Conventional Ventilation Research Articles

Knowledge and practice of using airway pressure release ventilation mode in ARDS patients: A survey of physicians

BackgroundLimited data is available on awareness and clinical management of the airway pressure release ventilation (APRV) mode of ventilation for acute respiratory distress syndrome (ARDS) patients among physicians who work at in adult critical areas. This study aimed to assess the knowledge and current practice of using APRV mode with ARDS patients and identify barriers to not using this mode of ventilation among physicians who work in adult critical areas in Saudi Arabia. MethodsBetween November 2022 and April 2023, a cross-sectional online survey was disseminated to physicians who work in adult critical areas in Saudi Arabia. The characteristics of the respondents were analyzed using descriptive statistics. Percentages and frequencies were used to report categorical variables. ResultsOverall, 498 physicians responded to the online survey. All responders (498, 100 %) reported that APRV is indicated in patients with ARDS, but 260 (52.2 %) did not know if there was an institutionally approved APRV protocol. Prone positioning was the highest recommended intervention by 164 (33.0 %) when a conventional MV failed to improve oxygenation in patients with ARDS. 136 (27.3 %) responders stated that the P-high should be set equal to the plateau pressure on a conventional ventilator while 198 (39.8 %) said that P-low should be 0 cmH2O. Almost half of (229, 46.0 %) responders stated that the T-high should be set between 4 and 6 s, while 286 (57.4 %) said that the T-low should be set at 0.4–0.8 s. The maximum allowed tidal volume during the release phase should be 4–6 ml/kg. Moreover, just over half (257, 51.6 %) believed that the maximum allowed P-high setting should be 35 cmH2O. One third of the responders (171, 34.3 %) stated that when weaning patients with ARDS while in APRV mode, the P-high should be reduced gradually to reach a target of 10 cmH2O. However, 284 (36.9 %) thought that the T-high should be gradually increased to reach a target of 10 s. Most responders (331, 66.5 %) felt that the criteria to switch the patient to CPAP would be to have an FiO2 ≤ 0.4, P-high ≤10 cm H2O, and T-high ≥10 s. Lack of training has been the most common barrier to not using APRV by 388 (77.9 %). ConclusionThere is a lack of consensus on the use of APRV mode, probably due to several barriers. While there were some agreements on the management of ventilation and oxygenation, there were variations in the selection of the initial setting of APRV. Education, training, and the presence of standardized protocols may help to provide better management.

Venovenous extracorporeal membrane oxygenation for respiratory failure refractory to high frequency percussive ventilation

BackgroundHigh frequency percussive ventilation (HFPV) has demonstrated improvements in gas exchange, but not in clinical outcomes. ObjectivesWe utilize HFPV in patients failing conventional ventilation (CV), with rescue venovenous extracorporeal membrane oxygenation (VV ECMO) reserved for failure of HFPV, and we describe our experience with such a strategy. MethodsAll adult patients (age >18 years) placed on HFPV for failure of CV at a single institution over a 10-year period were included. Those maintained on HFPV were compared to those that failed HFPV and required VV ECMO. Survival was compared to expected survival after upfront VV ECMO as estimated by VV ECMO risk prediction models. ResultsSixty-four patients were placed on HFPV for failure of CV over a 10-year period. After HFPV initiation, the P/F ratio rose from 76mmHg to 153.3mmHg in the 69 % of patients successfully maintained on HFPV. The P/F ratio only rose from 60.3mmHg to 67mmHg in the other 31 % of patients, and they underwent rescue ECMO with the P/F ratio rising to 261.6mmHg. The P/F ratio continued to improve in HFPV patients, while it declined in ECMO patients, such that at 24 h, the P/F ratio was greater in HFPV patients. The strongest independent predictor of failure of HFPV requiring rescue VV ECMO was a lower pO2 (p = .055). Overall in-hospital survival (59.4 %) was similar to that expected with upfront ECMO (RESP score: 57 %). ConclusionsHFPV demonstrated significant and sustained improvements in gas exchange and may obviate the need for ECMO and its associated complications.

Changes in respiratory mechanics in response to crystalloid infusions in extremely premature infants.

