Bench tests of simple, handy ventilators for pandemics: performance, autonomy, and ergonomy

BACKGROUND

It has been pointed out that in the wake of a virulent flu strain, patients with survivable illness will die from lack of resources unless more ventilators are made available. Numerous disaster-type ventilators are available, but few evaluations have been performed.

OBJECTIVE

To compare simple, lightweight, and handy ventilators that could be used in the initial care of patients with respiratory distress.

METHODS

We bench-tested 4 volume-cycled ventilators (Carevent ALS, EPV100, Pneupac VR1, and Medumat Easy) and 2 pressure-cycled ventilators (Oxylator EMX and VAR-Plus). We studied their general physical characteristics, sonometry, gas consumption, technical performance, ergonomy, and user-friendliness. With a test lung we assessed performance at F(IO(2)) of 0.50 and 1.0, set compliance of 30, 70, and 120 mL/cm H(2)O, and set resistance of 5, 10, and 20 cm H(2)O/L/s. To study user-friendliness and ergonomy we conducted, in randomized order, 7 or 8 objective, quantitative tests and 2 subjective tests.

RESULTS

Compliance and resistance strongly affected tidal volume with the pressure-cycled ventilators (from 418 ± 49 mL to 1,377 ± 444 mL with the VAR-Plus, at the lowest pressure level), whereas the volume-cycled ventilators provided a consistent tidal volume in the face of changing test lung characteristics.

CONCLUSIONS

We are concerned that the pressure-cycled ventilators did not provide a consistent tidal volume, and under certain conditions the volume delivered would be unsafe (too large or too small). Most of the volume-cycled ventilators proved to be technically efficient and reliable. Their reliability, portability, and ease of use could make them valuable in natural disasters and mass-casualty events.

Continuous positive airway pressure versus bilevel noninvasive ventilation in acute cardiogenic pulmonary edema: a randomized multicenter trial

STUDY OBJECTIVE

Patients with acute cardiogenic pulmonary edema may develop respiratory failure. Noninvasive respiratory support should be initiated rapidly to avoid tracheal intubation. The aim of this study is to compare the efficacy of continuous positive airway pressure (CPAP) delivered by the Boussignac CPAP device and bilevel positive airway pressure (bilevel PAP) in patients with acute respiratory failure caused by acute cardiogenic pulmonary edema.

METHODS

This prospective multicenter randomized study was conducted in 3 emergency departments. Patients were assigned to Boussignac CPAP through a facemask or to bilevel PAP, in addition to standard therapy. The main outcome was a combined criterion (tracheal intubation, death, or acute myocardial infarction). Complications, durations of ventilation, and hospitalization were also assessed.

RESULTS

After 1 hour of ventilation and at the end of the ventilation period, clinical parameters of respiratory distress and blood gas exchange significantly improved in each treatment arm. No significant differences were observed between the Boussignac CPAP and bilevel PAP arms for the combined criterion (5% versus 12%, respectively; odds ratio [OR] 0.4; 95% confidence interval [CI] 0.0 to 1.9) and also for severe complications (9% versus 6%; OR 1.5; 95% CI 0.3 to 9.9), duration of ventilation (median for both groups 2 hours; interquartile range [IQR] 1.2 to 3.0 hours), duration of hospitalization (CPAP 8.5 [IQR 6 to 14] days; bilevel PAP 10 [IQR 7 to 16] days), or intrahospital mortality (8% versus 14%; OR 1.8 [IQR 0.4 to 8.8]). Similar results were obtained among hypercapnic patients (PaCO2 >45 mm Hg). Whatever the ventilation support used, the combined criterion and severe complications were more frequently observed among hypercapnic patients.

CONCLUSION

Both Boussignac CPAP and bilevel PAP appeared effective in rapidly improving respiratory distress even in hypercapnic patients, but they were not different in terms of patient outcome.

