This is an excellent physiology-forward write-up, and the framing is exactly right: in severe metabolic acidosis, the peri-intubation killer often isn’t oxygenation, it’s loss of compensatory minute ventilation and rapid CO₂ rise → pH cliff → hemodynamic collapse. 
I especially appreciate the practical emphasis on VCV for predictable ventilation, using RR as the primary lever, and explicitly sanity-checking targets with Winter’s equation rather than default vent settings that are almost always too “gentle” for these patients. 
One bedside pearl I’d add: measure what the patient is doing before you take it away. Watching pre-intubation RR/VT (or NIV-delivered minute ventilation during preoxygenation) gives you a concrete “compensation target,” then re-check an ABG early (20–30 min) and titrate while vigilantly screening for auto-PEEP/air-trapping and hemodynamic intolerance. 
High yield, clinically honest, and very teachable; thank you for putting words and numbers to what many of us feel at the bedside!
Thank you for such a thoughtful and generous comment. Really appreciate you taking the time to engage so deeply with the physiology and share a practical bedside pearl—it adds a lot of value to the discussion.
One of the biggest challenges in managing these patients is deciding what tidal volume or minute ventilation we should actually target after intubation. ABG values help, but they are always retrospective. They tell us what *was* happening, not what is happening right now.
A common statement from experts is that no ventilator setting can truly match a patient’s physiological compensatory ventilation in severe metabolic acidosis. That is largely true. But if our goal is to get as close as possible, we first need to know what the patient was doing before we took over their breathing.
During preoxygenation, place the patient on NIV and observe the delivered tidal volume or minute ventilation. This represents the patient’s genuine compensatory effort. NIV applied after RSI drugs does not reflect true physiology and should not be used for this purpose.
Once this pre-intubation minute ventilation is known, it gives us a rational target after intubation. We may not fully reproduce it, but we can intentionally aim toward it.
Without knowing this baseline, ventilator adjustments become guesswork. We end up increasing and decreasing settings repeatedly, reacting to delayed numbers rather than physiology.
Please share your comments or difficulties with this approach if you had faced or will face if you try to adopt this before intubation. Open for discussion
Thank you for this insightful comment. Yes I guess everyone will definitely have some doubts regarding these patients, can discuss the problem faced here on these comments and they can be tackled bedside.
For Calculating appropriate minute ventilation, we can calculate approximate goal minute ventilation as mentioned in the REBEL EM article (cited as reference no 1)
This is a very high-yield physiology-forward reminder that the peri-intubation hazard in severe metabolic acidosis is often ventilation loss, not oxygenation; sedation/paralysis removes the patient’s life-saving compensation, PaCO₂ rebounds fast, and you can fall off a pH cliff before anyone has time to react. 
I really appreciate how you operationalize it: VCV for predictable minute ventilation, RR as the primary lever, and using Winter’s equation / pre-intubation minute ventilation as the “compensation target” rather than trusting default vent settings. 
Two bedside add-ons I’ve found helpful conceptually:
1. “Measure what you’re about to take away” (RR/VT/minute ventilation before induction, or NIV-delivered MV during preoxygenation) so the initial vent plan is anchored in reality.
2. Treat auto-PEEP like the hidden tax of high RR; set I:E intentionally, watch flow return to baseline, trend EtCO₂ (with the usual shock caveats), and get an early ABG to iterate quickly. 
Clinically honest, teachable, and exactly the kind of post that prevents avoidable arrests.
This is an excellent physiology-forward write-up, and the framing is exactly right: in severe metabolic acidosis, the peri-intubation killer often isn’t oxygenation, it’s loss of compensatory minute ventilation and rapid CO₂ rise → pH cliff → hemodynamic collapse. 
I especially appreciate the practical emphasis on VCV for predictable ventilation, using RR as the primary lever, and explicitly sanity-checking targets with Winter’s equation rather than default vent settings that are almost always too “gentle” for these patients. 
One bedside pearl I’d add: measure what the patient is doing before you take it away. Watching pre-intubation RR/VT (or NIV-delivered minute ventilation during preoxygenation) gives you a concrete “compensation target,” then re-check an ABG early (20–30 min) and titrate while vigilantly screening for auto-PEEP/air-trapping and hemodynamic intolerance. 
High yield, clinically honest, and very teachable; thank you for putting words and numbers to what many of us feel at the bedside!
Thank you for such a thoughtful and generous comment. Really appreciate you taking the time to engage so deeply with the physiology and share a practical bedside pearl—it adds a lot of value to the discussion.
Does non-invasive monitoring (Transcutaneous) of blood gas by Sentec (both tcPco2 and tcPcCo2 as PtC- can help in these patients?
Yes it can be used, but still this technology is new and needs more evidence support.
Great read!
My question is,, how much value does ETC02 add in this situation, as very often the lung physiology is also not optimal, and does not reflect pc02?
Very interesting question sir, So I answered it in a different note with literature references,
Have a look and get back for more discussion.
https://substack.com/profile/8658456-life-on-the-frontline/note/c-192447283?utm_source=notes-share-action&r=55kwo
and Thank you for reading and participating!
One of the biggest challenges in managing these patients is deciding what tidal volume or minute ventilation we should actually target after intubation. ABG values help, but they are always retrospective. They tell us what *was* happening, not what is happening right now.
A common statement from experts is that no ventilator setting can truly match a patient’s physiological compensatory ventilation in severe metabolic acidosis. That is largely true. But if our goal is to get as close as possible, we first need to know what the patient was doing before we took over their breathing.
During preoxygenation, place the patient on NIV and observe the delivered tidal volume or minute ventilation. This represents the patient’s genuine compensatory effort. NIV applied after RSI drugs does not reflect true physiology and should not be used for this purpose.
Once this pre-intubation minute ventilation is known, it gives us a rational target after intubation. We may not fully reproduce it, but we can intentionally aim toward it.
Without knowing this baseline, ventilator adjustments become guesswork. We end up increasing and decreasing settings repeatedly, reacting to delayed numbers rather than physiology.
Please share your comments or difficulties with this approach if you had faced or will face if you try to adopt this before intubation. Open for discussion
Thank you for this insightful comment. Yes I guess everyone will definitely have some doubts regarding these patients, can discuss the problem faced here on these comments and they can be tackled bedside.
Addition on how to set the initial parameters..
For Calculating appropriate minute ventilation, we can calculate approximate goal minute ventilation as mentioned in the REBEL EM article (cited as reference no 1)
This is a very high-yield physiology-forward reminder that the peri-intubation hazard in severe metabolic acidosis is often ventilation loss, not oxygenation; sedation/paralysis removes the patient’s life-saving compensation, PaCO₂ rebounds fast, and you can fall off a pH cliff before anyone has time to react. 
I really appreciate how you operationalize it: VCV for predictable minute ventilation, RR as the primary lever, and using Winter’s equation / pre-intubation minute ventilation as the “compensation target” rather than trusting default vent settings. 
Two bedside add-ons I’ve found helpful conceptually:
1. “Measure what you’re about to take away” (RR/VT/minute ventilation before induction, or NIV-delivered MV during preoxygenation) so the initial vent plan is anchored in reality.
2. Treat auto-PEEP like the hidden tax of high RR; set I:E intentionally, watch flow return to baseline, trend EtCO₂ (with the usual shock caveats), and get an early ABG to iterate quickly. 
Clinically honest, teachable, and exactly the kind of post that prevents avoidable arrests.