Extremely premature infants are at a higher risk of developing respiratory distress syndrome and circulatory impairments in the first few weeks of life. Administration of normal saline boluses to manage hypotension is a common practice in preterm infants. As a crystalloid, a substantial proportion might leak into the interstitium; most consequently the lungs in the preterm cohorts, putatively affecting ventilation. We downloaded and analyzed ventilator mechanics data in infants managed by conventional mechanical ventilation and administered normal saline bolus for clinical reasons. Data were downloaded for 30 min prebolus, 60 min during the bolus followed by 30 min postbolus. Sixteen infants (mean gestational age 25.2 ± 1 wk and birth weight 620 ± 60 g) were administered 10 mL/kg normal saline over 60 min. The most common clinical indication for saline was hypotension. No significant increase was noted in mean blood pressure after the saline bolus. A significant reduction in pulmonary compliance (mL/cmH2O/kg) was noted (0.43 ± 0.07 vs. 0.38 ± 0.07 vs. 0.33 ± 0.07, P = 0.003, ANOVA). This was accompanied by an elevation in the required peak inspiratory pressure to deliver set volume-guarantee (19 ± 2 vs. 22 ± 2 vs. 22 ± 3 mmHg, P < 0.0001, ANOVA), resulting in a higher respiratory severity score. Normal saline infusion therapy was associated with adverse pulmonary mechanics. Relevant pathophysiologic mechanisms might include translocation of fluid across pulmonary capillaries affected by low vascular tone and heightened permeability in extremes of prematurity, back-pressure effects from raised left atrial volume due to immature left-ventricular myocardium; complemented by the effect of cytokine release from positive pressure ventilation.NEW & NOTEWORTHY Administration of saline boluses is common in premature infants although hypovolemia is an uncommon underlying cause of hypotension. This crystalloid can redistribute into pulmonary interstitial space. In the presence of an immature myocardium and diastolic dysfunction, excess fluid can also be "edemagenic." This study on extremely premature infants (25 wk gestation) noted adverse influence on respiratory physiology after saline infusion. Clinicians need to choose judiciously and reconsider routine use of saline boluses in premature infants.

Study of temperature distribution and smoke movement by mobile ventilation during emergency rescue in tunnel fires

Mobile ventilation unit (MVU), as a convenient and maneuverable ventilation method, can provide forced airflow for emergency ventilation to reduce tunnel fire risk. Compared with the conventional natural ventilation and mechanical ventilation, this mobile ventilation method plays a crucial role in the current tunnel fire emergency rescue. To explore the effects of MVU on the temperature or smoke spread in tunnel fires, Computational Fluid Dynamics simulation, validated by the previous experimental data, is applied in the current study. A series of tests are conducted with fire heat release rate of 1–30 MW and MVU fan flow being up to 3 × 105 m3/h. The results show the maximum tunnel ceiling temperature presents exponential attenuation with increasing fan flow and its relational expression with fan flow and fire size is proposed. Furthermore, the temperature decay distribution between upstream and downstream area is obviously different and a new coefficient γ is imported to represent the difference by connecting the fan flow and fire size. Moreover, the smoke backflow length theoretical equation in the upstream area is obtained, which can provide effective guidance to tunnel fire emergency rescue with MVU.

Research advances on neurally adjusted ventilatory assist

Mechanical ventilation has, since its introduction into clinical practice, undergone a major evolution from controlled ventilation to diverse modes of assisted ventilation. Conventional mechanical ventilators depend on flow sensors and pneumatic pressure and controllers to complete the respiratory cycle. Neurally adjusted ventilatory assist (NAVA) is a new form of assisted ventilation in recent years, which monitors the electrical activity of the diaphragm (EAdi) to provide an appropriately level of pressure support. And EAdi is the best available signal to sense central respiratory drive and trigger ventilatory assist. Unlike other ventilation modes, NAVA breathing instructions come from the center. Therefore, NAVA have the synchronous nature of the breaths and the patient-adjusted nature of the support. Compared with traditional ventilation mode, NAVA can efficiently unload respiratory muscles, relieve the risk of ventilator-induced lung injury (VILI), improve patient-ventilator coordination, enhance gas exchange, increase the success rate of weaning, etc. This article reviews the research progress of NAVA in order to provide theoretical guidance for clinical applications.

