INTRODUCTION — Perioperative maintenance of adequate intravascular volume status is important to achieve optimal outcomes after surgery, but there are controversies regarding optimal composition and volume of intraoperative fluid therapy. This topic will review derangements and monitoring of intravascular volume status in this setting, as well as strategies for choosing appropriate composition, amount, and timing of intraoperative fluid administration.
Severe intravascular volume depletion in surgical patients is discussed in other topics. (See "Intraoperative management of shock in adults", section on 'Hypovolemic shock management' and "Massive blood transfusion".)
Routine management of maintenance and replacement fluids in nonsurgical settings is discussed separately. (See "Maintenance and replacement fluid therapy in adults".)
CAUSES AND CONSEQUENCES OF INTRAVASCULAR VOLUME DERANGEMENTS — Normovolemia/euvolemia should be maintained throughout the perioperative period to maintain adequate tissue perfusion. Both hypovolemia and hypervolemia are associated with postoperative morbidity [1-4].
Hypovolemia
Causes
●Preoperative factors – Preoperative hypovolemia may increase the risk of significant decreases in blood pressure during induction of anesthesia [5].
•Although preoperative fasting overnight for approximately 10 hours does not significantly reduce intravascular volume [6,7], the fasting period is limited to avoid preoperative dehydration [8]. Patients are encouraged to consume clear oral liquids up to two hours before surgery. (See "Preoperative fasting in adults".)
•Mechanical bowel preparation is associated with fluid loss from the gastrointestinal tract, which may reduce preoperative intravascular volume. Newer bowel preparations are designed to minimize this loss.
•Disorders such as bowel obstruction or pancreatitis may cause intravascular volume loss due to inflammation and interstitial edema. (See "Etiology, clinical manifestations, and diagnosis of volume depletion in adults", section on 'Etiology'.)
•Ongoing bleeding typically requires surgical hemostasis to allow adequate volume repletion. (See "Approach to shock in the adult trauma patient".)
●Surgery-related factors
•Surgical bleeding
•Coagulopathy due to hemodilution and/or hypothermia, which aggravates blood loss
•Decreased venous return due to:
-Abdominal insufflation during laparoscopy - (See "Anesthesia for laparoscopic and abdominal robotic surgery in adults", section on 'Hemodynamic complications'.)
-Compression of the inferior vena cava (eg, in the supine position during pregnancy) or other major veins (eg, portal vein)
•Positive pressure mechanical ventilation with large tidal volumes, high positive end-expiratory pressure, or lung recruitment maneuvers to reverse atelectasis. (See "Mechanical ventilation during anesthesia in adults", section on 'Recruitment maneuvers'.)
•Prolonged duration of surgery with evaporation and insensible fluid loss from exposed body cavities or wounds, particularly with an open abdominal cavity resulting in bowel edema and sequestration of fluid in tissues [9]. Conversely, minimal fluid losses occur during short less invasive surgical procedures [10].
•Any other factors preventing early transition (within 24 hours of surgery) from intravenous (IV) to oral fluid therapy [8].
Consequences — Hypovolemia results in reduced cardiac output and tissue perfusion. Persistent hypovolemia can lead to shock and multiorgan failure [11,12].
Hypervolemia
Causes — Development of hypervolemia is generally due to excessive volume administration. In many cases, intraoperative fluid is administered to treat hemodynamic instability due to vasodilation, surgical bleeding, myocardial dysfunction, or vascular permeability. This often results in postoperative fluid overload.
●Anesthesia-related factors
•General anesthetic agents – Most IV and inhalation anesthetic and adjuvant drugs including opioids cause dose-dependent vasodilation and myocardial depression that may lead to hypotension that is treated with fluid administration [13,14]. Unnecessarily deep anesthesia with hypotension may lead to excessive fluid administration. (See "Hemodynamic management during anesthesia in adults", section on 'Selection and dosing of anesthetic agents'.)
Hypotension that persists after reducing anesthetic depth (if appropriate), administration of appropriate amounts of fluid to replace surgical losses, and exclusion of other causes of hypotension should be treated with IV vasopressor/inotropic agents such as phenylephrine (table 1) rather than continuing administration of large amounts of fluid alone. (See 'Restrictive (zero-balance) strategy' below and "Hemodynamic management during anesthesia in adults", section on 'Vasopressor and positive inotropic agents'.)
•Neuraxial anesthesia – Sympathetic blockade during neuraxial anesthesia increases venous capacitance and dilates arteriolar resistance vessels, with resultant hypotension. However, rather than preloading with IV fluid to prevent hypotension, we use a vasopressor such as phenylephrine or norepinephrine (table 1).
●Surgery-related factors
•Treatment of surgical bleeding – Excessive administration of crystalloid or colloid together with transfusion of red blood cells results in dilution of coagulation factors, which may exacerbate bleeding and lead to additional transfusions and administration of fluid.
●Patient-related factors
•Congestive heart failure (CHF) with compensatory fluid retention
•Renal insufficiency, particularly if renal replacement therapy is inadequate
Consequences — Hypervolemia can result in reduced tissue perfusion due to tissue edema, with clinically significant postoperative fluid retention (ie, weight gain >10 percent above preoperative baseline). Postoperative fluid overload is associated with increased morbidity, length of stay in the intensive care unit, and mortality [15]. Specific systemic effects include the following:
●Respiratory effects – Increased extravascular fluid in lung tissue impairs oxygen exchange and increases risk for postoperative respiratory failure and pneumonia [16]. Some patients develop frank pulmonary edema, particularly those with a history of heart failure [17]. (See "Overview of the management of postoperative pulmonary complications", section on 'Pulmonary edema'.)
