Nitrous Oxide for the written and oral Anesthesia Boards

N2O
Effects on CNS	Mild depression of central nervous system (cerebral cortex) in conjunction with physiological levels of O2 (greater than 20%) Sensations depressed (sight, hearing, touch and pain ) It offers both hypnotic and analgesic characteristics. It decreases the propofol consumption and does not reduce the remifentanil consumption when given by a closed loop automated controller to maintain a similar Bispectral index (BIS) (1) In view of the limited evidence of human studies and the sufficient evidence of experimental studies, there is a significant association between exposure to nitrous oxide and Parkinson's disease. (2) Nitrous oxide exerts analgesia by inhibition of N-methyl-D-aspartate receptors. However, nitrous oxide anesthesia was not associated with decreased opioid administration, pain, or incidence of moderate to severe pain in the early postoperative phase. (3)
Effects on circulation	Blood pressure remains stable with only slight decrease Cutaneous vasodilation     No changes in heart rate and cardiac output   The pulmonary vascular resistance is increased due to constriction in pulmonary vascular smooth muscle, so nitrous oxide should be avoided in patients with pulmonary hypertension. (4) Nitrous oxide result in less depression of cardiac index when given with isoflurane than when given with halothane. (5)
Effects on respiration	Changes (drop) in rate and depth more likely due to anxiolytic effects Non irritating to pulmonary epithelium Slight elevation in resting respiratory minute volume at 50%/50% Nitrous oxide causes decrease in tidal volume and increase in respiratory rate. it also causes reduction in ventilatory response to hypoxia and hypercapnia. It decrease tracheal mucociliary flow and neutrophil chemotaxis. This may increase post operative complication. (4)
Effects on GI function	No clinically significant effect, unless there is a closed space (obstruction) N/V rarely seen unless hypoxia present
Effects on neuromuscular function	No direct relaxation of skeletal muscle Anxiolytic effects help relaxation Administration of nitrous oxide may increase motor activity with clonus and opisthotonus even in clinically used concentration.
Effects on hepatic function	It can be used in hepatic dysfunction
Effects on hematologic and immune systems	Long term exposure (greater than 24 hours) can produce transient bone marrow depression. Repeated use of nitrous oxide, particularly during lengthy procedures, may precipitate megaloblastic anemia and spinal cord degeneration. (4)
Other system	Uterine contractions not inhibited Pregnancy is a relative contraindication (avoid in first trimester) Nitrous oxide provided less effective pain relief than epidural anesthesia in labor pain management. (6)
Minimum alveolar concentration and pressures	Oil: gas partition coefficient = 1.4 Blood: gas partition coefficient = 0.47 MAC (%) = 105
Trace concentrations, O.R. pollution, personnel hazards	It is a compressed liquefied gas, an asphyxiation risk, and a dissociative anesthetic. Acute toxicity: N/V Exposure to Nitrous oxide causes short term decrease in mental performance, audio-visual ability and mental dexterity. Long term exposure can cause vitamin B12 deficiency, numbness, reproductive side effects (in pregnant females)
Advantages	No odor Fast induction and recovery Minimal cardio pulmonary depression Good analgesic
Clinical implications	general anesthesia  obstetrics  pain management (4)
References Liu N, Le Guen M, Boichut N et al. Nitrous oxide does not produce a clinically important sparing effect during closed-loop delivered propofol-remifentanil anaesthesia guided by the bispectral index: a randomized multicentre study.Br J Anaesth. 2014 Jan 31.  Mastrangelo G, Comiati V, dell'Aquila M, Zamprogno E. Exposure to anesthetic gases and Parkinson's disease: a case report. BMC Neurol. 2013 Dec 9;13:194. Duma A, Helsten D, Brown F, Bottros MM, Nagele P. The effect of nitrous oxide anesthesia on early postoperative opioid consumption and pain.Reg Anesth Pain Med. 2014 Jan-Feb;39(1):31-6. Amelia Banks, Jonathan G Hardman. Nitrous Oxide. Contin Edus Anaesth Crit Care Pain (October 2005) 5(5): 145-148 MS McKinney, JPH Fee. Cardiovascular effects of 50% nitrous oxide in older adult patients anesthetized with isoflurane or halothane. British Journal of Anesthesia. 1998; 80: 169-173.  Likis FE, Andrews JC, Collins MR, Lewis RM, Seroogy JJ, Starr SA, Walden RR, McPheeters ML. Nitrous oxide for the management of labor pain: a systematic review. Anesth Analg. 2014 Jan;118(1):153-67.   AnesthesiaExam Podcast  For Board Review and Practice Management Updates TEXT the word  ANESTHESIAEXAM to the number 33444  For more information, CME credit and MOCA and Primary Board Prep, For more information, CME credit and MOCA and Primary Anesthesiology Board Prep, Go to AnesthesiaExam.com For Basic and Advanced Anesthesia Exam Review,  Go to ABAStagedExams.com For CRNA Board Prep, go to CRNABoardPrep.com For the Pediatric Anesthesiology Board Review, Go to PedsAE.com David Rosenblum, MD specializes in Pain Management and is the Director of Pain Management at Maimonides Medical Center and AABP Pain Managment For evaluation and treatment of a Painful Disorder, go to www.AABPPain.com 718 436 7246 DISCLAIMER: Doctor Rosenblum IS HERE SOLELY TO EDUCATE, AND YOU ARE SOLELY RESPONSIBLE FOR ALL YOUR DECISIONS AND ACTIONS IN RESPONSE TO ANY INFORMATION CONTAINED HEREIN. This podcasts is not intended as a substitute for the medical advice of physician to a particular patient or specific ailment.  You should regularly consult a physician in matters relating to yours or another’s health.  You understand that this podcast is not intended as a substitute for consultation with a licensed medical professional.    Copyright © 2015 QBazaar.com, LLC  All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, recording or otherwise, without the prior written permission of the author.