Monitoring During
anaesthesia
Prof. Abdulhamid Al-Saeed, FFARCSI
Anaesthesia Department
College of Medicine
King Saud University
Lecture Objectives..
Students at the end of the lecture will be able to
knows:
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)
Monitoring: A Definition
• interpret available clinical data to
help recognize present or future
mishaps or unfavorable system
conditions
Monitoring in the Past
•Visual
monitoring of
respiration and
overall clinical
appearance
•Finger on pulse
•Blood pressure
(sometimes)
Finger on the pulse
Monitoring in the Present
• Standardized basic monitoring requirements
(guidelines) from the ASA (American Society of
Anesthesiologists), CAS (Canadian
Anesthesiologists’ Society) and other national
societies
• Many integrated monitors available
• Many special purpose monitors available
• Many problems with existing monitors (e.g., cost,
complexity, reliability, artifacts)
Standard
ASA monitoring for general anesthesia ,
monitored anesthesia care and regional
anesthesia :Oxygenation (oxygen analyzer, pulse
oximetry),
Ventilation (capnography, minute ventilation),
respiratory rate (under regional anesthesia)
Circulation (electrocardiogram [ECG], arterial
blood pressure, perfusion assessment),
 Temperature.
High Tech Patient Monitoring
Examples of Multiparameter Patient Monitors
High Tech Patient Monitoring
Transesophageal
Echocardiography
Depth of Anesthesia Monitor
Evoked Potential Monitor
Some Specialized Patient Monitors
Cardiovascular system.
The circulatory system is responsible for oxygen delivery to and
removal of waste products from the organs, and this must be
maintained during anesthesia.
Signs and symptoms of perfusion abnormalities
Central nervous system: mental status changes, neurologic
deficits.
Cardiovascular system: chest pain, shortness of breath,
ECG abnormalities, wall motion abnormalities on
echocardiogram.
Renal: decreased urine output, elevated blood urea
nitrogen and creatinine, decreased fractional excretion of
sodium.
Gastrointestinal: abdominal pain, decreased bowel sounds,
hematochezia.
Peripheral: cool limbs, poor capillary refill, diminished
pulses.
ECG.
 The ECG monitors the conduction of electrical impulses
through the heart.
 Rhythm detection is best seen in lead II.
ECG
Electrocardiogram
• Displays the overall electrical
activities of the myocardial cells
–
–
–
–
–
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
•
•
•
•
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
Arterial blood pressure.
 Automated noninvasive blood pressure is the most common
noninvasive method of measuring blood pressure in the
operating room.
 Invasive blood pressure monitoring uses an indwelling arterial
catheter coupled through fluid-filled tubing to a pressure
transducer.
 The transducer converts pressure into an electrical signal to
be displayed.
 Indications
– Need for tight blood pressure control (e.g., induced
hyper- or hypotension).
– Hemodynamically unstable patient.
– Frequent arterial blood sampling.
– Inability to utilize noninvasive blood pressure
measurements.
Arterial Blood Pressure
Central venous pressure (CVP) and cardiac output
 CVP is measured by coupling the intravascular space to a
pressure transducer using fluid-filled tubing.
 Pressure is monitored at the level of the vena cava or the right
atrium.
 Indications
 Measurement of the right heart filling pressures to assess
intravascular volume and right heart function.
 Drug administration to the central circulation.
 Intravenous access for patients with poor peripheral access.
 Indicator injection for cardiac output determination (e.g.,
green dye cardiac output).
 Access for insertion of pulmonary artery catheter.
 Range The CVP is normally 2 to 6 mm Hg
Central Venous Pressure
PULMONARY ARTERY
CATHETER
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)]
Respiratory system.
 pulse oximetry, capnography, a fraction of inspired oxygen
analyzer, and a disconnect alarm.
 Pulse oximeter
 combines the principles of oximetry and plethysmography to
noninvasively measure oxygen saturation in arterial blood.
 The pulse oximeter probe contains two light emitting diodes
at wavelengths of 940nm and 660 nm.
 Oxygenated and reduced hemoglobin differ in light
absorption (940 and 660 nm respectively).
 Thus the change in light absorption during arterial pulsation
is the basis of oximetry determination.
