Episode 20: pH Stat and Alpha Stat

In this episode I review two methods for managing arterial blood gasses in hypothermic patients, usually during cardiac surgery–pH Stat and Alpha Stat.

Check out this fantastic episode recap put together by Brian Park from Drexel Medical School: Show recap

10 Replies to “Episode 20: pH Stat and Alpha Stat”

  1. Hello I love your Podcasts thank you so much for helping all of us. I have my first call coming up and would greatly appreciate a lecture devoted to trauma. How to best in dues and prepare when caring for Incoming.

    1. Hi Deanna. Thanks for the comment. I’m so glad you enjoy the podcast. Great idea. I am in touch with some trauma anesthesiologists about doing an episode on trauma. Hopefully we can make it happen soon. Have a wonderful holiday and thanks for all you do out there every day!

      Best,
      Jed

  2. One source of confusion on this topic is nomenclature. “Correcting” seems to have different meanings based on method. All samples are run at 37C – got it. In alpha, does temperature correction mean I’m acknowledging physiology and although ABG may read normal, I know a respiratory alkalosis exists? Correction in pH seems to indicate the addition (or decreased removal) of CO2 – “correcting” the perturbation caused by hypothermia. Would one expect decreased pH since the cooled pt’s blood has added CO2 and the sample was warmed? Lastly, how do results affect management? Are decisions made based on corrected or uncorrected values?

    Dr Jed, thank you for this awesome addition to our community and for the reminders of the importance of our work.

    Blessings,
    Tracy

    1. Hi Tracy,

      You’re absolutely right. The nomenclature is confusing. “Temperature corrected” refers to what you do to address the blood gas. So pH stat is temperature corrected because you add CO2 to correct for the effects of temperature. So you are actually going to back calculate (or have a machine do it) to give you the pH and pCO2 at the patient’s ACTUAL temperature rather than at 37. Then you will add CO2 to bring the ACTUAL pH down to 7.4. And yes, once the patient is warmed, you will now have a relative acidosis which you will see as increased ETCO2 and you can breath off (once you are back on the vent) as quickly or slowly as you want. Management in Ph stat is based off of the actual value (what the pH is at the cooled temperature) and so your management is to add CO2 to correct the alkalosis. Management in alpha stat is to use the pH at 37 regardless of what the actual pH is and treat accordingly. I hope that helps!

      Best,
      Jed

  3. First of all, thank you for a great and highly relevant podcast. I am working my way through all of your episodes, and I will definitely get around to supporting the podcast on Patreon.

    A concept I did not hear you address in this podcast is the fact that the ionization constant of water changes according to temperature, thus causing “neutral pH” (defined as the pH at which [H+]=[OH-] ) to decrease with increasing temperatures. At body temperature, neutral pH is 6.8, which happens to be the (normal) intracellular pH.

    Conversely, neutral pH is higher at lower temperatures. As far as I understand, the ionization of intracellular proteins is not affected by pH per se, but by the ratio between [H+] and [OH-]. In other words, a decrease in temperature is associated with an increase in pH, but not necessarily a change in the ratio between H+ and OH- and therefore not a change in the degree of ionization of intracellular proteins. The pH point at which the intracellular proteins function optimally might also increase with hypothermia, and “correcting” this apparent alkalosis by increasing the PCO2 may lead to a relative intracellular acidosis, despite the fact that the actual measured pH is returned to “normal”, but “normal” for a patient at normal body temperature..

    English is not my first language, so in case the above is somewhat imprecisely worded, I would recommend the reference below for a more in-depth analysis:

    http://www.anaesthesiamcq.com/AcidBaseBook/ab1_6.php

  4. hi
    Thank you for clearing up what has always been a confusing concept ( pH stat versus alpha stat). I have been going through your podcasts to help prepare for my board exams and they have been great. Have you done any podcasts on Sepsis using the new definition and SOFA score in relation to anesthesia. I would love to hear your views on the subject.

    1. Hi Andrea,

      Thanks for the comment. There is still so much controversy and ongoing debate about sepsis definitions that I think it’s best to wait until we have more information before trying to evaluate it but will definitely keep it in mind in the future. Thanks!

  5. Great talk on pH! Although a majority of the talk was in regards to cardiac surgery, “pH stat” or “Temperature Corrected ABG’s” were always referred to as “temperature adjusted ABG’s” at the facility I worked at. We commonly used them for targeted temperature management/therapy for post arrest patients in the Trauma Neuro ICU at Mercy Hospital St. Louis. After being in anesthesia school for some time and revisiting this concept you spoke about it in a way that was understandable, and it helped me understand the value of utilizing pH stat vs alpha stat abg’s. Being a trauma unit, a majority of our post – arrest patients also had a combined head injury and elevated ICP’s which required extra diligence in management of ABG’s to prevent extremes in cerebral blood flow. A lot of these podcasts match up with content that I cover within classes and closely correlate with the organic/biochemistry topics covered. Keep doing what you’re doing, you are helping more people than you know.

    Stay classy sir,

    Kyle Smith RN BSN CCRN SRNA

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