Editorial II

Safe placement of central venous catheters: where should the tip of the catheter lie?

Central venous catheters are ubiquitous in modern hospital and ambulatory medicine, with up to 6 million insertions per year in the USA1 and 200 000 per year in the UK.2 Despite this, there is still considerable doubt as to what constitutes optimal practice in terms of catheter composition, route of placement and the minimization of complications such as catheter-related sepsis, thrombosis and vessel perforation.

In this issue of the journal, Schuster and colleagues describe an elegant post-mortem, radiological study of pericardial anatomy.3 This work is based on the premise that, in order to prevent atrial or ventricular perforation and subsequent cardiac tamponade, the central venous catheter tip should not lie within the boundaries of the pericardial sac. In seeking to prevent this dramatic but rare complication are we exposing the patient to other equally serious but more insidious complications? The answer is probably yes. These issues are explored in this editorial.

Catheters will generally function equally well for pressure measurement and fluid infusion if the tip is situated in any major vein, above or below the heart. For dialysis or the infusion of irritant/hypertonic fluids, a high rate of blood flow past the catheter tip is desirable and this requires the placement of the luminal opening in as large a vessel as possible. However, the package inserts of many central venous catheters give very strong warnings about the absolute requirement for catheter tips to lie outside the heart to avoid perforation and subsequent pericardial tamponade.4 In the USA, the Food and Drug Administration has issued advice emphasizing this point. This advice is based on numerous case series reporting the association between intracardiac placement of the catheter tip and (usually fatal) tamponade.1 57 Authors of recent case series have acted as expert witnesses in cases of litigation related to fatal tamponade.1 5 These experts may have been chosen for their polarized opinions. The outcome of such litigation has dictated the response of regulatory authorities and manufacturers. Despite this, the level of awareness of the issue amongst physicians, anaesthetists and radiologists was reported in 1995 to be low.5

Cardiac tamponade related to central venous catheterization follows a predictable pattern. Most cases occur in the first week after insertion.5 6 Chest pain, nausea, dyspnoea, cyanosis, tachycardia, hypotension, engorged neck veins and pulsus paradoxus may occur hours before decompensation. The correct clinical diagnosis is rarely made and cardiac arrest usually ensues, with a mortality exceeding 70%. In most cases, review of the chest radiograph taken before tamponade reveals the catheter to be inside the cardiac silhouette.5 At post-mortem, the fluid removed from the pericardium may be serous or serosanguinous, or may resemble the fluid being infused before tamponade. Interestingly, in a small proportion of patients it is not possible to find a definite track through the myocardium.

The incidence of tamponade is impossible to know precisely. Since the introduction of central venous catheterization in the 1950s, hundreds of millions of catheters have been inserted. Over the same period, the number of reported cases of associated tamponade is in the hundreds. Thus, even allowing for unrecognized and unreported cases, the scale of the problem is put into perspective. Experience with transvenous cardiac pacing is also instructive: the deliberate placement of transvenous pacing wires into the right atrial or ventricular wall very rarely results in tamponade.8 To prevent tamponade, it would appear reasonable to avoid placement of the catheter tip within the right ventricle or deep into the right atrium (RA). However, there is increasing recognition that placing the tip in positions above the RA is also associated with significant complications.

Perforation

Catheter perforation of the central veins has been widely reported and may result in pleural effusion, hydrothorax, haemothorax, hydromediastinum, pneumothorax and pneumomediastinum.911 Although the effects are less dramatic than for perforation of the heart, there is appreciable morbidity and finite mortality.10 Hydromediastinum resulting in cardiac tamponade has been reported,7 and perforation of the medial wall of the superior vena cava (SVC) can produce tamponade directly.6 This is explained by the finding by Schuster and colleagues that the pericardium may ascend alongside the medial wall of the SVC by up to 5 cm (mean 3 cm).3 Thus, placement just proximal to the atrium does not obviate the risk of tamponade.

Perforation is thought to occur as a result of mechanical trauma from the catheter tip or chemical damage from infused solutions.12 This results in two warning signs: visceral-type chest pain on infusion of drugs or parenteral nutrition solutions13 and a curved appearance of the distal catheter seen on chest x-ray.9

Factors affecting the risk of perforation by catheters (both venous and cardiac) are numerous. Stiffer catheters are more likely to perforate.14 Stiffness is a function of the composition of the catheter (Silastic probably being safest) and the number of the lumen (a function of the greater diameter and presence of ‘septa’ within the catheter). The angle that the catheter tip makes with the wall of the vein or heart is crucial; both in vitro14 and clinical evidence indicates that the more perpendicular the catheter to the wall, the greater the risk of perforation.11 15 Left-sided catheters pose a particular problem because the left innominate (brachiocephalic) vein forms a near right angle to the SVC. Catheters entering the SVC from the left therefore have a tendency to impinge on the lateral wall of the SVC. The resulting increased risk of perforation is well documented.9 11 15

A sharp, inflexible catheter tip increases the risk of perforation, as does excessive mobility of the tip (seen with brachial catheters upon movement of the arm). Fluid infused under high pressure or at a high flow rate may increase the risk of perforation; this may occur with the use of side ports as well as end ports. When myocardial perforation does occur in this situation, the risk of tamponade is greatly increased. Finally, it is likely that some perforations are due to trauma from the guidewire or dilator, particularly when tamponade occurs early after insertion.

