CVP, PA Pressure, Cardiac Output Measurements PDF

Central Venous Pressure, Pulmonary Artery Pressure, & Cardiac Output Measurements BIG FANCY WORDS  Objectives ◦ Introduce and discuss risks and benefits of central venous cannulization ◦ Review central line placement technique ◦ Discuss how the central venous pressure...

Central Venous Pressure, Pulmonary Artery Pressure, & Cardiac Output Measurements BIG FANCY WORDS  Objectives ◦ Introduce and discuss risks and benefits of central venous cannulization ◦ Review central line placement technique ◦ Discuss how the central venous pressure (CVP) waveform relates to cardiac cycle and its interpretation ◦ Introduce pulmonary artery (PA) catheters and discuss risks and benefits of their use ◦ Discuss pulmonary artery catheter placement, and how to “Float a Swan” ◦ Introduce and discuss various techniques for monitoring and calculating cardiac output ◦ Small review of echocardiography (continuation of last week) and the TEE probe with common views ◦ Present two small tables of common values for hemodynamic and cardiac values  Central Venous Catheterization ◦ Indicated for monitoring central venous pressure (CVP), administration of fluid to treat hypovolemia and shock, infusion of caustic drugs and total parenteral nutrition (TPN), aspiration of air emboli, insertion of transcutaneous pacing leads, and gaining venous access in patient with poor peripheral veins ◦ May also be used for continuous monitoring of central venous oxygen saturation (SCVO2) ◦ SCVO2 is used as a measure to assess adequacy of oxygen delivery ◦ Decreased SCVO2 (normal >65%) alerts the provider to the possibility of inadequate delivery of oxygen to tissues ◦ Low Cardiac Output ◦ Low hemoglobin ◦ Low arterial oxygen saturation ◦ Increased oxygen consumption ◦ Elevated SCVO2 (>80%) may indicate arterial/venous shunting or impaired cellular oxygen utilization (seen in cyanide poisoning)  Contraindications ◦ Include tumors, clots, or tricuspid valve vegetations that could be dislodged or embolized during cannulation ◦ Other contraindications are related to the cannulation site. The subclavian vein, for example, is contraindicated in patients receiving anticoagulants due to the inability to provide direct pressure in the event of an accidental arterial puncture ◦ Historically, many clinicians avoid puncturing the internal jugular vein on the side of a previous carotid artery surgical intervention due to concerns about unintentional artery puncture ◦ Presence of other central access or pacemaker leads may reduce the number of sites available for line placement ◦ Relative risk of dysrhythmias are common during placement. Incidence of 4.7% to 68.9%  Access Sites ◦ All sites of access carry inherent risks during placement and monitoring ◦ The subclavian vein is associated with greater risk of pneumothorax during insertion, but reduced risks during prolonged cannulation in critically ill patients ◦ Right internal jugular vein provides a combination of accessibility and safety ◦ Left Internal jugular vein has an increased risk of pleural effusion and chylothorax ◦ The external jugular veins can also be used as cannulation sites, but due to their acute angle joining the great veins, they are associated with slightly increased likelihood of failure to gain access to the central circulation than the internal jugular veins ◦ Femoral veins may also be cannulated, but are associated with increased risk of line-related sepsis ◦ Peripheral veins cannulated with long central access catheters are commonly referred to as Peripherally Inserted Central Catheter (PICC) lines  Technique ◦ Cannulation involves introducing a catheter into a vein so that the catheter’s tip lies within the central venous system within the thorax ◦ Optimal location of the catheter tip is just superior to or at the junction of the superior vena cava and right atrium ◦ The catheter tip being located within the thorax causes changes in central venous pressure (CVP) with inspiration depending upon whether ventilation is controlled or spontaneous ◦ Central venous pressure should be measured during end expiration, and is commonly done via electronic transducer (mmHg) or less commonly with a water column (cm H2O) ◦ The following slides will discuss placement technique along with a video of the process  Technique ◦ There are at least three techniques for cannulation ◦ Catheter over needle (similar to peripheral IV) ◦ Catheter through a needle (requires large-bore needle stick) ◦ Catheter over a guidewire (Seldinger technique) ◦ Seldinger technique is used for the overwhelming majority of central line placements (first described in 1953) ◦ For purposes of our discussion, we will be demonstrating placement of a line in the internal jugular from the right side ◦ We will break down the process in a step by step fashion, hopefully similar in nature to what was taught in the sim lab  Technique ◦ 1) Patient is placed in the Trendelenburg position to decrease the risk of air embolism and aid in distention of the