Dario Rodriquez

Bench Evaluation of 7 Home-Care Ventilators

BACKGROUND: Portable ventilators continue to decrease in size while increasing in performance. We bench-tested the triggering, battery duration, and tidal volume (VT) of 7 portable ventilators: LTV 1000, LTV 1200, Puritan Bennett 540, Trilogy, Vela, iVent 101, and HT50. METHODS: We tested triggering with a modified dual-chamber test lung to simulate spontaneous breathing with weak, normal, and strong inspiratory effort. We measured battery duration by fully charging the battery and operating the ventilator with a VT of 500 mL, a respiratory rate of 20 breaths/min, and PEEP of 5 cm H2O until breath-delivery ceased. We tested VT accuracy with pediatric ventilation scenarios (VT 50 mL or 100 mL, respiratory rate 50 breaths/min, inspiratory time 0.3 s, and PEEP 5 cm H2O) and an adult ventilation scenario (VT 400 mL, respiratory rate 30 breaths/min, inspiratory time 0.5 s, and PEEP 5 cm H2O). We measured and analyzed airway pressure, volume, and flow signals. RESULTS: At the adult settings the measured VT range was 362–426 mL. On the pediatric settings the measured VT range was 51–182 mL at the set VT of 50 mL, and 90–141 mL at the set VT of 100 mL. The VT delivered by the Vela at both the 50 mL and 100 mL, and by the HT50 at 100 mL, did not meet the American Society for Testing and Materials standard for VT accuracy. Triggering response and battery duration ranged widely among the tested ventilators. CONCLUSIONS: There was wide variability in battery duration and triggering sensitivity. Five of the ventilators performed adequately in VT delivery across several settings. The combination of high respiratory rate and low VT presented problems for 2 of the ventilators.

Effects of Simulated Altitude on Ventilator Performance

BACKGROUND Aeromedical transport of critically ill casualties requires continued safe operation of medical equipment at altitude. We evaluated performance of two ventilators in an altitude chamber. METHODS Two ventilators used by the United States Air Force (USAF) Critical Care Air Transport Teams were operated in an altitude chamber at barometric pressure of 754 mm Hg, 657 mm Hg, 563 mm Hg, and 428 mm Hg simulating altitudes of sea level, 4,000, 8,000, and 15,000 feet. At each altitude ventilators were set to deliver three tidal volumes (VT) from 0.25 L to 1.0 L. Airway pressure, timing, flow, and volumes were measured every breath. Measured parameters included VT, positive end-expiratory pressure (PEEP), inspiratory time, expiratory time, inspiratory flow, peak inspiratory pressure, expiratory flow, and respiratory rate. RESULTS The Impact 754 compensated for changes in altitude maintaining the set VT within 10% of the sea level VT. Tidal volume delivery of the 754 was less precise during operation of the compressor at an inspired oxygen concentration of 0.21. With each increase in altitude, the LTV VT increased. At 8,000 feet VT increased by 10% and at 15,000 feet VT increased by 30% (p<0.001). Respiratory rate was not affected by altitude with either device. CONCLUSIONS The Impact 754 compensates ventilator output to deliver the desired tidal volume regardless of changes in altitude and barometric pressure. The LTV-1000 does not compensate for changes in altitude resulting in delivery of increasing tidal volumes with falling barometric pressure. Clinicians should be aware of ventilator performance and ventilator limitations to provide safe and effective ventilation during transport.

Maximizing oxygen delivery during mechanical ventilation with a portable oxygen concentrator.

