IV crystalloids are generally considered first-line fluids except for children with hemorrhagic shock and dissociative shock In terms of crystalloid solution choice, several interventional trials in adults show decreased mortality and decreased kidney injury with preferential use of balanced fluids for resuscitation rather than 0.9% saline, though additional confirmatory trials are ongoing In children with septic shock, several studies demonstrate an association of increased mortality with hyperchloremia, which can be seen in the setting of large-volume saline resuscitation However, retrospective pediatric studies comparing balanced fluids to 0.9% saline have reported conflicting results and 0.9% saline has the relative benefits of low cost and universal compatibility compared to Plasma-Lyte and lactated Ringer’s (LR), respectively Until further data become available, use of crystalloids (either 0.9% saline or balanced fluids such as LR or Plasma-Lyte) is generally more common than colloids for initial fluid resuscitation due to their availability, ease of administration, and low cost There is evidence supporting a risk of kidney injury with the use of synthetic colloids, such as hydroxyethyl starch, and its use is currently not recommended by the Surviving Sepsis Campaign The use of blood products for volume expansion is another important consideration, especially in hemorrhagic shock The Advanced Trauma Life Support guidelines recommend resuscitation with crystalloid and blood products for classes III and IV hemorrhagic shock (see Chapter A General Approach to the Ill or Injured Child for more details on trauma) Based on early studies of adult septic shock and subsequent pediatric studies red blood cell (RBC) transfusion has typically been recommended to maintain a goal hemoglobin >10 g/dL and an ScvO2 >70% for children with fluid-refractory septic shock during the early stages of resuscitation However, while RBC transfusion can increase blood oxygen content, adverse effects can occur (e.g., transfusion-related acute lung injury, immune suppression, or circulatory overload) RBCs also tend to aggregate and obstruct the microcirculation in states of systemic inflammation and endothelial activation (as with sepsis), and transfused RBCs may be less efficient at delivering oxygen to vital organs due to a reduction in 2,3diphosphoglycerate content and other changes during storage Data from two adult randomized trials recently demonstrated that a hemoglobin threshold of to 7.5 g/dL before transfusion provided similar outcomes as a higher hemoglobin threshold Consequently, recent consensus guidelines for RBC transfusion in children were unable to reach consensus regarding the optimal transfusion threshold for critically ill children with unstable nonhemorrhagic shock