ARDS and Ventilation

Question 1

What is the new global definition of ARDS 2023? How does it differ from the Berlin 2013 defiintion

Answer 1

NB is “objective assessment” incorporated to exclude cardiogenic odema and iatrogenic intravascular overload

Question 2

What is the ARDS New Global Definition 2023

Answer 2

Additions are
1. Lung ultrasound by trained personal to diagnosed infiltrates (as an alternative to the use of CXR/CTChest)

2. PF ratio < 300 in the presence of PEEP > 5 OR HFNO2 > 30l/min
3. The addition of an SF ratio < 315 instead of a PF ratio is valid.

NB is “objective assessment” incorporated to exclude cardiogenic odema and iatrogenic intravascular overload.

Question 3

Name the trial that defined the Berlin 2013 ARDS definition

Answer 3

Acute respiratory distress syndrome: the Berlin Definition

Ranieri et al 2013

Question 4

Name the Research that defined the ARDS New Global Definition 2023

Answer 4

ARDS A New Global Definition

Matthay et al 2023

Question 5

Categorize the severity of ARDS and include the relative mortality

Answer 5

Mild PF 200 to 300 (27%)
Moderate PF 100 to 200 (32%)
Severe PF < 100 (45%)

Mortality in parenthesis was determined with all patients on a PEEP of 5+

Question 6

Summarise the pathophysiology of ARDS

Answer 6

Injury to the body –> inflammatory process
Disruption alveolar-capillary membrane

Question 7

What does the flow trigger do on the ventilator

Answer 7

Causes the ventilator to cycle back to inspiration

Question 8

What is peak inspiratory pressure

Answer 8

Pressure recorded at end inspiration
Dependent on volume or pressure delivered and airway resistance

Question 9

Define plateau pressure

Answer 9

Static transalveolar pressure at end inspiration during an inspiratory hold for an assisted breath

Question 10

Define PEEP

Answer 10

Positive end expiratory pressure
Pressure applied to the expiratory phase of a mechanical breath

Question 11

What is extrinsic PEEP and Intrinsic PEEP

Answer 11

Extrinsic PEEP - PEEP applied through a mechanical ventilator

Intrinsic PEEP (Auto-PEEP) - PEEP that is secondary to incomplete exhalation (airtrapping) e.g. asthma and COPD

Question 12

Compare CPAP and BIPAP

Answer 12

CPAP - Continuous Positive Airway Pressure

Positive pressure applied to both inspiration and expiration during spontaneous breathing in an awake and alert patient.
- no cycling of ventilator
- patient initiates all breaths

BIPAP - Bilevel Positive Airway Pressure

Awake patient who is breathing spontaneously
Ventilator alternates between higher inspiratory pressure (IPAP), augmenting patients own respiratory effort, and lower expiratory pressure (EPAP)
analogous to CPAP/PEEP

Question 13

What are the different types of ventilation

Answer 13

Volume cycled - inspiration ends when preset Vt is delivered

Pressure cycled - inspiration ends when preset pressure has been delivered

Time cycled - inspiration ends when inspiratory time has elapsed

Flow cycled - Inspiration ends when a preset inspiratory flow is reached

Question 14

Differentiate Volume controlled: CMV, A/C, IMV and SIMV modes of ventilation

Answer 14

CMV - Preset Vt. Fixed machine rate. Cannot be increased by patient. No spontaneous breathing by patient (Theatre only - patient paralysed)

A/C - Preset Vt. Pt can increase machine rate by triggering additional breaths.

IMV - Preset Vt. Fixed machine rate. Spontaneous breathing in between allowed. Stacking possible - machine breath on patient breath.

SIMV - Preset Vt. Fixed machine rate.
Spontaneous breathing in between allowed. Machine breaths only administered after patient exhalation complete (prevents stacking).

Question 15

Differentiate Pressure controlled: PSV, PCV, APRV/BIPAP, Volume targeted pressure control

Answer 15

PSV - Pt rate. Machine supports until set pressure. Vt determined by pressure set and lung compliance

PCV - Fixed machine rate. Vt determined by pressure set and compliance of lungs.

APRV - Airway Pressure Release Ventilation. The machine delivers intermittent positive pressure, the rate and duration of which can be set. The patient can breath spontaneously at the lower and high level of pressure.

