Breathlessness- Examinations Flashcards
Reasons to request an arterial blood gas
• Acid base balance disturbances= acidosis or alkalosis, Respiratory or Metabolic
• Respiratory disturbances= oxygenation and ventilation adequate. Hypoxemia, hypercapnia, respiratory failure
Values checked in an arterial blood gas
• PH
• PaO2
• PaCO2
• Bicarbonate (HCO3)
• Base excess
• Carboxyhemoglobin
• Methemoglobin
• Hemoglobin, lactate, sodium, potassium
Blood- pH values
• Normal 7.35-7.45
• <7.35= Acidaemia
• >7.45= Alkalemia
Arterial blood gas- bicarbonate values
• Normal range 22 – 26
• Can be altered as part of a primary metabolic derangement
• The kidneys can excrete or retain bicarbonate to counter a respiratory disturbance (compensatory mechanism)
• Use either Base excess or bicarbonate to look at metabolic status
• >26 mmol/l -> alkalosis
• <22mmol/l -> acidosis
Base excess values
• Range is -2 to +2
• Derived value -> not actually measured but calculated by the machine
• How much acid (H+) must be added or removed from blood to bring it’s PH back to normal
• BE < -2 = acidosis
• BE > +2 = alkalosis
Acid base balance
• The most important buffer system in the body is the carbonic acid-bicarbonate system
• H2O+CO2 = H2CO3 = HCO3-+H+
• Main enforcers are the kidneys and lungs= Adjusting ventilation affects CO2 concentrations, Rate of excretion of HCO3 and H+ controlled by the kidney
Metabolic acidosis- anion gap
• In blood the number of cations (+) is equal to anions (-)
• Adding all the measured cations and anions together gives a gap which reflects anions which are not measured (plasma proteins and organic acids)
• (sodium+potassium) - (chloride+bicarbonate) = Anion Gap
• Normal anion gap is 10-12
• If high represent additional anion (acid) in the blood
Arterial blood gas- PaCO2
• 4.5-6.0 Kpa
• Measures how good ventilation is
• >6.0 Kpa hypercapnia -> hypoventilation -> respiratory acidocis
• <4.5 Kpa hypocapnia -> hyperventilation -> respiratory alkalosis
• Type 2 respiratory Failure PaCo2 of > 6 Kpa
Causes of type 2 respiratory failure- PUMP failure
• Lungs -> COPD, severe asthma
• Outside the lungs -> fluid (effusion, ascites) , air ( pneumothorax) , fat(Obesity hypoventilation syndrome) , bones( scoliosis)
Causes of type 2 respiratory failure- nerve muscle complex (messenger carrier)
• Central- stroke, tumour, opoids, heroin
• Peripheral nerves- motor neuron diseases, bilateral diaphragm palsy
• Neuromuscular junction- myopathy, diaphragm palsy
Arterial blood gas- PaO2 (partial pressure of oxygen)
• In room air= >12 kpa (10 kpa for the elderly)
• <12 Kpa is hypoxemia
• <8kpa type 1 respiratory failure
• FiO2- fraction of oxygen in the inspired air, 21% or 0.21 of room air
Different devices used for air flow
• Nasal canulae, 2-4 L/min, 0.28-0.35
• Hudson mask, 6-10 L/min, 0.35-0.5
• Non re-breathe mask, 5-15 L/min, 0.6-0.9
• Venturi mask, 2-15 L/min, 0.24, 0.28, 0.31, 0.35, 0.40, 0.6
• Humidified oxygen, 2-15 L/min, 0.24-0.6
• High flow nasal oxygen, over 40L/min, 0.35-1ish with mouth closed
Causes of hypoxaemia
• Ventilation perfusion mismatching (e.g Pulmonary embolism)
• Right to left Shunt (cardiac or pulmonary)
• Decreased Oxygen Diffusion (e g Pulmonary fibrosis)
• Hypoventilation (Heroin overdose)
• Low oxygen content of air (at heights)
Blood gas-oxygen
• Rule of thumb to check for hypoxemia is “the Pao2 should be 10-15 kpa less then the FiO2”
• Example= on room air(Fio2 21%) you would expect the Pao2 to be -> 21-10= 11 Kpa (normally 10-14 kpa)
• If someone is on oxygen with a 40 % Venturi mask(FIo2 is 40%) , there PaO2 should be -> 40-15= 25 Kpa( 25-30 Kpa)
Alveolar arterial gradient (A-a)
• Difference between alveolar concentrations of oxygen and arterial concentrations of oxygen. Measure of the alveolar gas exchange
