Patients with serious illness or
injury or life-threatening states invariably require close observation
to detect changes in function or state. Electronic monitoring complements
the information gathered from direct physical examination by providing
(1) repetitive or continuous assessment that does not disturb the
patient, (2) a means for detecting the effect of interventions,
and (3) warning signals for physiological disturbances that permit
staff to observe multiple patients simultaneously. Current monitoring
devices also frequently have the capacity to store data that can
be reviewed subsequently for analysis. Because of the vital importance
of circulatory and respiratory function, much of the monitoring
in common use tracks activity of these systems, and such monitoring
is the focus of this section.
Monitoring of respiratory rate provides valuable clues about
disturbances in respiratory function (see Chapter 102). Processes that decrease respiratory system compliance
often cause the respiratory rate to increase; processes that depress
ventilatory drive cause the respiratory rate to decrease. Such monitoring may
be useful both in hospitalized patients and in those at home who
are at risk for breathing disturbances. Respiratory rate is assessed by
devices that monitor breathing movement, gas flow, or gas exchange.
Each approach is described briefly in the following sections and is
shown in Figure 106-1 and in the Table 106-1.
Common techniques for breath detection. Temperature or
CO2 concentration can be measured in gas at the nares or mouth
or through a tracheal tube. During inspiration, the gas is at room
temperature and has no CO2. During expiration, the gas
is warmed and contains CO2; thus, either temperature of
CO2 is a signal for the change from inspiration to expiration
or vice versa. With transthoracic impedance, two electrodes, placed
on opposite sides of the chest, detect a change in impedance as
the thoracic volume changes from inspiration to expiration. Inductance
plethysmograph uses two bands placed around the chest and abdomen
(shown by the coils). With chest and abdominal expansion during
inspiration, the bands lengthen, signifying an increase in thoracic
or abdominal circumference, and are used to calculate the changes
in thoracic (Vthorax ) or abdominal volume (Vabd ).
The sum of these changes is quantitatively related to the volume
entering or leaving the lungs with respiration.
Table 106-1. Common
Techniques for Monitoring Respiratory Function in Children |Favorite Table|Download (.pdf)
Table 106-1. Common
Techniques for Monitoring Respiratory Function in Children
|Source/Site and Method/Measurement||Comments and Precautions|
|Transthoracic Impedance||Simple, easy to use; not quantitatively related to change
in lung/chest wall volume; movement may appear like breath;
obstructive apnea not detected; breath can be undetected |
|Inductance Plethysmography||Provides estimate of relative tidal volume; signals apnea
when tidal volume below arbitrary threshold; can aid in determining etiology
of disordered breathing; false detection of breath, failure ...|
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