Plethysmograph cannot be the sole parameter in conjunction with GDT. However, it can be used as an adjunct parameter along with other clinical end points.

Borja, it seems that the plethysmographic has some technical limitations. For example, in order to calculate the POP variation, you have to use the raw signal and not the preprocessed signal from the monitor. However, yo could configure the bedside monitor to do so, but you will also have to deal with hypoperfusion in very sick patients. I think that pletysmographic signal has a lot of hidden information and that there is a great potential field of study.

Could be very nice as the techinque is widespread, although there are some concern about the known relationship with the amplitude of the signal and some other parameters that are related not only to fluid responsiveness (anesthesia depth, etc). Let me know if you need some ref.

Thanks for all your replies to me, are very useful.

Indeed, I also think the curve plethysmograpic hides a lot of information. And since it is a parameter routinely monitored, I think it could be very valuable, along with other parameters, to guide our fluid.

However, I think we have to consider several limitations:

1- Monitoring devices often vary the gain of the analysis of the POP. I have observed that many of these devices do not allow to set a fixed gain.

2- Filtering: I think this has to do with the constant part of the density of the signal (tissue), and the variable part of the density of the signal (blood flow). Dr Monge, how to get set the raw signal?

3- It seems very interesting interpretation of Dr. Kirk Shelley about the morphology of the curve. The explains that there is actually a mixture of the variation of arterial flow and venous flow. Even discussed the possibility of separating the two factors using both frequency domain (Fourier analysis) and time domain (envelope analysis) approaches.

4- I think also where monitoring (the finger, ear, forehead ..) states may produce different results.

5- Finally, there is obviously a problem with the signal related to hypoperfusion, and maybe anesthetic depth? (I would be happy if you could offer some reference about this interesting subject, Dr Martini).

But assuming these limitations ... there are many studies about the validity of the POP variation as a predictor of response to volume (Cannesson et al, and others).

It wouldn't be really interesting that monitoring devices incorporate POP variation routinely?

Thanks, and sorry for my very long answer.

Perhaps you might like to look at these...?

Lee QY, Redmond SJ, Chan GSH, Middleton PM, Steel E, Malouf P, Critoph C, Flynn G, O'Lone E, Lovell NH. Estimation of cardiac output and systemic vascular resistance using a multivariate regression model with features selected from the finger photoplethysmogram and routine cardiovascular measurements. Biomed Eng Online 2013; 12: 19. doi: 10.1186/1475-925X-12-19. (Designated Highly Accessed via BioMed Central)

Chan GSH, Fazalbhoy A, Birznieks I, Macefield VG, Middleton PM, Lovell NH. Spontaneous fluctuations in the peripheral photoplethysmographic waveform: roles of arterial pressure and muscle sympathetic nerve activity. American Journal of Physiology - Heart & Circulatory Physiology 2012. 302(3):H826-36

Middleton PM, Davies SR. Noninvasive hemodynamic monitoring in the emergency department. Curr Opin Crit Care 2011 Aug; 17(4):342-50

Middleton PM, Chan GS, Marr S, Celler BG, Lovell NH. Identification of high-risk acute coronary syndromes by spectral analysis of ear photoplethysmographic waveform variability. Physiol Meas 2011 Jun 27; 32(8):1181-1192.

Middleton PM, Tang CH, Chan GS, Bishop S, Savkin AV, Lovell NH. Peripheral photoplethysmography variability analysis of sepsis patients. Med Biol Eng Comput 2011 Mar; 49(3):337-47

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Thank you, very interesting. It seems there are several factors to consider in the plethysmography curve (also low, mid and high frequency are essential reflecting sympathetic and pressure contribution).

However, from a clinical point of view, and apply now, we might think that the amplitude variation of plethysmography curves, at least in mechanical ventilation and stable gain, would be helpful?

Perhaps as an intermediate step to PPV...

I think so.

If you can turn off the gain and avoid the filtering process, probably variations in the amplitude of plethismographic waveform could reflect preload-dependency during passive mechanical ventilation. I guess that same limitations for PPV should be also applied to POP variation.

As you pointed above, Maxime Cannenson has a lot of research on that field.

I know that you have now direct contact with him :)

And regarding your original question, there is a new paper about guiding fluid therapy using dynamic parameters (including pleth signal) in Crit Care. Authors are Benes and Michard.

