Clinical monitoring in the ICU

By: ABRAHA HAILU(MD)

Hemodynamic Monitoring

Overview

• Blood pressure monitoring– NIBP– IBP

• Central venous pressure monitoring

• Pulmonary artery pressure monitoring

• Mixed venous oxygen monitoring

• Cardiac output

Why monitor BP?

– Alterations inherent– Provides data for interpretation/therapeutic

decisions– Important for determining organ perfusion

(MAP most important, except with the heart)

Noninvasive Hemodynamic Monitoring

• Noninvasive BP

• Heart Rate, pulses

• Mental Status

• Mottling (absent)

• Skin Temperature

• Capillary Refill

• Urine Output

Indications for Arterial Blood Pressure

• Frequent titration of vasoactive drips• Major surgery involving large fluid shifts or EBL• CPB• Aortic surgery• Unstable blood pressures • Frequent ABGs or labs• Unable to obtain Non-invasive BP

Supplies to Gather

• Arterial Catheter• Pressure Tubing• Pressure Cable• Sterile Gown• Sterile Towels• Sterile Gloves

• Pressure Bag• Flush – 500cc NS• Suture (silk 2.0)• Chlorhexidine Swabs• Mask

Potential Complications Associated With Arterial Lines

• Hemorrhage

• Air Emboli

• Infection

• Altered Skin Integrity

• Impaired Circulation

Central Venous Pressure Monitoring

• CVP measures the filling pressure of the right ventricular (RV); it gives an estimate of the intravascular volume status and is an interplay of the:

(1) circulating blood volume (2) venous tone and (3) right ventricular function.

CVP

BLOOD VOLUME

(INCREASED VENOUS RETURN RAISES CVP

CARDIAC COMPETENCE (REDUCED VENTRICULAR FUNCTION RAISES CVP)

INTRATHORACIC AND INTRAPERITONEAL PRESSURE (RAISES CVP)

SYSTEMIC VASCULAR RESISTENCE (INCREASED TONE RAISES CVP)

NORMAL CVP MEASUREMENTS

• CVP monitoring should normally show measurements as follows:Mid Axilla: 0 - 8 mmHg An isolated CVP reading is of limited value;

a trend of readings is much more significant and should be viewed in conjunction with other parameters e.g. BP and urine output.

Indications for central venous catheter placement

i. Major operative procedures involving large fluid shifts and / or blood loss or Major trauma

ii. Diagnosis of RV failure: evidenced by high CVP in the presence of low Cardiac output

iii. Pharmacological intervention which is likely to result in changes in venous capacitance (Ex: drugs such as sodium nitroprusside can be used more safely if the CVP is known)

iv. fluid management, Intravascular volume assessment, when urine output is not reliable or unavailable (e.g.: renal failure)

v. Surgical procedures with a high risk of air embolism, such as sitting position craniotomies. In addition to monitoring, the central venous pressure (CVP) catheter may also be used to aspirate intracardiac air.

vi. Frequent venous blood sampling

vii. Venous access for vasoactive or irritating drugs

viii. Chronic drug administration

ix. Inadequate peripheral IV access

x. Rapid infusion of IV fluids

xi. Special Uses: vi. insertion of PA catheters

vii. insertion of transvenous pacing wires

viii.haemodialysis/plasmapheresis

Contraindications• Absolute:

SVC syndrome Infection at the site of insertion

• Relative:CoagulopathiesNewly inserted pacemaker wiresPresence of carotid diseaseRecent cannulation of the internal jugular veinContra lateral diaphragmatic dysfunctionThyromegaly or prior neck surgery

Central VenousCatheter Placement

Cannulation techniques:1. Catheter-over-the-needle

2. Catheter-through-the needle

3. Catheter-over-a-guidewire (seldinger technique)

sites

A. Central line from peripheral site (antecubital fossa commonly selected)

B. Femoral site

C. External jugular site

D. Subclavian site

E. Internal jugular site All have their own indications, contraindications,

advantages & disadvantages

Equipment Sterile gloves Sterile gown and mask (optional) Sterile prep solution Local anesthetic Syringes Sterile flush solution Suture material (might be included in the kit) Dressing material Manometer set (this may vary according to whether C.V.P. to be

transduced or not ) 500ml of0.9% Sodium Chloride. (500ml Sodium Chloride with 500

units heparin used in transduced circuits only) Pressure bag (only used in transduced circuits) Sedatives (if required)

• Central venous catheter kit: Different types of kits are availableAll have the use of the Seldinger over-the-

wiretechnique for placementLikewise, the type of catheter inserted varies

with its intended purpose:A multiple lumen catheter might be needed

to infuse several different types of vasoactive medications,

while a large-bore catheter is better for infusing a large volume of fluid or as a port for inserting a Swan-Ganz catheter.