Supraglottoplasty in Congenital Laryngomalacia Patient Without Tracheostomy

Laryngomalacia is the most common congenital anomaly of the larynx in neonates. This supraglottic obstruction leads to increased work of breathing and stridor. The most common associated symptoms are swallowing dysfunction, regurgitation, cough, and sleep-disordered breathing. Spontaneous improvement usually occurs over a period of 12 months to 2 years although the majority of cases of laryngomalacia bnegins its course without any long-term sequel. Despite its benign characteristics, 10% of cases require intervention. Nowadays, the treatment consists of either wait-and-see or surgery. For severe laryngomalacia, supraglottoplasty has become the mainstay of surgical management. In this study, we report 3 cases of laryngomalacia in neonates, where patients underwent supraglottoplasty using the carbon dioxide laser without tracheostomy under conventional ventilation.

Airway Pressure Release Ventilation in COVID-19-Associated Acute Respiratory Distress Syndrome-A Multicenter Propensity Score-Matched Analysis.

Background: There are limited and partially contradictory data on the effects of airway pressure release ventilation (APRV) in COVID-19-associated acute respiratory distress syndrome (CARDS). Therefore, we analyzed the clinical outcome, complications, and longitudinal course of ventilation parameters and laboratory values in patients with CARDS, who were mechanically ventilated using APRV. Methods: Respective data from 4 intensive care units (ICUs) were collected and compared to a matched cohort of patients receiving conventional low tidal volume ventilation (LTV). Propensity score matching was performed based on age, sex, blood gas analysis, and APACHE II score at admission, as well as the implementation of prone positioning. Findings: Forty patients with CARDS, who were mechanically ventilated using APRV, and 40 patients receiving LTV were matched. No significant differences were detected for tidal volumes per predicted body weight, peak pressure values, and blood gas analyses on admission, 6 h post admission as well as on day 3 and day 7. Regarding ICU survival, no significant difference was identified between APRV patients (40%) and LTV patients (42%). Median duration of mechanical ventilation and duration of ICU treatment were comparable in both groups. Similar complication rates with respect to ventilator-associated pneumonia, septic shock, thromboembolic events, barotrauma, as well as the necessity for hemodialysis were detected for both groups. Clinical characteristics that were associated with increased mortality in a Cox proportional hazards regression analysis included age (hazard ratio [HR] 1.08, 95% confidence interval [CI] 1.04-1.1; P < .001), severe acute respiratory distress syndrome (HR 2.62, 95% CI 1.02-6.7; P = .046) and the occurrence of septic shock (HR 17.18, 95% CI 2.06-143.2; P = .009), but not the ventilation mode. Interpretation: Intensive care unit survival, duration of mechanical ventilation, and ICU treatment as well as ventilation-associated complication rates were equivalent using APRV compared to conventional LTV in patients with CARDS.

Characteristics and Risk Factors Associated with SARS-CoV-2 Pneumonias in Hospitalized Pediatric Patients: A Pilot Study.

SARS-CoV-2 pneumonia in children has a lower incidence and severity compared to adults. Risk factors are adolescence and comorbidities. Our aims were to describe the characteristics of children admitted with SARS-CoV-2 pneumonia, identify risk factors associated with severity and compare the cases according to the variant of SARS-CoV-2. This was a descriptive and retrospective study, including patients aged 0-18 years hospitalized in a tertiary-care hospital between 1 March 2020 and 1 March 2022. Epidemiological, clinical, diagnostic and therapeutic data were analyzed. Forty-four patients were admitted; twenty-six (59%) were male and twenty-seven (61%) were older than 12 years. Thirty-six (82%) had comorbidities, the most frequent of which were obesity and asthma. Seven (15.9%) patients required high-flow oxygen, eleven (25%) non-invasive ventilation and four (9.1%) conventional mechanical ventilation. In critically ill patients, higher levels of anemia, lymphopenia, procalcitonin, lactate dehydrogenase (LDH) and hypoalbuminemia and lower levels of HDL-cholesterol were detected (all p < 0.05). Prematurity (p = 0.022) was associated with intensive care unit admission. Patients were younger during the Omicron wave (p < 0.01); no variant was associated with greater severity. In conclusion, pediatric patients with a history of prematurity or with anemia, lymphopenia, elevated procalcitonin, elevated LDH levels, hypoalbuminemia and low HDL-cholesterol levels may require admission and present more severe forms. Apart from age, no notable differences between SARS-CoV-2 variant periods were found.

