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MONITORING Prepare and monitor anaesthesia in animals MONITORING.

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Presentation on theme: "MONITORING Prepare and monitor anaesthesia in animals MONITORING."— Presentation transcript:

1 MONITORING Prepare and monitor anaesthesia in animals MONITORING

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

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

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

6 MONITORING Resting Signs Pupils & Eye position Jaw tone Heart rate & rhythm Respiratory rate Pulse quality MM & CRT Temperature Haemoglobin O 2 saturation (Pulse oximetry) Blood pressure ECG End-expiratory CO 2 (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 MONITORING 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 MONITORING Surgical stress map (timeline)

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

10 MONITORING Monitoring form e.g. AAS FORM

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

13 MONITORING Answers 1 1.Heart rate and rhythm 2.Pulse rate 3.MM colour 4.RR, depth and character 5.CRT 6.Temperature 7.Oxygen saturation 8.Pupil size and position

14 MONITORING Monitoring depth See anaesthesia stagesanaesthesia stages

15 MONITORING Anaesthetised Dog & Cat DogCat HR RR C 38 CRT < 2 sec SpO2 > 95% BP (diast) mmHg BP (syst) mmHg

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

17 MONITORING Answers 2 1.Pedal reflex 2.Jaw tone 3.Skin pricking 4.Anal pinching 5.Palpebral reflex 6.Corneal reflex 7.PLR 8.Response to visceral stimulus 9.Ear twitch 10.Cutaneous reflex 11.Reaction to painful stimulus 12.Righting reflex 13.Pharyngeal reflex 14.Laryngeal reflex

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

19 MONITORING 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 MONITORING Heart Rate Normal –Dog Report HR <80 to vet –Cat

21 MONITORING Oesophageal Stethoscope

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

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

24 MONITORING 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 MONITORING 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 MONITORING MM & CRT Best to assess gingival MM colour –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 MONITORING Pulse oximetry

28 MONITORING 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

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

34 MONITORING 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 = SpO 2 (S pulse O 2 ) –The pulse Hb O2 saturation (SpO 2 ) is an estimation of arterial Hb saturation, S a O 2 (S arterial O 2 ) –[cf arterial oxygen pressure = PaO 2 requires sampling blood and promptly measuring oxygen content]

35 MONITORING 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.hemeprotoporphyrin IX

36 MONITORING Haemoglobin with 4 O 2 Fe globin heme O2

37 MONITORING Haemoglobin with 3 O 2 Fe globin heme O2

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40 Acidosis > Hb unable to hold as much O 2 > more O 2 lost to tissues

41 MONITORING Acidosis > Hb unable to hold as much O 2 > more O 2 lost to tissues

42 MONITORING Clip-type Probe

43 MONITORING Probe Clip-type Probe

44 MONITORING Low SpO 2 … Decrease in arterial SO2 –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 MONITORING Interpreting SpO 2 % 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 MONITORING Probe interference Tight clips –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 MONITORING 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 MONITORING Normal S p O 2 … Does not mean that blood CO 2 is also normal Animals regulate their breathing rate mainly according to CO 2, not O 2 –Why is this so?

49 MONITORING SpO 2 & Anaemia If very low PCV (say 90%) but there may not be enough total oxygenated Hb to prevent hypoxaemia and hence tissue hypoxia

50 MONITORING Hypoxaemia defined… True arterial oxygen saturation (S a O2) < 90% or PCV < 15 %

51 MONITORING When is SpO2 too low? SpO 2 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 MONITORING Blood gases Oxygen –Blood sample measuring total O2 in blood plasma (Normal 85 – 105 mm Hg ) Arterial Oxygen Pressure = PaO2 –Is different from measuring O 2 in haemoglobin –Needs rapid processing –Equipment expensive Carbon dioxide

53 MONITORING Blood Pressure Arterial 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 MONITORING 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 (H 2 O)

55 MONITORING 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 MONITORING 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 MONITORING Doppler Blood Pressure

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59 Parks Doppler directions 1.Apply cuff so that the portion containing the occlusive bladder is over the artery to be occluded 2.Apply the Doppler transducer crystal over the artery but distal to the cuff & tape it snugly to the appendage

60 MONITORING Parks Doppler directions 1.Orientate the crystals so that they are perpendicular to the artery ( the artery must cross both the transmitting and receiving crystals) 2.Turn on the unit and listen for pulsatile blood flow 3.If the sound is not audible reposition the crystal

61 MONITORING Parks Doppler directions 4.Connect the sphygmomanometer to the cuff (scale 0-300mm Hg) 5.Inflate cuff until the blood flow can no longer be heard 6.Slowly open the valve so that the cuff gradually deflates, until blood flow can again be heard with each heart beat 7.The pressure on the manometer at this time is the systolic blood pressure