Volume targeted pressure control - Flow varies but volume is delivered at lowest possible pressure.

Question 16

Summarise the mechanisms of ventilator induced lung injury (VILI)

Answer 16

1. O2
   - Absorptive atalectasis
   - Toxic O2 radicals
2. Alveolar over-distension due to high Vt
   - Compromise alveolar integrity
   - Capillary leak
3. Atelectatic opening and closing
   - Shear stress, teairing
   - Cytokine cascade

Question 17

What is lung protective ventilation

Answer 17

Developed for ARDS but used in most patients:

Prevent:
1. Volutrauma: Vt < 6- 8 ml/kg. RR < 35 b/m)
2. Barotrauma: Pplat < 30. Ppeak < 35
3. Atelectrauma: PEEP 5 - 20
4. Oxytrauma: FiO2 < 50%
5. Permissive hypercarbia: pH > 7.2

Question 17

What is the differential for peak pressure >35 cm H20

Answer 17

1. High plateau pressure
   - ARDS/CHF/PTX/Pulm. haemorrhage/Large effusion/Right mainstem intubation
2. Low plateau pressure
   - Obstructive lung disease
   - Kink in circuit
   - Mucus plug ETT

Question 18

What is the differential diagnosis for low tidal volumes

Answer 18

1. Leak - insufficient airway pressure
2. Airway obstruction (upper/lower)
3. Pneumothorax

Question 19

Why is hypotension common after intubation

Answer 19

Multifactorial
1. Hypovolaemia
2. Analgaesia and anaesthesia
3. Acidosis
4. Immediate effects of PPV on venous return

If persistent –> consider PTX/air trapping
–> slow vent rate temporarily: auscultate, ultrasound, CXR.

Question 20

How do you optimise patient-ventilator synchrony

Answer 20

1. Adequate minute volume
2. Appropriate trigger threshold
3. Flow rates (some patients need higher)
4. AC sometimes tolerated better than IMV

Question 21

What is AutoPEEP

Answer 21

Dynamic hyperinflation
Airtrapping

Reflects inadequate time for expiration
- Prolonged expiratory time: bronchospasm
- Shortened expiratory time: high RR in ARDS

Question 22

What are the problems associated with autoPEEP

Answer 22

1. Haemodynamic compromise
2. Hypoventilation
3. Difficulty triggering ventilator

Question 23

How is AutoPEEP reduced

Answer 23

Decrease RR
Decrease inspiratory time (higher flow rate)
Bronchodilators
PEEP match

Question 24

List strategies to improve oxygenation

Answer 24

1. Increase alveolar O2 - Increase FiO2 - Decrease CO2 2. Increase PEEP - Increases FRC (stabilizes damaged alveoli, improves atalectasis improving VQ matching 3. Increase PIP (but less than 35 cmH2O) 4. Rescue strategies (not routinely recommended) - Recruitment maneuvre - Prone positioning 5. Sedation/Analgaesia (reduce WOB) 6. Increase mean airway pressure 7. Increase O2 delivery

Question 25

How do you optimise CO2 elimination

Answer 25

1. Increase Ve (RR or Vt) 2. Decrease inspiratory time 3. Decrease dead space 4. Improve lung perfusion

Question 26

What is the process for considering extubation in ICU

Answer 26

READINESS CRITERIA 1. Resolved indication for intubation and ventilation A - Adequate cough (VC > 10ml/kg). - Minimal secretions (suction < every 2 hours). - Oropharyngeal/upper airway patency. - GCS - Difficult airway B - RR < 35 - FiO2 < 50%. SaO2 > 90%. PEEP < 10 - Vt > 5 ml/kg - VC > 10 ml/kg - Ve < 10 L/min C - Haemodynamically stable - Normovolaemic - Minimum or no vasopressor D - Awake and co-operative - Sedation discontinued - Paralysis reversed E - Absence of sepsis/pyrexia - Electrolyte/endocrine abnormality SPONTANEOUS BREATHING TRIAL SPN-CPAP: FiO2 0.4. PSV 8. PEEP 5. --> 2nd minute if RSBI < 105 continue with SBT. --> 30 mins at least up to 2 hours. (30 minutes as effective as 2 hours: Perren et al 2002) FAIL (try again tomorrow) 1. RR > 35 2. SaO2 < 88% 3. HR > 140 (or > 20% increase) 4. SBP < 90 or > 180 5. Anxiety / sweating / paradoxical breathing PASS CUFF LEAK TEST 1. Suction above cuff before deflating 2. Qualitative: listen for turbulent air without stethoscope. 3. Vt before and after cuff deflated. If > 110 ml difference then sufficient movement past cuff to suggest minimal chance of post extubation stridor. STOP FEEDS for 4 HOURS ASPIRATE GASTRIC CONTENTS EXTUBATE