Techniques:• The sites and techniques for placing

central venous catheters are numerous

• Cannulation of internal jugular vein (IJV) was first described by English et al2 in 1969 Since then, it has steadily increased in

popularity as one of the methods of choice for CVP/RAP monitoring.

• The reason for this popularity relates to:it’s short, straight (right IJV), valveless course to

SVC and RA; and its position at the patient’s head, which provides

easy access by anesthetists in more intra

operative settingsthe success rate for its use exceeds 90% in most

series of adults and children

• For accurate measurement of CVP/RAP and also to aid aspiration of air in venous air embolism, the catheter tip is positioned ideally at

the SVC-RA junction,SVC or high up in the RA, away from the tricuspid

valve

• Cannulation of the IJV is relatively safe and convenient and various approaches exist for its cannulation

• The process of cannulation outlined in the following table

The pressure can be measured in at least two ways:

1. water manometer: the height of the column denoting the pressure

2. Pressure transducer: converts the pressure wave to an electrical

signal which can then be displayed

WATER MANOMETER:• Simple & inexpensive

• Any piece of open IV tubing can be used

• Specific problems include:Placement of the catheter in the right ventricleTR with a large reflux pressure waveGiant ‘a’ waves from the atrium ( cannon waves, A-V

dissociation & nodal rhythms)

Each of these will lead to CVP measurements which may be misleading, & markedly different from the real prassure

EQUIPMENT

(a) a sterile bag of fluids

(b) attached fluid administration set

(c) an IV extension set

(d) a manometer and

(e) a stopcock

a.

b.

c.

d.

e.

EQUIPMENT

IV extension set to entry port of patients central line.

IV giving setto fluid bag.

Stopcock(Three way tap)

DIRECTION OF FLOW

The white arrows indicate the direction of fluid flow.

(a). Initially the white knob is turned straight up, allowing fluid to flow from the fluid bag to the patient's catheter to assure the catheter is patent.. If fluid does not flow freely into the patient's catheter a valid CVP reading will not be obtained.

(b) Then the knob is turned toward the patient and fluid will fill the manometer. The manometer should not contain any air bubbles. If air is present in the manometer or fluid line, let the fluids run, overfilling the manometer until all air is purged from the system.

(c) Then turn the knob toward the fluids. The level of fluid in the manometer will fall (the fluid is running into the patient's catheter) until the height of the fluid column exerts a pressure equivalent to the patient's CVP

The top of the fluid column will slightly oscillate up and down as the pt’s heart beats and as the pt breathes.

a. c.b.

POSITION OF PATIENT

3-way tapmanometer

FluidBag

Patient in supine position

CentralVenousAccess

PRESSURE TRANSDUCER:• An electronic system with fast response time &

gives a more accurate wave representation• This enables maximum & minimum pressures to

be identified as well as visualization of the wave form which may supply information about the presence, for example of tricuspid incompetence

• Further more the mean pressure can be measured & this is usually the true CVP as it takes in to account the respiratory cycle

• Disadvantages: Complex in setting up the systemCostly Nursing staff need to be familiar with the

system There is always a risk of electronic problems

(such as ‘baseline drift‘ or mechanical damping of the system by unnoticed air bubbles in the line or transducer dome

• To maintain patency of the cannula a bag of normal saline or heparinised saline should be connected to the transducer tubing and kept under continuous pressure of 300mmHg thus facilitating a continuous flush of 3mls/hr

FACTORS AFFECTING THE MEASUREMENT OF CVP

• zeroing (Atmospheric pressure is thus the true zero value)

• Leveling (relative to an arbitrary reference level)

• where on the waveform to make the measurement: A primary purpose for measuring CVP is the assessment of cardiac

preload best measured at the base of the c wave The base of the c wave is used because this is the final pressure in

the ventricle before the onset of contraction and represents the final distending force for the ventricle, which is preload

• actual pressure across an elastic structure (transmural pressure)

we are restricted to making pressure measurements relative to atmospheric pressure.

