Search

Abstract Background Lung perfusion defects, mainly due to endothelial and coagulation activation, are a key contributor to COVID-19 respiratory failure. COVID-19 patients may also develop acute kidney injury (AKI) because of renal perfusion deficit. We aimed to explore AKI-associated factors and the independent prediction of standardized minute ventilation (MV)—a proxy of alveolar dead space—on AKI onset and persistence in COVID-19 mechanically ventilated patients. Methods This is a multicenter observational cohort study. We enrolled 157 COVID-19 patients requiring mechanical ventilation and intensive care unit (ICU) admission. We collected clinical information, ventilation, and laboratory data. AKI was defined by the 2012 KDIGO guidelines and classified as transient or persistent according to serum creatinine criteria persistence within 48 h. Ordered univariate and multivariate logistic regression analyses were employed to identify variables associated with AKI onset and persistence. Results Among 157 COVID-19 patients on mechanical ventilation, 47% developed AKI: 10% had transient AKI, and 37% had persistent AKI. The degree of hypoxia was not associated with differences in AKI severity. Across increasing severity of AKI groups, despite similar levels of paCO2, we observed an increased MV and standardized MV, a robust proxy of alveolar dead space. After adjusting for other clinical and laboratory covariates, standardized MV remained an independent predictor of AKI development and persistence. d-dimer levels were higher in patients with persistent AKI. Conclusions In critically ill COVID-19 patients with respiratory failure, increased wasted ventilation is independently associated with a greater risk of persistent AKI. These hypothesis-generating findings may suggest that perfusion derangements may link the pathophysiology of both wasted ventilation and acute kidney injury in our population.

Copyright of INSPILIP. Revista Ecuatoriana de Ciencia, Tecnología e Innovacion en Salud Pública is the property of Instituto Nacional de Investigacion en Salud Publica (INSPI) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Objective: Our study aimed to investigate the effects of different extracorporeal membrane oxygenation (ECMO) blood flow rates on lung perfusion assessment using the saline bolus-based electrical impedance tomography (EIT) technique in patients on veno-venous (VV) ECMO. Methods: In this single-centered prospective physiological study, patients on VV ECMO who met the ECMO weaning criteria were assessed for lung perfusion using saline bolus-based EIT at various ECMO blood flow rates (gradually decreased from 4.5 L/min to 3.5 L/min, 2.5 L/min, 1.5 L/min, and finally to 0 L/min). Lung perfusion distribution, dead space, shunt, ventilation/perfusion matching, and recirculation fraction at different flow rates were compared. Results: Fifteen patients were included. As the ECMO blood flow rate decreased from 4.5 L/min to 0 L/min, the recirculation fraction decreased significantly. The main EIT-based findings were as follows. (1) Median lung perfusion significantly increased in region-of-interest (ROI) 2 and the ventral region [38.21 (34.93–42.16)% to 41.29 (35.32–43.75)%, p = 0.003, and 48.86 (45.53–58.96)% to 54.12 (45.07–61.16)%, p = 0.037, respectively], whereas it significantly decreased in ROI 4 and the dorsal region [7.87 (5.42–9.78)% to 6.08 (5.27–9.34)%, p = 0.049, and 51.14 (41.04–54.47)% to 45.88 (38.84–54.93)%, p = 0.037, respectively]. (2) Dead space significantly decreased, and ventilation/perfusion matching significantly increased in both the ventral and global regions. (3) No significant variations were observed in regional and global shunt. Conclusions: During VV ECMO, the ECMO blood flow rate, closely linked to recirculation fraction, could affect the accuracy of lung perfusion assessment using hypertonic saline bolus-based EIT. [ABSTRACT FROM AUTHOR]

This is the first study to describe the daytime evolution of respiratory parameters in mechanically ventilated COVID-19 patients. The data base refers to patients hospitalised in the intensive care unit (ICU) at Arequipa Hospital (Peru, 2335 m) in 2021. In both survivors (S) and non-survivors (NS) patients, a remarkable decrease in respiratory compliance was observed, revealing a proportional decrease in inflatable alveolar units. The S and NS patients were all hyperventilated and their SatO2 was maintained at >90%. However, while S remained normocapnic, NS developed progressive hypercapnia. We compared the efficiency of O2 uptake and CO2 removal in the air blood barrier relying on a model allowing to partition between diffusion and perfusion limitations to gas exchange. The decrease in O2 uptake was interpreted as diffusion limitation, while the impairment in CO2 removal was modelled by progressive perfusion limitation. The latter correlated with the increase in positive end-expiratory pressure (PEEP) and plateau pressure (Pplat), leading to capillary compression, increased blood velocity, and considerable shortening of the air-blood contact time. [ABSTRACT FROM AUTHOR]

Background: Lung perfusion defects, mainly due to endothelial and coagulation activation, are a key contributor to COVID-19 respiratory failure. COVID-19 patients may also develop acute kidney injury (AKI) because of renal perfusion deficit. We aimed to explore AKI-associated factors and the independent prediction of standardized minute ventilation (MV)—a proxy of alveolar dead space—on AKI onset and persistence in COVID-19 mechanically ventilated patients. Methods: This is a multicenter observational cohort study. We enrolled 157 COVID-19 patients requiring mechanical ventilation and intensive care unit (ICU) admission. We collected clinical information, ventilation, and laboratory data. AKI was defined by the 2012 KDIGO guidelines and classified as transient or persistent according to serum creatinine criteria persistence within 48 h. Ordered univariate and multivariate logistic regression analyses were employed to identify variables associated with AKI onset and persistence. Results: Among 157 COVID-19 patients on mechanical ventilation, 47% developed AKI: 10% had transient AKI, and 37% had persistent AKI. The degree of hypoxia was not associated with differences in AKI severity. Across increasing severity of AKI groups, despite similar levels of paCO2, we observed an increased MV and standardized MV, a robust proxy of alveolar dead space. After adjusting for other clinical and laboratory covariates, standardized MV remained an independent predictor of AKI development and persistence. d-dimer levels were higher in patients with persistent AKI. Conclusions: In critically ill COVID-19 patients with respiratory failure, increased wasted ventilation is independently associated with a greater risk of persistent AKI. These hypothesis-generating findings may suggest that perfusion derangements may link the pathophysiology of both wasted ventilation and acute kidney injury in our population. [ABSTRACT FROM AUTHOR]

