Just Say NO: Inhaled Nitric Oxide Effect on Respiratory Parameters Following Traumatic Brain Injury in Humans and a Porcine Model

INTRODUCTION

The mechanism of post-traumatic brain injury (TBI) hypoxemia involves ventilation/perfusion mismatch and loss of pulmonary hypoxic vasoconstriction. Inhaled nitric oxide (iNO) has been studied as an adjunct treatment to avoid the use of high positive end-expiratory pressure and inspired oxygen in treatment-refractory hypoxia. We hypothesized that iNO treatment following TBI would improve systemic and cerebral oxygenation via improved matching of pulmonary perfusion and ventilation.

METHODS

Thirteen human patients with isolated TBI were enrolled and randomized to receive either placebo or iNO with measured outcomes including pulmonary parameters, blood gas data, and intracranial pressure (ICP) /perfusion. To complement this study, a porcine model of TBI (including 10 swine) was utilized with measured outcomes of brain tissue blood flow and oxygenation, ventilator parameters, and blood gas data both after administration and following drug removal and clearance.

RESULTS

There were no clinically significant changes in pulmonary parameters in either the human or porcine arm following administration of iNO when compared to either the placebo group (human arm) or the internal control (porcine arm). Analysis of pooled human data demonstrated the preservation of alveolar recruitment in TBI patients. There were no clinically significant changes in human ICP or cerebral perfusion pressure following iNO administration compared to controls.

CONCLUSIONS

iNO had no significant effect on clinically relevant pulmonary parameters or ICPs following TBI in both human patients and a porcine model. The pressure-based recruitment of the human lungs following TBI was preserved. Further investigation will be needed to determine the degree of utility of iNO in the setting of hypoxia after polytrauma.

Early empiric antibiotic use in COVID-19 patients: results from the international VIRUS registry

OBJECTIVES

COVID-19 escalated inappropriate antibiotic use. We determined the distribution of pathogens causing community-acquired co-infections, the rate, and factors associated with early empiric antibiotic (EEAB) treatment among hospitalized COVID-19 patients.

METHODS

The Society of Critical Care Medicine Discovery Viral Infection and Respiratory Illness Universal Study (VIRUS) COVID-19 Registry including 68,428 patients from 28 countries enrolled between January 2020 and October 2021 were screened. After exclusions, 7830 patients were included in the analysis. Azithromycin and/or other antibiotic treatment given within the first 3 days of hospitalization was investigated. Univariate and multivariate analyses were performed to determine factors associated with EEAB use.

RESULTS

The majority (6214, 79.4%) of patients received EEAB, with azithromycin combination being the most frequent (3146, 40.2%). As the pandemic advanced, the proportion of patients receiving EEAB regressed from 84.4% (786/931) in January-March 2020 to 65.2% (30/46) in April-June 2021 (P < 0.001). Beta-lactams, especially ceftriaxone was the most commonly used antibiotic. Staphylococcus aureus was the most commonly isolated pathogen. Multivariate analysis showed geographical location and pandemic timeline as the strongest independent predictors of EEAB use.

CONCLUSIONS

EEAB administration decreased as pandemic advanced, which may be the result of intensified antimicrobial stewardship efforts. Our study provides worldwide goals for antimicrobial stewardship programs in the post-COVID-19 era.

Weaning from mechanical ventilation in intensive care units across 50 countries (WEAN SAFE): a multicentre, prospective, observational cohort study

BACKGROUND

Current management practices and outcomes in weaning from invasive mechanical ventilation are poorly understood. We aimed to describe the epidemiology, management, timings, risk for failure, and outcomes of weaning in patients requiring at least 2 days of invasive mechanical ventilation.

METHODS

WEAN SAFE was an international, multicentre, prospective, observational cohort study done in 481 intensive care units in 50 countries. Eligible participants were older than 16 years, admitted to a participating intensive care unit, and receiving mechanical ventilation for 2 calendar days or longer. We defined weaning initiation as the first attempt to separate a patient from the ventilator, successful weaning as no reintubation or death within 7 days of extubation, and weaning eligibility criteria based on positive end-expiratory pressure, fractional concentration of oxygen in inspired air, and vasopressors. The primary outcome was the proportion of patients successfully weaned at 90 days. Key secondary outcomes included weaning duration, timing of weaning events, factors associated with weaning delay and weaning failure, and hospital outcomes. This study is registered with ClinicalTrials.gov, NCT03255109.

