resp Flashcards
Control of respiration
Central regulatory centres
* Central and peripheral chemoreceptors
* Pulmonary receptors
Central regulatory centres
- Medullary respiratory centre
- Apneustic centre (lower pons)
- Pneumotaxic centre (upper pons)
Central and peripheral chemoreceptors
Central: raised [H+] in ECF stimulates respiration
* Peripheral: carotid + aortic bodies, respond to raised pCO2 & [H+], lesser extent low pO2
Pulmonary receptors
- Stretch receptors, lung distension causes slowing of respiratory rate (Hering-Bruer reflex)
- Irritant receptor, leading to bronchoconstriction
- Juxtacapillary receptors, stimulated by stretching of the microvasculature
Chloride shift
CO2 diffuses into RBCs
* CO + H O —- carbonic anhydrase -→ HCO - + H+ 223
* H+ combines with Hb
* HCO - diffuses out of cell,- Cl- replaces it
Bohr Effect
Increasing acidity (or pCO2) means O2 binds less well to H
Haldane effect
↑ pO2 means CO2 binds less well to Hb
Tidal Volume (TV)
Volume inspired or expired with each breath at rest
* 500ml in ♂s, 350ml in ♀s
Inspiratory Reserve Volume (IRV) = 2-3 L
Maximum volume of air that can be inspired after normal tidal inspiration
* Inspiratory capacity = TV + IRV
Expiratory Reserve Volume (ERV) = 750ml
Maximum volume of air that can be expired after normal tidal expiration
Residual volume (RV) = 1.2L
Volume of air remaining after maximal expiration
* ↑ with age
* RV = FRC – ERV (Functional Residual Capacity - Expiratory Reserve Volume)
Vital Capacity (VC) = 5L
Maximum volume of air that can be expired after a maximal inspiration
* 4,500ml in ♂s, 3,500 mls in ♀s
* ↓ with age
* VC=IC+ERV
Obstructive lung disease
FEV1 - significantly ↓ FVC - ↓ or normal (FEV1/FVC) - ↓
Asthma
COPD
Bronchiectasis Bronchiolitis obliterans
Restrictive lung disease
FEV1 - ↓
FVC - significantly ↓ (FEV1/FVC) - normal or ↑
Pulmonary fibrosis
Asbestosis
Sarcoidosis
Acute respiratory distress syndrome Infant respiratory distress syndrome Kyphoscoliosis
Neuromuscular disorders
Causes of ↑ compliance
of ↑ compliance * Age
* Emphysema
Causes of ↓ compliance
- Pulmonary edema
- Pulmonary fibrosis * Pneumonectomy
- Kyphosis
Oxygen dissociation curve shifts
Shifts Right - Raised oxygen delivery - Raised acidity, Temp, 2-3 DPG
* Shifts Left - Lower oxygen delivery - Lower acidity, Temp, 2-3 DPG - also HbF,
carboxy/methemoglobin
Oxygen Dissociation Curve
describes the relationship between the percentage of saturated hemoglobin and partial pressure of oxygen in the blood. It is not affected by hemoglobin concentration, but affected by its quality (HbF, methemoglobin).
Basics
Oxygen Dissociation Curve RIGHT
Shifts to right = for given oxygen tension there is ↓ saturation of Hb with oxygen i.e. Enhanced oxygen delivery to tissues
Shifts to Right = Raised oxygen delivery
* Raised [H+] (acidity)
* Raised PCO2
* Raised 2,3-DPG
* Raised temperature
Oxygen Dissociation Curve LEFT
Shifts to left = for given oxygen tension there is ↑ saturation of Hb with oxygen i.e. ↓ oxygen delivery to tissues
- HbF, methemoglobin, carboxyhemoglobin
- Low [H+] (alkali)
- Low PCO2
- Low 2,3-DPG
- Low temperature
Left shift - affinrt
Left shift of the curve is a sign of hemoglobin’s ↑ affinity for oxygen (eg. at the lungs). Similarly, right shift shows ↓ affinity, as would appear with an ↑ in body temperature, hydrogen ion, 2,3- diphosphoglycerate (also known as bisphosphoglycerate) or carbon dioxide concentration (the Bohr effect)
Transfer factor
Raised: asthma, hemorrhage, left-to-right shunts, polycythemia
* Low: everything else
Transfer factor
he transfer factor describes the rate at which a gas will diffuse from alveoli into blood. Carbon monoxide is used to test the rate of diffusion. Results may be given as the total gas transfer (TLCO) or that corrected for lung volume (transfer coefficient, KCO)
Causes of a raised TLCO
Asthma
* Pulmonary hemorrhage (wegener’s, goodpasture’s)
* Left-to-right cardiac shunts
* Polycythemia
* Hyperkinetic states
* ♂ gender, exercise
Causes of a lower TLCO
- Pulmonary fibrosis
- Pneumonia
- Pulmonary emboli
- Pulmonary edema
- Emphysema
- Anemia
- Low cardiac output
KCO also tends to ↑ with age (used to diagnose or R/O interstitial lung disease). Some conditions may cause ↑ KCO with a normal or ↓ TLCO
Pneumonectomy/lobectomy * Scoliosis/kyphosis
* Neuromuscular weakness
* Ankylosis of costovertebral joints e.g. Ankylosing spondylitis
