Anaesthesiology - Anatomy Flashcards
Describe Central line
Locations for central line insertion
insertion of a thin, flexible catheter which is usually placed in a large vein going towards the heart. These catheters may have single or multiple lumens and can be inserted into neck or femoral veins.
Locations:
Internal jugular vein
Subclavian vein
Femoral vein
Describe PICC
PICC (peripherally inserted central catheter) are usually inserted in the upper arm through large peripheral veins (e.g. brachial, cephalic, basilic).
The tip of the line ends in the superior vena cava (SVC), so it is still considered a central line.
Indications for central line insertion
Venous access
1. Difficult peripheral venous access
2. Infusions of irritant or toxic substances e.g. concentrated ions, strong vasopressors, total parenteral nutrition (TPN), chemotherapy
3. Long term venous access required e.g. prolonged course of antibiotics in infective endocarditis
4. Potential major fluid shifts or blood loss during surgery
5. Multiple blood sampling needed
Monitoring
- Monitoring of central venous pressure (CVP) in certain types of surgery e.g. liver surgery, cardiac surgery, neurosurgery
Conduit for other procedures
1. Transvenous pacing
2. Renal replacement therapy/ plasmapheresis
3. Pulmonary artery catheter (PAFC) placement
4. Emergency aspiration of large air embolus
Contraindications for Central Line insertion
- Patient refusal (absolute contraindication)
- Infection over insertion site
- Coagulopathy, thrombocytopenia (correct before insertion)
- Uncooperative patient
- Inability to lie flat (unless having femoral line)
Outline the course of the IJV
starts as a continuation of the sigmoid sinus at the jugular foramen
» descends in the carotid sheath lateral to internal, then common carotid arteries together with the vagus nerve
» passes deep in space between the sternal & clavicular heads of sternocleidomastoid
» joins the subclavian vein at the sternal end of the clavicle to become brachiocephalic vein.
Define the anterior and posterior structures to the IJV
Anterior- skin, fat, platysma then sternocleidomastoid muscle once lower in neck, fascia
Posterior (from above)- lateral C1, preverterbral fascia, vertebral muscles, transverse cervical process, sympathetic chain, root of neck, pleura, thoracic duct (left side only).
Define the approaches to central line insertion at the IJV
High approach: Palpate the mastoid process & the sternal notch. Draw an imaginary line between these 2 landmarks and the entry point of your needle is the halfway point on this line. Palpate the carotid artery and ensure you are lateral to it.
Low approach: The internal jugular vein is accessed at apex of the triangle formed by the 2 heads of sternocleidomastoid. Also palpate and ensure you are lateral to the carotid artery.
Advantages & disadvantages
High approach: Less risk of pneumothorax, higher risk of hitting carotid artery
Low approach: Higher risk of pneumothorax
Complications of IJV insertion
Iatrogenic damage:
i. Carotid artery- bleeding, haematoma, stroke
ii. Pleura- pneumothorax
iii. Myocardium- arrhythmias, cardiac tamponade
iv. Nerves
* Vagus- hoarse voice
* Sympathetic chain- Horner’s syndrome
* Phrenic- dyspnoea, raised hemi-diaphragm
v. Thoracic duct- chyle leak, chylothorax (left sided insertion only unless patient has aberrant anatomy)
Related to indwelling catheter
* Thrombosis
* Vein stenosis
* Infection
* Kinking, line blockage
Related to actual insertion process
* Air embolism
* Guidewire loss, shearing of guidewire, retained foreign bodies
Procedures for placing IJV central line
a. Obtain informed consent
b. Trendelenberg position, with face turned to opposite side being cannulated
(This position will increase central venous pressure- making vein fuller and easier to visualise/cannulate and reduce the risk of air embolism)
c. Use ultrasound- visualise vein and carotid artery. Can aid in cannulating vein at 1st pass, avoid hitting the carotid artery, ensuring guidewire is in the vein before dilating. Is also helpful in patient with difficult surface landmarks e.g. those with a short, fat neck
d. Strict septic technique- full gowning, chlorhexidine skin prep & sterile field
e. Use local anaesthetic if patient is awake. Prime all lumens with saline
f.** Visualise internal jugular vein with USS** halfway along imaginary line drawn from mastoid process to sternal notch. Make sure you can see where the carotid artery is
g. Cannulate vein with needle via Seldinger technique (guidewire through needle). Watch the ECG for arrhythmias. Dilate before cannulating vein
h.** Ensure blood can be aspirated** from all lumens. Flush line with saline & suture into place
i. Safely dispose of all the sharps
Define Anatomical position for the tip of central line
Complications of misplaced central line
For neck lines, the line tip should lie in the superior vena cava (SVC) above the right atrium (RA). On CXR, the level of the carina is a useful landmark.
