Volume 2

Karl Bauer , ... Barbara S. Stonestreet , in Fetal and Neonatal Physiology (Fourth Edition), 2011

Intravascular Infusion of Isotonic Solutions

Rapid intravascular infusions of isotonic solutions, such as saline or Ringer's lactate, expand blood volume by only a fraction of the infused volume largely because of a loss of the infused fluid into the interstitial spaces. When adults of several species received intravascular infusions of isotonic crystalloid solutions, average intravascular retention was 20% to 50% of the infused volumes 30 to 60 minutes after rapid infusion. This is quite similar to the response in anesthetized newborn sheep, in that intravascular retention averaged only 30% to 40% after intravascular saline infusions. 26 Yet, in the unanesthetized ovine fetus, average intravascular retention after similar infusions was only 6% to 7% of the infused volume. 112 The reduced intravascular retention of crystalloid during fetal life is due largely to a high interstitial compliance–vascular compliance ratio, as well as a higher capillary filtration coefficient. 15 The increased capillary filtration coefficient permits very rapid fluid movements across the capillary membrane, and the high interstitial-to-vascular compliance ratio allows for extensive fluid shifts.

The reduced intravascular retention of fluid in the fetus compared with that of the adult may also be a primary factor in determining the urine flow responses to volume loading. It is well established that, after volume loading, normal adults will excrete the entire volume load through their kidneys over a period of several hours. Newborns of several species, including human and ovine, have a reduced capacity to excrete volume loads. This reduced excretory capacity can, in part, be attributed to the reduced intravascular retention. 113 With high intravascular retention in the adult, plasma renin activity and plasma concentrations of arginine vasopressin and atrial natriuretic factor all change in a direction appropriate for elevating urine flow. In the ovine fetus with a low intravascular retention, plasma arginine vasopressin and renin activity are unchanged, and atrial natriuretic factor undergoes only a transient increase. 113 Thus fetal urine flow rapidly returns to normal after rapid vascular volume expansion because the hormonal stimuli that promote urinary output are not maintained. 113 It has yet to be documented whether this is indeed the mechanism responsible for the diminished response to volume loading in human newborn infants.

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Fluid Distribution in the Fetus and Neonate

Robert A. Brace , in Fetal and Neonatal Physiology (Third Edition), 2004

Responses to Volume Loading

Rapid intravascular infusions of isotonic solutions, such as saline or Ringer lactate, expand blood volume by only a fraction of the infused volume owing largely to a loss of the infused fluid into the interstitial spaces. When adults of several species received intravascular infusions of isotonic crystalloidal solutions, intravascular retention averaged 20 to 50% of the infused volumes 30 to 60 minutes after rapid infusion. In the unanesthetized ovine fetus, similar infusions increased blood volume by only 6 to 7% of the infused volume. 67 This is quite different from the response in anesthetized newborn sheep, in that intravascular retention was similar to that of the adult and averaged 30 to 40% following intravascular saline infusions. 68 The reduced intravascular retention of crystalloid during fetal life is due largely to a high interstitial compliance/vascular compliance ratio as well as a higher capillary filtration coefficient. 6 The increased capillary filtration coefficient permits very rapid fluid movements across the capillary membrane, and the high interstitial to vascular compliance ratio allows for extensive fluid movements.

As might be expected, the plasma and interstitial protein concentrations are affected differently in the fetus than in the adult following volume expansion with crystalloid. In the fetus, the lymph/plasma protein concentration ratio decreases following volume expansion, 69 whereas this protein concentration ratio increases transiently in adult animals 12 and newborn sheep. 68

The reduced intravascular retention of fluid in the fetus compared with that of the adult may also be a primary factor in determining the urine flow responses to volume loading. It is well established that following volume loading, normal adults will excrete the entire volume load through their kidneys over a period of several hours. Newborns of several species, including human and ovine, have a reduced capacity to excrete volume loads. This reduced excretory capacity can, in part, be attributed to the reduced intravascular retention, 70 that is, with high intravascular retention in the adult, plasma renin activity and plasma concentrations of arginine vasopressin and atrial natriuretic factor all change in a direction appropriate for elevating urine flow. In the ovine fetus with a low intravascular retention, plasma arginine vasopressin and renin activity are unchanged, and atrial natriuretic factor undergoes only a transient increase. 70 Thus, fetal urine flow rapidly returns to normal following rapid vascular volume expansion because the hormonal stimuli that promote urinary output are not maintained. 70 It has yet to be documented whether this is indeed the mechanism responsible for the diminished response to volume loading in human newborn infants.

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Gastrointestinal Bleeding

Rajalakshmi R. Nair MD , in The Mont Reid Surgical Handbook (Sixth Edition), 2008

III. INITIAL MANAGEMENT

A. ASSESS THE MAGNITUDE OF HEMORRHAGE.

1.

Is the patient stable or unstable?

B. STABILIZE HEMODYNAMIC STATUS.

1.

Two large-bore intravenous lines (14–16 gauge)

2.

Begin resuscitation with isotonic solution.

3.

Place Foley catheter to facilitate monitoring of intravascular volume status.

