1. Prepare and monitor anaesthesia in animals
MONITORING
See

2. Best Practice in Anaesthesia
Photo from - Griet Haitjema, Senior Registrar - Veterinary Anaesthesia and Critical care
Murdoch University Veterinary Hospital

3. General GA monitoring rules
Monitoring continuous
Recording every 5 mins
The anaesthetist’s overall judgement is more important than any one parameter reading

4. Vital Signs for Anaesthesia
CNS vitals
Consciousness
Reflexes
Responses
Muscle tone
Other vitals
Cardiovascular
Respiratory
Urinary
Depth of anaesthesia
See Stages of Anaesthesia

5. Another classification
Signs continually present
Signs evoked by a stimulus
Responses
Reflexes

6. Resting Signs Pupils & Eye position Jaw tone Heart rate & rhythm
Respiratory rate
Pulse quality
MM & CRT
Temperature
Haemoglobin O2 saturation (Pulse oximetry)
Blood pressure
ECG
End-expiratory CO2 (Capnography)
Tongue curl (under light GA when as mouth opened)
Salivation (possible inadequate anaesthesia)
Urine output (1-2mL/kg/hr an indication of renal perfusion)

7. Other Signs tested for Palpebral reflex
Ear twitch (not a good guide to depth in cats)
Reaction to painful stimulus
Skin pricking
Corneal reflex
Pedal reflex
Anal pinching
PLR
Response to visceral stimulus
Cutaneous reflex
Righting reflex
Pharyngeal reflex
Laryngeal reflex

8. Surgical ‘stress map’ (timeline)

9. 5 mins How often to monitor?
Ideally check & record vitals every 5 minutes
5 mins

10. Monitoring form
e.g. ‘AAS’ FORM

12. Class activity 1
List 8 signs that can be monitored when a patient is under GA?

13. Answers 1 Heart rate and rhythm Pulse rate MM colour
RR, depth and character
CRT
Temperature
Oxygen saturation
Pupil size and position

14. Monitoring depth
See anaesthesia stages

15. Anaesthetised Dog & CatHR
80-140 RR
10-30
20-40 C
38
CRT
< 2 sec
SpO2
> 95%
BP (diast)
mmHg
BP (syst)
mmHg

16. Class Activity 2
List reflexes that can be monitored when a patient is under G/A

17. Answers 2 Pedal reflex Jaw tone Skin pricking Anal pinching
Palpebral reflex
Corneal reflex
PLR
Response to visceral stimulus
Ear twitch
Cutaneous reflex
Reaction to painful stimulus
Righting reflex
Pharyngeal reflex
Laryngeal reflex

18. Class activity 3
What are some types of monitoring devices?

19. Answers 3 Person ECG Pulse oximeter End tidal volume CO2 monitor
Oesophageal stethoscope & stethoscope
Respiratory monitors such as an Apalert
Doppler ultrasound & Dinamap
Thermometer

20. Heart Rate
Normal
Dog
Report HR <80 to vet
Cat

21. Oesophageal Stethoscope

22. Pulse rate & quality
Pulse strength & rate more useful information than HR
Measure
Lingual (under tongue, midline)
Femoral
Carotid
Pedal (dorsal)

23. Easy & Useful - 2 fingers on ventral midline of tongue
Lingual pulse
Easy & Useful - 2 fingers on ventral midline of tongue

24. Pulse rate & quality
Pulse beat should be felt just after each heart beat
Measure both HR & PR at same time
If not synchronised you have a ‘pulse deficit’
Strength of pulse gives a rough estimate of blood pressure

25. Oesophageal Stethoscope
Tube attached to a regular stethoscope
Permits auscultation of heart & lungs of draped patient
Intubate patient
Lubricate tubing (e.g. K-Y® gel)
Advance until heartbeat detected

26. MM & CRT Best to assess gingival MM colour CRT Pallor
Pain, haemorrhage, hypothermia, shock
Bluish-purple = cyanosis
Indicates hypoxia / hypoxaemia
Usually caused respiratory failure / airway obstruction
CRT
Useful but not reliable
Can have a good CRT in a euthanased animal!

