Respiratory failure and oxygen

Question 1

How is ARDS defined?

Answer 1

-Acute condition characterised by bilateral pulmonary infiltrates and severe hypoxaemia in the absence of evidence of cariogenic pulmonary oedema
-2 stages:
–Early stage = exudative injury with oedema
–Late stage = repair –> fibroproliferative changes –> scarring causing poor lung function

Question 2

What causes ARDS?

Answer 2

-Sepsis
-Trauma
-Direct lung injury (infection)
-Acute pancreatitis
-Long bone fracture / multiple fractures
-Head injury (sympathetic nervous stimulation which leads to acute pulmonary hypertension)

Question 3

How does ARDS present?

Answer 3

-Acute dyspnoea and hyperaemia
-Multi organ failure
-Rising ventilation pressures
(NB normal tidal volume = 6-10ml/kg)

Question 4

How would you manage ARDS?

Answer 4

-Treat underlying cause (eg abx if signs of sepsis)
-Negative fluid balance with diuretics
-Prone ventilation
-Mechanical ventilation using low tidal volumes

Question 5

What is the average tidal volume?

Answer 5

TV = volume inspired / expired with each breath at rest
-6-10ml/kg

Question 6

What is the inspiratory reserve volume?

Answer 6

-Max volume of air that can be inspired at the end of a normal tidal inspiration
-Average = 2-3L

Question 7

What is the expiratory reserve volume?

Answer 7

-Max volume of air that can be expired at the end of a normal tidal expiration
-Average = 750ml

Question 8

What is the residual volume?

Answer 8

-Volume of air remaining after maximal expiration
-1.2L, increases with age

Question 9

What is the functional residual capacity?

Answer 9

-Volume in the lungs at the end-expiratory position
-FRC = ERV + RV

Question 10

What is the viral capacity?

Answer 10

-Max volume of air expired after a maximal inspiration 4.5-5.5L
-Decreases with age

Question 11

What are O2 saturation targets with O2 therapy?

Answer 11

-Acutely ill patients = 94-98%
-Patients at risk of hypercapnia = 88-92%
-15L NRBM is first line therapy for critically ill patients

Question 12

What is the difference between T1 and T2 respiratory failure?

Answer 12

RF = disease of the lung / heart leads to failure to maintain adequate blood oxygen levels or increased CO2 levels
-TYPE 1 = arterial oxygen tension of <8kPa with normal or low arterial CO2
-TYPE 2 = presence of PaCO2 >6kPa and PaO2<8kPa

Question 13

What are the causes of T1 and T2 RF?

Answer 13

Type 1:
-COPD
-Pneumonia
-Pulmonary oedema
-Pulmonary fibrosis
-Asthma
-Pneumothorax
-PE
-Pulmonary hypertension
-Cyanotic CHD
-Bronchiectasis
-ARDS
Type 2:
-COPD
-Hypoventilation (drug overdose, weakness)

Question 14

What are the differences between CPAP and BiPAP?

Answer 14

CPAP = Continuous Positive Airway Pressure
-O2 delivered with positive pressure via face mask/hood
-Think - like breathing with your head stuck out a moving care
BiPAP = Biphasic Positive Airway Pressure
-CPAP + additional pressure to support inspiration
-Increases minute volume by increasing tidal volume

Question 15

What is the physiology of CPAP?

Answer 15

-Improves FRC + V/Q match
-Decreases atelectasis + leakage of fluid into lungs
-Splints airways open
-Decreases work of breathing

Question 16

What are the different indications for CPAP and BiPAP?

Answer 16

CPAP
-T1 RF
-Pulmonary oedema
-Fluid overload
-Atelectasis
-Chest infection
BiPAP
-Hypercapnoeic COPD exacerbations that are not improved by O2 therapy
-MSK conditions with RF
-Obesity, hypoventilation syndrome

Question 17

When is invasive ventilation indicated?

Answer 17

-RF that is not improved with other treatment
-RF w low conscious level
-Tiring on other treatment
-Airway compromise
-Sepsis, trauma, head injury