Presented by Dr Sonam Norbu Moderator Dr Aparna Sharma

1. Presented by Dr Sonam Norbu Moderator Dr Aparna Sharma

2. 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

3. 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

4. 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.

5. 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.

6. Arterial lines:frequent sampling,continous B.P-monitoring. • Intermitent stab:infrequent sampling. • Where to place- • Radial and ulnar. • Femoral. • Brachial. • Dorsalis pedis ,Axillary.

7. … 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.

8. .. ALLENS TEST.

9. CONTRAINDICATION FOR ARTERIAL PUNCTURE. • Infection at site. • Allen’s test negative. • On Anticoagulent therapy. • Severe peripheral vascular disease.

10. 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.

11. O2 SATURATION AND PULSE OXIMETRY • We can know arterial blood gases and arterial oxygen saturation from ABG machine with help of O2 dissociation curve.

12. O2 DISSOCIATION CURVE

13. 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.

14. 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).

15. 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.

16. 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.

17. 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.

18. 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.

19. 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)

20. 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.

21. 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.

23. 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.

24. 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.

25. RAMAN SPECTOMETRY(LIGHT SCATTERING GAS ANALYSIS) • PRINCIPLE: • A Laser emits monochromaticlight,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.

27. 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.

28. 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.

29. 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

30. 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

31. 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

32. 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

33. SIDE STREAM INFRARED ANALYSER

34. 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.

35. 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)

36. 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

37. 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 .

38. 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

39. 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)

40. 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

41. 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 colorless 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)

42. 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)

43. 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 )

44. 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)

45. 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

46. 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

47. 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)

48. 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)

49. 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.

50. UNUSUAL WAVEFORM…. • COPD,Bronchospasm, Upper airway obstruction- Expiration is progessively prolonged • Extubation,Esophagealintubation,complete breathing system disconnection-Sudden drop of ETCO2 to ZERO