Evaluation of Stroke Volume Variation Obtained by the FloTrac /Vigileo System to Guide Preoperative Fluid Therapy in Patients Undergoing Brain Surgery

The Journal of International Medical Research 2012; 40: 1175 1181 [first published online as 40(3) 11] Evaluation of Stroke Volume Variation Obtained by the FloTrac /Vigileo System to Guide Preoperative Fluid Therapy in Patients Undergoing Brain Surgery J LI, FH JI AND JP YANG Department of Anaesthesiology, The First Affiliated Hospital of Soochow University, Suzhou, Jiangsu, China OBJECTIVE: The accuracy of stroke volume variation (SVV) obtained by the FloTrac /Vigileo system in otherwise healthy patients undergoing brain surgery was assessed. METHODS: Anaesthesia was induced in 48 patients with minimal fluid infusion. Before surgery, fluid volume loading was performed by infusion with Ringer s lactate solution in 200 ml steps over 3 min, repeated successively if the patient responded with an increase in stroke volume of 10%, until the increase was < 10% (nonresponsive). RESULTS: A total of 157 volume loading steps were performed in the 48 patients. Responsive and nonresponsive steps differed significantly in baseline values of blood pressure, heart rate and SVV. Significant correlations were found between the change in stroke volume after fluid loading and values of blood pressure, heart rate and SVV before fluid loading, with SVV the most sensitive variable. CONCLUSION: Stroke volume variation obtained using the FloTrac /Vigileo system is a sensitive predictor of fluid responsiveness in healthy patients before brain surgery. KEY WORDS: FLUID THERAPY; HAEMODYNAMIC STABILITY; STROKE VOLUME VARIATION; BRAIN SURGERY; FLOTRAC /VIGILEO SYSTEM Introduction Haemodynamic stability and adequate cerebral perfusion are crucial in the treatment of patients with intracranial pathology. 1 In patients undergoing brain surgery, diuretics, preoperative fasting, induction of general anaesthesia and intraoperative bleeding may lead to hypovolaemia and poor cerebral perfusion. Fluid overload is also reported to increase complications and length of hospital stay after surgery. 2 It is, therefore, important that optimal presurgery fluid levels are achieved in patients undergoing neurosurgery. Conventional haemodynamic variables, such as blood pressure, heart rate (HR) and central venous pressure (CVP), are insensitive and sometimes misleading in the assessment 1175

of intravascular volume. 3 11 Although transoesophageal echo cardiography can be used to estimate the preload, there is difficulty in using this technique in most routine operations. 12,13 The FloTrac /Vigileo system provides automatic and continuous monitoring of cardiac output, stroke volume (SV) and stroke volume variation (SVV) based on arterial pulse contour analysis; 14 16 however, the usefulness of SVV obtained by the FloTrac /Vigileo system is 17 21 controversial. The aim of this study was to use a fluid volume loading step regime to assess the accuracy of SVV measured by the FloTrac /Vigileo system compared with commonly used variables. In addition, the optimal preoperative infusion volume for these patients was determined. Patients and methods STUDY POPULATION American Society of Anesthesiologists (ASA) physical status I or II 22 patients who were scheduled to undergoing elective brain surgery at The First Affiliated Hospital of Soochow University, Suzhou, Jiangsu, China, were enrolled sequentially into the study between March and September 2010. Patients with documented coronary or peripheral artery disease, pulmonary disease, diabetes mellitus, cardiac arrhythmias or coagulopathies were excluded from the study. Approval for the study was granted by the Ethics Committee of The First Affiliated Hospital of Soochow University, Suzhou, Jiangsu, China, and each patient or their carer provided written informed consent for participation. ANAESTHESIA All patients fasted for 8 h before surgery. Premedication consisted of intramuscular administration of 0.1 g phenobarbital and 0.5 mg atropine before arrival in the operating room. Following placement of a peripheral catheter (18 G) in the patient s left arm, Ringer s lactate solution was infused at 10 ml/h using an Alaris Asena GW infusion pump (Carefusion, San Diego, CA, USA). Anaesthesia was induced with 0.1 mg/kg midazolam, 3 µg/kg fentanyl, 2 mg/kg propofol and 0.1 mg/kg vecuronium and was maintained with 1.5 2.5% sevoflurane. The depth of anaesthesia was monitored by measuring the bispectral index, which was maintained between 50 and 60. After tracheal intubation, mechanical ventilation at 10 12 breaths/min and a tidal volume of 8 10 ml/kg was initiated to achieve an end-tidal carbon dioxide level of 28 32 mmhg. HAEMODYNAMIC MEASUREMENTS A 20 G catheter was inserted into the patient s radial artery to monitor blood pressure and was connected to the FloTrac /Vigileo system, version 3.01 (Edwards Lifesciences, Irvine, CA, USA) to collect SVV data, calculated as (maximum SV during expiration minimum SV during inspiration) / mean SV. 21,23 An Arrow 7 Fr pulmonary artery catheter (Teleflex, Reading, PA, USA) was inserted into the right internal jugular vein for fluid infusion and to monitor CVP, cardiac output and SV using a S/5 Carestation (Datex-Ohmeda, Helsinki, Finland). Independent research staff collected the data generated by the FloTrac /Vigileo system in order to maintain blinding in the study. EXPERIMENTAL PROTOCOL After 5 min of stable haemodynamic measurements, volume loading was performed by infusing 200 ml of Ringer s lactate solution over a period of 3 min. Haemodynamic variables were recorded 1 1176