●Gastrointestinal effects – Increased extracellular fluid in the bowel can lead sequentially to gastrointestinal edema, decreased gastrointestinal motility, and possibly ileus [18]. In patients undergoing bowel surgery, intestinal edema can increase tension at bowel anastomoses contributing to anastomotic dehiscence [16].
Occasionally, massive fluid resuscitation is associated with acute ascites [19]. Ascites and bowel edema can contribute to development of abdominal compartment syndrome [20]. (See "Abdominal compartment syndrome in adults".)
●Effects on hemostasis – Excess intravascular fluid dilutes clotting factors, which can contribute to or cause coagulation abnormalities. (See "Massive blood transfusion", section on 'Dilutional coagulopathy' and "Coagulopathy in trauma patients", section on 'Resuscitation-associated coagulopathy'.)
●Effects on wound healing – Marked tissue edema impairs wound healing. (See "Basic principles of wound healing".)
MONITORING INTRAVASCULAR VOLUME STATUS
Intraoperative monitoring challenges — Intravascular fluid status is monitored to maintain euvolemia with adequate tissue perfusion. Standard hemodynamic monitors include noninvasive blood pressure (BP) cuff and heart rate (HR) monitoring. In selected cases, one or more invasive monitors of dynamic hemodynamic parameters may be used to predict fluid responsiveness (ie, an increase in stroke volume [SV] and cardiac output [CO] following intravenous fluid administration (figure 1)) [21].
Challenges in estimating intravascular volume status during the intraoperative period include:
●Preoperative volume status may be suboptimal or unknown.
●Surgical volume losses may be continuously changing, but are difficult to quantify.
●Cardiovascular responses to anesthetic agents and dosing are occurring.
●Measured laboratory values do not reflect contemporaneous changes in intravascular volume status.
●Clinical methods routinely used to assess volume status in awake patients (eg, thirst, postural dizziness, lethargy, confusion) are unavailable in the anesthetized patient.
Traditional static parameters — Static parameters (eg, measurements of BP, HR, urine output [UO], central venous pressure [CVP]) have been traditionally used to provide supplemental data regarding intravascular volume status (see "Basic patient monitoring during anesthesia", section on 'Monitoring modalities'). However, sole use of these parameters to guide fluid therapy may result in either hypovolemia or hypervolemia. Even with continuous monitoring of these static parameters, significant intraoperative reduction in tissue perfusion may not be recognized [11,12,22].
●Blood pressure and heart rate – BP and HR responses to changes in intravascular volume status are not predictable in individual patients. Examples include:
•There is no correlation between BP and CO in patients undergoing major abdominal surgery [23].
•Healthy young patients with subclinical hypovolemia often have normal BP and HR because the stress response to surgery activates the sympathetic nervous system and the renin-angiotensin system, with release of vasoconstrictor hormones that increase BP. Although the resulting peripheral vasoconstriction favors maintenance of adequate perfusion to the heart and the brain, perfusion to other organs (eg, kidneys, gastrointestinal tract, skin) are reduced. Notably, general or neuraxial anesthesia may blunt these compensatory vasoconstrictive responses to decreased perfusion.
•Patients treated with beta-blockers may not manifest tachycardia as a compensatory response to hypovolemia.
●Central venous pressure – CVP measured from a central venous catheter (CVC) or pulmonary artery occlusion pressure (PAOP) measured from a pulmonary artery catheter (PAC) are sometimes used to provide supplemental data regarding intravascular volume status, but these parameters are inaccurate surrogates to determine cardiac preload, fluid responsiveness [24], or impending pulmonary edema [17,21,25-31].
●Urine output – Oliguria (UO <0.5 mL/kg per hour) is a commonly used indicator of hypovolemia. However, oliguria alone is not a sufficient indication for fluid administration in patients undergoing anesthesia and surgery. For example, inhalation anesthetics, as well as surgical stress, may reduce UO in patients who are actually euvolemic, leading to fluid overload if fluid is administered to treat oliguria [13,14].
Notably, intraoperative oliguria does not predict acute kidney injury (AKI) [4]. Data suggest that traditional targets that attempt to continuously maintain UO >0.5 mL/kg per hour are not warranted, although sustained oliguria may be associated with increased risk of renal injury, particularly if <0.3 mL/kg per hour [32-37].
●Mixed venous oxygen saturation – Measurements intended to track global oxygen (O2) delivery have limited utility to guide fluid therapy [38]. These include measurements of mixed venous O2 saturation from a PAC (SvO2) or central venous O2 saturation (ScvO2) from a CVC. Although SvO2 and ScvO2 are proportional to CO, tissue perfusion, and tissue O2 delivery, these measurements are also inversely proportional to tissue O2 consumption. Thus, values do not reflect changes in tissue perfusion during the perioperative period when O2 consumption is variable [38,39]. (See "Oxygen delivery and consumption".)
Dynamic parameters to assess volume responsiveness — Dynamic hemodynamic indices are used to assess fluid responsiveness and guide goal-directed fluid therapy in patients undergoing major invasive surgery, particularly for procedures with large expected blood losses or fluid shifts [8]. Compared with traditional static parameters, dynamic parameters provide superior assessment of response to a fluid challenge (ie, volume responsiveness) [26,38,40-45]. (See 'Goal-directed fluid therapy' below.)
The following parameters are examples:
Respiratory variations in arterial pressure waveform
●Measured variables – Variations in the intra-arterial pressure waveform that occur during respiration can be observed or measured to assess responses to fluid challenges (figure 1) [44-49]. These include pulse pressure variation (PPV), SV variation (SVV), systolic blood pressure variation (SPV), or change in inferior vena cava diameter. These variations occur during controlled mechanical ventilation because inspiration increases intrathoracic pressure, which reduces venous return, right ventricular (RV) filling volume, and SV. The opposite effects occur during expiration. If arterial vasomotor tone and cardiac function remain constant. these changes in venous return and SV create variations in pulse pressure and systolic BP (figure 2) [48]. Normal respiratory variations in these dynamic parameters are <10 percent [50]. Greater variations suggest fluid responsiveness and the likely need for fluid administration (figure 1) [24].
