ARTERIAL BLOOD GAS ANALYSISandEXPIRED GAS ANALYSIS

Presented by Dr Sonam NorbuModerator Dr Aparna Sharma

WHAT IS AN ABG

• ABG medical technique used to check gas levels in the blood.It typically involves using a thin needle and syringe to puncture an artery.

• COMPONENTS:PH/Paco2/Pao2/Hco3/O2sat/B.E i.s base excess

NORMAL VALUES

• PH:7.35-7.45• Paco2:35-45mmHg• Pao2:80-100mmHg• Hco3:21-27mEq/L• O2 sat-95-98 percent• Base excess:+/_2mEq/L

AMOUNT:needed for the analysis is as low as o.2ml of blood.

• Syringes should be Heparinized.

• Air bubbles should not be present:lead to inc PaO2 and dec paco2.

WHY ORDER AN ABG?

• AIDS in establishing a diagnosis.• Helps guide treatment plan.• Aids in ventilator management.• Improvement in acid/Base management

allows for optimal function of medications.• Acid/base status may alter electrolyte levels

critical to patient status/care.

• Arterial lines:frequent sampling,continous B.P-monitoring.

• Intermitent stab:infrequent sampling.Where to place-• Radial and ulnar.• Femoral.• Brachial.• Dorsalis pedis ,Axillary.

… ALLEN’S TEST.

• Instruct patient to clench his fist.• Apply occlusive pressure on both Radial and

Ulnar artery.• Blanching of pam and finger should occur.• Release the occlusive pressure on ulnar artery

and notice flushing of hand within 7-10 sec;denotes that ulnar artery supply is adequate and safe to prick Radial Artery.

.. ALLENS TEST.

CONTRAINDICATION FOR ARTERIAL PUNCTURE.

• Infection at site.• Allen’s test negative.• On Anticoagulent therapy.• Severe peripheral vascular disease.

SPO2 and SaO2

• Used interchangeably but they are not same.• When o2 saturation is measured by pulse

oximeter….SPO2.• CO-oximeter…Sao2.• Spo2 also called functional arterial o2

saturation.• Sao2….fractional arterial o2 saturation.

O2 SATURATION AND PULSE OXIMETRY

• We can know arterial blood gases and

arterial oxygen saturation from ABG

machine with help of O2 dissociation curve.

O2 DISSOCIATION CURVE

OXYGEN SATURATION and PULSE OXIMETRY…

• ABG machine calculates O2 saturation based on PH,Paco2, temp,by using normal adult o2 dissociation curve.

• Fetal Hb,low 2,3 DPG….curve shift Lt,

• Sickle cell,chronic hypoxia,cyanotic HD,chronic asthma,high altitude….curve shifts Rt.

O2 SATURATION and PULSE OXIMETRY…..

ADVANTAGE OF PULSE OXIMETRY.• Non invasive.• Portability.• Continous monitoring.• Ease of use(no calibration).• Rapidity(warn decrease in saturation before

sign and symptom).

ABG INTERPRETATION.

• First,does the patient have acidosis or alkalosis.

• Second,what is the primary problem-metabolic or respiratory.

• Third, is there any compensation by the patient-respiratory compensation is immediate while renal compensation takes time.

ABNORMAL VALUES.

PH<7.35:ACIDOSIS(Metabolic and/or Respiratory)

PH>7.45:ALKALOSIS(Metabolic and/or Respiratory)

PaCo2>45mmHg:Respiratory Acidosis.Paco2<35mmHg:Respiratory Alkalosis.HCo3<22meq/L:Metabolic acidosis.HCo3>26meq/L:Metabolic alkalosis.

PUTTING IT TOGETHER-RESPIRATORY SO,

• Paco2>45 with a PH <7.35 represents a Respiratory Acidosis.

• Paco2<35 with aPH >7.45 represents a Respiratory Alkalosis.

• For a primary respiratory problem ,PH and PCO2 moves in the opposite direction,for each deviation in Paco2 of 10mmHg in either direction,0.08PH units changes in the opposite direction.

PUTTING IT TOGETHER –METABOLIC and

• HCO3<22 and PH <7.35 represents a metabolic acidosis.

• HCO3>26 with a PH >7.45 represents a metabolic alkalosis.

• For a primary metabolic problem ,PH and HCO3 are in the same direction and Paco2 is also in the same direction.

COMPENSATION

• The body ‘s attempt to return the acid/base status to normal(i.s PH closer to7.4)

• Primary problem compensation• Respiratory acidosis....Metabolic Alkalosis(inc

bicarbonate reabsorption)

• Respiratory alkalosis….Metabolic Acidosis(dec bicarbonate reabsorption)

• Metabolic acidosis….Respiratory Alkalosis(dec PCO2 i.e hyperventilation)

• Matabolic alkalosis…Respiratory Acidosis(inc PCO2 i.e hypoventilation)

• In any uncompensated condition(alkalosis/acidosis)one of them will remain normal and other one will either inc or dec.

