Clinical Practice
The Diabetic Foot Ulcer: Hyperbaric Oxygen Therapy in the Treatment
of Refractory Ulcers
By Richard Belley and François Paquet
About the Authors
Richard Belley, MD, CCMF, B.Sc. and François Paquet, MD, CMFC (MU),
CSPQ practice at the Centre for Complex Wounds and the Diabetic Foot Clinic,
Hyperbaric Medicine Service, University Medical Centre affiliated to Hôtel-Dieu
de Lévis.
In Canada, 1.5 to 2 million people are diabetic; this represents about
5% of the population.1,2 The complications of diabetes are varied and
affect several organs. Peripheral neuropathy is the major cause of diabetic
ulcers with all their associated economic, social and psychological consequences.11
Between 5 and 15% 8,9 of diabetic patients will eventually
develop a foot ulcer.2,3 These ulcers are responsible for 85% of lower
limb amputations, diabetes remaining the single most important cause of
lower limb amputations.3,8,9
The purpose of this article is to examine in greater detail an adjunctive
therapy for refractory diabetic ulcers, hyperbaric oxygen therapy, a therapeutic
approach that can be combined with the standard treatment. The experience
gained in our community has helped us to better identify, assess and treat
diabetic ulcers by combining hyperbaric oxygen therapy with standard treatments.
First and foremost, we must remember that basic care is the cornerstone
of any treatment approach to diabetic ulcers. It is therefore essential
to put emphasis on the need to adhere strongly to basic principles so
that each complex wound clinic can optimally control each factor that
can be related to a delay in healing.3,5,6,9,10 One single
oversight will make us waste a lot of time. That's why the general message
to convey should be "No small wound is minor on a diabetic foot."
Vascular assessment prior to hyperbaric oxygen therapy (HBOT)
Despite our best efforts, it often happens that the status of the wound
fails to improve while we are unable to determine the uncontrolled factor.
It is no longer necessary to demonstrate the macro and microvascular circulatory
impairment in the diabetic patients process.2,3 During
the investigation to find out the status of the vessels, the vascular
laboratory is the first step (after the measure of the ankle/arm index)
to assess the peripheral vascular failure of the lower limb. The vascular
laboratory includes the measure of segmental pressures in the leg and
the use of Doppler. However, the results are often falsely reassuring
or difficult to interpret, mainly because of the non-compressibility of
the calcified arteries in the diabetic patient. We must remember that
the initial diagnostic assessment in a clinic should start by the measure
of the ankle/arm index. In the literature, it is understood that an index
lower than 0.6 suggests a more severe distal peripheral disease2,3;
however, it is possible that the result is biased as we have just mentioned.
So, more tests can be done to check the presence and the extent of the
disease before proceeding to a more extensive assessment such as angiography;
they include measures of the toe pressure, transcutaneous measures of
the partial oxygen pressure (PtcO2) and Duplex measures.
Although little investigation by transcutaneous oxymetry is available
in Quebec, it evaluates the vascularization and the perfusion on a microvascular
level. Consultation with a vascular surgeon becomes relevant if significant
abnormalities in the physical or laboratory results are observed. The
transcutaneous oxymetry laboratory allows us to give examples of following
results:
- Normal values are greater than 50 mm Hg.16,17
- Values of 35 to 40 mm Hg are considered sufficient to ensure adequate
healing in terms of oxygen intake.17,18,21,23,24
- A PtcO2 value lower than 20 mm Hg indicates a 39-fold risk of non-healing.15,21,24
- Patients who had an amputation with PtcO2 values > 40 mm Hg have
a good healing rate, from 20 to 40 mm Hg a more difficult healing and
< 20 mm Hg a poor rate of healing.22,24,25
- Diabetic patients with PtcO2 values > 30 mm Hg at the trans-metatarsal
level have a healing potential 8 times greater than those with values
< 30 mm Hg.3,24
The arteriography of the lower limb still remains the gold standard in
the assessment of the arterial system, especially when surgery is considered.