FINDINGS

Between Oct 4, 2017, and June 25, 2018, 10 232 patients were screened for eligibility, of whom 5869 were enrolled. 4523 (77·1%) patients underwent at least one separation attempt and 3817 (65·0%) patients were successfully weaned from ventilation at day 90. 237 (4·0%) patients were transferred before any separation attempt, 153 (2·6%) were transferred after at least one separation attempt and not successfully weaned, and 1662 (28·3%) died while invasively ventilated. The median time from fulfilling weaning eligibility criteria to first separation attempt was 1 day (IQR 0-4), and 1013 (22·4%) patients had a delay in initiating first separation of 5 or more days. Of the 4523 (77·1%) patients with separation attempts, 2927 (64·7%) had a short wean (≤1 day), 457 (10·1%) had intermediate weaning (2-6 days), 433 (9·6%) required prolonged weaning (≥7 days), and 706 (15·6%) had weaning failure. Higher sedation scores were independently associated with delayed initiation of weaning. Delayed initiation of weaning and higher sedation scores were independently associated with weaning failure. 1742 (31·8%) of 5479 patients died in the intensive care unit and 2095 (38·3%) of 5465 patients died in hospital.

INTERPRETATION

In critically ill patients receiving at least 2 days of invasive mechanical ventilation, only 65% were weaned at 90 days. A better understanding of factors that delay the weaning process, such as delays in weaning initiation or excessive sedation levels, might improve weaning success rates.

FUNDING

European Society of Intensive Care Medicine, European Respiratory Society.

Oxygenation and Respiratory System Compliance Associated With Pulmonary Contusion

BACKGROUND

Blunt pulmonary contusions are associated with severe chest injuries and are independently associated with worse outcomes. Previous preclinical studies suggest that contusion progression precipitates poor pulmonary function; however, there are few current clinical data to corroborate this hypothesis. We examined pulmonary dynamics and oxygenation in subjects with pulmonary contusions to evaluate for impaired respiratory function.

METHODS

A chest injury database was reviewed for pulmonary contusions over 5 years at an urban trauma center. This database was expanded to capture mechanical ventilation parameters for the first 7 days on all patients with pulmonary contusion and who were intubated. Daily [Formula: see text]:[Formula: see text], oxygenation indexes (OI), and dynamic compliances were calculated. Pulmonary contusions were stratified by severity. The Fisher exact and chi square tests were performed on categorical variables, and Mann-Whitney U-tests were performed on continuous variables. Significance was assessed at a level of 0.05.

RESULTS A TOTAL OF

1,176 patients presented with pulmonary contusions, of whom, 301 subjects (25.6%) required intubation and had available invasive mechanical ventilation data. Of these, 144 (47.8%) had mild-moderate pulmonary contusion and 157 (52.2%) had severe pulmonary contusion. Overall injury severity score was high, with a median injury severity score of 29 (interquartile range, 22-38). The median duration of mechanical ventilation for mild-moderate pulmonary contusion was 7 d versus 10 d for severe pulmonary contusion (P = .048). All the subjects displayed moderate hypoxemia, which worsened until day 4-5 after intubation. Severe pulmonary contusion was associated with significantly worse early hypoxia on day 1 and day 2 versus mild-moderate pulmonary contusion. Severe pulmonary contusion also had a higher oxygenation index than mild-moderate pulmonary contusion. This trend persisted after adjustment for other factors, including transfusion and fluid administration.

CONCLUSIONS

Pulmonary contusions played an important role in the course of subjects who were acutely injured and required mechanical ventilation. Contusions were associated with hypoxemia not fully characterized by [Formula: see text]: [Formula: see text], and severe contusions had durable elevations in the oxygenation index despite confounders.

