Despite lengthened NPO periods for PM surgical case starts, the goal-directed fluid therapy algorithm did not result in an increased fluid administration rate for PM cases compared to AM cases. This finding agrees with suggestions from previous studies that the NPO period does not significantly impact resuscitative fluid requirement.1,3,5,14 Our study design adds to the growing evidence supporting withholding NPO period fluid replacement, while introducing reduced opportunity for inter-provider variability to influence fluid administration rates by employing the goal directed fluid therapy algorithm.
Our observation of greater epidural use, longer case duration, and greater use of laparoscopy in the AM group likely reflects two scenarios more likely to receive goal-directed fluid therapy: same-day surgery admit laparoscopic abdominal surgery with controlled ventilation and complex, and longer-duration, open abdominal surgeries with increased epidural usage that practically benefit from beginning earlier in the day. Surgical block times typical of scheduling laparoscopic surgery may simply finish earlier in the day as well. Regardless, whether looked at without correction, or when these factors are corrected for using modeling, we find no evidence to support the hypothesis that later cases with longer NPO times required more fluid.
NPO time difference between AM and PM surgical case starts differed by a surprisingly small number of hours (less than 3), when we expected closer to 5. The small difference likely reflects both variation in how patients follow NPO guidelines, and the fact that the recorded NPO time remains subject to both recall and reporting bias.
AM starts actually received more fluid than PM starts; this may reflect patient pathology, condition, and greater insensible loss typical of more complex surgery as previously noted, though this result remains difficult to interpret in such a broad and multifactorial setting. Nevertheless, the variables affecting this previous result, namely, possible different ASA classifications among the AM vs. PM patient groups 16–18, the possible differential epidural placement for different cases 19–20, the possible difference in the number of laparoscopic procedures in the AM vs PM groups 21–22, different possible urine loss in cases of differing nature23–24, possible different patient demographics in weight25–27 or in age28–30, the different pragmatic scheduling need for surgical procedures of longer duration in the AM vs the PM groups31–33, and the possible different hemodynamic heat rate parameter between surgical cases of different nature among the AM vs PM groups34–36, have all been accounted for in the literature with evidence showing the clear benefit of following the GDFT algorithm and therefore this indeed shows the reason for the establishment of the fluid therapy algorithm as a highly encouraged tool to be used for fluid resuscitation. Ultimately, all of these differences most likely reflect typical surgical scheduling practices and may actually better guide practical application of our results to fluid administration in AM and PM case starts in real world environments.
Based on these results in conjunction with previously published data, we believe there is strong evidence supporting a change in focus from “replacing NPO time deficits” to thinking more about patient and surgical complexity. Obvious factors including presenting diagnosis, comorbidities, age, body habitus, expected blood loss, and case duration should be accounted for along with fluid responsiveness. Given the preponderance of variability in the literature with regards to the reliability of void urine output during surgery as a marker of resuscitation, void urine output in our study did indeed independently predict recommended fluid administration from the Goal Directed Fluid Therapy algorithm, in line with the earlier studies in literature that did suggest the predictable nature of void urine for fluid resuscitation 23–24. These data thus strongly support and importantly reinforce that a one-size fits all approach to fluid therapy does not benefit the surgical patient and should end where in use, shifting attention to the benefit of using the GDFT algorithm for resuscitation with our study’s supportive evidence of avoiding the NPO periods as a guide for excess fluid administration.
Limitations
The primary limitation of this study is the retrospective design. As with all retrospective studies, selection and information bias cannot be completely accounted for, and may confound the interpretation of the results. Missing or invalid data points in our database may have reduced the size and power of our study, but because the proportion of excluded and missing data was similar between the two groups, we believed the validity of the study remained intact. Additionally, excluding patients with EBL greater than 500 milliliters for reasons discussed above, while reducing variability, may have also introduced some selection bias. However, we used generalized linear models to help mitigate possible confounding factors and strengthen our results. The method of monitoring fluid responsiveness varied within our cohorts and we do not have specific records of which methods were used in which patients. There may be unaccounted bias in the approaches used between the AM and PM cohorts. Finally, the types of fluid used during resuscitation obviously differed from case to case and were not standardized. Despite this, there were not significant overall group differences, and we attempted to account for this in our results by creating multiple parallel analyses using different recommended replacement ratios from the literature. The consistent non-significant findings regardless of the approach used are reassuring that our findings are not approach-dependent.