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Surgery I > Anesthetic monitorings > Flashcards

Anesthetic monitorings Flashcards

1
Q

OBJ: Become familiar with the techniques used to monitor anesthetic depth in veterinary patients

A
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2
Q

OBJ: Understand how to use and interpret data form monitors used for:

  • blood pressure
  • Heart rate
  • Cardiac electrophysiologic activity (electrocardiogram)
  • Hemoglobin saturation with O2
  • Ventilatory function and exhaled carbon dioxide
A
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3
Q

What is Anesthetic Monitorings?

A
  • Observational monitoring of the animals responses to:
    • Increases or decreasing delivery of an anesthetic
    • Noxious stimuli
    • Charge in the patient’s body position
  • Recording and responding to information from monitoring equipment
    • ECG
    • Blood pressure monitor
    • Pulse oximeter
    • Capnography
    • Thermometer
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4
Q

Why monitor anesthetic depth?

A
  • Ensure lack of patient awareness, recall, pain and movement
  • Negative effects of anesthetics are associated with increasing depth of anesthesia
    • Hypotension
    • Hypoventilation
    • Decreases in cardiac output
    • Decreases in peripheral perfusion
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5
Q

What are the “stages and Planes’ of anesthesia?

A
  • Refers to Guedel’s classification of stages of anesthesia
    • published 1937
    • Stage 1 - 4
    • Based on older, no longer used anesthetics such as ether
    • NO longer useful
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6
Q

in what ways is Anesthetic depth described?

A
  • “too light”
    • responds to noxious stimuli
      • movement
      • tachypnea
      • increasing heart rate and blood pressure
  • “too deep”
    • no response but undesirable effects of the anesthetic may occur
  • “just right”
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7
Q

How should anesthetic depth be monitored?

A
  • Ongoing moment to moment assessment
    • Changes in depth can be quite subtle
    • No reliable or practical single piece of equipment to assess depth
    • Do not focus on just a single parameter to judge depth of anesthesia
  • Develop observational skills and understand how to respond
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8
Q

What are the subjective measures for judging anesthetic depth?

A
  • Eye position
  • palpebral reflex
  • lacrimation
  • Jaw tone, muscular relaxation
  • character of breathing
  • Patient’s response to position changes
  • patient’s motor response to noxious stimuli
    • first noxious stimuli is often the towel clamp
  • Hemodynamic responses to noxious stimuli
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9
Q

What does the palpebral reflex during isoflurane anesthesia mean?

A
  • Dogs / Cats
    • Present = very light
    • Absent dos not guarantee a surgical plane of anesthesia
  • Horses:
    • slight palpebral reflex often present during surgical planes of anesthesia
  • Cattle / small ruminants
    • may or may not be present
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10
Q

How does one check the palpebral reflex?

A
  • Gently touch medial and lateral canthus
  • Do NOT tap on the eyelid - can elicit a corneal response
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11
Q

What are the positions of the globe and pupil during isoflurane anesthesia?

A
  • Very Light:
    • pupil may still be centrally positioned
    • palpebral reflex present
    • lacrimation present
  • Increasing depth:
    • pupil positioned ventromedially
    • lacrimation markedly decreased
  • Excessive depth:
    • Pupil centrally located
    • NO palpebral
    • little to no lacrimation
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12
Q

How should jaw tone be assessed for anesthetic depth? when is it not useful?

A
  • Reflection of muscle relaxation
  • Open jaw fully 2 times
    • requires both hands
      • one hand stabilizes maxilla
      • one hand moves the mandible
  • Should feel slight resistance when mouth is ½ - ⅔ open
  • Very light = tighter jaw
  • Deep = slack jaw
  • Not useful in very young patients (<8 wks)
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13
Q

What are the objective measurements for depth assessment?

A
  • End-tidal anesthetic agent monitoring
  • End-tidal carbon dioxide tension
    • increased depth, increased hypoventilation
  • Changes in blood pressure in response to noxious stimulus
  • Changes in ventilatory character
    • Thoracic movement
    • Abdominal movement
    • Response to stimulus
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14
Q

What is used to monitor the cardiovascular system during anesthesia?

A
  • Heart rate
  • Blood pressure
  • Mucous membrane color
  • Capillary refill time
  • Limb temperature
  • Pulse oximetry/plethysmography
  • ECG
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15
Q

What technique is used to monitor the heart rate during anesthesia?

