Quiz: Contemporary Fluid Strategies in the ICU

This patient meets the criteria for shock (ie, pallor, tachycardia, abnormal mentation, poor pulse quality, cold extremities) and should be treated with aggressive fluid therapy. The shock dose of isotonic crystalloids for dogs is 90 mL/kg,⁶ but that amount of fluid is rarely required. 

In the 1950s and 1960s, hemorrhagic shock models using anesthetized healthy dogs showed that removal of ≈30% of blood volume can reliably produce signs of hypovolemic shock.^7,8 These experimental models also showed that replacing blood loss with isotonic crystalloids required a much larger amount of fluid than that of the blood withdrawn, as isotonic crystalloids rapidly redistribute into the interstitial space. Thirty minutes after administration of an isotonic crystalloid bolus, only about one-third of the fluids infused remain within the intravascular space. Therefore, fluids must be given in a 1:3 ratio of blood loss to fluids infused.^7,8 With a total blood volume of ≈90 mL/kg for dogs, administration of a shock dose of fluids is equivalent to the entire blood volume.

Giving an entire shock dose of crystalloids has been called into question, however, over the past two decades, primarily because of concerns about sequelae from overzealous fluid resuscitation. Interstitial edema created by translocation of crystalloids after large-volume fluid administration can cause a barrier to oxygen diffusion, thus worsening tissue dysoxia (abnormal tissue oxygen utilization). It is therefore recommended that IV crystalloids be administered in aliquots of 20-30 mL/kg (ie, ¼-⅓ of the total shock dose) and the patient monitored for signs of continuing shock before additional boluses are administered.⁹ In one study, fluid boluses were effective in significantly increasing the systolic blood pressure of dogs presenting in hypotensive shock from a variety of causes.¹⁰ Of dogs that responded to fluid boluses in this study, only about one-third of the total shock dose was required to increase the blood pressure.

This patient meets the criteria for shock (ie, pallor, tachycardia, abnormal mentation, poor pulse quality, cold extremities) and should be treated with aggressive fluid therapy. The shock dose of isotonic crystalloids for dogs is 90 mL/kg,⁶ but that amount of fluid is rarely required. 

In the 1950s and 1960s, hemorrhagic shock models using anesthetized healthy dogs showed that removal of ≈30% of blood volume can reliably produce signs of hypovolemic shock.^7,8 These experimental models also showed that replacing blood loss with isotonic crystalloids required a much larger amount of fluid than that of the blood withdrawn, as isotonic crystalloids rapidly redistribute into the interstitial space. Thirty minutes after administration of an isotonic crystalloid bolus, only about one-third of the fluids infused remain within the intravascular space. Therefore, fluids must be given in a 1:3 ratio of blood loss to fluids infused.^7,8 With a total blood volume of ≈90 mL/kg for dogs, administration of a shock dose of fluids is equivalent to the entire blood volume.

Giving an entire shock dose of crystalloids has been called into question, however, over the past two decades, primarily because of concerns about sequelae from overzealous fluid resuscitation. Interstitial edema created by translocation of crystalloids after large-volume fluid administration can cause a barrier to oxygen diffusion, thus worsening tissue dysoxia (abnormal tissue oxygen utilization). It is therefore recommended that IV crystalloids be administered in aliquots of 20-30 mL/kg (ie, ¼-⅓ of the total shock dose) and the patient monitored for signs of continuing shock before additional boluses are administered.⁹ In one study, fluid boluses were effective in significantly increasing the systolic blood pressure of dogs presenting in hypotensive shock from a variety of causes.¹⁰ Of dogs that responded to fluid boluses in this study, only about one-third of the total shock dose was required to increase the blood pressure.

This patient meets the criteria for shock (ie, pallor, tachycardia, abnormal mentation, poor pulse quality, cold extremities) and should be treated with aggressive fluid therapy. The shock dose of isotonic crystalloids for dogs is 90 mL/kg,⁶ but that amount of fluid is rarely required. 

In the 1950s and 1960s, hemorrhagic shock models using anesthetized healthy dogs showed that removal of ≈30% of blood volume can reliably produce signs of hypovolemic shock.^7,8 These experimental models also showed that replacing blood loss with isotonic crystalloids required a much larger amount of fluid than that of the blood withdrawn, as isotonic crystalloids rapidly redistribute into the interstitial space. Thirty minutes after administration of an isotonic crystalloid bolus, only about one-third of the fluids infused remain within the intravascular space. Therefore, fluids must be given in a 1:3 ratio of blood loss to fluids infused.^7,8 With a total blood volume of ≈90 mL/kg for dogs, administration of a shock dose of fluids is equivalent to the entire blood volume.

Giving an entire shock dose of crystalloids has been called into question, however, over the past two decades, primarily because of concerns about sequelae from overzealous fluid resuscitation. Interstitial edema created by translocation of crystalloids after large-volume fluid administration can cause a barrier to oxygen diffusion, thus worsening tissue dysoxia (abnormal tissue oxygen utilization). It is therefore recommended that IV crystalloids be administered in aliquots of 20-30 mL/kg (ie, ¼-⅓ of the total shock dose) and the patient monitored for signs of continuing shock before additional boluses are administered.⁹ In one study, fluid boluses were effective in significantly increasing the systolic blood pressure of dogs presenting in hypotensive shock from a variety of causes.¹⁰ Of dogs that responded to fluid boluses in this study, only about one-third of the total shock dose was required to increase the blood pressure.

This patient meets the criteria for shock (ie, pallor, tachycardia, abnormal mentation, poor pulse quality, cold extremities) and should be treated with aggressive fluid therapy. The shock dose of isotonic crystalloids for dogs is 90 mL/kg,⁶ but that amount of fluid is rarely required. 

In the 1950s and 1960s, hemorrhagic shock models using anesthetized healthy dogs showed that removal of ≈30% of blood volume can reliably produce signs of hypovolemic shock.^7,8 These experimental models also showed that replacing blood loss with isotonic crystalloids required a much larger amount of fluid than that of the blood withdrawn, as isotonic crystalloids rapidly redistribute into the interstitial space. Thirty minutes after administration of an isotonic crystalloid bolus, only about one-third of the fluids infused remain within the intravascular space. Therefore, fluids must be given in a 1:3 ratio of blood loss to fluids infused.^7,8 With a total blood volume of ≈90 mL/kg for dogs, administration of a shock dose of fluids is equivalent to the entire blood volume.

