Anaesthesia for Thoracic Surgery Flashcards
what is the main anaesthetic consideration when opening the thorax?
ventilation
why is ventilation a concern when opening the thorax?
opening the thorax removes negative pressure in the pleural space
what is the impact of the removal of negative pressure through opening the thorax?
when the chest wall expands on inhalation there is little or no air entry into the lungs as the pressure in the lungs is the same as atmospheric pressure
ventilation is inadequate and gas exchange impaired
what is needed during thoracic surgery to ensure adequate ventilation?
manual or automatic IPPV throughout surgery
what is caused by opening the thoracic cavity?
atelectasis
what is decreased by atelectasis?
total lung capacity
vital capacity
functional residual capacity
what is commonly seen during thoracic surgery even with IPPV?
atelectasis
what can worsen atelectasis during thoracic surgery?
packing off lung lobes
manipulation of blood vessels altering supply
leak testing
pathology patient was admitted with
what is functional residual lung capacity?
gas left in the lungs after expiration
what is the role of functional residual capacity?
reserve gas exchange occurs between breaths
which surgical approach to the thorax is more painful?
sternotomy - more retraction required and more muscle damage than thoracotomy
what thoracic surgical approach is least painful?
thoracoscopy
what must be considered when patients are undergoing thoracoscopy?
large volume of CO2 insufflation
lungs can become compressed
when may ventilation be required from the start of abdominal surgery?
diaphragmatic hernia repair
why is thoracotomy so painful?
skin incision
nerve damage
retraction of ribs to allow access leading to muscle damage
inflammation at surgical site
what can be caused by poor analgesia during thoracic surgery?
hyperalgesia
what is the impact on patient ventilation following thoracic surgery?
ventilation less effective as lung inflation is compromised due to pain making patient unwilling to move their chest
what are the main reasons for thoracic surgery?
respiratory system
cardiovascular
oesophageal FB
thoracic duct ligation
what are the main respiratory system reasons for opening the thorax?
lung lobe torsion
bulla
neoplasia
abscess
what are the main considerations for thoracic surgery involving the respiratory system?
pre existing pneumothorax
hypoventilation
hypoxaemia
pre-disposed to decompensation
pathology already compromising respiration
what are the main cardiovascular system reasons for opening the thorax?
patent ductus arteriosus
persistent right aortic arch
pericardectomy
heart surgery
what are the main considerations for thoracic surgery involving the cardiovascular system?
CVS changes due to primary lesion or surgical manipulation
bleeding
hypotension
risk of arrhythmias
what are the main considerations for persistent right aortic arch?
paediatric
present with regurgitation
risk of aspiration
may be malnourished
what should you be aware of during PDA closure?
may be significant changes
bradycardia and hypertension
what are the main considerations for opening the thorax for non-respiratory/CVS reasons?
contamination risk
infection
pain
risk of aspiration
risk of regurgitation
sepsis
what is vital for thoracic surgery?
preparation
what is involved in preparation for thoracic surgery?
blood type
check blood availability
hypotension treatment plan (drugs/fluids)
pre oxygenation
check ventilator or IPPV facilities
ensure monitoring equipment ready
analgesia plan
what must happen before thoracic surgery?
patient is as stable as possible
how may patients be stabilised for thoracic surgery?
chest drainage
pre-oxygenation
fluids
what must be considered about pre-oxygenation?
must not cause further stress as may worsen respiratory function
method should be best available for patient
what is the aim with all anaesthetic drugs for thoracic surgery?
minimal CVS depression
analgesia
what drug type might be avoided in thoracic surgery patients?
alpha-2 agonists
ACP
what drugs may likely be needed during thoracic surgery?
inotropes (e.g. noradrenaline)
additional analgesia infusions (e.g. fentanyl)
what is etomidate used for?
induction
CRI
is etomidate licensed for animals in the UK?
no
what type of drug is etomidate?
IV
ultra short acting
nonbarbituate
what are the advantages of etomidate?
minimal CVS depression
what are the disadvantages of etomidate?
poor quality of induction unless premed is very good or the animal is very sick
what is the main benefit of fentanyl during anaesthesia?
MAC sparing
what is the benefit of giving MAC sparing drugs such as fentanyl during anaesthesia?
reduce CVS/respiratory system depression seen with volatile anaesthetic agents as the level can be reduced
what is the speed of onset of action of fentanyl?
within 5 minutes
what is the duration of analgesic effect of fentanyl?
20 minutes (lowest dose) to 40 minutes (highest dose)
what is the benefit of one lung ventilation?
isolation of one lung for ventilation if pathology only affects one
increases surgical exposure
what are the options available for one lung ventilation?
single lumen ET tube advanced into one bronchus
double lumen tube
endobronchial blocker
what is the main disadvantage of one lung ventilation?
placement difficult
must be very careful moving patients with endobronchial or double lumen tubes placed as trauma is possible
what is the benefit of a single lumen ET tube advanced into one bronchus for one lung ventilation?
easy (er)
what is the disadvantage of a single lumen ET tube advanced into one bronchus for one lung ventilation?
may not achieve effective one lung ventilation
risk of contamination between lungs
difficult in large dogs (>20kg) due to tube length
what is the benefit of endobronchial blockers for one lung ventilation?
effective
what is the disadvantage of endobronchial blockers for one lung ventilation?
bronchoscope required to place
needs skill and training to place
expensive
what is the benefit of double lumen tubes for one lung ventilation?
can be done blind
what is the benefit of double lumen tubes for one lung ventilation?
can be placed blind
what is the disadvantage of double lumen tubes for one lung ventilation?
bulky and difficult to place
not achievable in dogs >20-25kg due to tube length
how is an endobronchial blocker placed?
advanced through single lumen ET tube
what must be followed when using endobronchial blockers?
stated inflation volumes for the cuff to prevent bronchial wall damage
when should an endobronchial cuff be inflated?
only when one lung ventilation is needed
what should be avoided once an endobronchial blocker is placed?
movement of patient as this can cause the blocker to dislodge
what must be avoided once an endobronchial blocker is placed and the cuff inflated?
movement of the patient due to the risk of bronchial wall damage
why is the size of the patient for double lumen tubes limited?
size of human tubes
what is the best ventilation option for thoracic anaesthesia?
mechanical
make do with manual if necessary
what is the ventilator setting range for tidal volume?
