A pilot study has concluded that 0.5 mg of the blood pressure drug metaraminol has a variable effect on cardiac output and oxygen delivery in patients who develop hypotension during induction of anesthesia.
The researchers said they planned to test the drug at different doses as a treatment for hypotension in surgical patients.
In the study, Scottish researchers set out to test how effective metaraminol would be as a treatment. This commonly used blood pressure medication directly stimulates vascular α-receptors and indirectly stimulates noradrenaline.
To find out if the drug could improve cardiac index and oxygen delivery index in a group of hypovolemic, vasodilated patients, the investigators conducted a prospective observational trial of 11 patients undergoing major colorectal surgery with or without synchronous liver resection.
“This is a group purposefully dehydrated to reduce blood loss. They were vasodilated because the anesthetist involved establishes an epidural pre-induction of anesthesia,” said Alex Puxty, MBChB, an anesthesiologist at Glasgow Royal Infirmary, who presented the study at the 2014 annual meeting of the Society of Critical Care Medicine (abstract 291).
Clinicians measured each patient’s hemodynamics on a beat-to-beat basis and stopped collecting data when a patient moved to the operating theater.
The anesthetist was blinded to the invasive blood pressure during anesthesia induction, but had access to noninvasive blood pressure monitoring. Patients were given 0.5 mg of metaraminol at the discretion of the anesthetist, and changes in cardiac index and oxygen delivery index were measured at the highest mean arterial pressure.
During the study, physicians used 18 doses of metaraminol in 11 patients during 14 hypotensive events. Hypotension was defined as a mean arterial pressure less than 70 mm Hg.
The median absolute rise in arterial pressure was 41 mm Hg (interquartile range [IQR], 31-60). Whereas systemic vascular resistance index rose for all patients, cardiac index and oxygen delivery index increased on 12 occasions and decreased on two occasions. The median rise in cardiac index was 0.53 L/min/m2 (IQR, 0.3-0.84). The median decline in cardiac index was –0.13 L/min/m2 (IQR, –0.19 to 0.07). The median increase in oxygen delivery index was 92 mL/min/m2(IQR, 93-232.8), and the median decrease in oxygen delivery index was –25 mL/min/m2 (IQR, –36.9 to 13.3).
“We will be doing further studies to look at a longer period of the operation and also to measure other perfusion variables and strategies of giving metaraminol,” Dr. Puxty said.
Matthew A. Levin, MD, assistant professor in the Division of Cardiothoracic Anesthesia, Icahn School of Medicine at Mount Sinai, in New York City, said metaraminol is not commonly used to counter hypotension in anesthetized patients in the United States.
“Since the primary mechanism [of action] of metaraminol is systemic vasoconstriction, it is not surprising that it only had a small and variable effect on cardiac output,” Dr. Levin said.
“Without a better characterization of the baseline cardiac function of these patients presenting for elective surgery, it is hard to say that the changes in cardiac index and oxygen delivery index observed are clinically significant.”