• In any compensated condition: change in HCO3 and PCO2 will be in the same direction.

• In mixed disorder:change in HCO3 and PCO2 will be in the opposite direction.

MASS SPECTROMETRY.

• Technique by which concentration of gas particles in a sample can be determined according to mass-charge ratio.

• Used to measure inspired and end-tidal concentration of O2 ,nitrogen,CO2,nitrous oxide,and volatile anaesthetic agents.

• It measures concentrations in volumes percent,not partial pressure.

MASS SPECTROMETRY…

• Vaccum pump inside the mass spectrometer draws a gas sample from a side port in a breathing circuit.Gas sample is passed through an ionizer and molecules become positively charged ion and passed through a magnetic field.The ions with the highest mass to charge ratio are least deflected and follow acurved path with the greatest radius.

MASS SPECTROMETRY..ADVANTAGES:• Measure nearly every gas of importance to Anaesthesia.• Multiple agent detection.• Fast response time.• Convenience:easy to use and maintain.• Low cost.• Measurement of nitrogen:detects leaks in the aspiration

mechanism and inc in nitrogen in the breathing system.DISADVANTAGES.• Measurement of only preprogrammed gases.• Necessity for scavenging.• Long warm-up time.

RAMAN SPECTOMETRY(LIGHT SCATTERING GAS ANALYSIS)

PRINCIPLE:• A Laser emits monochromatic light,which interacts with

a gas molecule that has interatomic molecular bonds,some of its energy is converted into vibrational and rotational modes.• A fraction of the energy absorbed is reemitted at

different wavelengths:Raman scattering.• APPLIED:all gases present in the respiratory gas

mixture(CO2,O2,nitrogen,nitrous oxide,and up to three anaesthetic agents)• Monoatomic gases(helium,xenon,Argon)donot exhibit.

RAMAN SPECTOMETRY…

ADVANTAGES:• Multiple gas capability:can identify and measure

CO2,O2,nitrogen, nitrous oxide,hydrogen;• Multiple agent detection:mixture of volatile agents.• Fast response time:slower then mass spectrometry.• Portability.• Fast start up time.• No need for scavenging gases.• High degree of accuracy.• No Artifacts with propellants.

RAMAN SPECTOMETRY…

DISADVANTAGES:• SIZE: Large and heavy compared to IR monitors.

• Argon and Helium cannot be measured.

• Inaccuracy with fruit-flavored oils.

• Artifacts with Nitric oxide:Nitric oxide produces Nitrogen,nitrous oxide and isoflurane signals.

Carbon Dioxide Analysis:• Means for assessing metabolism, circulation, and ventilation

• ASA guidelines: Correct positioning of ET tube must be verified by

identifying CO2 in the expired gas

• Capnometry: Measurement of CO2 in gas mixture

• Capnography: Recording of CO2 Conc versus time

Standard requirements of Capnometer:

• CO2 reading shall be within ±12% of the actual value or ±4 mm Hg

• Must have a high CO2 alarm for both inspired and exhaled CO2

Technology:

• Infrared Analysis

• Chemical colorimetric analysis

Infrared Analysis:• Most common technology in use

• Principle: Gases with two or more dissimilar atoms in the molecule

(nitrous oxide, CO2, and the halogenated agents) have specific and unique

infrared light absorption spectra.

• Amount of infrared light absorbed is proportional to the concentration of

the absorbing molecules, the concentration can be determined

• Nonpolar molecules cannot be measured

• 2 technologies available:

Black body radiation

Microstream technology

Blackbody Radiation Technology:• Utilizes a heated element called a blackbody emitter as the source of

infrared light, produces a broad infrared spectrum .

• Optical detectors must be calibrated to recognize only infrared radiation

that is modulated at a certain frequency by using a spinning chopper

wheel.

• Analyzer selects the appropriate infrared wavelength, minimize

absorption by other gases that could interfere with measurement of the

desired component

• Then an electrical signal is produced and amplified, and the concentration

is displayed.

• For halogenated agents: separate chamber to measure absorption at

several wavelengths (single-channel, four-wavelength infrared filter

photometers) have filter for each anesthetic agent and one to provide a

baseline for comparison

SIDE STREAM INFRARED ANALYSER

Diverting type:

• Gas to be measured is pumped continuously through a measuring

chamber

• Filtered and pulsed light is passed through the sample chamber and also

through a reference chamber (has no absorption characteristics)

• Light is focused on an infrared photosensor

• Changing light levels on the photosensor produce changes in the

electrical current running through it

• Provides hundreds of readings for each respiratory cycle.

