Tox: salicylates

Question 1

Sources of salicylate poisoning

Answer 1

Bayer aspirin, cold medicines, antidiarrheals (bismuth), topical products (methylsalicylate), oil of wintergreen (very concentrated), aminosalicylates (IBD tx), combination products (decongestants, antihistamines, narcotics)

Question 2

Pathophys of salicylate poisoning

Answer 2

Weak acid. At normal pH, mostly ionized and cannot cross the BBB or renal tubules (for reabsorption).
Acidemia promotes non-ionized form, allowing salicylate to enter the brain and be reabsorbed by kidneys (reduced excretion).

Question 3

Mechanism of toxicity of salicylates

Answer 3

Direct stimulation of respiratory center -> hyperventilation, resp alkalosis.
GI-> stim of chemoreceptor trigger zone -> vomiting.
Uncoupling of oxidative phosphorylation -> anaerobic metabolism, AGMA, hyperthermia.
Permanent inhibition of platelet aggregation.
Otoxicity -> tinnitus, hearing loss (correlates with salicylate level).
Alterations in capillary integrity-> cerebral and pulmonary edema.

Question 4

Symptoms of salicylate poisoning

Answer 4

Acute:
Early -> TINNITUS, n/v, HEARING LOSS, HYPERVENTILATION, diaphoresis, hyperthermia.

severe tox -> cerebral edema, marked hyperthermia, seizure, pulmonary edema, hypoglycemia, cardiovascular collapse.

Chronic:
Symptoms similar but slower in onset, more nonspecific.
Pts often present with confusion, dehydration, metabolic acidosis.
Neuro symptoms such as confusion, hallucinations, agitation, coma.
Pulmonary and cerebral edema, seizures, renal failure more common with chronic toxicity.

Question 5

Typical acid base finding in salicylate poisoning

Answer 5

Mixed respiratory alkalosis AGMA

Question 6

Ballpark toxic dose, tox levels

Answer 6

In adults: 10-30g aspirin. In children, as little as 3g.

Most pts show signs intoxication when serum levels exceed 2.9-3.6mmol/L (usual therapeutic range 0.7-2.2mmol/L)

Question 7

Treatment of salicylate poisoning

Answer 7

Goal: keep salicylate ionized to inhibit movement into BBB and increase renal excretion.

Activated charcoal. Consider multidose activated charcoal for enteric formulation. Given q6h as enteric formulation forms large pill burden with delayed gastric emptying.
IVF to maintain renal perfusion (not forced diuresis though).
Urinary alkalinization.
Prevention of hypokalemia.
Hemodialysis for some.

Question 8

Describe considerations when intubating patients with salicylate overdose

Answer 8

Must AVOID respiratory depression/reducing pts respiratory rate as this will inhibit respiratory alkalosis and worsen the overall acidemia.
Consider giving bicarb prior to intubation.
Once intubated, hyperventilate to match pre-intubation pCO2.

Question 9

Describe the process of urinary alkalinization (how to do it, how to monitor)

Answer 9

Give NaHCO3 drip 1-2 mEq/kg IV bolus followed by infusion of 150mEq/L in D5 +/- KCl.
Goal is to alkalinize urine to pH 7.5-8.
Correct hypokalemia as hypoK will prevent urinary alkalinization.

Obtain lytes/metabolic panel and salicylate levels q1-2 hrs during treatmen.

Question 10

What are the indications for HD in salicylate poisoning

Answer 10

AMS
Pulmonary or cerebral edema
Failure of bicarb drip (increasing salicylate levels despite couple hrs on drip)
Renal failure/anuria.
Consider for acute levels >7.2 mmol/L and chronic levels >4.3 mmol/L.

Consider earlier HD if: elderly, chronic poisoning, severe acidemia, comorbidities.