By Q. Keldron. Rutgers University-Camden.
Lym- membrane to regulate the exchange of plasma solutes with phatic tissues (spleen and lymph nodes) produce 20% extracellular ﬂuid generic estrace 1mg mastercard breast cancer 6 months chemo. Lipid-soluble materials diffuse directly to 30% of the WBCs cheap estrace 1mg online breast cancer xrt, and reticuloendothelial tissues through the capillary cell membrane; water and water-soluble (spleen, liver, lymph nodes) produce 4% to 8% of WBCs. Almost all oxygen (95% to 97%) is transported in Lymphatics combination with hemoglobin; very little is dissolved in blood. The lifespan of a normal RBC is approxi- Lymphatic vessels, which are composed mainly of endothe- mately 120 days. They then stream to enter injured tissues and phagocytize the carry lymphocytes, large molecules of protein and fat, micro- injurious agent. For example, when a blood vessel is injured, platelets adhere to each other and Blood functions to nourish and oxygenate body cells, protect the edges of the injury to form a cluster of activated the body from invading microorganisms, and initiate hemo- platelets (ie, a platelet thrombus or plug) that sticks stasis when a blood vessel is injured. If cells to lungs for removal from the body not used, they circulate for approximately a week • Transports absorbed food products from the gastroin- before being removed by phagocytic cells of the testinal tract to tissues; at the same time, carries meta- spleen. In addition, these drugs may be given for pal- bidity and mortality, often stem from blood vessel abnormali- liation of symptoms without alteration of the underlying dis- ties. In turn, most vascular diseases result from the malfunction ease process. Dysfunctional endothelium is considered a major factor in atherosclerosis, acute coronary syndromes (symptomatic myocardial ischemia, asymptomatic myocardial infarction [MI], and MI with or Review and Application Exercises without ST-segment elevation), hypertension, and throm- boembolic disorders. In what circumstances do other parts of the heart take over forces and leads to vasospasm, thrombosis, growth of the in- as pacemaker? What is the effect of parasympathetic (vagal) stimulation Pathologic changes in the structure of the capillary and venu- on the heart? What is the effect of sympathetic stimulation on the heart in interstitial space (edema), a common symptom of cardio- and blood vessels? How does low or high blood volume influence blood Overall, cardiovascular disorders may involve any struc- pressure? List ﬁve chemical mediators produced by endothelial cells culatory system is a closed system, a disorder in one part of and their roles in maintaining cardiovascular function. How does endothelial cell dysfunction contribute to cardiovascular disorders? DRUG THERAPY IN CARDIOVASCULAR DISORDERS SELECTED REFERENCES Cardiovascular disorders usually managed with drug therapy Gokce, N. Endotheliopathies: Clinical include atherosclerosis, heart failure, cardiac dysrhythmias, manifestations of endothelial dysfunction. Schafer ischemia, myocardial infarction, hypertension, hypotension, (Eds. Philadelphia: restore homeostasis or physiologic balance between oppos- W. Cardiovascular drugs may be given to in- of medical-surgical nursing, 9th ed. Philadelphia: Lippincott Williams crease or decrease cardiac output, blood pressure, and heart & Wilkins. Explain the roles of potassium chloride, conduction, indications for use, principles of lidocaine, atropine, and digoxin immune fab therapy, and nursing process implications. Critical Thinking Scenario George Sweeney, a 72-year-old retired carpenter, was recently hospitalized with heart failure and started on captopril, an angiotensin-converting enzyme (ACE) inhibitor. Reﬂect on: Physiologically, what happens when the heart fails to pump adequately, and what symptoms are seen in the client? What criteria (objective and subjective) will you use to evaluate whether the ACE inhibitor is effectively managing Mr. Vital functions of the endothelium include maintaining equilibrium between vasodi- Heart failure (HF), also called congestive heart failure (CHF), lation and vasoconstriction, coagulation and anticoagulation, is a common condition that occurs when the heart cannot pump and cellular growth promotion and inhibition. Endothelial dys- enough blood to meet tissue needs for oxygen and nutrients. These are major factors in coronary artery disease and hypertension, the most common conditions leading to HF. Other causative factors include hyperthyroidism, excessive Causes of Heart Failure intravenous ﬂuids or blood transfusions, and drugs that decrease the force of myocardial contraction (eg, antidysrhythmic drugs) At the cellular level, HF stems from dysfunction of contrac- or cause retention of sodium and water (eg, corticosteroids, tile myocardial cells and the endothelial cells that line the estrogens, nonsteroidal anti-inflammatory agents).
