respiratory atef
TRANSCRIPT
Acute respiratory failure
Topics
Definition of acute respiratory failure Basic respiratory physiology Pathophysiology Respiratory monitoring Treatment
Definitions
acute respiratory failure occurs when:– pulmonary system is no longer able to meet
the metabolic demands of the body hypoxaemic respiratory failure:
– PaO2 60 mmHg when breathing room air
hypercapnic respiratory failure:– PaCO2 50 mmHg
Basic respiratory physiology
O2CO2
Pulmonary Ventilation and pressures
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Oxygen in
• Depends on– PAO2
– Diffusing capacity– Perfusion– Ventilation-perfusion matching
2A2A2A2A NPOHPCOPOPpressureAlveolar
Nitrogen
Water vapour
Carbon dioxide
Oxygen
PAO2= (PB-PH2O)FIO2 – CO2/0.8
PAO2= (760-47)0.21 -40/0.8=100
Alveolar Oxygen tension
How much oxygen is in the blood
PaO2
SaO2
Oxygen content (CaO2)
How much oxygen is in the blood
PaO2• The amount of dissolved oxygen in the plasma phase --
and hence the PaO2 -- is determined by alveolar PO2 and lung architecture only
SaO2• The percentage of hemoglobin molecule bounded with
oxygen.
Oxygen Content CaO2• CaO2 = Hb (gm/dl) x 1.34 ml O2/gm Hb x SaO2 + PaO2 x
(.003 ml O2/mm Hg/dl)
Oxygen dessociation Curve
Oxygen in
• Depends on– PAO2
• FIO2
• PACO2
• Ventilation• Alveolar pressure
– Ventilation-perfusion matching– Perfusion– Diffusing capacity
Carbon dioxide out
Largely dependent on alveolar ventilation
Anatomical dead space constant but physiological dead space depends on ventilation-perfusion matching
)V-(V xRR nventilatio Alveolar DT
Carbon dioxide out
• Patient Vt f Ve Description– A (400) (20) = 8.0 L/min slow and
deep– B (200) (40) = 8.o L/min fast/shallow
• Patient Va-Vd f Va Description – A (400-150)(20) = 5.0 L/min slow and deep– B (200-150)(40) = 2.0 L/min fast/shallow
Increase PaCO2
Increase work of breathing
Muscle fatigue
Shallow breathing followed by increase in RR
Acute Lung Compromise
Carbon dioxide out
Respiratory rate
Tidal volume
Ventilation-perfusion matching
Ventilation-perfusion matching
Dead space
Shunt
Pathophysiology
Pathophysiology
• Low inspired Po2
• Hypoventilation• Ventilation-perfusion mismatch
– Shunting– Dead space ventilation
• Diffusion abnormality
PAO2=105 mmHg PACO2=37 mmHg
75% 100%
Pathophysiology
• Low inspired oxygen concentration• Hypoventilation• Shunting• Dead space ventilation• Diffusion abnormality
FIO2
Ventilation without
perfusion(deadspace ventilation)
Diffusion abnormality
Perfusion without
ventilation
(shunting)
Hypoventilation
Normal
BrainstemSpinal cordNerve root
Airway
Nerve
Neuromuscular junction
Respiratory muscle
Lung
Pleura
Chest wall
Sites at which disease may cause ventilatory disturbance
Causes of respiratory failure
Respiratory Center in BrainBrain
Causes of respiratory failure
Respiratory Center in Brain Neuromuscular Connections
(peripheral nervous system)
Brain
Nerves
Causes of respiratory failure
Respiratory Center in Brain Neuromuscular Connections Thoracic Bellows
(intact rib cage and chest wall musculature)
Brain
Nerves
Bellows
Causes of respiratory failure
Respiratory Center in Brain Neuromuscular Connections Thoracic Bellows Airways (upper & lower)
Brain
Nerves
Bellows
Airways
Causes of respiratory failure
Respiratory Center in Brain Neuromuscular Connections Thoracic Bellows Airways (upper & lower) Alveoli
Brain
Nerves
Bellows
AirwaysAlveoli
All the links are disrupted !