Thrombosis and catheter-related sepsis

The overall thrombosis rate from central venous catheterization is between 30 and 70%.1618 Thrombosis occurs where there has been repeated trauma to the endothelium from the catheter tip.19 There is increasing evidence of a relationship between high placement of the catheter tip (upper SVC or above) and thrombosis.19 20 Although most thrombosis is either asymptomatic or results in catheter blockage alone, life-threatening sequelae are probably under-recognized. The incidence of pulmonary embolism from catheter-related thrombosis may be up to 60% for both short- and long-term catheterization;16 21 22 one study reported a mortality of 12%.22 In addition, thrombosis of the axillary or subclavian veins can lead to significant morbidity and requires anticoagulation; SVC obstruction is possible and may be fatal.19

Catheter-related sepsis (CRS) is a major problem, with a direct mortality rate of 25%.23 A clear relationship has been established between CRS and thrombosis,16 17 and when the two combine to produce septic thrombophlebitis the result is devastating. Although it is not clear whether infection predisposes to thrombosis or vice versa, the morbidity and mortality that potentially originate from thrombosis due to a high-lying catheter tip (with or without infection) is enormous, and in quantitative terms may far exceed that related to cardiac tamponade.

Extravasation

Extravasation of fluid or drugs from proximal side-holes is a potentially serious complication of catheters inserted to an inadequate depth.24

Positioning

A major problem in correctly siting central venous catheters is the lack of reliable surface landmarks. Although some authors recommend points such as the sternal angle as being at the level of the junction of the SVC and right atrium,11 most recommend a chest x-ray as the only practical, reliable test. Schuster and colleagues identify the carina as a radiological landmark below which the tip is likely to be within the pericardial sac.3 However, given that the SVC is only 6 cm long and the carina is roughly 3.5 cm higher than the SVC/atrial junction, placing the tip above the carina is likely to put it in a risk area for thrombosis or, particularly for left-sided catheters, into a position at higher risk of perforation. In addition, a frontal chest radiograph does not exclude a catheter position in smaller vessels (e.g. azygos vein) or an extravascular site adjacent to the correct site.

The use of right atrial electrocardiography during insertion of central venous catheters has been claimed to be of value.26 However, such a technique can tell the operator only whether the tip is within the atrium, not where it is within the venous system. The use of an image intensifier permits visualization of the tip position but is not available routinely. Ultrasound, although very useful for aiding insertion, is of limited value in confirming tip placement. It will show misplacement in the subclavian, axillary or internal jugular veins but is not suitable for imaging the SVC. Venography and even computed tomography are of value in situations where the line position is in doubt and reinsertion is undesirable.

Current guidelines on tip position focus only on the risk of tamponade. We believe that an unsatisfactory tip position above the heart should not be accepted purely to satisfy these guidelines. Whenever the catheter negotiates a sharp bend, the catheter must be passed a reasonable distance beyond the bend such that the axes of the catheter and vein are aligned. In the case of insertion from the left side, this may be achievable only by siting the tip in the right atrium. Reference to a stylized diagram of the heart and great veins may provide some guidance (Fig. 1).



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Fig 1 Stylized diagram of heart and great veins. Angles may be more acute in vivo.

 
Zone A (low SVC/upper right atrium). This is a suitable tip site from any access point in the upper body. We believe catheter tips can be sited safely within the upper right atrium provided they do not abut the atrial wall end-on or pass through the tricuspid valve or into the coronary sinus.6 13 20 25 26

Zone B (upper SVC). This is a suitable site for tips of catheters placed via the right internal jugular route.9 10

Zone C (mid-point, left innominate vein). This is a suitable site for the tip when the catheter is introduced from the left internal jugular or subclavian vein, and reduces the risk of SVC perforation.11

Conclusions

The catheter tip should be placed in as large a vein as possible, ideally outside the heart and parallel with the long axis of the vein such that the tip does not abut the vein or heart wall end-on.

There are complications associated with all tip positions and a lack of good evidence on which to base practice. There is no evidence that the complications of short-term versus long-term catheterization are qualitatively different, but the event rate per patient is likely to be higher with the latter, requiring meticulous attention to detail.

Individual clinical factors must dictate the choice of access point and site of the catheter tip. Ultimately, the risks of central venous catheterization will be minimized only by clinicians having a detailed knowledge of the complications of catheterization, a high index of suspicion that clinical deterioration may be due to the catheter, and a readiness to take action. Clinicians should audit their results and be prepared to justify individual practice.

S. J. Fletcher

A. R. Bodenham

The General Infirmary at Leeds

Leeds LS1 3EX

UK

References

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