Transient hyperaemic response to assess vascular reactivity of skin: effect of locally iontophoresed acetylcholine, bradykinin, epinephrine and phenylephrine

Reevaluating the epinephrine myth: A comprehensive review

ABSTRACT

The combination of local anesthetic drugs with epinephrine has conventionally been contraindicated in acral regions due to concerns of potential necrosis caused by compromised blood flow. However, this belief has been challenged since 2001, when studies demonstrated the safety and effectiveness of the combination. This review aims to analyze reported cases of acral area necrosis following the use of local anesthesia with epinephrine since 2001. A thorough search was conducted on PubMed and Google Scholar using specific keywords to identify articles reporting acral area necrosis caused using local anesthesia and epinephrine. Our search yielded eight publications describing a total of 13 cases of ischemic events in acral areas. These cases involved finger necrosis (five cases), scrotal skin necrosis (two cases), and eyelid necrosis (six cases), following the injection of a combination of epinephrine and lignocaine. The majority of affected patients were female who underwent surgical intervention and reconstruction. The use of epinephrine in local anesthesia offers significant advantages and is generally safe for acral areas. However, the risk of necrosis cannot be entirely eliminated, particularly in patients with compromised vascular function. Adhering to proper guidelines and selecting suitable patients can help mitigate the risk. Phentolamine serves as a potential rescue agent if vascular compromise occurs. Precautionary measures must be taken when using this combination in high-risk patients.

AST-120 Improves Microvascular Endothelial Dysfunction in End-Stage Renal Disease Patients Receiving Hemodialysis

PURPOSE

Endothelial dysfunction (ED) is a pivotal phenomenon in the development of cardiovascular disease (CVD) in patients receiving hemodialysis (HD). Indoxyl sulfate (IS) is a known uremic toxin that induces ED in patients with chronic kidney disease. The aim of this study was to investigate whether AST-120, an absorbent of IS, improves microvascular or macrovascular ED in HD patients.

MATERIALS AND METHODS

We conducted a prospective, case-controlled trial. Fourteen patients each were enrolled in respective AST-120 and control groups. The subjects in the AST-120 group were treated with AST-120 (6 g/day) for 6 months. Microvascular function was assessed by laser Doppler flowmetry using iontophoresis of acetylcholine (Ach) and sodium nitroprusside (SNP) at baseline and again at 3 and 6 months. Carotid arterial intima-media thickness (cIMT) and flow-mediated vasodilation were measured at baseline and 6 months. The Wilcoxon rank test was used to compare values before and after AST-120 treatment.

RESULTS

Ach-induced iontophoresis (endothelium-dependent response) was dramatically ameliorated at 3 months and 6 months in the AST-120 group. SNP-induced response showed delayed improvement only at 6 months in the AST-120 group. The IS level was decreased at 3 months in the AST-120 group, but remained stable thereafter. cIMT was significantly reduced after AST-120 treatment. No significant complications in patients taking AST-120 were reported.

CONCLUSION

AST-120 ameliorated microvascular ED and cIMT in HD patients. A randomized study including a larger population will be required to establish a definitive role of AST-120 as a preventive medication for CVD in HD patients.

Non-Invasive Measurement of Skin Microvascular Response during Pharmacological and Physiological Provocations

Introduction

Microvascular changes in the skin due to pharmacological and physiological provocations can be used as a marker for vascular function. While laser Doppler flowmetry (LDF) has been used extensively for measurement of skin microvascular responses, Laser Speckle Contrast Imaging (LSCI) and Tissue Viability Imaging (TiVi) are novel imaging techniques. TiVi measures red blood cell concentration, while LDF and LSCI measure perfusion. Therefore, the aim of this study was to compare responses to provocations in the skin using these different techniques.

Method

Changes in skin microcirculation were measured in healthy subjects during (1) iontophoresis of sodium nitroprusside (SNP) and noradrenaline (NA), (2) local heating and (3) post-occlusive reactive hyperemia (PORH) using LDF, LSCI and TiVi.