4.

Place nasogastric tube: This may help to differentiate between an upper and lower GI bleeding source. Saline lavage should be continued until the fluid aspirate is clear.

C. MONITOR FOR CONTINUED BLOOD LOSS.

1.

Generally, an intensive care unit setting is required.

2.

Continuous monitoring of vital signs with hourly urinary output

3.

Frequent laboratory tests to assess the adequacy of transfusion and correction of coagulopathy. The hematocrit should be maintained >30 ml/dl, especially in elderly patients with cardiovascular disease.

4.

Central venous pressure or pulmonary artery monitoring in unstable patient

5.

If bleeding persists despite transfusion of four to six units of packed red blood cells, further diagnostic testing or surgical intervention is required (see algorithm in Fig. 22-1 ).

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Colloids and blood products

Michael MG Mythen , Matthias Jacob , in Oh's Intensive Care Manual (Seventh Edition), 2014

Crystalloids have larger volumes of distribution depending on their composition 8 ( Fig. 96.4 and Table 96.1 ). Whereas isotonic solutions target the whole extracellular compartment, hypotonic preparations additionally load the intracellular space. Colloids or plasma substitutes initially target the intravascular compartment. Ideal properties include:

•

stable with a long shelf life

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pyrogen, antigen and toxin free

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free from risk of disease transmission

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intravascular volume effect lasts for several hours

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metabolism and excretion do not adversely effect the recipient

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no tissue storage

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no direct adverse effects (e.g. causing a coagulopathy).

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Chronic Intestinal Pseudo-Obstruction

LEONEL RODRIGUEZ , ALEJANDRO FLORES , in Pediatric Gastroenterology, 2008

Antroduodenal Manometry

Always abnormal in CIPO, a normal AD manometry excludes CIPO. Because the majority of centers use water perfusion systems, it is recommended to use isotonic solutions like Pedialyte instead of water to avoid water intoxication. AD manometry includes a recording of a fasting period followed first by stimulation of antral contractions by erythromycin, which also helps to prevent the antral inhibition from octreotide used later for the intestine stimulation. In CIPO, the AD manometry aids not only to confirm abnormal upper GI motility but also differentiate between neuropathic and myopathic subtypes. A normal AD manometry in the suitable clinical setting should raise the concern of pediatric falsification disorder, Munchausen syndrome by proxy, or PADS. Typical manometric findings in CIPO include antral hypomotility; in the neuropathic variety, the typical findings include absence of MMC during fasting and phase III–like activity during feeding. In the myopathic variety, the typical findings include low amplitude or absent contractions. Also, the absence of MMC is associated with need for total parenteral nutrition (TPN) and its presence with good response to jejunal feedings. The presence of waves that are simultaneous and/or of long duration should raise concern for a missed mechanical obstruction. When a patient has a jejunostomy, the manometry catheter can be placed via the stoma and a jejunal manometry performed (Fig. 23-2).

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Endoscopy in minimally invasive gynecologic surgery

Licia Raymond , Gretchen M. Lentz , in Comprehensive Gynecology (Eighth Edition), 2022

Fluid management

Hysteroscopy requires a mechanism for intrauterine distention to facilitate visualization . Most hysteroscopes have a mechanism for continuous flow of input and output fluid to optimize visualization within the uterine cavity. Isotonic solutions are considered the safest option, as opposed to electrolyte-free hypotonic solutions, which carry a higher risk of potentially life-threatening hyponatremia in association with excess fluid absorption. Saline has become the distention medium of choice for both office and operating room hysteroscopy.

Saline is an isotonic electrolyte solution that can be used with bipolar electrosurgical energy, laser energy, and mechanical interventions. Hypotonic electrolyte-free fluids are compatible with monopolar electrosurgical platforms and can also be used with mechanical instruments or laser. Carbon dioxide gas has had a role as a distention medium in diagnostic hysteroscopy but has the potential for gas embolism and is not conducive to operative interventions because visualization can be limited.

The continuous inflow of the distention solution to optimize visualization can have implications on patient hemodynamics. Fluid overload and the resultant altered physiology can cause life-threatening hyponatremia, cerebral edema, and congestive heart failure; therefore a team awareness of fluid balance with hysteroscopy is crucial. The lower safety profile of hypotonic fluids relative to isotonic solutions such as physiologic saline is due to the greater risk of hyponatremia and fluid overload per quantity absorbed. Because of well-documented complications that can arise from excessive hysteroscopic fluid absorption with any medium, an important safety measure with any hysteroscopic procedure includes judicious measurement of the fluid deficit, the difference between fluid in and fluid out.

Guidelines mandate discontinuation of a hysteroscopic procedure before a fluid deficit of 1 L with a hypotonic solution such as glycine or mannitol. Guidelines allow for a fluid deficit of 2.5 L with isotonic fluids such as saline (AAGL, 2013). Fluid management systems are available to provide a more precise measurement of fluid input and output and to heighten safety when high fluid volumes are anticipated. Certain fluid management systems allow for adjustment of flow pressures to optimize visualization. For more simple office-based procedures, fluid overload can be avoided by limiting from the onset the amount of fluid to be infused to an amount under the deficit guidelines.

