This was a large retrospective audit of current intravenous fluid prescribing practice in the five hospitals in the Wessex region. We found that early cessation of intravenous fluids in the postoperative elective surgical patient was common and in keeping with the approach promoted by enhanced recovery after surgery programmes. In those patients that continue to receive intravenous fluids, a considerable proportion appear to receive excessive or inadequate quantities of various electrolytes in relation to reference requirements. A small but important proportion appears to receive excessive volumes of water. The type of intravenous fluid administered varies according to the stage of the patient pathway. There was considerable variation in the volume of fluid administered in the operating theatre for three common elective procedures. Electrolyte disturbances were frequent and became more common as the postoperative days passed.
Data limitations
The majority of medical records in this audit were paper based and often subjectively of poor quality which may affect the results. We did not collect detailed data on individual patient perioperative risk scores in the form of ASA (American Society of Anaesthesiologists) grade or other perioperative risk scoring systems. We considered ASA grade to be insufficiently robust to determine perioperative risk, and other risk scoring systems were rarely used by anaesthetists in this audit.
When calculating intraoperative fluid administration data for the three common procedures, our ability to determine that these were uncomplicated was based on discharge summaries and anaesthetic charts. Neither of these two methods may have recorded all the technical difficulties or other ‘complications’ during the surgery that may have mandated higher than average intravenous fluid administration volumes. In addition, the length of time spent in the operating theatre was not recorded so we were unable to present intraoperative fluid administration volumes as ml.kg.h−1. Also, these patients were not matched in terms of perioperative risk score (e.g. ASA), co-morbidities, surgical complexity or operative time, although we did exclude non-elective patients and those with significant blood loss. Fluid balance charts were studied to help assess appropriateness of intravenous fluids. These were subjectively noted to be often of poor quality and do not record all losses, such as fluid sequestration in sepsis, so they do not provide all the information needed to assess whether the fluid administered is clinically appropriate. Fluid prescription charts were better in terms of completion.
Meaning of this audit
One of the principles of enhanced recovery after surgery protocols is an early return to oral intake to improve patient comfort, gut function and limit the detrimental effects of intravenous fluid (Guidelines for the Implementation of Enhanced Recovery Protocols
2009). Intravenous fluid guidelines (National Institute for Health and Care Excellence
2013; Powell-Tuck et al.
2011) also make reference to promoting the early return to oral intake. Over 50 % of the patients had a free oral fluid order on the day of their operation or postoperative day 1, indicating an attempt to return them to normal oral fluid intake. Of the patients, 32 % had no record of any free fluid order being made possibly because it was obvious that the patient could drink freely or that the hospitals have adopted an enhanced recovery approach and assumed free oral fluids can be given unless specifically documented otherwise. Poor medical record keeping is another possibility. At least some of these 32 % of patients would have been allowed to drink free oral fluids; therefore, the lack of documentation is unlikely to underestimate the already large number of patients with an early (day of operation or postoperative day 1) free fluid order.
The balanced crystalloid solutions were the most common postoperative fluid, with hypotonic crystalloids (dextrose-saline solutions) and 0.9 % sodium chloride as the next most common. There is increasing recognition that the traditional postoperative regime of 0.9 % sodium chloride and 5 % dextrose risks sodium, chloride and salt overload (De Silva et al.
2010). Sodium chloride (0.9 %), even when not given in excessive quantities, is associated with a variety of detrimental effects such as hyperchloraemic acidosis, reduced renal blood flow, increased chance of renal failure and increased in-hospital mortality after major abdominal surgery (Lobo
2012). Data from Wessex in 2007 found that over 70 % of postoperative fluid prescriptions were 0.9 % sodium chloride or 5 % dextrose (De Silva et al.
2010). This figure was reduced to 40 % in 2009 after a targeted education intervention (De Silva et al.
2010). It appears that this downward trend has continued as evidenced by our work.
Differences in intraoperative and postoperative fluid types is partially explained by the prescriber (anaesthetists in theatre vs junior doctors or non-anaesthetists postoperatively) and the different physiology occurring at the different time points.
Even the use of the balanced crystalloids can result in sodium overload and some hospitals and the NICE (National Institute for Health and Care Excellence
2013) advocate hypotonic dextrose-saline solutions as a means of giving water with minimal sodium to meet the maintenance requirements. It is not surprising that the greater use of hypotonic dextrose-saline solutions was seen in patients that went to the ICU postoperatively compared to HDU or ward, perhaps indicating better intravenous fluid prescribing practice or awareness of guidelines.
The inadequate doses of intravenous potassium required to meet the maintenance seen in our audit are in keeping with previous work (Lu et al.
