2012_PerioperativeFluidTherapy_BMJ

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Perioperative fluid therapyIntravenous fluid therapy is an important aspect of perioperative care, but doctors often prescribefluid with limited knowledge of its benefits and risks.This article provides an evidence based summaryof current best practice in the prescription of fluid for patients undergoing major non-cardiac surgery.

Rupert M Pearseclinical reader1, Gareth L Ackland clinician scientist, honorary consultant

2

1Barts and The London School of Medicine and Dentistry, Queen Marys University of London, London EC1M 6BQ, UK; 2University College

London/University College Hospitals NHS Trust, Wolfson Institute for Biomedical Research, London WC1E 6BT

Patient outcomes after major non-cardiac surgery can be

improved considerably through more effective perioperative

care.1 Factors such as advancing age, comorbidity, and complex

surgical procedures can result in postoperative morbidity and

mortality rates similar to those found with common acute

medical emergencies.1-3

Patients who survive postoperativecomplications experience functional limitation and reduced long

term survival.1-3 Doctors often prescribe intravenous fluid with

limited knowledge of the benefits and risks of this treatment.

Doctors in training commonly express frustration at the lack of

clear guidance on the optimal approach to fluid therapy. The

debate that followed recent UK guidelines aimed at standardising

best practice highlights the uncertainty in this area, even among

experienced practitioners.4 5

We review the evidence from clinical studies, systematic

reviews, and practice guidelines to provide a summary of current

best practice in the prescription of fluid for patients undergoing

major non-cardiac surgery.

What are the principles behind fluidtherapy?

In health, 60% of total body mass consists of water. Most water

resides within the intracellular compartment, separated from

extracellular water, which comprises the interstitial and plasma

volumes. The neuroendocrine response to surgery results in

retention of sodium and water with a reduction in maintenance

requirements. Conversely, absolute hypovolaemia (blood loss)

and relative hypovolaemia (such as epidural or inflammation

mediated vasodilatation) commonly result in a fluid deficit. For

most patients fluid losses are replaced during surgery and oral

intake of fluid is rapidly resumed after surgery. However, for

some procedures (such as gastrointestinal surgery, proximal

femoral fracture repair), the preoperative deficit and losses

during surgery vary widely and may not be adequately replaced.

Inadequate fluid replacement leads to reduced cardiac output

and oxygen delivery to injured tissues, which is associated with

an excess of postoperative complications. Excessive fluid

administration may also have adverse effects, including acidosis,

coagulation defects, and oedema of both lungs and peripheral

tissues (fig 1).6

It is also worth noting that postoperativeadverse events may be attributed to fluid prescribing when

associated factors are to blame. The tissue injury of surgery

results in a systemic inflammatory response associated with

both tissue oedema and hypovolaemia. Negative fluid balance

after surgery is associated with reduced mortality (odds ratio

0.50 (95% confidence interval 0.28 to 0.89)),7 although this may

reflect the degree of inflammatory response as well as excessive

fluid administration.8 Fluid restriction and diuresis may decrease

oedema in patients with poor ventricular function but also

increase the incidence of acute kidney injury.

How should we select the dose of

intravenous fluid?Perioperative maintenance fluid

The normal daily dietary requirements for water and electrolytes

are listed in table 1. However, retention of sodium and water

after surgery reduces their requirements. Additional amounts

should be given only to correct deficit or continuing losses.

Monitoring should include clinical examination, fluid balance

charts, regular weighing, and biochemical analyses (urea,

electrolytes, creatinine, bicarbonate).

It is often helpful to calculate the quantity of water, sodium,

and potassium prescribed in a given fluid regimen (table 2 ).

The optimal daily dose of water and electrolytes cannot be

provided by a single crystalloid solution, and a suitable daily

prescription for maintenance fluid will normally include more

than one formulation. Many fluid solutions contain large

quantities of sodium and chloride, which may result in nausea

Correspondence to: R Pearse Adult Critical Care Unit, Royal London Hospital, London E1 1BB [email protected]

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BMJ2012;344:e2865 doi: 10.1136/bmj.e2865 (Published 26 April 2012) Page 1 of 6

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Methods

We searchedvariousdatabases, includingClinical Evidenceand the CochraneCollaboration, for articles which woulddefine clinical practiceby using the search terms: surgery; fluid, intra-venous; perioperative; blood transfusion. We also consulted several UK and internationalexperts in formulating the contents of this review and sought comments on the final version.

