In Vitro Evaluation of Evacuated Blood Collection Tubes as a Closed-Suction Surgical Drain Reservoir
ABSTRACT
The initial negative pressures of evacuated blood collection tubes (EBCT) and their in vitro performance as a rigid closed-suction surgical drain (CSSD) reservoir has not been evaluated in the scientific literature despite being described in both human and veterinary texts and journals. The initial negative pressures of EBCT sized 3, 6, 10, and 15 mL were measured and the stability of the system monitored. The pressure-to-volume curve as either air or water was added and maximal filling volumes were measured. Evacuated blood collection tubes beyond the manufacture’s expiration date were evaluated for initial negative pressures and maximal filling volumes. Initial negative pressure ranged from −214 mm Hg to −528 mm Hg for EBCT within the manufacturer’s expiration date. Different pressure-to-volume curves were found for air versus water. Optimal negative pressures of CSSD are debated in the literature. Drain purpose and type of exudates are factors that should be considered when deciding which EBCT size to implement. Evacuated blood collection tubes have a range of negative pressures and pressure-to-volume curves similar to previously evaluated CSSD rigid reservoirs. Proper drain management and using EBCT within labeled expiration date are important to ensure that expected negative pressures are generated.
Introduction
The concept of surgical drainage has been present for centuries, with the principles for their use significantly refined by the end of the 19th century.1 Indications for surgical drainage include the ability to decrease the accumulation of bodily fluids that provide a media for bacterial growth, to decrease pressure within wounds, and to evacuate inflammatory mediators.1–6 Surgical drains are defined as either open (passive) systems or closed (active) systems. The most common type of open drain used in veterinary medicine is the Penrose drain.2 This is a collapsible latex tube that allows exudates to flow with gravity and pressure variation around the exterior drain surface. Active systems, otherwise referred to as closed-suction surgical drains (CSSD), have a negative pressure or vacuum reservoir that allows the attached drain tubing to function as a conduit for exudate evacuation. Closed-suction surgical drains overcome many of the limitations of open drainage systems. Major benefits include not requiring a bandage, limiting environmental contamination, minimizing dead space, the ability to be placed in body cavities, and being able to quantify and qualify exudates.1–4,7–9 The reported limitations of CSSD include the following: induction of the inflammatory response; retrograde bacterial contamination; decreased local tissue resistance; breakage of drain tubing within the wound during removal; prolongation of lymphatic drainage; postoperative hemorrhage; bowel perforation; and as a source of pain during both function and at removal.2,6,7,10–12
Closed-suction surgical drains have either a rigid or collapsible reservoir that affects their initial subatmospheric pressure (otherwise referred to as negative pressure). These negative pressure measurements have been previously reported in the literature.5,8,11,13,14 Different compression methods for various collapsible reservoir types (e.g., grenade, concertina, and pancake configurations) demonstrated a negative pressure range between −64 to −249 mm Hg. Closed-suction surgical drains with rigid reservoirs identified a greater initial negative pressure measurement range of −430 to −630 mm Hg. Larger collapsible reservoirs tended to have a lower initial negative pressure compared with their smaller correspondent, whereas with rigid reservoirs, greater initial negative pressures were seen with larger reservoirs. Distinctly different pressure-to-volume relationships were demonstrated between collapsible and rigid systems as well.11,15 Collapsible reservoirs had a rapid loss of negative pressure initially and maintained a lower proportion of pressure during filling. Rigid reservoirs maintained a higher percentage of their initial negative pressure throughout filling and demonstrated a more gradual slope of the pressure-to-volume curve.11,15
The use of evacuated blood collection tubes (EBCT)a connected to either a modified butterfly catheterb or to a commercially available prefenestrated drainage systemc has been described in the human and veterinary literature.2,16–19 The tube sizes of different gauged butterfly catheters remain constant so the limiting factor to flow is the resistance generated by the needle’s radius. A 19-gauge needle is the largest commercially available in this type of catheter and will thus minimize the resistance to flow when implemented into this type of drain. These small, fabricated drain systems have several benefits. Their small size enables placement into wounds that historically may have been managed with a Penrose system. They can also be placed in awkward areas like the head, neck, tail base, and distal extremities where larger CSSD are size-prohibitive. The materials needed to construct these systems are readily available to practitioners and the overall cost is relatively inexpensive when compared with commercially manufactured CSSD systems. Despite these drains being in numerous publications, to the authors’ knowledge, EBCT initial negative pressure and pressure-to-volume relationships have not been previously investigated. The only known reported negative pressure within EBCT was an unreferenced statement describing that a 10-mL red-topped EBCT has an initial negative pressure of −75 mm Hg.16