ABSTRACTObjective To investigate the influence of the dead space in disposable blood sampling needle on activated partial thromboplastin time (APTT), FVIII level and pharmacokinetic (PK) profiles in children with hemophilia.Methods Children (

Background Cranioplasty can be a challenging procedure in certain patients, such as those with scalp necrosis, or when performed after multiple surgical procedures. Herein, we present a patient in whom a part of the skull was placed inside out in a setting where the scalp wound could not be simply sutured because of multiple previous operations. Methods A 66-year-old patient with a history of multiple craniotomies to resect an intracranial tumor suffered significant skin flap necrosis after harvesting the superficial temporal artery for a bypass intending to ligate the internal carotid artery. He subsequently underwent a one-stage reconstruction surgery, in which the central part of the bone was excised, turned over, and fixed at the inner plate of the bone flap on the outside, and the outer plate on the inside. Results This technique reduced the skin tension and reduced the epidural dead space, allowing skin flap healing with acceptable cosmetic results. Conclusion "Inside out cranioplasty" is a valid option for one-stage reconstruction in the cases with scalp necrosis. [ABSTRACT FROM AUTHOR]

ABSTRACTEfficiently querying multiple spatial datasets is a challenging task in geoscience. The majority of spatial processing techniques use minimum bounding box (MBB) to approximate neighbouring spatial objects and and place them adjacent in the spatial index. However, due to the existence of redundant space in MBB of these methods, this problem can significantly reduce the query efficiency. In this paper, we propose a novel two-stage adaptive method of clipping the bounding box in spatial query, called IB-CBB (Intersection Based Clipped Bounding Boxes). The first stage employs a clipped bounding box, which records the redundant spatial spaces within the bounding box of the spatial index by calculating the clip points. As a result, the computational complexity of indexed child nodes in the query process is reduced. The second stage optimizes the above query algorithm by judging the intersection of the query box and the MBB of index node, significantly reducing the query time. Experiments demonstrate that IB-CBB outperforms the baseline method in terms of reducing the computational time.

Background: The dead space fraction (VD/VT) has proven to be a powerful predictor of higher mortality in acute respiratory distress syndrome (ARDS). However, its measurement relies on expired carbon dioxide, limiting its widespread application in clinical practice. Several estimates employing routine variables have been found to be reliable substitutes for direct measurement of VD/VT. In this study, we evaluated the prognostic value of these dead space estimates obtained in the first 7 days following the initiation of ventilation. Methods: This retrospective observational study was conducted using data from the Chinese database in intensive care (CDIC). Eligible participants were adult ARDS patients receiving invasive mechanical ventilation while in the intensive care unit between 1st January 2014 and 31st March 2021. We collected data during the first 7 days of ventilation to calculate various dead space estimates, including ventilatory ratio (VR), corrected minute ventilation (V˙Ecorr), VD/VT (Harris–Benedict), VD/VT (Siddiki estimate), and VD/VT (Penn State estimate) longitudinally. A time-dependent Cox model was used to handle these time-varying estimates. Results: A total of 392 patients (median age 66 [interquartile range: 55–77] years, median SOFA score 9 [interquartile range: 7–12]) were finally included in our analysis, among whom 132 (33.7%) patients died within 28 days of admission. VR (hazard ratio [HR]=1.04 per 0.1 increase, 95% confidence interval [CI]: 1.01 to 1.06; P=0.013), V˙Ecorr (HR=1.08 per 1 increase, 95% CI: 1.04 to 1.12; P < 0.001), VD/VT (Harris–Benedict) (HR=1.25 per 0.1 increase, 95% CI: 1.06 to 1.47; P=0.006), and VD/VT (Penn State estimate) (HR=1.22 per 0.1 increase, 95% CI: 1.04 to 1.44; P=0.017) remained significant after adjustment, while VD/VT (Siddiki estimate) (HR=1.10 per 0.1 increase, 95% CI: 1.00 to 1.20; P=0.058) did not. Given a large number of negative values, VD/VT (Siddiki estimate) and VD/VT (Penn State estimate) were not recommended as reliable substitutes. Long-term exposure to VR >1.3, V˙Ecorr >7.53, and VD/VT (Harris–Benedict) >0.59 was independently associated with an increased risk of mortality in ARDS patients. These findings were validated in the fluid and catheter treatment trial (FACTT) database. Conclusions: In cases where VD/VT cannot be measured directly, early time-varying estimates of VD/VT such as VR, V˙Ecorr, and VD/VT (Harris–Benedict) can be considered for predicting mortality in ARDS patients, offering a rapid bedside application.

Background: Large tissue defects following pelvic exenteration (PE) fill with fluid and small bowel, leading to the empty pelvis syndrome (EPS). EPS causes a constellation of complications including pelvic sepsis and reduced quality of life. EPS remains poorly defined and cannot be objectively measured. Pathophysiology of EPS is multifactorial, with increased pelvic dead space potentially important. This study aims to describe methodology to objectively measure volumetric changes relating to EPS. Methods: The true pelvis is defined by the pelvic inlet and outlet. Within the true pelvis there is physiological pelvic dead space (PDS) between the peritoneal reflection and the inlet. This dead space is increased following PE and is defined as the exenteration pelvic dead space (EPD). EPD may be reduced with pelvic filling and the volume of filling is defined as the pelvic filling volume (PFV). PDS, EPD, and PFV were measured intraoperatively using a bladder syringe, and Archimedes' water displacement principle. Results: A patient undergoing total infralevator PE had a PDS of 50 ml. A rectus flap rendered the pelvic outlet watertight. EPD was then measured as 540 ml. Therefore there was a 10.8-fold increase in true pelvis dead space. An omentoplasty was placed into the EPD, displacing 130 ml; therefore, PFV as a percentage of EPD was 24.1%. Conclusions: This is the first reported quantitative assessment of pathophysiological volumetric changes of pelvic dead space; these measurements may correlate to severity of EPS. PDS, EPD, and PFV should be amendable to assessment based on perioperative cross-sectional imaging, allowing for potential prediction of EPS-related outcomes. [ABSTRACT FROM AUTHOR]

