5.1 AAA for EVAR Flashcards
An 80-year-old gentleman presents for an elective repair of an 8 cm
infrarenal abdominal aortic aneurysm. You have been asked by surgeons to
review this patient in the preassessment clinic.
Past Medical History His past medical history includes a left pneumonectomy and thoracoplasty for tuberculosis 40 years ago and two occasions where he had angioplasty and insertion of coronary stents 5 and 8 years ago.
Drugs
Enalapril 5 mg oD
Atenolol 25 mg oD
Isosorbide mononitrate 20 mg BD
Paracetamol 1g PRN
social History
Ex-smoker for over 40 years
Drinks alcohol occasionally
on examination
Heart rate 76/min
Blood pressure 160/90 mmHg
BMI 33 kg/m2
Dependent ankle oedema, which he attributes to venous stasis.
summarise the case.
This 80-year-old patient presents as a high-risk patient with multiple
comorbidities for high-risk surgery. He is elderly with significant cardiac
history, poorly controlled hypertension, pre-existing moderate chronic
kidney disease, and significant restrictive lung disease. The size of his aortic
aneurysm and his poor physiological status puts him at increased risk of
perioperative cardiac and surgical complications, bleeding, and long-term
severe renal dysfunction.
I would like to take a full history, examination, and review and consider
additional investigations and ensure full optimisation of his comorbidities
before considering his options with both the patient and his surgeon.
Discuss assessment of risk.
Abdominal aortic aneurysms are incidental findings in two thirds of patients.
Surgery is recommended when they reach 55 mm.
At this stage there is less than 1% risk of spontaneous rupture.
By 60 mm there is more than 17% risk of spontaneous rupture.
We can see that simply the size of this gentleman’s
aneurysm places him at high risk from rupture without surgical intervention.
In terms of proceeding with surgery,
risk assessment should be done
taking into consideration the likelihood
of a perioperative cardiovascular event.
original cardiovascular risk scoring systems include
Goldman’s Criteria,
Detsky’s, and Lee’s Revised Cardiac Index.
The American College of Cardiology (ACC)/American Heart Association (AHA)
guidelines for Perioperative evaluation of Non-Cardiac Surgery
(2003) have been developed subsequently.
Patient Risk (cardiac risk by patient comorbidities)
- Minor
° Age > 70
° Abnormal ECG
° Nonsinus rhythm
° Uncontrolled hypertension
° Stroke
- Minor
- Moderate
° MI > 6 months
° Mild angina
° Compensated heart failure
° Diabetes
- Moderate
- Major
° MI < 6 months
° Unstable angina
° Decompensated heart failure
° Severe valvular heart disease
° Symptomatic arrhythmias
- Major
surgical Risk (cardiac risk by type of surgery)
- Minor (< 1%)
° Endoscopy/cataract surgery
° Plastics/breast surgery
- Minor (< 1%)
- Intermediate (1%–5%)
° Thoracic/head and neck surgery
° orthopaedic/minor vascular surgery
- Intermediate (1%–5%)
- Major (> 5%)
° Aortic/major vascular surgery
° Emergency surgery
° Prolonged surgery
- Major (> 5%)
This patients risk
From a surgical risk basis,
this is aneurysm surgery in the high-risk category and independently,
cardiac risk is more than 5% for undergoing surgery alone irrespective of comorbidities.
In recent times it is apparent that more comprehensive scoring systems
are needed to categorise patient risk.
A system known as EuroSCoRE is increasingly being used.
Could you go through his investigations and positive findings?
Bloods
His blood tests reveal that he has chronic kidney disease.
ECG
* PR interval is at the upper limit of normal (200 msec)
* Tall R waves in lateral leads V5 and V6 with mild ST segment depression
suggests left ventricular hypertrophy
* rSR pattern in V1 with T wave inversion in V1–V3, suggestive of right
bundle branch block
CXR
CXR reveals evidence of his previous surgery and signs within his
existing lung.
It demonstrates marked volume loss of the left hemithorax with shift of
the mediastinum and elevation of the hemidiaphragm. Also the pleura is
calcified.
Lung function test
Lung function tests reveal severe restrictive disease and a very low DLCo.
DLCo is a measurement of carbon monoxide take-up per unit time. It
measures alveolar/capillary function. DLCo < 80% is associated with
increased pulmonary complications, and a DLCo < 30% is associated with
increased morbidity.
A full history together with an echocardiogram and baseline ABGs would
help assess him further.
What methods are there for assessing his functional capacity?
Functional capacity assesses patient response to increased physical demand.
I would like to ask about his exercise tolerance.