Effects of mild induced hypothermia during experimental sepsis

OBJECTIVES

The potential advantages of lowering core temperature during sepsis are to lower energy requirement and to activate various cell-protecting pathways. We experimentally investigated whether postconditioning temperature modifications influence survival duration during experimental sepsis.

DESIGN

A prospective, randomized, experimental animal study.

SETTING

University laboratory.

SUBJECTS

Eighteen male Sprague-Dawley rats (median 326 g, range 310-347 g).

INTERVENTIONS

After anesthesia, experimental sepsis was induced by cecal ligation and perforation. The animals were subsequently assigned a core temperature range: normothermia (37 degrees C), hyperthermia (42 degrees C), and mild hypothermia (32 degrees C). Anesthesia and analgesia were continuously maintained until death.

MEASUREMENTS AND MAIN RESULTS

Plasma lactate and pyruvate concentrations were measured at sepsis induction (H0), 4 hrs later (H4), and/or at the time of death. A significant increase in lactate concentration was observed at the time of death in the 42 degrees C group (p = .04). Lactate-to-pyruvate ratio increased in the 32 degrees C (at H4) and 42 degrees C (at the time of death) groups (p = .04). A linear correlation between a longer survival duration and a lower assigned core temperature was observed (from 61 +/- 10 mins at 42 degrees C to 289 +/- 17 mins at 37 degrees C and to 533 +/- 69 mins at 32 degrees C; R = .959, p < .0001).

CONCLUSIONS

The current results demonstrate that postconditioning hypothermia was associated with increased survival duration during experimental sepsis. Whether the observed benefits on survival duration are due to potential impacts on energy metabolism or to an anti-inflammatory effect of hypothermia requires further investigation.

[Acute respiratory distress]

Acute respiratory distress is a common cause of emergency admission to hospital. Clinicians may face difficulties in terms of diagnosis (etiology), especially in older subjects, often presenting with multiple medical conditions. The Brain Natriuretic Peptid (BNP) assay is an interesting new diagnostic tool in this context, since it differentiates pulmonary dyspnea from pulmonary edema in these patients. However, this laboratory examination should be used with discretion and analyzed according to the clinical setting to avoid possible false positive results. Symptomatic treatment of respiratory distress (oxygen therapy and/or respiratory support) is essential. Except from some clearly identified medical conditions (for instance cardiogenic pulmonary edema in hypertensive subjects, acute asthma attacks or tension pneumothorax), the effect of a specific treatment is often limited, at least in terms of immediate outcome.

Gut dysfunction and endoscopic lesions after out-of-hospital cardiac arrest

BACKGROUND

Cardiac arrest induces severe mesenteric ischaemia. The objective of this study was to assess the frequency of gut dysfunction and endoscopic lesions following resuscitation after cardiac arrest, and to evaluate the potential value of gut endoscopy performance in these circumstances.

METHODS

This is a retrospective data files survey of 3617 patients from the database in a medical intensive care unit. A systematic review of medical and endoscopic files was performed within this database, using a standardised chart.

PATIENTS

One-hundred and thirty consecutive patients who survived up to 48 h were admitted to our unit after out-of-hospital cardiac arrest. Seventy-eight of these patients (60%) presented with early clinical signs of gut dysfunction and/or lesions. Thirty-six patients underwent gut endoscopies (26%) and were included in the survey.

RESULTS

Endoscopic lesions were observed in all cases; in 15 cases, gastrointestinal haemorrhage requiring intervention was identified. The occurrence of haemorrhagic and/or necrotic lesions was found to be associated with an initial rhythm of asystole, higher SAPS II values and epinephrine requirements, compared with cardiac arrest patients without such lesions.

CONCLUSION

The frequent occurrence of endoscopic lesions in the presence of gut dysfunction following a cardiac arrest could suggest systematic gut endoscopy in such patients. However, an alternative recommendation would be to watch these patients very closely, treat all with prophylactic proton pump inhibitors, and endoscope only those with evidence of bleeding.