D 50 mg 50 mg 50 mg 50 mg E 200 mg 300 mg 600 mg 800 mg C 400 mg 650 mg 1200 mg 1800 mg Use in Preventing Cardiovascular Disease Folate 300 mcg 400 mcg 600 mcg 800 mcg Niacin 10 mg 15 mg 20 mg 30 mg Folic acid and vitamin C are believed to have cardioprotective Pyridoxine 30 mg 40 mg 60 mg 80 mg effects order estrace 2mg on line menstruation cycle pregnancy. Folic acid is important in the metabolism of homo- cysteine cheap 1mg estrace with visa pregnancy yoga exercises, a toxic amino acid and a major risk factor for heart disease. Homocysteine is normally produced during metabo- Use in Older Adults lism of methionine, another amino acid. Several B vitamins, including folic acid, are required for the metabolism of ho- Vitamin requirements are the same as for younger adults. How- mocysteine to a nontoxic substance, and an increased blood ever, deﬁciencies are common in older adults, especially of vi- level of homocysteine occurs with folic acid deficiency. With vitamin B12, for example, it is estimated that arteries and leads to plaque formation, arteriosclerosis, and older adults absorb only 10% to 30% of the amount found in thrombosis. Other factors may also contribute to deﬁciencies, includ- effects by lowering blood levels of homocysteine. Although ing limited income, anorexia, lack of teeth or ill-ﬁtting den- the FDA requirement that folic acid be added to cereal grain tures, drugs that decrease absorption of dietary nutrients, and foods may be helpful, the folic acid intake that helps prevent disease processes that interfere with the ability to obtain, pre- cardiovascular disease is thought to be higher. Vitamin C is thought to help prevent cardiovascular disease Every older adult should be assessed regarding vitamin in- by its antioxidant effects. The atherogenic effects of blood take (from foods and supplements) and use of drugs that in- lipids, especially low-density lipoprotein (LDL) cholesterol teract with dietary nutrients. Vitamin C may help to prevent oxidation of LDL healthy and able to eat a varied, well-balanced diet. Overall, however, the effects of vitamin C on pre- tion, requirements may be increased during illnesses, espe- vention of coronary artery disease (CAD) are unclear. Overdoses, especially of studies indicate an increased risk for CAD only with a severe the fat-soluble vitamins A and D, may cause toxicity and vitamin C deﬁciency and that vitamin C has little effect on should be avoided. Tolerable ULs for older adults have ischemic heart disease and stroke after adjustment for other been established for some vitamins (D, 50 mg; E, 1000 mg; risk factors. More research is needed before vitamin C supple- C, 2000 mg; folate, 1000 mcg; niacin, 35 mg; pyridoxine, ments are recommended for cardioprotective effects. For a number of years, vitamin E was thought to have an- Use in Preventing Cancer tioxidant, cardioprotective effects similar to those of vitamin C. Vitamin A, its precursor beta carotene, and vitamin C are the main vitamins associated with prevention of cancer. Vitamin Use in Renal Impairment A and beta carotene may reduce cancers of the lung, breast, oral mucosa, esophagus, and bladder. Although vitamin A Patients with renal impairment usually have special needs in supplements are not recommended, increasing dietary intake relation to vitamin intake because of difﬁculties in ingesting of fruits and vegetables is desirable. Considerations include: anticancer effects stem from beta carotene or other compo- • In patients with acute renal failure who are unable to eat nents of fruits and vegetables. Large doses of vitamin C should be 200 mg or more from fruits and vegetables (ﬁve or more serv- avoided because urinary excretion is impaired. In addi- ings daily) are associated with reduced cancer risk, especially tion, oxalate (a product of vitamin C catabolism) may for cancers of the GI tract (eg, oral cavity, esophagus, stom- precipitate in renal tubules or form calcium oxalate ach, and colon) and lung. However, in other studies, vitamin stones, obstruct urine ﬂow, and worsen renal function. C supplements did