Superficial anesthesia

Topical anesthesia Local use of drugs of this kind on the mucous membranes of the nose, mouth, larynx, tracheobrachial tree, eyes, urinary tract, and gastrointestinal tract causes superficial anesthesia. 

The topical use of anesthetic agents before injection may produce superficial anesthesia. They are also of value in taking impressions or intraoral radiographs in patients with an excessive gag reflex. 

Local infiltration anesthesia is die injection of a local anesthetic druginto tissues. This type of anesfliesia may be used for dental procedures, die suturing of small wounds, or making an incision into a small area, such as that required for removing a superficial piece of tissue for biopsy. 

EC-IC arterial bypass involves the use of general anesthesia, open craniotomy, and end-to-side anastomosis of the superficial temporal artery to a branch of the middle cerebral artery (MCA) (Fig. 6.1). Currently, this technique is being used primarily in the setting of intracranial aneurysm therapy, moyamoya disease, and... 

Ketamine is a cyclohexanone derivative whose pharmacological actions are quite different from those of the other IV anesthetics. The state of unconsciousness it produces is trancelike (i.e., eyes may remain open until deep anesthesia is obtained) and cataleptic it has frequently been characterized as dissociative (i.e., the patient may appear awake and reactive but does not respond to sensory stimuli). The term dissociative anesthesia is used to describe these qualities of profound analgesia, amnesia, and superficial level of sleep. 

Recovery is sufficiently rapid with most intravenous drugs to permit their use for short ambulatory (outpatient) surgical procedures. In the case of propofol, recovery times are similar to those seen with sevoflurane and desflurane. Although most intravenous anesthetics lack antinociceptive (analgesic) properties, their potency is adequate for short superficial surgical procedures when combined with nitrous oxide or local anesthetics, or both. Adjunctive use of potent opioids (eg, fentanyl, sufentanil or remifentanil see Chapter 31) contributes to improved cardiovascular stability, enhanced sedation, and perioperative analgesia. However, opioid compounds also enhance the ventilatory depressant effects of the intravenous agents and increase postoperative emesis. Benzodiazepines (eg, midazolam, diazepam) have a slower onset and slower recovery than the barbiturates or propofol and are rarely used for induction of anesthesia. However, preanesthetic administration of benzodiazepines (eg, midazolam) can be used to provide anxiolysis, sedation, and amnesia when used as part of an inhalational, intravenous, or balanced anesthetic technique. 

Infiltration anesthesia is the injection of local anesthetic directly into tissue without taking into consideration the course of cutaneous nerves. Infiltration anesthesia can be so superficial as to include only the skin. It also can include deeper structures such as intra-abdominal organs when these too are infiltrated. The advantage of infiltration anesthesia and other regional anesthetic techniques is that it is possible to provide satisfactory anesthesia without disruption of normal bodily functions. 

Tetracaine, an ester of para-aminobenzoic acid (PABA), has been widely used for topical anesthesia of the eye. It is currently available in a 0.5% solution. Its onset, intensity, and duration of anesthesia are comparable with those of proparacaine and benoxinate (Figure 6-2). Onset of anesthesia sufficient to permit tonometry or other minor procedures involving the superficial cornea and conjimc-tiva is 10 to 20 seconds, and duration of anesthesia is 10 to 20 minutes. It has been reported, however, that the 1% solution produces anesthesia lasting nearly an hour. Tetracaine 1% has also been used successfully to provide anesthesia during phacoemulsification cataract surgery and intraocular lens implantation. 

Patients with a reported history of allergic responses to ester and amide anesthetics pose a challenge, especially when regional anesthesia is necessary. Two alternatives may be considered when minor ophthalmic surgical procedures are performed. A 1% solution of diphenhydramine may be prepared by diluting the 5% solution (Benadryl Steri-Vials) with sterile saline. Additionally, injecting preserved sterile saline alone has been shown to be effective for superficial surgical procedures such as papilloma removal and shave biopsies. 

The excision of small superficial conjimctival lesions, such as concretions, can usually be achieved with topical anesthesia alone.Two or three drops instilled at 1-minute intervals allow sufficient anesthesia for this purpose. Alternatively, a cotton pledget or cotton-tipped applicator soaked in anesthetic solution may be applied for 1 to 2 minutes before surgery.This local application allows anesthesia of deeper portions of the conjimctiva. 

Dry eyes have been reported after the systemic or ocular use of timolol (360). A sensation of dryness in the eyes can develop and is usually transitory. There can be a reduction in the Schirmer test and tear film break-up time. Symptomatic superficial punctate keratitis in association with complete corneal anesthesia has been observed (361). 

