Impact of the Prone Position in an Animal Model of Unilateral Bacterial Pneumonia Undergoing Mechanical Ventilation

Adverse Mechanical Ventilation and Pneumococcal Pneumonia Induce Immune and Mitochondrial Dysfunctions Mitigated by Mesenchymal Stem Cells in Rabbits

BACKGROUND

Mechanical ventilation for pneumonia may contribute to lung injury due to factors that include mitochondrial dysfunction, and mesenchymal stem cells may attenuate injury. This study hypothesized that mechanical ventilation induces immune and mitochondrial dysfunction, with or without pneumococcal pneumonia, that could be mitigated by mesenchymal stem cells alone or combined with antibiotics.

METHODS

Male rabbits underwent protective mechanical ventilation (8 ml/kg tidal volume, 5 cm H2O end-expiratory pressure) or adverse mechanical ventilation (20 ml/kg tidal-volume, zero end-expiratory pressure) or were allowed to breathe spontaneously. The same settings were then repeated during pneumococcal pneumonia. Finally, infected animals during adverse mechanical ventilation received human umbilical cord-derived mesenchymal stem cells (3 × 106/kg, intravenous) and/or ceftaroline (20 mg/kg, intramuscular) or sodium chloride, 4 h after pneumococcal challenge. Twenty-four-hour survival (primary outcome), lung injury, bacterial burden, immune and mitochondrial dysfunction, and lung transcriptomes (secondary outcomes) were assessed.

RESULTS

High-pressure adverse mechanical ventilation reduced the survival of infected animals (0%; 0 of 7) compared with spontaneous breathing (100%; 7 of 7) and protective mechanical ventilation (86%; 6 of 7; both P < 0.001), with higher lung pathology scores (median [interquartile ranges], 5.5 [4.5 to 7.0] vs. 12.6 [12.0 to 14.0]; P = 0.046), interleukin-8 lung concentrations (106 [54 to 316] vs. 804 [753 to 868] pg/g of lung; P = 0.012), and alveolar mitochondrial DNA release (0.33 [0.28 to 0.36] vs. 0.98 [0.76 to 1.21] ng/μl; P < 0.001) compared with infected spontaneously breathing animals. Survival (0%; 0 of 7; control group) was improved by mesenchymal stem cells (57%; 4 of 7; P = 0.001) or ceftaroline alone (57%; 4 of 7; P < 0.001) and improved even more with a combination treatment (86%; 6 of 7; P < 0.001). Mesenchymal stem cells reduced lung pathology score (8.5 [7.0 to 10.5] vs. 12.6 [12.0 to 14.0]; P = 0.043) and alveolar mitochondrial DNA release (0.39 (0.34 to 0.65) vs. 0.98 (0.76 to 1.21) ng/μl; P = 0.025). Mesenchymal stem cells combined with ceftaroline reduced interleukin-8 lung concentrations (665 [595 to 795] vs. 804 [753 to 868] pg/g of lung; P = 0.007) compared to ceftaroline alone.

CONCLUSIONS

In this preclinical study, mesenchymal stem cells improved the outcome of rabbits with pneumonia and high-pressure mechanical ventilation by correcting immune and mitochondrial dysfunction and when combined with the antibiotic ceftaroline was synergistic in mitigating lung inflammation.

EDITOR’S PERSPECTIVE

Short- and long-term respiratory outcomes in neonates with ventilator-associated pneumonia

BACKGROUND AND OBJECTIVE

Ventilator-associated pneumonia (VAP) is a common nosocomial infection in critical care settings and might have important long-term consequences in neonates. Our aim is to clarify the short- and long-term respiratory outcomes of neonates affected by VAP.

METHODS

Prospective, population-based, cohort study with 12 months follow-up based on clinical examinations and diary-based respiratory morbidity score, conducted in an academic tertiary referral neonatal unit with dedicated follow-up program.

RESULTS

A total of 199 inborn neonates consecutively ventilated for at least 48 hours were eligible for the study. One hundred fifty-one were finally enrolled and classified as "exposed" or "unexposed" to VAP, if they fulfilled (or not) VAP criteria once during their stay. Bronchopulmonary dysplasia (BPD) incidence was significantly higher in exposed (75%) than in unexposed babies (26.8%; relative risk [RR]: 2.8 [1.9-4.0]; _Adj RR: 3.5 [1.002-12.7]; P = .049; number needed to harm = 2.07), although the composite BPD/mortality did not differ. Exposed patients showed longer intensive care unit stay (87 [43-116] vs 14 [8-52] days; St.β = 0.24; P < .0001) and duration of ventilation (15 [10-25] vs 5 [4-8] days; St.β = 0.29; P < .0001) than unexposed neonates. Exposed patients also showed less ventilator-free days (11 [5-17.7] vs 22 [14-24] days; St.β = -0.15; P = .05) compared to unexposed. Respiratory infections, use of drugs, rehospitalization for respiratory reasons, home oxygen therapy, their composite outcome, and diary-based clinical respiratory morbidity score were similar between the cohorts.