• Normal A-a gradient= Alveolar hypoventilation (Opoid), Low oxygen content (at heights)
• Raised A-a gradient= Diffusion defect (Pulmonary fibrosis), V/Q mismatch (Pulmonary embolism), Right to left shunt (intrapulmonary or cardiac)
Oxygen- Haemoglobin dissociation curve
• A non linear relationship, after a certain saturation it drops steeply
• Oxygen is mainly carried combined to Hb
• Left shift= Higher Hb-O2 affinity (lower, CO2, higher pH, lower temperature)
• Right shift= Reduced Hb-O2 affinity (Higher COS, lower pH, higher temperature)
Hypoxaemia and Hypoxia
• Hypoxemia -> Low Oxygen in the blood , PaO2 <12 Kpa
• Hypoxia -> reduced oxygen delivery to the cells causing them to switch to anaerobic respiration
What can Hypoxia be due to
• Poor oxygenation of the blood aka hypoxemia
• Poor oxygen carrying capacity ( anemia )
• Poor delivery of oxygen/blood to the cells( Shock)
• Cells not being able to use the oxygen for aerobic respiration (e.g Cyanide poisoning)
Steps to interpreting an arterial blood gas
• 1st Step check the PH and determine whether it is academic or alkalemic
• 2nd step Check the PCO2 and decide whether it is a primary metabolic or respiratory disorder
• 3rd Step check at the Bicarbonate or base excess to confirm your conclusion about nature of disorder
• 4th Check the oxygen to rule out hypoxemia
Advanced steps for an arterial blood gas
• If metabolic acidosis -> Check the Anion gap to determine whether anion gap or normal anion gap acidosis
• For all disorders check compensatory response is adequate (change in PCO2 for metabolic, change In bicarbonate for respiratory)
• If Metabolic acidosis check the Pco2 is adequately reduced to rule out a superadded respiratory acidosis
• A-a gradient for hypoxemic patients
Arterial blood gas- ROME mneomonic
• Respiratory opposite= if the pH is up and Pco2 is down then its respiratory alkalosis. If the pH is down and the Pco2 is up then its respiratory acidosis.
• Metabolic equal= If the pH and HCO3 are up then its metabolic alkalosis. If the pH and HCO3 are down then its Metabolic acidosis
Arterial blood gas- rule of thumb
• Metabolic problems PH and PCO2 move in the same direction i.e. both go up
• In Respiratory Problems they tend to move in opposite directions
• Problem is mixed defect – both respiratory and metabolic acidosis etc
Metabolic acidosis
pH, PCO2, Bicarbonate and base excess all go down
Causes of metabolic acidosis- Diabetic ketoacidosis, Salicylate OD, Shock, Sepsis, Severe diarrhoea, Renal failure
Metabolic alkalosis
pH, Pco2, Bicarbonate, base excess all went up. Change to PCO2 is minimal
Causes of metabolic alkalosis
• Drugs – diuretics , steroids
• GI loss – vomiting ,Bulemia , diarrhoea etc
• Renal loss – aldosterone excess , liquorice
• Hypokalemia
Respiratory acidosis
• Acute respiratory acidosis= pH goes down, pCo2 goes up, Bicarbonate doesn’t change
• Chronic respiratory acidosis= pH doesn’t change, pCo2 goes up, Bicarbonate goes up
Obtaining chest x-rays
Well patients stand postero-anterior , the x-ray beam travels from back to front. The arms are lifted to the side, so that the scapulae are lifted out of the lung fields. If the patients are too unwell a portable x-ray can be used, and an antero-posterior chest x-ray is taken in the sitting or lying position
Technical analysis of the x-ray
RIPE
• R- Rotation
• I- Inspiration
• P- Projection
• E- Exposure
RIPE- RI
Rotation- the spinal processes should be aligned vertically. The medial ends of the clavicle should be equidistant from the spinous process
Inspiration- poor inspiration may be seen in unwell patients i.e. due to pain, exhaustion. 5-6 ribs should be visible anteriorly above the diaphragm (10 ribs posteriorly). The patient is asked to take a derp breath for the chest x-ray.
