Hemodynamic Monitoring

1. MAP -- arterial line
    right atrial pressure -- Swan-Ganz or CVP line
    PAS/PAD mean PAP--Swan-Ganz
    PCWP -- Swan-Ganz with balloon inflated
    Left atrial pressure -- left atrial catheter (rarely used)
    Sv02-monitoring-Swan-Ganz catheter with a fifth channel to measure sprectrophotometrically the Sv02

2. Arterial blood pressure is relatively easily measured non-invasively via a blood pressure cuff. Placement of an arterial line is used mostly only if frequent ABG sampling is required

3. Equipment used for arterial pressure monitoring
    a. 21 gauge needle
    b. catheter tubing
    c. 3 way stopcock --for extracting blood for sampling
    d. continuous flush device--to allow heparin in line to keep line patent and to increase flow after sampling
    e. connecting tubing
    f.  pressure transducer--converts mechanical pressure into electrical current. Changes in pressure will cause electrical current changes
    mounted on an IV pole at level of sampling site
    g. amplifier or monitor--allows you to read systolic and diastolic pressures, calculates MAP, and allows you to see the artial pressure waveform
    h. electrical cord which connects transducer with monitor
    i. pressurized IV bag (usually kept at 300 mm Hg to prevent arterial flow into catheter

4. Radial artery most common site for arterial pressure monitoring. Also brachial and femoral arteries used

5. Inserting Arterial line (radial artery)
    1. Gather necessary equipment (#3)
    2. Perform Allen Test to assess collateral ventilation
        A. Have patient clench fist (to blanche hand)
        B. Apply pressure simultaneously to ulnar and radial artery
        C. Release pressure on ulnar artery (keeping pressure on radial artery)
        D. An acceptable test is if color returns to the hand within 15 seconds.
    3. Palpate the radial artery with patient wrist slightly extended
    4. Cleanse area with alcohol and iodophor pad
    5. Insert needle with stylet attached into radial artery
    6. Remove stylet and observe drops of pulsating bright red blood
    7. Place guide wire into needle and advance it into artery.
    8. Apply pressure to artery to secure guide wire then remove needle
    9. Insert 3 FR catheter over guide wire into artery
    10. Attach stop cock and flush solution to catheter
    11. secure with tape and an arm board
    12. Frequently the catheter is sutured to the skin

6. Arterial waveform
    a. Upstroke--inotropic phase (systole)
    b. Just after pressure reaches its peak (systolic pressure), diastole begins when there is a notch in the waveform (Dicrotic notch)
    c. Dicrotic notch represents when the aortic valve closes
    d. baseline represents diastolic pressure
    e. Difference between peak and baseline represents pulse pressure

7. When pressure readings will be erroneous
    1. If transducer in not at level of extremity it will read incorrectly; if transducer is too high, it will read low. If low, it will read high.
    2. An artline pressure is usually 5 to 20 mm Hg higher than cuff pressure. If it is lower it could be due to artery spasm, poor positioning, or thrombosis

8. Complications of an arterial line
    1. infection--line should stay in more than 72-96 hours
    2. hemorrhage--make sure connections are tight
    3. embolism--clot formation at tip--requires frequent heparin infusion and good flushing after arterial sampling

9. CVP line--Incision into jugular or subclavian vein. Catheter advanced into right atrium via the superior vena cava.

10. Right atrial pressure should be equal to right ventricular filling pressure. It's therefore a measurement of right ventricular preload.

