Laminar Flow Systems Research Articles

Experimental analysis of airborne contaminant distribution in an operating room with different ventilation schemes

Experimental and numerical investigations were performed in a research operating room to compare laminar air flow and turbulent mixing ventilation systems in reducing the concentrations of airborne germs and surgical smoke in operating room air. In addition, measurements at scattered positions were conducted to find positions that are suited best for airborne monitoring in real-time during surgeries. In the experiments, particle counters were used to sample tracer aerosols originating from the wound area and the facial area of the thermal manikins representing surgical staff. The results showed that it is important to perform monitoring close to the areas with high hygiene requirements. Increasing the air change rate with turbulent mixing ventilation significantly reduced the number of airborne particles, however, not in the surgical microenvironment. Our findings show varying results considering the particle concentration using laminar air flow compared to turbulent mixing ventilation. With laminar air flow, higher contaminant levels are obtained in the areas with a high demand for contamination reduction. In contrast, laminar air flow was more effective in reducing the concentration of surgical smoke in the facial areas of the surgical staff. Regarding airborne germs, monitoring should be performed at the instrument tables and close to the wound area to evaluate the risk for surgical side infections. These results can support the development of guidelines and best practices for operating room ventilation design and maintenance to improve patient safety and reduce the risk of healthcare-associated infections.

Surface Cleanliness Maintenance with Laminar Flow Based on the Characteristics of Laser-Induced Sputtering Particles in High-Power Laser Systems.

In high-power laser systems, the primary cause of contamination of optical components and degradation of spatial cleanliness is laser-induced sputtering of particles. To mitigate this problem, laminar flow is frequently utilized to control the direction and transport of these particles. This study characterizes the properties of laser-induced sputtering particles, including their flying trend, diameter range, and velocity distribution at varying time intervals. A time-resolved imaging method was employed to damage the rear surface of fused silica using a 355 nm Nd: YAG pump laser. The efficacy of laminar flow in controlling these particles was then assessed, with a particular focus on the influence of laminar flow direction, laminar flow velocity, particle flight height, and particle diameter. Our results indicate that the optimal laminar flow velocity for preventing particle invasion is highly dependent on the maximum particle attenuation distance (or safety distance), which can vary by up to two orders of magnitude. Furthermore, a laminar flow velocity of 0.5 m/s can effectively prevent particle sedimentation. Future research will aim to optimize laminar flow systems based on these findings to achieve high surface cleanliness in high-power laser systems with minimal energy consumption.

Two-Phase Biocatalysis in Microfluidic Droplets.

This Perspective discusses the literature related to two-phase biocatalysis in microfluidic droplets. Enzymes used as catalysts in biocatalysis are generally less stable in organic media than in their native aqueous environments; however, chemical and pharmaceutical compounds are often insoluble in water. The use of aqueous/organic two-phase media provides a solution to this problem and has therefore become standard practice for multiple biotransformations. In batch, two-phase biocatalysis is limited by mass transport, a limitation that can be overcome with the use of microfluidic systems. Although, two-phase biocatalysis in laminar flow systems has been extensively studied, microfluidic droplets have been primarily used for enzyme screening. In this Perspective, we summarize the limited published work on two-phase biocatalysis in microfluidic droplets and discuss the limitations, challenges, and future perspectives of this technology.

Spreading of SARS-CoV-2 via Heating, Ventilation, and Air Conditioning Systems—An Overview of Energy Perspective and Potential Solutions

Abstract The role of heating, ventilation, and air conditioning systems (HVAC) in spreading SARS-CoV-2 is a complex topic and has not been studied thoroughly. There are some existing strategies and technologies for health and high performance buildings; however, applications to other types of buildings come at large energy penalty: cost; design, regulations and standards changes, and varied public perception. In the present work, different factors and strategies are reviewed and discussed and suggested mitigations and solutions are provided including the required air flowrates with the presence of infectors with and without mask and disinfection techniques including ultraviolet (UV) light. Experimental and numerical research in open literature suggests that the airborne transmission of SARS-CoV-2 is sufficiently likely. However, in situ detailed experimental studies are still needed to understand the different scenarios of the virus spread. Displacement ventilation, underfloor air distribution, chilled beams, radiant ceiling panels, and laminar flow systems have varied effectiveness. High-efficiency particulate arrestance (HEPA) filters and UV light can clean viruses but at high energy cost. Suggested solutions to reduce the infection probability include recommended levels of ventilation and a combination of virus sampling technologies including cyclones, liquid impinger, filters, electrostatic precipitators, and water-based condensation.

