MRCS Part B - Stations from yester year

Now please note, these stations are just to help give you an idea of what kind of topics could come up in the exam. There is no guarantee that they will come up again or even if they do the format maybe different as the exam structure has recently changed. MRCS OSCEs are designed to test your core surgical knowledge and ability. If you revise the theoretical stuff and ensure that you get experience in going to a variety of outpatient clinics as well as scrubbing in regularly in the OR then you should not have any problems.

Hope these are useful and good luck!

Clinical Skills and History Taking 

1. Examine this ladies neck I started peripherally with a thyroid status exam, but the examiner prompted me to go directly to the neck. She was an afrocarribean lady with what I thought was bilateral parotid enlargement:

Q's
• Causes of symmetrical bilateral parotid enlargement
• What is most likely cause in her (sarcoidosis)
• He asked me about other manifestations outside the neck

2. Examine this lump on a man's back: 

Large lipoma- I examined including assessing for fixity to muscle, transillumenence, draining lymph nodes etc

Q's
• What muscle was it overlying
 • What is blood supply and lymph drainage of that muscle (was Lat Dorsi)
• To describe how you would excise this lipoma
• Consent patient for procedure

 3. HISTORY: 

Very simple history for likely colorectal Ca,

Q's
• RF for colorectal ca
• Difference in presentation for IBD and colorectal ca --> why is this change in bowel habit Crohns or UC
• How you would investigate him
• Why CT pneumocolon is inferior to colonoscopy (you can biopsy with latter)

 4. CVS Exam:

Patient had AS

Q's
• Other causes of ESM --Hypertrophic cardiomyopathy
• How to investigate to see if fit for surgery- ECHO to look at EF and gradient across valve
• Any important considerations for anaesthesia? No epidural, cause hypotension which can be compensated in AS due to fixed output state

5. Hx and brief resp exam 

Completely normal exam, history of long-standing panic disorders

Q's
• Would you pass this lady in pre-assessment for an elective cholecystectomy
• What are the ASA gradings? - what would she be?
• Can you think of ways to optomise her- SSRI trial

Anatomy (3):

1. Upper limb, prosection, live patient and skeleton all in one: Rapid fire 20 questions e.g- where is the insertion of supraspinator, (demonstrate on skeleton), demonstrate pronation and supination (live pt) point out long head of biceps (pro-section)

 2. Unmanned prosection of mediastinum and thorax in saggital section. Lots of flags- just had to identify the structures - was v hard !

3. Manned station- very easy, lower GI/ Hepatobillary -prosection of bowels- asked blood supply, significance of water shed area and marginal artery of drummond. Also was given a colonoscopy picture of bowel ca and asked to identify it. Then asked dukes classification. Then hepatobillary anatomy on another prosection Skills

(2): Taking blood cultures Important points: patient was there- there were marks for interacting.

If you spoke to her, she told you she was IVDU and Hep +ve, so u had to take appropriate cautions-eye protection, and noting it on the form for the lab. Change needles before you fill bottles, and fill aerobic first. Offer to label them.
Also they had an obs chart and it said she was Pen allergic.
They said she had a new murmur, and was spiking on obs chart and asked for a differential. I said that I wld query infective endocarditis, they asked organism, I said staph, and they asked me if I want to write up Abx- I did, VANC--> she was penn allergic which was the trick of the station.

Scrubbing Self explanatory

Other stations: 

Critical Care: Definitions of sepsis, septicaemia, septic shock etc. Asked for intepretation of a HDU chart, and generally where and how to ressucitate a patient in shock, ABCDE...

Comm skills- Calming an eratic mother whose son had been in accident in playground and was on the table for an emergency splenectomy. Had to tell her risk and complications, long term e.g immunizations. and she was questioning why he was taken to surgery without consent, so u had to to know the legislation that the doc act in interest of child if no consenting adult is available in an emergency Comm skills- Discharge summary.

Information Giving- Polytrauma patient, needed to read notes in prep station and call trauma surgeon at home who is on call. He just asked questions to see if you knew the ATLS guidelines, and about management of open fractures.

Information Receiving (written stations)
ECG: AF with fast ventricular response- asked to inteprate rate/ rhythm, about reversible causes, and treatment
CT- Bilateral pleural effusions in a pancreatitic- asked about ARDS, and glasgow scoring
Erect Chest X-Ray- Perforated viscus

Website Renovation Part deux...

Hi all

So sorry but moving the website along has proven much more time consuming than I initially anticipated. I can however give you a sneak peak on www.iwanttobeasurgeon.com. There is still so much content to move over including anatomy and videos of clinical skills. However it will all be so much easier to access once its all up there :) You will note that we have added a new research skills section which will contain articles on how to conduct research, how to write up papers and how to get published. We will also be introducing a monthly journal club onto this blog and I hope you will be able to partcipate by adding your comments :)

Anyway, good luck everyone sitting exams and especially those who have been emailing questions to us. Please write back and let everyone know how you get on.