Impact on cerebral hemodynamics of the use of volume guarantee combined with high frequency oscillatory ventilation in a neonatal animal respiratory distress model.

No differences were observed at cerebral hemodynamic between respiratory assistance in HFOV with and without VG, being the latter ventilatory strategy equally safe. • Preterm have a situation of fragility of cerebral perfusion wich means that any mechanical ventilation strategy can have a significant influence. High-frequency oscillatory ventilation (HFOV) is an alternative to conventional mechanical ventilation (CMV). Recently, the use of volume guarantee (VG) combined with HFOV has been suggested as a safe strategy capable of reducing the damage induced by ventilation in immature lungs. Several studies have compared CMV and HFOV and their effects at hemodynamic level. It is known that the use of high mean airway pressure in HFOV can cause an increase in pulmonary vascular resistance with a decrease in thoracic venous return. • The possible impact of VAFO + VG on cerebral hemodynamics is unknown. Due the lack of studies and the existing controversy, we have carried out this research project in an experimental animal model with the aim of evaluating the cerebral hemodynamic repercussion of the use of VG in HFOV compared to the classic strategy without VG.

Total liquid ventilation in an ovine model of extreme prematurity: a randomized study.

This study aimed at comparing cardiorespiratory stability during total liquid ventilation (TLV)-prior to lung aeration-with conventional mechanical ventilation (CMV) in extremely preterm lambs during the first 6 h of life. 23 lambs (11 females) were born by c-section at 118-120 days of gestational age (term = 147 days) to receive 6 h of TLV or CMV from birth. Lung samples were collected for RNA and histology analyses. The lambs under TLV had higher and more stable arterial oxygen saturation (p = 0.001) and cerebral tissue oxygenation (p = 0.02) than the lambs in the CMV group in the first 10 min of transition to extrauterine life. Although histological assessment of the lungs was similar between the groups, a significant upregulation of IL-1a, IL-6 and IL-8 RNA in the lungs was observed after TLV. Total liquid ventilation allowed for remarkably stable transition to extrauterine life in an extremely preterm lamb model. Refinement of our TLV prototype and ventilation algorithms is underway to address specific challenges in this population, such as minimizing tracheal deformation during the active expiration. Total liquid ventilation allows for remarkably stable transition to extrauterine life in an extremely preterm lamb model. Total liquid ventilation is systematically achievable over the first 6 h of life in the extremely premature lamb model. This study provides additional incentive to pursue further investigation of total liquid ventilation as a transition tool for the most extreme preterm neonates.

A comprehensive optimization study of personal cooling radiant desks integrated to HVAC system for energy efficiency and thermal comfort in office buildings

Personal comfort systems (PCS) maintain the occupant's preferred thermal environment and expand his thermal comfort experience under varying environmental conditions. Among PCSs, radiant-based systems are popular due to their comfort and energy efficiency. A personal cooling radiant desk (PCRD) in conjunction with conventional heating, ventilation, and air conditioning (HVAC) has proven to reduce energy costs. A system's energy and thermal performance, however, depends on various factors making it important to identify the optimal design parameters of a PCRD coupled with HVAC system in an office space. To optimize the energy and thermal performance of the PCRD-HVAC system, a numerical/mathematical model is developed simulating different design parameters. The model uses an artificial neural network (ANN), combined with a multi-objective genetic algorithm (MOGA) to identify the optimal design parameters. The decision variables include the supply temperature, the temperature, and the flow rate of chilled water flowing inside the desk. The study's findings show that the optimal design parameters achieved a balance between thermal comfort and energy efficiency. The recommended design parameters result in an annual energy consumption of 3880 kWh and a predicted percentage of dissatisfied individuals (PPD) of 6 %. The experiment is carried out to validate the model showed a maximum relative error of only 12.54 %. The results of this study have important implications for designing sustainable cooling solutions for office spaces in hot climates. The successful optimization of the PCRD system highlights the importance of balancing energy efficiency and thermal comfort in designing sustainable cooling solutions.