The two aims of this study are to document the negative pressure within different-sized EBCT and document their pressure-to-volume relationship as they fill with air and water. We hypothesize different initial negative pressure measurements between tube sizes, and similar pressure-to-volume curves compared with previously evaluated rigid closed-suction surgical reservoirs.11,15
Materials and Methods
Setup
To obtain initial EBCT negative pressure readings, a 19-gauge 3/4 in.butterfly catheterb through a male-to-male luer connectorc was attached to the pneumatic pressure transducerd previously described by Grobmyer et al.8 The transducer was calibratede prior to data collection and then tarred to atmospheric pressure between each evaluated tube. Once assembled, the needle of the butterfly catheter was inserted through the rubber stopper of the EBCT and the pressure recorded. Three of the four EBCTa sizes tested were red-topped serum collection tubes obtained through local reference laboratories, each with a total collection volume of 3 mL, 6 mL, and 10 mL. The fourth set of EBCT was obtained as part of a commercially manufactured drainage systemf with a total stated collection volume of 15 mL. The 3 mL and 6 mL tubes were composed of rigid plastic, and the 10 mL and 15 mL tubes were composed of glass. All EBCT used in data acquisition were within the manufacturer’s labeled expiration date.
Checking System Stability
To verify that the system maintained negative pressure, five EBCT of each size were individually connected to the pressure transducer and left undisturbed for 12 hr, after which time a second negative pressure measurement was recorded.
Maximal Water Aspiration Volume
Maximal tube aspiration volume was determined as described by Halfacree et al.11 The tip opposite the 19-gauge needle was submerged in a water bath, the tube was primed with water, and the 19-gauge butterfly catheter needle was inserted into the EBCT. The system was left undisturbed for 1 hr, the catheter was removed from the EBCT, and the total volume of aspirated fluid was measured. This was repeated six times for each tube size.
Pressure-to-Volume Relationship
As described by Halfacree et al., the data to create the pressure-to-volume relationship were generated by the addition of 10% of the EBCT’s total stated collection volume in individual aliquots of air.11 A three-way stopcockg was fitted with a 22-gauge 1.5” needle, a syringe holding the 10% aliquot of air, and a male adapter plugh. This setup was inserted through the EBCT’s red rubber stopper at a separate site to the butterfly catheter connected to the pressure transducer. After instilling the aliquot of air, the syringe was closed to the EBCT via the three-way stopcock, the pressure recorded, and the syringe disconnected, allowing the next aliquot to be drawn into the syringe prior to reattachment. If the entire volume of air was contained in the syringe, once the three-way stopcock was opened, the pressures across the EBCT and syringe would equilibrate, thus preventing incremental measurements. Ten percent aliquots of air were instilled until the total collection volume had been reached or negative pressure was no longer measurable. Experiments were repeated 10 times for each of the 4 tube sizes.
The pressure-to-volume relationship was repeated in the same manner, adding distilled water rather than air. The syringe was filled with the total collection volume of fluid rather than 10% aliquots. When the three-way stopcock was opened, allowing communication between the EBCT and the syringe, pressures could not equilibrate across the system because only one of the containers (the EBCT) contained air. This allowed the syringe to remain connected to the system between 10% aliquot additions (Figure 1).
Citation: Journal of the American Animal Hospital Association 54, 1; 10.5326/JAAHA-MS-6519
Expired EBCT Analysis (Incidental Finding)
Expired EBCT were obtained from local referring hospitals. Initial negative pressures and maximal water aspiration volumes of 6 mL and 3 mL plastic EBCT 5 yr beyond the manufacturer’s labeled expiration date were measured with the same methodology detailed above. Ten tubes of each size were measured to obtain the initial negative pressures and six tubes of each size were measured to obtain their maximal water aspiration volume.
