Gas Analyzers
CO2 is less than 0.5%
COLORIMETRIC (Color is purple)
CO2 is Up to 2%
COLORIMETRIC (Color is tan)
CO2 exceeds 2%
COLORIMETRIC CO2 ANALYZERS (Color is yellow)
OXYGEN Analyzers (There are 2 common types)
Clark Electrode (Polarographic) and Galvanic Fuel Cell
-Measuring electrode -Reference electrode
Consists of 2 half cell electrodes. (THE PH ELECTRODE AND THE POTENTIOMETRIC METHOD)
Mainstream and Sidestream
Two methods in obtaining a gas sample for analysis (2 TECHNIQUES FOR MONITORING PETCO2)
OXYGEN ANALYZERS
Used to analyze the FiO2 of inspired gas
Capnometry
______is a noninvasive method that measures the end-tidal partial pressure of carbon dioxide in the expired gas. As with pulse oximetry ______ is based on the principle that carbon dioxide absorbs infrared light.
The reference electrode
contains a mercury/mercurous chloride rod Surrounded by a solution of potassium Chloride which creates a small electric voltage
Measuring half cell
contains a silver-silver chloride rod surrounded by a solution of fluid with a constant ph of 6.840 and is capped by a pH sensitive glass membrane
Capnography
is the technique of displaying CO2 measurements as waveforms (capnograms) throughout the respiratory
Galvanic fuel cells
use a gold anode and a lead cathode. Current is generated by the chemical reaction of potassium hydroxide and oxygen. The greater the oxygen, the more reaction with the potassium, the more current generated which is converted to %O2.
Mainstream (Flow-through or In-line)
⚫ Adapter placed in the breathing circuit ⚫ No gas is removed from the airway ⚫ Adds bulk to the breathing circuit ⚫ Electronics are vulnerable to mechanical damage
Indication
⚫ Continuous monitoring of adequacy of oxygenation/ventilation ⚫ Need for real time assessment of therapeutic intervention (TRANSCUTANEOUS OXYGEN AND CO2 MONITORING)
Precautions
⚫ False-negative or false-positive results may lead to inappropriate treatment ⚫ Tissue injury (burns/tearing) may occur at the sensor site because sensor heats to 43.5 C (TRANSCUTANEOUS OXYGEN AND CO2 MONITORING)
Sidestream (aspiration)
⚫ Gas is aspirated from an airway sampling site and transported through a tube to a remote CO2 analyzer ⚫ Provides ability to analyze multiple gases ⚫ Can be used in non-intubated patients ⚫ Potential for disconnect or leaks giving false readings ⚫ Withdraws 50 to 500ml/min of gas from breathing circuit (most common is 150-200ml/min) ⚫ Water vapor from circuit condenses on its way to monitor -A water trap is usually interposed between the sample line and analyzer to protect optical equipment
Factors affecting accuracy
⚫ Patient age: agreement between sensed gas and actual PaO2 or PaCO2 decreases with age. The best correlation occurs only in neonates. ⚫ Poor perfusion either localized or systemic. ⚫ Calibration must be done prior to application. ⚫ Response time: response time of the electrode varies due to skin thickness, temperature and patient age (TRANSCUTANEOUS OXYGEN AND CO2 MONITORING)
Contraindications
⚫ Patients with poor skin integrity and adhesive allergies (TRANSCUTANEOUS OXYGEN AND CO2 MONITORING)
CO-OXIMETRY (Measures)
⚫ SaO2%, MetHb, HbCO% ⚫ SaO2 is measured as a percentage of the Oxyhemoglobin compared with all measured forms of Hb including dyshemoglobin species (functional Hb) ⚫ Potential measurement errors occur in neonates with substantial quantities of fetal hemoglobin - May show increased levels of HbCO, decreased SaO2 ⚫ Usually run in tandem with arterial ABG
COLORIMETRIC CO2 ANALYZERS (no perfusion)
❖ If patient has______, ET could be in airway and color will still be purple
THE PO2 ELECTRODE AND THE POLAROGRAPHIC METHOD
-Blood is separated from the electrode terminals by the use of an O2 permeable membrane -Oxygen diffuses easily thru this membrane into the electrolyte solution -The Cathode attracts oxygen molecules where they react with the H2O in the electrolyte solution -The chemical reaction at the cathode consumes 4 O2 electrons which are rapidly replaced as the silver and chloride react at the Anode. The more electrons consumed, the greater the electron flow between the poles. -The current generated will be in direct proportion to the amount of dissolved oxygen present at the cathode -A Polarogram graph shows the direct relationship between the PO2 and the voltage at the cathode