Amel

Happy Holidays!

Merry Christmas everyone (not that I can be too cheerful as I am on nights all this week :( ). I have enjoyed blogging about exams and all things surgical this year and hope everyone who has stumbled across our humble blog has found some useful info. Congratulations to Romesh for becoming a member and good luck to everyone else who is planning on sitting the exams soon.

With core surgical applications sent off and interviews obtained, I will try to blog about the experience in the hope that it may help others planning to apply next year.

As for our blog and website, I will be making some changes after interviews. Firstly, I want to re-design the website so that navigation is easier and avoid flash to make it more accessible. In addition, I will be uploding much more content and have designed a quiz generator for practice questions.

So change is coming to IWTBAS - watch this space. As for anyone who has used this blog, I would be very useful if you could let us know how you got on in the exams/what more you would like to see on our blog.

With that Merry Christmas and Happy New Year!

Amel

More MRCS Exam stuff!

Sorry but it has been brought to my attention that I forgot to post the two clinical skills stations which
I received. They were both single examiner and 9 minutes in length.

1) The scenario was someone was involved in an RTA and you needed to put in a cannula and write up fluids. Things to remember are confirm patient ID, correctly insert cannula and write up drug chart. After this it becomes an ATLS viva where thy quiz you on management of trauma. Its not a difficult station if you stay calm.
2) The second station was to excise a benign appearing lesion as your consultant was going to do it but he had to run to theatre. You have to pick the blade and suture you need to use and mount the scalpel (I found this the trickiest bit as my hands were shaking). Remember to check consent form, infiltrate with local and give advise as to when to remove stitches, how long to leave dressing and when histology will be back. Also give follow up details.

Hope this helps!

MRCS Stations - Efficiency Of Time Critical

With the next sitting of MRCS rapidly approaching, I thought that I would post what stations I got in the exam in May to help give you an idea of what the exam was like. Obviously, you need to prepare for the probability that anything can come up but this may help give you a flavour of what to expect.


So the exam is done at the Royal College of Surgeons HQ in London if you're sitting at the English College. The exam is split over two floors with chaperones escorting you between stations. There was also a 20 minute break half way through the exam with tea and biscuits which I must admit was very welcome!


On the day, you register and put your things in a locker (do not forget to put away your mobile otherwise its an instant fail!). You are then split into two groups and do a circuit of 9 stations then a break followed by the second circuit. Here were my stations:

Rest station

Head and neck: asked to examine a neck. On exam patient had enlarged left lobe of thyroid. I examined her neck and then I said I would like to examine the rest of her thyroid system. So I looked for proximal myopathy, exophthalmos, lid lag, AF, myxoedema etc… when I was done I said that she was euthyroid but with an enlarged left lobe. I was asked for differential diagnoses, investigations and management plans. Then I was asked to talk about different cancers of thyroid (so I did the whole epidemiology, pathology, investigations and management of each…). Good station, I finished early and had a nice chat with examiner and patient.

Investigations station: I got a CXR which showed NG in bronchus as well as the patients notes and asked to comment (basically SHO did NG tube then left at 17:30 without handing over for anyone to check. Patient then NG fed erroneously and ends up in ITU with respiratory distress). The examiner was an anaesthetist who was very quick with questions so you had to answer quickly. Asked what management of patient was (obviously remove and replace tube immediately). Second was a CT abdo slice of px and blood results. Diagnosis was acute cholecystitis and gallstones in gall bladder. Asked about management. Simple station but it was rushed and you have to think fast.

Examination of Resp system: patient needed elective inguinal hernia repair. I immediately looked around room and spotted inhalers. He had hypo-expanded chest and expiratory wheeze. I diagnosed COPD and was asked how this affects his management. So I mentioned getting pulmonary function tests, optimisation of his COPD treatment, informing HDU as although it is normally a day case procedure he may have difficulties, let surgeon and anaesthetist know. I also mentioned consider use of regional anaesthesia.

HISTORY 1: Back pain in a gardener. Toe is numb. Pain radiates to right leg and increased urinary frequency. She was constipated but was using dihydrocodeine for back pain. My differential was L5/S1 herniation of disc or sciatica. I said I needed to thoroughly examine and exclude cauda equine (MRI if necessary). I said if suspect cauda equine admit immediately, otherwise MRI as outpatient, analgesia, physio and discuss scans with spinal surgeon in case needs decompression if disc prolapse.

HISTORY 2: basically woman with panic attacks. Asked to give a string of differentials so I said asthma, heart failure, vasovagal syncope, angina… For management I said investigate by doing bloods, CXR, echo, PFT and inform anaesthetist, surgeon as well as relatives as she may need support prior to surgery.