●Limitations – Each of the dynamic indices based on respiratory variation has advantages and disadvantages (table 2) [51-53]. Although generally superior to static parameters for assessment of fluid responsiveness (see 'Traditional static parameters' above), these dynamic indices may not be useful in certain situations such as [45]:
•During spontaneous ventilation
•During mechanical ventilation with low tidal volumes <8 mL/kg or high positive end-expiratory pressure >15 cm H2O [54]
•During open chest procedures [55,56]
•Patients with clinical abnormalities such as elevated intra-abdominal pressure, cardiac tamponade, significant auto-PEEP, nonsinus rhythm or other cardiac arrhythmias, right heart failure, or a requirement for vasoactive infusions [49,54,57]
Also, there are limitations in sensitivity and specificity. A 2018 systematic review calculated the pooled area under the curve (AUC) for PPV and for SVV (5017 patients; 68 studies) [53]:
•For PPV, AUC was 0.86 (95% CI 0.80-0.92), with a sensitivity of 80 percent (95% CI 74-85 percent) and specificity of 83 percent (95% CI 73-91 percent)
•For SVV, AUC was 0.87 (95% CI 0.81-0.93), with a sensitivity of 82 percent (95% CI 75-89 percent) and specificity of 77 percent (95% CI 71-82 percent)
Thus, indices based on respiratory variations are interpreted with caution and should consider the clinical setting and clinical data such as the physical examination and static parameters such as filling pressures, UO, or SvO2 or ScvO2 [45]. (See 'Traditional static parameters' above.)
Notably, although hemodynamic indices of respiratory variation can be computed (manually or automatically), visual estimation is often adequate to guide fluid therapy [45,46]. In one study, determination of the need for a fluid bolus based on visual estimation of SPV in the intra-arterial waveform was compared with computed values; only 1 percent of treatment decisions were incorrect when based solely on visual estimation (figure 1) [46].
Changes in mean arterial pressure and/or SV induced by lung recruitment maneuvers (eg, ventilation with positive pressure held at 30 cm H2O for 30 seconds) can also be used to predict volume responsiveness [58].
Ultrasound technologies
Esophageal doppler technology — Esophageal Doppler devices use a flexible transesophageal Doppler ultrasound probe to measure blood flow velocity in the descending thoracic aorta to derive estimates of SV [44,59,60]. Such devices may be useful when indices based on respiratory variation in the intra-arterial waveform cannot be used. (See 'Respiratory variations in arterial pressure waveform' above.)
Echocardiography — Left ventricular (LV) size and intravascular volume status can be quickly estimated using transesophageal echocardiography (TEE) or transthoracic echocardiography (TTE). This is typically accomplished in the transgastric midpapillary short-axis view by qualitative visual assessment of LV cavity size. Underfilling of the left ventricle caused by acute hypovolemia is easily recognized in a patient with hyperdynamic systolic function and decreased end-diastolic and end-systolic LV cavity dimensions (movie 1). Quantitative measurements of the internal diameter or cross-sectional area of the LV at end-diastole can also be made (image 1 and image 2 and table 3) [61,62]. Changes from baseline (normovolemia) are monitored using these qualitative and/or quantitative assessments. (See "Intraoperative transesophageal echocardiography for noncardiac surgery", section on 'Assessment of left ventricular volume'.)
Point-of-care ultrasound (POCUS) transthoracic echocardiography can also be used to assess left and right atrial and ventricular chambers to estimate intravascular volume status [63]. One study noted good correlation between pulse pressure variation (PPV) during the respiratory cycle and the collapsibility index and distensibility index of the inferior vena cava measured using transthoracic echocardiography during mechanical ventilation [64]. (See "Overview of perioperative uses of ultrasound", section on 'Point-of care ultrasound (POCUS)'.)
Noninvasive technologies — Several types of noninvasive commercially available technologies that measure CO and/or assess fluid responsiveness have been studied (eg, pleth variability index, pulse wave analysis [pulse wave transit time or pulse contour analysis], carbon dioxide rebreathing, and thoracic electrical bioimpedance or bioreactance devices) [65-68]. A 2017 meta-analysis concluded that the percentage error of these devices for measurements of CO can be significant compared with standard thermodilution techniques [69].
Measurement of laboratory values — Increased serum lactate levels or lactic acidosis on sequential arterial blood gases can be an important indicator of reduced global tissue perfusion. However, these laboratory values do not provide information regarding contemporaneous clinical intravascular volume status since they are measured intermittently and do not immediately reflect acute changes. (See "Etiology, clinical manifestations, and diagnosis of volume depletion in adults", section on 'Clinical manifestations'.)
CHOOSING FLUID: CRYSTALLOID, COLLOID, OR BLOOD
Crystalloid solutions — Crystalloids are solutions of electrolytes and sterile water that may be isotonic, hypotonic, or hypertonic with respect to plasma. Balanced electrolyte solutions (also termed buffered crystalloid solutions) that have an electrolyte composition similar to plasma with the addition of a buffer (eg, lactate) are most widely used [70]. Examples include lactated Ringer's solution (also termed Hartmann's solution) or Plasmalyte.
We typically select a balanced electrolyte crystalloid solution for routine perioperative fluid administration to maintain intraoperative normovolemia. During major surgical procedures, we administer approximately 3 mL/kg per hour to replace sensible and insensible losses and support basal metabolic rate, and we administer fluid boluses (typically 250 mL) in volume responsive patients to optimize intravascular volume (see 'Dynamic parameters to assess volume responsiveness' above), and replacement of lost blood with crystalloid on a 1.5:1.0 volume basis until a blood transfusion threshold is met. We avoid dextrose-containing solutions due to the putative adverse effects of hyperglycemia [71].
