Presentation on theme: "Fluid and Electrolyte Balance IN SURGICAL PATIENTS By; Col. Abrar Hussain Zaidi."— Presentation transcript:
Fluid and Electrolyte Balance IN SURGICAL PATIENTS By; Col. Abrar Hussain Zaidi
INTRODUCTION One of the most critical aspects of patient care is management of the composition of body fluids and electrolytes. Most diseases, many injuries, and even operative trauma have a great impact on the physiology of fluids and electrolytes in the body. A thorough understanding of the metabolism of salt, water, and electrolytes and of certain metabolic responses is essential to the care of surgical patients.
A prerequisite: to understand the fluid and electrolyte management is; knowledge of the extent and composition of the various body fluid compartments.
INTRODUCTION BODY WEIGHT Fluids % Solids %
INTRODUCTION [cont] The main fluid in the body is water
Distribution of Water 60% of body weight is body water. water is distributed in three main compartments; separated from each other by cell membranes. a. The intracellular compartment - area within the cell. b. Extra-cellular compartments 1. The interstitial compartment (between and around cells) 2. The intravascular compartment
Distribution of Water
Plasma % Interstitial % Intracellular % Total % Water [Remaining -Solids - 40%:fat, protein, carbohydrates, minerals]
Distribution of Water Infants have a higher percent of water than adults do as much as 77%. The total water content of the body decreases most dramatically during the first 10 years at old age, - only 45% of the total body weight. Men tend to have higher percentages of water (about 65%) than women (about 55%) mainly because of their increased muscle mass and lower amount of subcutaneous fat. Fat has less water content than any other body tissue. This also accounts for a lower than normal water percentage in obese people.
Regulation of fluid balance CONSIDERATIONS [in health or disease] INTAKE VS OUT PUT GASTROINTESTINAL TRACT HYPOTHALAMUS/PITUTARYGLAND/Hormones STARLING FORCES OF EQUILIBTIUM KIDNEYS
Regulation of fluid balance Water in the body is in a constant state of motion. Shifting between the three major fluid compartments of the body and in addition being continuously lost from, and taken into, the person. In a normal, healthy human being : WATER INPUT = WATER OUTPUT. Maintaining this ratio : is of prime importance in maintaining health. Approximately 90% of the body's water intake comes via the gastro-intestinal tract. The remaining 10% is called metabolic water and is produced as the result of various chemical reactions in the cells of the body's tissues.
Regulation of fluid balance water loss from the body (healthy adult) GASTRO-INTESTINAL TRACT(FAECES)6% LUNGS(WATER VAPOUR) 13% SKIN(DIFFUSION & SWEAT) 19% KIDNEYS(URINE) 62%
Regulation of fluid balance The mechanisms for the regulation of body fluids: 1- center in the hypothalamus. receives input from the digestive tract helps in the control of thirst. 2- Hypothalamic-pituitary axis 3- Anti Diuretic Hormone (ADH) Main regulator of fluid volume and extracellular osmolarity
Regulation of fluid balance ADH - increases the permeability of the distal convoluted tubules and the collecting tubules in the kidneys. This allows more water to be reabsorbed in the kidneys. This is manifest if the body is short of fluid intake (such as during sleep) and results in a concentrated, darker coloured urine of reduced volume. Absence of ADH occurs when the individual is over-hydrated such as at a party if a lot of beer, cider, alcopops etc. are being drunk Here the urine is dilute, pale or colourless and of high volume. Primary factors involved in the triggering of ADH production are osmoreceptors and baroreceptors (pressure receptors). Secondary factors include, stress, pain, hypoxia, severe exercise, surgery (especially anaesthetics such as cyclopropane and nitrous oxide).
Regulation of fluid balance [cont] A reduction of around 8-10% of body volume of water will result in ADH secretion.[ haemorrhage or excess perspiration in desert] Volume changes-Sensed by- Pressure receptors located in the atria of the heart and the pulmonary artery and vein Relay their messages to the hypothalamus via the vagus nerve Thirst response Changes in osmolality Chemoreceptors in hypothalamus Chemoreceptors in carotids
Regulation of fluid balance [cont] The integrity blood vessels walls - barrier to the free passage of fluid between interstitial fluid and blood plasma. These capillary walls are permeable to water and small solutes but impermeable to large organic molecules such as proteins. The blood plasma tends to have a higher concentration of such molecules when compared to the interstitial fluid. Much of this interstitial fluid is taken up by the lymphatic system and eventually finds its way back into the blood stream.