[Indications and practical issues concerning oxygen therapy]

INTRODUCTION

The initiation of oxygen therapy for acute or chronic respiratory failure is a common medical intervention, both for hospital in-patients and in out-of-hospital emergency settings. Oxygen therapy is also frequently initiated by paramedics or nurses, without any initial medical prescription, in acutely ill patients.

STATE OF THE ART/PERSPECTIVES

It is important to remember that oxygen is a pharmaceutical drug, and its prescription should therefore be considered within treatment guidelines. Two main pathological situations may be encountered: tissue hypoxia and acute/chronic hypoxemia.

CONCLUSION

Physicians should be aware of the clinical signs that may indicate the presence of hypoxia and the pathological situations that may lead to hypoxemia. They must also be aware of the potential complications, in particular CO(2) retention in patients with chronic type II respiratory failure as well as the overall indications, and practical issues concerning oxygen therapy.

Physiologic effects of noninvasive ventilation during acute lung injury

A prospective, crossover, physiologic study was performed in 10 patients with acute lung injury to assess the respective short-term effects of noninvasive pressure-support ventilation and continuous positive airway pressure. We measured breathing pattern, neuromuscular drive, inspiratory muscle effort, arterial blood gases, and dyspnea while breathing with minimal support and the equipment for measurements, with two combinations of pressure-support ventilation above positive end-expiratory pressure (10-10 and 15-5 cm H2O), and with continuous positive airway pressure (10 cm H2O). Tidal volume was increased with pressure support, and not with continuous positive airway pressure. Neuromuscular drive and inspiratory muscle effort were lower with the two pressure-support ventilation levels than with other situations (p < 0.05). Dyspnea relief was significantly better with high-level pressure-support ventilation (15-5 cm H2O; p < 0.001). Oxygenation improved when 10 cm H2O positive end-expiratory pressure was applied, alone or in combination. We conclude that, in patients with acute lung injury (1) noninvasive pressure-support ventilation combined with positive end-expiratory pressure is needed to reduce inspiratory muscle effort; (2) continuous positive airway pressure, in this setting, improves oxygenation but fails to unload the respiratory muscles; and (3) pressure-support levels of 10 and 15 cm H2O provide similar unloading but differ in their effects on dyspnea.

Impact of a nurses' protocol-directed weaning procedure on outcomes in patients undergoing mechanical ventilation for longer than 48 hours: a prospective cohort study with a matched historical control group

INTRODUCTION

The aim of the study was to determine whether the use of a nurses' protocol-directed weaning procedure, based on the French intensive care society (SRLF) consensus recommendations, was associated with reductions in the duration of mechanical ventilation and intensive care unit (ICU) length of stay in patients requiring more than 48 hours of mechanical ventilation.

METHODS

This prospective study was conducted in a university hospital ICU from January 2002 through to February 2003. A total of 104 patients who had been ventilated for more than 48 hours and were weaned from mechanical ventilation using a nurses' protocol-directed procedure (cases) were compared with a 1:1 matched historical control group who underwent conventional physician-directed weaning (between 1999 and 2001). Duration of ventilation and length of ICU stay, rate of unsuccessful extubation and rate of ventilator-associated pneumonia were compared between cases and controls.

RESULTS

The duration of mechanical ventilation (16.6 +/- 13 days versus 22.5 +/- 21 days; P = 0.02) and ICU length of stay (21.6 +/- 14.3 days versus 27.6 +/- 21.7 days; P = 0.02) were lower among patients who underwent the nurses' protocol-directed weaning than among control individuals. Ventilator-associated pneumonia, ventilator discontinuation failure rates and ICU mortality were similar between the two groups.

DISCUSSION

Application of the nurses' protocol-directed weaning procedure described here is safe and promotes significant outcome benefits in patients who require more than 48 hours of mechanical ventilation.

