Efficacy of Inhaled 50% Equimolar Nitrous Oxide/Oxygen Gas Premix (Kalinox®) as Compared to Topically Administered 5% Eutectic Mixture of Lidocaine/Prilocaine (EMLA®) in Chronic Leg Ulcer Debridement

Study design: Prospective, controlled, single-center, cross-over design study. The study protocol was approved by the local ethical committee.

Study setting/participants: The study is performed in a highly specialized secondary care vein center. Patients with chronic foot and leg ulcer disease that are scheduled for repetitive ulcer debridement are eligible for the study and included into the study provided that written informed consent is obtained and no exclusion criteria are present.

Debridement procedure: For debridement, disposable sterile scalpel blades, ring curettes, and sterilized reusable scissors and forceps are used. The intended sharp mechanical debridement is proceeded as long as it is tolerated by the patient or terminated as planned. It will immediately be discontinued if the patient asks for it due to intolerable pain or discomfort.

Analgesia methods: For analgesia during debridement, either a topically administered eutectic mixture of 5% lidocaine/prilocaine (EMLA®) or an inhaled premix of 50% nitrous oxide/50% oxygen (Kalinox®) are used. The 5% lidocaine/prilocaine cream is administered as a thick layer directly onto the wound with a scoop and the wound is sealed with a polyurethane foil. After 30 minutes of exposure time, the foil is removed and debridement is started immediately. For analgesia with the inhaled 50% nitrous oxide/50% oxygen premix, the patient is asked to hold an inhalation rebreather mask with on-demand-valve tightly placed onto the face after being instructed on how to inhale the gas premix. After 3 minutes of exposure time to the gas premix, debridement is started immediately. Gas inhalation is sustained until final wound dressing is applied. During the entire procedure with each analgesia method, vital signs such as non-invasive blood pressure, heart rate and peripheral oxygen saturation (SpO2) are be recorded.

Allocation of the analgesia regimen: After study enrollment, patients are consecutively numbered starting at one. Even numbered patients have the first debridement done with topical administration of lidocaine/prilocaine cream, followed by inhaled nitrous oxide/oxygen premix for the second debridement, and again followed in an alternating way by both tested analgesia methods up to a maximum of 4 interventions. Uneven numbered patients receive inhaled nitrous oxide/oxygen premix first, followed by topical lidocaine/prilocaine cream. After 4 debridement in total with 2 sets of each analgesia method, the study period for each single patient will be secluded. A maximum of 4 data sets per patient will be brought to data analysis.