Statistical Analysis
Differences between continuous variables were analyzed by the use of a paired Sample t test and a repeated measures analysis of variance. All data collection was completed by a single investigator (B.H.). Data are normally distributed and presented as mean ± standard deviation. Values of P < .05 were considered significant.
Results
Maximal Initial Negative Pressure
There were significant initial negative pressure differences between all EBCT sizes (P < .0001; Table 1).
Checking System Stability
All EBCT sizes had significant pressure losses when left undisturbed for 12 hr (Table 1).
Maximal Volume of Water Aspirated
The volume of water aspirated by the 3 mL EBCT was significantly lower than the stated collection volume (P = .001). The volume aspirated by the 15 mL EBCT was significantly higher than the stated collection volume (P = .034). There was no statistically significant difference of the collected volumes within the 6 mL or 10 mL EBCT (P = .102 and P = .771, respectively; Table 1).
Pressure-to-Volume Relationship
All EBCT sizes had significant losses in negative pressure when the first 10% aliquot of either air or water was instilled. The pressure losses were more gradual in all tube sizes with the incremental addition of water compared with air (Figures 1–3).
Citation: Journal of the American Animal Hospital Association 54, 1; 10.5326/JAAHA-MS-6519
Citation: Journal of the American Animal Hospital Association 54, 1; 10.5326/JAAHA-MS-6519
Expired EBCT Findings
Evacuated blood collection tubes 5 yr beyond the manufacture’s expiration date, sized 3 mL and 6 mL, had significant losses of initial negative pressures and significant lower maximal water aspiration volumes. The 3 mL expired EBCT had an initial negative pressure of −113.9 mm Hg (±1.6) and a maximal water aspiration volume of 1.4 mL (±0). The 6 mL expired EBCT had an initial pressure of −202 mm Hg (±0.74) and a maximal water aspiration volume of 3.3 mL (±0.1).
Discussion
The results of this study confirm our hypotheses. The initial pressure of EBCT varies between tube sizes, with larger tubes generating more negative pressure. The pressure-to-volume curves are similar to previously evaluated CSSD rigid reservoirs. Different pressure-to-volume curves were noted in all EBCT sizes with the addition of fluid compared with air. The ideal gas law (pressure of the gas × volume of the gas = amount of gas in moles × universal gas constant × temperature of the gas) accounts for these findings in both this study and previously evaluated CSSD with rigid reservoirs.11,15
Discretion must be exercised when incorporating the results of this in vitro study in the clinical setting. Water may not accurately mimic how these drains perform because of its lower viscosity compared with body fluids. More viscous exudates evacuated from wounds may affect how the systems behave in vivo. Schnetler’s in vitro paper took into account Poiseuille-Hagen’s equation evaluating different viscosities when assessing the functionality of high- and low-pressure CSSD.15 A complete review of the Poiseuille-Hagen’s equation is beyond the scope of this discussion, but it is important to consider that flow is inversely proportional to the fluid viscosity. Keeping the drain pressure, diameter, and length constant, a lower flow rate was demonstrated when packed red blood cells were aspirated by the drains compared with water.15 Schnetler’s work with collapsible and rigid collection reservoirs also demonstrated the in vitro median pressure required to dislodge clotted blood from within drainage tubing. Negative 112.5 mm Hg was needed to dislodge a clot and a more negative pressure (<−260 mm Hg) was needed to keep 80% of the drainage tube from becoming obstructed. The compressible drains did not generate enough negative pressure to keep 80% of the drain tubing clear from clotted blood.15 In our study, the 3 mL EBCT had a maximal initial negative pressure of −213 mm Hg, which, if extrapolated to Schnetler’s findings, would fall short of this requirement as well. The 6 mL, 10 mL, and 15 mL EBCT fell beneath the −260 mm Hg threshold when they were fluid-filled by 40, 50, and 70% of their total collection volume, respectively. Combining our findings to Schnetler’s work would suggest when using a 6, 10, or 15 mL EBCT, they should be changed prior to filling to their maximum capacity to keep drain tubes clear and functional when viscous exudates or clotted blood are encountered.