CONCLUSION

Neonatal VAP seems associated to higher incidence of BPD, longer ventilation, and intensive care stay but it does not affect long-term respiratory morbidity.

Mechanical ventilation and Streptococcus pneumoniae pneumonia alter mitochondrial homeostasis

Required mechanical ventilation (MV) may contribute to bacterial dissemination in patients with Streptococcus pneumoniae pneumonia. Significant variations in plasma mitochondrial DNA (mtDNA) have been reported in sepsis according to the outcome. The impact of lung stretch during MV was addressed in a model of pneumonia. Healthy or S. pneumoniae infected rabbits were submitted to MV or kept spontaneously breathing (SB). Bacterial burden, cytokines release, mitochondrial DNA levels, integrity and transcription were assessed along with 48-hour mortality. Compared with infected SB rabbits, MV rabbits developed more severe pneumonia with greater concentrations of bacteria in the lungs, higher rates of systemic dissemination, higher levels of circulating inflammatory mediators and decreased survival. Pulmonary mtDNA levels were significantly lower in infected animals as compared to non-infected ones, whenever they were SB or MV. After a significant early drop, circulating mtDNA levels returned to baseline values in the infected SB rabbits, but remained low until death in the MV ones. Whole blood ex-vivo stimulation with Streptococcus pneumoniae resulted in a reduction of polymorphonuclear leukocytes mitochondrial density and plasma mtDNA concentrations. Thus, persistent mitochondrial depletion and dysfunction in the infected animals submitted to MV could account for their less efficient immune response against S. pneumoniae.

Linezolid and atorvastatin impact on pneumonia caused by Staphyloccocus aureus in rabbits with or without mechanical ventilation

Pneumonia may involve methicillin-resistant Staphylococcus aureus (MRSA), with elevated rates of antibiotics failure. The present study aimed to assess the effect of statins given prior to pneumonia development. Spontaneously breathing (SB) or mechanically ventilated (MV) rabbits with pneumonia received atorvastatin alone, linezolid (LNZ) alone, or a combination of both (n = 5 in each group). Spontaneously breathing and MV untreated infected animals (n = 11 in each group), as well as uninfected animals (n = 5 in each group) were used as controls. Microbiological features and inflammation were evaluated. Data are presented as medians (interquartile range). Linezolid alone tended to reduce pulmonary MRSA load in both SB and MV rabbits, but failed to prevent bacteremia (59%) in the latter. Linezolid alone dampened TNF-α lung production in both SB and MV rabbits (e.g., 2226 [789] vs. 11478 [10251] pg/g; p = 0.022). Statins alone did the same in both SB and MV animals (e.g., 2040 [133]; p = 0.016), and dampened systemic inflammation in the latter, possibly through TLR2 down-regulation within the lung. However, the combination of LNZ and statin led to an increased rate of bacteremia in MV animals up to 75%. Statins provide an anti-inflammatory effect in rabbits with MRSA pneumonia, especially in MV ones. However, dampening the systemic inflammatory response with statins could impede blood defenses against MRSA.

Prone positioning for intramedullary nailing of subtrochanteric fractrures, the techniques of intraoperative fluoroscopy and reduction: A technique note

The treatment of subtrochanteric fractures is a challenge for orthopaedic trauma surgeons. Three positions have been described previously: supine on a fracture table, supine on a flat radiolucent table, and the lateral decubitus position on a flat radiolucent table. Each one has its advantages and limitations. In this article we describe a prone position for intramedullary nailing of subtrochanteric femoral fractures. This position has the advantages including: 1) an easy approach to reduce and maintain the reduction of fracture by adjusting only the leg plate on injured side, 2) perfect intraoperation fluoroscopic imaging on both anteroposterior view and lateral view, and 3) an easy approach to establish an appropriate entry point even in obese patients.

Sepsis risk factors in infants with congenital diaphragmatic hernia

BACKGROUND

Congenital diaphragmatic hernia (CDH) is a rare congenital anomaly and remains among the most challenging ICU-managed disease. Beside severe pulmonary hypertension, lung hypoplasia and major abdominal surgery, infective complications remain major determinants of outcome. However, the specific incidence of sepsis as well as associated risk factors is unknown.

