Fluid administration during and after surgery is an essential part of postoperative care to maintain the patients' fluid and biochemical balance. Abdominal surgical procedures are associated with dehydration from preoperative fasting, bowel preparation, and intra- and postoperative fluid and electrolyte loss. So, perioperative fluid management has been a topic of much debate over years and has intensified especially over the past several years.

The controversies include the type of fluid, the timing of administration and the volume administrated. Following much discussion and ongoing controversy on colloids versus crystalloids and the ideal composition of the various intravenous solutions, the main focus more recently has been on the volume of fluids.

Fluid therapy strategies have been developed and implemented in clinical practice over several decades. The data suggest that aggressive or liberal intraoperative fluid resuscitation is harmful during open abdominal operation, whereas a restrictive fluid protocol has better outcomes, including fewer postoperative complications and a shorter discharge time.

However, a restrictive fluid regimen has several limitations. Overly restricted or inadequate fluid administration may lead to insufficient intravascular volume, tissue hypoperfusion, cellular oxygenation impairment and potential organ dysfunction, prolonged recovery of bowel function, and impair tissue oxygenation, which might ultimately impair wound healing including healing of anastomosis.

Recently, the pleth-variability index (PVI) derived from respiratory variations in peripheral perfusion index (PI) has been suggested to be an effective dynamic indicator of fluid responsiveness. Different from other invasive dynamic indices, PVI provides clinicians with a numerical value obtained non-invasively. PVI is calculated as [(PI max - PI min)/PI max] X 100, where PI max and PI min represent the maximal and the minimal value, respectively, of the plethysmographic perfusion index (PI) over one respiratory cycle. PI is the ratio between pulsatile and non-pulsatile infrared light absorption from the pulse oximeter, and it is physiologically equivalent to the amplitude of the plethysmographic waveform. A PVI value of >13% before volume expansion discriminated between fluid responders and non responders with 81% sensitivity and 100% specificity.

Inclusion Criteria:

1. Adult patients scheduled for colorectal surgery
2. American Society of Anesthesiologists grade I-II.

Exclusion criteria:

1. patient refusal.
2. psychiatric disorders.
3. pregnancy and lactation.
4. preexisting neurological dysfunction ( history of cerebrovascular stroke CVS)
5. Allergy to any protocol medication.
6. metastatic cancer.
7. Inflammatory bowel disease.
8. Coronary artery disease with impaired cardiac function.
9. Diabetes mellitus.
10. Renal insufficiency (serum creatinine level more than 180 μmol/l).
11. unexpected intraoperative findings (small bowel obstruction, inoperable).
12. accidental massive intraoperative haemorrhage.