Baseline FiO2 Research Articles

Impact of Pharmacologic Patent Ductus Arteriosus Treatment on Acute Respiratory and Oxygenation Metrics in Very Low Birth Weight Infants.

Hypoxemia and respiratory compromise occur in very low birth weight (VLBW, <1,500 g) infants and may be associated with shunting across patent ductus arteriosus (PDA). The impact of pharmacologic PDA treatment on acute hypoxemia and respiratory metrics is unclear. This study aimed to determine whether pharmacologic PDA treatment is associated with acute improvement in hypoxemia and respiratory metrics in VLBW infants. At a single center (2012-2022), all VLBW infants with echocardiographic evidence of PDA and without exclusions were classified as having received or not received pharmacologic PDA treatment (PDA-T and PDA-NT). Mean daily fraction of inspired oxygen (FIO2) and Respiratory Acuity Score (RAS, PMID 30374050) were compared at baseline (day 0) and 3 days after the start of treatment. For PDA-T infants with archived 0.5 Hz (every 2-second) oxygen saturation (SpO2) data, mean daily SpO2 and the percentage of time with severe hypoxemia (SpO2 <80%) were compared before and after treatment. Severe hypoxemia was further analyzed after stratification by clinical variables (sex, medication, gestational age, and postnatal age). We analyzed 125 VLBW infants with PDA, of whom 66 received pharmacologic PDA treatment. We analyzed a subgroup of 43 PDA-T infants with every 2-second SpO2 data available. PDA-T infants had higher baseline FiO2 and RAS and lower SpO2 than PDA-NT infants (p < 0.05). Compared to baseline, RAS decreased from a median of 258 (interquartile range [IQR]: 171, 348) to 254 (IQR: 174, 419), 3 days after the start of treatment (p = 0.012), but median FiO2 increased from 37% (IQR: 28, 46) to 40% (IQR: 29, 52; p = 0.008). SpO2 and the percent time with severe hypoxemia were unchanged. In this 10-year, retrospective, single-center analysis, pharmacologic PDA treatment in VLBW infants was not associated with a major improvement in acute measures of oxygenation or level of respiratory support. · Infants with pharmacologically treated PDA had worse baseline respiratory and oxygenation metrics.. · RAS decreased but FiO2 increased 3 days after pharmacologic PDA treatment.. · Pharmacologic PDA treatment did not acutely improve SpO2 or severe hypoxemia..

In vivo assessment of a modification of a domiciliary ventilator which reduces oxygen consumption in mechanically ventilated patients.

There are instances where hospitals may experience a relative shortage of oxygen, for example, future pandemics, natural disasters or wartime. We developed a modification to a domiciliary ventilator that captures oxygen normally vented during expiration into the atmosphere, delivering it to the patient. The modification significantly increases PaO2 in mechanically ventilated patients at their baseline FiO2 and baseline FiO2 +1, +2 and +3 L/min compared to no modification. The modification reduces walled oxygen consumption by median (IQR) -1.0 (-1.25 to -1.00) L/min whilst maintaining PaO2. This modification may be a valuable in circumstances where there is a relative shortage of oxygen.

Comparing low-dose (DART) and enhanced low-dose dexamethasone regimens in preterm infants with bronchopulmonary dysplasia.

Determining the optimal dexamethasone dosage for facilitating extubation in extremely low birth weight (ELBW) infants with bronchopulmonary dysplasia (BPD) remains uncertain. This study aims to compare the effectiveness of low-dose (DART) and enhanced low-dose dexamethasone regimens in achieving successful extubation in these infants. We conducted a retrospective cohort study at the Women's Wellness and Research Center (WWRC) involving ELBW infants who received dexamethasone for BPD prevention or treatment, or for extubation between January 1st, 2015, and December 31st, 2019. Our goal was to assess successful extubation within various time points of treatement. A total of 77 patients, matched in gestational age and BW, were enrolled in the study, receiving a total of 121 dexamethasone courses. Low-dose dexamethasone courses were administered 75 times to 49 infants, while 46 courses of enhanced low-dose were given to 28 infants. Treatment commenced at 30.8 ± 3.4 weeks post-menstrual age, compared to 32.1 ± 2.5 weeks in the enhanced low-dose group (p = 0.014). The median (IQR) course duration was seven (3-10) days in the low-dose group, while it was 10 (8-14) days in the enhanced low-dose group (p < 0.001). The median (IQR) course dose was 0.73 (0.53-0.86) mg/kg in the low-dose group and 1.27 (0.97-2.05) mg/kg in the enhanced low-dose group (p < 0.001). There were no differences in extubation success at any time point between the two groups at 72 h and seven days after treatment initiation, by course completion, and within seven days after treatment completion. However, regression analysis identified several predictors of successful extubation; baseline FiO2, course duration, and duration of invasive mechanical ventilation were negatively associated with successful extubation at various time points, while received dose per kg and cumulative dose positively correlated with successful extubation at different time points. No significant differences were observed in secondary outcomes, including death or BPD. The choice between low-dose and enhanced low-dose dexamethasone regimens may not significantly impact extubation success. However, careful consideration of dosing, ventilation status, and treatment duration remains crucial in achieving successful extubation. This study highlights the need for personalized dexamethasone therapy in ELBW infants.