27. Pulse oximetry

28. Pulse Oximeters How they work
Measure the absorption of infrared light by haemoglobin in a peripheral tissue bed.
The light absorption characteristics of haemoglobin vary with SpO2
Measure the difference in 2 wavelengths (red & blue) of arterial pulsating blood and the fixed signals from skin, tissue and venous blood

32. Application sites
Clip type sensors – tongue, lip, ear if non pigmented, paw, toes, thin skin folds on extremities (e.g. above hock)
Reflector sensors – light source & receiving sensor are on the same side of the skin surface, taped to a hairless skin surface
Rectal sensors – unreliable as faecal matter interferes with light transmission and probe movement cause vasoconstriction

33. Placement of sensor
Handle area (e.g. tongue) gently as rough handling causes vasoconstriction
Clipping hair at application site helps

34. Pulse oximetry
Measures the relative absorption (saturation) of the haemoglobin molecule with oxygen in an artery
An arterial vessel is distinguished by detecting its pulsation
Abbreviation = SpO2 (SpulseO2)
The pulse Hb O2 saturation (SpO2) is an estimation of arterial Hb saturation, SaO2 (SarterialO2)
[cf arterial oxygen pressure = PaO2 requires sampling blood and promptly measuring oxygen content]
Reprinted from RESPIRATORY CARE (Respir Care 1991;36: ) AARC Clinical Practice Guideline
Pulse Oximetry
PO 1.0 PROCEDURE:
Pulse Oximetry (SpO2) PO 2.0 DESCRIPTION/DEFINITION:
Pulse oximetry provides estimates of arterial oxyhemoglobin saturation (SaO2) by utilizing selected wavelengths of light to noninvasively determine the saturation of oxyhemoglobin (SpO2).(1-6) PO 3.0 SETTING:
Pulse oximetry may be performed by trained personnel in a variety of settings including (but not limited to) hospitals, clinics, and the home.(7,8) PO 4.0 INDICATIONS:
4.1 The need to monitor the adequacy of arterial oxyhemoglobin saturation(1,4,6,9)
4.2 The need to quantitate the response of arterial oxyhemoglobin saturation to therapeutic intervention(4,9,10) or to a diagnostic procedure (eg, bronchoscopy)
4.3 The need to comply with mandated regulations(11,12) or recommendations by authoritative groups(13,14)
PO 5.0 CONTRAINDICATIONS:
The presence of an ongoing need for measurement of pH, PaCO2, total hemoglobin, and abnormal hemoglobins may be a relative contraindication to pulse oximetry. PO 6.0 HAZARDS/COMPLICATIONS:
Pulse oximetry is considered a safe procedure, but because of device limitations, false-negative results for hypoxemia(4) and/or false-positive results for normoxemia(15,16) or hyperoxemia(17,18) may lead to inappropriate treatment of the patient. In addition, tissue injury may occur at the measuring site as a result of probe misuse (eg, pressure sores from prolonged application or electrical shock and burns from the substitution of incompatible probes be-tween instruments).(19) PO 7.0 DEVICE LIMITATIONS/VALIDATION OF RESULTS:
7.1 Factors, agents, or situations that may affect readings, limit precision, or limit the performance or application of a pulse oximeter include
7.1.1 motion artifact(2,5,8,9,20)
7.1.2 abnormal hemoglobins (primarily carboxyhemoglobin [COHb] and met-hemoglobin [metHb])(1,3,5,8,9,21)
7.1.3 intravascular dyes(1,3,8,9)
7.1.4 exposure of measuring probe to ambient light during measurement(2,3,8,9)
7.1.5 low perfusion states(1,3,4,8,9,21)
7.1.6 skin pigmentation(5,9,10,21)
7.1.7 nail polish or nail coverings with finger probe(9)
7.1.8 inability to detect saturations below 83%(22) with the same degree of accuracy and precision seen at higher saturations(9,10,21,23,24)
7.1.9 inability to quantitate the degree of hyperoxemia present(17)
Hyperbilirubinemia has been shown not to affect the accuracy of SpO2 readings.(25,26)
7.2 To validate pulse oximeter readings, incorporate or assess agreement between SpO2 and arterial oxyhemoglobin saturation (SaO2) obtained by direct measurement(1,4,5,21)--these measurements should be initially performed simultaneously(4,21) and then periodically re-evaluated in relation to the patient's clinical state.(6,27,28)
