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A Comprehensive Educational Website (established 1998)

Designed, Produced, and maintained (Edition 12, 2022) by 

Bhavani Shankar Kodali MD

Updated September 2022

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2018-04-28 12:33:41Susana Garcia DiezDear Mr Shankar Kodali,
I am Susana Garcia a Medical Student and I am ending my "end of degree work" ( it is like a thesis but "smaller"), and I chose capnography at prehospital setting because I work at an Ambulance as EMT and I consider capnography very useful but " around" me only use it for CPR. So...I need use your pictures at my work, but only if you allow me to do it.
Thanks a lot by your attention,
"a capno fan"
2017-12-04 07:49:10MichaelDear Prof Kodali,
Thank you for your wonderful website. I had a past exam question asking what the capnograph of a tension capnothorax from a laparoscopic fundoplication would look like. Could you provide any help with this? Page 4 of 6 of the mcqs on this link gives the options. Thanks for your help
2017-12-02 01:03:44Peter Cheng, DODear Dr. Kodali:

Thank you for a great website for learning capnography and for you many papers.

As I have ordered the Respironics NM3 monitor for volumetric capnography (Vcap) to optimize mechanical ventilation, do you know any anesthesiologists with Vcap expertise with whom I may visit?

Additionally, I also wish to learn esophageal pressure monitoring to assess pleural pressure.

Your list of names is greatly appreciated.

Merry Christmas and Happy New Year!

Thank you.

