Forum topic

Lynn, I have always followed your belief on this,and refused nurses or docs to pulsatile flush  my port line if they were even able to get their hands near me.  Just a wee bit of background, yes I am an R.N and a user of  CVADs for long term PN.. and for the past 2yrs had a port. From week 2 of its life had problems with fibrin sheath formation.. I have kept the line clear and clean with the use of  DuralockC, a  med not available in the  USA. and so for the past 11mths been having frequent infusions of urokinase.. [Cathflo not available here]  IF I stick to the prescription of only clearing the line once ever 2wks I started having  "brain farts" I am not a doc so shall not give them the label of  T.I.As in the past 4mths...  the last proved to me anyway that  the bits are coming from the fibrin sheath.. I was  preparing for an infusion when doing a positive flush of moderate strength I had sudden weakness in the leg, luckily  seat was behind me and I quickly connected up the waiting  urokinase..  I really do wonder if a nurse was doing the flush etc what her response would have been.. would they pick up that it was  a possible  TIA??

I am now doing urokinase the moment that a sheath reforms over the cath line.. and havent had another one since... to me it has proven that it is possible for the fibrin to have temporary  thrombolitic problems for the patient...  and with my crazy sense of humour all I could think of was.... that beats any ER  time of less than 3mins to have infusion running after an episode.

 I know that a study of one will never prove anything to anyone.. but I do know that when I get it removed come about Dec, I shall be lying down and not talking after the reporting from Lynn of such cases having an air emboli, which I have been told by many is just a myth..

What I do wonder is if that it had been a biofilm extra hard lump of something going up to the cerebral area, maybe I wouldnt have been living as usual.

BTW I did purchase the INS standards but cant get it to go to my eReader.. so have to slowly read it via the screen.. as I want to challenge the hospital I have to attend, on their pulsatile policy.. I remember when it came in here, and being told by a biomed, that one that only works in a bowl shaped vessel not a long thin line apart from shearing off hard matter.

 I am no expert, but just one who knows the consequences.

I guess nobody here has seen Lynn Manly's (Navilyst) real time invivo porcine flouroscopy clips of PICC flushing? I recall the "pulsitile" technique provided the least amount of catheter movement in the vessel.

Don't we start and stop flushing every time we access/de-access a catheter? Is the assumption that increasing the start and stop cycles of the syringe plunger will increase the likely hood biofilm release? 

From what I have read, I agree; biofilm attaches very firmly to many surfaces. I agree pulsitile flushing is not "cleaning" the catheter walls. Although I have seen transparent tubing and transparent luer access devices clear of blood completely with a pulsitile flushing. Whereas a constant flushing technique left a residual amount of blood  in the tubing or device. Whether that is true for a biofilm layden catheter also, I don't know.

I also think that any thing that might get dislodged from the PICC will get caught in the pulmonary system and not go cerebral....thoughts/comments?

Peter

All those wonderful OHSU monthly tips emphasize "Pulsatile" flushing

I find it nearly impossible to flush 10mLs NS in one continuous stream

Perhaps I have a poor understanding of the mechanics of flushing

It makes sense that there is some flow rate or psi that could trigger a  shear of biofilm. Is shear strength controlled by the bacteria colony size (as suggested in the "it's all about biofilm" article) or does it vary from species of critter, is it the material of the catheter, is it the median flow rate the biofilm is subjected to? What sets the shear strength of the biofilm? Is it stable or dynamic and is any thing we can do about it?

My point about the Navilyst trial is that out of all the techniques tried, pulsitile flushing caused the least amount of catheter movement, while power injecting caused the greatest catheter movement. Catheter movement is directionally proportional to fluid movement within the catheter. The faster one pushes the fluid through the catheter, the greater the catheter movement.

 If I extrapolate this data to biofilm shear. It would seem that we want to have a flushing technique  which causes the least amount of stress on the biofilm. That would be the technique that moves the catheter the least amount in the vessel. Pulsitile flushing caused the least amount of catheter movement, not slow and steady.

So is there evidense for a steady flush not causing biofilm shear?

So does the INS oppose using pulsatile flushing, or do they consider it a 'non-call' due to lack of evidence?  What about device manufacturers such as Bard that specifically recommend using pulsatile flushing? I completely agree that at this point any recommendation should prominently qualify it's strength with the degree of evidence to support the recommendation, although it seems like the INS is not very consistent with that rule.

My facility does educate staff to use a pulsatile flush with SOLO PICC's since that is what the manufacturer recommends.  We have had good results with this; when we approached Bard with our concerns about the high rates of occlussion we were experience with SOLO's, we were reminded to make sure we use a pulsatile flush, after we educated the staff on this our SOLO occlusion rates dropped significantly, still higher than heparin flushed PICC's, but much better than previous to using a pulsatile flush.  

