Investigations Flashcards
Acidosis
Metabolic
— increased acid production e.g. ketones (DKA), lactate (shock)
— acid ingestion e.g. salicylates
— failure to excrete hydrogen ions e.g. renal failure, distal renal tubular acidosis, carbonic anhydrase inhibitors
— loss of bicarbonate e.g. proximal renal tubular acidosis, D+V, GI fistula
Respiratory
— increased PaCO2 secondary to alveolar hypoventilation
Anaemia
Aetiological Classification
* impaired RBC production
— abnormal bone marrow - aplastic anaemia, myelofibrosis
— essential factors deficiency - iron, B12/folate, EPO (renal disease)
— stimulation factor deficiency - anaemia in chronic disease, hypothyroidism, hypopituitarism
* excessive destruction of RBCs
— intracorpuscular defect - membrane (hereditary spherocytosis), enzyme (G6PD deficiency), Hb (thalassaemia, haemoglobinopathies)
— extracorpuscular defect - mechanical (microangiopathic haemolytic), infective (clostridium titani), antibodies (SLE), hypersplenism
* blood loss
— acute - trauma, acute GI bleed
— chronic - parasitic infection, chronic NSAID use
Morphological Classification
* macrocytic (MCV >94, MCHC >31)
— B12 deficiency - pernicious anaemia
— folate deficiency - nutritional
— drug-induced abnormal DNA synthesis - anti-convulsant, chemotherapy
* microcytic hypochromic (MCV <80, MCHC <31)
— IDA - chronic blood loss, decreased intake, increased demand, malabsorption
— abnormal globin synthesis (thalassaemia, SCD)
* normochromic normocytic
— blood loss
— increased plasma volume (pregnancy)
— hypoplastic marrow
— endocrine - hypothyroidism, adrenal insufficiency
— renal and liver disease
Anion Gap
- (Sodium (+ Potassium)) - (Chloride + Bicarbonate)
- Normal = 8-16mEq/L
Raised anion gap
— accumulation of organic acids
— impaired hydrogen excretion
— lactate - metformin
— toxins - CO, CN, alcohol, toluene, ethylene glycol, salicylates
— ketones - DKA
— renal - uraemia
Normal anion gap
— loss of bicarbonate from Extracellular fluid (GI causes)
— Addisons
— CA inhibitors (acetazolamide)
— chloride excess
Low anion gap
— decreased unmeasured anions (albumin, dilution)
— increased unmeasured cations (multiple myeloma, increased calcium/magnesium, lithium OD)
— non random analytical errors
C-Spine X-ray
A - adequacy
A - alignment
— Atlantic-occipital
— vertebral - anterior vertebral line, posterior vertebral line, spinolaminar line, interspinous line
B - bony landmarks
C - cartilaginous space
D - disc space
S - soft tissue
CPET
Dynamic, non invasive assessment of the cardiopulmonary system at rest and during exercise.
Determine the functional capacity of an individual.
- electromagnetically braked cycle ergometer (with predetermined ramp of pedalling resistance - hand ergometer/treadmill as alternative)
- rapid gas analyser for breath by breath expired gas concentrations (IR)
- pressure differential pneumotachograph for spirometry and RR
- continuous 12-lead ECG
- continuous SpO2
- NIBP
Nine panel plot
* cardiovascular system 2, 3, 5
* ventilation 1, 4, 7
* VQ relationships 6, 8, 9
VO2peak = maximum oxygen consumption (<15mlO2/kg/min represents an increased risk of Perioperative complications)
Anaerobic threshold = the point at which the cardiopulmonary system is unable to meet the oxygen demand of the muscles and switches to anaerobic metabolism (AT <11mlO2/kg/min would put the patient into a higher-risk group)
Patterns of Physiological Limitation
* Cardiac - reduced VO2peak, early onset AT, typically limited by leg fatigue/angina, peak HR does not reach max, higher ventilatory equivalent for CO2, BP not increasing normally with exercise
* Respiratory - reduced VO2peak, exhaustion due to ventilatory limitation prior to AT, elevated VE for VO2/VCO2, decreasing tidal volumes, low O2 sats, limited by dyspnoea
* Pulmonary Vascular Disease - reduced VO2peak, elevated HR disproportionate to work rate, desaturation with progressive exercise, low ETCO2, early onset AT
CSF Results
Normal:
* clear and colourless
* WCC 0-5 cells/uL (predominantly lymphocytes)
* RBC 0-5/uL
* Protein 0.15-0.45g/L (or <1% of the serum protein concentration)
* Glucose 2.8-4.2mmol/L (or >60% of the serum glucose concentration)
* opening pressure 10-20cmH2O
Bacterial Meningitis
* cloudy/turbid fluid
* elevated WCC >100/uL (primarily polymorphonuclear leukocytes)
* Elevated protein >0.5g/L
* low glucose (<40% serum)
* elevated pressure >25cmH2O
* CSF microscopy, gram stain + culture, PCR, blood cultures, imaging for other pathology?
