Vasopressors dosing

In clinical practice, however, norepinephrine often is initiated after vasopressor doses of dopamine (4 to 20 mcg/kg per minute) alone or in combination with dobutamine (5 mcg/kg per minute) fail to achieve desired goals Doses of dopamine and dobutamine are kept constant or stopped altogether, or in some instances, dopamine is kept at low doses for purported renal protection. It may be more rational to use norepinephrine because it is more potent than dopamine and is more effective at increasing MAP. It has combined strong i activity and less potent f) 1 -agonist effects while maintaining the vasodilatory effects of /S2-receptor stimulation. 

Untoward effects of both E and NE (usually to a lesser degree) are anxiety, headache, cerebral hemorrhage (from vasopressor effects), cardiac arrhythmias, especially in presence of digitaUs and certain anesthetic agents, and pulmonary edema as a result of pulmonary hypertension. The minimum subcutaneous lethal dose of E is about 4 mg, but recoveries have occurred after accidental overdosage with 16 mg subcutaneously and 30 mg intravenously, followed by immediate supportive treatment. 

Pentobarbital is commonly loaded at a dose of 10 to 15 mg/kg over 1 to 2 hours, followed by a continuous infusion of 0.5 to 4 mg/kg per hour. Therapy can be tapered off after 12 to 24 hours of seizure control as evident on the EEG.35 One metaanalysis reported a lower incidence of treatment failure with pentobarbital (3%) when compared to midazolam (21%) or propofol (20%), although the risk of hypotension requiring vasopressor therapy was higher when pentobarbital was used.36 This relative efficacy for pentobarbital must be considered... 

Vasopressin levels are increased during hypotension to maintain blood pressure by vasoconstriction. However, there is a vasopressin deficiency in septic shock. Low doses of vasopressin increase MAP, leading to the discontinuation of vasopressors. However, routine use of vasopressin is not recommended because of lack of evidence of efficacy. Vasopressin is a direct vasoconstrictor without inotropic or chronotropic effects and may result in decreased cardiac output and hepatosplanchnic flow. Vasopressin use may be considered in patients with refractory shock despite adequate fluid resuscitation and high-dose vasopressors.24,27-28... 

Stress-induced adrenal insufficiency complicates 9% to 24% of septic patients and is associated with increased mortality. Adrenal-insuffident patients are identified by a adrenocorticotropic hormone (ACTH) stimulation test. Patients are given 250 meg ACTH and a cortisol level is checked within 30 to 60 minutes. Responders are defined as a greater than 9-mcg/dL increase in cortisol and non-responders as a less than 9-mcg/dL increase in cortisol. Septic shock patients refractory to resuscitation and vasopressors, and with adrenal insufifidency (non-responders to the ACTH test) should be administered intravenous hydrocortisone 200 to 300 mg per day in three divided doses for 7 days.24,44... 

Formulate appropriate doses of medications involved in patient therapy and revise as needed. Patient parameters may change frequently, thus requiring different doses and/or medications. Examples include antibiotic therapy, sedatives, insulin, fluids, or vasopressors. 

Vasopressin causes vasoconstrictive effects that, unlike adrenergic receptor agonists, are preserved during hypoxia and severe acidosis. It also causes vasodilation in the pulmonary, coronary, and selected renal vascular beds that may reduce pulmonary artery pressure and preserve cardiac and renal function. However, based on available evidence, vasopressin is not recommended as a replacement for norepinephrine or dopamine in patients with septic shock but may be considered in patients who are refractory to catecholamine vasopressors despite adequate fluid resuscitation. If used, the dose should not exceed 0.01 to 0.04 units/min. 

Corticosteroids can be initiated in septic shock when adrenal insufficiency is present or when weaning of vasopressor therapy proves futile. A daily dose equivalent to 200 to 300 mg hydrocortisone should be continued for 7 days. Adverse events are few because of the short duration of therapy. 

Avoid continuous IV therapy Acute tolerance develops during continuous IV administration. High concentration/low volume (250 ml) vasopressor solutions administered with the aid of an infusion control device allows for maximum dosing flexibility because fluids and drugs can be regulated independently and the development of tolerance is minimized. 