To minimize this problem, pressures are made at end expiration when pleural pressure is closest to atmospheric pressure

INFORMATION FROM THE CVP WAVEFORM

• Besides the actual pressure measurement there is much information that can be gained from examining the waveforms

WAVEFORMS IN CVPconsists of three upwards (a, c, & v waves) and two

downward defections (x and y descents). 1. ‘a’ wave by right atrial contraction and occurs just

after the P wave on the ECG.2. The ‘c’ wave due to isovolumic ventricular contraction

forcing the tricuspid valve to bulge upward into the RA3. The pressure within the RA then decreases as the

tricuspid valve is pulled away from the atrium during right ventricular ejection, forming the X descent.

4. The RA continues to fill during late ventricular systole, forming the V wave

5. The Y descent occurs when the tricuspid valve opens and blood from the RA empties rapidly into the RV during early diastole

THE CVP WAVEFORM• Reflects changes in right atrial pressure

during the cardiac cycle

INFORMATION OBTAINED FROM CVP WAVEFORMS

• Loss of A wave and irregular rhythm AF/AFL• Cannon A waves junctional rhythm, complete heart

block, ventric arrhythmias, TS,, PS, RVH, PHTN• Early/Holosystolic Cannon V waves (C-V Waves) TR• Prominent A and V waves, steep X, Y descent

pericardial constriction (“M”sign)

The a and v waves

• Typically the a wave is greater than or equal to the v wave in the CVP tracing of a normal person.

• The y and x descents get deeper with a spontaneous inspiration; this can be used to time inspiratory eventsWith positive-pressure ventilation they get smaller

• In patients following cardiac surgery the a wave is often smaller than the v wave and is likely due to decreased right ventricular function

M marks the appropriate place for measurement.The bottom tracing shows the overlap tracing with pulmonary arterypressure (PAP). This also can be used for timing the end of diastole and the place to make the measurement.

shows a tracing from a young woman who had a major bleed following a hysterectomy

Tricuspid regurgitation

• a small a wave and a massive v wave that begins with the onset of systole, which is consistent with the v wave being due to tricuspid regurgitation rather than filling of a noncompliant atrium

• This CVP pattern would make insertion of a pulmonary artery catheter very difficult because it would be hard to recognize when the catheter has crossed the tricuspid valve.

This indicates severe TR. It must be appreciated that the peak of the v wave, which is 35 mmHg, will still have an important impact on upstream structures such as the liver and kidney

Rhythm disorders

• Recognition of the wave pattern can be helpful for interpreting rhythm disorders

• Figure below shows the CVP tracing of a patient with episodes of ventricular tachycardia

• Intermittent cannon a waves can indicate the presence of pacemaker syndrome

Cannon A waves

“M sign” from Pericardial Constriction

The y descent• The presence of a large y descent

indicates restriction of right ventricular filling

• This can be due to intrinsic stiffness of the ventricular wall or occur in a ventricle that is excessively volume-loaded.

• In either case, further volume loading is unlikely to change cardiac output.

Tamponade

• Equalization of right and left atrial pressures suggests either cardiac tamponade or a restrictive process.

• These diagnoses can be distinguished by examining the x and y descents

• Loss of the x and y descent argues strongly for tamponade, whereas the presence of a prominent y descent argues against tamponade

• The reason why the x and y descents are lost in tamponade is that the pericardial fluid keeps the pressure inside the pericardium constant.

• The only time that fluid can enter the pericardial sac is during systole when the ventricles empty and allow the atria to fill.

• During diastole this volume is transferred to the ventricle, again maintaining constant pericardial volume and pressure.

• There is thus no period where pericardial pressure falls and thus no x or y descent.

