Acute eosinophilic pneumonia in the deployed military setting.

RATIONALE: Acute eosinophilic pneumonia (AEP) is a rare but important cause of severe respiratory failure most typically caused by cigarette smoking, but can also be caused by medications, illicit drugs, infections and environmental exposures. There is growing evidence that disease severity varies and not all patients require mechanical ventilation or even supplemental oxygen. OBJECTIVES: To compare patients with AEP treated at Landstuhl Regional Medical Center (LRMC) to those in other published series, and to provide recommendations regarding diagnosis and treatment of AEP. METHODS: A retrospective chart review was completed on forty-three cases of AEP which were identified from March 2003 through March 2010 at LRMC, Germany. RESULTS: Tobacco smoking was reported by 91% of our patients. Only 33% of patients in our series had a fever (temperature > 100.4 °F) at presentation. Peripheral eosinophilia (>5%) was present in 35% on initial CBC, but was seen in 72% of patients during their hospital course. Hypoxemia, as measured by PaO2/FiO2 ratio, seemed to be less severe in patients with higher levels of bronchoalveolar (BAL) eosinophilia percentage. CONCLUSIONS: Based on our experience and literature review, we recommend adjustments to the diagnostic criteria which may increase consideration of this etiology for acute respiratory illnesses as well as provide clinical clues we have found particularly helpful. Similar to recent reports of initial peripheral eosinophilia correlating with less severe presentation we found that higher BAL eosinophilia correlated with less severe hypoxemia.

Health care response to CCHF in US soldier and nosocomial transmission to health care providers, Germany, 2009.

In 2009, a lethal case of Crimean-Congo hemorrhagic fever (CCHF), acquired by a US soldier in Afghanistan, was treated at a medical center in Germany and resulted in nosocomial transmission to 2 health care providers (HCPs). After his arrival at the medical center (day 6 of illness) by aeromedical evacuation, the patient required repetitive bronchoscopies to control severe pulmonary hemorrhage and renal and hepatic dialysis for hepatorenal failure. After showing clinical improvement, the patient died suddenly on day 11 of illness from cerebellar tonsil herniation caused by cerebral/cerebellar edema. The 2 infected HCPs were among 16 HCPs who received ribavirin postexposure prophylaxis. The infected HCPs had mild or no CCHF symptoms. Transmission may have occurred during bag-valve-mask ventilation, breaches in personal protective equipment during resuscitations, or bronchoscopies generating infectious aerosols. This case highlights the critical care and infection control challenges presented by severe CCHF cases, including the need for experience with ribavirin treatment and postexposure prophylaxis.

Vocal cord dysfunction related to combat deployment.

OBJECTIVES: Several etiologies for vocal cord dysfunction (VCD), a syndrome of dyspnea, noisy breathing, and inspiratory vocal cord closure are suggested; there is no consensus on the predisposition to its development. One previously identified psychiatric etiology is combat stress. METHODS: A retrospective review of military personnel evaluated at Landstuhl Regional Medical Center with a new VCD diagnosis post-deployment was conducted. Medical records were reviewed for existing pulmonary, sinus, esophageal, or psychiatric disorders and determined their VCD evaluation. RESULTS: Forty-eight patients were identified with VCD symptoms after combat deployment. For military personnel with VCD, symptoms were associated with several etiologies. Fifty-two percent reported symptoms were related to high stress/anxiety, whereas 39% reported symptoms during exercise; 16% had onset with acute respiratory illness and 7% were trauma related. The combination of a truncated inspiratory flow volume loop and negative methacholine challenge had a 72% positive predictive value. CONCLUSIONS: Common etiologies with VCD onset during deployment are anxiety/stress, exercise, or combination of factors. Spirometry with abnormal flow volume loop plus negative methacholine challenge testing offers a reasonable predictive value for diagnosing VCD. For deployed military with these findings, laryngoscopy for upper airway disorders should be conducted.

