Question of the Day... Pseudomembranous colitis

This question was taken from May Edinburgh 2013 exam.

Question:

What is pseudomembranous colitis? What is the organism responsible and what is the pathophysiology?

Answer:

Pseudomembranous colitis is inflammation of the bowel associated with clostridium dificile and is a cause of antibiotic-associated diarrhoea.

Pathophysiology

The use of broad spectrum antibiotics such as cephalosporins or penicillin based antibiotics such as amoxicillin cause alteration of the normal bowel flora. The antibiotic kills off other competing bacteria in the intestine and any bacteria that remains has less competition for space and nutrients. Clostridium dificile may colonize the gut usually but when over-extensive growth due to less competition, in conjunction with toxins produced by the Clostridium dificile results in pseudomembranous colitis

Pseudomembranous colitis

The pseudomembranes on the mucosa of the colon or rectum is diagnostic. The pseudomembranes are composed of an exudate made of inflammatory debris, white blood cells.

For your information... Anti-platelet medication

There are several commonly used anti-platelet medications that are used in medical practice but for the purposes of MRCS I suggest learning about 2.

Aspirin
Inhibits the production of thromboxane A2, which then prevents further platelet aggregation at the site of a platelet plug.

Clopidogrel (Plavix)
Irreversibly inhibits an ADP chemoreceptor on platelets, also preventing further platelet aggregation at the site of a platelet plug.

For you information... Haemostasis

This question is taken from the London Feb 2013 exam.

Question:
What are the stages of haemostasis?

Answer:
Haemostasis is a process that causes bleeding to stop. There are 3 steps that occur in rapid sequence.

1. Vasoconstriction (vascular spasm): The damaged blood vessels contract as the first response to injury. This reduces blood flow to the area and limits the amount of blood loss. It is triggered by local pain receptors as well as local chemicals released by the damaged endothelial cells.
2. Platelet plug formation: Platelets adhere to the damaged endothelium to for a platelet plug and seals up the break in the vessel wall. They then release chemical mediators such as adenosine diphosphate (ADP), serotonin and thromboxane A2 that potentiate more platelets to adhere to the platelet plug.
3. Activation of the coagulation pathway: The platelet plug is reinforced by activation of the coagulation pathway and the subsequent products. Fibrinogen is converted to fibrin by thrombin. Clot regulation occurs through a negative feedback loop to prevent excessive clotting.

Mnemonics... Pancreatitis

Here is a common but neat way to remember the causes of Pancreatitis:

I - Idiopathic

G - Gallstones
E - Ethanol (Alcohol consumption)
T - Trauma

S - Steroids
M - Mumps
A - Autoimmune (SLE, RA)
S - Scorpion sting
H - Hyperlipidaemia
E - ERCP (Iatrogenic)
D - Drugs

For Your Information... Granuloma

What is a Granuloma?

A granuloma is a collection of activated macrophages!

Question of the Day... Critical Limb Ischaemia

This question is taken from the May Edinburgh 2013 Exam.

Question:
What are the diagnostic criteria for critical limb ischaemia?

Answer:
There are 3 main criteria for critical limb ischaemia.

1. Rest pain
2. Tissue loss
3. Ankle pressure of <50mmHg, ABPI <0.4, or Toe pressure of <30mmHg

Critical limb ischaemia is where the occlusion is no longer acute and the viability of the limb is threatened, requiring immediate management.

It is classically described with the 6 Ps:

Paraesthesia

Pain

Pallor

Pulselessness

Paralysed

Perishingly cold

Management of Critical Limb Ischaemia

In MRCS, the thing that you must remember is everything comes back to 1st principles. So when asked about management, first you talk about confirming the diagnosis (i.e investigations) then you talk about treatment. When talking about treatment, always start with A, B, and C.

A: Airway - intact

B: Ensure Oxygen is given

C: Ensure aggressive fluid resuscitation to avoid Reperfusion Syndrome. Place the patient on cardiac monitoring and monitor Urea and Electrolytes regularly. Consider doing an ABG and Lactate to further monitor acidosis and ischaemia

Management of CLI

In a nutshell!

Question of the Day... General Anatomy

These questions are taken from the Singapore Oct 2013 MRCS Part B OSCE Exam.

Question:

Name the 1st 2 branches of the ascending aorta.

Answer:
The ascending aorta has 2 branches, the Right and Left coronary arteries. The RCA arises from the anterior aortic sinus and the LCA arises from the posterior aortic sinus. You need to know 2 main branches from each coronary artery and what it supplies

RCA
The 2 main branches of the RCA:

1. Posterior interventricular branch
2. Right marginal branch

LCA

The 2 main branches of the LCA"

1. Anterior interventricular branch
2. Left circumflex artery

Question:

What is the course of the splenic artery?

Answer:

The splenic artery arises as one of the branches of the coeliac trunk and runs along the superior surface of the pancreas in the lienorenal ligament to the hilum of the spleen.

