Pharmacology & Poisoning
Question 25 of 89
An 87 year old man is brought to the Emergency Department following an accidental overdose of his bisoprolol. He cannot recall how many tablets he has taken today. Which of the following is NOT a typical feature of beta-blocker toxicity?
Answer:
The key feature in severe poisoning is cardiovascular collapse.- Cardiac features
- Bradycardia, hypotension, pulmonary oedema, syncope and cardiogenic shock may develop.
- Conduction abnormalities such as first or second degree AV block and intraventricular conduction delays may occur.
- Dysrhythmias have also been reported and can include asystole.
- Some beta blockers are associated with risk of VT associated with prolongation of QRS duration (e.g. propranolol) or prolongation of QT duration (e.g. sotalol - increases risk of torsade de pointes).
- Other features
- Bronchospasm and occasionally CNS-mediated respiratory depression may occur.
- Hypoglycaemia and hypocalcaemia are rare.
Beta-Blocker Toxicity
Pharmacology & Poisoning
Last Updated: 12th February 2021
Clinical features
The key feature in severe poisoning is cardiovascular collapse.
- Cardiac features
- Bradycardia, hypotension, pulmonary oedema, syncope and cardiogenic shock may develop.
- Conduction abnormalities such as first or second degree AV block and intraventricular conduction delays may occur.
- Dysrhythmias have also been reported and can include asystole.
- Some beta blockers are associated with risk of VT associated with prolongation of QRS duration (e.g. propranolol) or prolongation of QT duration (e.g. sotalol - increases risk of torsade de pointes).
- CNS features
- Beta blockers which are more lipid soluble (carvedilol, labetalol, metoprolol, oxprenolol, pindolol and propranolol) are more likely to cross the blood brain barrier causing drowsiness, confusion, convulsions, hallucinations, dilated pupils and in severe cases coma.
- Hydrophilic beta blockers (acebutolol, atenolol, bisoprolol, esmolol, nadolol, sotalol) have few CNS effects.
- Other features
- Bronchospasm and occasionally CNS-mediated respiratory depression may occur.
- Hypoglycaemia and hypocalcaemia are rare.
Management
- Maintain a clear airway and adequate ventilation in patients who are unconscious. Early tracheal intubation may be of benefit in severe poisoning.
- The benefit of gastric decontamination is uncertain. Consider activated charcoal (charcoal dose: 50 g for adults; 1 g/kg for children) if the patient presents within 1 hour of ingestion of more than a potentially toxic dose.
- This agent is cardiotoxic and careful assessment of the ECG is required. Perform a 12-lead ECG in all patients who require assessment. Repeat 12-lead ECGs are recommended, especially in symptomatic patients or in those who have ingested sustained release preparations. Check cardiac rhythm, QRS duration and QT interval.
- Observe all patients who require assessment for at least 6 hours after ingestion and 12 hours after ingestion of modified release preparation. Patients who are asymptomatic after this time with a normal ECG can then be considered for discharge with advice to return if symptoms develop.
- In symptomatic patients, or patients with an abnormal ECG, consider early discussion with HDU/ITU.
- Bradycardia
- For symptomatic bradycardia give atropine intravenously, 0.5-1.2 mg for an adult or 0.02 mg/kg for a child. Repeat doses may be necessary. Dobutamine or isoprenaline may be considered if bradycardia is associated with hypotension. Temporary pacemaker insertion may be required, alternatively external pacing may be used.
- Hypotension
- Ensure adequate fluid resuscitation. Treat brady and tachyarrhythmias appropriately. Consider early referral to critical care for patients with fluid-resistant hypotension, as these patients can deteriorate extremely rapidly.
- Vasopressors and inotropes can be initiated in an emergency through peripheral venous access. THIS SHOULD ONLY BE DONE UNDER THE DIRECTION OF AN EXPERIENCED PHYSICIAN (SpR AND ABOVE).
- Glucagon and high-dose insulin
- Glucagon is a treatment option for severe hypotension, heart failure or cardiogenic shock.
- In severe cases an insulin and dextrose infusion has been shown to improve myocardial contractility and improve systemic perfusion. It is particularly useful in the presence of acidosis.
- Metabolic acidosis
- If metabolic acidosis persists despite correction of hypoxia and adequate fluid resuscitation consider correction with intravenous sodium bicarbonate. Rapid correction is particularly important if there is prolongation of the QRS interval.
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