10-15ml/kg
(maybe 8-10ml/kg for cats)
what is the ventilator setting range for tidal volume during thoracic surgery to aid visualisation?
6ml/kg
how can you judge tidal volume settings are correct?
observe thorax
adapt to monitoring
what is the ventilator setting range for Peak inspiratory pressure?
8-12 cm H2O
when may PIP settings be altered?
if open or closed thorax
increase if recruitment
what is the ventilator setting range for respiratory rate?
10-30 bpm
when may respiratory rate settings be altered during ventilation?
adapt to animal
increase if tidal volume reduced
what is the ventilator setting range for I:E ratio?
1:2 max
what should I:E ratio be adapted to?
RR
does IPPV require NMBA?
not necessary in most cases
what are the main issues associated with ventilation?
CVS depression
trauma
re-expansion pulmonary oedema
why can ventilation lead to CVS depression?
decreased venous return
how can the CVS depressive effects of ventilation be reduced?
limit I:E ratio to at least 1:2
how can the risk of trauma during ventilation be reduced?
limit pressure/volume applied to the chest
how can re-expansion pulmonary of ventilation be reduced?
be careful not to over expan lungs at the end of surgery - allow them to reopen over time
what monitoring techniques will be used for anaesthesia for thoracic surgery?
blood gas
capnography
oxygen monitoring
as well as standard
what must you be aware of when using capnography with an open thorax?
EtCO2 unlikely to reflect PaCO2
why are there differences between EtCO2 and PaCO2 in animals with an open thorax?
altered ventilation and perfusion relationships in different areas of the lungs
how can PaCO2 be used to inform EtCO2 in patients with an open thorax?
PaCO2 reading obtained from art line
calculate difference between PaCO2 and EtCO2
use this to inform required EtCO2 level to keep PaCO2 between 35-45mmHg
how should oxygen levels be monitored during thoracic surgery?
SpO2 as a minimum
PaO2 if possible
how is hypoxaemia detected during surgery?
PaO2 via art line
how can hypoxaemia be managed?
check patient on 100% FiO2
check ET tube patency
ensure CVS function optimised
how can you alter ventilation to manage hypoxaemia?
switch to manual IPPV and give larger breaths
alveolar recruitment manoeuvre
introduce PEEP
reduce Fi inhaled agent
re-expand collapsed lung - communicate with surgeon
what may affect ET tube patency during thoracic surgery?
endobronchial blocker may have become dislodged and blocked the ET tube lumen
secretions may block tube lumen
how can you ensure CVS function is optimised during thoracic surgery?
ensure anaesthetic depth is appropriate
ensure circulating blood volume is adequate (IVFT?)
confirm surgeon isn’t decreasing venous return
what is the alveolar recruitment manoeuvre?
temporary airway pressure is increased during mechanical ventilation so as to open up the collapsed alveoli
what pressure is needed for a alveolar recruitment manoeuvre?
30 cmH2O airway pressure for a breath
what are the main supportive therapies used for thoracic surgery patients?
IVFT
hypothermia management
what analgesia is needed for a thoracic surgery patient?
combination of local and systemic techniques
what drug types may be used for analgesia following thoracic surgery?
full mu agonists
LA
NSAIDs
what full mu agonists may be used for thoracic surgery?
methadone
fentanyl
morphine epidural
what local anaesthetic techniques may be used for thoracic surgery?
intercostal nerve block (lateral thoracotomy)
LA down chest drain at end of surgery
LA infiltration around sternotomy site
why must NSAIDs be used with caution post-op?
if patient has had unstable BP throughout NSAIDs should not be given due to prostaglandin effects
when should the end of IPPV be timed with during thoracic surgery?
chest closure and drainage as won’t be able to breathe spontaneously before this
describe the process of weaning from the ventilator
turn off ventilator
support respiration with IPPV
gradually decrease IPPV to allow PaCO2 to rise
decrease anaesthetic and analgesic drugs
reverse NMBA, if used, before stopping IPPV completely
continue until breathing spontaneously
what techniques can be used to aid pulmonary re-expansion?
alveolar recruitment manoeuvre
when is an alveolar recruitment manoeuvre useful?
following lavage atelactasis
when is the risk of re-expansion pulmonary oedema higher?
if lungs collapsed for more than 12 hours
what is a vital part of the recovery process from thoracic surgery?
weaning patient on to room air
oxygen supplementation if needed
IVFT
what monitoring is needed for patients in recovery from thoracic surgery?
pulse ox
assess chest drain for air, blood or fluid
what should be done if the patient isn’t saturating adequately in recovery?
assess chest drain for air, blood or fluid
supplement O2
when can oxygen toxicity occur?
> 6 hours on high FiO2
when may a blood transfusion be necessary?
if >20% blood loss - check PCV
how can you check if a patient is actively bleeding from a chest drain?
PCV of fluid from chest drain
what are the key factors involved in anaesthesia for thoracic surgery?
IPPV**
pain management
basic support (temp, fluids)
good anaesthesia protocol: MAC sparing and good analgesia
