Measurement of Blood Gas, pH, and Electrolyte Data

1. Blood gases
   • Provide accurate measurement of PO2, PCO2, pH, hemoglobin saturation, and bicarbonate

   • Requires arterial blood, drawn in appropriate equipment and transported quickly (10-15 min) on ice to the lab

   • Erroneous results from room temp specimens (cellular metabolism) and specimens with air bubbles or improper capping (equilibration with air)

   • Check ulnar artery patency before radial artery draws!!!!

2. Serum electrolytes
   • Uses a standard serum specimen

   • "Chem 7" electrolyte panel includes sodium, potassium, chloride, CO2 content (bicarb), BUN, creatinine, glucose

     

   • Issues of frequency and utility for this test panel

     Do you really need one every day in a hospitalized patient (usually not)? Are chloride and CO2 content really helpful (usually not, unless a specific problem is suspected)?

   • CO2 content not a particularly accurate measure of bicarbonate.

   The CO2 content can provide a useful quick-and-dirty check for metabolic acid-base problems, but use a blood gas bicarb for calculations. The CO2 content reference range is so broad (partly because it allows for equilibration with air and cellular metabolism) that it overlaps into areas that would indicate significant acidosis or alkalosis in a blood gase bicarbonate measurement.