Juan Carlos Villalba González, MD
Comité Editorial Revista Colombiana de Anestesia y Reanimación Anestesiólogo Hospital Cardiovascular del Niño de Cundinamarca

How do we approach fluid management during surgery? The answers are based on physiological, hemodynamic, pathological, pharmacodynamic and occasionally, geographical concepts (1).

What type of solution should we choose? A few limitations can be mentioned. In our country -and probably in other countries of the region-some preparations are not available. Such is the case of dextrose in 0.45 % saline solution (or at least it is not broadly marketed). The use of gels is limited in some countries; in the particular case of the United States, gels were removed from the market due to the high frequency of allergic reactions. This has somewhat restricted clinical research and the subsequent use and development of the products. The pharmaceutical industry develops new synthetic colloids (i.e., hidroxietilstarch) that exhibit less side effects (renal damage [2], allergic reactions and clotting disorders).

These new solutions have a lower molecular weight and molar substitution (hidroxyethyl groups over the number of glucose units) less than 0.5 (3). Although the consensus is intended for adult patients, some of its conclusions can be extrapolated to children. For example, our pediatric colleagues usually administer isotonic solutions that may cause post-operative hyperglycemia. Holliday and Segar's formula for fasting fluid maintenance in pediatric patients evolved into the 4-2-1 rule; however, this rule has lost popularity as a result of new preoperative fasting guidelines that prescribe the intake of clear fluids up two hours prior to surgery (3). In addition to the adapted Holliday and Segar's formula corrected for fasting when required, several other simple formulae have been published. However, it was found that in healthy adults with no fasting fluid replacement the blood volume remained unchanged (4).

The follow-up of fluid balance measuring inputs and losses is essentially the roadmap for managing fluids and clinical signs; such is the case of capillary refilling as part of the basic instruments for perfusion monitoring. Urinary output is also part of this evaluation, though its relationship with volemia and perfusion not always represents the reality of the situation. Urinary output should be measured to assess the systemic volume, with two concepts in mind: low urinary output is not always an indication of a decreased systemic output (increased sympathetic tone due to surgical stress, in addition to anti-diuretic hormone release) and an intraoperative decrease of urinary output is not necessarily linked to renal dysfunction.

In terms of surveillance and follow-up of plasma volume, other technologies have been developed in addition to the traditional measurements to assess volume. There are new output measurement systems based on Doppler waves or changes in the amplitude of the pulse curve, that theoretically show an improved correlation to intravascular volume, as opposed to the traditional central venous pressure (CVP) measurement or the wedge pressure poorly related to the effective volume. However, this new technology does not show yet any superiority as compared to conventional monitoring. Moreover, follow-up using technologies to assess volemia, has not provided conclusive results in terms of reduced mortality (5).

The use of drugs for improving the hemodynamic performance in critical patients has shown discouraging results. In a meta-regression analysis, low dose Dopexamine (a β-2 dopa-agonist) (6) was found to reduce mortality in critical patients; later on, Gopal et al. (7), showed the opposite results in a meta-analysis. The Editorial in Anaesthesia: "Meta-analyses of the effects of dopexamine in major surgery: do all roads lead to Rome?" (8), discusses the arguments, strengths and weaknesses of these two trials (meta-regression versus meta-analysis) and concludes that for the time being, the use of dopexamine in critical patients shall be decided on a patient-by-patient basis, until an adequate trial settles the conlict.

The long debate over crystalloids and colloids has yielded some positive results in favor of colloids on very specific issues; for the time being, a Cochrane's review on surgical patients shows no difference in terms of major outcomes when any of the two solutions were administered (9,10).

With regards to the amount of fluid to be replaced, a strict luid management policy makes the difference. Exaggerated luid replacement causes edema and weight gain during the postoperative period. Such weight gain has a negative impact delaying healing, affects the lungs and slows down the gut peristalsis in patients undergoing colorectal surgery (11), in addition to increasing mortality (although it's impossible to determine whether it was the cause or the effect) (12).

On the other hand, an intensive fluid treatment in patients undergoing abdominal surgery increases tissue oxygenation, but excess luids may affect clotting, cardiac and lung function, healing, intestinal anastomosis, renal failure and extended hospital stay. The use of vasopressors instead of luids for regional anesthesia patients focuses on managing vasodilation and is corrected in the immediate postoperative period. Chappell's review article offers three conclusions: a) a luid-consuming third space does not exist; b) evaporation losses are maximum 1 ml/kg/hr, even under gut exposure, a concept that differs from the idea of replacing up to 8 cm³/kg/h of surgery; c) extracellular deficit after usual fasting is low.

Fluid therapy shall be managed rationally and taking into consideration the individual patient's conditions in terms of any positive and deleterious effects. Side effects are a constant challenge and should not be neglected.

