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Anaesthetic challenges in obese Paediatric patients
Prof.N. Krishnan
Professor of Anaesthesiology
Madras Medical College
Institute of Child Health & Hospital for Children
Childhood Obesity

The World Health Organization and the International Obesity Task Force have both recognized
that obesity is fast becoming a global epidemic. Obesity is associated with an increase in total
body weight (TBW), an increase lean body weight (LBW), and increase fat mass.

Total body weight (TBW) is the patient’s actual body weight.
 Ideal body weight (IBW) :Weight believed to be maximally ideal for good
healthof a person, based chiefly on height but modified by factors such as
gender, age, build, and degree of muscular development.
IBW = [ BMI at 50th percentile for the child’s age] x ( Height [m] )2
Lean body weight: [ LBW] = IBW + 0.3 X [TBW-IBW]
 Lean body mass is a component of body composition, calculated by subtracting body
fat weight from total body weight
Lean Body Mass (or the ideal body weight plus 20%)

Body mass index: BMI = Weight
(Kg)/Height2 (m2),
BMI, weight (kg)/height2 (m2), is a measure of ideal weight range.BMI, however, cannot be used as such
in Paediatric patients because of growth and differences in the distribution of fat and muscles, body
shape or bone density occurring at puberty.Growth in childhood has traditionally been measured using
the widely validated growth charts for boys and girls up to the age of 18 with height and weight indices
expressed in centiles.Gender-specific BMI charts were produced and the centiles for 'overweight' and
'obese' were defined by projecting back from where they crossed the BMI of 25 and 30 curves,
respectively, at the age of 18 yr.
(1) BMI of more than percentile 85 of the BMI at the child’s age means overweight.
(2) a BMI of more than percentile 95 means obesity.
(3) a BMI of more than percentile 99 means super obesity.
 With increasing obesity, fat mass increases to a greater extent than LBW, and the ratio of
LBW to TBW decreases. There are regional differences in the perfusion of adipose
tissue. Abdominal and visceral fat receive less blood flow than subcutaneous adipose
tissue.The increase in cardiac output is strongly related to the increase in LBW.Cardiac
output is a significant predictor of early distribution kinetics.The increase in cardiac
output associated with obesity results increased hepatic and renal blood flow.
Changes in various systems in body due to obesity
Changes in respiratory systems:
Lung Volumes: A reduction in lung volumes is well associated with the increase in body
mass.There is reduced Chest Wall Compliance, (of up to 30%) due to the heavy chest wall,and splinted
diaphragm, the reduction in Lung Compliance due to increased pulmonary blood volume, Decreased
Functional Residual Capacity(FRC), Vital Capacityand inspiratory capacity.With the onset of anaesthesia,
a supine position and the abnormally high elevation of the diaphragm (due to increased visceral and
abdominal wall fat) all combine to cause ventilation-perfusion mismatch. Respiratory Mechanics.
Respiratory resistances are increased.
Gas Exchange. The increased body mass and metabolically active adipose tissue leads to
increased oxygen consumption and carbon dioxide production.Minute ventilation is thus increased to
achieve normocapnia. Oxygenation decreases with the increase in body mass due to the are
underventilation of lungbases, airway closure and atelectasis, thus producing pulmonary "shunt" and
hypoxaemia. Thus reduction in compliance, together with increased respiratory demand results in an
increased work of breathing.
Obstructive Sleep Apnea:The disease is caused by passive collapse of the pharyngeal airway
during deeper planes of sleep, resulting in snoring and intermittent airway obstruction.
Changes in Cardiovascular system
Obesity is associated with a number of cardiac risk factors. These include hypertension,
ischaemic heart disease (IHD), cardiomyopathies, cardiac failure, arrhythmias, sudden cardiac death and
dyslipidaemias. Venous insufficiency, cerebrovascular and peripheral vascular disease. Increased
visceral fat is a cardiovascular risk factor even when the BMI is normal.
Childhood obesity causes increased blood volume and stroke volume with a resulting increase in
cardiac Output. The increase in cardiac output is strongly related to the increase in
LBW.Hypertension is particularly common in obesity. These patients also have an increased absolute
blood volume and increased cardiac output. Thus left ventricular stroke work is increased and left
ventricular hypertrophy can result. Left and right cardiac failure can both occur. Venous return is also
reduced. An obese abdomen will directly compress venous return from the legs (also increasing the risk
of deep vein thrombosis (DVT) and pulmonary embolism). Once ventilated, higher inflation pressures and
application of PEEP further reduces venous return, which may result in a fall in cardiac output. The risk of
pulmonary embolus and DVT is doubled in the obese. Other causative factors for this increase include
hypoxia-induced polycythemia, cardiac failure, decreased fibrinolysis and immobilization.
Changes in Gastrointestinal system:
Due to the increased abdominal mass, gastroesophageal reflux disease is frequent. There is an
increased incidence of hiatus hernia in the obese. The volume and acidity of gastric contents is often
increased.Need to give oral H receptor antagonists (e.g. ranitidine 150mg) or proton pump inhibitors
2
routinely 1-2 hours preoperatively, and if in doubt, perform rapid sequence induction.Nonalcoholic fatty
liver disease (NAFLD) is present in 50–60% of obese children
Changes in Endocrine:
Resistance to insulin and the metabolic syndrome is present in 39% of moderately obese and in
50% of severely obese adolescents.Non-insulin dependent diabetes mellitus (and its associated
microvascular and macrovascular changes) is much more common in the obese caused by insulin
resistance and inadequate insulin production.A preoperative fasting blood glucose level should be obtained,
because undiagnosed type 2 DM is frequent
Psychology
Some form of depression with a poor body image and loss of self-esteem are often present in
obese Paediatric patients. The relationship with lean peers is poor (teasing, marginalization).
Other miscellaneous changes:
Some pathologies specific to the Paediatric age group are
(1) slipped capital femoral epiphysis;
(2) tibia vara (Blount disease): repetitive trauma from overweight on the medial tibial growth plate results
in growth plate suppression and varus deformity of the tibia;
(3) cholelithiasis, because bile is supersaturated with cholesterol;
(4) polycystic ovary syndrome with clinical signs of hyperandrogenism (hirsutism, irregular menses);
(5) idiopathic intracranial hypertension (pseudotumour cerebri), probably caused by increased
intrathoracic pressure, decreasing venous outflow from the head.
Pharmacology
Calculation of the optimal drug doses for induction and maintenance of anesthesia are based on the
patients total body weight (TBW), ideal body weight (IBW), and lean body weight (LBW).Obese children have
significantly higher total body water, body volume, lean mass, fat mass and bone mineral content. They
also have an increased hydration of lean mass which is attributed to increased extracellular water.
Drug administration:The dosage of medicines in children is usually calculated on a milligram per
kilogram basis. Drug dosing in obese children presents a particular challenge. Dose calculation using
total body weight for many of the anaesthetic agents may lead to overdose and subsequent adverse
physiological sequelae. Therefore, the calculation of drug dosing on ideal body weight or even lean body
mass may be preferred.
Loading Dose