— gram positive diplococci - pneumococcal
— gram negative diplococci - meningococcal
— gram positive rods/coccobacilli - listerial
Viral Meningitis
* usually clear
* elevated WCC >100/uL (primarily lymphocytes)
* elevated protein > 0.5g/L
* normal glucose >60% serum
* normal or elevated pressure
* viral PCR
Tuberculous Meningitis
* opaque, if left to settle it forms a Fibrin web
* WCC elevated - typically lymphocytes
* protein elevated - 1-5g/L
* low glucose
* elevated opening pressure
Fungal Meningitis
* clear or cloudy
* elevated WCC (typically more modest elevations)
* elevated protein
* low glucose
* elevated opening pressure
SAH
* blood stained initially, with xanthochromia (yellowish appearance) >12hrs later
* WCC elevated
* RBC elevated
* protein elevated
* normal glucose
* elevated opening pressure
MS
* clear
* WCC 0-20/uL (primarily lymphocytes)
* protein mildly elevated 0.45-0.75g/L
* glucose normal
* normal opening pressure
* oligoclonal bands present on electrophoresis
GBS
* clear
* WCC normal
* protein markedly elevated >5.5g/L
* glucose normal
* opening pressure normal or elevated
CXR
Projection
Rotation
Inspiration
Penetration
Airway - trace trachea to hila - shifts, foreign bodies, other abnormalities, hilar mass
Breathing - lung from apices to diaphragm, pleura - pulmonary opacifications (air space/interstitial/nodular), air bronchograms, Kerley A/B/C lines
Circulation - heart - trace borders, cardiothoracic ratio, mediastinum - silhouette sign, mediastinal mass (anterior/middle/posterior
Diaphragm - costophrenic and cardiophrenic angles
Everything else
— bone - deposits, fractures
— intervention - tubes, lines, drains, pacemaker, valves
— tissue - surgical emphysema
The trachea is central and the hila are normal. Lung fields are clear with no air or fluid collection. There is no free air under the diaphragm and the angles are clear. The bones and soft tissues appear normal.