Moreno Valley, CA
2017-08-09 13:29:34K. DayIs there any way to monitor CO2 production/emission in mobile, healthy people throughout the day?
2017-07-24 17:41:18Laura Wellnitz Hi Dr. Kodali,
really enjoy this web site
I would like to have your permission to utilize some of your material for training our nursing team on Capnography...Would be used only for education and not publication.
Chula Vista
2017-03-21 13:35:29ruggero ruggeriexcellentniguarda hospital milan
2017-03-18 09:05:01Bhavani KodaliTo answer the question below, It should not as long as pulmonary circulation is not interrupted. Here, it is not interrupted. Boston
2017-03-17 17:36:36Julie WatanaDo use of CO2 used as an interventional radiology contrast (angiogram) significantly effect ETCO2 readings?West Hills, CA
2017-03-14 11:29:37Bhavani Shankar KodaliSee below answer for Question raised by Alex same as that of Chin's QuestionBoston
2017-03-14 11:27:13Bhavani Shankar KodaliBelow is the answer for question raised by ChinBoston
2017-03-14 11:26:14Bhavani Shankar KodaliHere it is not related to cardiac output. Yes cardiac output can alter the the ETCO2. However, here the mechanism is different and can happen without changes in cardiac output. Sedation with unobstructed airway can result in high ETCO2 due to hypercarbia. But if airway is partial obstructed impeding the flow, ETCO2 can be decreased until airway obstruction is rectified. Another cause of low ETCO2 is hypoventilation to the point that the tidal volume has decreased considerably and the sampling gas does not reflect true alveolar CO2. Boston
2017-03-14 05:24:20chindear Dr Kodali and Team,
Thank you for such a wonderful website. I've learn so much from your library. I have one question regarding capnography of oversedation(low etco2) vs hypoventilation(high etco2). My assumption is oversedation caused CVS compromise which in turn, result in decrease pulmonary blood flow and low etco2. Is this correct?
2017-03-09 13:54:10João MachadoGood afternoon,
You have an excellent site, very educative, I'm brazilian anesthesiologist and I use so lot your site.
Recentelly a saw an interesting capnogram in a cardiology pacient surgery. How I do to send you this case?
Do you have a e-mail?
Campos, Rio de Janeiro, Brazil
2017-03-02 07:26:56AlexCongratulations for your website!! It is helping me a lot. I can´t understand how during a deep sedation a central hypoventilation can decrease the PECO2 ? Could you explain it? Thanks in advanceSpain
2016-11-05 10:33:03Bhavani Kodali Hypoventilation does not per se increase dead space but rather decrease alveolar ventilation. Because of cone front effect due to laminar flow of gases (flow is relatively more in the center of the airway tubes than in the periphery. Because of this phenomenon, the alveolar ventilation does occur with tidal volume less than anatomical dead space. Therefore as hypoventilation occurs, end tidal CO2 will increase. But when hypoventilation is significant enough, the end-tidal gases may not represent alveolar gases and end tidal CO2 can be significantly lower than PaCO2. Under these circumstances a deep ventilation given via positive pressure bag will enable true alveolar sampling (squeeze PCO2) and will reflect PETCO2 closer to PaCO2. I hope you understand now.
During hyperventilation, there is no such issue and therefore end tidal gases represent decreased arterial PCO2 and hence decreased PETCO2.
2016-10-31 21:45:45Laila SamyThank you for this website.
I would like if you could explain to me why you say the PETCO2 will increase with hypoventilation and decrease with hyperventilation. I thought that hypoventilation will increase your dead space, increasing your PaCO2 and decreasing the PETCO2.
2016-08-16 21:48:41Jerry JensenAwesome Website!!! I Love It!!!VSC ICU Buffalo Grove IL
2016-08-14 09:32:05Yishaiwonderful web site I love it, excellent for teaching as well.
a small comment regarding the cause of cardiac oscillations, see Suarez-Sipmann et al. 2012 in J Clin Monit Comput
2016-08-03 16:28:55Christine Neal Wonderful informative website. I am interested in how CO2 poisoning would effect EtCO2 monitoring. Thank you very much. SSM Health St. Louis Mo
2016-03-04 11:08:30Dan CraddockOutstanding dynamic graphs, easy to understand content, My complements to Dr. Kodali for a job well done. St. Petersburg FL
2015-11-16 16:30:42Paul Burleigh BSS, NRPFantastic article providing online 'realtime' analyzation of Capnography for hospital and pre-hospital healthcare personnel! Thanks!!Ohio
2015-11-16 16:30:34Paul Burleigh BSS, NRPFantastic article providing online 'realtime' analyzation of Capnography for hospital and pre-hospital healthcare personnel! Thanks!!Ohio
2015-11-03 10:20:20Bhavani Shankar Kodali MDYou can contact the following. They have the unit
Treymed, Inc.
2015-11-02 18:12:13J Alberto Neder, MDDear Dr. Kodali,
I'm currently looking for a portable device that provides volume capnography (and exportable key variables) in spontaneous breathing subjects (NOT to be used in ICU/anesthesia). Any commercially-available option ?
Many thanks,
Yours sincerely,
J Alberto
Kingston, Canada
2015-07-30 15:41:37Dr. Hakeem YusuffHello,
I am preparing a manuscript for Clinical medicine (Journal of the Royal College of Physicians) on sedation for non-anaesthetists. I would like permission to use images showing oxygen delivery devices with capnography sampling ports. Please can you advice me on how to go about this. Thank you.
Manchester UK
2015-05-28 17:03:14Kyna Kozak RVT VTS(anesthesia) Awesome awesome as always, great to see this website being used so much... so many don't use capnography as much as they should...Alberta Canada
2015-03-27 18:39:41Bhavani KodaliMy website contains several capnograms, but no card system. You can develop your own by downloading the capngrams and make your cards. United States
2015-03-25 14:14:01donna kijakWe have several Microstream capnography quikcards. we have them posted in our post op pt. rooms. The word abnormal is not spelled correctly. It is "abormal". Patients have been pointing it our to us. Do you have different cards available for us?aspirus wausau hospital
2015-02-24 07:02:22Jay SheltonQuick question.
How do results of mainstream and sidestream capnography compare? As mainstream is BTPS and sidestream has time to cool and goes through a drying filter is it ATPD? Does this alter the value reported in mmHg?
Cleveland Ohio USA
2014-12-22 01:19:34Dr. Scott Allan LangGreat site - thank you.

I encountered a capnogram I had never seen before. Phase 3 was step-wise (almost looiked like cardiogenic oscillations). There was no valve malfunction I could detect. Any ideas?
Alice Springs, NT, Australia
2014-12-09 17:21:44Ted SmithI wanted to take this opportunity to introduce a revolutionary new endoscopy mask: The Panoramic Oxygen Mask (POM)! This one-of-a-kind mask provides oral and nasal modifiable membrane ports to allow scopes and tubes to pass through the mask itself! The POM has been certified to provide Fio2 levels at 90% and can reduce Hypoxic events! The POM also provides a capnography port for end-tidal Co2 monitoring! The POM is perfect for those patients who suffer from apnea or whom are overweight. Please visit for more information including videos and case studies.