While we don't specifically recommend a pulsatile flush in general, you'll find it's frequently used due to the effect of observation since when using clear tubing and clear caps, the beneficial effects of a pulsatile flush become fairly obvious.  As somebody who often draws off of a VAMP 10 or more times a shift, I can tell you from experience that a pulsed "fast-flush" is the only way to clear both the line and the sample port.  You can hold down the fast flush for 20 minutes if you want and there will still be blood that doesn't seem affected by the flow, yet after just a few pulses it's gone.  This is due to some basic principles of fluid dynamics.  While it varies depending on the viscosity, the "no-slip condition" applies to every fluid flowing in a tube to one degree or another.  This states that the fluid at the boundary (inner wall of the tube) will flow much slower (even stationary at the boundary) than the fluid in the center of the lumen.  As laminar flow forms shortly after the flow is initiated, it inhibits transverse flow and diffusion from near the boundary, leaving the area near the boundary unflushed.  This is effect is even more prominent in areas of irregularity such as valves and ports.  I've noticed some recommendations falsly claim that a pulsatile flush causes turbulence, which it does not, it causes agitation.  For true turbulent flow to occur in a smooth walled tube, you would need to acheive a Reynolds number of greater than 5x10^5, which would be really difficult to do with a flush.  What pulsatile flushing does is de-establishes the laminar flow and allows for transverse flow (agitation), which greatly improves flushing throughout the cross section of the lumen without using additional shear force.

Pulsatile flushing by itself does not increase peak shear force, it only creates an inconsistent shear force.  It is possible that an inconsistent shear force (aka rate of flow) may cause some biofilm breakage if the bending caused by the pulsatile flow exceeds the ductile capacity of the biofilm, although the few pulses caused by a flush is nothing compared the the repetative pulses caused by an IV pump.  I think an argument could be made that non-pulsatile flushing actually increases the shear force since a common reaction to seeing blood remain while flushing is to flush faster which increases the shear force.  

The theoretical benefits of pulsatile flushing are more clear when you look at flow through an irregular tube, such as the valve of a SOLO.  The SOLO valve causes turbulence behind the valve, resulting in stagnant areas of flow when a constant flow is used which would be very likely to occlude the valve over time if it's used for blood draws.  Unlike agitation which facilitates flushing, turbulence is non-chaotic and actually quite consistent with it's flow, producing areas of high flow and others with no flow at all with a consistent flow rate.  A pulsatile flow breaks these persistent eddies that form behind the valve and will diffuse some of the blood into the center of the lumen with each pulse.  

If the theories and observation that support a more effective flush with a pulsatile flush are true and the decreased rate of occlussions that we've seen at our faciltity are due to a pulsatile flush, that would suggest that pulsatile flushing actually decreases the risk of CRBSI's since we know that increased occlussion rates coincide with increased infection rates.  Better flushing of the fluid near the boundary in theory would also help decrease the formation of biofilm, since reducing the amount of biofilm 'building blocks' near the wall of the lumen should mitigate the formation of biofilm.  It would definitely be interesting to see these theories validated and quantified, but for now it would seem that the list of theoretical "pro's" greatly outweighs the theoretical "cons".  

There is one reference for steady flushing available by donlan in a microbiology journal.  The rapid and pulsitile flushing increase the potential for bacterial adhesion to the catheter wall.

It has to do with the renolds factor.  You are correct.  There is nothing to support pulsitile flushin

Donlan RM, Costerton JW. (2002) Biofilms: Survival Mechanisms of Clinically Relevant Microorganisms. Clinical Microbiology reviews .

            "Great post Wade, now I just have to research what your talking about. Any links or sites would be appreciated."

The preferred source would be a physics textbook, but since I can't link to that online we'll have to settle for wikipedia.  (The video is probably the most useful of the links)

If you scroll part way down this page you'll find a good explanation of fluid flow in a tube incorporating laminar flow and the no-slip condition.

You can also familarize yourself with the no-slip condition, laminar flow, and what shear stress is when discussing fluid flow (scroll down).  If you were really bored (or wanted to be) you could also look at viscosity/Newtonian and Non-Newtonian fluids.  

This video is a really good example of how fluids can get stuck along the walls of a lumen, and how some mild agitation can resolve the problem.

        "I would challange that with; try just gently tapping the the plunger with one finger (hardly moving .25cc of fluid) and you can clear that residual blood after a continous flush with just a few taps and 1cc of fluid injection."

The "fast flush" I was referring to is how we flush a transduced pressure line.  It's just a valve on the transducer that flushes the line, so theres no syringe involved.  The "Fast flush" actually flushes slower than most Nurses probably flush using a syringe, it's just called a fast flush becuase it flushes faster than the continuous flush which is only a few cc's an hour.  When we "pulse" the fast flush, it's just quick taps of the valve which results of a flow of less than 0.25ml per "tap".  As you point out, all it takes a very small amount of non-laminar flow to allow for transverse flow and mixing of differing solutions in the cross-section of the lumen.

        "I can not find the reference to steady catheter flushing in the article?"

My understanding (and correct me if I'm wrong Denise) is that these studies indirectly suggest that pulsatile flushing causes increased biofilm adhesion based on the findings of some of these studies that show increased adhesion with increased shear force.  In my view this represents a number false assumptions which are:  1) Pulsatile flushing causes increased shear stress.  2)Pulsatile flusing is not effective at mitigating biofilm development because it does not provide any additional cleaning force to the walls of the catheter, yet somehow at the very same time it may be unsafe because it applies more force to walls of the catheter which may dislodge biofilm, and 3) that given the choice, poorly adhered biofilm is better than well adhered biofilm.