Effects of dichloroacetate and ubiquinone infusions on glycolysis activity and thermal sensitivity during sepsis

Energy-metabolism disturbances during sepsis are characterized by enhanced glycolytic fluxes and reduced mitochondrial respiration. However, it is not known whether these abnormalities are the result of a specific mitochondrial alteration, decreased pyruvate dehydrogenase (PDH) complex activity, depletion of ubiquinone (CoQ(10); electron donor for the mitochondrial complex III), or all 3. In this study we sought to specify metabolism disturbances in a murine model of sepsis, using either a PDH-activator infusion (dichloroacetate, DCA) or CoQ(10) supplementation. After anesthesia, Sprague-Dawley rats received intravenous saline solution (control; n = 5), DCA (n = 5; 20 mg/100 g), or CoQ(10) (n = 5; 1 mg/100 g), before the induction of sepsis. Increased plasma lactate levels and increased muscle glucose content were observed after 4 hours in the control group. In the DCA group, a decrease in the muscle content of lactate (P <.05) and an increase in muscle glucose content (P <.05) were observed at 4 hours, but no lactatemia variation was noted. In the CoQ(10) group, only increased plasma lactate levels were observed. Increased muscle glycolysis fluxes were observed after 4 hours in the control group, but to a slighter degree in both the DCA and CoQ(10) groups. Only DCA restored a normal temperature sensitivity in the hyperthermia range, but we noted no differences in survival time. In conclusion, only DCA infusion restores normal glycolysis function.

Noninvasive continuous positive airway pressure in elderly cardiogenic pulmonary edema patients

OBJECTIVE

To compare the physiological effects and the clinical efficacy of continuous positive airway pressure (CPAP) vs standard medical treatment in elderly patients (> or =75 years) with acute hypoxemic respiratory failure related to cardiogenic pulmonary edema.

DESIGN

A prospective, randomized, concealed, and unblinded study of 89 consecutive patients who were admitted to the emergency departments of one general, and three teaching, hospitals.

INTERVENTION

Patients were randomly assigned to receive standard medical treatment alone ( n=46) or standard medical treatment plus CPAP ( n=43).

MEASUREMENTS

Improvement in PaO(2)/FIO(2) ratio, complications, length of hospital stay, early 48-h and overall mortality, compared between the CPAP and standard treatment groups.

RESULTS

Study groups were comparable with regard to baseline physiological and clinical characteristics (age, sex ratio, autonomy, medical history, cause of pulmonary edema). Within 1 h, noninvasive continuous positive airway pressure led to decreased respiratory rate (respiratory rate, 27+/-7 vs 35+/-6 breaths/min; p=0.009), and improved oxygenation (PaO(2)/F(I)O(2), 306+/-104 vs 157+/-71; p=0.004) compared with baseline, whereas no differences were observed within the standard treatment group. Severe complications occurred in 17 patients in the standard treatment group, vs 4 patients in the noninvasive continuous positive airway pressure group ( p=0.002). Early 48-h mortality was 7% in the noninvasive continuous positive airway pressure group, compared with 24% in the standard treatment group ( p=0.017); however, no sustained benefits were observed during the overall hospital stay.

CONCLUSION

Noninvasive continuous positive airway pressure promotes early clinical improvement in elderly patients attending emergency departments for a severe pulmonary edema, but only reduces early 48-h mortality.

Influence of the humidification device during acute respiratory distress syndrome

OBJECTIVE

To evaluate the effects of the humidification device on respiratory, hemodynamic and gas exchange parameters in acute respiratory distress syndrome (ARDS) patients.

DESIGN

A prospective open study.

SETTING

A medical intensive care unit of a university hospital.

PATIENTS

Acute respiratory distress syndrome patients, with hypercapnia (PaCO(2)>60 mmHg).