However, this examination is quite invasive and its use is limited by
the risk of acute renal failure secondary to the injection of a contrast
medium in this type of patients who often have some degree of nephropathy.
Another advantage of arteriography is the possibility of performing an
angioplasty when deemed necessary. The RMI and the new generations of
computerized axial tomography (CAT scans) can also be used to assess,
up to some extent, the arterial tree of the lower limb, the angio-RMI
having the advantage of using gadolinium, a contrast medium having no
or very little nephrotoxicity.
Treatment
The treatment of a diabetic foot ulcer may seem simple at first, but it
is shown to be very close to an art based on a multidisciplinary team
with expertise in wound care. It must be kept in mind that the wound frequently
becomes chronic in this category of patients and this significantly increases
the risk of infection, osteomyelitis, or ultimately amputation.
The general principles of wound care are:
1) controlling the pain,3
2) removing dead tissues from the wound by an appropriate method of debridement;
3) controlling the humidity and the environment by an appropriate dressing;
4) eliminating weight-bearing on the wound;10,12
5) treating the infection if necessary;
6) establishing an appropriate frequency for the follow-up and the changing
of dressings with the home care nursing personnel (through the CLSC) and
the wound care physician.13
Of course, before doing anything else, the vascular problem must be solved
either by surgery (bypass) or by angioplasty. Similarly, a wound with
a delay in healing and an oxymetry showing an ischemia without the possibility
of revascularization could possibly benefit from hyperbaric oxygen therapy.
Hyperbaric oxygen therapy (HBOT)
Hyperbaric oxygen therapy is the administration of 100% oxygen in a pressurized
environment. This treatment remains physiologically attractive because
of the increase of tissue oxygenation. Since the haemoglobin cannot carry
more than four oxygen molecules by molecule, the total carried oxygen
is a maximum of 20.4 mL of oxygen per 100 mL of blood in ambient air.
The dissolved oxygen part in plasma is only 0.31 mL of oxygen per 100
ml of blood plasma. However, under hyperbaric environment, it is possible
to achieve rates of 5.2 mL of oxygen per 100 mL of blood at 2.4 ATA (absolute
atmosphere), which is the treatment level most often used. Those levels
make it possible to reach tissue oxygen rates that are sufficient to resume
the healing process in selected patients where a local tissue ischemia
remains the main reason for non-healing. For example, in the transcutaneous
oxymetry laboratory, we see patients with distal values lower than 10
mm Hg that increase under hyperbaric conditions to more than 200 mm Hg.
It is known that one of the main factors in stimulating the fibroblasts
to produce collagen is an oxygen rich environment; this is one of the
reasons that may explain the improvement observed in these patients.25
In short, the main factors related to hyperbaric oxygen therapy that
showed an effect are the following:24,25,26,27,28,29,30,31
- Intermittent correction of tissue hypoxia;
- Reduction of local edema by local vasoconstriction. What's most important
is maintaining a capacity to deliver oxygen to tissues greater than
it would be without hyperbaric oxygen therapy;
- Increase of host response:
- Increase of macrophage response in the phagocytosis process;
- Direct effect of oxygen on anaerobic bacteria;
- Suppression of exotoxin production by certain types of bacteria;
- Increase of ulcer metabolism:
- Increase of fibroblast replication and collagen synthesis;
- Epithelialization;
- Prevention of negative impacts related to reperfusion (reperfusion
injury), a leucocyte-mediated process;
- Induction of cytokine receptors and cytokinine:
- Angiogenesis;
- Increase of osteoclast and osteoblast function.
Several articles demonstrated the clinical impact of these pathophysiological
notions.17,26,27,28,29,30,31,32 Finally, we must remember
that hyperbaric oxygen therapy will never replace basic wound care.
While we can see in our clinic of complex wounds more than 500 new patients
per year suffering from a diabetic foot ulcer, approximately less than
one out of 50 patients is eligible to treatments by hyperbaric oxygen
therapy.
To complete this information, we suggest the excellent article, about
the diabetic foot, written by Inlow S, Orsted H and Sibbald G, which can
be found on the CAWC Website (www.cawc.net).
References
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