Results

Iontophoresis of SNP increased perfusion (LSCI: baseline 40.9±6.2 PU; 10-min 100±25 PU; p<0.001) and RBC concentration (TiVi: baseline 119±18; 10-min 150±41 AU; p = 0.011). No change in perfusion (LSCI) was observed after iontophoresis of NA (baseline 38.0±4.4 PU; 10-min 38.9±5.0 PU; p = 0.64), while RBC concentration decreased (TiVi: baseline 59.6±11.8 AU; 10-min 54.4±13.3 AU; p = 0.021). Local heating increased perfusion (LDF: baseline 8.8±3.6 PU; max 112±55 PU; p<0.001, LSCI: baseline 50.8±8.0 PU; max 151±22 PU; p<0.001) and RBC concentration (TiVi: baseline 49.2±32.9 AU; max 99.3±28.3 AU; p<0.001). After 5 minutes of forearm occlusion with prior exsanguination, a decrease was seen in perfusion (LDF: p = 0.027; LSCI: p<0.001) and in RBC concentration (p = 0.045). Only LSCI showed a significant decrease in perfusion after 5 minutes of occlusion without prior exsanguination (p<0.001). Coefficients of variation were lower for LSCI and TiVi compared to LDF for most responses.

Conclusion

LSCI is more sensitive than TiVi for measuring microvascular changes during SNP-induced vasodilatation and forearm occlusion. TiVi is more sensitive to noradrenaline-induced vasoconstriction. LSCI and TiVi show lower inter-subject variability than LDF. These findings are important to consider when choosing measurement techniques for studying skin microvascular responses.

Age-associated induction of cell membrane CD47 limits basal and temperature-induced changes in cutaneous blood flow

OBJECTIVE

We tested the hypothesis that the matricellular protein thrombospondin-1 (TSP1), through binding to and activation of the cell receptor CD47, inhibits basal and thermal-mediated cutaneous blood flow.

BACKGROUND

Abnormal and decreased cutaneous blood flow in response to temperature changes or vasoactive agents is a feature of cardiovascular disease and aging. The reasons for decreased cutaneous blood flow remain incompletely understood. Furthermore, a role for matricellular proteins in the regulation skin blood flow has never been proposed.

METHODS

C57BL/6 wild type, TSP1-null, and CD47-null 12- and 72-week-old male mice underwent analysis of skin blood flow (SkBF) via laser Doppler in response to thermal stress and vasoactive challenge.

RESULTS

Young and aged TSP1- and CD47-null mice displayed enhanced basal and thermal sensitive SkBF changes compared with age-matched wild type controls. Nitric oxide-mediated increases in SkBF were also greater in null mice. TSP1 and CD47 were expressed in skin from young wild type mice, and both were significantly upregulated in aged animals. Tissue 3',5'-cyclic guanosine monophosphate, a potent vasodilator, was greater in skin samples from null mice compared with wild type regardless of age. Finally, treating wild type animals with a CD47 monoclonal antibody that inhibits TSP1 activation of CD47 enhanced SkBF in both young and aged animals.

CONCLUSIONS

These results suggest that secreted TSP1, via its cognate receptor CD47, acutely modulates SkBF. These data further support therapeutically targeting CD47 to mitigate age-associated loss of SkBF and maximize wound healing.

Association between endothelial dysfunction and acute brain dysfunction during critical illness

BACKGROUND

Acute brain dysfunction (delirium and coma) during critical illness is prevalent and costly, but the pathophysiology remains unclear. The relationship of acute brain dysfunction with endothelial function, which is impaired in critical illness and may contribute to alterations in cerebral blood flow and blood-brain barrier permeability, has not been studied. This study sought to determine whether systemic endothelial dysfunction is associated with acute brain dysfunction during critical illness.

