Second gas effect

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During induction of general anesthesia when a large volume of 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 "concentration effect" and the "second gas effect". These effects occur because of the contraction of alveolar volume associated with the uptake of the nitrous oxide. Previous explanations by Eger and Stoelting have appealed to an extra-inspired tidal volume due to a potential negative intrapulmonary pressure associated with the uptake of the nitrous oxide.

There are two extreme breathing patterns and that the extra-inspired tidal volume is an artificial construct associated with one of these patterns.^[1] Thus it is the volume change that actually causes the effects.

Stedman's medical dictionary

When a constant concentration of an anesthetic like 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.

References

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Errata British Journal of Anaesthesia 1997;79:268

v t e Anesthesia (outline)
Types	General Spinal Epidural Conduction anesthesia Local Topical Intercostal nerve block Sedation / Twilight anesthesia Dental (Inferior alveolar nerve) Neuroleptanalgesic anesthesia
Techniques	Airway management Anesthesia provision in the US Arterial catheter Bronchoscopy Capnography Dogliotti's principle Drug-induced amnesia Intraoperative neurophysiological monitoring Nerve block Penthrox inhaler Tracheal intubation
Scientific Principles	Blood–gas partition coefficient Concentration effect Fink effect Minimum alveolar concentration Second gas effect
Measurements	ASA physical status classification system Baricity Bispectral index Direct Fick method Entropy monitoring Fick principle Goldman index Guedel's classification Mallampati score Neuromuscular monitoring Thyromental distance
Instruments	Anaesthetic machine Anesthesia cart Boyle's machine Gas cylinder Laryngeal mask airway Laryngeal tube Medical monitor Odom's indicator Relative analgesia machine Vaporiser Double-lumen endotracheal tube Endobronchial blocker
Drugs	Benzodiazepine Etomidate General anaesthetic Inhalational anaesthetic Infiltration analgesia Ketamine Local anesthetic Methohexital Methoxyflurane Midazolam Neuraxial blockade Opiate Propofol Thiopental Thiopentone
Complications	Emergence delirium Allergic reactions Anesthesia awareness Local anesthetic toxicity Malignant hyperthermia Perioperative mortality Postanesthetic shivering Postoperative nausea and vomiting Postoperative residual curarization
Fields of study	Cardiothoracic Geriatric Oral sedation dentistry
Professions	Anesthesiologist Anesthesiologist assistant Nurse anesthetist Operating Department Practitioners Certified Anesthesia Technician Certified Anesthesia Technologist Anaesthetic technician
History	A.C.E. mixture Helsinki Declaration for Patient Safety in Anaesthesiology History of general anesthesia History of neuraxial anesthesia History of tracheal intubation
Organizations	American Association of Nurse Anesthetists American Society of Anesthesia Technologists & Technicians American Society of Anesthesiologists Anaesthesia Trauma and Critical Care Association of Anaesthetists of Great Britain and Ireland Association of Veterinary Anaesthetists Australian and New Zealand College of Anaesthetists Australian Society of Anaesthetists International Anesthesia Research Society