NUR 301 CH 14: Patients With Coronary Vascular Disorders

A patient asks the nurse how long he will have to wait after taking nitroglycerin before experiencing pain relief. What is the best answer by the nurse?

3 minutes Rationale: Nitroglycerin may be given by several routes: sublingual tablet or spray, oral capsule, topical agent, and intravenous (IV) administration. Sublingual nitroglycerin is generally placed under the tongue or in the cheek (buccal pouch) and ideally alleviates the pain of ischemia within 3 minutes.

Post-cardiac surgery assessment of renal function should be performed hourly for the first 12 to 24 hours. Identify the laboratory result that the nurse knows is a primary indicator of possible renal failure.

A serum BUN of 70 mg/dL Rationale: These four laboratory results should always be assessed, post cardiac surgery. Serum osmolality (N = >800 mOsm/kg) should also be included. A BUN reading of greater than 21 mg/dL is abnormal; a reading of greater than 60 mg/dL is indicative of renal failure. The lab results in the other choices are all within normal range.

You are caring for a client with CAD. What is an appropriate nursing action when evaluating a client with coronary artery disease (CAD)?

Assess the characteristics of chest pain. Rationale: The nurse should assess the characteristics of chest pain for a client with CAD. Assessing the client's mental, emotional status, the skin of the client, or for drug abuse will not assist the nurse in evaluating the client for CAD.

A client with angina pectoris must learn how to reduce risk factors that exacerbate this condition. When developing the client's care plan, which expected outcome should a nurse include?

"Client will verbalize the intention to stop smoking." Rationale: A client with angina pectoris should stop smoking at once because smoking increases the blood carboxyhemoglobin level; this increase, in turn, reduces the heart's oxygen supply and may induce angina. The client must seek immediate medical attention if chest pain doesn't subside after three nitroglycerin doses taken 5 minutes apart; serious myocardial damage or even sudden death may occur if chest pain persists for 2 hours. To improve coronary circulation and promote weight management, the client should get regular daily exercise. The client should eat plenty of fiber, which may decrease serum cholesterol and triglyceride levels and minimize hypertension, in turn reducing the risk for atherosclerosis (which plays a role in angina).

A client with an acute myocardial infarction is receiving nitroglycerin by continuous I.V. infusion. Which client statement indicates that this drug is producing its therapeutic effect?

"My chest pain is decreasing." Rationale: Nitroglycerin, a vasodilator, increases the arterial supply of oxygen-rich blood to the myocardium. This action produces the drug's intended effect: relief of chest pain. Headache is an adverse effect of nitroglycerin. The drug shouldn't cause a tingling sensation around the mouth and should lower, not raise, blood pressure.

When assessing a client who reports recent chest pain, the nurse obtains a thorough history. Which client statement most strongly suggests angina pectoris?

"The pain occurred while I was mowing the lawn." Rationale: Decreased oxygen supply to the myocardium causes angina pectoris. Lawn mowing increases the cardiac workload, which increases the heart's need for oxygen and may precipitate this chest pain. Anginal pain typically is self-limiting, lasting 5 to 15 minutes. Food consumption doesn't reduce angina pain, although it may ease pain caused by a GI ulcer. Deep breathing has no effect on anginal pain.

A man has just arrived in the ER with a possible myocardial infarction (MI). The electrocardiogram (ECG) should be obtained within which time frame of arrival to the ER?

10 minutes Rationale: The ECG provides information that assists in diagnosing acute MI. It should be obtained within 10 minutes from the time a patient reports pain or arrives in the emergency department. By monitoring serial ECG changes over time, the location, evolution, and resolution of an MI can be identified and monitored.

The nurse is reviewing the results of a total cholesterol level for a patient who has been taking simvastatin (Zocor). What results display the effectiveness of the medication?

160-190 mg/dL Rationale: Simvastatin (Zocor) is a statin Frequently given as initial therapy for significantly elevated cholesterol and low-density lipoprotein levels. Normal total cholesterol is less than 200 mg/dL.

In order to be effective, percutaneous transluminal coronary angioplasty (PTCA) must be performed within what time frame, beginning with arrival at the emergency department after diagnosis of myocardial infarction?