Abdo Exam: Asked to examine abdo of patient with abdo pain but patient kept refusing to let me see her abdo so I examined her by piece meal. I also forgot to look at obs chart first so examiner got upset at that (even though he had it hidden in his hand). Handed a piece of paper with urine analysis. There was bilirubin in her urine though she was not jaundiced. Pain was epigastric. I said cholecystitis, pancreatitis, gastritis as differentials and ran ourt of time. Everyone else said they had a tough time with the patient and examiner as neither were helpful. Examiner didn’t ask clear questions.

HISTORY 3: primary school teacher with change in bowel habit, LIF pain and mucous PR. She is adopted and does not know her biological family. So I gave IBD, hereditary bowel ca and said if she was old I may hink diverticulitis but she was only 30!. I would investigate with flex then colonoscopy if needed, barium enema/CT depending on scope results.

  

EXAM Ortho: hip exam of someone with pain in left hip, has scar on right hip, reduced flexion of left hip, fixed flexion deformity on right and small leg length discrepancy (I asked to measure his leg length so examiner got a tape measure out of his pocket). Tested trendelneberg which was normal. I gave differential of OA and then he asked what else so I said RA reluctantly. I said I wanted to do an xray of his hips. Asked about management so I said analgesia, physio, hip replacement if indicated but he wanted to know what else (think he wanted me to say bisphosphonates and calcichew which slipped my mind despite orthogeris).

TELEPHONE: 10 minutes to read patient notes investigations etc in one room then asked call the trauma consultant). Scenario is RTA of 23 year old male. ?free fluid in left paracolic gutter and absent pulses. ?compartment syndrome/critical leg ischaemia and possible head injury. Asked what I would do and said CT head and abdo if stable. Asked how to investigate leg. I said I would also consent patient for laparotomy, fasciotomy and possible leg amputation.  Then ran out of time.

REST

Anatomy 1: examiner pointed at bladder, vas deferens, seminal vesicles etc… asked about blood supply and posterior relations of bladder. Also types of bladder cancer (yay shistosomiasis!)

  

Anatomy 2: surface anatomy of ankle. Asked to point out peroneus longus, brevis and tertius. Where do they originate and insert? What happens to foot if tibialis anterior and posterior contract together? Where is EHL and EDL (Surface marking). What are the roots fof the knee and ankle reflexes. Demonstrate knee and ankle jerk. Demonstrate foot pulses. If patient had crush injury what is he at risk of? Sensory distribution of deep peroneal, saphenous, sural and S1?

Anatomy 3: Abdomen. Asked to find ascending colon on cadaver. Where is appendix, caecum and ileum. Demonstrate internal and external oblique. Nerve supply to external oblique. What makes the conjoint tendon and the nerve supply? Which nerve gets damaged in inguinal hernia repair and how does it present? Asked to name all the positions that the appendix can lie in. why does pain refer to RIF? 

CRITICAL CARE 1: 2 examiners, both anesthetists. Given vignette of patient who had TURP and is now confused, hypotensive and hyponatraemic. I said Trans uretheral resection of prostate syndrome likely diagnosis but differentials maybe sepsis, hypovolaemic shock and explained why it was not these things. Asked why TURPS occurs, so I said due to the osmotic actions of glycine the asked what glycine is. I said an amino acid. Then asked why confusion?  So I said that glycine breaks down into ammonia and causes confusion.  Asked what other conditions this occurs in and I said hepatic encephalopathy. Asked management so i said in ITU/HDU and went through how to carefully manage his acute issues.

PATHOLOGY: vignette of someone with gastric ca. asked about epidemiology, pathophysiology, investigations and management. Shown another vignette of patient at 6 months post op now with swollen abdomen so I said ascites likely die to peritoneal mets. Asked how to investigate and overall management in light of all this.

COMM SKILLS: given ten minutes to read patients notes and investigations. Then to explain to patient with obstruction and perforation why he needs surgery. Also explained stoma formation, complications, how long he needs it for…

CRITICAL CARE 2: 2 examiners and 20 minute station. Vignette on someone who had accident, swollen leg, renal impairment etc… discussed that problems due to crush syndrome and resulting rhabdomyolysis. Talked about acute management of his rhabdomyolysis.      

1)  All in all a fair exam in that examiners do give you a chance to prove yourself but you effectively only have 6 minutes to examine/take history and present findings in order to be able to answer as many questions as possible to score points. Most people have the knowledge but you need to compose yourself and be professional at all times! I hope this helps a little in preparing for the exams and I wish you all the best of luck.

Books etc to prepare for MRCS OSCE

When preparing for my OSCES I asked my friend Essie who had already sat and passed her exams for advice on which books to revise with. Although I didn't use al the books she recommended due to time limitations, here are the books I did use:

1. Instant Anatomy: great little book for brushing up on blood vessels, nerves etc... to be used as memory aid rather than for learning from scratch. The free podcasts from the website are also really good.
2. Netter's anatomy atlas. Excellent for learning anatomy from scratch.
3. Get Through MRCS: Anatomy Vivas by Simon Overstall. This book is amazing. 96 pages of anatomy vivas and model answers which really help with structuring answers for exam. It was the one book I couldn't have done on demand.  
4. Master Pass: MRCS Picture Questions Book 2 by Tang and Praveen. This book covered Trauma and Orthopaedics, Transplant, Vascular, Paediatric and Breast surgery. It has amazing pictures and excellent explanations. Can be used as a learning aid.
5. MRCS clinical question book by Catherine Parchment Smith. This book was good for structuring your clinical examinations and useful for anticipating questions around each topic. I dipped into it occasionally but did not use it very much as I was happy with my clinical examinations. Good for targeting weak areas or checking your examinations are in good shape.
6. Rafftery's MRCS book. I used this book for Part A and the pathology section for Part B.

