June Capnography Log

June 27, 2006 Croup

5 year old asthmatic, not responding to his home nebs. Satting at 100% on room air, no wheezes, but a sore throat and barking cough. I gave him humidified 02.

Here's the strip. (He's having a slight inspiratory problem):

June 22, 2006 - Journal Club - Challenged

I just got back from our journal club, where we did three articles on ETC02, which I have listed under the monitoring section. I am a little discouraged because the club advisor, a doctor who I love discussing subjects with challenged me on the utility of capnography for the non-intubated patient and I didn't argue as persuasively as I thought I could. I am partially handicapped by my non-M.D. level of physiology understanding. His point was we need studies to prove the use of capnography in the field and that I shouldn't let it guide my judgement. I was trying to say that until the studies are done, I can at least let it help confirm my judgement. Capnography by itself is just a number and a wave form. It needs to be seen in the context of everything. The one benefit to being challenged is it will force me to sharpen my arguements as well as my understanding. It is new territory and I am learning something with each experience. I do wish I was more informed so I could be sure that what I am writing here is reliable and not BS.

June 22, 2006 - ?COPD ?CHF ?Pneumonia

77 year old female with increasing respiratory distress. Only respiratory history was COPD, but she sounded like she had rales. Pale diaphoretic, warm, some pedal edema. Heart rate 108. Respirations in the high 30's. Sat in the 80's. She had a nice straight up wave form. I held off on a treatment and held off on Lasix and just went with 02 by nonrebreather and nitro, and she started breathing much better. Heart rate and respiratory rate improved steadily. Sat came up to mid 90's. Did capnography change the way I practiced? No, but it gave me more confidence in not giving a treatment, which I am always leary of doing when I sense CHF. At the hospital she had a temp of 100.7.

Here's her trend summary of HR and RR.

June 21- Unresponsive, Fever, Hyperglycemia

Unresponsive Incontinent obese 30-year-old male with kidney transplant and insulin dependent diabetes, not taking his insulin for several days and with infected feet for which he was recently seen for sepsis. Patient is hot diaphoretic, temp of 103 at the hospital, pupils dilated non-reactive, our blood sugar was 377, hospital's was 666, HR-140, BP- 200/100, Respiratory rate between 25 and 45 over a minute, but at times almost apnenic. No fruity acetone breath. Patient thrashing around. Glascow Comma between 6 and 9. Extremely difficult extrication from basement during which as we carried the person vertically up steep stairs on scoop, I thought he had coded during period of apnea. In the ambulance, patient Sats at 99% on 100% 02, Capnography steady betwen 35 and 38. We don't have RSI, the patient had a gag reflex. After seeing capnography and SAT, I felt a little better about his prospects for coding on the way in. He was at least perfusing, and did not appear to be, in my guess, in extreme acidosis. At the hospital, he was paralayzed and intubated.

Below is a trend strip showing an erratic respiratory rate.

Here are some wave forms.

The forms are mostly upright, but note the irregularity. I have figured out that you can measure the respiratory rate of a single breath just as you measure a QRS complex, using your field guide. Just measure from end of inspiration to end of inspiration. In this brief segment (sorry for not capturing the apnea (I was carrying the patient or too busy doing other things) the respiratory rate ranges from 25 to 45.

What was the guy's problem? He was certainly septic. He was hyperglycemic, but he wasn't in DKA. His ETC02 was too high. If he was acidotic, his ETCO2 should have been lower. I checked back with the hospital later and found their lab work showed his arterial CO2 was 40. Pretty close to our reading. Unlike our differing blood sugar -- so much for our just calibrated glucometer. I wouldn't rule out neurological damage. I suspected maybe some drugs on board, but he was clean.

Here's two studies on ETC02 in diabetic ketoacidosis.

End-tidal carbon dioxide predicts the presence and severity of acidosis in children with diabetes reveals that ETCO2 can help discriminate between patients with DKA and those without. Bottom line, Children without DKA had a mean ETCO2 of 37, those with DKA had a mean of 22.

Capnometry for noninvasive continuous monitoring of metabolic status in pediatric diabetic ketoacidosis. In this study initial ETC02 of patients in DKA was 18.6 +/- 10.8 torr. They also concluded that ETCO2 in patients with DKA provided an accurate measurement on arterial CO2.

I will post this later as a case study.

June 20 - Concordance Between Capnography and Arterial Blood Gas Measurements

dnvermedic posed an interesting question in a comment on this blog.

we had a copd pt. today that was super-sick - had been sob for a few weeks and was getting worse. didn't go to the hospital because he couldn't get to a bus. ironically, we weren't there to see him - we were there to see his significantly less ill family member - saw him huffing and puffing in the corner and jumped on it.

anyway, he was breathing 40+ times a minute, sats were in the low-mid 80s on a nrb with a albuterol neb attached. we decided to put the capnography cannula on him and had a strangely normal looking waveform and a strangely normal co2 level. labs showed up later with co2 level in the 60s (i do realize abg will have a different # than exhaled co2, but still...) - besides copd, lung ca that was supposed to have been treated, he was also suffering from respiratory acidosis.

after this long babble, my question is this - have you heard of getting incorrect co2 levels when the waveform is good? i told the doc i was surprised to see that he didn't have high co2 levels on the capnogram, and the doc couldn't come up with an answer for that.

thought i'd ask...

I promised I would look into his question and get back with the best answer I could find. Again, I must state at the outset, that I am not an M.D. I’m just a paramedic trying to learn about capnography, and lacking a standard text written for paramedic addressing all our prehospital questions(I’m learning that there is much that no one really knows the answers too, because capnography is new to the emergency and new to the prehospital setting), I have to try to piece answers together.