not decrease the occurrence of stomach or • In patients with chronic renal failure (CRF), deﬁciencies colorectal cancer. Thus, the cancer-preventing effects of fruits of water-soluble vitamins are common because many 466 SECTION 5 NUTRIENTS, FLUIDS, AND ELECTROLYTES foods that contain these vitamins are restricted because Use in Critical Illness of their potassium content. In addition, vitamin C is re- absorbed from renal tubules by a speciﬁc transport pro- Patients with critical illnesses often experience vitamin deﬁ- tein. When the transport protein becomes saturated, ciencies unless they are prevented by early supplementation. Vitamin C is Patients receiving enteral nutrition should usually be given removed by dialysis, and, therefore, patients receiving DRI-equivalent amounts of all vitamins. The optimal re- resections (short bowel syndrome) may be able to take most placement dose is unknown but probably should not ex- vitamins orally or by GI tube.
In liver disease estrace 2 mg with visa pregnancy leg pain, small doses of all diuretics are usually may occur with potassium-losing diuretics (eg cheap estrace 2 mg mastercard menstrual odor treatment, hydro- indicated because diuretic-induced electrolyte imbal- chlorothiazide, furosemide). Bumetanide may be a daily of hydrochlorothiazide) useful alternative, because it can be given in smaller b. Sustained-release tablets are usually better mide, the initial dose is usually metolazone 2. Giving a potassium-sparing diuretic along with the sired response is achieved. If an adequate diuretic effect potassium-losing drug occurs with the first dose of metolazone, the dose of d. Hydrochlorothiazide vocate this approach as preferable to supplemental 50 mg may also be used with furosemide and may be potassium or combination diuretic therapy, but its safer than metolazone because of its shorter duration effectiveness is not clearly established. Use in Edema You are working on a cardiac unit, caring for clients after bypass When diuretics are used to manage clients with edema, the surgery. Vellara has Lasix 80 mg ordered bid to pull off extra ﬂuid underlying cause of the edema should be addressed, not just that is retained from the surgery. When managing such clients, it is prefer- you look through the chart as you document the medication you gave. You note that the nursing assistant has charted the following: able to aim for a weight loss of approximately 2 lb (1 kg) per Vital signs: 142/88 (lying) 108/60 (sitting), AP 96 and regular, day. CHAPTER 56 DIURETICS 827 minimal daily requirement of potassium is unknown, kidneys and may increase the incidence of patent ductus arte- usual recommendations are 40 to 50 mEq daily for riosus and neonatal respiratory distress syndrome. Potassium loss with diuretics may furosemide may be given with indomethacin to prevent non- be several times this amount. In both tations for having high potassium content; actually, preterm and full-term infants, furosemide half-life is prolonged large amounts must be ingested. To provide 50 mEq but becomes shorter as renal and hepatic functions develop. Some of these closely monitored in children because of frequent changes in foods are high in calories and may be contraindi- kidney function and ﬂuid distribution associated with growth cated, at least in large amounts, for obese clients. Ototoxicity, which is associated with high Also, the amount of carbohydrate in these foods may plasma drug levels (>50 mcg/mL), can usually be avoided by be a concern for clients with diabetes mellitus. Hyperkalemia (serum potassium level >5 mEq/L) may cause less ototoxicity and thus may be preferred for chil- may occur with potassium-sparing diuretics. The fol- dren who are taking other ototoxic drugs (eg, premature and ill lowing measures help prevent hyperkalemia: neonates are often given gentamicin, an aminoglycoside anti- a. The sium supplements in clients with renal impairment half-life of bumetanide is about 2 hours in critically ill infants b. Avoiding excessive amounts of potassium chloride and 1 hour in children. Maintaining urine