What generates the waveform seen in arterial line monitoring? (Hint: It’s basically a Fourier analysis of two separate sine waveforms from two sources)
- Ejection of blood from LV into aorta during systole
- Peripheral arterial runoff of this same SV during systole
(The second is a sine wave displaced on the x-axis to the right with smaller amplitude)
In a normal A-line reading, what does the peak and trough represent?
Peak = peak systolic pressure
Trough = end diastolic pressure
What are the indications for A-line palcement?
- The need for real-time BP control (for example, pt has ruptured aneurysm(s))
- Anticipated or known hemodynamic instability
- The need to monitor response to vasoactive drugs in a continuous fashion
- Procedures that involve significant blood loss or fluid shifts
- Monitoring the safety of anesthetic techniques in significant procedures (cardiopulmonary bypass, deliberate hypotension, etc..)
- Inability to use NIBP
- The need for frequent ABG readings
What are the absolute contraindications for A-line placement?
- Localized infection at site of insertion
- Preexisting ischemia or nerve damage at insertion site
- Raynoud’s phenomenon
- Trauma to area proximal of insertion site
What are some relative contraindications for A-line placement?
- Failure to demonstrate collateral flow
- AV fistula in limb of placement site
- Evidence of disrupted lymphatics in limb of placement site
What fluid should you use in the set up of an A-line?
Saline or heparin (risk of HIT though)
How does the site and distance of A-line placement effect its waveform?
- Amplitudes of wave increases (sys increases, dias, decreases)
- MAP decreases
- Waveform narrows
- Delay in pressure pulse
Describe the effects of distal waveform amplification in A-line readings and why it occurs.
- Wider waveform
- Slurred dichrotic notch (slower)
- Delayed upstroke
- More prominent diastolic wave
> > Occurs at more distal A-line placement. Delayed upstroke and slurred dichrotic notch makes sense in the context of increased distance from aortic arch. Wider waveform and more prominent diastolic wave = due to harmonic resonance. (Correct this if I’m wrong, this is just my guess)
What is the effect of decreased arterial distensability (less compliant) on A-line readings?
Note: esp seen in elderly patients
- Delayed systolic peak
- Wider diastolic trough
- Early return of pulse waves, which causes increased pulse pressures
What should you do after you place the A-line catheter and connect it to the T-connector (which is connected to the transducer)?
- Aspirate 2 mL of blood to confirm placement and suck out any air.
- Flush the line with LESS than 3 mL of fluid. (More than that has demonstrated retrograde flow back to cerebral circulation)
What are some identifiable characteristics of overdamped pressure waveforms?
- Diminished pulse pressure
- Slurred upstroke
- Absent dichrotic notch and other sharp characteristics of a normal a-line waveform
What are some causes of an overdamped A-line pressure waveform?
- Arterial obstruction
- Catheter obstruction or clot (assess patency with flushing and aspiration)
- Pressure tubing kinks
- Air in tubing
- Transducer failure
- Loss of flush pressure (pressurize bag again)
What are some identifiable features of an underdamped A-line reading?
- Overshoot, ringing, or resonance (Everything becomes much more amplified)
- Systolic peak overestimates intra-arterial blood pressure (compare to NIBP reading if possible)
- Multiple sharp peak waves (so you can’t really tell which one is the dichrotic notch, although you can estimate)
Complications of A-lines? (There are many..)
- Distal ischemia (interruption of arterial flow)
- Pseudoaneurysm
- Arterial-venous fistula (inadvertently creating a connection between artery and vein)
- Hemorrhage
- Infection
- Peripheral neuropathy
- Misuse of equipment
- Misinterpretation of data
How does height affect A-line readings (BP #s)? (Numbers) –> How can you estimate effect of height on bp readings?
Every 15 cm of height difference = 10 mm Hg
too low = increase in BP, gravity
