Assessing fluid responsiveness is critical to evaluating whether patients are responding to fluid loading, itself key to resuscitating hemodynamically unstable patients. Specifically, fluid responsiveness is defined as a 10-15% increase in stroke volume after receiving 500 ml of crystalloid over 10-15 minutes (1). As such, fluid responsiveness serves as a relatively novel concept used to optimize circulation and organ perfusion while avoiding futile and potentially damaging fluid administration in critically ill patients (2). Ensuring such hemodynamic stability reduces overall surgical complications and minimizes time spent in the intensive care unit (ICU) (3). The plethysmographic (pleth) variability index (PVI) (Masimo Corp., Irvine, CA, USA) is derived from an algorithm developed allowing for non-invasive, automated and continuous hemodynamic monitoring.
PVI calculations reflect respiratory variations in pulse oximetry plethysmographic waveform amplitudes, based off of the perfusion index (PI), or the ratio of absorbed infrared light in pulsatile and non-pulsatile tissues (4). This technology has been gaining clinical prevalence, receiving Federal Drug Administration (FDA) approval in August 2020 for use as an indicator of fluid responsiveness on mechanically ventilated patients (5).
Reports of the efficacy of the pleth variability index in various contexts remain inconsistent to date. One study found PVI to be an inaccurate predictor of fluid responsiveness in patients undergoing kidney transplantation (6), while another found the PVI to be unable to predict fluid responsiveness with sufficient accuracy in patients undergoing orthotopic liver transplantation (7). The PVI was also considered less reliable than other metrics reflecting fluid responsiveness, including pulse pressure variation (PPV) and stroke volume variation (SVV), for predicting fluid responsiveness in critically ill patients receiving a vasoconstrictor drug such as in the form of norepinephrine (8). Finally, in a large number of critically ill patients, PVIs cannot be calculated due to spontaneous breathing activity, low tidal volume, minimal respiratory system compliance, and/or cardiac arrhythmias. The PVI is thus best suited for the operating theatre than the ICU (1).
In contrast, a number of studies have also found that the PVI can accurately reflect fluid responsiveness in clinical patients across the lifespan. One study found that in infants, in whom hemodynamics can be rapidly affected even with small fluid losses, the PVI was useful in infants undergoing myelomeningocele repair (9). In spontaneously anesthetized children, the PVI was found to be of value, though no cut off threshold could be recommended given the overlap between baseline PVI in fluid responsive and nonresponsive patients (10). Finally, the PVI has been used to successfully predict mean arterial pressure (MAP) reduction in a cohort of geriatric patients (11).
Broadly, systematic reviews conducted in 2012 and 2016 found that the PVI can effectively predict fluid responsiveness (12). Sandroni et al., in particular, found this prediction to be more accurate the larger the fluid bolus. Chu et al., in the same vein, found that patients who are expanded with a colloid solution, increasing micro- and microcirculatory volumes, are even better suited to PVI assessments. Consistently, studies have found that PVI is only able to predict preload responsiveness in patients with a high perfusion level (PI>4%) (13).
The PVI, while remaining aware of its limitations, can serve as a robust marker of fluid responsiveness in certain operative contexts. This said, its use remains controversial in acute non-surgical contexts. In the end, recommendations in 2020 are to use an integrated approach to the assessment of fluid responsiveness (14).
References
1. Monnet X, Marik PE, Teboul JL. Prediction of fluid responsiveness: an update. Vol. 6, Annals of Intensive Care. Springer Verlag; 2016. p. 111.
2. Cherpanath TGV, Geerts BF, Lagrand WK, Schultz MJ, Groeneveld ABJ. Basic concepts of fluid responsiveness. Netherlands Heart Journal. 2013.
3. Grocott MPW, Mythen MG, Gan TJ. Perioperative Fluid Management and Clinical Outcomes in Adults. Anesth Analg. 2005 Apr;100(4):1093–106.
4. Nilsson LM. Respiration signals from photoplethysmography. In: Anesthesia and Analgesia. Anesth Analg; 2013. p. 859–65.
5. FDA approves Masimo’s Pleth variability index (PVi) – Medical Devices [Internet]. Available from: https://medicaldevicescommunity.com/md_news/fda-approves-masimos-pvi/
6. Le Guen M, Follin A, Gayat E, Fischler M. The plethysmographic variability index does not predict fluid responsiveness estimated by esophageal Doppler during kidney transplantation. Medicine (Baltimore). 2018 May 1;97(20):e10723.
7. Konur H, Erdogan Kayhan G, Toprak HI, Bucak N, Aydogan MS, Yologlu S, et al. Evaluation of pleth variability index as a predictor of fluid responsiveness during orthotopic liver transplantation. Kaohsiung J Med Sci. 2016 Jul 1;32(7):373–80.
8. Monnet X, Guérin L, Jozwiak M, Bataille A, Julien F, Richard C, et al. Pleth variability index is a weak predictor of fluid responsiveness in patients receiving norepinephrine. Br J Anaesth. 2013 Feb 1;110(2):207–13.
9. İçli D, Yörükoğlu HU, Aksu C, Gürkan Y, Etüş V. Pleth Variable Index in infants undergoing myelomeningocele repair. Vol. 58, Journal of Clinical Anesthesia. Elsevier Inc.; 2019. p. 81–2.
10. Weber F, Rashmi BK, Karaoz-Bulut G, Dogger J, de Heer IJ, Prasser C. The predictive value of the Pleth Variability Index on fluid responsiveness in spontaneously breathing anaesthetized children—A prospective observational study. Paediatr Anaesth. 2020 Oct 1;30(10):1124–31.
11. A Yü. The utility of the pleth variability index in predicting anesthesia-induced hypotension in geriatric patients. Turkish J Med Sci. 2020;
12. Sandroni C, Cavallaro F, Marano C, Falcone C, De Santis P, Antonelli M. Accuracy of plethysmographic indices as predictors of fluid responsiveness in mechanically ventilated adults: A systematic review and meta-analysis. Vol. 38, Intensive Care Medicine. Springer; 2012. p. 1429–37.
13. Broch O, Bein B, Gruenewald M, Höcker J, Schöttler J, Meybohm P, et al. Accuracy of the pleth variability index to predict fluid responsiveness depends on the perfusion index. Acta Anaesthesiol Scand. 2011 Jul 1;55(6):686–93.
14. Noninvasive monitoring: fluid responsiveness using the pleth variability index & continuous hemoglobin — insights from UCI CMO Dr. William Wilson [Internet]. Available from: https://www.beckershospitalreview.com/patient-safety-outcomes/noninvasive-monitoring-fluid-responsiveness-using-the-pleth-variability-index-continuous-hemoglobin-insights-from-uci-cmo-dr-william-wilson.html
