Brian Locke

Arterial Line

Contraindications and complications

Vascular injury?

Indication

  • arterial BP readings (note: central = axillary, fem are more reliable and do not correlate all that well). MAP is still the most reliable indicator (as it is a surrogate for the perfusion pressure)
  • frequent blood gas

###Materials

  • 2% chlorhexadine skin prep dispensers
  • 2% lidocaine (1-3 ml), with syringe and 25g needle
  • sterile drape
  • 20g cannula (kit) 22g = micropuncture, larger for axillary/femoral. (they are color coded). Cook vs Arrow
  • extension to transducer, 3 way tap to connect to cannula

Site

Most commonly, radial artery of non-dominant hand. Other options: femoral (central), dorsalis pedis, ulnar, brachial, axillary (central).

Deep dive to different locations here: https://emcrit.org/pulmcrit/a-line/

Brachial

Complication rates: https://journals.lww.com/anesthesia-analgesia/Fulltext/2014/02000/Brachial_Artery_Catheterization___An_Assessment_of.9.aspx

Femoral

Possibly safer than billed? Can be converted for IR procedures, ECMO, etc.

Axillary

Have patient place arm behind head.

###Technique (Radial)

  • support wrist in slight dorsiflexion -palpate artery

  • steeper line of entry (45 degree entry). When flash is achieved, lower to 30 degree.

##Invasive Blood Pressure Monitoring

Radial arterial lines (probably all peripheral) likely significantly underestimate the central BP (e.g. https://pubmed.ncbi.nlm.nih.gov/28523028/) – if need to know, go for fem or axillary.

###Dampening the amount that a pressure wave transmits from the blood and through the tubing to the transducer. Reference

Over-damped = not transmitting pressure, such as if there is air in the tubing (compressible), a clot in the catheter, kinked/stiff tubing, or catheter is against a wall. Will be indicated by a loss of the dicrotic notch. MAP will still be accurate, but systolic will be underestimated, diastolic will be overestimated, and pulse pressure will be underestimated.

Under-damped = ringing vibrations in the tube. Exagerated dicrotic notch. Overestimate of systolic, underestimate of diastolic, overestimate of pulse pressure. Caused by long tube, many stopcocks, and tachycardia/high cardiac output.

Dicrotic notch = upstroke in the descending part of the tracing due to closure of aortic valve pushing fluid into aorta.

Square Wave test

you flush a high pressure wave of saline/heparin through the line, then see how much it reverberates in the line to estimate how easily pressure is transmitted through the system. Over-damped = 1 oscillation; perfect = 2 oscillations; under-damped = many.