2025/08/06 by Michael Ess, Dileep N. Lobo · 1 voice
Medicine · #Hemodynamic Monitoring and Therapy #Electrolyte and hormonal disorders #Trauma, Hemostasis, Coagulopathy, Resuscitation
paper · doi:10.1093/bjs/znaf179
openalex publication_date 2025/08/06 · openalex created_date 2025/10/30 · openalex updated_date 2026/07/29
Intravenous fluids and electrolytes are drugs and, like any drug, lead to dose-dependent responses, with too little or too much leading to adverse events and impaired clinical outcomes1–4. On surgical wards, fluid prescribing is often left to the most junior team members, who may be inexperienced1,5,6. Body water accounts for approximately 60% of body weight and the body water compartments are subdivided into intracellular and extracellular compartments, with the latter comprising the interstitial fluid space and the intravascular compartment (Fig. 1)7,8. About 20% of infused isotonic crystalloids, such as 0.9% sodium chloride (saline), Hartmann’s solution, Ringer’s lactate, and Plasma-Lyte-148, are retained in the intravascular compartment, with the rest being distributed in the interstitial space. On the other hand, although theoretically colloids should be retained in the intravascular compartment, in practice about 30–50% of infused colloids are distributed in the interstitial space. Thus, all fluids have the propensity to produce oedema. Hypotonic crystalloids, such as 5% dextrose and 0.18% saline/4% dextrose, are distributed through all the body water compartments and, although they are appropriate solutions to provide free water, they can cause cellular swelling and hyponatraemia when given in excess. Body water compartments and distribution of infused fluids (redrawn from Lobo et al.8) The aim of this article is to outline ten steps that will improve perioperative fluid prescribing and, hence, postoperative outcomes (Fig. 2). Ten steps towards better perioperative fluid and electrolyte therapy (images from https://www.freepik.com) The first step to better fluid prescribing is careful assessment and reassessment of the volume status of the patient and to decide if the patient requires intravenous fluids or not. As mentioned in the National Institute for Health and Care Excellence (NICE) guideline for intravenous fluid therapy in adults2, an airway, breathing, circulation, disability, and exposure (ABCDE) approach should be used to assess the patient, considering trends and context, rather than just spot observations (Table 1). Assessment will help determine if the patient is hypovolaemic, euvolaemic, or hypervolaemic (Table 2)2,8. It is important to note that patients rarely have all the signs and symptoms of either dehydration or fluid overload. Complex patients can have signs of both an intravascular deficit and interstitial fluid overload. If unsure, a senior clinician should be consulted. Assessment criteria NEWS, National Early Warning Score. Assessment criteria NEWS, National Early Warning Score. Some signs and symptoms of hypovolaemia, euvolaemia, and hypervolaemia Patient is thirsty Dry mucous membranes Cool peripheries Diminished skin turgor Shock RR >20 breaths/min Systolic BP <100 mmHg HR >90 beats/min Low JVP Postural hypotension Oliguria Confusion History of fluid loss/low intake NEWS ≥5 45° passive leg raise suggests fluid responsiveness Veins are well filled Extremities are warm BP and HR are normal Normal capillary refill time (<2 s) Normal skin turgor NEWS <3 Patient is oedematous Inspiratory crackles present ± shortness of breath Raised JVP Gallop rhythm History/charts showing fluid overload/surplus Increase in weight as a result of fluid retention NEWS ≥5 Patient is thirsty Dry mucous membranes Cool peripheries Diminished skin turgor Shock RR >20 breaths/min Systolic BP <100 mmHg HR >90 beats/min Low JVP Postural hypotension Oliguria Confusion History of fluid loss/low intake NEWS ≥5 45° passive leg raise suggests fluid responsiveness Veins are well filled Extremities are warm BP and HR are normal Normal capillary refill time (<2 s) Normal skin turgor NEWS <3 Patient is oedematous Inspiratory crackles present ± shortness of breath Raised JVP Gallop rhythm History/charts showing fluid overload/surplus Increase in weight as a result of fluid retention NEWS ≥5 RR, respiratory rate; BP, blood pressure; HR, heart rate; JVP, jugular venous pressure; NEWS, National Early Warning Score. Some signs and symptoms of hypovolaemia, euvolaemia, and hypervolaemia Patient is thirsty Dry mucous membranes Cool peripheries Diminished skin turgor Shock RR >20 breaths/min Systolic BP <100 mmHg HR >90 beats/min Low JVP Postural hypotension Oliguria Confusion History of fluid loss/low intake NEWS ≥5 45° passive leg raise suggests fluid responsiveness Veins are well filled Extremities are warm BP and HR are normal Normal capillary refill time (<2 s) Normal skin turgor NEWS <3 Patient is oedematous Inspiratory crackles present ± shortness of breath Raised JVP Gallop rhythm History/charts showing fluid overload/surplus Increase in weight as a result of fluid retention NEWS ≥5 Patient is thirsty Dry mucous membranes Cool peripheries Diminished skin turgor Shock RR >20 breaths/min Systolic BP <100 mmHg HR >90 beats/min Low JVP Postural hypotension Oliguria Confusion History of fluid loss/low intake NEWS ≥5 45° passive leg raise suggests fluid responsiveness Veins are well filled Extremities are warm BP and HR are normal Normal capillary refill time (<2 s) Normal skin turgor NEWS <3 Patient is oedematous Inspiratory crackles present ± shortness of breath