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Nursing2015 Critical Care

July 2014, Volume 9 Number 4 , p 12 - 16


  • Jennifer A. Gibson MSN, RN
  • Dione Breht Nordby MSN, RN


Sympathetic nervous system (SNS) activation is a critical compensatory mechanism that helps to increase cardiac output (CO) and oxygenation to meet the increased metabolic demands associated with stress or the "fight-or-flight" response.In clinical practice, we frequently administer medications that influence the SNS by stimulating, or inhibiting, different adrenergic receptors in order to produce specific, desired physiologic effects. Such effects are usually induced to counteract adverse hemodynamic changes that are associated with different disease states including: sepsis, dysrhythmias, asthma, hypertensive crises, and coronary artery disease (CAD).The body's nervous system is divided into two major branches: the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS contains the brain and the spinal cord. The PNS is subdivided into the somatic and autonomic nervous systems. The autonomic nervous system is further divided into the parasympathetic (cholinergic) and sympathetic (adrenergic) nervous systems. This article focuses on the SNS.Adrenergics, also known as adrenergic agonists or sympathomimetics, stimulate the SNS by binding to adrenergic receptors and causing a response. Substances that produce a sympathomimetic response are called catecholamines. Catecholamines include: epinephrine, norepinephrine, and dopamine. Adrenergic blockers, also known as antagonists or sympatholytics, bind to adrenergic receptors and inhibit or block SNS stimulation.Adrenergic receptors are further divided into alpha-adrenergic receptors and beta-adrenergic receptors. When stimulated, adrenergic receptors cause specific physiologic responses. Both types of adrenergic receptors are further differentiated into alpha1, alpha2, beta1, and beta2 receptors.1Innervated organs and tissues tend to have a predominance of one type of receptor. For example, the skeletal muscle vasculature has both alpha1 and beta2 receptors, but the beta2 receptors predominate.2 Similarly,

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