INTERVENTION

A progressive reduction of the humidification system dead space (DSh). The following five conditions were tested sequentially: (1). heat and moisture exchanger (internal volume=95 ml) with a tracheal closed-suction system (internal volume=25 ml; total DSh=120 ml), (2). heat and moisture exchanger (internal volume=45 ml) with the closed-suction system (DSh=70 ml), (3). heat and moisture exchanger (internal volume=25 ml) with the closed-suction system (DSh=50 ml), (4). heated humidifier with the closed-suction system (DSh=25 ml) and (5). heated humidifier alone (DSh=0 ml). Recordings were performed at baseline and every 30 min after each artificial dead-space reduction. All ventilatory settings remained constant during the measurement periods.

RESULTS

Ten ARDS patients were included. A significant PaCO(2) decrease was observed at each humidification system dead-space reduction, compared to baseline: PaCO(2 )=80.3+/-20 mmHg at DSh(120) compared to PaCO(2 )=63.6+/-13 mmHg at DSh(0) ( p<0.05). No changes were observed for hemodynamic and ventilatory parameters between the different humidification devices.

CONCLUSION

Artificial airway dead-space reduction allows a significant PaCO(2) reduction. Independently of any respiratory mechanical changes, this very simple maneuver may be of importance when low tidal volume ventilation is used in ARDS patients, and when PaCO(2) lowering is warranted.

[Cardiogenic pulmonary edema in the elderly]

Heart failure of elderly patients is a frequent disease. It is responsible for recurrent hospitalizations and an important mortality rate. The diagnosis of cardiogenic pulmonary edema may be difficult in elderly patients. In more than 50% of cases, echocardiography shows evidence of diastolic heart failure. Medical treatment mainly relies on high doses nitrates. Non invasive ventilation decreases cardiogenic pulmonary edema morbidity and early mortality.

Noninvasive mechanical ventilation in acute cardiogenic pulmonary edema

Acute cardiogenic pulmonary edema is a frequent life-threatening emergency. During the last 10 years, increasing attention has focused on the use of noninvasive ventilation to treat patients with various forms of acute respiratory failure. Numerous physiologic data and clinical studies support the use of noninvasive ventilation during cardiogenic pulmonary edema. Noninvasive ventilation results in rapid improvement of clinical signs of respiratory distress and gas exchange and decreases the need for endotracheal intubation for patients in the ICU with acute hypercapnic respiratory failure related to cardiogenic pulmonary edema. However, no sustained benefit (, decreased late mortality) or benefit for less severe forms of cardiogenic pulmonary edema has been demonstrated yet. Moreover, there are still few data that support the use of a specific mode of ventilation over the others.

Temperature sensitivity of glycolysis during sepsis

OBJECTIVE

To investigate the temperature sensitivity of glycolysis during sepsis.

DESIGN

A prospective, randomized, controlled animal study.

SETTING

The Physiological Department of a University Hospital.

SUBJECTS

Ten male Sprague-Dawley rats, weighing 400-500 g.

INTERVENTIONS

The rats were assigned to either a septic (n = 5) or a sham-control group (n = 5). After anesthesia (H0), experimental sepsis was induced by a cecal ligation and perforation, and the left lateral gastrocnemius was sampled. Four hours later (H4), a second anesthesia was performed to sample the contralateral muscle. The sham-control group underwent the same procedures, but the cecum was neither ligated nor incised.

MEASUREMENTS AND MAIN RESULTS

Glycolytic flux (J(B), the rate at which glycogen can be used in muscle) and the transition time (t99 : the time required for the transition from aerobic to anaerobic metabolism) were measured by using spectrophotometry. The measurements were performed at seven different temperature levels, ranging from 32 to 42 degrees C. For each measured variable, the temperature sensitivity of glycolysis was assessed by computing the Q10 values, which is the variation ratio of the measured variable, attributed to a 10 degrees C temperature increase. In control rats, anesthesia and surgical procedures induced a J(B) increase (7.9 +/- 1.6 at H0 vs. 11.9 +/- 2.1 micromol x min-1 x g(tissue) at H4, p<.05) without any t99 variation. Whatever the group (control or septic), the same temperature variation induced an effect that was approximately three times higher in the hypothermia (<37 degrees C) than in the hyperthermia range (>37 degrees C; p<.05). However, a loss in thermal sensitivity was observed in septic rats in the hyperthermia range (Q10 = 1.2 +/- 0.1 for septic animals vs. 2.3 +/- 0.4 for control animals; p<.05).