Efficiently querying multiple spatial datasets is a challenging task in geoscience. The majority of spatial processing techniques use minimum bounding box (MBB) to approximate neighbouring spatial objects and and place them adjacent in the spatial index. However, due to the existence of redundant space in MBB of these methods, this problem can significantly reduce the query efficiency. In this paper, we propose a novel two-stage adaptive method of clipping the bounding box in spatial query, called IB-CBB (Intersection Based Clipped Bounding Boxes). The first stage employs a clipped bounding box, which records the redundant spatial spaces within the bounding box of the spatial index by calculating the clip points. As a result, the computational complexity of indexed child nodes in the query process is reduced. The second stage optimizes the above query algorithm by judging the intersection of the query box and the MBB of index node, significantly reducing the query time. Experiments demonstrate that IB-CBB outperforms the baseline method in terms of reducing the computational time. [ABSTRACT FROM AUTHOR]

Abstract The circle breathing system was unsafe for spontaneous breathing because of hypercapnia during anesthesia. Few studies have examined the minimizing dead space in breathing tubing. This study investigated one‐way valves in the breathing tubing during spontaneous breathing in piglets. Six female piglets aged 68–71 days spontaneously breathed sevoflurane for 4 h randomly via traditional or anti‐rebreathing tubing. Arterial carbon dioxide tension (PaCO2) and respiratory characteristics were used to assess spontaneous breathing efficiency. mRNA‐based methods, immunohistochemistry, and histology were used to assess the lungs. After induction, all piglets had mild hypercapnia. Those who breathed via traditional tubing experienced severe hypercapnia and required assisted ventilation (mean [95% confidence interval for mean]: 3 [0.5; 5.5] times) over 4 h. Piglets who breathed via anti‐rebreathing tubing were able to normalize without assisted ventilation in less than 3 h and maintained. PaCO2 was higher in the traditional group than the anti‐rebreathing group at 3 and 4 hours (46.3 [42.1; 50.5] vs. 38.3 [34.1; 42.5] mmHg, p = 0.020; 46.3 [42.6; 50.0] vs. 40.7 [37.0; 44.4] mmHg, p = 0.040). However, one‐way valves increased resistance to breathing. For the lungs, mRNA‐based methods indicated higher expressions of cyclin‐dependent kinase, cell division cycle 20, and cyclin B2 in the traditional group; immunohistochemistry identified higher expression of phosphorylated histone 2AX in the traditional group; histology showed similar damage between the groups. These findings suggest that one‐way valves inside breathing tubing reduced dead space during spontaneous breathing and enhanced inhalation anesthesia advantages in the circle breathing system.

This is the first study to describe the daytime evolution of respiratory parameters in mechanically ventilated COVID-19 patients. The data base refers to patients hospitalised in the intensive care unit (ICU) at Arequipa Hospital (Peru, 2335 m) in 2021. In both survivors (S) and non-survivors (NS) patients, a remarkable decrease in respiratory compliance was observed, revealing a proportional decrease in inflatable alveolar units. The S and NS patients were all hyperventilated and their SatO2 was maintained at >90%. However, while S remained normocapnic, NS developed progressive hypercapnia. We compared the efficiency of O2 uptake and CO2 removal in the air blood barrier relying on a model allowing to partition between diffusion and perfusion limitations to gas exchange. The decrease in O2 uptake was interpreted as diffusion limitation, while the impairment in CO2 removal was modelled by progressive perfusion limitation. The latter correlated with the increase in positive end-expiratory pressure (PEEP) and plateau pressure (Pplat), leading to capillary compression, increased blood velocity, and considerable shortening of the air-blood contact time.

Abstract Background Inhaled sedation during invasive mechanical ventilation in patients with acute respiratory distress syndrome (ARDS) has received increasing attention. However, inhaled sedation devices increase dead-space ventilation and an undesirable effect is the increase in minute ventilation needed to maintain CO2 removal. A consequence of raising minute ventilation is an increase in mechanical power (MP) that can promote lung injury. However, the effect of inhaled sedation devices on MP remains unknown. Methods We conducted a bench study to assess and compare the effects of three devices delivering inhaled sevoflurane currently available in ICU (AnaConDa-50 mL (ANA-50), AnaConDa-100 mL (ANA-100), and MIRUS) on MP by using a test lung model set with three compliances (20, 40, and 60 mL/cmH2O). We simulated lung-protective ventilation using a low tidal volume and two levels of positive end-expiratory pressure (5 and 15 cmH2O) under ambient temperature and dry conditions. Following the insertion of the devices, either the respiratory rate or tidal volume was increased in 15%-steps until end-tidal CO2 (EtCO2) returned to the baseline value. MP was calculated at baseline and after EtCO2 correction using a simplified equation. Results Following device insertion, the EtCO2 increase was significantly greater with MIRUS (+ 78 ± 13%) and ANA-100 (+ 100 ± 11%) than with ANA-50 (+ 49 ± 7%). After normalizing EtCO2 by adjusting minute ventilation, MP significantly increased by more than 50% with all inhaled sedation devices compared to controls. The lowest increase in MP was observed with ANA-50 (p 50% with all devices after normalizing EtCO2 by adjusting minute ventilation. Conclusion Inhaled sedation devices substantially increased MP in this bench model of protective ventilation, which might limit their benefits in ARDS.