Natural Course of Muscular Strength, Physical Performance, and Musculoskeletal Symptoms in Hospitalized Patients With COVID-19

ObjectiveTo investigate the course of muscle strength, musculoskeletal symptoms and physical performance over time in hospitalized COVID-19 patients, and their relation with disease severity at admission. DesignProspective cohort study. SettingPandemic clinic of Gazi University Hospital, Ankara, Turkey. Participants76 adult COVID-19 patients (aged >18 years) were enrolled in the study between March 2021 and May 2021 (N=76). The participants were grouped as “mild,” “moderate,” and “severe” according to clinical and radiological findings. Main Outcome MeasuresThe fraction of inspired oxygen (FiO2), oxygen saturation (SpO2), hand grip strength (HGS), 5-times sit and stand test (5XSTS), modified Borg scale at rest (mBorg-rest), modified Borg scale during activities of daily living (mBorg-ADL), Barthel index, and visual analog scale for myalgia (myalgia-VAS) values were recorded on the first day of hospitalization and in the first, third, and 12th weeks. Outcome measures were compared between disease severity groups. In addition, the changes in these outcome measures over time were also examined. ResultsThere were 15 (19.7%) participants in the mild, 20 (26.3%) in the moderate, and 41 (53.9%) in the severe groups. At the baseline evaluation, SpO2 (P<.001), FiO2 (P<.001), 5XSTS (P=.002), mBorg-rest (P=.016), and mBorg-ADL (P<.001) were different in 3 groups, but there were no differences for HGS, Barthel index, and myalgia-VAS score. HGS, 5XSTS, myalgia-VAS, and mBorg-ADL scores improved significantly over time in all the groups (P<.001, P≤.001, and P<.001, respectively). At the end of 12 weeks, only 5XSTS was different between the groups. 5XSTS was significantly longer in the severe group (P=.010). ConclusionAlthough significant improvement was observed in the muscle strength, physical performance, and musculoskeletal symptoms of patients with COVID-19 over time, the physical performance of these patients did not reach normal standards. We conclude that post-COVID-19 rehabilitation programs are needed to optimize the physical performance of the patients.

342. Secondary Infections following Tocilizumab for Treatment of COVID-19 Pneumonia

BackgroundGuidelines recommend use of tocilizumab (TCZ), an inhibitor of pro-inflammatory IL-6 signaling, for hospitalized patients with progressive severe or critical Coronavirus disease 2019 (COVID-19). The incidence of infectious complications following the use of TCZ for COVID-19 has not been well-described.MethodsWe conducted a retrospective, observational matched cohort study of severely ill, hospitalized adult patients with confirmed COVID-19 who were treated with TCZ between 2/24/2021 and 6/1/2021. The intervention group, comprised of patients who received a single dose of TCZ, was matched based on c-reactive protein (CRP) and fraction of inspired oxygen (FiO2) with a control group who did not receive TCZ, and were hospitalized between 10/12/2020 and 3/6/2021. The primary outcome of the study was diagnosis of a bacterial or fungal infection after day 3 of the index hospitalization. Secondary outcomes included all-cause mortality during the study period and length of stay. Results75 patients who received TCZ were identified during the study period, and matched 1:1 with 75 control patients. Baseline CRP and FiO2 were similar between groups, while the median age in the TCZ group was younger (61 versus 71 years), reflecting the epidemiology of the outbreak during the TCZ and control study periods. 15 bacterial and fungal infections were identified in the TCZ group (20.0%) and 4 (5.3%) infections in the control group (p = 0.012). The majority of infections in both groups were bacterial, with a disproportionate number of bloodstream infections in the TCZ group [7 (9.3%) vs 2(2.6%); p = 0.166]. 28 patients (37.3%) died in the TCZ group compared to 39 (52.0%) in the matched control (p = 0.068). Median time to discharge was similar between TCZ and control patients (11 versus 12 days; 95% CI -2,2).ConclusionSecondary infections in adult patients with severe and critical COVID-19 were more common in patients who had received TCZ. Prospective studies are needed to confirm and further describe this association.Disclosures All Authors: No reported disclosures

Acute Responses to Oxygen Delivery via High Flow Nasal Cannula in Patients with Severe Chronic Obstructive Pulmonary Disease-HFNC and Severe COPD.

