Pharmacology and Nutrition

LEARNING OUTCOMES

1.       Explain the common drug use in Cardiovascular System.

2.       Explain nursing consideration when administering drug in Cardiovascular system.

 

Cardiac Stimulants and Depressants

The heart is a complex blood-pumping organ which contains specialized cardiac muscle and a unique system for generating and conducting electrical impulses. The most powerful generator of electrical impulses in the heart is the sinoatrial (SA) node (Figure 28–1). When the SA node generates an electrical impulse, a contraction of the atrium occurs. The impulse then proceeds through the atria to the atrioventricular (AV) node, which usually acts to coordinate atrial and ventricular contraction. However, the atrioventricular node can act as a pacemaker when the generator of impulses from the SA node is suppressed. Rhythms generated by the SA node are referred to as sinus rhythms. Those emanating from the AV node are called nodal rhythms. Electrical activity through the SA and AV nodes is dependent, to a great extent, on the influx of calcium through channels in the cardiac cell membrane into the cell. The entire contraction of the heart is known as a systole. Although both the atria and the ventricles have systole and diastole periods (the atria in systole when the ventricles are in diastole and the atria in diastole when the ventricles are in systole), the systole in the ventricles is considered the heartbeat, because it is audible and palpable. Systole occurs about 60–100 times each minute in adults and more rapidly in children and infants, depending on their age. For example, infants have a normal heart rate of 120–160 beats per minute, with the normal rate for toddlers being 90–140 beats, for preschoolers 80–110 beats, school-age children 75–100 beats, and adolescents 60–90 beats. Each systole is normally followed by a period of cardiac muscle relaxation known as diastole.

Heart rate is primarily controlled by the autonomic nervous system (ANS). Parasympathetic (cholinergic) nerve endings (vagal fibers) are located in close proximity to the SA node and other areas of the atria and ventricles. With stimulation of these nerves (vagal stimulation), the neurotransmitter acetylcholine is released at the junction of the nerve and the cardiac muscle (myocardium). This acts to slow the heart rate by inhibiting impulse formation and electrical conduction in the heart. Sympathetic (adrenergic) nerve fibers also innervate various portions of the heart. When these are stimulated, the neurotransmitter norepinephrine is released. This action tends to increase heart rate by promoting impulse formation and electrical conduction in the heart. Sympathetic stimulation also tends to reduce the time interval between consecutive generations of impulses. It therefore reduces the duration of the refractory period, i.e., the time between consecutive muscle contractions. Drugs can change several aspects of cardiac action. They can: increase or decrease the force of myocardial contraction. Drugs that increase the force of contraction are said to exert a positive inotropic effect on the heart. Those that reduce the force of contraction are said to exert a negative inotropic effect. increase or decrease heart rate by altering the rate of impulse formation at the SA node. Drugs that increase heart rate are said to exert a positive chronotropic effect. Those slowing heart rate are said to exert a negative chronotropic effect. increase or decrease the conduction of electrical impulses through the myocardium. Drugs that increase the rate of electrical conduction are said to exert a positive dromotropic effect. Those that slow conduction is said to exert a negative dromotropic effect

CARDIAC GLYCOSIDES

Digoxin and similar drugs belong to a chemical class usually referred to as the cardiac glycosides. They are all derived from natural sources and have been recognized for centuries for their medicinal qualities. Although commonly employed in ancient civilizations as emetics, diuretics, heart tonics, and even as rat poisons, the cardiac glycosides have emerged during the last century as popular and effective agents for the treatment of congestive heart failure.

This condition is often the result of the sustained presence of one or more underlying cardiovascular diseases in the client. Congestive heart failure is often characterized by: cardiac distention resulting from the inability of the ventricles to pump the entire volume of blood with which they are presented cardiac hypertrophy caused by the heart’s adaptation to prolonged stretching sodium and water retention caused, in part, by diminished renal blood flow These effects result in weight gain, edema, shortness of breath, pulmonary congestion, and a variety of other symptoms.

Cardiac glycosides usually provide effective treatment for congestive heart failure by exerting a positive inotropic action on the heart. In so doing, they increase the force of myocardial contraction and thereby improve the mechanical efficiency of the heart as a blood-pumping organ. This ultimately results in a reduction in heart size and increased blood flow to the kidneys. Improved renal blood flow causes a diuretic effect, which eventually reduces the concentration of sodium and water in the body. Cardiac glycosides also tend to exert negative chronotropic and dromotropic actions on the heart, thereby making them potentially useful agents in the treatment of various cardiac arrhythmias.

Note: Taking digitoxin or digoxin with meals may decrease gastric irritation.

Do not administer if pulse is less than 60 beats per minute (adults), 90 beats per minute (infants), or 70 beats per minute (children up to adolescence).

Report heart rates below these levels to the physician. Also report heart rates of 100 or more per minute.

