Monitoring adequacy of alpha-adrenoceptor blockade following systemic phentolamine administration.
Systemic phentolamine administration has been suggested as a diagnostic tool for identifying patients with sympathetically maintained pain (SMP) (Raja et al. 1991). The dose of phentolamine to produce adequate blockade of peripheral alpha-adrenoceptor function has, however, not been previously determined. In this study, the effects of two different doses of phentolamine on peripheral sympathetic vasoconstrictor function were investigated. One-hundred and seventeen (117) patients with chronic extremity pain underwent 130 phentolamine diagnostic tests using two different doses of phentolamine (0.5 mg/kg over 20 min (n = 60) and 1 mg/kg over 10 min (n = 59)). Eleven (11) patients did not receive phentolamine during the test. Cutaneous temperature was measured in the distal extremity before and after administration of phentolamine. In a subset of patients, baseline blood flow and sympathetically mediated vasoconstrictor response (SMR) to deep inhalation were measured on glabrous skin using laser Doppler flowmetry. SMR was elicited with a 5-sec maximal inspiratory gasp. A dose-related increase in cutaneous temperature was observed. In addition, baseline blood flow increased and SMR was attenuated after both doses of phentolamine, but to a greater degree after the 1 mg/kg dose. However, SMR was not completely attenuated, even after administration of the higher phentolamine dose. These results indicate that a phentolamine dose of 1 mg/kg over 10 min more completely blocks alpha-adrenoceptor function than a dose of 0.5 mg/kg over 20 min. We therefore recommend that to ensure adequate alpha-adrenoceptor blockade the higher phentolamine dose be used in the phentolamine diagnostic test for SMP.
Raja
Srinivasa N
SN
Department of Anesthesiology and Critical Care Medicine, The Johns Hopkins Hospital, Baltimore, MD 21287, USA Department of Neurosurgery, The Johns Hopkins Hospital, Baltimore, MD 21287, USA.
Turnquist
Jennifer L
JL
Meleka
Sherif
S
Campbell
James N
JN
D000293:Adolescent; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000328:Adult; D000368:Aged; D002908:Chronic Disease; D004305:Dose-Response Relationship, Drug; D005121:Extremities; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010146:Pain / Q000175:diagnosis; D010646:Phentolamine / Q000494:pharmacology*; D012039:Regional Blood Flow / Q000187:drug effects; D012119:Respiration / Q000502:physiology; D012867:Skin / Q000098:blood supply / Q000294:innervation; D012881:Skin Temperature / Q000187:drug effects; D013564:Sympathetic Nervous System / Q000187:drug effects* / Q000502:physiology; D014661:Vasoconstriction / Q000187:drug effects* / Q000502:physiology
D000317:Adrenergic alpha-Antagonists; D010646:Phentolamine