METHODS

In this prospective cohort study, adult medical/surgical intensive care unit patients in shock and/or respiratory failure were enrolled. Endothelial function was assessed at enrollment using peripheral artery tonometry to calculate the reactive hyperemia index, with lower reactive hyperemia index indicative of worse endothelial function. Patients were assessed for coma and delirium with the Richmond Agitation-Sedation Scale and Confusion Assessment Method for the Intensive Care Unit. Multivariable linear regression was used to analyze the association between reactive hyperemia index and (1) delirium/coma-free days among all patients and (2) delirium duration among survivors, both over a 14-day period.

RESULTS

One hundred forty-seven patients with median age of 57 yr and median Acute Physiology and Chronic Health Evaluation II score of 26 were enrolled. After adjusting for age, severity of illness, severe sepsis, preexisting cognitive function, medical versus surgical intensive care unit admission, and prehospital statin use, lower reactive hyperemia index (worse systemic endothelial function) was associated with fewer delirium/coma-free days (P = 0.02) and more delirium days (P = 0.05).

CONCLUSIONS

In this study, critically ill patients with lower vascular reactivity indicative of worse systemic endothelial function had increased duration of acute brain dysfunction.

Characterisation and mechanisms of bradykinin-evoked pain in man using iontophoresis

Bradykinin (BK) is an inflammatory mediator that can evoke oedema and vasodilatation, and is a potent algogen signalling via the B1 and B2 G-protein coupled receptors. In naïve skin, BK is effective via constitutively expressed B2 receptors (B2R), while B1 receptors (B1R) are purported to be upregulated by inflammation. The aim of this investigation was to optimise BK delivery to investigate the algesic effects of BK and how these are modulated by inflammation. BK iontophoresis evoked dose- and temperature-dependent pain and neurogenic erythema, as well as thermal and mechanical hyperalgesia (P < 0.001 vs saline control). To differentiate the direct effects of BK from indirect effects mediated by histamine released from mast cells (MCs), skin was pretreated with compound 4880 to degranulate the MCs prior to BK challenge. The early phase of BK-evoked pain was reduced in degranulated skin (P < 0.001), while thermal and mechanical sensitisation, wheal, and flare were still evident. In contrast to BK, the B1R selective agonist des-Arg9-BK failed to induce pain or sensitise naïve skin. However, following skin inflammation induced by ultraviolet B irradiation, this compound produced a robust pain response. We have optimised a versatile experimental model by which BK and its analogues can be administered to human skin. We have found that there is an early phase of BK-induced pain which partly depends on the release of inflammatory mediators by MCs; however, subsequent hyperalgesia is not dependent on MC degranulation. In naïve skin, B2R signaling predominates, however, cutaneous inflammation results in enhanced B1R responses.

The effect of a new topical local anaesthetic delivery system on forearm skin blood flow reactivity

Different topical local anaesthetics have varying effects on skin blood flow and vascular reactivity. We compared the vasoactive properties of Rapydan, a new topical local anaesthetic, with those of Ametop and EMLA creams in 20 healthy volunteers. Blood flow and vascular reactivity in the forearm skin were assessed by laser Doppler flowmetry and the transient hyperaemic response ratio respectively, before and after the application of EMLA (for 60 min), Ametop (for 30 and 60 min) and Rapydan (for 30 min). Application of EMLA had no effect on skin blood flow (median (IQR [range]) change from baseline -0.9% (-63 to 414 [-38.5 to 51.3] %, p = 1.0)) or mean (SD) transient hyperaemic response ratio (from 2.86 (0.86) to 3.17 (1.3), p = 0.38). The application of Ametop for 60 min produced a greater median (IQR [range]) increase in blood flow from baseline (508 (-55 to 998 [148-649]) %) than Rapydan applied for 30 min 160 (-77 to 997 [45-301]) %, p = 0.001), and a similar decrease in mean (SD) transient hyperaemic response ratio (from 2.69 (1.16) to 1.08 (0.26) and from 2.83 (0.84) to 1.49 (0.93) respectively, p = 0.57).