We avoid administration of a large volume of normal saline (NS; 0.9 percent), as this has been associated with hyperchloremic acidosis [72-85]. Risk for other adverse outcomes, particularly acute kidney injury (AKI), has been associated with NS in several observational and randomized studies [73,74,86-89]. However, results are not consistent in patients who do not receive large volumes of NS or are not critically ill [72,81,90-92]. A 2017 meta-analysis of randomized trials that included 1096 surgical patients noted that perioperative administration of buffered (ie, balanced) electrolyte solutions was associated with a lower incidence of minor metabolic derangements, particularly mild metabolic acidosis compared with NS, but did not demonstrate an effect on mortality or renal replacement therapy (RRT); however, most of these patients were not critically ill [72]. Another 2018 meta-analysis of randomized trials in more than 3700 unselected critically ill or perioperative adult patients did not find a significant reduction in mortality (odds ratio [OR] 0.90, 95% CI 0.69-1.17) or incidence of RRT (OR 1.12, 95% CI 0.80-1.58) with administration of balanced electrolyte solutions rather than NS; however, most of these patients received a low fluid volume [92]. Similarly, a 2020 single-center alternating cohort trial of infusion of large volumes of saline versus lactated Ringer’s solution noted comparable outcomes including renal, respiratory, infectious, and hemorrhagic complications in 8616 patients undergoing major noncardiac surgical procedures [91].
Colloid solutions — Colloids are human plasma derivatives (eg, human albumin, fresh frozen plasma [FFP]) or semisynthetic preparations (eg, hydroxyethyl starch [HES], gelatins) [93]. Colloids may be dissolved in isotonic saline or in a solution with a balanced electrolyte concentration similar to plasma [93].
Some clinicians prefer to use colloids in selected patients or situations in attempts to expand microvascular volume with minimal capillary leakage in fluid responsive patients, thereby minimizing the total quantity of administered fluid and edema formation [94]. For example, during blood loss, colloids may be administered on a 1:1 volume basis until a transfusion threshold is met [94,95]. Administration of 20 percent albumin results in a long-lasting plasma volume expansion lasting into the postoperative period [96,97]. In one study of patients undergoing open abdominal surgery, the intravascular half-life of 20 percent albumin was 9.1 (5.7 to 11.2) hours [96]. (See "Intraoperative transfusion of blood products in adults", section on 'Red blood cells'.)
However, evidence that colloid solutions are superior to balanced electrolyte crystalloid solutions is scant [98-102]. A study using closed loop administration of balanced HES for open abdominal surgery noted lower morbidity on postoperative day two and better disability-free survival at follow-up one year after surgery, compared with closed loop administration of balanced crystalloid solution [100,101]. A small study of administration of 20 percent albumin in the postoperative period after cardiac surgery noted less positive fluid balance and volume of fluid boluses and lower requirements for a vasopressor (norepinephrine) [103].
Overall, we minimize use of colloids since they do not provide significant hemodynamic benefits over crystalloids. When we do select a colloid to expand microvascular volume, we use albumin rather than HES.
Albumin — Human serum albumin is available in both 5 and 25 percent solutions. In some parts of the world, human serum albumin is available as 4 and 20 percent solutions. Human albumin 5 percent has a volume effect (ie, the percent of fluid administered that remains intravascular) of 70 percent, while albumin 25 percent solution is isosmotic with plasma (table 4). Human albumin is pasteurized and does not transmit any known infectious diseases. (See "Plasma derivatives and recombinant DNA-produced coagulation factors", section on 'Albumin'.)
Notably, albumin is more expensive than other solutions, and may not be safer or more efficacious than synthetic colloids (eg, HES) or balanced crystalloid solutions [90,98,104-106]. (See 'Hydroxyethyl starches' below and 'Crystalloid solutions' above.)
Hydroxyethyl starches — HES solutions are synthetic colloids, identified by three numbers corresponding to concentration, molecular weight, and molar substitution (ie, the average hydroxyethyl groups per one glucose unit) (table 4). As an example, Hespan is HES 6 percent (600/0.75) with a volume effect of 100 percent and a high molar substitution of 0.75. Due to concerns regarding renal toxicity and effects on hemostasis, administration of HES solutions is restricted in Europe and North America [90].
A 2018 systematic review in critically ill patients with medical and surgical diagnoses noted a higher incidence of RRT in those receiving HES solutions compared with those receiving crystalloids (risk ratio [RR] 1.30, 95% CI 1.14-1.48; 8527 participants, nine studies) [98]. Also, a 2010 systematic review in mixed surgical and nonsurgical patient populations found an overall increased risk of author-defined kidney failure in surgical and medical patients receiving HES solutions (including some who received highly substituted HES products) compared with those receiving various other types of fluid therapy [107]. Furthermore, administration of HES solutions in cardiac surgical patients increased risk of postoperative bleeding and transfusion compared with albumin [108].
However, data are not consistent. A 2022 meta-analysis of randomized trials (seven trials; 2398 patients) noted that intraoperative intravascular volume replacement with 6 percent hetastarch 130/.04 during open abdominal surgery was not associated with increased risk of AKI after 30 postoperative days compared with using crystalloid solutions (eg, lactated Ringers, Plasmalyte, NS) [109]. Furthermore, randomized trials comparing outcomes after administration of 6 percent hetastarch 130/.04 versus 5 percent albumin noted similar risk for AKI and other serious postoperative complications with either colloid [106,110]. Notably, risk of HES-induced renal toxicity and other complications is likely influenced by the molar substitution level in the specific product, with less risk for more recently developed low substituted HES products such as 6 percent hetastarch 130/.04 [111]. Nevertheless, in 2021, the FDA required additional warnings about the risk of death, bleeding, and AKI [112].
