical School, Boston, Massachusetts

ABSTRACT. A clinically useful diagnostic method has been developed for detecting and quantitating periods of apnea in pediatric patients. This procedure, called the pediatric pneumogram, permits the continuous recording on magnetic tape, for periods of up to 13 hours, of the respiratory pattern of infants utilizing an impedance technique. This test has been employed successfully in a variety of infants to evaluate respiratory activity and has permitted the objective docu-mentation of apneic and cyanotic episodes, as well as an assessment of the effectiveness of therapy. Pediatrics, 55:599,

1975, IMPEDANCE PNEUMOGRAM, APNEA, RESPIRATORY MONI-TORING.

Apnea is frequently observed in prematurely born infants and its morbidity has promoted much investigation into its pathophysiology. Apnea, as suggested by recent studies, is also associated with the events leading to the sudden infant death syndrome. Despite the increasing appreciation of apnea as a clinical problem, its recognition and

quantitation have presented difficulty.

This report describes a simple diagnostic method for evaluation of respiratory activity. With the information derived from this proce-dure, the frequency and severity of apnea can be

assessed and appropriate therapeutic intervention determined. Furthermore, the procedure may be employed to document the effectiveness of a prescribed therapy.

METHOD Patients

Patients were selected for study from the

Children’s Service Intensive Care and Interme-diate Care Units of the Massachusetts General

Hospital. Infants were studied who were observed

to have episodes of apnea, cyanosis, or bradycar-dia, unexplained on the basis of cardiopulmonary disease, seizures, sepsis, or hypoglycemia.

Respiratory activity was monitored contin-uously using the impedance pneumographic

tech-nique.7 This method is based on the principle that

volume changes within an induced electrical field

are accompanied by changes in electrical

resist-ance.

The electronics for measuring respiration by the impedance change method require a high-frequency oscillator (50 to 100 kHz) which sends a current (not exceeding 0.3 ma) through electrodes

placed on the chest wall of the infant. The small

changes in electrical resistance accompanying each breath are measured electronically. This

technique is widely employed in on-line apnea

monitors.

The impedance signal is recorded on magnetic tape utilizing a 1-lb 4 x 4 inch tape-recording

(Received September 13; revision accepted for publication November 19, 1974.)

Supported in part by the Pediatric Intensive Care Fund and

in part by Clinical Data, Inc.

ADDRESS FOR REPRINTS: (I.M.S.) Medical Director, Clinical Data, Inc., 358 Chestnut Hill Avenue, Boston,

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device especially designed for this

This device permits 13 hours of continuous recording of respiration on a single tape cassette. Most importantly, use of the device does not hinder care and handling of the infant.

At the beginning of each recording, the output signal from the impedance circuit is examined and the gain of the signal adjusted to permit the recording of respiration in infants of varying

size.

The nurses caring for each infant were asked to keep a log of the infant’s activities during the recording session and to note any apneic episodes,

either personally observed by the nursing staff or suggested by the triggering of a 20-second apnea

alarm system connected to the impedance

circuit.

The recorded tapes of respiration were then

reviewed on specialized playback equipment. #{176}In the playback operation, the recorded pneumo-graphic pattern was visually displayed and exam-med by a trained technician. Observed periods of apnea and changes in amplitude and respiratory rhythm were printed out for further examination and interpretation. Visual analysis of a 13-hour

recording may be completed in under 15

minutes.

The magnitude of the change in thoracic

impe-dance accompanying respiration is complex and depends upon the tidal volume, the size of the

infant, and the position of the electrodes. Although the relationship between impedance changes and tidal volume is not linear, it is, however, possible to detect both periods of apnea

and changing patterns of respiration.7

RESULTS

Continuous recordings of respiratory activity were easily obtained in infants ranging from 1 to

10 kg. in weight. To date, more than 50 infants

have been examined by this technique.

An example of a recording obtained from a normal infant without recognized significant apnea is shown in Figure 1, top. Respiratory activity is displayed as an undulating wave in which inspiration results in an upward deflection

from the baseline and the succeeding expiration

in a downward deflection returning to the base-line.

It will be noted in this tracing that the

respira-tory activity is relatively regular at a rate of 64

breaths per minute (paper speed, 5 mm/second). It will also be observed that the time of day (3:28)

#{176}Clinical Data, Inc., Boston, Massachusetts.

and a patient number (* 0000099) are printed

along with each 45-second block of data to permit proper identification and correlation of the respi-ratory activity with nursing observations taken during the recording.

