Some science behind the scenes
Ether is a class of organic compounds that contain an ether group — an oxygen atom connected to two alkyl or aryl groups. Thus whenever you see the name ‘ether’ being used to describe an anaesthetic or an inhalant, the terminology is not precise and serves only to make things more complex.
There are, in practise any number of ethers, for example, methyl ether, dimethyl ether and dipheylether. To make this area even more complex, IUPAC rules are not always followed for their naming and sometimes the names used before the rules for nomenclature was formalised are used – so spotting an ether is not easy. Diethyl ether, for example, is not only called ‘ether’ but has been called ‘sweet oil of vitriol’. By contrast methyl ether is known as ‘anisole’ because it was originally found in aniseed.
In this section we are only looking at diethyl ether. Its formula is (C2H5)2O. It is a colorless, highly volatile flammable liquid with a characteristic odour. Its uses include:
- As an anaesthetic - Diethyl ether was one of the early anaesthetics, but its use has now been virtually discontinued partly because it is flammable , but also because it has some unpleasant side effects
- As a solvent - It is particularly important as a solvent in the production of cellulose plastics such as cellulose acetate
- As a fuel - Diethyl ether is used as a starting fluid for diesel and gasoline engines because of its high volatility and low autoignition temperature. For the same reason it is also used as a component of the fuel mixture for carbureted compression ignition model engines.
- In the laboratory - Diethyl ether is a common laboratory solvent. It has limited solubility in water, therefore it is commonly used for liquid-liquid extraction.
Due to its application in the manufacturing of illicit substances, it is listed in the Table II precursor under the United Nations Convention Against Illicit Traffic in Narcotic Drugs and Psychotropic Substances.
Diethyl ether has been known for hundreds of years. There are apparent records of its use by Jābir ibn Hayyān in the 8th century and Raymundus Lullus in 1275. The name "sweet oil of vitriol" (oleum dulce vitrioli) was invented by Valerius Cordus who synthesised it in 1540—the name reflects the fact that it is obtained by distilling a mixture of ethanol and sulfuric acid (then known as oil of vitriol. Theophrastus Bombastus von Hohenheim, better known as Paracelsus, discovered ether's analgesic properties. The name ether was given to the substance in 1730 by August Siegmund Frobenius.
Ether was used in the UK as an anaesthetic in the early 1800s. British doctors were aware of the anaesthetic properties of ether as early as 1840 where it was widely prescribed in conjunction with opium. In those days it was sometimes used in place of chloroform because it had a higher therapeutic index - a larger difference between the recommended dosage and a toxic overdose.
Diethyl ether is susceptible to peroxide formation, and can form explosive diethyl ether peroxide. Ether peroxides are higher boiling and are contact explosives when dry.
It is extremely flammable. The autoignition temperature of diethyl ether is 160 °C (320 °F), therefore it can be ignited by a hot surface without a flame or spark.
Clinically “Induction requires about 15 minutes, the level in the visceral compartment, which includes brain and heart, rises slowly and continues to rise throughout the whole course of anesthesia”.
“At the end of 1 hour, the patient's brain is equilibrated with a concentration of approximately 2 per cent and the level still rises because a concentration of 5 per cent is being inhaled. If anesthesia were continued for 4 or 5 hours, the brain concentration would continue to rise and the patient would be at a deep level of anesthesia”.
- Heart – Diethyl ether does not directly depress the myocardium, but instead stimulates the sympathetic system and can cause tachycardia and hypertension
- Immune response – there are cases where diethyl ether has resulted in an impaired immune response after anaesthesia [Meyer]
- Dermatitis – there is a low risk, but a risk nevertheless of contact dermatitis [Meyer]
- Tracheobronchial secretions - Secretions all over the respiratory lining are markedly increased. During anaesthesia doctors sometimes use a premedication of atropine to help with this.
- Gastrointestinal effects - Ether has the highest incidence of nausea and vomiting among all the inhalational agents.
- Respiratory system: - respiration is stimulated. Only at very high doses is the respiration inhibited. Ventilatory responses to hypoxia and hypercarbia are preserved
- Cerebral - Intracranial tension is increased - you may get a headache
- Bronchial muscles – Diethyl ether is a potent bronchodilator.
- Hepatic and renal functions – unlike Halothane, the functions of the liver and the kidney are well preserved.
- Uterus - Uterine relaxation may be seen in deeper planes
- Uteroplacental barrier – Diethyl ether readily crosses the placenta and can cause respiratory depression in newborn.
- Metabolic systems – Diethyl ether releases catecholamines and can cause hyperglycemia. So is not used in diabetics.
Alzheimer's disease and anesthesia - Papon MA, Whittington RA, El-Khoury NB, Planel E. ; Département de Psychiatrie et Neurosciences, Centre Hospitalier de l'Université Laval Québec, QC, Canada.
Cognitive disorders such as postoperative cognitive dysfunction, confusion, and delirium, are common following anesthesia in the elderly, with symptoms persisting for months or years in some patients. Alzheimer's disease (AD) patients appear to be particularly at risk of cognitive deterioration following anesthesia, and some studies suggest that exposure to anesthetics may increase the risk of AD. Here, we review the literature linking anesthesia to AD, with a focus on the biochemical consequences of anesthetic exposure on AD pathogenic pathways.
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