Monitoring Anaesthesia Flashcards
What can show the depth of anaesthesia?
*Heart and resp rate
*Palpebral reflex
*Corneal reflex
*Eye position
*Nystagmus
*Pupillary diameter
*Lacrimation
*Salivation
*Tongue curl
*Laryngeal/pharyngeal reflexes
*Anal reflex
*Jaw tone
*Pedal reflex
What do the mucus membranes tell us during anaesthesia?
*Should be pink (cats; pale pink)
*Abnormal colours; pale, blue, white, brick red, purple
*CRT is an indicator of perfusion
*CRT should be less than 2 seconds
How should respiration be during anaesthesia?
*Pattern should be regular and deep
*Abnormal patterns include abdominal, paradoxical
and periodic.
Why is temperature important during anaesthesia?
*Hyperthermia increases oxygen
consumption
*If patient becomes hypothermic, may get
cardiovascular, respiratory, clotting
and ECG changes
What is pulse oximetry?
*Non invasive method
*Measures percentage of oxygenated haemoglobin in blood
*Represented as SpO2 (%)
*LED on one side of probe, emits light at different wavelengths
What will pulse oximetry tell you and not tell you?
*Useful if respiratory or cardiovascular disease
*Will tell you if pulse is present
*Will tell you that there is perfusion
*Will tell you the oxygen saturation of the Hb
* WILL NOT TELL YOU VENTILATORY STATUS OF PATIENT
What problems can occur with pulse oximetry?
Problems can occur when:
*Human hand me downs
*Lack of perfusion
*Ambient light
*Abnormal haemoglobin
*Movement
*Thick, pigmented or hairy tissues
What is Capnometry?
Is the monitoring of the partial pressure
or concentration of carbon dioxide in respiratory
gases. If these partial pressure values are plotted
against time, a capnograph is produced.
What information does a capnograph give?
*CO2 production, *perfusion of the lungs, *alveolar ventilation, *respiratory patterns, *elimination of
CO2 from the breathing system.
What is the normal capnograph reading for a dog and cat?
35 to 45 mm Hg in dogs and 28 to 32 mm Hg in cats.
What are the advantages and disadvantages of main stream and side stream capnography?
Mainstream capnometers place the measurement chamber within the airways. This allows for an
almost instantaneous measurement of CO2
. Some drawbacks of mainstream capnometry include:
easily damaged;
presence increases dead space;
difficult to use in spontaneously breathing patients; and
water condensation often occurs on the sensor (Figure 1).
Sidestream capnometers sample air aspirated out of the airway through fine bore tubing to a
measurement chamber outside the device (Figure 2).
An advantage of sidestream analysis is the units often measure other gases (that is, oxygen and
anaesthetics). Slight delays in measurement may occur due to movement of the sample through
the tubing. Secretions from the airway may easily obstruct the tubing.
Neither is clearly superior and the choice between them is most often a personal preference.
Why might the capnograph trace read too low?
Too low ETCO2
*Too light
*Cardiogenic
*Tidal volume very small
*Sampling line occlusion
*Ventilator disconnected
*Endo-oesophageal
intubation
Why might the capnograph trace read too high?
Too high ETCO2
*Too deep
*Airway obstruction
*Chest wall movement
impaired
*Excessive production
*Fresh gas flow too low
*Soda lime exhausted
Is hypo or hypercapnia a problem?
*CO2 is the ‘drive for ventilation’
*Cerebral vasoconstriction if CO2 levels decrease
below approx 22 mmHg
*Hypercapnia will cause cerebral vessel vasodilation
*Sympathetic nervous system stimulant
How does Rebreathing show on a capnogram?
How does slow expiration time appear on a capnogram?
How does hypoventilation appear on a capnogram?
How does hyperventilation appear on a capnogram?
How do spontaneous respiratory efforts during mechanical ventilation appear on a capnogram?
How do Cardiogenic oscillations appear on a capnogram?
What does an ECG do?