Question of the Day... Flail chest

Question:
Describe the features of a flail chest.

Answer:
Flail chest is when there is a free segment of the thoracic wall. This usually means 3 or more ribs broken at 2 points causing the segment to lose bony continuity with the rest of the chest wall.

Question:
How much bloods loss can be anticipated from a rib fracture?

Answer:
Up to 150mls of blood loss from rib fractures.

Question:
What are the implications of a flail segment?

Answer:
There are 4 main implications of a flail segment.

1. The inability to generate adequate negative intrathoracic pressure for inspiration due to the free segment can cause respiratory fatigue and subsequently Type II respiratory failure. This is a failure of ventilation, not of oxygen transfer therefore the patient will have hypercapnia.

2. Presence of a flail segment is indicative of high impact forces. As the chest wall is relatively pliable, a large amount of force is required to cause rib fractures. Such high forces may indicate the presence of other injuries.

3. There may be other underlying injuries. Haemothorax, pneumothorax, pulmonary contusions, diaphragmatic ruptures and cardiac trauma, including cardiac tamponade, are all possible concurrent diagnoses.

4. Infection and pneumonia in later stages is also a complication due to the inability to ventilate the lower lobes of bilateral lungs due to pain, or due to cardiac contusions.

Mnemonics... Bronchopulmonary segments

Another mnemonic to help remember the bronchopulmonary segments of the right and left lung

Right

A PALM Seed Makes Another Little Palm

Upper

Apical
Posterior
Anterior

Middle

Lateral
Medial
Superior

Basal

Medial
Anterior
Lateral
Posterior

Left

ASIA ALPS

Upper

Apicoposterior - 2 segments
Anterior

Lingula

Inferior
Superior

Basal

Anteromedial
Lateral
Posterior
Superior

Question of the day... Airway managment

Question:
What techniques of airway management do you know?

Answer:
Airway management techniques can be divided into 2 broad categories.

1. Simple techniques

These measures are quick and temporary techniques.

Jaw thrust

Chin lift

Adjuncts e.g. OPA and NPA

 

Suction

2. Definitive techniques

These measures can protect the airway for longer periods of time.

Nasotracheal

Orotracheal intubation

Surgical airway

- surgical cricothyroidotomy

- needle cricothyroidotomy

- tracheostomy

Question of the Day... Central Venous Pressure

Question:
Explain the procedure for orotracheal intubation.

Answer:

1. Gather all equipment and required medications
1. Laryngoscope
2. Endotracheal tube
3. Stylet/bougie
4. Tape to secure ETT
5. 10ml Syringe to inflate cuff with air
6. Sedative such as midazolam
7. Paralytic e.g. sux
8. Ventilator
9. Capnograph
2. Pre-oxygenate with 100% Oxygen for 3-5 mins
3. Position patient - sniffing the air position
4. Administer medication
1. Should be given with running IV fluids
5. Laryngoscopy
1. Pass ETT just beyond vocal cords
6. Intubation
7. Inflate cuff
8. Check position via auscultation and capnograph
9. Secure ETT
10. Check CXR if applicable

It's usually easier to watch than read.

For your information... Pneumothorax

There are 3 types of pneumothoraces:

SIMPLE:
A simple pneumothorax occurs when air gets trapped between the potential space of the visceral and parietal pleural. This causes compression of the lung and can cause pain and shortness of breath. Signs include decreased breath sounds on the affected side, tachycardia, tachypnoea, resonance on percussion and occasionally subcutaneous emphysema.

Diagnosis is with chest X-ray.

XR of Pneumothorax

Treatment:

1. Administering 100% Oxygen
2. Insertion of a tube thoracostomy
1. This can be a small calibre tube as there is only air in the pleural cavity. Consider a large bore tube if pleural effusion, haemothorax, or chylothorax also present.
3. If persistent, surgical methods may be required to control the pneumothorax
1. VATS and pleurodesis - either powder or mechanical
2. Pleurectomy

TENSION PNEUMOTHORAX:
This is when a one way valve effect causes air to rapidly build up in the pleural cavity without the ability to be released, causing pain and severe SOB. The compression effect causes a variety of physiological changes, the most severe being cardiogenic shock due to compression of the heart from the air. This results in decreased cardiac output as the heart is unable to be filled and can rapidly lead to collapse and death. Signs of a tension pneumothorax include the above as well as a deviated trachea to the contralateral side of the lesion, hyper-resonance on the affected side, raised JVP and haemodynamic instability.

Diagnosis is clinical.

Treatment:

1. Immediate insertion of a needle thoracostomy
2. Large bore IV cannula is placed in the mid-clavicular line, 2nd intercostal space
3. Correct placement is confirmed with hissing sound of air escaping
4. Follow up with definitive tube thoracostomy

OPEN PNEUMOTHORAX:
An open pneumothorax is when there is a free communication with the external environment resulting in the body's inability to generate negative intra-thoracic pressure leading to respiratory fatigue and eventually failure.

