Skip to main content

Changes in urinary electrolytes during acute respiratory acid-base modifications

Introduction

The renal system compensates respiratory disorders of acid-base equilibrium by modifying the urinary electrolyte composition [1]. Such a condition mainly involves changes in urinary ammonium excretion as a reaction to prolonged periods of acid-base disequilibrium, leaving the renal response to acute derangements unexplored. We aimed to determine the acute variations of urinary ammonium [NH4+]u, sodium [Na+]u, potassium [K+]u and chloride [Cl]u concentrations following controlled minimal respiratory acid- base imbalances, and to further investigate whether urinary anion gap ([AG]u = [Na+]u + [K+]u - [Cl]u) and sodium and chloride difference ([Na+]u - [Cl]u) might unveil an early activation of the renal response.

Methods

Patients admitted to the ICU after major surgery were enrolled, during intubation and sedation. Patients with chronic renal failure were excluded. A urinary catheter was connected to the quasi- continuous urinary analyzer KING®, measuring [NH4+]u, [Na+]u, [K+]u and [Cl]u over time. Based upon the arterial pH (pHa) at entrance, patients were randomly assigned to controlled hypoventilation (30% reduction of minute ventilation if pHa ≥7.40) or hyperventilation (30% increase of minute ventilation if pHa <7.40) for 2 hours. Samples for blood gas analysis were collected every 30 minutes.

Results

Thirty patients were enrolled; 20 were hypoventilated, 10 hyperventilated. At 2 hours from ventilation change, pHa was respectively decreased from 7.44 ± 0.02 to 7.34 ± 0.02 and increased from 7.37 ± 0.03 to 7.44 ± 0.02 (P < 0.001) in the two groups. Mean [NH4+]u rose by 2.6 ± 3.3 mEq/l in hypoventilated patients and fell by 2.5 ± 2.4 mEq/l in the hyperventilated (P < 0.001). No difference in mean [K+]u was observed at any time, while [Na+]u and [Cl]u progressively decreased in both groups (P < 0.05). [Na+]u was reduced by 48 ± 43 mEq/l during hypoventilation and by 32 ± 41 mEq/l during hyperventilation (P = 0.14), while [Clļu decreased by 29 ± 69 and by 46 ± 66 mEq/l respectively (P = 0.93). Whereas [AG]u did not differ between groups, [Na+]u - [Cl]u variation of hyperventilated patients was greater than that of hypoventilated (17 ± 34 vs. -18 ± 54 mEq/l, P < 0.05).

Conclusion

During acute respiratory modifications, changes in urinary ammonium can be observed within the first 2 hours even while maintaining arterial pH within a physiologic range. This response seems to be better associated with changes in the difference between urinary sodium and chloride rather than anion gap.

References

  1. 1.

    Ramadoss J, et al.: Can J Physiol Pharmacol. 2011, 89: 227-231. 10.1139/Y11-008

    PubMed Central  CAS  Article  PubMed  Google Scholar 

Download references

Author information

Affiliations

Authors

Corresponding author

Correspondence to M Ferrari.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Ferrari, M. Changes in urinary electrolytes during acute respiratory acid-base modifications. Crit Care 18, P430 (2014). https://doi.org/10.1186/cc13620

Download citation

Keywords

  • Minute Ventilation
  • Urinary Sodium
  • Electrolyte Composition
  • Ammonium Excretion
  • Renal Response