Special Techniques and Situations

Controlled hypotension is generally used to reduce surgical blood loss or provide a “bloodless” operating field.(1) Typically it is accomplished with vasodilators, beta-blockers, deep inhalational anesthesia, or calcium channel blockers. Longer-acting medications (beta blockade, inhalation agent) may be suitable in procedures in which there is little risk for rapid blood loss; however, rapidly reversible medications (nitroglycerin/sodium nitroprusside) are more prudent to use in procedures that have a high risk for blood loss.(1) Controlled hypotension has disparate effects on each of the major organ systems. Neurologic:, Cardiovascular:, Renal:, Hepatic:, Monitoring may change depending on the goals of the procedure in which controlled hypotension is used. If main objective is to lower perfusion pressure to improve operating conditions an arterial line may suffice but if the goal is to reduce surgical blood loss then CVP monitoring and an arterial line may be warranted. The addition of a drug with vasodilating properties (e.g., morphine) may be useful in the premedication of a patient undergoing hypotensive anesthesia. A balanced mix of volatile agents and a vasodilating agent (nitroglycerin/sodium nitroprusside/short acting beta blocker or calcium channel blocker) is best as an anesthetic technique based purely on volatile agents may cause profound cardiac depression. Short-acting beta blockers are not recommended in patients 2 years of age or younger, as cardiac output is heart rate dependent in this age group. Also beta blockers may cause hypoglycemia and thus glucose levels must be evaluated periodically. Monitoring should include pulse oximetry, etCO₂, ECG, temperature, CVP, MAP, and ABGs at specific intervals to evaluate hematocrit, blood glucose, and acid–base status. Arterial line pressures are typically taken from the radial artery although femoral arterial lines are adequate as well. Dorsalis pedis arterial lines have been noted to be inaccurate in the literature and thus should be used with caution. Once the desired MAP has been achieved, CVP should be recorded and maintained throughout the procedures to ensure the patient is normovolemic. Urine output should be monitored and be at least 0.5 to 1 ml/kg/h. Urine output is a simple way to determine if renal perfusion is adequate.