A
  • Stethoscope on the thorax
  • Esophageal stethoscope
  • Palpation of peripheral pulse
  • ECG monitor
  • Pulse oximeter reading of the heart rate
  • Doppler peripheral flow signal
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16
Q

What values are normal for heart rate during anesthesia?

A
  • Acceptable rate varies with species and within species
  • Drug influences:
    • alpha 2 agonists
    • Opioids
    • Anticholinergics
    • Body temperature
    • Think in terms of functional rate
  • Anything less than 60 is NOT necessarily bad
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17
Q

What is an esophageal stethoscope?

A
  • Passed through the mouth into the esophagus
  • Balloon tipped end is positioned over the heart
  • Listen and adjust position for where heart sounds are loudest
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18
Q

Where can the peripheral pulse be palpated during anesthesia?

A
  • Dogs / cats
    • lingual, dorsal pedal, femoral, coccygeal, metacarpal, metatarsal
  • Horses:
    • facial, mandibular, auricular, palatine, greater metatarsal
  • Ruminants:
    • Auricular, digital, saphenous, palatine
  • Swine:
    • auricular, femoral, digital
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19
Q

What can the mucous membranes be used to evaluate during anesthesia?

A
  • Gives some indication of peripheral perfusion and Oxygenation
  • Color:
    • pink but not pale
    • Cyanosis difficult to recognize unless very hypoxemic
      • requires 5 grams of desaturated hemoglobin per deciliter of blood to detect cyanosis
    • Pale can represent poor perfusion and/or anemia
  • Capillary refill time:
    • Should occur in less than 2 sec
    • reflection of peripheral blood flow
20
Q

What is a doppler ultrasound for blood pressure?

A
  • Paired piezoelectric ultrasound crystals over an artery
  • Blood pressure cuff proximal to the crystals
  • An ultrasound signal is sent out and back to the crystal and detects flow through an artery
    • crystal detects a change in frequency of the ultrasound when it comes back
    • transforms that information to an audible signal
  • Blood pressure cuff inflated until the sound is gone
  • gradually deflate - when sound occurs that is SYSTOLIC pressure
21
Q

What is the appropriate sized doppler ultrasound cuff? what happens if the cuff size isn’t appropriate?

A
  • Height should be 40-60% of the circumference of the appendage (leg / tail) where the cuff is placed
  • Too small = overestimate pressure
  • Too big = underestimate pressure
22
Q

How does an Oscillometric Blood Pressure Monitor track blood pressure during anesthesia?

A
  • Based on detection of arterial wall movement
    • Machine inflates a cuff to a point where it occludes flow through an artery
    • Deflates cuff
    • Blood starts to flow turbulently through the artery
      • machine detects movement from the blood flow - SYSTOLIC pressure
    • MAgnitude of ocillations increases to a maximum then decreases
      • maximum is MEAN blood pressure
      • as the cuff decreases, flow in vessel becomes laminar and no oscillations are detected - DIASTOLIC pressure
23
Q

What is Direct Blood Pressure Monitoring?

A
  • Catheter placed in peripheral artery
  • A transducer converts the mechanical pressure signal to an electrical signal
  • Digitized and displayed on a monitor
    • Wave form
    • Numbers corresponding to systolic, diastolic, and mean arterial pressure
24
Q

OBJ: Understand the principles of oxygen saturation of hemoglobin and how we monitor this with a pulse oximeter