Differences in oxygen delivery methods to treat hypoxemia have the potential to worsen CO2 retention in chronic obstructive lung disease (COPD). Oxygen administration using high flow nasal cannula (HFNC) has multiple physiological benefits in treating respiratory failure including reductions in PaCO2 in a flow-dependent manner. We hypothesized that patients with COPD would develop worsening hypercapnia if oxygen fraction was increased without increasing flow rate. We evaluated the acute response to HFNC in subjects with severe COPD when flow remained constant and inspired oxygen was increased. In total, 11 subjects with severe COPD (FEV1 < 50%) on supplemental oxygen with baseline normocapnia (PaCO2 < 45 mm Hg; n = 5) and hypercapnia (PaCO2 ≥ 45 mm Hg; n = 6) were studied. Arterial blood gas responses were studied at three timepoints: Baseline, HFNC at a flow rate of 30 L/min at resting oxygen supplementation for 1 h, and FiO2 30% above baseline with the same flow rate for the next hour. The primary endpoint was the change in PaCO2 from baseline. No significant changes in PaCO2 were noted in response to HFNC applied at baseline FiO2 in the normocapnic and hypercapnic group. At HFNC with FiO2 30% above baseline, the normocapnic group did not show a change in PaCO2 (baseline: 38.9 ± 1.8 mm Hg; HFNC at higher FiO2: 38.8 ± 3.1 mm Hg; p = 0.93), but the hypercapnic group demonstrated significant increase in PaCO2 (baseline: 58.2 ± 9.3 mm Hg; HFNC at higher FiO2: 63.3 ± 10.9 mm Hg; p = 0.025). We observed worsening hypercapnia in severe COPD patients and baseline hypercapnia who received increased oxygen fraction when flow remained constant. These data show the need for careful titration of oxygen therapy in COPD patients, particularly those with baseline hypercapnia when flow rate is unchanged.

Influence du cimentage et du score ASA sur l’état cardiovasculaire pendant une arthroplastie bipolaire pour fracture cervicale fémorale : une étude multicentrique cas-contrôle

BackgroundLittle is known about how bone cement and American Society of Anesthesiologists (ASA) classification influence the cardiovascular system in elderly patients with femoral-neck fractures treated with cemented hemiarthroplasty. Therefore, we performed a case-control study to investigate these questions and compared the following: (1)≥ASA III with≤ASA II patients who underwent cemented hemiarthroplasty; (2) cemented with cementless hemiarthroplasty in≥ASA III patients. HypothesisASA classification influences the cardiovascular system during cemented hemiarthroplasty and bone cement influences intraoperative blood pressure [IBP] in patients rated≥ASA III. Materials and methodsThis multicenter, prospective study included patients with acute displaced femoral-neck fractures. Baseline data, medical history, anesthesia, FiO2, vasopressor use, femoral component, IBP, SpO2, and complications were evaluated. Of 200 patients, 100 were cemented (mean age, 77±10years), and 100 were cementless (mean age, 78±9years). Cemented hemiarthroplasty employed a third-generation technique (plugging, irrigating, drying and filling the canal with cement under pressurization). ResultsSystolic blood pressure (SBP) decreased significantly during cementing, versus pre-rasping in≤ASA II patients (from 117.9±24.5 [range: 65–199] to 106.9±20.3 [range: 59–172]; p=0.007), in≥ASA III patients (from 129.5±21.0 [range: 90–169] to 110.4±17.9 [range: 79–157]; p=0.006), and post-stem-insertion, versus pre-rasping in≤ASA II patients (from 117.9±24.5 [range: 65–199] to 103.9±20.7 [range: 53–178]; p=0.0004), and in≥ASA III patients (from 129.5±21.0 [range: 90–169] to 111.2±24.6 [range: 70–156]; p=0.009). In≥ASA III patients, SBP decreased significantly during cementing or rasping, versus pre-rasping in cemented patients (from 129.5±21.0 [range: 90–169] to 110.4±17.9 [range: 79–157]; p=0.006), in cementless patients (from 115.0±17.7 [range: 85–150] to 100.7±15.7 [range: 75–142]; p=0.004), and post-stem-insertion, versus pre-rasping in cemented patients (from 129.5±21.0 [range: 90–169] to 111.2±SD [range]; p=0.009), and in cementless patients (from 115.0±17.7 [range: 85–150] to 89.4±17.5 [range: 58–140]; p<0.0001). There were no lethal complications. ConclusionsThis study indicate a similar hemodynamic change intraoperatively between≤ASA II patients and≥ASA III patients in the cemented group, and between patients with cemented and cementless hemiarthroplasty in the≥ASA III patients. With modern hemiarthroplasty techniques, bone cement might be as safe as cementless techniques in elderly,≥ASA III patients. Level of evidenceIII, multi-center case control cohort study.

The influence of bone cement and American Society of Anesthesiologists (ASA) class on cardiovascular status during bipolar hemiarthroplasty for displaced femoral-neck fracture: A multicenter, prospective, case-control study.

