Discussion
To our knowledge, this is the first study that has observed the impact of intraoperative crystalloid resuscitation during emergency exploratory laparotomy in the trauma population. Although there has been a large amount of research published concerning the effects of crystalloid on human physiology, morbidity and mortality, there is a lack of data within the trauma population. Here, we have shown that there is a wide distribution of the type and volume of intraoperative crystalloid administered during trauma laparotomy. A moderate correlation was demonstrated between the amount of crystalloid given and the time in the operating room, but no correlation was seen when comparing crystalloid volume and EBL or pRBC administration. Furthermore, no correlation was demonstrated between the crystalloid used as the primary resuscitative fluid and end resuscitation markers. In addition, the type of anesthesia provider did not have an impact on the amount of crystalloid, type of crystalloid administered, or postoperative resuscitation markers.
The patients were stratified based on transfusion requirements to examine discrete patient populations, as it would be expected that patients in more severe hemorrhagic shock would receive more blood products and less crystalloid volume. Patients requiring ≥5u of pRBCs represented a massive transfusion group as most cases were completed within 4 hours.25 As up to 92% of trauma patients do not receive blood products, we found it important to study patients who did not require transfusion to represent the majority of the trauma population.6 Our aim was to stratify patients in a way that was most natural to the progression of trauma patients being admitted to the emergency department and expediently taken to the operating room. Most of the information available at this time would consist of laboratory values and clinically based on patient hemodynamic status.
Given DCR strategies, it was not surprising that there were significant differences in the ISS, RI, EBL, and resuscitation markers, as these populations were defined by the amount of blood products received. Overall, the blood product resuscitation at our institution followed the optimal 1:1 FFP:pRBC strategy, which has demonstrated increased survival.27 Colloids were used during the resuscitation of all groups, but were given to a higher proportion of the ≥5u cohort. Although colloids have often been thought of as a superior resuscitative fluid to crystalloids, no studies have demonstrated a clear mortality benefit, reduction of blood transfusion, or need for renal replacement therapy.28
As expected, patients who required more transfusions had a higher ISS, required more blood-based resuscitation, required more vasopressor support, and had more metabolic derangements on arrival and exit from the operating room. All cohorts showed a trend toward improvement based on postoperative resuscitation makers, demonstrating ongoing resuscitation with crystalloid and/or blood products. There was also a significant decline in GFR at the end of the case in the cohorts requiring more transfusion. This was likely due to the severity of shock, as prior research has demonstrated the development of acute kidney injury following hypotension and hypoperfusion.29 The effect of vasopressors on renal function has largely shown increased renal perfusion, but the results are mixed, and in our study did not suggest renal protection.30
Most patients received two types of crystalloid during laparotomy, with NS and LR most often administered simultaneously at the beginning of the case. This was likely due to anesthesia providers choosing LR to be the primary resuscitative fluid but requiring NS to be administered with pRBC due to the concern that calcium could chelate the anticoagulating citrate and clot the pRBC within the intravenous line. When Normosol was used, it was only after the administration of NS and/or LR, with the transition to Normosol occurring after approximately 1 hour of operative time. There have been many publications suggesting that balanced crystalloids are a superior choice of resuscitative fluid due to a decreased morbidity and mortality in critically ill, non-critically ill, and non-emergent surgical patients.21–24 Self et al
24 demonstrated a lower incidence of persistent renal dysfunction and new renal replacement therapy in non-critically ill patients receiving Normosol as compared with NS. Semler et al
23 demonstrated a decreased rate of death, persistent renal dysfunction, and new renal replacement therapy in critically ill patients receiving Normosol as compared with NS. The major limitations in comparing these studies remain the population; Shaw et al purposefully excluded the trauma population, and Semler et al and Self et al included all patient populations (medical and surgical). This is the first study to look specifically at only the trauma population and specifically those undergoing emergency laparotomy.
The majority of patients in this study received NS as part of their intraoperative resuscitation, whereas only a minority of patients received Normosol. A mild correlation between the amount of NS received and Cl− concentration was demonstrated in some cohorts, but was not consistent. No correlation was seen between increased NS use and acidosis immediately postoperatively. In the literature, this relationship has been described, with increased NS administration resulting in hyperchloremic acidosis.14–16 18 19 However, as most patients received both NS and LR—often times simultaneously—the effects of the more balanced LR may have mitigated the negative consequences associated with higher volumes of NS administration. Given the emergent and often severe physiologic derangements, immediate postoperative laboratory values may have also been skewed by the use of intraoperative pharmacologic therapies. We also were unable to demonstrate superiority or inferiority of one type of fluid over another when comparing postoperative resuscitation markers. This was again likely confounded by the use of multiple crystalloid types during the operation in the majority of patients. There are limited available data or ability to ascertain retrospectively why a shift in crystalloid type was made during each case, but potential explanations may include fluid availability/convenience, acid/base status, clinical state, which fluid was started in the ED, or provider bias.
