Anaesthesia intravenous anaesthetics

The other method used is infusion of intravenous anaesthetics such as propofol, etomidate (for induction) and the barbiturates such as thiopental and pentobarbital. Investigations into the mechanism of anaesthesia have made use of all these compounds in order to identify a common mode of action linked to likely mechanisms within the CNS. 

Intravenous anaesthetics are mainly used for rapid induction of anaesthesia, which is then maintained by an inhalational agent. They also serve to reduce the amount of maintenance anaesthetics. 

It is a new intravenous anaesthetic agent with poor analgesic property. It has a briefer duration of action than thiopentone. It produces little cardiovascular and respiratory depression. A single intravenous dose produces loss of consciousness within 10 seconds and a state of anaesthesia. 

The ideal intravenous anaesthetic agent Mechanism(s) of intravenous anaesthesia Pharmacokinetics and metabolism Rapidly acting intravenous anaesthetics Non-barbiturate intravenous anaesthetics Slower-acting intravenous anaesthetics Other drugs INTRODUCTION... 

Induction of anaesthesia. Propofoi is the preferred intravenous anaesthetic where a rapid induction with a rapid ciear-headed recovery is desired (as in day surgery). The rapid redistribution of this drug may iead to sub-hypnotic piasma concentrations and great care must be taken to ensure adequate anaesthesia in the eariy operative phase. 

The EEC changes associated with ketamine anaesthesia are quite unlike those seen with other intravenous anaesthetics and consist of fast 3 activity mixed with high-voltage 5 waves. While ketamine-induced myoclonic and seizure-like activity has been seen in normal (non-epileptic) patients, ketamine appears to possess anticonvulsant properties. 

INTRAVENOUS ANAESTHETICS (e.g. thiopentone sodium, propofol) BETA-BLOCKERS Risk of severe hypotensive episodes during induction of anaesthesia (including patients taking timolol eye drops) Most intravenous anaesthetic agents are myocardial depressants and vasodilators, and additive 1 BP may occur Monitor BP closely, especially during induction of anaesthesia... 

Phencyclidine ( angel dust ) was made in a search for a better intravenous anaesthetic. It is structurally related to pethidine. Phencyclidine was found to induce analgesia without unconsciousness, but with amnesia, in man (dissociative anaesthesia). The postoperative course, however, was complicated... 

Anaphylactic reactions result from the interaction of antigens with specific IgE antibodies, which have been formed by previous exposure to the antigen. Anaphylactoid reactions are clinically indistinguishable from anaphylaxis but do not result from prior exposure to a triggering agent and do not involve IgE. Intravenous anaesthetics and muscle relaxants can cause anaphylactic or anaphylactoid reactions and, rarely, they are fatal. Muscle relaxants are responsible for 70% of anaphylactic reactions during anaesthesia and suxamethonium accormts for almost half of these. 

Although intravenous anaesthetics can inhibit in-vitro the activity of PMNs, " their in-vivo effect on the phagocyte-dependent immune system is not clearly defined especially in cases of short term anaesthesia. Our study indicates that PMN CL, if analyzed by an appropriate statistical test, seems to be modified also by short term intravenous anaesthesia. In fact, both discriminant analysis (Table 2) and regression analysis between luminol- and lucigenin-dependent CL (Figure 1) indicate that PMN CL is modified also after many hours of a short time intravenous anaesthesia. In... 

Today, either inhalation or intravenous anaesthetics or a combination of the two is used to produce general anaesthesia. 

Intravenous anaesthetics can be used for short surgical procedures of 10-20 minutes. Their elimination from the body is too slow to allow rapid control of the depth of anaesthesia needed for long procedures. They are most often used for induction because, even the fastest acting inhalation anaesthetics take a few minutes to act and cause excitement before anaesthesia is produced, which would be unpleasant for the patient. It also means that the amount of inhalation anaesthetic can be reduced. 

Ketamine produces a different effect to other intravenous anaesthetics analgesia, sensory loss, amnesia and muscle paralysis are produced without loss of consciousness, so-called dissociative anaesthesia, and with minimal respiratory depression. 

Intravenous anaesthetics are used to induce general anaesthesia, followed by an inhalation anaesthetic for maintenance, and for short surgical procedures. Propofol is commonly used for both induction and maintenance anaesthesia. 

What are the advantages of using intravenous anaesthetics for induction of general anaesthesia and why are they generally unsuitable for sole use in lengthy operations ... 

A placebo-controlled study in women undergoing abdominal hysterectomy found that a dexmedetomidine infusion started 15 minutes before induction of anaesthesia caused a dose-dependent reduction in isoflurane MAC (by 35% and 47% with dexmedetomidine plasma levels maintained at 0.37 and 0.69 nanograms/mL, respectively). In another study, dexmedetomidine reduced the ED50 dose requirement ofisoflurane for anaesthesia (motor response) in 9 healthy subjects. Dexmedetomidine plasma levels of 0.35 and 0.75 nanograms/mL reduced the requirements for isoflurane by about 30% and 50%, respectively. Subjects who had received dexmedetomidine took longer to wake up. Dexmedetomidine has sedative, analgesic and anxiolytic effects and therefore, like other sedatives, may reduce the dose requirements of anaesthetics. However, it may also affect the distribution of thiopental and possibly other intravenous anaesthetics. 

The predisposing factors are similar with all intravenous anaesthetics. This was the experience of several groups, including Clarke et al. (1978) and ourselves (Assem 1977 b). The reactions were most frequent in asthmatic and allergic patients (suffering from other allergies). They were particularly frequent in those who had a previous anaesthesia within the preceding few weeks, especially if it was with the same anaesthetic. 

Figure 10.19(a) Plasma viscosity before and after induction of anaesthesia (11 patients) with intravenous anaesthetic formulations containing Cremophor EL (b) the duration of this effect - a plot showing the viscosity of plasma at a shear rate of 11.5 s " as a function of time in minutes. Taken from Gramstad and Stovner [135] with permission. 

Local anaesthetics can be applied topically, deposited around peripheral nerves, or infiltrated into tissues. Central neural blockade can be produced by injection into the subarachnoid or epidural spaces. Less common uses are for intravenous regional anaesthesia and attenuation of cardiovascular responses to tracheal intubation. The membrane-stabilising effect of local anaesthetics has been utilised in the treatment of myocardial arrhythmias. 

Prilocaine is suitable for most types of local anaesthetic block but is not suitable for epidural use in obstetrics because of the need for repeat administration. Its main uses are for infiltration anaesthesia and intravenous regional anaesthesia where its low toxicity makes it the drug of choice. Levobupivacaine... 

CALCIUM CHANNEL BLOCKERS ANAESTHETICS - LOCAL Case reports of severe 1 BP when bupivacaine epidural was administered to patients on calcium channel blockers Additive hypotensive effect both bupivacaine and calcium channel blockers are cardiodepressant in addition, epidural anaesthesia causes sympathetic block in the lower limbs, which leads to vasodilatation and 1 BP Monitor BP closely. Preload intravenous fluids prior to the epidural... 

LEVODOPA ANAESTHETICS -GENERAL-VOLATILE AGENTS Possible risk of arrhythmias Uncertain Monitor EGC and BP closely. Consider using intravenous agents for maintenance of anaesthesia... 

---