Face Mask Capnography

Guest post by Terrance McGovern

End-tidal capnography is frequently used in the ED for monitoring patients at risk for hypoventilation.  Some departments stock the luxury oral/nasal sampling devices, but many of us have to make due with a nasal-only apparatus or fashion our own using a nasal cannula; these will not capture CO2 exhaled from the mouth. You can easily use a conventional face mask to build a capnometer that will continuously sample nasal and oral exhaled breaths, and provide supplemental oxygen. 

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If you use a non-rebreather mask with both exhalation valves activated, you must keep the reservoir insufflated with oxygen. To deactivate the exhalation valves, peel off the rubber gasket pictured most prominently in step 4.

If you provide high-flow oxygen, this will dilute the exhaled CO2 and the ETCO2 number will be artificially low, but the waveform is intact–if the wave amplitude is too small, change the monitor scale from max of 50 (default on most monitors) to max of 20.

Thanks to Brendan Milliner for his assistance/face.


addendum: similar setup described by an obscure author in the air medical journal.

The Usual State of Readiness


Emergency providers are routinely called upon to react to complex scenarios that demand specific life-saving maneuvers, immediately and without warning.  The most important impediment to performing well in these situations is your own catecholamines, and the most important catecholamine reduction strategy is preparation. The extent to which you are prepared to immediately react is your usual state of readiness, and it has two parts: cognitive and material.

Cognitive readiness requires that you consider emergency scenarios and decide on a plan. This starts with a textbook (by textbook I of course mean the internet) and reading what others think you should do in a given emergency scenario. The hard part of cognitive readiness is keeping up with the endlessly changing, endlessly disagreeing opinions, and deciding how to shape them into a plan that you like and that works for you in your environment. Logistics are key.

As medical knowledge expands forever faster, perhaps the most important knowledge of all is knowing what you need to know, and knowing what you can look up. This is not an either/or so much as a spectrum of how close information needs to be to your brain. There are plans that have to live in your brain (management of a completely obstructing airway foreign body), facts that you can take 30 seconds to look up (weight-based dose of atropine), and lists that you can review at your desk (the differential diagnosis of anisocoria). Memory fails when catecholamines are high; planning for emergency scenarios involves the development and deployment of emergency references. Your emergency references must be instantly available, instantly familiar and navigable, and damn reliable. Your plan for emergency scenarios takes into account how close aspects of that plan need to be to your brain and incorporates your emergency references.

As you develop cognitive readiness, the plans you develop for emergency scenarios start with a textbook but proceed in your imagination. I call this invisible simulation, and I find that I do a lot of it in the shower. The more you invisibly simulate emergency scenarios, the more likely the demand to immediately act will be met with calm. It is the combination of recognizing when to act immediately, and doing so calmly, that is the defining characteristic of an emergency professional.

Material readiness is simpler than cognitive readiness but often neglected. Material readiness is having the equipment you need, when you need it, where you need it. Nurses and technicians are often charged with this responsibility, however, when you need suction and it’s not there, the technician being reprimanded later does not get the blood out of your patient’s airway. You will do well to make a habit, at the start of every shift, of verifying that the most important equipment is ready and in a location known to you.

It might seem like a daunting task to cognitively and materially prepare for all the scenarios that might call for immediate action, after all, anything could roll through the doors at any time, right? Well, yes, but not really.

Asphyxiation. We focus on airway preparation for good reason. The best time to go through your airway checklist is before the patient arrives. Of particular interest is the scalpel. It has been said (by me) that there are two kinds of emergency physicians: those who always carry a scalpel in their pocket, and those who will, later on in their career, always carry a scalpel in their pocket.

Suffocation. Your adrenals will appreciate it if you have a well-rehearsed plan for managing the severe asthmatic. Also, having the capability to immediately initiate noninvasive ventilation–without calling for a machine, mask, or respiratory therapist–is worth fighting for. When you are forced to intubate a patient who could have been managed with NIV, you have done your patient a disservice.

Exsanguination and serious trauma. Do you know how to get your hands on uncrossmatched blood immediately? Do you have a good sense of the key interventions to consider in the first few minutes of a trauma resuscitation?

Cardiac arrest. Do you know exactly how to use your defibrillator? What about if the paddles or pads are disconnected? Can you initiate emergency pacing? Do you have a command of ACLS pulseless arrest, or your own algorithm? Do you know how to lyse a diagnosed or strongly suspected pulmonary embolism in cardiac arrest? Do you have a plan for treating cardiac tamponade? For tension pneumothorax, all you need is your scalpel and your finger.

Difficult access. Do you know where your IO device is and how to use it?

The uncontrollably violent patient. Do you know how to activate the highest alert to hospital security? Do you know what drug to use if you only have one shot?

Anaphylaxis. Do you know exactly which preparation of epinephrine to use and how much? Also see asphyxiation, above.

Status epilepticus. Do you have a clear set of priorities when managing the seizing patient? Which drug are you going to reach for first, and what dose? What if you don’t have an IV/IO?

Contamination. Do you know where all your personal protective equipment is, including those fancy masks? How you will make a patient covered in something dangerous safe to bring into your department?

Poisoning. How do you access your antidotes (digoxin immune Fab, lipid emulsion, hydroxocobalamin, etc)?

There are other scenarios that require immediate action, but start with these ten. Be warned that spending too long in the shower will upset your roommate.


Electromechanical Dissociation / TVP

This patient suffered a brady-asystolic arrest and a transvenous pacer was placed in the emergency department.

We are accustomed to relying on the monitor’s ECG tracing to determine heart rate; however, a good pulse oximeter waveform better reflects the number of perfusing beats. Note the heart rate, as measured by the pulse ox, is reported in purple in the upper-right corner of the monitor. At this point we had achieved electrical capture but not mechanical capture.

Watching the pulse oximetry graph is a slick way to guide pacemaker insertion. Cardiac sonography and placing a finger on the patient’s neck to assess the pulse are alternatives.


Strayer Transvenous Pacemaker Instruction Sheet


Dirty Epinephrine Drip

I take a milligram of crash cart epi, just because it’s the most available and already in a syringe, and put it into a 1 liter bag of NS. Attach to IV and titrate to effect using the knob. If the patient has a full or mostly-full bag of IVNS already hanging, I’ll just grab the crash cart epi and dump it in. Nothing could be faster.

1 mg epinephrine in 1000cc NS = 1 microgram/cc

20 drops/cc


2 drops per second = 6 mcg/min

Flow rates of various vascular catheters

standard pink IV:
20 gauge (.8 mm) x 30 mm angiocath
max flow rate = 60 ml / minute

standard green IV:
18 gauge (1 mm) x 30 mm angiocath
max flow rate = 105 ml / minute

standard grey IV:
16 gauge (1.3 mm) x 30 mm angiocath
max flow rate = 220 ml/min

procedural IV:
18 gauge x 64 mm angiocath
max flow rate = 85 ml/min

medial (blue) & proximal (white) lumen of triple lumen catheter:
18 gauge x 190 / 180 mm
max flow rate = 26 ml/min

distal (brown) lumen of triple lumen catheter:
16 gauge x 200 mm
max flow rate = 52 ml/min

cordis / introducer:
8.5 french (2.8 mm) x 100 mm
max flow rate = 126 ml / minute
max flow rate with pressure bag @ 300 mmHg: 333 ml / minute


from ETM course large bore IV access showdown

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from Traylor 2016 ACEP Abstract