Respiratory variation in CVP

• The respiratory pattern in CVP can be used to predict fluid responsiveness

• patients who have no inspiratory fall in CVP are on the flat part of their cardiac function curve and will not respond to fluids whereas patients who have an inspiratory fall in CVP are on the ascending part of the cardiac function curve and may or may not respond to fluids, depending how close they start to the plateau

• Patients with an inspiratory fall in CVP are also more likely to have a fall in cardiac output with the application of PEEP

Complications of central venous catheterization

• Complications of central venous cannulationArterial puncture with hematoma Arteriovenous fistula HemothoraxChylothorax Pneumothorax Nerve injury Brachial plexus Stellate ganglion (Horner’s syndrome) Air emboli Catheter or wire shearing

• Complications of catheter presenceThrombosis, thromboembolism Infection, sepsis, endocarditisArrhythmias Hydrothorax

MANAGEMENT OF A PATIENT WITH A CVP LINE

• Monitor the patient for signs of complications

• Label CVP lines with drugs/fluids etc. being infused in order to minimise the risk of accidental bolus injection

• If not in use, flush the cannula regularly to help prevent thrombosis. A 500ml bag of 0.9% normal saline should be maintained at a pressure of 300mmHg.

• Ensure all connections are secure to prevent exsanguination, introduction of infection and air emboli

• Observe the insertion site frequently for signs of infection.

• The length of the indwelling catheter should be recorded and regularly monitored.

• CVP lines should be removed when clinically indicated

REMOVAL OF CENTRAL LINE

• THIS IS AN ASEPTIC PROCEDURE• THE PATIENT SHOULD BE SUPINE WITH HEAD

TILTED DOWN• ENSURE NO DRUGS ARE ATTACHED AND RUNNING

VIA THE CENTRAL LINE• REMOVE DRESSING• CUT THE STITCHES• SLOWLY REMOVE THE CATHETER• IF THERE IS RESISTENCE THEN CALL FOR

ASSISTANCE• APPLY DIGITAL PRESSURE WITH GAUZE UNTIL

BLEEDING STOPS• DRESS WITH GAUZE AND CLEAR DRESSING EG

TEGADERM

PULMONARY ARTERY AND PULMONARYCAPILLARY WEDGE PRESSURE

MONITORING• The introduction of pulmonary artery catheter

(PAC) in clinical medicine one of the most popular and important advances in monitoring.

• With this catheter: PAP, PCWP & CVP can be measured easily under most circumstances provides an accurate

estimate of the diastolic filling (preload) of the left heart

Cardiac output determination using thermo-dilution technique is an equally important use of this catheter

Why PCWP?

• The filling pressure of the right and left ventricle depends on the blood volume, venous tone, ventricular compliance, contractility and after load.

• The left ventricle (LV) is less compliant with greater after load than the right ventricle (RV) and the left sided filling pressure is normally higher than the right

• Under normal circumstances, the right side of the heart and lungs are merely passive conduits for blood and it is possible to discern a relationship between the central venous pressure and the left atrial pressure.

• In health, it is possible to make reasonable assumptions about the relationship between the CVP and the LAP and manipulate the circulation according to the measurements of the CVP

• However, in a critically ill patient and a patient with cardiovascular disease, no such assumptions can be made and conclusions about left heart based on measurements of CVP may be invalid

• Since there are no valves between the pulmonary capillaries and the left atrium, PCWP is a reflection of the LAP.

• During diastole, when mitral valve is open, the PCWP reflects LVEDP.

• LVEDP is an index of left ventricular end-diastolic volume

Indications For PAP & PCWP Monitoring

A. Cardiac problems/surgery: Poor LV function (EF<0.4; LVEDP> 18 mm Hg) Recent MI Pts with right heart failure Procedures involving CPB Complications of MI eg. MR, VSD, ventricular aneurysm. Combined lesions eg. CAD+MR or CAD+AS Complicated lesions eg. IHSS Hemodynamically unstable pts requiring inotropes or IABP counterpulsation Major procedures with large fluid shifts and/or blood loss in pts with CAD

B. Non-cardiac situations: Shock of any cause or MOF Severe pulmonary disease , COPD , PHTN, or PE Pts requiring high levels of PEEP Bleomycin toxicity Complicated surgical procedure Massive trauma Hepatic transplantation

PA (Swan-Ganz) Catheter description

• The standard 7F thermo-dilution pulmonary artery catheter consists of a single catheter 110 cm in length containing four lumina.

• It is constructed of flexible, radio-opaque polyvinyl chloride.

• 10 cm increments are marked in black on the catheter beginning at the distal end.

• At the distal end of the catheter is a latex balloon of 1.5 cc capacity.