60 minutes Rationale: The 60-minute interval is known as "door-to-balloon time" for performance of PTCA on a diagnosed MI patient. The 30-minute interval is known as "door-to-needle time" for administration of thrombolytics post MI. The time frame of 9 days refers to the time for onset of vasculitis after administration of streptokinase for thrombolysis in an acute MI patient. The 6 to 12 month time frame refers to the time period during which streptokinase will not be used again in the same patient for acute MI.

The nurse has been asked to explain the cause of angina pain to a patient's family. Choose the best statement. The pain is due to:

A lack of oxygen in the heart muscle that causes the death of cells. Rationale: Impeded blood flow, due to blockage in a coronary artery, deprives the cardiac muscle cells of oxygen thus leading to a condition known as ischemia.

Which of the following methods to induce hemostasis after sheath removal post percutaneous transluminal coronary angioplasty (PTCA) is the least effective?

Application of a sandbag to the area Rationale: Several nursing interventions frequently used as part of the standard of care, such as applying a sandbag to the sheath insertion site, have not been shown to be effective in reducing the incidence of bleeding. Application of a vascular closure device has been demonstrated to be very effective. Direct manual pressure to the sheath introduction site has been demonstrated to be effective and was the first method used to induce hemostasis post PTCA. Application of a pneumatic compression device post PTCA has been demonstrated to be effective.

After percutaneous transluminal coronary angioplasty (PTCA), the nurse suspects that a patient, who is on bed rest, may be experiencing the complication of bleeding. The nurse's initial action should be to do which of the following?

Apply manual pressure at the site of the insertion of the sheath. Rationale: The immediate nursing action would be to apply pressure, which may stop the bleeding. If the bleeding does not stop, the health care provider needs to be notified.

A nurse is caring for a client who is exhibiting signs and symptoms characteristic of a myocardial infarction (MI). Which statement describes priorities the nurse should establish while performing the physical assessment?

Assess the client's level of pain and administer prescribed analgesics. Rationale: The cardinal symptom of MI is persistent, crushing substernal pain or pressure. The nurse should first assess the client's pain and prepare to administer nitroglycerin or morphine for pain control. The client must be medically stabilized before pulmonary artery catheterization can be used as a diagnostic procedure. Anxiety and a feeling of impending doom are characteristic of MI, but the priority is to stabilize the client medically. Although the client and his family should be kept informed at every step of the recovery process, this action isn't the priority when treating a client with a suspected MI.

The nurse plays an important role in monitoring and managing potential complications in the patient who has recently undergone a coronary artery bypass graft (CABG). The nurse should be alert to which of the following respiratory complications?

Atelectasis Rationale: Respiratory complications that may occur include atelectasis. An incentive spirometer and the use of deep breathing exercises are necessary to prevent atelectasis and pneumonia. Elevated blood sugar levels, hyperkalemia, UTI, and are complications that can occur but are unrelated to the respiratory system.

Which diagnostic is a marker for inflammation of vascular endothelium?

C-reactive protein (CRP) Rationale: C-reactive protein (CRP) is a marker for inflammation of vascular endothelium. LDL, HDL, and triglycerides are not marker of vascular endothelium inflammation. They are elements of fat metabolism.

Which complication of cardiac surgery occurs when there is fluid and clot accumulation in the pericardial sac, which compresses the heart, preventing blood from filling the ventricles?

Cardiac tamponade Rationale: Cardiac tamponade is fluid and clot accumulation in the pericardial sac, which compresses the heart, preventing the blood from filling the ventricles. Fluid overload is exhibited by high PAWP, CVP, and pulmonary artery diastolic pressure as well as crackles in the lungs. Hypertension results from postoperative vasoconstriction. Hypothermia is a low body temperature that leads to vasoconstriction.

Which of the following medications is given to patients diagnosed with angina and is allergic to aspirin?

Clopidogrel (Plavix) Rationale: Plavix or Ticlid is given to patients who are allergic to aspirin or given in addition to aspirin to patients at high risk for MI. Norvasc, Cardizem, and Plendil are calcium channel blockers.

A client comes to the Emergency Department (ED) complaining of precordial chest pain. In describing the pain, the client describes it as pressure with a sudden onset. What disease process would you suspect in this client?

Coronary artery disease Rationale: The classic symptom of CAD is chest pain (angina) or discomfort during activity or stress. Such pain or discomfort typically is manifested as sudden pain or pressure that may be centered over the heart (precordial) or under the sternum (substernal). Raynaud's disease in the hands presents with symptoms of hands that are cold, blanched, and wet with perspiration. Cardiogenic shock is a complication of an MI. Venous occlusive disease occurs in the veins, not the arteries.