The topical anesthetics in general use in the horse are 0.5% proxymetacaine (proparacaine) and 0.5% tetracaine (amethocaine). The rate of onset and duration of clinical anesthesia of the ocular surfaces using these agents in the horse is not known. However, in general, repeated instillations at 30-60 s intervals over a 5 min period will superficially desensitize the normal eye for around 15 min. In the presence of conjunctival hyperemia, there is likely to be accelerated loss of the drug into the systemic circulation and instillation of the anaesthetic agent at shorter intervals for a longer period may be necessary to desensitize the ocular surfaces effectively. 

Inhalation and ingestion are harmful and may be fatal. The major effect from acute inhalation is CNS depression. It produces dizziness, tiredness, headache at lower concentrations (<1500 ppm), anesthesia in the range of 1500-3000 ppm, and may cause death at high levels (e.g., 40 000 ppm). A dose of 10 ml (14.8 g) of chloroform can cause CNS depression and death due to respiratory and cardiac arrest. The oral lethal dose is estimated to be between 0.5 and 5gkg (loz to 1 pint) for an average 70 kg man. Short-term inhalation of chloroform at 900 ppm can cause dizziness, fatigue, and headache. Skin contact may result in irritation and redness and high levels can cause sores. Eye contact with liquid chloroform may result in painful irritation of the superficial eye structures, burns, and may cause corneal necrosis and ulcers. 

This depth of abrasion provides only low-quality topical anesthesia and the peel itself will be painful and too superficial. 

Objectively the keratinocyte touch is still negative -although the fingers can be felt to brake slightly as they slide from the healthy zone to the abraded zone, they still slide easily over the skin. Grade 1 sandpaper abrasion does not provide adequate topical anesthesia, and the peel is still painful and too superficial. 

Lidocaine hydrochloride is a topical/local anesthetic preparation. It stabilizes neuronal membranes by inhibiting the ionic fluxes required for the initiation and conduction of impulses, thereby affecting local anesthetic action. It is indicated as a topical anesthetic for use on normal intact skin for local analgesia or genital mucous membranes for superficial minor surgery and as pretreatment for inhltration anesthesia... 

The introduction of a eutectic mixture of lidocaine (2.5%) and prilocaine (2.5%) (EMLa) bridges the gap between topical and infiltration anesthesia. The efficacy of this combination lies in the fact that the mixture of prilocaine and lidocaine has a melting point less than that of either compound alone, existing at room temperature as an oil that can penetrate intact skin. EMLA cream produces anesthesia to a maximum depth of 5 mm and is applied as a cream on intact skin under an occlusive dressing, for procedures involving skin and superficial subcutaneous structures (e.g., venipuncture and skin graft harvesting). EMLA must not be used on mucous membranes or abraded skin, as rapid absorption across these surfaces may result in systemic toxicity. 

ABSORPTION, FATE, AND EXCRETION For sedative-hypnotic use, the barbiturates usually are administered orally (Table 16-3) absorption is rapid and nearly complete. The onset of action varies from 10-60 minutes, depending on the agent and the formulation, and is delayed by the presence of food in the stomach. When necessary, intramuscular injections of solutions of the sodium salts should be placed deeply into large muscles to avoid the pain and possible necrosis that can result at more superficial sites. The intravenous route usually is reserved for the management of status epilepticus (phenobarbital sodium) or for the induction and/or maintenance of general anesthesia (e.g., thiopental or methohexital). 

EMLA is a eutectic mbcture of 2.5% lidocaine and 2.5% prilocaine, which, when mbced, form a liquid that is formulated into a water-oil emulsion. EMLA is available as a cream, a gel and an anesthetic disc. Only the cream and gel are available in the USA. The cream is approved for use on intact skin for local anesthesia or genital mucosa for superficial minor surgery and as pretreatment for infiltration anesthesia. The gel is approved for adults who require localized anesthesia in periodontal pockets during scaling and/or root planning [1]. 

The back was shaved, taking care to avoid superficial and deep lesions on the skin. All rats underwent anesthesia by an intramuscular injection of 30 mg/kg of ketamine. It was decided to use 0.5 mL of hydrochloric acid (52 %) applied on the back of the rats for 15 s in a circular area of 2 cm in diameter (Fig. 4.46). 

Sensory systems Topical ocular anesthesia abuse is often misdiagnosed as acanthamoeba keratitis (a parasitic disease) and early identification to prevent ocular complications including superficial pxmctate keratitis, persistent epithelial defects, stromal/ring infiltrates, comeal oedema, endothelial damage and ocular inflammation is important. Local anesthetics may cause direct toxicity to the comeal epithelium, stroma and endothelium. Preservatives in the anesthetics may also contribute to toxicity. Patient demographics may include a health care association and/or psychiatric illness [25 ]. Evisceration of the eye after persistent topical anesthetic use has been described [26 ]. 

Anesthesia is not required for superficial chemical peelings. Mild tranquilizers can be used in very anxious patient in medium-depth and deep peelings. 

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