BACKGROUND Transportation of the critically ill or injured war fighter requires the coordinated care and judicious use of resources. Availability of oxygen (O2) supplies for the mechanically ventilated patient is crucial. Size and weight of cylinders makes transport difficult and presents an increased risk of fire. A proposed solution is to use a portable oxygen concentrator (POC) for mechanical ventilation. We tested the SeQual Eclipse II POC paired with the Impact 754 and Pulmonetics LTV-1200 ventilators in the laboratory and evaluated the fraction of inspired oxygen (FIO2) across a range of minute volumes. METHODS Each ventilator was attached to a test lung and pressure, volume, flow, and inspired oxygen (FIO2) was measured by a gas or flow analyzer. Ventilators were tested at a tidal volume (VT) of 500 mL; an inspiratory time of 1.0 second; respiratory rates of 10, 20, and 30 breaths per minute; and positive end-expiratory pressure of 0 and 10 cm H2O. The LTV 1200 was tested with and without the expiratory bias flow. The Eclipse II was modified to provide pulse dosing on inspiration at 3 volumes (64, 128, and 192 mL) and continuous flow at 1 L/min to 3 L/min. Six combinations of ventilator settings were used with each POC setting for evaluation. O2 was injected at the ventilator gas outlet and patient y-piece for pulse dose and continuous flow. Additionally, continuous flow O2 was injected into the oxygen inlet port of the LTV 1200, and a reservoir bag, on the inlet port of the Impact 754. All tests were done with both ventilators using continuous flow, wall source O2 as a control. We also measured the FIO2 with the concentrator on the highest pulse dose setting while decreasing ventilator VT to compensate for the added volume. RESULTS The delivered FIO2 was highest when oxygen was injected into the ventilator circuit at the patient y-piece using pulse dosing, with the VT corrected. The next highest FIO2 was with continuous flow at the inlet (LTV), and reservoir (Impact). Electrical power consumption was less during pulse dose operation. SUMMARY Oxygen is a finite resource, which is cumbersome to transport and may present a fire hazard. The relatively high FIO2 delivered by the POC makes this method of O2 delivery a viable alternative to O2 cylinders. However, patients requiring an FIO2 of 1.0 would require additional compressed oxygen. This system allows O2 delivery up to 76% solely using electricity. An integrated ventilator or POC capable of automatically compensating VT for POC output is desirable. Further patient testing needs to be done to validate these laboratory findings.

Management of the Artificial Airway

Management of the artificial airway includes securing the tube to prevent dislodgement or migration as well as removal of secretions. Preventive measures include adequate humidification and appropriate airway suctioning. Monitoring airway patency and removing obstruction are potentially life-saving components of airway management. Cuff pressure management is important for preventing aspiration and mucosal damage as well as assuring adequate ventilation. A number of new monitoring techniques have been introduced, and automated cuff pressure control is becoming more common. The respiratory therapist should be adept with all these devices and understand the appropriate application and management.

Managing endotracheal tube cuff pressure at altitude: a comparison of four methods.

BACKGROUND Ascent to altitude results in the expansion of gases in closed spaces. The management of overinflation of the endotracheal tube (ETT) cuff at altitude is critical to prevent mucosal injury. METHODS We continuously measured ETT cuff pressures during a Critical Care Air Transport Team training flight to 8,000-ft cabin pressure using four methods of cuff pressure management. ETTs were placed in a tracheal model, and mechanical ventilation was performed. In the control ETT, the cuff was inflated to 20 mm Hg to 22 mm Hg and not manipulated. The manual method used a pressure manometer to adjust pressure at cruising altitude and after landing. A PressureEasy device was connected to the pilot balloon of the third tube and set to a pressure of 20 mm Hg to 22 mm Hg. The final method filled the balloon with 10 mL of saline. Both size 8.0-mm and 7.5-mm ETT were studied during three flights. RESULTS In the control tube, pressure exceeded 70 mm Hg at cruising altitude. Manual management corrected for pressure at altitude but resulted in low cuff pressures upon landing (<10 mm Hg). The PressureEasy reduced the pressure change to a maximum of 36 mm Hg, but on landing, cuff pressures were less than 15 mm Hg. Saline inflation ameliorated cuff pressure changes at altitude, but initial pressures were 40 mm Hg. CONCLUSION None of the three methods using air inflation managed to maintain cuff pressures below those associated with tracheal damage at altitude or above pressures associated with secretion aspiration during descent. Saline inflation minimizes altitude-related alteration in cuff pressure but creates excessive pressures at sea level. New techniques need to be developed.