I would very much like to send samples for your review of this product. Please contact me if interested.
Los Angeles CA
2014-11-24 12:36:39Karen KraftDr. Kodali, I use your website to educate myself on capnography monitoring in the perianesthesia setting and as a basis to teach my staff. May I use your animated capnograms as part of a PowerPoint presentation for colleagues?
Karen Kraft BSN RN CPAN
Mercy Hospital St. Louis MO / Gonzaga University
2014-10-25 05:59:34Dr.Shirish MoreAt present, I am working in emergency medical services. And I want more and more material to improve my knowledge.Bombay-Maharastra-India
2014-10-13 16:13:44Maynard RamseyGreat site, I'm wondering about how to test mainstream CO2 sensors. Thoughts or a reference.
2014-09-15 21:43:01John FeketyDr. Kodali - I want to add my thank you to the thousands you have already received. As both a paramedic and an instructor your web site has given me a whole new perspective on capnography. I have referred to capnography in EMS as the best thing since sliced bread and one of the most, if not the most, advancements in prehospital care. I will be recommending your site to all of my colleagues and students so that they can expand their understanding of capnography and make better use of it in their practice. Thank you again for your invaluable contribution.. Pennsylvania, USA
2014-08-02 16:00:37jasmine sadler Hello Dr,Shankar Kodali my name is jasmine sadler , I love your site and how you have it set up. I am currently working towards my thesis paper in Toronto to finish my Osteopathic manual practioner degree, Would you be ok with me asking you some questions about my thesis and your thoughts, I would really appreciate it, thank you in advance jasminetoronto, canada
2014-08-02 09:18:55Aldo BarrantesDr. Kodali, felicitaciones por esta magnífica página, es de muchísima utilidad para nuestra práctica clínica y sobre todo una guía excelente para la enseñanza. Muchas bendiciones y siga adelantePerú
2014-07-08 12:04:02Mark RichardsonDr. Kodali, I have an odd clinical case I would like you input on. My department uses capnography to help guide our choice in treatments, particularly with respiratory patients. This case has called some of our decision making processes into question. We would really appreciate your expertise. You can email me at the above address. Thank you.Delaware County Memorial Hospital EMS Department
2014-07-08 11:54:53Mark RichardsonThis is a wonderful website! My department has implemented capnography into our clinical practice using a lot of the information found here. Upper Darby, PA
2014-06-11 11:16:18Sally Martin, RNThis is a very useful website. Please consider replacing "anesthesiologists" (unless the physician is what you mean) with "anesthesia providers" since the majority of anesthesia delivered in this country is delivered by non-physicians. Thank you.
2014-05-06 14:39:18Bhavani Shankar KodaliReply to below query by Zachary:

If a patient has cardiac arrest and CPR is being performed, there will be small appreciable waveforms seen on the capnography screen. These waveforms confirm that the endotracheal tube is correctly placed in the trachea. Since the CPR generates low cardiac output, the physiological dead space is relatively high resulting in lower overall end-tidal CO2 values. These values may range up to 25 mm Hg in a well performed CPR. The effectiveness of CPR can be judged by end-tidal PCO values. Every effort has to be made to keep end-tidal PCO2 values close to 20 mm Hg. An abrupt increase in PCO2 values (36 mm Hg as an example) may indicate return of spontaneous circulation (ROSC).
Hence the value of capnography during CPR is 1. confirm ET position, 2, effectiveness of CPR, 3. ROSC.
Ventilation during CPR is based on the standard principles of CPR in ACLS
United States
2014-05-05 13:55:42Zachary BeattyHey Doc,
First I have to say thanks for putting this website together. It is very informative and helpful. Now, my question. I am a firefighter/paramedic with the Glenview Fire Department in Illinois. We often have guys asking about the "ventilating to a number" utilizing the end tidal CO2 value during cardiac arrest. From my basic understanding of capnography, during cardiac arrest we should follow the AHA guidelines for ventilation due to the fact that the end tidal CO2 value is not only a function of the ventilation rate, but also one of cardiac output and cellular metabolism. An example I hear brought up a lot, is a pt in arrest that is not within that "optimum" 35-45 mm hg range. The question is then do we ventilate according to the end tidal value or to AHA recommendations. My thinking is that if the pt has a lower value, it is due to the decrease in cardiac output (as we know cardiac output during CPR is not as good as the "real thing") and the decrease in cellular metabolism. Therefore, the lower value in this case is not due to ventilating the pt to much and does not mean that we need to adjust our ventilation rate to the value. I feel that the utilization of capnography to determine ventilation rates is more applicable to the pt that is "alive." However, I also understand that if we have a derangement in the value with a pt that is alive, we still need to examine if the problem is a ventilation rate problem or if it stems from a cardiac output or cellular metabolism problem. This is my basic understanding when it comes to this portion of capnography, and if I am wrong, please feel free to correct me. Once again, I appreciate the effort that is put into this site and I look forward to hearing from you!