Regulation of fluid balance [cont] Starling forces Water and small solutes such as sodium (Na+), potassium (K+), calcium (Ca++), etc. can be freely exchanged between the plasma and the interstitial fluid. This exchange depends mainly upon the hydrostatic and osmotic forces of both of these fluid compartments. Further regulation of these electrolytes is controlled by the action of the kidneys.
Regulation of fluid balance [cont] Starling forces Cell membranes are completely permeable to water, the effective osmotic pressures in the two compartments are considered to be equal. Any condition that alters the effective osmotic pressure in either compartment results in redistribution of water between the compartments. An increase in effective osmotic pressure in the extracellular fluid, which would occur typically as a result of increased sodium concentration, would cause a net transfer of water from the intracellular to the extracellular fluid compartment. This transfer of water would continue until the effective osmotic pressures in the two compartments were equal. Conversely, a decrease in the sodium concentration in the extracellular fluid will cause a transfer of water from the extracellular to the intracellular fluid compartment. Depletion of the extracellular fluid volume without a change in the concentration of ions will not result in transfer of free water from the intracellular space.
Regulation of fluid balance [cont] The intracellular fluid shares in losses that involve a change in concentration or composition of the extracellular fluid, but shares only slowly in changes involving loss of isotonic volume alone. For practical considerations, most losses and gains of body fluid are directly from the extra-cellular compartment.
Regulation of fluid balance [cont] Overall, there is near equilibrium between fluid forced out of the capillaries and the fluid absorbed back. [This is because the lymphatic system collects the excess fluid forced out at the artery end and eventually drains it back into the veins at the base of the neck.] This is known as Starling's Law of the Capillaries. A similar situation exists between the interstitial fluid and the intracellular fluid More complicated by the presence of ion pumps and carriers.
Homeostasis All the body's fluid compartments are in osmotic equilibrium (except for transient changes). The ions and small solutes that constitute the ECF are in equilibrium with similar concentrations in each sub compartment. The ECF volume is proportional to the total Na content.
Electrolytes Electrolytes are the chemicals dissolved in the body fluid. The distribution has important consequences for the ultimate balance of fluids. Sodium chloride is found mostly in extra- cellular fluid, while potassium and phosphate are the main ions in the intracellular fluid.
ELECTROLYTE DISTRIBUTION--- Total Positive ions -meq/liter Extra cellular Intracellular Function Sodium fluid balance, osmotic pressure Potassium Neuromuscular excitability acid- base balance Calcium 5- bones, blood clotting Magnesium 2 26 enzymes
Electrolyte Distribution Total Negative ions -meq/liter Extra cellular Intracellular Function Chloride fluid balance, osmotic pressure Bicarbonate acid-base balance Proteins osmotic pressure Phosphate energy storage Sulfate 1 20 protein metabolism
Reminder WATERthe main fluid Electrolytes State of equilibrium in the composition and concentration of the constituents in all compartments Regulatory machanisms Sterling forces Role of hypothalamus and ADH Thirst Other hormones [aldosteron,steroids] Kidneys
Disorders of fluid & Electrolyte Balance CLASSIFICATION OF BODY FLUID CHANGES three general categories: (1) Disorders of volume (2) Disorders of concentration (3) Disorders of composition. Although these disturbances are separate entities –they are interrelated.