min after the end of the infusion and each patient was documented as having a responsive volume loading step (VLS) (increase in SV 10%) or a nonresponsive VLS (increase in SV < 10%). For patients with a responsive VLS, further infusions of 200 ml of Ringer s lactate solution over 3 min were performed as for the first infusion, until a nonresponsive VLS was reached. If a nonresponsive VLS was reached after the first 200 ml fluid infusion, an additional VLS was performed to confirm the result, and the haemodynamic variables were recorded. No changes in anaesthetic management were made during the course of the study. STATISTICAL ANALYSES Data were analysed using the SPSS statistical package, version 15.0 (SPSS Inc., Chicago, IL, USA). Haemodynamic variables in responsive and nonresponsive patients were analysed using an independent samples t-test. The relationship between changes in SV and changes in haemodynamic variables was assessed using Pearson s correlation coefficient. Receiver operating characteristic (ROC) curves were generated for mean arterial pressure (MAP), cardiac output, CVP, HR and SVV to assess the ability of different haemodynamic variables to discriminate between positive and negative responses to fluid challenge. The ROC curves were compared according to the method of Hanley and McNeil. 24 The mean volume of fluid infused was the volume needed to optimize presurgery fluid levels after a preoperative fast following the induction of general anaesthesia. Unless otherwise stated, data are presented as mean ± SD. Results This study enrolled 48 patients (28 males, 20 females) aged 23 68 years (mean ± SD 44 ± 9.3 years), with mean ± SD height 167.3 ± 10.2 cm and mean ± SD weight 61.4 ± 13.3 kg. There were 18 patients with intracerebral aneurysm, 14 with arteriovenous malformation, 11 with meningioma and five with large glioma. The 48 patients received a total of 157 VLS; 108 VLS were followed by an SV increase 10% (responsive) and 49 VLS were followed by an SV increase < 10% (nonresponsive). In four of the 157 VLS, nonresponsiveness was reached after the first fluid loading and, therefore, according to the protocol a second loading was performed; the results showed no further SV increase and these data were excluded from the statistical analysis. The median number (range) of VLS administered was 3.0 (1 5) per patient, equating to a mean ± SD requirement of 694 ± 235 ml of crystalloid fluid per patient as the optimal preoperative infusion volume. Responsive and nonresponsive VLS differed significantly in the pre-vls values of MAP, HR and SVV (P < 0.001 for each variable), but not in CVP and cardiac output values (Table 1). Significant correlations were found between the change in SV after fluid loading and the values of MAP, HR and SVV before fluid loading (P < 0.001 for all three variables). No significant correlation was found between changes in SV and the values of CVP or cardiac output before fluid loading (Table 2). The areas (± SE) under the ROC curve were 0.699 ± 0.054 for MAP, 0.649 ± 0.061 for cardiac output, 0.542 ± 0.062 for CVP, 0.683 ± 0.064 for HR and 0.889 ± 0.033 for SVV (Fig. 1). Only the area for SVV was statistically different from that for other variables (P < 0.001). With a cut-off point of 11.5% for SVV, sensitivity was 81% and specificity 83%. Thus, an SVV of > 11.5% would predict an increase in SV of > 10% in response to volume loading with a sensitivity of 81% and a specificity of 83%. 1177

