“Sorry.” You shake your head no as you explain for the third time that he cannot have anything to eat or drink. “Tony, you know the drill. You’re going to the operating room today. I know it’s time for breakfast, but you can’t have anything. I’m sorry.”

Tony, age 33, sustained second- and third-degree burns on 24% of his body when his pants caught fire during a camping trip. Today, he’s making his second trip in three days to the OR for skin graft surgery. 

Tony’s lips are dry and cracked. There are bluish hollows under his eyes. Despite having a peripheral IV line with IV fluid containing a mixture of 5% dextrose with 0.45% normal saline (D5.45NS) infusing at 125 milliliters per hour since being ordered NPO, Tony’s urine output is only 40 milliliters in the past two hours.

Maintaining a physiologic balance of body fluids in both volume and composition is critical to maintaining overall physiologic homeostasis. When caring for surgical patients, it’s important for the nurse to effectively monitor patients’ balance of fluid intake and output and fluid and electrolyte status in an effort to maintain homeostasis. Major disturbances in fluid and electrolyte balance can rapidly alter cardiovascular, neurologic, and neuromuscular functions.

Preoperative fluid and food restrictions, intraoperative fluid and blood loss, and the stress of surgery all contribute to fluid volume derangement in the surgical patient. Bowel preparations, nasogastric suctioning, vomiting, and certain disease states also place patients at risk for fluid volume deficit before surgery. Anesthesia and the trauma of the surgical procedure further reduce fluid volume. And after the procedure, recovery from anesthesia and surgery causes fluid shifts and imbalances.

Nurses need to understand intake and output management from the preoperative to the postoperative period to effectively care for surgical patients. This module discusses how fluid derangements occur in the surgical patient starting in the preoperative period and continuing through postoperative recovery. Which fluids are used to correct these imbalances and how the replacement is calculated are also addressed.^1-3

Fluid fundamentals

Fluids and electrolytes play an important role in the human body. The adult human body is largely composed of fluid: approximately 60% water depending on age, gender, and body mass. Muscle tissue contains more water than the same amount of adipose tissue. Therefore, men generally have higher water content due to more lean body mass — more muscular tissue — than women. Bodily fluids serve many essential functions such as maintaining body temperature, transporting necessary oxygen and nourishment to cells, and removing waste products of cellular metabolism.⁴

Electrolytes are the substances found in the intracellular fluid (ICF) and extracellular fluid (ECF). Electrolytes dissociate into ions, which are charged particles, when dissolved in water. Correct electrolyte balance is essential for contractility of muscles, regulating acid-base balance, transmitting nerve impulses, regulating water distribution, generating adenosine triphosphate needed for cellular energy, and clotting blood. The major cations, or positively charged electrolytes, are sodium, potassium, calcium, and magnesium. The major anions, or negatively charged electrolytes, are chloride, phosphate, bicarbonate, and plasma proteins. ICF and ECF have essentially the same electrolytes but in different concentrations. Potassium and phosphorus dominate in the ICF, while sodium and chloride dominate in the ECF. The renal and pulmonary systems maintain fluid and electrolyte balance. The anesthetics used in surgery alter the normal physiologic state — including electrolyte levels — of the surgical patient.⁴

Intra vs. extra

Total body water is divided into two compartments: ICF and ECF.¹ The ICF is the fluid found within cell membranes. The ECF are those fluids found in the compartments outside the cells of the body: plasma, intravascular fluids, fluids in the GI tract, and cerebrospinal fluid. The extracellular and the intracellular fluid compartments are separated by a cell membrane. Hypovolemia, or volume depletion, refers to a loss of ECF. Fluids and electrolytes move between the intracellular and extracellular spaces to facilitate body processes. These processes are acid-base balance, tissue oxygenation, response to drug therapies, and response to illness. The intravascular fluid (IVF) and the interstitial fluid (ISF) are the two compartments of extracellular fluid. The capillary membrane separates the IVF and the ISF compartments. The intravascular space is the fluid compartment accessible to the clinician and the chief focus of fluid therapy. The three goals of fluid therapy during surgery are to provide maintenance fluids, replace fluids lost as a result of surgery and anesthesia, and to correct electrolyte imbalances.^1,4

Replacement fluids in the OR

Because most cases of hypovolemia are caused by a loss of ECF, replacement with isotonic crystalloids, which have a composition similar to ECF, is appropriate. Examples of isotonic solutions are lactated Ringer’s and 0.9% normal saline. Solutions containing dextrose are not usually administered intraoperatively because of the risk of hyperglycemia, or high blood sugar. Hyperglycemia can result in osmotic diuresis, which is increased urination caused by the presence of certain substances, such as dextrose, in the kidney tubules. This furthers volume depletion.

