Total intravenous anaesthesia. A technique based on alphaxalone/alphadolone and pentazocine

Synthetic neuroactive steroids as new sedatives and anaesthetics: Back to the future

Since the 1990s, there has been waning interest in researching general anaesthetics (anaesthetics). Although currently used anaesthetics are mostly safe and effective, they are not without fault. In paediatric populations and neonatal animal models, they are associated with learning impairments and neurotoxicity. In an effort to research safer anaesthetics, we have gone back to re-examine neuroactive steroids as anaesthetics. Neuroactive steroids are steroids that have direct, local effects in the central nervous system. Since the discovery of their anaesthetic effects, neuroactive steroids have been consistently used in human or veterinary clinics as preferred anaesthetic agents. Although briefly abandoned for clinical use due to unwanted vehicle side effects, there has since been renewed interest in their therapeutic value. Neuroactive steroids are safe sedative/hypnotic and anaesthetic agents across various animal species. Importantly, unlike traditional anaesthetics, they do not cause extensive neurotoxicity in the developing rodent brain. Similar to traditional anaesthetics, neuroactive steroids are modulators of synaptic and extrasynaptic γ-aminobutyric acid type A (GABA_A ) receptors and their interactions at the GABA_A receptor are stereo- and enantioselective. Recent work has also shown that these agents act on other ion channels, such as high- and low-voltage-activated calcium channels. Through these mechanisms of action, neuroactive steroids modulate neuronal excitability, which results in characteristic burst suppression of the electroencephalogram, and a surgical plane of anaesthesia. However, in addition to their interactions with voltage and ligand gated ions channels, neuroactive steroids interact with membrane bound metabotropic receptors and xenobiotic receptors to facilitate signaling of prosurvival, antiapoptotic pathways. These pathways play a role in their neuroprotective effects in neuronal injury and may also prevent extensive apoptosis in the developing brain during anaesthesia. The current review explores the history of neuroactive steroids as anaesthetics in humans and animal models, their diverse mechanisms of action, and their neuroprotective properties.

A History of Intravenous Anesthesia in War (1656-1988)

The practice of anesthesia in war places significant restraints on the choice of anesthetic technique used; these include, but are not limited to, safety, simplicity, and portability. Ever since intravenous anesthesia became a practical alternative, there have been military doctors who felt that this technique was particularly suited to this environment. The challenge, as in civilian practice, has been to find the appropriate drugs as well as simple and safe delivery systems. The urgency of war has always stimulated innovation in medicine to counteract the ongoing development of weapons of war and their effects on the human body and to achieve improved survival as public expectations rise. This article traces the development of and the use of intravenous anesthesia by military physicians for battle casualties. The story starts long before the era of modern anesthesia, and the discussion concludes in the dog days of the cold war. The rapidly increasing interest in intravenous anesthesia in both civilian and military practice since the early 1990s is left for other authors to examine.

Ketamine and military anasthesia. The effect of heavy papaveretum premedication and Althesin induction on the incidence of emergence phenomena

An anaesthetic technique suitable for military field anaesthesia was sought which would attenuate the psychic side effects of ketamine. Heavy premedication with 30 mg of papaveretum and induction of anaesthesia with Althesin were evaluated. A combination of the two lowered the incidence of side effects, but they still occurred frequently enough to pose problems. Ketamine sequelae are considered incompatible with the battlefield environment.

Total intravenous anaesthesia

Total intravenous anaesthesia is a feasible alternative to the use of inhalational agents and the rationale behind such a technique is presented. The various intravenous agents are discussed, particularly with regard to their suitability for this form of anaesthesia, and their physiological effects compared with those of the inhalational anaesthetics. Some of the problems associated with the use of total intravenous anaesthesia are mentioned.

Total intravenous anaesthesia by an intermittent technique. Use of methohexitone, ketamine and a muscle relaxant

Good quality anaesthesia with smooth recovery can be induced by methohexitone 40 mg, ketamine 100 mg, diazepam 5 mg and alcuronium 15-20 mg and maintained with methohexitone 30 mg and ketamine 10 mg at 5-minute intervals and controlled ventilation with 30% oxygen in air. The technique is economical in running and capital costs and may have special implications for avoiding atmospheric pollution, for use in developing countries, and in emergency situations.