Here goes.

Generally speaking, studies have shown that End Tidal C02 obtained through capnography correlates well with arterial blood gas measurements of carbon dioxide. The most recent study – of patients with acute asthma – showed a high concordance (see clinical Studies). Similar studies in the past have shown concordance for people with healthy lungs, pediatrics with upper and lower airway disease, people with seizures and diabetic ketoacidosis.

There seems to be a problem however in patients with severe lung disease who have an excess of dead space. This can cause a perfusion/ventilation mismatch. There is carbon dioxide in the blood that cannot be ventilated off because there are not enough healthy alveoli for the needed exchange to take place. Thus the blood gas will be higher than the End Tidal C02. The blood will be poor in oxygen and rich in carbon dioxide

For a more detailed explanation, click this e-medicine link:

Respiratory Failure

For a nice layman’s explanation go to this message board link:



In the textbook Capnography Clinical Perspectives, in Chapter 23: PetC02 Monitoring for Patients with ARDS, the chapter author describes:

a study of patients with ARDS (Acute Respiratory Syndrome) where end tidal C02 accurately predicted blood gases “for the majority of patients in the study (65% or 20 of 31) with mild to moderately severe forms of ARDS. PETC02 did not accurately predict PAC02 for patients with more severe forms of ARDS (35%) requiring higher levels of ventilatory support and more compromised arterial blood gas exchange."

The bottom line for EMS people is to keep in mind that for COPDers and other people with severe lung disease, our End Tidal numbers might not be as reliable an indicator of arterial blood gas as it is with other patients.

Additionally, in Chapter 30 of the text, Ventilation/Perfusion Abnormalities and Capnography, the author mentions several limitations to the accuracy of capnography. (He is writing about mechanically ventilated ICU patients, but this should also be applicable to EMS patients.)

1. The composition of respiratory gas mixture may affect the capnogram, such as the use of high 02 concentrations in critically ill patients.

4. Contamination of the monitor or sampling system.

7. A low cardiac output state may result in an artificially low PetCO2 value.

The chapter concludes:

“Mismatching of ventilation and blood flow is common, and may become very severe in diseased lungs...Capnographic features such as absolute PETCO2 value, capnographic wave-form interpretation, as well as the (a-ET)PCO@ differences need to be interpreted in view of the presence of V/Q(ventilation/perfusion) inequality from lung disease or hemodynamic factors."

In paramedic speak:

Capnography like all of our tools needs to put in the context of the whole picture.

Severe lung disease and low cardiac output can lead to lower End tidal C02 values than the actual arterial blood gas values.

And just how much high flow 02 affects the value? I don’t know. This might be a good area for a study.

Lacking that study, in my practice, I will try to follow up as much as I can and get an arterial blood gas value from the hospital and compare it to my ETCO2 value on interesting cases.


Thanks again to denvermedic for raising such an excellent question!

June 14, 2006 COPDer with reproducible back pain.

Went to a medical center where the staff treated a COPDer with reproducible back pain as if her were having an MI. In addition to bottoming his pressure for a period(prior to our arrival), he began to have some trouble breathing. His wave form was straight up -- no wheezing, but his C02 number was only 19-20. I upped his 02 from 2 to 3. His SAT went from 91% to 95% and his ETC02 went up to 30. He was breathing better. I'm going to try to make note of the changes in ETC02 in COPDers with 02 added.

June 10, 2006 - COPDer with Pneumonia

60 year old female in a nursing home with a history of Lupus and COPD. Extreme tachypnea. Rate of 60. Sat 88% on cannula at 2 lpm. Fever of 103. Lung sounds decreased, some rhonchi. No wheezing. Put her on the capnography.

ETC02 - 20. The waveform indicates rebreathing. She is taking a new breath before she has let out the last breath.

I put her on a nonrebreather at 15 lpm.

90 seconds later, her ETC02 has risen(28), along with her SAT (94), which is now 94%. Her respiratory rate declines to 37. The waveform is showing less rebreathing.

Eight minutes later, she has been doing much better. Her respiratory rate has stabilized -- still too high at 37. Her Sat is 99-100%, Her ETC02 is 32. Her wave form is upright.

When I tried to put her back to a cannula -- the same thing happened. Rebreathing wave form, increasing RR, decreasing SAT, decreasing ETC02. I put her back on the nonrebreather, everything straightened out.

At the ER, the nurse said I had her on too much 02 for a COPDer. I went over my findings, including the capnography, and also mentioned that the hypoxic drive therory was pretty much that -- just a theory that wasn't really bourne out by clinical findings. The patient stayed on a mask. X-rays confirmed massive pneumonia.

I came across an interesting article by a respiratory therapist named Jeff Whitnack called:

Death of the Hypoxic Drive Theory

Very interesting reading. Here's an excerpt:

In the May 98 issue of Clinical Pulmonary Medicine is an article titled Acute Respiratory Failure in Chronic Obstructive Pulmonary Disease” by Schiavi. In it the author concludes that…… “....The traditional idea that oxygen induces hypoventilation by suppressing hypoxic ventilatory drive at the level of peripheral chemoreceptors is no longer tenable.”

Here's the guy's home page, which includes a link to his powerpoint presentation.

Home Page

June 3, 2006

A tech at the hospital told me they were getting capnography machines and an -inservice had been scheduled.

I had a good trauma today -- a patient with a destroyed pelvis from a wraparound a telephone pole. Heart rate in the 150's. I keep wanting to put the capnography on, but there was always one more thing I had ahead of me on the priority list. I'm curious what kind of reading I would have gotten.