output, the major route for elimi- potassium loss and hypokalemia. Spironolactone accumulates nating potassium from the body in renal failure, and dosage should be reduced. Use in Children Use in Older Adults Although they have not been extensively studied in children, diuretics are commonly used to manage heart failure, which Thiazide diuretics are often prescribed for the management often results from congenital heart disease; hypertension, of hypertension and heart failure, which are common in older which is usually related to cardiac or renal dysfunction; bron- adults. Older adults are especially sensitive to adverse drug chopulmonary dysplasia and respiratory distress syndrome, effects, such as hypotension and electrolyte imbalance. Thi- which are often associated with pulmonary edema; and edema, azides may aggravate renal or hepatic impairment. With rapid which may occur with cardiac or renal disorders such as the or excessive diuresis, myocardial infarction, renal impair- nephrotic syndrome. IV chlorothiazide chlorothiazide or equivalent doses of other thiazides and usually is not recommended. Risks of adverse effects may exceed beneﬁts at cause hyperglycemia, hyperuricemia, or hypercalcemia in chil- doses of hydrochlorothiazide greater than 25 mg. With loop diuretics, older adults are at greater risk of ex- cessive diuresis, hypotension, ﬂuid volume deﬁcit, and pos- Although metolazone, a thiazide-related drug, is not usu- sibly thrombosis or embolism. With potassium-sparing diuretics, hy- advantages over a thiazide because it is a stronger diuretic, perkalemia is more likely to occur in older adults because of causes less hypokalemia, and can produce diuresis in renal fail- the renal impairment that occurs with aging.
When the capacitance is dis- charged buy discount estrace 1 mg breast cancer 6 cm, a large but transient current ﬂows through Changes induced in the PSTH of single units the coil 1mg estrace with amex menstruation green discharge, some several thousand amperes` within The PSTH of a FDI unit in Fig. Thecurrentproducesamagneticﬁeldofupto anodal electrical stimulation produces an early peak 3 tesla oriented perpendicular to the coil (see Barker, with a sharp increase and short duration, prob- Jalinous & Freeston, 1985). The skull presents a low ably due to the D wave activating the motoneurone impedance to magnetic ﬁelds of this frequency, and monosynaptically (Day et al. Increasing the the magnetic ﬁeld induces eddy currents in superﬁ- stimulus intensity recruits further peaks which fol- cial layers of the brain at right angles to the ﬁeld. This is illustrated in the neural tissue is stimulated electrically with both Fig. What differs is the later by a second peak due to the I2 wave (pyrami- method of delivery. Electrical currents induced by the magnetic ﬁeld These ﬂow parallel to the surface of the brain. The Disadvantages magneticﬁeldfallsoffrapidlywithdistancefromthe The major problem with transcranial electrical stim- coil: with a typical 12 cm-diameter round coil, ulation is that only a small fraction of the current the strength falls by half at a distance of 4–5 cm from ﬂows into the brain. Experi- between the electrodes on the scalp and produces ments in monkeys suggest that, even at the highest strong discomfort, local pain and contraction of the stimulus intensities, there is no signiﬁcant activa- scalp muscles. Magnetic stimulation Stimulation using different coils Like electrical stimulation, transcranial magnetic With standard round coils, the induced current in stimulationofthemotorcortex(TMS)readilyevokes the brain ﬂows from an annulus underneath the Stimulation of the motor cortex 43 coil, which is usually some 8–12 cm in diameter. The following excitation of cortical elements oriented direction of current ﬂow in the coil is optimal for paralleltothesurface,suchasstellatecellsorcortico- stimulation of the left hemisphere when counter- cortical connection ﬁbres (see Rothwell, 1997). Coilswound in a ﬁgure-of-8 shape provide a more focal stimulus, TMS can also activate pyramidal and the lowest threshold