Since HES products impair platelet reactivity and decrease circulating plasma concentrations of coagulation factor VIII and von Willebrand factor, administration may result in weakening of clot formation and more transfusions of blood products including FFP, cryoprecipitate, and platelets compared with other fluid choices [98,113-115]. A 2018 systematic review of randomized trials in critically ill patients noted a higher incidence of transfusion in those receiving starch solutions compared with those receiving crystalloids (RR 1.19, 95% CI 1.02-1.39; 1917 participants, eight studies) [98]. HES products with low molar substitution (eg, pentastarch and tetrastarch) may have less effect on hemostasis [116]. One 2008 meta-analysis of randomized trials compared HES solutions with low (0.4) versus a somewhat higher (0.5) molar substitution, noting significantly less blood loss (404 mL) and red blood cell (RBC) transfusion (137 mL) in patients receiving the low substituted product (seven trials; 449 patients) [117]. Subsequently, a 2020 randomized trial noted similar coagulation, platelet count, and platelet function parameters with use of 6 percent hetastarch 130/.04 for plasma volume replacement compared with 5 percent albumin [118]. Furthermore, a multicenter retrospective study noted that bleeding rates did not change after switching from HES solution to albumin for musculoskeletal surgical procedures (3078 total patients) [119].
Gelatins — Gelatins are not used in the United States because of their short duration of action (two to three hours) due to rapid excretion in the urine, possible effects on coagulation, and a relatively high incidence of anaphylaxis [90,93,120]. (See "Perioperative anaphylaxis: Clinical manifestations, etiology, and management", section on 'Colloids and plasma expanders'.)
Gelatins are used in some countries because they are inexpensive and have a volume effect of 70 to 80 percent (table 4) [121].
Blood transfusion
●Red blood cells – RBCs are used to replace intraoperative blood loss when a transfusion threshold is met, as discussed separately. (See "Intraoperative transfusion of blood products in adults", section on 'Red blood cells'.)
●Plasma – Decisions regarding transfusion of plasma derivatives of human blood (eg, fresh frozen plasma [FFP], cryoprecipitate) are based on estimates of the amount of current and expected ongoing blood loss and evidence of intractable microvascular bleeding indicating abnormal hemostasis, ideally with confirmation by diagnostic test results. In patients with disseminated intravascular coagulation, administration of colloid lacking coagulation factors may exacerbate depletion of natural anticoagulants needed to prevent microthrombosis; thus, plasma rather than albumin is typically preferred for volume replacement in these patients [122]. Further discussions regarding transfusion are available in a separate topic. (See "Intraoperative transfusion of blood products in adults", section on 'Plasma' and "Intraoperative transfusion of blood products in adults", section on 'Cryoprecipitate'.)
CHOOSING A FLUID MANAGEMENT STRATEGY — Our intraoperative fluid management strategy and selection of noninvasive or invasive monitoring is based on the expected blood loss and the likelihood of nonhemorrhagic fluid shifts (eg, from open body cavities and wounds) during the planned surgical procedure (see 'Monitoring intravascular volume status' above). Other factors influencing these decisions include patient comorbidities (eg, anemia, congestive heart failure [CHF], chronic obstructive pulmonary disease [COPD]) and planned postoperative disposition (eg, home, hospital ward, intensive care unit).
Minimally/moderately invasive surgery — For most relatively brief minimally or moderately invasive surgery with planned early postoperative ambulation, we administer 1 to 2 L of a balanced electrolyte solution for procedures that will not incur significant fluid shifts or blood loss. This volume of fluid is typically administered during surgery over a period of 30 minutes to two hours. Such empiric but limited fluid administration for less invasive surgery in ambulatory patients addresses the mild dehydration caused by preoperative fasting and is associated with less risk for postoperative nausea and vomiting (PONV) or pain compared with controls receiving minimal fluids [123,124]. In patients with a history of CHF or COPD, fluid is administered cautiously (eg, in increments), with a total volume in the lower end of this range.
Major invasive surgery — For adult patients undergoing major invasive surgical procedures, we select one of the following strategies:
Restrictive (zero-balance) strategy — For invasive major surgery with expected blood loss <500 mL, we typically employ a restrictive zero-balance approach that minimizes fluid administration, particularly if no invasive monitoring of dynamic hemodynamic parameters is planned (eg, intra-arterial catheter, transesophageal echocardiography [TEE] or esophageal Doppler probe). With this approach, only the fluid that is lost during surgery is replaced, including the following strategies [12]:
●During the intraoperative period, patients receive a balanced electrolyte crystalloid solution administered at a rate of approximately 3 mL/kg per hour to replace sensible and insensible losses and support metabolic rate [11].
●For blood loss, additional fluid may be administered. Studies suggest that the optimal crystalloid-to-blood volume ratio is approximately 1.5:1.0, and that the optimal colloid-to-blood ratio is 1:1, until a threshold for red blood cell (RBC) transfusion is reached [125-128]. (See 'Crystalloid solutions' above and 'Colloid solutions' above.)
●We avoid "preloading" of crystalloids prior to a neuraxial block or induction of general anesthesia.
●We avoid replacement of nonanatomic "third space" losses since evidence suggests that this practice has no benefit and may cause morbidity [9,129,130].
●We avoid extremely deep anesthesia (eg, bispectral index values <40) that may result in hypotension treated with unnecessary additional fluid. If necessary, vasopressor agents such as phenylephrine or ephedrine may be employed to treat hypotension caused by administration of anesthetic agents and/or neuraxial block [131,132]. (See "Accidental awareness during general anesthesia", section on 'Brain monitoring' and "Hemodynamic management during anesthesia in adults", section on 'Hypotension: Prevention and treatment'.)
