The oxygen debt response correlated significantly with base deficit and lactate, but not blood pressure. The dogs that received
the 30 percent immediate resuscitation showed the mildest organ dysfunction with a complete recovery at seven days. Early,
small volume, hypotensive resuscitation may prove to be the best treatment for resuscitation in patients with hemorrhagic
Colloids versus crystalloids
The debate over colloids versus crystalloids for resuscitation has existed for more than five decades now and will likely
not be over anytime soon. Although evidence-based medicine is the preferable method of making therapeutic decisions for patients,
it is the vulnerability of the present evidence on this matter that intensifies the controversy. There are enough studies
on the issue to sustain 11 systematic reviews or meta-analyses or quantitative data syntheses. However, the suboptimal quality
of most of the primary studies, which is subsequently imparted to the systematic reviews, does nothing to ameliorate the situation.
In reality, the use of colloid or crystalloid fluids varies considerably and depends primarily on personal choices, availability,
clinical experience and cost.
If a review of the literature examining colloid versus crystalloid resuscitation for the critically ill patient is performed,
the combined results suggest that the choice of resuscitative fluid has a small or no effect on mortality. In contrast, however,
considering only trauma patients, the results suggest that the use of colloids carries an increase in mortality. Should crystalloids
therefore remain preferable in the initial treatment of animals with traumatic shock?
The use of synthetic colloids has been shown to alter the coagulation profile and immune response. There has been extensive
research in Europe investigating novel synthetic colloid products that do not interfere with coagulation and perhaps even
positively modulate the inflammatory response following infusion and prevent or correct capillary leak syndromes. By increasing
the C2:C6 ratio and decreasing the molar substitution to 0.4, a new hydroxyethyl starch (HES) product with a molecular weight
of 130,000 has been introduced in Europe (Voluven®).
This solution has minimal effects on coagulation, does not accumulate in plasma after multiple dosing, and may help to minimize
endothelial damage and "seal the leaks" in the capillaries, as other HES preparations have also claimed to do.
Small volume resuscitation
The use of hypertonic saline (HS) for resuscitation has been studied extensively. HS increases the blood volume by 2.5- to
3-times the volume infused and HSD by 3- to 4-times the volume infused, making these fluids impressively efficient compared
to isotonic crystalloids (0.8 times volume infused) or even synthetic colloids (about 2 times the volume infused for Hetastarch
and Dextran 70). The benefits of hypertonic, small volume resuscitation have repeatedly been shown to restore hemodynamic
stability, restore splanchnic organ perfusion, attenuate neutrophil migration, reduce increases in post-resuscitation intracranial
pressure, decrease cardiac troponin-I levels and lower pulmonary capillary wedge pressures.
There have been numerous studies in both experimental and clinical dogs examining the use of HSD for resuscitation from severe
burns, pyometra with septic shock, traumatic shock, endotoxemia, hemorrhagic shock and gastric dilatation volvulus. Results
are favorable overall, with an increase in mean arterial blood pressure, cardiac output, oxygen delivery and consumption,
superoxide dismutase levels and minimal side effects were noted.
Future strategies and directions
Shock-induced depletion of energy stores was first recognized in the 1940s by Le Page. It is clear that the ATP levels in
the liver, kidney and gastrointestinal tract are depleted rapidly, and correspondingly the metabolites are elevated during
and after resuscitation from shock. Since hypoxanthine and xanthine are well-known substrates for xanthine oxidase, their
accumulation during ischemia indubitably contributes to a burst of free-radical activity during reperfusion of the tissues.
Thus, it is well proven that lipid peroxidation by oxygen-derived free radicals plays a large role in the morbidity and mortality
associated with shock. Much of the current research is focusing on pharmacologic agents that might be used in conjunction
with fluid therapy to limit the extent of depletion of cellular and tissue ATP by increasing ATP levels in the tissues and
lowering xanthine and hypoxanthine levels during, and after, resuscitation. These include glutamine, crocein, ketone bodies
and pyruvate-containing fluid strategies.
Perfluorochemicals are chemically synthetic molecules that consist primarily of carbon and fluorine atoms, and have been used
to dissolve oxygen since 1966. The use of perfluorocarbon solutions to replace red blood cells for oxygen delivery was first
demonstrated in 1968. Subsequent studies in 1994 and 1995 have looked at these solutions for the treatment of hemorrhagic
shock in dogs. The use of perfluorocarbon resuscitation resulted in greater survival compared to lactated Ringer's solution.
Further research may shed more light on these fluids.