Low Lung Volumes, Atelectasis & Ventilation Flashcards
important concepts
FUN CAN HAPPEN AT COOL, NEW CARNIVALS AND THEMEPARKS
- Functional residual capacity (FRC)
- Closing capacity (CC)
- Hypoxemic pulmonary vasoconstriction
- Atelectasis
- Critical opening pressure
- Newtonian Law of Viscosity
- Collateral ventilation
- Alveolar interdependence
- Time constraints
(1) Functional residual capacity (FRC)
¬ Volume of gas in the lung after a normal expiration
o Participates in gas exchange during inspiration and expiration
¬ Balance between inward recoil of lungs and outward recoil of chest wall
Changes with Position
• Avoid head tilt down, or supine/slumped positions
• Upright standing or sitting has the highest amount of FRC
o With gravity, the diaphragm and abdominal contents are pushed down allowing more room for expansion
Changes with Age
• After 40, in supine the patients closing capacity will encroach on the FRC causing collapse or closure of airways
• Beyond 60, in upright the closing capacity will encroach on the FRC
• Risks of airway closure and decreased ventilation
(2) Closing capacity (CC)
¬ Volume of air in lung when small airways in dependent lung start to collapse during expiration (trapping air inside)
¬ Healthy, young individual (approximately):
o CC = RV (residual volume)
o CC < FRC
¬ If CC ≥ FRC during normal expiration there may be a collapse of airways in dependent lung areas, resulting in reduced ventilation to those areas
3) Hypoxemic Pulmonary Vasoconstriction
• Protective response
• V/Q mismatch > dec. PaO2
• Constriction of pulmonary vessels = hypoxaemic pulmonary vasoconstriction
o This will divert blood to areas with greater ventilation
♣ inc. perfusion to areas of ventilation
♣ This will inc. PaO2
Atelectasis RF
Risk Factors: • Surgical incision (abdominal/thoracic/cardiac) • Previous respiratory condition • Smoking history • Obesity • Age • Impaired cognitive function • Monotonous pattern of mechanical ventilation • Body position
Allie’s S’s that Risk of Post-Surgical Atelectasis:
• Surgery • Splinting (/sore) • Shallow breathing • Supine, slumped • Secretions • Surfactant • Synthetic (mechanical) ventilation • Sighs \+ Smoking history \+ Size (obesity
Types of atelectasis
Micro (occurs commonly during surgery):
• Patchy areas of atelectasis not resulting in shift of structures
Plate:
• Small areas of collapse
Compression: • Tumour external to Bronchi • Pneumothorax • Pleural effusion • Cardiomegaly
Absorption:
• If bronchus or bronchiole is blocked
• Or, if high FiO2 (oxygen therapy)
Surfactant impairment (affected by): • Anaesthesia • Supplemental O2 (dry) • Mechanical ventilation • Infection Pre-term neonate
Atelectasis effects
¬ Ventilation-perfusion mismatch o Hypoxaemia ( PaO2) o In some cases hypercapnia ¬ FRC ¬ Compliance ¬ Very difficult to re-inflate ¬ WOB ¬ O2 Consumption
Signs and symptoms of atelectasis
Palpation
• Chest wall movement (unilaterally or bilaterally)
• Temperature
Auscultation
• or absent breath sounds
• and/or fine end-inspiratory crackles
Special tests
o SpO2, PaO2
o CXR
NB. These signs may not all be present.
To Reverse Atelectasis
Three important concepts to reverse Atelectasis:
- Critical Opening Pressure > Pressure needed to overcome surface tension and achieve initial reinflation of collapsed regions
- Slow Laminar Flow (Newtonian Law of Viscosity) > Sticky surfaces peel apart more easily when the action is done SLOWLY
- Inspiratory Hold
a. Collateral ventilation> Interaction between collateral regions of the lungs to achieve ventilation
b. Alveolar interdependence > The walls of surrounding alveoli recoil, pulling the collapsed alveolus open
c. Surfactant release
d. Time constants > Compliance x Resistance of an alveolar unit ( inc. Resistance = longer time to fill)
Inspiratory hold/plateau can allow for different time constants
Medical Management of atelectasis
- Pain relief
- Bronchoscopy
- Drainage of pneumothorax/pleural effusion
- Removal of tumour/obstruction
- Recruitment manoeuvres (if ventilated)
- Surfactant therapy
