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Monitoring in ICU

Central Venous Access (central line)

Most patients in ICU will have some form of central line – usually small bore multilumen catheters. The indications for central venous access are listed in table 2 and types of central lines listed in table 3. Central venous pressure (CVP) is a very useful parameter to measure in the haemodynamically unstable patient. It can be used to guide fluid therapy, especially when administering a fluid challenge. The CVP is most reliable when measured from the superior vena cava via lines inserted from the internal jugular or subclavian veins. The transducer is zeroed at the level of the heart (mid axillary line at the 4th intercostal space).

Indications for central venous access

Drug administration including vasoactive agents and parenteral nutrition

Fluid administration

Measurement of central venous pressure (CVP)

Access for haemofiltration or dialysis

Venous access when peripheral access is difficult

Table 2. Indications for central venous access.


Types of central lines

Multilumen – several lumens exist so that multiple infusions are possible.

Wide bore – may be multilumen. Used for rapid administration of fluid, other catheters may be passed down the large lumen – e.g. PAF catheter or pacing wires

Single lumen – often tunnelled - usually for parenteral nutrition or chemotherapy. Not often used in ICU (multiple lumens required, as lines often need to be changed in ICU)

Table 3. Types of central lines.

Insertion of central lines

Insertion should follow general guidance as above. A trainee should only attempt central venous access if properly supervised or competent to do so.

It is recommended that ultrasound guidance is used to guide central line placement. Portable ultrasound machines are available in most units.


Preparation of operator and site

First clear the proposed site of all clothing, sheets etc and ensure you have easy access to the patient, with a clutter free sterile field. For access to veins in the neck, lay the patient flat, check the landmarks and check the vein with the ultrasound. Tip the bed head down; this manoeuvre fills the veins, making them a larger target, and reduces the chance of air embolism. This head down tilt can be delayed (occasionally omitted by an experienced operator) until the site is prepped and draped if it is disadvantageous to the patient e.g. uncomfortable, breathless or raised Intracranial pressure.
 
Full asepsis should be used for central line insertion, with maximal barrier precautions as applied to any other surgical procedure that carries a risk of infection
 
Scrub - wear a hat and mask, wash hands, don a surgical gown and gloves in an aseptic manner.
 
Site – use appropriate antiseptic solution (e.g. chlorhexidine 2%) to prepare the site then drape large sterile field. You are now ready to insert the central line.

Insertion of central line

The Seldinger technique is used – this is used for insertion of many devices in medicine.

After appropriate preparation of the patient and site, a large vein is located with a relatively large bore needle or cannula. Prior to this a small bore, “seeker needle” can be used to confirm vein location. A wire is passed down the large bore needle or cannula into the vein, then the needle or cannula is removed while the wire is left in situ. After dilating the tract, the catheter is passed over the wire into the vein.
 
Common veins accessed by central lines include internal jugular, subclavian and femoral. The site used depends on the skill and experience of the operator and on the existence of any relative contra-indications. For example, in case of coagulopathy the subclavian vein is less likely to be used. In case of difficulty in lying flat the femoral can be used.
 
The internal jugular vein is often used first or in an emergency because of ease of access intra-operatively and a reduced risk of pneumothorax compared to subclavian. It is also easy to press on if bleeding occurs.

The extent to which the line is inserted depends on the site as described in the table below.

Right internal jugular

usually 12-14 cm depending on patient's build

Left internal jugular

usually 14-16 cm depending on patient's build

Subclavian

usually 14-16 cm depending on patient's build and insertion point

Femoral

usually 16-20 cm

Table 4. Depth of line insertion according to site.

 

Complications relating to central venous access can be classified in to those occurring either early or late, see table 5.


Early complications

Damage to veins or adjacent structures, e.g. artery, nerve or thoracic duct

Pneumothorax (especially subclavian route)

Arrhythmias

Air embolism

Puncture of great vessels or heart

Late complications

Infection (reduced incidence at subclavian)

Extravasation of irritant drugs

Air embolism (if left open)

Bleeding

Catheter breakage

Catheter knotting

Penetration of vessel wall or heart

Table 5. Complications of central venous lines.

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