John J. Marini

Non-pulmonary factors strongly influence the stress index

PurposeA quantitative measure of the airway pressure–time tracing during passive inflation [stress index (SI)] has been suggested as an indicator of tidal lung recruitment and/or overinflation. If reliable, this simple index could help guide positive end-expiratory pressure (PEEP) and tidal volume selection. The compartment surrounding the lungs should impact airway pressure and could, therefore, affect SI validity. To explore the possibility, we determined SI in a swine model of pleural effusion (PLEF).MethodsUnilateral PLEF was simulated by instilling fluid (13xa0ml/kg—moderate, 26xa0ml/kg—large) into the right pleural space of five anesthetized, paralyzed, mechanically ventilated pigs. Animals were ventilated with constant flow ventilation: tidal volume (VT) 9xa0ml/kg, f set to end-tidal CO2 (ETCO2) of 30–40xa0mmHg, inspiratory to expiratory ratio (I/E) 1:2, PEEP 1 or 10xa0cmH2O. Respiratory system mechanics and computed tomography (CT) were acquired at end-inspiration and end-expiration to determine % tidal recruitment and overinflation.ResultsPrior to PLEF instillation, SI values derived at PEEPxa0=xa01 and 10xa0cmH2O were 0.90 and 1.22, respectively. Moderate PLEF increased these SI values to 1.06 and 1.24 and large PLEF further increased SI to 1.23 and 1.27 despite extensive tidal recruitment and negligible overdistention by CT. The initial half of the tidal pressure curve produced SI values (range 0.82–1.17) that were significantly lower than those of the second half (0.98–1.37).ConclusionsIn the presence of pleural fluid, SI indicated overinflation when virtually none was present and tidal lung recruitment predominated. When the extrapulmonary environment is abnormal, caregivers are advised to interpret the SI with caution.

Evaluating Humidity Recovery Efficiency of Currently Available Heat and Moisture Exchangers: A Respiratory System Model Study

OBJECTIVES: To evaluate and compare the efficiency of humidification in available heat and moisture exchanger models under conditions of varying tidal volume, respiratory rate, and flow rate. INTRODUCTION: Inspired gases are routinely preconditioned by heat and moisture exchangers to provide a heat and water content similar to that provided normally by the nose and upper airways. The absolute humidity of air retrieved from and returned to the ventilated patient is an important measurable outcome of the heat and moisture exchangers’ humidifying performance. METHODS: Eight different heat and moisture exchangers were studied using a respiratory system analog. The system included a heated chamber (acrylic glass, maintained at 37°C), a preserved swine lung, a hygrometer, circuitry and a ventilator. Humidity and temperature levels were measured using eight distinct interposed heat and moisture exchangers given different tidal volumes, respiratory frequencies and flow-rate conditions. Recovery of absolute humidity (%RAH) was calculated for each setting. RESULTS: Increasing tidal volumes led to a reduction in %RAH for all heat and moisture exchangers while no significant effect was demonstrated in the context of varying respiratory rate or inspiratory flow. CONCLUSIONS: Our data indicate that heat and moisture exchangers are more efficient when used with low tidal volume ventilation. The roles of flow and respiratory rate were of lesser importance, suggesting that their adjustment has a less significant effect on the performance of heat and moisture exchangers.

Cigarettes-induced acute eosinophilic pneumonia: a case report

BackgroundIdiopathic acute eosinophilic pneumonia is a rare disease. It presents with acute febrile illness, respiratory insufficiency, pulmonary infiltration and high eosinophil levels in Bronchoalveolar lavage fluid. Pathogenesis is not well understood, but may relate to the exposure to exogenous substances.Case presentationWe present a case of 20-year-old man, who developed idiopathic acute eosinophilic pneumonia after smoking cigarettes and required intubation with mechanical ventilation. His symptoms resolved quickly after corticosteroids therapy.ConclusionAcute eosinophilic pneumonia should be considered in the differential diagnosis of a patient with acute febrile respiratory illness, diffuse bilateral pulmonary infiltrates and recent modification in smoking habit.

Reliability of transpulmonary pressure-time curve profile to identify tidal recruitment/hyperinflation in experimental unilateral pleural effusion.