internal jugular vein ◦ 2) Practice sterile technique when placing a central venous line, paying attention to full aseptic technique. Utilize hand scrub, sterile gloves, gown, mask, hair cover, bactericidal skin prep (alcohol- based solutions are preferred), and sterile drapes ◦ 3) Locate the two heads of the sternocleidomastoid muscle and the clavicle to form 3-sides of a triangle ◦ 4) If the patient is awake use a small gauge need to infiltrate the area of approach with local anesthetic ◦ 5) Locate the internal jugular vein. Many institutions now use real-time ultrasound guidance to aid in anatomic identification ◦ 5.5) If ultrasound is not available or does not provide an adequate image, use of landmarks is indicated. Advance a needle along the medial border of the lateral head of the sternocleidomastoid toward the ipsilateral nipple, and an angle of 30o to the skin while pointing just lateral to the carotid artery pulse ◦ 6) While advancing the needle, aspirate continuously to obtain venous blood and confirm the needles' location in a vein  Technique ◦ 7) Depending on the kit and equipment available, a secondary needle may be inserted along with the locator needle, with the locator needle being removed once the secondary needle/needle with catheter is located within the vein. Many modern central access kits have a syringe with needle that will allow for advancement of the guide wire through the syringe without the need for both a locator need and placement needle (this will be demonstrated in a video coming up shortly) ◦ 8) Transduction of free blood flow to confirm venous vs arterial pressure using IV extension tubing, or tubing included in the access kit, is recommended before introducing the guidewire ◦ 9) Once the guidewire has been inserted as noticed either by ectopy on the EKG (NOT RECOMMENDED) or preferably by ultrasound confirmation, a dilator is advanced over the wire ◦ 10) Prepare the catheter for placement by flushing each of the ports to remove air using either saline or LR. Cap off each port that is not to be used, leaving the most distal port open to allow the guide wire to pass through the catheter during placement ◦ 11) Pass the catheter over the guidewire, being careful to not lose control of the wire in this process, and once the catheter is in place, remove the guidewire. Upon removing the wire be sure to place a finger or thumb over the connection point on the catheter to help eliminate the possibility of aspiration of air ◦ 12) Connection of the appropriate monitoring tubing or infusion tubing should be secured, followed by placement of a sterile dressing. Final confirmation of adequate placement is confirmed by chest x-ray Technique Technique Technique Video  Risks of Cannulation ◦ Risks of central venous cannulation include: ◦ Line infection ◦ Bloodstream infection ◦ Air or thrombus embolism ◦ Arrythmias indicating the catheter tip is in the right atrium or ventricle ◦ Hematoma ◦ Pneumothorax ◦ Hemothorax ◦ Hydrothorax ◦ Chylothorax ◦ Cardiac perforation ◦ Cardiac tamponade ◦ Trauma to nearby nerves and arteries ◦ Thrombosis  Clinical Considerations ◦ Central venous pressure (CVP) approximates right atrial pressure ◦ Ventricular volumes are related to pressures through compliance, with highly compliant ventricles able to accommodate volume with minimal changes in pressure ◦ Noncompliant ventricles have larger swings in pressure with less volume change ◦ As a result, any one CVP measurement will reveal only limited information about ventricular volumes and filling ◦ A very low CVP may indicate a volume-depleted patient, but moderate to high pressure readings may reflect volume overload, poor ventricular compliance, or both ◦ Using CVP in conjunction with other measure of hemodynamic performance may be a better indicator of a patient’s volume responsiveness ◦ Stroke volume ◦ Cardiac output ◦ Blood pressure ◦ Heart rate ◦ Urine output ◦ Common normal CVP values: 0-8mmHg, or 5-10 cm H2O (10cm H2O = 7.5 mmHg)  CVP Waveform ◦ The shape of the waveform corresponds to the events of cardiac contraction ◦ The waveform consists of five different waves which will be described individually: ◦ a waves are from atrial contraction. They are absent in atrial fibrillation and exaggerated in junctional rhythms (known as “cannon” a waves) ◦ c waves are due to tricuspid valve elevation during early ventricular contraction ◦ v waves reflect venous return against a closed tricuspid valve ◦ x and y descents are caused by the downward displacement of the tricuspid valve during systole and tricuspid valve opening during diastole CVP Waveform  Pulmonary Artery Catheter (PA) ◦ Pulmonary artery catheters (PA or Swan-Ganz catheter) were introduced into routine practice in operating rooms and in coronary and critical care units in the 1970s ◦ These catheters provide measurements of both cardiac output (CO) and pulmonary artery (PA) occlusion and are used to hemodynamic therapy ◦ Pulmonary artery occlusion pressure or wedge pressure, in the absence of mitral stenosis, permit