CONCLUSIONS

This study demonstrates that glycolysis is more sensitive to temperature in the hypothermia range than in the hyperthermia range. The loss in thermal sensitivity at >37 degrees C in septic rats suggests that sepsis may induce a dysregulation of glycolysis. From an energetic point of view, this signifies that hyperthermia may by itself impair energy metabolism without improving energy production and thus must be treated during sepsis.

A prospective survey of early 12-h prone positioning effects in patients with the acute respiratory distress syndrome

OBJECTIVES

To evaluate of the oxygenation effects of 12-h prone positioning (PP) in ARDS patients and to assess the safety of such a procedure.

DESIGN AND SETTING

Prospective observational study in a medical intensive care unit (12 beds) of a university hospital.

PATIENTS

51 consecutive ARDS patients.

INTERVENTION

PP for at least 12 h daily until recovery or death.

MEASUREMENTS AND RESULTS

Arterial blood gases were collected before and during PP and 1 h after return to supine. Turning adverse events, cutaneous bedsores, and enteral nutrition intolerance were specifically monitored and collected daily by a referring physician. In total 224 PP sessions were performed. Oxygenation improved 1 h after the turn and continued improving over the 12-h period (4). The beneficial effect persisted 1 h after return to supine (01). We considered 96% patients responders: 45% as early responders and 53% persistent responders (persistent benefit after return to supine). Four significant adverse events occurred during the 448 turning maneuvers (0.9%). Stage III ulceration and stage IV necrosis cutaneous bedsores occurred in ten patients (20%). Enteral nutrition intolerance was reported in 25% but without inability to meet patient's caloric requirement.

CONCLUSIONS

Twelve-hour PP is a safe procedure and allows a continuous oxygenation improvement throughout the entire session.

Prospective evaluation and outcome of patients admitted for syncope over a 1 year period

AIMS

Syncope is a frequent and potentially dangerous symptom. The epidemiological data are based on series mainly collected 20 years ago in the U.S.A. and do not adequately assist in the management of patients admitted now for this symptom in Europe.

METHODS AND RESULTS

To evaluate prospectively the epidemiological aspects and the management of the patients admitted in the emergency department of an adult university hospital for a 'verified' syncope, charts of all the patients consecutively admitted between June 1999 and June 2000 were systematically reviewed by a member of the cardiology staff. Those with a loss of consciousness were selected and those with a definite syncope were included in the study group and followed until they were discharged from the hospital. Among the 37,475 patients who presented to the emergency department, 454 (1.21%) had a definite syncope. For 296 it was the first episode and 169 (mean age 43+/-23 years) were discharged straight away; 285 (mean age 66+/-19 years; P<0.0001) were admitted to internal medicine (n=151), cardiology (n=65), neurology (n=44), endocrinology (n=14) and surgery (n=11) services. In 75.7% of all the patients a diagnosis was reported but it was inadequate to explain a syncopal episode in 56 cases (16.3%). Management differed by department: 36% of the patients had 'neurological' investigations mainly in internal medicine and neurology. Except in cardiology very few had 'cardiological' investigations particularly tilt test and electrophysiological studies (5%).

CONCLUSION

Syncope is a frequent symptom but its cause often remains unknown partly due to inadequate management. Precise and simple guidelines are urgently needed.

