RHC

Pulmonary artery catheters (PACs) are an invasive measurement of hemodynamic parameters within the heart using multiple lumens and a balloon tip to assist with placement

 

The following measures can be directly obtained from a PAC:

  • Central venous pressure (CVP): Pressure in vena cava, often an indicator of volume status
  • Right atrial pressure (RAP): Measure of volume status/RV preload
  • Right ventricular pressure (Systolic, end-diastolic): surrogate for PA pressure and preload
  • Pulmonary arterial pressure (PAP; systolic, diastolic, and mean): diagnosing pHTN
  • Pulmonary artery wedge pressure (PAWP; a-wave, v-wave, and mean): Wedging PAC into a small pulmonary arterial branch
    • Surrogate for LAP and LVEDP (preload)
  • Cardiac output, thermodilution (COt, L/min): Room temperate saline bolus is injected via proximal PAC lumen and the temperature drop is measured by thermistor on the PAC tip
  • Mixed venous oxyhemoglobin saturation (SvO2): % of O2 bound to hemoglobin in blood returning to the right side of the heart
    • Measurement of total body O2 extraction

 

A PAC can be used to calculate the following:

  • Systemic vascular resistance (SVR = 80 x [MAP-CVP]/ CO, in dynesseccm-5):  differentiation of types of shock, guides titration of afterload-reducing therapy in HFrEF
  • Transpulmonary gradient (TPG = mean PAP - PAWP, in mm Hg):  measure of pre-capillary contribution in pulmonary hypertension due to left heart disease
  • Pulmonary vascular resistance (PVR = [TPG]/ CO, in Wood units = mm Hg/L/min, customary unit. Multiply by 80 to convert to dynesseccm-5): Gold standard for estimation of the severity of pre-capillary pulmonary HTN
  • Cardiac output, Fick equation (COf, in L/min): VO2/ [(SaO2 - SvO2) x Hb x 13.4)]. VO2 is oxygen consumption, generally assumed value based on patient size and age
  • Cardiac index (CI = CO/body surface area, in L/min/m2)

 

Important equations:

-    Systemic vascular resistance (SVR = 80 x [MAP-CVP]/ CO, in dynesseccm-5): differentiates types of shock, and guides titration of afterload-reducing therapy in HFrEF

-    Transpulmonary gradient (TPG = mean PAP - PAWP, in mm Hg):  measure of pre-capillary contribution in pulmonary hypertension due to left heart disease

-    Pulmonary vascular resistance (PVR = [TPG]/ CO, in Wood units = mm Hg/L/min, customary unit. Multiply by 80 to convert to dynesseccm-5): Gold standard for estimation of the severity of pre-capillary pulmonary HTN as well as to determine a patient’s possible candidacy for heart transplant in left heart failure (goal for PVR <3)

-    Cardiac output, Fick equation (COf, in L/min): VO2/ [(SaO2 - SvO2) x Hb x 13.4)]. VO2 is oxygen consumption, generally assumed value based on patient size and age; SaO2 measured via pulse oximetry or ABG; SvO2 measured as above

-    Cardiac index (CI = CO/body surface area, in L/min/m2)

 

Complications of pulmonary artery catheters include:

  • Arrhythmias: sustained VT, RBBB (3rd degree AV block if patient has a pre-existing LBBB)
  • Myocardial, vessel, or valve rupture
  • Pulmonary artery perforation
  • Pulmonary infarction, Thromboembolism
  • Infection, particularly endocarditis of the pulmonary valve
  • Venous air embolisms
     

 

Interpretation of PAC Values:

PAC Values

 

 

 

 

Normal Values

Interpretation

Right Atrium

0-7 mmHg

Elevated with disruption in forward cardiac flow or increase in intravascular volume  (ie RV disease, valvular disease, pHTN, L to R shunt, systolic/diastolic heart failure, tamponade, constrictive and restrictive cardiomyopathies)

Right Ventricle  Pressure (mmHg

RV Systolic: 15- 25

RV Diastolic : 3-12

Elevated with diseases that elevate PA pressure and pulmonic valve disorders. Severe RVP elevations are generally chronic while acute conditions typically have RVSP <40-50.

Pulmonary Artery Pressure (mmHg)

PAP systolic: 15-25

PAP diastolic: 8-15

Mean PAP: 10 - 19

Elevated by acute conditions (PE, hypoxemia induced pulmonary vasoconstriction) or chronic conditions (all classes of pHTN, diagnostic criterion is mean PAP > 20 mm Hg)

Pulmonary Artery Wedge Pressure

4-12 mm Hg

Increased with elevated LVEDP: systolic or diastolic heart failure, mitral and aortic valve disorders, hypervolemia, R to L shunts, tamponade, constrictive/restrictive CM

Cardiac Index

2.8-4.2 L/min/m^2

Low CI: systolic/diastolic heart failure, severe valvular disorder (MR, AS), RV failure, pHTN, cardiogenic shock. Elevated CI (high-output state): sepsis, anemia, thyrotoxicosis, A-V shunt

Mixed venous oxyhemoglobin

Saturation (SvO2)

65-70%

<50%: Cardiogenic or hypovolemic shock

>65%: Distributive shock (sepsis)

High  SvO2 = decreased O2 demand or “high flow” states such as sepsis.

Low SvO2 = decreased O2 delivery (low flow, blood loss less O2 supply to same demand)

Systemic Vascular Resistance

800-1000 dynes-sec/cm^5

High SVR: Cardiogenic shock, other low cardiac output, hypovolemia, late septic shock.

Low SVR: May be due to early septic shock, anaphylaxis or other neurogenic shock, drugs (vasodilators, nitrates), hypercarbia

Transpulmonary Gradient &

Pulmonary Vascular Resistance

<12 mm Hg

 

 

<2 Wood units

Measures of intrinsic pulmonary vascular disease. In group II pHTN, elevations indicated combined pre- and post-capillary pulmonary hypertension (PH “out of proportion” to expected from L heart disease)