Diabetic Foot Sepsis/Amputations

Guidelines

Microbiology

Clinical Classification of Diabetic Foot Infection

Differential Diagnosis

Initial Examination and Assessment

Management of Diabetic Feet Ulcers

Diabetic Foot Sepsis

Evaluate for Limb Ischaemia

Local Context

Amputations

---

This is an extremely common problem which results in major morbidity, mortality, and extensive use of hospital resources. Important risk factors include neuropathy, peripheral vascular disease and poor glycaemic control. Minor trauma may precipitate wounds that heals slowly and precipitates infection which may ultimately  lead to major limb amputation. Principles of acute management are similar to other soft tissue infections, except that the microbiological profile mandates a broader spectrum of antimicrobial cover.  In an ideal world multidisciplinary team involvement (TOE and FLOW) is the norm .  Early referral to physiotherapy and rehab services are essential. Start making plans about rehab, placement and after hospital care as soon as possible. 

 Guidelines

Guidelines by the Infectious Disease Society of America(IDSA) (2012) and the International Working Group on the Diabetic foot (IWGDF) can be reviewed. Multiple classification systems for degree of ischaemia (Fontaine , Rutherford ) , diabetic foot ulcers ( Meggit-Wagner , University of Texas , PEDIS, Saint Elian , IDSA) are available. The Society of Vascular Surgery (SVS) Wound , Ischaemia and Foot Infection (WIFI) classification system is the latest trying to combine all the components to stage the patient and define risk of limb loss.

 Microbiology

Infections are mostly polymicrobial. Superficial diabetic foot infections including cellulites and infected ulcers in antibiotic naïve patients are likely due to aerobic gram positive cocci (Staphylococcus aureus , Streptococcus agalactiae, Streptococcus pyogenes and coagulase negative staphylococci). Deeper chronic infected ulcers previously treated with antibiotics may involve the above as well as enterococci, Enterobacteriaceae, Pseudomonas aeruginosa and anaerobes. Wounds with extensive local inflammation , necrosis , malodorous drainage or gangrene with systemic toxicity likely have an anaerobic component (anaerobic streptococci  Bacteroides,  Clostridium species). Dependant on certain risk factors and area and hospital specific infectious profiles MRSA , Pseudomonas aeruginosa (role uncertain even when present in cultures) and extended spectrum belta lactamase producing gram-negative rods can be involved.

Clinical Classification of Diabetic Foot Infection 

Uninfected	Wound lacking purulence or any manifestations of inflammation.
Mild	Presence of more than ≥ 2 manifestations of inflammation, but any erythema extends ≤ 2cm around an ulcer . Involves only superficial tissues with  no local complications or systemic toxicity.
Moderate	Patient is systemically well and metabolically stable , but has ≥ 1of the following : cellulitis extending beyond 2 cm, lymphatic streaking, spread beneath the superficial fascia, deep tissue abscess, gangrene, and involvement of muscle, tendon, joint or bone.
Severe	Systemic toxicity or metabolic instability (fever , chills , tachycardia , hypotension , confusion, vomiting , leucocytosis , severe hyperglycaemia).

 Differential Diagnosis

1. Acute Charcot neuro osteo- arthropathy – May present  acute or subacute; with warm , swollen red foot. Not treating associated infection in a patient with Charcot’s can be disastrous and not providing acute complete offloading in patient with Charcot’s incorrectly diagnosed as infection can exacerbate deformity
2. Fracture and other trauma associated injuries.
3. Chronic Venous Stasis.
4. Acute Deep Venous Thrombosis.
5. Crystal-associated arthritis.

 Initial Examination and Assessment

• Remove the patient’s shoes, socks, bandages and dressings and examine their feet for evidence of neuropathy, inflammation and/or infection, ischaemia, deformity, ulceration, Charcot arthropathy. Document any identified new and/or existing diabetic foot problems.
• A flame shaped area of erythema on the plantar surface of the foot often indicate deep space foot infection and needs urgent attention. Crepitus , bullae  and fluctuation are also worrying features.
• Underlying osteomyelitis is suspected with grossly visible bone or ability to probe to bone and with large sausage shaped digits.
• Examine the patients for signs and symptoms of systemic sepsis.
• Evaluate glycaemic control and be alert for diabetic keto-acidosis.
• Xray the affected foot (gas , foreign body, evidence of osteomyelitis , septic arthritis or Charcot’s).
• MRI may be indicated to diagnose osteitis , but not routinely done.
• Use pressure relieving support surfaces and strategies.

