Fluid resuscitation

RateIntravenous fluids to increase intravascular volume is a frequent intervention.

Fluid administration distributes initially to the intravascular compartment, and then to the interstitial and intracellular compartments.

Fluid influx into the interstitial compartment is reabsorbed into the circulation to the lymphatic system.

The factors affecting fluid distribution include: serum, oncotic, pressure, endothelial integrity, capillary hydrostatic pressure, fluid infusion rate and volume.

Intravenous fluids commonly prescribed for hospitalized patients are administered for multiple reasons including for rehydration, as a vehicle or carrier for medication, and to produce direct physiologic effects on cardiac output and electrolyte concentrations as medications.

Fluids remain the core effort in resuscitation of the critically ill.

Fluid challenges for the main stay for patients with signs of poor perfusion and critical illness.

Critically ill patients receive IV fluids in four forms: fluid challenge, fluid bolus, maintenance or replacement fluid, or as part of parenteral nutrition, and medication diluent or carrier.

A fluid challenge refers to the administration of a small volume of IV fluid, about 250 cc, over a short period of time (10 minutes), and assessing a patient’s response to the fluid with changes in cardiac output, heart rate, arterial blood pressure, or urinary output.

A fluid bolus refers to the administration of a larger volume of IV fluid of 502,000 cc, over short. Of time (15 minutes), with the intention of increasing intravascular volume.

Maintenance fluids are the replacement of IV fluid at lower rates of a longer periods of time with the aim of meeting daily needs for water, electrolytes, nutrition, and replacement of measured losses.

Significant amounts of fluid IV to administer medication or carriers is also a goal of fluid resuscitation.

Mortality is decreased when critically ill patients receive early fluid resuscitation during septic shock and hemorrhagic shock.

Saline 0.9% sodium chloride is the most commonly used fluid for resuscitation.

IV fluid solutions are classified as crystalloid solutions, which contain water and electrolytes, or colloid solutions which contain water, electrolytes, and a larger compound.

The most common crystalloid solutions are 0.9% sodium chloride and balanced or buffered crystalloid solutions, such as Ringer lactate.

Crystalloids solutions are readily available and inexpensive.

Balanced crystalloids are fluids who sodium and chloride concentrations are similar to plasma.

Colloids are administered as often as crystalloids.

Colloids minimize resuscitation volumes utilized.

Colloids may sustain intravascular volumes longer than crystalloids.

When comparing colloids with isotonic crystalloid fluids there is no difference demonstrated in a heterogeneous ICU patient population, with a small potential benefit with colloid as adjunctive therapy in patients with sepsis..

Hydroxyethyl starch is the most frequently used colloid.

Hydroxyethyl starch is a synthetic colloid, derived from partially hydrolyzed plant starch.

Hydroxyethyl starch associated with greater degree of renal damage and mortality, although studies are inconsistent on these matters.

In a meta analysis and systemic review hydroxytryptamine starch was associated with increased renal injury and mortality when used for acute volume resuscitation, and its use is not warranted (Zarychanski R et al).

Crystallized fluid therapy with buffered crystallized therapy compared with saline in the ICU acute kidney injury incidence difference not occur (Young P et al).

