Cardiorespiratory effects of spontaneous breathing in two different models of experimental lung injury: a randomized controlled trial

Relationship between ETCO2 and PaCO2 under Changing Capnogram in Ventilated Infants with NAVA: An Observational Study

This observational study evaluated the validity of end-tidal CO2 (ETCO2) as a surrogate for arterial PCO2 (PaCO2) in infants on neurally adjusted ventilatory assist (NAVA), particularly considering the influence of variable spontaneous breathing on capnography waveforms. The study involved 16 infants, analyzing 50 paired ETCO2 and PaCO2 values. Deming regression analysis highlighted a notably stronger correlation for maximum ETCO2 (r2 = 0.6783, p <0.0001) compared to mean ETCO2 (r2 = 0.5686, p <0.0001) and demonstrated a significantly weaker association for minimum ETCO2 (r2 = 0.1838). These findings emphasize the superior predictive value of maximum ETCO2 in estimating PaCO2, advocating its reliable use in clinical monitoring, especially given the dynamic capnography associated with NAVA's variable pressures. The results suggest ETCO2's potential to enhance noninvasive respiratory management, reduce the frequency of blood sampling, and improve overall care for infants requiring mechanical ventilation.

Measurement of Electrical Impedance Tomography-Based Regional Ventilation Delay for Individualized Titration of End-Expiratory Pressure

RATIONALE

Individualized positive end-expiratory pressure (PEEP) titration might be beneficial in preventing tidal recruitment. To detect tidal recruitment by electrical impedance tomography (EIT), the time disparity between the regional ventilation curves (regional ventilation delay inhomogeneity [RVDI]) can be measured during controlled mechanical ventilation when applying a slow inflation of 12 mL/kg of body weight (BW). However, repeated large slow inflations may result in high end-inspiratory pressure (P_EI), which might limit the clinical applicability of this method. We hypothesized that PEEP levels that minimize tidal recruitment can also be derived from EIT-based RVDI through the use of reduced slow inflation volumes.

METHODS

Decremental PEEP trials were performed in 15 lung-injured pigs. The PEEP level that minimized tidal recruitment was estimated from EIT-based RVDI measurement during slow inflations of 12, 9, 7.5, or 6 mL/kg BW. We compared RVDI and P_EI values resulting from different slow inflation volumes and estimated individualized PEEP levels.

RESULTS

RVDI values from slow inflations of 12 and 9 mL/kg BW showed excellent linear correlation (R² = 0.87, p < 0.001). Correlations decreased for RVDI values from inflations of 7.5 (R² = 0.68, p < 0.001) and 6 (R² = 0.42, p < 0.001) mL/kg BW. Individualized PEEP levels estimated from 12 and 9 mL/kg BW were comparable (bias -0.3 cm H₂O ± 1.2 cm H₂O). Bias and scatter increased with further reduction in slow inflation volumes (for 7.5 mL/kg BW, bias 0 ± 3.2 cm H₂O; for 6 mL/kg BW, bias 1.2 ± 4.0 cm H₂O). P_EI resulting from 9 mL/kg BW inflations were comparable with P_EI during regular tidal volumes.

CONCLUSIONS

PEEP titration to minimize tidal recruitment can be individualized according to EIT-based measurement of the time disparity of regional ventilation courses during slow inflations with low inflation volumes_. This sufficiently decreases P_EI and may reduce potential clinical risks.

Effect of inspiratory synchronization during pressure-controlled ventilation on lung distension and inspiratory effort

Background

In pressure-controlled (PC) ventilation, tidal volume (V_T) and transpulmonary pressure (P_L) result from the addition of ventilator pressure and the patient’s inspiratory effort. PC modes can be classified into fully, partially, and non-synchronized modes, and the degree of synchronization may result in different V_T and P_L despite identical ventilator settings. This study assessed the effects of three PC modes on V_T, P_L, inspiratory effort (esophageal pressure–time product, PTP_es), and airway occlusion pressure, P_0.1. We also assessed whether P_0.1 can be used for evaluating patient effort.

Methods

Prospective, randomized, crossover physiologic study performed in 14 spontaneously breathing mechanically ventilated patients recovering from acute respiratory failure (1 subsequently withdrew). PC modes were fully (PC-CMV), partially (PC-SIMV), and non-synchronized (PC-IMV using airway pressure release ventilation) and were applied randomly; driving pressure, inspiratory time, and set respiratory rate being similar for all modes. Airway, esophageal pressure, P_0.1, airflow, gas exchange, and hemodynamics were recorded.