Very Respectfully,

Zachary P Beatty
Glenview Fire Department

Glenveiw Fire Department
2014-04-20 16:33:56Bhavani Shankar Kodali MDResponse to Derek Flaherty BVMS, DVA, DipECVAA, MRCA, MRCVS, FHEA, Professor of Veterinary Anaesthesia and Analgesia.

Thank you for your question. Actually, both the groups may be correct.
Classically, the Beer–Lambert law was first devised independently where Lambert's law stated that absorbance is directly proportional to the thickness of the sample, and Beer's law stated that absorbance is proportional to the concentration of the sample. The modern derivation of the Beer–Lambert law combines the two laws and correlate the absorbance to both, the concentration as well as the thickness (path length) of the sample.

Beer Law does apply to CO2 absorption as it is concentration based. How far the components of Lambert's Law applies here is the debate. Although the thickness of the sample physically fixed (chamber), the thickness can vary depending on the concentration of a given gas.

Professor James Philip MD, our Bio-medical Engineering Director and the architect of GASMAN gives his view as follows:
Thank you for inviting me to comment.

If the Beer-Lambert law is not the mathematics of IR light attenuation, how do the conflicting anesthesiologists explain the math?

If it is whether the path length variation counts, it counts in the sense that path length must be constant after a capnometer is calibrated with a known gas sample.

Indeed, as my esteemed colleague Dr. Kodali and explains, there are techniques other than NDIR (non-dispersive IR spectroscopy) that can be used for CO2 monitoring, Mass Spectrometer, Raman Spectrometer. They so not use the Beer-Lambert law. However, none of the current clinical products use this.
2014-04-14 12:02:42Derek FlahertyI have just set a test for our anaesthesia residents and asked them about the physical principles underlying measurement of CO2 in respired gases. All of them came back and described the Beer-Lambert Law. At first I thought they were just getting confused with pulse oximetry, but the more I mulled it over, the more I thought that the B-L law might actually be involved, and, on searching the web, a number of sites do say that the B-L law is used in capnography. However, the senior anaesthetists here continue to disagree - please can you clarify?Scotland
2014-02-13 20:36:12Bhavani Shankar KodaliThe Quiz section - Links have been fixed and working well.United States
2014-02-13 04:59:37Martin DanicekHi,
I ´d like to try your Capnography quiz, but it´s not working. Can you please fix it? Or do you have somenthing simillar like this quiz?
Thank for your answer.
Regards, Martin Danicek.
Czech rep.
2014-01-31 19:12:17Bhavani KodaliThank you very much for encouraging commentsBoston
2014-01-31 08:57:10srobona chatterjeethis site is superb. i am in practice for 25 years (internal medicine) and never got formally taught about capnography--now i feel as smart as my residents :-) thank you. chapel hill, nc
2014-01-09 10:55:03Patrick J. MurphyHello Dr. Kodali,
Nonin Medical may be interested in becoming a sponsor of Could you let me know what opportunities might be available to Nonin as a sponsor? Also, aside from the website, are there other opportunities for Nonin to work with you to educate more clinicians on the importance of capnography?

I look forward to hearing from you.
United States
2013-12-30 19:34:26Bhavani KodaliThank you regarding encyclopedia capnograms. They are working now and I fixed them. The site has become big and sometimes it is difficult for me to know which pages are not working. This is despite checking the site when it gets upgraded.Boston
2013-12-30 07:13:42Rajdev ToorBrilliant site, previously used it for my part 1 ANZCA exams 2 years ago. Now using it for my final prep. first time at the new look edition of your site today. However, upon clicking the capnograms link, I am unable to open up any of the capnograms from the encyclopaedia. It keeps saying "error 404 - page not found". I get the same response with every group I tried clicking. Brisbane
2013-12-15 19:06:42Bhavani KodaliTo answer a question about teaching, the power point presentations on sedation and CPR can be downloaded for teaching.
2013-11-22 13:03:13Lynne HigginbothamI am creating an educational power point to test for competency in Capnography for our facility. I would like to get permission to use some of the images in your presentations.Thank youMercy San Juan Medical
2013-11-13 11:13:24Matthew BronkExcellent lecture for my residents and staff that need to learn about capnography for sedation. I would like to print out your powerpoint to give to my residents, if that would be OK. It has your name on it and I would not claim it as my lecture...just want to be able to print it out 4 per page so they have something to take notes on. Thanks,
Dr Bronk
Barksdale AFB, LA
2013-11-07 14:10:04Scott ElderDr. Kodali,
Is there any research out there supporting the use of capnography in PCEA where fentanyl is used? Epidural narcotics in the amount of 2ug/ml. Thanks
Boise VAMC
2013-09-17 03:18:28amitchauhanthis site has made capnography as easy as it could be
2013-07-25 12:31:46BJWGreat site! I've referenced it in presentations. I was curious if you had information or articles about management of capnography/ETCO2? Specifically how to treat and manage a rise in ETCO2. Perhaps a protocol or an algorithm?


