The use of topical anesthetic cream and tape is becoming common practice for alleviating pain and decreasing the stress of percutaneous cannulation. However, relatively slow onset times (lidocaine tape, Penles® (Wyeth Lederle Japan, Tokyo, Japan) 60–120 min; local anesthetic cream, EMLA® cream 60–90 min) and variable anesthetic results remain a deterrent to widespread clinical use and patient acceptance (1–5). In addition, even following the manufacturer’s recommendations for administration, there is room for improvement in the degree of anesthesia (3). Thus, enhanced transdermal delivery of a local anesthetic by the use of electrical or physical energy (6) or skin pretreatments such as stripping with adhesive tape and cleaning with benzine that attenuate the barrier effect of the skin have been studied (7).
Hydrating or moisturizing the skin with warm steam has been used for cosmetic skin care. Also, exposing the skin to water increases its permeability (8–10). We, therefore, hypothesized that applying warm steam to the skin would enhance the effect of topically applied local anesthetics. Lidocaine tape (Penles®) is a preparation of lidocaine in the form of a self-adhesive tape for cutaneous topical anesthesia (1,2,11). The tape (30.5 × 50.0 mm) consists of a thin film backing with a lidocaine-containing hypoallergenic polymer adhesive. The polymer adhesive contains crystalline base form of lidocaine (18 mg per 12 mg polymer) at a concentration of 60%. In this study, we investigated whether skin pretreatment with a warm steamed towel could increase the effect of the local anesthetic-impregnated tape.
Phase 1 Experiment
After receiving local ethics committee approval and written informed consent, 14 healthy female volunteers were recruited in this prospective, single-blinded, randomized controlled trial. Exclusion criteria were concomitant sedative or analgesic medication, chronic pain syndrome, neurological disease, or a skin lesion at the site of local anesthetic tape placement.
The surface of both forearms was swabbed with 70% isopropyl alcohol solution to remove excess skin oils. Pretreatment was performed on one forearm by applying a steamed towel (45°C ± 2°C) for 5 min. We changed the towel at 1.5-min intervals to maintain the temperature of the skin at 45°C. No pretreatment was applied on the other forearm as a control. A coin was tossed to decide which arm to use for control. Then, lidocaine-impregnated tape (Penles®) was applied to both forearms for 30 min.
Both arms were tested for degree of anesthesia in the superficial and the deeper layer of the skin. The skin was touched 5 times with a 27-gauge needle to determine the presence or absence of pain. A score of superficial anesthesia was obtained from each volunteer by noting the number of the painful sensation of the 5 pinprick touches given (0–1 point scale for each of 5 needle touches) before the application of warm steam and after the 30 min application of the lidocaine tape (7,11,12). When a pinprick induced some pain, although attenuated, it was scored as 0.5. Degree of anesthesia in the deeper layer was tested after 30 min application of the tape. Under sterile condition, a 27-gauge needle was marked to a length of 3 mm. Then, the needle was inserted vertically in the center area of the application of the tape to a depth of the mark and the pain was scored using 10-cm visual analog scale (VAS) (0 = no pain, 10 = worst pain imaginable) (11,12). The application of a warm steamed towel and data recording were each performed blindly by separate investigators.
Phase 2 Experiment
After receiving local ethics committee approval and written informed consent, another 14 healthy female volunteers were recruited in this prospective, single-blinded, randomized controlled trial. Exclusion criteria were the same as in the phase 1 experiment.
The surface of both forearms was swabbed with isopropyl alcohol solution. In the same manner as the phase 1 experiment, pretreatment (warm steam) was performed on one forearm and no pretreatment was applied on the other forearm as a control. A coin was tossed to decide which arm to use for control. Then, placebo tape, 30.5 × 50.0 mm (Tegaderm; 3M Health Care, St. Paul, MN), was applied to both forearms for 30 min. Both arms were tested for degree of anesthesia in the superficial layer of the skin as in the phase 1 experiment.
A pilot study with 5 volunteers showed that the mean (sd) of a superficial anesthetic score after a 30 min application of the lidocaine tape was 1.9 (1.5) and 4.1 (1.1) on the steamed forearm and the untreated arm, respectively. Mean (sd) of VAS of deeper insertion was 4.1 (1.5) on the steamed arm and 6.6 (1.7) on the untreated arm. Therefore, the sample size was chosen to show a difference of 2.0 (1.5) and 2.0 (1.5) on a superficial anesthetic score and VAS score of deeper anesthesia, respectively, with a significance level of 0.01 (α = 0.01) and a power of 90% (β = 0.10). Data are presented as median (range). An anesthetic score and VAS were compared using Wilcoxon’s signed-ranks test. A P value <0.05 was considered statistically significant.