Results

V_T was significantly lower during PC-IMV as compared with PC-SIMV and PC-CMV (387 ± 105 vs 458 ± 134 vs 482 ± 108 mL, respectively; p < 0.05). Maximal P_L was also significantly lower (13.3 ± 4.9 vs 15.3 ± 5.7 vs 15.5 ± 5.2 cmH₂O, respectively; p < 0.05), but PTP_es was significantly higher in PC-IMV (215.6 ± 154.3 vs 150.0 ± 102.4 vs 130.9 ± 101.8 cmH₂O × s × min⁻¹, respectively; p < 0.05), with no differences in gas exchange and hemodynamic variables. PTP_es increased by more than 15% in 10 patients and by more than 50% in 5 patients. An increased P_0.1 could identify high levels of PTP_es.

Conclusions

Non-synchronized PC mode lowers V_T and P_L in comparison with more synchronized modes in spontaneously breathing patients but can increase patient effort and may need specific adjustments.

Clinical Trial Registration Clinicaltrial.gov # NCT02071277

Electronic supplementary material

The online version of this article (doi:10.1186/s13613-017-0324-z) contains supplementary material, which is available to authorized users.

Identification and examination of a novel 9-bp insert/deletion polymorphism on porcine SFTPA1 exon 2 associated with acute lung injury using an oleic acid-acute lung injury model

The pulmonary surfactant-associated protein (SFTPA1, SP-A) gene has been studied as a candidate gene for lung disease resistance in humans and livestock. The objective of the present study was to identify polymorphisms of the porcine SFTPA1 gene coding region and its association with acute lung injury (ALI). Through DNA sequencing and the PCR-single-strand conformation polymorphism method, a novel 9-bp nucleotide insertion (+) or deletion (-) was detected on exon 2 of SFTPA1, which causes a change in three amino acids, namely, alanine (Ala), glycine (Gly) and proline (Pro). Individuals of three genotypes (-/-, +/- and +/+) were divided into equal groups from 60 Rongchang pigs that were genotyped. These pigs were selected for participation in the oleic acid (OA)-ALI model by 1-h and 3-h injections of OA, and there were equal numbers of pigs in the control and injection groups. The lung water content, a marker for acute lung injury, was measured in this study; there is a significant correlation between high lung water content and the presence of the 9-bp indel polymorphism (P < 0.01). The lung water content of the OA injection group was markedly higher than that of the control group and lung water content for the +/+ genotype was significantly higher than that of the others in the 1-h group (P < 0.01). No differences in the expression of the SFTPA1 gene were found among individuals with different SFTPA1 genotypes, indicating that the trait is not caused by a linked polymorphism causing altered expression of the gene. The individuals with the -/- genotype showed lower lung water content than the +/+ genotype pigs, which suggests that polymorphism could be a potential marker for lung disease-resistant pig breeding and that pig can be a potential animal model for human lung disease resistance in future studies.

Impact of ventilator adjustment and sedation-analgesia practices on severe asynchrony in patients ventilated in assist-control mode

OBJECTIVES

Breath-stacking asynchrony during assist-control-mode ventilation may be associated with increased tidal volume and alveolar pressure that could contribute to ventilator-induced lung injury. Methods to reduce breath stacking have not been well studied. The objective of this investigation was to evaluate 1) which interventions were used by managing clinicians to address severe breath stacking; and 2) how effective these measures were.

SETTING

Sixteen-bed medical ICU.

PATIENTS AND INTERVENTIONS

Physiological study in consecutively admitted patients without severe brain injury, who had severe breath stacking defined as an asynchrony index greater than or equal to 10% of total breaths. During 30 minutes before (baseline) and after any intervention employed by the managing clinician, the ventilator flow, airway pressure, and volume/time waveforms were continuously recorded and analyzed to detect normal and stacked breaths. The initial approach taken was assigned to one of three categories: no intervention, increase of sedation-analgesia, or change of ventilator setting. Nonparametric Wilcoxon-Mann-Whitney tests and multiple regression were used for statistical analysis. Quantitative data are presented as median [25-75].

