Respiratory Flashcards
What pathological signs are seen in asthma?
- Smooth wall hyperplasia
- Thick mucus plugs
- Thickened basement membranes (Deposition type IV collagen
- Mucosal odema (abnormal mucuciliary clearance
- Eosinophilia of submucosa and secretions
- increased mast cells in smooth muscle
What makes the diagnosis of asthma more likely?
Raised exhaled nitric oxide
What % of children with asthma will have a positive skin prick test to dust mite?
80%
What is the most common trigger of asthma exacerbation?
viruses- up to 85%. Most common is Rhinovirus
What blood test result might you get in children with asthma?
Otherwise unexplained raised eosinophilia
What percentage of children aged 1-4 years with wheeze DO NOT go on to have asthma at school age or later?
50%
How is preschool wheeze classified?
- Intermittent preschool wheeze (episodic, infrequent (>every 8 weeks)and viral)
- Frequent preschool wheeze (frequent, viral induced)
- Preschool asthma (multi-trigger wheeze)
What are the DDX of children with conditions characterised by cough? (other than asthma)
CF Pertussis Airway abnormality (tracheomalacia- more generalised, bronchomalacia- more localised) PBB Habitual cough
What are the DDX of children with conditions characterised by wheezing? (other than asthma)
Upper airway dysfunction
Inhaled FB with partial airway obstruction
Tracheomalacia
What are the DDX of children with conditions characterized by breathlessness? (other than asthma)
Hyperventilation
Anxiety
Poor ETT
How would you manage a child who is having wheeze triggered by viral illnesses less frequently than every 8 weeks (under 5 years old)?
Salbutamol only
How would you manage a child who is having wheeze triggered by viral illnesses more frequently than every 8 weeks (under 5 years old)?
Trial Flixotide for 8 weeks then reasses
How would you manage a child who is having wheeze triggered by viral illnesses AND in between illnesses (under 5 years old)?
Trial Flixotide for 8 weeks then reasses
How would you manage child >5 years old with suspected asthma?
Trial inhaled CCS. Reassess in 8 weeks. If no response check technique and review after 12 weeks of proper treatment. Consider PFTS
What would you see on spirometry is a child with asthma
Obstructive pattern
- concave loop
- FEV1 decreased
- FEV1/FVC reduced
Bronchodilator responsive of at least 12%
Normal DOES NOT exclude a dx of asthma
What causes a raised fractional exhaled nitric oxide level?
Suggests eosinophilic inflammation which may be caused by:
Asthma, eczema, allergic rhinitis, atopy, allergic bronchitis
Not diagnostic
What causes a lowered fractional exhaled nitric oxide level?
Smokers
Early phase of allergy
Some asthma phenotypes such as neutrophilic asthma
Why can you not use LABA’s without a combined inhaled corticosteroid
Can cause salbutamol resistance with a parodoxical bronchospasm resulting in increased mortality in scute exacerbations requiring Salbutamol
What kind of ICS are there?
Beclomethasone dipropionate (1/2 the strength of flixotide)
Beclamethasone dipropionate ultra fine (same strength as flixotide)
Fluticasone
Budenoside (1/2 the strength of flixotide)
What are the low dose ICS?
- low dose achieves 80-90% max efficacy in children
Beclomethasone dipropionate (1/2 the strength of flixotide) = 200mcg/day
Beclamethasone dipropionate ultra fine (same strength as flixotide) = 100mcg/day
Fluticasone = 100mcg/day
Budenoside (1/2 the strength of flixotide) = 200mcg/day
What is the next step in a child whose asthma is not controlled with a LOW dose ICS?
Add in a LABA
If >12 could use single maintenance and reliever therapy
When do you use Montelukast?
in <5 years old
- if frequent severe exacerbations (instead of ICS)
- or add frequent exacerbations not controlled with just ICS
in >5 year olds
- instead of ICS for frequent exacerbations
- or add if frequent exacerbations not controlled by STANDARD ICS + LABA
When do you step up to standard dose of ICS
If a child’s asthma is not controlled with a low dose ICS + LABA (or SMART if over 12yrs)
What are the STANDARD doses of ICS?
Beclomethasone dipropionate (1/2 the strength of flixotide)= 400-500ncg/day
Beclamethasone dipropionate ultra fine (same strength as flixotide) = 200mcg/day
Fluticasone= 200-250mcg/day
Budenoside (1/2 the strength of flixotide)= 400mcg/day
What is a HIGH dose of ICS?