Diffusing Capacity of the Lungs for Carbon Monoxide (DLCO)
Indirectly measures the ability of the lungs to transfer oxygen to the blood
DLCO = Va x Kco (Va = surface area of the lung available for gas exchange, Kco = rate of alveolar capillary blood CO uptake)
Normal = >75% of predicted (up to 140%)
<60% predicted is associated with increased mortality in thoracic surgery
<80% associated with increased pulmonary complications
- Causes of increased DLCO
- exercise, supine, pulmonary haemorrhage, polycythaemia, left to right shunt (e.g. ASD), obesity, mild LVF, asthma, pregnancy, morning
- Causes of decreased DLCO
- post exercise, standing, valsalva, lung resection, emphysema, interstitial lung disease, anaemia, evening, drugs (e.g. bleomycin, amiodarone), PAH, PE, CTEPH, cardiac insufficiency
** Specific Patterns**
* Normal DLCO with restrictive pattern
* kyphoscoliosis, morbid obesity, neuromuscular weakness, pleural effusion
- Normal DLCO with obstructive component
- alpha-1 antitrypsin deficiency, asthma, bronchiectasis, chronic bronchitis
- Low DLCO with restriction
- asbestosis, berylliosis, hypersensitivity pneumonitis, idiopathic pulmonary fibrosis, langerhans cell histiocytosis, lymphangitic spread of tumour, miliary TB, sarcoidosis, silicosis (late)
- Low DLCO with obstruction
- CF, emphysema, silicosis (early)
- Low DLCO with normal PFTs
- CTEPH, CHF, CTD with pulmonary involvement, dermatomyositis/polymyositis, IBD, early ILD, primary pulmonary hypertension, RA, SLE, systemic sclerosis, granulomatosis with polyangitis
ECG Changes
ST elevation
- MI
- LBBB
- myocarditis
- hyperkalaemia
- LVH
- pericarditis
- hypothermia
- PE
- cardiac trauma
- SAH/raised ICP
- normal variant (early repolarisation)
- ventricular aneurysm
T wave inversion
- normal in leads III, AVR, V1-2
- MI
- LBBB, RBBB
- SAH/raised ICP
- LVH + RVH
- cardiomyopathies
- PE
- ECT
- drugs
- electrolyte disturbance
- persistent juvenile pattern
Left Axis Deviation (+ve QRS in lead I, -ve QRS in lead II)
- LVH
- LBBB
- mediastinal shift
- LAFB
- inferior MI
- primum ASD
- pre-excitation
- hyperkalaemia
Right Axis Deviation (-ve QRS in lead I, +ve QRS in lead II)
- RVH
- PE/COPD/Cor pulmonale
- mediastinal shift
- LPFB
- secundum ASD
- pre-excitation
- hyperkalaemia
- dextrocardia
- normal variant (tall, slim)
LBBB - widened QRS “WiLLiaM,” LAD, TWI laterally
RBBB - widened QRS “MoRRoW”
Bifascicular Block - RBBB with axis deviation
Trifascicular Block - bifascicular block with prolonged PR interval
AV nodal Block - prolonged PR (I, II Mobitz 1/2, III)
Left anterior fascicular block - small inferior r waves, small lateral q waves, dominant r waves laterally, dominant S waves inferiorly, slightly wide qrs (<120ms) —> exclude inferior MI and other causes of left axis deviation
Left posterior fascicular block - small r wave laterally, small inferior q waves, dominant inferior R waves and lateral S waves, slight prolongation of QRS —> exclude lateral MI and other causes of right axis deviation
Left atrial hypertrophy - notched p in lead II (p mitrale), wide deep negative p wave in V1
Right atrial hypertrophy - tall/peaked p wave (p pulmonale)
Left ventricular hypertrophy - voltage criteria (e.g. S in V1 + tallest R V5-6 >35mm), no voltage criteria (e.g. ventricular activation time >50ms in V5-6 + strain)
- hypertension
- aortic stenosis
- aortic regurgitation
- mitral regurgitation
- HOCM
- coarctation
- normal variant (young/thin)
Right ventricular hypertrophy - increased QRS in V1-3 +/- ST depression or TWI
- chronic lung disease (COPD, pulmonary arterial hypertension, PE)
- pulmonary stenosis
- mitral stenosis
- HOCM
- Right ventricular cardiomyopathy
- CHD
ECGs
Hyperkalaemia - tented T wave, prolonged PR, flattened P wave, prolonged QRS, sine wave —> VF
