Specific diseases and anaesthesia Flashcards
What are the criteria of the STOP BANG assessment?
- S - Snoring
- T - Tiredness during daytime, often with headache
- O - Observed apnoeas
- P - Pressure (HTN)
- B - BMI > 35
- A - Age > 50
- N - Neck circumference > 41 cm women, > 43 cm men
- G - Gender (male)
What score on STOP BANG constitutes high risk of OSA?
≥ 5
What is the AHI?
Apnoea / Hypnea Index. The number of apnoeas or hypnoeas lasting > 10s recorded in 1 hour.
What are the risk stratifications for the AHI?
- ≥5 mild
- ≥15 moderate
- ≥30 severe
What constitutes a significant desaturation in OSA?
desaturations >4% if ≥5 in 1 hour.
Which features of OSA does nocturnal CPAP most improve?
- CCF
- platelet aggregation
- dysrhythmias
Which features of OSA should prompt to postpone surgery and optimise?
- Untreated CCF
- Hypercapnoea with PaCO2 > 6.5
What is the most common and most severe muscular dystrophy?
Duchennes Muscular Dystrophy
What is the incidence of DMD?
1 in 3500 male LB
Define muscular dystrophy
A group of inherited disorders characterised by progressive muscle weakness without evidence of denervation
What are the cardiac effects of DMD?
- Cardiomyopathy
- Conduction defects
- Heart Failure
What are the respiratory effects of DMD?
scoliosis resulting in restrictive lung defects improper secretion management recurrent chest infections Failure to wean from ventilation Respiratory muscle weakness
What are the neurological effects of DMD?
Learning disability
What is the typical life expectancy in DMD?
15-25 years
What is pseudohypertrophy?
Muscle enlargement in muscular dystrophy caused by replacement of muscle with fat and fibrous tissue
What are the biochemical abnormalities found in DMD?
Raised CK
What are the common operations in DMD?
Orthopaedic - scoliosis corrections Cardiac - angiography, valve replacement Ophthalmic - Cataracts Incidental - Dental work 2nd to low IQ
Why should you perform lung function tests in DMD?
VC less than 20ml/kg associated with increased mortality
List 3 acquired, non drug related causes of Long-QT
Subarachnoid haemorrhage Anorexia Nervosa Hypothermia
How do you diagnose long QT?
QTc greater than 440 ms
What is your perioperative anaesthetic management of Long QT?
- Seek cardiologist opinion
- Check electrolytes
- Perform ECG with valsalva
- Stop any drugs that increase QTc
- Continue beta blockers
- Avoid suxamethonium
- Obtund pressor response to laryngoscopy
- Avoid use of reversal (use sugammadex)
- Consider transvenous pacing
What causes long QT?
Depolarisation abnormality Malfunction in cardiac ion channels
What is porphyria?
Group of disorders characterised by an inherited or acquired abnormality in the enzymes relating to haem synthesis.
What is the pathophysiology of porphyria?
Failure in haem synthesis. Accumulation of porphyrins and precursors (ALA, aminolaevulinic acid, and PBG, porphobilinogen)
Which enzyme is an important rate limiting step in porphyria?
ALA synthetase
What is the incidence of porphyria?
1 in 20,000
How is a diagnosis of porphyria confirmed?
Urinary ALA and porphobilinogen
What are the different types of porphyria?
Acute Intermittent Variagate Hereditary
Which premedication drugs are considered SAFE in porphyria?
NONE
Which induction agents are considered SAFE in porphyria?
Propofol only
Which maintenance agents are considered SAFE in porphyria?
Most volatiles Nitrous Oxide
Which analgesics are considered SAFE in porphyria?
Paracetamol Aspirin Fentanyl, Alfentanyl, Morphine, Pethidine, Codeine
Which local anaesthetics are considered SAFE in porphyria?
Bupivacaine Prilocaine
Which uterotonics are considered SAFE in porphyria?
Oxytocin
Define BMI
Body mass divided by the square of the height expressed in units of kg/m2
BMI = Mass / Height2
What is the WHO BMI classification?
- < 18.5 Underweight
- 18.5 - 24.9 Normal
- 25 - 29.9 Overweight
- 30 - 34.9 Obese 1
- 35 - 39.9 Obese 2
- > 40 Obese 3 (previously ‘morbid obesity’)
What is morbid obesity?
