Applied physiology

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Applied physiology IIRespiration, oxygen
therapy Molnár ZsoltAITI
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Anatomy, physiology - the missing link
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Upper airway

• The nose
• Clears
• Heats (32-36)
• humidifies (90)

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The larynx

• Which is the narrowest part?

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The larynx

• Which is the narrowest part?
• Cricoid and acute surgery

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The larynx

• Which is the narrowest part?
• Cricoid and acute surgery
• Epiglottis
• Tracheostomy

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Anatomy - thorax

• Breathing
• Inspiration active
• Expiration passive
• End expiratory pause
• Intrapleural pressure
• Normal value 2-3 cmH2O
• Coughing, sneezing gt 60 cmH2O
• Peak inspiratory flow (PIF)
• PIF at rest 20-30 l/min

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Gas exchange

• Function of breathing
• Oxigenation
• CO2-elimination
• Acute respiratory failure
• Type I hypoxic
• Type II hypercapnic
• Mixed or global

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Alveolar oxygenation
PiO2 150 mmHg
PAO2FiO2 x (PB-PH2O) PaCO2/R
PvO240 mmHg
PAO2
120 mmHg
PA-aO2 ? 20 mmHg
PaO2100 mmHg
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Venous admixture
PvO240 mmHg
120
PaO2 (12040)/2 80 mmHg
PA-aO2 40 mmHg
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Closing capacity (CC)

• Normal lungs
• CC in ERV
• FRCgtCC
• ALI/ARDS
• CC in VT
• FRCltCC

VT
ERV
FRC
CC
RV
CC
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Atelectasis and venous admixture
O2
PvO240 mmHg
120 mmHg
PaO2 (12040)/2 80 mmHg
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Atelectasis and venous admixture
O2
PvO240 mmHg
180 Hgmm
PaO2 (12040)/2 80 mmHg instead PaO2
(18040)/2 120 mmHg
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Degree of venous admixture
0
5
10
400
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20

• Iso-shunt diagram
• Nunn JF. Appl. Resp Physiol., 1993

300
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PaO2 Hgmm
200
30
100
50
0,2
0,6
1,0
FiO2
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Oxygen therapy
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O2 therapy - indications

• Respiratory distress (resp. rategt24/min or
  laboured breathing)
• Asthmatic attack
• Hypotension (RRsyst lt 100 mmHg)
• Signs of abnormal heart function
• Metabolikc acidosis (act HCO3 lt 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

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Variable performance devices
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Features

• Breathing cycle
• Inspiration expiration end expiratory pause
• Peak inspiratory flow (PIF)
• At rest 20-30 l/min
• Forced inspiration gt60 l/min
• Variable performance devices
• Fresh gas flow lt PIF
• Performance depends on patients breathing
  pattern
• Types
• Nasal specs - Face mask Mask with reservoire
  balloon

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O2-rotameter

• 3 O2 ports/bed
• Flow0-16 L/min

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Nasal specs

• FiO2 30
• Flow 2-6 L/min
• Comfortable, cheap
• Dries nasal mucous tissues

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Face mask

• Increases dead space
• Flow 5-10 L/min
• FiO2 50
• Humidification unsolved

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Mask with a reservoire

• Flow 5-15 L/min
• Balloon
• FiO2 80
• Humidification unsolved

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Oxygen therapy
Fix performance devices
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Features

• Independent from patients breathing pattern
• Reason
• High fresh gas flow gt PIF
• Types
• Venturi-masks
• Anaesthetic breathing curcuits Mapleson-systems
• Respirators

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Daniel Bernoulli

• Bernoullis principle
• increase in the speed of the fluid occurs
  simultaneously with a decrease in pressure or a
  decrease in the fluid's potential energy

1700-1782
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Giovanni Battista Venturi

• Venturis 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

• Venturis 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
8 LPM 50 O2
1008 X21 (8X)50
4 0.3X 13 X Fresh gas
flow 13 8 21 LPM
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From Venturi to Vinturi

• 21st century

1746-1822
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Venturis injector humidification
O2
Air

• 20-50 FiO2
• 60-30 L/min
• Bernoulli effect
• Humidification
• Warm water container
• Heating wire

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Side effects of oxygen therapy

• Insignificant comparing to the benefits
• Claustrophoby
• Dry mucous membranes
• Respiratory depression (COPD)
• Hyperoxia

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Monitoring
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Pulsoximetry
Pletismograph and Oximeter
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The pulsoximeter

• Continuous
• Doesnt replace blood gas tests

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The pulsoximeter

• Reliability
• SaO2 70-100 (inaccuracy lt 5)
• SpO2 gt 94 SaO2gt90
• 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 1017

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First move in the care of a critically illGive
oxygen!
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