Hypokalaemia - tall, wide P waves, prolonged PR, flattened/inverted T wave, decreased ST segments, U waves, SVT/VEs/AF/VT
Hypercalcaemia - short QT, J waves, VF
Hypocalcaemia - prolonged QTc (long ST), Torsades, AF
Hypermagnesaemia - decreased HR, prolonged PR/QRS/QT, AV block
Hypomagnesaemia - flattened T wave, U waves, prolonged PR/QRS/QT, decreased ST segments, atrial/ventricular arrhythmias
Hypothermia - J waves, prolonged PR/QRS/QT, VEs, AF, bradycardia, arrest (VT/VF/asystole), shivering artefact
Digoxin therapy - reverse tick ST depression, biphasic T waves, prominent U waves
ECT therapy - arrhythmia, diffuse T wave inversion
PE - deep S in I, q in III, inverted T in III (20%), RV strain pattern (34% - TWI V1-4 +/- inf leads), sinus tachycardia (44%), ST/T changes (50%)
Pericarditis (4 stages) - diffuse ST elevation with PR depression —> resolution of stage 1 with T wave flattening —> deep T wave inversion —> resolution
STEMI - minutes - hyperacute T waves —> ST elevation; hours - Q waves and TWI; days - ST normalisation; weeks - persistent Q waves, T waves normalise
* LAD occlusion - septal V1-V2, anterior V3-V4, lateral V5-V6+aVL
* LCX (+RCA) occlusion - posterior V7-9 + left axis deviation
* RCA occlusion - inferior II, III, aVF + right axis deviation
ECGs in Pregnancy
Normal Findings
* Tachycardia
* Left axis deviation
* Small q waves
* T wave inversion in lead III
* ST depression and TWI/flattening in inferior/lateral leads
* atrial and ventricular ectopics
Hypercalcaemia (Hyperparathyroidism)
Malignancy
— primary
— bony metastases
Increased intake
— milk alkali syndrome
Vitamin D metabolic disorders
— hypervitaminosis D (vitamin D intoxication)
— idiopathic hypercalcaemia of infancy
— rebound hypercalcaemia after rhabdomyolysis
Renal Failure
Adrenocortical insufficiency
Disorders related to high bone-turnover rates
— hyperthyroidism
— prolonged immobilisation
— thiazide use
— vitamin A intoxication
— multiple myeloma
Hyperchloraemia
Usually associated with Hypernatraemia, and inversely to bicarbonate.
Drugs
* acetazolamide, aspirin OD, steroids, oestrogens
* thiazides, androgens
* IV NaCl replacement
Metabolic
* respiratory alkalosis - decreased C, K, Mg, increased Cl
* metabolic acidosis (normal anion gap metabolic acidosis)
Endocrine
* hypothalamic lesion (increased Na, decreased thirst perception)
* adrenocortical hyper function
Renal
* renal tubular acidosis
* acute renal failure
* diabetes insipius
GIT
* dehydration
* prolonged diarrhoea
Fictitious
* bromide toxicity
Hyperkalaemia
Increased intake
— IVI
— oral (potassium supplements)
— blood transfusion
— GI haemorrhage
Decreased renal excretion
— renal failure (acute and chronic)
— adrenocortical insufficiency - hypoaldosteronism, Addisons
— chronic active hepatitis
— obstructive uropathy
— drugs (ACEI, K-sparing diuretics, ARBs, heparin, beta blockers, phenylephrine, digoxin, trimethoprim, amiloride)
Increased release of potassium out of tissues
— trauma/tissue injury
— crush injuries
— malignant hyperthermia
— rhabdomyolysis
— suxamethonium
— intense physical activity
— tumour lysis syndrome
— haemolysis
— burns
— ischaemia
Trans cellular shift
— metabolic acidosis (DKA etc)
— respiratory acidosis
Artefactual
— haemolysed sample
— laboratory error
— leukocytosis, thrombocytosis
— sample taken from IV running potassium containing fluid
Hypermagnesaemia
Iatrogenic
— hyperalimentation
— IV and oral magnesium
— laxatives, enemas, antacids (especially in elderly and renal failure)
Renal Failure
Other
— perforated viscus with continued oral intake
— tumour lysis (increased K, Mg, PO4 and decreased Ca)
— rhabdomyolysis
— hypothyroidism, Addisons, adrenocortical insufficiency
— lithium therapy