an estimation of the left ventricular end-diastolic pressure (LVEDP) ◦ May also be used to estimate ventricular volume depending on ventricular compliance ◦ PA catheters are also used to perform measurements of cardiac output, allowing for determination of a patient’s stroke volume (SV)  WARNING!1!!1 Next slide has lots of abbreviations and mind-bending explanations about how various cardiac values can be used to help guide care, tread carefully  Pulmonary Artery Catheter (PA) ◦ Using these catheters allows for the diagnosis and monitoring of patients based on obtained measurements ◦ Patients with a diminished SVR, such as those with vasodilatory shock (sepsis), may show an increased SV ◦ Conversely, a reduction in SV may be secondary to poor cardiac performance or hypovolemia ◦ Determination of a “wedge” or pulmonary capillary occlusion pressure (PCOP) by inflating the small balloon at the end of the catheter estimates LVEDP (Left Ventricular End Diastolic Pressure) ◦ Decreased SV in the setting of low PCOP/LVEDP indicates hypovolemia and the need for fluid volume administration ◦ A heart that is “full” (or volume overloaded), which is reflected by a high PCOP/LVEDP and low SV, indicates the need for a positive inotropic drug (helps with ventricular contraction) ◦ Normal or increased SV in the setting of hypotension could be treated with the administration of vasoconstrictor drugs to restore SVR in a vasodilated patient  Pulmonary Artery Catheter (PA) ◦ Use of these correlations and PA catheters became synonymous with treatment approaches to patients with hypovolemia, sepsis, and heart failure in the perioperative intensive care setting and for cardiac anesthesia ◦ Conversely, several large observational studies have shown that patients managed with PA catheters have had worse outcomes than similar patients who were managed without PA catheters ◦ Several other studies indicate that though use of PA catheters to guide patient management may do no harm, they also offer no specific benefits ◦ Despite numerous reports of its questionable utility and the increasing number of alternative methods to determine hemodynamic parameters, these catheters are still utilized more often in the US than elsewhere ◦ Alternative techniques include: ◦ Transpulmonary thermodilution CO measurements ◦ Pulse contour analyses of the arterial pressure waveform ◦ Methods based on bioimpedance measurements across the chest ◦ PA catheters should be considered whenever cardiac index, preload, volume status, or degree of mixed venous blood oxygenation needs to be known Whew….. That’s Over  Pulmonary Artery Catheter (PA) ◦ There are several designs of PA catheters available, but the most popular design integrates five (5) lumens into a 7.5 FR catheter, 110-cm long, with a polyvinylchloride body ◦ The lumens house the following: ◦ Wiring to connect the thermistor near the catheter tip to a thermodilution cardiac output (CO) computer ◦ An air channel for inflation of the balloon ◦ A proximal port 30 cm from the tip for infusions, CO injections, and measurements of right atrial pressures ◦ A ventricular port at 20 cm for infusion of drugs ◦ A distal port for aspiration of mixed venous blood samples and measurements of PA pressure  Technique ◦ PA catheter insertion requires central venous access which can be accomplished using Seldinger’s technique ◦ Instead of a central venous catheter, a dilator and sheath combination is threaded over the guidewire, the guidewire and dilator are removed leaving the sheath in place which contains a lumen to accommodate the PA catheter ◦ Prior to insertion, the catheter is checked by inflating and deflating its balloon and filling all three lumens with IV fluid to remove air. The distal port is connected to a transducer and zeroed to the patient’s midaxillary line ◦ The PA catheter is then advanced through the introducer and into the internal jugular vein ◦ At approximately 15 cm, the distal tip should enter the right atrium, and a central venous tracing should confirm intrathoracic positioning ◦ The balloon is inflated to the manufacturer’s recommendations (usually 1.5 mL) to protect the endocardium from the catheter tip and to allow flow through the right ventricle to direct the catheter forward. NOTE: THE BALLOON IS ALWAYS DEFLATED DURING WITHDRAWL  Technique ◦ Advancement of the catheter may produce ectopy or arrythmias on the EKG. Transient ectopy is common and rarely requires treatment ◦ A sudden increase in systolic pressure on the distal tracing indicates the catheter tip is in the right ventricle ◦ Entry into the pulmonary artery (PA) normally occurs by 35 to 45 cm and is noted by a sudden increase in diastolic pressure ◦ In order to keep the catheter from knotting, the balloon should be deflated, and catheter withdrawn if pressure changes do not occur at the expected distances ◦ Once the tip of the catheter enters the PA, minimal additional advancement results in a pulmonary artery occlusion pressure (PAOP) waveform. A normal PA tracing should reappear