Twice that of standard dose
What other preventors are there other than ICS in asthma treatment?
Leukotriene receptor antagonists - i.e montelukast
Mast cell stabilisers- cromones such as sodium cromoglicate and Nedocromil sodium
Theophylline
As a paediatrician, what add on’s would you consider of asthma Mx of children on max therapy?
Oral CCS Omalizumab (Anti-immunoglobulin E) Mepolizumba (Anti-leukin 5) Tiotropium Bromide (long acting muscarinc antagonist) Theophylline
What is Omalizumab?
Monoclonal antibody, prevents immunoglobulin E from binding to mast cells
SC injection
Used in severe uncontrolled asthma as a preventor
Given every 2-5 weeks depending on response
When do you prescribe a low dose ICS in children other than children with frequent wheeze?
In children 5 years or older who present with a severe exacerbation of wheeze regardless of what symptoms they have at baseline
What is the expected FEV1 of children with asthma depending on the control?
Well controlled - FEV1 >80% of predicted/personal best Not well controlled - 60-80% predicted -75-80% personal best Poor control - <60% predicted -<75% personal best
What is the average tidal volume of a child?
approx 6-7ml/kg
What is Inspiratory Capacity?
Maximum inspired effort (including inspired TV)
What is Expiratory reserve volume and the Inspiratory reserve volume?
ERV-max forced expiration EXCLUDING expired TV
IRV- max force inspiration EXCLUDING inspired TV
What is Elastance?
property of a substance to oppose deformation or stretching? = change in pressure/change in volume
What is compliance?
property of a substance to undergo deformation or stretching (the reciprocal of Elastance) = change in volume/change in pressure
-Compliance is the rate of change of volume in response to pressure
In a normal healthy lung at low volume, relatively little negative pressure outside (or positive pressure inside) needs to be applied increase lung volume. However lung compliance decreases with increasing volume. Therefore, as the lung increases in size, more pressure must be applied to get the same increase in volume
AFFECTED by FRC –> use to standardise
What is Resistance in respiratory?
amount of pressure required to generate flow across of gas across the airways
Cau use Poiseuille’s law
R = 8ln/πr^4 (l=length, n=viscosity, r = radius)
What happens to the resistance when the radius is halved?
resistance is inversely proportional to the radius^4
therefore 1/2 the radius = increase the resistance by 16
What diseases can have minimal respiratory distress even with severe respiratory failure (hypoxemia and acidosis)?
Any disease where they cannot mount a sufficient effort to appear in respiratory distress like neuromuscular diseases such as:
Gullian Barre syndrome
Myasthenia Gravis
What contributes to Pulmonary vascular resistance in the third trimester of pregnancy?
The tunica media of the pulmonary arteries in the fetus becomes more muscular
Why are young infants particularly susceptible to pulmonary vasoconstrictive stimuli (hypoxemia, acidosis, hypercarbia)?
The tunica media of the pulmonary arteries are more muscular.
In children and adolescence the pulmonary vascular resistance (PVR ) is approx 15% of the Systemic vascular resistance (SVR)
In day 3 of life the PVR is approx 50% of the SVR
The PVR only decreases to approx 15% after 2-3 months of life
What are the 2 main cytokines made by the alveolar macrophages that activate the inflammatory cascade?
Tumour necrosis factor- α
Interleukin-1β –> stimulate other cytokines, ROS, prostaglandins which stimulate WCC migrations into lung tissue which can cause injury to vessels and alveoli epithelium
What two findings can be found in SIDS autopsy which are higher than normal in explained deaths?
Petechial haemorrhage (68-95%) - and are more extensive than explained causes Pulmonary oedema
What is Leigh disease? (subacute necrotizing encephalopathy)
Inherited, rare, neurodegenerative conditions
Characterized by Psychomotor regression in the first year of life. Death occurs usually in 2-3 years from respiratory failure
Also get Vomiting, poor feeding, FTT, seizures, hypotonia, ophthalmoplegia, nystagmus
What is Brugada syndrome?
Cardiac channelopathy resulting in arrthymia SCN5a (sodium channel) receptor defect Arrythmia can be at rest or triggered by a fever No cure, but could use a pacemaker Occurs in children and in adults Genetic component Occurs in 1 -30/10,000 M>F Higher rates in Asian ethnicity
Why are nasal passages important in resistance to air flow?
contribute to 50% of resistance to air flow in normal children
Congenital severe narrowing can be caused by malformed nasal bones which are often associated with a high and narrow hard palate
What is choanal atresia?
