Critical care: respiratory Flashcards
What is ARDS?
-Syndrome of respiratory failure
-Formation of non-cardiogenic oedema–> reduced lung compliance and hypoxaemia refractory to oxygen therapy
Berlin definition:
-Bilateral diffuse pulmonary infiltrates on CXR/CT
-Acute onset within 7 days
-PaO2:FiO2 ratio <300mmhg with PEEP or CPAP >5cmH2O
-Alveolar oedema not explained by fluid overload or cardiogenic causes
Pulmonary wedge pressure:
-Pressure measured by wedging a pulmonary artery catheter with an inflated balloon into a small pulmonary arterial branch
PaO2:FiO2 ratio
PaO2/FiO2 ratio is the ratio of arterial oxygen partial pressure (PaO2 in mmHg) to fractional inspired oxygen
Ie how much inspired oxygen gets into the blood stream
How would you classify ARDS causes
Direct lung injury
Indirect lung injury
ARDS direct lung injury causes
-Pneumonia
-Aspiration of gastric contents
-Fat emboli
-Smoke inhalation injury
ARDS indirect lung injury causes
-Sepsis
-Severe trauma
-Major burns
-Acute pancreatitis
-Multiple blood transfusion
Describe phases of ARDS pathophysiology
Exudative phase
Proliferative phase
Fibrotic phase
Describe exudative phase ARDS pathophysiology
-Alveolar damage initiated from the initial tissue injury
-Cytokines and inflammatory mediators–> alveolar and endothelial injury.
Describe proliferative phase ARDS pathophysiology
-Restoration of alveolar-capillary membrane integrity, by the fibroblasts and type-2 pneumocytes
-New surfactant is produced
Describe fibrotic phase of ARDS
-fibrin deposition leading to ‘scarring’ of the lung tissue.
-can lead to long-term oxygen or even ventilation dependency.
What is CPAP and how does it work?
-Form of invasive or non-invasive ventilation
-continuous pressure is given throughout respiratory cycle to increase functional residual volume and improve hypoxia
-This decreases work of breathing and prevents alveolar collapse
What type of respiratory failure is CPAP applicable for?
Type 1
Define respiratory failure
Type 1 (hypoxaemic)
-PaO2 <8 kpa
-Normal or reduced PaCO2
Type 2
-PaO2 <8 kPa
-PaCO2 is >6.7kPa
What are the indications for a tracheostomy
Maintain airway in:
-Congenital pathologies (tracheal stenosis)
-Following surgical procedures e.g. laryngectomy
-Emergency setting e.g. laryngeal trauma/oedema, inhalation injury
-If prolonged intubation expected
What are the two methods of performing a tracheostomy?
-Percutaneous
-Surgical
Name the types of tracheostomy tubes
-Metal or plastic
-Cuffed or uncuffed
-Fenestrated or unfenestrated
What are the advantages of tracheostomies?
-Expedites extubation and weaning
-Decreases work of breathing
-Avoids continued vocal cord injury
-Improves bronchopulmonary hygeine
-Improves ability of pt to communicate
What are the disadvantages of tracheostomies?
-Long-term risk of tracheal stenosis
-Blockage of tracheostomy tube leading to airway compromise
-Dislodged tracheostomy tube
Name some complications related to performing a tracheostomy
-Bleeding
-Pneumothorax
-Vascular injury
-Oesophageal trauma
-Death
When would you consider extubation?
-Resolution/stabilisation of disease process
-Intact cough/gag reflex - protected airway
-Spontaneous respirations
-FiO2 <40%
-PEEP <8
-PaO2 >10kPa (if no pre-existing lung disease)
-pH >7.35
-Good muscle strength
-Neurologically intact
Indications for intubation
-Acute respiratory failure
-Acute ventilatory failure
-Surgery
-Raised ICP to avoid hypoxia/hypercarbia
-Trauma (chest injury and lung contusion)
-Severe LVF with pulmonary oedema
-GCS <8
-ARDS
-Prophylactic establishment of airway e.g. smoke inhalation
-Raised ICP to avoid hypoxia/hypercarbia
What is IPPV
-Lungs are intermittently inflated with positive pressure
-Intubation is required to facilitate IPPV
Pulmonary embolus definition
-A pulmonary embolism (PE) refers to a blockage of the pulmonary artery by a substance that has travelled there in the bloodstream.