Disorders of fluid & Electrolyte Balance Fluid volume excess Fluid volume deficit Electrolyte excess Electrolyte deficit Proportionate fluid and electrolyte excess/loss Disproportionate fluid and electrolyte Excess/loss
Disorders of fluid & Electrolyte Balance If an isotonic salt solution is added to or lost from the body fluids, only the the extracellular fluid volume is changed. The acute loss of an isotonic extracellular solution, such as intestinal juice, is followed by a significant decrease in the extracellular fluid volume and little, if any, change in the intracellular fluid volume. Fluid will not be transferred from the intracellular space to refill the depleted extracellular space as long as the osmolarity remains the same in the two compartments. Addition of hyper or hypotonic fluid to extra- cellular compartment –[ i.e. –change in osmolality] –leads to fluid shift [think of a small bag of salt put in water]
Disorders of fluid & Electrolyte Balance If water alone is added to or lost from the extracellular fluid, the concentration of osmotically active particles changes. If the extracellular fluid is depleted of sodium, water will pass into the intracellular space until osmolarity is again equal in the two compartments.
Disorders of fluid & Electrolyte Balance The concentration of most other ions within the extracellular fluid compartment can be altered without significant change in the total number of osmotically active particles, thus producing only a compositional change. For instance, a rise of the serum potassium concentration from 4 to 8 mEq/L would have a significant effect on the myocardium, but it would not significantly change the effective osmotic pressure of the extracellular fluid compartment. Normally functioning kidneys minimize these changes considerably, particularly if the addition or loss of solute or water is gradual.
Distributional change An internal loss of extracellular fluid into a nonfunctional space, such as the sequestration of isotonic fluid in a burn, peritonitis, ascites, or muscle trauma This transfer or functional loss of extracellular fluid internally may be extracellular (e.g., peritonitis), or intracellular (e.g., hemorrhagic shock), or both (e.g., major burns). In any event, all distributional shifts or losses result in a contraction of the functional extracellular fluid space.
Disorders of fluid & Electrolyte Balance Most commonly---The problems occur when the level of sodium, potassium, or calcium is abnormal. Electrolyte levels Often change when water levels in the body change. Prefix "hypo-" Refer to a low levels Prefix "hyper-" Refers to high levels For example, a low level of potassium is called hypokalemia, a high level of sodium is called hypernatremia.
Disorders of fluid & Electrolyte Balance Older people more likely to develop abnormalities- more likely to become dehydrated or overhydrated. [the poor kidneys function ]. Certain drugs- including diuretics and some laxatives, can increase the risk of developing electrolyte abnormalities. Bed ridden state can increase the risk of developing electrolyte abnormalities because getting fluids and food may be difficult. Chronic disorders fever, vomiting, or diarrhea can result in electrolyte abnormalities. Operative trauma Children very sensitive to fluid electrolyte changes
Diagnosis Electrolyte abnormalities Clinical examination Measuring electrolyte levels in blood or urine. Determine the cause of the abnormalities. Treatment principles Treat the disorder causing the abnormality Assess the extent of disorder The extent of volume deficit/ecxcess The extent of electrolyte def./excess Assess the normal need for age /weight Define the mode of correction
FLUID disorders Volume changes A. Volume deficit/hypovolemia/Dehydration Volume of body fluids smaller than normal Fluid output exceeds intake for an extended period IF volume shrinks and not treated-- ICF volume and plasma volume decrease; B Volume excess/hypervolemia/ Overhydration Volume of body fluids larger than normal; Fluid intake exceeds output (for example, giving excessive amounts of intravenous fluids or giving them too rapidly )
FLUID/VOLUME - EXCESS OVERHYDRATION When more fluid is consumed than can be excreted The blood vessels overfill, and fluid moves from the blood vessels into the INTERSTITIAL SPACE causing edema. causes. Cardiac failure - heart cannot pump blood adequately. Kidney disorders -s cannot excrete enough water. Antidiuretic hormone (Forces kidneys to retain more water). Overproduction of ADH caused by ; pneumonia and stroke and by drugs such as carbamazepine Drugs, especially nonsteroidal anti-inflammatory drugs Foods that are high in sodium – fluids retion /overhydration. Intravenous fluids or blood transfusions too rapidly.
FLUID/VOLUME - EXCESS OVERHYDRATION Clinical Features / Diagnosis Oedema -Swelling in the legs or,in the lower back [if people are confined to bed]. D/D -chronic venous insufficiency -Lyphoedema Dyspnea/Shortness of breath because fluid backs up in the lungs. worse when a person lies down The person may wake up shortly after lying Puffiness of face
FLUID/VOLUME - EXCESS OVERHYDRATION Clinical Features / Diagnosis Swelling and enlargement of organs- Cardio/hepatomegaly The ENGORGMENT OF veins in the neck- JVP CVP raised Blood tests –Urea/ electrolytes or other substances that indicate how well the kidneys are functioning. A chest x-ray –Hiler shadows fluid in the lungs. Cardiac size /heart failure.