Complications if line goes into RA:
- risk of eroding through the myocardium causing tamponade or myocardial perforation
- trigger arrhythmias
- damage to the tricuspid valve or enter the coronary sinus
Describe anatomical course of subclavian vein
Subclavian vein is the continuation of the axillary vein, it becomes the subclavian vein at the lateral border of the 1st rib. It runs under the clavicle anterior to the subclavian artery, separated from it by the anterior scalene. At the sternal edge of the clavicle, it joins the internal jugular vein to become the brachiocephalic vein.
The phrenic nerve runs posterior to the vein and the thoracic duct joins the left subclavian vein close to its junction with the left internal jugular. The lung pleura lies inferior to the medial aspect of the vein
Define central line insertion point for Subclavian vein
Complications of subclavian vein cannulation
inserted at a point just below the clavicle at point dividing it into its medial 2/3 and lateral 1/3. The needle should be advanced with the tip pointing towards the sternal notch, aspirating all the time.
Complications:
* potential lung injury, haemothorax, tracheal injury, recurrent laryngeal nerve injury
* higher risk of pneumothorax compared to internal jugular cannulation
* harder to apply manual pressure in the event of bleeding.
Define the anatomical course of the femoral vein
Femoral vein is the continuation of the popliteal vein at the adductor hiatus. It ascends the anteromedial thigh into the femoral triangle where it lies medial to the femoral artery in the femoral sheath. It is joined by the deep femoral vein & the saphenous veins before this point. It continues as the external iliac vein as it passes under the inguinal ligament. The needle insertion point is 2cm below the inguinal ligament, medial to the femoral artery.
Contraindications and complicatins of femoral vein cannulation
Contraindications
* Patient refusal (absolute contraindication)
* Infection over insertion site
* Coagulopathy, thrombocytopenia (correct before insertion)
* Uncooperative patient
* intra-abdominal haemorrhage, abdominal trauma
Complications
* femoral nerve damage, bladder/ bowel perforation,
* haematoma, retroperitoneal bleeding, femoral artery damage, vein stenosis, pseudo-aneurysm formation.
* High risk of thromboembolic complications and infection
Advantages and drawbacks of neck vein central lines
- More accurate CVP measurement
- More comfortable than femoral vein
- Easier to insert with USS
- Lower risk of pneumothroax (High approach + USS)
- Can apply pressure for excessive bleeding (not for subclavian vein); excess pressure can cause stroke
- Easier to keep clean (IJV line may be contaminated by saliva bacteria in intubated pt)
- Safe with low complication rate
Advantages of drawbacks femoral vein central lines
- For use in emergency, no need to lie flat (esp if pt is dyspnoeic)
- No pneumothroax risk
- Easy to apply pressure if bleeding, no risk of stroke if high pressure applied to bleeding site
- Hard to keep clean, easily contaminated by groin bacteria
- Safe with low overall complication rate
Define central neuro-axial block
Administration of medication (usually local anaesthetic) into the subarachnoid or epidural space to produce anaesthesia and analgesia.
