VentWorld    VentWorld    ventworld.infopop.cc  Hop To Forum Categories  RC Professionals    Servo i versus PB 840
Page 1 2 3 4 5 
Go
New
Find
Notify
Tools
Reply
  
Servo i versus PB 840
 Login/Join
 
Member
Picture of JeffWhitnack
posted Hide Post
I don't discount the entire article. I just disagree with a primary premise which sets control and support modes as being separate poles. It doesn't matter who has more of any published data. There are tons of experts out there disagreeing about a host of issues--Xopenex of benefit or a fraud, Crystalloids or Colloids (and for what populations). More to the point, with NAVA you probably have a bunch of people also disagreeing. I might find some MD's paper touting PAV and then say "How dare you have the audacity to "...

If you have an interest in using NAVA then you will be using PAV, albeit with a NAVA trigger (apparently for both insp and exp).
 
Posts: 171 | Location: Palo Alto, CA USA | Registered: November 14, 2002Reply With QuoteReport This Post
Member
Picture of Jeffrey Haynes lungscience-education.com
posted Hide Post
We use the Servo-i; I like it a lot. There are a couple of features on the 840 that are superior to the servo:

1. a heated housing for the exp filter
(filters on the servo fill with H2O requiring
a change every 24-48 hours)
2. a choice of square wave or ramp flow in vc.
The servo only offers square wave.
 
Posts: 4 | Registered: July 06, 2008Reply With QuoteReport This Post
Member
posted Hide Post
I am curious to the comment about the 840 being 'superior' to the Servoi because you can select a ramp in VC.

Isn't the definition of VC, constant flow? Why then would you want to change it to a ramp (decelerating flow)? Have you ever considered the mechanics or physics of what the vent has to do to achieve this while still delivering a constant flow? It must alter i-time. Pressure control is by definition decelerating flow. It would make logical sense if you want decelerating flow, but still want a volume target, you would choose PRVC (VC+ for the 840, I think).

In the end it make not make any clinical difference as to how you get there. But to say the 840 is superior because of this feature is silly.
 
Posts: 21 | Registered: December 10, 2007Reply With QuoteReport This Post
Member
Picture of JeffWhitnack
posted Hide Post
Ramp flow was described as a superior feature. Not that this one superior feature makes it necessarily a superior ventilator.

Volume control is usually called flow controlled vs. pressure controlled.

You can control the flow with any number of "routines". A ramp is just one of them. With PMax on the Drager it's still ultimately flow controlled. But the "signal" to ramp down is pressure. But when the breath is "said and done" it's essentially a volume controlled breath. As opposed to PRVC, Autoflow in SIMV or CMV, VC+...which are all really pressure controlled breaths. The target, as far as the breath jumping out the gate, is really pressure. Albeit volume feedback does adjust this pressure. And if the Ti time is short enough, risetime high..the ramp aspect might be very slight compared to VC mode with ramp flow setting.
 
Posts: 171 | Location: Palo Alto, CA USA | Registered: November 14, 2002Reply With QuoteReport This Post
Member
posted Hide Post
Jeff you are correct. The statement was that it's a superior feature, but I still don't understand why one would make that comment.

From every textbook I have read Volume control ventilation is delivered with constant (square) flow. If you set a flowrate of 60 lpm and then ask the vent to make the flow decelerate it has to alter another parameter. In the case of the 840 it changes the inspiratory time. Many don't even realize when they input the settings and then hit the ramp button other numbers change.

This is straight from the 840 ops manual as to what happen when you change the from square to ramp or visa versa.

Flow pattern
The flow pattern setting defines the gas flow pattern of volumecontrolled(VC) mandatory breaths. The selected values for VT and VMAX apply to either the square or descending ramp flow
pattern. If VT and VMAX are held constant, TI approximately
halves when the flow pattern changes from descending ramp to
square (and approximately doubles when flow pattern changes
from square to descending ramp), and corresponding changes to
the I:E ratio also occur. Changes in flow pattern are phased in
during exhalation or at the start of inspiration. The settings for flow pattern,Vt, f,and VMAX are interrelated, and
changing any of these settings causes the ventilator to generate
new values for the other settings.