FLUID/VOLUME EXCESS -Treatment a- Restrict the fluids b-Help the body excrete the excess water. Diuretics - kidneys to excrete the excess can be taken by mouth or I/V. Thiazides- often used first- mild and tend tohave few side effects. Frurosemide more potent. Potassium-sparing diuretic.
FLUID/VOLUME EXCESS -Treatment Consume less salt also helps. If edema is due to poor circulation rather than overhydration Increase physical activity. Usually, the blood vessel disorder that is causing poor circulation is treated. Correct the cause of overhydration. Give i/v fluids with caution Treat Heart failure and kidney disorders. Discontinue drugs if cause or limit its use- NSAIDs- arthritis Overproduction of antidiuretic hormone –restrict fluid intake
FLUID/VOLUME - DEFICIT Dehydration Dehydration means not having enough water in the body.
FLUID/VOLUME - DEFICIT Dehydration Causes Hot weather-sweating is increased Fever-sweating +tachypnea Diarrhea -water is lost in the stool Vomiting - water is lost in the vomit Diabetes - the body produces more urine Kidney disorders- kidneys unable to concentrate urine as needed Problems with walking, because getting water is difficult Dementia- sense of thirst is reduced and the ability to get water impaired Diuretics- increase the of water and salt excretion
FLUID/VOLUME - DEFICIT Dehydration Clinical features a-mild b-Moderate c-Severe
FLUID/VOLUME - DEFICIT Dehydration Clinical features-General Dry skin Fast pulse low blood pressure Low urine out put- [ The kidneys try to conserve -olig urea / an-urea] Sunken eyes
FLUID/VOLUME - DEFICIT Dehydration Older people and Children More prone to dehydration Sense of thirst is less kidneys function less well Can not help themselves
FLUID/VOLUME - DEFICIT Dehydration Clinical features Mild [10-20%] May not be noticed Skin and the membranes of the nose and eyes become dry. Confusion / sluggishness. Tachycardia Moderate [ 20-30%] Above symptoms + Light-headedness Fainting Postural hypotension Oligurea + urine becomes dark. Severe [ 40% or above] Above +Sunken eyes Fall in blood pressure that can be life threatening. Shock
FLUID/VOLUME - DEFICIT Dehydration Treatment involves replacing lost fluids. How rapidly -? Mild dehydration - 2 to 3 liters of water to drink over a period of a few hours. Moderate dehydration - Add some salt (sodium) and other electrolytes. Rehydration formulas (available without a prescription) Severe Dehydration -INTRAVENOUS REPLACEMENT. I/V also for those who cannot swallow, and those who are in a coma. If electrolytes must also be replaced, they are given intravenously with the fluids.
Concentration Changes/ Electrolytes Disorders Sodium is primarily responsible for the osmolarity of the extracellular fluid space: determination of the serum concentration of sodium generally indicates the tonicity of body fluids. Hyponatremia and hypernatremia can be diagnosed on clinical grounds -- signs and symptoms generally are not present until the changes are severe. Clinical signs of hyponatremia or hypernatremia occur early and with greater severity when the rate of change in extracellular sodium concentration is very rapid. Changes in concentration should be noted early by laboratory tests and corrected promptly.
Disorders Of Sodium Balance Hyponatremia: result from Not consuming enough sodium in the diet, Excreting too much salt (in sweat or urine), or Overhydration when a person drinks a lot of water without consuming enough salt (sodium chloride), typically during hot weather when a person also sweats more. The sodium level may decrease when large amounts of fluids that do not contain enough sodium are given intravenously. Diuretics help the kidneys excrete excess sodium and excess water. However, diuretics may cause the kidneys to excrete more sodium than water, resulting in a low sodium level.
