When using therapeutic agents that can cause methemoglobinemia (methHb), which of the fol-lowing is important to prevent adverse effects?

a. Checking the frequency of ventilation
b. Frequent monitoring for methHb to weigh the risk against the benefit
c. Occasional monitoring for sickle cell ane-mia
d. Frequent monitoring for abnormal body temperature (high or low)

ANS: B
Methemoglobin (metHb) is an abnormal form of the molecule, in which the heme-complex nor-mal ferrous iron ion (Fe2+) loses an electron and is oxidized to its ferric state (Fe2+). In the ferric state, the iron ion cannot combine with O2. The result is a special form of anemia called methe-moglobinemia. As with HbCO, clinical abnormalities come from the associated increased affinity for O2 and loss of oxygen-binding capacity. The most common cause of methemoglobinemia is the therapeutic use of oxidant medications such as nitric oxide, nitroglycerin, and lidocaine. When using these therapeutic agents, frequent monitoring for metHg is important to weigh the risk against the benefit.