Positioning + Lung Function

Question 1

What does V/Q ratio stand for?

Answer 1

Ventilation and perfusion

Question 2

What factors influence ventilation?

Answer 2

Pleural pressure - more -ve = less potential

Altered lung expandability (compliance)

Altered airway resistance

Lung volume

Dead space

Shunt (wasted perfusion)

Question 3

What factors influence perfusion? (2)

Answer 3

Wasted ventilation (e.g. pulmonary embolism)

Circulatory disorders

Question 4

What are the five uses of body positioning?

Answer 4

Maximise ventilation
Maximise diaphragmatic function
Optimise V/Q matching
Decrease work of breathing
Drain sputum

Question 5

What is the effect of giving more oxygen to a patient on a ventilator?

Answer 5

Nitrogen levels which maintain alveoli to stay open are decreased meaning alveoli are more likely to collapse (absorption atelactasis)

Question 6

Describe the mechanics of being on a ventilator (4)

Answer 6

The air is forced into the lungs

Pushing the diaphragm down passively

The airflow takes the path of least resistance (I.e. to the top of the lung)

Increased perfusion at lower (dependent) regions and decreased ventilation so V/Q mismatch

Question 7

What are the three types of dead space?

Answer 7

Anatomical, alveolar and physiological

Question 8

What is anatomical dead space?

Answer 8

Volume of gas left in mouth, trachea and bronchioles, as we breathe; not used in gas exchange

Question 9

What is alveolar dead space?

Answer 9

Volume of gas in alveoli that should be involved in gas exchange but is not due to lack of blood supply

Question 10

What is physiological dead space?

Answer 10

Anatomical and alveolar added together

Question 11

Define Ventilation

Answer 11

Ventilation is the movement of air in and out of the lungs

Question 12

Define Perfusion

Answer 12

Blood flow in the capillary beds

Question 13

What is the principle for gas exchange to occur

Answer 13

V/Q matching - ventilation and perfusion need be in the same place at the same time for gas exchange to occur

V/Q ratio quantifies this match - normal blood gases = 0.8

Question 14

Explain the V/Q ratio

Answer 14

V & Q increase independently from top to bottom of the lung
This change occurs in the vertical plane regardless of body position
Q is increased to a greater extent because gravity exerts a greater effect on blood (liquid) than inspired air (gas)

Question 15

Explain the ventilation gradient

Answer 15

V follows a V gradient down the lung where V occurs more at the dependent (lower) regions in both upright and side lying because V is primarily gravity dependent in the spontaneously breathing adult (self-ventilation)

Alveoli in the NON-DEPENDENT (upper) regions are already inflated because gravity has greater effect on them meaning they stretched open so already at maximum expansion/nearing
Alveoli in the DEPENDENT (lower) regions of the lung are stretched to a lesser extent because intrapleural pressure is less -ve at the bottom than the top of the lung due to gravity so have a greater potential to expand

In side-lying the lower lung has a greater potential to expand because the lower hemi-diaphragm is pre-stretched by abdominal pressure & therefore has a mechanical advantage over the upper hemi-diaphragm causing twice the excursion

Question 16

Explain the perfusion gradient

Answer 16

Q follows a Q gradient down the lung tissue - some in upper lung but majority of blood flow is lower lung.
Q occurs most in lower region (base of alveoli) both in upright and side-lying position because Q is gravity dependent in the spontaneously breathing adult
Q gradient changes with exercise and posture

Question 17

How can positioning optimise V/Q matching

Answer 17

Position with knowledge of the V and Q gradients to decrease amount of V and Q in compromised lung areas

Question 18

How can positioning decrease WOB

Answer 18

Position to optimise diaphragm, decrease active fixation of shoulder girdle which uses muscular contraction = results in relaxed muscles of respiration thus lower energy demand

Question 19

How can positioning drain sputum

Answer 19

Position with knowledge of respiratory tree to move sputum more centrally so it can be coughed out.

Question 20

Explain Postural Drainage

Answer 20

The drainage of secretions, by the effect of gravity, from one or more lung segments to the central airways

Each position places the target lung segment(s) superior to the carina

Held for 3 –15 minutes dependent on patients symptoms

PD consists of very specific positions for specific segments; Often these positions have to be modified secondary to the patient’s condition or tolerance e.g. side lying with no head down tilt could be described as ‘modified PD’ or positioning

Question 21

Clinical application of PD

Answer 21

Clinical application of true PD limited by:

• More active clearance techniques being promoted
• Precautions/unhelpful side effects e.g. WOB
• Patients unable to tolerate due to co-pathologies, surgery etc.

Clinical adjuncts to PD include:

• Other clearance techniques incl. Manual techniques, ACBT (adjuncts often used in modified PD)
• Pre-PD bronchodilation - salbutamol (fast-acting bronchodilators)/humidification - saline nebulisers