Pulmonary Artery Catheter Measurements
The pulmonary artery catheter directly measures pressures in the superior vena cava, right atrium, right ventricle, and pulmonary artery, along with cardiac output, and modern catheters can also measure mixed venous oxygen saturation, right ventricular end-diastolic volume, and right ventricular ejection fraction. 1
Direct Measured Parameters
The PAC provides several directly measured hemodynamic values:
- Right atrial pressure (RAP): Normal values 2-8 mmHg, reflecting right ventricular preload, though it rarely correlates with left atrial pressures in acute heart failure patients 2
- Right ventricular pressure: Systolic values normally 15-30 mmHg and end-diastolic values 2-8 mmHg 2
- Pulmonary artery pressure: Systolic 15-30 mmHg, diastolic 4-12 mmHg, mean 9-18 mmHg 2
- Pulmonary capillary wedge pressure (PCWP): Normal values <12 mmHg, estimating left ventricular filling pressure 1, 2
- Cardiac output: Measured via thermodilution, with modern catheters providing semi-continuous measurements 1
- Mixed venous oxygen saturation (SvO₂): Provides estimate of oxygen transport and body oxygen consumption/delivery ratio 1
Calculated/Derived Parameters
From the directly measured values, the PAC enables calculation of:
- Cardiac index (CI): Cardiac output divided by body surface area, with normal values >2.5 L/min/m² (decreased if <2.2 L/min/m²) 2
- Pulmonary vascular resistance (PVR): Calculated as (mean PAP - PCWP) / CO, with normal values <2-3 Wood units 2
- Systemic vascular resistance (SVR): Calculated as (MAP - RAP) / CO, with normal values 800-1200 dynes·s·cm⁻⁵ 2
Critical Measurement Pitfalls
PCWP is not an accurate reflection of left ventricular end-diastolic pressure in patients with mitral stenosis, aortic regurgitation, ventricular interdependence, high airway pressure, or stiff left ventricle (due to left ventricular hypertrophy, diabetes, fibrosis, inotropes, obesity, or ischemia). 1, 2
Additional measurement limitations include:
- Severe tricuspid regurgitation can overestimate or underestimate cardiac output measured by thermodilution 1, 2
- Pressures must be measured at end-expiration during spontaneous breathing when intrathoracic pressure approaches atmospheric 2
- Transducer zeroing must be performed at the mid-thoracic line for accurate pressure readings 2
- Positive end-expiratory pressure (PEEP) ventilation affects CVP and other pressure measurements 1
Clinical Application Algorithm
The European Society of Cardiology provides a therapeutic approach based on PAC measurements 1:
- Low CI (<2.2 L/min/m²) + Low PCWP (<14 mmHg) + SBP >85 mmHg: Indicates hypovolemia; therapy is fluid loading 2
- Low CI + High PCWP (18-20 mmHg) + SBP >85 mmHg: Indicates cardiogenic shock with adequate pressure; use vasodilators (nitroprusside, nitroglycerin) and IV diuretics 1, 2
- Low CI + High PCWP + Low SBP: Indicates severe cardiogenic shock; use inotropic agents (dobutamine, dopamine) and vasoconstrictive inotropes if SBP is critically low 1, 2