Most common congenital anomaly of the nose
freq 1/1700 live births
Can be unilateral or bilateral bony (90%) septum between the nose and pharynx
Or can be a unilateral or bilateral membranous (10%) septum between the nose and pharynx
Most cases are a mixture of bony and membranous atresia
50-70% of children have other congenital anomalies - particularly CHARGE syndrome
10-20% of patients with CA have CHARGE
What is CHARGE syndrome?
C- coloboma
H- heart disease
A- atresia chonae
R- retarded growth and development or CNS anomalies or both
G- genital anomalies, hypogonadism or both
E- ear anomalies, deafness or both
Mutations in the CHD7 gene which is involved in CHROMATIN organization
What is Perforation of the nasal septum?
Generally acquired after birth secondary to infection
- Syphilis, TB, trauma (delivery)
- Rarely developmental
- CPAP nasal cannulae
If recognised early can be corrected with immediate realignment using blunt probes, cotton applicators and topical anaesthesia.
If late- surgical resection much later in life to avoid disturbance of mid face growth
What is Pyriform aperture stenosis?
Rare birth defect where the anterior opening of the nose is narrow secondary to overgrowth of the maxillary bone.
Cause of severe nasal obstruction and respiratory distress
Dx made by CT
Rx- surgery using a drill to enlarge the stenotic anterior bone apertures
What are the most common congenital midline nasal masses?
In descending order of frequency Dermoids Gliomas Encephalocoeles Haemangiomas Congenital nasolacrimal duct obstruction with cystic extension into the nasopharynx (presents as a mass)
What presents at birth as a midline nasal mass that is firm?
Gliomas and heterotropic brain tissue
How does a congenital dermoid cyst present and what are the complications?
Can present with dimple or pit on the nasal dorsum with or w/o hair.
Complications:
- recurrent infection of the dermoid cyst o
- intracranial fistula or sinus resulting increased risk of intracranial infection
How are congenital midline nasal masses diagnosed and treated
CT for bony detail (used most) + flexible scope
MRI for sagittal views to look at Intracranial extension
Rx is surgical - approach dependent on type and size of mass
What presents at birth as a midline nasal mass that is soft and enlarge with valsava/crying?
Encephalocoeles
What can tumours, septal perforations and other acquired abnormalities of the nose and paranasal sinuses present as?
Epistaxis
What is an acquired cause of saddle-nose deformity in children?
Septal haematoma caused by trauma which if there is a delay in Rx can result in necrosis of the septal cartilage
What is bromhydrosis
Generalised offensive body odour which can be present with an intranasal foreign body
What can nasal polyps be a sign of?
Undiagnosed CF in child <12 years (most common childhood cause of nasal polyposis)
Chronic sinusitis and allergic rhinitis
Aspirin sensitivity and asthma (called the Samter Triad. Uncommon)
How are lung compliance and elastic recoil related?
Lung compliance, or pulmonary compliance, is a measure of the lung’s ability to stretch and expand (distensibility of elastic tissue).
Low compliance indicates a stiff lung (one with high elastic recoil) and can be thought of as a thick balloon – this is the case often seen in fibrosis. High compliance indicates a pliable lung (one with low elastic recoil) and can be thought of as a grocery bag – this is the case often seen in emphysema.
What sinuses are present at birth?
Ethmoid and maxillary. But only the Ethmoid has presence of air spaced (pneumatized)
When are maxillary sinuses pneumatized?
Age 4 years
When are the sphenoid sinuses present?
Age 5 years
When do the frontal sinuses begin development?
Age 7-8 years and aren’t fully developed until adolescence
What are the most common organisms involved in acute bacterial sinusitis?
Strep pneumoniae (~30%) Haemophilus influenzae (~20%) (50% Beta lactamase +ve) Moraxella Cattarhalis (~20%) (100% BL +ve) Uncommonly Staph aureus (incl MRSA)
How can retropharyngeal abscesses occur?
Extension of localised infection of the oropharynx
Penetrating trauma
Dental infection
Osteomyelitis of the verterbrae
What age group is a retropharyngeal abscess most common and why?