OBJECTIVE: To evaluate the agreement between the Tafonius large animal ventilator-integrated volumetric capnography (vCap) software and the Respironics NICO noninvasive cardiac output monitor reference system. ANIMALS: Data were collected from 56 healthy adult horses undergoing general anesthesia. METHODS: Animals were placed under general anesthesia and connected to the Tafonius large animal ventilator circle system. A flow partitioning device with CO2 and flow sensors was utilized to couple the endotracheal tube to the NICO monitor. Tafonius CO2 and flow sensors are incorporated into the Y-piece of the breathing circuit. Arterial blood samples were collected to determine the partial pressure of arterial carbon dioxide (PaCO2) immediately before data collection. The PaCO2 was input into the Tafonius and NICO monitor, and dead space ventilation (%Vd), end-tidal CO2 partial pressure (ETco2), mixed-expired CO2 partial pressure (Peco2), and expired tidal volume (VT) were calculated over a single breath. Multiple measurements were completed for each patient, with a total of 200 paired data points collected for analysis. Data were assessed for normality, and Bland-Altman analysis was performed. Bias and 95% limits of agreement were calculated. RESULTS: The limits of agreement for %Vd of the ventilator-derived measurements fell within ± 10% of the NICO monitor reference method. CLINICAL RELEVANCE: Our results indicate that, when compared to the NICO monitor method, the Tafonius-integrated vCap software provides clinically acceptable values of PECO2, VT, and %Vd in healthy adult horses. [ABSTRACT FROM AUTHOR]

Abstract Between 2017 and 2021, the Brazilian Unified Health System (BUHS) administered a total of 527,903,302 doses of immunizations. Each immunization results in the presence of a residual volume (RV) due to syringe dead space (DS). The International Organization for Standardization 7886-1 allows a DS of up to 0.07mL in sterile single-use hypodermic syringes with volumes less than 5mL. This study aims to quantify the DS of immunization devices used in Brazil, study the best combinations of needles and syringes to minimize RV, estimate the number of wasted doses from 2017 to 2021, and evaluate the impact on the BUHS. Pneumococcal 10 vaccine with a 25x6mm needle and a regular 1mL syringe exhibited a significantly higher average RV (0.0826mL) and waste rate (14.42%). It was observed that for some intramuscular vaccines, there is less waste when using a 20x5.5mm needle compared to a 25x6mm needle. The use of syringes with plunger stoppers that penetrate the syringe barrel, denoted as low dead space syringes, results in less RV and an estimated difference in the waste rate of approximately 10% compared to the regular syringe. The estimated number of wasted doses from 2017 to 2021 by BUHS is approximately 32 million doses.

Coronavirus disease 2019 (COVID-19) pneumonia can lead to acute hypoxemic respiratory failure. When mechanical ventilation is needed, almost all patients with COVID-19 pneumonia meet the criteria for acute respiratory distress syndrome (ARDS). The question of the specificities of COVID-19-associated ARDS compared to other causes of ARDS is of utmost importance, as it may justify changes in ventilatory strategies. This review aims to describe the pathophysiology of COVID-19-associated ARDS and discusses whether specific ventilatory strategies are required in these patients.

The impact of dead space volume on the working processes of a positive-displacement piston hybrid power machine (PDPHPM) with two suction valves is investigated. Due to the fact that the process of back expansion in this machine proceeds with variable gas mass, an expression for determining the volume coefficient at variable mass of expanding gas is obtained. The numerical experiment carried out using the previously developed mathematical model established the effect of the dead space volume on the instantaneous integral characteristics of the machine. It is shown that an increase in the dead space volume leads to increase in the duration of the expansion process (despite a decrease in the mass of the expanding gas), a decrease in the coolant consumption, a significant decrease in the flow coefficient, and a slight decrease in the indicator isothermal efficiency. [ABSTRACT FROM AUTHOR]

To evaluate the accuracy with which veterinary anaesthetists and nurses of different experience draw up small volumes of liquid. Prospective blinded randomized study. A group of seven European College of Veterinary Anaesthesia and Analgesia (ECVAA) diplomates, six ECVAA residents and six anaesthesia nurses participated in the study. For each participant, five target volumes between 0.01 and 1.0 mL were randomly allocated. They were drawn up 20 times in random order using a 1 mL syringe attached to a 23 gauge needle. A total of 1900 measurements were analysed. An investigator filled the syringe and needle dead space with water for injection before each experiment. The change in mass of the syringe once filled to the target volume was used to calculate the actual volume of liquid drawn up. Large errors were made with measurements < 0.04 mL, so they were excluded from the statistical analysis. There was a significant effect of the target volume (p < 0.001) and of the order (p < 0.01). For each mL increase in the target volume, the absolute error decreased by 4% and from the first to the hundredth withdrawal each participant's absolute error decreased by 1%. The target volume was underestimated in 52.3% of measurements, 42% were overestimated and 5.7% were on target. None of the between-subject predictor variables approached significance. Accuracy of veterinary anaesthetists and nurses in drawing up medications decreases as the target volume becomes smaller. Small veterinary patients receive small volumes of anaesthetic drugs with higher risks of overdosing compared with larger dogs. Years of experience and staff grade are not associated with greater accuracy. Large percentage errors may be seen with target volumes less than 0.04 mL. Dilutions are recommended for volumes > 0.19 mL in 1 mL syringe. [ABSTRACT FROM AUTHOR]