Giving an entire shock dose of crystalloids has been called into question, however, over the past two decades, primarily because of concerns about sequelae from overzealous fluid resuscitation. Interstitial edema created by translocation of crystalloids after large-volume fluid administration can cause a barrier to oxygen diffusion, thus worsening tissue dysoxia (abnormal tissue oxygen utilization). It is therefore recommended that IV crystalloids be administered in aliquots of 20-30 mL/kg (ie, ¼-⅓ of the total shock dose) and the patient monitored for signs of continuing shock before additional boluses are administered.⁹ In one study, fluid boluses were effective in significantly increasing the systolic blood pressure of dogs presenting in hypotensive shock from a variety of causes.¹⁰ Of dogs that responded to fluid boluses in this study, only about one-third of the total shock dose was required to increase the blood pressure.

Although the obvious effects of overzealous fluid administration include volume overload, pleural effusion, pulmonary edema, and tissue edema, these are not the only components of resuscitation injury. 

At the cellular level, cell swelling and dysfunction can occur as sodium and water translocate into the cell.¹¹ Tissue hypoxia also can occur, as oxygen has a greater distance to travel through the interstitial edema in order to reach the cell. Cells begin to function less efficiently, increasing their oxygen demand. Decreased blood viscosity from administration of crystalloids can result in vasoconstriction and reduced tissue perfusion.¹²

Dilutional coagulopathy (ie, clotting factors diluted by blood loss and administration of coagulation factor-free fluids) has been identified in both humans and animals.^13,14 Loss of oncotic pressure, hypoalbuminemia, and tissue edema can lead to impaired healing. Excessive fluid administration has been linked to acute respiratory distress syndrome and multiorgan failure in human patients. Increased bleeding during trauma has been attributed to the effects of both dilutional coagulopathy and increased venous pressure causing premature clot removal.^13,14 

Together, all of these adverse effects represent what is known as resuscitation injury.

Answer B is incorrect, as acute kidney injury has been associated with infusion of artificial colloids but not with crystalloid solutions.

Answer C is incorrect, as hypoperfusion, lactate accumulation, intracellular acidosis, and cell death are all effects of underresuscitation, which can lead to multiorgan failure, but are not effects from overzealous fluid resuscitation.

Answer D is incorrect, as pleural effusion, pulmonary edema, and peripheral edema are the clinical syndromes that can occur with overzealous fluid administration but do not take into account the molecular and cellular level effects that make up resuscitation injury.

Although the obvious effects of overzealous fluid administration include volume overload, pleural effusion, pulmonary edema, and tissue edema, these are not the only components of resuscitation injury. 

At the cellular level, cell swelling and dysfunction can occur as sodium and water translocate into the cell.¹¹ Tissue hypoxia also can occur, as oxygen has a greater distance to travel through the interstitial edema in order to reach the cell. Cells begin to function less efficiently, increasing their oxygen demand. Decreased blood viscosity from administration of crystalloids can result in vasoconstriction and reduced tissue perfusion.¹²

Dilutional coagulopathy (ie, clotting factors diluted by blood loss and administration of coagulation factor-free fluids) has been identified in both humans and animals.^13,14 Loss of oncotic pressure, hypoalbuminemia, and tissue edema can lead to impaired healing. Excessive fluid administration has been linked to acute respiratory distress syndrome and multiorgan failure in human patients. Increased bleeding during trauma has been attributed to the effects of both dilutional coagulopathy and increased venous pressure causing premature clot removal.^13,14 

Together, all of these adverse effects represent what is known as resuscitation injury.

Answer B is incorrect, as acute kidney injury has been associated with infusion of artificial colloids but not with crystalloid solutions.

Answer C is incorrect, as hypoperfusion, lactate accumulation, intracellular acidosis, and cell death are all effects of underresuscitation, which can lead to multiorgan failure, but are not effects from overzealous fluid resuscitation.

Answer D is incorrect, as pleural effusion, pulmonary edema, and peripheral edema are the clinical syndromes that can occur with overzealous fluid administration but do not take into account the molecular and cellular level effects that make up resuscitation injury.

Although the obvious effects of overzealous fluid administration include volume overload, pleural effusion, pulmonary edema, and tissue edema, these are not the only components of resuscitation injury. 

At the cellular level, cell swelling and dysfunction can occur as sodium and water translocate into the cell.¹¹ Tissue hypoxia also can occur, as oxygen has a greater distance to travel through the interstitial edema in order to reach the cell. Cells begin to function less efficiently, increasing their oxygen demand. Decreased blood viscosity from administration of crystalloids can result in vasoconstriction and reduced tissue perfusion.¹²

Dilutional coagulopathy (ie, clotting factors diluted by blood loss and administration of coagulation factor-free fluids) has been identified in both humans and animals.^13,14 Loss of oncotic pressure, hypoalbuminemia, and tissue edema can lead to impaired healing. Excessive fluid administration has been linked to acute respiratory distress syndrome and multiorgan failure in human patients. Increased bleeding during trauma has been attributed to the effects of both dilutional coagulopathy and increased venous pressure causing premature clot removal.^13,14 

Together, all of these adverse effects represent what is known as resuscitation injury.

Answer B is incorrect, as acute kidney injury has been associated with infusion of artificial colloids but not with crystalloid solutions.

Answer C is incorrect, as hypoperfusion, lactate accumulation, intracellular acidosis, and cell death are all effects of underresuscitation, which can lead to multiorgan failure, but are not effects from overzealous fluid resuscitation.

Answer D is incorrect, as pleural effusion, pulmonary edema, and peripheral edema are the clinical syndromes that can occur with overzealous fluid administration but do not take into account the molecular and cellular level effects that make up resuscitation injury.

Although the obvious effects of overzealous fluid administration include volume overload, pleural effusion, pulmonary edema, and tissue edema, these are not the only components of resuscitation injury. 

At the cellular level, cell swelling and dysfunction can occur as sodium and water translocate into the cell.¹¹ Tissue hypoxia also can occur, as oxygen has a greater distance to travel through the interstitial edema in order to reach the cell. Cells begin to function less efficiently, increasing their oxygen demand. Decreased blood viscosity from administration of crystalloids can result in vasoconstriction and reduced tissue perfusion.¹²

Dilutional coagulopathy (ie, clotting factors diluted by blood loss and administration of coagulation factor-free fluids) has been identified in both humans and animals.^13,14 Loss of oncotic pressure, hypoalbuminemia, and tissue edema can lead to impaired healing. Excessive fluid administration has been linked to acute respiratory distress syndrome and multiorgan failure in human patients. Increased bleeding during trauma has been attributed to the effects of both dilutional coagulopathy and increased venous pressure causing premature clot removal.^13,14 

Together, all of these adverse effects represent what is known as resuscitation injury.