7.3 To help assure consistency of care (between institutions and within the same institution) based on SpO2 readings, assess
7.3.1 selection of proper probe and appropriate placement (the probe is at-tached to its intended site);
7.3.2 for continuous, prolonged monitoring, the Hi/Low alarms are approprately set;
7.3.3 specific manufacturer's recom-mendations are complied with, the device is applied and adjusted correctly to monitor response time(5,29) and electrocardio-graphic coupling;(20)
7.3.4 strength of plethysmograph waveform or pulse amplitude strength; assure that device is detecting an adequate pulse.
7.4 SpO2 results should be documented in the patient's medical record and should detail the conditions under which the readings were obtained:
7.4.1 date, time of measurement, and pulse oximeter reading; patient's position, activity level, and location;(4) during monitoring, assure that patient's activity is according to physician's order;
7.4.2 inspired oxygen concentration or supplemental oxygen flow, specifying the type of oxygen delivery device;
7.4.3 probe placement site(4) and probe type;
7.4.4 model of device (if more than one device is available for use);
7.4.5 results of simultaneously obtained arterial pH, PaO2, and PaCO2, and directly measured saturations of COHb, MetHb, and O2Hb4 (if direct measurement was not simultaneously performed, an additional, one time statement must be made explaining that the SpO2 reading has not been validated by comparison to directly measured values);
7.4.6 stability of readings (length of observation time and range of fluctuation, for continuous or prolonged studies, review of recording may be necessary);
7.4.7 clinical appearance of patient--subjective assessment of perfusion at measuring site (eg, cyanosis, skin temperature); (9)
7.4.8 agreement between patient's heart rate as determined by pulse oximeter and by palpation and oscilloscope.(2,17,28,30)
7.5 When disparity exists between SpO2, SaO2 readings, and the clinical presentation of the patient, possible causes should be explored before results are reported. Discrepancies may be reduced by monitoring at alternate sites or appropriate substitution of instruments or probes.If such steps do not remedy the disparity, results of pulse oximetry should not be reported; instead, a statement describing the corrective action should be included in the patient's medical record, and direct measurement of arterial blood gas values should be requested. The absolute limits that constitute unacceptable disparity vary with patient condition and specific device. Clinical judgment must be exercised.
PO 8.0 ASSESSMENT OF NEED:
8.1 When direct measurement of SaO2 is not available or accessible in a timely fashion, a SpO2 measurement may temporarily suffice if the limitations of the data are appreciated.(9,10)
8.2 SpO2 is appropriate for continuous and prolonged monitoring (eg, during sleep, exercise, bronchoscopy).(1,6,7,9,10,14,31)
8.3 SpO2 may be adequate when assessment of acid-base status and/or PaO2 is not requir-ed.(1,4,9,10)
PO 9.0 ASSESSMENT OF OUTCOME:
The following should be utilized to evaluate the benefit of pulse oximetry:
9.1 SpO2 results should reflect the patient's clinical condition (ie, validate the basis for ordering the test).
9.2 Documentation of results, therapeutic in-tervention (or lack of), and/or clinical decisions based on the SpO2 measurement should be noted in the medical record.
PO 10.0 RESOURCES:
10.1 Equipment: pulse oximeter and related accessories (probe of appropriate size)--the oximeter should have been validated by the manufacturer by a comparison of its values (and consequently its calibration curve) with directly measured oxyhemoglobin saturation.(17,32)