Transportable extracorporeal lung support for rescue of severe respiratory failure in combat casualties.

BACKGROUND: Advances in oxygenator membrane, vascular cannula, and centrifugal pump technologies led to the miniaturization of extracorporeal lung support (ECLS) and simplified its insertion and use. Support of combat injuries complicated by severe respiratory failure requires critical care resources not sustainable in the deployed environment. In response to this need, a unique international military-civilian partnership was forged to create a transportable ECLS capability to rescue combat casualties experiencing severe respiratory failure. METHODS: A multidisciplinary training and consultative relationship developed between the US military at Landstuhl Regional Medical Center (LRMC) and the University Hospital Regensburg (UHR), a German regional "lung failure" center with expertise in ECLS. ECLS circuits used were pumpless arteriovenous extracorporeal lung assist (NovaLung iLA) and pump-driven venovenous extracorporeal membrane oxygenation (PLS Quadrox D Membrane Oxygenator with Rotaflow Centrifugal Pump). US casualties supported by ECLS between June 2005 and August 2011 were identified from the LRMC Trauma Program Registry for review. RESULTS: UHR cared for 10 US casualties supported by ECLS. The initial five patients were cannulated with arteriovenous circuits (pumpless arteriovenous extracorporeal lung assist), and the remaining five were cannulated with pump-driven venovenous circuits (extracorporeal membrane oxygenation). Four patients were cannulated in the war zone, and six patients were cannulated at LRMC after evacuation to Germany. All patients were transferred to UHR for continued management (mean, 9.6 ECLS days). In all cases, both hypoxemia and hypercapnia improved, allowing for decreased airway pressures. Nine patients were weaned from ECLS and extubated. One soldier died from progressive multiple-organ failure. CONCLUSION: ECLS should be considered in the management of trauma complicated by severe respiratory failure. Modern ECLS technology allows these therapies to be transported for initiation outside of specialized centers even in austere settings. Close collaboration with established centers potentially allows both military and civilian hospitals with infrequent ECLS requirements to use it for initial patient stabilization before transfer for continued care. LEVEL OF EVIDENCE: Therapeutic/care management study, level V.

Diffuse alveolar hemorrhage: a rare manifestation of trauma.

OBJECTIVE: Fat emboli syndrome (FES) is a disorder associated with both acute lung injury and acute respiratory distress syndrome. Both FES and diffuse alveolar hemorrhage (DAH) are bronchoscopically definable entities that may share a common etiology. We conducted a chart review analysis to examine the relationship between FES and DAH. METHODS: Retrospective chart review. RESULTS: Three cases of concurrent FES and DAH were identified. Long bone fracture and/or orthopedic procedures preceded all the events and were the likely inciting source for eventual acute lung injury. Bronchoalveolar lavage-evident DAH and FES was found in all these cases in association with hemoptysis and lung-attributed blood loss. Lung-protective ventilation and standard supportive care approaches proved sufficient in attaining good outcomes. CONCLUSION: Combined FES and DAH can occur in association with orthopedic injury and repair and are likely an under-recognized entity.

The introduction of extracorporeal membrane oxygenation to aeromedical evacuation.

OBJECTIVE: To review the principles of extracorporeal membrane oxygenation (ECMO) and to describe the recent advancements in ECMO technology that permit use of this rescue therapy for severe lung injury in combat casualties. METHODS/RESULTS: Lung protective ventilation has defined the state-of-the-art treatment for acute lung injury for more than a decade. Despite the benefits provided by a low tidal volume strategy, lung injury patients may experience deterioration in gas exchange to the point that other rescue interventions are needed or the patient succumbs to progressive respiratory failure. When this occurs in combat casualties, management of the patient in an austere environment and movement to definitive care become problematic. Recent advances in ECMO technology permit long-range transport of these critically ill casualties with greater physiologic reserve and potentially less mortality. CONCLUSIONS: Advances in ECMO technology now enable the stabilization and aeromedical evacuation of even the most critically ill combat casualties with severe lung injury.

