Case Study: Ventilating Severe Metabolic Acidosis!

March 9, 2026

AI Summary

5 min read

Case Study: Ventilating Severe Metabolic Acidosis

A mid-50s man found down at a bus stop, altered, with a blood sugar over 600. Medics gave Narcan with no response. In the ER, he had seizure-like activity, desaturated to 70%, and was intubated with concern for aspiration. The team started low tidal volume ventilation—about 6 mL per kg—to protect against ARDS. But the waveforms told a different story than expected.

The pressure waveform showed peak inspiratory pressure in the single digits, barely above PEEP. The flow waveform showed the patient pulling flow in a nearly straight line throughout inspiration, then blowing out hard at the end. The volume waveform didn't show the expected exponential rise. These were not the waveforms of a passive, well-supported patient. They were the waveforms of a patient fighting the ventilator.

The Core Problem: Matching Pre-Intubation Physiology

When you intubate a patient with severe metabolic acidosis—likely DKA given the blood sugar over 600 and positive ketones—you inherit a problem. Before intubation, the patient was breathing hard and fast to compensate for the acidosis. After intubation, you need to match that minute ventilation. But you cannot simply set a high rate and high volume and expect it to work.

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What you'll learn

1 (00:00) **Case Introduction & Initial Ventilator Settings** - A mid-50s man found down with altered mental status, sugar >600, and seizure-like activity leads to intubation with low tidal volume settings (6-7 mL/kg) due to aspiration concern.
2 (01:34) **Expected vs. Actual Waveforms in PRVC** - The host describes what PRVC waveforms should look like in a passive patient and contrasts them with the abnormal waveforms seen.
3 (03:27) **Identifying Dyssynchrony: Delayed Cycling** - The waveforms show multiple dyssynchronies, especially delayed cycling, where the patient pushes against the ventilator to trigger expiration.
4 (04:28) **Linking Waveforms to Clinical Context: DKA/HHS** - The patient’s history (altered, sugar >600) suggests metabolic acidosis (DKA/HHS), which drives high respiratory effort.
5 (05:40) **Ventilating the Passive Patient with Metabolic Acidosis** - For a paralyzed patient, you cannot simply increase rate and volume; you must calculate time constant to set a safe rate and avoid auto-PEEP.
6 (08:57) **The Active Patient: PRVC Limitations and Patient Effort** - As the patient wakes and breathes spontaneously, PRVC reduces support as the patient pulls more volume, making it counterproductive.
7 (10:38) **ICU Fellow’s Advice: Pressure Control with Low Driving Pressure** - The fellow’s recommendation to use “lowest driving pressure” is critiqued, as driving pressure is only valid in passive patients with zero flow at end-inspiration.

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Show Notes

My approach to ventilating severe metabolic acidosis! Often needing to balance harm of the acidosis with harm of the ventilator and creating a balance of these 2 forces while we fix the underlying pathophysiology!