Modifying Candidacy and Management to Improve Extracorporeal Support During Supply-Demand Mismatch

BackgroundCandidacy for venovenous extracorporeal membrane oxygenation is dictated by ECMO to Rescue Lung Injury in Severe ARDS (EOLIA) criteria. We evaluated the effect of modifying candidacy on the basis of escalating demand and limited resources. MethodsWe retrospectively reviewed adult patients diagnosed with COVID-19–related severe acute respiratory distress syndrome who failed to respond to conventional ventilation and required extracorporeal support at our institution. Candidacy was restricted with a published probability model because of supply-demand mismatch and high mortality observed after the first surge. Age <55 years, mechanical ventilation days <3, and minimal comorbidities were prioritized. Primary outcomes included time to decannulation, extubation, tracheostomy, discharge, and death. Hospital and intensive care unit length of stay and hospitalization costs were evaluated. Predictors included cannulation strategy, before and after criteria implementation, use of cytoreductive techniques, timing of tracheostomy, and body mass index. Propensity score matching, multistate Cox proportional hazards models, and generalized linear models were used. ResultsOur sample comprised 105 patients, 26 from before criteria implementation (“before” phase) and 79 after (“after” phase). Propensity score results indicated no significant differences in death (P = .152) and costs (P = .063) between the groups. Patients who received cytoreductive therapy had lower total costs (P = .033). Those who underwent single-site cannulation had higher probability of decannulation (P = .009), discharge (P < .001), tracheostomy (P < .001), and extubation alive (P < .001) and lower risk of death (P = .017). ConclusionsModifying candidacy by objective criteria with the use of adjunctive therapies may improve outcomes and lower costs during periods of supply-demand mismatch.

Comparison of conventional mechanical ventilation and high-frequency oscillatory ventilation in congenital diaphragmatic hernias: a systematic review and meta-analysis

Outcomes of conventional mechanical ventilation (CMV) and high-frequency oscillatory ventilation (HFOV) in patients with congenital diaphragmatic hernia (CDH) were compared through a systematic review and meta-analysis. Outcome measures included mortality and incidence of chronic lung disease (CLD). Odds ratio (OR) and 95% confidence interval (95%CI) were evaluated. Subgroup analyses were performed according to the strategy for applying HFOV in CDH patients. Group A: CMV was initially applied in all CDH patients, and HFOV was applied in unstable patients. Group B: chronologically analyzed. (CMV and HFOV era) Group C: CMV or HFOV was used as the initial MV. Of the 2199 abstracts screened, 15 full-text articles were analyzed. Regarding mortality, 16.7% (365/2180) and 32.8% (456/1389) patients died in CMV and HFOV, respectively (OR, 2.53; 95%CI 2.12–3.01). Subgroup analyses showed significantly worse, better, and equivalent mortality for HFOV than that for CMV in group A, B, and C, respectively. CLD occurred in 32.4% (399/1230) and 49.3% (369/749) patients in CMV and HFOV, respectively (OR, 2.37; 95%CI 1.93–2.90). The evidence from the literature is poor. Mortality and the incidence of CLD appear worse after HFOV in children with CDH. Cautious interpretation is needed due to the heterogeneity of each study.

Natural ventilation in high-rise office building – Comfort and energy performance

AbstractThe application of natural ventilation strategies in high-rise office buildings is considered one of the most promising trends to address high energy performance and enhance the indoor thermal comfort levels in interior office spaces. In this regard, this study attempts to assess the potential of natural ventilation strategies of a specific, previously investigated, envelope design of a high-rise office building located in a temperate climate zone. Different summer natural ventilation approaches were tested using the building energy simulation program IDA ICE 4.8, evaluating thermal comfort and energy demand. The findings indicated that considerable energy savings can be achieved, compared to conventional mechanical ventilation and air conditioning systems.