Expert consensus on nursing management for patients undergoing primary percutaneous coronary intervention during the COVID-19 pandemic.

Expert consensus on nursing management for patients undergoing primary percutaneous coronary intervention during the COVID-19 pandemic.

Cost Effectiveness of Laminar Flow Systems for Total Shoulder Arthroplasty: Filtering Money from the OR?

Laminar flow ventilation systems were developed to reduce surgical contamination in joint arthroplasty to avoid periprosthetic joint infection (PJI). The goals of this study are to evaluate the cost-effectiveness and economic viability of installing and maintaining a laminar flow system in an operating room. A Monte Carlo simulation was used to evaluate the cost effectiveness of laminar flow. The variables included were cost to treat PJI, incidence of PJI, cost of laminar flow, years of operating room use, and arthroplasty volume as the dependent variable. Laminar flow would be financially-justified when 1,217 (SD: 319) TSA cases are performed annually with assumed 10% reduction in PJI from laminar flow and 487 (SD: 127) with assumed 25% reduction. In a high volume OR, laminar flow costs $25.24 per case (assuming 10% reduction) and $8.24 per case (assuming 25% reduction). Laminar flow would need to reduce the incidence of PJI by 35.1% (SD: 9.1) to be a cost-effective strategy. This analysis demonstrates the substantial arthroplasty volume and large reduction in PJI rates required to justify the installation and maintenance costs of this technology. This high cost of implementation should be considered prior to installing laminar flow systems.

Laminar flow does not affect risk of prosthetic joint infection after primary total knee replacement in Asian patients

The role of laminar flow (LAF) is contradictory with several studies failing to replicate risk reduction. The 2016 World Health Organization guidelines identified this lack of good comparative studies. To analyse the use of LAF and the incidence of prosthetic joint infections (PJIs) in Asian patients undergoing total knee replacement (TKR). Patients who underwent standard cemented posterior-stabilized TKR from 2004 to 2014 were reviewed from a prospectively collected single-surgeon database. Revision, traumatic and/or inflammatory cases were excluded. The type of airflow used was identified. The technique and surgical protocol for all procedures were similar. Tourniquets and inserted drains were routinely used. Patellar resurfacing was not performed. Patients were followed up at the outpatient clinics at regular intervals up to two years. At each visit, the patient was assessed for the occurrence of PJI. Of the 1028 procedures, 453 (44.1%) were performed in an LAF operating theatre (OT) whereas 575 (55.9%) were performed in a non-LAF OT. There were no significant differences between the two groups in terms of age, gender, or side of procedure. The overall incidence of PJI was 0.6% (N= 6). Three (50%) occurred in an LAF OT whereas three (50%) occurred in a non-LAF OT. This was not statistically significant. Laminar flow systems are costly to procure and maintain. With modern aseptic techniques, patient optimization, and use of prophylactic antibiotics, laminar flow does not appear to further reduce risk of PJI in Asian patients after TKR.