Disorders Of Sodium Balance Hyponatremia [cont] High ADH levels which signals the kidneys to retain water. caused by : pneumonia stroke drugs -anticonvulsants -carbamazepine) antidepressant -selective serotonin reuptake inhibitors (SSRIssuch as sertraline). poorly controlled diabetes heart failure, liver failure, Renal disorders.
Disorders Of Sodium Balance Hyponatremia -Symptoms confusion, drowsiness, muscle weakness, and seizures. A rapid fall in the sodium level often causes more severe symptoms than a slow fall. Treatment A low sodium level - restored to a normal by gradually and steadily giving sodium and water Orally/intravenously.
Disorders Of Sodium Balance Hypernatremia: caused by ; Dehydration Excessive loss of fluid without loss of salt Addition of excessive salt without proportionate fluid volume symptoms Typically--- thirst is the first symptom. weakness and sluggishness. A very high sodium level can cause confusion, paralysis, coma, and seizures.
Disorders Of Sodium Balance Hypernatremia - Treatment Oral plain fluids - If the sodium level is slightly high. Intravenous fluids - If the sodium level is very high. Once the body's fluids are replaced, the high level of sodium returns to a normal level.
Disorders Of Potacium Balance Hypokalemia: causes Diarrhea or vomiting for a long time. Enterocutaneos fistulaeuse Diuretic. Symptoms Mild decrease -- no symptoms. The body tends to produce less insulin. As a result, the level of sugar in the blood may increase. Moderate -- fatigue, confusion, and muscle weakness cramps. Severe -- paralysis and abnormal heart rhythms (arrhythmias). [ people who take digoxin [for heart failure), abnormal rhythms develop when the potassium level is even moderately low.
Disorders Of Potacium Balance Hypokalemia-Treatment Potassium supplements by mouth as a tablet or liquid or eating foods rich in potassium. Potassium-sparing diuretic –In People on diuretics - reduces the amount of potassium excreted. IV-supplement in surgical cases
Disorders Of Potacium Balance Hyperkalemia: A high potassium level (hyperkalemia) is much more dangerous than a low potassium level. Most common causes Renal failure Drugs that reduce the amount of potassium excreted by the kidneys. diuretic spironolactone and angiotensin-converting enzyme (ACE) inhibitors (used to lower blood pressure). When a person who takes one of these drugs also eats potassium-rich foods or takes a potassium supplement, the kidneys cannot always excrete the potassium.
Disorders Of Potacium Balance The first symptom of a high potassium level may be an abnormal heart rhythm. Electrocardiography (ECG) may help with the diagnosis. This procedure can detect changes in the heart's rhythm that occur when the potassium level is high.
Disorders Of Potacium Balance Hyperkalemia. Treatment Stop eating potassium-rich foods and stop taking potassium supplements. Drugs that cause the body to excrete excess potassium, such as diuretics. If the potassium level is very high or is increasing, treatment must be started immediately. If the heart rhythm is abnormal, calcium is given intravenously. This treatment helps protect the heart. Then diuretics – Frusemide prevents potassium from being re- absorbed are given to reduce the amount of potassium in the body. These drugs may be given intravenously, taken by mouth, or given as enemas.
Disorders Of Calcium Balance Hypocalcemia: result when a disorder such as; A widespread infection in blood and other tissues (sepsis). Hypoparathyroidism- if the parathyroid glands are removed or damaged during neck surgery. Deficiency of vitamin D. [Vitamin D helps the body absorb calcium ] Certain drugs, such as the anticonvulsants phenytoin and phenobarbital, can interfere with the processing of vitamin D, resulting in a deficiency of vitamin D. Several disorders, such as an underactive thyroid gland (hypothyroidism) and pancreatitis, can result in a low calcium level.
Disorders Of Calcium Balance Hypocalcaemia -Clinical Features weak ness, numbness in the hands or feet. confusion or seizures Muscle twitching / tetany +latent tetany Treatment involves taking calcium supplements by mouth. Or I/V Treat the Cause.
Disorders Of Calcium Balance Hypercalcemia: a-Excessive intake – milk alkali syndrome b-Exessive brake down of bone and release of calcium into the bloodstream. Calcium may be released when cancer spreads to the bone Paget's disease. Sarcoidosis Hyperparathyroidism.
