BREATHING
KIRSTIE MCPHERSON
ANAESTHETICS SPR UCLH
the centre for
Anaesthesia
UCL
AIMS
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How is breathing affected by anaesthesia?
Who is most at risk?
What can you do about it?
Common problems
How is breathing affected by anaesthesia?
General Anaesthesia
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Loss of pharyngeal tone
Obstruction
Soft Palate
Base of Tongue
Epiglottis
Airway management
Neuraxial blockade and regional anaesthesia
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Less commonly affects breathing
Opiates
Local anaesthetic
“High blocks”
Intercostal muscles
Diaphragm
Hypoventilation
Who is most at risk?
What can you do about it?
Preoperatively
Preoperatively
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Assessment
History
Risk-stratification (scoring systems)
Medical optimisation
Investigations
Multi-disciplinary meetings
Surgical options
Planning post-operative destination
Intraoperatively
• Pre-operative monitoring & IV access
• Pre-oxygenation
• Induction of anaesthesia
Apnoea
Airway obstruction
Take over ventilation & secure airway
How Anaesthesia affects Ventilation
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Loss of airway patency
Ability to manage secretions is lost
Airway obstruction
hypoxaemia
hypercapnia
The O2 in the FRC is the lung’s store of O2
Important to Preoxygenate
Apnoea and time to desaturation
Intraoperatively: General anaesthesia
Spontaneous Ventilation
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Ventilatory response to
CO2
• Respiratory rate indicator
of pain
BUT
• Prone to hypoventilation
• Some types of surgery
require muscle paralysis
Controlled Ventilation
• Prevent atelectasis
• Can control end-tidal CO2
BUT
• Can cause barotrauma &
volutrauma
• Higher risk of awareness
Assessment of breathing under anaesthesia
Saturations
• Oxygenation not ventilation
• Waveform
Capnography: End-Tidal CO2
• Adequacy of ventilation
• Confirms circuit is intact
• Immediate information
• Flat line: failure of ventilation
• Slow rising initial phase:
• Upper airway obstruction
Inspired O2
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Tidal Volume (6-8ml/kg)
Frequency
Pressure limits
PEEP
Lung protective strategies
Normocarbia
Postoperatively
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Reverse muscle relaxation
Suction
High flow Oxygen
Extubation
Supplemental Oxygen
Monitoring in recovery
Postoperative Problems
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Prevention better than Cure
Inadequate reversal
Atelectasis
Pneumonia
Asthma
Pain and hypoventilation
Analgesia
Poor mobility
Case Scenario
• Mrs Miggins is a 44 year old lady who had an
emergency laparotomy and repair of perforated
duodenal ulcer 5 days ago
• There were no intra-operative complications
• Blood loss 450ml
• PMH: Asthma, chronic back pain
• She is a non-smoker
• Medications: Salbutamol and beclometasone
inhalers, cocodamol (as required)
• NKDA: (Tolerates NSAIDS)
Deterioration
5 days post op, she is drowsy and less responsive
BP 102/68mmHg
HR 110 bpm
RR 8 breaths/min
SpO2 92% RA (FiO2 0.21)
Temp 36.7C
BM 3.9 mmol/L
U.O 20 ml/h
GCS 14/15 (eyes open to command)
Can you comment on the drug chart?
Summary
• Important to understand the changes in
physiology under anaesthesia
• Identify those most at risk for complications
• Protective strategies with mechanical ventilation
• Think OXYGENATION and VENTILATION