Phase 1 Experiment
The median (range) of the age, height, and weight of the volunteers were 35.5 (22–56) yr, 158.5 (151–167) cm, and 49.5 (40–70) kg. The median (range) of superficial anesthetic score was 5 (4–5) on both arms before warm steaming. After the application of the lidocaine tape, however, the score on the steamed arm was statistically lower than that on the untreated arm (median [range]: 2 [0–5] versus 4 [1–5]; P < 0.01) (Figure 1). Also, the VAS for degree of anesthesia of deeper layer was significantly smaller on the steamed arm than on the untreated arm (median [range]: 4.5 [0–8] versus 8 [2–10]; P < 0.01) (Figure 2). Pretreatment with a warm steamed towel did not cause any skin problems.
Phase 2 Experiment
The median (range) of the age, height, and weight of the volunteers were 29.5 (22–54) yr, 158 (146–169) cm, and 45.8 (38–53) kg. The median (range) of superficial anesthetic score was 5 (4–5) on both arms before warm steaming and did not change after the application of the placebo tape. Pretreatment with a warm steamed towel did not cause any problem on the skin.
The present study was not a double-blind design because the volunteers knew which side was steamed, so that there is a possibility that the subjects were biased, as pain is a subjective sensation. We therefore performed the phase 2 experiment using placebo tape. When combined with the results of the phase 2 experiment, the phase 1 experiment showed that skin pretreatment with a warm steamed towel enhanced the effect of a lidocaine-impregnated tape on anesthesia of the superficial as well as the deeper layer of the skin. In the phase 1 experiment, however, some volunteers gave an apparent exaggeration in pain scores. The insertion of a needle through the skin is painful. Painful experience leads to heightened anxiety and fear of needle insertion, “needle phobia”(3), which might have induced this exaggeration. Also, as there were no anesthetic effects of warm steaming or placebo tape, we could not determine the degree of anesthesia in the deeper layer in phase 2 experiment for ethical reasons.
Topical anesthetic cream and tape have been used for venous and arterial cannulation (2,4,5). The ideal topical local anesthetic preparation should profoundly anesthetize the skin with a rapid onset of action (3). Even following the manufacturer’s recommendation for the administration of topical anesthetic tape and cream, however, we usually experience a failure in its clinical use because application of anesthetics is short and the onset slow. Therefore, relatively slow onset times (Penles®; 60–120 minutes; EMLA® cream 60–90 minutes) remain a deterrent to widespread clinical acceptance (1–5).
The main factor modulating transdermal absorption speed is penetration of the stratum corneum, where the main route for the transdermal penetration is the intercellular matrix (3). The use of electrical energy, iontophoresis, or physical energy, ultrasound, enhances transdermal delivery of a local anesthetic through the stratum corneum (6,13,14). Also, skin pretreatments influencing stratum corneum structure, such as stripping with adhesive tape and cleaning with benzine, shorten the onset of anesthesia by dermal patch from 60 to 30–45 minutes (7).
Water disrupts the architecture of the intercellular space of the stratum corneum (9,10). The change induced by hydration can also increase the permeability of the skin and the transdermal penetration of drugs (8–10). Warm steaming provides hydration and moisture for the skin and thus the procedure has been used for cosmetic skin care. Although we did not investigate the effect of warm steaming on the stratum corneum microscopically in the present study, the enhanced anesthetic effect of a topical lidocaine tape indicated that the application of a warm steamed towel might have induced disruption of the stratum corneum structure, thereby increasing the transdermal penetration of topically applied lidocaine.
In our institutions, nurses keep steamed towels at 45°C and wipe the patient’s body with them. Before the present study, we applied warm steamed towels on the forearms of some volunteers and investigated whether this procedure induced their discomfort and any skin problem. In fact, the application of a warm steamed towel was a comfortable procedure for them and did not cause any skin problems. However, we do not exclude the possibility of thermal injury during warm steaming. Moreover, we need to assess the temperature of a steamed towel and the duration of the application according to the applied skin area because the epidermis and dermis thicknesses affect the temperature and burn injury distributions (15,16).
There are some limitations to our present study. The results obtained here may not be reproducible from other sites, such as the back of the hand, where the epidermal layer is thicker (7). Also, as observed in the present study, some patients have an apparently exaggerated response to the insertion of a needle probably because of heightened anticipatory anxiety and fear, or “needle phobia”(3). Thus, the temperature of the steamed towel and the period of the application of warm steam and lidocaine tape must be changed, depending on the region of the skin and the patients (16). Also, the nature of the pain stimuli may be different between pinprick and insertion of a fine needle versus IV cannulation. Therefore, we should investigate whether the present procedure increases the anesthetic effect of lidocaine tape on venipuncture.
In conclusion, skin pretreatment with a warm steamed towel enhanced the anesthetic effect of topical lidocaine tape. Therefore, this procedure might help to overcome the current limitations of topically applied local anesthetics and reduce the experience of pain, especially in children.
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