3-4 years of age
65% with have had recent URTI sx
Decreased as kids get older as retropharyngeal nodes involute after the age of 5 years
What are the sx of a Retropharyngeal abscess?
Fever, misery, decreased oral intake, drooling
Sometimes can get stiff neck, sore throat, torticollis
Muffled voice, stridor, resp distress, OSA
May get bulging of posterior pharyngeal wall (<50% in infants)
What are the sx of a lateral pharyngeal abscess?
Fever, dysphagia, prominent bulge of the lateral pharyngeal wall, sometimes with medial displacement of the tonsil
What are the DDx of a retro/lateral pharyngeal abscess?
Epiglottis FB Meningitis (if neck stiffness) Lymphoma Haematoma Vertebral osteomyelitis
How is retro/lateral pharyngeal abscess diagnosed and treated?
Incision, drainage and culture of an abscessed node is definitive
CT scan may show abscess and position but only accurately identifies abscess in 63%
XR of soft tissue taken in inspiration with neck extended may show increased width or an air fluid level in the retropharyngeal space.
Treat with IV abx +/- I&D (orgs usually GAS, anaerobes and Staph). >50% can be treated with IV Abx alone
Usually 3rd generation cephalosporin +/- clindamcyin for anaerobic coverage
Treatment usually a few day IV followed by a few days oral
What are the complications of a retro/lateral pharyngeal abscess?
Airway obstruction, rupture leading to aspiration pneumonia, extension to mediastinum, thrombophlebitis of internal jugular vein and erosion of the carotid sheath
What is an uncommon but characteristic infection of the parapharyngeal space?
Lemierre disease
- extension of infection to cause thrombophlebitis of internal jugular vein and embolic abscesses to the lungs
- present in adolescence and young adults with hx of recent pharyngitis
- Fever, hypoxia, tacypnoea, resp distress
- caused by FUSOBACTERIUM NECROPHORUM
What is peritonsillar cellulitis/abscess
Bacterial invasion through the tonsillar capsule
More common than deep space neck infections (i.e retropharyngeal abscess)
Typically presents in adolescence with recent pharyngitis
Sx: sore throat, fever, dysphagia, trismus,
Clinically diagnosed: Asymmetrical tonsillar bulge
Can also do CT if can’t visualise throat due to trismus
Orgs: GAS, mixed anaerobes
Rx: Surgical drainage and IV abx
Complications: Fail on Abx requiring tonsillectomy, ore repeat aspiration
Rare complication: Rupture of abscess with aspiration pneumonitis
What are the most common organisms in epiglottitis in an immunised child?
Strep pyogenes
Strep pneumoniae
Staph Aureus
What is acute epiglottitis?
Bacterial, rapidly progressive illness affecting the epiglottis and aryepiglottic folds
Starts usually with high fever, sore throat–> toxic, respiratory distress (though may be first sign), stridor (late sign and indicates obstruction.
Patient looks toxic, drooling, tripoding with neck hyperextended to keep the airway open and reduce pain.
brief period of air hunger and RESTLESSNESS is a severe sign as will rapidly deteriorate with cyanosis and coma
How is epiglottis diagnosed and treated?
Direct visualization of the cherry red swollen epiglottis and aeryglottic folds on laryngoscopy.
If unsure of clinical diagnosis could do neck XR in hyperextension to reveal the “thumb sign” of swollen epiglottis.
Need to secure air way first before doing anything because as many as 6% of children w/o a secured artificial airway (intubation) will die (c/f 1% in secured airways)
Pulmonary oedema is sometimes associated with acute airway obstruction
Rarely- meningitis, arthritis and other invasive infections may be found with HiB
Treatment after airway secure are IV abx (respond well after 2-3 days) such as ceftriaxone, cefotaxime for 7-10 days
What is spasmodic croup?
occurs in children aged 1-3 years
similar to croup except often no viral prodrome or fever in child and family.
Sudden
Often in the evening or night with mild to moderate coryza, hoarse voice, cough, anxious/distressed
Much improved within hours and the next day mild hoarse voice and cough
Thought to be related to more of an allergic reaction than viral antigens
What are the DDX of upper airway obstruction?
