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Problems with the PCO2 electrode!
- Degradation and Protein contamination of membrane slows diffusion of CO2 across membrane
- Electrolyte depletion
- Routine maintenance is important
Problems with PO2 electrode!
- Electrode contamination and degradation – alters diffusion of O2
- Depletion of electrolyte
- Tip must be “polished” periodically
PCO2 electrode measures CO2 by!
CO2 is hydrated in electrolyte and forms H ions, voltage develops proportional to CO2
PO2 Electrode measures O2 by!
O2 is reduced; electrons flow from anode to cathode proportional to # of molecules of reduced O2 , current is measured (amperometric)
What devices are used to measure Hb?
- Co Oximetry
What are the two forms of Hb that a pulse ox can measure?
O2Hb and reduced Hgb (RHb)
Some factors that might cause a pulse ox to read inaccurate?
- Vascular dyes
- Nail polish
- Skin pigment
- Ambient light
Drift with colibration!
- difference between current & previous calibrations
- Indicates electrode’s stability
When and where are you more likely to get a vein instead of an artery?
More likely in hypotensive patient & with femoral artery puncture
- Isolated result outside of control limit
- Minor significance
- Should be observed carefully, but disregarded
Recurrent measurable deviation away from the mean
- Progressive measurement either increasing or decreasing
- Causes – aging electrode, protein contamination
- Relatively abrupt change in measurement followed by a cluster or plateau
- Causes – bubbles on sensor tip, temp change, contaminated calibrants
- Extent to which repeated measurements of same “known” can be reproduced
- Defined in terms of variability based on standard deviation (SD) of a series of measurements
- Index of dispersion of repeated measurements
- Indicated by pattern of “hits” at a target
- Extent to which a “known” results in value approximating that “known”
- Mean of repeated measurements approximates “known”
- Or, how closely measured results reflect the true / actual value
- Problems are usually characterized by systematic errors
- Indicated by closeness to the “bull’s-eye” of a target
Most heat skin site to 40-45 C ̊to arterialize capillary blood flow: ↑temp - ↓response time
Why is Transcutaneous monitoring done?
Continuous monitor of oxygenation and ventilation
Precautions for Transcutaneous monitoring!
- Move electrode every 2-6 hours to prevent burns especially in neonates
- Both sensors require calibration & periodic recalibration (q 2-6 hours)
- 5-30 minutes warm-up may be required for equilibration after sensor placement
- Can trend oxygenation when PaO2-PtcO2 gradient is established
- Close correlation in neonates, patients with normal cardiac output
- Patients with severe leukocytosis (Leukemia) will demonstrate very fast metabolic changes (↓PaO2)
- Samples from such patients should be drawn in glass syringe, iced, analyzed immediately
Air in sample!
- If PaO2 < 158mmHg, air bubble will cause PaO2 to increase
- If PaO2 > 158mmHg, air bubble will cause PaO2 to decrease
Mixed venous blood!
- Mixed venous – average of all venous blood returning to the heart
- Obtained from a catheter in the pulmonary artery
How can you identify an mixed venous sample!
- Suspected when patient’s clinical status is better than ABGs suggest
- Crosscheck with pulse oximeter or ask another therapist to obtain a new sample
Recommended amount of heparin!
- Lithium heparin
- 1000 U/ml
- 0.05 mls per 1.0 ml of blood sample
What is the primarily result of too much heparin?
Excessive volume causes decrease in CO2 and ↓pH
What sample is more vournable to heparin?
PCO2 and infants
What are the effects of metabolism on blood gases?
- Decrease in pH
- Decrease in PaO2
- Increase in CO2
Room temp blood gases should be analyzed within...
Iced samples blood gases should be analyzed within...
Effects of temperature on normal blood gases!
- ↑temp → ↑PaO2 and ↑PaCO2
- Both should be reported
- Problem: Normal blood gases at various temps are unknown
Which electrode is least accuracte?
- Measurement of unknowns (“blinded samples”) & comparing with other labs using same method (interlaboratory)
- Provides measure of absolute accuracy of laboratory
Degree of dispersion or scattering of values from the average
- During puncture
- During transportation (ice slush for more uniform cooling if delay >30 minutes)
- Wrong patient
- Sample Handling
- Incorrect therapy or documentation
- Failure to mix sample
- Failure to allow time for analysis to “end-point”
- Verbal reports
- •Importance of “read back”
- Posting to wrong patient
- Failure to report “critical” values
- Correct interpretation
- Redraw, repeat on another analyzer if necessary!!!
Standards for RC departments and Pulmonary Labs guidelines!
2013 patient safety goals!
- IDENTIFY PATIENTS CORRECTLY
- IMPROVE STAFF COMMUNICATION
- USE MEDICINES SAFELY
- PREVENT INFECTION
- IDENTIFY PATIENT SAFETY RISKS
- PREVENT MISTAKES IN SURGERY
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