This can be done by using the Duke Activity Status Index,
which quantifies numbers of METs
(metabolic equivalents),
a measure of basal oxygen consumption (i.e. at rest).
1 MET equates to 3.5 ml o2/kg/min.
What do various METs represent
- 7–10 METs suggests good function
(e.g. carrying shopping upstairs, cycling, jogging). - 4–7 METs suggests moderate function
(e.g. climbing two flight of stairs without stopping). - 1–4 METs suggests impaired function
(e.g. basic ADLs, eating, dressing, walking on flat surface).
Tests of functional capacity
- Exercise ecG (Bruce Protocol):
Looking for evidence of ischaemia
while walking on a treadmill which goes
through intervals of walking on a flat
surface to graduated inclines. - 6-minute walk test:
To record the furthest distance walked at own pace
back and forth along a 30 m walkway
in 6 minutes on a flat surface. - incremental shuttle walk test:
Externally paced,
incremental distance walked back and forth,
final result measured in this is the number of shuttles,
which can help predict Vo2 max. - Pharmacology induced stress testing
Pharmacology-induced stress testing:
Dobutamine Stress Echo,
thallium scan;
echocardiographic or nuclear medicine imaging changes
based on drug injected to look for any
regional wall motion abnormality or cold spots depending on the test.
This may be useful if unable to walk due to arthritis or other conditions.
cardiopulmonary exercise testing (CPET)
This is usually done on a bicycle
with assessment of both ECG and
analysis of gases and
is valuable in considering when the aerobic metabolism
crosses over to anaerobic metabolism in a patient
and assessing maximal oxygen consumption
at peak exercise.
It provides many other parameters that can
help uniquely assess cardio respiratory risk in combination.
How is eVAR performed?
Endovascular repair of abdominal aortic aneurysms
involves a joint procedure performed by a
radiologist in conjunction with a vascular surgeon.
An aortic stent graft is placed via femoral arteries
to extend both above and below the edges of the aneurysm.
one or both groins may be used.
Local anaesthetic is used for the entry site,
but regional or general anaesthesia
may also be given,
though less frequently.
Arterial blood pressure monitoring is ideal.
It is not suitable if there is significant
peripheral vascular disease or
atherosclerotic plaques.
What are the benefits of eVAR versus open surgery?
Mortality of EVAR versus open repair is quoted as 0.9% versus 4.3%
according to AAAQIP report from 2009–2010.
Advantages
* Shorter, less invasive procedure
- Less associated bleeding
- Early ambulation
- Reduced hospital stay
____________________________________
Disadvantages
* Costly.
- Technically difficult
- Reasonable incidence of poor seating
of the graft and therefore leak around the graft
How will you discuss risk with the patient?
I would explain risk to the patient in terms of the patient’s comorbidities
and the surgery they are undergoing.
I will need a full history and possible additional investigations in order to provide a more comprehensive picture.
It is important to use terms that the patient can understand
such as percentages or use of ‘common’ or ‘rare’.
The Royal College of Anaesthetists has produced guidance and a patient information leaflet relating to aortic surgery that I could give the patient.
________________________________________
In this case there is the risk of his age and comorbidities,
which may lead him to a higher risk of a heart attack
and chest infection around the time of his operation,
the higher risk of bleeding given the size and length of
operation, and the possibility of long-term dialysis.
This should be balanced against his high risk of
spontaneous rupture given the size of the aneurysm.
It is important that all concerns are addressed before proceeding from both
the anaesthetic and surgical side.
Despite his high risk, how would you anaesthetise him?
I would give him a general anaesthetic. Ensure he has taken all his regular
medications except an ACE inhibitor preoperatively.
Preinduction
* Full noninvasive monitoring
- Awake mid-thoracic epidural after
informed consent under aseptic technique - Invasive arterial monitoring
induction
- Intubation with the use of high-dose opiate
and propofol intravenous
induction with use of a muscle relaxant - Central venous line for assessment of fluid status and provision of
vasopressors, blood, and multiple drugs if needed - Cardiac output monitoring would also be helpful
- Maintaining his mean arterial pressure within
15% of his baseline where
possible will help reduce risk of hypoperfusion to organs - Optimal positioning
- Fluid and body warmers and temperature monitoring
- Nasogastric tube to empty the stomach
During the operation he has a massive bleed when the clamp is released. How will you manage this?
This will require good communication within the theatre team to avoid
adverse sequelae.
The clamp should be reinstated and then both medical
and surgical aspects managed.
From a surgical perspective,
it is important that there is no ongoing surgical
site bleeding and this should be addressed.
The bleeding may have in part been related to haemodynamic changes associated with the release of the clamp.
