2. DEFINITION
Decreased arterial oxygen content in blood as
measured by pulse oximetry or arterial blood
gas analysis,
Usually transient as a result of atelectasis
and/or alveolar hypoventilation
3. Presentation
SpO 2 <90%
PaO 2 <60 mmHg
Patient is frequently lethargic and may be uncooperative
or agitated.
Tachycardia and hypertension may be associated with
hypoxia.
Tissue cyanosis may be seen in severe cases
9. Riskfactors
• Reduced FRC (obesity, intestinal obstruction,
pregnancy) reduces oxygen reserves.
• Failure to preoxygenate exacerbates any airway
difficulties at induction.
• Laryngospasm can result in negative pressure
pulmonary oedema.
• Head and neck surgery (shared access to the airway)
increases the risk of undetected disconnection.
10. Continue…
• History of congenital heart disease or detection
of a heart murmur (left to right communication).
• Chronic lung disease.
• Sickle cell disease.
• Methaemoglobinaemia (interpreted as
deoxyhaemoglobin by pulse oximeters).
11. Diagnosis;pre-requisite
• FiO 2 : use an oxygen analyser at all times.
• Ventilation: cross-check rise and fall of chest with
auscultation over stomach and in both axillae,
• Capnograph trace, measured expired tidal volume,
and airway pressure.
• Measurement error: does patient appear cyanosed?
Beware in anaemia when 5g/dl deoxyhaemoglobin
may not be visible.
• Aspiration/airway secretions: auscultate and
aspirate using tracheal suction catheter ― litmus
paper.
12. Differential diagnosis
• Suspect tension pneumothorax (particularly following
central line insertion) if IPPV and trachea shifted away
from a hyperresonant lung field with diminished breath
sounds. Neck veins may be engorged; Treat
immediately by decompressing the pleural cavity with
an open cannula placed in the 2nd intercostal space in
the mid- clavicular line.
• Suspect hypovolaemia if patient has HR >100bpm, RR
>20bpm,capillary return >2s, cool peripheries,
collapsed veins, a narrow and peaked arterial line
trace, or marked respiratory swing to either CVP or
arterial line trace.
13. Differential diagnosis
• Suspect air or gas embolus if patient had a pre-existing low CVP
and open venousbed. Signs are variable but may include sudden
decrease ETCO 2 ,
• Decrease SpO 2 , loss of palpable pulse, PEA, and subsequent
rise in CVP.
• Suspect fat embolus or cement reaction in the presence of
multiple bony injuries or long bone intramedullary surgery.
• Malignanthyperthermia: especially if accompaniedby increase
ETCO 2 , increase RR, Increase HR.
• Anaphylaxis—cardiovascularcollapse 88%, erythema 45%,
bronchospasm36%, angio-oedema 24%, rash 13%, urticaria 8.5%.
14. Differential diagnosis
• Suspect cardiac failure if patient has HR >100bpm, RR
>20bpm, engorged central veins, capillary return >2s,
cool peripheries,
• pulmonary oedema, or worsening SpO 2 with fluid
challenge.
16. Immediatemanagement
• 100% oxygen; check FiO 2 ; expose patient and check
for central cyanosis; check ventilation bilaterally;
hand ventilate on a simple system giving 3–4 large
breaths
• initially to recruit alveoli; secure airway;
endotracheal suction; initially remove any PEEP;
• Give adrenaline if accompanied by poorly palpable
pulses
17. Immediatemanagement
• ABC —expose the chest, all the breathing circuit, and
all airway connections.
Administer 100% O 2 by manual ventilation—at least 3–
4 large breaths initially will help to recruit collapsed
alveoli
(and gives continuous tactile feedback about the state
of the airway).If no improvement
18. Immediatemanagement
• Confirm FiO 2: if there is any doubt about inspired
oxygen concentration from the anaesthetic machine,
use a separate cylinder supply
• As a last resort use room air via a self-inflating bag =
21% O 2 ).
• Misplaced ETT —cross-check rise and fall of chest
with auscultation over stomach and in both axillae
and the capnograph trace
19. Immediatemanagement
• Ventilation problem : simplify the breathing system
until the problem is removed, i.e. switch to bag rather
than the ventilator,
• Use a Bain circuit instead of the circle system,
• Try a self-infl ating bag, + mask rather than ETT, etc.
20. Immediatemanagement
• Diagnosis of the source of a leak or obstruction: is not
as important initially as oxygenation of the patient.
• Make the patient safe first then use a systematic
approach. The fastest way to isolate the problem is
probably by division. For instance,
• Does breaking the circuit at the ETT connector leave
the problem on the patient side or the anaesthetic
machine side?
21. ManagementATPOSTOP
• Provide supplemental O 2 via nasal cannula or face
mask to maintain adequate oxygenation.
• Insert an artificial airway if airway obstruction is
present.
• Intubation and mechanical ventilation may be required
if the patient does not respond to supplemental O 2 .
• Arterial blood gas analysis is useful to determine PaO
2 and PaCO 2
• Cardiovascular support may be necessary in extreme
cases of arterial hypoxia.