Raised JVP Gallop rhythm History/charts showing fluid overload/surplus Increase in weight as a result of fluid retention NEWS ≥5 RR, respiratory rate; BP, blood pressure; HR, heart rate; JVP, jugular venous pressure; NEWS, National Early Warning Score. Most surgical patients can maintain an adequate oral intake of fluid and electrolytes, but, if intravenous fluids are necessary, possible indications include resuscitation, replacement, or maintenance (Fig. 3)8. Indications for intravenous fluid therapy and interactions between the indications (redrawn from Lobo4) An intravascular volume deficit necessitates resuscitation to replenish the deficit and restore intravascular volume9. Initially, 500 ml of an isotonic crystalloid, such as Hartmann’s solution, Ringer’s lactate, or Plasma-Lyte-148 (Table 3), should be given over <15 min. A colloid, such as gelatin (Geloplasma or Gelofusine) or albumin, could be used, but gelatin should be avoided for patients with sepsis and albumin should be considered for patients with severe sepsis. A smaller volume of 250 ml should be considered for patients at risk of heart failure, those with significant kidney disease, or those who are particularly frail or have a low body weight. The patient should then be reassessed to see whether a further bolus of 250–500 ml is required. Expert help should be sought if 2 l of fluid has been infused or there are signs of shock. Composition of commonly used crystalloids USP, United States Pharmacopeia. Composition of commonly used crystalloids USP, United States Pharmacopeia. If there are existing fluid and electrolyte deficits or ongoing losses, the patient should be given maintenance fluids and like-for-like replacements for what is/has been lost. A typical example of this is a patient with a high-volume aerodigestive fistulae. Prescribing an appropriate fluid for replacement will depend on where the losses have come from and therefore knowledge of the electrolyte content of various outputs from the gastrointestinal tract is essential for appropriate replacement2,8. Maintenance fluids may need to be added to or subtracted from calculations for replacement fluids. Maintenance fluids are necessary when the patient does not require immediate resuscitation or replacement, but cannot meet their fluid and electrolyte needs orally or enterally. Normally, over 24 h, patients require about 25–30 ml/kg of water and 1 mmol/kg of sodium and potassium2. They also need 400 calories (50 g of dextrose) to prevent starvation ketosis. Care must be taken in patients with obesity and prescriptions should be based on ideal body weight2. There is no ideal maintenance solution, but 0.3% KCl/0.18% saline/4% dextrose or Maintelyte (Table 3) could be used. However, infusing a large volume of these crystalloids (>2.5 l/24 h) can lead to hyponatraemia. Ideally all intravenous fluids should be administered via infusion pumps to minimize errors. The practice of prolonged starvation before elective surgery leads to the patient arriving in the anaesthetic room in a state of fluid deficit, which may necessitate a fluid bolus before the induction of anaesthesia to prevent post-induction hypotension. Most anaesthetic societies now recommend that patients should be starved of solid food for 6 h and should be allowed to drink clear liquids for up to 2 h before the induction of anaesthesia. The patient awaiting emergency surgery should be prescribed appropriate intravenous fluids if unable to eat and drink. As the exact timing of commencement of anaesthesia is sometimes unpredictable, the Centre for Perioperative Care in the UK recommends a ‘SipTilSend’ policy, where patients are allowed to drink up to 170 ml/h of water, black tea, black coffee, or squash until the operating team sends for the patient, unless there are contraindications10. Although 0.9% saline is often considered the staple crystalloid for infusion, the high chloride content (154 mmol/l) risks development of hypercholraemic acidosis, which has deleterious effects on kidneys, the gastrointestinal tract, coagulation, and cardiovascular and respiratory functions, as well as deleterious effects with regard to postoperative complications8,11–13. Balanced crystalloids, such as Hartmann’s solution, Ringer’s lactate, and Plasma-Lyte-148, are generally preferred to 0.9% saline and have been shown to cause fewer major adverse kidney events than saline11,13,14. Indications for 0.9% saline infusions include situations where there are high chloride losses (such as aerodigestive fistulae, profuse diarrhoea, and hypokalaemic, hypochloraemic metabolic alkalosis caused by vomiting or high nasogastric tube aspirates). The aim of intraoperative intravenous fluid therapy is to maintain intravascular volume, cardiac output, and tissue perfusion, while avoiding salt and water overload. If the patient is euvolaemic, large volumes of intravenous fluid are not necessary intraoperatively, and most patients require balanced isotonic crystalloids at a rate of 1–4 ml per kg per h to maintain homeostasis15. Some patients develop intravascular volume deficits intraoperatively, which require correction by administration of goal-directed boluses of intravenous fluids. The aim of goal-directed fluid therapy is to maintain intravascular normovolaemia, guided by changes in stroke volume, as measured using a minimally invasive cardiac output monitor, and is beneficial in high-risk patients having high-risk surgery15,16. In addition to the background crystalloid infusion, isotonic crystalloid or colloid