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What is Hemodynamics

The study of forces/pressures within the vascular system that will influence the circulation of the blood

Will be determined through cardiac contractility, blood volume, and vascular smooth muscle tone 

Valuable tool for the assessment of CVS function and the adequacy of intravascular fluid volume

Used to assess effectiveness of therapies such as drugs, fluids, etc.


Liquids and Pressures

Liquids are essentially not compressible

When in a sealed container the pressure of a liquid will vary with vertical position

When in a sealed container the pressure of the liquid will be the same for all points that are at the same vertical level 



Pascal’s Principle

A change in the pressure applied to an enclosed fluid is transmitted undiminished to every portion of the fluid and to the walls of the containing vessel. 

So by using Pascals Principal and IV line will should that changes in pressure are transmitted from the catheter to the transducer via the fluid filled IV line


Pressure Transducer System-The Transducer

A strain gage

Changes the mechanical signal (the pressure) to an electronic signal (the number displayed on the monitor)

As the pressure is applied to the diaphragm, the strain gauge wire will be lengthened changing the resistance. This will change the electrical current the flows through the wire, which will be interpreted by a computer as a proportional change in pressure. The computer will display a numeric pressure value or waveform


Pressure Transducer System-Levelling

This is the process of placing the transducer at the same level as the phlebostatic axis (the mid-axillary line and 4th rib) which approximates the right atrium


Pressure Transducer System-Zeroing

All hemodynamic monitoring is referenced to atmospheric pressure, which by convention is zero

The process involves turning the stopcock (closest to the transducer) off to the patient and open to atmospheric pressure (the reference pressure)

Wait a few seconds for equilibration and “zero” the monitor

Is done at set-up and at the start of each shift


Arterial Pressure Monitoring

Arterial pressure is the most frequently measured hemodynamic parameter.


Methods of Arterial Pressure Assessment

  • Non-Invasive
    • Blood pressure cuff
    • Doppler method (ultrasound)
  • Invasive (indwelling arterial catheter)
    • Direct


Indications for Continuous Arterial Monitoring

  • Hypotension/Hypertension
    • Unstable
      • Shock, Hypertensive Crisis, etc
  • Frequent Need for ABGs and Blood Work
    • Prolonged ICU Stay
    • Unstable respirtory failure
  • Patients requiring Inotropic Support
    • Drugs used to increase the force of myocardial contractility
    • Give continuous feedback to the effectiveness of this therapies 
  • Patient recieving vasoactive drugs
    • These drugs will alter vascular tone
    • Give continuous feedback to the effectiveness of this therapies 




Common Sites for Arterial Lines



Dorsalis pedis



Complications of an Indwelling Catheter

  • Infection
    • ​Improper sterile technique
    • Risk will increase over time
  • Hemorrhage
    • Dislodged catheter
      • 18 g catheter will allow 500 ml loss/min
    • Stop cock left open
    • Decreased clotting ability
    • Also bleeding at insertion site
  • Ischemia
    • Embolism
    • Thrombus
    • Arterial Spasm
      • All of the above will result in pallor distal to the insertion site
    • Is often accompanied with pain and numbness, and can produce tissue necrosis if not address



Arterial Pressure Waveform

The arterial pressure wave represents the impulse of the left ventricular contraction, conducted through the aortic valve and vesself along a fluid column (of blood), up a catheter, up another fluid column (of hard tubing), and then to the transducer.




Arterial Pressure Waveform-Dicrotic Notch 

The diacrotic notch represents the closure of the aortic valve

When systolic pressure is <50-60mmHg there will be an absence of dicrotic notch, and the pressure tracing is dampened and may not be accurate (falsly low numbers) 






Arterial Pressure Waveform-Pulsus Paradoxus

The effects of the respirtory system will not be generally seen due to the scale used to monitor BP-Changes less than 10 mmHg are not noticeable (Pulsus Paradoxus)

Pulsus paradoxus is when there is an abnormally large (>10 mmHg) decrease in pulse strength (stroke volume, systolic blood pressure, and therefore the pulse wave amplitude during inspiration

Pathology of respiratory variation may be:  cardiac tamponade, constrictive pericarditis, or restrictive cardiomyopathy, asthma (negative intrathoracic pressure created by the resp muscles during insp.

