Ketamine dosing in obese adolescents

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Whilst ketamine is widely used in children of all ages, previous studies (Green et al, 2009) have shown that adverse events associated with ketamine are more common in adolescents (including airway adverse events and vomiting).

Additionally, there is a lack of clarity for calculating the ketamine dose in obese adolescent patients – should it be based on ideal body weight  (Wulfsohn, 1972) or standard mg/kg doses as most guidelines suggest? Standard paediatric guidelines don’t tend to include a max dose – so what are we supposed to do?

This study investigates the dose of ketamine required to achieve adequate sedation in adolescents.

Street MH, Gerard JM, A fixed-dose ketamine protocol for adolescent sedations in a pediatric emergency department, Journal of Pediatrics, 2014

Who was studied?

This was a prospective, observational cohort study.

The study included patients presenting to the Emergency Department aged between 12 and 18 years old and weighing greater than 35kg, who required procedural sedation. They had to meet criteria for ASA Class I or II.

Patients were excluded if they had: craniofacial, airway, and cardiorespiratory abnormalities, previous sedation-related events, neurological masses, or were undergoing an oral procedure.

There were 43 patients – mean age 13.9 years, mean weight 68.8kg, and mean BMI 24.4.

39.5% had a BMI greater than 25.

What was the intervention?

The normal sedation policy was was followed, with pre-oxygenation and ongoing physiological observations. No benzodiazepines or antiemetics were given before sedation.

50mg of IV ketamine was given to each patient (over 30-60 seconds) and then sedation was assessed. Further doses of 25mg IV ketamine were administered until adequate sedation was achieved.

Sedation was measured using the Ramsay Sedation Score (RSS), and ‘adequate sedation’ was when the RSS was 5 or greater.

All patients were managed with the same guidelines. However for data analysis, the patients were split into those with a BMI over 25 and those with a BMI of 25 or less. Data was collected to record the dose of ketamine required to achieve adequate sedation.

What were the measured outcomes?

The main outcome was provider satisfaction with sedation which was based on a 0-100 point scale rating.

Adverse events were noted during the procedure, and families were contacted at 12-24 hours post-procedure to grade their satisfaction and record any other adverse events.

Heights, weights, and BMIs were calculated for all patients.

What did the results show?

81.4% of the cohort achieved adequate sedation after just 50mg of ketamine. All the remaining subjects achieved adequate sedation following a further 25mg dose.

Mean sedation time was 27.4 minutes and mean time to discharge was 116.9 minutes. Time to discharge was shorter in the overweight group.

A similar proportion of people from both the overweight and non overweight groups achieved adequate sedation with the 50mg ketamine dose. Based on actual body weight, the overweight group received less ketamine per kg.

Satisfaction was the same between the groups immediately post-procedure, and also on follow-up. 95.3% of families were satisfied or very satisfied with the sedation.

Were these any ketamine side effects?

  • 2.3% (one patient) had desats which recovered with repositioning
  • 18.6% developed nausea during recovery
  • 14% vomited during recovery
  • 2.3% (one patient) developed agitation which required midazolam

There was no difference in adverse events between the two groups.

No patient required over 75mg of ketamine to achieve initial adequate sedation (but bear in mind that patients did require further doses during the procedure as top-ups). Those in the overweight group required a median dose of 0.79 mg/kg to achieve adequate sedation.

Ketamine dosing in obese adolescents is a poorly understood area. This study indicates that there is no need to give the standard 1-2mg/kg ketamine initially. A fixed dose of 50/75mg should be sufficient to achieve adequate sedation in the obese adolescent population.

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About 

Tessa Davis is a paediatric emergency registrar from Glasgow and Sydney, but currently living in London. Tessa tries to spend time with her 3 kids in between shifts. @tessardavis | + Tessa Davis | Tessa's DFTB posts

One Response to "Ketamine dosing in obese adolescents"

  1. AzA J
    AzA J 3 years ago .Reply

    Thanks for linking an excellent article Tessa. Given the rise in childhood obesity, and subsequently in adolescents too, i had wondered how to approach this, but will try this approach.
    Now just to solve the mystery of the obese infant too…

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