By A. Samuel. Stillman College.
Other questions involve electrode conﬁgurations 80mg tadapox sale, electrical currents discount 80mg tadapox with mastercard, and pulse shapes, as well as the impor- tant issues of safety and biocompatibility. Preferential Stimulation of Retinal Cell Layers The advantage of stimulating retinal cells other than ganglions was mentioned ear- lier. Experimentally, it has been shown that phosphenes could be elicited in patients with advanced outer retinal degeneration via electrical stimulation (Potts and Inoue, 1970; Weiland et al. These electrically elicited responses require and indicate the presence of functioning retinal cells. As the human RGC axons exit the eye, they become myelinated and form the optic nerve. The cell bodies (somas) of these ganglion cells are mapped over the surface of the retina in a manner that approximates the projection of the visual world onto the surface of the retina. However, at any particular location on the sur- face of the retina, axons from distant sites overlay the individual ganglion cell bodies. If these superﬁcial passing axons were preferentially stimulated, groups of ganglion cells from large areas of the retina would be excited. One might expect the visual perception of such a stimulus to appear as a wedge. On the other hand, if the gan- glion cell bodies or deeper retinal cells were stimulated, one would expect the visual perceptions to be focal spots. RP patients that were stimulated with 50–200-mm- diameter platinum disk electrodes reported seeing spots, not wedges, of light (Humayun et al. To explore the possibilities of retinal electrical stimulation, a computational model of extracellular ﬁeld stimulation of the RGC has been constructed (Greenberg et al. The model predicted that the stimulation threshold of the RGC soma is 58– 73% lower than a passing axon, even though the axon was closer to the electrode. Nevertheless, a factor of less than 2 does not explain the source of visual perceptions observed during previous experiments with intraocular patients. Postmortem morphometric analysis of the retina of RP patients revealed that many more inner nuclear layer cells retain functionality (e. Early electrophysiological experiments showed that cathodic stimulation on the vitreous side of the retina depolarizes presynaptic end terminals of the photoreceptors (Knighton, 1975a,b) and bipolar cells (Toyoda and Fujimoto, 1984). Recently, latency experiments in frog retinas showed that higher currents stimulate the RGC directly, while lower currents activate other cells (photoreceptors, bipolar cells) (Greenberg, 1998). Another ﬁnding in those experiments was that shorter stimulating pulses (<0. There are well- deﬁned relationships between the threshold current and the duration of the stimulus pulse required for neuronal activation (West and Wolstencroft, 1983). As the dura- tion of the stimulus pulse decreases, the threshold increases exponentially. Also, as the pulse duration increases, the threshold current approaches a minimum value, called the rheobase. A chronaxie is the pulse width for which the threshold current is twice the rheobase current. Greenberg (1998) showed that deeper retinal cells have unusually long chronaxies compared with RGCs. It can be specu- lated from these results that there is a preferential stimulation of RGC cells or axons for short pulses and deeper cellular elements for long pulses.
However generic tadapox 80 mg with mastercard, iron deﬁciency is common in by direct injection into a vein or as a continuous IV in- young children and teenage girls buy discount tadapox 80mg on line, and an iron supplement is fusion. In children who eat poorly, a combined vitamin/mineral tion (50 mL contains 44. Monitor arterial blood gases and serum potassium lev- for infants and children. Overtreatment of acidosis with sodium a physician, dentist, or nurse practitioner. Serum potassium levels Children must be guarded against excessive ﬂuoride may change from high to normal levels initially (because ingestion and possible toxicity. Fluoride supplements acidosis causes potassium to be drawn into the blood- are used more often than formerly and numerous stream) to severely low levels as potassium reenters cells preparations are available for oral (tablets, chewable with treatment of acidosis. Thus, potassium replacement tablets, solutions) or topical (liquid rinse solutions or is likely to be needed during treatment of acidosis. During severe acidosis, effective ventilation measures should be kept out of the reach of children; supple- are needed, along with sodium bicarbonate to remove ments prescribed for children should be used only with carbon dioxide from the blood. In lactic acidosis, larger doses of sodium bicarbonate tions should be reminded to spit them out and not to may be required than in other types of acidosis. If supplements are given, dosages should be discussed lactic acid by body metabolism. All minerals and All minerals and electrolytes are toxic in overdose and electrolytes are toxic in overdose. If KCl and other electrolyte preparations are used to treat should not be exceeded. In addition, doses must be carefully nutritional status and use of drugs that interact with dietary measured and given no more often than prescribed to nutrients. Accidental ingestion of iron-containing medications and prevent either deﬁciency or excess states. To help Use in Renal Impairment combat accidental poisoning, products containing iron must be labeled with a warning and products with 30 mg Several mineral–electrolyte products are contraindicated in or more of iron (eg, prenatal