57. Obesity Flashcards
How can you classify obesity
There are numerous classification systems for categorising the relationship
between height and weight. The two commonest are:
body mass index (BMI) is a useful method and is calculated by BMI
= weight (kg)/height squared (m2)
22–25 is normal.
25–30 is considered overweight.
> 30 is obesity.
> 40 or >35 with obesity-related comorbidity is morbid obesity
What are the problems that her obesity may pose for anaesthesia?
Cardiovascular
Increased blood volume and cardiac output leading to cardiomegaly,
left ventricular hypertrophy (therefore reduced compliance and diastolic
function) and a potential for left ventricular failure.
Hypertension and ischaemic heart disease are common.
Venous access can sometimes be difficult.
Thromboembolism risk is increased.
Obese patients have less water per unit of body weight,
they tolerate hypovolaemia badly and
they may also compensate poorly for changes
of position during anaesthesia.
Respiratory
- Increased work of breathing.
mass effect of chest weight, which
reduces chest wall compliance - Reduced compliance (both chest wall and lung) and reduced FRC will
pre-dispose to atelectasis, increased shunt and hypoxia. These patients
must be pre-oxygenated as they desaturate much quicker than non-obese
(3–5 times). - Pulmonary vasoconstriction, pulmonary hypertension and right ventricular
hypertrophy. - Oxygen consumption and carbon dioxide production are increased.
- Obstructive sleep apnoea is relatively common and 5% have Pickwickian
syndrome in which there is a loss of the sensitivity to hypercarbia resulting
in a combination of hypoxia, cor pulmonale and polycythaemia. - There is a higher incidence of difficult laryngoscopy ?
Number of studies of patient undergoing bariatric
surgery that demonstrate there is no greater incidence of Cormack and Lehane grade
3 and 4 views in the morbidly obese than in controls of normal body habitus - increased adipose tissue of the neck and upper chest may
make bag-valve-mask ventilation difficult
Gastrointestinal
Increased acidity and volume of gastric contents.
Hiatus hernia and gallstones are common associations.
Increased intra-abdominal pressure.
There is a higher risk of regurgitation and aspiration requiring rapid
sequence induction if a difficult airway is not anticipated.
Tracheal extubation should be undertaken with the patient awake
Endocrine
Morphological
Endocrine
There is an association with glucose intolerance.
Morphological
Positioning
Transferring
Monitoring (arterial line may be needed if NIBP is problematic)
How would you assess this lady’s airway
History
Symptoms of obstructive sleep apnoea including snoring and
daytime hypersomnolence.
The patient’s partner may give a
useful description of apnoeic episodes.
Previous anaesthetic charts should be reviewed to determine if
there were problems with airway maintenance in the past.
Examination
Assessment of head and neck movement
Mouth opening
Mandibular movement
Thyromental distance
Nostril patency
Investigations Indirect laryngoscopy may be useful.
Radiology
The incidence of difficult intubation in morbid obesity is around 13%
The incidence of difficult intubation in morbid obesity is around 13%
Altered anatomy: Increase in soft tissue
Reduced head and neck mobility
Large tongue
Short neck
Large breasts
Anterior larynx
Restricted mouth opening
Tell me how you would anaesthetise this lady.
Having taken a history, examined the patient and performed appropriate
investigations, consideration should be given to pre-medication. Anti-emetics
and sodium citrate may be prescribed and an anticholinergic agent should be
given if fibre-optic intubation is to be performed
If a difficult intubation is not anticipated, then the patient should be
pre-oxygenated (in the head up position if possible) for at least 3 minutes and
a rapid sequence induction performed with cricoid pressure. All difficult
airway adjuncts should be immediately available. Once the airway is secured
with an endotracheal tube, the patient should be ventilated. Compared with
non-obese patients a higher FiO2 and the addition of PEEP may be required to
help prevent basal atelectasis. However, the addition of PEEP may adversely
affect venous return and cardiac output
A combination of general and regional anaesthesia has many advantages
but:
Regional blocks can be technically difficult as anatomical landmarks may be
obscured. Longer needles may be necessary.
Epidural local anaesthetic dose requirements are reduced as the volume of
the epidural space is reduced.
Analgesia
with intravenous paracetamol, an NSAID such as parecoxib and
morphine would be reasonable.
Anti-emetics should not be forgotten and
post-operative analgesia could be provided with a combination of regular
paracetamol and brufen with PCA morphine.
Important post-operative considerations include:
Extubate awake, sitting up.
HDU care, may need CPAP.
Oxygen and oximetry.
Obstructive sleep apnoea is most common some days after surgery
Adequate analgesia to allow deep breathing/coughing.
Physiotherapy
DVT prophylaxis
Ideal weigh
t: there are simple empirical formulae to approximate a patient’s ‘ideal’
weight. One such estimates the optimum weight by subtracting from the height in
centimetres 105 (for women) and 100 (for men).
Neurohumoral mechanisms underlying obesity:
In addition to the array of social,
psychological and cultural factors that are associated with food and eating, there are
highly complex regulatory neurohumoral mechanisms that are processed in the
hypothalamus.
These control appetite and satiety, and substances so far identified
include, leptin, ghrelin, adiponectin, peptide YY3–36 and insulin
Obese subjects predictably have high plasma leptin
concentrations secondary to their increased adipocyte mass, but they can have reduced
leptin sensitivity
Ghrelin is an orexigenic peptide that is released in the stomach and
inhibited by gastric distension. YY3–36 has the same effect on stimulating appetite but is released in the small bowel. As a simplification, there are anorectic and orexigenic
neurohumoral factors which regulate energy balance. In obese individuals, the balance
between the two systems is disrupted. It is probable that there is a genetic component.
Abdominal obesity:
there has been more interest recently in abdominal obesity as a
predictor of cardiovascular disease, hypertension and diabetes. Visceral fat appears to
provoke chronic low-grade inflammation that may trigger both insulin resistance
and the hypertension, atherosclerosis and diabetes mellitus that characterize the
metabolic syndrome.
Mortality:
the morbidly obese individual has only a 1 in 7 chance of reaching a
normal life expectancy, and their mortality for all forms of surgery averages twice
that of the non-obese population. Problems affect most systems.
Bariatric surgery:
The financial costs of
obesity are such that bariatric surgery is becoming more common in the NHS. There
is good evidence that it can reverse some of the complications such as hypertension
and diabetes mellitus. Following roux-en-Y gastric bypass surgery, for example, 60%
of patients with type 2 diabetes will revert to normal glycaemic status
usually laparoscopic and include gastric banding, in which an adjustable band
encircles the upper part of the stomach to create a small pouch; surgical gastroplasty,
which reduces the effective size of the stomach; sleeve gastrectomy which leaves a
small residual stomach; gastric bypass surgery, which causes weight loss by malabsorption;
duodenal switch surgery; and intragastric balloon insertion.