Association between air changes and airborne microbial contamination in operating rooms

BackgroundControl of airborne microbial contamination is important in operating rooms (ORs). To keep airborne contamination low, guidelines should highlight the importance of air turnover. The aims of the study were: (1) to verify the association between air turnover and airborne contamination in ORs; and (2) to identify a statistical relationship between air turnover and airborne microbial contamination. MethodsA cross sectional study was carried out from November 2014 to July 2017 in the teaching Hospital of Siena. Nineteen ORs (14 with turbulent and 5 with laminar flow ventilation) were surveyed a total of 59 times under operating conditions. Air samples were collected with an air sampler. Petri dishes, incubated at 36 °C for 48 h, were used to quantify colony forming units in the samples (CFU). The data was transformed to evaluate several statistically significant nonlinear associations between air turnover, quantified as air changes per hour (ACH) and CFU per cubic meter of air (p < 0.05). ResultsA log-linear regression model provided the best fit between ACH and CFU for laminar (p = 0.013; R2 = 0.3911) and turbulent flow systems (p = 0.002; R2 = 0.3443). The corresponding model was: ln(CFU) = (a − b*ACH), where the regression parameters were estimated at a = 4.02 and b = 0.037 for laminar flow and a = 5.24 and b = 0.067 for turbulent flow. ConclusionsItalian guidelines indicate microbial load limits of 20 and 180 CFU/m3 for operating rooms with laminar and turbulent flow ventilation, respectively. The model allowed us to evaluate the minimum number of ACHs to keep CFU within these limits. Ad hoc measurements in other environments can be used to calibrate the relationship between ACH and CFU.

The Impact of Patient and Surgical Factors for Primary Knee Arthroplasty Infection

Objective:The aim of this study was to identify risk factors for Prosthetic joint infection (PJI) following TKA.Method:The New Zealand Joint Registry database was analyzed, using revision surgery for PJI at 6 and 12 months as primary outcome measures. Statistical associations between revision for infection, with common and definable surgical and patient factors were tested. 64,566 primary TKAs have been recorded on the registry between 1999 and 2012 with minimum 12 months follow-up.Results:Multivariate analysis showed significant associations with revision for PJI (p<0.05) between male gender (odds ratio (OR) 1.85), previous surgery (osteotomy OR 2.45, ligament reconstruction OR 1.85), the use of laminar flow (OR 1.6) and the use of antibiotic-laden cement OR 1.93). There was a trend towards significance (p=0.052) with the use of surgical helmet systems (SHS) at 6 months (OR 1.53).Conclusion:These findings show patient factors remain the most important in terms of predicting early PJI following TKA. Furthermore, we found no evidence that modern SHSs reduce PJI risk and laminar flow systems may actually increase risk in TKA. The use of this registry data assists estimation of potential risk of PJI for individual patients, which is important for both informed consent and interpretation of institutional infection rates.

The impact of patient and surgical factors on the rate of infection after primary total knee arthroplasty: an analysis of 64,566 joints from the New Zealand Joint Registry.

The aim of this study was to identify risk factors for prosthetic joint infection (PJI) following total knee arthroplasty (TKA). The New Zealand Joint Registry database was analysed, using revision surgery for PJI at six and 12 months after surgery as primary outcome measures. Statistical associations between revision for infection, with common and definable surgical and patient factors were tested. A total of 64 566 primary TKAs have been recorded on the registry between 1999 and 2012 with minimum follow-up of 12 months. Multivariate analysis showed statistically significant associations with revision for PJI between male gender (odds ratio (OR) 1.85, 95% confidence interval (CI) 1.24 to 2.74), previous surgery (osteotomy (OR 2.45 95% CI 1.2 to 5.03), ligament reconstruction (OR 1.85, 95% CI 0.68 to 5.00)), the use of laminar flow (OR 1.6, 95% CI 1.04 to 2.47) and the use of antibiotic-laden cement (OR 1.93, 95% CI 1.19 to 3.13). There was a trend towards significance (p = 0.052) with the use of surgical helmet systems at six months (OR 1.53, 95% CI 1.00 to 2.34). These findings show that patient factors remain the most important in terms of predicting early PJI following TKA. Furthermore, we found no evidence that modern surgical helmet systems reduce the risk of PJI and laminar flow systems may actually increase risk in TKA. The use of this registry data assists the estimation of the risk of PJI for individual patients, which is important for both informed consent and the interpretation of infection rates at different institutions. Infection rates in TKA are related to both individual patient and surgical factors, and some modern methods of reducing infection may actually increase infection risk.

