Measurements & Monitoring
Prof. Abdulhamid Al-Saeed, FFARCSI
Chairman Anaesthesia Department
College of Medicine
King Saud University
Pulse Oximetry
Physical Principle
Within the probe are two light emitting diodes (LED's), one in the visible red
spectrum (660nm) and the other in the infrared spectrum (940nm). The beams
of light pass through the tissues to a photodetector. During passage through the
tissues, some light is absorbed by blood and soft tissues depending on the
concentration of haemoglobin. The amount of light absorption at each light
frequency depends on the degree of oxygenation of haemoglobin within the
tissues
Microprocessor can select out the absorbance of the pulsatile fraction of blood
Within the oximeter memory is a series of oxygen saturation values obtained from
experiments performed in which human volunteers were given increasingly
hypoxic mixtures of gases to breath. The microprocessor compares the ratio of
absorption at the two light wavelengths measured with these stored values, and
then displays the oxygen saturation digitally as a percentage and audibly as a
tone of varying pitch. As it is unethical to desaturate human volunteers below
70%, it is vital to appreciate that oxygen saturation values below 70% obtained
by pulse oximetry are unreliable.
A pulse oximeter gives NO information
on any of these other variables:
• The oxygen content of the blood
• The amount of oxygen dissolved in the blood
• The respiratory rate or tidal volume i.e.
ventilation
• The cardiac output or blood pressure
Incomptencies
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Critically ill with poor peripheral circulation
Hypothermia & VC
Dyes ( Nail varnish )
Lag Monitor
Signalling 5-20 sec
PO2
 Cardiac arrhythmias may interfere with the oximeter
picking up the pulsatile signal properly and with
calculation of the pulse rate
 Abnormal Hb ( Met., carboxy)
Capnography
• Capnography is the graphic display of
instantaneous CO2 concentration versus time
(Time Capnogram)
• Or expired volume (Volume Capnogram) during
a respiratory cycle.
• Methods to measure CO2 levels include infrared
spectrography, Raman spectrography, mass
spectrography, photoacoustic spectrography and
chemical colorimetric analysis
Physical Principle
• The infrared method is most widely used and most
cost-effective.
• Infrared rays are given off by all warm objects and are
absorbed by non-elementary gases (i.e. those composed
of dissimilar atoms), while certain gases absorb
particular wavelengths producing absorption bands on
the IR electromagnetic spectrum.
• The intensity of IR radiation projected through a gas
mixture containing CO2 is diminished by absorption; this
allows the CO2 absorption band to be identified and is
proportional to the amount of CO2 in the mixture.
Types
Side stream Capnography
• The CO2 sensor is located in the main unit itself (away
from the airway) and a tiny pump aspirates gas samples
from the patient’s airway through a 6 foot long capillary
tube into the main unit.
• The sampling tube is connected to a T-piece inserted at
the endotracheal tube or anaesthesia mask connector
Other advantages of the side stream capnograph
• No problems with sterilisation, ease of connection and
ease of use when patient is in unusual positions like the
prone position
Main stream Capnograph
• Cuvette containing the CO2 sensor is inserted between the
breathing circuit and the endotracheal tube.
• The IR rays traverse the respiratory gases to an IR detector within
the cuvette.
• To prevent condensation of water vapour, which can cause falsely
high CO2 readings, all main stream sensors are heated above body
temperature to about 40oC.
• It is relatively heavy and must be supported to prevent endotracheal
tube kinking.
• Sensor’s window must be kept clean of mucus and particles to
prevent false readings.
• Response time is faster
The Alpha angle
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The angle between phases II and III, which
has
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increases as the slope of phase III
increases.
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The alpha angle is an indirect indication of
V/Q
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status of the lung.
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Airway obstruction causes an increased
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slope and a larger angle.
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Other factors that affect the angle are the
response time of the capnograph, sweep
speed, and the respiratory cycle time.
The Beta angle
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The nearly 90 degrees angle between phase
III and the descending limb in a time
capnogram has been termed as the beta
angle.
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This can be used to assess the extent of
rebreathing. During rebreathing, there is an
increase in beta angle from the normal 90
degrees.
Clinical Applications
Monitoring NMJ
DEPOLARISING BLOCK
• Fasiculation
• No tetanic fade
• No post-tetanic potentiation
• Anticholinesterases increase block
• Potentiation by other depolarisers May
develop Phase 2 block
NON-DEPOLARISING BLOCK
• No fasiculation
• Tetanic fade
• Post-tetanic facilitation
• Anticholinesterases decrease block
• Antagonism by other depolarisers No
change in character of block
Train of four (TO4)
• Fade is prominent with non-depolarising blockers and at 0.5 Hz is greatest
by the 6th twitch. Using four twitches at 0.5 second intervals (TO4) was
popularised by Ali and from these the ratio of T4/T1 (the "TO4 Ratio") can
be derived. The degree of paralysis is estimated from the number of
twitches present, or if four are present the TO4 ratio.
• Counting the number of palpable twitches is quite a good guide to deeper
levels of paralysis; two or more twitches usually implies reasonably easy
reversal and some return of muscle tone, while virtually no response
suggests difficulty with reversal, weak cough at best, and very little muscle
tone.
• TO4 ratios around 0.25 are commonly estimated at between 0.1 and 0.7,
while at 0.5 some 40% of and at 0.7 fewer than 10% of observers can
reliably detect any fade at all. Consequently the presence of any detectable
fade indicates the presence of some paralysis and furthermore even if all
four twitches appear normal many patients are in fact partly paralysed.
• It cannot be used to assess very deep levels of block (no T1!) and is not
very sensitive to assessing adequacy of reversal.
