Intravascular fluid volume,
Left ventricular filling pressure,
Systemic blood pressure,
and ultimately, oxygen delivery to tissues
Rational approach to fluid management
In addition to surgical considerations (blood loss, evaporative loss, third spacing), certain conditions and changes that occur during the perioperative period can make the management of fluid balance a challenge, including preoperative:
fluid volume status, preexisting disease states,and the effect of anesthetic drugs on normal physiology
Management of fluid therapy
Management of fluid therapy may influence intraoperative and postoperative morbidity and mortality.
Providing sufficient intravascular fluid volume is essential for adequate perfusion of vital organs.
Although quantitative considerations are of primary concern, oxygen carrying capacity, coagulation, and electrolyte and acid-base balance are also of critical importance.
Preoperative assessment of intravascular fluid volume is important before induction of anesthesia.
Common causes of preoperative hypovolemia:
Bowel preparations, vomiting, diarrhea, diaphoresis, hemorrhage, burns, and inadequate intake
Redistribution of intravascular fluid volume without evidence of external loss is another important cause of preoperative volume depletion.
Examples: patients with sepsis, adult respiratory distress syndrome, ascites, pleural effusions, and bowel abnormalities.
Often, these processes are accompanied by increased capillary permeability resulting in loss of intravascular fluid volume to interstitial and other fluid compartments.
Evaluation of intravascular fluid volume relies on indirect measurements such as systemic blood pressure, heart rate, and urine output because measurements of fluid compartments are not readily available.
Even with sophisticated monitoring techniques (pulmonary artery catheters, arterial oxygen saturation), the adequacy of intravascular fluid volume replacement and tissue oxygen delivery to individual vital organs cannot be precisely determined.
For these reasons, clinical evaluation of intravascular fluid volume is necessary