Paracentesis: Delivering a faster, more convenient technique
30 June 2015
Authors: Sarah Hinds, student on the MSc in Bioengineering at UCD, School of Engineering and Materials Science; Derek Farrell, David Farrell and Frank Kelly, Department of Clinical Engineering, St Vincent’s University Hospital; Prof Aiden McCormack Hepatologists Liver Transplant Unit, St Vincent’s University Hospital
A project was carried out to address the need to find a safer and more efficient method of conducting an outpatient procedure called large volume paracentesis (LVP). This procedure involves the aspiration of five litres or more of fluid from the peritoneal cavity of patients suffering from ascites. The current procedure uses passive drainage (gravity only) and can take up to 10 hours. The project conducted a review of the current procedure and identified numerous areas for potential improvement.
An analysis of potential solutions was also carried out and a number of commercially available products were reviewed for the above purpose. An active drainage solution using wall suction was proposed and tested within the hospital. The revised procedure reduced drainage time by 75 per cent revealing the benefits of utilising wall suction for LVP.
Paracentesis is a surgical puncture of the peritoneal cavity for aspiration of ascitic fluid, which most commonly builds up in patients suffering from cirrhosis of the liver.  In St Vincent’s University Hospital (SVUH) a typical paracentesis procedure will drain an average of 10 litres of fluid and can take up to 10 hours. This procedure is currently carried out using passive drainage, relying entirely on gravity to remove the ascitic fluid. This is also the case in the majority of hospitals in Ireland who have also reported similar durations for the procedure.
Reviewing current literature, much shorter durations have been reported and this is mainly due to the implementation of active drainage for the procedure though wall or portable suction. [2, 3] The aim of this project was to propose and implement a safer and more efficient method of carrying out Large Volume Paracentesis. Numerous aspects of the procedure were considered including set up process, catheter selection, fluid drainage and fluid disposal.
There are a number of reasons for investigating a revised approach for large volume paracentesis. Firstly and foremost, numerous studies have reported that reducing the procedure time through active drainage is safe for the patient [4, 5, 6] provided albumin is administered intravenously.
One study carried out by Gottardi et al. reported on the risk of complications after LVP. Of the 515 paracentesis carried out, technical problems occurred in 5.6 per cent. The most frequent complication (5 per cent of the 5.6 per cent) was a leak of ascites at the puncture site.  It was noted by the staff at SVUH that the risk of continual leakage increases with procedure duration. Therefore, a reduction in procedure time offers improvement in terms of efficiency and from a safety perspective.
A more efficient procedure would significantly reduce costs by both minimising the work load for medical staff and decreasing the time a patient is confined to a hospital bed. Currently, the majority of LVP procedures are carried out on day patients who leave the hospital upon completion of the procedure. Although this is the case, the prolonged procedure results in the patients spending the entire day confined to a bed. With an average of three LVPs carried out per week in SVUH, this is a significant factor to consider.
Clinical need analysis
The initial focus of the project was taking the steps required in order to identify the clinical need(s). Interviews with both front and back end users were conducted and a task analysis for LVP was completed through observation of three separate LVP procedures. A number of areas for improvement were identified as follows:
Fluid disposal procedure: The nurse must fill two one-litre open top jugs and dispose of fluid in the sluice up to 50m away. This is carried out at least five times per procedure.
Fluid drainage: Currently ascitic fluid flows passively from the patient into a catheter drainage bag which collects a maximum of two litres before it is emptied. The ascitic fluid flow rate is unnecessarily slow.
Numerous factors required consideration when investigating a potential solution including cost, feasibility and development time. The proposed solution aimed to reduce drainage time and increase safety for the staff and patient, while minimising cost and set up time. The necessary equipment for the revised procedure included a low vacuum wall suction regulator, a 12 litre canister with roll stand (Iskus Medical Supplies) and a standard suction tube (cut in half). This is shown in figure 1. The suction tube can be connected directly to a BD Bonanno general purpose catheter using the luer lock provided in the catheter pack. Although wall suction is available at each bed on the ward, the set up can also be used in conjunction with portable suction.
The set up time for the revised procedure is similar to the previous set up time and requires few additional components. Vacuum outlets are available at each bed on St Brigid’s ward where LVPs are carried out. One standard suction tube can be cut, with one half connecting the catheter to the canister and the other half connecting the canister to the vacuum regulator as shown in figure 2 below.
In terms of patient safety, the application of suction is not problematic, but it is important that certain safety measures are employed such as controlling the level of pressure that the patient is subjected to and monitoring the volume of fluid being removed. The level and type of suction applied will ultimately depend on the regulator used. This will regulate the vacuum pressure from the main system and maintain the pressure at which it is set, unless it is manually altered.
