Monitoring In Anesthesia

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Monitoring In Anesthesia

• Prof. Abdulhamid Al-Saeed, FFARCSI
• Anaesthesia Department
• College of Medicine
• King Saud University

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Monitoring A Definition

• interpret available clinical data to help
  recognize present or future mishaps or
  unfavorable system conditions

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Patient Monitoring Management

• Involves
• Things you measure (physiological measurement,
  such as BP or HR)
• Things you observe (e.g. observation of pupils)
• Planning to avoid trouble (e.g. planning
  induction of anesthesia or planning extubation)
• Inferring diagnoses (e.g. unilateral air entry
  may mean endobronchial intubation)
• Planning to get out of trouble (e.g. differential
  diagnosis and response algorithm formulation)

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Monitoring in the Past

• Visual monitoring of respiration and overall
  clinical appearance
• Finger on pulse
• Blood pressure (sometimes)

Finger on the pulse
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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)

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ASA Monitoring Guidelines

• STANDARD I
• Qualified anesthesia personnel shall be present
  in the room throughout the conduct of all general
  anesthetics, regional anesthetics and monitored
  anesthesia care.
• http//www.asahq.org/publicationsAndServices/stan
  dards/02.pdf

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ASA Monitoring Guidelines

• STANDARD II
• During all anesthetics, the patients
  oxygenation, ventilation, circulation and
  temperature shall be continually evaluated.
• http//www.asahq.org/publicationsAndServices/stan
  dards/02.pdf

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CAS Monitoring Guidelines

• The following are required
• Pulse oximeter
• Apparatus to measure blood pressure, either
  directly or noninvasively
• Electrocardiography
• Capnography, when endotracheal tubes or laryngeal
  masks are inserted.
• Agent-specific anesthetic gas monitor, when
  inhalation anesthetic agents are used.

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CAS Monitoring Guidelines

• The following shall be exclusively available for
  each patient
• Apparatus to measure temperature
• Peripheral nerve stimulator, when neuromuscular
  blocking drugs are used
• Stethoscope either precordial, esophageal or
  paratracheal
• Appropriate lighting to visualize an exposed
  portion of the patient.

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High Tech Patient Monitoring
Examples of Multiparameter Patient Monitors
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High Tech Patient Monitoring
Transesophageal Echocardiography
Depth of Anesthesia Monitor
Evoked Potential Monitor
Some Specialized Patient Monitors
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Pulse Oximetry
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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.
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• 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

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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)

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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

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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.

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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 patients 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

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• 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.
• Sensors window must be kept clean of mucus and
  particles to prevent false readings.
• Response time is faster

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• 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.

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Clinical Applications
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Monitoring NMJ

• DEPOLARISING BLOCK
• Fasiculation
• No tetanic fade
• No post-tetanic potentiation
• Anticholinesterases increase block
• Potentiation by other depolarisers May develop
  Phase 2 block

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• NON-DEPOLARISING BLOCK
• No fasiculation
• Tetanic fade
• Post-tetanic facilitation
• Anticholinesterases decrease block
• Antagonism by other depolarisers No change in
  character of block

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• 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.

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• 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.

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• 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.

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• 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.

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Arterial Blood Pressure
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• 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

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• Factors causing Overdamping
• 1- Narrow tubing
• 2- Long elastic tubings(Compliant )
• 3- High density fluid
• 4- Air bubbles
• 5- Clot formation

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Central Venous Pressure
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PULMONARY ARTERY CATHETER
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Pulmonary Artery Catheter
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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)

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• 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)

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ECG
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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

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• 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

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ECG
Standard Limb Leads Unipolar Chest Leads
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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

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Temperature Monitoring

• Rationale for use
• detect/prevent hypothermia
• monitor deliberate hypothermia
• adjunct to diagnosing MH
• monitoring CPB cooling/rewarming
• Sites
• Esophageal
• Nasopharyngeal
• Axillary
• Rectal
• Bladder

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Detecting Mishaps Using Monitors

• 8. Pneumothorax
• 9. Air Embolism
• 10. Hyperthermia
• 11. Aspiration
• 12. Acid-base imbalance
• 13. Cardiac dysrhythmias
• 14. IV drug overdose
• Source Barash Handbook

• 1. Disconnection
• 2. Hypoventilation
• 3. Esophageal intubation
• 4. Bronchial intubation
• 5. Circuit hypoxia
• 6. Halocarbon overdose
• 7. Hypovolemia

These mishaps
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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
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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) ..

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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

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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) ..

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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- ...

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Question NO. 19

• brief the mechanism of action of this monitor
• 
  
• Name 4 factors affecting the accuracy of this
  monitor?
• 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 EXCEPTA.
  electrocauteryB. high cardiac output statesC.
  infrared lights near the sensorD. intravenous
  dyesE. severe hemodilution