Ventilation

Question 1

What contributes to the pressure in the ventilator?

Answer 1

Hint - P=F/A

Pressure = force/area

As force is set by the ventilator, area is the only variable. The area can affected by airway pressure (resistance), and lung compliance (elastic pressure)

Question 2

What is Peak Pressure?

Answer 2

Hint- Max prox insp

It is the maximal pressure in the proximal airways at the end of inspiration. It is suggestive of the airway resistance

Question 3

What is plateau pressure? What target do we aim for?

Answer 3

Plateau pressure occurs after inspiration is complete and a breath hold has been initiated. It is a surrogate marker of lung compliance

Target less than 28cm H20

Question 4

How do you define elevated peak pressure?

Answer 4

Difference between peak pressure and plateau pressure is >5cmH2O

Question 5

What are the causes of high peak pressure?

Answer 5

Broncospasm
Retained secretions
Mucous plug
ETT tip occlusion

Question 6

What are the cause of a high plateau pressure >35cmH20?

Answer 6

PTX
Pulm Oedema
ARDS
Pneumonia

Question 7

In APRV, what would you do if the patient becomes hypercapnic?

Answer 7

Increase P High, and T low will increase CO2 clearance

Question 8

In APRV, how can you improve recruitment and oxygenation?

Answer 8

Increase T high, P high and decreasing T low

Question 9

What strategies can help lessen hypercarbia in the sedated patient?

Answer 9

Increase RR
Decrease deadspace
Lighten sedation to encourage spont ventilation

Question 10

What are the indications for mechanical ventilation?

Answer 10

Acute or chronic Resp failure
Impending Resp failure
Apneoa

Question 11

What is the difference between CPAP and BiPAP?

Answer 11

• CPAP raised the baseline pressure that patients breath from, but provides no inspiratory support. This uses Positive end expiratory pressure to maintain alvelolar recruitment and sents open the upper airway
• Bilevel positive airway pressure offers both inspiratory and expiratory pressure support and can be useful in patients who are hypoventilating

Question 12

What is driving pressure? What is the ideal pressure?

Answer 12

Is the amount of pressure necessary to sustain a volume of gas in a given patient’s lungs. It is calculated by Plateau Pressure - PEEP and thought to be a better variable in optimising ventilation in ARDs. The cur off point appears to be about 15cm H20 as increasing mortality is seen above this.

Question 13

How does HFNC give therapeutic benefits?

Answer 13

Hint - room air, flush, PEEP

• The high flow prevents dilution with room air allowing high concentrations of oxygen to be delivered
• the flow allows washing of C02 from the upper airway, reducing anatomical deadspace, leading to decreased minute ventilation
• the high flow when meet with expiratory flow against and closed mouth can provide PEEP for 1cm H20 per 10L of flow