A global approach to energy metabolism in an experimental model of sepsis

Disturbances in energy metabolism during sepsis are not clearly understood. The aim of the study was to globally assess the energy drive in septic rat myocytes, studying both glycolysis rates and mitochondrial maximal activities together, using recent in vitro techniques. Measurements were assessed before (H0) and 4 h after sepsis induction (H4). Hyperlactatemia was observed in all septic animals ([lactate] = 1.2 +/- 0.3 mmol/L at H0 versus 3.3 +/- 0.6 mmol/L at H4; p < 0.001). An enhanced glycolysis rate was observed in both aerobic ( J(A) = 7.2 +/- 0.9 at H0 versus 18.2 +/- 4.1 nmol glucose/min/g at H4; p < 0.05) and anaerobic ( J(B) = 7.5 +/- 1.2 at H0 versus 15.4 +/- 3.4 micromol glucose/min/g at H4; p < 0.05) fluxes, associated with a selective significant pyruvate-malate-dependent oxygen consumption rate decrease (V O(2)-PM = 0.144 +/- 0.008 at H0 versus 0.113 +/- 0.007 micromol O(2)/h/mg at H4; p < 0.05). This oxygen consumption decrease can be interpreted either as a complex I and/or a complex I-ubiquinone relation alteration. Our results are consistent with the hypothesis that an altered mitochondrial function during sepsis is responsible, at least in part, for hyperlactatemia, which is thus a consequence of an increased glycolysis rate.

Biphasic-flow induced ventilation allows simultaneous ventilation in several animals, using a single multiple output ventilator--a preliminary report

Biphasic-flow induced ventilation (BiFIV) is a variable time-cycled tracheal gas insufflation mode, using a specific multiluminal endotracheal tube. Some recent studies have reported efficiency of this new ventilatory mode in experimental in vitro and in vivo settings. We hypothesized that this ventilatory mode could be able to deliver simultaneous efficient ventilation for several animals, using a single ventilator prototype. The study was performed in three groups of three domestic pigs with a normal lung compliance. Each pig was initially anaesthetized, intubated with the specific endotracheal tube, and ventilated with a conventional ventilatory device. The animals were then simultaneously ventilated under BiFIV, using a single ventilator prototype, for each group of three animals. Physiological parameters and arterial blood gases were recorded at each study phase. All animals but one survived the experiment. We did not observe any significant differences in arterial gas exchange, under both ventilatory modes. Oxygenation was as efficient for each three animals ventilated under BiFIV, using a single ventilator device, as under conventional ventilation, using three separate ventilators (PaO2 = 112+/-17 mmHg under conventional ventilation versus 115+/-16 mmHg under BiFIV). In conclusion, variable time-cycled tracheal gas insufflation may allow an efficient multiple ventilation on several animals, using a single multiple output ventilatory device, in a normal lung animal model. If validated on subsequent pathological models, it could thus be interesting in laboratory and/or mass casualty situations.

Helium-oxygen breathing in the early emergency care of acute severe asthma: a randomized pilot study

The aim of this study was to establish whether a clinical trial, comparing helium-oxygen (HeO2) breathing to standard therapy, would be feasible during the out-of-hospital care of adult patients with severe asthma. Although the primary outcome in a definitive trial will be a decrease in morbidity, the present study primarily examined: (1) if the strategy could be successfully implemented in emergency ambulatory units; (2) if the research staff could enroll enough patients, given the resources. Nine patients were included in the conventional treatment group, and seven patients in the HeO2 group. Patients randomized to the HeO2 group breathed the mixture for a 12-hour period. Clinical and biological parameters improved for all patients. There was no trend towards a HeO2 benefit, whether during the initial out-of-hospital nor the ICU care. No patient was intubated within the study period. HeO2 breathing was considered to be simple to initiate, and no side effects were reported. In conclusion, while HeO2 breathing is easy to apply, even in the out-of-hospital setting, the few enrolled patients did not appear to benefit from this treatment. Regarding our low inclusion rate and the lack of positive effect trend, we believe that a large definitive trial will be difficult to initiate in such an emergency care setting.