Consequently, should a blockage occur, the pressure will remain at the set level. However, the procedure is not constantly supervised, with nursing staff checking on the patient approximately every 15 minutes. It is therefore important to consider the risk of the regulator being manually altered or set incorrectly. Safe pressures ranges for LVPs are poorly documented. Although high fluid removal rates are reported in studies, few indicate the pressure level employed for the procedure. On study carried out by Reed et al. aimed to implement an active drainage solution for LVP. The pressure recommended from this study was -100 mm Hg.  As a result, it was decided that a low vacuum (pediatric) suction regulator with a negative pressure range of 0-150mmHg would be most suited for the procedure.
An alternative to using a paediatric regulator for the procedure is to ultilise the readily available high vacuum suction regulators in conjunction with a disposable negative pressure relief valve, which would ensure that the patient is never subjected to pressures higher than the given release pressure. Such a valve, the VRV II, is manufactured by Quest Medical and distributed in Ireland through John Bannon Medical Supplies. This valve can be placed in line between the catheter and canister as shown in figure 3. Figure 3: The Quest Medical VRV II negative pressure relief valve [Quest Medical Supplies Product Catalogue
Numerous tests were completed prior to carrying out the procedure on a patient. Figure 4 shows fluid (water) drainage times achieved for various pressures using the BD Bonanno catheter. As can be seen, the flow becomes less efficient at negative pressures above 125 mmHg most likely due to increased turbulence in the flow.
Numerous factors in addition to the pressure applied, contribute to the rate of flow. The flow of various body fluids through catheters has been demonstrated to follow Poiseuille’s law.  The law states that flow is not only proportional to the pressure difference, but it is also proportional to the radius of the cylindrical tube raised to the 4th power and inversely proportional to the length of the tube and the liquid viscosity. From this, it can be seen that the radius of the catheter plays by far the most prominent role in determining the flow rate.
The revised procedure was used to complete an LVP on the ward. The equipment was set up as shown in figure 2 and the vacuum pressure was set to the recommended 100 mm Hg. Portable ultrasound was used to identify the most suitable position for the catheter placement. The patients’ vitals were monitored every 15 minutes. Upon inserting the catheter, it was connected to the suction tube using the luer lock provided and the regulator was switched on. The procedure was monitored carefully, noting the time taken to drain each 250ml increment.
The procedure was successful and the patient did not experience any adverse effects from the suction. Figure 5 shows drainage times for both the active drainage procedure and a previous passive drainage procedure (same patient) both carried out using the BD Bonanno catheter. As can be seen, significant improvements were made, with the active drainage solution taking a total of 65 minutes giving a reduction in procedure time of three hours and 18 minutes. The flow rate decreased with time for both active and passive drainage.
LVPs carried out under active drainage are significantly faster than free drainage procedures and can be easily introduced for day patients in St Brigid’s ward. Utilising wall suction, which is available at each bedside, the overall procedure time may be reduced. Although a small additonal cost (€40) is required per procedure, numerous savings can also be associated with active drainage including the reduced bed time required for each day patient and the reduction in workload for the nursing staff in relation to the revised fluid disposal technique.
The only potentially serious complication which requires consideration, as with the standard manual technique, is hypotension which is related to the removal of a large volume of ascitic fluid in one procedure. However, as discussed above, this may be prevented by simultaneous administration of intravenous albumin infusion. [1, 2] One observation however was that albumin was required much sooner than with passive drainage (within the first eight minutes) meaning that this needs to be arranged prior to the procedure rather than during it.
This project demonstrates that drainage times for large volume paracentesis procedures may be significantly reduced by up to 75 per cent through the implementation of active drainage. The required equipment is readily available to any hospital and may also be used in conjunction with portable suction should wall suction be unavailable on site. The benefits to patient and nursing time combined with increased safety and reduced workload justify the continuation of this active drainage solution on St Brigid’s ward.
Sarah Hinds is a student on the MSc in Bioengineering at UCD, School of Engineering and Materials Science; Derek Farrell, David Farrell and Frank Kelly, Department of Clinical Engineering, St Vincent’s University Hospital; Prof Aiden McCormack Hepatologists Liver Transplant Unit, St Vincent’s University Hospital
 Tito L, Gines P, Arroyo V. et al Total paracentesis associated with intravenous albumin management of patients with cirrhosis and ascites. Gastroenterology 1990. 98146–151.151
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 Reed et al. (2011) Introduction of a low-pressure suction system for day case large volume paracentesis: results from a Scottish teaching hospital, Gut 2011;60:A245 doi:10.1136/gut.2011.239301.520
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