Oxygen management in mechanically ventilated patients: A multicenter prospective observational study.

PURPOSE: To observe arterial oxygen in relation to fraction of inspired oxygen (FIO2) during mechanical ventilation (MV). MATERIALS AND METHODS: In this multicenter prospective observational study, we included adult patients required MV for >48h during the period from March to May 2015. We obtained FIO2, PaO2 and SaO2 from commencement of MV until the 7th day of MV in the ICU. RESULTS: We included 454 patients from 28 ICUs in this study. The median APACHE II score was 22. Median values of FIO2, PaO2 and SaO2 were 0.40, 96mmHg and 98%. After day two, patients spent most of their time with a FIO2 between 0.3 and 0.49 with median PaO2 of approximately 90mmHg and SaO2 of 97%. PaO2 was ≥100mmHg during 47.2% of the study period and was ≥130mmHg during 18.4% of the study period. FIO2 was more likely decreased when PaO2 was ≥130mmHg or SaO2 was ≥99% with a FIO2 of 0.5 or greater. When FIO2 was <0.5, however, FIO2 was less likely decreased regardless of the value of PaO2 and SaO2. CONCLUSIONS: In our multicenter prospective study, we found that hyperoxemia was common and that hyperoxemia was not corrected.

Inspiratory Tube Condensation During High-Flow Nasal Cannula Therapy: A Bench Study.

BACKGROUND: High-flow nasal cannula (HFNC) therapy provides better humidification than conventional oxygen therapy. To allay loss of vapor as condensation, a servo-controlled heating wire is incorporated in the inspiratory tube, but condensation is not completely avoidable. We investigated factors that might affect condensation: thermal characteristics of the inspiratory tube, HFNC flow, and ambient temperature. METHODS: We evaluated 2 types of HFNC tubes, SLH Flex 22-mm single tube and RT202. Both tubes were connected to a heated humidifier with water reservoir. HFNC flow was set at 20, 40, and 60 L/min, and FIO2 was set at 0.21. Air conditioning was used maintain ambient temperature at close to either 20 or 25°C. We weighed the tubes on a digital scale before (0 h) and at 3, 6, and 24 h after, turning on the heated humidifier, and calculated the amount of condensation by simple subtraction. The amount of distilled water used during 24 h was also recorded. RESULTS: At 25°C, there was little condensation, but at 20°C and HFNC flow of 20, 40, and 60 L/min for 24 h, the amount of condensation with the SLH was 50.2 ± 10.7, 44.3 ± 17.7, and 56.6 ± 13.9 mg, and the amount with the RT202 was 96.0 ± 35.1, 72.8 ± 8.2, and 64.9 ± 0.8 mg. When ambient temperature was set to 20°C, condensation with the RT202 was statistically significantly greater than with the SLH at all flow settings (P < .001). CONCLUSIONS: Ambient temperature statistically significantly influenced the amount of condensation in the tubes.

Hyperoxemia in mechanically ventilated, critically ill subjects: incidence and related factors.

BACKGROUND: Excessive supplemental oxygen causes injurious hyperoxemia. Before establishing the best P(aO2) targets for mechanically ventilated patients, it is important to understand the incidence of hyperoxemia and related factors. We investigated oxygenation in mechanically ventilated subjects in our ICU and evaluated factors related to hyperoxemia (P(aO2) > 120 mm Hg) at 48 h after initiation of mechanical ventilation. METHODS: We retrospectively reviewed the medical records of patients admitted to our ICU from January 2010 to May 2013. Inclusion criteria were 15 y of age or older and administration of mechanical ventilation for > 48 h. Patients at risk of imminent death on admission or who had received noninvasive ventilation were excluded. We collected subject demographics, reasons for mechanical ventilation, and during mechanical ventilation, we collected arterial blood gas data and ventilator settings on the first day of intubation (T1), 48 h after initiation of mechanical ventilation (T2), and on the day of extubation (T3). Multivariable logistic regression analysis was performed to clarify independent variables related to hyperoxemia at T2. RESULTS: For the study period, data for 328 subjects were analyzed. P(aO2) statistically significantly increased over time to 90 (interquartile range of 74-109) mm Hg at T1, 105 (89-120) mm Hg at T2, and 103 (91-119) mm Hg at T3 (P < .001), coincident with decreases in F(IO2) of 0.4 (0.3-0.5) at T1, 0.3 (0.3-0.4) at T2, and 0.3 (0.3-0.35) at T3 (P < .001). Hyperoxemia occurred in 15.6% (T1), 25.3% (T2), and 22.4% (T3) of subjects. Multivariable logistic regression analysis revealed that hyperoxemia was independently associated with age of < 40 y (odds ratio 2.6, 95% CI 1.1-6.0), Acute Physiology and Chronic Health Evaluation II scores of ≥ 30 (odds ratio 0.53, 95% CI 0.3-1.0), and decompensated heart failure (odds ratio 1.9, 95% CI 1.1 to 3.5). CONCLUSIONS: During mechanical ventilation of critically ill subjects, P(aO2) increased, and F(IO2) decreased. One in 4 subjects were hyperoxemic at T2, and hyperoxemia persisted until T3.