Define types of neuro-axial blocks
- Spinal anaesthesia- deposition of drugs into the subarachnoid space, which usually contains around 20ml CSF. The enlarged dural sac inferior to the conus medullaris is the target site for injection
- Epidural anaesthesia- deposition of drugs into the epidural space. This space is defined as the space within the spinal canal that is outside of the dura mater
- Caudal anaesthesia- access to the epidural space via the sacrococcygeal membrane is a popular technique in children
- Combined spinal-epidural anaesthesia- combines effect of spinal & epidural
Define the anatomical boundaries of the epidural space
Extends from the foramen magnum to the sacrococcygeal membrane.
Boundaries
* Internal- dura mater
* Posterior- ligamentum flavum
* Anterior- posterior longitudinal ligament
* Lateral- intervertebral foramina
Contents of the epidural space
Epidural fat
Epidural blood vessels- Batson’s plexus, a valveless communication between pelvic & cerebral veins
Lymphatics
Spinal nerve roots
Connective tissue (reason why some blocks are “patchy”)
Define the depth of epidural space from skin
- Depth of space 6mm lumbar, 1mm cervical
- Negative pressure (transmission of negative intra-pleural pressure from paravertebral space)
- Distance from skin 2-9cm (deeper in the obese)
Define all the structures traversed from skin to epidural space
Which structure gives resistance during needle puncture
Ligamentum flavum gives ‘gripping’ sensation
The needle is advanced through the ligamentum flavum whilst pushing on the syringe plunger, but it is difficult to inject the saline. Once the needle tip reaches the epidural space with its negative pressure, there is a sudden loss of resistance and saline can be easily injected.
Landmarks for neuroaxial block
C7 bony prominence at the base of neck
T7-8 lower border of scapula
L4 line drawn at level of uppermost point of iliac crest
Compare spinal and epidural anesthesia
Define the anatomical components of the larynx
The larynx separates the lower airway from the upper airway. It sits in the anterior neck at the level of C4-C6. Laterally lies the carotid sheath & the thyroid lobes. It is made up of:
a. Cartilages
Unpaired- thyroid, cricoid & epiglottis (hyoid is a bone and not strictly part of the larynx) cartilages
Paired- arytenoids, cuneiform & corniculate cartilages
b. Ligaments and membranes
c. Muscles
Define the cartilages of the larynx
Unpaired- thyroid, cricoid & epiglottis (hyoid is a bone and not strictly part of the larynx) cartilages
Paired- arytenoids, cuneiform & corniculate cartilages
Define the nerve supply to the larynx
The larynx is supplied by branches of the vagus nerve. (Tongue base & vallecula are supplied by the glossopharyngeal nerve)
- Superior laryngeal nerve
Internal branch- sensation to glottis, supraglottis & inferior epiglottis
External branch- motor to cricothyroid muscle which tenses the vocal cord - Recurrent laryngeal nerve- supplies all other intrinsic muscles of the larynx and sensation to the subglottis
Method to prevent aspiration during rapid sequence of induction of anesthesia
The cricoid cartilage is the only complete ring of cartilage that makes up the larynx. The theory is that applied backwards pressure on this cartilage of 20-44N should occlude the oesophagus and prevent passage of regurgitated stomach contents into the patient’s trachea. It is a component of rapid sequence induction of anaesthesia.
Define emergency front of neck access
Emergency front of neck access (FONA)- cricothyroid membrane may be punctured to access the lower airway below the level of the vocal cords in an emergency e.g. cannot intubate, cannot ventilate situation to perform needle or surgical cricothyroidotomy.
A cannula or special tube is inserted to provide means of TEMPORARY emergency oxygenation.
The cricothyroid membrane can be identified using USS in difficult patients and the site marked prior to commencing anaesthesia if needed.
Brachial plexus anatomy
Approaches for brachial plexus block
Define the location for each brachial plexus block
Limitations of brachial plexus blocks