• When inflated, the balloon extends slightly beyond the tip of the catheter but does not obstruct it

Balloon is useful in three ways:

(1) it prevents the tip of the catheter from contacting the right ventricular wall during passage and hence reduces the incidence of arrhythmias during insertion

(2) it acts to float the catheter into the PA

(3) inflation of the balloon allows the measurement of PCWP

Distal catheter lumen terminates at the tip of the catheter;It is used to:

measure chamber pressures; PAP & PCWP obtain samples of the mixed venous blood

Proximal catheter lumen terminates 30 cm from the catheter tip placing it in the right atrium (RA) when the distal opening is in the PA. It: carries the injectate necessary for cardiac output computation Can be used to measure the CVP (RAP) can be used to infuse vasoactive drugs

The third lumen carries the electrical leads for thermistor, which is positioned at the catheter surface, 4 cm proximal to the tip

PULMONARY ARTERY CATHETER

Components of a Pulmonary Artery Catheter

Components of Swan-Ganz

• Normally has four [4] ports• Proximal port – [Blue] used to measure

CVP/RAP and injectate port for measurement of cardiac output

• Distal port – [Yellow] used to measure PAP• Balloon port – [Red] used to determine

pulmonary wedge pressure;1.5 special syringe is connected

• Infusion port – [White] used for fluid infusion

Types of PA catheters1.1. The thermo dilution catheter:The thermo dilution catheter:

is the one described above; using this catheter, thermo dilution cardiac output & other divided haemodynamic parameters may be measured

2.2. Pacing:Pacing: Some PAC’s have the capacity to provide

intra cardiac pacing

3.3. Mixed venous oxygen saturation:Mixed venous oxygen saturation: Special fiber-optic PAC can be used to monitor

mixed venous oxygen saturation SVO2 continuously by the principle of absorption and reflectance of light through blood

The normal SVO2 is 75%normal SVO2 is 75% and a 5– 10 % increase or decrease is considered significant

A significant decrease in SVO2decrease in SVO2 may be due to:(a) a decrease in the cardiac output

(b) increase in metabolic rate

(c) decrease in arterial oxygen saturation.

4. 4. Ejection fraction catheter :Ejection fraction catheter :New-catheters with faster thermistor response times

can be used to determine the right ventricular ejection right ventricular ejection fraction in addition to the cardiac outputfraction in addition to the cardiac output

5. 5. Continuous cardiac output measurement :Continuous cardiac output measurement :Continuous cardiac output measuring PACs contain

an integrated thermal filament at level of the RVThis filament is activated in a programmed sequence

to provide small amounts of heat, which is then detected in the PA by a thermistor

The data by the device yields a rapidly updated, near continuous value for cardiac output

Insertion procedure :

• is a simple, rapid and effective technique

• Most anaesthesiologists and critical care physicians choose RIJV approach to insert PAC

• Prior to insertion, all lumina of the PAC are flushed and distal port is connected to transducer system with a continuous wave from display

• With the patient supine and in 30 degree Trendelenberg position, the head is turned to the left side

• The appropriate area of the neck is surgically prepared and draped

• The RIJV is identified with a 22G needle Then an 18G thin walled 5 cm teflon catheter is placed into the vein and threaded down the vessel for a short distance

• The guide wire’s flexible end is passed through the 18 G catheter into the superior vena cava (SVC) and the 18 G catheter removed.

• The skin hole around the guide wire is enlarged with a no. 11 scalpel blade to allow introduction of the dilator set

• The dilator set consists of an internal vessel dilator and an external 10 G catheter sheath

• This combination is passed into the IJV over the guide wire by a twisting motion until the catheter sheath is in the SVC

• Then the 7 F Swan Ganz catheter, which has been filled with fluid and attached to a transducer, is passed through the sheath into the SVC

• Location of the catheter tip in a central vein is confirmed by the pressure changes related to respiration or coughing

• With the catheter in RA, the balloon is inflated with 1.5 ml of air and the PAC is advanced

• Further advancement of the catheter will produce a dramatic change in the pressure tracing as the tip of the catheter enters the RV Pressure changes from that characteristic of RA to a phasic pressure in the range of 25 /0 mm Hg, typical of RV

• The catheter is advanced through the RV until it enters the main PA

• This can be recognized by an increase in the diastolic pressure (25/12mm Hg.) Usually there is no change in the systolic pressure

• The catheter is advanced still further until it wedges in a branch o the PAwedges in a branch o the PA

• It will usually have the appearance of an atrial pressure pattern with a, c and v atrial pressure pattern with a, c and v wave components transmitted wave components transmitted retrogradely from retrogradely from LA(PCWP=8-12 mm LA(PCWP=8-12 mm Hg)Hg)

• PCW position is verified by:the characteristic waveform, a mean pressure lower than the mean PAP

andthe ability to withdraw arterialised blood.

