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?
Propofol
Nitrous oxide
Lignocaine
Halothane
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.
General Anesthesia