●Administration of a total volume of balanced electrolyte solutions that modestly exceeds zero fluid balance is appropriate in patients with evidence of hypovolemia [133].
A potential disadvantage of this approach is that hypovolemia may not be clinically appreciated. Also, if hypotension occurs, it may be difficult to determine the etiology (eg, surgical volume losses or other causes such as cardiovascular responses to anesthetic agents). However, in most studies, restrictive fluid therapy has been associated with better outcomes than traditional liberal or fixed-volume approaches for major elective surgical procedures [11,12,22,90,134-136].
A modified approach was described in a 2014 randomized trial in 166 patients undergoing radical cystectomy employing a restrictive approach (1 mL/kg/hour) combined with low-dose norepinephrine infusion during the initial portion of the surgery, subsequently followed by hydration (3 mL/kg/hour) during the last part of the surgical procedure [137]. This so-called "restrictive deferred hydration" approach was associated with fewer complications (RR 0.70, 95% CI 0.55-0.88) and a lower median duration of hospital stay (15 days, range 11 to 27) than a liberal approach with 6 mL/kg/hour (17 days, range 11 to 95).
Notably, variability in study design has resulted in inconsistent results. A randomized trial in 3000 patients undergoing major abdominal surgery noted that a restrictive (zero-balance) fluid regimen was associated with a higher rate of acute kidney injury (AKI) compared with a liberal fluid regimen (8.6 versus 5 percent; RR 1.71, 95% CI 1.29-2.27) [34]. A limitation of this study was its pragmatic design in that perioperative care was not standardized and there was a wide variation in the anesthetic and analgesic techniques, including the use of epidural analgesia, variable intraoperative hemodynamic management, and variable postoperative care. The total fluid volume administered (balanced electrolyte solutions in both groups) during and up to 24 hours after surgery was 3.7 versus 6.1 L in the restrictive and liberal groups, respectively. These volumes were lower than traditional liberal fluid strategy totals [133]. A retrospective observational study also noted an association between use of a restrictive strategy with AKI in patients undergoing cystectomy (odds ratio [OR] 0.79, 95% CI 0.68-0.91) [138].
Taken together, these studies suggest that hypovolemia should be recognized and appropriately treated with fluid to avoid hemodynamic compromise and organ ischemia (see 'Goal-directed fluid therapy' below). However, excessive perioperative fluid administration should also be avoided since this can cause tissue and organ edema [3,133,139]. (See 'Avoid traditional liberal or fixed-volume approaches' below.)
Goal-directed fluid therapy — For invasive major surgery with anticipated significant blood losses (eg, >500 mL) and/or fluid shifts, we typically employ a goal-directed approach to fluid administration using one or more invasive dynamic hemodynamic parameters to achieve a prespecified goal (see 'Dynamic parameters to assess volume responsiveness' above) [1]. With this approach, we ensure that intravascular volume status is optimal before adding vasopressor therapy to achieve optimal blood pressure [8]. Clinical questions regarding goal-directed therapy (GDT) that remain unanswered include which types of patients are most likely to benefit, optimal timing of the use of GDT (preoperative, intraoperative, and/or postoperative), which outcome measures or endpoints are optimal, which combinations of therapies constitute the best approach (eg, fluids with or without vasopressors or inotropic agents), and how long the regimen should be maintained during the postoperative period.
Specific techniques
●As with a restrictive strategy, patients receive balanced electrolyte crystalloid solution administered at a rate of approximately 3 mL/kg per hour during the intraoperative period to replace sensible and insensible losses and support metabolic rate [11].
●A disadvantage of GDT is that it requires invasive monitoring of dynamic hemodynamic parameters [8,12,59,140]. We consider the following factors in selection of monitoring modalities:
•In most patients undergoing major surgery, we use the intra-arterial waveform tracing for automated measurements of pulse pressure variations (PPV) or stroke volume variation (SVV), or visually estimated or manually calculated PPV or systolic pressure variations (SPV), in order to determine responses to fluid boluses (typically 250 mL increments) [141]. For some patients, fluid boluses are administered in 100 mL increments to avoid excessive fluid administration and consequent hypervolemia (figure 1 and figure 2) [142]. (See 'Hypervolemia' above.)
•For high-risk patients undergoing a surgical procedure with expected blood loss >1000 mL, significant nonhemorrhagic fluid losses, and/or likely prolonged duration, we typically use a commercially available device that provides automated calculation of PPV, SVV, or SPV by analyzing the intra-arterial waveform tracing to assess responses to fluid challenges. An alternative is use of an esophageal Doppler device to estimate stroke volume (SV) [65]. TEE is another option, allowing visual qualitative evaluation or quantitative measurements of the left ventricular (LV) cavity size to monitor fluid responsiveness (movie 1 and image 1 and image 2 and table 3). (See 'Dynamic parameters to assess volume responsiveness' above.)
●For a GDT approach, fluid is administered to achieve a prespecified goal:
•If respiratory variations in the arterial pressure waveform (PPV or SPV) are >10 to 15 percent, then the patient is assumed to be fluid responsive and we administer fluid boluses of a balanced electrolyte crystalloid solution (typically in 250 mL increments) [24,50,142]. Once change in the monitored dynamic parameter is <10 percent, fluid administration is stopped to avoid hypervolemia.
•If SV estimates are used for dynamic hemodynamic monitoring, the typical goal of therapy is to achieve and maintain optimal intravascular volume with maximum SV. The new SV value after fluid administration has resulted in <10 percent change is recorded as the new baseline goal value (representing the maximum SV to be maintained). (See 'Respiratory variations in arterial pressure waveform' above.)
