A 40 year old dental assistant presents with increased weakness and fatigue. Lab tests reveal megaloblastic anemia. Which of the following is most likely responsible for the presence of anemia?
High-Yield Explanation
Answer: b) Nitrous oxideNITROUS OXIDE (laughing gas)Has second gas effect during induction & diffusion hypoxia after discontinuation of anesthesia in recovery phase.As N2O is used in high concentration (70-80%) it leads to entry of N2O in blood at a rate higher than minute (1 lit/min) volume.N2O has low blood solubility. So it rapidly diffuse into alveoli & dilutes the alveolar air-Partial Pressure of O2 in alveoli is reduced i.e. diffusion hypoxiaDiffusion hypoxia is prevented by administering 100% oxygen for 5-10 min after discontinuing N2OPoynting effect: Entonox (50% O2 & 50% N2O) & mixture of gases (O2 & N2O) keeps them in gaseous form.If another potent anesthetic eg. Halothane is added, it also will be delivered to the blood at a rate higher than minute volume & the induction will be faster.N2O is a good analgesic but weak anaesthetic and poor muscle relaxant. Hence it is not a complete anaesthetic.N2O has blood gas coefficient of 0.47 and has fast inductionIt has MAC value of 104; Hence Potency is lowN2O is used as a carrier gas given in a mixture of 33% O2 and 66% N2OContraindications for N2O:Middle ear surgeries and tympanoplastyLaparoscopic surgeriesAcute intestinal obstruction and volvulusMicrolaryngeal surgeriesPneumothorax, pneumoperitoniumEye surgeriesPneumoencephalos.It should be avoided in patients with pulmonary hypertensionAdverse effects: bone marrow depression (agranulocytosis, megaloblastic anemia) and even neurological deficiencies (peripheral neuropathies and pernicious anemia).NOTE:Nitrous oxide is one of the most common anesthetics used in dental procedures. Prolonged exposure to nitrous oxide results in the development of megaloblastic anemia.Mechanism: Nitrous oxide oxidizes the cobalt in methylcobalamin to produce physiologically inactive B12.The resultant deficiency leads to megaloblastic anemia. Severe forms even present with myelosuppression and sub-acute combined degeneration.Side effects of nitrous oxide:Methylcobalamin deficiencyPneumothorax and pneumoperitoneumMethemoglobinemia.