REFERENCES

1. Powell-Tuck J, Gosling P, Lobo D, Allison S, Carlson GL, Gore M, et al. British Consensus Guidelines on Intravenous Fluid Therapy for Adult Surgical Patients (GIFTASUP). [Internet] Available from: http://www.ics.ac.uk/intensive_care_professional/standards_and_guidelines/british_consensus_gui-delines_on_intravenous_fluid_therapy_for_adult_surgical_patients_giftasup_2008. Accesed on April,2010.

2. Claus RA, Sossdorf M, Hartog C. The effects of hydroxyethyl starch on culture renal epithelial cells. Anesth Analg. 2010,110(2):300-1.

3. Bailey AN, McNaull PP, Jooste E, Tuchman J B. Perioperative cristalloid and colloid fluid Management in children: where are we and how did we get here? Anesth Analg. 2010;110(2):375-90.

4. Jacob M, Chappell D, Conzen P, Finsterer U, Rehm M. Blood volume in normal after preoperative overnight fasting. Acta Anaesthesiol Scand. 2008;52(4):522-9.

5. Leibowitz A. Hemodynamic monitoring: from central venous pressure to pulse contour analysis. ASA Reflecher Courses in Anesthesiology. 2009;37(1):119-29.

6. Gopal S, Jayakumar D, Nelson P N. Meta-analysis on the effect of dopexamine on in-hospital mortality. Anaesthesia. 2009;64(6):589-94.

7. Pearse RM, Belsey JD, Cole JN, Bennett ED. Effect of dopexamine infusion on mortality following major surgery: individual patient data meta-regression analysis of published clinical trials. Crit Care Med. 2008;36(4):1323-9.

8. Pandit JJ. Meta-analyses of the effects of dopexamine in major surgery: do all roads lead to Rome? Anaesthesia. 2009; 64(6):585-8.

9. Perel P, Roberts I. Colloids versus crystalloids for fluid resuscitation in critically ill patients. Cochrane Database Syst Rev. 2007;(4):CD000567.

10. Bunn F, Trivedi D, Ashraf S. Colloid solutions for fluid resuscitation. Cochrane Database Syst Rev. 2008;(1):CD001319.

11. Grocott MP, Mythen MG, Gan TJ. Perioperative fluid management and clinical outcomes in adults. Anesth Analg. 2005;100(4):1093-106.

12. Chappell D, Jacob M, Hofmann-Kiefer K, Conzen P, Rehm M. A rational aproach to perioperative fluid magement. Anesthesiology 2008;109(4):723-40.

1. Powell-Tuck J, Gosling P, Lobo D, Allison S, Carlson GL, Gore M, et al. British Consensus Guidelines on Intravenous Fluid Therapy for Adult Surgical Patients (GIFTASUP). [Internet] Available from: http://www.ics.ac.uk/intensive_care_professional/ standards_and_guidelines/british_consensus_guidelines_ on_intravenous_fluid_therapy_for_adult_ surgical_patients__giftasup__2008. Accesed on April,2010.        [ Links ]

2. Claus RA, Sossdorf M, Hartog C. The effects of hydroxyethyl starch on culture renal epithelial cells. Anesth Analg. 2010,110(2):300-1.        [ Links ]

3. Bailey AN, McNaull PP, Jooste E, Tuchman J B. Perioperative cristalloid and colloid fluid Management in children: where are we and how did we get here? Anesth Analg. 2010;110(2):375-90.        [ Links ]

4. Jacob M, Chappell D, Conzen P, Finsterer U, Rehm M. Blood volume in normal after preoperative overnight fasting. Acta Anaesthesiol Scand. 2008;52(4):522-9.        [ Links ]

5. Leibowitz A. Hemodynamic monitoring: from central venous pressure to pulse contour analysis. ASA Reflecher Courses in Anesthesiology. 2009;37(1):119-29.        [ Links ]

6. Gopal S, Jayakumar D, Nelson P N. Meta-analysis on the effect of dopexamine on in-hospital mortality. Anaesthesia. 2009;64(6):589-94.        [ Links ]

7. Pearse RM, Belsey JD, Cole JN, Bennett ED. Effect of dopexamine infusion on mortality following major surgery: individual patient data meta-regression analysis of published clinical trials. Crit Care Med. 2008;36(4):1323-9.        [ Links ]

8. Pandit JJ. Meta-analyses of the effects of dopexamine in major surgery: do all roads lead to Rome? Anaesthesia. 2009; 64(6):585-8.        [ Links ]

9. Perel P, Roberts I. Colloids versus crystalloids for fluid resuscitation in critically ill patients. Cochrane Database Syst Rev. 2007;(4):CD000567.        [ Links ]

10. Bunn F, Trivedi D, Ashraf S. Colloid solutions for fluid resuscitation. Cochrane Database Syst Rev. 2008;(1):CD001319.        [ Links ]

11. Grocott MP, Mythen MG, Gan TJ. Perioperative fluid management and clinical outcomes in adults. Anesth Analg. 2005;100(4):1093-106.        [ Links ]

12. Chappell D, Jacob M, Hofmann-Kiefer K, Conzen P, Rehm M. A rational aproach to perioperative fluid magement. Anesthesiology 2008;109(4):723-40.        [ Links ]