In addition to books I also bought 2 apps on my iphone. Netter's flash cards were useful but I did not learn much from them and it was an expensive app (£20). Rohen's anatomy app is excellent (£15) as it uses dissections and really handy for exam practice as you get dissections in 2 of the anatomy stations.

I also bought the OSCE Cases online course from Pastest as it was on offer for £69. Although they need to do alot of work on the format and increase the content, I thought that Prof Ellis' anatomy lectures were amazing and the OSCE tutorials on the different examinations were excellent. I would not pay more than £69 for the course as it is but if they improve it (Alot of improvements need doing) then it may rival more expensive courses. 

Internet wise, the following free website was absolutely amazing. It allows you to create your own anatomy quiz and uses dissections. The link is http://ect.downstate.edu/courseware/haonline/quiz/practice/u7/quiztop7.htm . Definitely worth trying out. I also discovered Acland's atlas of human anatomy which is a video atlas. You can download/view on University of Warwick's website and youtube. I thought it was very useful as a break from books.

As for critical care, I used the notes I made from the RCS Course that I went on instead of a book. However, if you don't go on the course, these two books cover everything you will need (we got given them free for the course):

1. Surgical Critical Care Vivas by Kanani
2. Applied Surgical Physiology Vivas by Kanani and Elliot

Anyway, I may have gone a little OTT with learning resources but I managed to use all of the above materioals in one way or another to target my weaknesses and it seems to have worked. The trick is to not use everything at once but to start with one or two books and add other learning materials as needed because your weak spots will become evident. Closer to the exam you can start whittling down the books you need.  

Change is coming to IWTBAS

Great news y'all. We have launched the website finally! Although it is still far from finished there are a few pages to keep you occupied for the time being.

Amel

MRCS Courses

Enjoying watching the soccer this weekend but thought I'd give you the low down on the course I went on.

I found it super difficult to pck a course as very little info is available and because they are so expensive I felt more apprehensive about making a bad choice. AFter much debate and searching, I wittled it down to 3 course:
1) The St Thomas' 7 day course costing £1200. So ths course was highly recommended by my Reg because he said they got you to practise stations on real patients. However, as it is very popular, I couldn't get a place on he course.

2) The PASTEST MRCS revision course. Costs £799 and you also get the online revision course for free. This course is run over a weekend so its only 2 days. I didn't go as I wanted something longer. A riend went and said it was excellent. Apparently you get grilled all day as the course is mostly in OSCE format and you go around in circuits. He felt it was very useful.

3) The Royal College of Surgeons' Applied sciences for the MRCS course. This is a 5 day course at the Royal College in London and costs £1000. I went on this course and thought it was fantastic. They explained what the format of the exam would be like, taught anatomy on cadavers in small groups and gave lectures on pathology and critical care. There were also lectures and an opportunity to practise comm skills stations. I think the highlights of the course were the lectures on critical care (very comprehensive) and the anatomy demonstrations. You also get critical care viva and a physiology viva books for free. The two problems with the course is that it didn't cover clinical examination or neuroanatomy.

I don't think you need a course to pass the exam but the royal college course really helped me prepare as I was most concerned with anatomy and critical care. Much of the stuff covered on the course came up in one way or another on the course. Hope you found this useful and if you have any experiences of the other courses please share with us.

Amel

Physiology of The Respiratory System III: Blood flow, Gas exchange and the regulation of Ventilation

Thank you for still sticking with us, I know respiratory physiology isn't everyone's cup of tea but it is essential to know the basics as they frequently come up in exams. So in this final blog on the matter, I'll give an overview of the important concepts goerning blood flow, gas exchange and reglation.

Blood Flow
A good understanding of pulmonary anatomy will be useful to tackle this bit. Pulmonary blood flow is regulated by levels of pCO2 and pO2. Hypoxia or hypercapnia result in vasoconstriction which allows blood to be diverted to better oxygenated areas (this is called hypoxic vasoconstriction). Flow is determined by perfusion pressure and resistance. The three pressures that determine blood flow in the lung are:

1. Hydrostatic pressure in the pulmonary arterioles
2. Pressure in the pulmonary veins
3. Pressure of air in the alveoli

The blood flow in the lung can be divided into zones:

1. Zone 1: this is the apex of the lung. Blood flow is low in this region as alveolar pressure is similar to pressure  in the pulmonary arterioles so smaller vessles become compressed. 
2. Zone 2: here the pressure in the arterioles is higher than alveolar pressure so blood flow is better.
3. Zone 3: The pressure in the arterioles is at its greatest in comparison with the pressure in the alveoli thus blood flow is highest here. This area corresponds with the bases and explain why vasculitic disease affects the bases.

