Agreement between two plasma bicarbonate assays in critically ill patients

Area of Science:

• Clinical Chemistry
• Critical Care Medicine
• Biomedical Engineering

Background:

• Plasma bicarbonate concentration is a key indicator of acid-base balance.
• The Henderson-Hasselbalch equation is commonly used for its calculation, but its reliability is questioned in critically ill patients.
• Discrepancies in bicarbonate measurement can impact clinical decision-making.

Purpose of the Study:

• To evaluate the agreement between two commonly used plasma bicarbonate assays in critically ill patients.
• To compare bicarbonate measurements derived from the Henderson-Hasselbalch equation with those from a spectrophotometric enzymatic technique.
• To determine the clinical significance of any observed discrepancies.

Main Methods:

• A comparative study design was employed using routine daily blood samples from critically ill patients.
• Paired arterial blood samples were analyzed concurrently using two distinct bicarbonate measurement methods.
• Bland-Altman analysis was utilized to assess the agreement and quantify bias between the two assays.

Main Results:

• A significant bias of -1.6 mmol/l (95% CI: -1.2 to -2.0 mmol/l) was observed when comparing the enzymatic method to the calculated method.
• The limits of agreement ranged from -5.85 mmol/l to 2.65 mmol/l, indicating substantial variability.
• The study revealed poor agreement between the two plasma bicarbonate assays.

Conclusions:

• The findings indicate poor agreement between calculated and enzymatic plasma bicarbonate assays in critically ill patients.
• This discrepancy holds clinical importance, potentially affecting patient management and treatment strategies.
• Further research is recommended to investigate the underlying causes of this unreliability and to improve bicarbonate measurement accuracy.