products) must be packaged clients with renal impairment, including magnesium and as individual doses. All iron-containing preparations potassium chloride (severe impairment with oliguria or should be stored in places that are inaccessible to young azotemia), because of potential accumulation and toxicity. They are listed in the follow- ysis and receiving supplemental erythropoietin therapy, two ing table. The ULs for magnesium indicate maximum iron preparations have been developed to treat iron deﬁciency intake from pharmaceutical preparations; they do not anemia. Sodium ferric gluconate complex (Ferrlecit) and iron include intake from food and water. Birth– 7–12 1–3 4–8 9–13 14–18 Mineral 6 months months years years years years Use in Hepatic Impairment Calcium No data No data 2. Also, overdoses of chromium Magnesium No data No data 65 mg 110 mg 350 mg 350 mg Selenium 45 mcg 60 mcg 90 mcg 150 mcg 280 mcg 400 mcg and copper are hepatotoxic and should be avoided. Use in Critical Illness Use in Older Adults Electrolyte and acid–base imbalances often occur in critically Mineral–electrolyte requirements are the same as for younger ill clients and are usually treated as in other clients, with close adults, but deﬁciencies of calcium and iron are common in monitoring of serum electrolyte levels and avoiding exces- older adults. Numerous factors may contribute to deﬁcien- sive amounts of replacement products. Diuretic drugs, frequently prescribed for cardiovascu- The home care nurse has the opportunity to assess household lar disorders in older adults, may cause potassium deﬁciency members and the environment for indications of mineral– unless serum levels are carefully monitored and preventive electrolyte deﬁciency or excess. For example, nutrients, when mineral supplements are indicated or should decreased renal function promotes retention of magnesium be avoided, and safety factors related to iron supplements or and potassium. Hyperkalemia also may occur with the use of exposure to lead in homes with small children. Give oral mineral–electrolyte preparations with food or To decrease gastric irritation.
Milrinone can be used alone or with other drugs such as dobutamine and Digoxin Toxicity nitroprusside cheap tadapox 80mg overnight delivery. Its dosage should be reduced in the presence of Digoxin has a low therapeutic index (ie tadapox 80 mg visa, a dose adequate for renal impairment. Dose-limiting adverse effects of the drugs therapeutic effects may be accompanied by signs of toxicity). Milrinone has a long half-life of approxi- doses mately 80 hours and may accumulate with prolonged infusions. Rapid loading or digitalization, whether by one or more large doses or frequent administration of small doses 3. Impaired renal function, which delays excretion of Human Natriuretic Peptide B-type digoxin 4. Age extremes (young or old) Nesiritide (Natrecor) is the ﬁrst in this new class of drugs to 5. Electrolyte imbalance (eg, hypokalemia, hypomagne- be used in the management of acute HF. Produced by recom- semia, hypercalcemia) binant DNA technology, nesiritide is identical to endogenous 6. Hypoxia due to heart or lung disease, which increases human B-type natriuretic peptide, which is secreted primarily myocardial sensitivity to digoxin by the ventricles in response to ﬂuid and pressure overload. Hypothyroidism, which slows digoxin metabolism and This drug acts to compensate for deteriorating cardiac func- may cause accumulation tion by reducing preload and afterload, increasing diuresis and 8. Concurrent treatment with other drugs affecting the secretion of sodium, suppressing the renin–angiotensin– heart, such as quinidine, verapamil, or nifedipine aldosterone system, and decreasing secretion of the neuro- hormones endothelin and norepinephrine. Onset of action is immediate with peak effects attained in 15 minutes with a Phosphodiesterase Inhibitors bolus dose followed by continuous IV infusion. Administra- tion should be by a separate IV line because nesiritide is in- Inamrinone (Inocor), formerly amrinone, and milrinone IV compatible with many other drugs. Hemodynamic monitoring (Primacor) are cardiotonic-inotropic agents used in short- of pulmonary artery pressure is indicated to determine drug term management of acute, severe HF that is not controlled effectiveness. Clearance of the drug is proportional to body by digoxin, diuretics, and vasodilators. The drugs increase weight and partially by the kidneys; however, no adjustment levels of cyclic adenosine monophosphate (cAMP) in myo- in dosing is required for age, gender, race/ethnicity, or renal cardial cells by inhibiting phosphodiesterase, the enzyme that function impairment. They also relax vascular smooth ducted on the use of nesiritide for more than 48 hours. The effects of these drugs are additive to those Endothelin Receptor Antagonists This new class of drugs relaxes blood vessels and improves blood ﬂow by targeting endothelin-1 (a neurohormone) that is produced in excess in heart failure. Endothelin-1 causes Nursing Notes: Apply Your Knowledge blood vessels to constrict, forcing the ailing heart to work harder to pump blood through the narrowed vessels. Studies Your assessment of Pamela Kindra reveals the following: indicate that endothelin antagonist drugs improve heart func- 118/92, 110, 32 and labored. Respiratory assessment reveals tion, as measured by cardiac index; animal studies indicate coarse rhonchi and wheezing bilaterally. Urine output has been that structural changes of heart failure (eg, hypertrophy) may less than 30 cc per hour and she has gained 12 pounds over the be reversed by the drugs.