Blood Gas electrode and quality assurance

Does not

In the PCO2 electrode, blood (dose /dose not )come in direct contact with the pH -sensitive glass.

anode

In the electrical system of the Clark electrode ,the silver is positively charged and serves as the

Quality Assurance in blood gas analysis

It is a systemic process used to monitor, document and regulate The accuracy and reliability of laboratory measurement

Sodium chloride solution

Cathode and anode are placed in

1-calibration 2- quality control

Elimination of pre analytic errors :

Analytical error

Errors that occur during the actual analysis of the sample The performance of electrode

Cathode : platinum- Anode : a silver /silver chloride + Cathode and anode are are placed in the electrolyte (Sodium chloride solution )

PO2 electrode ( Clark electrode )

1-O2 electrode (the Clark electrode) 2-pH electrode(the snaz electrode) 3-CO2 electrode (severingaus)

Types of electrode :

1-clot 2-reagent replacement 3-electrode replacement 4-recommended time between calibration has been exceed 5-After repairs or adjustment are completed

When more frequent QC is required?

1-at the start of each day 2- after any daily maintenance 3-if the analyzer or process is useless frequency twice a week only, then a QC sample needs to be analyzed only onthe days that patient samples are analyzed

When should a QC sample be analyzed?

Blood comes in contact with a co2 Modified pH electrode permeable membrane , the membrane made of silicone rubber ,Teflon, on the other side of the membrane is a bicarbonate solution that is in direct contact with the pH sensitive glass. Chemical reaction occurs within the bicarbonate solution as CO2 diffuses in.

pCO2 Electrode (Severinghaus)

pH measured by potentiometer in method What does means potentiometry ? The measurement of potential (voltage) between two electrode 1-measuring electrode (ion sensitive ) pH-sensitive glass allows hydrogen ions to diffuse into it . The tip is made of a special glass (sensitive only to H+) 2-reference electrode (constant potential electrode) known pH is present to compare the unknown voltage against. inan internal buffer solution with a fixed pH (=7) • Constantly gives a fixed and stable potential 2-reference electrode

pH electrode (sans electrode)

electrodes measure changes in electrical current of voltage and equate these changes with chemical measurement.

pH, PaCO2, PaO2 are measured directly by special electrodes (electrochemical devices) contained in a machine made for that purpose.

To initiate the electrical current and the measurement of oxygen ,the battery supplies the platinum cathode with a voltage of approximately 700 millivolts, this voltage attract oxygen molecules to the cathode where they react with water. The current generated in the circuit will be in direct proportion to the amount of dissolved oxygen present at the cathode.

pO2 electrode (clarck Electrode)

True

two)levels of controls should be run at least once per shift.

points calibration adjusts the electronic responses to 2 standards (Is done automatically at least every 8 hours and after electrodes maintenance)

1 point calibration is an adjustment of the electronic response to a single standard (Before each sample or routinely every 20-30 min)

Non analytical errors

An error that occurs before or after actual analysis (improper sampling technique )

It is a medical machine that measures pH and blood gas i.e.; (pCO2) and (pO2), in whole blood. It may also measure electrolytes ( K, Na, Ca, and Cl) and metabolites as (glucose, lactate, and bilirubin).

Blood Gas analyzers

PCO2 is a modified PH electrode (Measuring /reference ) it contains : -An inner PH electrode - surrounded by an internal fill solution (bicarbonate HCO3) -covered by an outer semi terrible silicon membrane selective to CO

PCO2 electrode :

Quality control After analysis, each result of the QC sample is compared to its known value If the results all fall within 95 -100% of the known values, the patient results will be correct

Quality Control sample is usually made of a liquid Its values are already known It is analyzed in exactly the same way as a patient sample

Quality control

Samples with known blood gas values that are periodically run to ensure that the machine is operating correctly are called

Voltage

The PCO2 electrodes actually measures (voltage/current) change .

Clark electrode

The PO2 electrode that incorporates a semipermeable membrane to prevent contact of the blood with the electrode terminal is called the

Silver chloride

The anode ion Clark electrode :

Platinum

The cathode in Clarke electrode is

Quality control

The periodic checking of an instrument performance to ensure calibration , stability and reliability is called -

The reference electrode in the PO2 electrode is made of (silver chloride

There (is/is not) actual flow of electrical current in the pH electrode.