Second gas effect

Last updated

During induction of general anesthesia, when a large volume of a gas (e.g. nitrous oxide) is taken up from alveoli into pulmonary capillary blood, the concentration of gases remaining in the alveoli is increased. This results in effects known as the second gas effect [1] and the "concentration effect". These effects occur because of the contraction of alveolar volume associated with the uptake of the nitrous oxide. Previous explanations by Edmond I. Eger and Robert K. Stoelting have appealed to an extra-inspired tidal volume due to a potential negative intrapulmonary pressure associated with the uptake of the nitrous oxide. [2]

Contents

There are two extreme breathing patterns and the extra-inspired tidal volume is an artificial construct associated with one of these patterns. [3] Thus it is the volume change that actually causes the effects.[ citation needed ]

An applicable example from Stedman's medical dictionary

When a constant concentration of an anesthetic such as halothane is inspired, the increase in alveolar concentration is accelerated by concomitant administration of nitrous oxide, because alveolar uptake of the latter creates a potential subatmospheric intrapulmonary pressure that leads to increased tracheal inflow.

See also

Related Research Articles

<span class="mw-page-title-main">Nitrous oxide</span> Colourless non-flammable greenhouse gas

Nitrous oxide, commonly known as laughing gas, nitrous, nitro, or nos, is a chemical compound, an oxide of nitrogen with the formula N
2
O
. At room temperature, it is a colourless non-flammable gas, and has a slightly sweet scent and taste. At elevated temperatures, nitrous oxide is a powerful oxidiser similar to molecular oxygen.

<span class="mw-page-title-main">Halothane</span> General anaesthetic

Halothane, sold under the brand name Fluothane among others, is a general anaesthetic. It can be used to induce or maintain anaesthesia. One of its benefits is that it does not increase the production of saliva, which can be particularly useful in those who are difficult to intubate. It is given by inhalation.

<span class="mw-page-title-main">Isoflurane</span> General anaesthetic given via inhalation

Isoflurane, sold under the brand name Forane among others, is a general anesthetic. It can be used to start or maintain anesthesia; however, other medications are often used to start anesthesia, due to airway irritation with isoflurane. Isoflurane is given via inhalation.

<span class="mw-page-title-main">Sevoflurane</span> Inhalational anaesthetic

Sevoflurane, sold under the brand name Sevorane, among others, is a sweet-smelling, nonflammable, highly fluorinated methyl isopropyl ether used as an inhalational anaesthetic for induction and maintenance of general anesthesia. After desflurane, it is the volatile anesthetic with the fastest onset. While its offset may be faster than agents other than desflurane in a few circumstances, its offset is more often similar to that of the much older agent isoflurane. While sevoflurane is only half as soluble as isoflurane in blood, the tissue blood partition coefficients of isoflurane and sevoflurane are quite similar. For example, in the muscle group: isoflurane 2.62 vs. sevoflurane 2.57. In the fat group: isoflurane 52 vs. sevoflurane 50. As a result, the longer the case, the more similar will be the emergence times for sevoflurane and isoflurane.

<span class="mw-page-title-main">Cyclopropane</span> Chemical compound

Cyclopropane is the cycloalkane with the molecular formula (CH2)3, consisting of three methylene groups (CH2) linked to each other to form a triangular ring. The small size of the ring creates substantial ring strain in the structure. Cyclopropane itself is mainly of theoretical interest but many of its derivatives - cyclopropanes - are of commercial or biological significance.

<span class="mw-page-title-main">Theories of general anaesthetic action</span> How drugs induce reversible suppression of consciousness

A general anaesthetic is a drug that brings about a reversible loss of consciousness. These drugs are generally administered by an anaesthetist/anesthesiologist to induce or maintain general anaesthesia to facilitate surgery.

<span class="mw-page-title-main">Anaesthetic machine</span> Medical device to supply a mix of life-support and anaesthetic gases

An anaesthetic machine or anesthesia machine is a medical device used to generate and mix a fresh gas flow of medical gases and inhalational anaesthetic agents for the purpose of inducing and maintaining anaesthesia.

<span class="mw-page-title-main">Anesthetic</span> Drug that causes anesthesia

An anesthetic or anaesthetic is a drug used to induce anesthesia ⁠— ⁠in other words, to result in a temporary loss of sensation or awareness. They may be divided into two broad classes: general anesthetics, which result in a reversible loss of consciousness, and local anesthetics, which cause a reversible loss of sensation for a limited region of the body without necessarily affecting consciousness.

Awareness under anesthesia, also referred to as intraoperative awareness or accidental awareness during general anesthesia (AAGA), is a rare complication of general anesthesia where patients regain varying levels of consciousness during their surgical procedures. While anesthesia awareness is possible without resulting in any long-term memory of the experience, it is also possible for victims to have awareness with explicit recall, where they can remember the events related to their surgery.

<span class="mw-page-title-main">Desflurane</span> Chemical compound

Desflurane (1,2,2,2-tetrafluoroethyl difluoromethyl ether) is a highly fluorinated methyl ethyl ether used for maintenance of general anesthesia. Like halothane, enflurane, and isoflurane, it is a racemic mixture of (R) and (S) optical isomers (enantiomers). Together with sevoflurane, it is gradually replacing isoflurane for human use, except in economically undeveloped areas, where its high cost precludes its use. It has the most rapid onset and offset of the volatile anesthetic drugs used for general anesthesia due to its low solubility in blood.