Early Ventilator Management for Infants With Congenital Diaphragmatic Hernia: Impact of a Standardized Clinical Practice Guideline

BackgroundInfants with congenital diaphragmatic hernia (CDH) experience high morbidity and mortality due to pulmonary arterial hypertension and hypoplasia. Mechanical ventilation is a central component of CDH management. Our objective was to evaluate the impact of a standardized clinical practice guideline (implemented in January 2012) on ventilator management for infants with CDH, and associate management changes with short-term outcomes, specifically extracorporeal membrane oxygenation (ECMO) utilization and survival to discharge. MethodsWe conducted a retrospective pre-post study of 103 CDH infants admitted from January 2007–July 2021, divided pre- (n = 40) and post-guideline (n = 63). Clinical outcomes, ventilator settings, and blood gas values in the first 7 days of mechanical ventilation were compared between the pre- and post-guideline cohorts. ResultsPost-guideline, ECMO utilization decreased (11% vs 38%, p = 0.001) and survival to discharge improved (92% vs 68%, p = 0.001). More post-guideline patients remained on conventional mechanical ventilation without need for escalation to high-frequency ventilation or ECMO, and had higher pressures and PaCO2 with lower FiO2 and PaO2 (p < 0.05). ConclusionsStandardized ventilator management optimizing pressures for adequate lung expansion and minimizing oxygen toxicity improves outcomes for infants with CDH. Level of EvidenceIII.

Outdoor thermal condition based-segmented intermittent demand-controlled ventilation for constant-air-volume system

The outdoor air supply is mandatory for healthy built environments but consumes a large amount of building energy. The demand-controlled ventilation method adjusts the outdoor air supply for both indoor air quality and high energy efficiency. However, the conventional demand-controlled ventilation method does not apply to the constant-air-volume ventilation system. Since the constant-air-volume ventilation system is widely used in practice for outdoor air supply, this study proposes a novel demand-controlled ventilation method, i.e., the segmented intermittent demand-controlled ventilation, to improve the energy efficiency of the constant-air-volume ventilation system with indoor air quality. The proposed method intermittently supplies outdoor air to reduce the amount of outdoor air supply for energy saving of ventilation fan while satisfying indoor air quality. Moreover, the proposed method divides the working time into segments and adjusts the outdoor air supply of each segment according to the outdoor weather for cooling/heating energy saving. This study reveals the detailed mechanisms of energy saving of the proposed method and develops an optimization algorithm to maximize the energy saving of the proposed method with indoor air quality. The proposed method is tested for both cooling and heating scenarios in different climate zones. The results show that compared with the conventional methods and the existing intermittent demand-controlled ventilation, the proposed method achieves weekly energy savings of 18.0%–62.4% and 4.3%–6.8% respectively. The proposed method can contribute to the development of low-carbon and healthy built environments.

Comparison of Bubble CPAP Versus Conventional Ventilation in Neonates Having Respiratory Distress

Objective: To compare the outcomes of bubble continuous positive airway pressure (B-CPAP) versus ventilator continuous positive airway pressure (V-CPAP) in neonates experiencing respiratory distress. Methodology: This randomized controlled trial was conducted at the Department of Neonatology, Children's Hospital, Pakistan Institute of Medical Sciences (PIMS), Islamabad, from March 1, 2021, to August 31, 2021. A total of 150 neonates of both genders who presented with respiratory distress and were delivered at &gt;32 weeks of gestation, weighing &gt;1500 grams. The neonates were then randomly allocated to two groups using a lottery method. Treatment failure was defined as a neonate's inability to maintain a SpO2 greater than 90% or an arterial partial pressure (PaO2) greater than 50 mmHg with a maximal CPAP of &gt;7 cm of water and a FiO2 greater than 0.6 or the necessity of mechanical ventilation. Results: Of these, 82 (54.7%) were male, and 68 (45.3%) were female, resulting in a male-to-female ratio of 1.2:1. The mean gestational age was 36±2.49 weeks in the B-CPAP group and 35.52±1.36 weeks in the V-CPAP group. The mean birth weight was 2381±506.4 grams in the B-CPAP group and 2187.3±427.49 grams in the V-CPAP group. Out of the 75 neonates in the B-CPAP group, 10 (13.3%) were classified as treatment failures, while 19 (25.3%) out of 75 neonates in the V-CPAP group met the criteria for treatment failure, according to our operational definition. Although the failure rate was slightly higher in patients receiving V-CPAP for the management of respiratory distress, these differences were not statistically significant (p-value= 0.052). Conclusion: In the treatment of neonatal respiratory distress, there was no significant difference in the failure rate between bubble CPAP and ventilatory CPAP. Regardless of the neonate's gender, birth weight, gestational age, or Silverman score, bubble CPAP may be considered as the primary mode of respiratory support for neonates with respiratory distress.