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

OBJECTIVE 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). METHODS 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. RESULTS 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. CONCLUSIONS 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.

Hypoxemia during aeromedical evacuation of the walking wounded.

BACKGROUND Hypobaric hypoxemia is a well-known risk of aeromedical evacuation (AE). Validating patients as safe to fly includes assessment of oxygenation status as well as oxygen-carrying capability (hemoglobin). The incidence and severity of hypoxemia during AE of noncritically injured casualties have not been studied. METHODS Subjects deemed safe to fly by the validating flight surgeon were monitored with pulse oximetry from the flight line until arrival at definitive care. All subjects were US military personnel or contractors following traumatic injuries. Noninvasive oxygen saturation (SpO2), pulse rate, and noninvasive hemoglobin were measured every 5 seconds and recorded to electronic memory. Patient demographics and physiologic data were collected by chart abstraction from the Air Force Form 3899, patient movement record. The incidence and duration of hypoxemic events (SpO2 < 90%) and critical hypoxemic events were determined (SpO2 < 85%). RESULTS Sixty-one casualties were evaluated during AE from Bagram Air Base to Landstuhl Regional Medical Center. The mean (SD) age was 26.2 (6) years, Injury Severity Score (ISS) was 8 (11), and mean SpO2 before AE was 96% (2%). The mean (SD) transport time was 9.3 (1.3) hours. Patients were monitored before AE for a brief period, yielding a total recording time of 10.28 hours. The mean (SD) hemoglobin at the time of enrollment was 13.2 (3.5) g/dL (9.4–18.0 g/dL). Hypoxemia (SpO2 < 90%) was seen in 55 (90%) of 61 subjects. The mean duration of SpO2 less than 90% was 44 minutes. The mean (SD) change in SpO2 from baseline to mean in-flight SpO2 was 4% (1.2%). Thirty-four patients (56%) exhibited an SpO2 less than 85% for 11.7 (15) minutes. CONCLUSION Hypoxemia is a common event during AE of casualties. In patients with infection and concussion or mild traumatic brain injury, this could have long-term consequences. LEVEL OF EVIDENCE Epidemiologic/prognostic study, level V.

Performance of portable ventilators for mass-casualty care.

INTRODUCTION Disasters and mass-casualty scenarios may overwhelm medical resources regardless of the level of preparation. Disaster response requires medical equipment, such as ventilators, that can be operated under adverse circumstances and should be able to provide respiratory support for a variety of patient populations. OBJECTIVE The objective of this study was to evaluate the performance of three portable ventilators designed to provide ventilatory support outside the hospital setting and in mass-casualty incidents, and their adherence to the Task Force for Mass Critical Care recommendations for mass-casualty care ventilators. METHODS Each device was evaluated at minimum and maximum respiratory rate and tidal volume settings to determine the accuracy of set versus delivered VT at lung compliance settings of 0.02, 0.08 and 0.1 L/cm H20 with corresponding resistance settings of 10, 25, and 5 cm H2O/L/sec, to simulate patients with ARDS, severe asthma, and normal lungs. Additionally, different FIO2 settings with each device (if applicable) were evaluated to determine accuracy of FIO2 delivery and evaluate the effect on delivered VT. Ventilators also were tested for duration of battery life. RESULTS VT decreased with all three devices as compliance decreased. The decrease was more pronounced when the internal compressor was activated. At the 0.65 FIO2 setting on the MCV 200, the measured FIO2 varied widely depending on the set VT. Battery life range was 311-582 minutes with the 73X having the longest battery life. Delivered VT decreased toward the end of battery life with the SAVe having the largest decrease. The respiratory rate on the SAVe also decreased approaching the end of battery life. CONCLUSION The 73X and MCV 200 were the closest to satisfying the Task Force for Mass Critical Care requirements for mass casualty ventilators, although neither had the capability to provide PEEP. The 73X provided the most consistent tidal volume delivery across all compliances, had the longest battery duration and the least decline in VT at the end of battery life.