While isotonic solutions are the first line of fluid volume replacement, some surgical patients require more aggressive therapy, which can include both colloid solutions and blood component therapy. Colloids <www.anesthesia-analgesia.org/cgi/reprint/101/2/601.pdf> are solutions containing osmotically active substances of high molecular weight that do not easily cross the capillary membrane. This draws fluid into the intravascular space and causes a sustained increase in intravascular volume. Because colloids tend to remain intravascularly, there is less peripheral edema, and a smaller volume is required for resuscitation. The downside is that colloids are expensive and can cause coagulopathy. Examples of colloid solutions are albumin 5% and 25% (Albuminar), dextran (dextran 40), and hetastarch (Hespan).

Surgical patients may also receive blood or blood component transfusion therapy. Packed red blood cells (PRBC) are the most common blood product administered. PRBCs maintain intravascular blood volume and improve oxygen-carrying capacity and oxygen transport to tissues. Fresh frozen plasma, platelets, and cryoprecipitate — a blood product prepared from plasma — are given intraoperatively to improve coagulation as well as increase fluid volume in the surgical patient. Amount and type of blood component therapy are documented on the anesthesia intraoperative record.¹

Heart basics

The cardiovascular system is composed of the heart and the vasculature that carries blood to provide nutrients to all cells in the body. Blood pressure is the product of cardiac output and peripheral vascular resistance (BP = cardiac output x peripheral vascular resistance). Cardiac output is the volume of blood being pumped by the heart. It is equal to the heart rate multiplied by the stroke volume. Thus, variation in extracellular fluid volume, the contractile state of the heart, and vascular tone determine variation in blood pressure.

Hypotension is defined as a blood pressure 20% less than baseline or preoperative blood pressure and is an indicator of hypovolemia. Decreased vascular resistance causes relative hypovolemia by interfering with venous return to the heart. Decreased vascular resistance (vasodilation) can be related to medication, general anesthesia, or regional anesthesia. Veins are very distensible and contain approximately 60% of blood volume. Hypervolemia — fluid volume excess — is defined as too much fluid in the vascular space, a condition that results in hypertension and is usually not seen in the surgical patient. Hypertension is defined as a blood pressure 20% to 30% above baseline. The venous system’s ability to accommodate large volume changes helps to buffer the intravascular volume during periods of hypervolemia or hypovolemia and thereby helps to maintain cardiac output.^1,3,4

The latest on fasting

Fluid volume derangements begin in the preoperative period. In the past, surgical patients did not eat or drink anything for eight to 12 hours before the surgery because the use of anesthesia required an empty stomach.⁵ Induction of anesthesia causes loss of airway reflexes. Aspiration is defined as the inhalation of either oropharyngeal or gastric contents into the lower airways.⁶ Inhalation of these contents can lead to aspiration pneumonia and aspiration pneumonitis. Aspiration of a massive amount of gastric contents, also known as Mendelson’s syndrome, can produce acute respiratory distress within one hour of aspiration. The acidity of aspirated gastric contents results in chemical burns to the tracheobronchial tree. An empty stomach on induction of anesthesia reduces this risk.

In 1999, the American Society of Anesthesiologists (ASA) Task Force on Preoperative Fasting set forth a revised standard, calling for cessation of clear liquids two hours before surgery and a light meal no later than six hours before surgery.⁷ According to the ASA, patients may be less anxious, better hydrated, and have fewer headaches and nausea after surgery when these revised practice guidelines are followed.⁵ However, most institutions still follow the NPO after midnight protocol. This restriction of food and fluid decreases the risk of aspiration but causes a greater fluid volume deficit in patients.

The indication for surgery and concurrent medical conditions may also contribute to this deficit. Vomiting, diarrhea, and fever cause dehydration. Bowel preparations, nasogastric suctioning, and certain medications (e.g., diuretics, steroids) further add to fluid volume deficits. Preoperative laboratory values are reviewed by the nurse and anesthesia team to assess for these fluid and electrolyte imbalances, which are corrected before surgery.

