Hemodynamic Monitoring Flashcards
Goals of the CV System
- deliver oxygen and nutrients
- remove waste
Hemodynamics
- mvmt of blood through the closed circulatory system
influenced by:
- BP
- blood flow
- characteristics of blood (viscosity, hydration, etc)
MAP Formula
MAP = CO x SVR
CO = HR x SV
Blood Flow Formula
Systolic Pressure
- max pressure
- pressure exerted when heart beats (systole)
- reflects volume and speed of ejection and compliance of the aorta
Diastolic Pressure
- minimum pressure
- pressure exerted in between heart beats
- reflects vascular resistance and compentence of the aortic valve
Circle of Life Visual
MAP
- best indicator of tissue perfusion!
- average driving pressure of blood during the cardiac cycle
- MAP used to titrate pressures for induced hypotension or calculation of CPP
Pulse Pressure
PP = SBP - DBP
- reflects difference in volume ejected from LV into arterial vessels and volume that is already there
- function of SV and SVR
Widened PP
- increased SV and decreased SVR
- sepsis
Narrow PP
- decreased SV and increased SVR
- atherosclerosis
Arterial Pressure Monitoring
NIBP: auscultation or automatic (oscillometric)
Art Line: continuous pressure transduction
Auscultation
- normal laminar flow in arteries produces little vibration and no sound
- when artery is constricted, blood flow becomes turbulent causing the artery to vibrate and produce sounds
Karotkoff Sounds
- turbulent flow that occurs when cuff pressure is >diastolic and <systolic></systolic>
<p>- tapping sounds associated w turbulent flow</p>
<p> </p>
</systolic>
Automatic Oscillometric Approach
- even when sounds are barely audible, the oscillometric method can pick up the vibrations
Automatic BP Monitoring
- measures oscillations in machine umbilical cable
- measures MAP (point of max oscillation amplitude) and calculates SBP and DBP from formulas that examine the rate of change of the pressure pulsations
- SBP identified as the pressure at which the pulsations are increasing and are at 25% to 50% of max
- DBP is the most unreliable measurement and is recorded when the pulse amplitude has decreased to a small fraction of its peak value
Comparison of BP Measurements Between Korotkoff Sounds and Oscillometry (Visual)
Limitations of Oscillometric Measurement
- Motion artifact
- Bruising at cuff site
- Nerve damage
- Arterial or intravenous occlusion during inflation.
- If proximal to pulse oximeter, damping of pulse ox waveform and reading
- If SBP below 80, NIBP often over estimates MAP.
- Must have correct cuff size
- Dysrhythmias make values difficult to interpret or increase cycle time.
BP Cuff Sizing
- ensure bladder length is 80% of arm circumference
Troubleshooting Automatic NIBP
- air leaks at cuff, tubing, or connection to unit
- pt must keep arm still
- disconnect and reconnect to reset
- most default to q5 min, increase to q2.5 min for induction
Invasive Arterial BP Monitoring
• Most accurate way to monitor beat to beat blood pressure and easy access to blood gas monitoring.
– Hemodynamic instability or predicted instability.
– Surgical procedure with anticipated significant blood loss or fluid shifts
– Monitoring of induced hypotension
– Monitoring response to vasoactive drugs
– NIBP is not feasible (burns, obese, shock)
– Repeated blood sampling
Invasive Art Line Waveform
- shape depends on force generated by ventricle
- speed of ejection
- compliance of arterial vessels
- rate of forward blood runoff (dependent on resistance to forward flow or SVR)
Troubleshooting Pressure Monitoring System
- keep it simple: minimize stopcocks, long tubing
- remove air bubbles
- zero line to midaxillary or phlebostatic axis (RA)
Location of Phlebostatic Axis
- 4th intercostal space midaxillary line
- location of RA, where the tip of a CVP would lie
- if below, BP will be erroneously high
- if above, BP will be erroneously low
Pressure Transducers: Normal vs Dampened/Overdampened (Visual)
Art Line Complications
- Distal ischemia, pseudoaneurysm
- Hemorrhage, hematoma
- Aterial embolization
- Local infection, sepsis
- Peripheral neuropathy
- Misinterpretation of data
Systolic Pressure Variation
- mechanical ventilation
- pulsus paradoxus is >10mmHg
- normally doesn’t exceed 10mmHg
Pulse Pressure Variation
- normal should not exceed 13%
- (PPV) = (PPmax – PPmin) / PPmean
CVP Monitoring
- indication of RVEDV or Preload (fluid status)
- normal 6-10