-Most commonly an embolus from DVT in leg
-Other causes include AF, right mural thrombus post MI, neoplastic cells or fat cells e.g. from tibial fracture
What ECG changes would you expect in pe?
-Often no changes
-Sinus tachycardia
RV strain: TWI V1-V4 and/or avf + 3
S1Q3T3
-Large S wave V1
-Large Q wave in V3
-T wave inversion lead 3
What are the risk factors for developing PE?
Wells score is useful predictor of PE/DVT assessing:
-Symptoms of DVT
-Advanced age
-Immobilisation >: 3 days
-Recent surgery
-Previous history DVT/PE
-Malignancy
Other risk factors include pelvic or leg trauma, pregnency, genetic predisposition
Describe mechanism of action of heparin
Binds to anti-thrombin 3 which inhibits factors IX, X, XI and XII and prevents conversion of fibrinogen to fibrin
Describe mechanism of warfarin
Competitive inhibitor vitamin K, which is co-factor for production of factor 2, 7, 9, 10
When would thrombolysis be indicated for PE?
May be indicated in PE with haemodynamic compromise: however, would require input from respiratory/ITU teams
Absolute contraindications for thrombolysis
-Active internal bleeding
-Recent spontaneous intracranial bleeding
Relative contraindications for thrombolysis
-Major surgery within 10 days
-Ischaemic stroke within 2 months
-GI bleed within 10 days
-Major trauma within 15 days
-Recent CPR
-Platelet count <100
-Severe uncontrolled hypertension
Explain O2 dissociation curve
-greater affinity hb for o2 after binding first molecule
-left shift: greater affinity
-right shift: lesser affinity
-Demonstrates relationship between pO2 and blood oxygen concentration
-Shape of curve reflects increasing ability of hb to take up o2 following binding of first molecule
-Left shift increases o2 affinity and so o2 is less readily available for use in tissues
-Right shift of curve decreases o2 affinity so it is more readily available for use in tissues
What are the causes of left shift in oxygen dissociation curve?
-Decrease in temperature
-Decrease in 2,3 diphosphoglycerate
-Alkalosis
-carbon monoxide poisoning
What is 2,3 diphosphoglycerate?
-Present in RBCs
-Binds with greater affinity to deoxygenated haemoglobin (ie haemoglobin in respiring tissues)
-Decreases affinity for oxygen and promotes release of remaining molecules
How does dissociation curve in foetal hb differ from adult?
-Curve is shifted to left and therefore has greater affinity to o2
-Readily takes up o2 from maternal adult hb
How is cO2 transported in body?
-As bicarb ions
-Dissolved in plasma
-Bound to hb as carbamino-compounds
How would you classify pneumothorax?
-Traumatic
-Spontaneous
-Tension
Describe traumatic pneumothorax causes
Results from penetrating or blunt injury to chest
Iatrogenic - complications of invasive medical procedures such as:
–Central line placement
–Thoracocentesis
–Lung biopsy
Accidental
Describe and classify sponteneous pneumothorax
Occurs without preceding trauma or precipitating event
-Primary: No obvious lung disease
-Secondary: complication of lung disease
Describe tension pneumothorax
-air is trapped in the pleural space under positive pressure
-Mediastinal structures are displaced
-cardiopulmonary function is compromised
How would you classify causes of tension pneumothorax
Iatrogenic
Non iatrogenic
What are the iatrogenic causes of tension pneumothorax
-Central line
-Mechanical ventilation
-Incorrect chest drain insertion
-CPR
-Needle lung biopsy
-Liver biopsy/surgery
-Neck surgery
Non-iatrogenic causes tension pneumothorax
-Blunt and penetrating trauma
-Asthma
-COPD
-Pneumonia
-Pertussis
-TB
-Lung abscess
-CF
What are clinical features of tension pneumothorax?
-Respiratory distress
-Raised JVP
-Tracheal deviation
-Reduced breath sounds
-hyper-resonance
-shock
-distended neck veins
Describe immediate management for tension pneumothorax
-100% O2
-Needle thoracocentesis: large bore cannula inserted into 5th intercostal space mid axillary line
What procedure would you perform for tension pneumothorax after needle thoracocentesis?