Disorders Of Calcium Balance Hyperparathyroidism- the cause is production of an excessive amount of hormone by a tumor in the parathyroid gland. lung cancers, can also produce Ectopic parathyroid hormone.
Disorders Of Calcium Balance Hypercalcaemia: Symptoms; A slight increase in the calcium level may not cause any symptoms. A very high level can result in dehydration because it causes the kidneys to excrete more water. A very high level can also cause loss of appetite, nausea, vomiting, and confusion. A person may even go into a coma and die.
Disorders Of Calcium Balance Hypercalcemia:Treatment High calcium level rapid treatment is needed. fluids intravenously Steroids calcitonin and bisphosphonates - given intravenously for short periods of time. [ decrease the amount of bone being broken down /decrease calcium released into the bloodstream. Treat the cause of the high calcium level. Paget's disease, bisphosphonates are often taken by mouth Tumor of parathyroid gland,-surgery
Mixed Volume and Concentration Abnormalities Mixed volume and concentration abnormalities may develop as a consequence of the disease state or occasionally as a result of inappropriate parenteral fluid therapy. Clinical picture associated with a combination of fluid abnormalities will be an algebraic composite of the signs and symptoms of each state. Like signs produced by both abnormalities will be additive, and opposing signs will nullify one another. For example, the tendency for the body temperature to fall with an extracellular volume deficit may be counteracted by the tendency for it to rise with severe hypernatremia.
Mixed Volume and Concentration Abnormalities One of the more common mixed abnormalities is an extracellular fluid deficit and hyponatremia. This state is readily produced in the patient who continues to drink water while losing large volumes of gastrointestinal fluids. It may also occur in the postoperative period when gastrointestinal losses are replaced with inadequate volumes of only 5% dextrose in water or a hypotonic sodium solution. An extracellular volume deficit accompanied by hypernatremia may be produced by the loss of a large amount of hypotonic salt solution, such as sweat, in the absence of fluid intake.
Mixed Volume and Concentration Abnormalities The prolonged administration of excessive quantities of sodium salts with restricted water intake may result in an extracellular volume excess and hypernatremia. This may also occur when pure water losses (such as insensible loss of water from the skin and lungs) are replaced with sodium- containing solutions only. Similarly, the excessive administration of water or hypotonic salt solutions to the patient with oliguric renal failure may rapidly produce an extracellular volume excess and hyponatremia.
Mixed Volume and Concentration Abnormalities Normally functioning kidneys may minimize these changes to some extent and compensate for many of the imprecise replacements associated with parenteral fluid administration. In contrast, the patient in anuric or oliguric renal failure is particularly prone to develop these mixed volume and osmolar concentration abnormalities. Fluid and electrolyte management in these patients, therefore, must be precise. Unfortunately, the fact that a patient with normal kidneys who develops a significant volume deficit may be in a state of functional renal failure often is not appreciated.
Composition Changes Compositional abnormalities of importance include: changes in acid-base balance Acidosis-metabolic/respiratory Alkalosis-metabolic respiratory Mix abnormalities changes in the concentration of potassium, calcium, and magnesium.
Principles of fluid and management in surgical patients Define the daily normal requirements-Maintenance Define the deficits and correct it Define the over load and make restrictions Define the electrolyte status Normal individual requirment of 2,000–2,500 mL water daily. The minimum amount of urinary output that is required to excrete the catabolic end products of metabolism is approximately 800 mL. Urine faeces ml A 750-mL insensible water loss occurs daily via the skin and respiratory tract-losses increase with hypermetabolism, fever, and hyperventilation.
Principles of fluid and management in surgical patients Maintenance. Maintenance fluids should be administered at a rate that is sufficient to maintain a urine output of 0.5–1.0 mL/kg per hour. Maintenance fluid requirements can be approximated on the basis of body weight as follows: 100 mL/kg per day for the first 10 kg, 50 mL/kg per day for the second 10 kg, and 20 mL/kg per day for each subsequent 10 kg. Maintenance fluids in general should contain Na+ (1–2 mmol/kg per day) and K+ [0.5–1.0 mmol/kg per day (e.g., D5/0.45% NaCl + 20–30 mmol K+/L)].
