Pleth Variability Index in Orthopedic Surgery: Reply

We thank Kehlet and Foss¹  and Gelman²  for their correspondence and interest in our randomized study on goal-directed fluid management published in Anesthesiology.³  Limitations in our choice of hospital length of stay as a clinically significant primary outcome were rightly raised. One such limitation, highlighted by Kehlet and Foss, is its variability among health care systems but also within time according to the evolution of care. The primary outcome of the OPVI (Optimization using the Pleth Variability Index) study (real length of hospital stay after knee or hip arthroplasty) was chosen by the OPVI group as a clinically relevant surrogate measure of postoperative morbidity. The length of hospital stay used to calculate the sample size was based on the 2014 national French database, the year the study was approved by the ethics committee.⁴  We agree that nowadays the length of stay is substantially shorter because of progressive implementation of enhanced recovery after surgery protocols in many surgical procedures, recently including knee and hip arthroplasty.

Another issue raised was the study population. The OPVI trial included intermediate-risk surgical patients because they represent the wide majority of patients worldwide and because they were not previously evaluated in this setting. It was deemed ethical for our group to exclude high-risk surgical patients because the Pleth Variability Index was not yet validated as a hemodynamic monitoring device at the time of our study.

Gelman emphasized that patients who were treated with goal-directed hemodynamic therapy received more fluids than the patients in the control group. Indeed, in the OPVI trial, twice as many patients received a fluid loading in the Pleth Variability Index group than in the control group, and the cumulative volume of fluid infused throughout the surgery was significantly larger in the Pleth Variability Index group than in the control group, whereas we observed no difference in regard to vasopressor use. We advance two theories to explain this. On the one hand, this result could be related to the fact that the study population did not benefit from using the hemodynamic algorithm through dedicated monitoring, as suggested by the low volumes of fluid loading used and the low incidence of postoperative complications. On another side, the Pleth Variability Index may not be reliable enough to allow effective hemodynamic optimization in a surgical setting. Using a cut-off value of 13% to discriminate preload dependency may not be sufficiently precise and suited to individualized goal-directed hemodynamic therapy. Dynamic changes in Pleth Variability Index or arterial pulse pressure variation may be more precise than a universal value of 13%, because many confounding factors are known to increase or decrease this cut-off value.⁵  Further studies are necessary to assess Pleth Variability Index in patients who undergo surgery requiring larger volume loadings,⁶  using changes in Pleth Variability Index more than a static cut-off value, to further specify the clinical utility of this device.

The authors declare no competing interests.

*OPVI participating clinical centers: Caen University Hospital (Sandrine Lemoine, M.D., Ph.D., Jean-Luc Hanouz, M.D., Ph.D., Georges Daccache, M.D., Ph.D., William Greub, M.D., Michel Pegoix, M.D., Maxence Le Goff Coupernot, M.D., Jean- Jacques Parienti, M.D., Ph.D., and Marc-Olivier Fischer, M.D., Ph.D.), Amiens Picardie University Hospital (Diane Taing, M.D., Ossama Abou Arab, M.D., Stéphane Bar, M.D., Emmanuel Lorne, M.D., Ph.D.), Lille University Hospital (Marion Houard, M.D., Serge-André Carron, M.D., Arnaud Alluin, M.D., and Benoît Tavernier, M.D., Ph.D.), Hospital of Catholic Institute of Lille (Chems-Eddine Bouchakour, M.D., Vincent Colas, M.D., Christophe Canevet, M.D.), and Rouen University Hospital (Vincent Compère, M.D., Ph.D.). Data Monitoring Committee: François Fournel, A.A.S., Blandine Lecrux, A.A.S., Sandrine Rot, A.A.S. (Clinical Research Department, Caen University Hospital, France); Domitille Tristam (Clinical Research Department, Hospital of Catholic Institute of Lille, France); Artak Petrosyan, Julie Bellet (Clinical Research Department, Lille University Hospital, France); and Sandrine Brisset (Clinical Research Department, Amiens Picardie University Hospital, France).