In the Balanced Solutions Intensive care study (BASICS), A double blind, randomized trial assessed the administration of a balanced solution during ICU stay compared with saline solution resulted in a 90 day mortality that was not significantly reduced.
No evidence that the risk of death or acute kidney injury among critically ill patients in the ICU was lower with the use of balanced multi electrolyte solutions than  with saline (New Zealand ICU Society clinical trials group).
Albumin is the most frequently used colloid in ICU settings, but compared with saline It is not reduce sepsis mortality.
Hemorrhaging shock is ideally treated with a balanced approach of packed red blood cells, fresh frozen plasma, and platelets.
Among patients who do not have hypotension from blood loss controversy exists about the ideal fluid to use for resuscitation.
In children fluid boluses may be associated with worse outcomes that may be related to cardiovascular claps than those receiving continuous infusions.
Higher fluid perfusion rates are suggested to improve hemodynamic parameters such as mean arterial pressure, and cardiac output at a greater speed.
Faster infusion rates, however, may rapidly expand the intravascular space resulting in more fluid into the tissues, with worsening tissue edema and reducing fluid reabsorption from the interstitial to the intravascular space, leading to organ failure.
A systematic review of 85 studies report that a rapid infusion rate of less than 30 minutes is associated with a higher probability of increasing stroke volume or cardiac output in response to fluid administration, likely more effectively increasing venous return, and preload: 80% of studies use a volume of fluid of 500 cc.
In a randomized trial of 10,520 patients in ICU‘s, treatment with fluid bolus is at 333 mL per hour versus 999 mL per hour resulted in a 90 day mortality of 26, 27%, respectively, the difference that was not statistically significant.
Among critically ill patients requiring fluid challenges,  Infusing at a slower rate compared with a faster rate did not reduce 90 day mortality. (The BASICS randomized clinical trial).
Studies suggest that rapid administration of chloride-rich solutions that is .9 point percent sodium chloride can be detrimental to kidney function, vascular smooth muscle function, and vasomotor tone, as well as promoting Inflammation compared with balanced solutions with compositions that more closely mimic electrolyte composition.
Prospective obsessional observational studies and crossover trials as well as retrospective investigations suggest small, but potentially important, increases in acute kidney injury, need for kidney replacement therapy, and mortality when chloride-rich solutions are compared with balance solutions in critically ill patients.
Despite multiple studies there is insufficient data to guide management in critically ill patients who require significant volume resuscitation.
Fluid therapy for sepsis: multiple pathways responsible for maintaining intravascular volume, venous return, cardiac output, and tissue perfusion are disrupted by sepsis.
Assessing whether  IV fluid administration is indicated, requires an evaluation of medical history, physical exam, laboratory evaluation and diagnostic imaging/ultrasound to assess the etiology of shock.
Approximately 57% of patients with sepsis are fluid responsive at presentation.
Dynamic measurements by passive leg raising or pulse pressure variation can identify patients who are fluid responsive.
An increasing cardiac output with passive leg raising identifies patients whose cardiac output would increase with the fluid bolus.
Fluid losses, increase venous capacitance, decreased venous resistance, all reduce the effective intravascular volume in sepsis, and may decrease venous return, cardiac output, and tissue perfusion.
Intravenous fluid therapy can increase blood volume in the vasculature, increase venous return to the heart, cardiac output, and volume of oxygen delivered to tissues.
A fluid bolus increases blood pressure by a greater amount when the arteries are stiff and noncompliant, compared with when the arteries are flexible and compliant in the changes in arterial pressure after fluid
administration depend on arterial elastance.
Fluid administration during sepsis may increase a patient’s cardiac output without increasing blood pressure.
During initial fluid therapy, hemodynamic improvements with increased cardiac output, increased, arterial pressure, and improved tissue perfusion can occur: the presence of excessive fluid administration can cause fluid extravasation and interstitial edema, with sepsis due to endothelial damage.
Tissue edema due to increased venous pressure can cause organ dysfunction and potential complications.
Point of care ultrasound can evaluate the etiology of shock and predict fluid responsiveness, facilitates assessment of cardiac function, characterizes pre-load, responsiveness and evaluates patients for complications of fluid accumulation.
Point of care ultrasound can evaluate the inferior vena cava and patterns of venous flow in the liver and kidneys, and may identify tissue edema informing about the decision to continue or to withhold fluid therapy.
Goals for fluid therapy in shock include normalization of blood pressure, normalization of capillary refill time, lactate clearance, and normalization of urinary output.
Fluid administration for sepsis has four phases for critical illness: resuscitation, optimization, stabilization, and evacuation.
In the resuscitation phase, the goal is to rapidly reverse hypoperfusion, administering fluid boluses and frequently administering vasopressors.
Findings for hypoperfusion include: altered level of consciousness, low arterial blood pressure, decreased urinary output, livedo reticularis, prolonged capillary fill time of three seconds or greater, and elevated serum lactate.
During the resuscitative phase fluid responsiveness is evaluated and the underlying cause for the hemodynamic abnormality is pursued.
The fluid resuscitation phase therapy is continued until the mean arterial pressure no longer increases with fluid administration, and the goals of resuscitation are attained, the patient is no longer immediately life threatened or complications of fluid therapy arise.
The optimization phase aims to attain perfusion to organs and tissues, and stabilization phase has the goal of maintaining homeostasis and facilitating organ dysfunction resuscitation.
The evacuation phase of fluid therapy is a result of that critically ill adults with sepsis may experience edema and organ failure due to excess accumulation of fluid administration during the critical illness and have a reduced capacity for fluid elimination.
It may be necessary to facilitate fluid removal in  patients who cannot adequately manage spontaneous reduction of fluid,  with the use of pharmacologic or kidney replacement therapy.

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