Pharmacology & Poisoning
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Question 31 of 89
A 21 year old known drug user is brought into ED with a GCS of 7 and RR of 6. He did not respond until a total of 800mcg of naloxone was given, his GCS improved to 12 and RR to 12. About 90 minutes later his GCS has dropped to 10. Your consultant requests that you start a naloxone infusion. Which of the following is the most appropriate starting rate?
Answer:
- Intravenous infusions of naloxone are often useful where repeated doses are likely to be required.
- Start with an hourly infusion rate equal to around 60% of the doses required to adequately reverse respiratory depression.
- For example - if 800 micrograms was required (either as a single dose or two 400 micrograms doses) then start the infusion at 500 micrograms per hour. The infusion will then require to be titrated to the desired clinical effect.
Opioid Toxicity
Pharmacology & Poisoning
Last Updated: 21st June 2022
Clinical features
- Drowsiness
- Coma
- Respiratory depression
- Pinpoint pupils
Management
- Administer naloxone (an opioid antidote):
- Initially give 400 micrograms intravenously.
- If no response after 1 minute, give 800 micrograms for up to 2 doses at 1 minute intervals.
- If there is still no response (after a total of 2 mg) give a further 2 mg dose (a 4 mg dose may be required in patients exposed to highly potent opioids and those who are severely poisoned).
- Failure of a definite opioid overdose to respond to large doses of naloxone suggests that another CNS depressant drug or brain damage is present.
- Doses can be given subcutaneously or intramuscularly, but only if the intravenous route is not feasible — intravenous administration has more rapid onset of action.
- The duration of action of naloxone is shorter than that of all opioid analgesics - REPEATED DOSES OF NALOXONE MAY BE REQUIRED.
- Note: The primary aim of treatment is to reverse the toxic effects of opioids such that patients are no longer at risk of respiratory arrest, airway loss, or other opioid-related complications, it is not to restore a normal level of consciousness. In some circumstances restoring a normal level of consciousness is entirely inappropriate.
- If the person is unconsciousness and not breathing, or if there are no signs of life, commence CPR with chest compressions, if able to do so — where possible, without significantly delaying starting or continuing the CPR, administer naloxone too.
- Acute withdrawal from opioids produces a state of sympathetic excess and can cause complications such as pulmonary oedema, ventricular arrhythmia, and severe agitation. Use naloxone reversal of opioid intoxication with caution in patients suspected of opioid dependence.
- Cardiac arrest in opioid overdose is usually secondary to a respiratory arrest and associated with severe brain hypoxia. Prognosis is poor. Once cardiac arrest has occurred, follow standard resuscitation guidelines.
Intravenous infusions following resuscitation:
- Intravenous infusions of naloxone are often useful where repeated doses are likely to be required.
- Start with an hourly infusion rate equal to around 60% of the doses required to adequately reverse respiratory depression.
- For example - if 800 micrograms was required (either as a single dose or two 400 micrograms doses) then start the infusion at 500 micrograms per hour. The infusion will then require to be titrated to the desired clinical effect.
- For adults, a solution containing 10 mg (25 vials) made up to a final volume of 50 mL with dextrose will produce a 200 micrograms/mL solution for infusion using an IV pump (dose adjusted to clinical response).
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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 |