Loading dose is usually based on the volume of distribution (VD). With an increased volume of
drug distribution, Elimination Half-Life might be prolonged (e.g. diazepam}.
Lipophilic drugs have increased volume of distribution. Lipophilic drugs distribute freely into fat tissue
resulting in greater distribution. A larger dose may be needed for adequate response. Some recommend
dosing lipophilic medications on TBW however this should be assessed on a case by case basis where
the risks of toxicity are considered.Hydrophilic drugs remain unchanged. Hydrophilic drugs are generally
loaded based on ideal body weight (IBW).
Maintenance dose selection is based on clearance rate for drugs predominantly determined by
renal and hepatic function. Drug clearance might be altered in obese individuals whose hepatic and renal
clearance may be increased in correlation with LBW .
Anaesthetic drug dose should ideally be as follows:
Thiopental sodium: Lean body weight (more rapid awakening).
Propofol: (induction bolus) Lean body weight / (maintenance infusion) Total (actual) body weight
Etomidate: Lean body weight
Succinylcholine: Total (actual) body weight
Pancuronium: Ideal body weight
Rocuronium: Ideal body weight
Vecuronium:Ideal body weight
Cisatracurium: Ideal body weight
Fentanyl:Lean body weight
Alfentanil: Lean body weight
Remifentanil: Lean body weight
Midazolam :(bolus dose)Total (actual) body weight (infusion)Ideal body weight
Paracetamol: Lean body weight
Neostigmine: Total (actual) body weight
Sugammadex: Total (actual) body weight or ideal body weight + 40%
Of the inhalational anesthetics, sevoflurane provides more hemodynamic stability and less airway
irritability when compared to desflurane and can be used for induction. Desflurane has a lower bloodlipidsolubility, provides a faster restoration of protective airway reflexes and perhaps a more rapid
recovery profile than sevoflurane in obese individuals. Isoflurane has a high blood-lipid solubility which
markedly increases recovery time in obese individuals compared to sevoflurane and desflurane.
Agent
B/G
Fat / blood
N2O
DES
ISO
SEVO
0.47
0.42
1.4
0.65
2.3
2.7
45
48
ANAESTHESIA FOR OBESE CHILDREN
The Preanesthetic Examination
The preanesthetic physical examination of obese children should include thorough airway
assessment,height, weight and BMI assessment using age specific and gender-specific curves. Blood
pressure, heart rate, fasting blood glucose level, and preoperative pulse oximetry should be obtained. If
cardiac disease is suspected, an echocardiography and electrocardiogram should be obtained.
Pulmonary function tests should be carried out if respiratory comorbidity is likely.Screening for obstructive
sleep apnoea may indicate the need for overnight oximetry, formal sleep studies, and other respiratory
function tests, including arterial blood gas analyses.The children should be examined and investigated to
rule out any other congenital or inborn errors associated with obesity.
No anesthetic technique has been found to be superior to another with respect to important
patient outcomes (eg, mortality, cardiopulmonary complications). Obese children all have a much higher
risk of bronchospasm, laryngospasm, and oxygen desaturation peri operatively than their non-obese
making this a high-risk group of children presenting for surgery. If possible general anesthesia should be
avoided to minimize airway and drug-related respiratory problems. However, general anesthesia may be
necessary for certain surgical procedures. Modifications of the approach to general anesthesia in obese
patients may be needed.
Premedication of the obese patient should ideally allow anxiolysis without abolishing airway
reflexes or preventing patient cooperation prior to induction of general anesthesia.
Preparation for induction.
Monitoring:



