Resp Flashcards
driving pressure
ΔP = VT/CRS (resp system compliance)
Bedside - Pplat - PEEP
providing lung-protective ventilatory strategy that is adapted to the size of the aerated lung
Has been assessed in retropective analysis of RCT patients
Aim for driving pressure of <15
transpulmonary pressure definition
TPP is the difference between the alveolar pressure (Palv) and pleural pressure (Ppl).
TPP is the net distending pressure applied to the lung.
How to measure alveolar pressure (Palv)
difficult to measure instantaneously during flow, but equalises to airway pressure at states of zero flow with airway occluded.
Classically measured as inspiratory pause pressure after complete tidal volume.
How to measure pleural pressure (Ppl).
estimated from oesphageal pressure (Pes.) with a thin wall latex
oesophageal ballon inserted via the NG or OG route.
Its measurement is prone to error;
- Malposition – gastric (one of third balloon placements in study below challenging)
- Positioning: supine vs erect (addition of mediastinal weight)
- Assumption that pleural pressures even through the chest
- Extrinsic factors – obesity, rising intra-abdominal pressure
Rationale for using transpulmonary pressure
the effects of chest wall compliance are negated and a true measure of lung distension is obtained. This may allow the safe tolerance of higher plateau pressures.
May have a role in obesity, raised intra-abdominal pressure and air trapping.
More accurate prevention of ventilator associated lung injury may be obtained by using TPP, e.g.:
Limit recruitment maneuvers to TPP 25 cmH2O
Setting PEEP to TPP 0-10 cmH2O
Limiting volutrauma by setting VT to a TPP 25 cmH2O
Determination of respiratory muscle work in spontaneous ventilation
Assessment of ventilator dys-synchrony
Estimation of auto-PEEP in spontaneously breathing patients
POssible causes of a patient “not being able to get enough air” ie causes of vent asynchrony
Patient factors
- Airway / trache – blocked, displaced or too small diameter
- Respiratory e.g. pneumonia, PE, PTX
- Cardiac – ongoing ischaemia, cardiac failure, fluid overload
- Neuromuscular – weakness, fatigue
- Sepsis
- Metabolic
- Central – increased respiratory drive, pain, agitation
Ventilator factors
- Unsuitable mode
- Triggering threshold too high
- Inspiratory flow rate too low
- Prolonged inspiratory time
- Inappropriate cycling
- Inadequate pressure support
- Inadequately set tidal volume
- Ventilator malfunction
Methods of determining PEEP
Use the ARDSNet PEEP/FiO2 escalation tables (setting the PEEP according to the severity of the oxygenation failure)
Titrate PEEP according to maximum compliance, i.e. set the PEEP which achieves the highest static compliance
Set the PEEP using the lower inflection point of the pressure volume curve (the point that indicates the pressure at which alveolar recruitment is maximal.
The measurement requires paralysis and - ideally - serial static measurements
Use a staircase recruitment (or derecruitment) manoeuvre to find the lowest PEEP at which the maximal oxygenation is maintained.
