Anaesthesia for peripheral vascular disease
Take home messages
- Patients with peripheral vascular disease are sicker than they look
- Anaesthetic technique is less important than homeostasis
- Peripheral vascular revascularisation is high risk surgery with a combined death and non-fatal MI rate of more than 5%
It's all plumbing
I’m fairly strongly of the opinion that the vast majority of medicine is plumbing, and peripheral vascular disease is a prime example.
- Oxygen is good
- Oxygen travels in blood
- Blood flow is therefore helpful
- Blocked pipes are bad
Tip top FRCA stuff here.
Peripheral vascular disease is a progressive blockage process of arteries throughout the body, most notably supplying the limbs.
To begin with this process will be asymptomatic, as the blood supply remains sufficient to serve the aerobic respiration requirements of the limb and its various muscles, however as it progresses, the patient will notice intermittent claudication, a deep aching muscular pain associated with insufficient oxygenation and a metabolic lactic acidosis from anaerobic respiration.
This will worsen in severity, with the onset of pain occurring sooner on exertion, and with greater intensity.
- Aorto-iliac occlusion will cause buttock claudication
- Common femoral occlusion will cause thigh claudication
- Tibioperoneal disease will cause foot claudication
Eventually it will reach the point where even at rest the arterial supply to the limb is insufficient, and without intervention the limb will become ischaemic and unsalvageable.
Let's complicate it further
At any point along this progressive stenotic journey, there remains an omnipresent risk of acute limb ischaemia, usually from an embolic phenomenon causing abrupt occlusion of the remaining lumen.
Without urgent intervention, this represents a severe threat to live and/or limb.
How bad is it?
If your blood vessels are so clogged up with atheroma that your limbs aren’t getting enough blood for aerobic respiration, then the prognosis is unsurprisingly poor.
It’s not just PAD
If the blood vessels to the limbs are stenosed and unhappy, it’s highly likely that the blood vessels elsewhere are having a similarly bad time.
- Most patients with significant PAD also have substantial coronary artery disease
- It is here where most of the post-operative mortality and morbidity resides
What comorbidities do patients with PAD have?
- Diabetes
- Coronary artery disease
- Renal failure
- Chronic obstructive pulmonary disease
Operate vs Optimise
Ah the eternal dilemma in comorbid patients - do you crack on and operate to fix the problem, or do you try and optimise as much as possible first to make the operation safer?
- This is going to be assessed on an individual basis
- You try and optimise as much as you can without delaying surgery
No surprises here.
How can you optimise a patient prior to surgery?
This is a multidisciplinary process that requires input from anaesthetist, surgeon, GP, cardiology, endocrinology, respiratory, physiotherapy and anyone else who needs to be involved.
- Start a statin if not already on one
- Stop smoking and start nicotine replacement (4-6 weeks before surgery)
- Cardiac meds should be optimised and continued
- If on β blockers, continue them, but don't necessarily start β blockers at this stage unless other indication
- Fix anaemia
- Diabetic control
- Treat hypertension*
- Antiplatelet therapy**
*ACE inhibitors reduce ischaemic events even if normotensive.
**Clopidogrel is better than aspirin.
How to fix it?
As with any pathology involving a blocked tube, you have essentially two options:
- Clear the blockage
- Bypass the tube
PVD is the same - you can do an angioplasty, an endarterectomy or revascularisation with a bypass, either autologous or prosthetic.
If you can't restore adequate perfusion to the limb, then the only remaining option is amputation.
Who should be offered amputation?
- Patients not suitable for either endovascular intervention or revascularisation
- Patients with severe comorbidities that mean they won't be able to use the limb even if they do manage to restore blood flow
- Patients with irreversible ischaemic damage to the limb
How do I anaesthetise them?
Just for a change, we’re going to suggest that the specific technique you use is less important than ensuring strict homeostatic control.
You can do many of these procedures under loco-regional anaesthesia, with all of the benefits of avoiding general anaesthesia and its inherent risks, especially in those with significant cardiorespiratory disease.
However many of these patients aren’t going to be able to lie flat and still for prolonged periods of time, necessitating general anaesthesia.
How would you conduct your general anaesthetic?
- Big IV access
- Minimum AoA monitoring
- Arterial line (awake if worried about instability at induction)
- Judicious use of balanced crystalloid and peripheral vasopressor infusions
- Catheter and urine output monitoring
- Central venous access is usually not necessary unless you’re finding the vasopressor requirement increasing dramatically
- Cautious, opioid-heavy induction
- Endotracheal intubation and positive pressure ventilation
You can use your buzzphrases of 'maintain preload and avoid sudden changes in systemic vascular resistance' that score you marks in literally any exam question.
What are the benefits of regional anaesthesia?
- Avoids respiratory risk of GA
- Reduced postoperative cognitive dysfunction
- Better postoperative analgesia
Not suitable if patient severely coagulopathic or unable to lie still for the procedure.
What are the benefits of general anaesthesia?
- Respiratory control
- Duration of procedure not an issue
- Possible volatile and opioid preconditioning benefits
What are your anaesthetic priorities intraoperatively?
- Avoid hypotension - aim for within 20% of patient's normal pressures
- Avoid tachycardia
- Avoid sudden changes in peripheral vascular resistance
- Judicious fluid therapy to maintain preload without causing overload
- Analgesia
- Antiemetics
- Glucose control
- Normothermia
- Coagulation control - monitoring ACT and giving heparin as needed
- Monitoring blood loss as this can be substantial and insidious
Heparin and ACT
If you're used to general and orthopaedic surgeons exclaiming that they can't possibly operate with an INR above 1.4, it comes as somewhat of a culture shock when a vascular surgeon says,
"Give five thousand units of heparin as I make a hole in this major artery."
So it takes a little getting used to.
You can measure the activated clotting time (ACT) as a point of care test like a blood glucose or haemacue, and give boluses of IV heparin as required.
How does unfractionated heparin work?
- Increases activity of Antithrombin
- The antithrombin-heparin complex inhibits factors 2a and 10a
Pain control
Ischaemia is painful, as is reperfusion injury.
Furthermore, many of these patients have been dealing with chronic pain for a while, and will have upregulated spinal pain pathways with increased sensitivity, hyperalgesia and potentially allodynia.
Consider adjuncts such as pregabalin (start 25mg and titrate up to effect) for chronic ischaemic pain.
This may need continuing post operatively as well.
What are the impacts of pain in peripheral vascular surgery?
- Increased sympathetic activity
- Tachycardia
- Hypertension
- Vasoconstriction
These are bad for the heart and bad for the graft or anastomosis.
Avoid NSAIDs for the obvious cardiac and renal badness in elderly patients.
Monitoring
The show doesn't stop once the drapes come off. While the primary vascular blockage may now be relieved and the circulation to the affected limb vastly improved, the patient is by no means out of the woods yet.
Frequently, proximal vessels including the aorta demonstrate severe disease and carry significant risk of recurrent embolisation (especially after hours of endovascular poking).
So they need close monitoring on a specialist vascular ward or high dependency unit as indicated.
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References and Further Reading
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