Obstructive sleep apnoea

 

Disease:

Pathophysiology

·      Hypotonia

·      Obstruction

·      Apnoea

·      Hypoxaemia

·      SNS +++

·      Partial arousal

·      Restored patency

·      Note OHS is present in 15%

Complications

Vessels:

·      Systemic hypertension

·      Pulmonary hypertension

Heart:

·      Arrhythmias (AF)

·      Cor pulmonale

·      Coronary artery disease

Blood:

·      Polycythaemia

·      Stroke

Significance

·      Risk of many peri-op complications

·      Risk highest if undiagnosed/untreated

 

Assessment:

STOPBANG

Parameters:

·      Snoring

·      Tired

·      Observed apnoea

·      Pressure (hypertension)

·      BMI >35

·      Age >50

·      Neck >43cm male, 41cm female

·      Gender (male)

Red flags:

·      Apnoeic period

·      Heroic gasps

·      Daytime somnolence

Risk group:

·      Low: 0-2 (good NPV)

·      Intermediate: 3-4

·      High: 5-8 (good PPV)

·      HCO3 improves specificity

Polysomnography

Apnoea-hypopnoea index:

·      Apnoea: cessation for >10 sec, + SpO2 ↓4%

·      Hypopnoea: airflow ↓50% for >10 sec, SpO2 ↓4%

Severity in adults:

·      Mild: 5-15

·      Mod: 15-30

·      Sev: >30

Severity in children:

·      Mild: 2-5

·      Mod: 5-10

·      Sev: >10

Other parameters:

·      Respiratory effort-related arousals

·      Respiratory disturbance index

·      Oxygen desaturation index (>6 sec, SpO2 ↓4%)

·      Nadir SpO2

·      T90 SpO2 (% time spent <90%)

Other

Overnight oximetry:

·      Not as good as PSG, but faster turnaround

·      Oxygen desaturation index (ODI3%): number of desat per hour

·      Same numbers as AHI (5-15, 15-30, >30)

Blood tests:

·      ↑Hb

·      ↑Hct

·      ↑HCO3

TTE:

·      RVSP

·      TAPSE

 

Intra-op issues:

Airway

Difficulties:

N.B. controversial – but safest to assume

·      Bag-mask ventilation

·      Intubation (±extubation)

·      FONA

Reasons:

·      If slim: anterior larynx

·      If obese: crowded cavities, hostile positioning, rapid desaturation

Breathing

·      Not really

Circulation

If pulmonary hypertension:

·      Risk of RV ischaemia

·      Risk of RV failure

 

Post-op disaster:

Problem

·      Airway obstruction + narcosis = death

o   1st night peak: due to drugs

o   3rd night peak: due to proper sleep

Risk factors

Patient:

·      BMI: >40

·      OSA: severe, untreated*

·      Cardioresp comorbidities: PHTN, severe, untreated

·      Abnormal upper airway

Anaesthetic:

·      Intra-op: general > sedation > other

·      Post-op: opioid*, benzo

Surgery:

·      Operation: affects airway, affects breathing

·      Post-op orders: supine, no CPAP*

Analgesic options

Prefer:

·      Regional

·      Paracetamol

·      COX2i

·      Clonidine

·      Atypical opioid

·      Ketamine

·      Lignocaine

Avoid:

·      Pure opioid

·      Long-acting opioid

·      Benzo

Observation levels

·      If effective CPAP, probably everyone is low risk

·      Low risk: regular ward bed

·      Medium risk: regular ward bed + continuous oximetry

·      High risk: HDU

 

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