Monitoring a patient

Question 1

Stethoscopes

Answer 1

• Allows for measurement of rate and rhythm
• Rate should be steady and strong, not weak or thready
• Also allows for measurement of rhythm
• We can also listen to the chest - listening for any crackles, difficulties or abnormalities
• Normal HR for dogs = 60-100 bpm
• Normal HR for cats = 160-200
• Normal respiratory rate for dogs = 10-30 bpm
• Normal respiratory rate for cats = 20-30 bpm
• Cardiac output can’t be appreciated so this method should be used in conjunction with a palpation of a pulse

Question 2

Oesophageal stethoscopes

Answer 2

• Used to measure heart rate
• Provides an opportunity to manually check heart rate and rhythm when access to the heart externally is restricted
• Using regular stethoscope during surgery could break sepsis and therefore is not always possible
• Oesophageal stethoscopes provide an alternative route for monitoring patients heart rate and rhythm
• Consists of a hollow tube and a cuff with multiple holes that connect to an ear piece
• It is placed within the oesophagus to the level of the heart base
• Sometimes it is possible to count respiration rate as well

Question 3

Electrocardiogram (ECG)

Answer 3

• Allows us to understand the electrical activity of the heart
• An ECG gives a visual representation of the hearts electrical activity and quality/rate of the contraction of the myocardium
• Electrical activity starts at the Sino-atrial node
• Electrical current passes through the bundle of His to the Purkinje fibres which distribute the impulse to the contracting muscle cells
• Active contraction (systole) pumps blood out of the heart
• Diastole is point of relaxing

Question 4

ECG wave

Answer 4

• P wave - contraction of the atria (depolarisation of SA node)
• PR interval - AV node stimulated and slowly conducts from atria to ventricles to allow a coordinated ventricular contraction
• QRS complex - contraction of ventricles
• T wave - repolarisation for next contraction

Question 5

ECG placement

Answer 5

• Red = Right forelimb
• Yellow = Left forelimb
• Green = Left hind limb
• Black = Right hind limb
• White = general placement on the side

Question 6

ECG considerations

Answer 6

• Describes electrical activity of the heart
• Rhythm can be traced on the graph and any abnormalities or changes can determine certain systemic abnormalities and cardiac pathology
• It does not indicate cardiac output and may remain minutes after cardiac arrest
• More use as a diagnostic tool than a monitor
• Should never be used as sole indicator

Question 7

Capnography

Answer 7

• Based on measurement of exhaled CO2 (end tidal CO2)
• This is usually measured by gas withdrawn from a small tube placed between the circuit and the ET tube
• Normal end tidal CO2 volumes are 40-50mm Hg
• If end tidal CO2 is high then it suggests hypoventilation, low levels suggest hyperventilation
• Very useful and easy to use but very expensive

Question 8

Pulse oximetry

Answer 8

• Non-invasive technique which monitors the degree to which Hb is saturated with O2 (SpO2)
• This measurement relies on the fact that Oxy haemoglobin and reduced haemoglobin absorb red and infra-red light to differing extents
• The monitor also often displays the animal’s heart rate
• The probe may be attached to various sites on the body including: tongue, non-pigmented skin

Question 9

Hypoxaemia

Answer 9

• The threshold for hypoxaemia is usually at an arterial oxygen tension of 60 mm Hg
• This corresponds to a Hb oxygen saturation of 90%
• Thus, during anaesthesia, oxygen saturation needs to be maintained above 90%
• When we supply the patient with oxygen we should expect oxygen saturation nearer to 100%
• Pulse oximeters work by picking up the proportion of oxygen-carrying haemoglobin in the red blood cells. The result is then given as a percentage on the monitor

Question 10

Pulse oximetry considerations

Answer 10

• Gives no indication of available haemoglobin
• Lack of perfusion will prevent a signal being obtained e.g. tissue compression of the probe
• Movement of the probe can reduce accuracy and prevent an adequate signal being obtained
• Light interference from surgical lights can cause inaccuracies
• Pulse oximeter does not measure the oxygen content of the blood
• Other forms of monitoring must be used in conjunction with the pulse oximeter

Question 11

Blood pressure

Answer 11

• Blood pressure provides the driving force for tissue perfusion
• In general anaesthesia, we aim to maintain arterial blood pressure above 70-80 mm Hg
• Low blood pressure can cause damage to kidneys and other tissues
• Normal blood pressure in conscious animals…
• Systolic Dog = 110-190 mmHg
• Systolic Cat = 120-170 mmHg
• Diastolic Dog = 55-110 mmHg
• Diastolic Cat = 70-120 mmHg

Question 12

Direct blood pressure monitoring

Answer 12

• Invasive and is one of the most useful indicators of cardiovascular function
• The central venous pressure (CVP) is the pressure measured in the central veins close to the heart
• It indicated mean right arterial pressure and is frequently used as an estate of right ventricular preload
• It is measured in the thoracic vena cava using a long IV catheter which is inserted into the thoracic VC via the jugular vein
• This catheter is attached to a pressure transducer which, in turn, is attached to a monitor
• Risks of introducing infection and haematoma formation