Certain disease states, such as diabetes mellitus, liver disease, or renal insufficiency, increase a patient’s risk for fluid and electrolyte imbalances. Burns cause an increase in permeability at the site of injury and throughout the microvasculature. This causes a tremendous shift of fluid from the plasma volume to the interstitial space. The burn patient is therefore intravascularly depleted. Patients who have undergone procedures requiring administration of IV dyes, such as an arteriogram or pyelogram, may experience osmotic diuresis because of urinary excretion of water and electrolytes. This diuresis causes hypovolemia. All of these factors must be considered as the patient enters the surgical suite.^2,4

First, second, and third

The surgical patient requires fluid therapy to replace losses that accompany surgery. Evaporative loss from exposed viscera and manipulation of tissues during surgery lead to redistribution of fluid from the intravascular space to the interstitial space. Fluid spacing is a term used to classify the distribution of water in the body. First spacing is the normal distribution of fluid in both the extracellular and intracellular compartments. Second spacing refers to an excess accumulation of interstitial fluid (edema). The interstitial compartment acts as an overflow reservoir for the intravascular compartment. Third spacing occurs when fluid accumulates in areas that normally have no fluid or only a minimum amount of fluid, such as the peritoneal, pleural, and pericardial cavities. Third spacing traps fluid away from the normal fluid compartments and results in a deficit in extracellular fluid volume. This redistributed, or third-spaced, fluid is nonfunctional. Surgical trauma causes third spacing because traumatized, inflamed, or infected tissue — as occurs with burns, extensive injuries, surgical dissections, or peritonitis — can sequester large amounts of fluid in its interstitial space. This fluid shift cannot be prevented by fluid restriction and is at the expense of both the functional extracellular and the intracellular fluid compartments.

Calculation of fluid replacement depends on the extent of the surgical procedure. For example, a patient undergoing a laparoscopic procedure has a relatively low amount of exposed viscera, while a patient undergoing an exploratory laparotomy has a large amount of exposed viscera. Thus, the exploratory laparotomy patient requires more aggressive fluid replacement.^1,2,4

How much fluid?

During the intraoperative period, the anesthesia team replaces fluids according to the length of time a patient is NPO, the fluids lost to surgery and anesthesia, and the patient factors that influence fluid management. Fluid estimates for otherwise healthy adults undergoing elective operations are —

• GI losses of 100 milliliters to 200 milliliters a day
• Insensible losses of 500 milliliters to 1,000 milliliters a day
• Urinary losses of 1,000 milliliters a day
• Predicted daily maintenance requirement of 2,500 milliliters a day

The calculation below can be used to estimate maintenance fluid requirements —

• 4ml/kg/hr for the first 0 to 10kg
• 2ml/kg/hr for the next 11 to 20 kg
• 1 ml/kg/hr for weight greater than 21 kg

Deficit is defined as the time the patient is NPO to the time surgery begins. The deficit can be estimated by multiplying the normal maintenance rate by the length of the fast. For the average 70 kilogram person fasting for eight hours, this amounts to —

• (40 + 20 + 50) ml/hour x 8 hours = 880 ml.2,8

Fluids lost to bowel preparations and nasogastric suctioning are added into this calculation of deficit. Bowel preparations are considered to cause a deficit of 1,000 milliliters. Fluid therapy for surgical patients includes administration of crystalloids to compensate for preoperative fluid deficit, maintenance fluids to compensate for evaporative losses from exposed viscera and to provide solute for excretion of waste, and fluids to replace surgical fluid losses (e.g., third-space loss and blood loss).¹

Maintenance is defined as the time of incision to closure and is dependent on the type of surgical procedure performed. For surgical procedures deemed minor, an estimate of 4ml/kg/hr is used, moderate surgical procedures warrant 6 ml/kg/hr, and extensive surgeries 8 ml/kg/hr. Another factor taken into consideration is blood loss. Blood loss is replaced 3:1 with isotonic crystalloid solution, 1:1 with colloid solution, and 1:1 replacement blood products.²

The schedule for fluid replacement during the surgical procedure is —

• First hour: 1/2 the deficit + maintenance + blood replacement
• Second hour: 1/4 the deficit + maintenance + blood replacement
• Third hour: 1/4 the deficit + maintenance + blood replacement

These calculations are a guideline for fluid replacement. Fluids will be titrated based on patient response and coexisting diseases.^9-11