Dual Burst Stimulation (DBS)
• 50Hz train of 3 repeated 0.75 seconds later by an identical train of
three. Each group of three twitches results in one twitch, and hence
only two twitches available for comparison. Since the first twitch
sums T1, T2 and T3, while the second sums T4, T5, and T6, it is
easy to see how the presence of fade would be easier to notice and
there is data to support this. As the level of block increases,
response to the second burst is lost as the third twitch of TO4 is lost;
the first burst is retained until a little after you lose all response to
TO4. Surgical paralysis is generally OK if only one response is
present; the patient is reversible if two are present, particularly if the
second is strong. TO4 is better for quantifying the intensity of
"surgical" paralysis, whereas DBS is better for noting persistance of
fade after reversal. If you use NMB's so that there is just no
response to DBS, the patient will be a little more paralysed than if
there was just no response to TO4.
• Tetanic stimulation
• Continuous stimulation at either 50 or 100 Hz is so painful as to
preclude its use in conscious patients, and is difficult to quantify, but
is probably the most useful and emulates physiological maximal
responses. Tetany is more sensitive to both residual and deep
paralysis than any other form of monitoring. The presence of any
persisting strength during tetany is a good indicator of the patient's
ability to maintain muscle tone.
• Comparing two bursts of tetany (each 3-5 seconds long) with a gap
of 3 seconds results in post-tetanic potentiation of the response to
the second burst. When assessing adequacy of reversal the initial
part of the second response (potentiated) can be compared to the
last part of the first (faded).
• If fade is present it is becomes more obvious with this rather than
any other method.
• Post-Tetanic Count (PTC)
• This consists of counting 1 Hz twitches 3 seconds after 5
seconds of 50Hz tetany and can give an approximate
time to return of response to single twitches and hence
permits assessment of block too deep for any other
technique. A Post-Tetanic Count (PTC) of 2 by palpation
suggests no twitch response for about 20-30 minutes,
PTC of 5 about 10-15 minutes.
• This is clearly the best method for monitoring paralysis
for patients in whom you seek to prevent diaphragmatic
movement, ie micro-neurosurgery; it is best to use
infusions of drugs and aim for PTC of 2.
Arterial Blood Pressure
Damping is the tendency of the system to resist
oscillations caused by sudden changes
• Overdamping The waves tend to faltten thus
underestimating systolic reading and
Overestimating diastolic reading
• Underdamping magnify the waves with
overshooting, thus overestimating systolic
reading and uinderestimating diastolic reading
Factors causing Overdamping
1- Narrow tubing
2- Long elastic tubings(Compliant )
3- High density fluid
4- Air bubbles
5- Clot formation
Central Venous Pressure
Pulmonary Artery Catheter
Haemodynamic Profiles Obtained
from PA Catheters
• SV = CO / HR (60-90 mL/beat)
• SVR = [(MAP – CVP) / CO]  80
(900-1500 dynes-sec/cm5)
• PVR = [(MPAP – PCWP) / CO]  80
(50-150 dynes-sec/cm5)
• O2 delivery (DO2)
= C.O.  O2 content
• Arterial O2 content (CaO2)
= ( Hb  1.38 )  (SaO2)
• Mixed venous O2 content (CvO2)
= ( Hb  1.38 )  (SvO2)
• O2 consumption (VO2)
= C.O.  (CaO2-CvO2)
SvO2 = SaO2 – [VO2 / (Hb  13.8)(CO)]
ECG
Electrocardiogram
• Displays the overall electrical
activities of the myocardial cells
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Heart rate & dysrhythmias
Myocardial ischaemia
Pacemaker function
Electrolyte abnormalities
Drug toxicity
• Does NOT indicate mechanical
performance of the heart:
– Cardiac output
– Tissue perfusion
Full (12)-lead ECG
– Standard limb leads (bipolar)
– Precordial leads (unipolar)
5-lead system
– Unipolar + bipolar
– RA, LA, RL, LL, C
3- lead system
Bipolar with RA, LA, LL
V5 usually used
– Best compromise between detecting ischaemia and diagnosing
arrhythmia
May come with
ST-segment analysis
ECG
Standard Limb Leads
Unipolar Chest Leads
Artifacts in ECG Monitoring
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Loose electrodes or broken leads
Misplaced leads
Wrong lead system selected
Emphysema, pneumothorax,
pericardial effusion
• Shivering or restlessness
• Respiratory variation and
movement
• Monitor Pulse Oximetry, Invasive
ABP
Question NO. 8
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1- Identify the monitor Tracing?
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2- What is the Name & Cause of
the Notch on the descending
limb of the trace?
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3- Name two different Clinical
informations could be
interpreted from this tracing?
a) ……………………………..
b) ……………………………..
Question NO. 10
• 1- Identify the Rhythm in the shown ECG Strip?
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-----------------------------------------------------• 2- What is your first line of management in case
of Unstable patient
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• 3- What is the normal QRS duration
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Question NO. 14
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1- Identify the tracing
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2- Name the different phases of the trace
I  ………………………
II  ……………………..
III  …………………….
IV  ……………………..
3- What different clinical informations
could be interpreted from the trace
a)
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b)
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Question NO. 15
• 1- Name the different waves on the trace?
• -----------------------------------------------• 2- Define Central Venous Pressure?
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• 3- What are the main determinants
regulating CVP?
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A-………………………………….
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B- ………………………………...
Question NO. 19
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brief the mechanism of action of this monitor :
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Name 4 factors affecting the accuracy of this monitor?
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If P50 of oxyhemoglobine dissociation curve is 40; is this
curve shifted to the right or left; mention 3 possible causes?
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• 36-Each of the following factors may
lead to error in readings using pulse
oximetry EXCEPT:
A. electrocautery
B. high cardiac output states
C. infrared lights near the sensor
D. intravenous dyes
E. severe hemodilution