Geoeconomic variations in epidemiology, ventilation management, and outcomes in invasively ventilated intensive care unit patients without acute respiratory distress syndrome: a pooled analysis of four observational studies

Background

Geoeconomic variations in epidemiology, the practice of ventilation, and outcome in invasively ventilated intensive care unit (ICU) patients without acute respiratory distress syndrome (ARDS) remain unexplored. In this analysis we aim to address these gaps using individual patient data of four large observational studies.

Methods

In this pooled analysis we harmonised individual patient data from the ERICC, LUNG SAFE, PRoVENT, and PRoVENT-iMiC prospective observational studies, which were conducted from June, 2011, to December, 2018, in 534 ICUs in 54 countries. We used the 2016 World Bank classification to define two geoeconomic regions: middle-income countries (MICs) and high-income countries (HICs). ARDS was defined according to the Berlin criteria. Descriptive statistics were used to compare patients in MICs versus HICs. The primary outcome was the use of low tidal volume ventilation (LTVV) for the first 3 days of mechanical ventilation. Secondary outcomes were key ventilation parameters (tidal volume size, positive end-expiratory pressure, fraction of inspired oxygen, peak pressure, plateau pressure, driving pressure, and respiratory rate), patient characteristics, the risk for and actual development of acute respiratory distress syndrome after the first day of ventilation, duration of ventilation, ICU length of stay, and ICU mortality.

Findings

Of the 7608 patients included in the original studies, this analysis included 3852 patients without ARDS, of whom 2345 were from MICs and 1507 were from HICs. Patients in MICs were younger, shorter and with a slightly lower body-mass index, more often had diabetes and active cancer, but less often chronic obstructive pulmonary disease and heart failure than patients from HICs. Sequential organ failure assessment scores were similar in MICs and HICs. Use of LTVV in MICs and HICs was comparable (42·4% vs 44·2%; absolute difference –1·69 [–9·58 to 6·11] p=0·67; data available in 3174 [82%] of 3852 patients). The median applied positive end expiratory pressure was lower in MICs than in HICs (5 [IQR 5–8] vs 6 [5–8] cm H₂O; p=0·0011). ICU mortality was higher in MICs than in HICs (30·5% vs 19·9%; p=0·0004; adjusted effect 16·41% [95% CI 9·52–23·52]; p<0·0001) and was inversely associated with gross domestic product (adjusted odds ratio for a US$10 000 increase per capita 0·80 [95% CI 0·75–0·86]; p<0·0001).

Interpretation

Despite similar disease severity and ventilation management, ICU mortality in patients without ARDS is higher in MICs than in HICs, with a strong association with country-level economic status.

Funding

No funding.

Assessment of Detectable Serum Tobramycin Concentrations in Patients Receiving Inhaled Tobramycin for Ventilator-Associated Pneumonia

BACKGROUND

Inhaled tobramycin can be used for empiric or definitive therapy of ventilator-associated pneumonia (VAP) in mechanically ventilated patients. This is believed to minimize systemic exposure and potential adverse drug toxicities including acute kidney injury (AKI). However, detectable serum tobramycin concentrations have been reported after inhaled tobramycin therapy with AKI.

METHODS

This retrospective, observational study evaluated mechanically ventilated adult subjects admitted to ICUs at a large, urban academic medical center that received empiric inhaled tobramycin for VAP. Subjects were separated into detectable (ie, ≥ 0.6 mg/L) or undetectable serum tobramycin concentration groups, and characteristics were compared. Independent predictors for detectable serum tobramycin concentration and new onset AKI during or within 48 h of therapy discontinuation were assessed.