2013) and our anecdotal observations. Although it is possible that some patients received potassium supplementation by other means (i.e. orally), the increasing incidence of hypokalaemia as the postoperative period progresses suggests that inadequate intravenous (and other) potassium supplementation is a true finding and is a problem that requires addressing. There are a number of potential reasons behind this but fear of intravenous potassium and the belief that the balanced crystalloid solutions contain adequate potassium for all patients are possible explanations. Hypokalaemia in the postoperative patient has been associated with slower return of gut function as well as other complications, and there is a suggestion that preventing hypokalaemia in the postoperative stage may improve outcomes (Lu et al.
2013).
Postoperative hyponatraemia was common and is multifactorial. It is not possible to determine the causes without a detailed notes analysis of the affected patients. As Fig.
8 demonstrates, mean serum sodium declined by 2.6 mmol.l
−1 in the 356 subjects in whom pre- and postoperative day 1 serum sodium values were available. This is despite the vast majority of intraoperative intravenous fluid therapy consisting of balanced crystalloid solutions. Therefore, the decline in mean serum sodium compared to pre-operative values is most likely to represent the physiological stress response to surgery. This is a spectrum of changes that occur throughout various body systems (neuroendocrine, metabolic, immunological and haematological) in response to surgical incision and trauma. Neuroendocrine changes are particularly relevant to perioperative fluids because the release of catecholamines and cortisol, vasopressin and aldosterone result in retention of sodium and water (often water in excess of sodium hence hyponatraemia), loss of potassium, reduced creatinine clearance and urine output. These effects can last well beyond the operative period into the postoperative phase.
Hyponatraemia can cause a variety of neurological and other symptoms but, more importantly, has been associated with increased risk of in-hospital and long-term mortality in a variety of patient groups (Lu et al.
2013). The mean drop in serum sodium from postoperative day 1 to postoperative day 2 was 0.21 mmol.l
−1. When only looking at those patients who received any dextrose solutions on postoperative day 1, the mean drop was 2.9 mmol.kg
−1. This raises the possibility that the use of dextrose solutions on postoperative day 1 is associated with subsequent hyponatraemia (compared to other fluids) and should be avoided. It should be noted that the pre-operative mean serum sodium was lower in this group. With the relatively small number of subjects, the retrospective nature of the audit and the large number of contributory factors, it is not possible to suggest causation. From our limited data, it would appear that the use of hypotonic dextrose-saline on postoperative day 1 was not associated with hyponatraemia and therefore, the recommendation made in several fluid guidelines (National Institute for Health and Care Excellence
2013; Woodcock
2014) that this is the preferred fluid is reasonable based on the results of this audit.
The range of intraoperative fluid doses for three index procedures was wide and in keeping with a recent two-centre observational study in America of fluid administration for uncomplicated elective abdominal surgery with minimal blood loss (Lilot et al.
2015). This found wide variability of crystalloid administration both within and between anaesthesia providers (Lilot et al.
2015). In that study, for most procedures, 50 % of patients received 4–10 ml.kg
−1.h
−1 of crystalloid (corrected for urine output and estimated blood loss) but 50 % fell outside of this wide range with some patients receiving as much as 35 ml.kg
−1.h
−1 (Lilot et al.
2015). Although a patient’s fluid requirements will vary and depend on a number of factors, it would be surprising to see such a wide range of physiological needs during similar surgical episodes, raising the possibility that variation is due to variation in individual anaesthetists’ fluid approach.
The lack of correlation between the volume of postoperative day 1 fluids and body weight is interesting. In terms of absolute volumes given, if clinicians were calculating fluid doses on a millilitre per kilogram basis, we might expect absolute volumes to increase with body weight. We saw the opposite of this with smaller patients getting larger volumes of fluids. This suggests that practitioners are thinking in terms of ‘number of bags’ for a ‘standard’ patient and not taking into account weight.
Unanswered questions and future research
Most intravenous fluid trials take place in the operating theatre. We have demonstrated the type of intravenous fluid prescribed varies depending on whether the patient is in the postoperative ward or in theatre. The type of prescriber is likely to be different as well. Some previous intravenous fluid research has excluded the first postoperative day from any analysis because fluid prescriptions during this period may have been complicated by surgery-induced fluid and electrolyte shifts and any postoperative fluid prescriptions completed by the anaesthetist (Walsh and Walsh
2005). Being a continuum, any future research should cover the intraoperative and postoperative phases, something that has been recognised as important by an international trial looking at fluid therapy during and after major abdominal surgery Myles PS & Wallace SK (
2015). Interestingly, prostatectomies in the American study (Lilot et al.
2015) had a much narrower range of fluid administered because a fluid protocol exists. A similar fluid protocol intervention may be needed in Wessex.
Education of junior doctors can make an impact on their prescribing choices (De Silva et al.
2010) but there is always a risk that any relatively short lived intervention only lasts a limited period of time before traditional practice starts to re-establish itself. The variation in intraoperative fluid volumes observed in theatre means that there is a quality improvement work that might be required in this environment as well.