Closing the "care in the air" capability gap for severe lung injury: the Landstuhl Acute Lung Rescue Team and extracorporeal lung support.

BACKGROUND: The success of US Air Force Critical Care Air Transport Teams (CCATT) in transporting critically ill and injured patients enabled changes in military medical force deployment and casualty care practice. Even so, a subset of casualties remains who exceed even CCATT capabilities for movement. These patients led to the creation of the Landstuhl Acute Lung Rescue Team (ALeRT) to close the "care in the air" capability gap. METHODS: The ALeRT Registry was queried for the period between November 1, 2005, and June 30, 2010. Additionally, Landstuhl Regional Medical Center critical care patient transfers to host nation medical centers were reviewed for cases using extracorporeal lung support systems. RESULTS: For the review period, US Central Command activated the ALeRT on 40 occasions. The ALeRT successfully evacuated patients on 24 of 27 missions launched (89%). Three patients were too unstable for ALeRT evacuation. Of the 13 remaining activations, four patients died and nine patients improved sufficiently for standard CCATT movement. The ALeRT initiated pumpless extracorporeal lung assistance six times, but only once to facilitate evacuation. Two patients were supported with full extracorporeal membrane oxygenation support after evacuation due to progressive respiratory failure. CONCLUSIONS: ALeRT successfully transported 24 casualties from the combat zones to Germany. Without the ALeRT, these patients would have remained in the combat theater as significant consumers of limited deployed medical resources. Pumpless extracorporeal lung assistance is already within the ALeRT armamentarium, but has only been used for one aeromedical evacuation. Modern extracorporeal membrane oxygenation systems hold promise as a feasible capability for aeromedical evacuation.

Reversal of hemorrhagic shock-associated hepatic ischemia-reperfusion injury with N-acetylcysteine.

BACKGROUND: The underpinning pathophysiology, prevalence, and clinical relevance particular to hemorrhagic shock-induced liver damage have been explored only recently. Importantly, several investigators have revealed that an aberrant periportal endothelial response, characterized by the early release of oxidizing mediators, perpetuates and eventually amplifies the extent of hepatic reperfusion injury. CASE: We present a case that illustrates the clinical impact of hepatic ischemia-reperfusion injury and a potential means of ameliorating the attendant self-propagating hepatic destruction. CONCLUSION: Reversal of hemorrhagic shock may lead to the induction of a hepatic oxidation response with a resultant furthering of liver injury. Antioxidants such as N-acetylcysteine may represent a tolerable and logical means of attenuating the aberrant oxidant cascade and stabilizing or reversing ischemic-reperfusion hepatopathy.

A review of the surgical treatment options for the obstructive sleep apnea/hypopnea syndrome patient.

Obstructive sleep apnea/hypopnea syndrome (OSAHS) is a medical condition that has received significant attention within the medical community and mainstream media due to its potentially serious physiological consequences and relatively frequent occurrence within the general population. From the military perspective, the impact on individual readiness for deployment, and the potential degradation of performance in critically important military duties, often results in tremendous expenditures of training resources, time, and expertise to replace the military member with a suitable substitute or release of the individual from active duty. This article reviews common surgical techniques for clinical management of OSAHS patients in a presentation format for primary care and sleep medicine specialists, as well as surgeons interested in the philosophies of surgical management of sleep disordered breathing. Presentation of risks and benefits of surgical treatment are discussed in a manner to facilitate communication between patient and health care provider.

High-frequency percussive ventilation revisited.

High-frequency percussive ventilation (HFPV) has demonstrated a potential role as a rescue option for refractory acute respiratory distress syndrome and as a method for improving inhalation injury outcomes. Nevertheless, there is a lack of literature examining the practical application of HFPV theory toward either improving gas exchange or preventing possible ventilator-induced lung injury. This article will discuss the clinically pertinent aspects of HFPV, inclusive of high- and low-frequency ventilation.