The impedance pneumograph has been used successfully in a variety of pediatric patients to demonstrate changing patterns of respiration and apnea. The following cases illustrate the informa-tion derived from these recordings.

CASE REPORTS

Case 1

M.F. is a 2.5-kg, 7-day-old, 38-week gestation, normal female infant. The normal respiratory pattern of this infant as revealed in a 13-hour recording is shown in Figure 1, top. Twelve episodes of apnea of five to seven seconds in duration were detected; an example of one such episode is shown in Figure 1, center. Longer periods of apnea were not observed.

It can also be noted in Figure 1, center, that, during the period of apnea, the impedance changes reflecting cardiac contraction can be seen as 1- 2-mm undulating waveforms; hence, heart rate may also be determined by the exami-nation of the tracing during the apneic intervals. In this case, the heart rate was approximately 135 beats per minute. At times, impedance changes due to cardiac contraction can also be seen superimposed on the respiratory waveform, as shown in Figure 1, bottom.

Case 2

M.P. is a 1.3-kg, 39-day-old, 28-week gestation male infant with frequent and prolonged apnea. A

13-hour recording revealed 47 episodes of apnea longer than ten seconds duration. Twenty-six episodes were longer than 20 seconds in duration and 12 of these resulted in bradycardia to rates

less than 100 beats per minute.

Examples of these periods of apnea are shown in Figure 2. In Figure 2, top, two apneic episodes are shown, one 17 seconds in duration and the other 8 seconds long. The cardiac rate was 165 beats per minute. In Figure 2, bottom, the period of apnea lasted longer than 29 seconds and during this episode the cardiac rate decreased from 135 to 80 beats per minute.

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FIG. 1. Top, Recording of rhythmic respiration in M.F., a normal 2.5-kg infant. Inspiration (I) is

recorded as an upstroke and expiration (E) as a downstroke. Respiratory frequencv, 64/minute;

paper speed, 5 mm/second; time, 3:28; patient ID, 0000099. Center, Recording of two

seven-second apneic spells occurring at end-expiration in M.F. Respiratory frequency, 82/minute excluding apneic period; heart rate, 130 beats/minute. Bottom, Recording of rhythmic respiration with superimposed cardiac impedance (C). Respiratory frequency, 32/minute; heart

rate, 160 beats/minute.

observed after respiration had spontaneously

recommenced and the nurses then attributed the

alarm to “lead failures.” In a few instances, the

alarm apparently was not consciously heard and

no observation or action was taken until a second alarm signaling bradycardia also occurred.

Case 3

C.R. is a 2.6-kg, 32-day-old, 36-week gestation

male infant with repeated spells of bradycardia

and cyanosis referred for evaluation of a cyanotic episode experienced at home.

A 13-hour recording revealed 12 episodes of apnea of longer than 10 seconds, two of which

were longer than 15 seconds in duration. All 12 spells exceeding ten seconds in duration were

associated with bradycardia beginning at seven to

nine seconds of apnea. A typical example of such

a period of apnea is shown in Figure 3. It will be

noted that this apneic spell was 25 seconds in

duration and that the heart rate decreased from 150 beats per minute to 85 beats per minute.

It is of interest that this infant was referred for

evaluation of episodes of bradycardia, and was

not clinically observed to have apnea. In this case, the apnea was preceded by the bradycardia as

shown by the recording.

The sensitivity and effectiveness of the pediat-nc pneumogram in detecting apnea was corn-pared to nursing observations in nine infants who were being monitored on apnea alarm systems. The results are shown in Table I. As will be noted,

in six of the nine cases, the pneumogram record-ings revealed two to three times as many episodes

(4)

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Fi;. 2. i()), Recording of two apneic episodes (left, 17 seconds; right, 8 seconds) in M.P., a 1.3-kg

infant. Heart rate, 135 beats/minute. Bottom, Recording of an apneic episode ill NIP. Apnea

lasted 29 seconds and heart rate fell from 135 to 80 beats per niinute.

F1;. 3. Recording of a 17-second apneic spell in CR., a 2.6-kg, 32-day-old, 36-week gestation

infant. heart rate is 150 l)eats per minute which decreases suddenly after seven seconds of apuca

and reaches 80 beats/minute at 17 seconds.

DISCUSSION

The pediatric pneumogram has proven to be a

simple, easily obtained, diagnostic study which

Illay be performed in-hospital or at the patient’s

home. Respiratory rate, rhythm, relative

anipli-ttide of inspiration, frequency, and duration of

apnea as well as any resultant bradycardia may be

objectively quantified by this procedure.