Bacterial tracheitis
Croup
Epiglottitis
Diptheritic croup (unimms. gray white patches on tonsils)
FB
Retropharyngeal or peritonsillar abscess
Extrinsic compression from laryngeal web, vascular ring)
Intraluminal obstruction from laryngeal papilloma, haemangioma (often recurrent sx)
Angioedema allergic/anaphylactic/trauma
Hyopcalcemic tetany (angioedema)
EBV
Tumours or malformations of the larynx
Ingestion of hot liquids or caustic poisons
What are the complications of viral croup?
Occur in 15%
middle ear infection
viral LRTI
Secondary bacterial tracheitis –> if STAPH AUREUS can cause Toxic shock syndrome
What is bacterial tracheitis?
Acute bacterial infection of the upper airway. Often follows viral illnes (particularly croup).
More common in vaccinated pops than epiglottitis
Orgs: Staph aureus (most common), Moraxella, Haemophilus influenzae
Age: mean age 5-7 years
Sx: high fever, toxicity, can lie flat, don’t drool. May have brassy or seal bark cough
Dx: Mucosal swelling at level of cricoid cartilage and purulent, copious, thick secretions. + absence of sx of epiglottitis
Rx: anti-staph agents, consider coverage for MRSA.
50% will need intubation
Complications: Toxic shock in staph. Subglottic narrowing
What are the most common congenital laryngeal anomalies which causes stridor in an infant?
- Laryngomalacia
- 60% - Congenital subglottic stenosis
- Vocal cord paralysis
What is laryngomalacia?
- Congenital softening of the larynx including epiglottic folds
- insp and low pitched stridor. Worse with feeding and crying
- onset around 2 weeks of life and increase in severity for up to 6 months
- If mod to severe WOB need to do radiographs
- Dx by laryngoscopy - Classic “delta sign”
- Can get associated laryngeal reflux (aggressively treat)
- most get better with time, some require surgery
What is congenital subglottic stenosis?
Congenital narrowing of the airway below the vocal cords and involves the cricoid
- 2nd most common cause of stridor
- Inspiratory or biphasic stridor
- Can get recurrent or persistent croup
-First sx often occur with an URTI
Dx: Lateral CXR and laryngoscopy
Rx: Anterior laryngeal decompression (cricoid split) or laryngotracheal reconstruction
DDX: laryngomalacia, vocal cord paralysis, haemangioma, papilomatosis
What is congenital vocal cord paralysis?
unilateral or bilateral vocal cord paralysis
3rd most common cause of congenital stridor
Often idiopathic but can be associated with:
-myelomeningocoele, Arnold-Chiari malformation, Hydrocephalus
Sx: Bilateral
Airway obstruction manifested as high pitched inspiratory stridor/cry
Sx: Unilateral
Aspiration, choking,coughing; cry is weak and breathy; minimal stridor if any
Note that unilateral cord paralysis can be caused by surgery after congenital cardiac repair or TOeF
Dx: laryngoscopy whilst awake + IX for other associated issues as above
Rx: Usually resolved spontaneously in 6-12 months. If Bilateral may need temporary tracheostomy
If unilateral and aspirating may need injecting of affected cord to move it medially
What are congenital laryngeal webs +/- atresia and why are they important?
Membrane like structure involving the vocal cords and may extend down. May get airway obstruction
Can be related to SUBGLOTTIC STENOSIS.
Dx: laryngoscopy. Can sometimes see a web on lateral XR
Rx: Incision/dilatation. laryngotracheal reconstruction if have subglottic stenosis
Laryngeal atresia presents as a complete glottic web . Commonly associated with TRACHEAL AGENESIS and TOeF
Congenital subglottic haemangioma
Haemangioma involving the region of the subglottis
Sx of airway obstruction occur in the 1st 1-2 months of life
Sx: biphasic (worse on inspiration) stridor, barking cough, hoarseness, recurrent or persistent croup
May have a facial haemangioma in the BEARD region
Dx: laryngoscopy but CXR may show asymmetric narrowing of the subglottic larynx
What are the DDX of wheezing in children?
- Infection
- viral
- bacterial (chlamydia, TB, histoplasmosis - Asthma
- Central airway abnormalities
- malacia of the airways
- TOeF (particularly H type)
- laryngeal cleft with aspiration - Extrinsic airway anomalies
- vascular ring (esp double carotid arch compressing on oesophagus and trachea)
- Mediastinal lymphadenopathy (tumour, infection)
- Mediastinal mass/tumour
- oesophageal FB
What are more DDX of wheezing in children?
