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Cerebral blood flow during the acute therapy of severe hypertension with oral clonidine
C S Greene1, D D Gretler, K Cervenka
1Department of Emergency Medicine, University of Chicago, IL 60637.
Insights
Clonidine effectively treats severe hypertension by lowering blood pressure. Its impact on cerebral blood flow (CBF) varies, increasing in patients with low initial CBF and decreasing in those with high initial CBF.
Area of Science:
- Neurology
- Cardiovascular Medicine
- Pharmacology
Background:
- Acute treatment of severe hypertension poses a risk of reduced cerebral blood flow (CBF) and central nervous system ischemic injury.
- Understanding the effects of antihypertensive medications on CBF is crucial for patient safety.
Purpose of the Study:
- To investigate the impact of acute clonidine treatment for severe hypertension on cerebral blood flow (CBF).
- To determine if clonidine affects CBF and to identify factors influencing these changes.
Main Methods:
- Studied 13 patients with severe hypertension (diastolic blood pressure > 115 mm Hg).
- Administered oral clonidine and measured CBF before and after blood pressure reduction.
- Analyzed the relationship between initial CBF and changes in CBF post-treatment.
Main Results:
- Oral clonidine effectively reduced blood pressure in 12 of 13 patients.
- Mean group CBF did not significantly change, but 9 patients showed >10% alterations (5 increases, 4 reductions).
- CBF changes were dependent on initial CBF levels: increases in patients with low pretreatment flow, decreases in those with high initial flow.
Conclusions:
- Clonidine is effective for acute severe hypertension treatment.
- Clonidine's effect on CBF is influenced by baseline CBF levels, with no significant adverse effects observed.
- These findings highlight the importance of assessing baseline CBF when using clonidine in hypertensive patients.
Abstract:
A major risk associated with the acute treatment of severe hypertension is a reduction in cerebral blood flow (CBF) with ischemic injury to the central nervous system. The authors studied CBF before and after the acute treatment of severe hypertension (diastolic blood pressure greater than 115 mm Hg) with clonidine in 13 patients. One patient did not reach goal blood pressure (diastolic blood pressure 105 mm Hg or a decrease by 30 mm Hg) after clonidine alone. In the remaining 12 patients, oral clonidine reduced supine blood pressure from 201.7 +/- 5.0/126.3 +/- 2.1 mm Hg to 149.4 +/- 5.3/96.8 +/- 1.7 mm Hg over an average time period of 85 +/- 7 minutes. Although mean CBF for the group did not change (72.6 +/- 4.2 v 73.7 +/- 3.5 mL/100 mg/min), a significant (greater than 10%) change occurred in 9 of the 12 patients (5 increases and 4 reductions). The magnitude and direction of the change were dependent upon initial CBF (r = -0.65, P less than .05); patients with low pretreatment CBF experienced an increase, whereas those with high initial flow exhibited a decrease. No significant adverse effects were observed. These data confirm previous reports that clonidine is effective in the acute treatment of severe hypertension and demonstrate that its effects on CBF are determined by the pretreatment levels of flow.