Current Evidence for the Use of Laminar Flow in Reducing Infection Rates in Total Joint Arthroplasty.

Since the introduction of laminar air flow in orthopaedic theatres by Sir John Charnley, it has widely become accepted as the standard during orthopaedic procedures such as joint arthroplasty. We present a review of available current literature for the use of laminar flow operating theatre ventilation during total joint arthroplasty and examines the effectiveness of laminar flow ventilated operating theatres in preventing post-operative wound infection. Results of our findings suggest that while bacterial and air particulate is reduced by laminar air flow systems, there is no conclusive effect on the reduction of post-operative wound infections following total joint arthroplasty. We conclude that a combination of strict aseptic technique, prophylactic antibiotics and good anaesthetic control during surgery remains crucial to reduce post-operative surgical infections.

Self-calibrating highly sensitive dynamic capacitance sensor: towards rapid sensing and counting of particles in laminar flow systems.

In this report we propose a sensor architecture and a corresponding read-out technique on silicon for the detection of dynamic capacitance change. This approach can be applied to rapid particle counting and single particle sensing in a fluidic system. The sensing principle is based on capacitance variation of an interdigitated electrode (IDE) structure embedded in an oscillator circuit. The capacitance scaling of the IDE results in frequency modulation of the oscillator. A demodulator architecture is employed to provide a read-out of the frequency modulation caused by the capacitance change. A self-calibrating technique is employed at the read-out amplifier stage. The capacitance variation of the IDE due to particle flow causing frequency modulation and the corresponding demodulator read-out has been analytically modelled. Experimental verification of the established model and the functionality of the sensor chip were shown using a modulating capacitor independent of fluidic integration. The initial results show that the sensor is capable of detecting frequency changes of the order of 100 parts per million (PPM), which translates to a shift of 1.43 MHz at 14.3 GHz operating frequency. It is also shown that a capacitance change every 3 μs can be accurately detected.

Comparison between mixed and laminar airflow systems in operating rooms and the influence of human factors: Experiences from a Swedish orthopedic center

The importance of laminar airflow systems in operating rooms as protection from surgical site infections has been questioned. The aim of our study was to explore the differences in air contamination rates between displacement ventilation and laminar airflow systems during planned and acute orthopedic implant surgery. A second aim was to compare the influence of the number of people present, the reasons for traffic flow, and the door-opening rates between the 2 systems. Active air sampling and observations were made during 63 orthopedic implant operations. The laminar airflow system resulted in a reduction of 89% in colony forming units in comparison with the displacement system (P < .001). The air samples taken in the preparation rooms showed high levels of bacterial growth (≈ 40 CFU/m(3)). Our study shows that laminar airflow-ventilated operating rooms offer high-quality air during surgery, with very low levels of colony forming units close to the surgical wound. The continuous maintenance of laminar air flow and other technical systems are crucial, because minor failures in complex systems like those in operating rooms can result in a detrimental effect on air quality and jeopardize the safety of patients. The technical ventilation solutions are important, but they do not guarantee clean air, because many other factors, such as the organization of the work and staff behavior, influence air cleanliness.

Dissolution of Weak Acids Under Laminar Flow and Rotating Disk Hydrodynamic Conditions: Application of a Comprehensive Convection–Diffusion–Migration–Reaction Transport Model

A steady-state mass transfer model that incorporates convection, diffusion, ionic migration, and ionization reaction processes was extended to describe the dissolution of weak acids under laminar flow and a rotating disk hydrodynamics. The model accurately predicted the experimental dissolution rates of benzoic acid, 2-naphthoic acid, and naproxen in unbuffered and monoprotic buffers within the physiological pH range for both hydrodynamic systems. Simulations at various flow rates indicated a cube root dependency of dissolution rate on the flow rate for a given bulk pH value for the laminar hydrodynamic system, as proposed earlier by Shah and Nelson (1975. J Pharm Sci 64(9):1518-1520) for neutral compounds. The model has limitations in its ability to accurately predict the dissolution of weak acids under certain conditions that imposed steep concentration gradients, such as high pH values, and for polyprotic buffer systems that caused the numerical solution to be unstable, suggesting that alternative numerical techniques may be required to obtain a stable numerical solution at all conditions. The model presents many advantages, most notably the ability to successfully predict the complex process under physiological conditions without simplifying assumptions, and therefore accurately representing the system in a comprehensive manner.