Postoperative dreaming. A comparison of the incidence following pentazocine and morphine premedication

The incidence of postoperative dreaming following the use of morphine and pentazocine as premedicants in an otherwise standard anaesthetic sequence is compared in healthy volunteers. No statistically significant difference was demonstrated between the two drugs. The causes of psychotomimetic problems in the postoperative period and the difficulty of precise definition of hallucinations are discussed.

Althesin infusions for maintenance of anaesthesia

The intravenous anaesthetic Althesin may be administered by continuous intravenous infusion for maintenance of general anaesthesia, sedation in patients in intensive care units or during investigational procedures. Published reports of experience with this technique are reviewed, with particular attention to the rates of administration employed and the influence of other anaesthetics and analgesic agents used concurrently.

Total intravenous anaesthesia with low dose ketamine and Althesin. Assessment of a technique for minor surgery in difficult situations

In 38 patients subjected to minor surgery, totally intravenous anaesthesia with low dose ketamine and Althesin produced adequate operating conditions in 92% of patients with minimal cardiorespiratory disturbance. Problems arose from muscular hypertonus, spontaneous movement and occasionally salivation. Initial recovery was quicker and the incidence of side-effects lower, than those reported when ketamine was used as the sole agent. The technique could be useful in difficult situations as an alternative to inhalation anaesthesia or other intravenous techniques.

The in vivo metabolism of Althesin (alphaxalone + alphadolone acetate) in man

Gas chromatograph-mass spectrometry has been used to study the metabolism of Althesin (alphaxalone and alphadolone acetate) in man. Two metabolites, 20 alpha-reduced alphaxalone and alphadolone, as well as the two parent steroids, have been detected in the plasma during and after an infusion of Althesin. The main urinary metabolites were alphaxalone and 20 alpha-reduced alphaxalone, with smaller amounts of alphadolone, all of which were excreted mainly as the glucuronide conjugates. No alphadolone acetate was detected in the urine. In 3 patients in whom bile was collected over the 1st 24 h post-operation from an indwelling T-tube, it has not been possible using the methods described to detect in bile the presence of the parent steroids, or any of their probable metabolites.

Liver enzyme studies with continuous intravenous anaesthesia

A battery of liver function tests was carried out before operation and on the 3rd--5th and 13th--15th postoperative days in patients anaesthetised with continuous infusion of thiopentone, Althesin or etomidate for an intermediate operation. Some derangement of enzyme activity was found in one quarter to one third of the patients, and was most marked after Althesin. The findings are compared with published data on ketamine, which had an effect on enzyme activities similar to that of Althesin. On pooling data from different studies it became very apparent that large doses of intravenous anaesthetics cause a greater derangement of liver function than that which occurs using a balanced technique for the same operation.

Alphaxalone infusion during cardiopulmonary bypass

A continuous infusion of alphaxalone (as Althesin) was used to maintain anaesthesia for patients undergoing open heart surgery. Plasma levels of the drug were measured at intervals during the procedure. It was found that alphaxalone was adequatley removed from the circulation, despite a period of cardiopulmonary bypass and hypothermia, and provided suitable anaesthesia for this type of surgery.

Althesin for neuroanaesthesia

Althesin was used as a induction agent then diluted and administered as a controlled infusion for 60 patients undergoing 66 procedures. Increment doses of fentanyl were given to provide additional analgesia. There was delayed awakening in 7 patients (12.1%), 3 of whom responded rapidly to narcotic reversal with naloxone. Intracerebral pathology and surgical trauma contributed to the slow recovery in the other 4 patients. Evidence is presented that Althesin infusions reduce the narcotic requirement. Althesin anaesthesia provides good neurosurgical conditions without delay in recovery.

Anaesthesia for tracheal resection. Modified use of the Carden Tube

Surgical procedures involving sharing of the airway between the anaesthetist and surgeon, such as bronchoscopy, microlaryngeal surgery and tracheal resection impose special problems on the anaesthetist. The surgeon requires unrestricted surgical access, whereas the anaesthetist must ensure adequate and safe pulmonary ventilation and anaesthesia. This case report describes a two stage technique for management of the airway and ventilation during tracheal resection for stenosis. Initially a modified Carden tube with a ventilating injector was used through a tracheostomy stoma and subsequently an orotracheal tube was substituted. Anaesthesia was maintained entirely by the inravenous route. The surgical access was unrestricted and there was no pulmonary contamination.