Fielding Chapter 11: Fluid Overload

What does the presence of fluid overload require?

Either excessive fluid administration or inadequate renal excretion

Fluid Overload in Renal Failure

• Kidneys may be unable to remove the required amount of fluid from the extracellular fluid volume (ECFV) to maintain normal water balance

  • Most commonly occurs due to a decreased GFR

  • Less commonly, GFR may be normal but the kidneys eliminate an inappropriately low amount of water

Conditions Where Renal Function is Adequate but the Kidneys are “Tricked” Into Allowing Fluid Overload

• Increased capillary permeability, hypoproteinemia, changes in interstitial compliance, heart failure

  • In increased capillary permeability, increased fluid accumulates within the interstitium and ECFV and total body water (TBW) will gradually exceed normal volumes but intravascular volume may be decreased or normal so the kidneys do not perceive a fluid overload

  • In heart failure, the kidneys perceive that additional intravascular volume is need in order to maintain cardiovascular function and this volume is maintained despite the excessive total body water and extracellular fluid volumes

What are risk factors for fluid overload?

Hypoproteinemia

Heart failure

Renal failure

Systemic inflammation

Blood product administration

Hypoproteinemia and Fluid Overload

• Many conditions that result in hypoproteinemia are also associated with systemic inflammation

  • Difficult to delineate the contribution of hypoproteinemia, increased vascular permeability, and interstitial matrix compliance changes

• Albumin concentrations less than 1-1.5 g/dL or total protein concentrations less than 4.0 g/dL have been anecdotally implicated as a threshold for edema formation in horses, there is no research to support these conclusions

• In cases with hypoproteinemia where IV fluid administration will be initiated, the risk of edema formation may be higher

• In cases where edema is present, identification of hypoproteinemia should not exclude the search for other causes contributing to a state of fluid overload

Renal Failure and Fluid Overload

• Patients with compromised renal function will be at increased risk for fluid overload if they are unable to excrete the quantity of fluid that is being administered

• Acute kidney injury is recognized with as little as a 0.3 mg/dl increase in serum creatinine concentrations so a single measurement of creatinine at the middle or upper end of a normal range may still be associated with renal insufficiency

• Fractional excretion of sodium may be another means for identifying more subtle changes in renal function and patients at higher risk for fluid overload

Systemic Inflammation and Fluid Overload

• Systemic inflammatory response can cause changes in renal function, cardiac function, capillary permeability, interstitial compliance, and plasma protein concentrations that can lead to fluid overload

• Interstitial compliance is the change in interstitial volume resulting from a change in interstitial pressure

  • By creating greater negative pressure, it is possible for the interstitium to help increase net movement of fluid out of the vascular space

Blood Product Administration and Fluid Overload

• Volume of transfused products and rate of transfusion were shown to be independent risk factors for fluid overload

• Overload doesn't appear to be commonly identified with blood/plasma transfusions in equine medicine

Aggressive Fluid Resuscitation and Fluid Overload

• In healthy horses, rates of 80 ml/kg/h seem to well tolerated over a 30 minute period

• It seems likely that high rates of crystalloid fluid administration (>20-40 ml/kg/h for a prolonged period) could result in fluid overload particularly in patients with other risk factors

Using Changes in Body Weight to Recognize Fluid Overload

• Body weight on presentation can be challenging to evaluate as patients may be severely dehydrated and a gain in body weight after fluid administration may be appropriate

• Body weight change doesn't address the location of the excess fluid

• In general, a patient who is at risk for fluid overload and consistently gains weight each day may be accumulating excess fluid

Using CVP to Recognize Fluid Overload

• CVP represents the pressure within the intrathoracic vena cava

• Elevated CVP (>15 cmH2O) may indicate the potential for fluid overload

• A rise in CVP (>4 cmH2O) in response to a fluid challenge could indicate a risk for edema formation unless hypovolemia is present and baseline CVP is low

• Ability to detect volume overload in horses in unclear

Pulmonary Function Deterioration as a Sign of Fluid Overload

• Horses with systemic inflammation may be at risk for pulmonary disease (ARDS) as well as fluid overload

  • The excess fluid may not be a direct cause of the pulmonary dysfunction; rather the systemic inflammatory response may be the primary cause of excessive pulmonary fluid

• Pulse oximetry and arterial blood gas monitoring are practical means of monitoring oxygenation and pulmonary function

Bioimpedance Analysis (BIA) to Recognize Fluid Overload

• Bioimpedance analysis (BIA) is designed to be able to determine the amount of water accumulating in different fluid compartments and quantify the size of the ECFV, ICFV, and TBW

  • Appears to detect acute volume changes in healthy horses

  • Evidence that BIA may be influenced by electrolyte imbalances, which are common in critically ill patients

  • Relatively non-invasive but requires patients to remain still for short periods and avoid contact with metal

Pulse Pressure Variation to Recognize Fluid Overload

• Pulse pressure variation (PPV) can be used to evaluate the need for fluid volume in patients undergoing mechanical ventilation

  • Calculated value is based on the difference between systolic and diastolic arterial pressure during the inspiratory and expiratory phases of positive pressure ventilation

What pulse pressure variation indicates the need for additional IV fluids?

