METHOD

A retrospective study was performed over the year between January 2001 and January 2002. All neonates on the neonatal unit at our district general hospital who required a percutaneous long line during this period were included in the study. Long lines were inserted by paediatric clinicians using their standard procedure. Two standard types of lines were used: Premicath 27G (Vygon, Cirencester, UK) and Epicutaneo-cava Katheter 24G (Vygon). After insertion, a plain radiograph was taken, using the CR system, to ascertain the line position. The viewing system used is Kodak Direct View PACS version 4.2. Soft copy images are viewed on 2K portrait monitors, and hard copy films are printed at true size.

Both hard and soft copy (console) images were assessed by three independent observers. The hard copy films were reviewed by observers 1 and 3, and soft copy images by observers 2 and 3. Assessment was made as to whether the line tip position could be confidently identified or not.

RESULTS

All lines could be visualised using both techniques. With the hard copy reporting technique, the line tip could be accurately identified in 30/45 cases by both observer 1 and 3. There was discrepancy of opinion on two films, but overall there was excellent statistical agreement (κ = 0.90) with both observers confidently identifying the tip in 30 cases. With the soft copy reporting technique, the line tip could be accurately identified in 43/45 cases by both observer 2 and 3, with perfect agreement (κ = 1.0). The significance of the difference was assessed using McNemars test. All combinations of observers and methods were compared. All combinations revealed a significant difference in the visibility of the line tip using the two different reporting techniques (p = 0.002). Overall 66.7% of line tips were confidently identified on hard copy images and 95.6% using the soft copy reporting technique. The difference in the percentage of visible line tips between the two techniques was 28.9% (95% confidence interval 10.2% to 36.7%). Owing to the small numbers involved, no conclusion could be made in differentiating the two types of long line used.

DISCUSSION

Accurate positioning of intravenous long lines is important to avoid potential complications that may result from misplacement. Retrospective studies have suggested overall long line complication rates of 28–88%,^2,9 mechanical complication rates of 13–53%,² and perforation rates of 3–29%.^4,7,9 Mortality resulting from perforation and cardiac tamponade has been estimated at 0.76–1%.^4,7 After reports of complications associated with right atrial tip position, and subsequent Department of Health recommendations,¹⁰ there has been a move towards positioning the line tip within the distal superior vena cava for upper limb placement and distal inferior vena cava for lower limb placement.^1,3,6 To allow for migration and patient movement, it is recommended that the line tip lie at least 0.5–1.0 cm outside the cardiac outline in premature or small infants and 1.0–2.0 cm outside in larger infants.^1–3

The narrow calibre, poorly opaque lines used, however, may be difficult to visualise using conventional radiography. Reece et al¹¹ prospectively assessed line visibility on their regional neonatal intensive care unit, and found that 50% (31/62) of patients required a repeat radiograph, with the use of intravenous contrast to clarify the position of the line and tip which was not visible on the original film. They concluded that “intravenous contrast should be routinely used in the assessment of long line position in the neonate”. This policy is currently the standard protocol for imaging neonatal long lines in many centres nationally, and was adopted locally for a short period until the introduction of CR and PACS within the hospital.

The main advantage of CR and PACS over conventional radiography lies in its superior contrast resolution and the ability to allow alteration of image contrast and brightness after processing. This can be used to compensate for suboptimal exposure and improve overall image quality without the need for a repeat radiograph. The major limitation is a reduction in spatial resolution compared with conventional images, although this difference is negligible with the current high quality viewing hardware available.

At our centre a plain radiograph is performed after line insertion using CR. Neonatal films are printed as hard copy images and returned to the neonatal unit for review by clinical staff. On occasion there has been doubt over line tip position, and repeat films with contrast have been felt necessary. In many of these cases, however, review of the images using the viewing console, with the benefit of contrast and brightness windowing and image inversion has resulted in improved confidence in determining tip position and avoided the need for repeat films, with its associated radiation risk. Rarely, difficulties may arise out of hours or when radiological review is not possible, and on these occasions, a repeat film with intravenous contrast may be performed.

Review of our hard copy films revealed that the line tip could be accurately identified in 30/45 cases. Of the 15 lines that were poorly visualised, it was felt that exact information on line position was required in four cases, and repeat imaging with intravenous contrast was recommended. Visibility was significantly improved, however, when the same films were viewed on the PACS console at the time of reporting. The tip could be accurately identified in 43/45 cases (95.5%) and in neither of the two poorly visualised cases was it felt necessary to re-image, as exact determination of the tip position was unlikely to influence clinical management. Overall, 13 more lines (29%) could be seen using soft copy rather than hard copy reporting, and repeat imaging could be avoided in four cases (9%).

Although the overall numbers are small and there is need for further controlled trials, these findings lead us to conclude that the use of soft copy reporting of radiography images significantly improves the accuracy in determining neonatal long line position and tip, and in many cases may obviate the need for further imaging or repeated films with contrast.

This may have implications for the provision of CR/PACS access on the neonatal unit, for review by clinical teams and indeed has resulted in the installation of viewing consoles with windowing and image inversion facilities on our neonatal unit locally. Access is of particular importance out of normal working hours and when immediate radiological review may not be possible.