Respiratory monitoring By Dr. Ahmed Mostafa Assist. prof. of anesthesia & I.C.U

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.


• 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.



• 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.



• 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


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).


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.



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◄ ◄◄


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.


Types:

1. Side stream(Diverting):


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.


Types:



Types:




CO ₂ waveform


CO ₂ waveform


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.


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.


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.


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.


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.



• Other capnogram abnormalities:

Obstruction, bronchospasm or COPD



Spontaneous respiratory effort (Curare cleft)



Cardiac oscillations.



Incompetent expiratory valve or exhausted CO2absorbent



Incompetent inspiratory valve

Anesthetic Gas Analysis


Indications:- Analysis of anesthetic gases is useful

during any procedure requiring inhalation anesthesia.

- There are no contraindications to analyzing these gases.


Techniques:

1-Mass spectrometry.

2-Raman spectroscopy.

Both are primarily of historical interest.

3-Infrared spectrophotometry.

4-Piezoelectric 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.


Infrared spectrophotometry


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


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 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.


- 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.


- 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.


pH electrode


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.


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,


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.


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.



• CO2 + H2O → H2CO3 → H+ + HCO3-

• Hydrogen ions are produced in proportion to

the pCO2 and are measured by the pH-

sensitive glass 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.

?

Thank you

Dr. Ahmed Mostafa

Documents

Respiratory monitoring By Dr. Ahmed Mostafa Assist. prof. of anesthesia & I.C.U