Little is known about how bone cement and American Society of Anesthesiologists (ASA) classification influence the cardiovascular system in elderly patients with femoral-neck fractures treated with cemented hemiarthroplasty. Therefore, we performed a case-control study to investigate these questions and compared the following:≥ASA III with≤ASA II patients who underwent cemented hemiarthroplasty; and cemented with cementless hemiarthroplasty in≥ASA III patients. ASA classification influences the cardiovascular system during cemented hemiarthroplasty and bone cement influences intraoperative blood pressure [IBP] in patients rated≥ASA III. This multicenter, prospective study included patients with acute displaced femoral-neck fractures. Baseline data, medical history, anesthesia, FiO2, vasopressor use, femoral component, IBP, SpO2, and complications were evaluated. Of 200 patients, 100 were cemented (mean age, 77±10 years), and 100 were cementless (mean age, 78±9 years). Cemented hemiarthroplasty employed a third-generation technique (plugging, irrigating, drying and filling the canal with cement under pressurization). Systolic blood pressure (SBP) decreased significantly during cementing, versus pre-rasping in≤ASA II patients (from 117.9±24.5 [range, 65-199] to 106.9±20.3 [range, 59-172]; p=0.007), in≥ASA III patients (from 129.5±21.0 [range, 90-169] to 110.4±17.9 [range, 79-157]; p=0.006), and post-stem-insertion, versus pre-rasping in≤ASA II patients (from 117.9±24.5 [range, 65-199] to 103.9±20.7 [range, 53-178]; p=0.0004), and in≥ASA III patients (from 129.5±21.0 [range, 90-169] to 111.2±24.6 [range, 70-156]; p=0.009). In≥ASA III patients, SBP decreased significantly during cementing or rasping, versus pre-rasping in cemented patients (from 129.5±21.0 [range, 90-169] to 110.4±17.9 [range, 79-157]; p=0.006), in cementless patients (from 115.0±17.7 [range, 85-150] to 100.7±15.7 [range, 75-142]; p=0.004), and post-stem-insertion, versus pre-rasping in cemented patients (from 129.5±21.0 [range, 90-169] to 111.2±SD [range]; p=0.009), and in cementless patients (from 115.0±17.7 [range, 85-150] to 89.4±17.5 [range, 58-140]; p<0.0001). There were no lethal complications. This study indicate a similar hemodynamic change intraoperatively between≤ASA II patients and≥ASA III patients in the cemented group, and between patients with cemented and cementless hemiarthroplasty in the≥ASA III patients. With modern hemiarthroplasty techniques, bone cement might be as safe as cementless techniques in elderly,≥ASA III patients. III, multicenter case-control cohort study.

Effects of short-term hyperoxia on erythropoietin levels and microcirculation in critically Ill patients: a prospective observational pilot study

BackgroundThe normobaric oxygen paradox states that a short exposure to normobaric hyperoxia followed by rapid return to normoxia creates a condition of ‘relative hypoxia’ which stimulates erythropoietin (EPO) production. Alterations in glutathione and reactive oxygen species (ROS) may be involved in this process. We tested the effects of short-term hyperoxia on EPO levels and the microcirculation in critically ill patients.MethodsIn this prospective, observational study, 20 hemodynamically stable, mechanically ventilated patients with inspired oxygen concentration (FiO2) ≤0.5 and PaO2/FiO2 ≥ 200 mmHg underwent a 2-hour exposure to hyperoxia (FiO2 1.0). A further 20 patients acted as controls. Serum EPO was measured at baseline, 24 h and 48 h. Serum glutathione (antioxidant) and ROS levels were assessed at baseline (t0), after 2 h of hyperoxia (t1) and 2 h after returning to their baseline FiO2 (t2). The microvascular response to hyperoxia was assessed using sublingual sidestream dark field videomicroscopy and thenar near-infrared spectroscopy with a vascular occlusion test.ResultsEPO increased within 48 h in patients exposed to hyperoxia from 16.1 [7.4–20.2] to 22.9 [14.1–37.2] IU/L (p = 0.022). Serum ROS transiently increased at t1, and glutathione increased at t2. Early reductions in microvascular density and perfusion were seen during hyperoxia (perfused small vessel density: 85% [95% confidence interval 79–90] of baseline). The response after 2 h of hyperoxia exposure was heterogeneous. Microvascular perfusion/density normalized upon returning to baseline FiO2.ConclusionsA two-hour exposure to hyperoxia in critically ill patients was associated with a slight increase in EPO levels within 48 h. Adequately controlled studies are needed to confirm the effect of short-term hyperoxia on erythropoiesis.Trial registrationClinicalTrials.gov (www.clinicaltrials.gov), NCT02481843, registered 15th June 2015, retrospectively registered

Hypoxic guard systems do not prevent rapid hypoxic inspired mixture formation

Because a case report and theoretical mass balances suggested that hypoxic guard systems may not prevent the formation of hypoxic inspired mixtures (FIO2 ≤ 21 %) over the clinically used fresh gas flow (FGF) range, we measured FIO2 over a wide range of hypoxic guard limits for O2/N2O and O2/air mixtures. After IRB approval, 16 ASA I-II patients received sevoflurane in either O2/N2O (n = 8) or O2/air (n = 8) using a Zeus(®) anesthesia machine in the conventional mode. After using an 8 L/min FGF with FDO2 = 25% for 10 min, the following hypoxic guard limits were tested for 4 min each, expressed as [total FGF in L/min; FDO2 in %]: [0.3;85], [0.4;65], [0.5;50], [0.7;36], [0.85;30], [1.0;25], [1.25;25], [1.5;25], [2;25], [3;25], [5;25], and [8;25]. In between these [FGF;FDO2] combinations, 8 L/min FGF with 25% O2 was used for 4 min to return to the same baseline FIO2 (25%) before the start of the next combination. This sequence was studied once in each patient receiving O2/air (n = 8), but twice in each patient who received O2/N2O (n = 8) to examine the effect of decreasing N2O uptake over time, resulting in three groups: early O2/N2O, late O2/N2O, and O2/air group. The [FGF;FDO2]-FIO2 relationship was examined. The overall [FGF;FDO2]-FIO2 relationship in the three groups was similar. In all 1, 1.25, and 1.5 L/min FGF groups, FIO2 decreased below 21% in all but one patient; this occurred within 1 min in at least one patient. In the 0.7 L/min O2/air group and the 3 L/min late O2/N2O and O2/air groups, FIO2 decreased below 21% in one patient. Current hypoxic guard systems do not reliably prevent a hypoxic FIO2 with O2/N2O and O2/air mixtures, particularly between 0.7 and 3 L/min.