BACKGROUND: The dead-space-to-tidal-volume ratio (VD/VT) has been used to successfully predict extubation failure in children who are critically ill. However, a singular reliable measure to predict the level and duration of respiratory support after liberation from invasive mechanical ventilation has remained elusive. The objective of this study was to evaluate the association between VD/VT and the duration of postextubation respiratory support. METHODS: This was a retrospective cohort study of subjects who were mechanically ventilated and admitted to a single-center pediatric ICU between March 2019 and July 2021, and who had been extubated with a recorded VD/VT. A cutoff of 0.30 was chosen a priori, with subjects divided into 2 groups,VD/VT < 0.30 and VD/VT 6 0.30, and postextubation respiratory support was recorded at specified time intervals (24 h, 48 h, 72 h, 7 d, and 14 d). RESULTS: We studied 54 subjects. Those with VD/VT 6 0.30 had a significantly longer median (interquartile range) duration of respiratory support after extubation (6 [3--14] d vs 2 [0--4] d; P 5 .001) and longer median (interquartile range) ICU stay (14 [12--19] d vs 8 [5--22] d; P 5 .046) versus the subjects with VD/VT < 0.30. The distribution of respiratory support did not differ significantly betweenVD/VT at the time of extubation (P 5 .13) or at 14 d after extubation (P 5 .21) but was significantly different during the intervening time points after extubation (24 h [P 5 .01], 48 h [P < .001], 72 h [P < .001], and 7 d [P 5 .02]). CONCLUSIONS: VD/VT was associated with the duration and level of respiratory support needed after extubation. Prospective studies are needed to establish if VD/VT can successfully predict the level of respiratory support after extubation. [ABSTRACT FROM AUTHOR]

To evaluate early measurement of the arterial to end-tidal carbon dioxide (PaCO 2 -PetCO 2) gap, a surrogate for physiologic dead space, and its association with clinical outcomes in intubated adults in the emergency department (ED). Observational cohort study of invasively mechanically ventilated adults in an academic medical center (years 2009 to 2016). The association of the PaCO 2 -PetCO 2 gap was evaluated with respect to clinical outcomes; the primary outcome was in-hospital mortality. 519 patients were included. 325 (63%) patients had an elevated (>5 mmHg) PaCO 2 -PetCO 2. Patients with an elevated PaCO 2 -PetCO 2 were significantly older, had higher APACHE II scores, more frequently had chronic obstructive pulmonary disease (COPD), had lower arterial oxygen to fraction of inspired oxygen (P:F) ratios, and were more likely to be intubated for exacerbation of COPD or sepsis. There was no difference in mortality for patients with an elevated PaCO 2 -PetCO 2 (25% vs 26%) in unadjusted analysis (p = 0.829) or adjusted analysis (aOR = 0.81 [95% CI: 0.53–1.26]), as compared to a non-elevated PaCO 2 -PetCO 2. An elevated PaCO 2 -PetCO 2 gap is common in the post-intubation period in the ED, but not significantly associated with clinical outcomes. • An elevated PaCO 2 to PetCO 2 gap is a surrogate for physiologic dead space. • An elevated PaCO 2 to PetCO 2 gap is common among intubated adults in the ED. • Elevated gap was associated with age, illness severity, and intubation for COPD and sepsis. • There was no difference in mortality stratified by PaCO 2 to PetCO 2 gap. [ABSTRACT FROM AUTHOR]

OBJECTIVES: Acute respiratory distress syndrome (ARDS) is associated with high ventilation-perfusion heterogeneity and dead-space ventilation. However, whether the degree of dead-space ventilation is associated with outcomes is uncertain. In this systematic review and meta-analysis, we evaluated the ability of dead-space ventilation measures to predict mortality in patients with ARDS. DATA SOURCES: MEDLINE, CENTRAL, and Google Scholar from inception to November 2022. STUDY SELECTION: Studies including adults with ARDS reporting a deadspace ventilation index and mortality. DATA EXTRACTION: Two reviewers independently identified eligible studies and extracted data. We calculated pooled effect estimates using a random effects model for both adjusted and unadjusted results. The quality and strength of evidence were assessed using the Quality in Prognostic Studies and Grading of Recommendations, Assessment, Development, and Evaluation, respectively. DATA SYNTHESIS: We included 28 studies in our review, 21 of which were included in our meta-analysis. All studies had a low risk of bias. A high pulmonary dead-space fraction was associated with increased mortality (odds ratio [OR], 3.52; 95% CI, 2.22-5.58; p < 0.001; I² = 84%). After adjusting for other confounding variables, every 0.05 increase in pulmonary-dead space fraction was associated with an increased odds of death (OR, 1.23; 95% CI, 1.13-1.34; p < 0.001; I² = 57%). A high ventilatory ratio was also associated with increased mortality (OR, 1.55; 95% CI, 1.33-1.80; p < 0.001; I² = 48%). This association was independent of common confounding variables (OR, 1.33; 95% CI, 1.12-1.58; p = 0.001; I² = 66%). CONCLUSIONS: Dead-space ventilation indices were independently associated with mortality in adults with ARDS. These indices could be incorporated into clinical trials and used to identify patients who could benefit from early institution of adjunctive therapies. The cut-offs identified in this study should be prospectively validated. [ABSTRACT FROM AUTHOR]

