Hypervolemia

The weight gain is the outcome signal - In postsurgical ICU patients, weight gain greater than 10% of preoperative weight carried a mortality of 31.6% against 10.3% in those who stayed under 10%, and mortality kept climbing with further gain. Postoperative weight against the preoperative baseline is the cheapest measure of how much fluid you left behind.

What it does to the lungs - Postoperative pulmonary edema has been documented when administered volume exceeded 67 mL/kg/h, a rate that shows up in real practice. Even in healthy volunteers, 40 mL/kg of lactated Ringer's over 3 hours produced significant falls in forced vital capacity and FEV1 that persisted 8 hours past the end of the bolus, with a median 0.85 kg weight gain still present at 24 hours.

What it does to the gut - In an animal anastomosis model, bowel manipulation alone raised intestinal tissue weight 5% to 10% at the anastomosis and 5 cm from the suture line. Adding intraoperative crystalloid at 5 mL/kg/h added another 5%, and that edema was still present at the anastomosis 5 days later. That is the argument for restraint in bowel surgery specifically.

The quieter costs - Gross tissue edema lowers tissue oxygen tension and impairs wound healing. Prolonged ileus and impaired coagulation belong on the same list and are now getting the attention pulmonary edema and cardiac compromise have always had.

Static numbers will not tell you - Urine output and blood pressure are the traditional intraoperative surrogates and they are poor ones. Volume status is better read from dynamic indices that exploit the respiratory cycle in a positive-pressure-ventilated patient: stroke volume variation, pulse pressure variation, systolic pressure variation and the pleth variability index.

Why the dynamic indices work - Positive-pressure inspiration drops left ventricular preload; exhalation refills it, effectively test-dosing volume responsiveness on every breath. On the steep part of the Frank-Starling curve the stroke volume swings with each breath, so a high stroke volume variation means the patient will respond to preload. Flat curve, minimal variation — more fluid only overloads the heart.

Goal-directed rather than calculated - Goal-directed therapy titrates to a measured endpoint such as cardiac output instead of to a formula. Continuous cardiac output was historically thermodilution through a central catheter; esophageal Doppler monitoring and arterial-waveform devices such as FloTrac/Vigileo and PiCCO plus give the same read with less invasion.

Know who arrives already wet - Renal failure, congestive heart failure, liver failure and excess sodium intake all set the patient up before you start. In these patients the room for the standard formula is small and the pulmonary consequence arrives faster.

Hypervolemia is an increase in circulating blood volume. Medically it follows renal failure, congestive heart failure, liver failure, excessive sodium intake, or any other failure of sodium regulation — sodium is retained, water follows, plasma volume rises. Uncontrolled, it fills the extravascular spaces as peripheral edema, pulmonary edema and ascites.

Perioperatively the cause is usually us. The traditional intraoperative fluid equation — maintenance, NPO deficit, estimated blood loss, and third-space losses — rests on research performed more than 50 years ago and was built to prevent hypovolemia at almost any cost. It produces a high prevalence of postoperative fluid overload, with surgical patients gaining an average of 3 to 10 kg after major procedures. The target has shifted from avoiding hypovolemia to maintaining euvolemia.