I really isn't an issue of 'to ramp or not to ramp'. It's more an issue 'do you even understand what the ventilator is doing'. If I surveyed 100 PB 840 users my guess is that less than 10% understand what the ventilator is doing to achieve the ramp flow pattern in VC.

Again it probably is of zero clinical significance, but is makes me cranky when people call something a 'superior' feature and they don't even understand it.
 
Posts: 21 | Registered: December 10, 2007Reply With QuoteReport This Post
Member
Picture of Jeffrey Haynes lungscience-education.com
posted Hide Post
I think you need a vacation Seatac!! Yes I understand how the ventilator works, and I'm not saying that the 840 is a superior machine, I love the servo-1. The only point that I was trying to make was that having the option of ramp in the VC mode is a nice (better adjective?)feature because the ramp may be more synchronous for spontaneously breathing patients than square wave. The one problem with the PRVC mode when you want a target tidal volume is that it does not guarrantee any level of support to reach that target. For example, if you set your target at 500 mL and the patient increases their VT to 700 mL because of physiologic stress, the response of the machine is to reduce support in an attempt to decrease the VT to the 500 mL target. I have seen many patients receiving 2-3 cm H2O of inspiratory support when they exceed the target VT. Jeff
 
Posts: 4 | Registered: July 06, 2008Reply With QuoteReport This Post
Member
Picture of JeffWhitnack
posted Hide Post
First let me re-emphasize that I an NOT a cheerleader for any one type or brand of ventilator. We RT's often just have to work with whatever ventilator we find selected at whatever institution we work at.

I used to work with Evita (pre XL). I really liked it, but it would be real hilarious to see it implemented where I now work. I have mixed feelings about how Autoflow hides the PC "wolf" in VC "sheeps" clothing---not really the fault of the vent, but often MD's and RT's are totally unaware that the patient is really on PC. I also don't buy into Smartcare, though I admire the software and all---I would just turn in upside down and use it to ensure that the "stable non-fatiguing mode is actually such.

I also used to work with the Servo 300A. I have mentioned my dislike of it's features---PS flow termination of 5%, Automode (same reasons as Smartcare, MMV, etc.---but with a "where's the PRVC to VS weaning beef?" anyway. But the Servo I has fixed those problems. And the clinical staff of Servo or Marquet I have met have been great.

I am also very interested in other vents---Hamiltons ASV and PV curves, GE's FRC routine, Newports PS flow termination criteria (best I've seen...I just don't like PS unless for short TC SBT) and so on. I could probably go on about any ventilator and, depending on which angle, either make the vent vendors beam or become livid with rage. We should never fall too much in love with any ventilator. Often people become "true believers" in the new vent their hospital has purchased. Then several years later when newer vents and modes/adjuncts appear they are derided as "bells and whistles".

OK, having said all that. On to the question of "does the ramp waveform make volume controlled ventilation into something else?" I don't think it does. It still is a flow controlled mode, just now flow is controlled with a decreasing, yet pre set flowrate. In old 7200 flow would decay to 5% of set peak and insp time would be about doubled from square wave. This isn't necessarily a problem if either 1) increasing insp time is OK or 2) the RT just increases the peak flow to decrease insp time. Flow rate 60 in square wave, increase flowrate to 120 and put in ramp (one hospital tried to write me up for this and I came back from lecture from Marini conference where Dr. Ravenscraft described setting flow 120 for an asthmatic, in textbook I found such a high rate used, etc.).

In the old Hamilton vent I recall one had a whole smorgasbord of flow profiles to choose from (only used that ventilator VERY briefly and the name escapes me as well as the exact flow profiles). LTV's VC is halfway between square and ramp of the 840 (roughly).