10.2 Personnel: Pulse oximetry is a relatively easy procedure to perform. However, if the procedure is not properly performed or if it is performed by persons who are not cognizant of device limitations or applications, spurious results can lead to inappropriate intervention.
Level I--personnel trained in the technical operation of pulse oximeters, oxygen delivery devices and related equipment, measurement of vital signs, and record keeping--may perform and record results of pulse oximetry but should be supervised by Level II personnel.
Level II--health care profes-sionals trained in patient assessment, disorders of acid-base, oxygenation and ventilation, and diagnostic and therapeutic alternatives--evaluate patients and recommend and/or make changes in therapy based on assessment.
PO 11.0 MONITORING:
The clinician is referred to Section 7.0 Validation of Results. The monitoring schedule of patient and equipment during continuous oximetry should be tied to bedside assessment and vital signs determinations. PO 12.0 FREQUENCY:
After agreement has been initially established between SaO2 and SpO2, the frequency of SpO2 monitoring (ie, continuous vs 'spot check') depends on the clinical status of the patient, the indications for performing the procedure and recommended guidelines.(14,31) For example, continuous SpO2 monitoring may be indicated throughout a bronchoscopy for detecting episodes of desaturation,(3,31) whereas a spot check may suffice for evaluating the efficacy of continued oxygen therapy in a stable postoperative patient. However, it must be emphasized that direct measurement of SaO2 is necessary whenever the SpO2 does not confirm or verify suspicions concerning the patient's clinical state. PO 13.0 INFECTION CONTROL:
No special precautions are necessary, but Universal Precautions (as described by the Centers for Disease Control(33,34)) are recommended.
13.1 If the device probe is intended for multiple patient use, the probe should be cleaned between patient applications according to manufacturer recommendations.
13.2 The external portion of the monitor should be cleaned according to manufacturer's recommendations whenever the device remains in a patient's room for prolonged periods, when soiled, or when it has come in contact with potentially transmissible organisms.
Cardiopulmonary Diagnostics Guidelines Committee: Kevin Shrake MA RRT, Chairman, Springfield IL Susan Blonshine RPFT RRT, Lansing MI Robert Brown BS RPFT RRT, Madison WI Robert Crapo MD, Salt Lake City UT Rick Martineau BS RPFT RRT, Reno NV Gregg Ruppell MA RPFT RRT, St Louis MO Jack Wanger MBA RPFT RRT, Denver CO
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Welch JP, DeCesare MS, Hess D. Pulse oximetry: instrumentation and clinical applications. Respir Care 1990;35:
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Tremper KK, Barker SJ. Pulse oximetry. Anesthesiology 1989;70:
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ECRI Health Devices Alert, 1990-A-26. Plymouth Meeting PA: ECRI, June 29, 1990.
Barrington KJ, Finer NN, Ryan CA. Evaluation of pulse oximetry as a continuous monitoring technique in the neonatal intensive care unit. Crit Care Med 1988;16:
Cahan C, Decker MJ, Hoekle PL, Strohl KP. Agreement between noninvasive oximetric values for oxygen saturation. Chest 1990;97:
Hannhart B, Habberer J-P, Saunier C, Laxenaire MC. Accuracy and precision of fourteen pulse oximeters. Eur Respir J 1991;4:
Severinghaus JW, Naifeh KH. Accuracy of response of six pulse oximeters to profound hypoxia. Anesthesiology 1987;67:
Severinghaus JW, Naifeh KH, Koh SO. Errors in 14 pulse oximeters during profound hypoxia. J Clin Monit 1989;5:72-81.
Veyckemans F, Baele.P, Guillaume JE, Willems E, Robert A, Clerbaux T. Hyperbilirubinemia does not interfere with hemoglobin saturation measured by pulse oximetry. Anesthesiology 1989;70:
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Interested persons may copy these Guidelines for noncommercial purposes of scientific or educational advancement. Please credit AARC and Respiratory Care Journal.