Ventilation and Perfusion
The ventilation to perfusion ratio varies through out the lung and depends on the pressure in the arterioles:

• V/Q = infinity in alveoli that are ventilated but not perfused.
• V/Q = zero in alveoli that are perfused but not entilated.
• At the apex, V/Q = 3 which means that the alveoli are ventilated better than they are perfused. Whilst at the bases V/Q = 0.6 which indicates that the alveoli are perfused better than ventilated. 
• The ideal V/Q is found 2/3 of the way up the lungs.

 Gas Exchange
The diffusion of gases is affected by:

1. Pressure gradient: this is the partial pressure and involves the flow of air from an area of high pressure to lower pressure
2. Diffusion coefficient: this is the ease with which a gas can diffuse and is determined by its solubility in water as well as molecular weight.
3. Tissue factors: the tissue at site of diffusion should have a large surface area and short diffusion distance.

Sysemic venous blood is pumped into the pulmonary arteries from the right ventricle. This blood has a pO2 of 5.3 kPa and pCO2 of 6 kPa whereas alveolar pO2 is 13.7 and pCO2 is 5.3.  Thus oxygen will diffuse into the bood as it has a lower partial pressure whilst carbon dioxide will diffuse into the alveoli. This results in oxygenated blood transported back to the heart via the pulmonary veins. Physiological shunting (passage of blood through the lungs without going through the alveoli) occurs as bronchial blood mixes with the oxygenated blood therefore the partial pressure of oxygen in systemic blood is lowered to 13kPA. Pathological causes of shunting include pneumonia, ASD, VSD and Patent ductus arteriosus.

Oxygen is predominantly transported by haemoglobin and only a miniscule amount is dissolved. The oxygen dissociation curve shows the relationship between the partial pressure of oxygen and the concentration of oxygen in the blood. The position of the curve is altered by several factors:

1. Right shift decreases oxygen affinity thus oxygen is released at higher partial pressure. This is caused by raised temperature, increase in levels of 2,3-diphosphoglycerate (2,3-DPG) and increased H+. Right shift of the dissociation curve is called the Bohr effect.
2. Left shift increases oxygen affinity and thus oxygen is released at lower partial pressure. 

Foetal Haemoglobin and Myoglobin
Adult Hb has two alpha and two beta chains whilst foetal Hb has two gamma chains as well as two alpha. The change in globin chain results in greater affinity for oxygen thus allowing the foetus to extractblood from the maternal circulation. The curve for HbF is to the left of adult Hb as there is greater affinity for oxygen. Myoglobin has an even greater affinity for oxygen and so its curve is even further to the left as it is an oxygen storage molecule which only releases O2 when the partial pressure has dropped significantly. The function of myoglobin is to provide additional oxygen during anaerobic respiration.


Carbon Dioxide
CO2 is transported in three ways:

1. Carbamino groups which are formed between CO2 and proteins/peptides. 
2. Dissoved
3. HCO3- makes up arund 70% of transported carbon dioxide. It forms when carbon dioxide diffuses into red blood cells and reacts with water to give carbonic acid which dissocites to H+ and HCO3-. The H+ binds haemoglobin and the bicarbonate diffuses into the plasma. The reverse of this process occurs in the alveoli (bicarb diffuses into the cell to produce CO2 which can be expired).

The CO2 dissociation curve differs from that of oxygen as it has no plateau phase as blood can not become saturated with CO2, carbon dioxide is far more soluble than oxygen and the normal rnge for CO2 is narower (5.3-6kPa). The curve is influenced by partial pressure of oxygen thus the amount of CO2 carried increases as oxygen levels fall (this is called the Haldane effect).