"The effects of goal directed fluid therapy based on dynamic paramters on post surgical outcome: a meta-analysis of randomized controlled trials"

Thanks! I'll read it ASAP... ;)

Hi everybody, I'm following this thread as this area is a research interest of mine - I'm currently studying the response of the processed POP to a fluid challenge so I will be checking out the references supplied here. Thanks in particular to Manuel for alerting me to the new meta-analysis paper.

I am very greatful about the interest about the topic and your learnings. I think plethysmographic curve variation become a help in goal directed therapy  in same scenarios with same types of patients.   Along with others parameters clinic and methabolic  we  are able to  know more  the phisiosiology of patient  like reponsiveness of fluitotherapy and how we must treat patients with inotropic perhaps more early and better

Interesting topic. Phenomenon (plethysmograiphic curve variation) is another (PPV and SVV) indirect presentation  of volume status and depends besides on hemodynamic/ventilatory conditions on hematological conditions an peripheral circulatory conditions as well. In this object plethysmography is very difficult to use for the interpretation of volume responsiveness. In think its to early to use this phenomenon to guide volume therapy or in management protocols as GDT.   

I agree with Rob De Wilde. Further, indirect measures such as POPV can't discriminate between hypovolaemia and diastolic dysfunction which could result in inappropriate fluid administration. There's some way to go before POPV (which is also likely to be severely affected by vasoconstriction, hypothermia, inflammatory mediators, tissue oedema) could be accepted as a surrogate for other assessment tools such as transthoracic echo etc.

According to the comments, we'll have to wait until the investigation of POP waveform provide more light... :(

However, I think that the height variation of the ascending phase of POP curve can probably, at present, have a great sensitivity to discriminate fluid-responder patients, and be an intermediate step towards the PPV, taking into account the clinical context .

Interestingaspect, however one must realize that currently the pletysmogram is automatically by software in the anesthesia monitoring equipment

Here is a review article published in this month's Anesthesia and Analgesia which may be helpful in this area. I haven't yet read it myself though.

Addison PS. A Review of Signal Processing Used in the Implementation of the Pulse Oximetry Photoplethysmographic Fluid Responsiveness Parameter. Anesth Analg 2014;119:1293–306.

Most of the attempts at using the PPG waveform have been based on the baseline variability, which is affected by a number of variables. Some work has been done using waveform morphology, and we showed some years ago that the PPG waveform has a great similarity to intra-arterial waveforms, particularly in that there is a reflected component which alters the shape, and which is affected by vasodilatation. What is perhaps eventually going to be of more use is to use the PPG to monitor the degree of autonomic tone and response by frequency domain analysis, and observing the power at both the 0.1Hz area (sympathetic tone) and the ~0.25Hz area (the respiratory frequency), which is affected by volume status. 

Thanks, Paul, that's really interesting. Meanwhile, do you think a POP curve with high quality signal and constant gain factor could be helpful to suspect a responder patient to volume?

I mean, with tools we have now in operating room.. is it possible?

The review which Alan cited in A&A included:

"In summary, it is this author’s belief that the use

of more signal information over significantly longer periods

of time but with the emphasis on both the quality and temporal

relevance of the information would appear the most

fruitful way forward in the development of a robust, fully

automated ΔPOP algorithm."

I usually realize about the good correlation between POP variation and PPV, when I watch a good signal quality, but I don't have an assay to be sure of it.

I send an example with two pictures.

I find very interesting an article published by Aymen Allian and Kirk Shelley in Best Practice and Research Clinical Anesthesiology in December on plethysmography.

In that article, they recognize that, after many years studying the usefulness of this curve as functional hemodynamic parameter, find three limitations:

1- The factors that modulate the curve (venous and arterial flow, sympathetic tone ...)

2- To know more about interaction between tidall volume and respiratory and circulatory systems.

3- Improve systems for signal filtering to isolate only the respiratory effect on the curve.

And interestingly, recommend a practical way to use plethysmography variation in the actual scene : or by measuring the POP variation (The clinical cutoff appears to be approximately 15%), or by establishing a monitoring speed 12.5 mm / s, and if there is little or no modulation, despite adequate ventilation, one can be confident that the patient is not hypovolemic. In other words, there are very few causes for a "false negative".

I think it's a very practical way to use POP to guide our fluid.

Hi 

Its a very useful tool in children especially in infants and smaller children. There are new literature to state this. 

I can provide references if you need .

Yes, please! Thanks...

I'm out of the country and will do it on my return next week 

cheers