Now I suppose when one uses (not that anyone hardly ever does) Pmax setting in VC. Then one sets a peak (or initial flow) AND a pressure setting. Flow charges ahead until it "bonks" into the pressure level selected. Then it ramps down or "hugs" that pressure until the breath is delivered. Any time left over is an inspiratory pause. If the breath can't be delivered via combination of set VT, Ti, set initial flowrate, pressure setting then an alarm sounds. So one is then forced to always have an inspiratory pause to allow room for some variance. It's also OK for an inspiratory pause to be set in PC. But let someone set an inspiratory pause in regular VC and many RT's are then seen muttering about "you need an order to do that!" as if some unholy act was committed.


The other question is if RT's understand what they are doing when they use the ramp---that insp time is extended. On the 840 one can touch the flowrate in VC and the Ti displays.


When I used VC on 7200 I would always use the ramp and increase flowrate to at least 70 or 80 peak. The drop off is pretty steep. I think it tends to distribute VT better. But a while back Marini (in FOCUS article) described how he likes to use a square wave when the main goal is mobilizing secretions--so secretions aren't pushed back. He also mentioned episodic Peep releases, etc. March/April 2007 issue titled "INHALED BRONCHODILATORS IN AIRFLOW OBSTRUCTION
TOO MUCH OF A GOOD THING?" (he starts off talking about BD's then moves on).
 
Posts: 171 | Location: Palo Alto, CA USA | Registered: November 14, 2002Reply With QuoteReport This Post
Member
posted Hide Post
Wow these questions keep coming around. It is a tough question to answer because they all really do the job so well.

I have used both SI and 840 vents. I like both. The Servo is very vesitile and and somewhat portable. The functions are all very similar but it lacks PAV. With the advent of Dr. Sinderby's NAVA system it has a lot of bang for the buck I am sure. Now if Maquette and PB could just come together what a caddy that would be.

The 840 in my humble opinion is a very responsive vent, but arguably the ultrasonic flowsensors in the Servo are likely just as much so. They are both measure distal to the patient and therefore likely lacking somewhat in smaller populations.

The graphics on the Servo I are amazing and because I am told they are "non buffered" you get real time data. I don't know about the 840 but I really like the 840 split screen.

One other note as far as versitility the Servo I can be adapted for an MRI environment which is kinda handy, as the 840 can not.

Cleaning is not really an issue. The cassette is cleanable and the 840 has expiratory water trap and filters which are cleanable. Disposable circuits sort of did away with the Star heater age for the 300's and expiratory heaters for excess rain out.

So likely not a really strong answer to your question. Here we have quite a variety of vents and are fortunate in some respects however they all do the job well.
 
Posts: 45 | Registered: July 23, 2005Reply With QuoteReport This Post
Junior Member
posted Hide Post
Not going to get drawn into a middle school style of debate, but this is my experience.

I work for a busy LA area trauma center and we use 840s. They have been outstanding with regard to turn around time and flexability for different patient types.

We use Bi_Level routinely and it has made a major impact on our outcomes. We have had the best Pulmonary outcomes in the state 3 years running.

I have never used the Servo I so I can't comment on it, but from all I've heard you'll do well with either the 840 or the Servo I.
 
Posts: 2 | Registered: September 15, 2008Reply With QuoteReport This Post
Member
posted Hide Post
Before anybody starts talking about which vent is the best, you should first take a poll of the doc's that are going to do the ordering and see where they stand as far as understanding what the perticular vent has to offer and can they apply it. No sense buying a Cadillac just to drive to the mailbox at the end of the driveway.
 
Posts: 3 | Registered: September 29, 2008Reply With QuoteReport This Post
  Powered by Social Strata Page 1 2 3 4 5  
 

VentWorld    VentWorld    ventworld.infopop.cc  Hop To Forum Categories  RC Professionals    Servo i versus PB 840

© Copyright Equipment Simulations LLC, 2000-10. All rights reserved.