Regulation

• Neurological: this occurs via the medulla oblongata, Pons, cerebral cortex and Limbic system. In the medulla inspiratory neurons rhythmically fire action potentials which stimulate the diaphragm and external intercostals to contract this is followed by intervening periods of inactivity when expiration occurs. Expiratory neurons in the medulla are inacive during quietrespiration but during increased respiration fire action potentials to stimulate the internal intercostals and abdo muscles to contract thus producing forced expiration. In the pons, the apneustic centre prolongs inspiration and reslts in short expiratory efforts whilst the pneumotaxic centre inhibits inspiritory neurons to shorten inspiration. Neither of these centres are essential for respiration. The cerebral cortex can override neurons in the medulla to increase ventilation or reduce it/hold breath. Finally, in extreme emotional states, the limbic system may influence respiration.
• Chemical: central and peripheral chemoreceptors monitor changes in arterial PCO2, pH and PO2. Central chemoreceptors are found in the CNS close to the resp centre in the medulla and are especially sensitive to changes in pCO2. As CO2 diffuses into the blood in the brain, it reacts with water to give H+ which causes a fall in pH. This fall stimulates the central chemoreceptors which increases the resp rate in an attempt to blow off CO2. The opposite occurs with low CO2. Peripheral chemoreceptors are located in the carotid bodies and are less important than central chemoreceptors. They respond to changes in arterial pH and low levels of pO2. Thus a fall in arterial pH due to metabolic acidosis will stimulate respiration and thus lower the level of CO2 to bring pH back to normal. The response to low oxygen is only seen when pO2 is less than 8kPa. The importance of this mechanism is witnessed in chronic lung disease whereby persistently elevated carbon dioxide levels cause the patient to become accustomed to it and thus lose the effect low pCO2 has on chemoreceptors. Thus they rely on low levels of pO2 to stimulate respiration and is called the hypoxic drive. 

Hypoxia, hypoxaemia and respiratory failure
Hypoxia is a reduction of oxygen in the tissues and is classified as:

1. Hypoxic hypoxia: due to low arterial pO2 and caused by high altitude, PE, hypoventilation, lung fibrosis and pulmonary oedema.
2. Anaemic hypoxia: decrease in amount of haemoglobin which leads to a decrease in oxygen and is due to haemorrhage, reduced red cell production, haemolysis and carbon monoxide poisoning.
3. Stagnant hypoxia: due to low blood flow which maybe due to vasoconstriction or reduced cardiac output.
4. Histotoxic hypoxia:  this occurs when the enzymes involved in cellular respiration become poisoned and thus are unable to use oxygen. The main cause of this is cyanide poisoning.

Hypoxaemia is a reduction in the concentration of oxygen in arterial blood. It is caused by:

1. Hypoventilation: this may result from CNS depression, trauma, neuromuscular disorders and chest wall deformity. It may be treated using oxygen therapy.
2. Impaired diffusion: this can be caused by asbestosis, sarcoidosis and ARDS. It maybe treated by oxygen therapy.
3. Shunt: this is not improved by oxygen therapy.
4. V/Q mismatch: this usually occurs in chronic lung disease and results in mismath between ventilation and perfusion.
5. Reduction in inspired Oxygen tension

Respiratory failure is present if PaO2<8kPa and is subdivided into:

• Type I: PaCO2 < 6kPa and is due to ventilation-perfusion mismatching. The PaCO2 is normal or low as the increase in ventilatory rate results in compensation by remaining alveoli for any increase in CO2. Causes of Type I resp failure include pneumothorax, pneumonia, contusion, PE and ARDS.
• Type II: PaCO2 > 6kPa. This is largelydue to hypoventilation and caused by COAD, neuromuscular disorders, airway obstruction, central respiratory depression and chest wall deformity.

Well that's it for respiratory physilogy, hope it was useful.

Amel

Physiology of The Respiratory System II: Lung Function Tests

The assessment of lung volumes is important in dignosing respiratory disease and monitoring progression. Spirometry is used to measure lung volumes. It is important to know the definition of each lung volume in order to be able to intepret spirometry findings and their relevance:

• Tidal Volume (TV): air breathed in and exhaled during quite respiration
• Inspiratory reserve volume (IRV): maximum volume of air that can be inspired on top of normal inspiration
• Expiratory reserve volume (ERV): maximum amount of air that can be forcefully expired after normal expiration
• Functional residual capacity (FRC): volume of gas left in the lungs after expiration during normal breathing. This can be determined using the helium dilution method. This involves the patient breathing normally from a spirometerfilled with a known volume of helium and air thus as they breath in and out, the helium is diluted into the air that is left in the lungs 

FRC = (initial helium concentration of spirometer) x Volume/(final helium concentration) 

• Residual volume (RV): volume remaining after maximal expiration. It can't be measured directly but is calculated as RV= FRC - ERV
• Total lung capacity (TLC): the sum of all volumes plus the residual volume
• Vital capacity (VC):volume of air expelled from maximal inspiration to maximal expiration

Dead space
The concept of dead space is important to grasp as this is the volume of air which does not take part in gas exchange. The are two types:

1. Anatomical: the volume of gas which does not mix with air in the alveoli. It can be determined using Fowler's method. This involves the patient breathing through a tube connected to a nitrogen analyser. The patient initial takes a single breath of pure oygen, holds their breath for several seconds and breathes out. This will determine deadspace as only the alveoli will have maximal concentrations of nitrogen whilst the higher up airways will have purer concentrations of oxygen as they did not participate in gas exchange. Thus if a curve is drawn, air initially expired will not have nitrogen as it is part of the anatomical deadspace whilst nitrogen concentrations will increase as alveolar air is expired.
2. Physiological: this is the volume of gas that reaches the alveoli but due to a lack of perfusion does not take part in gs echange. It can be determined using the Bohr equation

Volume of deadspace= Volume expired CO2(1-(Fraction of expired CO2/Fraction of alveolar CO2))

Alveolar Ventilation rate
This is the rate at which gas exchange occurs in the alveoli.
Alveolar ventilation rate= (TV-dead space) x Respiratory rate

Peak Expiratory Flow rate
This is a cheap and simple test that can be performed at the bedside. A patient is asked to take a maximal inspiration and then blow out as fast as possible into the peak flow meter. It is useful in assessing the severity of asthma attacks and monitoring treatment.

