1. Respiratory monitoringBy
Dr. Ahmed Mostafa
Assist. prof. of anesthesia & I.C.U.

2. Precordial & Esophageal Stethoscopes
Indications:
Many anesthesiologists believe that all anesthetized patients should be monitored with a precordial or esophageal stethoscope, though this practice is gradually changing as anesthesiologists rely on capnography and pulse oximetry to monitor pulmonary function.
Contraindications:
Esophageal varices or strictures.

3. Precordial & Esophageal Stethoscopes
A precordial stethoscope (Wenger chest-piece) is a heavy, bell-shaped piece of metal placed over the chest or suprasternal notch. Various chest pieces are available, but the child size works well for most patients. The bell is connected to the anesthesiologist by extension tubing.

4. Precordial & Esophageal Stethoscopes

5. Precordial & Esophageal Stethoscopes
The esophageal stethoscope is a soft plastic catheter (8–24F) with balloon-covered distal openings. Although the quality of breath and heart sounds is much better than with a precordial stethoscope, its use is limited to intubated patients. Temperature probes, ECG leads, ultrasound probes, and even atrial pacemaker electrodes have been incorporated into esophageal stethoscopes.

6. Precordial & Esophageal Stethoscopes

7. Precordial & Esophageal Stethoscopes
Value:
Confirmation of ventilation.
Quality of breath sounds (e.g. stridor, wheezing).
Regularity of heart rate.
Quality of heart tones (muffled tones are associated with decreased cardiac output).
The confirmation of bilateral breath sounds after tracheal intubation, however, is made with a binaural stethoscope.

8. Pulse oximetry

9. Pulse oximetry
It is a continuous, noninvasive method that records the arterial oxygen saturation and heart rate.
It analyzes the absorption of infrared light by the examined circulatory area.
The most frequent indications of pulse oximetry are continuous monitoring of oxygenation in critical periods.
Its aim is to indicate hypoxia early and to prevent the development of severe hypoxia.

10. Examples of pulse oximetry probes

11. Pulse oximetry
Principles: 1- Optical oximetry principle: 2- Plethysmography:

12. Pulse oximetry
1- Optical oximetry principle: The level of saturation of the blood with oxygen can be calculated via the following formula:

13. Pulse oximetry
1- Optical oximetry principle:

14. Pulse oximetry 1- Optical oximetry principle:
If blood is illuminated with light of a given wavelength, the oxygen concentration can be concluded from the intensity of the reflected (transmitted) light.
Light of different wavelengths (at least two) is used.
In the event of the red or infrared detection of oxy and deoxy-hemoglobin, the light source can be a LED (Light-emitting diode) or a laser.
The most frequent LED wavelengths are 660 nm (red) and 940 nm (infra-red).
After reflection, only a part of the light reaches the detector

15. Pulse oximetry 1- Optical oximetry principle:
Only a small fraction of the pulsating part carries the information. Since this pulsation is characteristic only of the arterial blood, the plus (variable) absorption due to the pulse added volume of arterial blood is used to calculate the level of arterial oxygen saturation.
The intensity measured at the isobestic wavelength is characteristic of the amount of blood and not its oxygen content.
The arterial oxygen saturation of healthy people is constant (97–99%), while the saturation of venous blood is on average 75%.

16. Pulse oximetry 2. Plethysmography principles:
Is a method for measuring volumes.
It is possible to draw conclusions on the degree of blood flow.

17. Pulse oximetry Limitations: Movement of the patient. Wrong placement.
Ambient light.
Circulating dyes.
Nail polish
Pigmented skin

18. Pulse oximetry Limitations:
Peripheral circulatory dysfunction (by definition, the method can be used only if the pulse (the heart rhythm) is regular. In the event of low cardiac output and vasoconstriction, it is difficult to distinguish the real signal from the background noise.
The presence of other compounds, e.g. hemoglobin (which is increased in malaria and liver diseases).

19. Pulse oximetry Limitations:
Carbon monoxide poisoning. The red and infrared absorbance of carboxyhemoglobin is identical to that of hemoglobin. so, in heavy smokers the actual SpO ₂ is 2–4% lower, while in cases of carbon monoxide poisoning it is 20–40% lower than the measured normal.

