Noninvasive Monitoring in The
Intensive Care Unit
Iskander Al-Githmi, MD,FRCSC, FCCP
Assistant Professor of Surgery
King Abdulaziz University
Learning Objectives
• Know the different noninvasive monitoring
techniques commonly use in ICU.
• Know the advantages and limitation of the
different noninvasive monitoring methods.
• Know the different technologies used in
noninvasive monitoring.
• Correlate findings observed during noninvasive
monitoring with the patient’s changing
physiology.
Goals of Monitoring
• Assessment of vital organs function
• Detection of early life-threatening complications
• Determine the needs for intervention.
Respiratory Monitoring
• Pulse Oximetry
• Capnography
Pulse Oximetry
• Measures four types of hemoglobin: deoxyHb,
oxyHb, carboxyHb and metHb.
• Estimate functional hemoglobin saturation.
Principles of Pulse Oximetry
Principles of Pulse Oximetry con’t
• Spectorphotometry
• Discriminate between oxyHb and deoxyHb by
the difference in light absorption at 660nm and
940nm
• Estimate heart rate by measuring cyclic changes
in light transmission.
Absorption Spectra
Pitfalls and Limitations
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Margin of error is +/- 4% at Sao2 95%
Margin of error is upto 15% at SaO2 <70%
Does not measure arterial oxygen (PaO2)
Wide Pao2 level 60-160mmHg at O2-Dissociation curve
Is not a substitute for arterial blood gas
SPO2= O2Hb+COHb
SPO2>90%even with COHb 70%
Methylene blue underestimate the saturation
Low perfusion e.g. low cardiac output
Extreme anemia
Oxygen - dissociation Curve
Capnometry
• Clinical practice:
• Confirmation of endotracheal tube placement
• Estimation of arterial CO2 with End-Tidal CO2
• Monitoring the integrity of patient-ventilator
system
• Provide a noninvasive means of facilitating
weaning from mechanical ventilation
The principles of capnometry
• Main stream and side stream analyzer
• Infrared spectrometry
• CO2 absorption takes place at 4.3 micm
Normal capnogram
• Phase I: inspiratory baseline
• Phase II: expiratory upstroke
• Phase III: expiratory plateau
PaCo2 – PETCo2 gradient
• PETCo2 is usually 1-3mmHg lower than PaCo2
• The difference between PETCo2 and PaCo2 is
caused by V/Q mismatch
• PETCo2 does not reflect PaCo2 in the presence
of V/Q mismatch
• PaCo2 – PETCo2 gradient is usually < 5mmHg
• The gradient increased when cardiac output
decreased
Limitations
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Alteration of dead space ventilation
Breathing patterns
Patient stability
Tidal volume
V/Q ratio
Capnogram abnormalities
Sudden loss of ETCO2
Sudden loss ETCO2
Possible causes:
• Airway disconnection
• Dislodgment of ET tube
• Total obstruction of ET tube
Gradual decrease in ETCO2 to non zero level
Gradual decrease in ETCO2 to non zero level
Possible causes:
• Leak in the circuit
• Partial disconnection from ventilator
Gradual decrease in ETCO2 level
Gradual decrease in ET CO2
Possible causes:
• Hypothermia
• Pulmonary embolism
• Cardiopulmonary bypass
Rise in baseline ETCO2
Rise in baseline ETCO2
Possible causes:
• Defective exhalation valve
• Rebreathing of previously exhaled CO2
Quiz
Question 1
The capnograph also has a use in correctly and exactly identifying
end expiration during the analysis of haemodynamic wave forms.
This would classically be seen when measuring the Pulmonary
Artery Wedge Pressure at end expiration.The point of end expiration
is seen at:
a. Just after the peak on the capnography waveform.
b. Just before the peak on the capnograph waveform.
c. In the exact middle of the capnography waveform.
d. In the middle of the capnography "trough".
Question 2
Capnography has a place in confirming endotracheal tube
placement but should be used in conjunction with other,
simpler techniques. What is the most correct sequence
of events in confirming endotracheal tube placement?
a. Visualise the tube with laryngoscopy / observe and
auscultate the chest and epigastrium / check the
capnogram.
b. Visualise the tube with laryngoscopy / check the
capnogram / observe and auscultate the chest and
epigastrium
Question 3
The Capnograph may also be used in the ICU to avoid constant
arterial sampling for ABGs and also to monitor patients with brains
injuries who need to be kept with a normal PaCO2.
This is possible because of a correlation between the maximum
partial pressure of CO2 (PetCO2) at end expiration and the arterial
CO2 levels. With normal ventilation and perfusion the gradient
between PetCO2 and PaCO2 should be between 1-5 mm Hg.
The following statement is most true:
a. Capnography is unreliable in the case of massive pulmonary
embolism.
b. Capnography is unreliable in the case of ARDS.
c. Once a PetCO2 to PaCO2 gradient is established, capnography
completely obviates the need for ABGs.
d. Once a PetCO2 to PaCO2 gradient is established capnography can
be reliable used.
Question 4
Cardiac arrest can produce a flat
capnograph trace, due to low pulmonary
blood flow, even if the endotracheal tube
is correctly placed above the carina.
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True
False
Question 5
Severe bronchospasm can produce a flat
capnograph trace even if the
endotracheal tube is correctly placed.
a. True
b. False
Question 6
12 year-old was rescued by a firefighter form a smoke
field room of a burning 12-story apartment building.
The following procedures are appropriate, except
which of the following:
a.
b.
c.
d.
a careful inspection of the upper airway passage to
detect signs of inhalation injury
A chest x-ray on admission to look for inhalation injury
A 24 hour hospital observation
A normal oxygen hemoglobin saturation by pulse
oximetry to exclude the presence of CO poisoning
Question 7
The following statement about pulse oximetry are true except which of
the following:
a.
b.
c.
d.
Modern pulse oximetry uses two wavelength of light, red and
infrared to discriminate between oxygenated and deoxygenated
blood
Pulse oximetry is not affected by low cardiac output state
Different form of dyshemoglobinemia can affect the accuracy of
oxyhemoglobin measurement by pulse oximetry
The pulse oximetry degrades with oxygen saturation <65%