Paradoxical pulse = pulsus paradoxus







Arterial Pressure Waveform-Catecholamines

Increasing circulating catecholamines can make the inotropic phase become steeper and form a point which may be higher than the pressure in the volume displacement phase





 Central Venous Pressure Monitoring (CVP line)

Pressure of the blood in the right atrium or vena cava during diastole

Normal = ≤ 6 mmHg

Triple-lumen central venous pressure (CVP) catheter designed for placement through the internal or external jugular vein. The tip ends in the right atrium. The catheter does not have a balloon; air is never injected into ports.

Reflects preload of RV



Clinically, CVP can also be estimated by Jugular Venous Distention (JVD)

Normal JVD < 3 cm above the sternal angle

At the patient’s bedside (pt in semi-fowler’s position @ 45°) end exhalation

Qualified as normal, ↑’d or markedly ↑’d

Most common cause of JVD is Rt sided heart failure – Rt – sided failure may be secondary to left sided failure or chronic hypoxemia (pulmonary vasoconstriction)


CVP Indications

  • Assess circulating blood volume
  • Assess right ventricular function
  • CVP Line can be used for:
    • rapid infusion of fluid/blood/drugs
    • blood samples
    • parenteral nutrition
    • poor peripheral access
    • temporary cardiac pacemakers, hemodialysis catheters


Common Routes for CVP

  • Common
    • Jugular vein
      • Lower risk of pneumothorax
      • Requires CXR for placement and r/o pneumo
      • Catheter is less stable, can be subjcet to kinking, breakage, and accidential removal 
    • Subclavian vein
      • Higher risk of pneumothorax
      • Require CXR for placement and r/o pneumo
      • Close to the artery meaning there is a greater chance of bleeding, also is more difficult to place
      • More stable after insertion
  • Rare
    • Femoral vein
      • Require CXR for placement
      • Easiest to place, lower risk of complication, less reliable because the catheter is farther from the right atrium (waveform may be dampened), 
      • Patient must be supine



CVP Risks and Complications




Air embolism


Pneumothorax (site dependent)


CVP Line Placement

CVP is placed in the vena cava or right atrium


CVP – Respiratory Variations

Respirtory induced pressures change is a normal variation on the CVP waveform

If there is no variation on the waveform and the patient is breathing, we must assume that the CVP is inaccurate. At this point we should check for kinks/air in the tubing, stopclock error, small clot or kink in the catheter. 

It is very rare for no variation to be caused by hypoventilation or small Vt. One way to trouble shoot is to have the patient take a big breath in and watch the waveform

Pressure readings should be done at the end of expiration 

During spontaneous breathing, inspiration will cause a decrease in CVP

During positive pressure ventilation inspiration will cause an increase in CVP


CVP – Technical Consideration

The CVP line has to be zeroed when at level with the right atrium (aka phlebostatic axis)

The ~location of the right atrium is found at thephlebostatic axis which is the intersection of the midaxillary and a line drawn from the 4th intercostal space at the right side of the sternum. 

If it's positioned below the phlebostatic axis, readings will be artificially elevated; if it's above this point, the pressures will be falsely low. Leveling needs to be redone whenever the stopcock is moved from the position where the original referencing was done.


Pulmonary Artery Catheters
(PAC) Complications

Pain, infection, bleeding, air embolism, thrombus, pneumothorax (site dependant)

Catheter can irritate the heart which can cause dysrhythmias 

Perforation of the heart or pulmonary artery, 

Pulmonary rupture from overfilling balloon, which can result in the patient coughing up blood tinged sputum 

It is not common anymore but there can be significant heart defects caused by the PAC. For example the catheter can loop in the ventricle which can cause knotting or valve damage (resistance upon removal is NOT normal)



PAC Measures

Left atrial filling pressure


PAP- Volume ejected by the RV and resistance of flow through the pulmonary vasculature



SVR-Via systemic arterial pressure and PA end diastolic pressure 

SvO2 (measured at PA port)-some have continuous monitoring via reflection spectrophotometry

Ca-vO2 – can assess for left to rt shunt by measuring from CVP (Proximal port) and PA distal

Even though you can tell a lot of information the real question is whether or not you need all this information for how invasive 


PAC Uses

  • Cardiac output measurements – thermodilution
  • Route for mixed venous sampling - C(a-v)O2
    • SvO2
  • Administration of drugs
  • Pacing


PAC Catheters

A multi-lumen catheter made of radiopaque pvc, with 4 to 6 lumens

Thermistor lumen port for measurement of C.O.

