Obesity hypoventilation syndrome

 

Pathophysiology

·      Obesity

·      Impaired mechanics

·      Chronic hypoventilation

·      Chronic hypercapnoea ± hypoxia

·      Note OSA is present in 90%

Complications

·      Pulmonary hypertension in 66%

·      Cor pulmonale

Peri-op issues

·      A: expect difficulty

·      B: aim for patient’s normal PaCO2; assume OSA

·      C: assume PHTN

Significance

·      High risk of severe pulmonary hypertension

·      High risk of severe peri-op complications

·      Not much evidence for peri-op management

·      Should get NIV pre-op and post-op

·      Should go to HDU

 

Assessment:

Hx/Ex

·      BMI >30 (esp. >50)

·      Basically STOPBANG minus the apnoeas

ABG

·      ↑PaCO2 >45

·      ↑HCO3 (can be venous)

·      ↓PaO2

·      Normal A-a gradient

Sleep studies

·      Continuous CO2 monitoring required

·      OHS worse during sleep

Echo

·      Likely difficult TTE

·      Pulmonary hypertension

·      RV dysfunction

 

Optimisation:

IPPV

·      Normalises PaCO2 and PaO2 in >50% patients

·      Peak improvement at 1 month

·      CPAP vs BiPAP?

Oxygen

·      <50% require O2 initially

·      <10% require O2 once stabilised

·      O2 dangerous if given without IPPV

 

 

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