Abstract
Objective
To determine if there is a difference in the rate of early infection in hip fracture surgery performed under laminar flow and conventional turbulent ventilation.
Method
The impact on the rates of early surgical site infection (SSI) in patients who sustained a hip fracture after our trauma theatre was moved from a laminar to a non-laminar flow theatre was assessed. Data was retrospectively collected for six months prior to the merging of the trauma service and six months after. For each operation: age, gender, American Society of Anesthesiologists (ASA) grade, dementia, diabetes, immunosuppressants, anticoagulation, smoking status, duration of surgery, administration of peri-operative antibiotics, surgeon grade, skin closure method, and SSI were extracted from the hospital electronic notes with input from the trust's SSI surveillance team.
Results
259 hip fracture operations were performed during this period. Seven patients were excluded due to incomplete information. There were 95 patients in the laminar flow group and 157 in the non-laminar flow group. There were no SSIs in the laminar flow group and a 3.2% SSI rate (Fishers exact p = 0.16) in the non-laminar flow group. Three were superficial infections and two deep. This difference was not statistically significant. Patient characteristics were included in a Firth logistic regression model which did not show a significant change in the odds ratio.
Conclusion
A higher incidence of early SSI was found when hip fracture surgery was performed under non-laminar flow conditions but this difference was not statistically significant. Larger studies may change this outcome.
Keywords: Laminar flow, Hip fracture, Neck of femur fracture, Surgical site infection
1. Introduction
Surgical site infections (SSI) are one of the leading causes of hospital acquired infections.1 Over 1600 SSIs were detected between April 2016 and March 2017 from 139,691 procedures in 201 NHS hospitals and 8 independent sector NHS treatment centres.2 It is known that SSIs are associated with prolonged hospitalization, increased morbidity, and costs.3,4 Reducing the burden of SSIs has been well researched and amongst other methods, the use of laminar flow in operating theatres has been and is still in current use. The cornerstone trial which supports the use of laminar flow was performed between 1974–79.5 This was a randomised study which found a significant reduction in the rate of deep SSIs in total hip and knee arthroplasties when performed under laminar flow compared to conventional ventilation. However, the study did not control for the administration of prophylactic antibiotics nor could the results of the trial be reproduced in later studies. As a result, its benefit as a preventative measure has fell into uncertainty. Bischoff et al. completed a recent systematic review and meta-analysis demonstrating that laminar flow does not reduce the risk of SSI in total hip and knee arthroplasty or abdominal surgery compared to conventional turbulent ventilation.6
Following a reconfiguration of the trauma service in November 2016 at NHS Lanarkshire, all trauma operations including those for fractured neck of femurs except total hip arthroplasty was performed in a theatre with conventional turbulent ventilation. The aim of this study is to determine if there is a difference in the rate of early surgical site infection in patients who sustained a hip fracture and underwent surgery in laminar flow versus conventional turbulent ventilation.
2. Materials and methods
Consecutive patients who underwent surgery for fractured neck of femur in the Department of Trauma & Orthopaedics at Hairmyres Hospital between May 2016 and May 2017 were eligible for this study. This included patients who were admitted six months prior to the change of the trauma theatre from laminar to non-laminar flow on 1st November 2016 to six months thereafter. The trauma theatre moved following the merging of the trauma service at NHS Lanarkshire. Inclusion criteria included adults admitted with a fractured neck of femur in the above time frame and underwent surgery. Patients who did not undergo surgery were excluded.
In this study, the data was collected retrospectively using the hospital electronic system. This included: Age, Gender, American Society of Anesthesiologists (ASA) grade, the presence or absence of dementia and diabetes, Drug history most notably concentrating on immunosuppressants and anticoagulants, Smoking status, Duration of surgery, Administration of peri-operative antibiotics, Grade of the surgeon, Method of skin closure, and Documentation of surgical site infection (SSI). The hospital's SSI team were also involved in identifying surgical site infection.
The primary endpoint was the incidence of surgical site infection.
3. Results
A total of 252 patients were included of which 95 patients were found in the laminar flow group and 157 in the non-laminar flow group. The median age was 83 years (54–101 years) in the laminar flow group and 82 years (51–100 years) in the non-laminar flow group. The distribution of females to males was 2:1 in both groups.