This can be minimised by giving a fluid bolus and maintaining
vascular tone with vasopressors when clamp is next released.
It is also important to ensure that the current bleed has been dealt with and blood and other products transfused appropriately if needed and haemodynamic parameters restored before a repeat attempt at releasing the clamp.
Define massive transfusion,
Massive transfusion occurs when there is
more than 50% blood volume transfused
in 4 hours or 10 units in 24 hours.
products available, and transfusion triggers for each product.
Products available are
red cells,
fresh frozen plasma,
platelets,
cryoprecipitate.
Adjuncts include
fibrinolytics, such as tranexamic acid,
aprotinin,
recombinant factor 7,
prothrombin concentrate.
Principles around bleeding
The main principles are to
recognise it early,
maintain tissue perfusion and oxygenation
by considering oxygen delivery,
arrest the cause of bleeding
(surgical versus coagulopathy),
and use blood products appropriately and in a timely fashion.
Until bleeding is controlled,
it is recommended to give
products in a ratio of 1:1:1 (red cells:FFP:platelets).
Transfusion triggers during ongoing bleeding
- Hb < 10
- APTT > 1.5 times normal
- Platelets < 50 or < 75 with ongoing haemorrhage
- Fibrinogen < 1.5
other goals to achieve
Temperature > 36 degrees
Ionised Ca2+ > 1.1
pH > 7.2
What are his options for analgesia?
In view of his poor lung function and undergoing a laparotomy,
I feel that a thoracic epidural is in his best interests.
I will discuss the procedure with the patient
and make appropriate plans for removal later given perioperative
heparin use.
This should be performed awake preinduction and should
facilitate postoperative deep breathing and together with regular chest
physiotherapy help reduce the risk of postoperative respiratory infection.
The alternative would be to perhaps perform
transversus abdominis plane blocks and use a fentanyl/morphine PCA with regular paracetamol.
It should be borne in mind that due to his age
he is likely to be opiate sensitive and
due to his additional risk of further renal impairment postoperatively he
may have difficulty clearing opiates,
which may impair his recovery and
cooperation with physiotherapy.
What will decide the criteria for extubation at the end of the operation and where will he go postoperatively?
Providing he has normal acid base, temperature, reasonably corrected
haematological and electrolyte parameters and is fully reversed,
it would be ideal to plan for an early wakening
and extubation to assess neurology and
encourage early chest physiotherapy.
With his comorbidities, intensive care would be necessary
in the first instance until both ventilation and kidney
function have been assessed as adequate.
Preoperative cardiopulmonary exercise testing (CPET)
may have helped plan
postoperative care if he has undergone this.
What will decide the criteria for extubation at the end of the operation and where will he go postoperatively?
Providing he has normal acid base, temperature, reasonably corrected
haematological and electrolyte parameters and is fully reversed,
it would be ideal to plan for an early wakening
and extubation to assess neurology and
encourage early chest physiotherapy.
With his comorbidities, intensive care would be necessary
in the first instance until both ventilation and kidney
function have been assessed as adequate.
Preoperative cardiopulmonary exercise testing (CPET)
may have helped plan
postoperative care if he has undergone this.
What has the AAQIP set out
In recent years various studies have looked at the use of CPET to help
stratify risk in patients undergoing aneurysm surgery.
In the UK the national vascular society has recommended the use of the AAAQIP (Abdominal Aortic Aneurysm Quality Improvement Project) preoperative care bundle (2011), which incorporates the following:
- Preoperative assessment and risk scoring
- CT angiography to aid decision making between open repair or EVAR
- Assessment by a vascular anaesthetist
- Case reviewed at an MDT meeting involving both surgeon and radiologist
- Patient to be given evidence-based written information
Can you discuss relevance of CPET in more depth with respect
to elective AAA surgery?
CPET has become a routine part of preassessment for elective aneurysm
surgery and helps plan postoperative care. Some variables of significance
are as follows.
Vo2 max of 15 ml/kg/min is thought to be equivalent to four METs and hence
predictive of poor functional capacity below this value. A value of at least
20 ml/kg/min is desirable for abdominal aortic aneurysm surgery.
AT, or anaerobic threshold, denotes the Vo2 value when there is a switch
from aerobic to anaerobic metabolism and therefore when oxygen demand
is greater than supply. An AT of 11 ml/kg/min is thought to be needed
to undergo significant surgery, and below this there may be a need for
postoperative critical care. In addition, below this value on a case-by-case
basis there may be a preference for EVAR instead of an open procedure.
A low-peak Vo2, AT, and ventilatory equivalent for Co2 have been shown to
be associated with poor outcomes after this surgery.
