Trivia check: in a pre-oxygenated, isoflurane-maintained dog on a rebreathing system, which monitor typically alerts you to hypoventilation first — EtCO2 rising past about 55 mmHg on capnography, SpO2 dipping, or HR drifting — and why? I usually see the capnogram climb within 1–2 minutes after reducing minute ventilation on a 25 kg Lab, long before SpO2 moves, but I’m curious if your protocols show the same pattern.
EtCO2 flags it first for me too; my practical tweak is set the high EtCO2 alarm to 50 mmHg and watch inspired CO2 — if the baseline climbs above 0–2 mmHg while the peak crosses “55 mmHg,” that’s rebreathing (absorber/APL) more than pure hypoventilation… Do you see the plateau slope steepen before the number jumps on your setup?
Capnography usually leads because “pre-oxygenation buys time,” so I set a high EtCO2 alarm at 50–55 mmHg plus a short apnea alarm and start a couple of controlled breaths as soon as the plateau climbs. Do you see the alveolar plateau lengthen or a subtle shark-fin before the number jumps? Caveat: with low cardiac output or a kinked sampling line, EtCO2 can under-read, so I confirm perfusion and the line before chasing ventilation.