Answer B is incorrect, as acute kidney injury has been associated with infusion of artificial colloids but not with crystalloid solutions.

Answer C is incorrect, as hypoperfusion, lactate accumulation, intracellular acidosis, and cell death are all effects of underresuscitation, which can lead to multiorgan failure, but are not effects from overzealous fluid resuscitation.

Answer D is incorrect, as pleural effusion, pulmonary edema, and peripheral edema are the clinical syndromes that can occur with overzealous fluid administration but do not take into account the molecular and cellular level effects that make up resuscitation injury.

While veterinarians tend to use these three terms interchangeably, volume, hydration, and fluid balance do differ.

Intravascular volume refers to blood volume (ie, amount of fluid in all blood vessels). Patients that are hypervolemic have high blood volumes primarily residing within the venous system. It is important to realize that the venous system is the capacitance system and administering fluids primarily affects venous pressures. The arterial system is less affected by volume despite the common misconception that large volumes of fluids can lead to hypertension.¹⁵ Engorged peripheral veins, pulmonary edema, pleural effusion (especially in cats), peripheral edema, and ascites are all signs of hypervolemia. 

Overall volume status refers to the patient’s total body water, including all three fluid compartments (ie, intravascular, interstitial, intracellular). Typically, hydration and intravascular volume are directly related, except in cases with vascular leak (eg, systemic inflammatory response syndrome [SIRS], sepsis).

Hydration refers to the interstitial and intracellular compartments.¹⁶ Typical signs of overhydration include development of peripheral edema, chemosis, and serous nasal discharge. Signs of underhydration (ie, dehydration) include sunken eyes, tacky mucous membranes, and prolonged skin tenting.

Fluid balance is the objective measure of net fluid gain or loss over a set period (usually 24 hours) across all fluid compartments. It can be calculated based on the patient’s fluid intake and output or can be estimated based on body weight. Positive fluid balance means the patient either has higher intake than output or has gained weight over the set time period. Clinical signs attributed to positive fluid balance are used to identify fluid overload and can be a mixture of any of the clinical signs as described.¹⁷

While veterinarians tend to use these three terms interchangeably, volume, hydration, and fluid balance do differ.

Intravascular volume refers to blood volume (ie, amount of fluid in all blood vessels). Patients that are hypervolemic have high blood volumes primarily residing within the venous system. It is important to realize that the venous system is the capacitance system and administering fluids primarily affects venous pressures. The arterial system is less affected by volume despite the common misconception that large volumes of fluids can lead to hypertension.¹⁵ Engorged peripheral veins, pulmonary edema, pleural effusion (especially in cats), peripheral edema, and ascites are all signs of hypervolemia. 

Overall volume status refers to the patient’s total body water, including all three fluid compartments (ie, intravascular, interstitial, intracellular). Typically, hydration and intravascular volume are directly related, except in cases with vascular leak (eg, systemic inflammatory response syndrome [SIRS], sepsis).

Hydration refers to the interstitial and intracellular compartments.¹⁶ Typical signs of overhydration include development of peripheral edema, chemosis, and serous nasal discharge. Signs of underhydration (ie, dehydration) include sunken eyes, tacky mucous membranes, and prolonged skin tenting.

Fluid balance is the objective measure of net fluid gain or loss over a set period (usually 24 hours) across all fluid compartments. It can be calculated based on the patient’s fluid intake and output or can be estimated based on body weight. Positive fluid balance means the patient either has higher intake than output or has gained weight over the set time period. Clinical signs attributed to positive fluid balance are used to identify fluid overload and can be a mixture of any of the clinical signs as described.¹⁷

While veterinarians tend to use these three terms interchangeably, volume, hydration, and fluid balance do differ.

Intravascular volume refers to blood volume (ie, amount of fluid in all blood vessels). Patients that are hypervolemic have high blood volumes primarily residing within the venous system. It is important to realize that the venous system is the capacitance system and administering fluids primarily affects venous pressures. The arterial system is less affected by volume despite the common misconception that large volumes of fluids can lead to hypertension.¹⁵ Engorged peripheral veins, pulmonary edema, pleural effusion (especially in cats), peripheral edema, and ascites are all signs of hypervolemia. 

Overall volume status refers to the patient’s total body water, including all three fluid compartments (ie, intravascular, interstitial, intracellular). Typically, hydration and intravascular volume are directly related, except in cases with vascular leak (eg, systemic inflammatory response syndrome [SIRS], sepsis).

Hydration refers to the interstitial and intracellular compartments.¹⁶ Typical signs of overhydration include development of peripheral edema, chemosis, and serous nasal discharge. Signs of underhydration (ie, dehydration) include sunken eyes, tacky mucous membranes, and prolonged skin tenting.

Fluid balance is the objective measure of net fluid gain or loss over a set period (usually 24 hours) across all fluid compartments. It can be calculated based on the patient’s fluid intake and output or can be estimated based on body weight. Positive fluid balance means the patient either has higher intake than output or has gained weight over the set time period. Clinical signs attributed to positive fluid balance are used to identify fluid overload and can be a mixture of any of the clinical signs as described.¹⁷

While veterinarians tend to use these three terms interchangeably, volume, hydration, and fluid balance do differ.

Intravascular volume refers to blood volume (ie, amount of fluid in all blood vessels). Patients that are hypervolemic have high blood volumes primarily residing within the venous system. It is important to realize that the venous system is the capacitance system and administering fluids primarily affects venous pressures. The arterial system is less affected by volume despite the common misconception that large volumes of fluids can lead to hypertension.¹⁵ Engorged peripheral veins, pulmonary edema, pleural effusion (especially in cats), peripheral edema, and ascites are all signs of hypervolemia. 

Overall volume status refers to the patient’s total body water, including all three fluid compartments (ie, intravascular, interstitial, intracellular). Typically, hydration and intravascular volume are directly related, except in cases with vascular leak (eg, systemic inflammatory response syndrome [SIRS], sepsis).