Performance of ventilators compatible with magnetic resonance imaging: a bench study.

BACKGROUND: Magnetic resonance imaging (MRI) is indispensable for diagnosing brain and spinal cord abnormalities. Magnetic components cannot be used during MRI procedures; therefore, patient support equipment must use MRI-compatible materials. However, little is known of the performance of MRI-compatible ventilators. METHODS: At commonly used settings, we tested the delivered tidal volume (V(T)), F(IO2), PEEP, and operation of the high-inspiratory-pressure-relief valves of 4 portable MRI-compatible ventilators (Pneupac VR1, ParaPAC 200DMRI, CAREvent MRI, iVent201) and one ICU ventilator (Servo-i). Each ventilator was set in volume control/continuous mandatory ventilation mode. Breathing frequency and V(T) were tested at 10 breaths/min and 300, 500, and 700 mL, respectively. The Pneupac VR1 has fixed V(T) and frequency combinations, so it was tested at V(T) = 300 mL and 20 breaths/min, V(T) = 500 mL and 12 breaths/min, and V(T) = 800 mL and 10 breaths/min. F(IO2) was 0.6 and 1.0. At the air-mix setting, F(IO2) was fixed at 0.5 with the Pneupac VR1, 0.45 with the ParaPAC 200DMRI, and 0.6 with the CAREvent MRI. PEEP was set at 5 and 10 cm H2O, and pressure relief was set at 30 and 40 cm H2O. RESULTS: V(T) error varied widely among ventilators (-28.1 to 25.5%). As V(T) increased, error decreased with the Pneupac VR1, ParaPAC 200DMRI, and CAREvent MRI (P < .05). F(IO2) error ranged from -13.3 to 25.3% at 0.6 (or air mix). PEEP error varied among ventilators (-29.2 to 42.5%). Only the Servo-i maintained V(T), F(IO2), and PEEP at set levels. The pressure-relief valves worked in all ventilators. CONCLUSIONS: None of the MRI-compatible ventilators maintained V(T), F(IO2), and PEEP at set levels. Vital signs of patients with unstable respiratory mechanics should be monitored during transport and MRI.

Humidification performance of two high-flow nasal cannula devices: a bench study.

INTRODUCTION: Delivering heated and humidified medical gas at 20-60 L/min, high-flow nasal cannula (HFNC) creates low levels of PEEP and ameliorates respiratory mechanics. It has become a common therapy for patients with respiratory failure. However, independent measurement of heat and humidity during HFNC and comparison of HFNC devices are lacking. METHODS: We evaluated 2 HFNC (Airvo 2 and Optiflow system) devices. Each HFNC was connected to simulated external nares using the manufacturer's standard circuit. The Airvo 2 outlet-chamber temperature was set at 37°C. The Optiflow system incorporated an O2/air blender and a heated humidifier, which was set at 40°C/3. For both systems, HFNC flow was tested at 20, 40, and 50 L/min. Simulating spontaneous breathing using a mechanical ventilator and TTL test lung, we tested tidal volumes (VT) of 300, 500, and 700 mL, and breathing frequencies of 10 and 20 breaths/min. The TTL was connected to the simulated external nares with a standard ventilator circuit. To prevent condensation, the circuit was placed in an incubator maintained at 37°C. Small, medium, and large nasal prongs were tested. Absolute humidity (AH) of inspired gas was measured at the simulated external nares. RESULTS: At 20, 40, and 50 L/min of flow, respective AH values for the Airvo 2 were 35.3 ± 2.0, 37.1 ± 2.2, and 37.6 ± 2.1 mg/L, and for the Optiflow system, 33.1 ± 1.5, 35.9 ± 1.7, and 36.2 ± 1.8 mg/L. AH was lower at 20 L/min of HFNC flow than at 40 and 50 L/min (P < .01). While AH remained constant at 40 and 50 L/min, at 20 L/min of HFNC flow, AH decreased as VT increased for both devices. CONCLUSIONS: During bench use of HFNC, AH increased with increasing HFNC flow. When the inspiratory flow of spontaneous breathing exceeded the HFNC flow, AH was influenced by VT. At all experimental settings, AH remained > 30 mg/L.

Correction: Temperature of gas delivered from ventilators.

[This corrects the article on p. 6 in vol. 1, PMID: 25705400.].