20. Capnography & capnometry

21. Capnography and capnometry
Principle: It is based upon the Beer-Lambert law (This law demonstrates a linear relationship between the light absorption and the absorbing material; in the case of capnography, the higher the CO₂ concentration, the higher the light absorption will be at a definite infrared wavelength (Infrared absorption photometry) . The absorption maximum of CO₂ is at 4250 nm, but N₂O, H₂O and CO can also absorb at this wavelength.

22. Capnography and capnometry

23. Capnography and capnometry
Uses:
Confirmation of endotracheal tube intubation.
Monitoring breathing and mechanical ventilation.
Demonstration of respiratory disorders (e.g. Bronchospasm) and effectiveness of therapy.
Monitoring of circulatory insufficiency.
Demonstration of hyper metabolic states.
►►►Diagnosis of air embolism◄ ◄◄

24. Capnography and capnometry
Types:
Side stream(Diverting):
The gas sample is taken through a small tube, and analyzed in a separate chamber. The results are very reliable(less accurate at higher respiratory frequency); the time delay is 1–60 s.

25. Capnography and capnometry
Types:
Side stream(Diverting):

26. Capnography and capnometry
Types:
2. Main stream (Flow through):
The tube is larger, which adds dead space. The reaction time is only 40 ms, and it is very accurate. Calibration is difficult and “rebreathing” detection is too difficult.

27. Capnography and capnometry
Types:
2. Main stream (Flow through):

28. Capnography and capnometry
Types:
2. Main stream (Flow through):

29. Capnography and capnometry

30. Capnography and capnometry
CO ₂ waveform

31. Capnography and capnometry
CO ₂ waveform

32. Capnography and capnometry
CO ₂ waveform: three main phases can be distinguished in the normal capnogram:
Phase I: is characteristic of the
airways.
Phase II indicates transitional gas.
Phase III demonstrates the changes
in the alveolar gas.

33. Capnography and capnometry
CO ₂ waveform:
Exhalation characteristic mostly of the anatomic dead space begins in phase I.
In phase II, the alveolar gas begins to mix with the dead space gas, and hence the CO₂ concentration rapidly rises.
Phase III corresponds to the elimination of CO₂ from the alveoli.

34. Capnography and capnometry
CO ₂ waveform:
The end-tidal CO₂ (ETCO ₂)
concentration is equal to the
maximum in phase III.
ETCO₂ is usually approximately
0.4 kPa (2–5 mm Hg) lower than
Pa CO₂.
Phase IV indicates inspiration.

35. Capnography and capnometry
CO ₂ waveform: Alfa angle: The angle between phases II and III, increases as the slope of phase III increases. The alpha angle is thus an indirect indication of V/Q status of the lung.

36. Capnography and capnometry
CO ₂ waveform: Beta Angle: - Nearly 90 degrees angle . - Increase during rebreathing. - Delayed response time particularly in children, can produce increase in the beta angle.

37. Capnography and capnometry

38. Capnography and capnometry
Other capnogram abnormalities:
Obstruction, bronchospasm or COPD

39. Capnography and capnometry
Other capnogram abnormalities:
Spontaneous respiratory effort (Curare cleft)

40. Capnography and capnometry
Other capnogram abnormalities:
Cardiac oscillations.

41. Capnography and capnometry
Other capnogram abnormalities:
Incompetent expiratory valve or exhausted CO2absorbent

42. Capnography and capnometry
Other capnogram abnormalities:
Incompetent inspiratory valve

43. Anesthetic Gas Analysis

44. Anesthetic Gas Analysis
Indications:
Analysis of anesthetic gases is useful during any procedure requiring inhalation anesthesia.
There are no contraindications to analyzing these gases.

45. Anesthetic Gas Analysis
Techniques: 1-Mass spectrometry. 2-Raman spectroscopy. Both are primarily of historical interest. 3-Infrared spectrophotometry. 4-Piezoelectric Analysis.

46. Anesthetic Gas Analysis
Infrared spectrophotometry
Most commonly used.
Based on the Beer–Lambert law.
The absorption of infrared light passing through a solvent (inspired or expired gas) is proportional to the amount of the unknown gas.