Differential hypertrophy and atrophy among all types of cutaneous innervation in the glabrous skin of the monkey hand during aging and naturally occurring type 2 diabetes

Diabetic neuropathy (DN) is a common severe complication of type 2 diabetes. The symptoms of chronic pain, tingling, and numbness are generally attributed to small fiber dysfunction. However, little is known about the pathology among innervation to distal extremities, where symptoms start earliest and are most severe, and where the innervation density is the highest and includes a wide variety of large fiber sensory endings. Our study assessed the immunochemistry, morphology, and density of the nonvascular innervation in glabrous skin from the hands of aged nondiabetic rhesus monkeys and from age-matched monkeys that had different durations of spontaneously occurring type 2 diabetes. Age-related reductions occurred among all types of innervation, with epidermal C-fiber endings preferentially diminishing earlier than presumptive Adelta-fiber endings. In diabetic monkeys epidermal innervation density diminished faster, became more unevenly distributed, and lost immunodetectable expression of calcitonin gene-related peptide and capsaicin receptors, TrpV1. Pacinian corpuscles also deteriorated. However, during the first few years of hyperglycemia, a surprising hypertrophy occurred among terminal arbors of remaining epidermal endings. Hypertrophy also occurred among Meissner corpuscles and Merkel endings supplied by Abeta fibers. After longer-term hyperglycemia, Meissner corpuscle hypertrophy declined but the number of corpuscles remained higher than in age-matched nondiabetics. However, the diabetic Meissner corpuscles had an abnormal structure and immunochemistry. In contrast, the expanded Merkel innervation was reduced to age-matched nondiabetic levels. These results indicate that transient phases of substantial innervation remodeling occur during the progression of diabetes, with differential increases and decreases occurring among the varieties of innervation.

Bradykinin is a potent pruritogen in atopic dermatitis: a switch from pain to itch

Histamine, substance P, serotonin and bradykinin were applied by iontophoresis to lesional and visually non-lesional skin of 14 patients with atopic dermatitis, and normal skin of 15 healthy volunteers. Itch could be evoked by light stroking of skin with a cotton swab (alloknesis) in all lesional skin sites, but not in non-lesional or normal skin. Substances were applied in the same skin area before and 3 h after administration of placebo or antihistamine (olopatadine hydrochloride: H1-receptor-blocker). Intensities of itch and pain sensation and areas of flare and wheal were measured. All the substances induced significantly more intense itch in lesional skin than in non-lesional skin of patients. Even bradykinin, which evoked only weak itch and pain of similar intensities in non-lesional skin of patients and in healthy volunteers, induced intense itch in lesional skin, while the simultaneously increased pain did not suppress the itch sensation, indicating central sensitization. Histamine- and substance P-induced itch was almost completely suppressed by antihistamines, whereas bradykinin- and serotonin-induced itch was not. This suggests that substance P is a histamine-dependent pruritogen also in lesional skin under sensitized conditions but that bradykinin and serotonin are histamine-independent pruritogens in lesional skin. It is concluded that serotonin and bradykinin, classic endogenous algogens, can turn into potent histamine-independent pruritogens in lesional skin of atopic dermatitis.

Digital anesthesia with epinephrine: an old myth revisited

BACKGROUND

The prohibition against the use epinephrine with local anesthetics for digital blocks or infiltrative anesthesia is an established dogma in dermatologic surgery. Major textbooks reinforce this teaching suggesting that there is substantial risk of digital gangrene caused by local anesthesia containing epinephrine.

OBJECTIVE

To provide a comprehensive literature review of the cases of digital necrosis associated with the use of local anesthesia containing epinephrine.

METHODS

A PubMed search of the National Library of Medicine database using the terms "lidocaine" and "epinephrine" and "finger" with no specified limits was performed.