62 MONITORING Parks Doppler 8.Be sure to deflate the cuff so that no pressure remains in it between readings 9.If the cuff remains pressurised it will restrict blood flow to the limb causing catecholamine release and cardiovascular stimulation 10.In cats the Doppler tends to underestimate the systolic blood pressure therefore add 15 mm Hg to the reading

63 MONITORING Ventilation Monitors Respiratory Rate –Apalert© Expired CO 2 –Capnograph Minute Respiratory Volume –Wrights Respirometer

64 MONITORING 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 MONITORING 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 MONITORING Apnoea monitor Detects temperature change of exhaled air –Thermistor wont work if exhaled air is cool

67 MONITORING Respiratory Rates To measure RR –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 MONITORING Normal respiration cycle Inspiration 1-1½ sec Expiration 2-3 sec

69 MONITORING 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 MONITORING Apneustic respiration Prolonged pauses after inspiration, followed by expiration –Seen with dissociative anaesthetics (like Ketamine)

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

72 MONITORING 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 MONITORING Capnography Monitoring pulmonary ventilation Pulmonary ventilation (minute ventilation) = Respiratory Rate (f) x Tidal Volume (V T ) Normal respiratory rate (f) –10 – 20 breaths / min Normal tidal volume (V T ) –10 – 20 mL / kg Normal minute ventilation –200 mL / kg / min Capnometry –measuring CO 2 concentration in a gas mixture Capnography –graphical display of changes in CO 2 concentration over time

74 MONITORING Principles CO2 moves easily across the alveolar membranes and rapidly equilibrates between the blood and alveolar compartment In the absence of ventilation-perfusion impairment, CO 2 concentration in alveoli is almost the same as concentration in arterial blood (Arterial CO 2 is about 5 mmHg higher than alveolar CO 2 ) During general anaesthesia, the difference is larger (~10 mmHg) Highest concentration of CO 2 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 CO 2 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 MONITORING Capnography (Expired CO 2 ) Corresponds with alveolar and therefore arterial CO 2 Also measures RR Conscious animals = 40mm Hg Anaesthetised dogs = 40-50mm Hg Hypoventilation > 55 mm Hg

76 MONITORING Capnography

77 MONITORING Using capnography Sampling –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 ETCO 2 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 MONITORING Capnogram (CO 2 -ogram) Normal patient Expiration Inspiration II I III O

79 MONITORING Capnogram I = Inspiratory baseline –Fresh gas containing no CO 2 passing through analyse II = Expiratory upstroke –Begin of exhalation –Dead space elimination from respiratory tract –CO 2 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 CO 2 of gases from previous exhalation Expiration Inspiration II I III O

80 MONITORING High CO 2 (hypr-capnia) Most common cause- –Inadequate removal, in relation to CO 2 production, of alveolar CO 2 due to hypoventilation Less common cause –Inadequate removal of CO 2 from breathing circuit, e.g. Exhausted soda lime Inadequate fresh gas flows in non-rebreathing circuits Rare –Abnormally high CO 2 production, e.g. Fever Malignant hyperthermia

81 MONITORING Sudden drop in ET-CO 2 Sudden decrease in ETCO 2 –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 MONITORING Low CO2 (hypo-capnia) Ventilation of alveoli is increased (hyperventilation) removing CO 2 at an abnormally high rate and exceeding rate of production False low CO 2 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 MONITORING Interpreting the curve Elevated baseline = Rebreathing of CO 2 –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 CO 2

84 MONITORING 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 MONITORING Capnography Summary Normal ETCO 2 –35 – 45 mmHg High ETCO 2 (>55mmHg) –Hypoventilation Low ETCO 2 –Low, abnormally high / normal PaCO2 Normal capnogram is a square wave Sudden changes in ETCO 2 and in the waveform may be due to problems with –Patient –Endotracheal tube –Breathing circuit –Sampling system

86 MONITORING 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 MONITORING 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 MONITORING 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 MONITORING 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 MONITORING Alligator clips (not too tight!)

91 MONITORING ECG Hold (R side down)

92 MONITORING 4 Cables but 6 Lead Combinations

93 MONITORING Typical Lead II trace

94 MONITORING 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 MONITORING Temperature Place a probe oesophageal or rectally for continuous monitoring Hypothermia –Causes prolonged recovery from GA –Most heat loss in 1 st 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 MONITORING Warmth post op Heat mats Heat lamps Heat blanket Hot H 2 O bottles Hot oat bags

97 MONITORING Overheating Problems –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 38.5 o C

98 MONITORING 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 MONITORING Tissue Hypoxia The major concern in anaesthesia Causes include – O2 supply (poor respiration) blood O2 – blood supply (poor perfusion) cardiac output

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

101 MONITORING The VN More valuable to the vet than all the monitoring equipment combined Helen Keates

102 MONITORING The End


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