Annals of Surgical Oncology
DOI: 10.1245/s10434-008-0139-0
Stroke Volume Variation as a Predictor of Intravascular Volume Depression and Possible Hypotension During the Early Postoperative Period After Esophagectomy Makoto Kobayashi, MD, PhD,1 Masayoshi Koh, MD,2 Takashi Irinoda, MD, PhD,1 Eiji Meguro, MD, PhD,1 Yoshiro Hayakawa, MD, PhD,1 and Akinori Takagane, MD, PhD1
1
Surgical Division, Hakodate Goryoukaku Hospital, 38-3 Goryoukaku-cho, Hakodate City, Hokkaido 040-8611, Japan Anesthetic Division, Hakodate Goryoukaku Hospital, 38-3 Goryoukaku-cho, Hakodate City, Hokkaido 040-8611, Japan
2
Background: Perioperative hypotension during esophagectomy results from hypovolemia caused by a shift of extracellular fluid from the intravascular to the extravascular compartment. Fluid management is often difficult to gauge during major surgery because there are no reliable indicators of fluid status, and some patients still experience cardiorespiratory instability. In this retrospective study, we evaluated stroke volume variation (SVV), calculated by using a new arterial pressure-based cardiac output measurement device, as a predictor for fluid responsiveness after esophageal surgery. Methods: Eighteen patients undergoing esophagectomy with extended radical lymphadenectomy were monitored by the FloTrac sensor/Vigileo monitor system during the perioperative and immediate postoperative period. Fluid responsiveness was assessed and compared with concurrent SVV and central venous pressure (CVP) values, and routine hemodynamic variables. Results: Eleven of 18 patients needed additional volume loading within the first 10 postoperative hours as a result of hypotension. The maximum SVV value of fluid resuscitated patients was >15% in all cases, whereas six of seven patients without postoperative hypotension had maximum SVV values of 0.05). Conclusion: We conclude that SVV, as displayed on the Vigileo monitor, is an accurate predictor of intravascular hypovolemia and is a useful indicator for assessing the appropriateness and timing of applying fluid for improving circulatory stability during the perioperative period after esophagectomy.
Over the past decade, morbidity and mortality associated with radical esophagectomy have both improved,1 whereas postoperative management has remained problematic.2 In particular, hypotension often occurs during the perioperative and immediate
Address correspondence and reprint requests to: Makoto Kobayashi, MD, PhD; E-mail:
[email protected] Published by Springer Science+Business Media, LLC 2008 The Society of Surgical Oncology, Inc.
postoperative periods associated with major surgery, such as extended radical lymphadenectomy for esophageal cancer, and it is almost certainly caused by hypovolemia. While postoperative hemorrhage needs to be ruled out, most cases of hypovolemic hypotension seem to be due to a shift of extracellular fluid from the central to peripheral compartments, and it has been suggested that this is a direct consequence of the development of a third space associated with increased vascular permeability caused by
M. KOBAYASHI ET AL.
hypercytokinemia.3 The destruction of the lymphatic tract due to interruption of the pulmonary lymph outflow tract as a result of mediastinal lymphadenectomy and removal of the thoracic duct also promotes deterioration of circulatory dynamics.4 With the introduction of minimally invasive surgery,5 corticosteroid administration to prevent hypercytokinemia,6,7 and treatment with a specific neutrophil elastase inhibitor,8 postoperative management of esophageal cancer is safer than ever. However, it is also true that some patients still experience cardiorespiratory instability; especially those with poor preoperative nutrition and those receiving neoadjuvant chemoradiotherapy.9,10 Even when it is thought that sufficient fluid has been administered, it is sometimes difficult to determine whether intravascular fluid depression has been relieved by monitoring routine hemodynamic parameters. An added complication is that although appropriate fluid transfusion is often crucial to avoid the deleterious effects of overresuscitation, underresuscitation, or inappropriate resuscitation, it is also reported that static indicators of cardiac preload, such as central venous pressure (CVP), pulmonary artery occlusion pressure, and cardiac end-diastolic dimensions, may be unreliable in detecting volume responsiveness in critically ill patients.11 The FloTrac sensor in combination with the Vigileo monitor (Edwards Lifesciences, Tokyo, Japan) is a recently introduced arterial pressure-based system for continuously monitoring cardiac output (CO), which has applicability in the critical care setting. The FloTrac sensor is a less invasive hemodynamic monitoring device than those used for thermodilution assessment, and it can be used to monitor continuously CO, stroke volume, and stroke volume variation (SVV) through a peripheral arterial pressure line. In addition, other CO devices require calibration to correct for the patient’s changing vascular tone, whereas the FloTrac sensor/Vigileo monitor system needs no calibration because it continuously adjusts for the patient’s ever-changing vascular tone by use of a novel algorithm incorporated within the Vigileo monitor, which is applied to the digitized arterial pressure wave.12 The usefulness of SVV in assessing fluid responsiveness has previously been reported in patients with reduced cardiac function.13 We started routinely using the FloTrac sensor/Vigileo monitor system during esophageal surgery, including an assessment of its advantages for perioperative management after radical esophagectomy, in May 2006. This followed early findings that indicated that SVV was very good at predicting the development of Ann. Surg. Oncol.
hypercytokinemia-induced intravascular hypovolemia in patients undergoing major surgery. Here we report retrospective results from the first 18 patients undergoing surgery for esophageal cancer in whom the FloTrac sensor/Vigileo monitor system was used to assess fluid responsiveness as an integral part of routine postoperative management follow-up and care. In addition, we compared SVV with CVP in terms of reliability in predicting fluid responsiveness during the perioperative and postsurgical periods.
MATERIALS AND METHODS Between May 2006 and September 2007, 18 men of mean ± standard deviation age 66.8 ± 4.8 (range, 61– 73) years underwent perioperative monitoring with the FloTrac sensor/Vigileo monitor system after curative esophagectomy for esophageal squamous cell carcinoma at Hakodate Goryoukaku Hospital. The tumor, node, metastasis system classification according to the Guidelines for the Clinical and Pathologic Studies on Carcinoma of the Esophagus (Japan Society for Esophageal Diseases, 9th edition) was as follows: stage I, n = 5; stage II, n = 5; stage III, n = 4; and stage IVa, n = 4. Tumor location was upper thoracic esophagus, n = 3; middle thoracic esophagus, n = 13; and lower thoracic esophagus, n = 2. Two-field lymph node dissection was performed in 5 patients and three-field dissection in 13 patients. A combination of general (intravenous propofol) and epidural (bupivacaine) anesthesia was used to manage perioperative anesthetic requirements during surgery. The surgical approach for tumor resection for all patients was made by intercostal thoracotomy through a 10- to 12-cm skin incision, preserving the latissimus dorsi and serratus anterior muscle. After subtotal esophagectomy and extended mediastinal lymph node dissection, reconstruction via stomach and cervical esophagogastrostomy was performed. All patients were selected for posterior mediastinal reconstruction via a gastric tube, and a hand-sutured anastomosis was conducted at the neck site. During the surgical procedure, fluid was administered at a rate of 12 to 15 mL/kg/h of crystalloids. Perioperative dopamine or furosemide was not permitted. After surgery, all patients were immediately transferred to the intensive care unit (ICU) under tracheal intubation. Mechanical ventilation was adjusted to supply tidal volumes of 8 to 10 mL/kg of preoperative body weight with pressure-support ventilation. Midazolam and morphine were admin-
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istrated intravenously for sedation during tracheal intubation. Fluid administration in the early postoperative period was started at a rate of 3.5 mL/kg/h and continued until an extravascular to intravascular shift was observed. Patients were considered to be hypotensive when systolic blood pressure could not be maintained above 80 mm Hg for longer than 15 minutes, at which time additional volume loading was provided. If the serum albumin concentration dropped below the normal range (3.4 to 5.4 g/dL), 250 mL of 5% plasma protein fraction was administered. In lieu of corticosteroid treatment to treat hypercytokinemia, sivelestat sodium hydrate, a specific neutrophil elastase inhibitor (Elaspol, Ono pharmacy, Tokyo, Japan), was administrated intravenously at a rate of 0.2 mg/kg/h on completion of surgery. To avoid the possibility of intravascular hypoperfusion, our policy is not to use low-dose dopamine or loop diuretics to protect against oliguria until after adjustments have been made for volume depression. After confirming circulatory stability and a shift toward diuresis, the rate of fluid administration was immediately decreased to 1.5 mL/kg/h to avoid congestive heart failure developing as a consequence of overhydration. Patients were then weaned from assisted mechanical ventilation.
Assessment of Hemodynamic Parameters Before surgery, hemodynamic monitoring was initiated via a 22-gauge elastic catheter that was inserted into the radial artery and connected to a FloTrac sensor. CO and SVV were measured every 20 seconds according to the algorithm housed within the Vigileo monitor. Other parameters routinely monitored included, continuous electrocardiography, pulse oximetry, end-tidal CO2 and arterial blood pressure (ABP). A central venous catheter was inserted into the internal jugular vein, and CVP was measured continuously during the perioperative period with a low-pressure transducer. All raw data from the Vigileo monitor were recorded directly onto a computer and were subsequently reviewed and analyzed statistically. To assess hemodynamic variability associated with volume loading mean SVV, CVP and CO were determined 30 minutes before and 30 minutes after fluid administration. To investigate the relation between changes in preload and postload variables, changes (D) in SVV, CVP, and CO were calculated by the following formulas:
DSVVð%Þ ¼ preload SVV postload SVV DCVP ðmm HgÞ ¼ postload CVP preload CVP DCO ¼ ðpostload CO preload COÞ=preload CO.
Statistical Analysis All data are expressed as mean ± SD, unless stated otherwise. The v2 test for independence was used to assess the relationship between SVV and the development of postoperative hypotension. To determine whether changes in hemodynamic variables (DSVV, DCVP) were related to the increased ratio in CO (DCO) after additional volume loading, both linear regression and Pearson’s correlation coefficient were calculated by StatView software (Abacus Concepts, Berkeley, CA). Values of P < 0.05 were considered statistically significant. RESULTS The mean duration of surgery was 303 ± 58 minutes, and mean blood loss was 280 ± 320 mL. Postoperatively, 11 of 18 patients required additional volume loading within the first 10 hours due to hypotension, and 3 of these received blood transfusions. The mean duration under mechanical assist ventilation after surgery was 1.7 ± 0.7 days. The mean lengths of ICU and hospital stay after surgery were 3.6 ± 1.4 days and 16.0 ± 3.2 days, respectively. There was no significant difference in cardiac function, as assessed by echocardiographically measured ejection fraction before surgery, in patients who needed fluid resuscitation after hypotension (69.1 ± 7.2%) compared with those who did not (66.1 ± 8.8%; P = 0.390, Mann-Whitney U-test). Furthermore, there was no statistically significant difference in the volume of fluid administered (14.1 ± 3.8 vs. 16.1 ± 3.5 mL/kg/h; P = 0.2204, Mann-Whitney U-test), blood loss (241 ± 165 vs. 427 ± 332 mL; P = 0.092, MannWhitney U-test), or operating time (293 ± 39 vs. 294 ± 70 minutes; P = 0.9025, Mann-Whitney Utest) between the group requiring fluid resuscitation versus the group that did not. Importantly, in this series of patients who had undergone esophagectomy with extended radical lymphadenectomy and who developed intravascular volume depression, ICU management with appropriate fluid replacement for critical hypotension (as predicted by SVV changes on the Vigileo monitor) resulted in resuscitation and recovery in all cases and no clinically Ann. Surg. Oncol.
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FIG. 1. Postoperative SVV, CO, and CVP in a patient with circulatory instability after esophagectomy in a 69-year-old man. Duration of surgery was 237 minutes; blood loss was 127 mL. Pathological classification according Japanese guidelines (see Materials and Methods) was pT3 pN0 M0 pIM0; pStage II. SVV, stroke volume variation; CO, cardiac output; CVP, central venous pressure; PPF, plasma protein fraction.
important medical problems such as renal dysfunction, respiratory failure, cardiac insufficiency, or death occurred. Furthermore, there were no complications associated with the use of the FloTrac sensor/Vigileo monitoring system in this cohort of patients. Figure 1 shows a typical graphical presentation for SVV, CO, and CVP in a patient who underwent esophagectomy with three-field lymph node dissection. This patient experienced postoperative hypotension and required fluid resuscitation in the ICU. The initial SVV of the patient at the time of entering the ICU was 8%, but it gradually increased to 15% to 20% by postoperative hour 4. Shortly thereafter, systolic ABP decreased to 80 mm Hg, but SVV still increased to 26%. ABP once again dropped to 20%, and hypotension reoccurred. After additional fluid resuscitation, the circulation stabilized, and SVV was finally maintained near 10%. During these events, CVP values showed almost no response before or after volume loading, whereas the change in SVV observed graphically on the Vigileo monitor clearly predicted hypotension resulting from intravascular hypovolemia. In contrast, Fig. 2 shows the typical graphical presentation for SVV, CVP, and CO in a patient with stable circulation without any hypotensive events. CO and ABP remained stable, Ann. Surg. Oncol.
and SVV remained 15% at any stage during the 12 hours after surgery. In contrast, maximum SVV values in the patient group with hypotension were >15% in all cases (n = 11), even though the initial SVV value was 15% is statistically significantly higher than in patients with maximum SVV of 60% of patients develop hypotension on the operative day.14 Postoperative hypotension is often associated with a further reduction in intravascular volume caused by unusual shift of extracellular fluid into the third space.3 Even though an effective strategy for hypercytokinemia can be adopted that uses corticosteroids or a specific neutrophil elastase inhibitor such as sivelestat, and even though early weaning from mechanical ventilation is possible,8 some patients still experience severe circulatory instability. The usual protocol in our institute Ann. Surg. Oncol.
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FIG. 4. Responsiveness of CO according to changes in CVP and SVV after fluid loading. DSVV (%) = preload SVV - postload SVV; DCVP (mm Hg) = postload CVP - preload CVP; DCO = (postload CO - preload CO)/preload CO; SVV, stroke volume variation; CO, cardiac output; CVP, central venous pressure.
for the perioperative management of patients undergoing esophagectomy is to administer fluid during anesthesia at a rate of 15 mL/kg/h of crystalloids. After transfer to the ICU, fluid administration starts at a rate of 3.5 mL/kg/h. Our strategy for minimizing effects related to the adverse release of the neutrophil elastase is to administer sivelestat rather than a corticosteroid, and we also avoid the use of dopamine and furosemide. By means of this protocol, in 18 patients with esophageal cancer undergoing radical esophagectomy, 15 patients (83%) were successfully extubated within 2 days after surgery without complication, and the mean period was 1.7 days after surgery. Seven of 18 patients avoided hypotension and escaped additional volume loading, but 11 patients (61%) needed fluid resuscitation to treat intravascular hypovolemia. Precise control of fluid balance is a primary goal of postoperative management after surgery, but traditional hemodynamic monitoring parameters (heart rate, mean arterial pressure, and CVP) are often insensitive and sometimes misleading in the assessment of circulating blood volume.15 From May 2006, our institute introduced the FloTrac sensor/Vigileo monitor system for tracking SVV during the perioperative period of esophagectomy. It was reported that SVV calculated from stroke volume changes within the respiratory cycle under mechanical ventilation could be used to assess the volume status and cardiac preload of critically ill16 and cardiac surgery patients.17 Our early clinical experience of applying the FloTrac sensor/Vigileo monitor system to patients with esophageal cancer, also demonstrated that monitoring changes in Ann. Surg. Oncol.
SVV accurately predicted the development of hypotension in patients undergoing esophageal surgery. In our series, the initial value of SVV on entering to the ICU was15% in all cases, and the occurrence rate of hypotension was statistically significantly higher (P = 0.0012) in these patients (Fig. 3). These data indicate that an increase in SVV above 15% might usefully be used to predict the development of hypotension and the need for additional fluid during the early postoperative period, even when traditional parameters (e.g., mean arterial pressure, CVP, heart rate) may not highlight such changes. In the literature concerning the accuracy of SVV for estimating fluid responsiveness after cardiac surgery, it has been reported that real-time monitoring of SVV is a more sensitive and specific predictor than CVP and other hemodynamic parameters.18 Our SVV-based data is the first pertaining to esophagectomy patients and confirms that SVV also has excellent predictive qualities in this group of patients undergoing esophageal surgery. Comparing CVP and SVV for their predictability in assessing fluid responsiveness (Fig. 4) indicated that a decrease in SVV values was significantly correlated to CO improvement (r = 0.638, P = 0.049), but no such correlation between CVP and CO value existed. CVP, which is a commonly used parameter for the evaluation of intravascular volume status,11,17 demonstrated no predictive value for cardiorespiratory instability during the perioperative period after esophagectomy.
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Although the usefulness of SVV is clearly demonstrated in our data, the clinical use of this hemodynamic parameter has certain limitations. First, this monitoring method can only be used in mechanically ventilated patients without arrhythmias. Moreover, severe peripheral constriction and aortic regurgitation may affect absolute values. Nevertheless, despite these limitations, we suggest that the FloTrac sensor/ Vigileo monitor system provides marked advantages over more traditional vital sign monitoring systems alone in postoperative fluid resuscitation after esophageal surgery. Because individual responses to surgical stress from this form of surgery vary and are difficult to predict, perioperative cardiorespiratory instability is more unpredictable than after cardiac surgery.19 Even though relatively large amounts of fluid were transfused during the surgical procedures reported, postoperative hypotension resulting from intravascular hypovolemia still occurred unexpectedly. This is a predicament for the physician, who has difficult decisions to make with regards fluid resuscitation. Persistent hypotension can lead to serious tissue hypoperfusion and organ distress, while excessive fluid replacement may lead to congestive heart failure and pulmonary edema during volume resuscitation. To maintain low mortality rates in esophagectomy, a safer and more exact fluid management method is required. On the basis of our experience to date, we conclude that SVV, as displayed on the Vigileo monitor, is an accurate predictor of intravascular hypovolemia and is a useful indicator for assessing the appropriateness and timing of applying fluid for improving circulatory stability during the perioperative period after esophagectomy. A larger, prospective trial is needed to help ascertain the overall effectiveness of SVV/ Vigileo monitoring. ACKNOWLEDGMENT We thank Steve Clissold, PhD (Content Ed Net), who provided assistance with English language and whose work was funded by Edwards Lifesciences, Japan.
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