The nurse is reviewing the laboratory results for a patient having a suspected myocardial infarction (MI). What cardiac-specific isoenzyme does the nurse observe for myocardial cell damage?

Creatine kinase MB Rationale: There are three creatine kinase (CK) isoenzymes: CK-MM (skeletal muscle), CK-MB (heart muscle), and CK-BB (brain tissue). CK-MB is the cardiac-specific isoenzyme; it is found mainly in cardiac cells and therefore increases when there has been damage to these cells. Elevated CK-MB is an indicator of acute MI; the level begins to increase within a few hours and peaks within 24 hours of an infarct.

The nurse is administering a calcium channel blocker to a patient who has symptomatic sinus tachycardia at a rate of 132 bpm. What is the anticipated action of the drug for this patient?

Decreases the sinoatrial node automaticity Rationale: Calcium channel blockers have a variety of effects on the ischemic myocardium. These agents decrease sinoatrial node automaticity and atrioventricular node conduction, resulting in a slower heart rate and a decrease in the strength of myocardial contraction (negative inotropic effect).

A nurse is monitoring the vital signs and blood results of a 53-year-old male patient who is receiving anti-coagulation therapy. Which of the following does the nurse identify as a major indication of concern?

Hematocrit of 30% Rationale: Hematocrit is a measurement of the proportion of blood volume that is occupied by red blood cells. A lowered hematocrit can imply internal bleeding.

The nurse is discussing risk factors for developing CAD with a patient in the clinic. Which results would indicate that the patient is not at significant risk for the development of CAD?

High-density lipoprotein (HDL), 80 mg/dL Rationale: A fasting lipid profile should demonstrate the following values (Alberti et al., 2009): LDL cholesterol less than 100 mg/dL (less than 70 mg/dL for very high-risk patients); total cholesterol less than 200 mg/dL; HDL cholesterol greater than 40 mg/dL for males and greater than 50 mg/dL for females; and triglycerides less than 150 mg/dL.

Which of the following is inconsistent as a condition related to metabolic syndrome?

Hypotension Rationale: A diagnosis of metabolic syndrome includes three of the following conditions: insulin resistance, abdominal obesity, dyslipidemia, hypertension, proinflammatory state, and prothrombotic state.

When the nurse notes that the post cardiac surgery patient demonstrates low urine output (< 25 mL/hr) with high specific gravity (> 1.025), the nurse suspects:

Inadequate fluid volume Rationale: Urine output of less than 25 mL/hr may indicate a decrease in cardiac output. A high specific gravity indicates increased concentration of solutes in the urine, which occurs with inadequate fluid volume. Indices of normal glomerular filtration are output of 25 mL or greater per hour and specific gravity between 1.010 and 1.025. Overhydration is manifested by high urine output with low specific gravity. The anuric patient does not produce urine.

Which of the following is the most important postoperative assessment parameter for patients undergoing cardiac surgery?

Inadequate tissue perfusion Rationale: The nurse must assess the patient for signs and symptoms of inadequate tissue perfusion, such as a weak or absent pulse, cold or cyanotic extremities, or mottling of the skin. Although the nurse does assess blood sugar and mental status, tissue perfusion is the higher priority. Assessing for activity intolerance, while important later in the recovery period, is not essential in the immediate postoperative period for patients undergoing cardiac surgery.

The nurse is educating a patient diagnosed with angina pectoris about the difference between the pain of angina and a myocardial infarction (MI). How should the nurse describe the pain experienced during an MI? (Select all that apply.)

It is viselike and radiates to the shoulders and arms. It is substernal in location. It is sudden in onset and prolonged in duration. Rationale: Chest pain that occurs suddenly, continues despite rest and medication, is substernal, and is sometimes viselike and radiating to the shoulders and arms is associated with an MI. Angina pectoris pain is generally relieved by rest and nitroglycerin.

As part of health education for a patient with an abnormal fasting lipid profile, the nurse explains that an excess of this lipid leads to the formation of plaque in the arteries. Identify the lipid.

