Everything Respiratory for CICM Primary

Definitions

100

The volume of gas remaining in the lungs at the end of normal expiration. Also described as the equilibrium point between elastic recoil of lungs and chest wall.

FRC

200

What and where is the "respiratory pacemaker"?

Pre-Botzinger complex in medulla

300

What is hysteresis?

·  The phenomenon whereby the transmural pressure required to distend an elastic body, such as the lungs, is greater during expansion compared to during contraction, for a given volume

400

List atleast 3 non-respiratory functions of the lung

- blood reservoir (~450mls blood)

- immune functions (IgA, filtration, muco-ciliary elevator, alveolar macrophages, protective reflexes)

-metabolic/endocrine functions

   Production of surfactant

• Reduces alveolar surface tension and increases lung compliance
• Contributes to stability of alveoli (prevents smaller alveoli from emptying into larger alveoli)

• Protein synthesis
• 
  
  • Collagen and elastin form part of the structural framework of the lungs
• Metabolism of vasoactive substances
• 
  
  • Since the entire cardiac output passes through the lungs (unlike any other organ apart from the heart), it is well suited to modulate circulating substances
  • Activation of vasoactive substances
  • 
    
    • Inactive angiotensin I is converted to active angiotensin II by ACE on the surface of capillary endothelial cells
  • Inactivation of vasoactive substances
  • 
    
    • Bradykinin is 80% inactivated by ACE in the lungs
    • Serotonin is almost completely removed by uptake and storage in the lungs (rather than metabolised)
    • Noradrenaline is 30% removed by the lungs
    • PG E2 and F2α and leukotrienes are largely metabolised in the lungs
  • Unaffected by passage through the lungs
  • 
    
    • Angiotensin II
    • Vasopressin
    • Histamine
    • Dopamine
    • PG A2 and prostacyclin

500

What is venous admixture?

•  The amount of mixed venous blood that would have to be added to pulmonary end-capillary blood to produce the observed drop in arterial pO2 from the pO2 in pulmonary end-capillary blood

Up in (Lung) Space

100

Please describe the difference between lung volumes and lung capacities.

Volumes are measured whereas lung capacities are combination of 2+ lung volumes

200

What is physiological dead space?

• Physiological dead space is the part of the tidal volume that does not participate in gas exchange
• Everything that behaves physiologically or functionally like dead space, ie anatomical + alveolar dead space

300

What is a normal FRC

• 30ml/kg supine
• 40ml/kg erect

400

Which west zone corresponds to Part > Palv >Pven?

West Zone 2

500

Please list atleast 4 factors that can affect pulmonary vascular resistance

• Hypoxic pulmonary vasoconstriction
  • Helps to optimize V/Q matching
  • In response to low
    • Alveolar pO2 (major role)
    • Mixed venous pO2 (minor role)
• Lung volume
  • PVR is minimal at FRC
    • Below FRC, less radial traction on extra-alveolar vessels → ↑resistance
    • Above FRC, intra-alveolar capillaries are stretched → ↑resistance
• Pulmonary artery pressure
  • ↑PAP → ↓PVR
  • This is due to
    • Recruitment (mainly in West zones 1–2)
    • Distension (mainly in West zone 3)
• Other factors
  • Hypercapnia and acidosis → ↑resistance
  • Hypothermia → ↑resistance
  • Autonomic innervation
    • Sympathetic →
      • α1 → pulm v/c (from noradrenergic nerves)
      • β2 → pulm v/d (from circulating adrenaline)
    • Parasympatheic →
      • M3 → pulm v/d
  • Endocrine factors
    • Eicosanoids
      • TXA2 → pulm v/c
      • Prostacyclin → pulm v/d
    • Endothelin
      • ETA → pulm v/c
      • ETB → pulm v/d
    • Histamine
      • H2 → pulm v/d
    • Vasopressin
      • V1 → pulm v/d

No Oxygen

100

What PaO2 on an ABG will correspond to type 1 respiratory failure? Bonus 50 points what is a P/F ratio and what's considered normal

<60mmHg

P/F ratio = PaO2 / FiO2, typically utilised in ARDS, normal >300

200

What are the 4 types of hypoxia?

1. Hypoxemia

2. Anemic

3. Circulatory

4. Histotoxic

300

What is the alveolar gas equation

PaO2 = FiO2 x (pB - pH20) - (PaCO2/R)

400

List atleast 3 factors that can LEFT shift the oxygen dissociation curve

- decrease pCO2

- decrease H+ conc

- decrease 2,3 DPG

- decrease temp

- HbF

500

List atleast 4 causes of hypoxemia. Bonus 50 points for which cause classically doesn't respond to supplemental oxygen

1. Low inspired partial pressure of O2
   • Low concentration of O2 (FiO2)
   • Low barometric pressure (PB)
2. Hypoventilation
3. Diffusion limitation
4. Shunt
5. V/Q mismatch

Follow the Law

100

What is the Bohr effect?

• Describes the phenomenon whereby increased CO2 in blood results in a reduced affinity of haemoglobin for O2, causing a right shift in the ODC
• CO2 loading assists with O2 unloading in blood

200

What gas classically undergoes diffusion limited gas transfer and thus is utilised for measurements in PFTs?

Carbon Monoxide (CO)

300

What factors affect the ability of a gas to diffuse?

• V̇gas = A / T . D . (P1 – P2)
  • V̇gas – rate of diffusion of a gas
  • A – surface area available for diffusion
  • T – thickness of the diffusion pathway (alveloar membrane thickness)
  • D – diffusion coefficient
  • (P1 – P2) – partial pressure gradient over the diffusion pathway (alveolar to capillary blood gradient)

400

The amount of gas dissolved in a liquid is proportional to the partial pressure of the gas that is in equilibrium with the liquid, at a constant temperature

Henry's Law

500

Which gas law is the cornerstone that sats probes works from?

Beer-Lambert Law

• The absorbance (A) of light passing through a medium is proportional to the concentration (C) of the medium and the path length (L)

Equipment/Measurement

100

List atleast two potential sources of error with sats probes.

- dysHb (carboxy Hb - high) (MetHb - low)

- dyes (methylene blue - low)

- perfusion related (shock or venous pulsations)

- interference with ambient light

200

How can we measure anatomical dead space?

Fowler's method

300

What is the formula for calculating static compliance in an intubated patient?

• Static compliance can be calculated by tidal volume / (Pplateau – PEEP)

400

What wavelengths of light are oxygenated and deoxygenated Hb absorbed for sats probes?

660nm for deoxy

940nm for oxy

500

What is Reynold's number?

• Whether flow is laminar or turbulent is predicted by Reynolds No:
• Re = 2rvd/η
• 
  
  • r – radius
  • v – average velocity
  • d – density
  • η viscosity
• In a straight smooth tube when
• Re < 2000 → flow is mainly laminar
• Re 2000 – 4000 → mixture of laminar and turbulent flow
• Re > 4000 → flow is mainly turbulent