CVP Lecture 1 PDF

Monitoring Central Venous Pressure “CVP” Objectives • Define central venous pressure (CVP) • Relate CVP to right and left heart failure • Describe all factors that increase and decrease CVP • Understand the relationship of CVP and Venous Return • Know the sites for CVP insertion • Evaluate the CVP...

Monitoring Central Venous Pressure “CVP” Objectives • Define central venous pressure (CVP) • Relate CVP to right and left heart failure • Describe all factors that increase and decrease CVP • Understand the relationship of CVP and Venous Return • Know the sites for CVP insertion • Evaluate the CVP waveform and all it’s components • Understand clinical relevancies of EKG rhythm changes on CVP Definition • Central Venous Pressure (CVP) • • Known as right atrial pressure (RAP) it describes the pressure of blood in the vena cava (great thoracic veins) as it returns deoxygenated to the heart. CVP indirectly REFLECTS the amount of blood (VOLUME) returning to the heart, and the ability of the heart to pump the blood into the arterial system. Central Venous Pressure (CVP) • Very good approximation of right atrial pressure, which is a major determinant of right ventricular end diastolic volume (RVEDV) • This can be seen as “Preload” for the right heart • Direct means of assessing right heart function • Indirect means of assessing left heart function Chamber Pressure and Saturation Chamber Pressure (mmHg) O2 Saturation (%) Right Atrium (0 to 8) 65 to 80 Right Ventricle [15 to 25] / [0 to 8] 65 to 80 Pulmonary Artery [15 to 25] / [8 to 15] 60 to 80 Mean Pulmonary 10 to 20 -- PCWP (6 to 12) -- Left Atrium (0 to 10) 95 to 99 Left Ventricle [90 to 140] / [0 to 10] 95 to 99 Aorta [90 to 140] / [60 to 90] 95 to 99 Mean Arterial 70 to 105 -- ( ) Mean pressure Questions about the CVP Why is CVP a direct assessment of RV filling pressure? • CVP correlates with RVEDP (filling pressure) • The ventricle is preloaded by venous return • This correlation is possible because, when the TV is open RA-RV communication occurs • This means pressures equilibrate at end RV diastole RA and RV Equilibration Why is CVP an indirect assessment of LV function? Normally, RVEDP and LVEDP correlate well : LVEDP = ( 2 x RVEDP ) + 2 So if: RVEDP (CVP) = 4 LVEDP = (2 x 4) + 2 LVEDP (LAP) = 10 This ONLY pertains to healthy hearts When differences occur in left and right heart function the correlation goes out the window Failing LV (RV compensates-for now) Factors that affect CVP Factors That INCREASE CVP • • • • • • • • Hypervolemia (volume overload / perfusionist overfilling) Forced exhalation Tension pneumothorax Heart failure Pleural effusion Decreased cardiac output Cardiac tamponade Mechanical ventilation and the application of positive end-expiratory pressure (PEEP) Factors That DECREASE CVP • Hypovolemia (perfusionist underfilling) or • Hypovolemia (volume loss-bleeding) • Deep inhalation • Shock • • https://www.suto ri.com/item /respiratory-pump-0747 Inspiration causes the lungs, right atrium, right ventricle, superior vena cava, and inferior vena cava, to expand. When these expand, the vascular and cardiac pressures fall. https://www.cvphysiology.com/Cardiac%20Function/CF018 Respiratory Activity (Abdominothoracic or Respiratory Pump) https://www.cvphysiology.com/Cardiac%20Function/CF018 • • • • • • https://www.sutori.com/item/respiratory-pump-0747 The respiratory system also affects venous return. During inspiration, the intrapleural pressure: the pressure between organs in the thoracic cavity (example, the pressure between the heart and the lungs), becomes more negative. This causes the lungs, right atrium, right ventricle, superior vena cava, and inferior vena cava, to expand. When these expand, the vascular and cardiac pressures fall. The right atrial pressure is important for the pressure gradient of venous return. When right atrial pressure falls, venous return pressure increases. CVP and Venous Return Since CVP reflects blood returning to the heart under nominal amounts of pressure, this measurement is correlated to venous return CVP and Venous Return Venous Return Circulatory system has pulmonary and systemic circulations. Balance is achieved by Starling’s law: • Venous return is the flow of blood back to the heart. Venous return must equal cardiac output when averaged over time. (a closed loop system). • Otherwise, blood would accumulate in either the systemic or pulmonary circulations. Venous Return Circulatory system has pulmonary and systemic circulations. Balance is achieved by Starling’s law: how to think it through…progression… • If systemic venous return is suddenly increased, RV preload increases causing an increase in SV and increased pulmonary blood flow. • The LV then experiences an increase in pulmonary venous return, which in turn increases LV preload and SV. Venous return will match cardiac output over time Venous Return • Venous return to the heart from the venous vascular beds is via a pressure gradient (venous pressure - right atrial pressure) and venous resistance • Therefore, increases in venous pressure will lead to an increase in venous return. (It’s a gradient) • Although the above relationship is true for the hemodynamic factors that determine the flow of blood from the veins back to the heart, it is important not to lose sight of the fact that blood flow through the entire systemic circulation represents both the CO and the venous return, which are equal. Factors Affecting Venous Return Remember: Your Volume is Mostly Venous 6 Factors Affecting Venous Return I. II. Musculo-venous pump: Contraction of limb muscles during normal locomotion (walking, running, swimming) promotes venous return by the muscle pump mechanism. (n/a on CPB) https://www.sutori.com/item/skeletal-muscle-pump286c Decreased venous capacitance: Sympathetic (fight or flight) activation of veins decrease venous compliance, increase venous tone, increase CVP and venous return, which increases blood flow through the circulatory system. 