Interpretation basics Flashcards by Elizabeth McCabe

What are the normal value ranges on an ABG?

pH = 7.35 - 7.45
PaCO2 = 4.7 - 6.0 kPa
PaO2 = 11 - 13 kPa
HCO3- 22-26 mEq/L
Base excess (BE) -2 to +2 mmol/L

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What are the thresholds for hypoxaemia and respiratory failure on ABG O2 sats?

PaO2 <10kPa on air = hypoxaemia
PaO2 <8kPa on air = respiratory failure as severely hypoxaemix

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What is the basic criteria for type 1 and type 2 respiratory failure?

Type 1 - hypoxaemia and normocapnic
Type 2 - hypoxaemia and hypercapnia

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What is the typical cause of Type 1 respiratory failure?

V/Q mismatch = volume of air in lungs does not match blood flow to lungs

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What can cause a low ventilation to normal perfusion mismatch in the lungs?

Asthma attack
Pulmonary odema

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What can cause a norm ventilation to low perfusion mismatch in the lungs?

Pulmonary embolism

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Why is O2 low and CO2 norm in type 1 respiratory failure?**

PaO2 dec and PaCO2 increases
Increased respiratory drive - trigger inc overall alveolar ventilation (RR),
This corrects PaCO2 but not PaO2

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What is the typical cause of Type 2 respiratory failure?

Alveolar hypoventilation (not breathing enough per minute)
Stops adequate oxygenation and elimination of CO2 from their blood (cause PaCO2).

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What are the different causes of alveolar hypoventilation in type 2 respiratory failure?

Inc resistance due to airway obstruction e.g COPD
Dec movement of lung tissue/chest wall pneumonia, rib#. obesity
Decreased strength of respiratory muscles e.g MND, GBS
Drugs depression resp efforts e.g opiods

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What is the equation underpinning why CO2 has an acidic affect in the body?

CO2 + H2O <—–> H2CO3 <—-> HCO3- + H+

The first part of this reversible reaction is catalysed in both direction by carbonic anhydrase.

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What conditions can cause respiratory acidosis?
what are the shows on an ABG?

Low pH high paCO2
Asthma and COPD
Respiratory Depression

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What conditions tend to cause respiratory alkalosis?

Due to hyperventilation
Anxiety
Pain
PE
Pneumothorax

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What conditions tend to cause metabolic acidosis?

Either increased acid production or acid ingestion
Decreased acid excretion or increased rate of gastrointestinal/renal HCO3- loss

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What equation is used to work out the cause of metabolic acidosis?

The Anion Gap
Na+ - (Cl- + HCO3-)
Artificial measure used to determine the presence of unmeasured anions mainly albumin.
Measures the balance of neg and positive ions in the blood - how many more cations than anions.

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What is the normal anion gap?

= 4 to 12 mmol/L?

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What are the causes of a high anion gap?

DKA
Lactic acidosis
Aspirin OD
Renal failure
Increased production/ingestion or reduced excretion of H+ by the kidneys

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What are the causes of anormal anion gap?

GI loss (diarrhoea, ileostomy etc)
Renal tubular disease
Addisons disease

Loss of bicarb, replaced by chloride in the plasma, results in stable overall anion concentration

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What are the main causes of metabolic alkalosis?

Decreased H+ conc, leading to increased bicarb or direct result of increased bicarb
For example - GI loss of H+ (DV), renal loss of H+ (diuretics, HF, nephrotic syndrome), iatrogenic.

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What are the difference compensation systems for alkalosis/acidosis?

Metabolic system - compensates slowly over days - by dec or inc HCO3-
Respiratory system - compensates quickly by retaining or blowing off CO2.

What additional blood results should by analysed in a ABG?

Na+ and Cl- = for anion gap is metabolic acidosis
Look at K+ as can be cause of cardiac arrest
Lactate - predictor of how unwell
Glucose - high or low, DKA or hypoglycemic

What is the first step when interpreting any results?

Confirm patient details
Confirm date and time of test
What was the clinical indication for this test?
Are there any previous tests for comparison?

How should the quality of a CXR by assessed?

RIPE
Rotation - medial aspect of clavicle should be equidistant from the spinous process, spinous process vertical to vertebral bodies
Inspiration - 5-6 ant ribs, lung apicies, costophrenic angles and lateral rib edges should be visible
Presentation - AP or PA
Exposure - vertebrae should be visible behind heart if very white is over exposed, left hemiD should by visible to the spine

What is the A-E approach for CXR analysis?