ulmonary arteries vasoconstrict
vasoconstriction of the pulmonary arteries. This allows blood to be divered to better aerated areas of the lung and improves the efficiency of gaseous exchange
The following can cause Asthma:
Isocyanates
* Platinum salts
* Soldering flux resin
* Glutaraldehyde
* Flour
* Epoxy resins
* Proteolytic enzymes
↑ possibility of asthma
Wheeze, breathlessness, chest tightness and cough, worse at night/early morning
* History of atopic disorder
* Wheeze heard on auscultation
* Unexplained peripheral blood eosinophilia
↓ possibility of asthma
Prominent dizziness, light-headedness, peripheral tingling
* Chronic productive cough in the absence of wheeze or breathlessness
* Repeatedly normal physical examination
* Significant smoking history (i.e. > 20 pack-years)
* Normal PEF or spirometry when symptomatic
For patients with an intermediate probability of asthma further investigations are suggested. The guidelines state that spirometry is the preferred initial test:
FEV1/FVC < 0.7: trial of treatment
* FEV1/FVC > 0.7: further investigation/consider referral
Stepwise management of stable asthma
1st Inhaled short-acting β2 agonist as required (e.g Sulbutamol PRN)
2nd Add inhaled steroid at 200-800 mcg/day (beclometasone dipropionate or equivalent)
400 mcg is an appropriate starting dose for many patients. Start at dose of inhaled steroid appropriate to severity of disease
. Add inhaled long-acting β2 agonist (LABA)
2. Assess control of asthma:
* Good response to LABA - continue LABA
* Benefit from LABA but control still inadequate: continue LABA and ↑ inhaled
steroid dose to 800 mcg/day* (if not already on this dose)
* No response to LABA: stop LABA and ↑ inhaled steroid to 800 mcg/ day.* If control
still inadequate, institute trial of other therapies, leukotriene receptor antagonist or SR theophylline
Consider trials of:
* Increasing inhaled steroid up to 2000 mcg/day
* Addition of a fourth drug e.g. Leukotriene receptor antagonist, SR theophylline, β2
agonist tablet
Leukotriene Receptor Antagonists:
.g. Montelukast (causes Churg-Strauss syndrome), zafirlukast
* Have both anti-inflammatory and bronchodilatory properties
* Should be used when patients are poorly controlled on high-dose inhaled corticosteroids and a
long-acting β2 agonist
* Particularly useful in aspirin-induced asthma
* Associated with the development of churg-strauss syndrome
Fluticasone
s more lipophilic and has a longer duration of action than beclometasone
Hydrofluoroalkane
now replacing chlorofluorocarbon as the propellant of choice. Only half the usually dose is needed with hydrofluoroalkane due to the smaller size of the particles
Long acting β2 agonists (LABA)
bronchodilators but also inhibit mediator release from mast cells. Recent meta- analysis showed adding salmeterol improved symptoms compared to doubling the inhaled steroid dose
Moderate asthma
PEF > 50% best or predicted
* Speech normal
* RR < 25 / min
* Pulse < 110 bpm
severe asthma
PEF 33 - 50% best or predicted
* Can’t complete sentences
* RR > 25/min
* Pulse > 110 bpm
life threatening asthma
- PEF < 33% best or predicted
- SpO2 < 92%
- Silent chest, cyanosis or feeble respiratory effort
- Bradycardia, dysrhythmia or hypotension * Exhaustion, confusion or coma
asthma non responding to treatment
British Thoracic Society guidelines 2003 (updated 2004)
* Magnesium sulphate recommended as next step for patients who are not responding (e.g. 1.2 -
2g IV over 20 mins)
* Little evidence to support use of IV aminophylline (although still mentioned in management
plans)
* If no response consider IV salbutamol
* If the patient is developing respiratory acidosis (pH <7.35) consider intubation
COPD causes
Smoking.
* Alpha-1 antitrypsin deficiency
* Cadmium (used in smelting)
* Coal
* Cotton
* Cement
The following investigations are recommended in patients with suspected COPD:
To demonstrate airflow obstruction: post- bronchodilator spirometry: FEV1/FVC < 70%
* Chest x-ray: hyperinflation, bullae, flat hemidiaphragm. Also important to exclude lung cancer
* Full blood count: exclude secondary polycythemia
* Body mass index (BMI) calculation
Chronic Management: COPD
General management
* Smoking cessation advice
* Annual influenza vaccination
* Pneumococcal vaccination
Bronchodilator therapy
* Short-acting β2-agoinst (SABA) or short-acting muscarinic antagonist (SAMA) is 1st line Rx.