• In humans, PPV values of 12-13% have been used to discriminate between patients who will benefit from additional IV fluids and those in whom additional fluids could be detrimental

  • PPV value greater than 13% would indicate the need for additional IV fluids

Pulse Pressure Variation Equation

When is treatment of fluid overload indicated?

• Fluid overload is contributing to impairment of normal pulmonary function and oxygenation is inadequate

• Fluid overload is contributing to impairment of normal cardiovascular function and perfusion is inadequate

• Renal function is impaired and the fluid overload is unlikely to improve with time

What are the main components of treatment for fluid overload?

• Modify/eliminate fluids being administered

• Increase renal excretion of fluids if possible

• Remove fluid accumulations (pleural, peritoneal) if possible

Treatment of Fluid Overload - Modification of the Fluid Therapy Plan

• In some cases can just decrease the rate of fluid administration

• For critically ill patients with poor perfusion, a high rate of fluids may be required to maintain cardiac output

  • If the rate of fluids can't be safely decreased you may be able to change fluid type

Treatment of Fluid Overload - Increased Renal Excretion of Fluid

• Common drugs used to induce diuresis in horses include furosemide and mannitol

  • In cases of impaired renal function, particularly oliguria or anuria, mannitol could result in further volume overload because it cannot be eliminated

  • Furosemide is generally effective in achieving a negative fluid balance but it has the potential to cause deterioration in renal function and worsen electrolyte imbalances

Furosemide in Renal Failure

• Controversy over the benefits of furosemide in renal failure

  • May decrease oxygen consumption in the loop of Henle and therefore be protective by decreasing potential ischemic injury

  • If furosemide is able to increase urinary flow, it could also improve intratubular obstruction

What is the most common treatment to increase renal excretion of fluid in horses?

• In horses, furosemide likely represents the most practical and safe option to induce fluid diuresis and resolve volume overload

  • It is possible that renal function and electrolyte balance may be negatively affected by furosemide

  • In some cases, continued fluid administration (even hypertonic fluid) in combination with furosemide may be needed to maintain an appropriate fluid balance

Treatment of Fluid Overload - Removal of Fluid Accumulations

• If there is large-volume fluid accumulation, removal may improve respiratory function (particularly in cases of pleural effusion) and help restore fluid balance

• If fluid removal is too rapid, severe hypotension can result

Prognosis in Fluid Overload

• Prognosis for survival following fluid overload depends on the inciting cause and the severity of overload

  • If the inciting cause can be resolved and renal function is adequate, fluid balance is likely to return to normal

  • If fluid accumulation is severe and due to renal failure following severe sepsis, the fluid accumulation may be difficult to resolve and the prognosis may be guarded/poor

• Renal function is one of the more significant determinants of prognosis in cases of volume overload

• In cases of severe overload, pulmonary function may be severely compromised and even if the underlying cause is treatable, respiratory failure may result before the excess fluid can be removed

  • Treatment with furosemide should be initiated as quickly as possible

Prevention of Fluid Overload - Selection of Fluid Type

• Colloid administration has been implicated in fluid overload but it depends on the rate and volume administered

• If colloids are required, the rate of fluid administration should be considered and moderated if possible

Prevention of Fluid Overload - Selection of Fluid Rate

• Often 50% of the "maintenance rate" may be used in high-risk patients

• Fluid boluses should be used only when absolutely necessary as they may cause a more rapid, albeit temporary, increase in central venous pressures than continuous rate administration

Prevention of Fluid Overload - Diuretic Treatment

Administration of a diuretic in conjunction or shortly following fluid resuscitation may help to mitigate fluid overload

Fluid Overload in Neonatal Foals

• Risk factors for fluid overload in neonates include kidney failure, heart failure, hypoproteinemia, and inflammatory conditions

• Many critical neonatal foals appear to be prone to fluid overload, particularly with the treatment of IV fluids

  • May be due to differences in capillary permeability or the compliance of their interstitium

• Treatment of neonatal foals with fluid overload has similar options to adults

  • Modifying fluid administration is one consideration, but increasing fluid urinary excretion may be required with significant volume overload

  • Furosemide infusions are very effective at removing excess fluid from foals, but fluid and electrolyte balance must be monitored