Management of Diabetic Feet Ulcers 

• Record the size and depth of the ulcer. Assess and record any signs of infection, ischaemia, neuropathy, gangrene or deformity.
• Debridement should only be done by healthcare professionals from the surgical team using the technique that best matches their expertise, clinical experience, patient preference and site of the ulcer.
• When choosing wound dressings, take into account the wound, patient preference and the clinical circumstances, and use wound dressings with the lowest acquisition cost.
• Offer off-loading techniques with the lowest acquisition cost. Use pressure-relieving support surfaces and strategies.
• Involve a multidisciplinary team, diabetic nurse, podiatry services whenever possible.
• Negative pressure wound therapy improves ulcer healing in randomized trials , but has no effect on ulcer recurrence and may be used if resources allow.

 Diabetic foot sepsis

• Patient needs to be hospitalized for moderate to severe foot infections. Mild infections can be treated on an outpatient basis.
• Wound management includes debridement of callus and necrotic tissue, wound cleansing and relief of pressure (offloading). Sharp as well as enzymatic debridement can be performed . Wound dressing must absorb exudate and provide a moist environment to healing. Avoidance of weight bearing (offloading) is generally more important than the kind of dressing used and can include total contact casts , cast walkers , special shoes (such as simple postop shoe , prescriptive shoes with orthotic insets , non prescription rocker sole shoes, wedge shoes also called half shoes ) , knee walkers and bedrest.
• Send a deep soft tissue sample (or abscess aspirate) for microbiological examination as superficial swabs are often unreliable ( Bacterial colonization not infection). In osteomyelitis bone biopsy is preferred.
• Blood cultures should be performed in severe infections.
• Manage fluid and electrolyte balance , glycaemic control and diabetic keto-acidosis as per standard guidelines.
• Start antibiotic therapy based on infection severity as well as likelihood of involvement of resistant organisms , using the antibiotic with the lowest acquisition cost appropriate for the clinical situation. No single drug or combination appears to be superior to others .Take into account local antibiotic guidelines as well as the microbiology results.
• Do not delay starting therapy for suspected osteomyelitis.
• The South African Antibiotic Stewardship program (SAASP) suggests flucloxacillin 500mg po 6 hourly as an outpatient for mild infection. For moderate infection that is not extensive without limb threat or systemic toxicity Co-amoxiclav 1g po 12 hourly may be used ( in other words cellulitis beyond 2cm, but no  deep infection or systemic toxicity). For most moderate and severe infections Co-amoxiclav 1.2 g 8 hourly IVI is indicated.
• In patients with penicillin allergy with mild/moderate infections Clindamycin 450mg po 8-hourly can be used with ciprofloxacillin 500mg po 12-hourly if gram negative organisms is suspected. With severe infections use Clindamycin 600mg iv 8-hourly PLUS ciprofloxacin 400 mg IV 8 hourly.

NB. Change to specific antibiotic regimen informed by identities and sensitivities of organisms cultured when these results become available. If the patient responded clinically well in may not be necessary to always change antibiotics even if some ( such as Pseudomonas) are not sensitive to prescribed regimen.