Principles of fluid and management in surgical patients Preoperative management. Correct the deficits Preexisting volume and electrolyte. Consideration - duration and route of loss -for extent and type of fluid and electrolyte abnormalities. Intr-aoperative fluid management Replacement of preoperative deficit Ongoing losses maintenance fluids for the duration of the case, hemorrhage, and third-space losses. Maintenance fluid requirement is calculated. Acute blood loss replaced with ; a volume of crystalloid that is three to four times the blood loss or with an equal volume of colloid or blood.
Principles of fluid and management in surgical patients Intra-operative insensible and third-space fluid losses dependent on : The size of the incision The extent of tissue trauma The dissection time and type Replaced with an appropriate volume of lactated Ringer's solution. Small incisions with minor tissue trauma (e.g., inguinal hernia repair) result in third-space losses of approximately 1–3 mL/kg per hour. Medium-sized incisions with moderate tissue trauma (e.g., uncomplicated sigmoidectomy) result in third-space losses of approximately 3–7 mL/kg per hour. Larger incisions and operations with extensive tissue trauma and dissection (e.g., pancreaticoduodenectomy) can result in third-space losses of approximately 9–11 mL/kg per hour or greater.
Principles of fluid and management in surgical patients Postoperative fluid management Careful clinical evaluation and monitoring Continued sequestration of extracellular fluid into the sites of injury or operative trauma can continue for 12 hours or more after operation. Urine output should be monitored closely and intravascular volume replenished to maintain a urine output of 0.5–1.0 mL/kg per hour. Gastrointestinal losses that exceed 250 mL per day from nasogastric or gastrostomy tube suction should be replaced with an equal volume of crystalloid. Mobilization of peri-operative third-space fluid losses typically begins 2–3 days after operation. Anticipation of postoperative fluid shifts should prompt careful evaluation of the patient's volume status and, if needed, consideration of diuresis before the development of symptomatic hypervolemia.
Parenteral fluid therapy A.Crystalloids, in general, are solutions that contain sodium as the major osmotically active particle. Crystalloids are relatively inexpensive and are useful for volume expansion, maintenance infusion, and correction of electrolyte disturbances. 1Isotonic crystalloids (e.g., lactated Ringer's solution, 0.9% NaCl) distribute uniformly throughout the extracellular fluid compartment so that after 1 hour, only 25% of the total volume infused remains in the intravascular space. Lactated Ringer's solution is designed to mimic extracellular fluid and is considered a balanced salt solution. This solution provides a HCO3– precursor and is useful for replacing GI losses and extracellular fluid volume deficits. In general, lactated Ringer's solution and 0.9% NaCl can be used interchangeably. However, 0.9% NaCl is preferred in the presence of hyperkalemia, hypercalcemia, hyponatremia, hypochloremia, or metabolic alkalosis.
2. Hypertonic saline solutions alone and in combination with colloids, such as dextran, have generated interest as a resuscitation fluid for patients with shock or burns. These fluids are appealing because, relative to isotonic crystalloids, smaller quantities are required initially for resuscitation. However, the intravascular hypertonic benefit rapidly dissipates as the fluid redistributes between the intravascular and extravascular spaces. Side effects of hypertonic solutions include hypernatremia, hyperosmolality, hyperchloremia, hypokalemia, and central pontine demyelination with rapid infusion. These solutions should be used with caution in patients with impaired renal function.
B.Hypotonic solutions (D5W, 0.45% NaCl) distribute throughout the total body water compartment, expanding the intravascular compartment by as little as 10% of the volume infused. For this reason, hypotonic solutions should not be used for volume expansion. They are used to replace free water deficits. C.Colloid solutions contain high–molecular-weight substances that remain in the intravascular space. Early use of colloids in the resuscitation regimen may result in more prompt restoration of tissue perfusion and may lessen the total volume of fluid required for resuscitation. However, there are no situations in which colloids have unequivocally been shown to be superior to crystalloids for volume expansion. Because colloid solutions are substantially more expensive than crystalloids, their routine use in hypovolemic shock remains controversial. The use of colloids is indicated when crystalloids fail to sustain plasma volume because of low colloid osmotic pressure (e.g., increased protein loss from the vascular space, as in burns and peritonitis). Synthetic and human-derived colloids carry minimal risk of transmitting infection.