Hydration refers to the interstitial and intracellular compartments.¹⁶ Typical signs of overhydration include development of peripheral edema, chemosis, and serous nasal discharge. Signs of underhydration (ie, dehydration) include sunken eyes, tacky mucous membranes, and prolonged skin tenting.

Fluid balance is the objective measure of net fluid gain or loss over a set period (usually 24 hours) across all fluid compartments. It can be calculated based on the patient’s fluid intake and output or can be estimated based on body weight. Positive fluid balance means the patient either has higher intake than output or has gained weight over the set time period. Clinical signs attributed to positive fluid balance are used to identify fluid overload and can be a mixture of any of the clinical signs as described.¹⁷

Clinical signs of hypovolemia (ie, low blood volume) include tachycardia, weak femoral pulses, and altered mentation. Clinical signs of overhydration include peripheral edema. Presence of red mucous membranes and rapid CRT are indicative of vasodilation from sepsis. Low urine production is likely from a combination of hypotension and low intravascular volume leading to poor renal perfusion. 

This dog represents one of the few cases in which the patient has a low blood volume, yet is overhydrated. Typically, hydration and volume are directly related. During conditions that cause SIRS, the vascular endothelium becomes leakier than normal, allowing water, solutes, and albumin to easily translocate into the interstitial space.¹⁸ In addition, this patient is a likely candidate to be severely hypoalbuminemic, as evidenced by pitting edema. Oncotic pressure is strongly correlated with albumin. As oncotic pressure decreases, fluid is less likely to stay within the intravascular space. Considering the endothelial leakage and hypoalbuminemia that commonly occur in patients with severe SIRS and sepsis, roughly 90% of a crystalloid bolus can leak from the blood volume into the interstitium in 30 minutes.¹⁸ This creates a difficult-to-treat condition in which the administered fluid volume does not remain in the vascular volume but instead leaches into the interstitial space.

This patient meets at least 3 of the 4 criteria for SIRS (ie, elevated body temperature, tachycardia, tachypnea).¹⁶ The fourth criterion is a WBC count outside the reference range (or >5% bands), but this information was not provided in the case summary. This dog also has known septic focus (septic abdomen) and thus meets criteria for sepsis.

Clinical signs of hypovolemia (ie, low blood volume) include tachycardia, weak femoral pulses, and altered mentation. Clinical signs of overhydration include peripheral edema. Presence of red mucous membranes and rapid CRT are indicative of vasodilation from sepsis. Low urine production is likely from a combination of hypotension and low intravascular volume leading to poor renal perfusion. 

This dog represents one of the few cases in which the patient has a low blood volume, yet is overhydrated. Typically, hydration and volume are directly related. During conditions that cause SIRS, the vascular endothelium becomes leakier than normal, allowing water, solutes, and albumin to easily translocate into the interstitial space.¹⁸ In addition, this patient is a likely candidate to be severely hypoalbuminemic, as evidenced by pitting edema. Oncotic pressure is strongly correlated with albumin. As oncotic pressure decreases, fluid is less likely to stay within the intravascular space. Considering the endothelial leakage and hypoalbuminemia that commonly occur in patients with severe SIRS and sepsis, roughly 90% of a crystalloid bolus can leak from the blood volume into the interstitium in 30 minutes.¹⁸ This creates a difficult-to-treat condition in which the administered fluid volume does not remain in the vascular volume but instead leaches into the interstitial space.

This patient meets at least 3 of the 4 criteria for SIRS (ie, elevated body temperature, tachycardia, tachypnea).¹⁶ The fourth criterion is a WBC count outside the reference range (or >5% bands), but this information was not provided in the case summary. This dog also has known septic focus (septic abdomen) and thus meets criteria for sepsis.

Clinical signs of hypovolemia (ie, low blood volume) include tachycardia, weak femoral pulses, and altered mentation. Clinical signs of overhydration include peripheral edema. Presence of red mucous membranes and rapid CRT are indicative of vasodilation from sepsis. Low urine production is likely from a combination of hypotension and low intravascular volume leading to poor renal perfusion. 

This dog represents one of the few cases in which the patient has a low blood volume, yet is overhydrated. Typically, hydration and volume are directly related. During conditions that cause SIRS, the vascular endothelium becomes leakier than normal, allowing water, solutes, and albumin to easily translocate into the interstitial space.¹⁸ In addition, this patient is a likely candidate to be severely hypoalbuminemic, as evidenced by pitting edema. Oncotic pressure is strongly correlated with albumin. As oncotic pressure decreases, fluid is less likely to stay within the intravascular space. Considering the endothelial leakage and hypoalbuminemia that commonly occur in patients with severe SIRS and sepsis, roughly 90% of a crystalloid bolus can leak from the blood volume into the interstitium in 30 minutes.¹⁸ This creates a difficult-to-treat condition in which the administered fluid volume does not remain in the vascular volume but instead leaches into the interstitial space.

This patient meets at least 3 of the 4 criteria for SIRS (ie, elevated body temperature, tachycardia, tachypnea).¹⁶ The fourth criterion is a WBC count outside the reference range (or >5% bands), but this information was not provided in the case summary. This dog also has known septic focus (septic abdomen) and thus meets criteria for sepsis.

Clinical signs of hypovolemia (ie, low blood volume) include tachycardia, weak femoral pulses, and altered mentation. Clinical signs of overhydration include peripheral edema. Presence of red mucous membranes and rapid CRT are indicative of vasodilation from sepsis. Low urine production is likely from a combination of hypotension and low intravascular volume leading to poor renal perfusion. 

This dog represents one of the few cases in which the patient has a low blood volume, yet is overhydrated. Typically, hydration and volume are directly related. During conditions that cause SIRS, the vascular endothelium becomes leakier than normal, allowing water, solutes, and albumin to easily translocate into the interstitial space.¹⁸ In addition, this patient is a likely candidate to be severely hypoalbuminemic, as evidenced by pitting edema. Oncotic pressure is strongly correlated with albumin. As oncotic pressure decreases, fluid is less likely to stay within the intravascular space. Considering the endothelial leakage and hypoalbuminemia that commonly occur in patients with severe SIRS and sepsis, roughly 90% of a crystalloid bolus can leak from the blood volume into the interstitium in 30 minutes.¹⁸ This creates a difficult-to-treat condition in which the administered fluid volume does not remain in the vascular volume but instead leaches into the interstitial space.

