Miscellaneous 1 Flashcards
What are the 4 main risks of IV contrast administration?
Anaphylaxis/allergy Renal impairment Lactic acidosis (secondary to metformin) Extravasation
What is the annual background radiation in Sieverts?
2.4mSV per year
What frequency would be used to look at deep structures in ultrasound?
Lower frequency
What is Duplex US?
Allows for velocity of a substance e.g. blood to be determined, assessing flow patters of blood within a vessel
Why is ultrasound not good at looking at bowel?
Waves don’t travel well through gas and become distorted resulting in significant artefact
What part of the adrenal is affected primarily in Addison’s disease?
Adrenal cortex - destruction via autoantibodies
4 causes of primary hypoadrenalism?
TB Bilateral adrenalectomy Metastatic Ca deposits WHFS (menigococcal sepsis)
What is the biochemical difference between primary and secondary hypoadrenalism? Why?
In secondary, e.g. due to long term steroids, aldosterone secretion is maintained and fluid/electrolyte disturbances less marked (aldosterone secreted in relation to RAS)
6 functions of glucocorticoid hormones?
Maintenance of immune system Stimulate gluconeogenesis Stimulate glycogenolysis Stimulate lipolysis Mobilise amino acids Inhibit glucose uptake by muscles
How would you manage adrenal insufficiency peri-operatively?
Pre-op assessment, do first on list Give usual AM medications and hydrocortisone IV at induction Depending on procedure and post-op recovery, double hydrocortisone dose for 24-48 hours before established back on usual oral medications Local hospital protocol
Management of Addisonian crisis?
ABCDE Correct hypoglycaemia IV Fluid resuscitation and correct electrolyte abnormalities Hydrocortisone 200mg stat then 100mg QDS Fludrocortisone 0.1mg OD Look for precipitants
Typical starting regime of steroids for primary adrenal insufficiency?
Hydrocortisone 20mg / 10mg per day Fludrocortisone 0.05-0.1mg OD
How is cardiopulmonary exercise testing performed?
Ramped protocol test using cycle ergometer, with cardiac monitoring attached and soft rubber facemask. Cycle for 3 mins unloaded then gradually increase load until symptomatic or after 10 minutes
What key piece of surgically relevant information does cardiopulmonary exercise give?
Anaerobic threhold, occuring at 47-64% of VO2Max - roughly equating to physiological reserve and risk of surgery
What is the relevance of VO2Max to surgical risk?
Over 20ml/kg/min = no increased risk 10-15ml/kg/min = increased risk Less than 10ml/kg/min = very high risk
How accurate is pulse oximetry to true HbSat level? When is it less reliable/not useful?
Accurate within 2%, however less at working out severity of hypoxia or in vasoconstriction or carbon monoxide poisoning. Also can’t provide information on alveolar hypoventilation
What 3 syndromes may phaeochromcytoma occur as part of?
NF1 VHL MEN2
Diagnosis of phaeochromocytoma is made by?
24 hour urine collection of catecholamine hormones and metabolites Plasma metanephrines
Imaging options for phaeochromoctyoma?
CT - contrast historically said to trigger crisis MRI I-MIG - radionucleotide scan to localise lesion and detect extra-adrenal lesions
Procedure of choice for phaeochromocytoma?
Laparosopic adrenalectomy
What is the biggest concern/operative risk for phaeochromcytoma surgery?
Hypertensive crisis - manage by ensuring alpha (phenoxybenzamine) then beta blockade
What is the order of blockade required in surgical management of phaeochromocytoma? What is used?
Alpha blockade first via phenoxybenzamine Then beta blockade
What BP changes can occur during phaeochromocytoma surgery? When?
Changes can occur during manipulation of gland (hypertensive) Hypotension may occur when adrenal veins secured
What forces govern the accumulation of fluid in the interstitium? What makes these up?
Starling’s Forces - capillary pressure, plasma colloid oncotic pressure vs interstitial fluid pressure and interstitial fluid osmotic pressure
What proportion of body fluid is interstitial?
1/6
What key part of plasma is not present in interstitial fluid? Why?
Protein - high molecular weight precludes filtration
How is excess interstitial fluid usually returned to vsacular system?
Lymphatics
4 factors favouring development of oedema (excess fluid in extracellular space)?
Increased hydrostatic pressure Hypoprotinaemia - low plasma oncotic pressure Venous/lymphatic obstruction Endothelial changes in capillary bed - acute inflammation or sepsis
Where is respiratory rhythm generated? What are these?
2 groups of neurones in medulla - dorsal inspiratory and ventral repiratory groups
Where do respiratory groups in medullar receive afferents from?
Cortex, pons, aortic and carotid bodies and lung (vagal nerve)
What is respiratory drive primarily influenced by? How?