 The ratio of the absorption at the two wavelengths is
analyzed by a microprocessor to record the oxygen
saturation.
Pulse Oximetry
Incomptencies




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)
Capnometry
What is Capnometry?
 Is the measurement of end-tidal carbon dioxide tension.
 This provides valuable information to the anesthesiologist.
 The presence of end tidal CO2 aids in confirming endotracheal
intubation.
 Alteration in the slope of the graph can give clues to the
presence of airway obstruction.
 A rapid fall in reading may signify extubation, air embolism or
low cardiac output with hypovolemia.
The Alpha angle
•
The angle between phases II and III, which
has
•
increases as the slope of phase III
increases.
•
The alpha angle is an indirect indication of
V/Q
•
status of the lung.
•
Airway obstruction causes an increased
•
slope and a larger angle.
•
Other factors that affect the angle are the
response time of the capnograph, sweep
speed, and the respiratory cycle time.
The Beta angle
•
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
Central nervous system (level of consciousness)
monitoring
 Bispectral index (BIS) assess central nervous system
depression during general anesthesia.
 It is based on the surface electroencephalogram (EEG),
which predictably changes in amplitude and frequency
as the depth of anesthesia increases.
Temperature monitoring
Indications
Infants and small children are prone to thermal lability due to
their high surface area to volume ratio.
Adults subjected to large evaporative losses or low ambient
temperatures (as occur with exposed body cavity, large
volume transfusion of unwarmed fluids, or burns) are prone
to hypothermia.
Malignant hyperthermia is always a possible complication, and
temperature monitoring should always be available.
Monitoring site
Tympanic membrane temperature
Rectal temperature
Nasopharyngeal temperature,
Esophageal temperature monitoring reflects the core
temperature well. The probe should be located at the
lower third of the esophagus and rarely may be
misplaced in the airway.
Blood temperature measurements may be obtained with
the thermistor of a PAC.
Neuromuscular blockade monitoring:
 Neuromuscular blockade is monitored during surgery to
guide repeated doses of muscle relaxants and to
differentiate between the types of block.
 All techniques for assessing neuromuscular blockade
use a peripheral nerve stimulator (PNS) to stimulate a
motor nerve electrically.
Detecting Mishaps Using Monitors
1. Disconnection
2. Hypoventilation
3. Esophageal intubation
4. Bronchial intubation
5. Circuit hypoxia
6. Halocarbon
overdose
7. Hypovolemia
These mishaps …
8. Pneumothorax
9. Air Embolism
10. Hyperthermia
11. Aspiration
12. Acid-base
imbalance
13. Cardiac dysrhythmias
14. IV drug overdose
Source: Barash Handbook
Detecting Mishaps with Monitors
•
•
•
•
•
•
•
•
Pulse oximeter
Capnograph
Automatic BP
Stethoscope
Spirometer
Oxygen analyzer
ECG
Temperature
1,2,3,4,5,8,9,11,14
1,2,3,9,10,12
6,7,9,14
1,3,4,13
1,2
5
13
10
Source: Barash Handbook
… are detected using these monitors
Question NO. 8
•
•
1- Identify the monitor Tracing?
•
2- What is the Name & Cause of
the Notch on the descending
limb of the trace?
………………………………
………………………………………
………
•
•
•
•
………………………………………
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?
-----------------------------------------------------2- What is your first line of management in case of
Unstable patient
…………………………………………………………
3- What is the normal QRS duration
……………………………………………………………
Question NO. 14
1- Identify the tracing
……………………………………………………
…………………………………
2- Name the different phases of the trace
I  ………………………
II  ……………………..
III  …………………….
IV  ……………………..
3- What different clinical informations could
be interpreted from the trace
a) ………………………………………………..
b) ………………………………………………..
Question NO. 15
1- Name the different waves on the trace?
-----------------------------------------------2- Define Central Venous Pressure?
……………………………………………………
……………………………………………………
3- What are the main determinants regulating
CVP?
A-………………………………….
B- ………………………………...
Question NO. 19
brief the mechanism of action of this monitor :
………………………………………………………………………………………
……………………………………………………………………………
……………………………………………………………………………
…
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?
…………………………………………………………………………
…………………………………………………………………………
…………………………………………………………………………..
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