Low-density lipoproteins (LDL) Rationale: When there is an excess of LDL, these particles adhere to vulnerable points in the arterial endothelium. Here, macrophages ingest then, leading to the formation of foam cells and the beginning of plaque formation. A harmful effect is exerted on the coronary vasculature because the small LDL particles can be easily transported into the vessel lining.

Which of the following discharge instructions for self-care should the nurse provide to a patient who has undergone a percutaneous transluminal coronary angioplasty (PTCA) procedure?

Monitor the site for bleeding or hematoma. Rationale: The nurse provides certain discharge instructions for self-care, such as monitoring the site for bleeding or development of a hard mass indicative of hematoma. A nurse does not advise the patient to clean the site with disinfectants or refrain from sexual activity for one month.

Upon discharge from the hospital, patients diagnosed with a myocardial infarction (MI) must be placed on all of the following medications except:

Morphine IV Rationale: Upon patient discharge, there needs to be documentation that the patient was discharged on a statin, an ACE or angiotensin receptor blocking agent (ARB), and aspirin. Morphine IV is used for these patients to reduce pain and anxiety. The patient would not be discharged with IV morphine.

A patient in the recovery room after cardiac surgery begins to have extremity paresthesia, peaked T waves, and mental confusion. What type of electrolyte imbalance does the nurse suspect this patient is having?

Potassium Rationale: Hyperkalemia (high potassium) can result in the following ECG changes: tall peaked T waves, wide QRS, and bradycardia. The nurse should be prepared to administer a diuretic or an ion-exchange resin (sodium polystyrene sulfonate [Kayexalate]); IV sodium bicarbonate, or IV insulin and glucose. Imbalances in the other electrolytes listed would not result in peaked T waves.

Which of the following medications is an antidote to heparin?

Protamine sulfate Rationale: Protamine sulfate is known as the antagonist to heparin. Alteplase is a thrombolytic agent. Clopidogrel (Plavix) is an antiplatelet medication that is given to reduce the risk of thrombus formation post coronary stent placement. The antiplatelet effect of aspirin does not reverse the effects of heparin.

The nurse is part of a triage team that is assessing a patient to determine if his chest pain is a manifestation of angina pectoris or an MI. The nurse knows that a primary distinction is that the pain of angina is:

Relieved by rest and nitroglycerin Rationale: One characteristic that can differentiate the pain of angina from a myocardial infarction is pain that is relieved by rest and nitroglycerine. There may be some exceptions (unstable angina), but the distinction is helpful especially when combined with other assessment data.

A patient complains to the nurse about chest pain and palpitations during and after his morning jogs. The patient's family history reveals a history of coronary artery disease (CAD). What should the nurse recommend to minimize cardiac risk?

Smoking cessation Rationale: The first line of defense for patients with CAD is a change in lifestyle, such as smoking cessation, weight loss, stress management, and exercise. A protein-rich diet, liquid diet, and mild meals will not minimize cardiac risk.

A patient with coronary artery disease (CAD) is having a cardiac catheterization. What indicator is present for the patient to have a coronary artery bypass graft (CABG)?

The patient has at least a 70% occlusion of a major coronary artery. Rationale: For a patient to be considered for CABG, the coronary arteries to be bypassed must have approximately a 70% occlusion (60% if in the left main coronary artery).

A nurse is educating a community group about coronary artery disease. One member asks about how to avoid coronary artery disease. Which of the following items are considered modifiable risk factors for coronary artery disease? Choose all that apply.

Tobacco use Obesity Hyperlipidemia Rationale: Modifiable risk factors for coronary artery disease include hyperlipidemia, tobacco use, hypertension, diabetes mellitus, metabolic syndrome, obesity, and physical inactivity. Nonmodifiable risk factors include family history, advanced age, gender, and race.

The patient has had biomarkers drawn after complaining of chest pain. Which diagnostic of myocardial infarction remains elevated for as long as 3 weeks?

Troponin Rationale: Troponin remains elevated for a long period, often as long as 3 weeks, and it therefore can be used to detect recent myocardial damage. Myoglobin returns to normal in 12 hours. Total CK returns to normal in 3 days. CK-MB returns to normal in 3 to 4 days.

Which of the following is also termed preinfarction angina?

Unstable angina Rationale: Preinfarction angina is also known as unstable angina. Stable angina has predictable and consistent pain that occurs on exertion and it relieved by rest. Variant angina is exhibited by pain at rest with reversible ST-segment elevation. In silent angina, there is evidence of ischemia, but the patient reports no symptoms.