Anesthesia’s effects

Anesthesia contributes to the fluid volume deficit of surgery. The vasodilatory effects of both regional and general anesthesia can result in hypovolemia.¹ Different types of anesthetic techniques are used based upon patient factors and type of surgery performed. The type of anesthetic chosen will have varying effects on patient hemodynamics and affect the amount of fluid replacement needed. Deep sedation, defined as a state in which the patient is asleep but easily arousable, does not have the degree of hemodynamic compromise as a general anesthetic.  General anesthesia involves a complete loss of consciousness. General anesthesia is a reversible state that provides analgesia, muscle relaxation, and sedation by IV or inhaled anesthetics. Inhaled general anesthetics are myocardial depressants. These may lead to dose-dependent decreases in myocardial contractility and blood pressure. This response may be accentuated in patients who are volume depleted, are over-diuresed, have poor ventricular function, or have autonomic neuropathy, as seen in patients with diabetes.³

Inhaled anesthetics (e.g., desflurane, sevoflurane, isoflurane) cause peripheral vasodilation. Spinal and epidural anesthesia involve using local anesthetics to block conduction pathways along spinal nerve roots to provide anesthesia to the body below the level of the injection site. This also causes vasodilation in all areas below the level of analgesia. Peripheral vasodilation causes pooling of blood, fluid volume deficit (a relative hypovolemia), and reduced venous return to the heart. Hypotension results secondary to this relative hypovolemia. Anesthesia providers manage this with IV fluid administration.^3,4

Fluid overload

Elderly patients and patients with congestive heart failure (CHF), renal insufficiency, or cirrhosis of the liver may not be able to handle fluid replacement therapy, and compensatory mechanisms that can be relied on in younger patients function less rapidly in older patients. The elderly have less compliant atrial and ventricular myocardium and decreased passive left ventricular filling. Elderly patients are less able to maintain the integrity of the extracellular space and other fluid compartments when challenged. These physiologic changes of aging place the elderly patient at risk for fluid volume overload.

In CHF — which is associated with systemic hypertension and/or coronary artery disease — the heart’s pumping power is weaker than normal. The more fluid in the blood vessels, the harder the heart must work to pump excess fluid through the body. Overaggressive fluid administration can place the CHF patient at risk for pulmonary edema. A patient with poorly functioning kidneys cannot diurese, causing fluid to remain in the vascular space resulting in volume overload. A patient in liver failure has generalized peripheral vasodilation and a hyperdynamic circulatory system with fluid and electrolyte imbalances that require judicious intraoperative fluid management. The anesthesia provider guides fluid therapy around these factors. Vasopressors may be used to maintain blood pressure and fluid volume.^2,9,10

After surgery

When care is transferred from the OR to the recovery room, a report is given to the nurse receiving the patient. The total amount of fluid given in crystalloid, colloid, and blood component therapy is reported and recorded in the MDA/CRNA anesthesia record. Estimated blood loss and urine output are reported, as are duration of surgery along with type of anesthesia administered.

In the recovery room, hypotension is a common occurrence and is usually caused by blood loss and inadequate replacement of introperative fluid. Manifestations of hypotension may include disorientation, nausea, loss of consciousness, chest pain, oliguria, and anuria. These can be attributed to the hypoperfusion that accompanies hypotension. A common dysrhythmia that occurs after surgery is sinus tachycardia — a heart rate greater than 100 beats per minute in adult patients. Tachycardia is an insensitive and nonspecific indicator of hypovolemia.⁴

To help patients regain homeostasis, nurses must understand the importance of returning their surgical patients to correct fluid and electrolyte balance. Patients entering the operating theater have a fluid volume deficit for a variety of reasons: Their disease process, NPO status, concurrent medical conditions, and current medical therapies all contribute. During the surgical period, the anesthesia provider replaces fluid intravenously based upon patient needs. These needs differ according to type of anesthesia administered, duration of surgery, type of surgery, and preexisting medical conditions. Inadequate fluid management can lead to changes in vital signs, such as hypotension and tachycardia, as seen in the recovery room. Hypovolemia can also cause nausea, confusion, and anuria.

The nurse’s understanding of fluid balance and related fluid management leads to positive patient outcomes.⁴ To reduce the risk of these untoward conditions and to help foster positive patient outcomes, nurses must understand fluid balance and fluid management in the surgical patient. The nurse must be able to recognize fluid volume deficit and implement evidence-based practices to replace fluid volume to maintain patient homeostasis and safety.