Shunting
• Intra-pulmonary– Pneumonia– Pulmonary oedema– Atelectasis– Collapse– Pulmonary haemorrhage or contusion
• Intra-cardiac– Any cause of right to left shunt
• eg Fallot’s, Eisenmenger, • Pulmonary hypertension with patent foramen ovale
Respiratory monitoring
Clinical
• Respiratory compensation• Sympathetic stimulation• Tissue hypoxia• Haemoglobin desaturation
Clinical
• Respiratory compensation– Tachypnoea– Accessory muscles– Recesssion– Nasal flaring
• Sympathetic stimulation• Tissue hypoxia• Haemoglobin desaturation
Clinical
• Respiratory compensation• Sympathetic stimulation
– HR– BP (early)– sweating
• Tissue hypoxia• Haemoglobin desaturation
Clinical
• Respiratory compensation• Sympathetic stimulation• Tissue hypoxia
– Altered mental state– HR and BP (late)
• Haemoglobin desaturation
Summary
• worry if• RR > 30/min (or < 8/min)• unable to speak 1/2 sentence without pausing• agitated, confused or comatose• cyanosed or SpO2 < 90%
• deteriorating despite therapy
• remember• normal SpO2 does not mean severe
ventilatory problems are not present
Treatment
Treatment
• Treat the cause• Supportive treatment
– Oxygen therapy– CPAP– Mechanical ventilation
Oxygen therapy
• Fixed performance devices
• Variable performance devices
Variable performance device
Time
Flow
30
0
6 l/min O2
6
100% O2
Variable performance device
Time
Flow
30
0
6
6 l/min O2
37% O2
24 l/min air
Fixed performance device
Time
Flow
30
0
100% O2 15 l/min
15 l/min air
60% O2 60% O2 30 l/min
Venturi mask
Other devices
•Reservoir face mask•Bag valve resuscitator
CPAP
• reduces shunt by recruiting partially collapsed alveoli
Mechanical ventilation
• Decision to ventilate– Complex– Multifactorial– No simple rules
Ventilate?
• Severity of respiratory failure• Cardiopulmonary reserve• Adequacy of compensation
– Ventilatory requirement• Expected speed of response
– Underlying disease– Treatment already given
• Risks of mechanical ventilation
Ventilate?
• 43 year old male• Community acquired pneumonia• Day 1 of antibiotics• PaO2 60 mmHg, PaCO2 30 mmHg, pH
7.15 on 15 l/min via reservoir facemask• Respiratory rate 35/min• Agitated
No Yes
Yes
• 43 year old male• Community acquired pneumonia• Day 1 of antibiotics• PaO2 60 mmHg, PaCO2 30 mmHg, pH
7.15 on 15 l/min via reservoir facemask• Respiratory rate 35/min• Agitated
Yes
• 43 year old male• Community acquired pneumonia• Day 1 of antibiotics• PaO2 60 mmHg, PaCO2 30 mmHg, pH
7.15 on 15 l/min via reservoir facemask• Respiratory rate 35/min• Agitated
Yes
• 43 year old male• Community acquired pneumonia• Day 1 of antibiotics• PaO2 60 mmHg, PaCO2 30 mmHg, pH
7.15 on 15 l/min via reservoir facemask• Respiratory rate 35/min• Agitated
Yes
• 43 year old male• Community acquired pneumonia• Day 1 of antibiotics• PaO2 60 mmHg, PaCO2 30 mmHg, pH 7.15
on 15 l/min via reservoir facemask• Respiratory rate 35/min• Agitated
Yes
• 43 year old male• Community acquired pneumonia• Day 1 of antibiotics• PaO2 60 mmHg, PaCO2 30 mmHg, pH
7.15 on 15 l/min via reservoir facemask• Respiratory rate 35/min• Agitated
Ventilate?• 24 year old woman• Presents to ER with acute asthma
– SOB for 2 days• Salbutamol inhaler, no steroids• PFR 60 L/min, HR 105/min• pH 7.25 PaCO2 51 mmHg, PaO2 315 mmHg on
FiO2 0.6• RR 35/min• Alert
No Yes
No
• 24 year old woman• Presents to A&E with acute asthma
– SOB for 2 days• Salbutamol inhaler, no steroids• PFR 60 L/min, HR 105/min• pH 7.25 PaCO2 51 mmHg, PaO2 315 mmHg on
FiO2 0.6• RR 35/min• Alert
No
• 24 year old woman• Presents to A&E with acute asthma
– SOB for 2 days• Salbutamol inhaler, no steroids• PFR 60 L/min, HR 105/min• pH 7.25 PaCO2 51 mmHg, PaO2 315 mmHg on
FiO2 0.6• RR 35/min• Alert
No
• 24 year old woman• Presents to A&E with acute asthma
– SOB for 2 days• Salbutamol inhaler, no steroids• PFR 60 L/min, HR 105/min• pH 7.25 PaCO2 51 mmHg, PaO2 315 mmHg on
FiO2 0.6• RR 35/min• Alert
No
• 24 year old woman• Presents to A&E with acute asthma
– SOB for 2 days• Salbutamol inhaler, no steroids• PFR 60 L/min, HR 105/min• pH 7.25 PaCO2 51 mmHg, PaO2 315 mmHg on
FiO2 0.6• RR 35/min• Alert
No
• 24 year old woman• Presents to A&E with acute asthma
– SOB for 2 days• Salbutamol inhaler, no steroids• PFR 60 L/min, HR 105/min• pH 7.25 PaCO2 51 mmHg, PaO2 315 mmHg on
FiO2 0.6• RR 35/min• Alert
No
• 24 year old woman• Presents to A&E with acute asthma
– SOB for 2 days• Salbutamol inhaler, no steroids• PFR 60 L/min, HR 105/min• pH 7.25 PaCO2 51 mmHg, PaO2 315 mmHg on
FiO2 0.6• RR 35/min• Alert
Thank you