RESULTS

Fifty-nine inhaled tobramycin courses in 53 subjects were included in the analysis, of which 39 (66.1%) courses administered to 35 (66.0%) subjects had detectable serum tobramycin concentrations. Subjects with detectable serum tobramycin concentrations were older (57.1 y ± 11.4 vs 45.9 ±15.0, P = .004), had higher PEEP (9.2 cm H₂O [7.0-11.0] vs 8.0 [5.6-8.9], P = .049), chronic kidney disease stage ≥ 2 (10 [29.4%] vs 0 [0%], P = .009), and higher serum creatinine before inhaled tobramycin therapy (1.26 mg/dL [0.84-2.18] vs 0.76 [0.47-1.28], P = .004). Age (odds ratio 1.09 [95% CI 1.02-1.16], P = .009) and PEEP (odds ratio 1.47 [95% CI 1.08-2.0], P =.01) were independent predictors for detectable serum tobramycin concentration. Thirty-seven subjects had no previous renal disease or injury, of which 9 (24.3%) developed an AKI. Sequential Organ Failure Assessment score (odds ratio 1.72 [95% CI 1.07-2.76], P = .03) was the only independent predictor for AKI.

CONCLUSIONS

Detectable serum tobramycin concentrations were frequently observed in critically ill, mechanically ventilated subjects receiving empiric inhaled tobramycin for VAP. Subject age and PEEP were independent predictors for detectable serum tobramycin concentration. Serum monitoring and empiric dose reductions should be considered in older patients and those requiring higher PEEP.

Variation in Early Management Practices in Moderate-to-Severe ARDS in the United States: The Severe ARDS: Generating Evidence Study

BACKGROUND

Although specific interventions previously demonstrated benefit in patients with ARDS, use of these interventions is inconsistent, and patient mortality remains high. The impact of variability in center management practices on ARDS mortality rates remains unknown.

RESEARCH QUESTION

What is the impact of treatment variability on mortality in patients with moderate to severe ARDS in the United States?

STUDY DESIGN AND METHODS

We conducted a multicenter, observational cohort study of mechanically ventilated adults with ARDS and Pao2 to Fio2 ratio of ≤ 150 with positive end-expiratory pressure of ≥ 5 cm H2O, who were admitted to 29 US centers between October 1, 2016, and April 30, 2017. The primary outcome was 28-day in-hospital mortality. Center variation in ventilator management, adjunctive therapy use, and mortality also were assessed.

RESULTS

A total of 2,466 patients were enrolled. Median baseline Pao2 to Fio2 ratio was 105 (interquartile range, 78.0-129.0). In-hospital 28-day mortality was 40.7%. Initial adherence to lung protective ventilation (LPV; tidal volume, ≤ 6.5 mL/kg predicted body weight; plateau pressure, or when unavailable, peak inspiratory pressure, ≤ 30 mm H2O) was 31.4% and varied between centers (0%-65%), as did rates of adjunctive therapy use (27.1%-96.4%), methods used (neuromuscular blockade, prone positioning, systemic steroids, pulmonary vasodilators, and extracorporeal support), and mortality (16.7%-73.3%). Center standardized mortality ratios (SMRs), calculated using baseline patient-level characteristics to derive expected mortality rate, ranged from 0.33 to 1.98. Of the treatment-level factors explored, only center adherence to early LPV was correlated with SMR.

INTERPRETATION

Substantial center-to-center variability exists in ARDS management, suggesting that further opportunities for improving ARDS outcomes exist. Early adherence to LPV was associated with lower center mortality and may be a surrogate for overall quality of care processes. Future collaboration is needed to identify additional treatment-level factors influencing center-level outcomes.

TRIAL REGISTRY

ClinicalTrials.gov; No.: NCT03021824; URL: www.clinicaltrials.gov.

Endocutter Staple Height Auto-adjusts to Tissue Thickness

BACKGROUND

Surgeon choice of the appropriate staple height has been cited as a factor in the mechanical integrity of a staple line. However, tissue measured at the industry standard 8 g/mm² is usually thicker than the formed staple height of the staples that hold it together. This means that the pressure that the staples apply must be greater than 8g/mm². Additionally, formed staple heights in tissue may be different than formed staple heights of the same cartridge type when fired without tissue. This means that there is likely a compressive limit to the individual staples deployed by the stapling system. The purpose of this study is to establish the degree to which staple heights of endocutter staples auto-adjust to tissue and the compressive limit to tissue that this infers.