Prevention of Surgical Site Infections in Bone and Joint Procedures

There is strong evidence that preoperative nasal S. aureus screening/decolonization will significantly reduce surgical site infections (SSIs) after joint prostheses implantation. There is some evidence that antibiotic-containing bone cement may lower SSI rates. Timely administration of perioperative systemic antibiotic prophylaxis is recommended for patients with implants who are undergoing dental treatment, urogenital surgery, upper endoscopy, sigmoidoscopy, or colonoscopy. Advanced skin disinfection by chlorhexidine-gluconate-impregnated cloths may be protective. There is evidence that clippers are favored for hair removal, rather than razors, but no significant advantage, as compared with other modes of hair removal, has been found. Antibiotic-coated intramedullary nails and antibiotic-impregnated bone grafts may be useful for the treatment of chronic bone infections. No recommendation can be made for wound dressing types. Laminar air flow systems do not seem to prevent SSI but may even cause harm, instead. There is a strong association between the annual number of surgical procedures and low SSI rates.

A laboratory-scale device for the straightforward production of uniform, small sized cell microcapsules with long-term cell viability

Microencapsulated and genetically engineered cells may be used for prolonged delivery of therapeutically active proteins. The objective of this study was to develop a simple, inexpensive and flexible laboratory-scale device for the production of cell microcapsules, especially capsules of small diameter (<300 μm). Many microencapsulation devices are expensive, difficult to assemble and to use, and often more suitable for large-scale experiments. However, the simplicity and low price of the encapsulation system should not limit the quality of capsules and reproducibility of the process: for successful in vitro and in vivo experiments it is important to be able to produce uniform, spherical microcapsules without deformities with high reproducibility. In addition, an advantage of the present procedure compared to other similar, co-axial laminar gas flow systems is the possibility to produce also small microcapsules, less than 200 μm in diameter, with narrow size distribution. First, design, optimization and reproducibility testing of this custom-built device were carried out. Second, microencapsulated retinal pigment epithelial cells (ARPE-19) capable of secreting soluble vascular endothelial growth factor receptor 1 (sVEGFR1) were engineered. The cells remained viable in alginate-poly-L-lysine-alginate microcapsules and secreted sVEGFR1 for prolonged periods.

Patterning osteogenesis by inducible gene expression in microfluidic culture systems

The development of transitional interfacial zones between adjacent tissues remains a significant challenge for developing tissue engineering and regenerative medicine strategies. Using osteogenic differentiation as a model, we describe a novel approach to spatially regulate expression and secretion of the bone morphogenetic protein (BMP-2) in a two-dimensional field of cultured cells, by flow patterning the modulators of inducible BMP-2 gene expression. We first demonstrate control of gene expression, and of osteogenic differentiation of the cell line with inducible expression of BMP-2. Then we design laminar flow systems, with patterned delivery of Doxycycline (Dox), the expression modulator of BMP-2. The patterned concentration profiles were verified by computational simulation and dye separation experiments. Patterned differentiation experiments conducted in the flow systems for a period of three weeks showed the Dox concentration dependent osteogenic differentiation, as evidenced by mineral deposition. In summary, by combining inducible gene expression with laminar flow technologies, this study provided an innovative way to engineer tissue interfaces.