Influence of Arterial Dissolved Oxygen Level on Venous Oxygen Saturation

Dissolved oxygen (i.e., unbound to hemoglobin) is often neglected as a determinant of central venous oxygen saturation (ScvO2) in review articles and textbooks. These statements may lead to potential misinterpretation of SCvO2 value across FiO2 changes. In this study, we aimed to explore the influence of PaO2 and FiO2 on ScvO2 in ventilated critically ill patients. This was a prospective observational study in two surgical intensive care units. Mechanically ventilated and sedated patients with cardiac output and ScvO2 monitoring and PaO2/FiO2 > 200 with inspiratory oxygen (FiO2) ≤ 0.5 were enrolled (cohort [ScvO2]). A second cohort of brain-injured patients with jugular venous oxygen saturation monitoring was studied to assess the application of the results to regional circulation (cohort [SjvO2]). Central venous oxygen saturation was measured at baseline FiO2 and at FiO2 = 1. We finally estimated the participation of the dissolved oxygen (PadissolvO2) to the ScvO2 variations. Twenty patients formed the cohort ScvO2 and eight formed the cohort SjvO2. Central venous oxygen saturation rose from 71% (69%-76%) to 84% (78%-88%) after increasing FiO2, whereas PaO2 rose from 100 (85-124) mmHg to 387 (360-449) mmHg. The rise of ScvO2 was mostly ascribable to the dissolved oxygen. The increase of ScvO2 was not explained by changes in cardiac output or hemoglobin levels. Jugular venous oxygen saturation rose from 71% (58%-78%) to 83% (78%-89%) after increasing FiO2. Arterial dissolved oxygen level can significantly influence the ScvO2 value. Therefore, PaO2 should not be overlooked while considering the ScvO2 value as a therapeutic goal. Interpretation of ScvO2 variations in response to a therapeutic challenge (i.e., fluid challenge, inotropic drug initiation) should be performed at constant FiO2.

High-Frequency Oscillatory Ventilation in Pediatric Acute Hypoxemic Respiratory Failure: Disease-Specific Morbidity Survival Analysis

BackgroundMultiple ventilatory strategies for acute hypoxemic respiratory failure (AHRF) in children have been advocated, including high-frequency oscillatory ventilation (HFOV). Despite the frequent deployment of HFOV, randomized controlled trials remain elusive and currently there are no pediatric trials looking at its use. Our longitudinal study analyzed the predictive clinical outcome of HFOV in pediatric AHRF given disease-specific morbidity.MethodsA retrospective 8-year review on pediatric intensive care unit admissions with AHRF ventilated by HFOV was performed. Primary outcomes included survival, morbidity, length of stay (LOS), and factors associated with survival or mortality.ResultsA total of 102 patients underwent HFOV with a 66 % overall survival rate. Survivors had a greater LOS than nonsurvivors (p = 0.001). Mortality odds ratio (OR) for patients without bronchiolitis was 8.19 (CI = 1.02, 65.43), and without pneumonia it was 3.07 (CI = 1.12, 8.39). A lower oxygenation index (OI) after HFOV commencement and at subsequent time points analyzed predicted survival. After 24 h, mortality was associated with an OI > 35 [OR = 31.11 (CI = 3.25, 297.98)]. Sepsis-related mortality was associated with a higher baseline FiO2 (0.88 vs. 0.65), higher OI (42 vs. 22), and augmented metabolic acidosis (pH of 7.25 vs. 7.32) evaluated 4 h on HFOV (p < 0.05).ConclusionHigh-frequency oscillatory ventilation may be safely utilized. It has a 66 % overall survival rate in pediatric AHRF of various etiologies. Patients with morbidity limited to the respiratory system and optimized oxygenation indices are most likely to survive on HFOV.