Clark Electrodes
-Function is similar to ABG machines
Oximetry
-Is the measurement of hemoglobin saturation using spectrophotometry -Try works because every substance emits its own unique pattern of light (absorption/emission). -Each form of hemoglobin (e.g., HbO2 , HbCO) has its own pattern of light absorption. -For example, HbO2 absorbs less red light and more infrared light
CAPNOMETRY
-Measures end tidal CO2: The maximum partial pressure of CO2 exhaled during a tidal breath just before the beginning of inspiration; expressed as PetCO2 -Respiratory context: inspired and expired gases sampled at the Y connector, mask or nasal cannula. -Gives insight into alterations in ventilation, cardiac output, distribution of pulmonary blood flow and metabolic activi
HOW ETCO2 WORKS
-Photo detector measures the amount of infrared light absorbed by airway gas during inspiration and expiration ⚫ CO2 molecules absorb specific wavelengths of infrared light energy ⚫ Light absorption increases directly with CO2 concentration - A monitor converts this data to a CO2 value and a corresponding waveform (capnogram)
TRANSCUTANEOUS OXYGEN AND CO2 MONITORING
-Provides continuous and non invasive estimates of arterial PO2 and PCO2 through a surface skin sensor. -Expressed as PtcO2 and PtcCO2 -Devices heat the skin to help vascularize the tissue increasing the permeability of O2 and CO2 from the capillary
voltage
-The Reference electrode creates a known (PH ELECTRODE)
PH ELECTRODE
-The Reference electrode creates a known voltage -The pH sensitive glass in the measuring electrode comes into contact with the blood. -H ions in the blood diffuse into the measuring electrode thru the glass -The difference in H ions on either side of the glass changes the potential charge within the measuring electrode -This change in voltage is compared with the reference electrode and converted into a pH reading. -The potential difference in current between the 2 electrodes creates the pH reading thus the name "Potentiometric Method"
LOCATION OF SENSOR
-The location of the CO2 sensor greatly affects the measurement -Measurement made further from the alveolus can become mixed with fresh gas causing a dilution of CO2 values and rounding of the capnogram
Potentiometric Method
-The potential difference in current between the 2 electrodes creates the pH reading thus the name (PH ELECTRODE)
COLORIMETRIC CO2 ANALYZERS
-Used to detect CO2 in exhaled gases -Simple, inexpensive, inline detector especially useful for detection of successful intubation
THE SEVERINGHAUS (PCO2 ELECTRODE)
1. Blood does not come into contact with the pH sensitive glass. 2. Blood comes into contact with a CO2 permeable membrane 3. On the other side of the membrane is bicarbonate solution that is in direct contact with the pH-sensitive glass 4. A hydrolysis reaction occurs within the bicarbonate solution as CO2 diffuses in. 5. This reaction results in the production of H Ions and a pH change of the bicarbonate solution. 6. The pH change is in direct proportion to the PCO2, thus the corresponding voltage change can be converted into
-pH Electrode -PCO2 Electrode -PO2 Electrode
Blood Gas Analyzers consist of a 3 electrode system
PULSE OXIMETRY
Measures the amount of O2 attach to your hemoglobin in your bloodstream and gives it as a percentage.
THE SEVERINGHAUS (PCO2 ELECTRODE)
Modified version of the pH electrode
T
Oxygen analyzers must be calibrated using R/A and 100% O2 T/F
⚫ High ambient light ⚫ Painted/false/long fingernails ⚫ Movement ⚫ Decreased local or systemic perfusion ⚫ Can be adversely affected by Hb variants: HbCO, Methemoglobin ⚫ Can be affected by vascular dyes (Methylene Blue, Indocyainie Green, Indi
Pulse Ox. (Is adversely affected by)
Polarogram
Shows the direct relationship PO2 (mmHg) and Amps
Clark Electrode
The most common oxygen electrode used in blood gas analysis is the (THE PO2 ELECTRODE AND THE POLAROGRAPHIC METHOD)
