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Hemodynamics med surg week 3
Nursing Care- Complex Health Problems II (11-63-375)
University of Windsor
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Hemodynamics
Hemodynamic Monitoring
Ongoing measurement of pressure, flow, and oxygenation in the cardiovascular system Invasive and non-invasive Why do it? o Adequacy of tissue perfusion o Adequacy of oxygen delivery o Oxygen delivery- amount of oxygen delivered to whole body from lungs
Cardiac Output
Essential for supply of oxygen and nutrients to all cells Amount of blood pumped by heart in one minute (N = 4-8 L/min) o C. O. = HR x SV (amount pumped per beat; N = 60- ml/beat) Cardiac Index (N = 2.5-4 L/min/m 2 ) o C. / Body Mass Index o An adjustment for C. based on body size
- Preload
- Afterload
- Contractility a. Strength of myocardial contraction b. Resistance that ventricles must overcome to eject contents c. Myocardial stretch/volume at end of diastole
What is the interaction between HR and CO?
Increasing HR results in?
o Always? Lower HR results in? o Always?
Heart Rate as Determinant of CO
In general, the higher the heart rate, the higher the cardiac output o Ex. HR x SV = CO o 60/min x 80ml= 4800 ml/min (4 L/min) o 70/min x80ml = 5600ml/min (5/min) BUT o Very high HRs decrease diastolic filling time, reducing SV and CO o HR below 50 will not further increase filling because heart is already full
Preload as Determinant of CO
Volume of blood in ventricles at end of diastole (amount available for ejection) Related to stretch of myocardial fibres o Starling’s law Relationship between myocardial stretch, volume, and pressure? Preload affected by o Vascular volume o Drugs (vasodilators/vasoconstrictors) o Sympathetic tone Vasoconstriction/vasodilation o Atrial kick o Heart failure
Right Ventricular Preload
Generally measured as right atrial pressure (RAP) or central venous pressure (CVP) Normal = 0-8mm Hg Reflects venous return to heart Factors that affect CVP/RAP o See previous slide o Right ventricular failure o Pulmonary embolism, pulmonary HTN
Left Ventricular Preload
Normal = 4-12mmHg See factors affecting preload Increased with LV failure Generally measured as left atrial pressure, pulmonary artery diastolic pressure, pulmonary artery occlusive pressure
Afterload as Determinant of CO
Afterload = resistance that ventricles must overcome to force valves open and eject blood Inversely related to stroke volume/cardiac output Each ventricle has its own afterload Factors affecting afterload o Valvular stenosis o Vascular resistance/tone (vasoconstriction/vasodilation) o Polycythemia o Vascular volume o Drugs (vasoconstriction/dilation)
Right Ventricular Afterload
Factors influencing SvO o Oxygen Delivery Factors Cardiac output Hemoglobin Arterial O 2 saturation o Tissue Metabolism O 2 extraction/consumption
Factors that decrease SvO
Decreased SVO 2 indicates: o Decreased O 2 delivery (Hgb, CO, or SaO 2 ) OR o Increased O 2 demand, leading to increased extraction
Factors that increase SvO
Elevated SVO 2 is most commonly due to sepsis (secondary to impaired ability to extract O 2 from arterial blood)
Assessment of CV system- Hemodynamic Monitoring
Measurement of pressure, flow and oxygenation within cardiovascular system o Arterial Pressure Monitoring Invasive and non-invasive o CVP Monitoring o Advanced Hemodynamic Monitoring via Pulmonary artery catheter (invasive) Minimally invasive hemodynamic monitoring (e., Vigileo) Non-invasive hemodynamic monitoring
Arterial Pressure Monitoring
Non-invasive- manual or automated Invasive Direct and continuous BP measurement Catheter placed directly in an artery o Rigid fluid filled tubing connects artery to transducer o Transducer converts mechanical energy (pressure) into electrical energy → graph Also allows arterial blood sampling Radial artery - most common site o Assess circulation prior to insertion: Allen test Transducer position o level with heart (4th intercostal space and mid-axillary line) – “phlebostatic axis” Zero the transducer o eliminates effect of atmospheric and hydrostatic pressures Keep pressure bag inflated o Maintains ~ 3-5 cc flush/hr to prevent clotting Alarms on; set at appropriate limits Keep insertion site visible Dressings, tubing changes Assess distal circulation
CVP Monitoring
CVP is a measure of _____________? CVP provides information about ___?
Measured in various ways, commonly by connecting a catheter in vena cava to a pressure monitoring system. Transducer or manometer must be leveled Insertion sites o Internal jugular o Subclavian vein o Femoral vein Tip in superior vena cava Intermittent CVP measurements using H 2 O manometer Continuous CVP with catheter connected to transducer and monitor
Advanced Hemodynamic Monitoring
Pulmonary artery catheter (invasive) Minimally invasive hemodynamic monitoring (e., Vigileo) Non-invasive hemodynamic monitoring
Pulmonary Artery Catheter
Invasive Measures right and left-sided intra-cardiac pressures To assess and establish/maintain adequate perfusion (C) Inserted in major vein and threaded → inferior or superior vena cava → RA → RV → pulmonary artery Provides measures of: o Preload: CVP/RAP, left sided preload (wedge) o Afterload: SVR (left side) and PVR (right side) o Pulmonary artery pressures o Cardiac output / cardiac index o SVO 2 o ++ Less commonly used than previously because: o Invasive with potential for significant complications o Availability of less invasive, more reliable approaches to achieve similar (or better) outcomes
Minimally Invasive Hemodynamically Monitoring
Prototype: FloTrac/Vigileo system o Less invasive approach to hemodynamic monitoring o Uses arterial waveform and complex calculations to determine stroke volume Larger pulse pressure reflects larger SV and thus higher CO Provide continuous data on: o CO; SV, SVR (and their “indexes), SVV (change in SV with each heartbeat) For certain patients (ventilated only), provides indicators of where preload is on the Frank-Starlings curve, thus indicating fluid “responsiveness” Passive leg raising o Provides an indication of fluid responsiveness (i., preload status) o Mimics fluid bolus without giving fluid. o Does leg raise increase SV? If yes, an indication of “fluid responsiveness” (needs fluid)
Non-Invasive Hemodynamic Monitoring
Uses a finger cuff with an infrared light system and an inflatable bladder to continuously measure BP and CO. Also provides measures of SV, pulse rate, SVV, SVR
Hemodynamics med surg week 3
Course: Nursing Care- Complex Health Problems II (11-63-375)
University: University of Windsor
