The care of obstetric patients requiring hemodynamic monitoring can be quite complex. It requires a basic understanding of pregnancy physiology, monitoring equipment, and applications of information gathered. In this chapter, we will review invasive and noninvasive hemodynamic principles provide the reader with a functional understanding of circulatory monitoring and ways to practically apply this understanding to normal and pathologic conditions in the gravid patient.
HEMODYNAMIC MONITORING AND EQUIPMENT
The interpretation of data gathered with hemodynamic monitoring is most useful when applied according to disease state and used to identify ominous changes before they result in clinical deterioration (Table 1-1). Responses to therapy can be closely followed with the help of hemodynamic monitoring using invasive and noninvasive techniques.
TABLE 1-1Derived Hemodynamic Parameters
J.C. Swan and W. Ganz first introduced this technology in 1970.1 The pulmonary artery catheter (PAC) is guided into the superior vena cava (SVC) by way of the internal jugular or subclavian vein, then into the RA, with blood flow it “floats” into the RV, past the pulmonary valve into the pulmonary artery and the inflated balloon tip will end up positioned or “wedged” into a branch of the pulmonary artery. Measurements should be taken at end-expiration (Fig. 1-1).
Pulmonary artery catheter (PAC) pressure and waveform. (Reproduced with permission from Urden L. Critical Care Nursing Diagnosis and Management. 7th ed. St. Louis: Elsevier/Mosby; 2014.)
Once “wedged”, the PAC waveform has a specific configuration, each portion relates to an action in the left atrial chamber. The “a-wave” correlates to atrial contraction, one will notice a rise in pressure on the waveform. Next is the “x-wave” which signifies atrial diastole and relaxation of the chamber in preparation for filling, one will notice a drop in pressure on the waveform. The next rise in pressure corresponds to passive left atrial filling and this is the “v-wave”. The “y-wave” denotes atrial emptying (Figs. 1-2 and 1-3).
CO is often measured with a PAC using thermodilution. A small volume of liquid with a lower temperature than the blood ...