Post on 17-Jan-2016
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Applied physiology – II:Respiration, oxygen therapy
Molnár Zsolt
AITI
Anatomy, physiology - the missing link…
Upper airway
• The nose:• Clears
• Heats (32-36)
• humidifies (90%)
The larynx
• Which is the narrowest part?
The larynx
• Which is the narrowest part?• Cricoid and acute surgery
The larynx
• Which is the narrowest part?• Cricoid and acute surgery• Epiglottis• Tracheostomy
Anatomy - thorax
• Breathing• Inspiration: active
• Expiration: passive
• End expiratory pause
• Intrapleural pressure:• Normal value: ±2-3 cmH2O
• Coughing, sneezing: > 60 cmH2O
• Peak inspiratory flow (PIF)• PIF at rest ~ 20-30 l/min
Gas exchange
• Function of breathing• Oxigenation
• CO2-elimination
• Acute respiratory failure• Type I: hypoxic
• Type II: hypercapnic
• Mixed or global
Alveolar oxygenation
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PvO2=40 mmHg
PAO2
PaO2~100 mmHg
120mmHg
PAO2=FiO2 x [(PB-PH2O) – PaCO2/R]
PA-aO2 20 mmHg
PiO2~ 150 mmHg
Venous admixture
Molnár ‘99
PvO2=40 mmHg
120
PaO2 = (120+40)/2 = 80 mmHg PA-aO2 = 40 mmHg
• Normal lungs:– CC in ERV– FRC>CC
• ALI/ARDS:– CC in VT
– FRC<CC
VT
FRCERV
RVCC CC
Closing capacity (CC)
Atelectasis and venous admixture
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PvO2=40 mmHg
PaO2 = (120+40)/2 = 80 mmHg
120mmHg
O2
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PvO2=40 mmHg
180Hgmm
O2
PaO2 = (120+40)/2 = 80 mmHginstead
PaO2 = (180+40)/2 = 120 mmHg
Atelectasis and venous admixture
• „Iso-shunt” diagramNunn JF. Appl. Resp Physiol., 1993
Degree of venous admixture
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100
200
300
400
PaO
2 Hgm
m
0 5% 10%
15%
20%
25%
30%
50%
FiO2
0,2 0,6 1,0
Oxygen therapy
O2 therapy - indications
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– Respiratory distress (resp. rate>24/min or laboured breathing)
– Asthmatic attack
– Hypotension (RRsyst < 100 mmHg)
– Signs of abnormal heart function
– Metabolikc acidosis (act HCO3 < 18 mmol/l)
– Suspected AMI
– Severe trauma and/or severe blood loss
– Sepsis
– Altered level of consciousness
– Drug overdose with confusion
– Smoke, CO, toxic gas inhalation
– Complications during labour
– Transport of the critically ill
– Every postoperative condition
Variable performance devices
Features
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• Breathing cycle• Inspiration – expiration – end expiratory pause
• Peak inspiratory flow (PIF): • At rest ~ 20-30 l/min
• Forced inspiration >60 l/min
• Variable performance devices• Fresh gas flow < PIF
• Performance depends on patient’s breathing pattern
• Types• Nasal specs - Face mask – Mask with reservoire balloon
O2-rotameter
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• 3 O2 ports/bed
• Flow:0-16 L/min
Nasal specs
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• FiO2 ~ 30%
• Flow: 2-6 L/min
• Comfortable, cheap
• Dries nasal mucous tissues
Face mask
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• Increases dead space
• Flow: 5-10 L/min
• FiO2 ~ 50%
• Humidification unsolved
Mask with a reservoire
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• Flow: 5-15 L/min
• Balloon
• FiO2 ~ 80%
• Humidification unsolved
Fix performance devices
Oxygen therapy
Features
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• Independent from patient’s breathing pattern• Reason:
• High fresh gas flow > PIF
• Types• Venturi-masks
• Anaesthetic breathing curcuits: Mapleson-systems
• Respirators
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• Bernoulli’s principle– „…increase in the speed of the fluid occurs
simultaneously with a decrease in pressure or a decrease in the fluid's potential energy”
Daniel Bernoulli
1700-1782
1738
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Giovanni Battista Venturi
• Venturi’s principle and injector– „…fluid velocity must increase through the
constriction to satisfy the equation of continuity, the gain in kinetic energy is balanced by a drop in pressure or a pressure gradient force”
1746-1822
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Giovanni Battista Venturi
100*8 + X*21 = (8+X)*50 4 = 0.3X
13 = XFresh gas flow = 13 + 8 = 21 LPM
8 LPM 50% O2
• Venturi’s principle and injector– „…fluid velocity must increase through the
constriction to satisfy the equation of continuity, the gain in kinetic energy is balanced by a drop in pressure or a pressure gradient force”
1746-1822
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From Venturi to Vinturi
• 21st century:
1746-1822
Venturi’s injector + humidification
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• 20-50% FiO2
• 60-30 L/min
• Bernoulli effect
• Humidification• Warm water container
• Heating wire
O2
Air
Side effects of oxygen therapy
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• Insignificant comparing to the benefits • Claustrophoby• Dry mucous membranes• Respiratory depression (COPD)• Hyperoxia
Monitoring
Pulsoximetry
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Pletismographand
Oximeter
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• Continuous
• Doesn’t replace blood gas tests
The pulsoximeter
• Reliability• SaO2 ~ 70-100% (inaccuracy < 5%)
• SpO2 > 94% ~ SaO2>90%Van de Louw A et al. Intensive Care Med 2001; 27: 1606
• Reaction time• 5-8s
• Desaturation reaction time: – Ear probes: 7.2-19.8
– Finger probes: 19.5-35.1
– On toes: 41-72.6 Bishop ML. Anesthessiol Review 1994; 256: 1017Molnár ‘99
The pulsoximeter
Motto
First move in the care of a critically ill:
Give oxygen!