Contact anesthetics

HEALTH SYMPTOMS inhalation (dizziness, headache, nausea, asphyxia, lowering of consciousness, irritates respiratory tract) contact (anesthetic effects, liquid may cause frostbite)... 

Olefins, Diolefins, and Acetylenes. Members of this category having up to four carbon atoms are both asphyxiants and anesthetics, and potency for the latter effect increases with carbon chain length. Skin-contact effects are similar to those of paraffins. 

Propylene is a colorless gas under normal conditions, has anesthetic properties at high concentrations, and can cause asphyxiation. It does not irritate the eyes and its odor is characteristic of olefins. Propjiene is a flammable gas under normal atmospheric conditions. Vapor-cloud formation from Hquid or vapor leaks is the main ha2ard that can lead to explosion. The autoignition temperature is 731 K in air and 696 K in oxygen (80). Evaporation of Hquid propylene can cause skin bums. Propylene also reacts vigorously with oxidising materials. Under unusual conditions, eg, 96.8 MPa (995 atm) and 600 K, it explodes. It reacts violentiy with NO2, N2O4, and N2O (81). Explosions have been reported when Hquid propylene contacts water at 315—348 K (82). Table 8 shows the ratio TJTp where is the initial water temperature, and T is the superheat limit temperature of the hydrocarbon. 

In the past, chloroform was used extensively as a surgical anesthetic, but this use was abandoned because exposure to narcotic concentrations often resulted in sudden death from effects on the heart and circulation or from severe injury to the Hver. In addition, chloroform for this and other consumer uses was harmed by FDA in 1976 with the discovery that it is carcinogenic in mice (38). When splashed into the eye, chloroform causes local pain and irritation, but serious injury is not expected. Skin contact for single, brief exposures ordinarily causes Htde or no local irritation. 

Thyssen JP. Menne T. Elberberg J. Plaschke P, 16 Johansen D Hypersensitivity to local anesthetics -update and proposal of evaluation algorithm. Contact Dermatitis 2008 59 69-78. 17... 

Breit S, Rueff F, PrzybiUa B Deep impact contact allergy after subcutaneous injection of local anesthetics. Contact Dermatitis 2001 45 296-297. Orasch CE, Helbling A, Zanni MP, Yawalkar N. Hari Y Pichler WJ T-cell reaction to local anaesthetics relationship to angioedema and urticaria after subcutaneous application-patch testing and LTT in patients with adverse reaction to local anaesthetics. Clin Exp Allergy 1999 29 1549-1554. 

Monophasic Action Potential in Anesthetized Guinea Pigs. Epicardia monophasic action potential recording using suction/contact pressure electrodes are emplaced, allowing simultaneous measurement of ECG and heartrate. 

Phenol can have beneficial effects when used for medical reasons. It is an antiseptic (kills germs) when applied to the skin in small amounts and may have antiseptic properties when gargled as a mouthwash. It is an anesthetic (relieves pain) and is a component of certain sore-throat lozenges and throat sprays or gargles. Small amounts of phenol in water have been injected into nerve tissue to lessen pain associated with certain nerve disorders. Phenol destroys the outer layers of skin if allowed to remain in contact with skin, and small amounts of... 

Pramoxine (Anusol Ointment, PrectoFoam NS, Others) [Topical Anesthetic] Uses Relief of pain itching from hemorrhoids, anorectal surg y topical for bums dermatosis Action Topical anesthetic Dose Apply freely to anal area q3h Caution [C, ] Disp Foam (Proctofoam-NS), cream, oint, lotion, gel, pads, spray SE Contact dermatitis, mucosal thinning w/ chronic use EMS None OD Unlikely... 

The most commonly used vasoconstrictors, the sympathomimetic drugs, are often added to local anesthetics to delay absorption of the anesthetic from its injection site. By slowing absorption, these drugs reduce the anesthetic s systemic toxicity and keep it in contact with nerve fibers longer, thereby increasing the drug s duration of action. Administration of lidocaine 1% with epinephrine results in the same degree of blockade as that produced by lidocaine 2% without the vasoconstrictor. 

Transcranial magnetic stimulation (TMS) is a novel treatment for psychiatric illness (George et ah, 1999 Pridmore and Belmaker, 1999). In the procedure, a current is passed around an insulated coil held in contact with the patient s head, causing a magnetic field to pass into the first few millimeters of cortex. Unlike ECT, a specific area of the brain is stimulated, the procedure does not require a general anesthetic, and a seizure does not occur. 

The metabolism of enflurane and sevoflurane results in the formation of fluoride ion. However, in contrast to the rarely used volatile anesthetic methoxyflurane, renal fluoride levels do not reach toxic levels under normal circumstances. In addition, sevoflurane is degraded by contact with the carbon dioxide absorbent in anesthesia machines, yielding a vinyl ether called "compound A," which can cause renal damage if high concentrations are absorbed. (See Do We Really Need Another Inhaled Anesthetic ) Seventy percent of the absorbed methoxyflurane is metabolized by the liver, and the released fluoride ions can produce nephrotoxicity. In terms of the extent of hepatic metabolism, the rank order for the inhaled anesthetics is methoxyflurane > halothane > enflurane > sevoflurane > isoflurane > desflurane > nitrous oxide (Table 25-2). Nitrous oxide is not metabolized by human tissues. However, bacteria in the gastrointestinal tract may be able to break down the nitrous oxide molecule. 

Pramoxine hydrochloride is a topical anesthetic that can provide temporary relief from pruritus associated with mild eczematous dermatoses. Pramoxine is available as a 1% cream, lotion, or gel and in combination with hydrocortisone acetate. Application to the affected area two to four times daily may provide short-term relief of pruritus. Local adverse effects include transient burning and stinging. Care should be exercised to avoid contact with the eyes. 

CAUTION This step should be carried out in a fume hood to avoid inhalation of the vapors. Chloroform is a known carcinogen. It is toxic by inhalation and has anesthetic properties. Contact with skin should be avoided. Prolonged inhalation or ingestion can lead to liver and kidney damage and may be fatal. 

Quinine and its derivatives, when brought in contact with sensory nerves, produce local anesthesia. This is used clinically in the form of the more soluble and less irritant double salts, especially quinine urea hydrochloride. The anesthesia is more lasting than with other local anesthetics it may persist for several days. This is indeed due to necrosis of the axis cylinders and sheaths, with subsequent regeneration. However, the concentrations above 0.25% sometimes produce considerable irritation, edema, and fibrous indurations and above 1% there may be sloughing. Its employment has therefore greatly diminished, although some clinicians consider these fears as exaggerated. 

When applied locally to nerve tissue in appropriate concentrations, local anesthetics (Figure 23.2) reversibly block the action potentials responsible for nerve conduction. They act on any part of the nervous system and on every type of nerve fiber. Thus, a local anesthetic in contact with a nerve trank can cause both sensory and motor paralysis in the area innervated. The necessary practical advantage of the local anesthetics is that their action is reversible at clinically relevant concentra-... 

All local anesthetics including cocaine paralyze the nerve fibers anywhere in their course, wherever they are brought into contact with them. When applied to mucous membranes or hypodermically, they select the portions peripheral to the main trunks, the thinner sheath of the terminal fibrils facilitating its penetration. It is therefore unnecessary to assume selective action on the histological sensory endings. 

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