boluses (200–250 ml) should be given to treat any objective evidence of hypovolaemia (>10% fall in stroke volume) to optimize intravascular volume and cardiac output15,16. In patients with haemorrhagic shock, an initial bolus of 1 l of warmed balanced isotonic fluid should be administered and further volumes should be based on the response to resuscitation. Early administration of blood products at a low ratio of packed red blood cells : plasma : platelets can help prevent coagulopathy and thrombocytopaenia17. Early and adequate control of bleeding is vital. In the event of major haemorrhage, replacement of blood loss with packed cells, fresh frozen plasma, and platelets at a ratio of 1 : 1 : 1 has been shown to be more beneficial than packed cells alone18. Maintenance fluids are required for patients unable to meet their fluid requirements by the oral and enteral routes after surgery. These should be tailored to the individual patient to avoid too much or too little fluid, in accordance with the NICE recommendations2 described in the ‘Assessment and indications for intravenous fluids’ section. Typically, a solution such as Maintelyte or 0.3% KCl/0.18% saline/4% dextrose should be used. Multiple bags of these can be given up to a total volume of 2–2.5 l/24 h. These can be prescribed as 1 l bags and should not be given more rapidly than 100 ml/h across the day. The early postoperative interval is characterized by a sodium and water retention phase, followed by a sodium diuresis phase19. Physiological oliguria often accompanies the sodium and water retention phase. The aim of perioperative fluid prescribing should be to achieve as near a state of zero fluid balance as possible. This ensures that the patient is not dehydrated or overloaded and helps maintain organ perfusion, prevents acid–base and electrolyte imbalances, and reduces complications and prolonged hospital stays. There is a relatively narrow range for safe intravenous fluid therapy and both hypovolaemia and hypervolaemia can cause adverse effects and complications (Fig. 4)3,4,15. Fluid balance charts should be completed accurately and monitored. When calculating fluid intake, it should be remembered that oral and intravenous fluids are given to administer medications and that both enteral and parenteral feeds contain fluid and electrolytes. A postoperative weight gain of ≥2.5 kg, indicative of fluid retention of ≥2.5 L has been associated with increased morbidity. Adverse effects of hypovolaemia and salt and water overload. Oral fluids and nutrition can, in most instances, be resumed soon after surgery in neurologically and haemodynamically stable, fully conscious patients with no signs of bleeding20. Early oral feeding has been shown to be beneficial in patients undergoing lower gastrointestinal surgery21, but caution may be necessary in patients undergoing upper gastrointestinal and pancreatic surgery20. It should also be remembered that, while it is only too easy to overload patients with intravenous salt and water, it is difficult to do so by the oral route. If patients are unable to eat after 5–7 days or meet ≥50% of their nutritional requirements through the oral route, enteral nutrition should be considered20. In the case of intestinal failure, parenteral nutrition may be necessary. Early dietitian review should be sought. Once artificial nutrition is commenced, intravenous fluids should be reduced or stopped to prevent overload. The interval of clearance of the inevitable salt and water overload that occurs during resuscitation, optimization, and stabilization is described as the de-escalation phase22. During this phase the aim should be to prevent further salt and water overload and to promote excretion of the accumulated excess, with the aim of restoring organ function and normal fluid balance. Salt and water intake, by whatever route, should be limited to that which meets maintenance requirements and replaces any additional losses, such as from intestinal fistulae or gastric aspiration. One of the major causes of avoidable fluid overload is a failure to make a timely adjustment of the fluid prescription from resuscitation to maintenance requirements. During the de-escalation phase, prescription of fluids should allow a small negative balance each day, as the patient’s ability to excrete a salt and water load returns (the sodium and water diuresis phase). The rate at which this transition can be achieved may vary according to the natural history and severity of the patient’s particular illness. This process requires careful monitoring to strike a balance between getting rid of the interstitial fluid overload and avoiding depletion of intravascular volume. Other means of de-escalation include small doses of diuretics and renal replacement therapy. However, de-escalation is best left to the expert, rather than the novice. Prescription of fluid and electrolytes, particularly in the perioperative interval, is an often-neglected area of training. Understanding of the pathophysiology of salt and water balance and careful attention to detail can lead to better prescribing and improved clinical outcomes. The authors have no funding to declare. Michael Ess (Conceptualization, Investigation, Methodology, Visualization, Writing—original draft, Writing—review & editing), and Dileep N. Lobo (Conceptualization, Investigation, Methodology, Project administration, Resources, Supervision, Visualization, Writing—original draft, Writing—review & editing) The authors declare no conflict of interest. Not applicable.