McKenna's Pharmacology for Nursing, 2e

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P A R T 5  Drugs acting on the autonomic nervous system

■ ■ Monitor blood pressure and pulse, assess

Prototype summary: Phenylephrine Indications: Treatment of vascular failure in shock or drug-induced hypotension; to overcome paroxysmal supraventricular tachycardia; to prolong spinal anaesthesia; as a vasoconstrictor in regional anaesthesia; to maintain blood pressure during anaesthesia; topically for symptomatic relief of nasal congestion and as adjunctive therapy in middle ear infections; ophthalmically to dilate pupils and as a decongestant to provide temporary relief of eye irritation. Actions: Powerful postsynaptic alpha-adrenergic receptor stimulant causing vasoconstriction and raising systolic and diastolic blood pressure with little effect on the beta-receptors in the heart. Pharmacokinetics: Route Onset Duration IV Immediate 15–20 mins IM, SC 10–15 mins 30–120 mins Topically Very little systemic absorption occurs T 1/2 : 47 to 100 hours; metabolised in the tissues and liver; excreted in urine and bile. Adverse effects: Fear, anxiety, restlessness, headache, nausea, decreased urine formation, pallor. ■ ■ Assess for contraindications or cautions: any known allergies to the drug to avoid hypersensitivity reactions ; presence of any cardiovascular diseases, which could be exacerbated by the vascular effects of these drugs; thyrotoxicosis or diabetes, which would lead to an increase in thyroid stimulation or glucose elevation ; chronic renal failure, which could be exacerbated by drug use ; renal or hepatic impairment, which could interfere with drug excretion or metabolism ; and current status of pregnancy and breastfeeding. ■ ■ Perform a physical assessment to establish baseline status before beginning therapy to determine effectiveness and during therapy to evaluate for any potential adverse effects. ■ ■ Assess level of orientation, affect, reflexes and vision to monitor for CNS changes related to drug therapy. Care considerations for people receiving α -specific adrenergic agonists Assessment: History and examination

peripheral perfusion and obtain ECG, if indicated, to determine drug effectiveness and evaluate for adverse cardiovascular effects. ■ ■ Assess urinary output to evaluate renal function and monitor for adverse effects of the drug. ■ ■ Evaluate person for nausea and constipation to assess adverse effects of the drug and establish appropriate interventions. ■ ■ Monitor laboratory test results, such as renal and liver function tests, to determine drug effects on renal and hepatic systems. ■ ■ Do not discontinue the drug abruptly because sudden withdrawal can result in rebound hypertension, arrhythmias, flushing and even hypertensive encephalopathy and death ; taper drug over 2 to 4 days. ■ ■ Do not discontinue the drug before surgery; document on the person’s chart and monitor blood pressure carefully during surgery. Sympathetic stimulation may alter the normal response to anaesthesia, as well as recovery from anaesthesia. ■ ■ Monitor blood pressure, orthostatic blood pressure, pulse, rhythm and cardiac output regularly, even with ophthalmic preparations, to adjust dose or discontinue the drug if cardiovascular effects are severe. ■ ■ When giving phenylephrine intravenously, ensure that an α -blocking agent is readily available to counteract the effects in case severe reaction occurs ; infiltrate any area of extravasation with phentolamine within 12 hours after extravasation to preserve tissue. ■ ■ Arrange for supportive care and comfort measures, including rest and environmental control, to decrease CNS irritation ; analgesics for headache to relieve discomfort ; safety measures, such as use of side rails and assistance with ambulation if CNS effects occur, to protect the person from injury ; and protective measures if CNS effects are severe. ■ ■ Provide thorough teaching about drug name, dose and schedule for administration; technique for administration if appropriate; measures to prevent potential adverse effects such as voiding before taking the drug and use of bowel training activities if constipation is a problem; safety measures such as avoiding driving and operating dangerous machinery if CNS effects occur, and getting up and down slowly if orthostatic hypotension is an issue; warning signs of problems; and importance of monitoring and follow-up. Implementation with rationale