• After achieving a wedge position, the balloon is allowed to deflate

• This should produce a typical PAP tracing

• Reinflation of the balloon should reproduce the wedge tracing with 1.5 ml of air.

• If less than 1.0 ml of air results in a wedge position, the catheter should be withdrawn to the point where 1-1.5 ml balloon inflation is associated with PCWP

INVASIVE HEMODYNAMIC MONITORING

PA Insertion Waves

Components of the Monitoring System

• Bedside monitor – amplifier is located insideThe amplifier increases the size of signal

• Transducer – changes the mechanical energy or pressures of pulse into electrical energy; should be level with the phlebostatic axis (intersecting lines from the 4th ICS,mid axillary line)

Phlebostatic Axis

Pulmonary Artery Pressure Monitoring

• Contraindications– AbsoluteAbsolute

• Tricuspid or Pulmonary valve stenosis• RA or RV masses• Tetralogy of Fallot

– RelativeRelative• Severe arrhythmias• Coagulopathy• Newly inserted pacemaker wires

Complications of Swan-GanzA. Complications of cannulationComplications of cannulation

Arterial puncture (carotid, subclavia) Haematoma, haemothorax Pleural effusion iv) Nerve injury (brachial plexus, stellate

ganglion) Emboli (air, catheter insertion)

B. Complications of catheter insertionComplications of catheter insertion Cardiac perforation Cardiac dysrhythmia , heart block Knotting Tricuspid, pulmonary valve injury

C. Complications of catheter presenceComplications of catheter presence Thrombosis, thromboembolism Infection, endocarditis, sepsis Pulmonary artery rupture iv) Pulmonary infarction

mmHg

Cardiac Output

• Volume pumped by ventricles each minute;

normal = 4 - 8 liters/minute

• Cardiac Output = Heart Rate x Stroke Volume

(CO = HR X SV)

• SV = amount of blood ejected from each ventricle with each contraction;

normal SV = 50 - 100 ml per contraction

Cardiac Index

• Cardiac output (CO) adjusted to body size

• Cardiac index (CI) = CO / body surface area

• Normal CI range = 2.5 to 4.3 L/min/m2

Low Cardiac Output

• Inadequate ventricular fillingdysrhythmias

hypovolemia

cardiac tamponade

mitral or tricuspid stenosis

constrictive pericarditis

restrictive cardiomyopathy

Low Cardiac Output

• Inadequate ventricular emptying

mitral/tricuspid insufficiency

myocardial infarction &/or disease

increased afterload (hypertension)

metabolic disorders (acidosis, hypoxia)

negative inotropic drugs (beta-blockers, calcium channel blockers)

High Cardiac Output

• Increased HR and/or contractility and/or decreased afterload– Sepsis

– Anemia

– Pregnancy

– Hyperthyroid crisis

Determinants of Cardiac Output & Stroke Volume

• Preload - Volume or pressure generated in the ventricles at end diastole

• Afterload – Resistance to ejection of blood from the ventricles

• Contractility – Force of ventricular ejection; difficult to measure clinically

Clinical Measurement of Preload

• Left ventricular end diastolic pressure = LVEDP; measures preload in left ventricle

– Pulmonary artery wedge pressure (PAWP) reflects LVEDP; normal = 8 - 12 mmHg

– If unable to wedge PAC, use PA diastolic

– PA diastolic (PAD); normal = 10 - 15 mmHg

– PAD indirectly reflects left atrial pressure, which indirectly reflects LVEDP

Clinical Measurement of Preload

• Central venous pressure = CVP; measures preload in the right ventricle

– Normal CVP = 2 – 8 mmHg

Factors that Affect Preload

• Anything that alters →

– Circulating blood volume

– Blood returning to the heart

– Ventricular filling time

Factors that Decrease Preload

Affect right & left ventricles (CVP & Wedge)

• Hypovolemia

• Patient position reducing venous return

• Vasodilatation causing blood to pool

• Reduced venous return due to mechanical ventilation - high PIP, high levels of PEEP

• Tension pneumothoraxBlood is not returning to the heart to fill the ventricles.