METHODS

This prospective, 4-year observational study took place in the pediatric intensive care and neonatal medicine department of the Paris South University Hospitals (Le Kremlin-Bicêtre, France), CDH national referral center and involved 62 neonates with CDH.

MAIN RESULTS

During their ICU stay, 28 patients (45%) developed 38 sepsis episodes. Ventilator-associated pneumonia (VAP: 23/38; 31.9 VAP per 1000 days of mechanical ventilation) and central line-associated blood stream infections (CLABSI: 5/38; 5.5 per 1000 line days) were the most frequently encountered infections. Multivariate analysis showed that gestational age at birth and intra-thoracic position of liver were significantly associated with the occurrence of sepsis. Infected patients had longer duration of mechanical and noninvasive ventilation (16.2 and 5.8 days, respectively), longer delay to first feeding (1.2 days) and a longer length of stay in ICU (23 days), but there was no difference in mortality.

CONCLUSIONS

Healthcare-associated infections, and more specifically VAP, are the main infective threat in children with CDH. Sepsis has a significant impact on the duration of ventilator support and ICU length of stay but does not impact mortality. Low gestational age and intra-thoracic localization of the liver are two independent risk factors associated with sepsis.

Mechanical Ventilation Alters the Development of Staphylococcus aureus Pneumonia in Rabbit

Ventilator-associated pneumonia (VAP) is common during mechanical ventilation (MV). Beside obvious deleterious effects on muco-ciliary clearance, MV could adversely shift the host immune response towards a pro-inflammatory pattern through toll-like receptor (TLRs) up-regulation. We tested this hypothesis in a rabbit model of Staphylococcus aureus VAP. Pneumonia was caused by airway challenge with S. aureus, in either spontaneously breathing (SB) or MV rabbits (n = 13 and 17, respectively). Pneumonia assessment regarding pulmonary and systemic bacterial burden, as well as inflammatory response was done 8 and 24 hours after S. aureus challenge. In addition, ex vivo stimulations of whole blood taken from SB or MV rabbits (n = 7 and 5, respectively) with TLR2 agonist or heat-killed S. aureus were performed. Data were expressed as mean±standard deviation. After 8 hours of infection, lung injury was more severe in MV animals (1.40±0.33 versus [vs] 2.40±0.55, p = 0.007), along with greater bacterial concentrations (6.13±0.63 vs. 4.96±1.31 colony forming units/gram, p = 0.002). Interleukin (IL)-8 and tumor necrosis factor (TNF)-αserum concentrations reached higher levels in MV animals (p = 0.010). Whole blood obtained from MV animals released larger amounts of cytokines if stimulated with TLR2 agonist or heat-killed S. aureus (e.g., TNF-α: 1656±166 vs. 1005±89; p = 0.014). Moreover, MV induced TLR2 overexpression in both lung and spleen tissue. MV hastened tissue injury, impaired lung bacterial clearance, and promoted a systemic inflammatory response, maybe through TLR2 overexpression.

Prone position in acute respiratory distress syndrome. Rationale, indications, and limits

In the prone position, computed tomography scan densities redistribute from dorsal to ventral as the dorsal region tends to reexpand while the ventral zone tends to collapse. Although gravitational influence is similar in both positions, dorsal recruitment usually prevails over ventral derecruitment, because of the need for the lung and its confining chest wall to conform to the same volume. The final result of proning is that the overall lung inflation is more homogeneous from dorsal to ventral than in the supine position, with more homogeneously distributed stress and strain. As the distribution of perfusion remains nearly constant in both postures, proning usually improves oxygenation. Animal experiments clearly show that prone positioning delays or prevents ventilation-induced lung injury, likely due in large part to more homogeneously distributed stress and strain. Over the last 15 years, five major trials have been conducted to compare the prone and supine positions in acute respiratory distress syndrome, regarding survival advantage. The sequence of trials enrolled patients who were progressively more hypoxemic; exposure to the prone position was extended from 8 to 17 hours/day, and lung-protective ventilation was more rigorously applied. Single-patient and meta-analyses drawing from the four major trials showed significant survival benefit in patients with PaO2/FiO2 lower than 100. The latest PROSEVA (Proning Severe ARDS Patients) trial confirmed these benefits in a formal randomized study. The bulk of data indicates that in severe acute respiratory distress syndrome, carefully performed prone positioning offers an absolute survival advantage of 10-17%, making this intervention highly recommended in this specific population subset.