PaCO2 CO2 generates hydrogen ions in CNS which stimulate central chemoreceptors - in periphery these are aortic and carotid bodies
How do catecholamine based inotropes work?
Beta adrenergic receptors to increase intracellular (myocyte) cAMP and mobilise calcium, or inhibit neuronal resorption of NA/Ad
What receptors do inotropes work on generally?
Beta 1 agonism directly on myocardium
When are inotropes best used?
Depresion of cardiac function to increase ouput and improve blood pressure, to in turn improve myocardial perfusion
How do vasoconstrictors/’pressors’ work? Receptors?
Alpha receptor agonism to act on peripheral tissues and cause constriction
Why are central lines required for inotropes?
Require MAP and CVP monitoring Direct entry to high flow system Reliable dosing
What is the difference in receptors between adrenaline and norad? How does this vary?
Adrenaline primarily beta 1 - cardiac, although is an alpha agonist at high doses Norad is alpha 1 agonist - pressor
How does dopamine work?
D1+2 receptor mediated renal and mesenteric vascular dilatation (and D2 - inhibits NA release) and beta 1 agonism at high doses to increase CO - good for cardiac issues and myocardial perfusion
How does dobutamine work?
Predominantly beta 1 agonism - weak beta 2 and alpha agonism
Phosphodiesterasae inhibitors - example and mechanism of action?
Milrinone Acts directly on cardiac phosphodiesterase to increase cardiac output
What effect do B2 agonism have?
Vasodilation
What does ABO incompatibility result in following transplant?
Early hyperacute organ rejection due to pre-existing antibodies
How does HLA matching impact on transplant outcomes? Which are most important clinically?
HLA A B C and DR are most important - greater number of mismatches the worse the outcome; T lymphocytes recognise antigens bound to HLA molecules, activate and then direct clonal response against the antigen
How long do fractures involving cancellous bone take to unite? How does this differ in cortical bone e.g. tibia, femur?
6 weeks Cortical takes 4-6 months (6 for femur)
Describe this image?
Displaced, comminuted fractured humerus with fracture callus surrounding site
What are the potential imaging modalities for suspected colorectal cancer? What is best?
Direct visualisation via colonoscopy is most sensitive and specific
Sigmoidoscopy
CT colonography
CT with faecal tagging
Barium enema
When would you perform an MRI for colorectal cancer?
If cancer below peritoneal reflection - MRI rectum
What is this and what does it show? What is the classic appearance?
Double contrast barium enema showing lesion of right colon
Classical apple core lesion suggesting colonic adenocarcinoma
What is the treatment for colonic cancer generally? Alternatives?
Generally surgical resection as only shot at cure
Stents, bypass and diversion stomas are palliative adjuncts
Why are colonic cancer surgeries chosen in the way they are?
Following lymphatic drainage, which follows arterial supply
What chemotherapy may be offered post-resection for colonic cancer?
5FU and oxaliplatin
What adjunct to surgery can be offered for rectal cancers and why?
Radiotherapy - as it is extraperitoneal
Often given neoadjuvant radiotherapy
What is normal arterial pH and what does this correspond to?
7.35-7.45, corresponding to H+ ion concentration of 40nmol/L
What is the main buffer system for pH? How does this work?
Bicarbonate present within blood, which can combine with hydrogen ions to form carbonic acid which then dissociates to CO2/H20
What are the main sites of acid-base excretion and conservation? Outline these
Lung - changes in respiratory rate allow for retention/excretion of CO2
Kidneys - can retain bicarbonate short term, and increase H+ ion excretion longer term
Outline how kidney manages acid-base balance?
PCT re-absorbs around 85% of filtered bicarbonate
Distal nephron secretes H+ ions into collecting duct, which are formed from carbonic acid dissociation in tubular cells
Result is excretion of H+ and retention of bicarb
What is usual acid-base state of urine? How is this mediated?
pH5-6
Due to hydrogen ion excretion, buffered by e.g. ammonium ions
What 6 things do ABG machines directly measure?
O2, CO2, pH, Na, K and Cl
What is the difference between standard and regular bicarb?
Bicarbonate is that which is actually present at time of analysis
Standard bicarbonate is calculated by adjusting CO2 to 5.3kPa
What is the anion gap and how is it calculated? Why is it useful?
AG = unmeasured anions - [Na + K] - [Bicarb + Cl]
Useful in metabolic acidosis as high AG suggests acid gain e.g. ketones, lactate vs normal AG which suggests bicarb loss
2 indications for cryoprecipitate?
Bleeding following massive transfusion
Haemophilia when factor concentrates not available
How to manage bleeding from liver surface?