• Other empiric parental regimens described in the literature for moderate to severe diabetic foot infections can be discussed with the microbiology department when patients are not responding ( although this often indicates a need for surgical debridement)
  • Other beta lactam antibiotics such as piperacillin-tazobactam has activity against Pseudomonas
  • Carbapenems - ertapenem often used, often has activity against ESBL producing organisms , but not Pseudomonas. Imipenem-cilastatin and meropenem has broad cover.
  • Combination regimens such as Metronidazole plus third and fourth generation cephalosporins or quinolones.
  • When MRSA is suspected/cultured : Vancomycin , Linezolid or Daptomycin  ( oral trimethoprim-sulfamethoxazole , doxycycline and clindamycin may have some activity)
• Duration of antibiotic therapy is variable: in mild infection this may be 1 – 2 weeks until there is evidence that the infection has resolved. Antibiotics need not be administered for the duration that the wound is open. After surgical debridement antibiotics is often administered for 2 – 4 weeks ( may be less if infection completely eradicated) initially parenterally and later changed to oral therapy if feasible. With residual osteomyelitis longer duration of antibiotic therapy may be needed. After a major limb amputation with the area of infection fully resected, a brief course of antibiotics usually a week,  is sufficient.
• Adequate Source Control surgery is essential. Surgical referral is indicated in most moderate infections especially in patients with deep abscess ( flame) , bone or joint involvement, crepitus, gangrene , necrotizing fasciitis and severe vascular insufficiency. In addition to surgical debridement, revascularization ( via angioplasty or bypass grafting) and/or major limb amputation  may be necessary. 
• Early surgery improves limb salvage vs delayed surgery and is more important than antibiotic regimen chosen . Resuscitation before surgery is extremely important in very ill patients , but should not unduly delay surgery, since source control is needed to treat overwhelming  infection.
• Infection in diabetic patients are often more extensive than expected. It is important to counsel the patient regarding this and that more extensive surgical procedures such as trans metatarsal ( forefoot ) amputation or guillotine (supra malleolar amputation) may be necessary ( important to get pre operative consent ).
• Important surgical points is to widely lay open plantar space infections with debridement of bone and tendons – especially infected tendons leads to foot infection spreading proximally.
• In cases where limb salvage is clearly not possible a decision has to be  made to either first perform a guillotine amputation above the ankle followed by a formal above or below knee amputation vs proceeding directly to a major limb amputation. Guillotine amputations are extremely valuable when the necrosis involves the foot , but the cellulitis extends to the below knee amputation level. In this case a two stage procedure with guillotine first followed by a formal amputation  once cellulitis has resolved is useful. The gullotine procedure can also be used as part of resuscitation of extremely ill patients since it requires only a short anaesthetic time.
• Negative pressure wound therapy ( vac dressing) is often used after extensive debridement for infection or necrosis or following partial foot amputation. Skin grafting then follows to obtain wound closure.
• In patients with osteomyelitis of the foot with extensive associated soft tissue infection the bone is normally resected. In cases of bony involvement with intact skin or a small sinus longer duration antibiotic treatment without surgery may be feasible and should be discussed with an orthopaedic surgeon.
• Advice regarding foot care remains critical. This includes the following:
  • Avoid smoking.
  • Do not go barefoot , even at home , and especially on hot decks and hot sand.
  • Visually inspect shoes before inserting foot ( may not feel foreign object due to neuropathy).
  • Test water temperature before stepping into bath , avoid warm water bottles to feet.
  • Trim toenails to shape of toe, and remove sharp edges with a nail file , do not cut cuticles.
  • Wash feet in lukewarm water , dry thoroughly ( including between toes) and check feet daily.
  • Shoes should be snug , but not tight , and customized if feet are misshapen or have ulcers.
  • Shocks should fit and be changed daily.

 Evaluate for Limb Ischaemia

• Obtain a history of any previous cardiovascular events and symptoms, including treatments and/or procedures.
• Inspect the limb for colour and temperature, gangrene or tissue loss and presence or absence of a peripheral pulse.
• Measure and document the ankle–brachial pressure where clinically possible and interpret the results.
• If ischemia and infection co-exist and the limb is deemed salvageable , arrange prompt specialist assessment via a tertiary Vascular Surgery service. If in doubt discuss the patient telephonically, and document the decision made.
• Be wary of performing toe amputation or transmetatrsal amputation in diabetics without foot pulses - this frequently leads to disaster with progressive necrosis; it is better to do angiography and PTA first and then amputate the toes. If such a patient is seen, discuss the management with vascular surgery team first, to review if the patient is a candidate for vascular intervention.
• Vascular surgery will not offer intervention for claudicants/ asymptomatic patients with no foot pulses – these are to be managed at district or secondary level and referred if truly incapacitated after attempts at failed conservative management.
• Vascular referral for potential revascularization is  indicated in patients with  chronic limb threatening ischaemia ( CLTI)  with  rest pain , non healing ulcers ( expect 50% reduction in wound size at 4 weeks) and gangrene that is not beyond the trans metatarsal level ie a forefoot amputation should still be possible after revascularization. The patient should be ambulant and have a reasonable life expectancy. Current smoking or poorly controlled diabetes is not a contra-indication to revascularization in limb threatening ischaemia, but outcomes will be worse. High risk patients with cardiac, renal and pulmonary conditions may still be considered for revascularization (preferably endovascular ) , but risk of mortality is higher and individual judgement will be required .
• Not all patients with CLTI deemed not to be candidates for revascularization by vascular surgery team has to receive a mandatory major limb amputation. Wound care and pain management may suffice ( especially with small wounds and limited gangrene)  with amputation for severe overwhelming infection , progressive gangrene and on request by patient for intolerable rest pain . In this scenario at least 40% of patients with gangrene and 25% with rest pain will be amputated within a year.