High-frequency percussive ventilation and low tidal volume ventilation in burns: a randomized controlled trial.

OBJECTIVES: In select burn intensive care units, high-frequency percussive ventilation is preferentially used to provide mechanical ventilation in support of patients with acute lung injury, acute respiratory distress syndrome, and inhalation injury. However, we found an absence of prospective studies comparing high-frequency percussive ventilation with contemporary low-tidal volume ventilation strategies. The purpose of this study was to prospectively compare the two ventilator modalities in a burn intensive care unit setting. DESIGN: Single-center, prospective, randomized, controlled clinical trial, comparing high-frequency percussive ventilation with low-tidal volume ventilation in patients admitted to our burn intensive care unit with respiratory failure. SETTING: A 16-bed burn intensive care unit at a tertiary military teaching hospital. PATIENTS: Adult patients ≥ 18 yrs of age requiring prolonged (> 24 hrs) mechanical ventilation were admitted to the burn intensive care unit. The study was conducted over a 3-yr period between April 2006 and May 2009. This trial was registered with ClinicalTrials.gov as NCT00351741. INTERVENTIONS: Subjects were randomly assigned to receive mechanical ventilation through a high-frequency percussive ventilation-based strategy (n = 31) or a low-tidal volume ventilation-based strategy (n = 31). MEASUREMENTS AND MAIN RESULTS: At baseline, both the high-frequency percussive ventilation group and the low-tidal volume ventilation group had similar demographics to include median age (interquartile range) (28 yrs [23-45] vs. 33 yrs [24-46], p = nonsignificant), percentage of total body surface area burn (34 [20-52] vs. 34 [23-50], p = nonsignificant), and clinical diagnosis of inhalation injury (39% vs. 35%, p = nonsignificant). The primary outcome was ventilator-free days in the first 28 days after randomization. Intent-to-treat analysis revealed no significant difference between the high-frequency percussive ventilation and the low-tidal volume ventilation groups in mean (± sd) ventilator-free days (12 ± 9 vs. 11 ± 9, p = nonsignificant). No significant difference was detected between groups for any of the secondary outcome measures to include mortality except the need for "rescue" mode application (p = .02). Nine (29%) in the low-tidal volume ventilation arm did not meet predetermined oxygenation or ventilation goals and required transition to a rescue mode. By contrast, two in the high-frequency percussive ventilation arm (6%) required rescue. CONCLUSIONS: A high-frequency percussive ventilation-based strategy resulted in similar clinical outcomes when compared with a low-tidal volume ventilation-based strategy in burn patients with respiratory failure. However, the low-tidal volume ventilation strategy failed to achieve ventilation and oxygenation goals in a higher percentage necessitating rescue ventilation.

Combat-associated drowning.

BACKGROUND: The purpose of this article is to describe the clinical course and outcome of drowning cases related to current US military combat operations. METHODS: This retrospective case series spans December 2002 to January 2009 of survivors transferred to an echelon IV military trauma center in Europe serving as the primary evacuation hub for ongoing combat operations. Patient demographics and the situational and clinical findings at the initial drowning scene were reviewed. A comprehensive analysis of care as each patient transitioned through the combat theater to the echelon IV trauma center in Europe was performed. RESULTS: Overall, mortality was 37.5% mortality rate (3 of 8 patients). Advanced modes of respiratory support such as high-frequency ventilation, airway pressure release ventilation, and extracorporeal membrane oxygenation were required in a majority of the cohort (6 of 8 patients). Limited-duration vasopressor infusions (7 of 8 patients) were also required to ensure adequate end-organ perfusion. Glasgow Coma Scale (GCS) scores and the need for cardiopulmonary resuscitation (CPR) at the scene of injury were associated with eventual patient mortality (100% mortality for an initial GCS score of 3 and 75% mortality for on-scene CPR). Survivor long-term morbidity was often related to the sequelae of acute respiratory distress syndrome and hypoxic encephalopathy. CONCLUSION: Drowning associated with combat operations was associated with severe acute respiratory distress syndrome and cardiovascular shock. GCS score and the need for CPR at the scene of injury were associated with eventual mortality because of anoxic brain injury in all cases.