when the balloon is deflated ◦ Wedging before maximal balloon inflation signals an overwedged position, and the catheter should be withdrawn slightly to minimize the chance of PA rupture from balloon overinflation ◦ Wedge readings should be obtained infrequently, and PA pressures should be continuously monitored to detect and overwedged position indicative of catheter migration ◦ Correct positioning of a PA catheter is confirmed by chest x-ray  Technique GUIDEWIRE & SHEATH CATHETER COVER Technique Video “Floating a Swan”  Contraindications and Complications ◦ Relative contraindications include: ◦ Left bundle-branch block (which could lead to complete heart block with pre-existing right bundle branch block) ◦ Infection, especially in patient who may already be bacteremic ◦ Thrombus formation in patients prone to hypercoagulation ◦ These catheters have numerous complications, including all of those associated with central venous cannulation ◦ Endocarditis ◦ Thrombogenesis ◦ Pulmonary infarction ◦ Pulmonary artery (PA) rupture (early indication may be trace hemoptysis) ◦ Hemorrhage ◦ Catheter knotting ◦ Arrythmias ◦ Conduction abnormalities ◦ Pulmonary valvular damage ◦ Complication risk increases with length of catheterization time which usually should not exceed 72 hours  Cardiac Output ◦ One of the primary reasons for placement of a PA catheter is calculation of stroke volume (SV) ◦ There are, however, several alternative less invasive methods to estimate ventricular function and assist in goal-directed therapy ◦ Each of the following methods will be discussed independently: ◦ Thermodilution ◦ Dye Dilution ◦ Pulse Contour Devices ◦ Esophageal Doppler ◦ Thoracic Bioimpedance ◦ Fick Principle ◦ Echocardiography  Thermodilution ◦ Cardiac output measurement via thermodilution uses the injection of a quantity of fluid (2.5, 5, or 10 mL) that is below body temperature (either room temperature or iced) into the right atrium that changes the temperature of blood in contact with the thermistor on the tip of a PA catheter ◦ The degree of change is inversely proportional to cardiac output (CO) ◦ Temperature change is minimal if there is a high blood flow ◦ Temperature change is greater when flow is reduced ◦ After injection, the temperature is plotted as a function of time to produce a thermodilution curve, which a computer uses to integrate the area under the curve and calculate CO ◦ Accurate measurements depend on rapid and smooth injection, precisely known injectant temperature and volume, correct entry of calibration factors for the specific type of PA catheter in use, and avoidance of measurements during electrocautery ◦ Tricuspid regurgitation and cardiac shunts invalidate results because only right ventricular output into the PA is being measured  Thermodilution ◦ A modified technique allows for continuous CO measurement with a special catheter and monitor system ◦ The catheter contains a thermal filament that introduces small pulses of heat into the blood proximal to the pulmonic valve and a thermistor that measures changes in PA blood temperature ◦ A computer determines CO by cross-correlating the amount of heat input with the changes in blood temperature ◦ Another transpulmonary system (PiCCO®) relies upon the same principles of thermodilution, but does not require PA catheterization ◦ A central line and a thermistor-equipped arterial catheter (usually placed in the femoral artery) are necessary ◦ Cold indicator is injected into the superior vena cava via a central line, the thermistor notes the change in temperature in the arterial system following the cold indicator’s transit through the heart and lungs and estimates CO  Thermodilution ◦ The PiCCO® system calculates SV variation and pulse pressure variation through pulse contour analysis, both of which can be used to determine fluid responsiveness ◦ Both SV and pulse pressure are decreased during positive-pressure ventilation ◦ Greater variations over the course of positive- pressure inspiration and expiration, lead to the idea the patient is more likely to improve hemodynamic measures following volume administration ◦ Pulse pressure variation and stroke volume variation become less reliable when arrythmias are present  Dye Dilution ◦ Injection of an indicator such as indocyanine green dye or lithium through a central venous catheter can be measured and analyzed from arterial blood samples with the appropriate detector ◦ The area under the resulting dye indicator curve is related to cardiac output ◦ Systems that analyze both arterial blood pressure and integrate it with CO can also calculate beat-to- beat SV ◦ A systems that uses lithium (LiDCOTM) has a small bolus of lithium chloride injected into the circulation which utilizes a lithium-sensitive electrode in an arterial catheter to measure decay in lithium concentration over time ◦ This device also uses pulse contour analysis similar to the PiCCO® thermodilution device to provide ongoing beat-to-beat determinations of CO and other calculated parameters ◦ Lithium