A client with chest pain doesn't respond to nitroglycerin. When he's admitted to the emergency department, the health care team obtains an electrocardiogram and administers I.V. morphine. The physician also considers administering alteplase (Activase). This thrombolytic agent must be administered how soon after onset of myocardial infarction (MI) symptoms?

Within 6 hours Rationale: For the best chance of salvaging the client's myocardium, a thrombolytic agent must be administered within 6 hours after onset of chest pain or other signs or symptoms of MI. Sudden death is most likely to occur within the first 24 hours after an MI. Physicians initiate I.V. heparin therapy after administration of a thrombolytic agent; it usually continues for 5 to 7 days.

Patients who are taking beta-adrenergic blocking agents should be cautioned not to stop taking their medications abruptly because which of the following may occur?

Worsening angina Rationale: Patients taking beta blockers are cautioned not to stop taking them abruptly because angina may worsen and myocardial infarction may develop. Beta blockers do not cause the formation of blood clots, internal bleeding, or thrombocytopenia.

A client with severe angina pectoris and ST-segment elevation on an electrocardiogram is being seen in the emergency department. In terms of diagnostic laboratory testing, it's most important for the nurse to advocate ordering a:

troponin level. Rationale: Troponin is a myocardial cell protein that is elevated in the serum when myocardial damage has occurred during a myocardial infarction (MI). It's the best serum indicator of MI and is more indicative of cardiac damage than creatine kinase. Hb values and liver panel components aren't as useful in the diagnosis of MI as a troponin level.

A client in the emergency department complains of squeezing substernal pain that radiates to the left shoulder and jaw. He also complains of nausea, diaphoresis, and shortness of breath. What should the nurse do?

Administer oxygen, attach a cardiac monitor, take vital signs, and administer sublingual nitroglycerin. Rationale: Cardiac chest pain is caused by myocardial ischemia. Therefore the nurse should administer supplemental oxygen to increase the myocardial oxygen supply, attach a cardiac monitor to help detect life-threatening arrhythmias, and take vital signs to ensure that the client isn't hypotensive before giving sublingual nitroglycerin for chest pain. Registration information may be delayed until the client is stabilized. Alerting the cardiac catheterization team or the physician before completing the initial assessment is premature.

A patient complains about chest pain and heavy breathing when exercising or when stressed. Which of the following is a priority nursing intervention for the patient diagnosed with coronary artery disease?

Assess chest pain and administer prescribed drugs and oxygen Rationale: The nurse assesses the patient for chest pain and administers the prescribed drugs that dilate the coronary arteries. The nurse administers oxygen to improve the oxygen supply to the heart. Assessing the blood pressure or the physical history does not clearly indicate that the patient has CAD. The nurse does not administer aspirin without the physician's prescription.

Which condition most commonly results in coronary artery disease (CAD)?

Atherosclerosis Rationale: Atherosclerosis (plaque formation), is the leading cause of CAD. Diabetes mellitus is a risk factor for CAD, but it isn't the most common cause. Myocardial infarction is a common result of CAD. Renal failure doesn't cause CAD, but the two conditions are related.

Which medication should a nurse have on hand when removing a sheath after cardiac catheterization?

Atropine Rationale: Removing the sheath after cardiac catheterization may cause a vasovagal response, including bradycardia. The nurse should have atropine on hand to increase the client's heart rate if this occurs. Heparin thins the blood; clients should stop taking it before the sheath removal. Protamine sulfate is an antidote to heparin, but the nurse shouldn't administer it during sheath removal. Adenosine treats tachyarrhythmias.

The nurse administers propranolol hydrochloride to a patient with a heart rate of 64 beats per minute (bpm). One hour later, the nurse observes the heart rate on the monitor to be 36 bpm. What medication should the nurse prepare to administer that is an antidote for the propranolol?

Atropine Rationale: Sheath removal and the application of pressure on the vessel insertion site may cause the heart rate to slow and the blood pressure to decrease (vasovagal response). A dose of IV atropine is usually given to treat this response.

A client comes to the emergency department complaining of chest pain. An electrocardiogram (ECG) reveals myocardial ischemia and an anterior-wall myocardial infarction (MI). Which ECG characteristic does the nurse expect to see?