We recognise the considerable variation in clinical practice in this area. The article focuses on key aspects of the topic affecting the majority

of patients who would benefit from a standardised and individual approach to fluid prescribing. Our aim is to provide simple guidance for theless experienced or less expert clinician who prescribes fluid on a regular basis. We stress the importance of recognising that fluids aredrugs and accordingly require expert guidance in their use.

and vomiting, metabolic acidosis,9 and impaired renal blood

flow.10 However, although hypotonic solutions are important

sources of water, they may cause severe hyponatraemia and

neurological impairment when used as replacement fluids.

Analysis of 38 randomised trials involving 1589 patients

undergoing major abdominal aortic surgery failed to identify

specific superior fluid regimens.11 Although crystalloid solutions

that contain bicarbonate may limit the deleterious effects of

chloride, the clinical and metabolic consequences of limiting

chloride-rich fluids remain unclear.9

Replacement of perioperative fluid deficit

The most important information required to assess intravascular

volume is provided by the clinical scenario; is it likely that the

patient is hypovolaemic? Estimates of fluid deficit based on

traditional physiological parameters such as heart rate, blood

pressure, and central venous pressure are not reliable. A

systematic review of 24 studies showed that central venous

pressure is a poor measure of fluid deficit (pooled correlation

between central venous pressure and change in cardiac output

0.11 (95% confidence interval 0.02 to 0.21)).12

Assessing the dynamic response of physiological variables to

a fluid challenge is a more instructive approach. The response

to the rapid administration of a fluid bolus (in our practice, 250

ml colloid solution) may be evaluated during surgery by

monitoring cardiac output and is best guided by an algorithm

for perioperative fluid and inotropic therapy (fig 2). This

treatment approach is associated with a mortality reduction of

37% and a two or three day reduction in length of hospital stay.13

The National Institute for Health and Clinical Excellence (NICE)

has endorsed the use of perioperative cardiac output monitoring

while acknowledging the need for further research.14

For most patients, resumption of oral fluid and light diet can

begin shortly after surgery. Patients undergoing major gut or

vascular surgery require individualised prescription of

intravenous fluid, and the clinical team should communicate to

ensure optimal fluid administration during and after surgery.These patients should be reassessed on a regular basis by

suitably trained staff.

After major surgery, a substantial proportion of patients will

become critically ill. In this scenario decisions regarding fluid

and inotropic therapy should be guided by senior medical advice.

This is best determined by objective, dynamic assessment of

cardiovascular performance in response to a fluid challenge and

may also be guided by a basic transthoracic echocardiogram to

assess left ventricular function. Lactate and central venous

saturation measured from a blood sample drawn from a central

venous catheter may also indicate hypovolaemia. This approach

is currently being evaluated in clinical trials. Initial care of

patients who become critically ill on a standard surgical wardcan be improved by input from critical care outreach staff.

However, this resource cannot replace prompt admission to a

critical care unit.2 3

What are the differences between

crystalloid and colloid solutions?

Intravenous fluids should be considered as conventional drugs,

with both beneficial and adverse effects. Differences in the

chemical structure of colloid and crystalloid solutions may

explain their diverse metabolic effects (table 2). There is no

evidence that resuscitation with colloids (including albumin)

reduces the risk of death or morbidity compared with

resuscitation with crystalloids (pooled relative risk 1.00 (0.91

to 1.09)).15 Safety concerns have emerged from several studiesregarding a potential increase in the risk of bleeding and acute

kidney injury with different colloids. However, systematic

review of these data is limited by the lack of statistical power

and inconsistent definitions of kidney injury.16 There are several

ongoing clinical trials comparing the effects of crystalloid and

colloid solutions. Until these studies are complete, wide

international variations in fluid prescribing practice are unlikely

to change.17

When should we transfuse blood to a

surgical patient?