The value of positive end-expiratory pressure and Fio2 criteria in the definition of the acute respiratory distress syndrome*

The criteria that define acute lung injury and the acute respiratory distress syndrome include PaO₂/Fio₂ but not positive end-expiratory pressure or Fio2. PaO2/Fio2 ratios of some patients increase substantially after mechanical ventilation with positive end-expiratory pressure of 5-10 cm H₂O, and the mortality of these patients may be lower than those whose PaO₂/Fio₂ratios remain <200. Also, PaO₂/Fio₂ may increase when Fio2 is raised from moderate to high levels, suggesting that patients with similar PaO₂/Fio₂ ratios but different Fio₂ levels have different risks of mortality. The primary purpose of this study was to assess the value of adding baseline positive end-expiratory pressure and Fio₂ to PaO₂/Fio₂ for predicting mortality of acute lung injury/acute respiratory distress syndrome patients enrolled in Acute Respiratory Distress Syndrome Network clinical trials. We also assessed effects of two study interventions on clinical outcomes in subsets of patients with mild and severe hypoxemia as defined by PaO₂/Fio₂. Analysis of baseline physiologic data and outcomes of patients previously enrolled in clinical trials conducted by the National Institutes of Health Acute Respiratory Distress Syndrome Network. Intensive care units of 40 hospitals in North America. Two thousand three hundred and twelve patients with acute lung injury/acute respiratory distress syndrome. None. Only 1.3% of patients enrolled in Acute Respiratory Distress Syndrome Network trials had baseline positive end-expiratory pressure < 5 cm H₂O, and 50% had baseline positive end-expiratory pressure ≥10 cm H₂O. Baseline PaO₂/Fio₂ predicted mortality, but after controlling for PaO₂/Fio₂, baseline positive end-expiratory pressure did not predict mortality. In contrast, after controlling for baseline PaO₂/Fio₂, baseline Fio₂ did predict mortality. Effects of two study interventions (lower tidal volumes and fluid-conservative hemodynamic management) were similar in mild and severe hypoxemia subsets as defined by PaO₂/Fio₂ ratios. At Acute Respiratory Distress Syndrome Network hospitals, the addition of baseline positive end-expiratory pressure would not have increased the value of PaO₂/Fio₂ for predicting mortality of acute lung injury/acute respiratory distress syndrome patients. In contrast, the addition of baseline Fio2 to PaO₂/Fio₂ could be used to identify subsets of patients with low or high mortality.

A influência de duas frações inspiradas de oxigênio no padrão respiratório de pacientes sob desmame ventilatório

An inspired oxygen fraction (FiO2) of 40% is often used for weaning patients, but lower FiO2 values are also recommended, if arterial oxygen pressure (PaO2)/ FiO2 >150-200 mmHg. This study aimed to compare respiratory variables and vital data values recorded during use of sufficient FiO2 (ideal) to maintain peripheral oxygen saturation at 92% with values recorded during use of FiO2 established at 40% (baseline) in weaning patients. Prospective cross-over study. Respiratory variables (respiratory frequency, tidal volume, occlusion pressure, inspiratory time/total time ratio) and vital data (blood pressure and heart rate) were collected sequentially at 30 and 60 minutes with baseline FiO2, followed by ideal FiO2. These were compared to a generalized linear model for repeated measurements. Comparisons between baseline and ideal FiO2 values, and arterial blood gases were evaluated by the Student's t or Wilcoxon tests. In 30 adult patients the median of ideal FiO2 was 25% (IQ25%-75% 23-28). This was significantly lower than baseline FiO2 (40%) (p< 0.001). No significant difference was found in the PaO2/ FiO2 ratio between baseline FiO2 (269±53) and ideal FiO2 (268±47). Tidal volume was significantly lower during use of ideal FiO2 (p=0.003) and blood pressure was significantly higher during use of baseline FiO2 (p=0.041), but there was no clinical significance. The remaining variables were not affected by reduction in FiO2. The ideal FiO2 did not influence remaining variables. These results suggest that FiO2 levels sufficient to ensure a SpO2>92% did not alter breathing patterns or trigger clinical changes in weaning patients.

Battery Life of the “Four-Hour” Lithium Ion Battery of the LTV-1000 under Varying Workloads

The objective of this study was to determine the effects of inspired oxygen concentration (FIO2), positive end-expiratory pressure (PEEP), and breath type on the battery life of the LTV-1000 external lithium ion battery (LiB). An LTV-1000 ventilator and external LiB were tested in the laboratory. The ventilator was operated using pressure and volume breaths set to deliver a tidal volume of 750 mL. FIO2 was varied from room air (0.21) to 1.0. PEEP was set a 0, 10, and 20 cm of H2O. Duration of operation was determined from measurements of delivered tidal volume. At a baseline of volume control at an FIO2 of 0.21 and a PEEP of 0 cm of H2O, the ventilator operated for 300 +/- 11.6 minutes. Increasing FIO2 to 1.0 reduced battery life to 247 +/- 2.1 minute (p < 0.001). The addition of PEEP to 20 cm of H2O reduced battery life to 211 +/- 3.5 minutes (p < 0.001). The combination of FIO2 of 1.0 and PEEP of 20 cm of H2O further reduced battery life to 188 +/- 6.3 minutes (p < 0.001). At the baseline FIO2 and PEEP (0.21 and 0 cm of H2O), the use of pressure control reduced battery life to 142 +/- 3.5 minutes. Battery life of the external LiB is significantly reduced by the use of pressure control, increasing PEEP, and increasing FIO2. This information is critical to resource planning for medical missions.