2013-07-14 15:19:12Jon SeiverthHello,

Does your Training CD have the 96 min of CPR video clip and similar articles, etc with it?


Perrysburg, OH
2013-06-28 13:50:38K. BairdI would love to hear how other hospitals are incorporating capnography into their programs, especially for monitoring patients receiving narcotics post-operatively. Are others monitoring all post-op pt's (and for how long), or just certain subpopulations (OSA, elderly, previous narcotic use), etc?? Any info will be helpful.NC
2013-06-28 12:00:11Mary Welch, RN, MSNExcellent content within this website... just want to say "Thanks" for the resource.

Cone Health, Greensboro, NC
2013-06-23 10:07:18Bhavani Shankar Kodali Anesthesiology 2013; 118:192–2013
In an article on this subject, I wrote for Anesthesiology, I used PETCO2. I think this is correct and should be used as standard nomenclature. It reflects what we mean ie partial pressure of end tidal CO2. ETCO2 can used if the measurements are being conveyed as CO2 concentration rather than partial pressure.
Brigham and Women's Hospital, Boston.
2013-06-17 21:00:29Bhavani Shankar Kodali To reply to David: You can download and use as read only document for presentation. Password not required for presentation
2013-06-17 16:11:18David FaginI tried to open the powerpoint presentation as I'm giving a capnography lecture to our sedation nurses and it says I need a passwordAtlanta Georgia
2013-05-16 05:38:02Ailsa BradburyFantastic website. I'm a veterinary anaesthetist but the principles are the same. Thank you so much for such a valuable resource and thank you for making it available to everyone.Manchester
2013-05-01 17:57:30Patrick MurphyWhat information can you provide regarding becoming a sponsor for Nonin Medical may have an interest in helping to sponsor the site.


Pat Murphy
Minneapolis, MN
2013-04-16 22:36:02bill steinsiek mdis your hospital using etco2 monitoring routinely postoperatively with patients on the surgical floors receiving pca NARCOTICS...TRYING TO GET A PROGRAM STARTED AT MY SMALL HOSPITAL BUT NEED A LISTING OF OTHER INSTITUTIONS ALREADY USING THE TECHNOLOGY ROUTINELY....THKS FOR YOUR REPLY...BILL STEINSIEK ashland oregon
2013-03-26 14:29:30Dr. Maria Orsini EdD, RNHi Dr. Kodali:
I have found your website and reading your articles very helpful for my job. I am the new Emergency Department nurse educator and I am trying to develop trainings for my nurses that are meaningful in practice and theory. I am trying to find more information on how to use capnography in rapid sequence induction (RSI). If you have any recommendations, I would truly appreciated as I would love to incorporate your comments into the class we are developing on RSI.
Thank you so much for designing and keeping up this website,
Durham VA
2013-02-24 11:44:18MuryumGod bless you Dr Kodali! This is an amazing resource !Hamikton, ont
2013-02-18 21:30:55Katrin SwindellsAs a veterinary criticalist (DACVECC) capnography is one of the most common monitors I use in patients with respiratory disease or paralysis due to Australian snake envenomation or tick paralysis. Your website has been an invaluable resource for myself, my residents when I was at Murdoch University, and the emergency clinicians and nurses I work with. I frequently provide your website address when I lecture to veterinarians. Thank you for all of the time and effort you have placed on this site. It is greatly appreciated by the veterinary community. KatrinWestern Australian Veterinary Emergency and Specialty
2013-01-16 07:46:24Katie MansfieldLove the site - it has explained capnography in clear English, and has been a huge help for my veterinary nursing degree program. However, I just wanted to point out to you that the link for veterinary capnography takes you to the paediatric page. It's from this page: , menu on the left hand side.
Otherwise thank you for a very informative, easy to understand web site,

Kind regards,
Katie Mansfield (student at Royal Veterinary College, London, UK)
United Kingdom
2012-12-30 15:32:24JohnGreat siteVirginia