Pulse oximetry: Oxygen saturation monitoring problems can often be overcome with the use of
an ear probe or in smaller children use of a wrap-around type saturation probe.
ECG monitoring: increased impedance due to a higher proportion of body fat may lead to a poor
signal.
Blood pressure:The sphygmomanometer cuff should be 20% greater than the diameter of the
upper arm , if the cuff is too small, the BP will be over-estimated. In the morbidly obese, invasive
BP monitoring is advisable.There may be practical difficulty in obtaining arterial access.

Temperature

Capnography
Positioning
Proper Positioning is important to prevent pressure necrosis during prolonged procedures. For
younger obese patients, additional padding and attention to bony prominences as with all patients may be
sufficient. The obese patients may require additional equipment that is not typically available. These
include:
●Special equipment for positioning.
●Large beds and operating tables – Designated weight limits may not remain valid if the patient is
shifted on the table, or the table is unlocked .

Additional arm supports to widen the table, or the use of two operating tables, may be necessary.
●Mechanical transfer mechanisms – Various means of mechanically assisting the transfer of
severely obese patients between stretchers and beds have been developed. These may improve
patient safety and prevent injury to care personnel.
●Additional personnel – Assistance may be needed to transfer and position patients safely.
●Extra-long needles – Normal length epidural, spinal, and nerve block needles may be insufficient to
access structures in severely obese patients.
●Ultrasound – Ultrasound may be used to assist in vascular access, nerve block, and neuraxial
procedures.

