Hypoxemia

Mechanisms

Mechanisms

* Low FiO2
Relative (inadequate for patient’s condition)
Absolute (problems delivering O2 to circuit)
* Inadequate VA
* V/Q mismatch
* Anatomic shunt
* Excess metabolic O2 demand
* Low cardiac output

Clinical Causes

Clinical Causes

* Inadequate ventilation
AIRWAY obstruction
HYPOVENTILATION during GA
* Endobronchial intubation
* Patients with increased A-a gradient
Pre-existing lung disease
>Pneumothorax
Pulmonary edema
Aspiration
Atelectasis
Pulmonary embolism
* Low cardiac output

Prevention

Prevention

* Check anaesthetic machine
O2 analyser & alarms
* Adequate Ventilation (esp tidal volume)
* Monitor & adjust FiO2
* High normal range tidal volume
* Caution with spontaneous ventilation in lung disease

Manifestations

Manifestations

* Pulse Oximetry
Malfunction can occur: check waveform & probe position
o Hypothermia
o Poor peripheral circulation
o Artifacts: diathermy, motion, ambient lighting
o Dyes
o Cyanosis
o Dark blood in surgical field
o Late signs
bradycardia , myocardial ischaemia & dysrhythmias, hypotension and cardiac arrest

Management

Management

* Assume low SpO2 = hypoxaemia
* Increase FiO2
Verify FiO2 increases
* Check pulse, BP
* Check EtCO2 & pulse oximeter (refer next slide)
* Hand ventilate - assess lung compliance, give large TV
* Check chest movements & auscultate chest
Exclude endobronchial intubation
* ABG’s
* Posture ­ sitting up

Verify Pulse Oximeter

Verify Pulse Oximeter

* do not fixate
Assess signal amplitude
Check waveform
Check position
Correlate reading with diathermy
Shield probe
Change site

Persistent hypoxemia causes

Persistent hypoxemia causes

* Pulmonary
Pneumothorax - consider CXR
Aspiration
Massive atelectasis
Pulmonary embolism
Aspiration of foreign body
Acute pulmonary oedema
* Extra-Pulmonary
Low cardiac output
Low Hb
Intracardiac shunting in CHD

Persistent hypoxemia management

Persistent hypoxemia management

* Use aggressive pulmonary toilet
Suction ETT
Consider bronchoscopy
* Consider addition of PEEP
Maintain large tidal volume 12-15ml/kg
* Restore circulating blood volume
Maintain CO and Hb levels (Hb>100g/L)
Consider inotropes

Unresolved hypoxemia

Unresolved hypoxemia

* Inform surgeons (earlier if appropriate)
Check retractors
Transfer to supine position
Terminate surgery ASAP
* Investigations in PACU
Incl. CXR, ABG’s
* Arrange transfer to ICU

Awake patient

Awake patient

* Detection ­ see previous slide
* Look for cause
Inadequate Ventilation ­ airway, depressed VA
Pulmonary and extra-pulmonary
Also diffusion hypoxaemia, laryngospasm, inadequate reversal, shivering
* Management
High flow O2 - CPAP - re-intubation
Drug reversal ­ relaxants, opioids