Neuroanaesthesia & neurocritical care
Electrolyte redistribution during acute respiratory acid–base changes: an in vivo study using apnoea testing
Main finding · pH-dependent change in strong ion difference (SID)Result — go to the resultChange in SID −11.7 meq L-1 95% CI −13.1 to −10.3Authors' conclusion
Acute respiratory acid-base disturbances produce in vivo Na and Cl redistribution associated with pH change that are modulated by haemoglobin concentration. The observed pH-dependent electrolyte redistribution is consistent with physiological buffering and can be reasonably approximated using a simple bedside pH-correction model.
Study context
- Population
- Patients undergoing apnoea testing for organ donation after determination of brain death
- Participants
- 263 participants
- Exposure
- pH-dependent change in strong ion difference during apnoea testing; derived model vs a simple bedside pH-correction method (ΔSID=−15×ΔpH)
- Outcome
- pH-dependent change in strong ion difference (SID)
Main finding
As reported in the abstract
Change in strong ion difference (SID)
−11.7 meq L-1
95% CI −13.1 to −10.3
P < 0.001
Per pH unit increase, as printed
Observational data: associations, not effects.
Further findings
Agreement between predicted and observed SID changes, derived model vs simplified pH-correction model · only modestly improved by using the derived model
pH during apnoea testing
- pH decreased from
- 7.40 (0.07)
- pH decreased to
- 7.23 (0.07)
- pH returned to
- 7.40 (0.08)
Individual electrolytes contributing to the pH-dependent SID change
- Sodium ion (Na), 52% of change
- −7.2 mM; P<0.001
- Chloride ion (Cl), 36% of change
- +3.7 mM; P<0.001
Effect modification of pH-SID relation
- Higher haemoglobin concentration associated with a higher pH-dependent SID change; together explaining 53% of within-patient variability
- 53%
Original publication
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