• Monochromatic analyzers use one wavelength to measure potent

inhalational agents

• Polychromatic analyzers use multiple wavelengths to both identify and

quantify the various agents

• Measuring cell is calibrated to zero (using gas that is free of the gases of

interest, usually room air) and to a standard level (using a calibration gas

mixture)

Non Diverting Type:

• Gas stream passes through a chamber (cuvette) with two windows,

placed b/w the breathing system and the patient

• Sensor (has both the light source and detector) fits over the cuvette

• Sensor is heated slightly above body temperature (to prevent

condensation)

• Infrared light passes through window on one side of the adaptor, sensor

receives the light on the opposite side

• Then light goes through three ports in a rotating wheel, containing

(a) a sealed cell with a known high CO2 concentration

(b) a chamber vented to the sensor's internal atmosphere

(c) a sealed cell containing only nitrogen

• Then passes through a filter (to isolate CO2 information)

• Signal amplified and sent to the display module

• Calibration done using: low calibration cell contains 100% nitrogen, high

cell contains a known partial pressure of CO2

• Corrections for nitrous oxide and oxygen entered manually

Microstream Technology:• Uses laser-based technology to generate infrared rays that match the

absorption spectrum of CO2

• it utilizes Smaller sample cell, low flow rate

• Emission source: Glass discharge lamp with an infrared transmitting

window

• Electrons (generated by a radio frequency voltage) excite nitrogen

molecules, Carbon dioxide molecules are excited by collision with the

excited nitrogen molecules These drop back to their ground state and

emit the signature wavelength of CO2

• This emission now passes through main optical detector and reference

detector .

• Measurements made every 25 msec

• Because of low sample flow and small sample cell, useful for measuring:

CO2 in very small patients

high respiratory rates

low-flow applications

unintubated patients

• Readings not affected by high concentrations of oxygen or anesthetic

gases

Advantages of Infrared Analysis:Multigas Capability

Volatile Agent Detection

Small, compact, lightweight

Quick response times (faster for CO2)

Short warm-up time

Convenience (no complicated calibrations)

Lack of interference from other gases (argon, low conc NO)

Detecting anaesthetic agent breakdown (desflurane to CO will show as

wrong or mixed agent)

Disadvantages of Infrared Analysis:• O2 and N2 cannot be measured

• Gas interference :

O2 causes broadening of CO2 spectrum l/t lower readings

N2O absorption spectrum overlaps with CO2 (l/t higher vlues): so need

either automatic or manual correction for N2O

He l/t underestimation of CO2

• Other substances l/t inaccuracies (ethanol, methanol, diethyl ether,

methane): give high volatile agent reading, polychromatic less affected

• Interference from Water vapors: Absorb infrared rays (l/t lower values)

• Slow response time (with rapid resp rates)

• Difficulty in adding new volatile agents

Chemical Carbon Dioxide Detection• Consists of a pH-sensitive indicator

• Principle: When the indicator is exposed to carbonic acid that is formed

as a product of the reaction between CO2 and water it becomes more

acidic and changes color

Technology:

Hygroscopic:CO2 detector contains hygroscopic filter paper that has

colorl ess base and indicator that changes color as a function of ph.

Hydrophobic;show s acolor change from blue to green to yellow;

Uses:

• For confirming tracheal intubation when a capnometer is not available

• Disposable so it may be useful to confirm tracheal intubation in patients

with respiratory diseases (e.g.SARS)

Advantages:

• Easy to use, small size, low cost

• Not affected by N2O, volatile anaesthetics

• Offers minimal resistance to flow

• CO doesn’t interfere

Disadvantages:

• Recommended to wait six breaths before making a determination

• False-negative results may be seen with very low tidal volumes

• Drugsused in the trachea or gastric contents can cause irreversible

damage to the device

• False-positive results can occur if CO2 in the stomach

• Semiquantitative, cannot give accurate measurement of CO2 (So use

limited to check endotracheal intubation)

CLINICAL SIGNIFICANCE OF CAPNOMETRY.