Question 13

Indirect blood pressure monitoring

Answer 13

• A Doppler robe contains 2 piezoelectric crystals which should sit at a right angle to a peripheral artery
• Common arteries used include the metacarpal, dorsal metatarsal, plater metatarsal and coccygeal artery
• The chosen site should be clipped of fur and contact improved with the application of ultrasound gel
• The probe should be taped into place over the artery before turning on the loudspeaker, and minor adjustments made to the positioning as necessary to obtain the best quality sound; this approach reduces placement time and loud positioning noise
• Headphones may be used to reduce theatre noise levels

Question 14

Oscillometer blood pressure monitoring

Answer 14

• Oscillometric BP can be obtained with the use of an inflatable cuff around the limb or tail base, which is attached to the monitor
• Measurement is automatic and allows detection of oscillations produced by the artery wall as the cuff deflates
• Oscillometric monitors systolic, mean and diastolic pressure, unlike the Doppler method which only detects systolic pressure
• Single measurements by this methods may underestimate arterial pressure by 5-20mm Hg, meaning oscillometric BP can only be used to observe trends and accuracy may be reduced in patients under 5kg

Question 15

Digital thermometer

Answer 15

• A thermometer is used to monitor patient temperature
• The tip of the thermometer is lubricated and placed into the rectum of the patient
• Normal range for dogs = 38.3-38.7°C
• Normal range for cats = 38.0-38.5°C
• We should check for hypothermia and hyperthermia

Question 16

Blood gas analysis

Answer 16

• The blood gas analyser measures pH, the partial pressure of O2 and the partial pressure of CO2
• This means that the sample should contain no air bubbles, which may be mis-read by the analyser and thus lead to inaccurate results
• From these main results, others such as plasma bicarbonate concentrations, base excess and the saturation of Hb with O2 can all be worked out
• The blood gas analyser represents the gold standard method of evaluating gas exchange. It provides information on: Oxygenation, ventilation and the acid base status of the patient

Question 17

Central nervous system

Answer 17

• Main purpose of monitoring the CNS is to assess the depth of the anaesthesia
• Depression of the cranial nerve reflexes gives indication of this
• The deeper the anaesthesia, the more reduced the reflex
  Examples:
• Palpebral
• Eye position
• Jaw tone
• Pupillary diameter
• Pedal

Question 18

Ideal plane of anaesthesia

Answer 18

• Palpebral = no response
• Eye position = pupil should be in the corner
• Jaw tone = slack
• Pupillary diameter = large
• Pedal = toes don’t move

Question 19

Light plane of anaesthesia

Answer 19

• Palpebral = Blinking
• Eye position = Central
• Jaw tone = Tight
• Pupillary diameter = Small
• Pedal = Toes move

Question 20

Deep plane of anaesthesia

Answer 20

• Palpebral = no response
• Eye position = central
• Jaw tone = slack
• Pupillary diameter = large
• Pedal = toes don’t move

Question 21

Cranial reflexes

Answer 21

• Cranial reflexes are checked on many different patients, however they are used commonly on those patients who are anaesthetised
• Typically, reflexes are checked to measure depth of anaesthesia, to consider if a patient is too light or deep in depth of anaesthesia

Question 22

Monitoring mm and CRT

Answer 22

• Mucous membranes can alter in colour slightly, with each colour indicative of particular complication
• Salmon pink = healthy
• Pale = sign of shock
• Yellow/jaundice = liver failure
• Blue/purple = lack of oxygen
• Brick red = infection
• CRT (capillary refill time) can also be used on the gums, pressing the gums will whiten them, when the finger is removed they should return to colour in 1-2 seconds. A slower CRT can indicate poor circulation or shock

Question 23

Anaesthesia complications

Answer 23

• Hypothermia - abnormally low body temperature which can be caused by anaesthetic drugs and surgery prep - may occur due to vasodilation during anaesthesia and the heat loss which may occur during evaporation of water from hibi-scrub, as well as having fur removed at the site or surgery
• Tachycardia - increased heart rate. This could mean the propofol may need increased or more pain relief needs to be given, as an increased heart rate may occur when the animal is feeling more pain during a particular part of the surgery or too lightly under anaesthetic
• Hypoxia - lack of oxygen to certain area, may be indicated by blue/purple mm’s or skin colour, and indicated the tissues are not oxygenating properly. This could indicate the anaesthetic equipment is not working properly or may have been set up wrong
• Bradycardia + bradypnea - slow heart rate and rest rate could mean that the patient is too deep under anaesthetic, could lead to heart failure and crash kit will be needed to administer drugs

Question 24

Monitoring charts

Answer 24

• Monitoring of the patient should be continual and a written record should be completed
• Should be started from when the pre-anaesthetic is given
• This is a record of the anaesthetic period
• It allows for harmful trends to be recognised and allows for timely and appropriate action to be taken
• Most will write a reading every 5 mins
• This document is a medical-legal document