Proper Electrocardiography-guided Placement Of A Central Venous ...

Methods used to optimise CVC placement

The veins most commonly used as CVC access routes are the internal jugular, subclavian, or femoral veins or the arm veins. There is a general evidence-based agreement for the preferential use of the right internal jugular vein based on its anatomy vis-à-vis the heart, as it presents a low risk of venous stenosis, thrombosis, and pneumothorax in that area. Traditionally, the central venous catheter insertion site has been determined by palpating anatomical references with a known relation to the vein to be cannulated.

The placement of the CVC tip is essential for it to work correctly. Ideally it should be placed in a vessel with a wide diameter, preferably outside the cardiac cavity and parallel to the vein axis to decrease the presence of lesions.

The ideal placement is in the extra-pericardial vena cava,8 due to the potential risk of vascular disruption or heart perforation with tamponade that has been demonstrated in case reports.9,10 Moreover, the high position of the catheter tip in the superior vena cava increases the risk of thrombosis.

The overall rate of complications is given by multiple factors, especially the experience of the medical staff, secondaries of percutaneous insertion, the catheter characteristics and type, the technique used, its indication and management while inserted.

Knowing at what distance the catheter tip will be inserted is necessary, since it can differ according to age, gender, or height. A series of formulas for positioning the CVC tip in adult patients according to height have been described.6 In a 1995 study some formulas that are still used today were validated (Table 1)

Table 1.

CVC insertion length.

Insertion site	Formula	In superior vena cava	In right atrium
Right subclavian	(Height/10)−2cm	96%	4%
Left subclavian	(Height/10)+2cm	97%	2%
Right internal jugular vein	(Height/10)−1cm	90%	10%
Left internal jugular vein	(Height/10)+4cm	94%	3%

Czepizak CA, O‘Callaghan JM, Venus B. Evaluation of formulas for optimal positioning of central venous catheters. Chest 1995; 107: 1662–1664.

A chest X-ray is considered the most commonly used method for verifying the CVC placement. The catheter tip should be above the carina, thus ensuring placement above the pericardial sac. It stands out for its simplicity, economy, and speed of use. A 95% general efficacy is reported independent of the puncture site, efficacy being understood as the ability to position the CVC tip in the superior vena cava (SVC) and not in the right atrium11,12 (Fig. 1).

Figure 1.

CVC in SVC on X-ray.12

Transoesophageal echocardiogram (TOE) enables the right atrium and superior vena cava near it to be visualised, enabling the CVC tip to be located even if it is 2cm or more from the terminal sulcus.11,13

The TOE enables two-dimensional vision and immediate correction in the case of misplacement; however, this requires an experienced operator.14

Three schematic zones have been proposed for the placement of the CVC tip.13

• –

  Zone A (lower SVC and LAD) would be a safe zone for left-sided CVC tip insertions since it would enable great parallelism between the catheter tip and the vertical.

• –

  This is an unsafe zone for right-sided insertions, therefore it is recommended they should be removed if placed in this zone.

• –

  Zone B (upper SVC and brachiocephalic vein junction) would result in a safe zone for right-sided CVC tip insertions. However, it would be dangerous for catheters with left accesses due to the probability of forming a >40° angle with the vertical with the resulting risk of perforation. In these cases, the authors recommend advancing them.

• –

  Lastly, zone C (proximal left brachiocephalic vein) would be a zone of questionable safety, only to be used for infusions over a short period and for fluid replacement (Fig. 2).

  Figure 2.

  Schematic zones for positioning the CVC tip.13

A study by Martinez et al.,15 assessed the validity of four tests to determine the CVC situation (venous return, central venous pressure waveform, arrhythmias, and difference between external measurement before and after the catheter placement) and position by comparing them on the chest X-ray. They found that the described tests are highly sensitive and non-specific for determining the position of the central venous catheter. Joining the four had more reliable values (Table 2).

Table 2.

Validity of clinical tests for determining the central venous catheter position.

Tests	Positive cases	Negative cases	Sensitivity	Specificity	+PV	−PV	Accuracy
Chest X-ray	37	10	1.0	1.0	1.0	1.0	1.0
Venous return	44	3	0.97	0.22	0.84	0.66	0.82
Central venous pressure	32	15	0.86	0.40	0.83	0.44	0.80
Arrhythmias	38	9	0.97	0.60	0.89	0.85	0.95
Measurement	42	5	0.97	0.12	0.8	0.50	0.89
Venous return+cvp+arrhythmias+measurement	31	16	0.86	0.90	0.96	0.66	0.87

Martínez F et al. Validez de las pruebas clínicas para determinar posición del catéter venoso central. Rev Med Inst Mex Seguro Soc 2009; 47 (6): 665–668.