Local Context: Diabetic foot sepsis is the commonest reason for amputation in the Western Cape

• Diabetics have 15x increased risk for lower extremity amputation.
• Patients with diabetes are almost twice as likely to require re-amputation as patients without diabetes. Long-term mean survival is also reduced in patients with diabetes.
• The neuropathic ulcer with foot pulses is a major problem; the main therapy is "offloading" not revascularization : vascular surgery does not have a role here. Clinical services with these skills are lacking in the Metro. Referral can be done to Pinelands Orthotic and Prosthetic Centre if no local service is available in this regard.

 

What must the day hospital/GP do?	Prevention prevention prevention = education of patients, families and nursing staff, glycemic control NB+++, daily meticulous foot care. Refer septic and progressive ulceration.
What must the EC doctor do?	Evaluate the patient, initiate resuscitation if indicated, check glucose, FBC, X-ray foot, and commence antibiotics. Refer suspected septic cases to surgery without undue delay.
What must the surgery intern do?	Re-evaluate the patient, check the results of the tests, be aware of co-morbidities (CRF/ IHD/ visual impairment/ obesity/ mobility problems, etc) arrange for admission to the ward, prescribe antibiotics, IV fluids, nursing instructions, plan social support and post-operative placement in patients requiring amputation. At the time of discharge- re-counsel the patient about diabetic management, and medications, speak with the family, and give access to online resources for continuing education.
What must the surgery MO/registrar do?	Respond to the EC/DH referral promptly telephonically and in person/ evaluate the patient, provide oversight on the diagnostic investigations, decide on the indication for surgery, obtain consent, book theatre, and perform the procedure.

 

Amputations

Indications:

• To remove ischemic, infected, or necrotic tissue.
• locally unresectable tumor.
• Peripheral artery disease and diabetes are the leading causes of amputation.

Preparation:

Prior to amputation, medical, prosthetic, rehabilitation, and, potentially, psychological consultation should be obtained. Involve physiotherapy, social workers and family members to prepare for early rehabilitation and home care.

Level of the amputation

• Dictated by the extent of the disease, healing potential and rehabilitation potential of the patient.
• Palpable pulse proximal to the level of amputation is associated with a healing rate of >90% percent.
• Absence of a palpable pulse does not imply that the incision will not heal, but should be complemented by ABI, and/or tcpO2 measurements.
• Role of special investigations: Although various objective tests can supplement the clinical examination, these tests have a wide variability in their sensitivity and should not be used to replace good clinical judgement.
• Patients with uncontrolled sepsis may undergo guillotine amputation at the lowest anatomical site proximal to the sepsis, this is typically above the ankle. This will allow for a formal below or above knee amputation once the sepsis is under control.

Antibiotics-  perioperative prophylactic antibiotics are indicated.

Thromboprophylaxis is to be used for all patients undergoing major lower extremity amputation (transtibial and above). Patients undergoing major lower extremity amputation are at high risk for thromboembolism. Without prophylaxis, deep vein thrombosis has been reported in up to 50 percent of patients following major lower extremity amputation.

Complications following lower extremity amputation are common

• medical complications related to preexisting conditions
• local complications related to the surgery,stump hematoma, infection, need for repeat amputation, phantom limb syndrome and flexion contracture.

Perioperative mortality rate

• Major amputation for PVD range from 3 -18% ( related to the patient’s medical comorbidities)
• 11-18 % for AKA amputation
• 4- 9% for BKA
• 2-7% for foot amputation (total or partial).
• Mortality rates for amputation performed for nonvascular indications are lower

---

Updated: April 2023