Lecture Title: Equipments &
Measurements Stations
Lecturer name:
Lecture Date:
Prof. Abdulhamid Al-Saeed,
Lecture Objectives..
Students at the end of the lecture will be
able to:know
Monitors : non-invasive blood pressure , ECG , pulse oximetry
capnography (CO2 monitor) and oxygen analyzer ,
temperature probe nerve stimulator
Specialized monitors : arterial line (invasive blood pressure)
central venous line (cvp monitoring) pulmonary artery
flotation catheter ( monitors function of right and left side
of the heart) BIS monitor (depth of anesthesia)
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.
• Describe the principles involved in pulse
oximetry.
• What are its limitations in clinical practice?
• Is it fast or slow as a monitor of oxygen
saturation?
A pulse oximeter gives NO information on any
of these other variables:
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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
• What is the physical principle?
• Discuss the end-tidal CO2 trace with
rebreathing.
• What are the types?
• Clinical Applications?
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 costeffective.
• 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.
•
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
• Discuss neuromuscular monitoring
• What is double burst?
• What is train-of-four (TOF)?
• Can you differentiate between depolarising
and non-depolarising agents?
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 PostTetanic 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
• Discuss arterial traces (including damped/resonant).
• What is Fourier analysis?
• What is bandwidth?
• What is a transducer, and when might this be used in
clinical practice?
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 underestimating 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
• 1.How does an ECG machine work?
2. What are amplifiers?
3. Define bandwidth and gain.
4. What is differential amplification?
5. What is the frequency of the ECG?
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
Reference book and the
relevant page numbers..
Thank You 
Dr.
Date: