This ongoing column is authored by members of the International Society for the Perioperative Care of the Obese Patient (ISPCOP), an organization dedicated to the bariatric patient.
Column Editor: Stephanie B. Jones, MD
Dr. Jones is Associate Professor, Harvard Medical School and Vice Chair for Education, Department of
Anesthesia, Critical Care and Pain Medicine, Beth Israel
Deaconess Medical Center, Boston, Massachusetts.
This month’s installment by: by Konstantin Balonov, MD
Dr. Balonov is Assistant Professor of Anesthesiology, Tufts University School of Medicine, Department of Anesthesiology, Tufts Medical Center, Boston, Massachusetts.
Funding: No funding was provided.
Disclosures: The authors do not have any conflicts on interest relevant to the content of this article.
Intraoperative fluid management in morbidly obese patients remains a controversial and under-researched topic. Minimizing the risk of the intraoperative complications requires precise assessment of the patient’s volume status. This article reviews current scientific views and concepts regarding fluid management in morbid obesity. Goal-directed therapy appears to be the most accurate approach in guiding fluid management. Dynamic parameters such as pulse pressure variation are considered to be the most reliable in assessing volume status and fluid responsiveness of the patient.
Bariatric Times. 2013;10(5):26–27.
Estimation of intravascular volume is one of the most important clinical skills of the anesthesiologist. Management of the fluid balance in patients with morbid obesity remains controversial, which, to great extent, can be attributed to the lack of randomized controlled studies. Current paradigms for fluid management in this patient population are based on studies that mostly compared liberal to restrictive approaches in a nonobese population.
Fluid Management Approaches: Benefits and Risks
Liberal fluid management can produce a positive fluid balance, weight gain, and congestive heart failure while a more restrictive approach may increase the risk of acute tubular necrosis and rhabdomyolysis. The benefits of the liberal approach as demonstrated in studies by Ettinger et al, Schuster et al, and Oggunnaike et al include the prevention of rhabdomyolysis and a decrease in postoperative nausea and vomiting. Patients with more liberal fluid management (40mL/kg vs. 15mL/kg total body weight [TBW]) also produced significantly higher urine output in the operating room, in the post-anesthesia care unit (PACU), and on Postoperative Days 0 and 1 as demonstrated by Wool et al. However, the same study failed to prove any changes in the incidence of rhabdomyolysis.
On the other hand, a restrictive approach to intra- and postoperative fluid management has been advocated by Brandstrup et al. Surgical patients whose fluid balance was managed in the more restrictive fashion demonstrated faster recovery of gastrointestinal (GI) function, better wound healing, and improvement in pulmonary function and tissue oxygenation. In the bariatric setting, as proposed by McGlinch et al, limiting intravenous fluids reduced the incidence of postoperative pulmonary dysfunction and hypoxia, and shortened hospital stay.
Recently, urine output as a guide for perioperative fluid management has been challenged. A study by Matot et al demonstrated low urine output in bariatric patients regardless of relatively high-volume fluid therapy. The authors concluded that their results potentially invalidate urine output as a reliable indicator of the fluid status in the patients with obesity and further investigation is required.
Steep head-up (reverse Trendelenburg) position in the presence of pneumoperitoneum represents another challenge for the intraoperative assessment of fluid balance. Under general anesthesia, this position is associated with a gravity-induced shift of blood volume to the lower part of the body, which frequently results in a significant decrease of cardiac output and blood pressure.[8,9]
Guiding Parameters for Administering Fluids to Patients with Obesity
While administering fluids in patients with morbid obesity undergoing bariatric procedures or any other type of surgeries, a promising technique is to assess fluid responsiveness, and include this parameter in the concept of goal-directed therapy (GDT), as proposed by many authors.[10,11] GDT encompasses a technique involving intensive monitoring and aggressive management of intraoperative hemodynamics. It is based on the achievement of certain values rather than estimating fluid status and calculating interventions. Fluid responsiveness is defined as an ability of the heart to increase stroke volume in response to volume expansion.
Dynamic parameters such as pulse pressure variation (PPV) and stroke volume variation (SVV), derived from arterial waveform analysis, have been suggested as the most reliable indicators of fluid responsiveness in mechanically ventilated patients as long as sinus rhythm is maintained. A recent study by Jain and Dutta demonstrated the value of SVV in the bariatric population. PPV or SVV values greater than 13 percent indicate fluid responsiveness, while patients with PPV below nine percent should be considered nonresponders. Twenty-five percent of the patients with PPV value between 9 and 13 percent represent the so called “gray zone,” when fluid responsiveness cannot be reliably predicted.
Plethysmographic waveform variation (PWV) obtained from the pulse oximetry waveform is a completely noninvasive dynamic parameter that can also be used to assess fluid responsiveness as described by Pizov et al. Its noninvasive nature, minimal additional cost, and practically universal availability represents a major benefit for its use. However, compared to arterial waveform analysis, the authors found some delay in detecting hypovolemia. In other words, PWV may be useful at levels of more profound hypovolemia. There are other new technologies for noninvasive assessment of the cardiac output, PPV, and SVV, such as the ccNexfin (Edwards Lifesciences, Amsterdam, Netherlands) that uses a finger cuff for assessment of blood pressure and derived variables. Based on a recent publication by Fischer et al, this technology was not sufficiently useful in a postoperative cardiac surgical population. On the other hand, early results from intraoperative use in a bariatric population suggest that ccNexfin may be comparable to invasive PPV determination.
The FloTrac (Edwards Lifesciences) is a minimally invasive system that calculates vascular tone and cardiac output by analyzing the waveform derived from the arterial line. Along with the SVV, it provides continuous CO and central venous oxygen saturation (ScvO2) if connected to a central venous line. The additional parameters provided by the FloTrac can be used in bariatric patients with significant cardiac comorbidities.
Pulse-contour analysis-based techniques, such as PiCCO (Pulsion Medical Systems SE, Munich, Germany) are a comprehensive modality for perioperative cardiovascular assessment as they provide not only real-time measurement of PPV, SVV, and cardiac output, but also useful newer parameters, such as Global End-Diastolic Index, intrathoracic blood volume, and extravascular lung water. This technology can be used in patients when certain conditions (e.g., significant arrhythmia) limit use of PPV or in high-risk patients with morbid obesity undergoing high-risk surgical procedures. Due to the high cost and invasiveness, these devices are often reserved for the sickest patients undergoing major surgical interventions.
When making decisions for intraoperative fluid management in patients with morbid obesity one should consider the following:
1. Potentially high incidence of rhabdomyolysis and acute tubular necrosis
2. Beneficial effect of limiting perioperative fluids on GI recovery and hospital stay
3. In laparoscopic bariatric procedures, urine output is an unreliable indicator
4. Pneumoperitoneum and head-up position have a significant negative effect on venous return
5. In low-to-moderate risk patients undergoing laparoscopic bariatric procedures, PWV can be used to estimate fluid responsiveness
6. Minimally invasive monitoring, such as PPV, is a reliable indicator of fluid responsiveness and should be used widely in bariatric patients with significant cardiac comorbidities or undergoing more invasive surgery.
7. In high-risk patients with morbid obesity undergoing high-risk surgical procedures, consider the use of advanced, invasive monitoring, such as FloTrack or PiCCO
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17. Personal communication, Roman Schumann, MD, Tufts Medical Center, 04/03/2013.