25
OBJ: Know what a capnograph is an how to use it to evaluate a patient's ventilatory status
26
OBJ: know why an ECG would be used during anesthetic monitoring
27
OBJ: know the benefits of monitoring temperature during anesthesia
28
What is the goal of oxygenation monitoring?
* Ensure an adequate oxygen concentration in the patient's arterial blood * Objective methods of monitoring oxygenation include * Arterial blood gas analysis * Pulse oximetry
29
What is a Oxygen Hemoglobin Saturation Curve?
* Saturation of hemoglobin (SO2) and partial pressure of oxygen in the blood (PO2) has a relatively linear relationship below a PO2 of about 40mmHg * Above a PO2 of about 80 mmHg the curve is relatively flat * Saturation changes very little * Difference between normoxemia and hypoxemia is only a few saturation points * Small changes in SO2 represent large changes in P)2 on the steep part of the curve
30
What does Pulse Oximetry do?
* Measures oxygen saturation of hemoglobin * Noninvasive * Continuous detection of pulsatile arerial blood in a tissue bed * Absorption or reflection of red and infrared light is used to detect % of oyhemoglobin vs deoxyhemoglobin * Must detect pulsatile flow * Measurement inaccurate or not present with poor peripheral flow * Provides a pulse rate
31
What is the cut off for being considered hypoxic?
\<60 mmHg
32
What are healthy Pulse Oximeter Readings?
* Healthy patients breathing \>95% O2 * saturation should be between 97 - 100% * Healthy patient breathing room air * saturation should be about 95% * patients with low saturation need to be evaluated for causes of hypoxemia
33
What can cause Pulse oximetry artifacts / inaccuracies?
* Motion artifact * Ambient light artifact * no longer a problem with most * Poor peripheral flow * hypotension * vasoconstriction * Electrical interference from cautery * Increased carboxyHb or metHb * do NOT carry oxygen * Can be differentiated by most pulse oximeter
34
What is Capnography?
* Measures and displays CO2 concentration in the expired air * End-tidal CO2 reflects partial pressure of CO2 in the alveoli * alveolar CO2 will be an accurate estimate of arterial CO2 * Continuous noninvasive measure of CO2 * reflects the patient's ventilatory status * Standard of care for monitoring human patients
35
What are the different types of capnographs?
* Sidestream * Mainstream
36
What is side stream capnography?
* Aspirate gas through a small tube that is connected to an adaptor between the endotracheal tube and the breathing circuit * Rate of gas aspiration varies with the machine * Datex-Ohmeda monitors 200ml/min * Nellcor microstream 50ml/min * Microstream monitors should be used on all small patients
37
What are Mainstream capnographs?
* Infrared light source and infrared detector are in the adaptor that is between the endotracheal tube and the breathing circuit * Adaptor between the breathing circuit and ET tube * Instantaneous reading with each breath
38
What is the Massimo Emma II?
* Mainstream capnograph * Small, portable * Designed for short term use * confirm ET placement * During CPR * Adult, pediatric, and neonatal adaptors * Used in some veterinary practices as reasonable alternative for capnography because of lower cost
39
Why would a capnograph fail to display a waveform?
* Esophageal intubation * Apnea or respiratory arrest * Cardiac arrest * Disconnected breathing circuit and adaptor from the ET tube * Obstructed ET tube
40
Why would the capnograph have high End-tidal CO2 Reading?
* Hypoventilation * common during anesthesia with isoflurane or sevoflurane * Normal CO2 35 - 45% * Rebreathing CO2 * Faulty breathing circuit * Inadequate O2 flow with a nonrebreathing circuit * Exhausted CO2 absorbent (soda lime) * Excessive dead space between the breathing circuit and the ET tube * Rebreathing of CO2 will cause an elevated baseline on the capnograph tracing * waveform does NOT return to baseline
41
What are Cardiogenic Oscillations?
* On the capnograph * Small, regular sawtooth pattern on the graph * Synchronized to heart rate * When the heart beats the changes in heart volume causes slight changes in intrathoracic pressure and changes in lung volume
42
What would inadequate sampling of alveolar gas result in? why does it happen?
* Can be a problem with small patients * particularly on nonrebreathing circuits * Underestimates alveolar CO2 * Capnograph will still give a value but it will underestimate alveolar CO2
43
What does Rapid Decline in End-tidal CO2 mean?
* CO2 has to get to the lung from pulmonary circulation * If there is rapidly declining ET-CO2 you need to be concerned about decreasing cardiac output and cardiac arrest
44
What is a ventilometer?
* Attaches to the expiratory limb of a breathing circuit * Measures volume of gas flowing through the tube on expiration * Can measure tidal volume and/or minute ventilation * Expensive ($1300) * secure it to the anesthetic machine so it is not dropped
45
What is an electrocardiogram?
* Measures and displays electrical activity of the heart * Continuous ECG necessary for accurate and rapid detection of any dysrhythmias or abnormalities in conduction * We place an ECG on all patients prior to induction of anesthesia * may not be in a standard lead configuration * We are using this to detect dysrhythmia
46
Why is temperature monitoring important during surgery?
* Hypothermia is common in our patients * Affects healing * Prolongs recovery from anesthesia * May induce shivering in recovering which increases oxygen demand * Preventing hypothermia is easier than treating hypothermia * Overwarming can also occur * multiple warm water blankets in use * Forced air warming
47
What is a normal capnograph waveform? what are its parts?

Surgery I (37 decks)

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