Using a PA catheter, titrate PEEP to achieve the smallest intrapulmonary shunt
Titrate PEEP according to the transpulmonary pressure
- Transpulmonary pressure = (Pplat - Pes)
- The ideal TPP is 0-10 in end-expiration and no more than 25 in inspiration
Using electrical impedance tomography, titrate PEEP to achieve the highest electrical impedance in the thorax (i.e. the greatest amount of aerated lung)
Sequential CT scans to visually determine a PEEP at which the greatest volume of lung is recruited during end-expiration
Patient-Ventilator Dyssynchrony definition
when the patient’s demands are not met by the ventilator,
Due to issues including;
(1) timing of inspiration
(2) adequate inspiratory flow for demand
(3) timing of the switch to expiration
(4) duration of inspiration
Indications for NIV
Strong indications -
Cardiogenic pulmonary oedema: improves survival, decreases rate of intubation (Cochrane review)
COPD: halves mortality when compared to invasive ventilation (Cochrane review)
Obesity hypoventilation sydrome: mainstay of chronic maintenance and rescue for acute respiratory failure (Carrillo et al, 2012)
Rib fractures and chest trauma: reduced mortality, intubation rate and infections (Chiumillo et al, 2013)
Weak indications -
Asthma: no mortality benefit, but prevents intubation, decreases ICU stay and imrpoves delivery of nebulised drugs (Lim et al, 2012)
Weaning COPD patients from invasive ventilation: improves mortality, reduces VAP risk (Cochrane review)
Elective extubation of patients without respiratory failure: Cooperative hypercapneic high-risk patients may benefit (Ferrer et al, 2006)
Ventilation for cystic fibrosis patients awaiting lung transplant: based on small-scale observational studies (Bright-Thomas et al, 2013)
Community-acquired pneumonia: useful in patients with pre-existing cardiac or respiratory disease (Carrillo et al, 2012)
Post-operative respiratory failure- “prophylactic NIV” - little data in support of this (Jaber et al, 2012)
Lung infection in the neutropenic patient: improves survival when compared to intubation (one small trial)
Limitations of therapy: if the patient requires intubation but is “not for “ intubation; NIV provides comfort (Azoulay et al, 2010)
Complications of NIV
Mask intolerance, agitation and claustrophobia Increased need for sedation Delay of intubation Aspiration Poor clearance of secretions Hypotension of hypovolemic patients Facial pressure areas Raised intracranial pressure Aerophagy (swallowing air) Damage to facial, nasal and oesophageal surgical sites or traumatic injuries, leading to surgical emphysema, pneumothorax and pneumomediastinum
mechanisms by which an ICU ventilator may cycle from inspiration to expiration
Time cycled.
Once the time programmed for inspiration (inspiratory flow time plus inspiratory pause time) is completed, the ventilator automatically cycles to expiration. This occurs independent of any patient effort or other variables.
Flow cycled.
Once flow has decreased to a pre-determined minimum value, (eg 25% maximum flow rate), the ventilator cycles to expiration. In lungs with poor compliance, the cycling threshold will be reached more quickly, resulting in a shorter time for inspiration and a smaller tidal volume. Used more in spontaneous modes
Pressure cycled.
Once a set pressure is reached, the ventilator will cycle to expiration. Non-compliant lungs will have smaller tidal volumes than compliant lungs. The most common application for this mode is as an alarm setting as a safety feature to prevent sustained or excessive high pressures.
Volume cycled
Once a set volume is reached, the ventilator will cycle to expiration (or inspiratory pause).
Dapsone
Pneumocystis prophylaxis in those with sulphonamide allergy
Side effects-
- methamoglobinaemia
- haemolytic anaemia
- agrnulocytosis
Methamoglobinaemia
Use a co-oximeter to measure oxygen saturation - the pulse oximeter will read about 82%.
Increase the oxygen carrying capacity of blood by transfusion of PRBCs
Aim for a high PaO2
Infuse methylene blue to reduce all the Fe3+ back into Fe2+
Infuse glucose - it is essential for the hexose monophosphate shunt, which produces the NADPH required for methylene blue to be effective
Types of ventilator associated lung injury
Barotrauma (due to disruption of Basement membrane, seen when transpulmonary pressure >50)
Volutrauma (also BM)
Atelectotrauma (why PEEP helpful)
Macroscopic shear injury - at junction of good and bad lung
Biotrauma - upregulation of pulmonary cytokine production
Oxygen toxicity - destruction of alveolar cells
Causes of wheeze
Extrathoracic causes
- Anaphylaxis
- Vocal cord paralysis
- Laryngeal stenosis
- Goiter with thoracic inlet obstruction
- Anxiety with hyperventilation
Intrathoracic central airway causes
- Tracheal stenosis
- Mediastinal tumours
- Hyperdynamic airway collapse due to tracehomalacia
- Mucus plugs
- Thoracic aortic aneurysm
- Foreign body inhalation
Intrathoracic lower airway causes
- Bronchitis or bronchiolitis
- COPD
- Pulmonary oedema - “cardiac asthma”
- Airway distortion due to mechanical causes, eg. bronchial mass, bronchiectasis, pneumothorax
- Exposure to inhaled irritant or corrosive agent, and this includes the aspiration of gastric contents
Why may NIV be helpful in asthma
positive pressure ventilation decreases effort of breating by applying a positive counter-pressure and thus decreasing the relative amount of intrathoracic pressure which must be generated by the patient’s muscles.