The primary cause of dyspnea on exertion in heart failure with preserved ejection fraction (HFpEF) is presumed to be the marked rise in pulmonary capillary wedge pressure during exercise; however, this hypothesis has never been tested directly. Therefore, we evaluated invasive exercise hemodynamics and dyspnea on exertion in patients with HFpEF before and after acute nitroglycerin (NTG) treatment to lower pulmonary capillary wedge pressure. Does reducing pulmonary capillary wedge pressure during exercise with NTG improve dyspnea on exertion in HFpEF? Thirty patients with HFpEF performed two invasive 6-min constant-load cycling tests (20 W): one with placebo (PLC) and one with NTG. Ratings of perceived breathlessness (0-10 scale), pulmonary capillary wedge pressure (right side of heart catheter), and arterial blood gases (radial artery catheter) were measured. Measurements of V ˙ / Q ˙ matching, including alveolar dead space (V d alv ; Enghoff modification of the Bohr equation) and the alveolar-arterial P o 2 difference (A-aDO 2 ; alveolar gas equation), were also derived. The ventilation (V ˙ e)/CO 2 elimination (V ˙ co 2) slope was also calculated as the slope of the V ˙ e and V ˙ co 2 relationship, which reflects ventilatory efficiency. Ratings of perceived breathlessness increased (PLC: 3.43 ± 1.94 vs NTG: 4.03 ± 2.18; P =.009) despite a clear decrease in pulmonary capillary wedge pressure at 20 W (PLC: 19.7 ± 8.2 vs NTG: 15.9 ± 7.4 mm Hg; P <.001). Moreover, V d alv (PLC: 0.28 ± 0.07 vs NTG: 0.31 ± 0.08 L/breath; P =.01), A-aDO 2 (PLC: 19.6 ± 6.7 vs NTG: 21.1 ± 6.7; P =.04), and V ˙ e / V ˙ co 2 slope (PLC: 37.6 ± 5.7 vs NTG: 40.2 ± 6.5; P <.001) all increased at 20 W after a decrease in pulmonary capillary wedge pressure. These findings have important clinical implications and indicate that lowering pulmonary capillary wedge pressure does not decrease dyspnea on exertion in patients with HFpEF; rather, lowering pulmonary capillary wedge pressure exacerbates dyspnea on exertion, increases V ˙ / Q ˙ mismatch, and worsens ventilatory efficiency during exercise in these patients. This study provides compelling evidence that high pulmonary capillary wedge pressure is likely a secondary phenomenon rather than a primary cause of dyspnea on exertion in patients with HFpEF, and a new therapeutic paradigm is needed to improve symptoms of dyspnea on exertion in these patients. [ABSTRACT FROM AUTHOR]

OBJECTIVES: To study: 1) the effect of prone position (PP) on noninvasive ventilation (NIV)-delivered mechanical power (MP) and 2) the impact of MP on physio-anatomical and clinical responses to early versus late PP in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pneumonia. DESIGN: Nonrandomized trial with inverse probability of treatment weighted-matched groups. SETTING: HUMANITAS Gradenigo Sub-ICU. PATIENTS: One hundred thirty-eight SARS-CoV-2 pneumonia patients with moderate-to-severe acute hypoxemic respiratory failure (Pao2/Fio2 ratio < 200 mm Hg) receiving NIV from September 1, 2020, to February 28, 2021 (Ethics approval: ISRCTN23016116). INTERVENTIONS: Early PP or late PP or supine position. MEASUREMENTS AND MAIN RESULTS: Respiratory parameters were hourly recorded. Time-weighted average MP values were calculated for each ventilatory session. Gas exchange parameters and ventilatory ratio (VR) were measured 1 hour after each postural change. Lung ultrasonographic scores and circulating biomarkers were assessed daily. MP delivered during the initial 24 hours of NIV (MP [first 24 hr]) was the primary exposure variable. Primary outcomes: 28-day endotracheal intubation and death. Secondary outcomes: oxygen-response, Co2-response, ultrasonographic, and systemic inflammatory biomarker responses after 24 hours of NIV. Fifty-eight patients received early PP + NIV, 26 late PP + NIV, and 54 supine NIV. Early PP group had lower 28-day intubation and death than late PP (hazard ratio [HR], 0.35; 95% CI, 0.19-0.69 and HR, 0.26; 95% CI, 0.07-0.67, respectively) and supine group. In Cox multivariate analysis, (MP [first 24 hr]) predicted 28-day intubation (HR, 1.70; 95% CI, 1.25-2.09; p = 0.009) and death (HR, 1.51; 95% CI, 1.19-1.91; p = 0.007). Compared with supine position, PP was associated with a 35% MP reduction. VR, ultrasonographic scores, and inflammatory biomarkers improved after 24 hours of NIV in the early PP, but not in late PP or supine group. A MP (first 24 hr) greater than or equal to 17.9 J/min was associated with 28-day death (area under the curve, 0.92; 95% CI, 0.88-0.96; p < 0.001); cumulative hours of MP greater than or equal to 17.9 J/ min delivered before PP initiation attenuated VR, ultrasonographic, and biomarker responses to PP. CONCLUSIONS: MP delivered by NIV during initial 24 hours predicts clinical outcomes. PP curtails MP, but cumulative hours of NIV with MP greater than or equal to 17.9 J/min delivered before PP initiation attenuate the benefits of PP. [ABSTRACT FROM AUTHOR]

Abstract Cumulative evidence has demonstrated that the ventilatory ratio closely correlates with mortality in acute respiratory distress syndrome (ARDS), and a primary feature in coronavirus disease 2019 (COVID-19)-ARDS is increased dead space that has been reported recently. Thus, new attention has been given to this group of dead space ventilation-related indices, such as physiological dead space fraction, ventilatory ratio, and end-tidal-to-arterial PCO2 ratio, which, albeit distinctive, are all global indices with which to assess the relationship between ventilation and perfusion. These parameters have already been applied to positive end expiratory pressure titration, prediction of responses to the prone position and the field of extracorporeal life support for patients suffering from ARDS. Dead space ventilation-related indices remain hampered by several deflects; notwithstanding, for this catastrophic syndrome, they may facilitate better stratifications and identifications of subphenotypes, thereby providing therapy tailored to individual needs.

Heat and moisture exchange filters create additional dead space, comparable in volume to physiological, in premature newborns. It makes carbon dioxide remove difficultу. Reducing the dead space volume by increasing the flow in the ventilator circuit can lead to the hypocapnia. Aim of the study was to determine the safety and efficiency of gas flow boost in the ventilator circuit to hypercapnia compensation created by the additional dead space. Material and methods. The effect of the additional dead space created by a heat and moisture exchange filter on hemoglobin saturation and partial pressure of carbon dioxide at the end of expiration in premature newborns at flows of 5 and 6 l/min was studied. Results and discussion. It has been demonstrated that flows of 5–6 l/min satisfactorily compensate for the effect of additional deadspace without hypocapnia. Conclusions. It is possible to recommend the widespread use of heat and moisture exchange filters in newborn weighing at least 1.0 kg during long-term transportation.