Although the amount of crystalloid received correlated with the amount of time spent in the operating room, we did not observe any correlation between EBL or pRBC and crystalloid volume. Despite increased blood loss in the ≥5u pRBC cohort, operative times and fluid administration per hour were similar. All cohorts received a median of 1 L/hour (or 10–11 mL/kg/hour) of crystalloid regardless of ongoing resuscitation with blood product with a total median volume of 2.5 L to 2.7 L administered in all cohorts. Although one might expect a positive correlation, there has been a paradigm shift in fluid resuscitation from a liberal to a more restricted approach, although no strong evidence has been demonstrated and there is renewed interest in intraoperative fluid resuscitation.31–37 Shin et al have recently demonstrated optimal postoperative outcomes are associated with crystalloid infusion rates of approximately 6 to 7 mL/kg/hour or 1 L of fluid for a 3-hour operative case in an non-emergent setting with minimal blood loss.36 Myles et al recently demonstrated that a restrictive resuscitation (median crystalloid volume of 1.7 L) was associated with a higher rate of kidney injury and no difference in disability-free survival as compared with a liberal resuscitation (medial crystalloid volume of 3.0 L).37 Although in our institution crystalloid appears to be given as a lower percentage of the total resuscitation as RI increases, our providers do not appear to reduce hourly administration of crystalloid across our three transfusion cohorts. Whether this level of hourly crystalloid administration is harmful for patients in any of these cohorts remains to be determined.
Within the trauma population, multiple studies have demonstrated the detrimental effects of large crystalloid volumes, specifically in those patients requiring massive transfusion.12–18 38 There remains a knowledge gap for those patients not receiving blood products at all. More specifically, however, trauma patients present unique physiologic changes compared with elective operative cases; they are more likely to arrive hypovolemic, acidotic, coagulopathic, and hypothermic.3 5 8 This presents unique challenges in managing resuscitation. Massive transfusion protocols have guided the actively hemorrhaging patients and have decreased morbidity and mortality.2–5 7 8 No protocols/guidelines have been developed to aid in the trauma population that are not actively hemorrhaging but require emergent operative intervention.
Each anesthesia attending oversaw/performed a median of 7 trauma laparotomies during the study design, which averages to only 2 to 3 cases per year. During each of these cases, there is also variability in the assisting provider based on resident and CRNA involvement. Multiple studies have demonstrated significant provider variability across individual anesthesia provider, surgical specialties, and regional hospitals.36 38–40 Lilot et al demonstrated wide interprovider and intraprovider variability when departmental fluid administration guidelines were not in place. They determined that most providers are inconsistent in their individual approaches based on a wide range of corrected volumes administered, and overall the volume of crystalloid administered is largely based on the individual giving the fluid and not based on patient or procedural factors.39 It has been suggested that protocols should be developed and rigorously implemented based on widespread provider variability in non-emergent abdominal operative intervention.36 39–41 Given the limited number of cases each anesthesia provider performs in a year, we agree that there may be a role for standardization of crystalloid usage in the intraoperative trauma population.
This study is limited in being a retrospective review, which comes with its own inherent difficulties. It is also a single institution review, which may have limited applicability to the global trauma population and other institutions. There is also concern for anesthesia provider bias during intraoperative resuscitation, as a small group of attendings performed the resuscitation on a higher number of cases. Given that our cohorts were intentionally different in the amount of pRBCs administered, the results may also be confounded by the use of blood products and other pharmacologic adjuncts used during massive transfusion, leading to improved resolution of hemorrhagic shock. Our results may also be skewed as the majority of patients received both NS and LR at the start of the operation instead of a single intravenous fluid throughout each case. However, this highlights an important point: there does not appear to be a standard choice in resuscitation fluid by anesthesia providers at our institution.
Based on the results of this study and following discussions with our own anesthesia department, we sought to determine why our fluid resuscitations seemed to be primarily NS-driven and with multiple types of crystalloids. It was discovered that anesthesia technicians set up the trauma operating room with NS as the default fluid for anesthesia providers to use. Normosol was historically regarded as cost prohibitive in our institution, but after further review it was determined that the cost is currently equivalent for all three crystalloids. An institutional change was made to have Normosol available as the primary resuscitative fluid to anesthesia providers. This change was based on the literature in non-trauma patient populations demonstrating the superiority of a balanced crystalloid fluid, the ability of Normosol to be infused with blood, and the decreasing cost of Normosol.19–24 Nevertheless, there remains a need for multi-institutional clinical trials to further evaluate the effects of the type of crystalloid resuscitation during trauma laparotomies and determine the ideal resuscitative crystalloid. A study mirroring the Vanderbilt group, in which the intravenous fluid administered is controlled from the emergency department to discharge, would be of value to identify the ideal crystalloid.23 24 Furthermore, future studies are needed to determine the cost of using a Normosol-derived intraoperative resuscitation protocol as compared with an unprotocolized resuscitation strategy.