CLIX Flashcards
Be familiar with the components of an Arterial Blood Gas: pH, pCO2, pO2, HCO3-, Base Excess, Anion Gap, p50, and the underlying physiology and anatomy for a normal result.
Units Reference range
pH 7.35 -7.45
pCO2 mmHg 35 - 45
pO2 mmHg 83 - 108
Oxygen saturation % 94 – 98
Bicarbonate mmol/L 18 – 26*
p50 mmHg 24 – 28
Base Excess mmol/L -2.0 to +3.0
Anion Gap: = (Na+) − (HCO3¯+ Cl¯)
Be able to interpret an Arterial Blood Gas analysis and to be able to distinguish between
metabolic and respiratory acidosis and alkalosis.
Correctly apply the compensation rules to identify a mixed acid-base disturbance
Metabolic acidosis: Winter’s formula: Expected level of pCO2 = 1.5 x bicarbonate level + 8 ±2 mmHg
Metabolic alkalosis: For every 1mmol/L↑ in HCO3─ above 24.4 mmol/L, pCO2↑above 40 mmHgby
0.6 - 0.75 mmHg, OR
Expected level of pCO2 = 0.7 x bicarbonate level + 20 ±5 mmHg
Respiratory acidosis: For every 10mmHg↑in pCO2 above 40 mmHg, HCO3 ─ ↑ above 24.4 mmol/L by
1 mmol/L (acute) or 4 mmol/L (chronic)
Respiratory alkalosis: For every 10mmHg↓in pCO2 below 40 mmHg, HCO3 ─ ↓ below 24.4mmol/L by
2 mmol/L (acute) or 5 mmol/L (chronic)
Understand the common causes of acid base disturbances and the underlying physiological
changes that have led to the presentations and results.
Understand the role of the ABG in interpreting oxygenation problems, the causes of shift in
the O2-Haemoglobin dissociation curve and carbon monoxide poisoning.
If the curve is shifted to the right, this means that the bond is weaker than normal, and that oxygen more readily
dissociates from haemoglobin as it passes through the tissues, and
oxygen delivery is therefore improved. In this situation, the P50 value is > 28mmHg.
When the curve is left-shifted, the affinity of haemoglobin and oxygen is increased (stronger binding) and oxygen delivery at tissue level is therefore decreased. The P50 value is < 24mmHg. As the blood flows past the respiratory membrane the haemoglobin avidly takes up oxygen when the curve is in the leftward position.
In summary, the p50 shows us the position of the curve, and infers the quality of oxygen delivery to the tissues. Factors which shift the curve to the right do so by exerting a conformational change in the haemoglobin molecule
by binding to the globin chain. This change lessens the strength of the bond between the iron and oxygen.
Understand the indications for an ABG, its limitations, its complications and the judicious use of ABG.
Clinical indications:
* Cardiorespiratory failure and/or Breathlessness (acute or chronic) to determine O2 or CO2.
* Metabolic disturbance eg DKA.
* Poisoning with drugs eg salicylate.
* CO poisoning (please note, cannot use haemoglobin saturation/O2 saturation probe for CO poisoning)
* Acute asthma with O2 saturation <92% (on air).
* Sepsis (lactate measurement)
Understand the difference between the ABG and VBG.
For patients who are not in shock, pH, Bicarbonate and base excess in VBG are close enough to arterial values to be useful.
Agreement with CO2 is not as good
Obviously, VBG does not provide useful information about O2 levels (whereas ABG does)
Be familiar with the components of spirometry and pulmonary function tests and the underlying physiology.
ERV Expiratory reserve volume
FRC Functional residual capacity
IC Inspiratory capacity
IRV Inspiratory reserve volume
RV Residual volume
TLC Total lung capacity
VC Vital capacity
VT Tidal volume
Be able to identify patterns of obstructive, restrictive and mixed changes in PFTs.