11. There will be elevations in CVP with increases in right ventricular preload or increased pressure downstream from the right atrium. Normally 4-10 mm Hg; if it goes up there may be:
    1. volume overload
    2. tricuspid or pulmonary valve stenosis
    3. pulmonary hypertension
    4. RT. ventricular failure
    5. Lt. Ventricular failure
    6. Pulmonary embolism
    7. Cardiac tamponade or pneumothorax

12. CVP readings will be low:
    1. Hypovolemia
    2. Excessive loss of fluid to interstital space ("third spacing")
    3. Sudden decrease in venous return (morphine administration)

13. CVP will decrease with spontaneous inspiration
    Usually goes up with PEEP or CMV
    If CVP drops with addition of PEEP, it signals that there has been a serious decrease in venous return

14. CVP will be a fair index of left ventricular preload and function if there are no valvular problems, pulmonary hypertension, lung disease etc.  Since it is more common to have left heart problems, accurate measurements require the use of a pulmonary artery or Swan-Ganz catheter.

15. Values obtainable via a Swan-Ganz catheter
    A. CVP, mean PAP (PAS & PAD) & PCWP
    B. Pulmonary Vascular Resistance (PVR)
    C. Cardiac output (Fick and Thermodilution)
    D. Mixed Venous gases
    E. Indwelling mixed venous saturations (if using catheter with light source)
    F. Oxygen Consumption
    G. If ABG done:
        a. C (a-v)02
        b. 02 extraction ratio

16. Swan-Ganz catheter(flow directed, baloon-tipped, pulmonary artery catheter)
    1. 100 cm long catherer marked in 10 cm increments
    2. 4 or 5 lumen catheter
        1. First or "proximal" lumen located at level of right atrium--used to measure CVP, infuse IV solution, insertion of cool liquid for thermodilution calculation of cardiac output.
        2. Distal lumen--located at very end. Used to monitor PAP (when balloon deflated), take wedge pressure (when balloon inflated), withdraw mixed venous gases, also to inject medications
    3. Thermistor--located 5 cm from tip. To record temperature for thermodilution calculations
    4. Balloon port--for inflated balloon
    5. light channel--to enable continuous measurement of Sv02.

17. Insertion-- Cut-down into jugular or subclavian vein or (rarely) femoral vein.
    Catheter is inserted while distal port is attached to a pressure tranducer. When catheter is pushed to right atrium, characteristic CVP wareform seen.
    Balloon inflated and allows venous return to take catheter tip thru tricuspid valve (see ventricular waveform), then thru pulmonnic valve into pulmonary artery (charteristic waveform is seen). When waveform changes to one similar to the CVP the catheter has become wedged. The balloon is then deflated and the pulmonary artery waveforms should be seen. The catheter is then sutured or somehow stabilized.

18. Waveforms--see Wilkins Figure 14-12

19. Swan usually seen in RLL or LLL on A-P chest x-ray

20. PAS and mean PAP will increase with:
    1. Volume overload
    2. Pulmonary vascular vasoconstriction (acidosis and hypoxemia)
    3. pulmonary disease resulting in loss of pulmonary capillary bed (emphysema, pulmonary fibrosis)
    4. mitral valve problems
    5. pulmonary embolism (if severe)
    6. left heart failure

21. Normally the PAD is 1-2 mm Hg higher than the PCWP.
    Oftentimes, when the PCWP is hard to obtain, the PAD is used as a useful approximation of the wedge pressure.  This approximation is not useful if, for any reason there is an increase in pulmonary vascular resistance (PVR)

22. Complications of a Swan-Ganz catheter Infection, Thrombosis, pulmonary hemorrhage, cardiac dysrthymias, and endocarditis. Usually not left in place for more than 72-96 hours.

23. Pulmonary Capillary Wedge Pressure (PCWP)
    A. Best Measurement of Left Ventruicular Preload we have
    B. Will increase in:
        a. Fluid overload
        b. Mitral valve problems
        c. Lt. heart failure
    C. Will decrease with hypovolemia

24. PCWP--normally about 10-15 mm Hg in critically ill patient
    A. If it goes above 18 mm Hg, you will begin to see signs of pulmonary congestion
    B. If above 30 mm Hg--classic cardiogenic pulmonary edema