MAIN RESULTS

Sixty-six of 254 (26%) mechanically ventilated patients exhibited severe breath-stacking asynchrony. A total of 100 30-minute sequences were recorded and analyzed in 30 patients before and after 50 clinical decisions for ongoing management (no intervention, n=8; increasing sedation/analgesia, n=16; ventilator adjustment, n=26). Breath-stacking asynchrony index was 44 [27-87]% at baseline. Compared with baseline, the decrease of asynchrony index was greater after changing the ventilator setting (-99 [-92, -100]%) than after increasing the sedation-analgesia (-41 [-66, 7]%, p<0.001) or deciding to tolerate the asynchrony (4 [-4, 12]%, p<0.001). Pressure-support ventilation and increased inspiratory time were independently associated with the reduction of asynchrony index.

CONCLUSIONS

Compared with increasing sedation-analgesia, adapting the ventilator to patient breathing effort reduces breath-stacking asynchrony significantly and often dramatically. These results support an algorithm beginning with ventilator adjustment to rationalize the management of severe breath-stacking asynchrony in ICU patients.

Nontraditional modes of mechanical ventilation: progress or distraction?

As technology continues to develop, a wide range of novel and nontraditional modes of mechanical ventilation have become available for the management of critically ill patients. Proportional assist ventilation, neurally adjusted ventilatory assist and adaptive support ventilation are three novel modes of ventilation, which attempt to optimize patient-ventilator synchrony. Improved interactions between patient and ventilator may be important in improving clinical outcomes. Another important priority for mechanically ventilated patients is lung protection, and nontraditional modes of ventilation that may be implemented to minimize ventilator-associated lung injury include airway pressure release ventilation and high-frequency ventilation. Novel and nontraditional modes of ventilation may represent important tools in the critical care environment; however, continued investigation is needed to determine the overall impact of these various approaches on outcomes for mechanically ventilated patients.

Partial ventilatory support modalities in acute lung injury and acute respiratory distress syndrome-a systematic review

PURPOSE

The efficacy of partial ventilatory support modes that allow spontaneous breathing in patients with acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) is unclear. The objective of this scoping review was to assess the effects of partial ventilatory support on mortality, duration of mechanical ventilation, and both hospital and intensive care unit (ICU) lengths of stay (LOS) for patients with ALI and ARDS; the secondary objective was to describe physiologic effects on hemodynamics, respiratory system and other organ function.

METHODS

MEDLINE (1966-2009), Cochrane, and EmBase (1980-2009) databases were searched using common ventilator modes as keywords and reference lists from retrieved manuscripts hand searched for additional studies. Two researchers independently reviewed and graded the studies using a modified Oxford Centre for Evidence-Based Medicine grading system. Studies in adult ALI/ARDS patients were included for primary objectives and pre-clinical studies for supporting evidence.

RESULTS

Two randomized controlled trials (RCTs) were identified, in addition to six prospective cohort studies, one retrospective cohort study, one case control study, 41 clinical physiologic studies and 28 pre-clinical studies. No study was powered to assess mortality, one RCT showed shorter ICU length of stay, and the other demonstrated more ventilator free days. Beneficial effects of preserved spontaneous breathing were mainly physiological effects demonstrated as improvement of gas exchange, hemodynamics and non-pulmonary organ perfusion and function.

CONCLUSIONS

The use of partial ventilatory support modalities is often feasible in patients with ALI/ARDS, and may be associated with short-term physiological benefits without appreciable impact on clinically important outcomes.

Chest wall mechanics and abdominal pressure during general anaesthesia in normal and obese individuals and in acute lung injury

PURPOSE OF REVIEW

This article discusses the methods available to evaluate chest wall mechanics and the relationship between intraabdominal pressure (IAP) and chest wall mechanics during general anaesthesia in normal and obese individuals, as well as in acute lung injury/acute respiratory distress syndrome.

RECENT FINDINGS

The interactions between the abdominal and thoracic compartments pose a specific challenge for intensive care physicians. IAP affects respiratory system, lung and chest wall elastance in an unpredictable way. Thus, transpulmonary pressure should be measured if IAP is more than 12 mmHg or if chest wall elastance is compromised for other reasons, even though the absolute values of pleural and transpulmonary pressures are not easily obtained at bedside. We suggest defining intraabdominal hypertension (IAH) as IAP at least 20 mmHg and abdominal compartment syndrome (ACS) as IAP at least 20 mmHg associated with failure of one or more organs, although further studies are required to confirm this hypothesis. Additionally, in the presence of IAH, controlled mechanical ventilation should be applied and positive end-expiratory pressure individually titrated. Prophylactic open abdomen should be considered in the presence of ACS.