Predictors of early acute lung injury at a combat support hospital: a prospective observational study.

BACKGROUND: Acute lung injury (ALI) is a syndrome consisting of noncardiogenic acute hypoxemic respiratory failure with the presence of bilateral pulmonary infiltrates and occurs in up to 33% of critically ill trauma patients. Retrospective and observational studies have suggested that a blood component resuscitation strategy using equal ratios of packed red blood cells (PRBCs) and fresh frozen plasma (FFP) may have a survival benefit in combat casualties. The purpose of this study was to determine whether this strategy is associated with an increased incidence of ALI. METHODS: We performed a prospective observational study of all injured patients admitted to an intensive care unit (ICU) at a combat support hospital who required >5 units of blood transfusion within the first 24 hours of admission. Baseline demographic data along with Injury Severity Score (ISS), pulmonary injury, presence of long bone fracture, blood products transfused, mechanical ventilation data, and arterial blood gas analysis were collected. The primary endpoint of the study was the development of ALI at 48 hours after injury. Those who did not survive to ICU admission were excluded from analysis. Follow-up (including mortality) longer than 48 hours was unavailable secondary to rapid transfer out of our facility. A multivariate logistic regression was performed to determine the independent effects of variables on the incidence of early ALI. RESULTS: During a 12-month period (from January 2008 to December 2008), 87 subjects were studied; of these, 66 patients met inclusion criteria, and 22 patients developed ALI at 48 hours (33%). Overall, the ratio of FFP to PRBC was 1:1.1. Those who developed ALI had a higher ISS (32 +/- 15 vs. 26 +/- 11; p = 0.04) and received more units of FFP (22 +/- 15 vs. 12 +/- 7; p < 0.001), PRBCs (22 +/- 16 vs. 13 +/- 7; p = 0.008), and platelets (5 +/- 11 vs. 1 +/- 2; p = 0.004) compared with those who did not develop ALI. Multivariate logistic regression analysis revealed that presence of pulmonary injury (odds ratio, 5.4; 95% confidence interval, 1.3-21.9) and volume of FFP transfused (odds ratio, 1.2; 95% confidence interval, 1.1-1.3) had independent effects on ALI at 48 hours. CONCLUSION: On the basis of this small, prospective, descriptive study of severely injured patients admitted to the ICU, we determined that the presence of pulmonary injury had the greatest impact on the incidence of early ALI. There was also an independent relationship between the amount of FFP transfused and the incidence of early ALI. Further studies are required to determine the effects of the development of early ALI from FFP transfusion on short- and long-term survival.

Intercontinental aeromedical evacuation of patients with traumatic brain injuries during Operations Iraqi Freedom and Enduring Freedom.

Traumatic brain injury contributes significantly to military combat morbidity and mortality. No longer maintaining comprehensive medical care facilities throughout the world, the US military developed a worldwide trauma care system making the patient the moving part of the system. Life-saving interventions are performed early, and essential care is delivered at forward locations. Patients then proceed successively through increasingly capable levels of care culminating with arrival in the US. Proper patient selection and thorough mission preparation are crucial to the safe and successful intercontinental aeromedical evacuation of critical brain-injured patients during Operations Iraqi Freedom and Enduring Freedom.

High-frequency percussive ventilation: pneumotachograph validation and tidal volume analysis.

INTRODUCTION: High-frequency percussive ventilation (HFPV) is an increasingly used mode of mechanical ventilation, for which there is no proven real-time means of measuring delivered tidal volume (V(T)). OBJECTIVE: To validate a pneumotachograph for HFPV and then exploit flow-sensor data to describe the behavior of both low-frequency and high-frequency breaths. METHODS: Sensor performance was gauged during changes in high-frequency (4-12 Hz) and low-frequency rate and ratio, mean airway pressure, oxygen concentration, heated or heated-humidified gas flow, and endotracheal tube diameter. Glass bottle (adiabatic V(T)) and test lung (adiabatically derived low-frequency V(T)) based adiabatic conditions provided both an initial source for analog-signal calibration and an accepted standard comparator to flow-sensor measurement of high-frequency and low-frequency (flow-sensor-derived) V(T)), respectively. RESULTS: Pneumotachography proved accurate and precise over an array of tested settings and conditions when analyzing both high-frequency (difference between mean +/- SD high-frequency V(T) and adiabatic V(T) was -0.2 +/- 1.8%, 95% confidence interval -0.5 to 0.9%) and low-frequency breaths (mean +/- SD difference between flow-sensor-derived low-frequency V(T) and adiabatically derived low-frequency V(T) was 0.6 +/- 2.4%, 95% confidence interval 0.1-1.1%). High-frequency V(T) and frequency exhibited an exponential relationship. During HFPV, flow-sensor-derived low-frequency V(T) had a mean +/- SD of 1,337 +/- 700 mL, 95% confidence interval 1,175-1,499 mL. CONCLUSIONS: Readily available pneumotachography provided accurate measurements of low-frequency and high-frequency V(T) during HFPV. In the setting of acute lung injury, typical HFPV settings may deliver injurious V(T).

Inhaled prostacyclin in combination with high-frequency percussive ventilation.

We present a case of severe acute respiratory distress syndrome pursuant to inhalation of a compressed gas computer keyboard cleaner. Despite the use of multimodal therapy to include empiric antibiotics, intravenous paralytics, intravenous concentrated albumin, high-dose corticosteroids as well as sustained high mean airway pressure mechanical ventilation by airway pressure release and high-frequency percussive ventilation (HFPV) modes, the patient demonstrated an unchanging arterial oxygen tension/fraction of inspired oxygen ratio of only 57 mm Hg. A trial of nebulized prostacyclin was initiated during HFPV leading to a significant improvement in arterial oxygen tension/fraction of inspired oxygen to 147 mm Hg. The improved oxygen tension allowed for a reduction in mean airway pressure and oxygen concentration as well the safe aeromedical evacuation of the patient from the combat theater. Further, prospective studies are required to validate the magnitude of response to inhaled prostacyclin during HFPV.

Cardiopulmonary exercise test interpretation using age-matched controls to evaluate exertional dyspnea.

BACKGROUND: Cardiopulmonary exercise testing (CPET) is one method to diagnose unexplained dyspnea in young adults, yet few normal reference values exist in this population. This study evaluated interpretation of maximal CPET in a young adult cohort with known pulmonary disorders using published reference values compared to age-matched normal controls. METHODS: A control population of 69 healthy military volunteers with normal chest radiographs, pulmonary function testing, and bronchoprovocation testing were compared to 105 patients with exertional dyspnea. Both groups underwent a standardized evaluation including CPET on a graded exercise treadmill to maximal exercise with expired gas analysis. RESULTS: Measurements from CPET in the dyspnea group were interpreted using published reference values compared to control population results (mean +/- 1.65 x SD). Statistical comparison of predicted normals (reference vs. control) of maximal oxygen consumption (> 83% vs. 82%), ventilatory anaerobic threshold (> 40% vs. 53%), respiratory rate (< 60 vs. 56 breaths/min), tidal volume to inspiratory capacity (< 80% vs. 111%), ventilatory equivalent for carbon dioxide production (< 40 vs. 38), and maximal voluntary ventilation minus minute ventilation (> 11 vs. -1 L/min) was performed. The overall specificity for tidal volume to inspiratory capacity improved using age-matched controls but sensitivity was decreased. Other parameters were not significantly different. CONCLUSIONS: The use of age-matched controls for CPET results in an increase in specificity and decrease in sensitivity for respiratory limitations to exercise, when compared to reference values. The study findings suggest that CPET may be insensitive in detecting mild disease in young healthy adults.

Feasibility study of noninvasive ventilation with helium-oxygen gas flow for chronic obstructive pulmonary disease during exercise.

BACKGROUND: Individually, noninvasive ventilation (NIV) and helium-oxygen gas mixtures (heliox) diminish ventilatory workload and improve exercise tolerance in patients with chronic obstructive pulmonary disease (COPD). NIV in combination with heliox may have additive effects on exercise tolerance in severe COPD. METHODS: We assessed the safety, tolerability, and efficacy of heliox and NIV during exercise in patients with severe COPD. SETTING: Pulmonary rehabilitation facility in an academic tertiary-care medical center. PROTOCOL: Twelve patients with severe COPD were enrolled. Using a sequential randomized placebo-controlled crossover study design, the patients performed 4 separate constant-work stationary bicycle cardiopulmonary exercise studies at 80% of maximal workload during application of sham NIV, NIV, 60:40 heliox with sham NIV, and 60:40 heliox with NIV. Tolerability, safety, and exercise duration as determined by constant-work cardiopulmonary exercise test were the primary outcome measures. Secondary outcome measures at peak exercise and iso-time included rate of perceived exertion, dyspnea, leg pain, heart rate, respiratory rate, systolic and diastolic blood pressure, tympanic temperature, and oxyhemoglobin saturation. RESULTS: No adverse effects occurred during or after application of NIV, heliox, or NIV with heliox. Exercise duration using heliox with NIV was significantly longer than both heliox (P = .01) and NIV (P = .007), but not placebo (P = .09). Relative to placebo, all treatment arms permitted lower respiratory rates at peak exercise. Heliox, with or without NIV, was associated with significant improvements in oxyhemoglobin saturation at peak exercise, relative to placebo or NIV alone. CONCLUSIONS: The adjunctive use of NIV with heliox during exercise proved both safe and tolerable in patients with severe COPD. The lack of demonstrable efficacy to any of the treatment arms relative to placebo (P = .09) may be the result of the small sample size (ie, type 2 error)-a conclusion emphasized by the large standard deviations and differences in treatment group variances in exercise duration alone.

Airway humidification during high-frequency percussive ventilation.

BACKGROUND: We were concerned about the risk of inadequate humidification during high-frequency percussive ventilation (HFPV). METHODS: We studied 5 humidifiers during HFPV with a lung model, at bias gas flows of 10 L/min, 30 L/min, and 50 L/min, and compared the results to those from a comparator ventilator/humidifier setup and to the minimum temperature (30 degrees C) and humidity (30 mg/L) [corrected] recommended by the American Association for Respiratory Care, at both regular room temperature and a high ambient temperature. Temperature was measured at the humidifier outflow point and at the artificial carina. Humidity was measured at the artificial carina. RESULTS: Of the 7 HFPV/humidifier combinations, 2 (the MR850 at a bias flow of 50 L/min, and the ConchaTherm Hi-Flow with VDR nebulizer) provided a carinal temperature equivalent to the comparator setup at room temperature, whereas one HFPV/humidifier combination (the ConchaTherm Hi-Flow with modified programming, at bias flows of 30 L/min and 50 L/min) provided a higher carinal temperature. At high ambient temperature, all of the setups delivered lower carinal temperature than the comparator setup. Only 2 setups (the ConchaTherm with modified programming at a bias flow of 50 L/min, and the ConchaTherm Hi-Flow with VDR nebulizer) provided carinal humidification equivalent to the comparator setup, without regard to ambient temperature; the other humidifiers were less effective. The ConchaTherm with modified programming, and the ConchaTherm with the VDR nebulizer provided the most consistent humidification. CONCLUSION: HFPV's distinctive gas-flow mechanism may impair gas heating and humidification, so all humidification systems should be tested with HFPV prior to clinical use.