Which of the following statements about continuous cardiac output monitoring are true?

A. Continuous cardiac output monitoring may unmask events not detected by intermittent cardiac output measurements.

D. The technique of thoracic electrical bioimpedance utilizes sensors to determine stroke volume by detecting changes in resistance to a small, applied alternating current.

DISCUSSION: Various techniques are available to measure cardiac output continuously. The advantages of continuous cardiac output monitoring, as compared with intermittent methods, are (1) previously undetected events may be unmasked; (2) more prompt recognition of adverse events may be achieved; and (3) earlier therapeutic intervention may be possible. Continuous cardiac output monitoring using the thermodilution method appears to be as accurate as the “standard” intermittent bolus method, but it does not require fluid injectates. In this method, a modified pulmonary artery catheter incorporating a thermal filament heats blood in the right ventricle at pulsed intervals, and a distal thermistor detects the temperature change, which can be related mathematically to cardiac output. The Fick method combines respiratory gas analysis with oximetery to determine oxygen consumption (V(overdot)O 2) and to estimate mixed venous and arterial oxygen content differences, respectively. Cardiac output (CO) is then determined from the formula: CO = V(overdot)O 2/ {C(a-v)O 2 × 10} @ V(overdot)O 2/ {SaO 2 - SvO 2) × (Hb) × (1.39) × 10}. Thoracic electrical bioimpedance is a technique by which the resistance to a small-amplitude alternating current (i.e., the impedance) is measured using various electrodes. The impedance change induced by each cardiac ejection is a function of the stroke volume, which then can be used to calculate the cardiac output.