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wikitox:3.1.1_hypotension [2018/09/01 09:00] (current)
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 +Link to [[:​wikitox:​3.4.10_pressor_agents_and_control_of_blood_pressure|3.4.10 Pressor Agents and Control of Blood Pressure]]
 +====== Hypotension ======
 +Kent R. Olson, MD
 +==== Initial Treatment ====
 +  * Patients with intoxication by CNS-depressant drugs often have a **“relative” hypovolemia due to decreased sympathetic nervous system activity** ​ leading to peripheral venodilatation and decreased arteriolar tone. This can usually be corrected by administration of intravenous fluids, preferably normal saline. The initial bolus should be at least 15-20 mL/kg (1-2 liters in the average adult). More fluids may be needed if the poison has caused significant volume loss (e.g., due to vomiting or diarrhea) or vasodilatation.
 +  * Sometimes it is appropriate to measure the **central venous pressure** ​ or left ventricular end-diastolic pressure. In some cases massive fluids have been given to sustain the circulation (e.g., 18-20 L in a patient with severe gastrointestinal fluid losses due to mushroom poisoning).
 +  * If blood pressure does not improve after fluid administration,​ consider **vasopressors** ​ or specific agents depending on the offending drug. In general, dopamine is effective for drug-induced hypotension of various types but if the cause of low blood pressure is loss of peripheral vascular resistance, a vasoactive presser such as norepinephrine or phenylephrine may be more appropriate.
 +==== Special Considerations ====
 +  * An unusual situation arises with overdoses of **beta-2 agonists** ​ (e.g., albuterol, salbutamol) or theophylline,​ in which beta-mediated vasodilatation is the primary cause of hypotension and reflex tachycardia is insufficient to raise the blood pressure; in such cases a trial of beta-blocker such as **propranolol** ​ (0.5-2 mg IV) may be effective in reversing the vasodilatation and raising the BP.
 +  * Hypotension and bradycardia due to **beta-adrenergic blocker overdose** ​ are often resistant to usual doses of beta-agonist drugs such as dopamine or isoproterenol,​ and in such circumstances high-dose **glucagon** ​ (50-10 mg IV bolus followed by an infusion of 5-10 mg/hour) may be effective. This is because glucagon increases intracellular cAMP by a receptor complex separate from the blocked beta receptor.
 +  * **[[:​wikitox:​|Calcium channel blockers]]** are a cause of severe and often fatal hypotension and bradycardia. Nifedipine and amlodipine, as vasodilators,​ usually cause hypotension with reflex tachycardia and this is often treated effectively with IV fluids alone. For other CCBs, or when IV fluids are insufficient,​ try intravenous **calcium**. Large doses are often needed (more than 1-2 ampoules) and serum calcium levels have been raised to the high teens with subsequent improvement. Case reports and animal studies suggest that **high-dose insulin-euglycemia therapy** ​ may salvage some calcium channel blocker patients who do not respond to other measures. The recommended dose of insulin is 0.5-1 U/kg bolus followed by 0.5 U/kg/hour infusion, with enough dextrose to maintain a normal blood sugar level.
 +  * Hypotension associated with **[[:​wikitox:​|tricyclic ]]** **[[:​wikitox:​|antidepressants]]**can be multifactorial:​ direct alpha blockade; neuronal norepinephrine depletion; cardiodepressant effects of sodium channel blockade; and hyperthermia are examples of pharmacologic effects and complications that can contribute to hypotension in a TCA patient. As a result, various strategies are employed starting with IV fluids, and followed by infusion of **dopamine** ​ and/or **norepinephrine** ​ (many authorities recommend starting with norepinephrine because of suspected alpha blockade and NE depletion), and **sodium bicarbonate** ​ boluses if the QRS complex is widened, suggesting sodium channel blockade. If the patient is **hyperthermic**,​ provide aggressive cooling measures such as neuromuscular paralysis and intubation, and evaporative cooling by wetting the skin and fanning.
 +==== Table. Selected causes of hypotension ====
 +|**Type of hypotension** |**Examples** |**Specific Treatment** |
 +|Hypotension with bradycardia|Beta blockers|Glucagon|
 +| |Calcium channel blockers|Calcium;​ hyperinsulin-euglycemia therapy|
 +| |Clonidine other centrally acting sympatholytics (eg, brimonidine,​ oxymetazoline,​ methyldopa)|Treatment supportive: IV fluids, dopamine if needed.|
 +| |Tricyclic antidepressants|Sodium bicarbonate;​ norepinephrine may be more effective than dopamine for hypotension.|
 +|Hypotension with tachycardia|Beta-2 agonists (e.g., albuterol, salbutamol)|IV fluids. Rule out true hypovolemia from gastrointestinal losses, bleeding; rule out septic shock.|
 +| |Theophylline|High levels associated with hypotension,​ ventricular arrhythmias,​ seizures; level of greater then 90-100 mg/L is an indication for urgent hemodialysis.|
 +| |Phenothiazines|Hypotension due to alpha-adrenergic blockade; give IV fluids and consider norepinephrine,​ phenylephrine.|
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