Average Crossflow Velocity in Laminar Flow Systems with Periodic Finned Surfaces

AbstractExperimental and CFD studies of the enhanced average crossflow velocity in a laminar flow system were performed. The experiments were carried out using working fluid with a kinematic viscosity of 1.8·10–6 m2/s. A steady flow Reynolds number in the laminar range of 0 &lt; Re &lt; 400 and oscillation Reynolds number in the range 0 &lt; Reosc &lt; 1000 were studied. The range of oscillation amplitude and frequency were 0.2 mm &lt; A &lt; 1.0 mm and 5 Hz &lt; f &lt; 90 Hz respectively. Three experimental configurations were studied, i.e., oscillating finned surface in a fluid at rest, which is similar to a batch configuration, steady finned flow and oscillating finned flow configurations. The acquired images were analyzed using particle image velocimetry (PIV) software. The study is also supported by CFD simulations using the software suit CFX 11.0 from ANSYS GmbH, Germany. The results of the flow visualization and PIV analyses reveal the formation of periodic vortices and increased transverse transport. The maximum enhancement of the average crossflow velocity was obtained at κ = 3. The oscillation parameters and shape of the fins have a significant influence on the flow patterns and the crossflow effects. A triangular finned geometry gives better performance considering the enhanced average crossflow velocity. In general, efficient fluid mixing is possible due to the complex flow structures generated.

Enhanced thermal stability and mismatch discrimination of mutation-carrying DNA duplexes and their kinetic and thermodynamic properties in microchannel laminar flow

This article reports the enhancement of thermal stability involving normal duplex and mutation-carrying DNA duplexes in microchannel laminar flow. The application of an in-house temperature-controllable microchannel-type flow cell is demonstrated for improved discrimination of mismatch base pairs such as A–G and T–G that are difficult to distinguish due to the rather small thermal destabilizations. Enhancement in thermal stability is reflected by an increased thermal melting temperature achieved in microchannel laminar flow as compared with batch reactions. To examine the kinetics and thermodynamics of duplex–coil equilibrium of DNA oligomers, denaturation–renaturation hysteresis curves were measured. The influence of microchannel laminar flow on DNA base mismatch analysis was described from the kinetic and thermodynamic perspectives. An increasing trend was observed for association rate constant as flow rate increased. In contrast, an apparent decrease in dissociation rate constant was observed with increasing flow rate. The magnitudes of the activation energies of dissociation were nearly constant for both the batch and microchannel laminar flow systems at all flow rates. In contrast, the magnitudes of activation energies of association decreased as flow rate increased. These results clearly show how microchannel laminar flow induces change in reaction rate by effecting change in activation energy. We anticipate, therefore, that this approach based on microchannel laminar flow system holds great promise for improved mismatch discrimination in DNA analyses, particularly on single-base-pair mismatch, by pronouncedly enhancing thermal stability.

Opal‐based isotopic proxies of paleoenvironmental conditions

The δ30Si and δ15Ndiatom of diatom opal provide a view of nutrient utilization in past oceans and are used to formulate and test hypotheses concerning Southern Ocean productivity and fluctuations in atmospheric CO2 over glacial cycles. Water column profiles of the Si and N isotopic composition of nutrients and the δ15Ndiatom of sediment core tops support the use of δ30Si and δ15Ndiatom as tracers of silicic acid and nitrate utilization, but some issues remain concerning the use of these proxies for paleoceanographic reconstructions. If average marine δ30Si changes over time, it could contribute to the observed down core variations in δ30Si. Reconstruction of deepwater δ30Si using opal from sponges or deep‐dwelling radiolarians would address this concern. Cleaning and measurement methods for δ15Ndiatom need to be standardized between laboratories and in general suffer from our lack of knowledge of how much organic matter a clean diatom frustule should contain and what its C/N ratio should be. Corresponding shifts in the δ15N and C/N of diatom opal with species composition suggests that changes in species composition contributes to the measured down core variations in N and possibly Si as well. This could be due to changes in the ecological niche represented in the sediments or, in the case of N, to species specific fractionation factors. Separation of opal sediments into something more closely resembling monospecific samples is a key development that needs to be made and may be possible using laminar flow systems like “split‐flow lateral‐transport thin fractionation” (SPLITT). In the meantime, information on the species composition of each sieved and cleaned sample analyzed needs to be collected alongside the isotopic data.