Try topical haemostatic agents
If not resolving, pack and remove 24 hours later
Specific management of open fractures?
Take photo
Remove any obvious debris
Cover with soaked towel
Give broad spec antibiotics and tetanus toxoid
Prepare for theatre and consider specialist orthoplastic centre
When and how should surgery be done for open fractures?
Ideally within 6 hours if possible with combined orthoplastic approach but do in daylight hours unless:
Immediate if vascular injury (consider CTA)
Within 12 hours if high velocity
Within 24 hours otherwise
Is CVP affected in neurogenic shock? What about cardiac output?
Not primarily - unless concommitant hypovolaemia, which may be masked by nature of neurogenic shock (no tachycardia)
Cardiac output may be same or elevated
At what level is neurogenic shock likely? Why?
T6 and above
Below this unlikely to cause sufficient sympathetic disruption
What level of spinal cord injuries may be associated with bradycardia? Why?
T1 and above
Unopposed vagal activity on heart
Management of neurogenic shock?
Vasopressor support e.g. NA on ICU with management of concomitant injuries
Often give fluids any way but will not work long term
Bradycardia may respond to atropine if present
How much blood in pleura will blunt costophrenic angle on CXR? Problems with supine? Best scan for haemothorax?
400ml in pleural space
No meniscus on supine XR - hazy opacity
GAST scan better at detecting
What is massive haemothorax usually due to?
Major vessel injury - hilar disruption
Will parenchymal lesions cause massive haemothorax?
Not usually - low pressure and cease spontaneously
Management of massive haemothorax?
Chest tube insertion
Thoracotomy
What is biggest risk factor for tension pneumothorax? How is this seen in ventilated patients?
Penetrating chest injury plus mechanical ventilation
In ventilated patients presents as cardiovascular disturbance, subcutaneous emphysema and increasing O2 requirements
6 CXR signs of tension pneumothorax?
Lung collapse towards hilum
Increased rib separation
Diaphragmatic depression
Increased thoracic volume
Ipsilateral heart border flattening
Contralateral mediastinal deviation
Management of tension pneumothorax?
Immediate needle decompression (2ICS, MCL w 14-16G needle) + definite wide bore chest drain insertion
Presentation, investigation and management of pyloric stenosis?
Presents aged 2-4 weeks with projectile vomiting, due to hypertrophy of circular muscles of pylorus
Diagnose via US/test feed
Ramstedt pyloromyomotomy
What is the classical biochemical disturbance of pyloric stenosis? Why?
Hypochloraemic metabolic alkalosis with hypokalaemia
Because protracted vomiting causes hydrogen ion and chloride ion loss, increasing gastric production and H+/K+ pump. Also hypovolaemia and acidic urine
How is acid produced in stomach? Explain the hypokalaemia in pyloric stenosis?
Parietal cells generate hydrogen and bicarbonate ions
H+ combines with chloride to form HCl whereas bicarbonate ions enter circulation
In kidney there is exchange between sodium and hydrogen ions - conserving sodium and excretion of hydrogen. As H+ loss progresses the kidney then exchanges sodium for K, resulting in loss of K
Why is atelectasis seen post surgery and what is the significance of this?
Multiple reasons - especially abdominal surgery, pain post-op and inadequate analgesia causes underventilation and basal atelectasis
Significance is due to underventilation - risk of HAP
4 ECG signs of PE?
Tachycardia - sinus, AF
S1Q3T3
RBBB
Signs of right heart strain
Why may pain occur in pancreatic cancer? When?
Invasion of coeliac plexus - late on
What is Trousseau’s sign?
Migratory superficial thrombophlebitis suggestive of pancreatitis
What is CA19-9 and why is it used?
Carbohydrate antigen 19-9 used for monitoring (but not diagnosis) in pancreatic cancer
2 side effects of Whipple’s procedure?
Dumping syndrome
Ulcers
What does actual amount of oxygen transported in blood depend on?
Haemoglobin concentration
Haemoglobin O2 saturation
What does globin bind to?
CO2 and H+ ions
What is 2,3 DPG and what does it bind to?
2,3 diphosphoglycerate - binds to beta chains of globin; chronic anaemia causes raised 2,3 DPG
How many oxygen molecules bind to each haemoglobin molecule?
4
Discuss the oxygen dissociation curve? Why is it the shape it is?
Describes relationship between percentage of saturated Hb and partial pressure of oxygen in blood.
Shape is sigmoidal because when Hb binds with a single O2 molecule, it conformationally changes protein structure to facilitate binding of next molecule which is not dependent on Hb concentration
What is the Bohr effect with relation to oxygen dissociation?
Shift in O2 dissociation curve to the right indicating reduction in oxygen affinity for Hb molecule, in metabolically more active tissue (and so facilitates oxygen release) - seen in high temp, high H+ concentration, high CO2 and high 2,3 DPG
What is the Haldane effect?