The pathophysiology of sleep apnea goes beyond anatomic predisposition to airway collapse and includes additional factors such as arousal threshold and loop gain. High loop gain is a prominent feature in central and complex sleep apnea (with a mixture of obstructive and central features) where relative hypocapnia can lead to respiratory instability and periodic breathing. Existing therapies, including continuous positive airway pressure (CPAP) and adaptive servo-ventilators, often inadequately treat sleep apnea with high loop gain features. Enhanced expiratory rebreathing space (EERS) targets prevention of the hypocapnia that triggers central events in sleep by increasing dead space in amounts less than typical tidal volumes. This is accomplished by covering traditional exhalation ports on positive airway pressure masks and adding small additional tubing with distal exhalation and safety valves. This technique reduces carbon dioxide (CO2) blow-off during arousals and the associated large recovery breaths, typically producing a maximal increase in resting CO2 by 1–2 mmHg, thus increasing the CO2 reserve and making it less likely to encounter the hypocapnic apneic threshold. Typically, the amount of EERS is titrated in response to central events and periodic breathing rather than aiming for a goal CO2 level. Ideally CO2 monitoring is used during titration of EERS and the technique is avoided in the setting of baseline hypercapnia. This method has been used in clinical practice at our sleep center for over 15 years, and retrospective data suggests an excellent safety profile and high rates of successful therapy including in patients who have previously failed CPAP therapy. Limitations include decreased effectiveness in the setting of leak and decreased tolerance of the bulkier circuit. EERS represents a simple, affordable modification of existing positive airway pressure modalities for treatment of central and complex sleep apnea. Areas of future study include randomized controlled trials of the technique and study of use of EERS in combination with adaptive ventilation, and pharmacologic adjuncts targeting high loop gain physiology.

ABSTRACT Introduction: By July 2023, Brazil had administered approximately 540 million COVID-19 vaccine doses. This study aimed to quantify wasted doses resulting from dead space in vaccine supplies. Methods: The vaccine supply was initially weighed, filled with distilled water, and expelled to simulate administration. Weighing it again after the application determined the dead space volume. Descriptive analyses calculated the waste rate/wasted dose count. Results: The estimated total number of wasted vaccine doses using supplies with the lowest dead space was 62,097,338. Conclusions: Syringe dead space is a crucial factor in dose wastage, directly influencing the number of wasted doses.

BackgroundHyperventilation and inadequate cardiac output (CO) increase are the main causes of exercise limitation in pulmonary hypertension (PH). Intrapulmonary blood flow partitioning between ventilated and unventilated lung zones is unknown. Thoracic impedance cardiography and inert gas rebreathing have been both validated in PH patients for non-invasive measurement of CO and pulmonary blood flow (PBF), respectively. This study sought to evaluate CO behaviour in PH patients during exercise and its partitioning between ventilated and unventilated lung areas, in parallel with ventilation partitioning between ventilated and unventilated lung zones.MethodsEighteen PH patients (group 1 or 4) underwent a cardiopulmonary exercise test (CPET) with a three-step loaded workload protocol. The steps occurred at 0%, 20%, 40%, and 60% of peak workload reached during a preliminary maximum CPET. Ventilatory parameters, arterial blood gases, CO, PBF, and intrapulmonary shunt (calculated as the difference between CO and PBF) were obtained at each step, combining thoracic impedance cardiography and an inert gas rebreathing technique.ResultsDead space ventilation observed throughout the exercise was about 40% of total ventilation. A progressive increase of CO from 4.86 ± 1.24 L/min (rest) to 9.41 ± 2.63 L/min (last step), PBF from 3.81 ± 1.41 L/min to 7.21 ± 2.93 L/min, and intrapulmonary shunt from 1.05 ± 0.96 L/min to 2.21 ± 2.28 L/min was observed. Intrapulmonary shunt was approximately 20% of CO at each exercise step.ConclusionsAlthough the study population was small, the combined non-invasive CO measurement seems a promising tool for deepening our knowledge of lung exercise haemodynamics in PH patients. This technique could be applied in future studies to evaluate PH treatment influences on CO partitioning, since a secondary increase of intrapulmonary shunt is undesirable.

Abstract In the three‐compartment model of lung ventilation‐perfusion heterogeneity (VA/Q scatter), both Bohr dead space and shunt equations require values for central “ideal” compartment O2 and CO2 partial pressures. However, the ideal alveolar gas equation most accurately calculates mixed (ideal and alveolar dead space) PAO2. A novel “modal” definition has been validated for ideal alveolar CO2 partial pressure, at the VA/Q ratio in a lung distribution where CO2 elimination is maximal. A multicompartment computer model of physiological, lognormal distributions of VA and Q was used to identify modal “ideal” PAO2, and find a modification of the alveolar gas equation to estimate it across a wide range of severity of VA/Q heterogeneity and FIO2. This was then validated in vivo using data from a study of 36 anesthetized, ventilated patients with FIO2 0.35–80. Substitution in the alveolar gas equation of respiratory exchange ratio R with modalR=R–1–PEtCO2/PaCO2 achieved excellent agreement (r2 = 0.999) between the calculated ideal PAO2 and the alveolar‐capillary Pc'O2 at the modal VO2 point (“modal” Pc'O2), across a range of log standard deviation of VA 0.25–1.75, true shunt 0%–20%, overall VA/Q 0.4–1.6, and FIO2 0.18–1.0, where the modeled PaO2 was over 50 mm Hg. Modal ideal PAO2 can be reliably estimated using routine blood gas measurements.