RIPE- PE
Projection- describe the direction of the x-ray beam in relation to the patient. Anterior posterior (AP) or Poster-oanterior (PA), the standard position is PA. The scapulae overlies the lung field on AP film.
Exposure- assessed by looking at the cardiac shadow. The vertebral bodies should only just be visible through the cardiac shadow. If very visible its an over penetrated film, low density lesions may be missed. If not visible, there is inadequate penetration, the lung fields will appear falsely white.
Chest x-ray ABCDE approach
A-airway
• Is the trachea central?
• Carina: located at the point the trachea divides into the right and left main bronchi
• Left main bronchus
• Right main bronchus: steeper angle, shorter and wider than the left. Therefore foreign bodies more likely to lodge here
• Hilar structure: pulmonary vessels, major bronchi and lymph nodes, should appear symmetrical in normal x-rays
Chest x-ray ABCDE approach
B-breathing
• The pleura should not be visible in well individuals, it can be thickened in mesothelioma
• Check that the lung markings extend all the way to the pleura (otherwise consider a pneumothorax)
• Divide each lung into 3 zones: upper, middle and lower
• Check that the lung markings cover the entire zone
• Look for any areas of increased opacity, comparing sides
Chest x-ray ABCDE approach
C-circulation
• Heart size: can only be assessed in PA films, the cardiothoracic ration should be <0.5
• Heart borders: on the right side it made up mainly on the right atrium, the left is predominantly the left atrium
• Loss of definition of the left heart border is associated with lingular consolidation
• Loss of definition of the right heart border is associated with middle lobe consolidation
• The width of the heart should be less than half the width of the distance from the lateral edges of the lungs
• Aorto-pulmonary window (the space between the aortic arch and the pulmonary arteries)- may be obscured by mediastinal lymphadenopathy is present
• Aortic knuckle (the aortic arch crossing the left main bronchus)- can appear irregular in aortic aneurysm
Chest x-ray ABCDE approach
D-diaphragm
• The right hemidiaphragm is higher than the left (normal is <3cm difference)
• The diaphragm should not separate from the underlying liver – air below the diaphragm suggests visceral perforation
• The costophrenic angles should be clearly defined with acute angles
• Blurring of the costophrenic angles occurs with consolidation or pleural effusions
Chest x-ray ABCDE approach
E-everything
• Bones- any fractures or lytic lesions
• Soft tissues- swellings or subcutaneous emphysema
• Drains/ pacemakers/ lines/ tubes/ artificial valves
Conduction in the heart
Discharge spreads from the SA node across the atrium to the AV node, There is a short pause before the conduction is spread to the ventricles via the bundle of His
Basic ECG SHAPE
• P wave- atrial depolarisation
• QRS- depolarisation of the ventricles
• T wave- repolarisation of the ventricles
ECG lead position
• Limb leads: I, II, III, aVR, aVL, Avf
• Chest leads: V1, V2, V3, V4, V5, V6
• Rhythm strip- recorded from lead 2
ECG leads and anatomy
• Lateral part of the heart: I, aVL, V5, V6
• Anterior parts of the heart: V1, V2, V3
• Inferior part of the heart: II, III, aVF
Systematic reading of an ECG
• Rate, rhythm, axis
• Abnormalities in the P wave, PR interval, QRS complex, ST segment and T wave
ECG- rate
• Add up the number of large squares between each QRS complex
• Divide 300 by that number to get the heart rate
• So if there is 5 squares between each complex 300/5= 60, so the heart rate is 60
ECG- rhythm
In normal sinus rhythm each QRS complex is preceded by a P wave with an equal distance between the QRS complex, this is the PR interval. Shows whether the rhythm is regular or irregular
ECG- axis
• The predominant axis of the normal heart spreads from the right atrium to the left ventricle, on an ECG this is lead II
• A normal axis is between 90 degrees and -30 degrees which is a big range
• The QRS complex is negative in aVR and positive in lead II
• If the QRS is positive in leads I and II then that means the axis is normal
P wave, PR interval and ST segment
P wave and PR interval= in sinus rhythm the length of the PR interval is consistent (normally between 3-5 small squares)
ST segment: the flat line between the QRS complex and the start of the T wave, the interval between ventricular depolarisation and repolarisation. ST segment elevation or depression suggests either myocardial infarction or ischaemia
QRS complex
• Key waves are the part of the QRS complex that goes downwards, large key waves suggest a recent myocardial infarction.