- Intrinsic airway anomalies
- airway haemangioma or tumour
- CAM
- bronchial or lung cyst
- congenital lobar emphysema
- CHD causing pulmonary HTN (vessels compress on bronchi)
- FB - Immunodeficiency states
- IgA immunodef
- B cell defs
- Bronchiectasis
- Primary ciliary dyskinesia - Mucociliary clearance def –> CF, PCD, bronchiectasis
- Aspiration i.e GOR
- Other
- anaphylaxis, heart failure
- inhalation injury
- interstitial lung disease, bronchiolitis obliterans, bronchopulmonary dysplasia
What single amino acid is deleted on the delta 508 gene in CF?
Phenylalanine
Apart from DeltaF508, what is only other prevalent gene in CF - which is found in 60% of Ashkenazi Jewish people?
W1282X
What modifier gene polymorphisms play a role in severity of progression of lung disease in CF?
- Transforming growth factor B1 (TGF-B1)- single nucleotide change results in defective function. TGF-B1 is important in proliferation and differentiation of cells.
Very important in immune function - Mannose- binding lectin. Important function in innate immunity. Variations in this are associated with severe disease and reduced survival
- IRFD1 gene- a transcriptional co-regulator which is important for neutrophil cell differentiation
Vitamin E deficiency as seen sometimes in CF, can present with what symptoms?
Haemolytic anaemia , peripheral neuropathy (including loss of DTR and vibration), retinopathy, ataxia and dementia
How is compliance calculated?
Compliance =change in volume /change in pressure
What are the key features of Lymphocytic interstitial pneumonia?
syndrome of fever, cough, and dyspnea, with bibasilar pulmonary infiltrates consisting of dense interstitial accumulations of lymphocytes and plasma cells
Does NOT cause fibrosis
Most COMMON form of interstitial lung disease in children
Associated with immunodeficiencies and autoimmune; some sporadic cases
Associated with perinatally acquired HIV ( in 25-40%)
Unknown cause ?immune dysregulation
O/E
Generalized lymphadenopathy, hepatosplenomegaly, parotid enlargement, clubbing, wheezing (occasional).
Ix:
Non-specific inflammation
High polyclonal hypogammaglobulinemia
Bibasal pulmonary infiltrates on CXR
What is Churg Strauss disease?
RARE in children
Syndrome associated with asthma + eosinophilia
Is a necrotising small vessel vasculitis
SX and signs:
Asthma, transient pulmonary infiltrates on CXR
Rash- palpable purpura, tender subcut nodules
Peripheral neuropathy
Occasional renal involvement
What is Sarcoidosis in children
UNCOMMON but has come up in exam questions.
A chronic granulomatous inflammatory disease (non-caseating epilthelioid).
in Kids <4 years: triad of skin, eye and joint involvement w/o typical lung disease
In >4 years: involves lungs, lymph nodes and eyes
SX:
General- fatigue, anorexia, weight loss, bone and joint pain, and anemia.
Lungs- cough, CP and exertional dyspnoea, fibrosis
Systemic- Extrathoracic lymphadenopathy, eye changes (uveitis, iritis), skin lesions (red-brown to purple maculopapular lesions), hepatic lesions and bone marrow involvement also occur frequently.
Parotid gland enlargement is a frequent finding in children with sarcoidosis, particularly early onset. (13%)
Neurologic involvement is rare but may cause seizures, CN or hypothalamic dysfunction.
The course is variable, treatment is supportive/symptomatic +/- corticosteroids to suppress acute manifestations.
How do you calculate the A-a (PAO2-PaO2) gradient (esp partial pressure of arterial oxygen)?
PAO2 = (pressure of inspired air - water vapour)x FIO2 -(PaCO2 x 1/R)
R= 0.8, FIO2 depends on if you are in air or on o2
PaC02 usually about 36mmhg
1/R =1/0.8 = 1.25
PAO2 = (760mmhg - 47mmhg) x FIO2 - (36mmhg x 1.25)
= 713mmhg x FI02 - 45
In normal people it the A-a gradient is about 20
What shifts the oxygen dissociation curve to the right? (Hb has less affinity for oxygen = increased RELEASE into tissues)
Increased temperature (Fever) Increased 2-3 DPG Decreased pH Increased C02 Adult haemaglobin
Note:If curve moves right a higher PO2 is required for Hb to bind a given amount of O2,
hence more oxygen is unloaded into tissues.