*Useful in monitoring animals will cardiovascular or
respiratory complications, animals with electrolyte
abnormalities or sepsis
*Need to know how to recognise and treat
arrhythmias
*Only indicates electrical activity of heart, not
mechanical
What should you interpret on the ECG?
*Is it regular?
*If no – then is it regularly irregular
*If it is regularly irregular, time it and see if it correlates with the breathing. If it does this is sinus
arrythmias.
*If it is irregularly irregular – then something more
sinister.
*Is there a p wave for every QRST complex
*If not – could be an AV block
What kind of AV blocks are there?
*1st degree – lengthening of P-Q interval
*2nd degree – missed QRS every so often, sounds like a
skipped beat
*3rd – p wave and QRS complex completely
mismatched
What should mean Blood Pressure be?
Mean bp should be 65-95mmHg.
Discuss oscillometric Blood pressure?
Uses a piezoelectric crystal in the cuff to sense movement of the arterial wall.
Cuff is inflated till movement stops and then slowly
release until systolic pressure reached.
Pressure will continue to release and record the mean and diastolic
pressure.
Discuss oscillometric Blood pressure considerations?
*Choose your cuff carefully.
*40% cirucumference of appendage.
*Not too tight or too wide, else will underestimate.
*Not too loose or too narrow else, will overestimate.
*Beware taping the cuff down too tightly.
How does blood pressure with a doppler work?
*Detects movement of RBCs in arteries
Which species is doppler blood pressure most useful?
Cat
Discuss some limitations of doppler blood pressure?
*Systolic blood pressure is fairly accurate but
overestimated.
*Diastolic blood pressure is underestimated
*Mean = ⅓ x pulse pressure + diastolic pressure
What is the most dangerous period for risk of death in an anaesthetic period?
*Post operative period found to be the most
common time for an animal to die in the peri
anaesthetic and peri-sedation period.
*Within three hours of recovery.
*60% of deaths in cats.
*50% of deaths in dogs.
*Cause of death unknown in many of these cases.
Why is the post operative period so dangerous?
*Many of the anaesthetic and sedative drugs
still on board.
*Tend to withdraw support and monitoring at the time.
How should airways be checked post GA?
*Check back of mouth and pharynx for any blood/fluid
*Suction if necessary
*Ensure pharyngeal packs are removed
*Leave endotracheal tube cuff up
– until dog is vigorously swallowing
– until first swallow in cat
*Ensure patent airway once extubated
*Have scissors or wire cutters available if jaws
sutured/wired closed
*Have an airway kit readily available if airway security is
of a concern
How to prepare for a difficult intubation?
*Pre oxygenate
*Range of endo-tracheal
tubes plus stylet
*Laryngoscope
*Suction
*Trans tracheal oxygen
*Tracheostomy kit
What is an armoured endotrachreal tube?
*Spiral of metal through wall of ETT resists
kinking
*A little more floppy to hold and more difficult
to place
*Internal diameter is smaller than a regular ETT
Discuss the risks of using mouth gags especially in relation to cats?
*Several publications of potential consequences of using mouth gags in cats for dental procedures
*Spring-loaded gags generate a constant force that can
contribute to bulging of soft tissue between mandible and tympanic bulla.
*Post-procedural blindness associated with decreased
maxillary blood flow when mouth opened maximally in cats.
*Respiratory arrest after global cerebral ischaemia reported in
one cat after spring loaded mouth gag placed.
*
What are the recommendations for opening cats mouths during dental procedures?
Recommendations include avoiding
spring loaded gags, not opening cat’s
mouths more than 30mm and if
wider opening is required, allow
periodic relaxation.
What are the pathophysiological effects of Hypothermia?
*CNS depression
*Bradycardia
*Hypotension
*Hypoventilation
*Decreased basal metabolic rate
*Decreased urine production
What are the consequences of Hypothermia?
*Slowed metabolism of medications and
hypoventilation which in turn lead to delayed recovery from anaesthesia.