Airway
Breathing
Cardiac
Diaphragm
Everything else

What should be considered in the Airway part of a CXR interpretation?

Trachea - central or deviated, if deviated pushed ( pleural effusion, tension pneumothorax) or pulled (consolidation with associated lobar collapse)

Carnia and bronchi - present

Hilar structures - no visible lymph nodes, same size,

What are some causes of hilar pathology on a CXR?

Enlargement - bilaters = sarcoidosis, unilateral/asymmetrical = underlying malignancy Abnormal position - pushing (enlarging mass) or pulled (global collapses)

What should be considered within the breathing section of CXR interpretation?

Lung markings present inc at edge of lungs (absence = pneumothorax) Are zones (three zones on each lungs - NOT LOBES) symmetrical? Are zones good side and colour Any increased airspace shadowing? Y=consolidation/malignancy Is the pleura visible? Y = mesothelioma Pattern of opacity - increased = fluid, decreased = air.

What does a visible pleura indicate on a CXR?

Not visible on healthy people Visible indicates pleural thickening Norm - mesothelioma - associated with asbestos exposure.

What is the cause of a pneumothorax?

Damage to pleura Air from outside in to pleura but can not bet out Air accumulates in pleural cavity Positive pressure on lungs - prevents expansion cause respiratory distress Trachea and structures pushed away from pneumothorax Compress heart and great vessels - leads to cardiovascular collapse and cardiac arrest.

What is the treatment for a tension pneumothorax?

Needle decompression.

What are the key parts of a cardiac analysis on a CXR?

Only comment on PA, AP makes bigger Heart should be no bigger that 50% thoracic width if >=cardiomegaly Borders clearly visible including right atrium as right border and left ventricle as left border.

What can cause loss of the heart borders on a CXR?

Loss of right border = right atrium = right middle lobe consolidation Loss of left border = left ventricle - lingular consolidation

What is important about the diaphragm on analysis of a CXR?

R hemi higher due to liver L - often gastric bubble due to stomach underneath Free gas under diaphragm - pneumoperitoneum - panic as bowel perforation Costoprhenic angles should be acute and visible - if missing/blunting due to fluid or flattening in hyperinflation COPD patients

What should be considered in he everything else part of examining a CXR?

Bones - fractures etc Soft tissue - breast tissue or hematoma Equip - NG, ECG leads, central lines, artificial heart valves, pacemakers. Aortic knuckle loss in AAA Aortopulmonary window - lost in mediastinal lymphadenopathy.

What are the three different categories of blood tests?

Haematology, biochemistry and coagulation

What blood bottles are used for haematology, biochemistry and coagulation during a blood test?

Haematology = purple top Biochemistry = Gold top Clotting screen = blue top

What blood tests are included within haematology?

FBCs WBC Platelets

What rests are included within a biochemistry blood test?

U&Es LFTs CRP Albumin

What tests are included in a clotting screen?

Coagulation screen INR D-dimer

How should changes in FBC, WBC and Platelets be indicative of?

FBC - low is bleed or anaemia, high polycythemia (COPD) WBC - high infection or steroid (leukocytosis), low immunodeficiency (leucopenia) Platelets - Thrombocytopenia acute -bleeding, viral infection, HELLP syndrome, DIC or chronic (cirrhosis, alcohol, iron deficient, HIV) Thrombocytosis - reactive, inflammation, malignancy.

What is the difference between a liver pathology and a biliary pathology in LFTs?

Liver - high ALT Biliary - high ALP

What does a low albumin indicate?

Poor nutritional intake Incorrect fluid distribution

How to interpret different elements of a clotting screen?

Coag screen - bleeding time for platelet function, PTT is a marker of liver function (too high not functioning) INR - used in warfarin patients - higher indicates longer clotting time D-dimer - low rules our thrombosis

What is the use of the pink blood bottle?

Cross match, Group and Saves

What is the use of the grey blood bottle?

Glucose Lactate Ethanol

What is the use of a dark green top blood bottle?

Ammonia

What is a pleural effusion? How does it tend to present on a CXR?

Accumulation of excessive fluid in the pleural space - hydrothorax (serous), haemothorax, empyema. Blunting of costophrenic angles, prominent upper zone vessels.

What is flash pulmonary oedema? How does it tend to present on a CXR?

Rapid onset acute pulmonary oedema Often precipitated by acute MI, mitral regurg/HF CXR findings: Fluid in alveolar walls, batting winging (increased vascular shadowing), kerley B lines (parelel lines at lung edges - represent interlobar septa), possible pleural effusions