• If abnormal, collect venous blood oxygenation samples
– Global tissue perfusion and oxygenation
High CVP
- persistant hypotension following fluid bolus and high CVP = myocardial congestion (MI, tamponade, tension pneumo)
Low CVP
low CVP, tachycardia, and hypotension = hypovolemia
CVP Catheter Types
- single lumen: rapid, high volume resuscitation or pressure monitoring
- multi lumen: drug therapy, nutrition support, pressure monitoring
CVP Waveform
- a -‐ atrial contraction, absent in a fib, larger in tricuspid stenosis, pulmonary stenosis and pulmonary HTN
- c – due to bulging of tricuspid valve into RA
- x -‐ atrial relaxation
- v -‐ rise in arterial P before tricuspid valve opens
- y -‐ atrial emptying as blood enters ventricle
CVP Waveform (Visual #2)
Pulmonary Artery Pressure Monitoring
• Better indicator of left heart pressure than CVP, especially when:
– LV function is impaired
– Significant valvular disease
– Pulmonary HTN
• PCWP – Best estimation of LVEDV (left V preload)
• CO – Thermodilution
• SVO2 (mixed venous oxygen saturation)
– Evaluate oxygen consumption and delivery
PA Catheters
- multi-lumen polyvinylchloride catheter w balloon at tip
- inflation of balloon ensures that blood flow will move balloon/catheter forward in the direction of blood flow
Insertion of PA Catheter
- R heart catheterization w large bore introducer sheath
- typically via subclavian or IJ veins
- seldinger technique (introducer then guidewire then catheter over wire)
Prior to Insertion of PA Catheter
- Flush all lumens with solution
- Check integrity of balloon
– Always deflate passively
- Prepare transducer system that has been leveled and zeroed.
- Connect lines to appropriate lumens
– PA pressure monitor is distal
– CVP pressure monitor is proximal
Catheter Insertion
- PA catheter is inserted to a depth of 20cm.
- A CVP waveform must be idenAfied to confirm that the PAC type is in the R vena cava or atrium.
- Balloon then fully inflated, blood will carry or float the catheter through the RA, RV and into the PA.
Progression of PA Catheter (Visual)
PA Catheter Measures
Systolic: 15-30 mmHg
Diastolic: 5-15
PACWP: 4-14
Thermodilution CO
- cold water injected through PA catheter and the change in temp from proximal to distal ends of catheter is measured and analyzed against time
- thermistor tip
Complications of CVP and PA Lines
- Infection
- Pneumothorax
- Vessel erosion or perforation
- Venous air embolism
- Hemorrhage (rupture of PA)
- Cardiac dysrhythmias
LiDCO
- lithium dilution cardiac output
- minimally invasive continuous CO monitoring
• Uses the pulse pressure analysis algorithm for continuous measurement of changes in CO
– Derive SV from arterial pressure waveform
– Calculate HR
– CO = SV*HR
– calibration
• Provides info on SV variation and pulse pressure variation
EKG
• Monitors electrical impulses through the heart
– HR
– Arrhythmias
– Myocardial ischemia
– Pacemaker function
– Electrolyte abnormalities
– NOT contractility or output! (PEA)
How does EKG monitoring work?
- Silver chloride electrode with a conductive gel which decreases the electrical resistance of the skin.
- A very small electrical signal is amplified and then broadcasted over a 0.01 to 250 Hz bandwidth.
- Prone to electrical interference
– Clean dry skin
EKG Lead Placement
• Lead II – Rhythm detection
– P waves
– Inferior portion of the heart supplied by the RCA
• Lead V5 – Bulk of the LV supplied by LAD placed 5th intercostal space anterior axillary line
• Lead I – Circumflex artery
Respiratory Impedence of EKG
- Impedance pnuemography
- In short, measures movement of the chest electrodes.
- Anesthesia monitors do not default to show this, but helpful with sedation cases.
Pulse Oximetry
- measurement of arterial Hgb oxygenation
- oxygenation and deoxygenated blood absorb light differently
oxyHgb: infrared, 940nm wavelength
REDuced Hgb: red, 660 nm
Pulse Ox: Beer-Lambert Law
- Measure “pulsatile signals across perfused tissue at two discrete wavelengths”
- Absorbance of light indicates state of hemoglobin
- Two Light Emi|ng Diodes (LEDs)
– Infrared (940 nm wave length) – oxyhemoglobin
– Red (660 nm wave length) -‐ REDuced hemoglobin
• Light detector
Light Absorbance Visual
Carboxyhemoglobin
- CO poison
- appears like oxyHgb at 660 nm
- raises appearance of oxygenated Hgb
- falsely HIGH readings
Methemoglobin
- benzocaine, methylene blue
- gives a sat of 85% no matter what the true oxygenation is