Question 27

Why should a spontaneous breathing trial not exceed 2 hours

Answer 27

Will lead to muscle fatigue and delay extubation.

Question 28

Should a SBT be done more than once a day

Answer 28

No. Will lead to muscle fatigue and delay extubation. (Don't overload or underload)

Question 29

What are important aspects of the act of extubating a patient in the ICU

Answer 29

1. Airway and oropharyngeal suction 2. Sit patient upright 3. Remove ETT during expiration 4. FMO2 + Nebs + Monitor

Question 30

What are the causes for failure of SBT

Answer 30

Inadequate respiratory center output (decreased drive) - Drugs - CNS damage - Hypothyroidism - Metabolic Alkalosis Increased respiratory workload - Increased minute ventilation (Pain/fever/anxiety) - Increased metabolic rate (Infection/feeding) - Increased Vd/Vt - Increased elastic workload (low compliance, PEEPi)

Question 31

Categorize the causes of difficulty in discontinuation of mechanical ventilation in the ICU

Answer 31

1. CNS: Inadequate RSP centre output (drugs/brain injury/thyroid/met. alkalosis) 2. Increased respiratory work load - Increased Ve (Hyperventilation/pain/anxiety) - Increased metabolic rate (Infection/feeding) - Increased Vd/Vt - Increased elastic workload (low compliance) - Increased resistive workload (Secretions/ETT/Vent circuit) 3. Respiratory pump failure - Chest wall (pl.effusion / pneumo / obesity / ascites etc) - Neuromuscular (Phrenic nerve injury / GBS ) 4. Muscle weakness - Electrolytes - Myopathy - Steroids 5. Left ventricular failure

Question 32

Define ARDS

Answer 32

Berlin 2013 definition New or worsening acute (<1 week) respiratory symptoms with characteristic bilateral and diffuse parenchymal opacification on chest imaging. Objective assessment such as echocardiography must exclude hydrostatic oedema (cardiac failure) or fluid overload if no risk factor present. Global Definition of ARDS 2023 Includes 1. Lung Ultrasound can also be used for diagnosis 2. SF ratio < 315 can be used instead of PF < 300 with PEEP > or = 5 or 3. HFNO2 of > 30L.min

Question 33

List and categorise the most common associations with ARDS

Answer 33

DIRECT INJURY (Primary) Pneumonia Gastric Aspiration Near drowning Inhalation injury Fat emboli Pulmonary contusion Pulmonary embolus INDIRECT INJURY (Secondary) Sepsis Polytrauma Acute pancreatitis Blood transfusion Cardiopulmonary bypass

Question 34

Define the pathological stages of ARDS

Answer 34

Phase 1 - Exudative (diffuse alveolar damage) - Diffuse neutrophilic alveolar infiltrate - Alveolar flooding - Capillary thrombosis Phase 2 - Proliferative (Subacute) - Proliferation of type 2 pneumocytes, squamous metaplasia, myofibroblasts and early collagen deposition Phase 3 - Fibrotic (Chronic) - Diffuse fibrosis with cyst formation Phase 4 - Recovery

Question 35

Summarise the management of a patient with ARDS

Answer 35

Supportive care 1. Treat underlying trigger (e.g. infection) 2. FASTHUGS IN BED 3. Lung protective ventilation 4. Salvage therapies - Prone positioning - Recruitment maneuvres 5. Neuromuscular blockers (< 48 hours) for pts with EARLY ARDS and PF < 150. 6. Conservative fluid management strategy without hypoperfusion 7. Steroids remain contraversial - currently not recommended.