• The R wave is the first upwards deflection after the P wave and the S wave is the downwards deflection.
• A normal QRS segment is less than 3 small squares, a broad complex is bigger then 3 squares and is either ventricular in origin or suggests a problem with conduction such as bundle branch block
T wave
• Represent ventricular repolarisation, changes in the T wave can occur in myocardial infarction, high or low levels of potassium, cardiomyopathy and in subarachnoid haemorrhage.
• The distance between the Q wave and the end of the T wave is the QT interval, this distance is related to the heart rate.
• The QT interval can lengthen with various metabolic and electrolyte issues, certain drugs or can be congenital.
• Abnormally prolonged QT is associated with arrhythmias
Spirometry
Medical screening test- registers amount of air a subject inhales or exhales, rate at which air is moved into or out of the lungs, performed using a spirometer.
Spirometers- wedge bellows, rotating vane, pneumotachographs, ultrasonic
Wedge bellow
• Bellows mounted in a box
• Bellows expand pushing the stylus upwards when patient expires
• Stylus moves across a pressure sensitive paper and makes a recording
• Bellows are calibrated so the stylus moves the appropriate distance to record the correct volume on the chart paper
• Electric motor drives the chart horizontally to give a record of volume against time
• Advantages: simple, reliable, accurate
• Disadvantages: expired measurements only, big and bulky. Recalibration requires specialist medical engineer, inside cannot be cleaned
What are you measuring using a spirometer
• RVC (litres) Relaxed Vital Capacity: max volume expired from full inspiration, but done at a relaxed or steady pace
• FEV1 (litres) Forced Expiratory volume in 1 second: maximum volume of air expired from the lungs in the first second of a forced
• FVC (litres) Forced Vital Capacity: maximum volume of air expired from the lungs during a forced and complete expiration from full inspiration
FEV/VC ratio or expiratory ratio
• FEV1 / VC%
• FEV1 expressed as a percentage of VC
• Largest acceptable FEV1 divided by largest acceptable VC multiplied by 100
Why do we perform spirometry
• Detect presence or absence of disease
• Quantify the extent of known disease
• Monitor deterioration of disease
• Measure effects of therapy
• Assess risk for surgical procedures
Contraindications: when not to perform spirometry
• Recent MI (within 1 month)
• Pneumothorax
• Recent thoracic, abdominal or eye surgery
• Haemoptysis of unknown origin
• Vomiting, generally unwell
• Confusion, dementia
What should patients avoid when performing a spirometer
• Short-acting bronchodilators for 4 hrs
Long-acting bronchodilators for 12 hrs
• Short-acting antichollinergics for 6 hrs
• Long-acting antichollinergics for 24 hrs
• Performing vigorous exercise 30mins
• Smoking 24hrs
• Wearing tight-fitting clothing
• Alcohol consumption 4hrs
•Eating a substantial meal 2hrs
How to perform spirometry
Should be performed with the patient sitting upright in a chair with both feet on the floor. Hold the spirometer in one hand, don’t have the other arm folded across chest
Test procedure- RVC
• Take in as deep a breath as possible through the mouth
• Place lips and teeth around the mouthpiece to make a tight seal
• Blow out at a steady speed until completely empty
