Diabetic Foot Amputation: Anesthetic Concerns and Perioperative Management
Case Summary and Diagnosis
What is the short summary of the case and the diagnosis?
This is a 54-year-old female,
a known case of type 2 diabetes mellitus on irregular treatment with oral hypoglycemic agents.
She presented with a one-week history of fever and a non-healing ulcer near the heel of the right leg that had been increasing for one month.
Examination revealed absent peripheral pulsations,
impaired vibration sense, skin changes, and orthostatic hypotension.
The diagnosis is type 2 diabetes mellitus complicated by diabetic peripheral neuropathy,
with a right diabetic foot, posted for below-knee amputation.
Is this an emergency surgery? How much time is there before the procedure?
While it may not be a "dire" emergency,
it is an urgent surgery. If the patient is in sepsis,
the source of infection should be controlled within 6 to 12 hours.
Delaying beyond this window means the patient is unlikely to improve.
The surgery is life-saving, not just limb-saving.
Preoperative Concerns and Considerations
What are the main anesthetic concerns for this patient?
The primary concerns are the acute and chronic complications of uncontrolled,
long-standing diabetes mellitus.
Acute complications include diabetic ketoacidosis (DKA),
hypoglycemia, hyperosmolar hyperglycemic state (HHS), and lactic acidosis.
Chronic complications include both microvascular and macrovascular issues.
The patient already shows signs of microvascular complications like peripheral neuropathy.
Why is autonomic neuropathy a specific concern, and how might it present in the history?
Autonomic neuropathy is a major concern because it affects multiple organ systems.
Cardiovascular involvement can lead to resting tachycardia,
exercise intolerance, and silent myocardial ischemia.
Gastrointestinal involvement can cause gastroparesis and esophageal dysmotility.
In the history, look for symptoms like syncopal attacks (from orthostatic hypotension),
dyspnea on exertion (instead of angina),
alternating diarrhea and constipation, dry skin, or heat intolerance with altered sweating.
What is the significance of infection in this patient?
The patient is very likely to have an infection,
which could lead to sepsis. It is important to assess for sepsis using tools like qSOFA.
Infection itself can affect the patient's physiology,
including causing thrombocytopenia and impacting erythropoiesis.
Preoperative Investigations and Optimization
What investigations are necessary and why?
- Complete Blood Count: To check hematocrit for anemia (due to chronic disease,
nutritional deficiency, or renal failure),
WBC count with neutrophils for infection, and platelet count (sepsis can cause low platelets).
- RBS and HbA1C: To assess current glycemic control (RBS of 300 was noted)
and long-term control over the past 8-12 weeks.
An HbA1C >9 or <5 indicates poor control and higher risk.
- Serum Electrolytes: Mainly to check potassium levels.
Potassium can be high in DKA (due to acidosis causing a shift out of cells and insulin deficiency)
and in renal failure. Sodium levels can indicate hydration status;
a normal or high sodium with hyperglycemia suggests water depletion.
- Renal Function Tests: To assess for diabetic nephropathy.
- ECG: To look for evidence of silent myocardial ischemia,
arrhythmias, or signs of hyperkalemia (peaked T waves).
- Echocardiogram: To evaluate for diabetic cardiomyopathy or other structural heart disease,
as the patient is at high risk for cardiac complications.
- Arterial Blood Gas: To rule out diabetic ketoacidosis given the high RBS.
- Urine Routine Examination: To check for proteinuria or ketones.
Other tests like CRP or procalcitonin may be done to assess the degree of infection.
A chest X-ray is routine but not strictly indicated without symptoms.
How can you assess exercise tolerance in this patient?
Exercise tolerance can be assessed using the six-minute walk test,
shuttle walk test, or stair climbing test.
A metabolic equivalent (MET) score of more than 4 is desirable.
This is roughly equivalent to a patient being able to climb two flights of stairs without difficulty.
One MET is the oxygen consumed at rest (approximately 3.5 mL/kg/min).
How should you optimize a patient with a high HbA1C?
Optimizing HbA1C ideally takes 2-3 months.
In urgent or emergency surgeries like this,
there is no time to wait. The patient should proceed to surgery,
but the risks associated with poor glycemic control must be communicated to the patient and their family.
What are the pre-operative medication orders for a diabetic patient on the morning of surgery?
- Schedule the patient as the first case.
- Oral Hypoglycemic Agents (OHA):
- Metformin: Skip the morning dose on the day of surgery due to the rare risk of lactic acidosis,
especially in patients with renal impairment.
- Sulfonylureas: Skip the morning dose; some recommendations suggest skipping the previous night's dose as well due to the risk of hypoglycemia.
- SGLT2 Inhibitors: Skip 24 to 72 hours before surgery due to the long half-life and risk of euglycemic ketosis.
Intraoperative Anesthetic Management
What are the anesthetic choices and which is preferred?
Regional anesthesia is preferred over general anesthesia or spinal anesthesia.
A regional technique keeps the patient awake,
allowing for continuous neurological assessment and avoiding the hemodynamic instability associated with general anesthesia in a potentially septic patient.
Why is spinal anesthesia not a good option?
Spinal anesthesia is relatively contraindicated due to several factors:
- It can cause profound hypotension,
especially in a patient with pre-existing autonomic neuropathy and potential sepsis.
- Coagulation may be deranged due to sepsis or other complications.
What specific nerve block is suitable for a below-knee amputation?
A popliteal sciatic nerve block is a good option,
but it must be combined with a block for the saphenous nerve.
The saphenous nerve, a branch of the femoral nerve, supplies the skin on the medial side of the leg.
A safer approach would be a proximal sciatic nerve block combined with a femoral nerve block to ensure complete anesthesia of the limb.
What additional monitoring is required for this high-risk case?
In addition to standard ASA monitors,
an invasive arterial line for continuous blood pressure monitoring is ideal.
This is crucial for a patient with autonomic neuropathy, potential sepsis, and cardiac concerns.
The patient should be closely monitored post-operatively,
as the risk of a perioperative myocardial infarction is high.
Postoperative Risks and Prognosis
Why is this patient at high risk for a perioperative myocardial infarction (MI)?
The surgical insult from an amputation triggers a significant inflammatory and procoagulant state.
These inflammatory markers and a tendency for thrombosis persist well into the postoperative period,
increasing the risk of an MI. A perioperative MI has a higher mortality than a non-surgical MI because the inflammatory trigger is not quickly removed.
What is the long-term prognosis for patients undergoing amputation?
This is a very high-risk case with significant long-term mortality.
Evidence suggests that around 60% of patients who have had an amputation are not alive five years after the procedure.