Report any evidence of irregular rhythm.

Observe client for toxicity, including symptoms of headaches, visual disturbances, nausea, vomiting, anorexia, or disorientation.

Clients taking diuretics other than potassium-sparing diuretics are at particular risk of developing toxicity.

Monitor potassium levels and encourage intake of potassium-rich foods. Client education is especially important.

This includes instruction in taking a radial pulse, as well as directions to notify the physician if indications of toxicity occur.

Hypothyroid clients are particularly sensitive to these drugs.

Monitor drug level.

 

ANTIARRHYTHMIC AGENTS

Although the rhythm of the heart is generally controlled by its principal pacemaker, the SA node, spontaneous electrical discharge or automaticity may occur anywhere in the heart under certain conditions. Any electrical activity initiated by such a spontaneous discharge is considered to be a rhythm disturbance, or arrhythmia

Antiarrhythmic drugs act to diminish or obliterate rhythm disturbances by: decreasing the automaticity of cardiac tissues distant from the SA node (i.e., at ectopic sites) altering the rate of conduction of electrical impulses through the heart altering the refractory period of cardiac muscle between consecutive contractions The selection of the most appropriate antiarrhythmic agent is dependent on the type of arrhythmia treated, the presence of other pathological conditions (e.g., heart failure, pulmonary disease), the relative safety of the drug as compared to other means of therapy, and the onset and/or duration of action of the drug. Most antiarrhythmic agents are administered intravenously (inamrinone lactate, milrinone lactate, digoxin, adenosine, diltiazem HCl, and others) until the heart has converted to normal sinus rhythm (NSR). Oral doses are used to maintain NSR

 

CARDIAC STIMULANTS USED TO TREAT SHOCK

 Adrenergic or sympathomimetic drugs are agents that mimic the action of the neurotransmitter norepinephrine. They may act to cause: vasoconstriction of peripheral blood vessels vasodilation of blood vessels in skeletal muscle increased heart rate (positive chronotropic effect) increase in the force of contraction of the heart (positive inotropic effect) increased rate of glycogenolysis in the liver and skeletal muscle stimulation of the CNS Not all sympathomimetic agents will produce each of these effects to the same degree. Their action is often dependent on their degree of selectivity for specific adrenergic receptors in the body. Some sympathomimetic agents have a selective action on alpha-adrenergic receptor sites

 

Note: Monitor the apical pulse for 1 minute before administration.

Record rate and rhythm of heartbeat.

Patient should be supine when IV doses are administered to prevent postural hypotension.

 

Sympathomimetic Agents Used in the Treatment of Shock

Note: An intravascular line is usually established so that these drugs can be given by IV. During emergency treatment the nurse must keep track of the names and dosages of drugs administered.

Monitor client’s vital signs and condition continuously when drugs are given IV.

Record intake and output on all clients. Infiltration may result in tissue necrosis.

NURSING IMPLICATIONS

Cardiac Glycosides

1. Always check the client’s apical pulse rate for 1 minute before administering these products.

2. Withhold these drugs if the pulse rate is less than 60 beats per minute in adults, less than 90 beats per minute in infants, and less than 70 beats per minute in children and adolescents.

3. Report bigeminy (if on monitoring) or significant deviations in the client’s heart rate or rhythm.

4. Assess the client for toxicity by checking the heart rate and rhythm and observing for neurological signs, such as headache, visual disturbances and changes in color vision and gastrointestinal symptoms such as nausea, vomiting and anorexia.

5. Monitor potassium level and report level less than 4 ml.

6. To minimize pain and possible tissue damage, intramuscular preparations must be given deep into a large muscle mass.

7. Teach the client and family members how to recognize signs of toxicity and assess heart rate.

 

Antiarrhythmic Agents

1. Assess the client’s apical pulse for 1 minute before administration.

2. Clients scheduled to receive lidocaine, tocainide, or procainamide should be questioned about allergy to local anesthetics.

3. Give quinidine at mealtimes to decrease gastrointestinal upset.

4. The client should always be supine when intravenous quinidine is administered.

 5. Clients receiving intravenous lidocaine or procainamide should be supine during administration.

6. Check vital signs on all clients following intravenous administration of antiarrhythmic drugs. Report signs of confusion or convulsions in clients following lidocaine or procainamide use.

7. Report evidence of granular deposits on the cornea of clients taking amiodarone.

8. Verapamil HCl may cause hypotension and disturbances of cardiac rhythm. Stop intravenous administration if the systolic blood pressure drops below 70–80 mm/Hg and if the pulse drops below 50 beats per minute.

 

Coronary Vasodilators

1. Assessment focuses on determining the frequency, nature, and precipitants of anginal attacks and the effectiveness of vasodilators in relieving angina.