47. Anesthetic Gas Analysis
Infrared spectrophotometry

48. Anesthetic Gas Analysis
Piezoelectric Analysis Uses oscillating quartz crystals, one of which is covered with lipid. Volatile anesth. dissolve in the lipid layer and change the frequency of oscillation, which, when compared to the frequency of oscillation of an uncovered crystal, allows the concentration of VA to be calculated

49. Anesthetic Gas Analysis
Piezoelectric Analysis Neither these devices nor infrared photo acoustic analyses allow different anesthetic agents to be distinguished. New dual-beam infrared optical analyzers do allow gases to be separated and an improperly filled vaporizer to be detected.

50. Oxygen Analysis

51. Oxygen Analysis To measure the FiO2 of inhaled gas:
Galvanic Cell (fuel cell):

52. Oxygen Analysis
2. Paramagnetic Analysis: Oxygen is a nonpolar gas, but it is paramagnetic and when placed in a magnetic field, the gas will expand, contracting when the magnet is turned off. By switching the field on and off and comparing the resulting change in volume (or pressure or flow) to a known standard, the amount of oxygen can be measured.

53. Oxygen Analysis
2. Paramagnetic Analysis:

54. Oxygen Analysis 3. Polargraphic (Clark’s-Oxygen) Electrode:
Has a gold (or platinum) cathode and a silver anode, both based in sodium chloride electrolyte solution, separated from the gas to be measured by a semipermeable membrane. Unlike the galvanic cell, a polarographic electrode works only if a small voltage (0.6 v.) is applied to two electrodes. The amount of current that flows is proportional to the amount of oxygen present.

55. Oxygen Analysis
3. Polargraphic (Clark’s-Oxygen) Electrode:

56. Oxygen Analysis 4. Spirometry: Can measure:
Airway pressures, volume, and flow.
Calculate resistance and compliance.
Display the relationship of these variables as flow– volume or pressure–volume loops.

57. Oxygen Analysis 4. Spirometry:
Low peak inspiratory pressure and high peak inspiratory pressure, which indicate either a ventilator or circuit disconnect, or an airway obstruction.

58. Blood gas measurement

59. Blood gas measurement
Blood gas analyzers report a wide range of results, but the only parameters directly measured are:
Partial pressures of oxygen (pO2): by the polarographic (Clark) oxygen electrode.
Blood pH: by pH electrode.

60. Blood gas measurement
Carbon dioxide (pCO2): by the Severinghaus or carbon dioxide electrode.
The hemoglobin saturation (HbO2%):%): is calculated from the pO2 using the oxygen-dissociation curve and assumes a normal P50 and that there are no abnormal forms of hemoglobin. Some blood gas analyzers incorporate a co- oximeter that directly measures the various forms of hemoglobin including oxy-hemoglobin, total hemoglobin, carboxy-hemoglobin and met-hemoglobin.

61. Blood gas measurement
The actual bicarbonate, standard bicarbonate, and base excess: are calculated from the pH and pCO2 using the Siggard- Anderson nomogram derived from a series of in vitro experiments relating pH, pCO2 and bicarbonate.

62. Blood gas measurement
pH electrode

63. Blood gas measurement
pH electrode If a glass membrane separates two solutions of different hydrogen ion concentration a potential difference develops that is proportional to the hydrogen ion gradient between the two.

64. Blood gas measurement
pH electrode A measuring silver/silver chloride electrode is encased in a bulb of special pH-sensitive glass and contains a buffer solution that maintains a constant pH. This glass electrode is placed in the blood sample and a potential difference is generated across the glass,

65. Blood gas measurement
pH electrode The potential is measured between a reference electrode (in contact with the blood via a semi- permeable membrane) and the measuring electrode. Both electrodes must be kept at 37° C, clean and calibrated with buffer solutions of known pH.

66. Blood gas measurement
The Severinghaus or CO2 electrode Modified pH electrode separated from the blood specimen CO2 semi-permeable membrane which diffuses from the blood sample across the membrane into the sodium bicarbonate solution, producing H ions and a change in pH.

67. The Severinghaus or CO2 electrode
Blood gas measurement
The Severinghaus or CO2 electrode
CO2 + H2O → H2CO3 → H+ + HCO3-
Hydrogen ions are produced in proportion to the pCO2 and are measured by the pH- sensitive glass electrode.

68. The Severinghaus or CO2 electrode
Blood gas measurement
The Severinghaus or CO2 electrode
The Severinghaus electrode must be maintained at 37 ° C, be calibrated with gases of known pCO2 and the integrity of the membrane is essential.

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70. Thank you
Dr. Ahmed Mostafa