• Confirm endotracheal intubation.• Assess adequacy of cardiac output.• Detect circuit disconnection. CAPNOGRAPHY.• Examined for• Height,frequency(R.R),• Rhythm.• Baseline(Normally zero)• Shape(top hat or sine wave )

Capnography cont…

• Phase 1: E (Inspiratory baseline)

• Phase 2: B to C (Expiratory upstroke), S shaped- represents transition

from dead space to alveolar space

• Phase 3: C to D (all from alveoli)

• End of Phase 3 (Point D): End tidal point (Max CO2)

• Alpha : Angle b/w Phase 2 & 3 (normal 100-110 degree)

• Beta: B/w end of phase 3 & Descending limb (90 degree)

The slope of phase 3 (C to D) increases:

With PEEP

Airway obstruction

V/Q mismatch

And so angle Alpha also increases

And angle Beta decreases

Angle Beta increases with:

Rebreathing

Prolonged response time

Dec ET CO2:

• Impaired peripheral circulation

• Pulmnonary embolism

• Increased patient dead space

• Hyperventilation-airway obstruction

• Hypothermia

• Use of muscle relaxants

• Leak in sampling line

• Leak around ET

• Heavy sedation

Increased ET CO2:

• Absorption of CO2 from peritoneal cavity

• Injection of NaHCO3

• Convulsions

• Hyperthermia

• Pain, anxiety, shivering

• Increased muscle tone (reversal of muscle relaxation)

• Hypoventilation

• Upper airway obstruction

• Rebreathing

• Increased circulation from tissues to lung (release of tourniquet)

UNUSUAL WAVEFORM;

• Leak in sample line: Brief peak at the end of plateau

• Partially paralysed (making intermittent resp effort) :Curare cleft

• Cardiogenic occilations:

Seen in pediatric pts

(d/t heart beating against

Lungs)

UNUSUAL WAVEFORM…

• Hyperventilation or inc in dead space ventillation:Low end-tidal co2 with a good alveolar plateau.

• Hypoventilation or inc co2 delivery to lungs.

Elevated end –tidal co2 with good Alveolar pleateau.

UNUSUAL WAVEFORM….

• COPD,Bronchospasm, Upper airway obstruction- Expiration is progessively prolonged

• Extubation,Esophageal intubation,complete breathing system disconnection-Sudden drop of ETCO2 to ZERO

OXYGEN ANALYSISOxygen:Standard requirements:

• Oxygen readings shall be within ±2.5% of the actual level

• The high and low oxygen level alarms must be at least medium

priority, oxygen concentration below 18% (should be high priority

alarm)

• It shall not be possible to set the low oxygen alarm limit below 18%

Technology used:

• Paramagnetic Technology

• Electrochemical Technology

Paramagnetic Oxygen Analysis:• Paramagnetic substances: Substances which locate themselves in the

strongest portion of the field when introduced into a magnetic field

• Oxygen is the only paramagnetic gas.

• Principle: When a gas that contains oxygen is passed through a magnetic

field, the gas will expand and contract, causing a pressure wave that is

proportional to the oxygen partial pressure.

• Reference and sample gases are pumped through the analyser

• Pressure difference is detected by the transducer and converted into an

electrical signal that is displayed as oxygen partial pressure or volumes

percent.

Eletrochemical Oxygen Analysis:• Consists of a sensor, analyzer box, display, and alarms

• Sensor is placed in the inspiratory limb

• Gel membrane (nonpermeable to ions, proteins, but is permeable to

oxygen)

• Technology:

Galvanic cell/ fuel cell

Polarographic electrode

Galvanic cell:(Fuel cell,Microfuel cell)

• Principle: Oxygen diffuses through the sensor membrane and electrolyte

to the cathode, where it is reduced, causing a current to flow

• Current generated is proportional to the partial pressure of oxygen in the

gas

Cathode: O2 + 2H2O + 4e- → 4OH-

Anode: 4OH- + 2Pb → 2PbO + 2H2O + 4e-

• Cathode is the sensing electrode, anode is usually consumed

• The chemical reaction is temperature dependent

Polarographic Electrode:(Clark electrode)

• Components: anode, a cathode, an electrolyte, and a gas-permeable

membrane

• Needs power source for inducing a potential between the anode and the

cathode

• Same principle as galvanic cell

Advantages:

• Easy to use, low cost, compact

• No effect from argon

Disadvantages:Maintenance:more then Galvanic cell monitor.

• Slow response time.

• Calibration:each day and every 8 hours.

Applications of Oxygen Analysis:

Detecting Hypoxic or Hyperoxic Mixtures:

• Oxygen monitor provides earlier warning of inadequate oxygen than

pulse oximetry

Detecting Disconnections and Leaks:• However not dependable

Detecting Hypoventilation:

• Normal: Difference b/w inspired and expired oxygen is 4% to 5%

End tidal Oxygen Measurement:

• Assess pt’s oxygen consumption (Malignant hyperthermia)

• To detect air embolism (inc ET O2)

• Nitrous Oxide:

Measurement technique:

• Infrared Analysis

• Significance:

Assess flowmeter function

Nitrogen:

• Previously measured using Raman spectroscopy or mass spectrometry

• Now no longer available

• Significance:

• Verifying adequate denitrogenation before induction (imp for

pediatric pt, in lung ds, dec FRC)

• Detecting air emboli (Inc ET N2)

Thank You