RESULTS

A total of 16 papers were referenced and only 6 papers dealt with digital anesthesia. A total of 50 cases of digital gangrene were reported, mostly in the early part of the 20th century. In 21 cases digital gangrene was associated with anesthetic mixed with epinephrine. Actual concentration of epinephrine was known in only 4 cases. Careful analysis of all cases of necrosis did not support epinephrine itself as a cause. Other contributing factors including older compounds (cocaine, eukaine, and procaine), non-standardized inaccurate methods of mixing epinephrine with lidocaine, inappropriate use of a tourniquet, postoperative hot soaks, infection, or large anesthetic volume were also present. None of the reported cases were associated with the use of a commercial lidocaine-epinephrine mixture.

CONCLUSION

A literature review failed to provide evidence to support the dogma that block or infiltrative anesthesia with lidocaine and epinephrine produces digital necrosis. Proper injection technique and adequate selection of patients (absence of thrombotic, vasospastic conditions, or uncontrolled hypertension) are mandatory to minimize complications. The addition of epinephrine, in fact, reduces the need for the use of tourniquets and large volumes of anesthetic and provides better and longer pain control during digital procedures.

The effect of glucose and mental stress on cutaneous microvascular endothelial function

Glucose and mental stress, independently, have been found to impair arterial endothelial function (an indicator of vascular health). The present study sought to determine whether the combination of glucose and stress would have a greater effect on microvascular endothelial function than each on its own. To assess endothelial function, surges in skin blood flow (reactive hyperemia), following the release of cuff pressure to the upper arm at 200 mmHg for 5 min, were measured with laser Doppler flowmetry in 40 young, healthy females. Endothelial function did not change significantly following a 5-min mathematics stressor or the consumption of 75 g of glucose. However, the combination of glucose and stress impaired endothelium-dependent dilatation 30 min after glucose consumption. These findings suggest that combinations of vascular risk factors may be more threatening to cardiovascular health than singularly occurring factors.

Non-selective and cyclo-oxygenase-2-specific non-steroidal anti-inflammatory drugs impair the hyperaemic response of skin to brief axillary artery occlusion

BACKGROUND

Cyclo-oxygenase-2 (COX-2)-specific inhibitors are marketed as safer analgesics than non-selective non-steroidal anti-inflammatory drugs. However, there has been conflicting evidence concerning endothelial function and cardiovascular risk after COX-2 inhibitor use. We investigated forearm skin vascular reactivity to brief axillary artery occlusion in healthy volunteers after a single dose of the non-steroidal anti-inflammatory drugs ibuprofen (non-selective) and rofecoxib (COX-2 specific).

METHODS

Ten healthy male volunteers were studied. Forearm skin blood flow was measured using laser Doppler flowmetry. Two non-invasive probes were placed on the volar surface of the forearm. The magnitude of hyperaemic response to brief (20 s) and prolonged (5 min) occlusion of the axillary artery was measured before and 2-3 h after administration of ibuprofen 800 mg or rofecoxib 25 mg. The transient hyperaemic response ratio (THRR), defined as the net peak hyperaemic flow-flux divided by the net baseline flow-flux, was calculated. Each volunteer received both drugs in random order at least 1 week apart.

RESULTS

Ibuprofen and rofecoxib increased net baseline blood flow (median (range): ibuprofen, from 23.3 (12.1-40.8) to 31.5 (17.4-77.3); rofecoxib, from 22.0 (14.6-41.0) to 29.9 (19.5-112.0); P<0.01). The net hyperaemic peak flow-flux after brief and prolonged occlusion was unchanged after both drugs. THRR was reduced by both drugs (ibuprofen, from 2.92 (2.38-3.86) to 2.09 (1.45-3.54); rofecoxib, from 3.36 (2.06-5.16) to 2.67 (1.15 -3.84); P<0.01).

CONCLUSIONS

Both COX-2 and non-selective non-steroidal anti-inflammatory drugs, when given to healthy volunteers as single therapeutic doses, decrease skin microvascular tone but do not impair maximal vasodilatory ability.