Paediatric obesity

We talk a lot about obesity in adults and the profound implications it can have on our anaesthetic plan and the risks involved, because it's something we see a lot of.

After all, in 2024 there were over a billion people living with obesity worldwide.

However we tend to talk a lot less about obesity in children, largely because it has (until recently) been a much less common problem.

This is changing.

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Around 170 million kids between 5 and 19 years old were obese in 2024, and 35 million children under the age of 5 were overweight.

Obese children also need surgery more often than children with a normal body habitus, so it's rather important to be aware of how it impacts your job as the anaesthetist.

What operations do children with obesity need?

Of course they might need any manner of operation that a child without obesity could require, however there are two categories of procedure that are disproportionately more prevalent among kids with obesity:

Adenotonsillectomy (for sleep apnoea)
Bariatric surgery

What's the definition of obesity?

Obesity is defined by body mass index, which is calculated using the formula:

Body weight/height²

How you feel about the validity of this physiological parameter is a separate issue, but for now it's the most widely used measure of 'overweightness' around the world.

The WHO definitions for children that you need to know are as follows:

For children aged 0 - 5 years

Overweight = Weight-for-height >2 standard deviations above the median
Obese = WFH >3 standard deviations above the median
Severely obese doesn't exist (yet)

For children aged 5 - 19 years

Overweight = BMI for age >1 standard deviation above the median
Obese = >2 SD

Why are more children becoming obese?

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The short (and arguably ill-informed) answer is 'calories in > calories out' which is biologically true but socially and logistically unhelpful when it comes to actually figuring out how to improve the situation.

Humans have evolved to survive on lean, infrequent meals that required a lot of walking, foraging or chasing something hairy and/or quick.

In vast swathes of the world, life has been becoming steadily more sedentary, more stressful and fuelled by more processed, calorie-dense but nutrient-poor low quality dopamine-triggering food and drink.

We've gone from chasing deer across plains for three days, to a society where pushing a button that tells a man on a scooter to bring Dr Pepper and pizza to your front door is cheaper and easier than getting hold of organic vegetables.

It's hard not to put on weight.

So it's important to recognise, and be sensitive to, the myriad features that contribute to people putting on excess weight, because it helps build a framework upon which you can start figuring out how to fix it.

The question could also be framed in an exam as 'what are the causes of childhood obesity?' which can be answered in a nicely structured format as follows:

Antenatal causes

Gestational diabetes
Maternal smoking leading to intrauterine growth restriction

Lifestyle causes

Sedentary lifestyle
Excessive consumption of particularly highly processed food and drink
Sleep deprivation

Lower socioeconomic status is not a 'cause' as such, but a definite risk factor.

Genetic causes

Polygenic factors
Melanocortin-4 receptor defects
Leptin deficiency

Medication side effects

Glucocorticoids
Antidepressants
Antiepileptics
Antipsychotics
Sulfonylureas

Endocrine causes

Hypothyroidism
Pseudohypoparathyroidism
Growth hormone deficiency
Hypercortisolism
Polycystic ovarian syndrome (PCOS)

Specific syndromes

Prader-Willi
Fragile X
Beckwith–Wiedemann

There are many more, but it's unlikely you'll need (or be able) to list more than one or two in an exam setting.

What are the effects of obesity in kids?

Many of the same principles apply as in adults, and this answer is best broken down by body system, addressing each in turn.

If you're asked this in an exam, start with a strong introduction such as,

"Obesity in children is an increasingly prevalent, multisystem disease that has a profound impact on every major system in the body, and therefore requires careful assessment and planning by the anaesthetist."

Then you can launch into your system-by-system response.

Airway

All of the soft tissues are enlarged, including the tongue, pharynx and neck, resulting in:

Obstructive sleep apnoea
Difficult facemask ventilation

The big thing (literally) is macroglossia, where excess tongue tissue increases its propensity to flop backwards after induction of anaesthesia and obstruct the airway.

Interestingly, obesity doesn't necessarily make intubation harder, although it does make positioning the head appropriately more difficult, and of course you have less time to get the deed done.

Respiratory

Excess weight on the chest and diaphragm leads to:

Reduced respiratory compliance
Reduced functional residual capacity
Hypoventilation
Increased closing capacity
Increased shunt
Air trapping

This means there is less of an oxygen reserve to play with during any apnoeic periods, and just to further complicate things, obese children have a higher oxygen demand as well, so they use it up even faster.

This is also worse when lying flat, as you might have guessed, hence the advice to ramp the patient when inducing anaesthesia.

Oh and they're also more likely to have asthma and bronchospasm, just to make it even more interesting.

Cardiovascular

We know that obesity tends to cause hypertension and the same is true in kids - obesity triples the risk of hypertension.

The cause of this is multifactorial and includes:

Increased blood volume and cardiac output
Sympathetic and RAAS activation
Insulin resistance
Renal sodium retention

Long term complications include:

Pulmonary hypertension (if OSA)
Right heart failure
Vascular disease
Left ventricular hypertrophy
Left atrial dilatation
Cor pulmonale

GI

There's increased pressure in the abdomen due to the excess abdominal wall adipose tissue.

This increases the incidence of GORD. (1 in 5 obese kids have GORD)

It's not certain if this increases the risk of aspiration, but it's not exactly going to reduce the risk is it?

There aren't currently any concrete guidelines on whether we should be adjusting fasting times for obesity in children.

What comorbidities are associated with obesity in children?