This decreases the work of breathing.
Additionally, it splints the constricted airways, allowing improved CO2 clearance
Very short notes of HFOV
- indications
- ventilation principles
- determinants of oxygen
- determinants of CO2
- indications
None anymore - maybe BPF, paeds - ventilation principles
Minimise FiO2, aiming for sats of 88%
Tolerate high CO2 to minimise leak
Maximise frequency and minimise tidal volume - determinants of oxygen
Mean airway pressure is the driving pressure which maintains open alveoli, and is the governing principle of oxygenation in HFOV.
And FiO2
- determinants of CO2 Amplitude of oscillation Frequency of oscillations Cuff leak Inspiratory time
Co-oximeter Oxy Hb 85%
Pulse oximeter oxygen saturation 95%
Carboxyhaemoglobin
Methaemoglobin
Radiofrequency interference
Co-oximeter Oxy Hb 98%
Pulse oximeter oxygen saturation 88%
Poor peripheral perfusion Ambient light Poor probe contact Dyes – methylene blue, indocyanine green Tricuspid regurgitation
Determinants of peak airway pressure.
lung compliance
tidal volume
airway resistance
PEEP
How to calculate compliance
Vt/ (Pplat - PEEP)
Contraindications of non-invasive ventilation
Decreased level of consciousness
Respiratory arrest
Vomiting
Hemodynamic instability
Poor clearance of secretions, eg. absent cough and gag
large sputum load and/or pneumonia
surgical or traumatic damage to the airways or oesophagus
Causes of auto-triggering of the. ventilator
- cardiogenic oscillations
- High sensitivity settings
- Circuit leaks
- Water condensation in the circuit
Or - external to the vent;
- Diaphragmatic “capture” of her pacemaker
- External movements (eg. nursing care)
Causes of autoPEEP
Machine factors:
- Blocked or faulty expiratory valve of the ventilator
- kinked expiratory limb of the ventilator tubing
- rain-out in the expiratory limb
- clogged water-sodden HME
- kinked ETT
- ETT clogged with sputum
- ETT being chewed on by the patient
Ventilator settings
- Short expiratory time
- High I:E ratio
Patient factors
- Bronchospasm
- Increased respiratory rate
All cause Increased resistance to expiratory flow
Indications for lung biopsy
diagnosis of lung disease cannot be established by less invasive means (eg. BAL, bronchoscopic biopsy, HRCT)
the lung disease is not responding to the current management
Management for the differentials is substantially different and a tissue diagnosis will alter the course of management
The management suggested has significant side effects, and a biopsy may prevent such management
Prognosis will be influenced by tissue diagnosis, and may be grounds for a palliative course of management
Complications of lung biopsy
pneumothorax
bronchopleural fistula
haemothorax
major vessel damage
failure to establish a diagnosis due to poor sampling
death
Methaemoglobinaema pathophysiology
the Fe2+ of iron is oxidised into Fe3+ = altered state of haemoglobin where ferrous ions (Fe2+) of haem are oxidised to the ferric state (Fe3+), which are unable to bind oxygen.
Indications for hyperbaric oxygen therapy
Carbon monoxide poisoning Arterial gas embolism, eg. decompression sickness Clostridial myonecrosis Necrotising fasciitis Refractory osteomyelitis Compromised skin grafts/flaps Severe burns Catastrophic anaemia (life without haemoglobin is possible) Compartment syndrome Burns Radiation necrosis
Contraindications for hyperbaric oxygen therapy
Untreated tension pneumothorax Therapy with the following drugs: Doxorubicin Cisplatin Disulfiram Mafenide
Adverse effects of hyperbaric oxygen therapy
Safe when limited 120 minutes
Myopia (revrsible)
Cataract formation
Rupture of the middle ear and cranial sinuses
Seizures
Claustrophobia
Pulmonary irritation and pulmonary oedema
Mechanisms for improved oxygenation when prone
Improved V/Q matching
More homogeneous ventilation:
- benefits include More uniform distribution of pleural pressure -> more uniform compliance; more uniform distribution of plateau pressure; and less cyclical atelectasis and alveolar overdistension.