6 Factors Affecting Venous Return III. Respiratory pump: During inspiration, the intrathoracic pressure is negative (suction of air into the lungs), and abdominal pressure is positive (compression of abdominal organs by diaphragm). IV. Vena Cava Compression: An increase in the resistance of the vena cava, when the thoracic vena cava becomes compressed decreases venous return. There is a pressure gradient between the infra- and supradiaphragmatic parts of the IVC, "pulling" the blood towards the right atrium. 6 Factors Affecting Venous Return V. Gravity: The effects of gravity on venous return seem paradoxical, when a person stands up hydrostatic forces cause the RAP to decrease and the venous pressure in the limbs to increase. This increases the pressure gradient for venous return from the dependent limbs to the right atrium; however, venous return decreases. The reason for this is when a person initially stands, cardiac output and arterial pressure decrease (because right atrial pressure falls). The flow through the entire systemic circulation falls because arterial pressure falls more than right atrial pressure; therefore the pressure gradient driving flow throughout the entire circulatory system is decreased. (orthostatic hypotension) 6 Factors Affecting Venous Return VI.Pumping Action Of the heart: During the cardiac cycle atrial pressure changes alter CVP. The CVP is altered because there is no valve between the heart's atria and the veins. Atrial pressure changes venous pressure and therefore alters venous return. Monitoring the Central Venous pressure Catheters and Insertion Sites CVP Insertion Sites CVP is monitored via a catheter inserted toward the right atrium Catheters differ: • • • • • • • in length, internal diameter, number of channels (access ports), method of insertion , material and means of fixation. Two lengths: 20 cm catheters for subclavian vein and • 60 cm catheters for femoral venous access • internal jugular vein lines Indications for Central Venous Cannulation Admission of fluids and electrolytes Drug therapy Access for monitoring central venous pressure Access for insertion of a pulmonary artery catheter Administration of blood and blood components Parenteral nutrition Insertion of trans-venous pacemaker Lack of accessible peripheral veins Coagulopathy Thrombolytic therapy Anticoagulation Contraindications for Central Venous Cannulation Infection at proposed site High risk of pneumothorax (PEEP, CPAP, emphysema) Severe vascular disease at proposed site Distorted vascular anatomy Suspected vena caval injury Combative patient Unsupervised, inexperienced operator CVP Insertion Sites Selection of the insertion site should be based both on the ease of placement and on the risks associated with the procedure. • Subclavian • Internal Jugular • External Jugular • Femoral • Antecubital Subclavian Vein is associated with a lower risk for infection Subclavian Vein Advantages n n n n Easy access Unrestricted neck and arm movement Less likely to displace catheter once in position Reduced incidence of thrombotic complications Disadvantages n n n n n n n Risk of air embolism Potential vessel damage Risk of pneumothorax Phrenic nerve or brachial nerve injury Possible tracheal perforation Possible endotracheal tube cuff perforation Risk of major complications increased in patients with prior surgery in the area, emphysema and mechanical ventilation Triple Lumen Subclavian Access Internal/External Jugular is associated with a low rate of severe mechanical complications in the intensive care unit as compared with subclavian access External jugular vein: easier access Internal Jugular Vein Advantages n n n n Relatively short / direct pathway for the catheter Reliable site for correct catheter placement Catheter displacement not likely Decreased chance of thrombotic complications Disadvantages n n n n n Risk of air embolism Potential vessel damage Risk of pneumothorax Possible tracheal perforation Possible endo-tracheal tube cuff perforation Jugular CVP Line Femoral Vein is associated with a higher risk for infection and thrombosis (as compared with the subclavian route) Femoral Vein Disadvantages Advantages § § § § § Readily available Been used by clinicians for central access longer than any other site Greater ease of insertion in elderly patients with convoluted subclavian and jugular veins No risk of pneumothorax Minimal risk of air embolism § § § § § Presence of smaller vessels may complicate insertion Possible increased risk of infection due to proximity to groin Difficult to maintain an intact, sterile dressing Thrombosis of femoral vein is high risk for pulmonary embolism Difficulty immobilizing leg; increased risk of catheter displacement Antecubital Site Antecubital Site Advantages n n No risk of pneumothorax or major hemorrhage Bleeding from site more easily controlled in patients with coagulopathies or anticoagulation Disadvantages n n n n n n n Difficult to locate in obese or edematous patients Advancement of catheter to central veins may be difficult Vein may not be large enough to accept largelumen catheter Access may be limited because of previous cutdown or venipuncture Venous spasm may prohibit catheter passage Catheter displacement more common Increased risk of vessel thrombosis Thank you