1.Albumin preparations ultimately distribute throughout the extracellular space, although the initial volume of distribution is the vascular compartment. Preparations of 25% albumin (100 mL) and 5% albumin (500 mL) expand the intravascular volume by an equivalent amount (450–500 mL). However, 25% albumin is indicated in the edematous patient to mobilize interstitial fluid into the intravascular space. The cost per liter of albumin is more than that of other colloid solutions and 30 times the cost of the intravascular volume-equivalent amount of crystalloid solutions. Consequently, albumin preparations should be used judiciously. They are not indicated in the patient with adequate colloid oncotic pressure (serum albumin >2.5 mg/dL, total protein >5 mg/dL), for augmenting serum albumin in chronic illness (cirrhosis or nephrotic syndrome), or as a nutritional source. 2.Dextran is a synthetic glucose polymer that undergoes predominantly renal elimination. In addition to its indications for volume expansion, dextran also is used for thromboembolism prophylaxis and promotion of peripheral perfusion. Dextran solutions expand the intravascular volume by an amount equal to the volume infused. Side effects include renal failure, osmotic diuresis, coagulopathy, and laboratory abnormalities (i.e., elevations in blood glucose and protein, interference with blood cross-matching).
a.Dextran 40 is the fraction of branched dextrose polysaccharide with an average molecular weight of 40 kd, available as a 10% solution in either 0.9% NaCl or D5W. Recommended dosing for acute volume expansion is 2 g/kg (20 mL/kg of 10% solution) per 24 hours. If use continues beyond 24 hours, the dosing should be reduced to 1 g/kg (10 mL/kg) per 24 hours. Use should not extend beyond 5 days. b.Dextran 70 is a polysaccharide with an average molecular weight of 70 kd that is available as a 6% solution in normal saline or a 5% solution in inert sugar. Recommended dosing for acute volume expansion should not exceed 1.2 g/kg (20 mL/kg) in the first 24 hours. If therapy is extended beyond 24 hours, the dose should not exceed 0.6 g/kg (10 mL/kg) daily. The usual adult dose for acute volume expansion is 30 g (500 mL). In emergent situations, dextrose 70 can be given at a rate of 1.2–2.4 g per minute (20–40 mL per minute). In normovolemic or nearly normovolemic patients, the rate of infusion should not exceed 0.24 g per minute (4 mL per minute).
3.Hydroxyethyl starch (hetastarch) is a synthetic molecule resembling glycogen that is available as a 6% solution in 0.9% NaCl. Hetastarch infusion, like 5% albumin, increases the intravascular volume by an amount equal to or greater than the volume infused. Hetastarch is less expensive than albumin and has a more favorable side effect profile than dextran formulations, making it an appealing colloid preparation. a.Indications include use as a plasma volume-expanding agent in shock from hemorrhage, trauma, sepsis, and burns. Urine output typically increases acutely secondary to osmotic diuresis and must not be misinterpreted as a sign of adequate peripheral perfusion in this setting. b.Elimination is hepatic and renal. Patients with renal impairment are particularly subject to initial volume overload and tissue accumulation of hetastarch with repeated administration. In these patients, initial volume resuscitation accomplished with hetastarch should be maintained with another plasma volume expander, such as albumin or crystalloid. c.Laboratory abnormalities include elevations in serum amylase to approximately twice normal without associated alteration in pancreatic function.
d.Dosing of hetastarch 6% solution is 30–60 g (500– 1,000 mL), with the total daily dosage not exceeding 1.2 g/kg (20 mL/kg) or 90 g (1,500 mL). In hemorrhagic shock, hetastarch solution can be administered at a rate of 1.2 g/kg per hour (20 mL/kg per hour). Slower rates of administration generally are used in patients with burns or septic shock. In individuals with severe renal impairment (creatinine clearance <10 mL per minute), the usual dose of hetastarch can be administered, but subsequent dosage should be reduced 50–75%. 2.