•If TEE is employed, hypovolemic and hypervolemic states can be quickly assessed by visual qualitative evaluation or quantitative measurements of LV cavity size. Fluid administration is stopped once normovolemia has been achieved (movie 1 and image 1 and image 2 and table 3). (See 'Echocardiography' above.)
●Although most studies evaluating GDT have used boluses of colloid fluid [143,144], we typically select a balanced crystalloid solution for fluid boluses. Randomized trials in patients undergoing elective abdominal surgery have found little difference in postoperative complications or any clinical benefit with use of a 6 percent hydroxyethyl starch (HES) colloid solution for fluid boluses compared with a balanced crystalloid solution to provide GDT [101,125]. (See 'Choosing fluid: Crystalloid, colloid, or blood' above.)
Comparison with other strategies — Variable benefits have been noted in comparisons of GDT with other fluid management strategies. Numerous limitations in study design may account for variable benefits of GDT compared with other fluid management strategies. These include clinical heterogeneity among trials with differing definitions for GDT, lack of well-defined endpoints, different types of fluid therapy, different devices used to monitor dynamic hemodynamic parameters, variations in management of the control group, different types of surgery, and small sample sizes [145-149]. In addition, most studies have included only limited information regarding anesthetic techniques and perioperative surgical care [146].
●Comparison with traditional liberal fluid strategies – GDT appears to be superior to traditional fixed-volume or liberal fluid approaches (see 'Avoid traditional liberal or fixed-volume approaches' below). A 2022 meta-analysis of randomized trials in noncardiac surgical patients noted a trend toward reduced mortality with GDT (OR 0.84, 95% CI 0.64-1.09) and shorter length of hospital stay (mean difference -0.72 days, 95% CI -1.10 to -0.25 days), with low certainty evidence for these primary outcomes compared with standard of care (76 trials; 9081 patients) [150]. In subgroup analyses, GDT was also favored for other outcomes (pneumonia, acute respiratory distress syndrome, surgical site infection, anastomotic leakage, and delirium) compared with standard of care, but with low or moderate certainty of evidence. A 2018 meta-analysis noted similar results with GDT compared with standard care (eg, lower risk of respiratory, renal, wound, and gastrointestinal complications, with shorter time to hospital discharge) [145].
However, data are not consistent [151-157]. In particular, GDT does not appear to offer additional benefits over a restrictive fluid approach for patients managed with protocols to achieve enhanced recovery after surgery (ERAS) [151,154-157]. The likely reason is that ERAS protocols implement multiple processes that each reduce the risk of perioperative fluid imbalances (eg, avoidance of preoperative dehydration, use of an intraoperative restrictive fluid approach, emphasis on early postoperative alimentation and ambulation). One meta-analysis assessing GDT in this setting found no benefit (or harm) with its use [151]. (See "Anesthetic management for enhanced recovery after major noncardiac surgery (ERAS)", section on 'Fluid management'.)
In some studies, administration of optimal fluid volume using a GDT approach was combined with attempts to achieve optimal hemodynamic management, thereby ensuring optimal tissue and organ perfusion in individual patients [149,158]. A 2018 meta-analysis of GDT (defined as fluid and/or vasopressor therapy titrated to hemodynamic goals (eg, cardiac output [CO]) was associated with lower risk of mortality (OR 0.66, 95% CI 0.50-0.87), pneumonia (OR 0.69, 95% CI 0.51-0.92), AKI (OR 0.73, 95% CI 0.58-0.92), wound infection (OR 0.48, 95% CI 0.37-0.63), and shorter length of hospital stay (-0.9 days; 95% CI -1.3 to -0.5 days), compared with fluid management at the discretion of treating clinicians (11,659 patients; 95 randomized trials) [145]. Another 2018 meta-analysis noted that studies using dynamic hemodynamic parameters to optimize intravascular volume and achieve optimal cardiac output (CO) or index (CI) reported less short-term mortality (OR 0.45, 95% CI 0.24-0.85) and less overall morbidity (OR 0.41, 95% CI 0.28-0.58), compared with standard fluid therapy (13 trials; 1100 total patients) [159]. Notably, data from other trials in this meta-analysis that employed GDT without attempts to optimize CO or CI that were analyzed separately did not note differences between GDT versus standard fluid management strategies (six trials; 524 patients) [159]. Similarly, a 2020 network meta-analysis noted that studies employing GDT aimed at optimizing intravascular volume as well as stroke volume and CO most effectively reduced the incidence of surgical site infections and other postoperative complications compared with usual care (43 trials; 8100 patients). One 2021 randomized trial employed computer-assisted individualized hemodynamic management that included a fluid management support system for GDT combined with a closed-loop system to titrate norepinephrine [160]. The investigators reported higher mean CI at the end of the procedure as well as lower total requirements for norepinephrine and lower fluid balances in patients receiving computer-assisted management, compared with those receiving manually directed GDT and manually titrated norepinephrine.
●Comparison with restrictive fluid strategies – Whether GDT is superior to a restrictive fluid strategy is less certain as there are limited data comparing GDT to this approach. In a 2019 meta-analysis of randomized trials in patients undergoing major noncardiac surgery, very low-certainty evidence suggested that restrictive fluid therapy does not affect the risk of complications (RR 1.61, 95% CI 0.78-3.34; five studies; 484 participants), but may increase the risk of all-cause mortality (risk difference [RD] 0.03, 95% CI 0.00-0.06) [144].
Avoid traditional liberal or fixed-volume approaches — Traditional liberal or fixed-volume approaches have been abandoned. Evidence suggests that these approaches resulted in administration of a large volume of crystalloid solution with likely fluid overload. Specifically, traditional fixed-volume approaches were based upon:
●Predetermined calculations that included administration of fluid to account for presumed preoperative deficits, as well as intraoperative blood and urinary losses.