* For patients who remain breathless or have exacerbations despite using short-acting
bronchodilators the next step is determined by the FEV1
COPD treatment
FEV1 > 50% (Stage I and II)
Long-acting β2-agoinst (LABA), for
example salmeterol, or:
* Long-acting muscarinic antagonist
(LAMA), for example tiotropium
COPD treatment
FEV1 < 50% (stage III and IV)
LABA + inhaled corticosteroid (ICS) in a
combination inhaler, or: * LAMA
For patients with persistent exacerbations or breathlessness
- If taking a LABA then switch to a LABA + ICS combination inhaler
- Otherwise give a LAMA and a LABA + ICS combination inhaler
Oral theophylline
- NICE only recommends theophylline after trials of short and long-acting bronchodilators or to
people who cannot use inhaled therapy - The dose should be reduced if macrolide or fluroquinolone antibiotics are coprescribed
Cor pulmonale
Features include peripheral oedema, raised
JVP, systolic parasternal heave, loud P2
* Use a loop diuretic for oedema, consider
long-term oxygen therapy
* ACE-inhibitors, calcium channel blockers
and alpha blockers are NOT recommended by NICE
Factors which may improve survival in patients with stable COPD
Smoking cessation - the single most important intervention in patients who are still smoking
* Long term oxygen therapy in patients who fit criteria
* Lung volume reduction surgery in selected patients
long-term oxygen therapy (L TOT).
sess
* Very severe airflow obstruction (FEV1 <
patients if any of the following:
30% predicted). Assessment should be ‘considered’ for patients with severe airflow obstruction (FEV1 30-49% predicted)
* Cyanosis
* Polycythaemia
* Peripheral oedema
* Raised jugular venous pressure
* Oxygen saturations ≤ 92% on room ai
LTOT
Assessment is done by measuring arterial blood gases on 2 occasions at least 3 weeks apart in patients with stable COPD on optimal management.
Offer LTOT to patients with
< 7.3 kPa or tothosewithapO2 of7.3-8kPaandoneofthe following:
* Secondary polycythaemia
* Nocturnal hypoxaemia
* Peripheral oedema
Pulmonary hypertension
Benefits of LTOT:
- ↓ secondary polycythemia
- ↓ sympathetic activity → ↓ cardiac
arrhythmia - Improve sleep quality
Oxygen saturation targets
Acutely ill patients: 94-98%
* Patients at risk of hypercapnia (e.g. COPD patients): 88-92% (see below)
* Oxygen should be ↓ in stable patients with satisfactory oxygen saturation
Management of COPD patients O2 saturation
Prior to the availability of blood gases, use a 28% Venturi mask at 4 l/min and aim for an oxygen saturation of 88-92% for patients with risk factors for hypercapnia but no prior history of respiratory acidosis
* Adjust target range to 94-98% if the pCO2 is normal
Situations where oxygen therapy should not be used routinely if there is no evidence of hypoxia:
Myocardial infarction and acute coronary syndromes
* Stroke
* Obstetric emergencies
* Anxiety-related hyperventilation
Non-invasive ventilation - key indications
COPD with respiratory acidosis pH 7.25-7.35
* Type II respiratory failure secondary to chest wall deformity, neuromuscular disease or
obstructive sleep apnoea
* Cardiogenic pulmonary edema unresponsive to CPAP
* Weaning from tracheal intubation.
Recommended initial settings for bi-level pressure support in COPD
Expiratory Positive Airway Pressure (EPAP): 4-5 cm H2O
* Inspiratory Positive Airway Pressure (IPAP): RCP advocate 10 cm H20 whilst BTS suggest 12-
15 cm H2O
* FiO2: not > 40%
* Back up rate: 15 breaths/min
Back up inspiration:expiration ratio: 1:3
* Keep SpO2: 88-92%
* ABG every 1-2 hours
INVESTIGATION: The British Thoracic Society (BTS) published guidelines in 2003 on the
investigation of patients with suspected pulmonary embolism (PE)
Computed Tomographic Pulmonary Angiography (CTPA) is now the recommended initial
lung-imaging modality for non-massive PE. Advantages compared to V/Q scans include speed, easier to perform out-of-hours, a ↓ need for further imaging and the possibility of providing an alternative diagnosis if PE is excluded
* If the CTPA is negative then patients do not need further investigations or treatment for PE
* Ventilation-Perfusion scanning (V/Q) MAY BE USED INITIALLY IF appropriate facilities exist, the chest x-ray is normal, and there is no significant symptomatic concurrent
cardiopulmonary disease
Massive PE + hypotension →
thrombolyse
Ongoing anticoagulation with warfarin (Target INR 2 – 3) length of treatment:
Calf DVT: at least 6 weeks
* Proximal DVT or PE where there is transient risk factors: at least 3 months
* Idiopathic venous thromboembolism or permanent risk factors: at least 6 months
Thrombolysis
Thrombolysis is now recommended as the first-line treatment for massive PE where there is
circulatory failure (e.g. Hypotension). Other invasive approaches should be considered where appropriate facilities exist
CAP) may be caused by the following organisms:
Streptococcus pneumoniae (accounts for around 80% of cases)
* Hemophilus influenzae
* Staphylococcal aureus
* Atypical pneumonias (e.g. due to Mycoplasma pneumoniae)
* Viruses