Anesthesia premedication

Clinical reports of patients who underwent chloroform anesthesia indicated that premedication with morphine caused serious respiratory depression when chloroform was co-administered. Thiopentone (thiopental Na, an ultra-short-acting barbiturate anesthetic) was associated with increased incidences of hypotension in chloroform-anesthetized patients (Whitaker and Jones 1965). 

Bronchial secretion. Premedication with atropine before inhalation anesthesia prevents a possible hypersecretion of bronchial mucus, which cannot be expectorated by coughing during intubation (anesthesia). 

For use as a narcotic analgesic supplement in general or regional anesthesia. For administration with a neuroleptic such as droperidol as an anesthetic premedication, for induction of anesthesia and as an adjunct in maintenance of general and regional anesthesia. 

As a sedative when used as premedication and following general anesthesia. 

In anesthesia drugs from several groups are used as premedication. Pre-anesthetic medication can decrease the anesthetic doses which otherwise would be required to induce anesthesia and so decrease the risk for adverse effects. Pre-anesthetic medication will increase the rate of induction of anesthesia and can reduce pre-operative pain and anxiety. Drugs include benzodiazepines for sedation and their muscle relaxant properties, opiates for pain relieve and anticholinergics or histamine Hi receptor antagonists against nausea and vomiting. Neuroleptics are also used as premedication for their antiemetic effects. 

Propofol can be used for induction as well as maintenance of anesthesia. It is very lipophilic and induction of anesthesia takes place within 30 seconds. After a single dose the patient awakes in approximately 5 minutes and after anesthesia by continuous intravenous administration of longer duration recovery may take 10-15 minutes. It can be used in combination with the usual range of premedications, analgesics, muscle relaxants and inhalation anesthetic agents. 

Pentazocine is indicated for relief of moderate pain in patients not receiving large doses of opioids. It is also used as premedication for anesthesia and as a supplement to surgical anesthesia. 

For sedative and possible amnestic effects during medical or surgical procedures such as endoscopy and bronchoscopy—as well as for premedication prior to anesthesia—oral formulations of shorter-acting drugs are preferred. 

Diazepam, lorazepam, and midazolam are used for preanesthetic medication and as adjuvants during surgical procedures performed under local anesthesia. As a result of their sedative, anxiolytic, and amnestic properties, and their ability to control acute agitation, these compounds are considered to be the drugs of choice for premedication. (The basic pharmacology of benzodiazepines is discussed in Chapter 22.) Diazepam and lorazepam are not water-soluble, and their intravenous use necessitates nonaqueous vehicles, which cause pain and local irritation. Midazolam is water-soluble and is the benzodiazepine of choice for parenteral administration. It is important that the drug becomes lipid-soluble at physiologic pH and can readily cross the blood-brain barrier to produce its central effects. 

The technique typically involves the use of intravenous midazolam for premedication (to provide anxiolysis, amnesia, and mild sedation) followed by a titrated, variable-rate propofol infusion (to provide moderate to deep levels of sedation), and a potent opioid analgesic or ketamine (to minimize the discomfort associated with the injection of local anesthesia and the surgical manipulations). 

Dosages and routes of administration For acute (postoperative) pain and for anesthesia, fentanyl is given by the intravenous route. For pre-medication in anesthesia and for break-through pain the compound can also been given as an oral-transmucosal formulation (Ashburn and Streisand, 1994). A transdermal patch has been developed for chronic pain treatment (Jeal and Benfield, 1997 O Siordin, 1998). The intravenous doses for premedication are 50-100 pg, oral-transmucosal systems contain 200-400 pg and patch formulations have a delivery rate of 25-100 pg/h. 

Saidman LJ, Eger El II (1964) Effect of nitrous oxide and narcotic premedication on the alveolar concentration of halothane required for anesthesia. Anesthesiol 25 302-306... 

For ex vivo assays, mice, rats, or guinea pigs from either sex receive the test compound or the vehicle (for controls) by oral, intraperitoneal or intravenous administration. At the end of the absorption time, blood is collected by caval venipuncture under pentobarbital sodium anesthesia and xylazine (8 rng/kg i.m.) premedication. 

The anesthetic effect of (+)-etomidate subsides within a few minutes owing to redistribution of the drug. Etomidate can provoke myoclonic movements that can be prevented by premedication with a benzodiazepine or an opioid. Because it has little effect on the autonomic nervous system, it is suitable for induction in combination anesthesia. Etomidate inhibits cortisol synthesis in subanesthetic doses and can therefore be used in the long-term treatment of adrenocortical overactivity (Cushing disease). 

Hypothermia is common during anesthesia, and adversely affects outcome. It primarily results from internal redistribution of body heat from the core to the periphery. Premedication with sedative agents can affect perioperative heat loss by altering core-to-peripheral heat distribution. This has been analysed in a prospective randomized study in 45 patients undergoing arthroscopic knee ligament reconstruction surgery (47). Heavy premedication caused initial hypothermia. Moderate premedication reduced perioperative heat loss. No premedication was associated with significantly lower intraoperative core temperatures than in sedated patients. 

Delirium during emergence from sevoflurane anesthesia has often been documented. Four patients, an adult and three children aged 3-8 years, who were able to recount the experience, have been reported (599). They had full recall of postoperative events, were terrified, agitated, and distressed, and hence presented with acute organic mental state dysfunction which was short-lived. Two were disoriented and had paranoid ideation. They were not in any pain or were not distressed by pain if it was present. The authors hypothesized that misperception of environmental stimuli associated with sevoflurane s particular mode of action may have been the underlying cause of this phenomenon. Anxiolytic premedication and effective analgesia did not necessarily prevent the problem. 

A 2-year-old girl with a past history of asthma, developmental delay, short neck, and lumbar lordosis, but no known genetic defect or syndrome underwent anesthesia with midazolam and paracetamol premedication, halothane and nitrous oxide induction, and isoflurane plus nitrous oxide for maintenance of anesthesia. Difficulty with mouth opening was noted and endotracheal intubation was difficult. Limb rigidity developed rapidly. Thiopental and cisatracurium were given and the muscle rigidity abated over the next 10 minutes. 

Two cases of drug allergy have been reported in a 37-year-old woman and a 66-year-old man, who received hydroxyzine for premedication before anesthesia (1,2). In these patients immediate skin tests with the implicated drug were positive. 

The effects of intramuscular premedication with either clonidine 2 micrograms/kg or midazolam 70 micrograms/ kg on perioperative responses to ketamine anesthesia have been assessed in a placebo-controlled study in 30 patients (14). Clonidine significantly reduced intraoperative oxygen consumption, mean arterial pressure, and heart rate compared with midazolam and placebo. Thus, clonidine was as effective as midazolam, the standard drug used for this purpose, in reducing the undesirable sympathetic stimulation of ketamine. 

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