Airway and respiratory

Asthma
Recurrent chest infections
Obstructive sleep apnoea

Cardiovascular

Heart failure
Hypertension
Atherosclerosis
LV hypertrophy

Neurological and psychological

Idiopathic intracranial hypertension
Anxiety and depression
Low self esteem
Poor academic performance

GI

GORD
Fatty liver disease

Endocrine

Type 2 Diabetes Mellitus
Metabolic syndrome
Polycystic ovarian syndrome
Hyperlipidaemia

Haematological

Anaemia (usually iron deficiency)

Remember that anaemia will make any respiratory or cardiovascular issues worse, by reducing the oxygen-carrying capacity of the blood.

Musculoskeletal

SUFE (slipped upper femoral epiphysis)
Blount's disease (bow legs)

What investigations should I order before surgery?

We're not just gas technicians anymore, we're perioperative physicians, and should be taking a proactive approach to the preoperative optimisation of our patient's comorbidities to improve their chances of the best possible outcome after surgery.

With that in mind, you could consider the following investigations for a child with obesity who is undergoing surgery:

Polysomnography to assess for presence and severity of sleep apnoea
Peak flow to assess asthma severity
Blood pressure
ECG
Echocardiography if any evidence of cardiovascular dysfunction
Full blood count and iron studies to look for anaemia
Thyroid function tests, urea and electrolytes
Serum lipids, liver function tests and ultrasound if concern for hepatic steatosis
HbA1c and fasting glucose and insulin if worried about TIIDM
Vitamin D level

It should come as no surprise that anaesthesia is higher risk in obese children, however this is not often clear to the child or their parents at the preoperative consenting stage.

Thankfully, anaesthesia has become unfathomably safe in recent years, however this brings with it an incredibly high expectation of what can safely be achieved with a syringe of propofol and a laryngoscope.

It is our duty to sensitively convey the increased risks of anaesthesia associated with obesity, so that we can tick the box of properly 'informed' consent.

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If you get the rapport right, you can also use this as an opportunity to signpost them towards weight-management support.

Specifics to consent for

There is an increased risk of:

Airway obstruction
Difficult face mask ventilation
Bronchospasm
Post op chest infection

Gas induction takes longer and IV induction is safest, however

IV access may be difficult
Regional anaesthesia may be more challenging

Induction and emergence may take longer.

How do I anaesthetise them?

Carefully, obviously, but paying particular attention to the following:

How do I estimate their weight for drug dosing?

Total body weight is the number the scales give you.

Ideal body weight = 50th centile BMI for age x height²
Adjusted body weight = IBW + 0.35 x (Total - ideal body weight)

What weight should I use for each drug?

The big caveat here is that we don't have a brilliant understanding of pharmacokinetics in kids with obesity, hopefully for obvious reasons, but the generally advice is as follows:

For the commonly used drugs, use the following:

Midazolam - total body weight
Propofol - ideal body weight
Fentanyl - adjusted
Remifentanil - adjusted
Morphine - ideal
Paracetamol and ibuprofen - adjusted
Ondansetron and dexamethasone - total
Rocuronium - ideal
Suxamethonium - total
Sugammadex - total
Atropine - total
Lidocaine - total
Bupivacaine - ideal
Penicillins - total
Gentamicin - adjusted

This box is for educational purposes to show that different drugs should use different weights. When making your own drugs up, always double check which weight you should be using from a verified source such as SOBA or the BNFc.

Preoperative

Be cautious with sedating premedication, especially where there is confirmed or suspected obstructive sleep apnoea
Ketamine or dexmedetomidine may be a better choice than benzodiazepines, or at least reduce the dose as there is risk of significant hypoventilation

Induction of anaesthesia

Intravenous induction is preferred due to difficult airway management but obviously it's going to depend on the individual child
Ramped position with external auditory meatus and sternal notch aligned
Induce in theatre to avoid added risk of transfer from anaesthetic room
Have a low threshold for intubating rather than using a supraglottic airway, even for minor procedures
SOBA recommend videolaryngoscopy as first line

The big risk is that you gas a kid down until they're nicely sat in the super-high-risk stage of anaesthesia, whereupon they obstruct, you can't bag them and it's then hard to find a vein and it all goes pear shaped.

Positioning

Minimise transfers and changes in position where possible
Flattening the patient will reduce respiratory compliance, increase airway pressures and atelectasis
Heavier patients are at increased risk of sliding off the table so use safety straps
Obesity carries the risk of pressure point injuries, so pay attention to pressure areas and use appropriate padding
Ensure your equipment is safe to use for the weight of your patient

Analgesia

Kids with OSA are more sensitive to hypoventilation after opioids
But kids with obesity may also have worse pain
So you can use opioids, but you need to balance these risks on an individual basis
As always, you're going to use your multi-modal opioid sparing analgesic techniques including the use of regional anaesthesia where appropriate.

Emergence and recovery

Remember that extubation is just as, if not more, risky as intubation.

Ramped position
Preoxygenation
Bite block or oropharyngeal airway
Adequate PEEP to avoid negative pressure pulmonary oedema
Full reversal of neuromuscular blockade
Wide awake extubation
Consider extubation onto NIV
Lower threshold than normal for admission to HDU or ITU postoperatively especially if severe OSA
Day case surgery is still possible, if they meet all the usual criteria - obesity alone is not necessarily an indication to stay overnight

Are there any studies to know about for the exams?

Yeah they like to ask about the PEACHY study.

It was a large, multicentre, prospective cohort study published in 2021 and was the first big study to estimate UK paediatric obesity prevalence perioperatively.

This study aimed to figure out: