Thomas C Blakeman

Asynchrony and dyspnea.

Patient-ventilator synchrony and patient comfort are assumed to go hand in hand, yet few studies provide support for this common sense idea. In reality, synchrony between the patient and ventilator is complex and can be affected by the ventilator settings, type of ventilator, patient-ventilator interface, and sedation. Inspections of airway pressure and flow waveforms are reliable methods for detecting asynchrony, and automated detection seems accurate. A number of types of asynchronies have been defined, and asynchrony during invasive and noninvasive ventilation have different calling cards. There is a clear association between asynchrony, ventilator-induced diaphragmatic dysfunction, and duration of mechanical ventilation. Whether these are cause and effect or simply associated remains to be determined.

Inter- and Intra-hospital Transport of the Critically Ill

Intra- and inter-hospital transport is common due to the need for advanced diagnostics and procedures, and to provide access to specialized care. Risks are inherent during transport, so the anticipated benefits of transport must be weighed against the possible negative outcome during the transport. Adverse events are common in both in and out of hospital transports, the most common being equipment malfunctions. During inter-hospital transport, increased transfer time is associated with worse patient outcomes. The use of specialized teams with the transport of children has been shown to decrease adverse events. Intra-hospital transports often involve critically ill patients, which increases the likelihood of adverse events. Radiographic diagnostics are the most common in-hospital transport destination and the results often change the course of care. It is recommended that portable ventilators be used for transport, because studies show that use of a manual resuscitator alters blood gas values due to inconsistent ventilation. The performance of new generation transport ventilators has improved greatly and now allows for seamless transition from ICU ventilators. Diligent planning for and monitoring during transport may decrease adverse events and reduce risk.

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.

Evaluation of 4 New Generation Portable Ventilators

BACKGROUND: Portable ventilators are increasingly utilized in the intra- and inter-hospital transport of patients. We evaluated 4 portable ventilators, Impact EMV, CareFusion LTV 1200, Newport HT70, and Hamilton T1, in terms of triggering, delivered tidal volume (VT) accuracy, battery duration, delivered FIO2 accuracy, and gas consumption. METHODS: Triggering was tested using a microprocessor controlled breathing simulator that simulated a weak, normal, and aggressive inspiratory effort using muscle pressures of −2, −4, and −8 cm H2O respectively. Delivered VT and FIO2 accuracy were evaluated across a range of operation. To determine gas consumption, the ventilators were attached to an E type oxygen cylinder and operated at an FIO2 of 1.0 until the tank was depleted. Battery duration was tested by operating each ventilator at an FIO2 of 0.21 until the device ceased to operate. RESULTS: Differences remain among devices in several aspects of the testing protocol. Gas consumption ranged from 9.2 to 16 L/min. Battery duration ranged from 101 to 640 min. Triggering performance varied among devices but was consistent breath to breath within the same device, using the fastest and slowest rise time settings. FIO2 accuracy varied at the low range on the 50 mL VT setting with one device, and at the high range on both the 50 mL and 500 mL VT settings with another. CONCLUSIONS: Manufacturers continue to improve the performance of portable ventilators. All the ventilators we tested performed well on VT delivery across a range of settings, using both the internal drive mechanism (FIO2 0.21) and compressed oxygen (FIO2 1.0). Two of the ventilators were unable to deliver accurate FIO2 across the range of VT. None of the devices was clearly superior to the others in all aspects of our evaluation.

Patient-Ventilator Asynchrony in a Traumatically Injured Population

BACKGROUND: Prolonged mechanical ventilation, longer hospital stay, and a lower rate of home discharge have been reported with patient-ventilator asynchrony in medical patients. Though commonly encountered, asynchrony is poorly defined within the traumatically injured population. METHODS: Mechanically ventilated trauma patients at an urban, level-1 center were enrolled. Breath waveforms were recorded over 30 min within the first 48 hours following intubation. Asynchronous breaths were defined as ineffective patient triggering, double-triggering, short-cycle breaths, and long-cycle breaths. Asynchronous subjects were defined as having asynchrony in ≥ 10% of total breaths. Demographic, injury, sedation/delirium scores, and clinical and discharge outcomes were prospectively collected. RESULTS: We enrolled 35 subjects: median age 47 y, 77.1% male, 28.6% with penetrating injuries, 16% with a history of COPD, median (IQR) Injury Severity Score 22 (17–27), and median (IQR) chest Abbreviated Injury Scale score 2 (0–6). We analyzed 15,445 breaths. Asynchrony was present in 25.7% of the subjects. No statistical differences between the asynchronous and non-asynchronous subjects were found for age, sex, injury mechanism, COPD history, delirium/sedation scores, PaO2/FIO2, PEEP, blood gas values, or sedative, narcotic, or haloperidol use. Asynchronous subjects more commonly used synchronized intermittent mandatory ventilation (SIMV) (100% vs 38.5%, P = .002) and took fewer median spontaneous breaths/min: 4 breaths/min (IQR 3–8 breaths/min) vs 12 breaths/min (IQR 9–14 breaths/min) (P = .007). SIMV with set breathing frequencies of ≥ 10 breaths/min was associated with increased asynchrony rates (85.7% vs 14.3%, P = .02). We found no difference in ventilator days, ICU or hospital stay, percent discharged home, or mortality between the asynchronous and non-asynchronous subjects. CONCLUSIONS: Ventilator asynchrony is common in trauma patients. It may be associated with SIMV with a set breathing frequency of ≥ 10 breaths/min, though not with longer mechanical ventilation, longer stay, or discharge disposition. (ClinicalTrials.gov NCT01049958)

Accuracy of Noninvasive Hemoglobin Monitoring in Patients at Risk for Hemorrhage

BACKGROUND Monitoring for acute blood loss is critical in surgical patients, and delays in identifying hemorrhage can result in poor outcomes. The current standard of care for monitoring patients at risk for bleeding is serial measurement of hemoglobin (Hgb) by standard laboratory complete blood count (CBC). Point-of-care testing (i.e., iSTAT) can be a rapid method of evaluating Hgb, and spectrophotometry-based devices (i.e., Radical-7) offer the advantages of being continuous and noninvasive. We sought to evaluate the accuracy of Radical-7 and iSTAT in measuring Hgb and assessing for blood loss when compared with the criterion standard CBC. METHODS Adult patients at risk for hemorrhage admitted to the surgical intensive care unit of a tertiary referral, Level I trauma center were eligible for this study. Serial CBC Hgb measurements were drawn as clinically indicated. The Radical-7 device was placed on the patient for noninvasive Hgb measurements (SpHb), and at each CBC measurement, concurrent iSTAT Hgb measurements were obtained. Bland-Altman analysis was used to compare the three methods of measuring Hgb with accuracy defined as measurements within 1.0-g/dL CBC Hgb. Concordance measurements were also performed to compare trends between values. RESULTS Eighty-eight patients were enrolled and underwent 572 CBC measurements. Bland-Altman analysis of SpHb versus CBC resulted in an estimated bias of 1.49 g/dL, with 95% limits of agreement of −2.2 g/dL to 5.0 g/dL. iSTAT versus CBC resulted in an estimated bias of −0.63 g/dL, with 95% limits of agreement of −3.4 g/dL to 2.2 g/dL. Changes in SpHb had concordance with CBC Hgb 60% of the time, compared with 76% for iSTAT versus CBC CONCLUSION Radical-7 SpHb was inaccurate when compared with CBC Hgb levels, and serial SpHb achieved concordance with CBC Hgb 60% of the time. As such, the clinical utility of Radical-7 as a rapid, noninvasive predictor of acute hemorrhage may be limited. LEVEL OF EVIDENCE Diagnostic study, level II; care management, level III.

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.

Oxygen supplies in disaster management

Mass casualty events and disasters, both natural and human-generated, occur frequently around the world and can generate scores of injured or ill victims in need of resources. Of the available medical supplies, oxygen remains the critical consumable resource in disaster management. Strategic management of oxygen supplies in disaster scenarios remains a priority. Hospitals have large supplies of liquid oxygen and a supply of compressed gas oxygen cylinders that allow several days of reserve, but a large influx of patients from a disaster can strain these resources. Most backup liquid oxygen supplies are attached to the main liquid system and supply line. In the event of damage to the main system, the reserve supply is rendered useless. The Strategic National Stockpile supplies medications, medical supplies, and equipment to disaster areas, but it does not supply oxygen. Contracted vendors can deliver oxygen to alternate care facilities in disaster areas, in the form of concentrators, compressed gas cylinders, and liquid oxygen. Planning for oxygen needs following a disaster still presents a substantial challenge, but alternate care facilities have proven to be valuable in relieving pressure from the mass influx of patients into hospitals, especially for those on home oxygen who require only an electrical source to power their oxygen concentrator.

Reducing Secondary Insults in Traumatic Brain Injury

OBJECTIVES To determine the alterations in intracranial pressure (ICP) during U. S. Air Force Critical Care Air Transport Team transport of critically injured warriors with ICP monitoring by intraventricular catheter (IVC). METHODS Patients with an IVC following traumatic brain injury requiring aeromedical evacuation from Bagram to Landstuhl Regional Medical Center were studied A data logger monitored both ICP and arterial blood pressure and was equipped with an integral XYZ accelerometer to monitor movement. RESULTS Eleven patients were studied with full collection of data from takeoff to landing. The number of instances of ICP>20 mm Hg ranged from 0 to 238 and duration of instances ranged from 0 to 3,281 seconds. The number of instances of ICP±50% of the baseline ICP ranged from 0 to 921 and duration of instances ranged from 0 to 9,054 seconds. Five of the patients did not experience ICP>20 mm Hg throughout their flight, but 10 patients showed instances of ICP±50% of baseline ICP. CONCLUSION Patient movement results in changes in ICP both from external stimuli (vibration, noise) and from acceleration and deceleration forces. During transport, Critical Care Air Transport Team crews should prioritize monitoring and correcting ICP including additional sedation and/or venting IVC.

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.