• Needs to be repeated until 3 relaxed manoeuvres that match within 5% or 100ml are performed. Up to 4 attempts should be made to achieve reproducibility
Test procedure- FEV1 and FVC
• Take in as deep a breath as possible through the mouth
• Place lips and teeth around the mouthpiece to make a tight seal
• Blow out as fast and forcefully as possible and to keep on blowing for as long as possible
• Fast start and expiration time >6 seconds
• Tests needs to be repeated until 3 forced manoeuvres that match FEV and FVC within 5% or 100ml are performed. Up to 9 attempts should be made to achieve reproducibility
A spirometry result can be rejected on the following grounds
• A leak at the mouth
• An obstructed mouthpiece due to tongue or teeth
• A poorly co-ordinated start to the test so that the blow starts slowly and “builds up” to a high flow.
• A cough within the first second of the test – may give spuriously high FEV1
• A cough during the test that is deemed to interfere with the blow
• Early termination of the blow – every subject should try to keep blowing for a minimum of 6 seconds
• The subject did not inspire fully – watch out for the “Ted Heath” who raises his shoulders but does not take a breath in!!
• The expiratory effort was submaximal.
• Unable to reproduce best effort
How many times to repeat spirometry
Asthmatics may struggle doing repeated tests due to bronchoconstriction
• Largest FVC & Largest FEV1 from different efforts can be reported (as long as within 5% or 100ml)
• Examine RVC & FVC- use whichever is largest to calculate ratio & call this VC
Calculating % Predicted= (Measured / Predicted) x 100
Normal values for spirometry
• FEV >80%
• FVC >80%
• FEV/VC >70%-80% (depends on age)
Obstructive lung disease- spirometry values
• FEV1- low
• FVC- normal/low
• FEV1/VC- <70%
Restrictive lung disease- spirometry values
• FEV1- low
• FVC- low
• FEV1/VC >70%
Airway obstruction
Narrowing of the airways due to: contraction of smooth muscle (bronchoconstriction), inflammatory changes and mucus secretions.
Hallmarks of obstructive lung disease
• Reduced Expiratory ratio (FEV1/VC%)
• Reduced FEV1
• Maintained VC
• Increased exhalation time
• Late or no plateau on volume-time curve
• Diseases: COPD, asthma, bronchiectasis, Sarcoidosis, Bronchial tumours
Hallmarks of restrictive lung problems
• Reduced VC and FEV1
• Normal or elevated expiratory ratio (FEV1/VC %)
• Reduced exhalation time
• Early plateau on volume time curve
• Intra pulmonary conditions: Pulmonary fibrosis, Sarcoidosis, Asbestosis, Fibrosing Alveolitis
• Extrapulmonary conditions: Kyphoscoliosis, Ankylosing spondylitis, Lung volume reduction surgery, Muscle weakness
Peak expiratory flow
A persons maximum speed of expiration as measured with a peak flow meter, a small hand-held device used to monitor a persons ability to breathe out air. It measures the airflow through the bronchi and thus the degree of obstruction in the airways.
When to use peak flow
• Peak flow is useful when you are considering obstructive airway conditions such as asthma.
• Due to the longer term obstructive nature of COPD, spirometry is of more value in the diagnosis of this.
Diagnosis in asthma
Diurnal variability of peak expiratory flow rate (PEFR) greater than 20% for at least three days in a week for two weeks is typical of asthma. OR
Improvement in PEF:
• 10 minutes after high-dose bronchodilator through a spacer.
• After a six-week course of inhaled steroids.
• After 14 days of 30 mg prednisolone.