Dopamine (Intropin) [Vasopressor/Adrenergic] Uses Short-tOTn use in cardiac decompensation secondary to X contractility when no hypovolemia is present T organ p fusion (at low dose) Action Renal dose 2-5 mcg/kg/min Inotropic dose 5-10 mcg/kg/min Pressor dose >10 mcg/kg/min Dose Adults Feds. 5-20 mcg/kg/min by cont inf, start at 5 and t by 5 mcg/kg/min to 20 mcg/kg/min max to effect (mix 400 mg in 250 mL DjW to make 1600 mcg/mL) (see Table 1-3) Caution [C, ] Contra Pheochromocytoma (adrenal gland tumor), VF, sulfite sensitivity Disp Inj 40, 80, 160 mg/mL, premixed 0.8, 1.6, 3.2 mg/mL SE Tach, vasoconstriction, 4- BP, HA, N/V, dyspnea Notes >10 mcg/kg/min X renal p fiision Interactions t Effects W/ a-blockers, diuretics, ergot alkaloids, MAOIs, BBs, anesthetics, phenytoin X effects W/ guanethidine EMS Correct hypovolemia before use use microdrip set or inf pump check soln- discolored... 

Phenylephrine, Nasal (Neo-Synephrine Nasal) (OTC) [Vasopressor/Decongestant] Uses Can be used prior to nasal intubation and NG tube insCTtion to reduce bleeding Action a-Adren gic agonist Dose Adults Feds. 1—2 sprays/nostril q4h (usual 0.25%).Caution [C, +/—] HTN, acute pancreatitis, H, coronary Dz, NAG, h5 pCTth5Toidism Contra Bradycardia, arrhythmias Disp Nasal soln (0.125-0.25%) SE Arrh5rthmias, HTN, nasal irritation, dryness, sneezing, HA Interactions May -1- effects OF nitrates EMS Ocular instillation may dilate pupil... 

Rarely is it necessary to keep a patient in bed for prolonged periods. Those with serious cardiovascular disease, should have their doses increased even more slowly, with blood pressure frequently monitored. Acute orthostasis can usually be managed by having the patient lie down with feet elevated. On rare occasions, volume expanders or vasopressors may be required. 

Metaraminol has a longer duration of action than some other vasopressors and care should be taken to avoid inducing hypertension. The dose is 0.5-5 mg as a slow intravenous bolus. If necessary, 15-100 mg may be diluted in normal saline (500 ml) and given by infusion. The dose of methoxamine is 2-5 mg intravenously. 

Vasopressin also plays an important role in the short-term regulation of arterial pressure by its vasoconstrictor action. It increases total peripheral resistance when infused in doses less than those required to produce maximum urine concentration. Such doses do not normally increase arterial pressure because the vasopressor activity of the peptide is buffered by a reflex decrease in cardiac output. When the influence of this reflex is removed, eg, in shock, pressor sensitivity to vasopressin is greatly increased. Pressor sensitivity to vasopressin is also enhanced in patients with idiopathic orthostatic hypotension. Higher doses of vasopressin increase blood pressure even when baroreceptor reflexes are intact. 

Further data have come from a review of the use of high doses of vasopressin (mean dose 0.47 U/minute) to replace noradrenaline (24). There were reductions in heart rate, cardiac index, and oxygen delivery. The authors recommended that the dose of vasopressin should not exceed 0.04 U/minute and that vasopressin should not be used as a single vasopressor agent in septic shock. 

Local anesthetics block the sodium channels, are cardiac depressants, and bring about a ventricular conduction defect and block that may progress to cardiac and ventilatory arrest if toxic doses are given. In addition, these agents produce arteriolar dilation. Circulatory failure may be treated with vasopressors such as ephedrine, metaraminol (Aramine), or mephentermine (Wyamine). Artificial respiration and cardiac massage may also become necessary. Among the local anesthetics, only cocaine blocks the uptake of norepinephrine, causes vasoconstriction, and may precipitate cardiac arrhythmias. 

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