35. Haemoglobin
Mammalian hemoglobins have molecular weights of about 64,500. Composed of four peptide chains called globins each of which is bound to a heme. Normal human hemoglobin is composed of a pair of two identical chains. Iron is coordinated to four pyrrole nitrogens of protoporphyrin IX, and to an imidazole nitrogen of a histidine residue from the globin side of the porphyrin. The sixth coordination position is available for binding with oxygen and other small molecules. Called oxyhemoglobin, HbO2 in the oxygenated form and carboxyhemoglobin, HbCO, when the oxygen is displaced by carbon monoxide. Binds reversibly with oxygen while the heme iron remains in the ferrous state. Autoxidation is prevented by the cover of hydrophobic groups of the globin. When the iron in hemoglobin is oxidized from the ferrous to the ferric state the compound is called methemoglobin and is accompained by loss of oxygen-binding capacity.

36. Haemoglobin with 4 O2 Fe O2 heme Fe O2 Fe O2 heme heme Fe O2 heme

37. Haemoglobin with 3 O2 Fe O2
heme Fe Fe O2
heme
heme Fe O2
heme
globin

40. Acidosis > Hb unable to hold as much O2 > more O2 lost to tissues

41. Acidosis > Hb unable to hold as much O2 > more O2 lost to tissues

42. Clip-type Probe

43. Clip-type Probe
Probe

44. Low SpO2 … Decrease in arterial SO2 Poor circulation
Oxygen deficiency
O2 delivered from tank?
ET tube – intubated, connected and sealed properly
Poor circulation
Vasoconstriction
Pain stimulus
Cardiac depression
Deep anaesthesia, bradycardia, arrhythmia
Low blood volume
Probe interference (see later)

45. Interpreting SpO2 % Normally good if > 95%
Should remain at least > 90-92%
If <92% look for a problem
Ok at 92% if otherwise stable and nothing else can be done to improve oxygenation
Cyanosis not apparent until at least <85%
Risk of some hypoxic organ injury if < 90%
Severe organ injury if < 60%

46. Probe interference Tight clips Patient movement Hair Tissue pigment
Tissue compressed by clips (>no blood)
May need to move periodically, especially in small animals like cats
Patient movement
Hair
Tissue pigment
Dry tongue
Add moisture

47. Pain! Pain, (tugging on ovaries, clamping uterus etc), causes:
Sympathetic response
Vasoconstriction
Pulse pressure may disappear
Pulse oximeter may not read a pulse!
Alarm goes off

48. Normal SpO2 … Does not mean that blood CO2 is also normal
Animals regulate their breathing rate mainly according to CO2, not O2
Why is this so?

49. SpO2 & Anaemia
If very low PCV (say <15%), one can have normal Hb saturation (>90%) but there may not be enough total oxygenated Hb to prevent hypoxaemia and hence tissue hypoxia

50. Hypoxaemia defined…
True arterial oxygen saturation (SaO2) < 90% or PCV < 15 %

51. When is SpO2 too low? SpO2 Interpretation 95 % Normal 92 %
Start looking for a reason
90 %
Hypoxaemia present
Try to improve oxygenation
85 %
Moderate to severe hypoxaemia Lowest acceptable 85(dogs),87(cats)
80 %
Life-threatening hypoxaemia

52. Blood gases Oxygen Carbon dioxide
Blood sample measuring total O2 in blood plasma (Normal 85 – 105 mm Hg )
Arterial Oxygen Pressure = PaO2
Is different from measuring O2 in haemoglobin
Needs rapid processing
Equipment expensive
Carbon dioxide

53. Blood Pressure Arterial blood pressure Venous blood pressure Systolic
Heart contraction phase
Diastolic
Heart relaxation phase
Mean arterial
A calculated value
= 1/3 systolic pressure + 2/3 diastolic pressure
Venous blood pressure
Central (Right atrial ~ Deep jugular pressure)
Peripheral

54. Blood Pressure Units Measured by weight of column of fluid
High pressure use heavy liquids like mercury (Hg)
Low pressure use lighter liquids like water (H2O)

55. Normal Blood Pressures
Systolic (dog & cat)
100mm Hg
Diastolic
80mm Hg
Problems with organ function if <90/60 for any length of time
i.e. 100/80