Less lung deformation:
Increased FRC:
Improved drainage of secretions:
Improved response to recruitment manoeuvres:
Improved mechanics of the chest wall in obesity
causes of right shift of ODC and what does it mean
increase temp, CO2 and 2,3DPG
Decreased pH
Hb has a decreased affinity for O2 and so delivery to the tissues is increased
Patient-ventilator dyssynchrony deifnition
increased work of breathing and decreased patient comfort because of a mismatch between the ventilator gas delivery pattern and the patient’s demands.
How to manage patient ventilatory dyssynchrony
- treating patient respiratory problems eg sputum, irritable airways
- checking ETT for kinking, secretion block, impinging on carina or between cords
- choosing the appropriate ventilator
- choosing the appropriate mode
- selecting sensitivity not too low or high
- choosing the appropriate ventilator rate
- setting appropriate flow rate
- sedating the patient to reduce agitation
- taking over ventilation if fatigue is apparent
Discussion
Chest physio techniques used
Manual lung hyperinflation
- Improves recruitment of atelectatic lung
- Mobilises bronchial secretions
- Improves lung compliance
Recruitment manoeuvres:
- Transiently improve oxygenation
Suctioning:
- Improves clearance of secretions
- Inspiratory muscle training
- May improve the chances of successful ventilator weaning
Chest shaking and vibration
- Aid mucociliary clearance
Chest wall compression
- Enhances expiratory manoeuvres and aids secretion clearance
Percussion
- May mobilise secretions
Neurophysiological facilitation of respiration
- Stimulates increased VT and cough
Positioning
- May reduce the work of breathing
Gravity-assisted positioning
- May enhance secretion clearance
Active cycle of breathing techniques (ACBT)
- Breathing exercises to remove excess secretions
Causes of Difficulty Weaning from Mechanical Ventilation
Respiratory load -> Increased work of breathing
- Inappropriate ventilator settings
- Reduced compliance
- Increased airway resistance
- Dynamic hyperinflation
- Endotracheal tube diameter
- Increased airway secretions or sputum retention
Cardiac load
- Heart failure
- Increased cardiac workload (eg. increased metabolic demand)
- Decreased oxygen-carrying capacity of blood, eg. anaemia or some sort of dyshaemoglobinaemia
Neurological causes
- Depressed central drive, eg. due to drugs
- Delirium
- Peripheral neurological dysfunction, eg. ICU-acquired weakness
- Pain, eg. due to a laparotomy wound
Musculoskeletal causes
- Muscular problems (eg. steroid myopathy) or NMJ problems (eg, myasthenia)
- Mechanical problems, eg. scolisosis-associated restrictive lung disease or a massive distended abdomen in ileus
- Skeletal problems, eg. chest trauma, flail segments
Metabolic disturbances
- Increased metabolic demand, eg. trauma, burns, sepsis
- Extremes of nutrtion, eg. obesity or cachexia
- Metabolic acidosis
pathological consequences of OSA
Hypertension
Pulmonary hypertension (due to chronic hypoxic vasoconstriction)
Right ventricular hypertrophy and right heart failure
Increased risk of myocardial infarction
Atrial fibrillation (3-4 fold higher odds)
Increased risk of stroke
Decreased seizure threshold (independently associated with epilepsy)
Diabetes (somehow, it is an independent risk factor)
Increased risk of post-operative reintubation
What useful information can be gained from respiratory pressure-volume loops in the management of the ICU patient?
PV loops require either steady state (super-syringe technique) or quasi-steady state techniques (slow constant flow) to minimise effects of flow characteristics on pressure.
The use of non constant flow requires mathematical computerised correction of the curve.
- graphical representation of lung compliance
- estimation of lower inflection point
- estimation of pressure required for complete alveolar recruitment
- adjusting PEEP to this may pervent derecruitment
estimation of pressure which causes alveolar overdistension - adjusting plateau pressure to this may prevent VILI
- estimation of the work of breathing
- estimation of the degree of airway obstruction
Limitations of the loops are as follows:
- Poor representation of heterogenous lung pathology
- Inconsistent agreement among observers as to where the lower inflection point is