- Normal
Inspiratory limb of loop is symmetric and convex. Expiratory limb is linear. - Restrictive disease (e.g. sarcoidosis, kyphoscoliosis)
Configuration of loop is narrowed because of ↓lung volumes but shape is basically normal. At comparable lung volumes, flow rates are normal. (Actually ↑ because airways held open by ↑elasƟc recoil) - Obstructive disease (e.g. COPD, asthma)
All flow rates ↓, but particularly expiratory flow rate is ↓↓
Understand the role of and be able to interpret pulmonary function testing in the diagnosis and monitoring of COPD.
Recognise the common causes of restrictive lung disease and their typical presentations.
Be able to utilise the DLCO to determine the cause of restrictive changes in pulmonary
function testing.
Whereas spirometry measures the mechanical properties of the lungs, the lung diffusing capacity test (DLco)
measures the ability of the lungs to perform gaseous exchange.
The ability of the lungs to pass oxygen from alveoli → pulmonary capillary blood can be affected by damage to or loss of
respiratory membrane as in emphysema, and by thickening of the membrane by fibrosis or inflammation (interstitial lung disease e.g. asbestosis)
The DLco test is more sensitive
Causes of ↓ DLco
Interstitial lung disease
Emphysema
Severe anaemia
Smoking
Late stage pulmonary oedema
Causes of ↑ DLco
Polycythaemia
Early left ventricular failure
Asthma
Be aware of the limitations of spirometry and pulmonary function testing and demonstrate
judicious use of investigations.
ABSOLUTE
* Active infection
* Thoracic/ Abdominal or Cerebral
aneurysms
* Current Pneumothorax
* Recent surgery to eyes/ ears/ abdomen
or neurosurgery
RELATIVE
* Respiratory infection in the previous 4-6 weeks
* Haemoptysis of unknown origin
* Conditions aggravated by forced expiration
* Pneumothorax
* Unstable angina/ recent MI/ uncontrolled
hypertension/ Pulmonary embolism
* History of stroke/ TIA/ thoracic, abdominal or eye
surgery
* Patient is too unwell
* Communication problems/ confusion
Understand the basic principles behind conventional radiography (X-ray-plain films).
Be able to describe the advantages and disadvantages of the main imaging modalities: x-ray, ultrasound, CT and MRI.
X-RAY
* Radioactive beams are projected through the body and then detected by the plate
* The xray plate starts off white, as the beams hit it turns black., Denser structures (bones, metal) absorb more of the beams and therefore appear whiter. More Xrays pass through air and thus air filled lungs will appear more black.
* Chest xray projections can be Posterior/Anterior (most common), Anterior/Posterior and Lateral.
* Usage: Skeletal, Lungs, Heart
* Screening -mammograms
* Benefits: cheap, widely available, portable
* Disadvantages: radiation (but low – x 38 CXRs = b/g radiation in 1 year), 2D image
Describe the normal anatomy of the chest and, understand changes to this in cardiac and respiratory disease and, why these may result in abnormalities on a chest X-ray.
HEART
Describe and interpret abnormalities on a chest X-ray seen in common chest conditions
List appropriate additional imaging investigations (other than a chest X-ray) that would bemost useful in the diagnosis and management of common presentations/conditions affecting the cardiovascular, respiratory system
Understand the limitations and risks associated with imaging and demonstrate judicious use of imaging as a choice of investigation.
Describe the normal anatomy and physiology of the kidney and understand the changes to
this in renal disease and, why these changes may result in abnormal renal function tests.
List commonly used investigations (blood and urine) that assess renal function and urinary
tract pathology.
Describe the composition and characteristics of normal urine and interpret abnormal urine
test characteristics in acute kidney injury and chronic kidney disease.
Explain the use of urinary PCR, ACR and 24 hour protein collection in assessing renal
pathology and interpret abnormal urine protein test results. .
Explain the use of first line blood tests including urea, creatinine, eGFR and electrolytes in assessing renal function and interpret common abnormalities seen in patients with renal disease.