25. Pulmonary edema has two basic causes:
    a. Hydrostatic pressure much greater than osmotic pressure, you will have a transudative fluid transfer into the interstitium first, then frank alveolar edema. (if PCWP > 30 mm Hg)
    b. Also can occur will increased pulmonary capilliary membrane permeability (membrane leak) as occurs in ARDS and IRDS. In this situation, the PCWP will be normal even though pulmonary edema pattern seen on x-ray.
    c. Because of this--alveolar edema with a normal PCWP is thought to be diagnostic of ARDS

26. Two methods of determining cardiac output
    1. Thermal dilution method
        a. Solution of known volume and temperature (once commonly iced, now more frequently at room temperature) is injected into the proximal port (rt. atrium) of Swan.
        b. Temperature change is then measured at thermister of catheter, located near the distal port in the pulmonary artery
        c. The greater the cardiac output, the smaller the resultant temperature change.
        d. Calculation allows you to estimate cardiac output based on the change in temperature.
    2. Fick equation
        Q = 02 consumption (V02)/Ca-v02
        5 = 250 cc/min / 5 cc 02/dl of blood x 10 dl/l
    To perform a FICK, one must measure the difference between the amount of 02 inspired and that expired to get 02 consumption. This can be done with a metabolic cart. An assumption is made that the 02 uptake is equal to the 02 consumption.

27. Pulmonary Vascular Resistance (PVR)
    R = P1 - P2/flow
    R = mean PAP - PCWP / Cardiac output (Q)
    = 16 - 6 / 5 = 2 mm HG/LPM
    PVR expressed in dynes/sec/cm To convert above in these units you multiply by 80.
    So, in above 2 x 80 = a PVR of 160 dynes/sec/cm
    Normal values are anywhere between 100 to 250.
    PVR increases with things described in objective #20.

    Systemic Vascular Resistance (SVR)
    SVR = [(MAP - CVP)/Q] x 80
    = 90 - 5/5 or 17 x 80 = 1360 dynes/sec/cm
    normal values are anywhere between 900 to 1400

28. Usually Cardiac output is calculated via the thermodilution method
    To estimate 02 consumption, you rearrange the Fick Equation for cardiac output.
    Since Q = V02/Ca-v02;
    Then V02 = Q x Ca-v 02 x 10.
                    = 5 x 5 x 10
                    = 250 cc 02/min

29. PCWP will decrease with spontaneous inspiration
    Usually goes up with PEEP or CMV
    If PCWP drops with addition of PEEP, it signals that there has been a serious decrease in venous return

30. Fluid Challenge
    Generally, it is not good to judge absolute values of PCWP or CVP as an index of optimum fluid volue for a given patient.
    Practice is to give "fluid challenge" of 200 cc of fluid in a short period of time to determine what efect it has on CVP or PCWP.  Since the vascular system is a compliant structure, volume increases will cause little change in pressure until it is stretched to elastic limit, then pressure will increase dramatically.
Challenge is tried only in hemodynamically unstable individuals, to see if more volume may improve cardiac output.
If volume causes < 3 mm Hg change in PCWP, then give more fluid.
If > than 7 mm Hg then do not give any more fluid.

31.                                     CVP    PAP    PCWP

hypovolemia                      low          low          low
tricuspid valve stenosis     high     N or low      N
pulmonic valve stenosis     high     N or low      N
cor pulmonale                      high      high            N
pulmonary hypertension N or high   high          N
ARDS                                  high          high          N
Pulmonary emboli              high          high          N
LV failure                          high           high     high
Mitral valve stenosis         high          high     high
Aortic Valve stenosis         high          high     high
Hypervolemia                      high          high     high

32. Intraaortic balloon pump
    1. Used on individuals in cardiogenic shock (low C.I. with high PCWP)
    2. Balloon placed in aorta which will inflate at end diastole and deflate at the beginning of systole
    3. The deflation will decrease LV afterload by reducing intraaortic pressures.
    4. The inflation will increase coronary artery blood flow

Cardiac Websites