hi this is Zack Fulkerson pulmonary and critical care fellow and I'd like to tell you about a story a story about a patient of mine who is transferred emergently from the ward to medical ICU for altered mental status and respiratory failure had to be emergently intubated and when they got to the ICU they were hypotensive and in shock this was my view after getting central access there was an army of nurses and respiratory therapists around everything was going normally the nurses were trying to find a place where the pulse oximeter would read the in tidal co2 was up and I solved this nothing in the room had changed at all the nurses were still going about their usual work and my question for you is this if you see something like this is this significant or not does it mean something or not if you don't know or simply aren't sure then I hope you'll join me for the next few minutes as we discuss wave form capnography in detail the overview of this talk is simple we're going to talk about physiology as it pertains to wave form capnography very briefly and then we're going to go immediately into applying that physiology to capnography examples with all that said let's get started to discuss the physiology we are going to make use of this diagram where pulmonary circulation is shown here at the bottom followed by alveoli in the middle and then your Airways and whatever mechanical tubing you have your patient connected to finally all of this is in line with the carbon dioxide detector shown here at the top in order to get co2 to register three things need to happen physiologically first we need to produce carbon dioxide in the peripheral tissues through aerobic metabolism second we need pulmonary perfusion we need all of that co2 to actually circulate to the lungs and finally ventilation not only do we need carbon dioxide to diffuse into the alveoli but also to make it up to our detector graphically we get something that looks like this where a plateau is formed during expiration and the end tidal co2 is recorded at the end of that plateau during inspiration the reading should be zero because typically we are breathing negligible amounts of carbon dioxide as a reminder our carbon dioxide can be measured through the artery as well and comparing these values can be valuable up metabolism circulation and ventilation it is metabolism and in Finland that tend to make the in title and the arterial co2 go in the same direction what I mean by that is that anything that causes the arterial co2 to go up such as hypoventilation or hyperthermia will also cause the intitle to go up the reverse is also true in that hyperventilation or decreased metabolism such as hypothermia will cause both the end tidal and arterial co2 to go down circulation can be more of a wild-card and can actually make the entitle and arterial co2 go in opposite directions you see in tidal co2 tends to be a little bit less than arterial co2 and this gap can increase any time we decrease the pulmonary perfusion or add alveolar dead space to demonstrate this let's add some dead space to our diagram and see what happens on the right there is no alveolar co2 because there's no perfume - this alveolus on the left the alveolar co2 is reflective of the arterial co2 once these two mix and make it to our carbon dioxide detector there's a substantial amount of dilution and the entitles of co2 decreases significantly causing a large gap between the entitle and arterial co2 all right now that we have some Physiology under our belts let's take a look at some common patterns that we're going to run into in the ICU this one you may recognize this is a normal cap immigrant but let's review it for a little bit notice during inspiration we're breathing negligible amounts of carbon dioxide and the reading should be zero during expiration we form a plateau that's almost flat but not quite and we measure the in tidal co2 at the end of expiration and now let's compare the normal with our first abnormal example now this starts off looking normal enough but notice that the in title is gradually decreasing this can happen in any situation that causes the arterial co2 to decrease such as hyperventilation or a decrease in metabolism but remember the in tidal co2 can also go down by anything that causes an increase in dead space such as decreased cardiac output a pulmonary embolism or hyper expanded alveoli our next example is basically the complete opposite you'll notice it gradually increasing in tidal co2 so this can be caused by anything that increases the arterial co2 such as hypoventilation or an increase in metabolism such as hyperthermia you'll also notice that the in title will go up anytime that you give your patient exogenous bicarbonate such as a bicarb push our next example starts off looking just like the previous one a gradually increasing in tidal co2 but here's the difference the in title isn't returning back down to zero during inspiration why it's because the patient is rebreathing the patient has too much mechanical dead space or the expert or eval is not working causing the patient to rebreathe other previously exhaled co2 the point being if you see a waveform that looks like this there may be something wrong with the ventilatory circuit itself our next example has a completely different waveform we've lost her nice Plateau and instead it's been replaced by something that looks more like a shark fin you may be thinking to yourself that it looks like it's taking a very long time for alveolar carbon dioxide to make it up to the detector and that's exactly what's going on there is an airway obstruction in this particular case most commonly this is caused by a small airway obstruction such as COPD or asthma but this could also be due to a very significant large airway obstruction such as a mucus plug foreign body or severely kinked endotracheal tube now this waveform starts off looking fairly normal but eventually we're going to lose that nice Plateau what's going on here is alveolar carbon dioxide is not making it to the detector instead it is actually leaking outside of the circuit you get this if you have a tracheostomy cuff or an endotracheal tube cuff that's poorly inflated or blown or perhaps you have a super chaotic airway that's not fit correctly in any case this is a leak in the circuit that should probably be addressed at the bedside for our next example I want you to imagine that you just intubated a patient and you use paralytics and let's say 45 minutes or an hour passed and the paralytics are shown to wear off and the patient is starting to try to initiate breast but isn't strong enough to trigger a full breath what you're going to see is you're gonna see a little cleft in the Plateau this is called a curare cleft and is seen anytime a patient is making an inspiratory effort but is not strong enough to actually trigger a full breath on the vent and finally we are back to a waveform that should look fairly familiar this is the waveform from our case the one where we should be asking ourselves is this normal or not this is an important waveform because it could represent a lot of bad things happening if you have a spontaneously breathing patient this could represent apnea this could also represent someone who is disconnected from the ventilator or the endotracheal tube is dislodged and in worst case scenario such as our patient this could reflect a cardiac arrest it should come as no surprise that a sudden drop in your in tidal co2 to zero could represent a cardiac arrest because this is the ultimate in terms of dead space there is no pulmonary perfusion that is occurring during a cardiac arrest and therefore no carbon dioxide making it to our detector with all that said let's talk about how to use cap nama tree to manage our coding patient once you start CPR you should be restoring pulmonary perfusion to some degree and this should be reflected by an increase in your end tidal co2 this can also provide a goal for you you want your entitled to be at least 10 if not greater than 15 and if you notice that you're in tidal co2 is drifting downward such as in this case it's probably time to change out the person doing CPR on the contrary if you notice a sudden increase in your in tidal co2 then the patient probably regained a pulse I particularly love capnography in the immediate post-arrest phase because I know that as long as my patient has measurable in tidal co2 they also have spontaneous circulation this concludes our review of wave form capnography I hope that you have found it useful thanks so much for tuning in and until next time this is exile Gerson so long