MATERIALS AND METHODS

Excised gastric remnants from laparoscopic sleeve gastrectomy were measured for tissue thickness at different external pressures. An optimized experimental staple line was then created in parallel to the clinical staple line. The doubly-stapled gastric sliver then underwent computed tomography with solid modeling software to measure staple heights.

RESULTS

Staple heights fired in gastric tissue were significantly different than industry labelled and control staple heights. Clinical staple heights were significantly shorter than measured tissue thickness at 8 g/mm². Staple height more closely approximated tissue thickness under 15 g/mm² of pressure, rather than the 8 g/mm² loading pressure used by industry for tissue thickness range labelling.

CONCLUSIONS

Staples deployed in human gastric tissue are taller than commercial labelling. The closed staple height corresponds to tissue thickness under 15g/mm² of pressure, not the labelled staple height. These results demonstrate that staple heights from modern endocutter staplers adjust to tissue, approximating a maximum compressive force just above 15g/mm².

A study of the possible factors affecting COVID-19 spread, severity and mortality and the effect of social distancing on these factors: Machine learning forecasting model

BACKGROUNDS

SARS-CoV-2 is affecting different countries all over the world, with significant variation in infection-rate and death-ratio. We have previously shown a presence of a possible relationship between different variables including the Bacillus Calmette-Guérin (BCG) vaccine, average age, gender, and malaria treatment, and the rate of spread, severity and mortality of COVID-19 disease. This paper focuses on developing machine learning models for this relationship.

METHODS

We have used real-datasets collected from the Johns Hopkins University Center for Systems Science and Engineering and the European Centre for Disease Prevention and Control to develop a model from China data as the baseline country. From this model, we predicted and forecasted different countries' daily confirmed-cases and daily death-cases and examined if there was any possible effect of the variables mentioned above.

RESULTS

The model was trained based on China data as a baseline model for daily confirmed-cases and daily death-cases. This machine learning application succeeded in modelling and forecasting daily confirmed-cases and daily death-cases. The modelling and forecasting of viral spread resulted in four different regions; these regions were dependent on the malarial treatments, BCG vaccination, weather conditions, and average age. However, the lack of social distancing resulted in variation in the effect of these factors, for example, double-humped spread and mortality cases curves and sudden increases in the spread and mortality cases in different countries. The process of machine learning for time-series prediction and forecasting, especially in the pandemic COVID-19 domain, proved usefulness in modelling and forecasting the end status of the virus spreading based on specific regional and health support variables.

CONCLUSION

From the experimental results, we confirm that COVID-19 has a very low spread in the African countries with all the four variables (average young age, hot weather, BCG vaccine and malaria treatment); a very high spread in European countries and the USA with no variable (old people, cold weather, no BCG vaccine and no malaria). The effect of the variables could be on the spread or the severity to the extent that the infected subject might not have symptoms or the case is mild and can be missed as a confirmed-case. Social distancing decreases the effect of these factors.

Healthcare disparities among anticoagulation therapies for severe COVID-19 patients in the multi-site VIRUS registry

Here we analyze hospitalized andintensive care unit coronavirus disease 2019 (COVID‐19) patient outcomes from the international VIRUS registry (https://clinicaltrials.gov/ct2/show/NCT04323787). We find that COVID‐19 patients administered unfractionated heparin but not enoxaparin have a higher mortality‐rate (390 of 1012 = 39%) compared to patients administered enoxaparin but not unfractionated heparin (270 of 1939 = 14%), presenting a risk ratio of 2.79 (95% confidence interval [CI]: [2.42, 3.16]; p = 4.45e−52). This difference persists even after balancing on a number of covariates including demographics, comorbidities, admission diagnoses, and method of oxygenation, with an increased mortality rate on discharge from the hospital of 37% (268 of 733) for unfractionated heparin versus 22% (154 of 711) for enoxaparin, presenting a risk ratio of 1.69 (95% CI: [1.42, 2.00]; p = 1.5e−8). In these balanced cohorts, a number of complications occurred at an elevated rate for patients administered unfractionated heparin compared to patients administered enoxaparin, including acute kidney injury, acute cardiac injury, septic shock, and anemia. Furthermore, a higher percentage of Black/African American COVID patients (414 of 1294 [32%]) were noted to receive unfractionated heparin compared to White/Caucasian COVID patients (671 of 2644 [25%]), risk ratio 1.26 (95% CI: [1.14, 1.40]; p = 7.5e−5). After balancing upon available clinical covariates, this difference in anticoagulant use remained statistically significant (311 of 1047 [30%] for Black/African American vs. 263 of 1047 [25%] for White/Caucasian, p = .02, risk ratio 1.18; 95% CI: [1.03, 1.36]). While retrospective studies cannot suggest any causality, these findings motivate the need for follow‐up prospective research into the observed racial disparity in anticoagulant use and outcomes for severe COVID‐19 patients.

