OSCE 4

What is this device?

Describe its safety features.

The original college description of this viva was :

"Monitoring. Examples included central venous catheter, arterial catheter for determination of  transpulmonary thermodilution and  pulse  contour  analysis  determination  of  cardiac output, bladder catheter, temperature probe, and transcranial doppler.
Twenty out of twenty-two candidates passed this section."

Instead, I made it all about central lines.

The safety features are:

• Flexible beveled atraumatic plastic tip
• Non-pyrogenic inert material
• Radioopaque, allowing the user to identify the tip position on CXRs
• Antibiotic and antiseptic impregnated to resist infection
• Pliable soft polyurethane line
• Flanged hub to assist in securing the device to the skin and prevent dislodgement
• Molded, flexible low-profile junction hub (to improve cleaning)
• Transparent hub-to-hub tubing to detect blood or air bubbles
• Clamps to prevent air embolism or blood loss
• Caps to prevent air embolism or blood loss
• Coloured hubs with gauge indicators
• Pressure injectable lumens are easily identified to prevent catheter rupture

What vessels are considered central vessels for the purpose of CVC insertion?

The ANZICS guideline defines a central line in terms of tip position; "the device must terminate in one of the great vessels ... or in or near the heart to qualify as a central line". 

Greater vessels, for the purpose of this definition, are also listed by ANZICS:

• pulmonary artery
• superior vena cava
• inferior vena cava
• brachiocephalic veins
• internal jugular veins
• subclavian veins
• external iliac veins
• common iliac veins
• femoral veins

What are the indications for central venous access?

There are only a few strong reasons for the insertion of a central venous access device:

• IV access
• Infusion of irritant substances
• CVP monitoring
• Advanced haemodynamic monitoring (PICCO, PA catheter)
• Central venous oxygenation monitoring

Extended indications also include:

• Inadequate peripheral access
• Extracorporeal therapies (ECMO, CRRT)
• IVC filter placement
• Venous stenting
• Transvenous pacing
• Catheter-guided thrombolysis
• Repeated blood sampling

What are the contraindications for central venous access?

Generic contraindications to CVC insertion at any site include:

• Obstructed vein (eg. clot)
• Stenosis of the vein
• Raised ICP (IJ line)
• Severe coagulopathy
• Respiratory failure with high FiO₂
• Contaminated site
• Traumatised site (eg. clavicle fracture and subclavian line)
• Burned site
• Uncooperative awake patient
• No absolute contraindications

At various sites, other contraindications can be invented, but they would all fall into the categories of "some bone broken or deformed near the site" or "the site itself is infected". For example, a previously fractured clavicle or severe kyphosis with forward rotation of the shoulders us a relative contraindication to subclavian line insertion. The possibilities are too numerous to list for all possible sites.

Which factors influence your choice of insertion site?

The NSW Health policy lists a series of factors which should be "considered" before inserting a CVAD, without offering much guidance on how one should react to them. These factors included:

• Obesity
• Bleeding diathesis:
  • Platelets less than 50
  • INR over 1.5
  • APTT over 50
  • Antiplatelet drugs: clopidogrel and ticagrelor especially
• Hypotension
• Previous surgery at the proposed site of insertion
• Previous central line at the same site
• Infection at the site
• Presence of LBBB (relevant to PA catheters only)
• Lymph node dissection in the same area
• Previous DVT in the limb being drained by the central vein you're looking at.

What determines whether you insert a central line into a right or left sided vein?

• It is easier to insert a right subclavian (more likely to end up with the tip in the correct position)
• It is easier to insert a left PICC (less likely to go up into the neck)
• It is better to insert a vascath into a right IJ because the relatively straight course of the catheter will promote better flow and fewer access pressure problems
• It is better to save the right IJ for a vascath if the patient is likely to require ECMO or dialysis at some stage in the near future
• The right IJ vein is bigger than the left: Ishuzuka et al (2010) found a 3-4mm difference in their diameter, on average
• Femoral vessels are bilaterally symmetrical (i.e. it does not matter which vein you access in terms of venous access alone). However, the right femoral artery is the favoured site for arterial angiography access, and in general the femoral arteries are ideal for this; so if a coronary angiogram IABP or ECMO are planned, one may wish to leave the groins alone.
• In a patient with some sort of severe one-sided lung pathology the IJ or subclavian line should be placed on the affected side, so that you do not cause a pneumo/haemothorax of the "good" lung.
• Left-sided lines (IJ and subclavian) tend to have a higher chance of damaging the thoracic duct. Teichgraber et al (2003) report a case where the guidewire from a left subclavian insertion attempt accidentally penetrated the thoracic duct, perforating it and causing a chylothorax. You'd have to be extremely unlucky and the rarity of this complication approaches case report status, but it needs to be considered in situations where thoracic duct damage would be for some reason disastrous.

