March 08, 2016

Nitrous Oxide for the written and oral Anesthesia Boards

4 minutes

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.

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David Rosenblum, MD specializes in Pain Management and is the Director of Pain Management at Maimonides Medical Center and AABP Pain Managment

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