I. Pendulum swings again: crystalloid or colloid fluid therapy?

Abstract

Since the 1980s, evidence has been accumulating that survivors of major surgery generate a higher postoperative cardiac output than non-survivors, and that achieving a supranormal oxygen delivery to the body’s major organs (DO2, normally .1000 ml O2 min ) in the perioperative period, using supplementary i.v. fluids combined with inotropes, could improve survival in high-risk patients. – 3 A recent Cochrane Systematic Review identified 31 studies (including 5292 participants) that studied the perioperative increase in global blood flow to explicit defined goals. Of these, 28 were single-centre and included ,200 participants. One large multi-centre studydominated the results of the analysis. While no difference in mortality was found, colloid-based, individualized goal-directed therapy (GDT) was associated with a reduced rate of major complications. No difference was observed between interventions using fluids alone compared with those using a combination of fluids and inotropes to achieve oesophageal Doppler-guided blood flow targets. Similar conclusions have been made with regard to the use of GDT in cardiac surgery. A randomized controlled trial of GDT in patients with proximal femoral fractures was concluded early because of slow recruitment, but demonstrated a clinically important trend towards favourable results with colloidbased GDT. However, colloid-based GDTapparently does not benefit ‘fit’ patients [who achieved anaerobic threshold (AT) .11 ml O2 kg min] compared with ‘unfit’ patients (AT 8.0–10.9 ml O2 kg 21 min) in a randomized controlled trial of 179 patients undergoing major colorectal surgery. In this population, ‘fit’ GDT patients had a longer length of hospital stay compared with controls, whereas there was no difference for ‘unfit’ patients. GDTpatients received an average of 1360 ml additional colloid compared with controls, indicating a detrimental effect of this additional colloid load despite GDT, although DO2 was not directly measured. 8 When considering the optimum fluid choice to achieve supra-normal DO2, colloids have a theoretical and intuitive advantage. Being composed of molecules .35 kDa, colloids have traditionally been thought to have greater fluid efficacy (i.e. they remain in the intravascular space for longer, thus contributing a greater effect on cardiac output) compared with crystalloids. These theoretical benefits of colloids led to their routine use in GDT. Studies in healthy volunteers have demonstrated that crystalloids tend to expand the intravascular volume by 20% of the infused volume; however, when physiological endpoints have been used in clinical studies, the fluid efficacy of crystalloids increases up to 60%. This discrepancy may be explained by a number of factors, including the time taken for fluid to equilibrate throughout the extracellular fluid, the vasodilating effect of anaesthetic-induced hypotension on vascular capacitance, and the impairment of fluid elimination because of the surgical stress response. While colloid has been the default fluid choice in most GDT studies to date, recent evidence from both the perioperative anaesthetic setting and from intensive care have raised concerns that these agents may produce adverse effects on renal function and coagulation. – 17 Recent studies have sought to compare the use of crystalloid solutions with colloids for GDT. – 20 Senagore and colleagues randomized 64 patients undergoing laparoscopic colectomy to receive standard therapy or oesophageal Doppler-guided GDT using either crystalloid (lactated Ringer’s) or colloid (hetastarch). While patients randomized to crystalloid GDT received slightly more intraoperative fluids (mean 3800 ml vs 3300 ml colloid), their length of hospital stay was similar to patients in the hetastarch group (72 h vs 76 h). In a German pilot study, patients (n1⁄450) undergoing cytoreductive surgery for ovarian cancer were randomized to receive either balanced crystalloid or balanced hydroxyethyl starch (HES) colloid. Oesophageal Doppler monitoring was used to guide fluid administration to optimize stroke volume. While patients in the colloid group achieved marginally better numerical haemodynamic stability, there was no difference in complication rates or length of intensive care unit or hospital stay. A recent study from York compared the use of Hartmann’s crystalloid solution with a balanced starch solution in 202 mediumto high-risk patients undergoing elective colorectal surgery, and using a LiDCO Rapid monitor (LiDCO, Cambridge, UK) to guide GDT. The primary outcome studied was the ability to tolerate enteral diet on the fifth postoperative day. No difference was seen between the crystalloid and colloid group in the primary outcome. While the crystalloid group received more fluid, again there was no difference in the British Journal of Anaesthesia Page 1 of 3 doi:10.1093/bja/aeu015