Elevated ST segment Rationale: Ischemic myocardial tissue changes cause elevation of the ST segment, an inverted T wave, and a pathological Q wave. A prolonged PR interval occurs with first-degree heart block, the least dangerous atrioventricular heart block; this disorder may arise in healthy people but sometimes results from drug toxicity, electrolyte or metabolic disturbances, rheumatic fever, or chronic degenerative disease of the conduction system. An absent Q wave is normal; an MI may cause a significant Q wave. A widened QRS complex indicates a conduction delay in the His-Purkinje system.

A patient's elevated cholesterol levels are being managed with Lipitor, 40 mg daily. The nurse practitioner reviews the patient's blood work every 6 months before renewing the prescription. The nurse explains to the patient's daughter that this is necessary because of a major side effect of Lipitor that she is checking for. What is that side-effect?

Increased liver enzymes Rationale: Myopathy and increased liver enzymes are significant side effects of the statins, HMG-CoA reductase inhibitors that are used to affect lipoprotein metabolism.

The nurse is caring for a patient who is having chest pain associated with a myocardial infarction (MI). What medication should the nurse administer intravenously to reduce pain and anxiety?

Morphine sulfate Rationale: The patient with suspected MI should immediately receive supplemental oxygen, aspirin, nitroglycerin, and morphine. Morphine is the drug of choice to reduce pain and anxiety. It also reduces preload and afterload, decreasing the work of the heart.

Postpericardiotomy syndrome may occur in patients who undergo cardiac surgery. The nurse should be alert to which of the following clinical manifestations associated with this syndrome?

Pericardial friction rub Rationale: The syndrome is characterized by fever, pericardial pain, pleural pain, dyspnea, pericardial effusion, pericardial friction rub, and arthralgia. Leukocytosis (elevated WBCs) occurs, along with elevation of the ESR.

When the patient diagnosed with angina pectoris complains that he is experiencing chest pain more frequently even at rest, the period of pain is longer, and it takes less stress for the pain to occur, the nurse recognizes that the patient is describing which type of angina?

Unstable Rationale: Unstable angina is also called crescendo or preinfarction angina and indicates the need for a change in treatment. Intractable or refractory angina produces severe, incapacitating chest pain that does not respond to conventional treatment. Variant angina is described as pain at rest with reversible ST-segment elevation and is thought to be caused by coronary artery vasospasm. Intractable or refractory angina produces severe, incapacitating chest pain that does not respond to conventional treatment.

A client has a blockage in the proximal portion of a coronary artery. After learning about treatment options, the client decides to undergo percutaneous transluminal coronary angioplasty (PTCA). During this procedure, the nurse expects to administer an:

anticoagulant. Rationale: During PTCA, the client receives heparin, an anticoagulant, as well as calcium agonists, nitrates, or both, to reduce coronary artery spasm. Nurses don't routinely give antibiotics during this procedure; however, because the procedure is invasive, the client may receive prophylactic antibiotics to reduce the risk of infection. An antihypertensive may cause hypotension, which should be avoided during the procedure. An anticonvulsant isn't indicated because this procedure doesn't increase the risk of seizures.

A client with severe angina pectoris and electrocardiogram changes is seen by a physician in the emergency department. In terms of serum testing, it's most important for the physician to order cardiac:

troponin. Rationale: This client exhibits signs of myocardial infarction (MI), and the most accurate serum determinant of an MI is troponin level. Creatine kinase, lactate dehydrogenase and myoglobin tests can show evidence of muscle injury, but they're less specific indicators of myocardial damage than troponin.

The nurse has been asked to teach a patient how to self-administer nitroglycerin. The nurse should instruct the patient to do which of the following? Select all of the teaching points that apply.

• Let the tablet dissolve in the mouth and keep the tongue still. The tablet can be crushed between the teeth but not swallowed. • Renew the supply every 6 months. • Take the tablet in anticipation of any activity that can produce pain. • Call emergency services if, after taking three tablets (one every 5 minutes), pain persists. Rationale: Nitroglycerine is very unstable and should be carried securely in its original container (capped, dark, glass bottle). The tablets should never be removed and stored in metal or plastic pillboxes. Nitroglycerine is also volatile and is inactivated by heat, moisture, air, light, and time. Therefore, storage and replacement is recommended every 6 months. Refer to Box 14-3 in the text.