Introduction		Care of the Central venous Catheter
Which central vein to cannulate?		What is Central Venous Pressure?
Types of central venous catheters		When should CVP be measured?
Different methods of insertion		How to measure the CVP
General preparation to obtain central venous access		Interpretation of the CVP
General technique for all routes		Short case examples of CVP interpretation
The Subclavian Vein		When may the CVP reading be unreliable?
The Internal Jugular Vein		Catheter removal
The External Jugular Vein		Pulmonary artery flotation catheters (PAFC)
The Femoral Vein		Further Reading
The Antecubital Veins

Introduction

Central venous access is the placement of a venous catheter in a vein that leads directly to the heart. The main reasons for inserting a central venous catheter are:

• measurement of central venous pressure (CVP)
• venous access when no peripheral veins are available
• administration of vasoactive/inotropic drugs which cannot be given peripherally
• administration of hypertonic solutions including total parenteral nutrition
• haemodialysis/plasmapheresis 

Which central vein to cannulate?

There are a number of central veins and for each of these there are a variety of techniques. It should be remembered that, with the exception of the external jugular, central veins are often deep and have to be located blindly. This is associated with risk to nearby structures, especially in the hands of the inexperienced operator. Veins commonly lie close to arteries and nerves, both of which can potentially be damaged by a misplaced needle. The subclavian vein also lies close to the dome of the pleura, damage to which can cause a pneumothorax. The choice of route will therefore depend on a number of factors as listed in table 1.

Table 1. Factors which determine the choice of central vein
Patient:	How long will the catheter be required? ie. long term / intermediate / short term Suitability of the vein for technique chosen e.g. for CVP measurement the tip of the catheter must be within the thorax. A femoral route therefore needs a long catheter
Operator:	Knowledge and practical experience of the technique -it is be better to have a few clinicians in each area who perform all the central venous cannulations and gain experience (a "central venous access team")
Technique characteristics:	Success rate for vein cannulation Success rate of central placement Complication rate. Applicability to patients of different ages Ease of learning Puncture of a visible and/or palpable vein or 'blind' venepuncture based on knowledge of anatomy
Equipment available:	Availability of suitable apparatus Cost Suitability of material for long term cannulation

Types of central venous catheters

Catheters are available which differ in length, internal diameter, number of channels (access ports), method of insertion (see below), material and means of fixation. Two useful lengths are 20cm catheters for subclavian and internal jugular lines, and 60cm catheters for femoral and basilic lines. 

Different methods of insertion

There are several basic methods of inserting the catheter after the vein has been found:

Catheter over the needle. This is a longer version of a conventional intravenous cannula and may be quickly inserted with a minimum of additional equipment. The catheter is larger than the needle, which reduces the leakage of blood from the insertion site, but using a larger needle to find the vein makes the consequences of accidental arterial puncture more serious. In addition it is easy to over-insert the needle. Catheter over guidewire (Seldinger technique). This is the preferred method of insertion. A small diameter needle (18 or 20 gauge) is used to find the vein. A guidewire is passed down the needle into the vein and the needle removed. The guidewire commonly has a flexible J-shaped tip to reduce the risk of vessel perforation and to help negotiate valves in the vein e.g the external jugular vein (EJV). Once the wire is placed in the vein, the catheter is passed over it until positioned in the vein. The wire should not be over-inserted as it may kink, perforate the vessel wall or cause cardiac arrhythmias. This technique allows larger catheters to be placed in the vein after the passage of appropriate dilators along the wire and a small incision in the skin at the point of entry. Catheter through the needle or catheter through cannula. The catheter is passed through a cannula or needle placed in the vein. The technique is becoming less popular as the hole made in the vein by the needle is larger than the catheter thatis passed leading to some degree of blood leakage around the site. If a problem is encountered during threading the catheter, withdrawal of it through the needle risks shearing part of the catheter off with catheter embolisation into the circulation. This technique is mainly reserved for the antecubital route.

(Continued ...)

---

© World Federation of Societies of Anaesthesiologists WWW implementation by the NDA Web Team, Oxford

---