Select the true statement regarding blood pressure when 1.5 MAC nitrous oxide–isoflurane is substituted for 1.5 MAC isoflurane–oxygen.

Select the true statement regarding blood pressure when 1.5 MAC nitrous oxide–isoflurane is substituted for 1.5 MAC isoflurane–oxygen.

• A. A Blood pressure is less than awake value, but greater than that seen with isoflurane–O2
• B. B Blood pressure is equal to awake value
• C. C Blood pressure is greater than awake value
• D. D Blood pressure is unchanged

Answer: (A)

The main concept is how the carrier gas affects hemodynamics at a given depth of anesthesia. Isoflurane lowers blood pressure mainly by causing vasodilation and some myocardial depression. When nitrous oxide is used as part of the 1.5 MAC mixture instead of oxygen, the overall depressant effect on blood pressure is reduced compared with isoflurane–oxygen alone. Nitrous oxide tends to preserve vascular tone and can have a less pronounced depressant impact, so the blood pressure remains below awake values but higher than the level seen with isoflurane–O2. In other words, arterial pressure is reduced from baseline due to anesthesia, but not as much as with isoflurane–O2.

The main concept is how the carrier gas affects hemodynamics at a given depth of anesthesia. Isoflurane lowers blood pressure mainly by causing vasodilation and some myocardial depression. When nitrous oxide is used as part of the 1.5 MAC mixture instead of oxygen, the overall depressant effect on blood pressure is reduced compared with isoflurane–oxygen alone. Nitrous oxide tends to preserve vascular tone and can have a less pronounced depressant impact, so the blood pressure remains below awake values but higher than the level seen with isoflurane–O2. In other words, arterial pressure is reduced from baseline due to anesthesia, but not as much as with isoflurane–O2.