Although the maximal fluid aspiration volume correlated well with the tubes’ stated total collection volumes, the 3 mL EBCT aspirated significantly less fluid than the stated collection volume (Table 1). This coupled with the significant negative pressure loss of all tube sizes over a 12-hr period would advocate changing EBCT reservoirs several times daily to ensure an anticipated amount of negative pressure is applied to the drainage system.
Based on the in vitro nature of the study, there are several limitations. The interaction of the fenestrated tube with the body in regard to clearance of tissue debris and clots was not addressed. Distilled water was used rather than body fluids, and different maximal fluid aspiration volume may change if more viscous fluids had been evaluated. The pneumatic pressure transducer reads the pressure at the tip of the butterfly catheter, and the dispersal of pressure throughout a wound once the tubing is fenestrated may vary. Disconnecting the syringe between aliquots of air in the pressure-to-volume portion of data acquisition was unavoidable in order to obtain incremental pressure measurements. There was a potential for air to be trapped between the three-way stopcock and the syringe tip. Although the amount of air that could have been introduced into the system at this point was minimal, it would not have been accounted for and potentially could have caused a more rapid rate of negative pressure loss.
An incidental finding of this study found that EBCT beyond the manufacturer’s labeled expiration date had initial negative pressures and maximal water aspiration volumes significantly lower than the EBCT evaluated that were not expired. The initial negative pressures were 46.8 and 44% lower and maximal water aspiration was 51.7 and 46% lower for the 3 mL and 6 mL EBCT, respectively. These tubes were all plastic and the manufacturer acknowledges plastic tubes will lose negative pressure over time. The expiration date is set on plastic tubes to ensure an accurate draw volume.20 Ideally, we would have evaluated 10 mL and 15 mL glass tubes beyond their expiration date, but tubes fitting this description were unavailable. Using EBCT within their expiration date will ensure both more accurate pressure estimation and stated volume accrual.
Optimal pressure gradients generated by CSSD reservoirs in the clinical setting remain a topic of debate in both human and veterinary surgery.21–25 To the authors’ knowledge, there are no in vivo experiments in the veterinary literature looking at different CSSD negative pressures. The goal of this study was not to define the optimal clinical applications of EBCT drains, but to determine what pressures these systems generate and how they behave in the bench-top setting. The majority of our understanding of the in vivo performance of CSSD stems from studies performed in human medical literature, with the results of these studies presenting conflicting findings.21–25 Some studies show there being less fluid production and shorter hospital stays with less negative drainage pressure, other studies show no difference between drains with different pressures, and other research shows better resolution of clinical signs using drains with more negative pressure. Further in vivo evaluation of CSSD in veterinary medicine is warranted to obtain a better understanding of drain performance and proper implementation in our patient population. Goals of these studies would be to identify how animals’ bodies interact with the fenestrated tubing, to determine the ideal negative pressures of CSSD reservoirs, to outline guidelines for reservoir maintenance, and to guide modification in design to ensure optimal clinical application.
Conclusion
Evacuated blood collection tubes fall within the negative pressure range of previously reported CSSD rigid reservoir systems. We confirm our hypotheses that different-sized tubes generate a variety of negative pressures and the pressure-to-volume curve is similar to previously evaluated rigid reservoirs. Changing the EBCT reservoirs after all air has been evacuated from the surgical wound and then multiple times daily will maximize the amount of negative pressure applied to the drain tubing. Evacuated blood collection tubes within their manufacture’s labeled expiration date will generate the expected pressures demonstrated by this study.
Pneumatic pressure transducer connected to the 19-gauge butterfly catheter via a male-to-male luer lock adapter has been inserted into the 15-mL evacuated blood collection tube. At a separate site of insertion sits a 22-gauge needle connected to a three-way stopcock capped with a male adapter plug on one end, and attached to a syringe holding the volume of water to be added incrementally to the tube.
Mean ± SD negative pressure (mm Hg) within the 3-mL and 6-mL evacuated blood collection tubes filling with incremental volumes (10% of total stated volume) of air (green and blue lines) or water (red and purple lines). SD, standard deviation.
Mean ± SD negative pressure (mm Hg) within the 10-mL and 15-mL evacuated blood collection tubes filling with incremental volumes (10% of total stated volume) of air (green and blue lines) or water (red and purple lines). SD, standard deviation.
Contributor Notes