What shifts the oxygen dissociation curve to the left? (Hb has MORE affinity for oxygen = Decreased release into tissues)
Decreased temperature Decreased 2-3 DPG Increased pH Decreased C02 Fetal haemaglobin
Note: If curve moves left a lower PO2 is required for Hb to bind a given amount of O2
• Therefore, there is increased affinity of Hb for oxygen in the lungs, but less available to tissues
Why is 2,3 DPG important in the oxygen dissociation curve?
• 2,3 DPG binds to beta-chain of deoxygenated Hb to liberate O2
• 2,3 DPG is increased in states requiring more O2 delivered to tissues e.g.
altitude, anaemia, chronic hypoxia, exercise, thyroid hormones, growth
hormones, androgens.
• Note HbF γ chains bind 2,3 DPG poorly. Hence HbF has increased affinity for O2.
• 2,3 DPG levels fall in stored blood reducing the ability of this blood to release O2 to tissues.
How do you associate the Sp02 with Pa02 (mmhg)?
Oxygen dissociation curve
• This answer can be determined from the
oxygen-haemoglobin dissociation curve
• As Pa02 falls, the haemoglobin saturation (sp02)
also falls, as haemoglobin releases oxygen
to the tissues.
• From a saturation of 90%, the dissociation
curve drops off sharply
• An 02 sat of 90% corresponds to a Pa02 of
60mmHg, the minimum oxygen
concentration providing enough oxygen to
prevent tissue ischaemia
This can be remembered by: Hb saturation (%) Approx Pa02 (mmHg) 70 40 80 50 90 60
What is Pulmonary sequestration?
Thoracic lesion which appears to have a SYSTEMIC blood supply as seen on antenatal USS (receives blood supply from systemic arteries and returns blood to right side of heart via vena cava)
CT- air-filled cysts of varying size. Thickening and collapse are present within the same areas
- It does not have any role in gas exchange
- Intrapulmonary sequestrations usually occur in lower lobes.
- Extrapulmonary sequestrations almost always involve left lung
- Can have cysts present in the lesion
What is Cystadenomatoid malformation?
- MOST COMMON congenital lung lesion
- Consists of hamartomatous or dysplastic lung mixed with normal lung
- Can be macrocystic or microcystic but DOES NOT have systemic blood supply
What is a Bronchogenic cyst?
- Bronchogenic cysts usually found on right near midline structure
- Appears as a single cyst which may have air fluid levels in infective states
What us congenital Lobar emphysema?
• Congenital lobar emphysema affects middle and upper lobes exclusively (not as
frequently seen on antenatal scans)
• Present with respiratory distress and hyperinflation
• A polyalveolar lobe is a form of congenital emphysema
What does a restrictive pattern show on PFTS?
Normal FEV1:FVC but FVC <70% of normal
What does an obstructive pattern show on PFTS?
FEV1:FVC <70%
What does respiratory muscle weakness pattern shown on PFTS?
FEV1:FVC ratio would be normal, but the FVC would be a lot lower
Vascular ring
Chronic wheezing exacerbation by crying, feeding, flexion of neck
Can get choking
Stridor that changes with position
Pneumonia
Xr- indentation of posterior wall of oesophagus
FRC
-Expiratory reserve volume and residual volume.
-Occurs at passive end of respiration
-At this point, the tendency for the lungs to collapse inwards is balanced by the tendency for the chest to spring outwards
- Determined by the compliance of the lung and chest wall
-
Inspiratory capacity
Inspiratory reserve + TV
Vital capacity
IRV + TV (IC) + ERV
factors affecting FRC
Loss of lung compliance causes a reduced FRC:
- Anything that reduces the outward mobility of the chest wall reduces its compliance: examples of this are severe obesity or constrictive bandages.
- Likewise, anything that reduces the volume of the lungs reduce their compliance, examples of this are pulmonary oedema, fibrosis, consolidation or increased intra-abdominal pressure.
Factors affecting compliance
Compliance changes in various disease states. For example, in fibrosis the lungs become stiff, making a large pressure necessary to maintain a moderate volume. Such lungs would be considered poorly compliant.
However, in emphysema, where many alveolar walls are lost, the lungs become so loose and floppy that only a small pressure difference is necessary to maintain a large volume. Thus, the lungs in emphysema would be considered highly compliant.