SUMMARY

Increased IAP markedly affects respiratory function and complicates patient management. Frequent assessment of IAP is recommended.

The effect of ventilator performance on airway pressure release ventilation: a model lung study

BACKGROUND

Using a model lung connected to six different ventilators, with each ventilator in the airway pressure release ventilation mode, we measured differences in intrinsic positive end-expiratory pressure (PEEPi) during the expiratory phase and calculated the inspiratory and expiratory pressure time product (PTP) as an index of work of breathing during the inspiratory phase.

METHODS

We compared 6 ventilators: Puritan-Bennett 840, Evita XL, Servo i, Avea, Hamilton G5, and Engström. With a constant inspiratory pressure level of 25 cm H(2)O and expiratory pressure level of 0 cm H(2)O, PEEPi was measured as the expiratory time was decremented from 1.0 second to 0.2 second in steps of 0.1 second. The inspiratory and expiratory PTPs were measured during the ventilator's inspiratory phase by simulating spontaneous breathing with a tidal volume of 300 mL, with a respiratory rate of 30 breaths/min and with expiratory flow rates of 0.5 L/s, 1.0 L/s, and 1.5 L/s.

RESULTS

In all ventilators, the progressive diminution of the expiratory time caused a significant increase in PEEPi (P< 0.001). With a 0.2-second expiratory time, PEEPi ranged from 9.4± 0.07 cm H(2)O for the Servo i to 15.7± 0.04 cm H(2)O for the Avea. The Servo i had a significantly lower inspiratory PTP than did the other ventilators (P< 0.001). When the expiratory flow rate was 0.5 L/s and 1.0 L/s, the expiratory PTP was lower with the Servo i and Evita XL than with the other ventilators (P< 0.001).

CONCLUSIONS

PEEPi varied significantly among ventilators. Inspiratory and expiratory work of breathing varied between ventilators when spontaneous breathing occurred during the ventilator's inspiratory phase.

Ovine smoke/burn ARDS model: a new ventilator-controlled smoke delivery system

BACKGROUND

Our current ovine smoke/burn acute respiratory distress syndrome (ARDS) model utilizes a manual bee smoker. This smoke delivery system lacks standardization and reproducibility, with 20% of sheep failing to meet ARDS criteria. Time to reach ARDS criteria and survival time are also variable. The mild volutrauma (15 mL/kg) applied after smoke/burn injury may also fail to induce ARDS within 24 h. We hypothesized that these inconsistencies were associated with the bee smoker and the mild volutrauma. In the current study, we addressed these problems to improve the consistency of the smoke/burn ARDS model.

METHODS

Adult female sheep (n = 10) were given a 40% total body surface area third degree cutaneous burn and 48 breaths (4 × 12) of cotton smoke under general anesthesia. A modified ventilator was then used to deliver a precise and consistent smoke volume (tidal volume) to the sheep. Additional barotrauma was induced by pressure control ventilation (40 cm H(2)0). When ARDS criteria (PaO(2)/FiO(2) < 200) were met, the ARDS Network low tidal volume ventilation protocol (6-8 mL/kg ideal body weight) was used.

RESULTS

Carboxyhemoglobin levels were 81.4% ± 5.6% immediately following smoke injury. All sheep met ARDS criteria within 24 h (12.5 ± 4.9 h). Mean survival time post-injury was 62.1 ± 26.4 h. White blood cells and granulocytes were significantly elevated at 24 h post-smoke/burn injury. Lung tissue at necropsy was consistent with ARDS.

CONCLUSIONS

The refinements made to the original ovine smoke/burn ARDS model produce a more reliable time to ARDS onset, injury severity, and time of death.

Year in review 2008: Critical Care--respirology

Original research contributions published in Critical Care in 2008 in the fields of respirology and critical care medicine are summarized. Eighteen articles were grouped into the following categories: acute lung injury and acute respiratory distress syndrome, mechanical ventilation, mechanisms of ventilator-induced lung injury, and tracheotomy decannulation and non-invasive ventilation.