Why TCA cause metabolic acidosis?
TCA are weak bases. increasing the serum pH with bicarbonate -> increases the proportion of non-ionised drug which -> increase in drug distribution throughout rest of body and away from heart. increased Na+ also overcomes the Na+ receptor blockade.
How does TCA cause hypotension?
Tricyclic Antidepressants TCAs can also cause sedation that results from blockade of H1 histamine receptors, and orthostatic hypotension, due to blockade of α1 receptors on blood vessels.
What does TCA overdose cause?
Tricyclic antidepressant overdose is poisoning caused by excessive medication of the tricyclic antidepressant (TCA) type. Symptoms may include elevated body temperature, blurred vision, dilated pupils, sleepiness, confusion, seizures, rapid heart rate, and cardiac arrest.
Why do you give Bicarb for TCA overdose?
The benefit of sodium bicarbonate in the setting of TCA overdose is probably due to both an increase in serum pH and the increase in extracellular sodium. Alkalization favors the neutral form of the drug and reducing the amount of active cyclic antidepressants.
Does TCA cause acidosis?
Gastrointestinal absorption may be delayed because of inhibition of gastric emptying and significant enterohepatic recirculation prolongs the final elimination. The amount of unbound tricyclic may also increase if the overdose causes respiratory depression resulting in an acidosis, which reduces protein binding.
How is TCA toxicity diagnosed?
Exam. Symptoms based on toxidrome: Myocardial Sodium channel antagonism: Reduced cardiac contractility and hypotension, widened QRS predisposing to VT and VF, Prolonged QT. Inhibition of noradrenalin and serotonin reuptake: CNS depression/coma, seizures.
Which TCA is least sedating?
Desipramine (Norpramin) It is a commonly used TCA that is relatively less sedating and tends to have fewer anticholinergic and antihistaminic adverse effects than other TCAs.
Why TCA cause seizure?
Flumazenil ( a benzodiazepine antagonist ) has been shown to induce seizures in TCA overdoses. Both flumazenil and TCA’s affect the GABA- chloride ionophore in the CNS.
How is TCA toxicity treated?
Administration of sodium bicarbonate might be beneficial for patients with severe or life-threatening TCA toxicity if a prehospital protocol exists for its use (Grades B/D). Benzodiazepines are recommended for TCA-associated convulsions (Grade D). Flumazenil is not recommended for patients with TCA poisoning (Grade D).
When do you administer sodium bicarbonate in TCA overdose?
Sodium bicarbonate may be considered for the treatment of QRS prolongation (>100ms) associated with TCA overdose (Grade E). The treatment of dysrhythmias or hypotension should include alkalinisation to a serum pH of 7.45 to 7.55.
How do you control a TCA overdose?
Management of Significant Tricyclic Overdose Secure IV access, administer high flow oxygen and attach monitoring equipment. Administer IV sodium bicarbonate 100 mEq (1-2 mEq/kg); repeat every few minutes until BP improves and QRS complexes begin to narrow. Intubate as soon as possible.
How does TCA cause seizure?
They also block alpha receptors peripherally and thus can cause hypotension. Furthermore, they block neurotransmitter reuptake (norepinephrine, serotonin) at central presynaptic terminals, and this may be the mechanism by which seizures are induced by TCA overdose.
What are the symptoms of a TCA overdose?
Symptoms may include elevated body temperature, blurred vision, dilated pupils, sleepiness, confusion, seizures, rapid heart rate, and cardiac arrest. If symptoms have not occurred within six hours of exposure they are unlikely to occur. TCA overdose may occur by accident or purposefully in an attempt to cause death.
Is there a low toxicity threshold for TCAS?
Low toxicity threshold of TCAs Therapeutic doses range from 2-4 mg/kg/d Toxicity is observed at doses of 10-20 mg/kg Ingestion of only two 50-mg tablets in a 10-kg toddler can be sufficient to produce symptoms of toxicity Pharmakinetics Absorbed rapidly from GI tract in the alkaline small intestine
What are the effects of TCAS on the myocardium?
TCAs have anticholinergic effects, cause excessive blockade of norepinephrine reuptake at the preganglionic synapse, direct alpha adrenergic blockade, and importantly they block sodium membrane channels with slowing of membrane depolarization, thus having quinidine-like effects on the myocardium.
What are the compensatory mechanisms of metabolic acidosis?
Compensatory mechanisms. Metabolic acidosis is either due to increased generation of acid or an inability to generate sufficient bicarbonate. The body regulates the acidity of the blood by four buffering mechanisms.