<span class="mw-page-title-main">Bispectral index</span> Technology for monitoring anesthesia

Bispectral index (BIS) is one of several technologies used to monitor depth of anesthesia. BIS monitors are used to supplement Guedel's classification system for determining depth of anesthesia. Titrating anesthetic agents to a specific bispectral index during general anesthesia in adults allows the anesthetist to adjust the amount of anesthetic agent to the needs of the patient, possibly resulting in a more rapid emergence from anesthesia. Use of the BIS monitor could reduce the incidence of intraoperative awareness during anaesthesia. The exact details of the algorithm used to create the BIS index have not been disclosed by the company that developed it.

<span class="mw-page-title-main">Nitrous oxide (medication)</span> Gas used as anesthetic and for pain relief

Nitrous oxide, as medical gas supply, is an inhaled gas used as pain medication, and is typically administered with 50% oxygen mix. It is often used together with other medications for anesthesia. Common uses include during childbirth, following trauma, and as part of end-of-life care. Onset of effect is typically within half a minute, and the effect lasts for about a minute.

<span class="mw-page-title-main">Inhalational anesthetic</span> Volatile or gaseous anesthetic compound delivered by inhalation

An inhalational anesthetic is a chemical compound possessing general anesthetic properties that is delivered via inhalation. They are administered through a face mask, laryngeal mask airway or tracheal tube connected to an anesthetic vaporiser and an anesthetic delivery system. Agents of significant contemporary clinical interest include volatile anesthetic agents such as isoflurane, sevoflurane and desflurane, as well as certain anesthetic gases such as nitrous oxide and xenon.

Minimum alveolar concentration or MAC is the concentration, often expressed as a percentage by volume, of a vapour in the alveoli of the lungs that is needed to prevent movement in 50% of subjects in response to surgical (pain) stimulus. MAC is used to compare the strengths, or potency, of anaesthetic vapours. The concept of MAC was first introduced in 1965.

<span class="mw-page-title-main">Methoxyflurane</span> Chemical compound

Methoxyflurane, sold under the brand name Penthrox among others, is an inhaled medication primarily used to reduce pain following trauma. It may also be used for short episodes of pain as a result of medical procedures. Onset of pain relief is rapid and of a short duration. Use is only recommended with direct medical supervision.

Dental anesthesia is the application of anesthesia to dentistry. It includes local anesthetics, sedation, and general anesthesia.

The Fink effect, also known as "diffusion anoxia", "diffusion hypoxia", or the "second gas effect", is a factor that influences the pO2 (partial pressure of oxygen) within the pulmonary alveoli. When water-soluble gases such as anesthetic agent N2O (nitrous oxide) are breathed in large quantities they can be dissolved in body fluids rapidly. This leads to a temporary increase in both the concentrations and partial pressures of oxygen and carbon dioxide in the alveoli.

In the study of inhaled anesthetics, the concentration effect is the increase in the rate that the Fa /Fi ratio rises as the alveolar concentration of that gas is increased. In simple terms, the higher the concentration of gas administered, the faster the alveolar concentration of that gas approaches the inspired concentration. In modern practice it is only relevant for nitrous oxide since other inhaled anesthetics are delivered at much lower concentrations due to their higher potency.

Blood–gas partition coefficient, also known as Ostwald coefficient for blood–gas, is a term used in pharmacology to describe the solubility of inhaled general anesthetics in blood. According to Henry's law, the ratio of the concentration in blood to the concentration in gas that is in contact with that blood, when the partial pressure in both compartments is equal, is nearly constant at sufficiently low concentrations. The partition coefficient is defined as this ratio and, therefore, has no units. The concentration of the anesthetic in blood includes the portion that is undissolved in plasma and the portion that is dissolved. The more soluble the inhaled anesthetic is in blood compared to in air, the more it binds to plasma proteins in the blood and the higher the blood–gas partition coefficient.

<span class="mw-page-title-main">Robert M. Epstein</span> American anesthesiologist

Robert Marvin Epstein (1928-2024) was an American anesthesiologist, a member of the National Academy of Medicine, and the Harold Carron Professor of Anesthesiology (emeritus) at the University of Virginia.

References

  1. Epstein, R.M.; Rackow,H.; Salanitre,E.; Wolf,G.L. (1964). "Influence of the Concentration Effect on the Uptake of Anesthetic Mixtures: The Second Gas Effect". Anesthesiology. 25 (3): 364–371. doi: 10.1097/00000542-196405000-00015 . PMID   14156577.
  2. Stoelting, R.K.; Eger,E.I. (1969). "An Additional Explanation for the Second Gas Effect: A Concentrating Effect". Anesthesiology. 30 (3): 273–277. doi: 10.1097/00000542-196903000-00007 . PMID   5778096.
  3. Korman, B.; Mapleson, W. W. (May 1997). "Concentration and second gas effects: can the accepted explanation be improved?". British Journal of Anaesthesia. 78 (5): 618–625. doi: 10.1093/bja/78.5.618 . PMID   9175984.