TABLE 1: Haemodynamic variables before volume loading in 48 patients scheduled for brain surgery, according to the responsiveness of stroke volume to the volume loading Statistical Variable Responsive a Nonresponsive b significance MAP, mmhg 67 ± 9 72 ± 9 P < 0.001 CO, l/min 4.4 ± 0.5 4.6 ± 0.5 NS CVP, mmhg 8.1 ± 1.2 8.2 ± 1.0 NS HR, beats/min 69 ± 7 64 ± 7 P < 0.001 SVV, % 13.4 ± 2.2 10.4 ± 1.3 P < 0.001 Data presented as mean ± SD. Volume loading was performed in steps after anaesthesia and before brain surgery. Each step consisted of infusion of 200 ml Ringer s lactate solution over 3 min. a Responsive, defined as an increase in stroke volume of 10% (occurred for 108 volume loading steps). b Nonresponsive, defined as an increase in stroke volume of < 10% (occurred for 49 volume loading steps). MAP, mean arterial pressure; CO, cardiac output; CVP, central venous pressure; HR, heart rate; SVV, stroke volume variation; NS, not statistically significantly different between groups (P 0.05; independent samples t-test). TABLE 2: Correlation of haemodynamic variables before volume loading with the change in stroke volume after volume loading in 48 patients scheduled for brain surgery Pearson s correlation Statistical Variable coefficient significance MAP 0.624 P < 0.001 CO 0.276 NS CVP 0.128 NS HR 0.578 P < 0.001 SVV 0.814 P < 0.001 Volume loading was performed in steps after anaesthesia and before brain surgery. Each step consisted of infusion of 200 ml Ringer s lactate solution over 3 min. MAP, mean arterial pressure; CO, cardiac output; CVP, central venous pressure; HR, heart rate; SVV, stroke volume variation; NS, not statistically significant (P 0.05). Discussion 23,25 27 Several clinical trials have studied SVV. The FloTrac /Vigileo system provides automatic and continuous monitoring of cardiac output, SV and SVV from a single arterial catheter. Previously used SVV monitoring devices, such as the PiCCO (Pulse index Continuous Cardiac Output; Pulsion Medical Systems, Munich, Germany) and the pulmonary artery catheter (PAC), are based on thermodilution methods and special catheters and skilled techniques are required. The FloTrac /Vigileo system combines ease of use with semi-invasive and continuous real-time monitoring. The potential for SVV obtained with this device to be able to predict fluid responsiveness has not previously been fully evaluated and opinions on the value of SVV obtained with the FloTrac /Vigileo system are divergent. 17 21 De Waal et al. 19 found that SVV obtained with the FloTrac /Vigileo system, using first-generation system software (version 1.01), which detected SVV every 10 min, failed to predict fluid responsiveness in coronary artery bypass graft patients. The 1178

1.0 0.8 Sensitivity 0.6 0.4 0.2 SVV HR MAP CO CVP 0 0 0.2 0.4 0.6 0.8 1 specificity FIGURE 1: Receiver operating characteristic curves for stroke volume variation (SVV), heart rate (HR), mean arterial pressure (MAP), cardiac output (CO) and central venous pressure (CVP) before volume loading as predictors of increase in stroke volume by > 10% after volume loading. Only the area for SVV was significantly different from that for other variables (P < 0.001) 1.0 shortcomings suggest that this version may not have been able to assess SVV accurately and further investigations with newer software versions were indicated. Lahner et al. 20 considered that SVV measured with the FloTrac /Vigileo system (version 1.07) also did not reliably predict fluid responsiveness in patients undergoing major abdominal surgery. In their study, cardiac output and SV were obtained by transoesophageal echocardiography (CardioQ ; Deltex Medical, Greenville, SC, USA). They concluded that the position of the probes might have been a source of inaccuracy in their study. In studies on patients with cardiovascular or pulmonary disease, SVV obtained with the FloTrac /Vigileo system could have been influenced by the disease itself, the patient s body position, thoracic pressure or the surgical operation that was performed. 5,19,21,23 For such cases, PAC or transoesophageal echocardiography may be the optimal choice, while the FloTrac /Vigileo system may be an attractive alternative for monitoring. Unlike previous studies, the present study focused on patients undergoing neurosurgery, specifically taking measurements between the induction of anaesthesia and the start of surgical procedures. During this period, most of the patients were hypovolaemic as a result of preoperative fast, diuresis and anaesthetic vasodilatation, thus controlling for the fact that rapid fluid infusion would be the major factor that might affect the haemodynamic variables assessed in this study with respect to their ability to predict fluid responsiveness using a VLS method. It was also considered that the VLS protocol could be used to determine the appropriate fluid volume needed by each patient. In the present study, 1179

