Pharmacology
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Anaesthesia
Your consultant decides to use ketamine for a patient requiring procedural sedation in the Emergency Department. At what receptor does ketamine primarily act:
Answer:
In contrast to most other anaesthetic agents, ketamine is a NMDA (N-methyl-D-aspartate) receptor antagonist. It is a non-competitive antagonist of the calcium-ion channel in the NMDA receptor. It further inhibits the NMDA-receptor by binding to its phencyclidine binding site.Ketamine
Pharmacology / Anaesthesia
Last Updated: 1st May 2023
Ketamine has hypnotic, analgesic and local anaesthetic properties. Ketamine is an NMDA receptor antagonist, but it may also have other actions. Ketamine produces so-called ‘dissociative’ anaesthesia. Transient psychotic effects including alterations in mood state, floating sensations, vivid dreams and hallucinations are common during emergence from ketamine anaesthesia. These usually resolve on full wakening. Benzodiazepine premedication e.g. with diazepam or midazolam reduces this delirium, which also occurs less often in children and the elderly.
The onset of action is slower than other induction drugs (unconsciousness in about 1 - 2 min for IV use), and the end point can be difficult to judge with patients staring into the distance for a short period of time. The duration of action of a single dose is approximately 5 - 10 minutes. Recovery is relatively slow.
Uses
Ketamine has a unique combination of cardiovascular effects. Unlike other induction drugs it has sympathetic effects with increased heart rate, increased blood pressure and an increased cardiac output; this makes ketamine useful in the shocked, unwell patient. It is used mainly for paediatric anaesthesia, particularly when repeated administration is required (such as for serial burns dressings).
Ketamine has a minimal effect on respiratory drive and protective airway reflexes remain well preserved, this makes ketamine an ideal anaesthetic drug to be used in the prehospital environment. Ketamine is also a bronchial smooth muscle relaxant and therefore has a special role in the management of severe asthma.
Contraindications
Ketamine is contraindicated in acute porphyrias, head trauma, stroke and raised intracranial pressure, hypertension and severe cardiac disease.
Side Effects
There is a high incidence of extraneous muscle movements and postoperative nausea and vomiting. Other common side effects include hypertension, tachycardia and transient psychotic effects.
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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 |
