UMEM Educational Pearls - By Harry Flaster

Pulse Checks in Cardiac Arrest: Your Fingers Are Not Reliable.

Summary:  Whenever possible, use an ultrasound or an arterial line for pulse checks.  Our fingers are not reliable. 

Key points:

1. It is very difficult to obtain a palpable pulse in a hypotensive patient, even in the best of conditions.  In cardiac arrest patients specifically, manual pulse checks are not a reliable method to detect return of spontaneous circulation (ROSC).  
2. Yet manual pulse checks remain the standard of care in ACLS algorithms.  
3. Better options to determine ROSC include ultrasound and arterial lines.  
4. End title CO2 is a useful adjunct, but should not replace ultrasound and arterial lines to determine ROSC.
5. There is a lack of evidence to determine a measured arterial pressure in which it is safe to stop chest compressions, but in the absence of an evidence based, established standard, a MAP > 50 or SBP > 60 can be used as a tentative guide.

Multiple studies have demonstrated that manual pulse checks are not a reliable method to determine ROSC.  Arterial lines and ultrasound are far more reliable methods.  However, using more accurate measures of circulation lead to an additional dilemma: at what MAP, SBP, or ultrasound measured flow should we stop chest compressions?  There is no agreed upon number, and as with most dilemmas in clinical medicine, the best answer is, “it depends”.  However, a MAP > 50 or SBP > 60 for most patients is a reasonable choice to stop chest compressions.  MAP < 50 or  SBP < 60 are unlikely to provide adequate perfusion to the brain, and chest compressions should be resumed.  

References:

1. https://pubmed.ncbi.nlm.nih.gov/35131404/
2. https://pmc.ncbi.nlm.nih.gov/articles/PMC6042301/
3. https://pubmed.ncbi.nlm.nih.gov/30902687/
4. https://pubmed.ncbi.nlm.nih.gov/36646373/
5. https://pubmed.ncbi.nlm.nih.gov/35792305/
6. https://emcrit.org/emcrit/further-disambiguating-pea/
7. https://emcrit.org/emcrit/pea-is-stupid/

Flow rates are, in theory, determined by Poiseuille’s Law, which states that the flow rate depends on fluid viscosity, pipe length, and the pressure difference between the ends of the pipe .  

Of course we won’t be calculating this during a resuscitation! Nor would it be useful if we did: the equation assumes laminar flow, whereas turbulent flow is more likely.  Nor is it practical to look up the viscosity of crystalloid/blood/plasma, which also dramatically impacts flow rates.   

Instead, remember this equation:  Larger + shorter = faster  

And keep in mind the following:

1. Excess IV tubing can decrease your flow rate no matter the size of your catheter
2. All connectors (J-loops, needlefree connectors, etc) will dramatically decrease your flow rate.  Do not add to the catheter if your goal is faster flow!

In practice, our friends in Australia actually put common catheters to the test, and provided these helpful results:

Or, as a picture:

Note, these flow rates were achieved using crystalloid.  Blood will be slower due to higher viscosity.

Show References