- BMI > 40 or;
- BMI > 35 with a recognised co-morbidity:
- T2DM
- Sleep disordered breathing
- HTN
- Cardiovascular disease
- Cerebrovascular disease
Define central obesity
- Waist circumference > 88 cm in a woman
- Waist circumference > 102 cm in a man; or
- A waist-to-height ratio > 0.55
What risks is OSA specifically associated with in the perioperative period.
OSA patients have double the incidence of:
- postoperative desaturation
- respiratory failure
- postoperative cardiac events
- ICU admission
What is obesity hypoventillation syndrome?
A triad of:
- Obesity (BMI > 35)
- Sleep disordered breathing (usually OSA)
- Daytime hypercapnoea (PaCO2 > 6 kPa)
What is the typical compliance with nocturnal CPAP for OSA?
Around 50%
Obesity Hypoventillation Syndrome - Pathophysiology
- Leptin intollerence / Resistance
- Reduction in CO2 chemoreceptor sensitivity
- Particularly susceptable to opiod respiratory depression
What are the cardiovascular sequelae of obesity?
- HTN
- Increased cardiac output and cardiac work
- Pulmonary HTN
- CCF
- Arrhythmias
- 2° to sino-atrial node dysfunction and fatty infiltration of the conducting system
- 1.5x RR for atrial fibrillation
- increased risk of sudden cardiac death
- increased incidence of prolonged QT interval
Which anaesthetic drugs should be dosed on Lean Body Weight?
- Induction agents
- Propofol (induction)
- Thiopental
- Fentanyl
- Non-depolarising Muscle Relaxants:
- Rocuronium
- Atracurium
- Vecuronium
- Morphine
- Paracetamol
- Bupivacaine
- Lidocaine
Which anaesthetic drugs should be dosed on Adjusted Body Weight
- Propofol (infusion)
- Antibiotics
- Low molecular weight heparin
- Alfentanil
- Neostigmine (maximum 5 mg)
- Sugammadex
Ideal Body Weight
IBW = height (cm) - x
(where x = 105 in females, x = 100 in males)
Lean Body Weight
The patient’s weight excluding fat. Many of the formulae for calculating lean body weight are complex but one of the most widely used is that of Janmahasatian et al.
Adjusted Body Weight
ABW = IBW + 0.4 x (TBW - IBW)
Adding 40% of the excess weight to the IBW
What is OS-MRS?
Obesity Surgery Mortality Risk Stratification
- BMI > 50 kg.m-2
- Male
- Age > 45 years
- Hypertension
- Risk factors for pulmonary embolism
- Previous VTE
- Venocaval filter
- Sleep disordered breathing
- Pulmonary HTN
What is the mortality for OS-MRS?
- Class A: 0-1 points: 0.2-0.3%
- Class B: 2–3 points: 1.1-1.5%
- Class C: 4–5 points: 2.4-3%
What are the main benefits of a pre-operative discussion in bariatric surgery?
- Promote smoking cessation
- Stress importance of VTE-prophylaxis and early mobilisation
- Plan management of medication before admission
- Remind patients to bring their own CPAP machine
- Commense “Liver Shrinking” diet
- Ensure CPAP adherance
What collar size is associated with a difficult airway?
> 60 cm
How much epidural catheter should be left in the space in bariatric cases
At least 5 cm to prevent catheter migration
Why might suxamethonium be a bad idea in bariatric cases?
Suxamethonium associated fasciculations increase oxygen consumption and have been shown to shorten the safe apnoea time. It is unlikely to wear off before profound hypoxia occurs.
List some general techniques to deliver a “Safe Sleep-Disordered-Breathing Anaesthetic”
- Avoid GA/Sedatives where possible
- Use short acting agents
- Use DoA monitoring to limit anaesthetic load
- Use neuromuscular monitoring to ensure complete reversal of block before waking
- Maximal use of local anaesthetic and multimodal opioid sparing analgesia
- Maintain head–up position throughout recovery
- Monitor of oxygen saturations until mobile
- Reinstate CPAP early
Which surgical fluids are considered safe in porphyria?
Glycine
Describe the basic pathophysiology of Acromegaly
- eosinophilic adenoma
- growth hormone production
