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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.

Figure 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

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