Vit D and pulmonary disease
There is growing evidence of the role of vitamin D in lung development and the pathogenesis of pulmonary disease. A review article by Konstantinopoulou and Tapia (2017) has collated the current research and evidence in this area.
A: Vitamin D has been shown to have a physiological role in type 2 pneumocyte maturation and thereby increase surfactant synthesis.
B: Vitamin D (calcitriol) has been shown to inhibit platelet-derived growth factor induced airway smooth muscle mass.
C: An animal-model study investigating the effect of vitamin D deficiency on somatic growth, lung function and lung structure, showed the Vitamin D deficient mice had reduced lung volumes at 2 weeks of age compared to matched controls.
D: Studies have shown a correlation with low maternal intake of vitamin D in pregnancy and recurrent wheezing in preschool children and development of asthma by five years of age.
E: Vitamin D insufficiency has been associated with lower mean FEV1. A study have also shown an inverse relationship between vitamin D levels and use of inhaled corticosteroids or leukotriene inhibitors.
Congenital central hypoventilation syndrome
-rare genetic disorder characterized by sleep-related hypoventilation, autonomic nervous system dysfunction, and increased risk for Hirschsprung disease and tumors of neural crest origin (neuroblastoma, ganglioneuroma, or ganglioneuroblastoma)
- PHOX2B mutations (90% polyalanine repeats)
- AD but 92% de novo
- Usually normal delivery. Symptoms of cyanosis and shallow breathing during sleep but no respiratory effort to counteract cyanosis (no response to hypoxia or hypercapnea)
- most neonates need intubation and ventilation but minimal rates, pressures and oxygen
- During wakefulness, the child with CCHS has an absent to diminished response to hypoxia and hypercapnia and has no subjective sensation of dyspnea or discomfort
See uptodate for more
CCHS and ROHHAD syndrome
-Both congenital central hypoventilation and ROHHAD syndrome are associated with tumours of neural crest origin. CCHS is primarily associated with neuroblastoma and ROHHAD with ganglioneuromas and ganglioneuroblastomas.
All have a lack of symptomatic response to hypoxia and have a lack of symptomatic response to hypercapnoea.
In general, both CCHS and ROHHAD are associated with autonomic dysfunction.
ROHHAD is distinguished from CCHS by unique clinical characteristics and lack of PHOX2B mutations.
- ROHHAD has ++ weight gain with assoc hyperphagia
- ROHHAD has mix OSA and central
- ROHAAD has hypothalamic/gonadal axis issues and hypopit sx
Estimating CO using Fick’s principle
O2 consumption (ml/min)/ Ao sats- venous sats (ml/l)
= CO (L/min)
How to calculate Qp:Qs
Sat Ao - Sat MV/Sat PV- Sat PA
Ao= aorta MV= mixed venous PV= pulmonary vein PA= pulmonary artery
Factors affecting clinical cyanosis
Fever, metabolic acidosis, adult Hb
–>shifts dissociation curve to the right
–> polycythemic patients have the easiest detectable cyanosis due to increase in Hb concentration
◾As a result, at a given arterial PO2, there is increased oxygen delivery to the tissues resulting in a greater concentration of reduced haemoglobin, and cyanosis appears more readily
Hypothermia, alkalosis, fetal Hb
–> Shift dissociation curve to the left
–> anaemia pts have less circulating Hb
Cyanosis harder to detect
Factors affecting oxygenation
◾FiO2
◾Mean airway pressure
◾Lung volume
Factors affecting ventilation (Co2)
◾Minute volume, which equals to tidal volume x resp rate
◾MV = VT x RR
A higher minute volume will remove more CO2 and thus decrease the arterial CO2 concentration
HF ventilation
High frequency ventilation (HFV) delivers small volumes of air, which are equal to or smaller than anatomic dead space, at an extremely rapid rate (300 to 1500 breaths per minute).
Each HF ventilator applies continuous distending pressure to maintain lung expansion and superimposes small tidal volumes at a rapid rate.
PaO2 is dependent on Paw (Mean airway Pressure) and FiO2.
PaCO2 is dependent on delta P and frequency.
Mean airway pressure has the most important effect on oxygenation, as altering to optimal levels will change lung volume, improve VP matching, and decrease shunting.
After second dose surfactant
- causes increased mean airway pressure (MAP) (from improvement in the compliance and hence increased lung expansion)
- increased MAP causes decreased venous return and hence, reduction in cardiac output reflected by increased HR and decreased MABP
