Tuesday, 18 August 2015

Variability in practice and factors predictive of total crystalloid administration during abdominal surgery: retrospective two-centre analysis. BJA January 2015.

This study is an analysis of the volume and type of crystalloid prescribed in two major hospitals in the US and the factors that determined the volume administered. This month Professor Garry Morgan sent an email to all of Westmead’s medical staff suggesting that the current prescription of maintenance fluids was suboptimal and potentially contributing to post operative complications. His email included an extract from a BJA editorial published in April that accompanied this paper.

Scientific evidence for best practice intra and post-operative fluid management is still limited and evolving. The purpose of this study was to determine what constitutes current practice in centres that do not have protocolised fluid administration and what factors determines that practice.

Patients were ASA 1-3, undergoing elective abdominal surgery between 2009 and 2011. Exclusion criteria included emergency cases, cases with intraoperative complications, blood loss greater than 500mls, those requiring colloids, blood products or procedures of duration less than 1 hour. The lengthy exclusion criteria were designed to produce as homogenous a surgical population as possible.

The data collection resulted in approximately 6000 patients that were used to build a regression model. In order to compensate for variability in patient size and duration of operation, fluid administration was recorded in mls/kg/hr.

The average rate of fluid administration was 7ml/kg/hr for the whole study population. For an 80 kg patient this results in an average rate of infusion of approximately 550ml/hr.

Determining factors analysed in the regression model included patient factors (HR, UO, MAP, Age, weight) procedural factors (blood loss, epidural used, type of surgery) and the individual surgeon and anaesthetist involved in the case. The regression model then allows you to assess the impact of each factor of interest, once all others have been adjusted for.
Perhaps unsurprisingly the single biggest factor affecting rate of fluid administration was who was giving the anaesthetic. There was significant variation of practice of each individual anaesthetist and significant variation between different practitioners. Average (mean) fluid infusion rates for an individual anaesthetist ranged from a low of 2.9ml/kg/hr (the fluid restrictors) to a high of 14ml/kg/hr (the liberal infusers).

More surprisingly was the fact that patient factors including haemodynamic parameters, urine output, age, weight and estimated blood loss had no impact on the volume of fluid infused at all. ASA 3 patients did received slightly less than ASA 1 patients undergoing the same procedure. The most significant factor was if the surgeon insisted on a restrictive approach.

This paper does not attempt to measure the impact the various fluid administration strategies had on patient outcomes but seeks to describe the current chaos with which intraoperative fluid management is occurring, with the single biggest factor that determines how much fluid the patient receives being who turns up to give the anaesthetic and what kind of mood they are in that day.

The accompanying editorial is also well worth reading. Some of the key points are:
  • Whilst the ideal fluid strategy remains controversial, it is unlikely that those giving an average of 3mls/kg/hr and those giving 14mls/kg/hr are both correct.
  • The scientific evidence for restrictive fluid administration is increasing but the studies accessing this also have significantly different ideas about what constitute ‘normal’ care
  • Adherence to ‘enhanced recovery’ strategies for optimal oral hydration and carbohydrate loading prior to surgery are showing benefit in the UK. The aim being for your patient to arrive in OT in a euvolaemic state and then to maintain this during the procedure.
  • Hartmann’s, Plasmalyte and normal saline are intended for resuscitation or volume replacement and are not maintenance fluids. Each bag of Hartmann’s contains twice the daily requirement of NaCl (the same amount of salt that is found in 10 bags of chips) and this sodium load leads to fluid retention, odema and surgical complications
  • 5% dextrose or 0.18% saline + dextrose are appropriate post surgical maintenance fluids and 1ml/kg/hr  (up to a maximum of 2L of 5% dextrose in a 24 hr period) should be sufficient fluid until oral hydration is established
  • Patients should be transitioned to oral hydration and IV lines discontinued as soon as possible
  • If this is not possible the patient and blood work should be reassessed and a tailored fluid strategy should be produced

Co-author author of the editorial Professor Mythen is interviewed on the subject for the BJA podcast from April:
http://www.oxfordjournals.org/podcasts/bja_114.05.01.mp3

DD

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