Left shift of oxygen dissociation curve in circumstances of decreased oxygen delivery to tissues and so less metabolically active - O2 displaces CO2 from Hb. In low H+, low temp, low 2,3 DPG.
7 things which cause left shift in O2 dissociation curve?
Low H+
Low temp
Low DPG
Low CO2
HbF
Methaemoglobin
Carboxyhaemoglobin
Where are the main chemoreceptor centres modulating respiratory activity and what are they sensitive to?
Central chemoreceptors - central surface of medulla, sensitive to changes in CSF pH
Peripheral chemoreceptors - carotid bodies and aortic arch, sensitive to O2 levels
How are central chemoreceptors stimulated? Where are they?
Stimulation via CO2 dissolution in CSF to carbonic acid and H+ ions, which stimulate receptors on medulla
How are peripheral chemoreceptors stimulated with regards to respiration?
Bifurcation of carotids (bodies) and arch of aorta - fire more in response to reduced pO2, increased H+ and increased pCO2 in arterial blood
In a well person, what is the single most important driver for increase in respiratory rate?
Increase in partial pressure of CO2
There are 3 respiratory centres involved in respiration. Where are they and what do they?
Medullary respiratory centre - inspiratory (dorsal) and expiratory (ventral) neurones
Apneustic centre - lower pons - stimulates inspiration by activating and prolonging inhalation. Overriden by pneumotaxic centre to end inspiration
Pneumotaxic centre - upper pons - inhibits inspiration to fine tune respiratory rate
What are the 2 main problems with laryngeal mask airways?
Potential for reflux of gastric contents because it doesn’t occlude trachea
Often not possible to use high pressure ventilation
Advantages of LMA airway?
Easy to insert
Do not require paralysis
What are tracheostomies used for? Why are they good?
Reduce work of breathing
Reduce anatomical dead space
Good for weaning intubated patients and facilitate awake ventilation
5 main risks of ET intubation?
Damage to dentition
Accidental intubation of oesophagus
Damage to oropharynx or trachea
Single lung intubation
Pneumothorax formation with PPV
What is the difference between paediatric and adult ET tubes other than size?
Paeds are uncuffed, adults are cuffed
How to avoid intubation of oesophagus during ET intubation?
Training and familiarity with landmarks
Auscultation of chest and abdomen following intubation
Attaching end tidal CO2 monitor to circuit
Describe this?
Intertrochanteric, displaced, angulated neck of femur fracture with comminution and separation of lesser trochanter
General management of fractured neck of femur?
Combined orthogeriatric approach
Full trauma assessment and management of comorbidities
Fascia iliaca nerve block and analgesia
Surgery within 36 hours; delay of over 48 associated with increased morbidity and mortality
Early mobilisation post op and intensive physio
Manage underlying causes and treat osteoporosis - bisphosphonate and calcium
What forms does calcium exist in in body and what form of calcium is biologically active?
Protein bound
Complexed
Ionised - biologically active
Where is the largest store of calcium in the body?
Skeleton
Describe renal homeostasis of calcium and phosphate?
Normally calcium and phosphate freely filtered at glomerulus
Majority of calcium ions diffuse out of PCT, rest actively filtered in DCT
Majority of phosphate actively filtered at PCT, diffuse out in DCT
2% of filtered Ca excreted, 10% of filtered PO4 excreted
3 actions of calcitonin?
Inhibits intestinal calcium absorption
Inhibits osteoclast activity
Inhibits renal tubular absorption of calcium
4 actions of active form of vitamin D? What is it?
1,25 dihydroxycholecalciferol
Increases intestinal absorption of calcium
Increases renal tubular reabsorption of calcium
Increases osteoclastic activity
Increases renal phosphate reabsorption
4 actions of PTH?
Increase bone resorption via activating osteoclasts
Increase renal tubular reabsorption of calcium
Increase synthesis of active form of vitamin D in kidney to increase gut absorption
Decrease renal phosphate reabsorption
What markers are used in SOFA scoring? Where is it appropriate?
Used in ICU patients primarily
Pa/FiO2
Platelets (low)
Bilirubin
MAP/inotropes required
GCS
Creatinine
Urine output
What 3 criteria are used in qSOFA?
Resp rate over 22
SBP under 100
GCS under 15
Specific goals in treating sepsis in terms of CVP, MAP, UO, SVC O2 and lactate?
CVP 8-12mmHg
MAP over 65
UO over .5ml/kg/hour
SVC O2 conc over 70%
Normal lactate
What haemodynamic parameters define septic shock?
MAP under 65 or lactate over 2 in presence of infective source
