PFT

• Degradation and Protein contamination of membrane slows diffusion of CO2  across membrane
• Electrolyte depletion
• Routine maintenance is important

• Electrode contamination and degradation – alters diffusion of O2
• Depletion of electrolyte
• Tip must be “polished” periodically

CO2 is hydrated in electrolyte and forms H ions, voltage develops proportional to CO2   

O2 is reduced; electrons flow from anode to cathode proportional to # of molecules of reduced O2  , current is measured (amperometric)

• Oximetry
• Co Oximetry
• Hemoxitry

O2Hb and reduced Hgb (RHb)

• Vascular dyes
• Nail polish
• Skin pigment
• Ambient light

• difference between current & previous calibrations
• Indicates electrode’s stability

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

Continuous monitor of oxygenation and ventilation

• 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

• If PaO2 < 158mmHg, air bubble will cause PaO2 to increase
• If PaO2 > 158mmHg, air bubble will cause PaO2 to decrease

• Mixed venous – average of all venous blood returning to the heart
• Obtained from a catheter in the pulmonary artery

• Suspected when patient’s clinical status is better than ABGs suggest
• Crosscheck with pulse oximeter or ask another therapist to obtain a new sample

• Lithium heparin
• 1000 U/ml
• 0.05 mls per 1.0 ml of blood sample

Excessive volume causes decrease in CO2 and ↓pH

PCO2 and infants

• Decrease in pH
• Decrease in PaO2
• Increase in CO2

30 minutes

2 hours

• ↑temp → ↑PaO2 and ↑PaCO2 
• Both should be reported
• Problem: Normal blood gases at various temps are unknown

PO2

• 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”

• Transcription
• Verbal reports
• •Importance of “read back”
• Posting to wrong patient
• Failure to report “critical” values
• Correct interpretation
• Redraw, repeat on another analyzer if necessary!!!

CLIA

• IDENTIFY PATIENTS CORRECTLY
• IMPROVE STAFF COMMUNICATION
• USE MEDICINES SAFELY
• PREVENT INFECTION
• IDENTIFY PATIENT SAFETY RISKS
• PREVENT MISTAKES IN SURGERY