Closing Capacity
This is the volume of the lungs at which airways at the base of the lung start to close. It is normally 10% of vital capacity and can be assessed by getting the patient to breath a maximal inspiration of 100% O2 then expiring fully through a nitrogen analyser. A graph can be plotted which will show 4 phases:

1. Pure dead space is exhaled so its 100% oxygen
2. a mixture of deadspace and alveolar gas (increasing concentration of nitrogen)
3. pure alveolar gas (reaches a plateu)
4. abrupt increase in nitrogen as airways at the base of the lung close and therefore not participating in gas exchange so the expired air is coming from the apex which has received less oxygen thus the nitrogen is more concentrated.

 Factors that affect the closing capacity include increasing age, supine position and anaesthesia which increase it.

Diffusion Capacity
This tests the diffusion capacity of the alveolar membrane and pulmonary vasculature. It is measured by inhaling small amounts of carbon monoxide and measuring its levels in the blood.Diffusion capacity is most commonly reduced in pulmonary oedema (as diffusion distance is increased) and emphysema (causes loss of alveolar surface area).

Flow-Volume and Volume-Time Curves
These can be plotted using spirometry results and are important because certain pathological processes such as obstructive lung disease cause typical curves.

Well that's it for now from me. Watch out for the third and final respiratory physiology tutorial. By the way if there are any specific topics you'd like us to cover/discuss just leave a comment/send an email and we'll get on to it.

Amel

Physiology of The Respiratory System I: Mechanics of Ventilation

Although I generally find physiology a tad on the dry side, a good foundation in this is vital for success in Surgical exams and patient care. I thought we could start with the respiratory system as I'm currently doing a Resp job.

Components of the Respiratory system

1. Nasal passages
2. Olfactory system
3. Conducting airways
• Nasopharynx
• larynx
• trachea
• bronchi
• bronchioles
• Alveoli

Functions of the respiratory system

1. Cleaning, humidification and warming/cooling of air: this is achieved by the nose hairs, mucociliary escalator and air flow through the conchae.
2. Respiratory gas exchange: flow of gases depends on pressure gradient between atmosphere and alveoli which can be represented as V (rate of air flow)  = Palveoli - Patmosphere/R (resistance). Thus bronchoonstriction leads to reduced air flow due to increased resistance.
3. Facilitation  of olfaction and sound production

Mechanics of Ventilation

Inspiration is an active process. At the start of inspiration the intrapleural pressure is about -4cmH2O. This decreases to around -9cmH2O when respiratory muscles contract to increase increase chest volume. This change in intrapleural pressure causes lung expansion and generation of of a negative intralaveolar pressure. The result of this is that atmospheric pressure is higher leading to air inhalation.  (NB at rest around 500mL of air is inhaled, during excercise pressure can decrease down to -30cmH2O and thus 2-3L of air can be inhaled).

Expiration is passive due to elastic recoil of the lung. However, during excercise, contraction of the accessory muscles of respiration (internal intercostals and abdominal muscles) can generate intrapleural pressures of up to +20cmH2O to expel air more quickly.


Pressures and forces acting on the Lung
Three forces act on the lung:

1. Elasticicity of the lungs: under normal conditions this keeps the lungs stretched whic results in a force that pulls inwards on the visceral pleura.
2. Surfactant: lines alveolar surfaces and produces surface tension thus producing an inward pressure which accounts for 2/3 of elastic recoil. Surfactant also increases lung compliance thus reducing work of breathing, prevents fluid accumulation in alveoli and reduces alveolar instability [ΔP (alveolar distending pressure) T (tension)/r (radius)] by stopping them from collapsing.
3. Negative intrapleural pressure: opposes the above two forces and is created by the chest wall and diaphragm pulling the parietal pleaura outwards. This results in the two layers of the pleura being pulled in opposite directions leading to a negative pressure.

 The pressure in the alveoli is equal to atmospheric pressure which is 0cmH2O. As intrapleural pressure is between -4 and -9cmH2O this results in a transmural pressure which keeps the lungs distended.

Compliance
This is the ease with which lungs can be inflated and can be expressed as:

Compliance = ΔV (change in volume)/ΔP(change in pressure)

It is governed by elsticity of the lung parenchyma and surface tension. Thus compliance is reduced in scarring or fibrosis of parenchyma, pulmonary oedema, deficiency of surfactant, reduced lung expansion (e.g. motor neurone disease/muscular paralysis), supine position, mechanical ventilation (due to reduced pulmonary blood flow), age and breathing 100% O2. Conversely, emphysema increases lung compliance to destruction of elastic fibres in the lung parenchyma. 