occurs when the induced axons directly current in the brain ﬂows from posterior to anter- ior at an angle approximately perpendicular to the ADwaveisproducedincorticospinalaxonstoupper line of the central sulcus (Mills, Boniface & Schubert, limb motoneurones when the coil is rotated or the 1992). Direct record- ingsofdescendingactivityobtainedinanaesthetised humansubjectsduringsurgeryhaveshownthatTMS Responses in upper limb muscles can produce D waves with a lower threshold than I Longer latency of EMG responses evoked by waves (Burke et al. An alternative possibil- produced by the two techniques is the time taken ity was raised by Nielsen, Petersen and Ballegaard for trans-synaptic activation of pyramidal neurones (1995). They found that the EMG responses evoked 44 General methodology by anodal stimulation 2–3 cm lateral to the vertex Conditioning stimulation occurred 1–2 ms earlier than those evoked from the Subliminal transcranial magnetic stimulation has vertex, and they interpreted this as direct stimula- been used extensively to investigate the corti- tion of corticospinal axons deep to cortex. In accor- cospinal control of all spinal cord circuits for dancewiththisinterpretation,epiduralrecordingsof which there are reliable methods of investigation corticospinal volleys in awake co-operative human (cf. It is impossible to focus the magnetic ﬁeld in order to restrict the extent of the induced current ﬂow only to speciﬁc cortical areas and, at rest, TMS induces responses in several muscles. A good way of focus- Critique: advantages, limitations, ing the stimulation on one muscle is to record the conclusions response from a voluntarily activated muscle, but it is then impossible to investigate changes in trans- Cortical stimulation may be used to evoke test mission produced by a voluntary contraction. It is responses and conditioning stimuli essential that the position of the coil on the scalp is stable throughout an experiment, and different Test responses methods have been proposed to ensure this. Man- During voluntary contraction, the recruitment ual ﬁxation against a reference grid marked on the sequence in a voluntarily activated motoneurone scalp is the simplest way (see Capaday, 1997). Alter- pool is similar for Ia and corticospinal inputs natively the position of the coil may be secured by a (cf. In any event, because fore be modiﬁed similarly by conditioning stimuli, thefocusingoftheresponseonaparticularmuscleis unless the conditioning volley alters (i) motor cortex dependentonthepositionofthecoiloverthescalp,it excitability (see below); (ii) presynaptic inhibition of is important that the subject does not move the neck Ia terminals mediating the afferent volley of the test during the session. A prac- Input–output relationship within the ticalconsequenceofthedifferenceinthesitesofacti- motoneurone pool vationinthehandareaisthatthresholdresponsesto electricalstimulation(duetodirectactivationofcor- As for the H reﬂex, the input–output relationship ticospinal axons) should be less affected by changes within the motoneurone pool is sigmoid, and it is incorticalexcitabilitythanthoseevokedbymagnetic important to set the stimulus intensity within the stimulation(duetotrans-synapticactivationofpyra- range corresponding to the steep (roughly linear) midal neurones). This has been used as a method part of the relationship (see Capaday, 1997). Eccles & Lundberg, 1957), small slow-twitch to large fast-twitch units (Bawa & and (ii) convergence from two different ﬁbre sys- Lemon, 1993). The intensity of the rest,Hreﬂexes and MEPs of similar size do not ne- stimuli is adjusted so that separate stimulation of cessarily recruit the same population of motoneu- either I or II does not elicit a post synaptic poten- rones (Nielsen et al. This could be because tial (PSP) in the motoneurone (ﬁrst two rows in the component of the corticospinal excitation trans- Fig. The consequence of this is then produces an EPSP in the motoneurone (last that a different modulation of the MEP and the H row inFig.
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