Obesity and OSA Flashcards
What are some conditions associated with obesity?
CVD
- HTN, IHD, cardiomyopathy, cor pulmonale, CVD< PVD, DVT, PE, sudden cardiac death
Resp
restrictive lung disease, OSA, asthma, obesity hypoventilation syndrome
Endocrine
DM, hypothyroidism, PCOS
Gastrointestinal
Hiatus hernia, GORD, non-alcoholic fatty liver disease
Genitourinary
CKD, female urinary incontinence, erectile dysfucntion
Malignancy
Breast, prostate, colorectal, cervical, endometrial cancer
Musculoskeletal
OA, back pain
How do we measure/define obesity?
Classic definition
- excess body fat due to dietary energy intake exceeding expenditure
Metabolic definition
- multiple hormonal/psychological feedback mechanism imbalance
not all obesity is the same
- central obesity (increased CVD, thrombosis, metabolic syndrome)
- peripheral fat confers minimal health risk
BMI is the form of measurement (weight kg/(height(m))squared)
Waist circumference - better to relate to disease.
- >94cm increased risk 102cm substantially increased men and 80cm or 88cm in Women
MRI measurement -
What is the relationship between surgical outcomes and obesity?
U shape - most deaths occuring with underweight and morbidly obese patients
Obesity paradox - does not increase risk of complications or death from elective surgery
Metabolic syndrome (centrally obese, hyperglycemic, HTN, dyslipidemia) risk is significantly higher
What are the physiological reasons obese patient’s have difficult ventilation/airways?
reduced mouth opening, hyperglossia, oropharyngeal crowding and a short/immobile neck make airway management more difficult
large breasts and reduced chest wall compliance - expiratory residual volume and functional residual capacity fall causing small airway closure resulting in mismatch of lung ventilation. This issue is compounded by general anaesthesia.
increased metabolic demand from excess fat and reduced functional residual capacity shortens time for apnoea before art oxygen saturation occurs.
Difficult bag mask ventilation in obese patients
common to get:
- difficult intubation
- aspiration
- airway trauma
- extubation issues
- asthma has a 2.5 fold increase in obese patients (mechanically squashed airways)
What are some of the respiratory investigations and ways to optimise perioperative care?
all patients get RR and pulse oximeter
- ABG if hypoxic at room air
- PFT if unexplained dyspnoea at rest with symptoms of obstructive lung disease (jagged peaks due to resistance)
What are the principles of pulmonary optimization in obese patients?
minimum 6 weeks cessation of smoking with NRT
inhaled corticosteroids, leukotriene inhibitors and long-acting beta agonists for treatment of asthma
antibiotics for infected sputum
PPI for GORD
periop diet/exercise
What is the mechanism between obesity and asthma?
- mechanical lung functional
- obesity inflammatory
- GORD
- OSA
- vocal cord dysfunction
- deconditioning
generally difficult to manage
- disconnect between expectations and outcomes
- excessive medications poorly responsive
- additional diagnoses
When is a patient suitable for day case surgery?
BMI <40 can provided comorbidities are optimised
BMI 40-50 day surgery can be appropriate in absence of major comorbidities (esp OSA)
BMI >50 day surgery is not recommended
What is the criteria for Bariatric surgery in Victoria?
- BMI >40 or >35 with two or more obesity related cormorbidities (HTN requiring meds, T2DM, dyslipidaemia, OSA, pulmonary HTN, non-alcoholic steatohepatitis)
- over 18 and under 65
- have attempted but not succeeded in achieving weight loss using non surg measures
What forms of weight loss surgery are there? How do they work?
Laparoscopic adjustable gastric banding (LAGB)
- small stomach pouch
- adjustable saline silicone tube adjusted by the volume of saline added by use of Huber-tipped needle inserted through skin
- lose 40-50% excess weight of 1-2 years
- has high revision rate for malpositioning, band erosion and port problems
Laparoscopic sleeve gastrectomy (LSG)
- 100-150ml sleeve after stomach surgically removed
- increased early surgical complications (bleeding, anastomotic leakage)
Roux-en-Y gastric bypass
- bypasses the stomach
- performed laparoscopically where the stomach is stapled off to create a small gastric puch with 15mls volume. Jejunum is divided and the cut end is attached to the small stomach pouch.
- 60% excess wieght
- higher complication rate (bleeding, anastomotic breakdown, bowel obstruction)
work through early satiety
most bariatic patients post surg require preop caloric restriction to shrink the liver and improve surgical access to stomach.
associated with long term reduction in mortality, decreased diabetes, reduced MI, stoke and cancer.
Explain the physiology around sleep and factors that control sleep
Light
- sensed by suprachiasmic nucleus, sends message to suprioer cervical ganglion. Sends message to pineal gland to inhibit melatonin (aides sleep)
Melatonin
- acts on oroxine (can inhibit neurotransmitters in thalamus or if oroxine inhibited gaga/ACH alertness)
Circadian Balance
- while we are awake body temperature rises, growth hormone released in first half of night, cortisol released in second half of night (REM)
- measured using actigraphy
Polysomnography (sleep study)
REM higher in children than adults (60% to 15) as compared to slow wave sleep and stage 1+2
What is the relationship between BMI and sleep loss?
- inversely related
- sleep loss changes appetite
- endocrine changes with sleep deprivation (slower glucose clearance, insulin release impaired, raised cortisol)
- reduced growth hormone
- reduced performance
- sleep loss reduces upper airway muscle activity
What is the categorised within sleep disordered breathing?
- OSA
- hypercapnic central sleep apnoea (CSA) including obesity hypoventilation syndrome (OHS)
- non-hypercapnic central sleep apn
What is the definition of OSA?
- OSA - recurrent apnoeas (>10 second pause in ventilation) or partial apnoeas (AHI or apnoea hypoxia index)
5-10 mild
15- 30 moderate
>30 severe
spO2 overnight can also be used >92% normal 88-92% mild 80-90% mod <80% severe
What is central sleep apnoea? What is obesity hypoventilation syndrome?
Hypercapnic CSA
- periods of hypoventilation >2mins duration
- mild forms only during REM sleep and CO2 returns to normal when patient returns to nonREM
Hypocapnia CSA
- cyclic loss of respiratory drive (stage 1-2 of non REM sleep)
- when CO2 signal to the central (brain stem) and peripheral (carotid body) chemoreceptors the drive to ventilation is exaggerated - abnormal autonomic control as hyperventilation occurs in response to apnoea.
- seen in advanced heart failure (Cheyne Stokes respiration)
- seen in some OSA patients given CPAP (CPAP induced CSA)
OHS
BMI >30 daytime hypoventilation (PaCO2 >45 and PaO2 <70) in the absence of other contributing factors