A meta-analysis of conventional assisted ventilation versus continuous lung recruitment maneuver in preterm infants.

A meta-analysis of conventional assisted ventilation versus continuous lung recruitment maneuver in preterm infants.

Bone Cement Fumes Generated in Laminar Airflow Versus Conventionally Ventilated Operating Rooms: Does the Mixing System Matter?

Bone cement is commonly utilized in a variety of orthopaedic procedures and contains methylmethacrylate (MMA) monomer. MMA is a colorless, clear, flammable liquid of intense odor. Its vapor concentration in the immediate breathing zone can vary considerably in the operative setting and, in higher concentrations, can become an occupational health hazard. Therefore, reducing MMA vapor is desirable. The aim of this study was to compare the MMA vapor levels emitted during mixing among 5 commercially available cement-mixing systems across 2 operative settings: an operating room (OR) with conventional ventilation (CV) and an OR with laminar airflow (LAF). A prospective, in vitro study was conducted at a single hospital in an OR with LAF and in an OR with CV. MMA vapor release during the cement preparation of a SAWBONES femoral canal was measured with use of a calibrated MiniRAE 3000. A total of 5 different vacuum cement-mixing systems were utilized to mix the same cement type according to the manufacturer instructions of each system. MMA vapor concentrations were measured during 5 phases of mixing, and each mixing system was randomly utilized 10 times in each OR. When comparing the MMA concentration levels of each system between the 2 settings, emissions remained generally higher in the CV setting for every system and in nearly every phase. Among the 5 systems analyzed, System #5, the only entirely closed system, had the lowest overall emissions for each of the 5 phases in the CV setting. This study demonstrated that an operative environment with LAF is conducive to clearing the fumes of MMA during mixing as well as limiting the amount of time that residual fumes linger after mixing. Additionally, the entirely closed cement-mixing system was the most effective in minimizing fume levels within the CV setting. Utilizing this closed system, especially in an OR with CV, may reduce exposure to MMA fumes from bone cement, potentially creating a more favorable working environment. This study provides evidence that a closed cement-mixing system utilized under vacuum in both an OR with CV and an OR with LAF is effective in keeping MMA fume levels below those considered harmful by the U.S. Occupational Safety and Health Administration.

Experimental study on air extraction performance of novel rooftop natural ventilators

The air extraction performance of novel rooftop natural ventilators was experimentally investigated and compared to the conventional turbine ventilator. The newly developed ventilator integrates a vertical-axis wind turbine with a static ventilator, where the wind turbine, equipped with 8C-type rotors and six rotor guide vanes, serves to drive the rotation of the static ventilator. The static ventilator is an exhaust cowl with curved guide vanes inside. The wind turbine, including 8C-rotors and 6 flat guide vanes, is 10 cm in height with a diameter of 21 cm. The dimensions of static ventilation are 7 cm in height, and 26 cm and 21 cm in bottom and top diameters, respectively, with curved guide vanes inside. Various heights of guide vanes (0.5 and 3 cm) and numbers of guide vanes (0, 6 and 12) were investigated. An open wind tunnel system was used to simulate the condition where the wind blows over the rooftop ventilator. The ventilator air extraction rates were determined using the mean air velocities, measured using a hot-wire anemometer at an open slot in a ventilation pipe connected to the ventilator. The results indicated that the rotating and non-rotating novel ventilators exhibited superior air extraction rates at most tested wind speeds compared to the rotating conventional turbine ventilator. The curved guide vanes inside the static ventilator played the most important role in the air extraction rate. This study suggests that a static ventilator with an adequate guide-vane design may be more suitable for rooftop ventilation than a conventional turbine ventilator.