1) There's no evidence to suggest pulsatile flushing increases shear stress.  Shear stress is the amount of pressure a fluid applies to the wall of the tube.  It does feel like it takes more pressure to "pulse" flush, although it appears that this is just how we perceive the pressure, and not what it actually is, just as a 50lb dumbell would seem much heavier if you were to lift it in incremental "stop/start" fashion compared to one continuous motion.  We did an experiement at work yesterday to try this out.  We took a triple lumen PICC (one Power and 2 Groshong lumens), and set up a way of measuring shear stress.  We mimicked an outlet pressure of about 10cm H2O (the typical mean CVP) and put a 3 way valve (with all three ports open) on the access port of the Power lumen with a Femostop manometer attached to the third port of the three-way.  We had all the nurses on the floor flush the line using both a pulsatile and continuous technique.  The manometer readings are a direct reading of shear stress, and we found that peak pressures using a pulsatile flush techique were 1/2 to more than a 1/3 less than using a continuous flush technique (depending on the Nurse).  Even so, every Nurse said they thought they were using more pressure in the pulsatile technique, which goes to show how much inertia can help in reducing work load (or at least how we perceive the work load).  This was by no means a rigorous scientific study, but it casts some serious doubt on the idea that pulsatile flushing increases shear stress.

Even if it does increase shear stress and increase adhesion, isn't that exactly what you would want?  Why would you want biofilm to be loosely adhered and on the verge of rupturing at any time?  Optimally, we would be preventing biofilm formation in the first place instead of worrying about strong vs weak adhesion, and it would seem that optimally effective flushing, particularly after a blood draw, would be the best way to do that, suggesting a pulsatile flush is preferred after a blood draw based on theory.

   You are correct that agitation is not a type of flow, which is part of why it works and why I made a point of differentiating turbulence from what happens with pulsed flushing.  You are also correct that given same other variables (dynamic viscosity,obstructions, surface friction, etc), the only thing that differentiates laminar flow from turbid flow is flow rate.  Because of this, it becomes fairly obvious that the effect of pulsed flushing is not attributable to turbulence when you consider flushing of a pressure line.  If the improved effectiveness of a pulsatile flush is due to increased shear force/flow rate, then when shouldn't see any difference in effectiveness when comparing the two techniques at the exact same flow rate/shear force.  The rate of flow when flushing a transduced pressure line is constant, the flush is either on or off, there is no way altering the flow rate when flushing.  If the effects of a pulsed flush were due to the creation of turbulent flow with a pulsed flush, then there would be no difference in flushing effectiveness when pulsing a pressure line since the rate is constant and therefore the reynolds number (which quantifies turbid flow) remains the same.  Yet flushing a pressure line of blood is where the difference seems to be the most noticible, possibly because you can't make up for the lack of flushing effectiveness by flusing with more force with a continuous flush.  I agree that the goal should be to flush with as little shear force as is necessary which is why I prefer a pulsed flush - you get a better flush while at the same time using less force.

   Laminar and turbulent flow aren't actually the only types of flow characteristics, flow can also be described in terms of compressible vs incompressible flow, Stokes flow, Viscid flow, RT instable flow (which best describes flushing blood using NS), etc.  I'm impressed that a Physiology textbook refers to laminar and turbid flows at all, although I'm not sure that a Physiology textbook contains everything there is to know about fluid dynamics.  The beneficial effect of pulsatile flushing is not actually fluid flow at all.  Flow occurs when fluid is displaced.  Improving flushing by clearing solutes from the boundary area is not dependent on fluid displacement through the tube.  For instance, some Nurses, when "helping" a pressure line clear itself of blood, will tap the line.  When the line is tapped even without any flow through the line, the blood will diffuse through the cross section of the lumen due to the agitation of the "tap", this is not due to fluid displacement but to agitation resulting in diffusion of solutes to the center of the lumen, no true fluid flow actually occurs making laminar vs turbid flow irrelevant.

   We tried another experiment today which I have pictures of but I can't get the pictures into a post.  We took tubing extensions and filled them with cranberry juice.  We then flushed one with 5cc's, and the other with 5cc's but with a stop/start every 0.5cc.  The Start-stop tubing was clear after 5cc while the other was still noticably pink.  This doesn't come to much of a surprise to Nurses that have observed numerous flushes and through experience have found that a pulsed flush better clears blood from a line.  It would be nice to see this confirmed and quantified through proper research, but in the meantime it is conisidered common wisdom by a large portion of the Nursing Community.  So if your goal is to better prevent the formation of biofilm in the first place, which I agree with, it would seem the best way to do this would be by starving potential biofilm formations by better clearing the line, particularly near the wall of the lumen, being able to do this with less shear force than a continuous flush would seem to be an added bonus.

I'm not sure that I disagree with the INS standard as I'm not totally clear what it is.  Am I going against the Standard by pulsatile flushing?  Or is there just no Standard that covers pulsatile flushing?    

So power injecting or flushing may equal a more powerful biofilm?