Normobaric hyperoxia reduces cardiac index in patients after coronary artery bypass surgery

The purpose of this study was to assess the hemodynamic changes in response to normobaric hyperoxia in patients immediately after coronary artery bypass surgery. Observational study. Single-center university hospital. Patients immediately after coronary artery bypass surgery. Change of fractional inspired oxygen concentration from baseline (< or =0.60) to 1.0 and return to baseline. Cardiovascular changes were assessed with a lithium dilution technique. Cardiac index decreased from 2.82 to 2.52 L/min/m2 (10.6%). Heart rate decreased from 85.9 to 82.5 beats/min (4.0%), and the systemic vascular resistance index increased from 1,858 to 2,304 dyne/s/cm5/m2 (24.1%). Stroke index or mean arterial pressure did not change significantly. On reducing the FIO2 from 1.0 to the baseline FIO2 , there was significant reversal of the previous changes in heart rate and systemic vascular resistance. Heart rate increased from 82.5 to 84.0 beats/min (1.8%), and the systemic vascular index decreased from 2304 to 1932 dyne/s/cm5/m2 (16.1%). The cardiac output did not return to baseline, and the mean arterial pressure decreased from 69.6 to 64.4 mmHg (7.6%). Exposing patients after coronary artery surgery to hyperoxia induces significant hemodynamic changes.

Evaluation of antihypoxemic maneuvers before tracheal aspiration in mechanically ventilated newborns

Periodical tracheal aspiration in mechanically ventilated patients is necessary to remove mucus from the airways. In children and adults, this procedure causes transient hypoxemia, which may be prevented by hyperoxia and/or hyperventilation. These findings, however, have not been sufficiently assessed in newborn infants. Thus we investigated the usefulness of hyperoxia and/or hyperventilation as antihypoxemic maneuvers before tracheal aspiration in newborn infants. Our design was a prospective, randomized, multiple crossover study. The setting was the NICU of a third-level pediatric hospital in Mexico City. Patients included 15 newborn infants under mechanical ventilation. Within a 12-hr period, every patient received, in random order, three antihypoxemic maneuvers during 1 min just before tracheal aspiration: hyperoxia (10% increase of baseline FiO2), hyperventilation (50% increase of ventilator cycling rate), or both. Additionally, a control (sham) maneuver was also applied. Pulse oximeter saturation (SpO2) was recorded before and after each antihypoxemic maneuver, and at 0, 15, 30, 60, and 300 sec after tracheal aspiration. Basal values of SpO2 (81.5 +/- 1.5%) increased with all three antihypoxemic maneuvers (SpO2 over 90%, P <0.05 to P <0.01). Immediately after tracheal aspiration a drop in the SpO2 could be detected in all infants. However, patients receiving hyperoxia showed higher SpO2 values (87.1 +/- 1.8%) than those observed with the sham maneuver (76.9 +/- 2.3%, P <0.01). From this point on, all newborn infants in all conditions (even those with sham maneuver) had spontaneous increments of SpO2 that at 300 sec were again higher than their respective basal values (P <0.05 to P <0.0005). At this time, SpO2 values from following the hyperoxia maneuver were still higher than those following the sham maneuver (P <0.05). Our results show that, similar to what occurs at other ages, tracheal aspiration in mechanically ventilated newborn infants causes transient hypoxemia, which can be partially prevented by previous application of antihypoxemic maneuvers, especially hyperoxia.

Measurement of functional residual capacity by nitrogen washout during partial ventilatory support.

Evaluation of an open circuit multiple breath nitrogen washout (MBNW) technique for measurement of functional residual capacity (FRC) during partial ventilatory support using corrections for gas viscosity, sampling delay time, and re-inspired nitrogen. Measurements in a lung model with known reference volume simulating spontaneous breathing and duplicate measurements in patients breathing spontaneously with partial ventilatory support. SETTING. Experimental laboratory and intensive care units of a university hospital. Eighteen patients with acute respiratory failure. Change of FiO(2) from baseline to 1.0. FRC was measured by MBNW during spontaneous breathing with continuous positive airway pressure, pressure support ventilation, proportional assist ventilation, automatic tube compensation, and airway pressure release ventilation. In the lung model, repeated measurements at three volumes were done with all partial ventilatory support modalities, and baseline FiO(2 )was varied with one mode and FRC. The mean of differences between MBNW (FRC(MBNW)) and reference was 28 ml (1.6%), and the 2.SD-interval was 84 ml (4.9%) for all modes. Measurements up to a baseline FiO(2) of 0.8 showed differences of 5 ml (-0.3%) and the 2.SD-interval of 38 ml (2.2%) between reference and FRC(MBNW). In 18 patients, 66 duplicate measurements revealed a mean difference of 30 ml (0.9%) with a coefficient of repeatability of 358 ml (13%) independent of ventilatory mode and chronological order. This study suggests that, using corrections for gas viscosity, sampling delay time, and re-inspired nitrogen, FRC can be determined with good repeatability in patients and good accuracy in a lung model during partial ventilatory support.