Chest drain
What are the indications for inserting chest drain?
-Pneumothorax
-Haemothorax
-Chylothorax
-Drain pleural fluid or empyema
-Peri-operative procedure e.g. thoracotomy, oesophageal surgery, cardiothoracic surgery
Name some complications following chest drain insertion
-Bleeding from an injured intercostal artery
-Accidental injury to the heart, arteries, lung, liver on right, spleen on left
- infection
-Air leaks in tube
-Dislodged tube
-Incorrect positioning of tube
-Insertion of chest tube can cause open or tension pneumothorax
Label spirometry graph
- Tidal volume
- Inspiratory reserve volume
- Inspiratory capacity
- Functional residual capacity
- Vital capacity
- Functional residual capacity
- Total lung capacity
Define tidal volume
The amount of air that moves in or out of the lungs with each respiratory cycle
Define inspiratory reserve volume
The amount of air a person can inhale forcefully after normal tidal volume inspiration
Define expiratory reserve volume
Expiratory reserve volume is the amount of air a person can exhale forcefully after a normal exhalation
Define functional residual capacity
the volume remaining in the lungs after a normal, passive exhalation
Define vital capacity
total amount of air exhaled after maximal inhalation
Define residual volume
the amount of air that remains in a person’s lungs after fully exhaling
Total lung capacity
the maximal volume of gas in the lungs after a maximal inhalation
How would you differentiate obstructive from restrictive lung disease on lung function test?
-Normal FEV1:FVC ratio around 80%
-In restrictive lung disease FEV1:FVC ratio >79%
-in obstructive lung disease <80%
Define FEV1:FVC ratio
-The ratio of the forced expiratory volume in the first one second vs forced vital capacity of the lungs.
-The normal value for this ratio is above 0.75-85, though this is age dependent.
Define inspiratory capacity
The maximum volume of air that can be inspired after reaching the end of a normal expiration
What are the different systems that regulate acid-base balance?
Respiratory
Kidney
Blood
Bone
Liver
How does respiratory system control acid/base balance?
-PCO2 controlled by alteraltions in alveolar ventilation
-CO2 crosses blood-brain barrier and dissoves in CSF forming H+ ions
-This stimulates central chemoreceptors in ventrolateral surface of medulla oblongata
How does kidney control acid/base balance?
-Controls bicarbonate ion which is important for long-term control and compensation of acid-base disturbances
How would you manage pt with post operative pneumonia?
-Resuscitate as per ccrisp protocols
-Oxygen
-Antibiotics
-Chest physio
-Discuss with critical care team
What are the defence mechanisms of the respiratory system?
-Airway mucus secretion
-Muco-ciliary action of upper respiratory tract
-Alveolar macrophages
What are the indications for intubation?
GCS <8
-Traumatic chest injury + pulmonary contusion
-Respiratory/ventilatory failure
-Prophylactic establishment of airway e.g. smoke inhalation
-Decreased level of consciousness/coma
-Upper airway obstruction
-Traumatic chest injury
-ALI/ARDS
-Respiratory failure
-Apnoea
-Neuromuscular disease
-Prophylactic establishment of an airway – eg smoke inhalational injuries, angioedema, drug overdose
If post op pneumonia pt does not improve, what type of respiratory support could be considered?
Non invasive ventilation (IPAP/EPAP)
Invasive ventilation
Describe negative feedback pathway that acts within respiratory centre of the brain
-High pO2, low pcO2: less ventilation
-Low pO2, more pCO2: more ventilation
-Arterial pCO2 detected by peripheral chemoreceptors in carotid and aortic bodies
-Send signals to medullary respiratory centre to alter rate of respiration
-Raised pO2, decreased pCO2 and drop in hydrogen ions discourage ventilation to retain more CO2 and restore normal CO2 levels
-Fall in pO2, increased pCO2 and rise in hydrogen ions encourage ventilation to blow off more CO2 and, therefore, restore normal CO2 levels
-These actions are a result of altered arterial pCO2 being sensed by peripheral chemoreceptors in carotid and aortic bodies
-These send signals to medullary respiratory centre to alter rate of respiration