Increased mortality among patients undergoing non-cardiacsurgery is associated with both preoperative anaemia (odds ratio

142 (131 to 154)) and perioperative haemorrhage.18 19

However, the benefits of blood transfusion are uncertain, and

further research is required in this area.20 The adverse effects

associated with transfusion are well described,21 and, for surgical

patients, include increased risks of postoperative infection and

increased recurrence after cancer surgery.22 23 Current guidelines

recommend transfusion when haemoglobin values fall below

70 g/L during the perioperative period but do not recommend

transfusion to achieve values >100 g/L.24 A recent large

randomised trial in patients undergoing proximal femoral

fracture repair, which randomised patients to transfusion triggers

of 100 g/L versus 80 g/L, did not show any differences in

functional outcome (odds ratio 1.01 (0.84 to 1.22)).25

Consideration should also be given to the use of techniques

which reduce transfusion requirements, including iron and

erythropoietin, antifibrinolytic therapy, and red cell salvage

devices.23 Systematic reviews indicate that use of autologous

transfusion of the patients own blood (donated before surgery)

is not associated with benefit and may increase transfusion

rates.26

How should we optimise perioperative

nutrition?

Surgical patients should be screened for nutritional deficit and

managed according to published guidelines for perioperativenutritional support.27 In the small proportion of patients who

present for surgery with a severe nutritional deficit, caution

should be taken with re-feeding after surgery either by enteral

or parenteral routes. The advice of a specialist dietician should

be sought. Most patients without disorders of gastric emptying



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Learning points

Perioperative fluid therapy is associated with potential benefits and harm, yet fluid prescribing practice varies much more widely thanwould be accepted for other drugs

The inflammatory responsegenerated by tissue injury causes complexchangesin fluid and electrolyte balance.Although maintenancerequirements are reduced, many patients require replacement of fluid losses

Careful monitoring should be undertaken using clinical examination, fluid balance charts, and regular weighing when possible

For most patients fluid losses during surgery can be replaced with resumption of oral fluid and light diet after surgery

Patients undergoing complex major surgery (such as major gastrointestinal surgery, proximal femoral fracture repair) experiencevariablefluid losses dueto tissue injury, inflammation, and blood loss. Forthese patients, evidencesupports an individualised approachto fluid therapy often involving cardiac output monitoring during surgery

Fluid restriction and diuresis may decrease oedema in patients with poor ventricular function but may increase the incidence of acutekidney injury. It is better to avoid excess fluid administration than to treat the consequences

Tables

Table 1| Normal daily requirements for fluid and electrolytes for a healthy adult

RequirementItem1.5 ml/kg/hourWater

11.5 mmol/kgSodium

1 mmol/kgPotassium

1.5 mmol/kgChloride

0.20.5 mmol/kgPhosphate

0.10.2 mmol/kgCalcium

0.10.2 mmol/kgMagnesium

145 kJ/kgEnergy



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Table 2| Constituents of commonly used crystalloid and colloid based intravenous fluids

Constituent

Fluid OtherGlucose (dextrose)Chloride (mmol/L)Potassium (mmol/L)Sodium (mmol/L)

Crystalloids

1541540.9% saline

50 g/L5% dextrose

40 g/L30300.18% saline + 4% dextrose

Lactate 29 mmol/L

Calcium 2 mmol/L

1115131Hartmanns solution

Bicarbonate 1000 mmol/L1000Sodium bicarbonate 8.4%

Colloids

Gelatin 40 g/L120154Gelofusine

Hetastarch 60 g/L154154Hetastarch

Hydroxyethylstarch 60 g/L

Acetate 34 mmol/L

Magnesium 1.5 mmol/L

1104137Volulyte

Albumin 45 g/L136 mmol/L150Human albumin 4.5%

Crystalloids have various indications, whereas use of colloids is generally limited to intravascular fluid resuscitation. No commonly available fluid provides the

correct combination of water and electrolytes for maintenance requirements.



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Figures

Fig 1Optimal perioperative fluid therapy requires a balance of the beneficial and adverse effects of intravenous fluid. Thisrequires an individualised approach to prescribing that is often neglected, resulting in poor patient outcomes

Fig 2Use of cardiac output monitoring to guide replacement fluid therapy during and immediately after major surgery ismuch more reliable than use of venous pressure. A physiological challenge with a small bolus of intravenous fluid willresult in an increase in venous return and hence stroke volume, but only in patients with a fluid deficit. Thus both inadequate

and excessive fluid administration may be avoided.



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2012_PerioperativeFluidTherapy_BMJ