The heart serves as the pump of the conduit. The conduit for fluid transport is the vascular system. Carried by hemoglobin to the capillaries, oxygen normally diffuses with great ease through the capillary membrane to the cells, most of which are located less than 50 micrometers from a capillary. Oxygen and glucose are transported from the intravascular space to the cell through a fluid medium. In contrast to 38 ATP molecules that are produced during aerobic metabolism, anaerobic metabolism produces lactate and only 2 ATP molecules per glucose molecule. These membrane transport systems occur in every cell in every organ, and require energy to function.Įnergy required to drive transmembrane ion exchange is supplied by cleavage of adenosine triphosphate (ATP). Membrane ion pumps also regulate intracellular calcium, hydrogen, chloride, magnesium, glucose and amino acid concentration.

The primary active pump for solute transport across the cell membrane is the sodium-potassium pump. Transmembrane ion pumps regulate intracellular water maintaining cellular and organelle integrity.

Fluid moves into the interstitial space when intravascular hydrostatic pressure is increased over COP, membrane pore size increases, or intravascular COP becomes lower than interstitial COP. The hydrostatic pressure within the capillary is the pressure forcing outward on the capillary 'membrane' generated by the blood pressure and cardiac output. Albumin is the most numerous and the smallest, approximately 69,000 daltons. The natural particles in blood that create COP are proteins-globulins, fibrinogen, and albumin. The amount of fluid that moves across the capillary 'membrane' depends on a number of factors, to include: capillary colloid oncotic pressure, hydrostatic pressure, and permeability. Any particle movement between the interstitium and the cell must occur through some transport mechanism (e.g., channel, ion pump, carrier mechanism).įluids are in a constant state of flux across the capillary endothelial membrane, through the interstitium and into and out of the cell. This membrane is freely permeable to water but not small or large molecular weight particles. The intracellular compartment is separated from the interstitial space by a cell membrane.

Fluids support the matrix and cells within the interstitial space. The interstitial compartment is that space between the capillaries and the cells. Gases such as oxygen and carbon dioxide diffuse freely through the capillary endothelial cell to enter or exit the intravascular compartment. This capillary 'membrane' is freely permeable to water and small molecular weight particles such as ions, glucose, acetate, lactate, gluconate, and bicarbonate. A capillary 'membrane, consisting of capillary endothelial cells and the subendothelial cell matrix separates the capillary intravascular space from the interstitial fluid compartment. Fluid movement from the intravascular to interstitial and intracellular compartments occurs at the capillary. There are 3 major fluid compartments intravascular, interstitial and intracellular. The ability to create an effective fluid resuscitation plan depends on understanding the pathophysiology of shock and the different body fluid compartments and the dynamics of fluid movement and distribution between fluid compartments.īody Fluid Compartments and Fluid Dynamics A positive outcome is optimized by rapid and aggressive fluid resuscitation, with hemostasis employed as required. Significant loss of intravascular volume, or hypovolemia, can result from many causes, to include: trauma, loss of plasma water during vomiting and diarrhea, extreme venodilation from systemic inflammation, and significant hemorrhage. Shock is a phenomenon of ineffective circulating volume. Decompensation will be directly related to Airway, Breathing and/or Circulatory failure. A rapid assessment must determine whether the animal has decompensated or is likely to decompensate. Small animals in crisis will present for a myriad of reasons: vomiting, diarrhea, bloat, urinary obstruction, dystocia, trauma.the list is endless. 'The single most important factor in successful resuscitation from shock is time: rapid expeditious therapy in the early stages may lead to good results, but adequate therapy that is delayed may be ineffective.' (Shoemaker, W.C)

Box diagram of body fluid compartments