ARDS and Ventilation Flashcards
What is the new global definition of ARDS 2023? How does it differ from the Berlin 2013 defiintion
NB is “objective assessment” incorporated to exclude cardiogenic odema and iatrogenic intravascular overload
What is the ARDS New Global Definition 2023
Additions are
1. Lung ultrasound by trained personal to diagnosed infiltrates (as an alternative to the use of CXR/CTChest)
- PF ratio < 300 in the presence of PEEP > 5 OR HFNO2 > 30l/min
- 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.
Name the trial that defined the Berlin 2013 ARDS definition
Acute respiratory distress syndrome: the Berlin Definition
Ranieri et al 2013
Name the Research that defined the ARDS New Global Definition 2023
ARDS A New Global Definition
Matthay et al 2023
Categorize the severity of ARDS and include the relative mortality
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+
Summarise the pathophysiology of ARDS
Injury to the body –> inflammatory process
Disruption alveolar-capillary membrane
What does the flow trigger do on the ventilator
Causes the ventilator to cycle back to inspiration
What is peak inspiratory pressure
Pressure recorded at end inspiration
Dependent on volume or pressure delivered and airway resistance
Define plateau pressure
Static transalveolar pressure at end inspiration during an inspiratory hold for an assisted breath
Define PEEP
Positive end expiratory pressure
Pressure applied to the expiratory phase of a mechanical breath
What is extrinsic PEEP and Intrinsic PEEP
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
Compare CPAP and BIPAP
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
What are the different types of ventilation
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
Differentiate Volume controlled: CMV, A/C, IMV and SIMV modes of ventilation
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).
Differentiate Pressure controlled: PSV, PCV, APRV/BIPAP, Volume targeted pressure control
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.
Summarise the mechanisms of ventilator induced lung injury (VILI)
- O2
- Absorptive atalectasis
- Toxic O2 radicals - Alveolar over-distension due to high Vt
- Compromise alveolar integrity
- Capillary leak - Atelectatic opening and closing
- Shear stress, teairing
- Cytokine cascade
What is lung protective ventilation
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
What is the differential for peak pressure >35 cm H20
- High plateau pressure
- ARDS/CHF/PTX/Pulm. haemorrhage/Large effusion/Right mainstem intubation - Low plateau pressure
- Obstructive lung disease
- Kink in circuit
- Mucus plug ETT
What is the differential diagnosis for low tidal volumes
- Leak - insufficient airway pressure
- Airway obstruction (upper/lower)
- Pneumothorax
Why is hypotension common after intubation
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.
How do you optimise patient-ventilator synchrony
- Adequate minute volume
- Appropriate trigger threshold
- Flow rates (some patients need higher)
- AC sometimes tolerated better than IMV
What is AutoPEEP
Dynamic hyperinflation
Airtrapping
Reflects inadequate time for expiration
- Prolonged expiratory time: bronchospasm
- Shortened expiratory time: high RR in ARDS
What are the problems associated with autoPEEP
- Haemodynamic compromise
- Hypoventilation
- Difficulty triggering ventilator
How is AutoPEEP reduced
Decrease RR
Decrease inspiratory time (higher flow rate)
Bronchodilators
PEEP match
List strategies to improve oxygenation
- Increase alveolar O2
- Increase FiO2
- Decrease CO2 - Increase PEEP
- Increases FRC (stabilizes damaged alveoli, improves atalectasis improving VQ matching - Increase PIP (but less than 35 cmH2O)
- Rescue strategies (not routinely recommended)
- Recruitment maneuvre
- Prone positioning - Sedation/Analgaesia (reduce WOB)
- Increase mean airway pressure
- Increase O2 delivery
How do you optimise CO2 elimination
- Increase Ve (RR or Vt)
- Decrease inspiratory time
- Decrease dead space
- Improve lung perfusion
What is the process for considering extubation in ICU
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
Why should a spontaneous breathing trial not exceed 2 hours
Will lead to muscle fatigue and delay extubation.
Should a SBT be done more than once a day
No. Will lead to muscle fatigue and delay extubation. (Don’t overload or underload)
What are important aspects of the act of extubating a patient in the ICU
- Airway and oropharyngeal suction
- Sit patient upright
- Remove ETT during expiration
- FMO2 + Nebs + Monitor
What are the causes for failure of SBT
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)
Categorize the causes of difficulty in discontinuation of mechanical ventilation in the ICU
- CNS: Inadequate RSP centre output (drugs/brain injury/thyroid/met. alkalosis)
- 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) - Respiratory pump failure
- Chest wall (pl.effusion / pneumo / obesity / ascites etc)
- Neuromuscular (Phrenic nerve injury / GBS ) - Muscle weakness
- Electrolytes
- Myopathy
- Steroids - Left ventricular failure
Define ARDS
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
List and categorise the most common associations with ARDS
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
Define the pathological stages of ARDS
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
Summarise the management of a patient with ARDS
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.