2. Sublingual or lingual nitroglycerin should be used at the first sign of an attack of angina.

3. Clients using nitroglycerin products, such as sublingual tablets, lingual spray, or ointment, plus those using amyl nitrite are advised to sit or lie down before using the product, as hypotension is possible. Alcohol may intensify hypotensive effects.

 4. A fresh supply of sublingual nitroglycerin tablets should be obtained every 3 months. Avoid storage in areas subjected to prolonged heat.

5. Nurses must avoid direct contact with topical preparations of nitroglycerin. Review the procedure for applying nitroglycerin ointment and the guidelines for use of a transdermal nitroglycerin system.

6. Intravenous nitroglycerin must only be administered using glass bottles and special administration sets. Do not mix other drugs with the nitroglycerin.

7. When both a beta-adrenergic blocking agent and a vasodilator are ordered, schedule administration of the blocking agent first.

8. Calcium channel blockers should be taken with meals or milk. Blood pressure should be routinely monitored.

Peripheral Vasodilators

1. Assessment includes inspection of the skin, auscultation, palpation, and interviewing.

2. Clients experiencing light headedness or dizziness when taking vasodilators should be advised to lie down until these side effects pass.

3. A flushed or warm feeling often results from the use of vasodilators and is not a cause for alarm.

 4. Clients with peripheral vascular illnesses require an education program focused on general hygiene and safety.

 

ANTICOAGULANTS

These drugs inhibit the action or formation of one or more clotting factors. None, however, is capable of exerting a fibrinolytic effect on existing clots.

Heparin is an agent found in mast cells located throughout the body. It has been found to be a potent inhibitor of the clotting process and has been used for more than 40 years in the prophylaxis and treatment of clotting disorders related to coronary occlusion, cerebral thrombosis, cerebral vascular accidents (CVAs), and many other diseases. Heparin indirectly interferes with the conversion of prothrombin to thrombin

Note:

These agents should be used with caution in clients with trauma, infection, hypertension, diabetes, or major surgery.

Prothrombin times should be taken every 4 to 6 weeks once the client has been stabilized. Monitor the client for the development of drug interactions.

KEY NURSING IMPLICATIONS

Anticoagulants

1. Report abnormal bleeding or indications of internal bleeding, such as headache, tarry stools, and changes in neurological status.

2. To avoid intramuscular injection of heparin, select a short needle and choose a site with adequate subcutaneous tissue.

3. The effects of heparin can be reversed through the intravenous use of protamine sulfate.

4. When heparin is administered by continuous intravenous infusion, an infusion pump is generally used to ensure a precise rate of infusion.

5. When administering heparin through a saline lock, disinfect the diaphragm, use a small-gauge needle and watch for signs of infiltration.

6. Contact the prescriber before administering the next dose of an oral anticoagulant if the prothrombin time is 30 seconds or greater.

7. Review the procedure for safe administration of heparin.

8. Monitor partial thromboplastin time (PTT) when administering heparin and contact the prescriber if PTT is not within prescribed parameters (usually 1.5–2.5 times normal [30–40 seconds]).

Comfort and Safety During Anticoagulant Therapy

1. Avoid intramuscular injections in clients on anticoagulants. If such injections are necessary, maintain pressure on the site for several minutes after injection.

2. Vitamin K1 (phytonadione) is used as an antidote for oral anticoagulants.

3. Avoid the use of aspirin and aspirin containing products

Anticoagulants

1. Clients are advised to avoid situations that could lead to trauma.

2. Clients are instructed to talk with the primary care provider before adding or subtracting any drug from their treatment program.

3. Drastic changes in diet, laxatives and mineral oil should be avoided.

 4. Identification and information about treatment should always be carried or a Medic-Alert tag worn.

5. Women on anticoagulants who are considering pregnancy must be referred to an obstetrician.

Thrombolytic Agents

1. Observe the client receiving streptokinase for allergic reactions. Observe all clients receiving thrombolytic agents for bleeding, changes in vital signs, and chest pain.

2. Reconstitute streptokinase with Sodium Chloride Injection or Dextrose (5%) Injection. Do not shake the vial to mix it.

3. Many clients develop reperfusion arrhythmias that require prompt identification and treatment following alteplase use.

4. To minimize bleeding, intravenous lines are established prior to initiating therapy with thrombolytic agents.

5. Apply manual pressure for 20 to 30 minutes, followed by application of a pressure dressing on all puncture sites during and following thrombolytic therapy.

6. Use preservative-free sterile water for injection to reconstitute alteplase.

7. Following the infusion of alteplase, the line is flushed with 5% Dextrose in water (D5W) or normal saline, to ensure administration of the entire dose.

8. Institute safety measures (e.g., padded siderails, routine vital signs, assessment of skin) to prevent unnecessary blood loss.

9. Monitor the client for the development of re occlusion of the coronary arteries.

10. Client and family education regarding drug therapy and lifestyle changes is an important nursing function.

Self check
1. Explain nursing responsibility when administering cardiac drugs.