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 that 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 1-1.Definitions, Terms, and Formulas |Favorite Table|Download (.pdf) TABLE 1-1. Definitions, Terms, and Formulas
|Parameter ||Abbreviation ||Formula ||Units |
|Pulse pressure ||PP ||BP syst – BP diast ||mm Hg |
|Mean arterial pressure ||MAP ||BP diast + 1/3PP ||mm Hg |
|Cardiac index ||CI || ||L/min/m2 |
|Stroke volume ||SV || ||mL |
|Stroke index ||SI || ||mL/beat/m2 |
|Systemic vascular resistance ||SVR || ||dyn/s/cm–5 |
|Systemic vascular resistance index ||SVRI ||SVR × BSA ||dyn/s/cm–5/m2 |
|Pulmonary vascular resistance ||PVR || ||dyn/s/cm–5 |
|Pulmonary vascular resistance index ||PVRI ||PVR × BSA ||dyn/s/cm–5/m2 |
|Left ventricular stroke work ||LVSW ||SV × MAP × 0.136 ||g/m |
|Left ventricular stroke work index ||LVSWI || ||g/m/m2 |
|Right ventricular stroke work ||RVSW || ||g/m |
|Right ventricular stroke work index ||RVSWI || ||g/m/m2 |
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 right atrium (RA); with blood flow it “floats” into the right ventricle (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. See Fig. 1-1. Measurements should be taken at end expiration.
Pulmonary artery catheter (PAC) pressure and waveform. (Reproduced with permission from Urden L, Critical Care Nursing Diagnosis and Management, 7th ed. Elsevier, 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...