Objective: Minute ventilation is a combination of alveolar ventilation (V'alv) and dead space ventilation which is also a result of multiplication of respiratory rate (RR) by tidal volume. V'alv is the volume of the air which reaches the alveoli per minute by definition. The aim of this study was to examine the effect of RR on V'alv in a pediatric physiologic bench setting. Method: In our study, respiratory parameters of a male child, approximately 1 year old, 78 cm in length and ideal body weight of 10 kg, were simulated. This model was ventilated in two different RR settings and with two different breathing circuits which has different dead space (DS) values. However amount of CO2 was kept same during whole bench. Static compliance, static resistance, end-tidal-carbondioxide, positive end expiratory pressure, peak inspiratory pressure, inspiratory time, expiratory-time values of each breathing circuit were taken as the mean and standard deviation of repeated measurements. Results: V'Alv decreased from 1.84+-0.3 L/m to 1.63+-0.5 L/m (p

Background: Ventilatory ratio (VR) has been proposed as an alternative approach to estimate physiological dead space. However, the absolute value of VR, at constant dead space, might be affected by venous admixture and CO2 volume expired per minute (VCO2).Methods: This was a retrospective, observational study of mechanically ventilated patients with acute respiratory distress syndrome (ARDS) in the UK and Italy. Venous admixture was either directly measured or estimated using the surrogate measure PaO2/FiO2 ratio. VCO2 was estimated through the resting energy expenditure derived from the Harris-Benedict formula.Results: A total of 641 mechanically ventilated patients with mild (n=65), moderate (n=363), or severe (n=213) ARDS were studied. Venous admixture was measured (n=153 patients) or estimated using the PaO2/FiO2 ratio (n=448). The VR increased exponentially as a function of the dead space, and the absolute values of this relationship were a function of VCO2. At a physiological dead space of 0.6, VR was 1.1, 1.4, and 1.7 in patients with VCO2 equal to 200, 250, and 300, respectively. VR was independently associated with mortality (odds ratio [OR]=2.5; 95% confidence interval [CI], 1.8-3.5), but was not associated when adjusted for VD/VTphys, VCO2, PaO2/FiO2 (ORadj=1.2; 95% CI, 0.7-2.1). These three variables remained independent predictors of ICU mortality (VD/VTphys [ORadj=17.9; 95% CI, 1.8-185; P<0.05]; VCO2 [ORadj=0.99; 95% CI, 0.99-1.00; P<0.001]; and PaO2/FiO2 (ORadj=0.99; 95% CI, 0.99-1.00; P<0.001]).Conclusions: VR is a useful aggregate variable associated with outcome, but variables not associated with ventilation (VCO2 and venous admixture) strongly contribute to the high values of VR seen in patients with severe illness. [ABSTRACT FROM AUTHOR]

This article summarizes the anatomical features of the lungs, airway and thorax pertinent to the physiology of breathing and discusses chemoreceptor detection mechanisms, brainstem centres and relays involved in the control of breathing. We will discuss lung mechanics including spirometry, lung compliance, airway resistance and the role of surfactant and consider how these can be affected by disease states. It is recommended to revise principles of arterial blood gas analysis in addition to this article. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Medical Equipment Journal is the property of Chinese Medical Equipment Journal Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Simple Summary: Mechanical ventilation is mandatory during ophthalmological surgeries when neuromuscular blocking agents are used. Ventilation of paediatric patients is more complicated because of their small size, the underdevelopment of their respiratory system and the lack of evidence-based guidelines for this age group. We presented two cases of severe hypoventilation during anaesthesia in paediatric dogs due to inadvertent ventilation mainly of the upper airways, and possible development of lung collapse. Both patients were ventilated using the same ventilator in a volume-controlled mode, and the actual level of hypercapnia was detected only when manual ventilation was used, and alveoli were properly ventilated. Adjustments in the volume-controlled ventilation failed to ventilate effectively, and manual ventilation was used for the remainder of the procedure until recovery. Both patients recovered well. Pressure-controlled ventilation, ventilators that take into consideration the compliance of the breathing system and the use of manual breathing, among other techniques, could contribute to better ventilation of those patients. A 2-month-old male 1.56 kg Yorkshire terrier (Case No. 1) and a 3-month-old male 2.3 kg Jack Russell Terrier (Case No. 2) were scheduled for ophthalmological surgery under general anaesthesia and neuromuscular blockade. For both patients, volume-controlled ventilation (VCV) was used with set tidal volumes (VT) of 13 mL/kg and 20 mL/kg for cases No. 1 and 2, respectively. The type of ventilator used did not take into account the intrinsic compliance of the breathing system; therefore, a significant part of the delivered VT was wasted in the expansion of the breathing system, and did not reach the patients, causing alveolar hypoventilation. Both cases developed low dynamic compliance (CD), and after a recruitment manoeuvre, EtCO2 of up to 116 mmHg and 197 mmHg were revealed for cases No. 1 and 2, respectively. The two cases had to be ventilated manually, using positive inspiratory pressures (PIP) of 20–25 mmHg, in order to improve alveolar ventilation and reduce the EtCO2, as adjustments to the VCV were ineffective. Both patients maintained an oxygen haemoglobin saturation between 94% and 100% throughout the procedure and they recovered well. Using a higher VT from the beginning, to compensate for the compliance of the breathing system, or the use of pressure-controlled ventilation (PCV), could have potentially helped to avoid these two incidences of severe hypercapnia. [ABSTRACT FROM AUTHOR]

Cumulative evidence has demonstrated that the ventilatory ratio closely correlates with mortality in acute respiratory distress syndrome (ARDS), and a primary feature in coronavirus disease 2019 (COVID-19)-ARDS is increased dead space that has been reported recently. Thus, new attention has been given to this group of dead space ventilation-related indices, such as physiological dead space fraction, ventilatory ratio, and end-tidal-to-arterial PCO2 ratio, which, albeit distinctive, are all global indices with which to assess the relationship between ventilation and perfusion. These parameters have already been applied to positive end expiratory pressure titration, prediction of responses to the prone position and the field of extracorporeal life support for patients suffering from ARDS. Dead space ventilation-related indices remain hampered by several deflects; notwithstanding, for this catastrophic syndrome, they may facilitate better stratifications and identifications of subphenotypes, thereby providing therapy tailored to individual needs. [ABSTRACT FROM AUTHOR]