Induction ketamine

Ketamine (Ketalar) is a rapid-acting general anesthetic. It produces an anesthetic state characterized by profound analgesia, cardiovascular and respiratory stimulation, normal or enhanced skeletal muscle tone, and occasionally mild respiratory depression. Ketamine is used for diagnostic and surgical procedures that do not require relaxation of skeletal muscles, for induction of anesthesia before the administration of other anesthetic drugp, and as a supplement to other anesthetic drags. 

Ngan Kee WD, Khaw KS, Ma ML, et al (1997) Postoperative analgesic requirement after cesarean section a comparison of anesthetic induction with ketamine or thiopental. Anesth Analg 85 1294-1298... 

Ketamine also can be contrasted to other intravenous drugs in its ability to cause cardiovascular stimulation rather than depression. The observed increases in heart rate and blood pressure appear to be mediated through stimulation of the sympathetic nervous system. In a healthy, normovolemic, unpremedicated patient, the initial induction dose of ketamine maintains or stimulates cardiovascular function. In contrast, patients with... 

A most important advantage of ketamine over other anesthetic agents is its potential for administration by the IM route. This is particularly useful in anesthetizing children, since anesthesia can be induced relatively quickly in a child who resists an inhalation induction or the insertion of an IV line. Ketamine has a limited but useful role as an IM induction agent and in pediatrics. 

Although the use of ketamine for anesthesia induction when seizure duration is insufficient has also been recommended, recent studies did not find this agent to be helpful (100, 101, 102 and 103). Disadvantages of ketamine include the following ... 

Of the intravenous agents, ketamine and thiopentone undergo complete placental transfer. Propofol is also rapidly transferred across the placenta, and propofol infusions should be used with caution during Caesarean section when a prolonged induction to delivery time is anticipated. However, neonates clear propofol rapidly and residual effects in healthy newborn are usually negligible. 

In 190 patients taking tricyclic antidepressants that could not be discontinued before surgery, who underwent general and 61 local or regional anesthesia, there were no changes in the cardiovascular effect of halothane, induction time with pentobarbital, propanidid, or ketamine, or the duration of depolarization or recovery time (160). The general conclusion was that it is safer to continue treatment with tricyclic antidepressants than to risk potential disruption from withdrawal before surgery. 

Disadvantages. Ketamine produces no muscular relaxation. It increases intracranial and intraocular pressure. Hallucinations can occur during recovery (the emergence reaction), but they are minimised if ketamine is used solely as an induction agent and followed by a conventional inhalational anaesthetic. Their incidence is reduced by administration of a benzodiazepine both as a premedication and after the procedure. 

Ketamine relaxes smooth muscles in the airways and may therefore be a useful induction agent in children with asthma (6). If endotracheal intubation is required, lidocaine 1-2 mg/kg intravenously before intubation has been recommended, although the use of a laryngeal mask airway may be more appropriate. When used in combination with midazolam by infusion, ketamine provides analgesia and prevents and relieves bronchospasm (7). 

Tachycardia and hypertension are common after anesthetic induction with ketamine, although the hypertension can be limited by the addition of diazepam (10). Nodal dysrhythmias can also occur (11). Because of possible... 

Waxman K, Shoemaker WC, Lippmann M. Cardiovascular effects of anesthetic induction with ketamine. Anesth Analg 1980 59(5) 355-8. 

The side-effects of reserpine include hypotension, bradycardia and increased gastrointestinal motility and diarrhea (Lloyd et al 1985), all resulting from decreased sympathetic tone and increased parasympathetic tone. The hypotensive effects of reserpine may take days to several weeks to occur but may persist for 1 to 6 weeks after the withdrawal of the dmg. Administration of induction agents, such as xylazine and ketamine, that produce hypotension may be fatal in horses treated with reserpine. 