dilution can be used in patients who have only peripheral venous access ◦ Contraindications: Lithium should not be administered to patients in the first trimester of pregnancy, background tracer buildup may affect use over time, and nondepolarizing muscle relaxants may affect the lithium sensor  Pulse Contour Devices ◦ Pulse contour devices use the arterial pressure tracing to estimate CO and other dynamic parameters, such as pulse pressure and SV variation with mechanical ventilation ◦ The indices provided by these devices are useful in determining if hypotension is likely to respond to fluid therapy ◦ Pulse contour devices reply upon algorithms that measure the area of the systolic portion of the arterial pressure trace from end diastole to the end of ventricular ejection ◦ Some devices rely first on transpulmonary thermodilution or lithium thermodilution to calibrate the machines for subsequent measurements  Esophageal Doppler ◦ This technique relies upon the Doppler principle to measure the velocity of blood flow in the descending thoracic aorta ◦ Blood in the aorta is in relative motion compared with the Doppler probe in the esophagus, and as red blood cells travel, they reflect a frequency shift, depending upon both the direction and velocity of their movement ◦ Blood flows toward the transducer reflect at a higher frequency than that which is transmitted by the probe ◦ Blood flows away from the transducer reflect at a frequency than that which was initially transmitted by the probe ◦ The Doppler equation is used to determine the velocity of blood flow in the aorta ◦ The equation calculates the SV of blood in the descending aorta, and knowing the heart rate allows for calculation of the portion of CO flowing through the descending thoracic aorta, which is approximately 70% of total CO. The monitor corrects for the other 30% allowing it to estimate the patient’s total CO ◦ This technique relies upon many assumptions and nomograms (mathematical device or model that shows the relationship between two variables) which may limit its ability to accurately reflect CO in a variety of clinical situations  Thoracic Bioimpedance ◦ Thoracic volumes can cause changes in thoracic resistance (bioimpedance) to low amplitude, high frequency currents ◦ If changes in bioimpedance are measured following ventricular depolarization, SV can be continuously determined ◦ This is a noninvasive technique that required six electrodes to inject microcurrents and to sense bioimpedance on both sides of the chest ◦ Increasing fluid in the chest results in less electrical bioimpedance which allows for mathematical assumptions and correlations to be made allowing for calculation of CO from changes in bioimpedance ◦ Disadvantages of such systems include susceptibility to electrical interference and reliance upon correct electrode positioning ◦ The accuracy of this technique is questionable in patients: ◦ With aortic valve disease ◦ Previous heart surgery ◦ Acute changes in thoracic sympathetic nervous function (i.e., spinal anesthesia) Thoracic Bioimpedance  Fick Principle ◦ The Fick Principle is the basis of all indicator-dilution methods of determining CO ◦ Mixed venous and arterial oxygen content are easily determined if a PA catheter and arterial catheter are in place ◦ The amount of oxygen consumed by an individual (VO2) equals the difference between arterial and venous oxygen content (Cao2 and Cvo2) multiplied by cardiac output  Echocardiography ◦ A powerful tool for use in diagnosing and assessing cardiac function perioperatively and intraoperatively via TTE and TEE ◦ Both can be employed preoperatively and postoperatively with TTE being completely noninvasive ◦ TEE is the ideal option to visualize the heart, and useful in the operating room where access to the patient's chest may be limited ◦ Disposable TEE probes are now available that allow them to remain positioned in critically ill patients for days during which intermittent examinations can be performed ◦ Anesthesia staff can use echocardiography in two ways, basic (hemodynamic) or advanced (diagnostic) ◦ Basic use allows for the determination of why a patient might be hypotensive, to see if the heart is adequately filled, contracting appropriately, not externally compressed, and devoid of any grossly obvious structural defects ◦ Advanced use allows for recommendations both therapeutic and surgical based upon TEE interpretations  Echocardiography ◦ Echocardiography has many uses, including: ◦ Diagnosis of the source of hemodynamic instability, including myocardial ischemia, systolic and diastolic heart failure, valvular abnormalities, hypovolemia, and pericardial tamponade ◦ Estimation of hemodynamic parameters, such as SV, CO, and intracavitary pressures ◦ Diagnosis of structural diseases of the heart, such as valvular heart disease, shunts, and aortic diseases ◦ Guiding surgical interventions, such as mitral valve repair TEE Probe TEE Views Who Likes Memorization? Common Hemodynamic Values Common Cardiac Values The End….. For Now