The effects of an intravenous nicardipine injection on baroreflex control of heart rate in man

Does intravenous landiolol, a β1-adrenergic blocker, affect stroke volume variation?

PURPOSE

There are no reports about the effect of bradycardia on stroke volume variation (SVV), and we hypothesized that induced bradycardia alters the value of SVV. Landiolol, an ultra-short-acting adrenergic β1-receptor blocking agent, was reported to induce bradycardia without decreasing blood pressure. The initial aim of this prospective study was to investigate changes in SVV values by induced bradycardia in patients with good cardiac function.

METHODS

At 30 min after anesthesia induction, if heart rate (HR) was >80 bpm, the patient was chosen as a subject. Ten ASA physical status I-II patients aged 38-75 years who were scheduled for elective abdominal surgery were included in this study. Baseline values were recorded, and then administration of landiolol was started at 125 μg/kg/min for 1 min and then continued at 40 μg/kg/min. SVV and other parameters were recorded at baseline and 3 min after continuous landiolol injection.

RESULTS

Landiolol significantly decreased systolic arterial pressure, and diastolic arterial pressure, contrary to our expectations, and also HR, SVV, cardiac output, stroke volume index, and pressure of end-tidal CO(2), whereas systemic vascular resistance values increased significantly.

CONCLUSIONS

SVV decreased after continuous administration of a β1-adrenergic blocker, probably because of a decrease in the difference of maximum stroke volume (SV) and minimum SV, or the downward shift of the Frank-Starling curve that occurred after landiolol administration. We believe that SVV values might be overestimated or misinterpreted when HR is decreased by landiolol and might not necessarily indicate that the patient is hypervolemic or normovolemic.

Do induced hypertension and hypotension affect stroke volume variation in man?

STUDY OBJECTIVE

To investigate changes in stroke volume variation (SVV) by both induced hypertension (pressor test) and hypotension (depressor test), and also by induced hypotensive anesthesia in patients with good cardiac function.

DESIGN

Prospective, controlled clinical study.

SETTING

University hospital.

PATIENTS

31 ASA physical status 1 and 2 patients, aged 39-62 years, who were scheduled for elective surgery.

INTERVENTIONS

We conducted three studies: a pressor test study, a depressor test study, and an induced hypotensive anesthesia study. In the pressor test, patients received a bolus of phenylephrine 0.001 mg/kg to increase systolic arterial pressure (SAP) by 30% to 40% compared with baseline. In the depressor test, patients received a bolus of nitroglycerine 0.005 mg/kg to decrease SAP by 30% to 40% compared with baseline. In the induced hypotensive anesthesia test, patients received intravenous (IV) nitroglycerine continuously until mean arterial pressure (MAP) was reduced to 60-70 mmHg.

MEASUREMENTS

When arterial pressure reached the target pressure for each study type, SVV and other parameters were recorded.

MAIN RESULTS

Induced hypertension (pressor test) decreased SVV, while induced hypotension (depressor test) and induced hypotensive anesthesia increased SVV.

CONCLUSIONS

SVV does not misinterpret preload dependency assessment of patients receiving medications to increase or to lower blood pressure.

The effects of butorphanol on baroreflex control of heart rate in man

The effects of butorphanol injection on baroreflex control of heart rate were investigated using both pressor and depressor tests in eighteen adult patients. Baroreflex sensitivity was attenuated after butorphanol injection in the pressor test using phenylephrine, whereas it was unchanged in the depressor test using nitroglycerine. No resetting of the baroreflex occurred after butorphanol injection. After the administration of butorphanol, plasma epinephrine and norepinephrine levels increased. These results suggest that it is safe to use butorphanol clinically even when a reduction in blood pressure due to hypovolemia or unclamping of the major artery is expected and that it is disadvantageous to administer the drug when an increase in blood pressure due to cross-clamping of the major artery is predicted.