143 Hemodynamics and Ventricular Function

Question 1

What is the PA catheter used for?

Answer 1

•Determine cause of pulmonary edema:

• –Cardiogenic vs. non-cardiogenic

•Determine type of shock:

• –Cardiogenic vs. hypovolemic vs. distributive (e.g., septic shock)
• Determine cardiac output (blood flow)
• Uses: diagnosis, guide treatment, monitor response to treatment
• –Differential diagnosis of pulmonary edema
• –Differential diagnosis of shock
• –Pulmonary hypertension
• –Right-sided heart failure (to determine etiology)

Question 2

Normal waveform of PA catheter

Answer 2

Question 3

SVR =

MAP =

CO =

EF =

Flow =

Pulmonary VR =

Answer 3

SVR = MAP - CVP / CO

MAP = (SBP + (2xDBP))/3

CO = HR x SV

EF = SV/EDV

Flow = deltaP / R

Pulmonary VR = (Mean PA pressure - Wedge pressure) / CO * 80

CVP = Right Atrial Pressure (PA cath)

Capillary Wedge Pressure = Estimator of LA pressure

Question 4

RV preload

LV preload

RV afterload

LV afterload

Answer 4

• •RV preload:
  
  • –Mean right atrial (RA) pressure
  • –RA pressure = central venous pressure (CVP)
• •LV preload:
  
  • –Mean left atrial (LA) pressure
• •RV afterload
  
  • –Pulmonary vascular resistance (PVR)
• •LV afterload
  
  • –Systemic vascular resistance (SVR)

Question 5

Limitations of increasing preload

Answer 5

Question 6

Ventricular compliance

Causes of decreasing compliance

Answer 6

•Ventricular compliance: influenced by

–Filling volume (­volume = ¯compliance)

–Wall thickness (­thickness = ¯compliance)

–Ventricular size (­size = ­compliance)

•Causes of decreasing compliance (prevents heart from expanding in diastole)

–­intrathoracic pressure, ­pericardial pressure, ­pressure or volume of opposite ventricle, myocardial ischemia, myocardial disease

Question 7

PA catheter measurements (Direct, Indirect)

Answer 7

Directly measured:

• –RA pressure (central venous pressure)
• –RV pressures
• –PA pressures
• –Pulmonary capillary wedge pressure (PCWP)
  
  • •an estimator of left atrial pressure
• –Cardiac output (CO)
• –Central venous (pulmonary artery) oxygen saturation (SvO2)

Calculated (not directly measured):

• –Stroke volume (CO/HR)
• –Systemic vascular resistance (SVR)
  
  • •Based on Ohm’s law (V = IR; R = V/I)
  • •Resistance = pressure difference across a circuit divided by flow through the circuit
  • •SVR = (MAP – CVP / CO) ´ 80
• –Pulmonary vascular resistance (PVR)
  
  • •PVR = (mean PA pressure – PCWP / CO) ´ 80

Question 8

Normal values

Answer 8

The “rule of 6’s”: these are approximations:

–RA ~ 6 mmHg

–RV ~ 24/6 mmHg

–PA ~ 24/12 mmHg

–PCWP <12 mmHg

•SV: 50-100 ml/beat

•Stroke volume index (SI): 25-40 ml/m2

•CO: 4-8 L/min, cardiac index (CI): 2.5-4 L/min/m2

–Indexed values (by BSA) account for body size

•SVR: 800-1200 dynes*sec/cm5

•PVR: < 240 dynes*sec/cm5

–Most normal subjects have a PVR 40-150 dynes*sec/cm5

Question 9

Sources of low vs high Stroke Volume

Answer 9

•Low SV:

• –Inadequate blood volume (bleeding)
• –Impaired ventricular contractility (ischemia/infarction, cardiomyopathy)
• –Cardiac valve dysfunction (e.g., mitral regurgitation)

•High SV:

• –Low SVR states (sepsis, liver disease, etc)

Question 10

PA catheter pressure in RA

Answer 10

Question 11

PCWP waveform

Answer 11

• •Catheter balloon stops forward blood flow in pulmonary arteriole
  
  • –Creates a static column of blood between catheter tip and left atrium
• •The LA pressure is transmitted thru the column of blood back to the catheter tip
• •PCWP: reflects LA pressure with waveform characteristics similar to RA waveform

Question 12

Effects of respiration on PA pressure waveforms

Answer 12

• •Cardiac chambers and great vessels:
  
  • –Subject to intrinsic pressure changes and
  • –Extrinsic pressure changes caused by breathing
• •Hemodynamic pressures fall during inhalation and rise during exhalation
• •Measure pressures at end-expiration
  
  • –When intrathoracic pressure is closest to zero

Question 13

Proper placement of PA line

Answer 13

want to go in lower “zone 3” of capillary area because Pressure of artery and pressure of venous are both higher than pressure of alveolar

Question 14

Cardiac Output/Index (2 methods of measuring)

Answer 14

•2 methods to determine CO with PA line

• –Fick cardiac output: oxygen is the “dye”
  
  • •If the “dye” gets diluted a lot that means that there was a lot of time that the “dye” was circulating = low cardiac output (and vice versa)
• –Thermodilution cardiac output: temperature-based measurement of CO
  
  • •Cold saline injected into RA port, temperature measured at distal (PA) port

Question 15

Central venous oxygen saturation (SvO2)

Answer 15

Question 16

Ddx shock

Answer 16

•Differential diagnosis of shock with the PA line:

• –Low CVP, low CO, high SVR: hypovolemia
• –High CVP, low CO, high SVR: cardiogenic
• –Low CVP, high CO, low SVR: “distributive”
  
  • •Sepsis
  • •Neurogenic
  • •Anaphylaxis
  • •Adrenal insufficiency