patients were infused with different volumes of fluid independently of body weight. The results showed that SVV was a more sensitive predictor of fluid responsiveness than CVP, MAP, cardiac output or HR, and indicated that the method used here may have an advantage over the conventional method based solely on the weight of the patient. Apart from their indications for surgery, the patients enrolled in this study were healthy, with ASA physical status I or II; thus, preoperative fluid responsiveness of patients with the same physical status could be predicted using the FloTrac /Vigileo system. The present study had several limitations. First, its scope was restricted to confirmation that SVV may be useful in determining fluid responsiveness. The study was undertaken in response to the differing conclusions reached in previous studies on SVV obtained with the FloTrac /Vigileo system and a recent meta-analysis by Peyton and Chong. 28 Secondly, the loading volume of 200 ml in each step may have led to an inaccurate titration result, though this could be remedied by studying additional cases and a larger data collection. The present study highlights a method for the individual tailoring of preoperative volume expansion and goal-directed fluid therapy using the FloTrac /Vigileo system, which is minimally invasive, easy to use and provides continuous real-time monitoring. Obtaining SVV using the FloTrac /Vigileo system was found to be a sensitive predictor of fluid responsiveness in healthy patients before brain surgery. Conflicts of interest The authors had no conflicts of interest to declare in relation to this article. Received for publication 19 January 2012 Accepted subject to revision 29 January 2012 Revised accepted 4 April 2012 Copyright 2012 Field House Publishing LLP References 1 Guidelines for cerebral perfusion pressure. Brain Trauma Foundation. J Neurotrauma 1996; 13: 693 697. 2 Brandstrup B, Tønnesen H, Beier-Holgersen R, et al: Effects of intravenous fluid restriction on postoperative complications: comparison of two perioperative fluid regimens: a randomized assessor-blinded multicenter trial. Ann Surg 2003; 238: 641 648. 3 Feissel M, Michard F, Mangin I, et al: Respiratory changes in aortic blood velocity as an indicator of fluid responsiveness in ventilated patients with septic shock. Chest 2001; 119: 867 873. 4 Tavernier B, Makhotine O, Lebuffe G, et al: Systolic pressure variation as a guide to fluid therapy in patients with sepsis-induced hypotension. Anesthesiology 1998; 89: 1313 1321. 5 Rex S, Brose S, Metzelder S, et al: Prediction of fluid responsiveness in patients during cardiac surgery. Br J Anaesth 2004; 93: 782 788. 6 Wiesenack C, Fiegl C, Keyser A, et al: Assessment of fluid responsiveness in mechanically ventilated cardiac surgical patients. Eur J Anaesthesiol 2005; 22: 658 665. 7 Michard F: Changes in arterial pressure during mechanical ventilation. Anesthesiology 2005; 103: 419 428. 8 Bendjelid K, Romand JA: Fluid responsiveness in mechanically ventilated patients: a review of indices used in intensive care. Intensive Care Med 2003; 29: 352 360. 9 Pinsky MR, Teboul JL: Assessment of indices of preload and volume responsiveness. Curr Opin Crit Care 2005; 11: 235 239. 10 Berkenstadt H, Margalit N, Hadani M, et al: Stroke volume variation as a predictor of fluid responsiveness in patients undergoing brain surgery. Anesth Analg 2001; 92: 984 989. 11 Michard F, Boussat S, Chemla D, et al: Relation between respiratory changes in arterial pulse pressure and fluid responsiveness in septic patients with acute circulatory failure. Am J Respir Crit Care Med 2000; 162: 134 138. 12 Vallée F, Fourcade O, De Soyres O, et al: Stroke output variations calculated by esophageal Doppler is a reliable predictor of fluid response. Intensive Care Med 2005; 31: 1388 1393. 13 Lee JH, Kim JT, Yoon SZ, et al: Evaluation of corrected flow time in oesophageal Doppler as 1180

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