AARC Clinical Practice Guideline: Management of Adult Patients with Tracheostomy in the Acute Care Setting

Management of patients with a tracheostomy tube includes many components of care provided by clinicians from various health care disciplines. In recent years, clinicians worldwide have demonstrated a renewed interest in the management of patients with tracheostomy due to the recognition that more effective and efficient management of this patient population is necessary to decrease morbidity and mortality and to optimize the value of the procedure. Commensurate with the goal of enhancing the care of patients with tracheostomy, we conducted a systematic review to facilitate the development of recommendations relevant to the care of adult patients with tracheostomy in the acute care setting. From our systematic review, clinical practice guidelines were developed to address questions regarding the impact of tracheostomy bundles, tracheostomy teams, and protocol-directed care on time to decannulation, length of stay, tracheostomy-related cost, tracheostomy-related adverse events, and other tracheostomy-related outcomes in tracheostomized adult patients in the acute care setting. Using a modification of the RAND/UCLA Appropriateness Method, 3 recommendations were developed to assist clinicians with tracheostomy management of adult patients in the acute care setting: (1) evidence supports the use of tracheostomy bundles that have been evaluated and approved by a team of individuals experienced in tracheostomy management to decrease time to decannulation, tracheostomy-related adverse events, and other tracheostomy-related outcomes, namely, improved tolerance of oral diet; (2) evidence supports the addition of a multidisciplinary tracheostomy team to improve time to decannulation, length of stay, tracheostomy-related adverse events, and other tracheostomy-related outcomes, namely, increased speaking valve use; (3) evidence supports the use of a weaning/decannulation protocol to guide weaning and removal of the tracheostomy tube to improve time to decannulation.

Bacillus Calmette-Guérin vaccine, antimalarial, age and gender relation to COVID-19 spread and mortality

•

COVID-19 is affecting different countries all over the world with great variation in infection rate and death ratio.

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Some reports suggested a relation between the Bacillus Calmette-Guérin (BCG) vaccine and the malaria treatment to the infection prevention.

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Some reports related infant's lower-susceptibility to the BCG vaccine. Some other reports a higher risk in males compared to females in such a COVI-19 pandemic.

•

Some other reports claimed the possible use of chloroquine and hydroxychloroquine as prophylactic in such a pandemic.

•

The-present commentary is to discuss the possible relation between those-factors and SARS-CoV-2 infection.

COVID-19 is affecting different countries all over the world with great variation in infection rate and death ratio. Some reports suggested a relation between the Bacillus Calmette-Guérin (BCG) vaccine and the malaria treatment to the prevention of SARS-CoV-2 infection. Some reports related infant's lower susceptibility to the COVID-19. Some other reports a higher risk in males compared to females in such COVID-19 pandemic. Also, some other reports claimed the possible use of chloroquine and hydroxychloroquine as prophylactic in such a pandemic. The present commentary is to discuss the possible relation between those factors and SARS-CoV-2 infection.

Risk Factors for the Development of Acute Respiratory Distress Syndrome Following Hemorrhage

BACKGROUND

The Pragmatic Randomized Optimal Platelet and Plasma Ratios (PROPPR) study evaluated the effects of plasma and platelets on hemostasis and mortality after hemorrhage. The pulmonary consequences of resuscitation strategies that mimic whole blood, remain unknown.