Blood pressure cuffs – Appropriately-sized blood pressure cuffs for noninvasive blood pressure
(NIBP) result in accurate readings.
Pre-oxygenation is ideally performed in the sitting or head-up (reverse Trendelenburg) position to
maintain oxygenation, as both the supine position and the induction of anesthesia decrease lung volumes
in the obese patient. A head-up or ramped position with the goal of horizontal alignment between the
external auditory meatus and the sternal notch which will improve laryngoscopic view.Preoxygenation can
be done via a tight-fitting facemask using 100 percent oxygen (O2) at a flow rate high enough to prevent
rebreathing (10 to 12 L/min), aiming for an end-tidal concentration of O2 greater than 90 percent in order
to maximize safe apnea time, Three minutes of tidal volume breathing or Eight Vital-capacity breaths over
60 seconds ,Manually-applied positive end-expiratory pressure (PEEP), or the use of Noninvasive
ventilation .
Induction :
IV induction can be used to rapidly induce a deep plane of anesthesia ready for airway
instrumentation. This technique may be preferable for patients with very severe OSA.But Venous access
may be more difficult in this group secondary to increased subcutaneous fat deposits The increased risk
and consequences of respiratory depression in obese patients indicate caution in the use of opioids,
sedatives Propofol, and anxiolytic medications like benzodiazepines. Opioid administration should be
minimized to decrease the risk of respiratory depression, particularly in patients with obstructive sleep
apnea. opioid-sparing multimodal analgesia like include the use of local or regional anesthesia,
nonsteroidal antiinflammatory drugs such as ketorolac, IV acetaminophen, ketamine, alpha-2 agonists
clonidine and dexmedetomidine and antiepileptic drugs pregabalin and gabapentin, and other
medications may reduce the risk of respiratory depression and other opioid-related side effects. Obesity
increases difficulty with mask ventilation and decreases the apneic period until desaturation occurs.
When using a neuromuscular blocking agent (NMB) for airway placement, it is reasonable to choose a
rapid acting ones like succinylcholine or rocuronium to decrease the interval between induction and
intubation, during which the patient must either be mask ventilated or be apneic.
There will be a lot of Morphological and functional variations of the respiratory system after the
induction and maintenance of anaesthesia and paralysis. Relaxation of the genioglossus muscle will
result in airway collapse .Increased pharyngeal fat decreases the upper airway caliber.passive collapse of
the pharyngeal airway during deeper planes of sleep, resulting in snoring and intermittent airway
obstruction. Positioning in an upright or lateral position, use of a jaw thrust maneuver, delivery of positive
pressure by face mask and placement of an oral airway may aid in relieving the obstruction. Severe
airway obstruction in a spontaneously breathing patient may result in a very high negative inspiratory
force generated although the patient is inhaling against the collapsed pharynx or closed glottis; the
increased pulmonary blood flow and pulmonary microvascular pressure that ensues can result in post
obstructive pulmonary edema.
Airway management — Obese patients tend to have short, fat necks making both mask
ventilation and direct laryngoscopy technically more challenging. Due to the reduced chest compliance
and sheer mass of the chest wall, higher inflation pressures are required to ventilate such patients. Obese
patients are more likely need intubation rather than a supraglottic airway LMA as LMA may not maintain a
seal at the higher airway pressures. Studies have shown using a laryngeal mask airway (LMA), choosing
size according to TBW significantly increases the oropharyngeal leak pressure and gives better
ventilating conditions in overweight children. When chosen second-generation devices designed for
controlled ventilation, which allow for higher seal pressures and provide a gastric vent may be used.
Obese patients are more likely to require controlled ventilation to prevent hypoventilation during
spontaneous respiration, and during positive-pressure ventilation. Obese patients should not be managed
with mask ventilation except for brief anesthetics like an exam under anesthesia. As there will be less
time to rescue the obese patient in a failed airway situation (cannot ventilate, cannot intubate) due to
rapid apneic desaturation devices for difficult intubation, medications, equipment and expert assistance
should be readily available for any patient having general anesthesia.
Maintenance agents — Anesthesia can be maintained with either an inhaled anesthetic agent
(eg, isoflurane, sevoflurane, desflurane, with or without nitrous oxide) or with an intravenous agent (most
often propofol). Slightly more rapid emergence and recovery occurred in patients with desflurane