Regional differences in Ventilation

In the upright position the apices are less ventilated than the bases. This is due to gravity and the fact that the pressure-volume curve is sigmoid shaped and thus the two parts lie on diferent areas of the curve. This is because the bases lie on the diaphragm and are compressed whereas the apices re already stretched by their own weight this inflation begins further along the pressure-volume curve.

Well that's it for now, I shall be writing another two posts on Respiratory phyiology. The next shall be on Lung Function tests and the final on Blood flow, Gas exchange and the regulation of Ventilation. For more info, I found the following webites useful: www.acbrown.com/lung/www.acbrown.com/lung/Lectures/RsVntl and www.medicine.mcgill.ca/physio/resp-web. Hope this has been useful.

Amel

MRCS Part B - Part deux

Going to meet Essie for coffee next week. She MRCS Part B in October and passed as an F1 (never having done a single surgical job). She'll give me an update on what came up, which books she used, how she revised etc... will keep you posted!

MRCS Part B

So the next Part B exam is coming up in May. As the exam is relatively new, it can be a bit of a cahllenge preparing as there isn't the wealth of information out there for other exams. The format for the exam is OSCEs with 18 stations (4 of them rest stations). On application (DEADLINE is 19th March!!) you are asked to decide he following:

1. Choose a region in which you will be assessed on Anatomy, History taking and physical exam.
2. Choose a region in which you will be examined on History taking and physical exam.
3. Choose a region on which you will be assessed on physical exam alone.
4. The rest of the exam will be basic surgical skills, communication etc...
5. The regions available are Thorax and Trunk, Head and neck, Limbs and Spine as well as Neuro. You can only pick one region per assessment and can't pick the same region more than once.

Advise from other people who have sat the exam and passed has been:

1. Revise your anatomy very well as there are anatomy stations. However, on applying you get to pick which region you would like to be examined on.
2. Read up on physiology and pathology.
3. There is no substitute for clinical experience so increase your exposure by going to clinic, theatre etc...remember people are supposed to sit the exam in their surgical training years although more and more junior people are sitting it early.
4. Get a good clinical tutor who can take you through examining patients correctly and test your knowledge as preparation for the exam.
5. If you work in groups and know people who are sitting the exam; revise together as you can get constructive feedback.
6. The area of going to revision courses is still contentious but most people go to courses in order to get a structure for their revision and polish their performance. I will try and research some of the courses and give feedback on this blog.

So here you are. A little breakdown of the exam. I must admit I'm finding it difficult to get meaningful advise about how to prepare for the exam but like any exam, I guess knowing your stuff well and seeing as many patients as possible is key to being successful.  Things that do not help in focusing on revision is knowing that you can only take this exam 4 times and the cost of the exam as well as revision courses/books. Its important to remember though that even failure in the exam itself should not be seen as a collossal negative as it can just act as a mock for the next time you sit it. Good luck and watch this space for more info on revision tools for Part A and B.

Amel

MRCS approaches

The spectre of MRCS looms ever closer and we will be blogging regular posts to help with preparation. Ideally, you should have started thinking about revisng for Part A by now as the exam's in April. Revision tips and advice will be published by Mr T very soon. From experience, I found that there are a few things that were vital in my passing the exam:

1) Anatomy revision: REVISE REVISE REVISE anatomy as the first paper has anatomy & Physiology only. I really liked "Instant Anatomy" (little orange book) as it was concise, split into logical chapters and had diagrams that were easy to memorise.

2) "Basic Sciences for the MRCS" by Rafftery is invaluable for learning physiology and if you want to brush on some pathology. The anatomy section is a little weak (as I unwittingly told the author whilst I was awaiting to sit the second paper and really didn't stop to think why someone who looked quite senior would ask what I thought of the book!!!) but you can't have everything. If you're good at learning anatomy from text rather than need viusal aids (as I do) then the anatomy sections will do very nicely for you. One thing to make note of is that although dry, make note of the little details like paths of major nerves and embryonic development as they do come up in the exam.

3) PASTEST question bank all the way! Honestly, I'm not being paid/sponsored by them before the accusations start flying but those questions were life savers. I did not revise any pathology as that was my strong point and I wanted to focus on anatomy and physiology which I was dire in. I did every single question on the database and the pathology was spot on! Its the exact same level and many of the exam questions were very similar.  Also make sure you dont just do EMQ/SBAs as although the exam is in that format, T/F questions will test your knowledge to a higher detail and all practise is useful to building knowledge. The anatomy and physiology questons were also very useful but you definitely need to revise these to a bit more detail for the exam.

4) Try to get a few days off as zeros/annual leave around the exam if at all possible so that you can touch up on areas of weakness.

Anyway, that's it for now. Watch this space for more MRCS Part A and B information from all of us.

Amel