56. Blood Pressure Devices
Using an occlusive pneumatic cuff
Generally around any accessible artery
e.g. distal to elbow/hock or on base of tail
Cuff width should be 40% of circumference
Types
Doppler ultrasonic device such as the Parks Doppler
Detects arterial blood flow
Pulse rate
Systolic arterial pressure
Oscillometric devices –such as the Dinamap
Estimates HR, systolic, diastolic & mean pressures
Very accurate if used in large/medium dogs
Pressure detected by the cuff bladder

57. Doppler Blood Pressure

59. Parks Doppler directions
Apply cuff so that the portion containing the occlusive bladder is over the artery to be occluded
Apply the Doppler transducer crystal over the artery but distal to the cuff & tape it snugly to the appendage

60. Parks Doppler directions
Orientate the crystals so that they are perpendicular to the artery ( the artery must cross both the transmitting and receiving crystals)
Turn on the unit and listen for pulsatile blood flow
If the sound is not audible reposition the crystal

61. Parks Doppler directions
Connect the sphygmomanometer to the cuff (scale 0-300mm Hg)
Inflate cuff until the blood flow can no longer be heard
Slowly open the valve so that the cuff gradually deflates, until blood flow can again be heard with each heart beat
The pressure on the manometer at this time is the systolic blood pressure

62. Parks Doppler
Be sure to deflate the cuff so that no pressure remains in it between readings
If the cuff remains pressurised it will restrict blood flow to the limb causing catecholamine release and cardiovascular stimulation
In cats the Doppler tends to underestimate the systolic blood pressure therefore add 15 mm Hg to the reading

63. Minute Respiratory Volume
Ventilation Monitors
Respiratory Rate
Apalert©
Expired CO2
Capnograph
Minute Respiratory Volume
Wrights Respirometer

64. Monitoring Ventilation
Movement of thorax
Movement of rebreathing bag
Auscultation (e.g. oesoph. stethoscope)
Condensation within ET tube
Movement hair/fluff at open end of ET tube
Respiration/apnoea monitors

65. Respiration/Apnoea Monitor
Apalert®
Alerts if apnoea
Connects to the ET tube and detects changes in gas temperature from inspiration to expiration
Gives an audible signal

66. Apnoea monitor Detects temperature change of exhaled air
Thermistor wont work if exhaled air is cool

67. Respiratory Rates To measure RR Normal: 10-20 breaths/min Chest rises
Rebreathing bag movements
Apnoea monitor
Normal: breaths/min
If <8 breaths/min look for a problem
Inform vet
May need to bag patient to maintain at least 8-12 breaths/min

68. Normal respiration cycle
Inspiration 1-1½ sec
Expiration 2-3 sec

69. Hyperventilation under GA
Stimulated by either
Pain of Surgery
Usually only temporary
Usually self-limiting because patient draws in more anaesthetic gas
High CO2, possibly caused by
Poor ventilation
Exhausted soda lime
Lightening anaesthesia

70. Apneustic respiration
Prolonged pauses after inspiration, followed by expiration
Seen with dissociative anaesthetics (like Ketamine)

71. Other respiration problems
Increased effort in inspiration
Upper airway obstruction
Increased effort in expiration
Lung problem
Abnormal noises
Whistles
Squeaks
Crackles

72. Respiratory sighs
With increasing GA some air sacs may not receive enough air to remain inflated
collapse of air sacs (alveoli) = atelectasis
Can reinflate these air sacs by gently bagging patient every 5 mins or so
Close pop-off
Squeeze bag gently so chest wall rises slightly
Re-open pop-off valve

73. Capnography Monitoring pulmonary ventilation
Pulmonary ventilation (minute ventilation) = Respiratory Rate (f) x Tidal Volume (VT)
Normal respiratory rate (f)
10 – 20 breaths / min
Normal tidal volume (VT)
10 – 20 mL / kg
Normal minute ventilation
200 mL / kg / min
Capnometry
measuring CO2 concentration in a gas mixture
Capnography
graphical display of changes in CO2 concentration over time