compared with sevoflurane, isoflurane due to lower fat blood coefficient .While nitrous oxide (N2O) may
be used to supplement a volatile agent or propofol, some obese patients with underlying respiratory
problems may not tolerate the decreased inspired oxygen concentration that accompanies the use of
N2O. Concern that rapid diffusion of N2O into the bowel obscures the view of the surgical field was not
confirmed in a study of obese patients undergoing laparoscopic bariatric surgery.
`
Morbidly obese patients during general anaesthesia should be ventilated with physiologic tidal
volumes (6-10 ml/Kg Ideal Body weight) and a respiratory rate to maintain normocapnia. In addition, an
application of 10 cmH2O PEEP after a recruitment manoeuvre associated with a FiO2 between 0.4 and
0.8 are recommended.
MANAGEMENT OF NEURAXIAL ANESTHESIA — In general, neuraxial anesthetic techniques with local
anesthetic (ie, without opioids) minimally affect respiratory drive, and are safe and appropriate choices for
obese patients. Spinal and epidural anesthesia at higher dermatomal levels (ie, thoracic levels) may lead
to respiratory difficulty. Landmarks tend to be more difficult to identify in obese patients and a greater
number of attempts are required to place spinal and epidural anesthetics. When planning a neuraxial
technique at higher levels, it is prudent to use a technique that allows control of the amount and interval of
dosing, such as an epidural or spinal catheter, rather than a “single shot” block.
Extubation — The obese patient should only be extubated in the operating room when fully awake and
after any neuromuscular blockade has been completely reversed, in addition to standard extubating
criteria. The head-up position is ideal at emergence, to improve oxygenation and decrease work of
breathing.Neuromuscular blockade may be reversed using Sugammadex or neostigmine .the
sugammadex group had a significantly faster recovery from NMB.
Following Extubation the following measures are used to maintain adequate oxygenation:
●Administration of oxygen, titrated to keep O2 at >90 percent (by face mask or nasal cannula)
●Positioning patient in head-up (sitting or semi-sitting) or lateral position (if surgically acceptable)
●Use of incentive spirometry or chest physiotherapy
●Administration of continuous positive airway pressure (CPAP) or noninvasive ventilation (NIV) in
patients with preoperative use, or with hypoxia unresponsive to incentive spirometry.
Postoperative Care
Obese children have an increased incidence of airway obstruction after operation and also
require a longer duration of stay in the post-anaesthesia care unit (PACU) after their procedure. In the
immediate postoperative period, oxygen therapy will be required and may need to be continued once the
child is on the ward. Constant observation with oxygen saturation monitoring is vital.
Adequate postoperative analgesia should be given however, large doses of sedating opioids may
increase the risk of delayed airway obstruction and so should be carefully titrated to minimize risk on the
ward or at home. The use of regional analgesia should be encouraged as much as possible .Control of
nausea and vomiting with use of multi-modal antiemetics.
Conclusion:Obesity is not rare in Paediatric patients and we should introduce the use of BMI charts in
our preoperative assessment to identify such patients and adapt our perioperativemanagement
accordingly. In obese children, perioperative morbidity is mainly related to airway and ventilation.Patients
with a history of obstructive sleep apnoea will require an overnight stay and may need monitoring in a
high-dependency unit. We should be careful with the use of drugs. Postoperative physiotherapy/incentive
spirometry and use of regional techniques such as epidural analgesia should reduce atelectasis and
postoperative respiratory failure. Early postoperative mobilization is vital for the safety of these cute
obese children.
References:
1. Anesthetizing the obese child Anette Mortensen1, Katja Lenz1, Hanne Abildstrøm2 & Torsten L. B.
LauritsenPediatric Anesthesia 21 (2011) 623–629 ª 2011 Blackwell Publishing Ltd.
2. Child obesity and Anaesthetic morbidity - Francis Vickerman’s- Current Opinion in Anaesthesiology
2008,21:308–312.
3. Childhood obesity and the anaesthetist- Jan Owen FRCA - Continuing Education in Anaesthesia,
Critical Care & Pain | Volume 12 Number 4 2012.
4. Dose adjustment of anaesthetics in the morbidly obese - J. Ingrande and H. J. M. Lemmens- British Journal
of Anaesthesia 105 (S1): i16–i23 (2010).
5. Complications of obesity in children and adolescents- SR Daniels- International Journal of Obesity (2009)
33, S60–S65.
6. Obesity & Anaesthesia - Dr KD Rooney www. world anaesthesia uk.com
7. Smith’sAnesthesia for Infants and Children- Eighth Edition
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