This patient meets at least 3 of the 4 criteria for SIRS (ie, elevated body temperature, tachycardia, tachypnea).¹⁶ The fourth criterion is a WBC count outside the reference range (or >5% bands), but this information was not provided in the case summary. This dog also has known septic focus (septic abdomen) and thus meets criteria for sepsis.

Although all of the answer choices are partially correct, calculating the fluid balance is the most objective measure of overall volume status. Fluid balance takes into account urine production, which is affected by renal perfusion and in turn reflects volume status of patients with normally functioning kidneys. Fluid balance also takes into account total net fluid gain in the interstitium. Measuring intake and output should be standard for every ICU patient. 

How is intake and output measured? 

• Intake is total fluids a patient receives in a 24-hour period, including medications and water consumption. Output typically measures urinary and GI losses, along with any losses occurring via drains. 
  • Output measurements involve, for example, placing an indwelling urinary catheter to ascertain output; weighing absorbent cage pads, blankets, and bandages; and determining total volume output collected from drains. In addition, respiratory and cellular fluid losses must be calculated (these insensible losses are typically one-third the patient’s maintenance fluid rate). 
• The author’s preferred method of calculating maintenance rate is (30 x BW [in kg]) + 70 = mL/day. 
  • However, a heavily panting dog can lose up to 9 mL/kg/hr of free water in respiratory losses alone, so the insensible losses are a rough estimate. 
  • There is no one ideal maintenance rate to use. Other formulas (eg, 2 mL/kg/hr, 40-60 mL/kg/day) are equally fine starting points. 
  • The key is to tailor the fluid therapy plan to the patient, not necessarily adhere to a single formula for all patients.

In a majority of patients, body weight can serve as an excellent measure of overall volume status. It is one of the easiest (and least expensive) ways to measure fluid gain or loss. Any weight gain or loss should be attributed to shifts in hydration. In this dog, the problem is linked to vascular leakage syndrome (vasculitis). Fluids being administered will move into the interstitial space (an example of third-spacing). Weight will reflect the hydration status but will not accurately reflect the intravascular volume status. In general, sick patients should be weighed at least twice daily. 

For a patient with normal renal function, the USG is normally a good reflection of intravascular volume. The flaw in this method is that patients with SIRS and vascular leakage can have high specific gravity in the face of overhydration because the kidneys concentrate urine based on renal blood flow. In this dog, a high USG and low urine output may be present, as the kidneys attempt to conserve fluid even in the face of overhydration. Alternatively, acute kidney injury is common in patients with SIRS and sepsis, which can also result in misleading USG results. Because this dog’s hypotension will alter renal blood flow, establishment of normal blood pressure is essential before evaluating urine output and USG. 

One of the easiest methods to determine tissue perfusion is by monitoring lactate levels. Lactate is a product of anaerobic metabolism, and its major producers are the GI tract and muscle. Lactate levels reflect intravascular volume but do not usually reflect hydration status. High lactate simply means that a tissue bed is not receiving sufficient oxygen through perfusion. In patients (such as this dog) with both hypovolemia and overhydration, high lactate would be expected from both poor perfusion and a diffusion barrier created by interstitial edema. However, lactate level typically does not correlate well with oxygen delivery in patients with SIRS. As a general rule, a high lactate level means tissue oxygenation is poor, but a normal lactate level does not mean everything is okay.²⁰

Although all of the answer choices are partially correct, calculating the fluid balance is the most objective measure of overall volume status. Fluid balance takes into account urine production, which is affected by renal perfusion and in turn reflects volume status of patients with normally functioning kidneys. Fluid balance also takes into account total net fluid gain in the interstitium. Measuring intake and output should be standard for every ICU patient. 

How is intake and output measured? 

• Intake is total fluids a patient receives in a 24-hour period, including medications and water consumption. Output typically measures urinary and GI losses, along with any losses occurring via drains. 
  • Output measurements involve, for example, placing an indwelling urinary catheter to ascertain output; weighing absorbent cage pads, blankets, and bandages; and determining total volume output collected from drains. In addition, respiratory and cellular fluid losses must be calculated (these insensible losses are typically one-third the patient’s maintenance fluid rate). 
• The author’s preferred method of calculating maintenance rate is (30 x BW [in kg]) + 70 = mL/day. 
  • However, a heavily panting dog can lose up to 9 mL/kg/hr of free water in respiratory losses alone, so the insensible losses are a rough estimate. 
  • There is no one ideal maintenance rate to use. Other formulas (eg, 2 mL/kg/hr, 40-60 mL/kg/day) are equally fine starting points. 
  • The key is to tailor the fluid therapy plan to the patient, not necessarily adhere to a single formula for all patients.

In a majority of patients, body weight can serve as an excellent measure of overall volume status. It is one of the easiest (and least expensive) ways to measure fluid gain or loss. Any weight gain or loss should be attributed to shifts in hydration. In this dog, the problem is linked to vascular leakage syndrome (vasculitis). Fluids being administered will move into the interstitial space (an example of third-spacing). Weight will reflect the hydration status but will not accurately reflect the intravascular volume status. In general, sick patients should be weighed at least twice daily. 

For a patient with normal renal function, the USG is normally a good reflection of intravascular volume. The flaw in this method is that patients with SIRS and vascular leakage can have high specific gravity in the face of overhydration because the kidneys concentrate urine based on renal blood flow. In this dog, a high USG and low urine output may be present, as the kidneys attempt to conserve fluid even in the face of overhydration. Alternatively, acute kidney injury is common in patients with SIRS and sepsis, which can also result in misleading USG results. Because this dog’s hypotension will alter renal blood flow, establishment of normal blood pressure is essential before evaluating urine output and USG. 

One of the easiest methods to determine tissue perfusion is by monitoring lactate levels. Lactate is a product of anaerobic metabolism, and its major producers are the GI tract and muscle. Lactate levels reflect intravascular volume but do not usually reflect hydration status. High lactate simply means that a tissue bed is not receiving sufficient oxygen through perfusion. In patients (such as this dog) with both hypovolemia and overhydration, high lactate would be expected from both poor perfusion and a diffusion barrier created by interstitial edema. However, lactate level typically does not correlate well with oxygen delivery in patients with SIRS. As a general rule, a high lactate level means tissue oxygenation is poor, but a normal lactate level does not mean everything is okay.²⁰

Although all of the answer choices are partially correct, calculating the fluid balance is the most objective measure of overall volume status. Fluid balance takes into account urine production, which is affected by renal perfusion and in turn reflects volume status of patients with normally functioning kidneys. Fluid balance also takes into account total net fluid gain in the interstitium. Measuring intake and output should be standard for every ICU patient. 

