2.23: Blood Gas Analysis
- Page ID
- 120628
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RELATED READING: Chapter 25. See Methods on CD-ROM for Blood Gas Analysis.
OBJECTIVES
Upon completion of this exercise, appropriate discussion, and related readings, the student will be able to:
- Verify calibration of a blood gas analyzer and adjust calibration if needed. (For many instruments these values are preset and it is not possible to adjust calibration.)
- Perform blood gas analysis as instructed.
- Discuss the effect of improper collection or handling of arterial samples on blood gas values.
METHOD
Whatever automated blood-gas instrument is available.
MATERIALS
- Arterial blood samples
- Blood Gas Analyzer
- Controls
GLOSSARY
Calibrator -the initial of the two standards used for calibration of pH, PCO2, and PO2 measurements on a blood-gas instrument.
Sloping reagent - the second of the two standards used for calibration of the pH, PCO2, and PO2 measurements on a blood-gas instrument. This sets the slope of the calibration line.
PROCEDURE
- Following the instructions given by your instructor, check the calibration of the blood gas analyzer and adjust the calibrator and slope setting as needed.
- Verify calibration by running appropriate controls. Record your results on the data sheet.
- Determine the gas values for the samples provided by your instructor. Record your results on the data sheet.
- Following the instructions given by your instructor, alter the sample in some way.
- Repeat the blood gas analysis on the altered sample and record the results on the data sheet.
- When all samples have been tested, leave the instrument in stand-by mode.
OPTIONAL EXERCISES
Sample Alteration: The following is a list of suggested activities that can be used to illustrate the error that can be induced by the improper handling of arterial samples when performing blood gas analysis.
- Introduce a small air bubble into the sample, recap, mix and return the sample to ice bath storage for 10 minutes. Retest the sample. Allow the sample to remain at room temperature for an additional 10 minutes, then retest.
- Introduce a moderate air bubble into the sample. Recap, mix and allow the sample to remain at room temperature for 10 minutes. Retest the sample.
- Uncap the syringe and place it in a 37°C incubator for 10 minutes. Retest the sample. (This would be similar to placing the sample on top of a warm instrument).
- Draw 0.5 mL of heparin into the sample. Recap, mix and retest the sample. Allow the sample to stand at room temperature for 10 minutes. Retest the sample.
- Allow the capped sample to remain at room temperature. Retest after 5, 10, and 15 minutes.
- Allow the capped sample to stand on ice in a vertical position for 10 minutes, allowing the plasma and cells to separate. Retest the sample without mixing.
| DATA SHEET, EXERCISE #23 |
NAME: ___________ DATE: ___________ |
RESULTS
| pH | PCO2 (mm Hg) | PO2 (mm Hg) |
TCO2 (mmol/L) | Base Excess (mmol/L) | O2 Sat. (%) | |
|---|---|---|---|---|---|---|
| Low Control | ||||||
| Medium Control | ||||||
| High Control | ||||||
| Sample 1 | ||||||
| Sample 2 | ||||||
| Sample 3 |
OPTIONAL EXERCISES
| Initial Sample Values | Altered Sample Values | |||
|---|---|---|---|---|
| Sample 1 | Sample 2 | Sample 3 | ||
| pH | ||||
| PCO2 (mm Hg) | ||||
| PO2 (mm Hg) | ||||
| TCO2 (mmol/L) | ||||
| Base Excess (mmol/L) | ||||
| O2 Saturation (%) | ||||
Note below how each sample was altered.
Discussion Questions
- What was done to alter the samples you tested?
- What blood-gas parameters were changed as a result of each sample manipulation?
- Briefly discuss why these changes occurred.
- Can you think of any circumstances in which a blood-gas sample received at room temperature might still be an acceptable specimen?
- Can you think of any circumstance in which a blood-gas sample containing a large air bubble might still be an acceptable specimen?