A Fisher's exact test was performed which showed there were no surgical site infections (SSI) in the laminar flow group but 3.2% (five patients) of patients in the non-laminar flow group (Fig. 1) suffered from SSI. Of the five cases, two were deep infections requiring two stage revision surgery and three were superficial infections treated with antibiotic therapy. The two deep infections occurred in patients who underwent cemented hemiarthroplasty. Of the three superficial infections, two cases occurred in patients who underwent cemented hemiarthroplasty and one patient had undergone intramedullary nail fixation. Although there was an observed difference this was not statistically significant. Each patient characteristic and those pertaining to the surgery were included in a Firth logistic regression model (Fig. 2) in order to understand if any of these characteristics were responsible for an observed higher incidence of SSI in the non-laminar flow group. A significant change in the odds ratio for laminar flow after adjusting for each of the characteristics was not found.
Fig. 1.
The rate of surgical site infections.
Fig. 2.
Odds ratio graph for firth logistic regressions rate of surgical site infections.
4. Discussion
Surgical site infections are one of the most commonly reported hospital-acquired infections worldwide.1 Therefore, its prevention is paramount to improve patient care and reduce costs. This retrospective study compared the incidence of early SSI in patients with a hip fracture who underwent surgery under laminar flow versus non-laminar flow conditions. The main finding of an observed higher incidence of early SSI when hip fracture surgery was performed in a non-laminar flow operating theatre was not statistically significant. The patient characteristics and various peri-operative factors included in this study were not responsible for the observed higher rate of SSI in the non-laminar flow group (Fig. 2). However, this result may change based on larger numbers of patients and surgical site infections.
The results of this study are in accordance with the evidence published in the literature. Biscoff et al. recently performed a systematic review and meta-analysis on this topic and found that after total hip and knee arthroplasty and abdominal surgery there was no difference in SSIs regardless of whether the procedure was performed under laminar flow or conventional ventilation systems. The study included data from several different countries and it depended upon national surveillance systems and registries which meant that multiple factors may have confounded their results. However, the authors do acknowledge this.6
In addition to studies negating the beneficial effect of laminar flow, there is also evidence to suggest that laminar flow may be detrimental. Hooper et al. used the New Zealand Joint Registry to retrospectively collect data between 1999 and 2008 on 88,113 case of hip and knee arthroplasty. The study compared rates of early revision (within six months of the index procedure) for deep infection in both total hip and knee arthroplasty performed in laminar and non-laminar flow theatres and with or without the use of space suits. It found a statistically significant increased rate of the requirement of revision surgery in cases conducted under laminar flow. 0.148% of patients that underwent hip arthroplasty under laminar flow conditions required revision surgery compared with a 0.061% revision rate of those performed in a turbulent airflow theatre (p value < 0.003). The results were similar in those who underwent total knee arthroplasty; 0.243% revision rate in laminar flow conditions compared with 0.098% in cases performed in turbulent air flow (p value < 0.001).7
Similarly, a retrospective cohort study conducted in 2008 in Germany based on the nation's nosocomial infections surveillance system also came to the similar conclusions. It analysed data collected between 2000 and 2004 in 20 hospitals on 99,230 procedures. It compared the rates of SSI in theatres with high efficiency particulate air filtered (HEPA) vertical laminar flow and those with HEPA turbulent air flow. The study discovered a statistically significant increase in the number of SSIs in hip arthroplasty performed under vertical laminar flow (1.85%) compared to turbulent air flow (1.31%, p < 0.001). Following the controlling of confounding factors, the negative effect of laminar flow remained.8
The strength of this study is that it was able to account for a variety of variables influencing surgical site infection. However, it has its limitations. This is a retrospective study and results may change in the setting of a randomised controlled trial. Such a study would require a very large number of participants in order to be sufficiently powered due to the low rate of SSIs in this cohort. Therefore, may not be practically possible.
5. Conclusion
This study has shown there is no benefit of laminar flow compared to conventional turbulent ventilation in reducing the risk of early surgical site infections in hip fracture patients. However, further studies incorporating a larger number of patients may show otherwise but in an healthcare system with ever increasing demands and financial burdens the efficacy and cost-effectiveness of this preventative measure has been placed into doubt.
Conflicts of interest
None (Please see ICMJE conflict of interest form).
Footnotes
Supplementary data to this article can be found online at https://doi.org/10.1016/j.jor.2019.08.026.
Contributor Information
A. Din, Email: mrazhardin@gmail.com.
P. Foden, Email: philip.foden@manchester.ac.uk.
Mo Mathew, Email: Mo.Mathew@lanarkshire.scot.nhs.uk.
K. Periasamy, Email: kumar.kumarranitha@gmail.com.
Appendix A. Supplementary data
The following is the Supplementary data to this article:
References
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