Factors that Increase Preload

• Intravascular volume overload

• Cardiac tamponade

• Restrictive cardiomyopathies

• Left ventricular dysfunction (↑ PCWP & CVP)

• Right ventricular dysfunction (↑ CVP)

Afterload

• Afterload is any resistance against which the ventricle must pump in order to eject its volume

– Systemic Vascular Resistance (SVR) reflects LV afterload• Normal Range = 800-1200 dynes/sec/cm-5

– Pulmonary Vascular Resistance (PVR) reflects RV afterload• Normal Range =100-250 dynes/sec/cm-5

Factors that Affect Afterload

• Volume & mass of blood ejected from the ventricle– Inverse relationship between afterload

and CO (↑CO = ↓afterload; ↓CO = ↑afterload)

• Compliance & diameter of the vessels into which the blood is ejected

• Aortic impedance, peripheral vascular resistance, and blood viscosity

Decreased Afterload (↓ SVR)

• Arterial dilatation from drugs such as nitroprusside, nitroglycerin, calcium channel blockers, beta blockers

• Shock (septic, anaphylactic, neurogenic)

• Hyperthermia (fever)

Increased Afterload (↑SVR)

• Accomplished by vasoconstriction – Hypothermia– Hypertension– Alpha agonists (pressors)

• Levophed, Dopamine, Phenylephrine, Epinephrine

– Low CO with hypovolemic or cardiogenic shock

• An effect of obstruction– Aortic/pulmonic stenosis

Increased Afterload (↑ PVR)

• Conditions exhibiting increased PVR– Pulmonary hypertension

– Hypoxia

– End-stage COPD (Cor pulmonale)

– Pulmonary emboli

Contractility = Inotropy

• Inherent ability of cardiac muscle to contract

• Reflected indirectly by stroke volume index (SVI) and the stroke work index for each ventricle (LVSWI & RVSWI)

• Influenced by myocardial oxygenation & functionality; electrolyte balance; +/- inotropes; amounts of preload and afterload

Factors/Meds Increasing Contractility

Positive Inotropes• Sympathic stimulation – “fight or flight”• Dobutamine • Epinephrine (Adrenalin)• Norepinephrine (Levophed)• Amrinone (Inocor)• Dopamine (5 – 10 mcg/kg/min)• Calcium; glucagon; caffeine• Digoxin (only oral inotrope)

Factors Decreasing Contractility

Negative inotropes

• Acidemia

• Hypoxia

• Beta blockers

• Anti-arrhythmics

Conditions Resulting in PCWP and LVEDP Discrepancies

• PCWP > LVEDPPCWP > LVEDP– Pos. press. ventilation– PEEP– Incr. Intrathoracic

pressure– Non-west zone III PAC

placement– COPD, Incr PVR– Left atrial myxoma– Mitral valve disease

• PCWP < LVEDPPCWP < LVEDP– Noncompliant LV– AR (premature closure

of mitral valve)– LVEDP > 25 mmHg

ASA Guidelines for PAC Use

Thermodilution Cardiac Output• Cardiac output-monitored in patients who are

hemodynamically unstable.

• Usually the PA catheter is used to measure CO

• Thermodilution technique is often used-a known amount of solution(saline or d5w) of known temperature(room or chilled) is injected rapidly into the right atrial lumen of the PA catheter. A drop in blood temp is detected by a thermister embedded in the catheter tip in the PA.

• CO is then calculated by a computer from the temperature waveform

• CO or CI will be decreased in hypovolemia, shock, heart failure

• Increases may be associated with sepsis prior to septic shock

Mixed venous oxygen saturation

• PA catheters have a sensor located on them which measures oxygen saturation of hemoglobin of pulmonary artery blood which is mixed venous blood

• Normal SVO2 at rest is 60-80%

• Blood gases may also be drawn from the PA line to determine mixed venous blood gas analysis and SVO2

• Don’t expect to be an expert--requires practice and experience as well as vast knowledge of hemodynamics.