There are reports that diazepam can produce paradoxical excitability immediately after i.v. administration to humans and small animals. Although this paradoxical effect is not well described in horses, diazepam should be administered with caution to mature horses when used as a sole agent. It can be used as the sole agent for sedation and restraint in young foals. Diazepam is recommended for i.v. use at doses of 0.02-0.1 mg/kg. Diazepam is primarily used in adult horses to provide muscle relaxation and for its anticonvulsant effect prior to anesthetic induction with ketamine. Diazepam (0.04 mg/kg) reduces the MAC of halothane by approximately 29% (Matthews et al 1990). Diazepam is considered the acute treatment of choice for status epilepticus in all species (see Ch. 9). Diazepam (0.02-0.04 mg/kg) is an appetite stimulant in horses, although its effect is of short duration (Brown et al 1976). 

Ketamine produces a rapid onset of anesthesia when given i.v. with recumbency occurring within 1 min (Kaka et al 1979). After i.m. administration, a combination of medetomidine and ketamine produced recumbency in feral horses with a mean induction time of 11 min, although 3 out of the 14 horses were still standing, sedated but not manageable (Matthews et al 1995). 

Ketamine has a short duration of effect after i.v. bolus administration. Ketamine induction after xylazme sedation generally provides 12-20 min duration of anesthesia (Muir et al 1977). The termination of the effects of ketamine in the CNS primarily results from redistribution of the drug from the brain to other tissues (Waterman et al... 

Ketamine is used as an i.v. anesthetic in the horse, always after adequate sedation. Ketamine can be used as an anesthetic induction agent, prior to intubation and maintenance with inhalation anesthesia. The typical dose used in the horse for induction of anesthesia is 2.2mg/kg i.v. xylazine (l.lmg/kg i.v.) followed by ketamine (2.2mg/kg i.v.) is the most common anesthetic technique used for short procedures in horses in the field. S atives other than xylazine may be used prior to ketamine anesthetic induction, for example detomidine... 

In the horse, induction with thiopental usually results in a brief increase in heart rate and a decrease in cardiac output but no significant change in arterial blood pressure. Arterial blood pressure is typically lower after thiopental induction than in ketamine-based anesthetic techniques (Bennett et al 1998, Muir et al 2000). However, when horses are placed on inhalation anesthetics for maintenance of anesthesia, the hemodynamic effects of the induction agents is short lived and the hypotension and reduced cardiac output typical of inhalation anesthesia predominates (Bennett et al 1998, Wagner et al 1996). Respiratory depression is significant with an accompanying increase in Paco2 and decrease in pH. 

Bennett R C, Steffey E P 2002 Use of opioids for pain and anesthetic management in horses. Veterinary Clinics of North America Equine Practice 18 47-60 Bennett R C, Taylor P M, Brearley J C et al 1998 Comparison of detomidine/ketamine and guaiphenesin/thiopentone for induction of anaesthesia in horses maintained with halothane. Veterinary Record 142 541-545 Bettschart-Wolfensberger R, Clarke K W, Vainio O et al 1999 Pharmacokinetics of medetomidine in ponies and elaboration of a medetomidine infusion regime which provides a constant level of sedation. Research in Veterinary Science 67 41-46 Bettschart-Wolfensberger R, Freeman S L. Jaggin-... 

Clarke K W, Song D Y, Alibhai H I et al 1996 Cardiopulmonary effects of desflurane in ponies, after induction of anaesthesia with xylazine and ketamine. Veterinary Record 139 180-185... 

Etomidate is a nonbarbiturate hypnotic without analgesic activity and is used for induction of general anesthesia, for supplementing subpotent anesthetics such as nitrous oxide in oxygen, and for maintenance of anesthesia for short operative procedures. Etomidate lowers cerebral blood flow, and similar to ketamine, methohexital, or thiopental, also reduces cerebral oxygen consumption (see also Table 16). 

Ketamine is used as a sole anesthetic agent for diagnostic and surgical procedures that do not require skeletal muscle relaxation. It is best suited for short procedures, but it can be used with additional doses for longer procedures. It is also used for the induction of anesthesia prior to the administration of other general anesthetics and to supplement low-potency agents, such as nitrous oxide. 

The onset and duration of an induction dose of ketamine are determined by the same distribution/redistribntion mechanism operant for all the other parenteral anesthetics. 

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