Operational Characteristics of a Normabaric Hypoxic System

Introduction: Several studies have demonstrated beneficial performance effects in endurance athletes following completion of approximately four weeks of “high-low” altitude training (Levine and Stray-Gundersen 1997; Rusko 1996). Athletes who utilize “high-low” altitude training typically live/sleep at a simulated or natural elevation > 2000 m, and train at a relatively low elevation (< 750 m). The Hypoxico Altitude TentTM (HAT) is a commercially available, normobaric hypoxic system that allows one individual to rest/sleep in an artificial altitude environment, and purportedly simulates a maximum elevation of 4200 m. The HAT has been marketed as a safe and effective way for athletes to “sleep high and train low”. However, there are minimal data on the safety and efficacy of these commercial simulated altitude systems, particularly among the population most likely to utilize them, i.e., elite athletes (Wilber 2001). Therefore, the purpose of this study was to evaluate the operational characteristics of the Hypoxico Altitude TentTM using international level athletes as subjects. Methods: Female (n = 3) and male (n = 7) U.S. National Team athletes slept in the HAT for five consecutive nights, ∼ 8 hrs per night, at a simulated altitude of 2500 m (FIO2 ∼15.3%). The athletes were distance runners, racewalkers, rowers, and paddlers who lived and trained at ∼150 m at the U.S. Olympic Training Center (Chula Vista, CA) during the non-sleep portion of the day. Included in this group were four athletes who competed in the 2000 Olympics. Temperature and relative humidity (RH) were measured every 30 min using a digital barotemp device (Fisher Scientific). Measurements of FIO2 and FICO2 were made every 30 min via zirconium oxide (S-3A; Applied Electrochemistry) and infrared (LB-2; Applied Electrochemistry) gas analyzers, respectively. A repeated measures ANOVA was used to evaluate mean differences over time. Results: Mean temperature within the HAT was 20 ± 2°C, which remained relatively stable provided the HAT was used in an air-conditioned room. Mean RH within the HAT was 86 ± 4%. For one subject, RH increased to as high as 95% by the end of an overnight exposure. [CO2] increased rapidly and stabilized within 60 min. Mean FICO2 over the duration of the 8-hr sleep period was 0.7 ± 0.1%, which was significantly higher (p < 0.05) compared with baseline values (0.03–0.04%). [O2] decreased by 10% to 15% in the initial 2 to 3 hrs of sleep. Mean FIO2 over the duration of the 8-hr sleep period was 14.4 ± 0.4% (∼3000 m), which was significantly lower (p < 0.05) versus the baseline FIO2 of 15.3 ± 0.2% (∼2500 m). Questionnaires collected each day within 30 min of awakening indicated minimal physical and/or psychological side effects. Discussion: The most important finding of the present study was the significant 16-fold increase in [CO2] inside the HAT that occurred in the initial 60 min of the 8-hr sleep period. Although mean FICO2 (0.7%) did not approach unhealthy levels (> 3.0%), we were concerned that it might compromise the overnight recovery of the athletes. This does not appear to have been true, as evidenced by the fact that the athletes reported minimal discomfort or side effects on post-sleep questionnaires. The other interesting finding was the significant decrement in FIO2 (10–15%) that occurred primarily in the initial 2 to 3 hrs of sleep. This progressive decrease in FIO2 was observed to a greater degree in taller/larger athletes, and therefore may be related to differences in thoracic cavity size and VE. We concluded that despite some concerns with [CO2] and [O2] stabilization, the HAT has the potential of providing a relatively comfortable normobaric hypoxic environment, thereby allowing athletes to “sleep high and train low”. Acknowledgements: Supported by the United States Olympic Committee

Oxygen uptake during peritoneal ventilation in a porcine model of hypoxemia.

Peritoneal ventilation (PV) can greatly increase PaO2 in hypoxemic rabbits. We tested the hypothesis that the peritoneum can provide a gas exchange surface for oxygen uptake in larger animals that, like humans, have a smaller relative peritoneal surface area and corresponding blood flow. Prospective, randomized, controlled animal study. University research laboratory. In six anesthetized pigs, a modified endotracheal tube (9.0-inner diameter) was inserted into the peritoneal cavity, and the peritoneal cavity was ventilated with oxygen in helium in gas phase. Measurements of peritoneal oxygen uptake and mixed venous oxygen saturation were made over 30 mins of: a) baseline FiO2 0.20, no PV; b) FiO2 0.20, PV; c) FiO2 0.20, PV, dopamine 5 microg/kg/min; d) baseline FiO2 0.15, no PV; e) FiO2 0.15, PV; and f) FiO2 0.15, PV, dopamine 5 microg/kg/min. Mixed venous oxygen saturation was 61% at the baseline FiO2 of 0.20 and 33% at an FiO2 of 0.15 and did not increase significantly from baseline with PV or with dopamine at either FiO2. Peritoneal oxygen uptake, measured with a waterseal spirometer, was 9.1+/-3.1 (SD) and 11.9+/-3.0 mL/min when lung FiO2 was 0.20 and 0.15, respectively, and 9.7+/-2.8 and 12.2+/-2.7 mL/min when FiO2 was 0.20 and 0.15 and dopamine was infused, respectively. Peritoneal ventilation does not result in clinically significant oxygen uptake or alter mixed venous oxygen saturation in a porcine model of hypoxemia.