The stress index (SI) is a parameter that characterizes the shape of the airway pressure–time profile (P/t). It indicates the slope progression of the curve, reflecting both lung and chest wall properties. The presence of pleural effusion alters the mechanical properties of the respiratory system decreasing transpulmonary pressure (Ptp). We investigated whether the SI computed using Ptp tracing would provide reliable insight into tidal recruitment/overdistention during the tidal cycle in the presence of unilateral effusion. Unilateral pleural effusion was simulated in anesthetized, mechanically ventilated pigs. Respiratory system mechanics and thoracic computed tomography (CT) were studied to assess P/t curve shape and changes in global lung aeration. SI derived from airway pressure (Paw) was compared with that calculated by Ptp under the same conditions. These results were themselves compared with quantitative CT analysis as a gold standard for tidal recruitment/hyperinflation. Despite marked changes in tidal recruitment, mean values of SI computed either from Paw or Ptp were remarkably insensitive to variations of PEEP or condition. After the instillation of effusion, SI indicates a preponderant over-distension effect, not detected by CT. After the increment in PEEP level, the extent of CT-determined tidal recruitment suggest a huge recruitment effect of PEEP as reflected by lung compliance. Both SI in this case were unaffected. We showed that the ability of SI to predict tidal recruitment and overdistension was significantly reduced in a model of altered chest wall-lung relationship, even if the parameter was computed from the Ptp curve profile.

Tracheal gas insufflation during late exhalation efficiently reduces PaCO2 in experimental acute lung injury

Abstract.Objective: Tracheal gas insufflation (TGI) reduces PaCO2 by flushing the tracheal and mechanical deadspace, and may have its maximum benefit when TGI gas is unopposed by significant expiratory gas flow. Thus, limiting TGI to the late expiratory period may diminish tracheal exposure to TGI gas while preserving the efficacy of TGI. This study examined the gas exchange consequences of such late-expiratory TGI. Design and setting: Randomized controlled trial, animal study. Materials: Eleven pigs. Interventions: After stable lung injury was established using oleic acid 11 pigs were ventilated using a standardized lung protective strategy. Phasic expiratory TGI was applied for 30xa0min stages during the last 20%, 40%, 60%, and 100% of expiration in random sequence. PaCO2 was continuously measured via an indwelling blood gas analysis system. Measurements and results: PaCO2 at baseline was 86.1±4.7xa0mmHg, and decreased progressively with increasing TGI duration of 20%, 40%, and 60%, but not 100%, of expiration (PaCO2=75.7±5.2, 68.8±3.6, 65.1±5.3 and 65.2±5.2xa0mmHg, respectively). For all stages the reduction in PaCO2 relative to baseline was significant. Trends of increasing PaO2 and airway pressure with increasing TGI duration were noted and most likely associated with a TGI-induced increase in lung volume. Conclusions: Under these conditions confining TGI to the final 60% of expiration achieved effective PaCO2 reduction, not significantly different from panexpiratory TGI, while limiting exposure of the trachea to TGI gas, and reducing the potential for TGI-induced hyperinflation. These findings suggest that TGI is most effectively applied in a phasic manner in late expiration, with its duration titrated to effect.

Is Automated Weaning Superior to Manual Spontaneous Breathing Trials

Weaning from mechanical ventilation involves the reduction or withdrawal of ventilatory support in proportion to the patients ability to sustain spontaneous ventilation. Protocolized weaning has been shown to reduce weaning duration; however, its weakness lies in the reliance on human intervention. Automated weaning is theoretically superior to manual weaning because of its ability to rapidly recognize deviations from desired behavior and enforce compliance with a standardized weaning strategy unencumbered by external influences. Whether currently available methods for automated weaning fulfill that potential to achieve superiority depends on patient type, care environment, and cause of ventilator dependence.

Consequences of Pleural Effusions for Respiratory Mechanics in Ventilated Patients

Pleural effusion can be part of the primary condition that precipitates the admission of a patient to an intensive care unit (ICU), or it may develop during the course of an ICU stay [1]. In the former case, such as pneumonia or thoracic trauma, the decision to drain the fluid collection is dictated by the infectious or hemorrhagic nature of the liquid. After admission, the cause usually relates to combinations of factors leading to lung edema, such as generous fluid administration, myocardial depression, increased capillary permeability, and hypoalbuminemia. If there is no suspicion of empyema or hemothorax, the decision to intervene in this scenario is less straightforward. Increasing expertise with ultrasound among intensivists may fuel temptation to drain all pleural fluid accumulations in mechanically ventilated patients.