●Additional fluid administered to compensate for calculated non-anatomic "third space" fluid losses during the surgical procedure. This practice is inappropriate, as it has been well-established that such third space losses do not exist [9,129,130].
●Large volumes of fluid as preloading before a neuraxial block.
●Replacement of initial blood loss with crystalloid volume that was three times the amount of lost blood. For example, if blood loss was estimated to be 500 to 1000 mL, then 1500 to 3000 mL of crystalloid was typically administered. This calculation is not supported by available data. Rather, optimal volume ratios to compensate for lost blood are estimated to be 1.5:1.0 for crystalloid and 1:1 for colloid, as discussed above [125-127]. (See 'Crystalloid solutions' above and 'Colloid solutions' above.)
These traditional fixed volume calculations for fluid administration resulted in a higher incidence of perioperative tissue and organ edema, and were associated with increased risk for adverse outcomes compared with restrictive or goal-directed approaches [3,11,12,16,22,59,140,161-166].
SUMMARY AND RECOMMENDATIONS
●Causes and consequences of intravascular volume derangements – Normovolemia/euvolemia should be maintained throughout the perioperative period to maintain adequate tissue perfusion. Both hypovolemia and hypervolemia are associated with postoperative morbidity.
•Hypovolemia – Hypovolemia is common due to preoperative, anesthesia-related, and surgery-related factors. Hypovolemia results in reduced cardiac output and tissue perfusion. Persistent hypovolemia can lead to shock and multiorgan failure. (See 'Hypovolemia' above.)
•Hypervolemia – Development of hypervolemia is generally due to excessive volume administration (eg, to treat hemodynamic instability). Hypervolemia can result in reduced tissue perfusion due to tissue edema and clinically significant postoperative fluid retention. (See 'Hypervolemia' above.)
●Monitoring intravascular volume status
•Traditional static parameters – Static physiological parameters such as blood pressure, heart rate, central venous pressure, and urine output are monitored during surgery to provide supplemental data regarding intravascular volume status. However, significant reduction in tissue perfusion may not be recognized. (See 'Traditional static parameters' above.)
•Dynamic hemodynamic parameters – Dynamic hemodynamic indices are used to assess responses to a fluid challenge (ie, volume responsiveness) and guide goal-directed fluid therapy in patients undergoing major invasive surgical procedures, particularly if large blood losses or fluid shifts are anticipated. These include:
-Respiratory variation using the intra-arterial waveform tracing for estimates or calculations of pulse pressure variations (PPV), stroke volume variation (SVV), systolic pressure variations (SPV) (figure 1 and figure 2 and table 2), or stroke volume (SV). (See 'Respiratory variations in arterial pressure waveform' above.)
-Ultrasound technologies including esophageal Doppler measurements of blood flow velocity in the descending thoracic aorta to estimate SV, or transesophageal echocardiography (TEE) or transthoracic echocardiography (TTE) for visual qualitative assessment or measurements of left ventricular cavity size (movie 1 and image 1 and image 2 and table 3). (See 'Esophageal doppler technology' above and 'Echocardiography' above.)
•Laboratory measurements – Increased serum lactate levels or lactic acidosis indicate reduced global tissue perfusion, but are measured intermittently and do not reflect acute changes. (See 'Measurement of laboratory values' above.)
●Selection of fluid (table 4)
•Balanced crystalloid solutions – We suggest a balanced electrolyte solution (eg, Ringer's lactate, Plasmalyte) rather than normal saline or colloid to maintain intraoperative normovolemia (Grade 2C), including replacement of sensible and insensible losses, fluid boluses (typically 250 mL) in volume responsive patients, and replacement of lost blood on a 1.5:1.0 volume basis until a transfusion threshold is met. (See 'Crystalloid solutions' above.)
•Colloid solutions – During blood loss, some clinicians prefer to administer colloid (eg, albumin) on a 1:1 volume basis until a transfusion threshold is met. We minimize colloid use due to insignificant hemodynamic benefits compared with crystalloids. We administer albumin rather than hydroxyethyl starch (HES) when a colloid is selected. (See 'Colloid solutions' above.)
•Blood transfusion – Red blood cells (RBCs) are used to replace blood loss when a transfusion threshold is met. Decisions regarding transfusion of plasma derivatives (eg, fresh frozen plasma [FFP]) are based on estimates of blood loss and evidence of abnormal hemostasis. (See 'Blood transfusion' above.)
●Selection of a fluid management strategy
•Minimally or moderately invasive procedures – For most adult patients undergoing minimally or moderately invasive surgical procedures, we administer 1 to 2 L of a balanced electrolyte solution to provide adequate intravascular hydration. (See 'Minimally/moderately invasive surgery' above.)
•Major invasive procedures – For major invasive surgical procedures, we suggest a restrictive (zero-balance) or a goal-directed therapy (GDT) approach to fluid administration (Grade 2B). (See 'Major invasive surgery' above.)
-Restrictive strategy – For procedures without significant anticipated blood loss (eg, <500 mL) and/or other fluid shifts, we use a restrictive approach replacing only fluid lost during the procedure (approximately 3 mL/kg per hour to replace sensible and insensible losses). (See 'Restrictive (zero-balance) strategy' above.)
-Goal-directed fluid therapy – For procedures with significant anticipated blood losses (eg, >500 mL) and/or fluid shifts, we use GDT with invasive dynamic hemodynamic parameters to achieve a pre-specified goal. (See 'Goal-directed fluid therapy' above and 'Dynamic parameters to assess volume responsiveness' above.)
•Avoid liberal fixed-volume strategies – We avoid traditional liberal or fixed-volume approaches that lead to administration of large volumes of crystalloid solution, tissue edema, and associated adverse outcomes. (See 'Avoid traditional liberal or fixed-volume approaches' above.)