How is intake and output measured? 

• Intake is total fluids a patient receives in a 24-hour period, including medications and water consumption. Output typically measures urinary and GI losses, along with any losses occurring via drains. 
  • Output measurements involve, for example, placing an indwelling urinary catheter to ascertain output; weighing absorbent cage pads, blankets, and bandages; and determining total volume output collected from drains. In addition, respiratory and cellular fluid losses must be calculated (these insensible losses are typically one-third the patient’s maintenance fluid rate). 
• The author’s preferred method of calculating maintenance rate is (30 x BW [in kg]) + 70 = mL/day. 
  • However, a heavily panting dog can lose up to 9 mL/kg/hr of free water in respiratory losses alone, so the insensible losses are a rough estimate. 
  • There is no one ideal maintenance rate to use. Other formulas (eg, 2 mL/kg/hr, 40-60 mL/kg/day) are equally fine starting points. 
  • The key is to tailor the fluid therapy plan to the patient, not necessarily adhere to a single formula for all patients.

In a majority of patients, body weight can serve as an excellent measure of overall volume status. It is one of the easiest (and least expensive) ways to measure fluid gain or loss. Any weight gain or loss should be attributed to shifts in hydration. In this dog, the problem is linked to vascular leakage syndrome (vasculitis). Fluids being administered will move into the interstitial space (an example of third-spacing). Weight will reflect the hydration status but will not accurately reflect the intravascular volume status. In general, sick patients should be weighed at least twice daily. 

For a patient with normal renal function, the USG is normally a good reflection of intravascular volume. The flaw in this method is that patients with SIRS and vascular leakage can have high specific gravity in the face of overhydration because the kidneys concentrate urine based on renal blood flow. In this dog, a high USG and low urine output may be present, as the kidneys attempt to conserve fluid even in the face of overhydration. Alternatively, acute kidney injury is common in patients with SIRS and sepsis, which can also result in misleading USG results. Because this dog’s hypotension will alter renal blood flow, establishment of normal blood pressure is essential before evaluating urine output and USG. 

One of the easiest methods to determine tissue perfusion is by monitoring lactate levels. Lactate is a product of anaerobic metabolism, and its major producers are the GI tract and muscle. Lactate levels reflect intravascular volume but do not usually reflect hydration status. High lactate simply means that a tissue bed is not receiving sufficient oxygen through perfusion. In patients (such as this dog) with both hypovolemia and overhydration, high lactate would be expected from both poor perfusion and a diffusion barrier created by interstitial edema. However, lactate level typically does not correlate well with oxygen delivery in patients with SIRS. As a general rule, a high lactate level means tissue oxygenation is poor, but a normal lactate level does not mean everything is okay.²⁰

Although all of the answer choices are partially correct, calculating the fluid balance is the most objective measure of overall volume status. Fluid balance takes into account urine production, which is affected by renal perfusion and in turn reflects volume status of patients with normally functioning kidneys. Fluid balance also takes into account total net fluid gain in the interstitium. Measuring intake and output should be standard for every ICU patient. 

How is intake and output measured? 

• Intake is total fluids a patient receives in a 24-hour period, including medications and water consumption. Output typically measures urinary and GI losses, along with any losses occurring via drains. 
  • Output measurements involve, for example, placing an indwelling urinary catheter to ascertain output; weighing absorbent cage pads, blankets, and bandages; and determining total volume output collected from drains. In addition, respiratory and cellular fluid losses must be calculated (these insensible losses are typically one-third the patient’s maintenance fluid rate). 
• The author’s preferred method of calculating maintenance rate is (30 x BW [in kg]) + 70 = mL/day. 
  • However, a heavily panting dog can lose up to 9 mL/kg/hr of free water in respiratory losses alone, so the insensible losses are a rough estimate. 
  • There is no one ideal maintenance rate to use. Other formulas (eg, 2 mL/kg/hr, 40-60 mL/kg/day) are equally fine starting points. 
  • The key is to tailor the fluid therapy plan to the patient, not necessarily adhere to a single formula for all patients.

In a majority of patients, body weight can serve as an excellent measure of overall volume status. It is one of the easiest (and least expensive) ways to measure fluid gain or loss. Any weight gain or loss should be attributed to shifts in hydration. In this dog, the problem is linked to vascular leakage syndrome (vasculitis). Fluids being administered will move into the interstitial space (an example of third-spacing). Weight will reflect the hydration status but will not accurately reflect the intravascular volume status. In general, sick patients should be weighed at least twice daily. 

For a patient with normal renal function, the USG is normally a good reflection of intravascular volume. The flaw in this method is that patients with SIRS and vascular leakage can have high specific gravity in the face of overhydration because the kidneys concentrate urine based on renal blood flow. In this dog, a high USG and low urine output may be present, as the kidneys attempt to conserve fluid even in the face of overhydration. Alternatively, acute kidney injury is common in patients with SIRS and sepsis, which can also result in misleading USG results. Because this dog’s hypotension will alter renal blood flow, establishment of normal blood pressure is essential before evaluating urine output and USG. 

One of the easiest methods to determine tissue perfusion is by monitoring lactate levels. Lactate is a product of anaerobic metabolism, and its major producers are the GI tract and muscle. Lactate levels reflect intravascular volume but do not usually reflect hydration status. High lactate simply means that a tissue bed is not receiving sufficient oxygen through perfusion. In patients (such as this dog) with both hypovolemia and overhydration, high lactate would be expected from both poor perfusion and a diffusion barrier created by interstitial edema. However, lactate level typically does not correlate well with oxygen delivery in patients with SIRS. As a general rule, a high lactate level means tissue oxygenation is poor, but a normal lactate level does not mean everything is okay.²⁰

On presentation, the patient is 7% dehydrated and weighs 4.5 kg.