Diagnosis is clinical

Treatment:

1. Fashioning of a 3 way flap to cover the opening
2. This allows air to be pushed out during expiration but stops air from entering during inspiration and allows adequate negative intra-thoracic pressure for inspiration
3. Follow up with definitive tube thoracostomy

Mnemonics... Risk factors for Atelectasis

Here is another round of atelectasis based mnemonics...

The 5 Ps - Risk factors for atelectasis

• Plump
• Pensioner
• Pain
• Pulmonary
• Pollution

Plump - Those with BMI >27

Pensioner - Age >60

Pain - Upper abdominal or thoracic surgery causing pain leading to lack of deep breathing

Pulmonary - COPD

Pollution - smokers

The 6 Ps - Management of atelectasis

• Position
• Pain management
• Prompt mobilisation
• Puffing air
• Positive Pressure
• Purge

Position - keep patients upright

Pain management - allowing patients to breathe deeply and recruit alveoli

Prompt mobilisation - allow patients to walk early

Puffing air - breathing exercises

Positive Pressure - CPAP

Purge - suctioning mucus

Question of the day... ARDS

How do you define ARDS?

ARDS (Acute Respiratory Distress Syndrome) is a combination of acute respiratory failure combined with non-cardiogenic pulmonary oedema. It is characterised by decreased lung compliance and hypoxaemia that is refractory to oxygen therapy.

The main features of ARDS are:

1. Diffuse pulmonary infiltrates

2. PaO2/FiO2 ratio of <200mg
- this indicates that the acute respiratory failure is refractory to oxygen therapy
- normal PaO2 = 80-100mmHg
- room FiO2 = 0.21 (21% O2 in atmospheric air)
- if PaO2 is not available, SaO2 can be used as a surrogate

3. Pulmonary wedge pressure <16mmHg
- this indicates that the left atrial pressure is normal, therefore that pulmonary oedema is not cardiogenic

For your information... Thoracic surgery incisions

The main ways to access the thorax:

Median Sternotomy

- allow access to mediastinum

Posterolateral thoracotomy

- most common

- allows access to lung, pericardium and lung, and the aorto-pulmonary window

Anterolateral thoracotomy

- follows the 5th intercostal space to the sternal edge

Clamshell (Bilateral anterior thoracotomy)

- below each nipple connecting at xiphisternum

Mediastinoscopy

- 2 FB above sternal notch

- allows viewing of subcarinal LN for disease staging and progression

Mnemonics... ARDS

It's mnemonic time! To remember things, I find that making my own mnemonics help greatly instead of using others. Hope you find this helpful.

The causes for ARDS (Acute Respiratory Distress Syndrome) can be divided into Localised and Systemic.

Localised

TEN CAPS

Trauma

Embolism (Fat - due to long bone fractures)

Near Drowning

Cardio-pulmonary bypass

Aspiration

Pneumonia

Smoke inhalation

This list is NOT in order of most likely to least likely, just a list to remember

Systemic

MADD TITS

Multi-trauma

Acute pancreatitis

Drugs

Disseminated Intravascular Coagulation

Toxic Inhalation

Transfusion (massive)

Sepsis

Again, not in order of probability.

For your entertainment, here is a picture of ten caps.

Question of the day... Chest tube insertion

Today I studied surface anatomy of the thorax. So many times I see my own chest in the mirror and don't think about what's going on underneath. But clinical question time.

Indications of a tube thoracostomy include:

1. Pneumothorax
• Open vs closed
• Simple vs tension
• The diagnosis of a tension pneumothorax is purely clinical and an immediate needle thoracocentesis should be performed in the midclavicular line in the 2nd intercostal space to relieve the tension before a definitive tube thoracostomy is performed 
2. Haemothorax
3. Haemopneumothorax
4. Hydrothorax
5. Chylothorax
6. Empyema
7. Pleural effusion
8. Patients with penentrating chest wall injury who are/about to be intubated
9. Those at risk of pneumothorax about to undergo air transport

Contraindications:

1. Need for emergent thoracotomy

Relative:

1. Coagulopathy
2. Pulmonary bullae - COPD
3. Adhesions - previous thoracic surgery
4. Loculated pleural effusions or empyema
5. Skin infection over chest tube insertion site

What are the borders of the triangle of safety when performing a tube thoracostomy?

• Medial - lateral border of the pectoralis major
• Inferior - 5th intercostal space, or above the 6th rib
• Lateral - mid axillary line
• Apex - below the axilla

Go above the rib because this means the intercostal neurovascular bundle runs in the subcostal groove and thus will not be injured.

My MRCS Part B Journey

Today I begin studying for my MRCS part B exam. Hopefully I'll have the discipline and will power to study hard, while reviewing what I've studied here every night. Then we can all help each other with our studies! For now I think I'll just read my way through the syllabus and make sure that I'll be studying what I need to know. For those of you who are considering taking your MRCS Part B, here is the syllabus:

NUS MRCS Instructions