Xenon as an Anesthetic?

RickSmith · 2008-04-19 17:41:15

Hi all,
Xenon is an attractive anesthetic on Earth but is little used because of its expense. However, it is a side product of liquefying oxygen cryogenically which industries are likely to do on Mars. Furthermore, it will be cheaper as Mars is some 80 degrees C colder than Earth which will significantly reduce the expense of cooling the air to liquid oxygen temperatures.

Xenon is about as common on Mars as Earth (a bit surprising as much of it is formed by radioactive decay of plutonium which Mars formed much less than Earth). There are 90 parts per billion (ppb) on Earth and 80 ppb on Mars.

Here is some information on Xenon as a anesthetic:

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Xenon: A modern anesthetic

Dr Sanjay Singh

Xenon is well known as an inert gas filled inside incandescent lamps. Although, named after a Greek word ‘stranger’, Xenon is becoming less and less of a stranger for anesthesiologist. Knowledge of the anesthetic properties of xenon goes back to 1939, where Behnke and Yarborough investigated for the US Navy, the reason for mental effects in deep sea diving. Lawrence published initial experiments with xenon anesthesia in 1946. With a minimum alveolar concentration of 0.63, it is more potent than N2O. However, the extremely high cost (approx USD 10.00 per liter) has hindered its wide clinical application. Xenon was completely forgotten for more than 30 years since the early clinical trials in 1950’s, until Lachmann, Erdmannand their colleagues at Rotterdam rediscovered it in 1990. Since then, there has been a growing interest in xenon, especially in Europe and Japan, and two multi-centre clinical trials have been completed in the European Union.

Xenon belongs to the group of noble gases and is found in very small concentration in the air (0.0000087 per cent). It is manufactured by fractional distillation of liquefied air, which is obtained as a by-product during the process of pure oxygen production. After several separation processes, a purity of 99.995 per cent can be obtained; only impurity being O2 and N2. The production of one liter of Xenon consumes 220-Watt hours of energy. Corresponding to its rarity, xenon is expensive. The current world production of xenon is approximately 10 million liters per year.

Only 1.5 million liter per year is utilized for medical purposes, with half of this amount being used for anesthetic purposes. Xenon has been used for decades to study blood flow and gas distribution in lung although recent technical developments have expanded its use in magnetic resonance imaging. The resurgence of xenon as anesthetic despite its rarity and high cost may invite natural wonder in this era of cost containment.

There are three major reasons for Xenon’s popularity:

* Pharmacological and clinical advantage
* Its usefulness as scientific tool
* Environment friendliness.

Pharmaco clinical advantage –Xenon exists as a monatomic gas under normothermic and normobaric conditions. Although virtually inert, the very large outer electron shell of xenon may get polarized and distorted by nearby molecules and permits xenon to interact with and bind to proteins such as myoglobin as well as bi-layer lipids. Xenon’s ability to interact with cell proteins and cell membrane constituents is presumably responsible for its anesthetic potency.

Xenon also inhibits plasma membrane Ca++ pump, an action similar to that of volatile anesthetics, which may be responsible for an increase in neuronal Ca++ concentration and altered excitability.

Franks et al found that xenon despite a relatively simple atomic structure, acts selectively by blocking the N-methyl-d-aspartate receptor. This NMDA receptor inhibitor is responsible for inhibition of nociceptive responsiveness of spinal dorsal horn neurons.

Xenon has been shown not to alter voltage gated ion channels in the myocardium, nor does it sensitises the myocardium to the dysrhythmogenic effects of epinephrine. Xenon has many properties of an ideal anesthetic gas. These include:

1. Non-inflammable and non explosive

2. Rapid induction and emergence due to its low blood gas partition coefficient (0.12), which is lowest of all known anesthetics.

3. Human minimum alveolar conc (MAC) value of 0.63 makes it suitable as an inhalation anesthetic in a mixture of 30 percent O2. It is 1.5 times more potent then N2O.

4. Sufficient analgesic and hypnotic effect in mixture with 30 per cent O2.

5. The absence of metabolism, low toxicity and devoid of teratogenicity.

6. Compared to another anesthetic regimen, xenon anesthesia produces highest regional blood flow in the brain, liver, kidney and intestine. Dangers of tissue hypoxia are greatly reduced. It therefore appears to be an interesting alternative for anesthesia in transplant surgery.

7. It may protect neural cells against ischemic injury. During cardiopulmonary surgery its neuro protective effect is confirmed.

8. Undisturbed ventilation and pulmonary function. Despite higher density than N2O it does not alter respiratory mechanics. Airway resistance is not increased.

9. Lack of cardiovascular depression is the most appealing characteristics of Xenon. Even with 80 per cent concentration of Xe, Ca++ flow in human cardiomyocytes remains unaffected. Myocardial performance Index (MPI) and contractility, as measured by measuring the velocity of circumferential fiber shortening (Vcfe) and left ventricular and systolic wall stress (LVESW) using Tran esophageal echocardiography did not show any depression. The unique combination of analgesia, hypnosis and lack of hemodynamic depression makes it a very attractive choice for patients. Though its limited cardiovascular reserve, makes it expensive.

10. Diffusion hypoxia is less than N2O.

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