Jen's ABG equipment study tips (2/17)

3 components to a blood gas analyzer

1. Electronic circuitry (displays visuals)

2. Electrolyte solution (promotes reactions + current)

3. blood gas electrodes (measures pH, PCO2 and PO2, all other values are calculated)

Measured values of ABG? Calculated ones?

Measured: pH PCO2 and PO2

Calculates all other values

Name of each electrode

pH: Sanz (measured @37C)

PCO2: Severinghaus (measured indirectly)

PO2: Clark/polarographic

Mean definition

Average calculated by dividing sum of all numbers in a group by number of entries

Standard deviation

High + low that represents 95% of where normal population falls when subjected to a certain test, being a measure of variance around the mean.

Aka., measure of spread from the average (mean).

Quality control

Control samples have their range of normal based on ±2 SD’s from the mean, being able to determine mean and SD by running 20 control samples through machine. All 3 levels (acidosis, alkalosis and normal) are run every 24h/shift through vials with a known concentration matching each level.

Calibration

When equipment is adjusted/corrected to mach the control standards to determine accuracy and precision

Accuracy vs precision

Accuracy = mean value of several measurements

Precision = how consistently same measurement will produce same results

Levey-Jennings chart

Functions to tell you whether an ABG machine is ready or not.

Control: shows if all QC (quality control) runs are w/i acceptability (±2 SD’s)
Trend: shows if QC’s start trending towards one side of SD (ex. can still use, but its trending out of control)
Random error: all w/i acceptability except one run (still ok!)
Out of control: 2+ out of acceptability.

What causes a “shift/drift” on L-J chart?

Electrode or sensor malfunction if protein is deposited on membrane or there’s a leak in the membrane, electrolyte, depletion or sensor failure.

What causes it to be “out of control” on L-J chart?

Temperature control failure to maintain 37C or thermometer inaccuracy.

What causes it to be “consistently high or low” on L-J chart?

Improper calibration of either inadequate or contaminated buffer or calibration gas.

What might cause clotting in system?

Mechanical problems with leak/improper fxn pump tubing or valves.

ABG sample troubleshooting air bubbles

Room air bubble causes pH, PO2 and SaO2 to rise and pCO2 to lower due to equilibrium.

ABG sample troubleshooting venous admixture

Risk of puncturing vein causing a decreased PO2, and increased PCO2 and SaO2.

ABG sample troubleshooting metabolism. What increases after prolonged sample duration? What decreases?

Cellular metabolism continues even after blood is collected so prolonged storage will cause decreased pH, pO2 and cGlu, and increased pCO2, cCa2 and cLac.

ABG sample troubleshooting heparin and dilution

anticoagulants dilute sample which can decrease pCO2.