Which factors influence your choice of central venous catheter?

The general principles as outlined in the local policy:

1. The minimum number of lumens should be used
2. TPN (or any lipid-rich solution for that matter) requires a dedicated lumen all to itself
3. Antimicrobial (instead of antiseptic) catheters should be saved for those who need them most

Patients who should be considered for an expensive minocycline/rifampicin coated line are identified by the ANZICS guideline as follows:

• Immunosuppressed patients.
• Those expected to have long term need for CVC
• Those at a high risk of CLABSI (eg, burns patients)
• If CLABSI rates in the unit have remained high in spite of good insertion technique and attention to routine maintenance

What are the minimum requirements for an appropriate environment in which to perform CVC insertion?

You need to have access to:

• Adequate lighting
• Adequate space around the patient
• Some means of assuring aseptic technique (i.e. a trolley and drapes?)
• Immediate access to cardiac resuscitation equipment and drugs
• Skilled assistants
• Electrical safety support (i.e. you need to be in a cardiac-protected electrical area, where there are Residual Current Devices (RCDs), Line Isolation Monitors (LIMs) and Equipotential earthing. You can recognise these areas in Australian hospitals by the redness of the power socket (normal sockets are white and uninterruptable power supply sockets are blue)

These characteristics are shared by ED resuscitation areas, ICU rooms, operating theatres, anaesthetic bays, endoscopy suites, angiography and interventional radiology suites, and potentially other locations around the hospital. 

At minimum, you should have:

• An ECG monitor
• A pulse oximeter
• A pressure transducer

The NSW Health policy recommends all patients must have some ECG monitoring.

How would you position a patient for right internal jugular venous puncture?

In summary:

• Flat
• Supine
• Trendelenburg position:  Bazaral et al (1981) tilted patients by 14 and found that this increased the crossectional area of the IJ by about 50%,
• A neutral head position, or only as much head rotation as is required to give access to the neck
  • Turning the head away from the puncture actually impedes the procedure because it puts the vein directly under the sternocleidomastoid (making an anterior approach especially difficult)

What are the anatomical landmarks for an infraclavicular approach to the subclavian vein?

• The index finger of the non-dominant hand should be on the supraclavicular notch, and the thumb should be on the needle, pushing it down (parallel to the floor.)
• Puncture should occur about 1-2cm inferior and lateral to the junction (that usually is at the level of the deltoid tuberosity of the clavicle, if you can identify it)
• The needle should pass under the junction of the medial one-third and lateral two-thirds of the clavicle.
• The needle tip should be directed at the index finger (or just superior to its tip)

What methods can be used to confirm venous placement?

There are several simple bedside methods which you can use to determine whether you are in a vein or artery.

• Create a simple manometer: attach minimum volume extension tubing to the CVC, stretch the tubing up and allow the blood level in the tubing to rise. Given the convertion of mercury manometry to blood, at a systolic BP of 120 mm Hg your "blood manometer" would read 1.63m, i.e. you'd run out of tubing. This is why we used mercury in those things.
• Attach the transducer to the needle. It's sterile and already attached - may as well use it before dilating the vessel
• Visual ultrasound confirmation - you'd have to actually visualise the needle in the central vein.
• Blood gas analysis - though you'd be surprised how often arterial oxygenation is so disappointing that it looks venous.

How does one estimate the appropriate depth for insertion?

What radiographic landmarks can be used to determine correct tip position?

 The NSW Health policy suggests that it is "reasonable" to expect your tip:

• above the cephalic limit of the pericardial reflection, which is
• at a level corresponding to the carina on a chest radiograph

Disclaimer: the viva stem above may be an original CICM stem, acquired from their publicly available past papers. Or, perhaps it is a slightly altered version of the original CICM stem. Or, it is a completely original viva stem, concocted by the monstrously amoral author of Deranged Physiology for nothing more than his own personal amusement. In either case, because the college do not make the main viva text or marking criteria available, almost everything here has been confabulated. It might sound like a plausible viva and it could be used for the purpose of practice, but all should be aware that it does not represent the "true" canonical CICM viva station.