Automated Control of Endotracheal Tube Cuff Pressure During Simulated Flight

BACKGROUND Successful mechanical ventilation requires that the airway be controlled by an endotracheal tube (ETT) with an inflatable cuff to seal the airway. Aeromedical evacuation represents a unique challenge in which to manage ETT cuffs. We evaluated three methods of automatic ETT cuff pressure adjustment during changes in altitude in an altitude chamber. METHODS Size 7.5 and 8.0 mm ETTs that are currently included in the Critical Care Air Transport Team allowance standard were used for the evaluation. Three automatic cuff pressure controllers—Intellicuff, Hamilton Medical; Pyton, ARM Medical; and Cuff Sentry, Outcome Solutions—were used to manage cuff pressures. The fourth group had cuff pressure set at sea level without further adjustment. Each ETT was inserted into a tracheal model and taken to 8,000 feet and then to 16,000 feet at 2,500 ft/min. Baseline cuff pressure at sea level was approximately 25 cm H2O. RESULTS Mean cuff pressure at both altitudes with both size ETTs was as follows: Control arm, 141 ± 64 cm H2O; Pyton, 25 ± 0.8 cm H2O; Cuff Sentry, 22 ± 0.3 cm H2O; and Intellicuff, 29 ± 6.6 cm H2O. The mean time that cuff pressure was >30 cm H2O using Intellicuff at both altitudes was 2.8 ± 0.8 minutes. Pressure differences from baseline in the control arm and with Intellicuff were statistically significant. Cuff pressure with the Cuff Sentry tended to be lower than indicated on the device. CONCLUSIONS Mean cuff pressures were within the recommended range with all three devices. Intellicuff had difficulty regulating the cuff pressure initially with increases in altitude but was able to reduce the pressure to a safe level during the stabilization period at each altitude. The Pyton and Cuff Sentry allowed the least variation in pressure throughout the evaluation, although the Cuff Sentry set pressure was less than the actual pressure. LEVEL OF EVIDENCE Therapeutic study, level V.

Performance of Portable Ventilators at Altitude

BACKGROUND Aeromedical transport of critically ill patients requires continued, accurate performance of equipment at altitude. Changes in barometric pressure can affect the performance of mechanical ventilators calibrated for operation at sea level. Deploying ventilators that can maintain a consistent tidal volume (VT) delivery at various altitudes is imperative for lung protection when transporting wounded war fighters to each echelon of care. METHODS Three ventilators (Impact 731, Hamilton T1, and CareFusion Revel) were tested at pediatric (50 and 100 mL) and adult (250–750 mL) tidal VTs at 0 and 20 cm H2O positive end expiratory pressure and at inspired oxygen of 0.21 and 1.0. Airway pressure, volume, and flow were measured at sea level as well as at 8,000, 16,000, and 22,000 ft (corresponding to barometric pressures of 760, 564, 412, and 321 mm Hg) using a calibrated pneumotachograph connected to a training test lung in an altitude chamber. Set VT and delivered VT as well as changes in VT at each altitude were compared by t test. RESULTS The T1 delivered VT within 10% of set VT at 8,000 ft. The mean VT was less than set VT at sea level as a result of circuit compressible volume with the Revel and the 731. Changes in VT varied widely among the devices at sea level and at altitude. Increasing altitudes resulted in larger VT than set for the Revel and the T1. The 731 compensated for changes in altitude delivered VT within 10% at the adult settings at all altitudes. CONCLUSION Altitude compensation is an active software algorithm. Only the 731 actively accounts for changes in barometric pressure to maintain the set VT at all tested altitudes.