Treatment of acute hypoxemic nonhypercapnic respiratory insufficiency with continuous positive airway pressure delivered by a face mask: A randomized controlled trial

CONTEXT

Continuous positive airway pressure (CPAP) is widely used in the belief that it may reduce the need for intubation and mechanical ventilation in patients with acute hypoxemic respiratory insufficiency.

OBJECTIVE

To compare the physiologic effects and the clinical efficacy of CPAP vs standard oxygen therapy in patients with acute hypoxemic, nonhypercapnic respiratory insufficiency.

DESIGN, SETTING, AND PATIENTS

Randomized, concealed, and unblinded trial of 123 consecutive adult patients who were admitted to 6 intensive care units between September 1997 and January 1999 with a PaO(2)/FIO(2) ratio of 300 mm Hg or less due to bilateral pulmonary edema (n = 102 with acute lung injury and n = 21 with cardiac disease).

INTERVENTIONS

Patients were randomly assigned to receive oxygen therapy alone (n = 61) or oxygen therapy plus CPAP (n = 62).

MAIN OUTCOME MEASURES

Improvement in PaO(2)/FIO(2) ratio, rate of endotracheal intubation at any time during the study, adverse events, length of hospital stay, mortality, and duration of ventilatory assistance, compared between the CPAP and standard treatment groups.

RESULTS

Among the CPAP vs standard therapy groups, respectively, causes of respiratory failure (pneumonia, 54% and 55%), presence of cardiac disease (33% and 35%), severity at admission, and hypoxemia (median [5th-95th percentile] PaO(2)/FIO(2) ratio, 140 [59-288] mm Hg vs 148 [62-283] mm Hg; P =.43) were similarly distributed. After 1 hour of treatment, subjective responses to treatment (P<.001) and median (5th-95th percentile) PaO(2)/FIO(2) ratios were greater with CPAP (203 [45-431] mm Hg vs 151 [73-482] mm Hg; P =.02). No further difference in respiratory indices was observed between the groups. Treatment with CPAP failed to reduce the endotracheal intubation rate (21 [34%] vs 24 [39%] in the standard therapy group; P =.53), hospital mortality (19 [31%] vs 18 [30%]; P =.89), or median (5th-95th percentile) intensive care unit length of stay (6.5 [1-57] days vs 6.0 [1-36] days; P =.43). A higher number of adverse events occurred with CPAP treatment (18 vs 6; P =.01).

CONCLUSION

In this study, despite early physiologic improvement, CPAP neither reduced the need for intubation nor improved outcomes in patients with acute hypoxemic, nonhypercapnic respiratory insufficiency primarily due to acute lung injury. JAMA. 2000;284:2352-2360.

Glycolysis in the human muscle: a new approach

The flow response time theory allows the global assessment of a metabolic pathway. This study describes the first application of this concept to explore glycolysis on human skeletal muscle extracts. The muscle extract is used to convert glucose or glucose-6-phosphate into glycerol-phosphate through the first part of glycolysis. The functioning of the experimental model is assayed by a continuous recording of the reduced nicotinamide adenine dinucleotide decay in a spectrophotometer. This measurement method was applied to normal and pathologic human skeletal muscles. The aerobic (J(A)) and anaerobic (J(B)) fluxes and the time (t99) needed for the transition from J(A) to J(B) were measured under a wide clinical temperature range (30 degrees C to 40 degrees C). The two studied muscle types (gluteus maximus and tibialis anterior) have similar glycolytic flux values, with an identical functional modality. The thermal response of glycolysis is not linear, with a high thermal sensitivity in the hypothermic range (30 degrees C to 38 degrees C) and a thermal insensitivity in the hyperthermic range (37 degrees C to 40 degrees C). On the same type of muscle (tibialis anterior), a pathologic process can induce different variations in the glycolysis patterns, but further data are needed to clear this point. The flow response time concept allows an accurate assessment of glycolysis in the human skeletal muscle, whether normal or pathologic. This approach is interesting for evaluating the global influence of different stimulations on a metabolic pathway, such as temperature variation.