Calculation of Anticipated Weight Gain with Rehydration 

• 4.5 kg × 0.07 = ≈0.32 kg
  • The patient is dehydrated by ≈0.32 kg. 
• Reminder
  • 1 mL = 1 g
  • 0.32 kg × 1000 g/kg = 320 g, or 320 mL
• The cat should gain 320 g (or 0.32 kg) when rehydrated. 
  • Over a 12-hour period, that means ≈26 mL/hr. But based on a daily maintenance rate of 60 mL/kg, the cat needs 11.25 mL/hr; hence, a total fluid rate of ≈38 mL/hr for the first 12 hours.
  • Note that any ongoing losses are not taken into consideration. 

Normosol-R is the preferred initial fluid choice. Research has shown that Normosol-R is superior to 0.9% NaCl because the former returns blood pH to normal faster than does 0.9% NaCl and the small amount of potassium contained in Normosol-R does not affect the rate of potassium decrease.²³ Realistically, any buffered isotonic crystalloid is likely to work, but published research has been on the use of Normosol-R.

Although answer choice A has the correct fluid type, the math is incorrect. Because the patient is 7% dehydrated and weighs 4.5 kg, the answer is off by a factor of 10 (see calculation above). 

For answer choice B, the math and the fluid selection are both incorrect. Again, the patient is 7% dehydrated and weighs 4.5 kg, so the answer is off by a factor of 10. In addition, a buffered fluid is recommended for treating blocked cats, and Normosol-R is the fluid investigated for these cases.²³

For answer choice D, the math is correct, but the fluid choice is not because Normosol-R is the preferred fluid choice.²³ 

On presentation, the patient is 7% dehydrated and weighs 4.5 kg.

Calculation of Anticipated Weight Gain with Rehydration 

• 4.5 kg × 0.07 = ≈0.32 kg
  • The patient is dehydrated by ≈0.32 kg. 
• Reminder
  • 1 mL = 1 g
  • 0.32 kg × 1000 g/kg = 320 g, or 320 mL
• The cat should gain 320 g (or 0.32 kg) when rehydrated. 
  • Over a 12-hour period, that means ≈26 mL/hr. But based on a daily maintenance rate of 60 mL/kg, the cat needs 11.25 mL/hr; hence, a total fluid rate of ≈38 mL/hr for the first 12 hours.
  • Note that any ongoing losses are not taken into consideration. 

Normosol-R is the preferred initial fluid choice. Research has shown that Normosol-R is superior to 0.9% NaCl because the former returns blood pH to normal faster than does 0.9% NaCl and the small amount of potassium contained in Normosol-R does not affect the rate of potassium decrease.²³ Realistically, any buffered isotonic crystalloid is likely to work, but published research has been on the use of Normosol-R.

Although answer choice A has the correct fluid type, the math is incorrect. Because the patient is 7% dehydrated and weighs 4.5 kg, the answer is off by a factor of 10 (see calculation above). 

For answer choice B, the math and the fluid selection are both incorrect. Again, the patient is 7% dehydrated and weighs 4.5 kg, so the answer is off by a factor of 10. In addition, a buffered fluid is recommended for treating blocked cats, and Normosol-R is the fluid investigated for these cases.²³

For answer choice D, the math is correct, but the fluid choice is not because Normosol-R is the preferred fluid choice.²³ 

On presentation, the patient is 7% dehydrated and weighs 4.5 kg.

Calculation of Anticipated Weight Gain with Rehydration 

• 4.5 kg × 0.07 = ≈0.32 kg
  • The patient is dehydrated by ≈0.32 kg. 
• Reminder
  • 1 mL = 1 g
  • 0.32 kg × 1000 g/kg = 320 g, or 320 mL
• The cat should gain 320 g (or 0.32 kg) when rehydrated. 
  • Over a 12-hour period, that means ≈26 mL/hr. But based on a daily maintenance rate of 60 mL/kg, the cat needs 11.25 mL/hr; hence, a total fluid rate of ≈38 mL/hr for the first 12 hours.
  • Note that any ongoing losses are not taken into consideration. 

Normosol-R is the preferred initial fluid choice. Research has shown that Normosol-R is superior to 0.9% NaCl because the former returns blood pH to normal faster than does 0.9% NaCl and the small amount of potassium contained in Normosol-R does not affect the rate of potassium decrease.²³ Realistically, any buffered isotonic crystalloid is likely to work, but published research has been on the use of Normosol-R.

Although answer choice A has the correct fluid type, the math is incorrect. Because the patient is 7% dehydrated and weighs 4.5 kg, the answer is off by a factor of 10 (see calculation above). 

For answer choice B, the math and the fluid selection are both incorrect. Again, the patient is 7% dehydrated and weighs 4.5 kg, so the answer is off by a factor of 10. In addition, a buffered fluid is recommended for treating blocked cats, and Normosol-R is the fluid investigated for these cases.²³

For answer choice D, the math is correct, but the fluid choice is not because Normosol-R is the preferred fluid choice.²³ 

On presentation, the patient is 7% dehydrated and weighs 4.5 kg.

Calculation of Anticipated Weight Gain with Rehydration 

• 4.5 kg × 0.07 = ≈0.32 kg
  • The patient is dehydrated by ≈0.32 kg. 
• Reminder
  • 1 mL = 1 g
  • 0.32 kg × 1000 g/kg = 320 g, or 320 mL
• The cat should gain 320 g (or 0.32 kg) when rehydrated. 
  • Over a 12-hour period, that means ≈26 mL/hr. But based on a daily maintenance rate of 60 mL/kg, the cat needs 11.25 mL/hr; hence, a total fluid rate of ≈38 mL/hr for the first 12 hours.
  • Note that any ongoing losses are not taken into consideration. 

Normosol-R is the preferred initial fluid choice. Research has shown that Normosol-R is superior to 0.9% NaCl because the former returns blood pH to normal faster than does 0.9% NaCl and the small amount of potassium contained in Normosol-R does not affect the rate of potassium decrease.²³ Realistically, any buffered isotonic crystalloid is likely to work, but published research has been on the use of Normosol-R.

Although answer choice A has the correct fluid type, the math is incorrect. Because the patient is 7% dehydrated and weighs 4.5 kg, the answer is off by a factor of 10 (see calculation above). 

For answer choice B, the math and the fluid selection are both incorrect. Again, the patient is 7% dehydrated and weighs 4.5 kg, so the answer is off by a factor of 10. In addition, a buffered fluid is recommended for treating blocked cats, and Normosol-R is the fluid investigated for these cases.²³

For answer choice D, the math is correct, but the fluid choice is not because Normosol-R is the preferred fluid choice.²³ 

As mentioned in the question 6 discussion, ongoing fluid losses were not taken into consideration. Thus, the calculated fluid rate is not accommodating the cat’s ongoing urinary losses, leading to additional weight loss. Ongoing dehydration, not overhydration, is therefore the primary concern, and the fluid therapy rate needs to be adjusted accordingly. 