Inflation lumen port to inflate/deflate balloon 

The proximal and distal lumen can be connected to a transducer to measure pressure. The pressure that is measured at the proximal lumen is CVP. The pressure that is measured at the distal lumen is PAWP (inflated) and PAP (deflated)

A sample of blood can be obtained from the distal lumen- A true mixed venous sample will come from when the cuff is inflated

The distal lumen will open into the pulmonary artery and the proximal lumen is open into the right atrium 


What can you do to PEEP if you want to change CO

Want to increase CO we can decreasePEEP



Preload is a volume reflected by pressure (more pressure=more volume).

There are situtions where the pressure will go up but volume will not change.


PAC Catheters- Proximal and Distal Lumen

Proximal lumen opening rests in the RA (CVP measurement)

  • Blood samples
  • Injection drugs
  • Thermal bolus

Distal lumen opening rests in the PA

  • Measure  PAP and PCWP
  • Can obtain mixed venous samples from here


PAC Insertion/ Placement-Right Atrium


Right Atrium: The balloon will be inflated here in order to reduce the risk of PVC, as well if the balloon is not inflated it may enter the inferior vena cava. When the tip of the catheter reaches the vena cava the CVP waveform will appear (small wiggly line) and only show pressures of 2-6 mmHg





PAC Insertion Right Ventricle

As the catheter passes through the tricuspid valve there will be a rapid increase in the height of the pressure waveform

At this point there will be a charateristic down stroke drop to near 0 mmHg which wil distinguish it from in the pulmonary artery

End diastolic pressure occurs just before the upstroke created by isovolumetric contraction

Should float easily into the PA from the RV can take minutes to ~ 1 hour (difficulties due to large, dysfunctional RV, Tricuspid regurg, PHTN, Pulmonary valve incompetence). 

Insertion through jug or SC should reach PA at about the 50 cm mark, if advancing and not getting PA insertion, possible curling in atrium or ventricle, withdraw to RA and re-insert = can use fluro. (femorals)

Flow from the heart will suck it into the right ventricle 


PAC Placement in “Wedged” Position

Wedge Position: Measure the backpressure from the left atrium

When balloon deflated = waveform should return to PA waveform – should not be left in wedged position

Overdistention could rupture the pulmonary artery – death


Diagram of normal pressures, waveforms, based on position of PAC in the heart.



Accurately Measuring Wedge Pressure

nFor PCWP to reflect left atrial pressures, blood flow must be uninterrupted between the catheter tip and the left heart - this condition only exists in Zone III

In this zone our zenous pressure will still stay patent , where in zone 2 will only be patent during relaxed exhalation (there will be an intrupption), and in zone to it is always closed (total deadspace ventilation)


Lung Zones

  • At a standing up relaxed position 
    • Alveoli in Zone 1 will be open due to gravity and this is where ventilation will occur first, but because they are already open they do not have any more ability to open and fill more (so even though air goes here first it is not where the most air goes)
      • Compliance is highest in this area 
    • The most air will go into zone 3 which is where the most ventilation will occur and will open the most
  • When looking at your V/Q ratio
    • Zone 1- High Ventilation Very Low Perfusion
    • Zone 2-The vessel pressure is not high enough to keep itself open during inhalation because it will be compressed when the alveoli is opening
    • Zone 3-More perfusion than ventilation (even though most ventilation occurs in zone 3). There is enough pressure in the capillary to remain open 


PCWP and Breathing

  • PCWP should be measured  when pleural pressure is near zero or close to zero (at end exhalation)
  • During mechanical PPV especially PEEP, PCWP can be overestimated from transmission of positive pressure to the catheter
  • PEEP < 10 cmH2O show limited effect on PCWP
    • The effect of PEEP on pleural pressures is enhanced with:
      • Increased lung compliance