74. Principles
CO2 moves easily across the alveolar membranes and rapidly equilibrates between the blood and alveolar compartment
In the absence of ventilation-perfusion impairment, CO2 concentration in alveoli is almost the same as concentration in arterial blood (Arterial CO2 is about 5 mmHg higher than alveolar CO2)
During general anaesthesia, the difference is larger (~10 mmHg)
Highest concentration of CO2 should occur at the sampling site
at the end of expiration (end tidal = ET)
Samples of gas are continuously aspirated by capnograph
Infrared analyser determines the CO2 concentration
Sampling port placed between breathing circuit and ET tube adaptor (150 – 300 ml / min)
Sampling site should be as close as possible to the patient in order to minimize dead space as much as possible

75. Capnography (Expired CO2)
Corresponds with alveolar and therefore arterial CO2
Also measures RR
Conscious animals = 40mm Hg
Anaesthetised dogs = 40-50mm Hg
Hypoventilation > 55 mm Hg
Used in anaesthesia and critical care, these monitors sample gas from the endotracheal tube adapter and track the inspired/expired CO2 wave form. From this the monitor can determine the respiratory rate, the inspired CO2 (normally zero) and the C02 concentration at the end of expiration ("End-Tidal or ET CO2); normally equivalent to the arterial CO2. In conscious animals this is usually around 40 mm Hg. During anaesthesia, ET CO2 increases in a linear fashion with increasing anaesthetic depth to 50 or 60 mm Hg in dogs and horses respectively. ET CO2 monitors should display the CO2 wave form in order to know that the sample is accurate. ET CO2 monitors do require calibration and maintenance.

76. Capnography

77. Using capnography Sampling Maintenance
Should be done from a site as close as possible to minimize dead space
Sample adaptor is most commonly placed between the ET tube adapter and breathing circuit
Non-rebreathing circuit with high fresh gas flow
Dilutes ETCO2
Sampling via a hypodermic needle inserted through and into the lumen of ET tube will provide more reliable readings
Maintenance
After use
Allow to run for a while so that the tubing can dry out
Clean and dry water traps
Sampling gases is continuous and also contains anaesthetic gases
Gases can be routed back into the breathing circuit in order to minimize environmental pollution and loss of gases from breathing circuit

78. Capnogram (‘CO2-ogram’)
Expiration
Inspiration II I
III a b O
Normal patient

79. Capnogram I = Inspiratory baseline II = Expiratory upstroke
Expiration
Inspiration
III II O I
I = Inspiratory baseline
Fresh gas containing no CO2 passing through analyse
II = Expiratory upstroke
Begin of exhalation
Dead space elimination from respiratory tract
CO2 concentration is increasing as alveolar air is reaching analyse
III = Expiratory plateau
Exhalation of pure alveolar gas
O = Inspiratory downstroke
Start of inhalation
Fresh gas “washing away” CO2 of gases from previous exhalation

80. High CO2 (hypr-capnia) Most common cause- Less common cause Rare
Inadequate removal, in relation to CO2 production, of alveolar CO2 due to hypoventilation
Less common cause
Inadequate removal of CO2 from breathing circuit, e.g.
Exhausted soda lime
Inadequate fresh gas flows in non-rebreathing circuits
Rare
Abnormally high CO2 production, e.g.
Fever
Malignant hyperthermia

81. Sudden drop in ET-CO2 Sudden decrease in ETCO2 Apnoea
Patient extubation
Obstruction of ET tube / breathing system
Abnormalities in pulmonary blood flow
Cardiac arrest
Decrease in cardiac output
Obstruction of pulmonary artery / branches
Pulmonary embolism
Surgical manipulation
Air embolism
Water / secretions accumulating within and obstructing sampling tubing

82. Low CO2 (hypo-capnia)
Ventilation of alveoli is increased (hyperventilation) removing CO2 at an abnormally high rate and exceeding rate of production
False low CO2 readings occur in
Tachypnoea
Alveolar gases are incompletely exhaled and/ or diluted by dead space gases and the response time of the analyser may be too slow
Use of non-rebreathing circuits using high fresh gas flows
High fresh gas flows may wash out the end tidal gases and dilute them