Key Points

• The cat produced 30 mL/hr of urine (total 120 mL over 4 hours), far in excess of the fluid maintenance rate being provided (11.25 mL/hr).
• The maintenance rate requires normal renal function, as previously discussed. 
  • Postobstructive diuresis, common in cats following urethral obstruction, occurs because of a variety of functional abnormalities, including tubular pressure necrosis, medullary washout, and alterations in antidiuretic hormone (ADH) responsiveness. 
  • In one study, 46% of cats with urethral obstruction had postobstructive diuresis defined as urine production >2 mL/kg/hr.²⁵
  • It is important to keep up with these losses until the kidneys regain normal function, especially since overall volume depletion can occur very quickly in these patients.²⁶ 

The ongoing loss should be calculated at 30 mL/hr, in addition to the cat’s base rate (maintenance plus dehydration) of ≈38 mL/hr for a total of ≈68 mL/hr. Simply increasing the fluid rate to 46 mL/hr would only add 8 mL/hr to the fluid treatment plan, which would not compensate for the rate of ongoing loss. 

Each time the urine collection bag is emptied (typically q4h), ongoing loss should be calculated and fluid rate reassessed. After the initial rehydration period of 12 hours, fluid rate and patient needs should again be reassessed to reflect the current overall volume status.

As mentioned in the question 6 discussion, ongoing fluid losses were not taken into consideration. Thus, the calculated fluid rate is not accommodating the cat’s ongoing urinary losses, leading to additional weight loss. Ongoing dehydration, not overhydration, is therefore the primary concern, and the fluid therapy rate needs to be adjusted accordingly. 

Key Points

• The cat produced 30 mL/hr of urine (total 120 mL over 4 hours), far in excess of the fluid maintenance rate being provided (11.25 mL/hr).
• The maintenance rate requires normal renal function, as previously discussed. 
  • Postobstructive diuresis, common in cats following urethral obstruction, occurs because of a variety of functional abnormalities, including tubular pressure necrosis, medullary washout, and alterations in antidiuretic hormone (ADH) responsiveness. 
  • In one study, 46% of cats with urethral obstruction had postobstructive diuresis defined as urine production >2 mL/kg/hr.²⁵
  • It is important to keep up with these losses until the kidneys regain normal function, especially since overall volume depletion can occur very quickly in these patients.²⁶ 

The ongoing loss should be calculated at 30 mL/hr, in addition to the cat’s base rate (maintenance plus dehydration) of ≈38 mL/hr for a total of ≈68 mL/hr. Simply increasing the fluid rate to 46 mL/hr would only add 8 mL/hr to the fluid treatment plan, which would not compensate for the rate of ongoing loss. 

Each time the urine collection bag is emptied (typically q4h), ongoing loss should be calculated and fluid rate reassessed. After the initial rehydration period of 12 hours, fluid rate and patient needs should again be reassessed to reflect the current overall volume status.

As mentioned in the question 6 discussion, ongoing fluid losses were not taken into consideration. Thus, the calculated fluid rate is not accommodating the cat’s ongoing urinary losses, leading to additional weight loss. Ongoing dehydration, not overhydration, is therefore the primary concern, and the fluid therapy rate needs to be adjusted accordingly. 

Key Points

• The cat produced 30 mL/hr of urine (total 120 mL over 4 hours), far in excess of the fluid maintenance rate being provided (11.25 mL/hr).
• The maintenance rate requires normal renal function, as previously discussed. 
  • Postobstructive diuresis, common in cats following urethral obstruction, occurs because of a variety of functional abnormalities, including tubular pressure necrosis, medullary washout, and alterations in antidiuretic hormone (ADH) responsiveness. 
  • In one study, 46% of cats with urethral obstruction had postobstructive diuresis defined as urine production >2 mL/kg/hr.²⁵
  • It is important to keep up with these losses until the kidneys regain normal function, especially since overall volume depletion can occur very quickly in these patients.²⁶ 

The ongoing loss should be calculated at 30 mL/hr, in addition to the cat’s base rate (maintenance plus dehydration) of ≈38 mL/hr for a total of ≈68 mL/hr. Simply increasing the fluid rate to 46 mL/hr would only add 8 mL/hr to the fluid treatment plan, which would not compensate for the rate of ongoing loss. 

Each time the urine collection bag is emptied (typically q4h), ongoing loss should be calculated and fluid rate reassessed. After the initial rehydration period of 12 hours, fluid rate and patient needs should again be reassessed to reflect the current overall volume status.

As mentioned in the question 6 discussion, ongoing fluid losses were not taken into consideration. Thus, the calculated fluid rate is not accommodating the cat’s ongoing urinary losses, leading to additional weight loss. Ongoing dehydration, not overhydration, is therefore the primary concern, and the fluid therapy rate needs to be adjusted accordingly. 

Key Points

• The cat produced 30 mL/hr of urine (total 120 mL over 4 hours), far in excess of the fluid maintenance rate being provided (11.25 mL/hr).
• The maintenance rate requires normal renal function, as previously discussed. 
  • Postobstructive diuresis, common in cats following urethral obstruction, occurs because of a variety of functional abnormalities, including tubular pressure necrosis, medullary washout, and alterations in antidiuretic hormone (ADH) responsiveness. 
  • In one study, 46% of cats with urethral obstruction had postobstructive diuresis defined as urine production >2 mL/kg/hr.²⁵
  • It is important to keep up with these losses until the kidneys regain normal function, especially since overall volume depletion can occur very quickly in these patients.²⁶ 

The ongoing loss should be calculated at 30 mL/hr, in addition to the cat’s base rate (maintenance plus dehydration) of ≈38 mL/hr for a total of ≈68 mL/hr. Simply increasing the fluid rate to 46 mL/hr would only add 8 mL/hr to the fluid treatment plan, which would not compensate for the rate of ongoing loss. 

Each time the urine collection bag is emptied (typically q4h), ongoing loss should be calculated and fluid rate reassessed. After the initial rehydration period of 12 hours, fluid rate and patient needs should again be reassessed to reflect the current overall volume status.