Electronic means of apnea detection and alarm are subject to both false-positive and false-nega-tive responses and therefore the examination of the analog signal is necessary to be certain that true apnea is present.

Recordings of the pediatric pneumogram

ob-tamed on infants who were being monitored

simultaneously on conventional apnea alarm devices while in an intensive-care unit have revealed and documented significant episodes of

apnea that were going undetected by both

nursing staff and apnea alarm system. Conversely,

these recordings have revealed instances where

the triggering of the 20-second apnea alarm has

been due to causes other than apnea, e.g., lead

failure, alarms which would have otherwise led to

erroneous diagnostic conclusions.

The importance of quantifying spells of apnea and their duration is primarily related to the

consequences of gas exchange and subsequent

tissue hypoxia. Although 20 seconds should

(5)

TABLE I

COMPARISON OF APNEIC EPISODES

( > 20 sec) DETECTED BY PEDIATRIC PNEUMOGRAM

AND NURSING STAFF/APNEA ALARM

Infant

No. ofEpiso des ofApnea

Pediatric Pneumogram Nursing Staff/ Apnea Alarm 1 2 3 4 5 6 7 8 9 25 8 11 42 4 6 1 26 14 11 1 3 TNTC#{176} 3 2 1 8 6

#{176}Toonumerou s to count.

( case 3) may be associated with bradycardia. For

this infant, five seconds was probably exceeding a safe limit. Similar conclusions regarding clinically safe periods of apnea were drawn by Daily et a!.

in a study of premature infants.’

It is important to recognize that this technique does not improve on-line, real-time monitoring and is of little value in those circumstances where immediate medical intervention is indicated. Furthermore, the technique is subject to the

artifacts of motion and lead failure of

conven-tional impedance monitoring.

Despite these drawbacks, the information derived from these recordings permitted a more accurate diagnosis of apnea. The pediatric

pneu-mogram is of diagnostic value in infants with

spells of apnea, bradycardia, or unexplained cyanosis whether sleep-related or associated with prematurity whether observed in-hospital by the professional staff or by the parents at home. This procedure should also prove to be a useful research tool for examining infants with sleep-related apnea who are at high risk for the sudden infant death syndrome.

REFERENCES

1. Daily, W. J.R., Klaus, M., and Meyer, H. B. P.: Apnea in

premature infants: Monitoring, incidence, heart rate changes, and an effect of environmental

temperature. Pediatrics, 43:510, 1969.

2. Sinclair, J. C.: The premature baby who “forgets to breathe.” N. Engl. J.Med., 282:598, 1970.

3. Reid, D. H. S., and Mitchell, R. G.: Recurrent neonatal apnea. Lancet, 1:786, 1966.

4. Naeye, R. L.: Pulmonary arterial abnormalities in the sudden infant death syndrome. N. EngI. J. Med., 289:1167, 1973.

5. Valdes-Dapena, M. A.: Sudden, unexpected, and unex-plained death in infancy-a status report-1973. N. Engl. J. Med., 289:1195, 1973.

6. Steinschneider, A.: Prolonged apnea and sudden infant death syndrome: Clinical and laboratory observa-tions. Pediatrics, 50:646, 1972.

7. Geddes, L. A., Hoff, H. E., Hickman, D. M., and Moore, A. G.: The impedance pneumograph. Aerospace

Med., 33:28, 1962.

8. Albisser, A. M., and Carmichael, A. B.: Factors in impedance pneumography. Med. Biol. EngI.,

12:599, 1974.

ACKNOWLEDGMENT

The authors would like to express our sincere appreciation to Ms. Marilyn Nash and Ms. Ann Leahy for their assistance

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1975;55;599

Pediatrics

Israel M. Stein and Daniel C. Shannon

Infants

Quantitating Apnea in

and

The Pediatric Pneumogram: A New Method for Detecting

Services

Updated Information &

http://pediatrics.aappublications.org/content/55/5/599

including high resolution figures, can be found at:

Permissions & Licensing

http://www.aappublications.org/site/misc/Permissions.xhtml

entirety can be found online at:

Information about reproducing this article in parts (figures, tables) or in its

Reprints

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(7)

1975;55;599

Pediatrics

Israel M. Stein and Daniel C. Shannon

Infants

Quantitating Apnea in

and

The Pediatric Pneumogram: A New Method for Detecting

http://pediatrics.aappublications.org/content/55/5/599

the World Wide Web at:

The online version of this article, along with updated information and services, is located on

American Academy of Pediatrics. All rights reserved. Print ISSN: 1073-0397.

References

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