*Thermoregulatory vasoconstriction decreasing oxygen
delivery to wounds and delayed wound healing
*Suppressed immune function increasing susceptibility
to infection
*Metabolic and cardiovascular changes including predisposition to dysrhythmias
*Decreased enzyme activity and platelet function which
can result in alterations to normal coagulation
*Shivering leading to increased oxygen requirements
How can you reduce the risk of hypothermia?
*Reducing the time a patient is anaesthetised by careful planning of preparation time
*Minimising wetting of the patient
*Maintaining high ambient temperature around the patient
*Use of heat and moisture exchangers between the
endotracheal tube and breathing system in anaesthetised
animals to reduce heat loss through evaporation
*Use of appropriate anaesthetic circuits (rebreathing
circuits, low flow rates, warmed air)
*Using warmed fluids fluid therapy / lavage
*Actively conserving body heat from the time that
premedication is given
*Placing animal on insulating material (Vetbed , blanket or
similar)
What is active core warming?
*Can be considered if hypothermia during
anaesthesia become severe (<34⁰C)
* Warm water enemas and bladder lavage –
fluids again can be warmed to 40-42.8C, but care should be taken not to over-distend the organs.
What is MRI compatible equipment?
*All equipment in MRI room must not contain
ferro-magnetic material
*Metal objects will become fast and dangerous
projectiles
*Strong magnet may also interfere with some monitors
*ECGs are often grossly distorted in MRI, unless
shielded
What is Pharyngostomy intubation?
*Trachea is intubated as usual
*Incision made over lateral aspect of pharynx
*ETT is pushed past incision and pulled back
out of side hole
*NB – do this without the connecter on!
*Pilot balloon always awkward – have some
artery forceps ready
*Need iv top up nearby
* Secured using roman sandal suture
*Remove at same time as you would remove an oro-tracheal tube
What is Transmylohyoid intubation?
*Normal oro-tracheal
intubation
*Incision at level of 1st
molar tooth over
mandible
*Blunt dissection through
mylohyoid muscle
*Mucosal incision over
haemostats
*Deflate cuff and push
endotracheal tube
aborally.
*Grasp pilot balloon and pull through incision before grasping end of endotracheal tube
What are the considerations for Oronasal or oroantral fistula surgery?
*Communication between oral cavity and anterior or caudal
respiratory tract
*Water and food contaminates respiratory tract so often see
respiratory infection
*Check and treat for signs of infection before anaesthesia
*Pre-oxygenation and oxygen supplementation in recovery
*Airway protection and sharing airway
*Daschunds overrepresented so care with positioning
*Large flaps have to be created by releasing periosteum
from mucosa
– Potential for blood loss
– Pain
How can Anaesthetics have effects on neoplasia?
*Peri-operative stressors will suppress the immune system
(Stress states suppress NK activity and promote metastasis: Low levels of NK activity associated with increased cancer
related morbidity and mortality in human studies)
*Stress activates angiogenesis
– Growth of new capillaries from
existing blood vessels, essential for growth of cancer cell into a
macroscopic metastasis
What are the benefits of local anaesthetics?
*Several studies demonstrate that tumour resection
under local anaesthesia has better long term
prognosis than if resected under general anaesthesia.
*Only true analgesic
*Attenuates surgical stress response
*Reduces release of adrenaline
*Prevents inhibition of immune system
*Reduces need for post-operative systemic opioids
How can you monitor anaesthesia with hands and eyes?
*Feel pulses
*Assess mucous membrane colour and capillary refill time
*Watch the bag and chest move
*Monitor the eye position and palpebral reflex
*Check the pedal reflex
*Assess jaw tone
*Check your levels of volatile agent in the vaporiser, and gases in the cylinders
*Monitor for blood loss in the surgical field.
What signs can be used to assess depth of anaesthesia?
o Heart and respiratory rate
o Palpebral reflex
o Corneal reflex
o Eye position
o Nystagmus
o Lacrimation
o Salivation
o Tongue curl
o Laryngeal/pharyngeal reflexes
o Anal reflex
o Jaw tone
o Pedal reflex
List potential causes for hypercapnia and hypocapnia?
What are the 3 phases of the capnograph trace?