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Dysnatremias in cancer

UMUT SELAMET , ALA ABUDAYYEH , in Onco-Nephrology, 2020

Treatment of hypervolemic hypo-osmolar hyponatremia

Hypervolemic hypo-osmolar hyponatremia treatment considerations include concern over the possibility of exacerbating hypervolemia when hypertonic saline is used for hyponatremia in symptomatic cancer patients. Thus the initial treatment choice for symptomatic patients is isotonic solution, with or without loop diuretics, with the goal of increasing serum sodium concentration by 1 to 2 mEq/L per hour, until symptoms subside. Once symptoms abate, free water restriction, with or without loop diuretics, is used with a goal serum concentration increase of less than 0.5 mEq/L/h. In contrast, initial treatment of asymptomatic patients is free water restriction and loop diuretics, depending on the severity of hypervolemia and if the patient is getting other sources of intravenous fluids (i.e., medications).

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Tumour ablation

David Kessel MB BS MA MRCP FRCR , Iain Robertson MB ChB MRCP FRCR , in Interventional Radiology: A Survival Guide (Third Edition), 2011

Minimizing collateral damage

Protecting adjacent viscera from thermal injury is an important consideration. Other organs and viscera can be displaced away from the intended ablation zone. Several techniques are described.

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Fluid displacement (hydrodissection) : sterile water or similar isotonic solution (e.g. dextrose) is used to separate the tumour and the organ deemed at risk by injection through a fine needle inserted between them.

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Balloon displacement: the use of fluid-filled balloons positioned between the kidney and adjacent viscera has also been described.

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Gas displacement: instillation of carbon dioxide or air to form an insulating thermal cushion is another successful technique.

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Retrograde or percutaneous antegrade infusion of chilled water during RFA of the kidney protects the adjacent collecting system from thermal injury during ablation of central tumours (Fig. 30.7).

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Volume 1

Richard H. Sterns , ... J. Kevin Hix , in Seldin and Giebisch's The Kidney (Fifth Edition), 2013

Pathophysiology

If non-permeant solutes other than sodium salts accumulate in the extracellular space, the extracellular fluid volume expands, reducing the concentration of the sodium normally present in this fluid compartment. Plasma osmolality varies, depending on the cause of the syndrome.

Retention of a sodium-free isotonic solution (e.g., infusion of isotonic mannitol in a patient with renal insufficiency who excretes the solute slowly) causes isotonic hyponatremia. Mannitol, a solute that is unable to permeate cell membranes, is confined to the extracellular space; the fluid infused with the solute is similarly confined. 304 Thus, the extracellular fluid expands, and the intracellular compartment is unaffected. Sodium-free hypotonic solutions containing impermeant solutes can be considered isotonic solutions to which water has been added; hyponatremia caused by these solutions is primarily extracellular, but plasma osmolality is slightly reduced and the intracellular compartment is slightly diluted.

Retention of a sodium-free hypertonic solution (e.g., infusion of hypertonic mannitol) causes hypertonic hyponatremia. 305 In this case, intracellular water is osmotically drawn to the extracellular fluid compartment, compounding the dilution of extracellular sodium caused by the infused diluent. Thus, the sodium concentration of the extracellular space is reduced, while the osmolality of both extracellular and intracellular fluid compartments is increased. 306 A similar phenomenon has been described after administration of IgG solutions containing maltose or sucrose. 307

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Case Studies: Acid-Base Problems

Neeta Kannan , ... John A. Kellum , in Critical Care Nephrology (Second Edition), 2009

Treatment

Treatment of DKA consists of insulin and fluids. Often, several liters of fluid are needed because patients may have intravascular volume depletion as well as dehydration. Appropriate treatment results not only in a resolution of the acidosis but also in normalization of the AGc or SIG as the ketoacids are eliminated or metabolized. The patient should undergo insulin therapy, starting with 0.1 unit/kg. Potassium replacement should also commence as soon as the insulin therapy is started. The serum potassium level should be monitored hourly for the first 4 to 6 hours of therapy. Crystalloid fluid treatment should also begin with an isotonic solution infused at a rate of approximately 1 L/hr for the first 2 hours, followed by infusion of half-isotonic solution at 250 to 500 mL/hr. Most textbooks suggest saline as the primary crystalloid solution, but this solution would invariably lead to hyperchloremic metabolic acidosis. Lactated Ringer's solution or bicarbonate-based solutions can be used instead, although one serious concern with such a decision is that rapid correction of metabolic acidosis may result in a rapid drop in the serum potassium concentration. If care is not taken to replace potassium before correction of the pH, life-threatening hypokalemia may result. Finally, with the use of bicarbonate-based solutions, overshoot alkalosis is also a concern. Thus, we recommend initial therapy with isotonic saline followed by lactate- or bicarbonate-based crystalloid solutions. Depending on the amount of water deficit present, the tonicity of the fluid can be altered, and depending on the extent of hyperchloremia, the chloride concentration can be adjusted.

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