Respiratory monitoring
ByDr. Ahmed Mostafa
Assist. prof. of anesthesia & I.C.U.
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.
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.
Precordial & Esophageal Stethoscopes
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.
Precordial & Esophageal Stethoscopes
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.
Pulse oximetry
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.
Pulse oximetryExamples of pulse oximetry probes
Pulse oximetryPrinciples:1- Optical oximetry principle:
2- Plethysmography:
Pulse oximetry1- Optical oximetry principle:
The level of saturation of the blood with oxygen can be calculated via the following formula:
SpO₂ is the level of oxygen saturation of the blood.
HbO₂ is the concentration of oxygenated hemoglobin.
Hb is the concentration of deoxygenated Hb.
Pulse oximetry1- Optical oximetry principle:
Pulse oximetry1- 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
Pulse oximetry1- 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%.
Pulse oximetry2. Plethysmography principles:- Is a method for measuring volumes. - It is possible to draw conclusions on the
degree of blood flow.
Pulse oximetryLimitations:
Movement of the patient.
Wrong placement.
Ambient light.
Circulating dyes.
Nail polish
Pigmented skin
Pulse oximetryLimitations:
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).
Pulse oximetryLimitations:
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.
Capnography & capnometry
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.
Capnography and capnometry
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◄ ◄◄
Capnography and capnometry
Types:
1. 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.
Capnography and capnometry
Types:
1. Side stream(Diverting):
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.
Capnography and capnometry
Types:
2. Main stream (Flow through):
Capnography and capnometry
Types:
2. Main stream (Flow through):
Capnography and capnometry
Capnography and capnometry
CO ₂ waveform
Capnography and capnometry
CO ₂ waveform
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.
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.
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.
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.
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.
Capnography and capnometry
Capnography and capnometry
• Other capnogram abnormalities:
Obstruction, bronchospasm or COPD
Capnography and capnometry
• Other capnogram abnormalities:
Spontaneous respiratory effort (Curare cleft)
Capnography and capnometry
• Other capnogram abnormalities:
Cardiac oscillations.
Capnography and capnometry
• Other capnogram abnormalities:
Incompetent expiratory valve or exhausted CO2absorbent
Capnography and capnometry
• Other capnogram abnormalities:
Incompetent inspiratory valve
Anesthetic Gas Analysis
Anesthetic Gas Analysis
Indications:- Analysis of anesthetic gases is useful
during any procedure requiring inhalation anesthesia.
- There are no contraindications to analyzing these gases.
Anesthetic Gas Analysis
Techniques:
1-Mass spectrometry.
2-Raman spectroscopy.
Both are primarily of historical interest.
3-Infrared spectrophotometry.
4-Piezoelectric Analysis.
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.
Anesthetic Gas Analysis
Infrared spectrophotometry
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
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.
Oxygen Analysis
Oxygen AnalysisTo measure the FiO2 of inhaled gas:
1.Galvanic Cell (fuel cell):
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.
Oxygen Analysis
2. Paramagnetic Analysis:
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.
Oxygen Analysis
3. Polargraphic (Clark’s-Oxygen) Electrode:
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.
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.
Blood gas measurement
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.
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.
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.
Blood gas measurement
pH electrode
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.
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,
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.
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.
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.
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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Thank you
Dr. Ahmed Mostafa