METHODS

A secondary analysis of the PROPPR study was performed. Injured patients predicted to receive a massive transfusion were randomized to 1:1:1 versus 1:1:2 plasma-platelet-red blood cell ratios at 12 Level I North American trauma centers. Patients with survival >24 h, an intensive care unit (ICU) stay, and a recorded PaO2/FiO2 (P/F) ratio were included. Acute respiratory distress syndrome (ARDS) was defined as a P/F ratio < 200, with bilateral pulmonary infiltrates, and adjudicated by investigators.

RESULTS

Four hundred fifty-four patients were reviewed (230 received 1:1:1, 224 1:1:2). Age, sex, injury mechanism, and regional abbreviated injury scale (AIS) scores did not differ between cohorts. Tidal volume, positive end-expiratory pressure, and lowest P/F ratio did not differ. No significant differences in ARDS rates (14.8% vs. 18.4%), ventilator-free (24 vs. 24) or ICU-free days (17.5 vs. 18), hospital length of stay (22 days vs. 18 days), or 30-day mortality were found (28% vs. 28%). ARDS was associated with blunt injury (OR 3.61 [1.53-8.81] P < 0.01) and increasing chest AIS (OR 1.40 [1.15-1.71] P < 0.01). Each 500 mL of crystalloid infused during hours 0 to 6 was associated with a 9% increase in the rate of ARDS (OR 1.09 [1.04-1.14] P < 0.01). Blood given at 0 to 6 or 7 to 24 h were not risk factors for lung injury.

CONCLUSION

Acute crystalloid exposure, but not blood products, is a potentially modifiable risk factor for the prevention of ARDS following hemorrhage.

Impact of Oxygenation Status on the Noninvasive Measurement of Hemoglobin

BACKGROUND

Noninvasive monitoring of hemoglobin (SpHgb) via pulse oximetry has the potential to alert caregivers to blood loss. Previous studies have demonstrated that changes in oxygenation may impact accuracy.

METHODS

Twenty normal volunteers were monitored using SpHgb at sea level, during ascent to 14,000 feet, at 14,000 feet with 100% oxygen delivery, and again at sea level. Each period consisted of 15 minutes of monitoring. SpHgb measurements were compared to a blood sample using Bland Altman analysis. The loss of the SpHgb signal was also recorded.

RESULTS

The mean difference in measured hemoglobin (Hgb) between a venous sample and SpHgb was -2.6 ± 0.96 at 14,000 feet. Ascent to 14,000 feet resulted in a predictable fall in SpO₂ and was associated with loss of the SpHgb signal for half the period of observation (7.4 minutes). In the other three conditions, SpHgb signal was missing 1 to 12.6% of the time. The nadir SpO2 was not predictive of the loss of SpHgb signal.

DISCUSSION

Changes in oxygenation in normal volunteers are associated with short-term SpHgb signal loss (<10 minutes), but no impact on the measured SpHgb.

Comparison of airway control methods and ventilation success with an automatic resuscitator

Mechanical ventilation in an austere environment is difficult owing to logistics, training, and environmental conditions. We evaluated the ability of professional caregivers to provide ventilatory support to a simulated patient using the Simplified Automated Ventilator (SAVe) with a mask hand attended ventilation, mask with single strap unattended ventilation, and supraglottic airway (King LT) ventilation. All three methods were performed using a SAVe with a set tidal volume of 600ml and respiratory rate of 10 breaths per minute. The simulator consisted of a head and upper torso with anatomically correct upper airway structures, trachea, esophagus, and lung which, also measured the delivered tidal volume, respiratory rate, inspiratory flow, and airway pressures. Volunteers used each airway control method to provide ventilation for 10 minutes in random order. Success of each technique was judged as a mean delivered tidal volume of > 500ml. The major finding of this study was that medical professionals using SAVe resuscitator and the manufacturer supplied face mask with single head strap failed to ventilate the airway model in every case.

KEYWORDS

SAVe, Ventilation, Airway management, Prehospital, Mask Ventilation.