83. Interpreting the curve
Elevated baseline = Rebreathing of CO2
Partial exhaustion of soda lime
Incompetent expiratory one-way valve
Slanted upstroke
Slow expiration
Uneven emptying of alveoli
Partially obstructed ET tube / expiratory tube of breathing circuit
Airway narrowing
COPD
Asthma
Bronchospasm
Abnormal plateau
Normal height = 35 – 44 mmHg
Elevation
Hypoventilation
Hyperthermia
Abnormally low
Hyperventilation
Ventilation perfusion (P/Q) mismatch + elevated arterial CO2

84. Interpreting the curve
Irregular plateau
Surgical manipulation of chest / abdomen  small volumes of air moving in and out of lungs
Cardiac oscillation
movement of pulmonary vasculature during cyclic filling and emptying pushes gas in and out of the lungs
Artificial ventilation
Patient is trying to fight ventilation a cleft may appear in the expiratory plateau
Slanted inspiratory downstroke
Airway obstruction
Obstruction caused by surgeon leaning on chest
Prolonged inspiratory downstroke
Faulty inspiratory one-way valve

85. Capnography Summary Normal ETCO2 High ETCO2 (>55mmHg) Low ETCO2
Hypoventilation
Low ETCO2
Low, abnormally high / normal PaCO2
Normal capnogram is a “square wave”
Sudden changes in ETCO2 and in the waveform may be due to problems with
Patient
Endotracheal tube
Breathing circuit
Sampling system

86. ECG Electrical activity of the heart
Cardiac rhythm disturbances
Ventricular premature contractions (VPCs)
Atrial fibrillation
Ventricular tachycardia
Ventricular fibrillation
Asystole
But cannot rely on this - can have a normal ECG and not have an effective heart muscle contraction! (EMD=electro-myographic dissociation)
Electrical interference may be a problem
Expensive?

87. Electrocardiogram ECG (or EKG)
With each heartbeat atria & ventricles cell membranes depolarise and repolarise – the electrical waves produced are measured on the surface of the body

88. Electrocardiogram
The wave is recorded as a voltage difference between 2 electrodes in various positions:
Lead I = Left arm to Right arm
Lead II = Right arm to Left leg (MOST USEFUL)
Lead III = Left arm to Left leg

89. ECG Leads All ‘Leads’ are applied at the start
A switch on the machine selects which are being used to measure voltage
Various clips used to attach to skin
Alligator
Human
Various contacts
+/- clip hair
To improve conduction
ECG gel, or
K-Y gel, or
Methylated spirit

90. Alligator clips (not too tight!)

91. ECG Hold (R side down)

92. 4 Cables but 6 ‘Lead’ Combinations

93. Typical Lead II ‘trace’

94. Usefulness of ECG in GA
ECG only gives electrical performance of heart, not the muscular performance and so is not to be relied upon
A heart can have a normal ECG but not be contracting properly
e.g. in ‘electro-myocardial dissociation (EMD)’

95. Temperature
Place a probe oesophageal or rectally for continuous monitoring
Hypothermia
Causes prolonged recovery from GA
Most heat loss in 1st 20 mins
Small animals most susceptible
Heat injury
Heating mats
Hot water bottles not wrapped in towel
Note that a hot wet towel can scald skin

96. Warmth post op Heat mats Heat lamps Heat blanket Hot H2O bottles
Hot oat bags

97. Overheating Problems Prevention of overheating Burns Overheating
‘Shock’ – due to vasodilation
Prevention of overheating
Monitor body temperature frequently
Do not leave patient unattended
Take away thermal support equipment once the body temperature reaches 38.5oC

98. Many reasons to get cold
Loss of brain thermoregulation
Vasodilating tranquillisers & anaesthetics
Cold tables
Skin prep solutions (alcohol)
Open body cavities
Reduced metabolic rate

99. ‘Tissue Hypoxia’ The major concern in anaesthesia Causes include
 O2 supply (poor respiration)
 blood O2
 blood supply (poor perfusion)
cardiac output

100. Note
Use as many methods and signs to assess the patient do not rely on one!!!

101. The VN
More valuable to the vet than all the monitoring equipment combined
Helen Keates # I
* 5 *

102. The End