Conventional Mechanical Ventilation Group Research Articles

High-Frequency Oscillatory Ventilation, Partial Liquid Ventilation, or Conventional Mechanical Ventilation in NewbornPiglets with Saline Lavage-Induced Acute Lung Injury

It has been reported that, in diseased lungs, either partial liquid ventilation (PLV) or high-frequency oscillatory ventilation (HFOV) can improve oxygenation better and with less lung injury than conventional mechanical ventilation (CMV). This study was intended as a preclinical comparison between the effects of HFOV, PLV and CMV on gas exchange, lung mechanics and histology. Fifteen anesthetized newborn piglets, with respiratory insufficiency due to repeated saline lung lavage, were allocated to either a PLV, HFOV or CMV (n = 5 each) strategy, and treated for 4 h. Within 30 min of commencing therapy, PLV, HFOV, and CMV improved arterial Po₂ (Pa,o₂), alveoloarterial oxygen gradient (P(A-a),o₂), oxygenation index (OI), venous admixture (va), and arterial Pco₂ (Pa,co₂). After 4 h, oxygenation parameters (Pa,o₂, P(A-a),o₂, OI and venous admixture) were significantly better in the HFOV group than in the PLV group; the CMV group showed a higher Pa,o₂ and lower OI than the PLV group. Gas exchange at the end of the experiment was not different from baseline in the HFOV and CMV groups. Lung histology and morphometry were performed after perfusion-fixation at endotracheal deflation pressure corresponding to mean airway pressure at the end of the experiment. Lung injury score and mean linear intercept were not different between the three treatment groups. We conclude that in this model, gas exchange improved significantly in all three ventilation strategies. Indices of oxygenation improved less during PLV. The saline lavage-induced acute lung injury model used as in this study, is less stable than previously thought. The final lung injury is not influenced by the ventilation strategy. We speculate that the impaired gas exchange during PLV is an expression of diffusion limitation and ventilation-perfusion mismatch in a recovering lung.

High frequency oscillatory ventilation attenuates the activation of alveolar macrophages and neutrophils in lung injury.

BACKGROUND: Recent investigations have shown that leukocyte activation is involved in the pathogenesis of ventilator-associated lung injury. This study was designed to investigate whether the inflammatory responses and deterioration of oxygenation in ventilator-associated lung injury are attenuated by high-frequency oscillatory ventilation (HFO). We analyzed the effects of HFO compared with conventional mechanical ventilation (CMV) on the activation of pulmonary macrophages and neutrophils in 10 female rabbits. RESULTS: After surfactant depletion, the rabbits were ventilated by CMV or HFO at the same mean airway pressure. Surfactant-depletion followed by 4 h mechanical ventilation hindered pulmonary oxygenation in both groups. Impairment of oxygenation was less severe in the HFO group than in the CMV group. In the HFO group the infiltration of granulocytes into alveolar spaces occurred more readily than in the CMV group. Compared with CMV, HFO resulted in greater attenuation of beta2-integrin expression, not only on granulocytes, but also on macrophages. CONCLUSIONS: In the surfactant-depleted lung, the activation of leukocytes was attenuated by HFO. Reduced inflammatory response correlated with decreased impairment of oxygenation. HFO may reduce lung injury via the attenuation of pulmonary inflammation.

A multicenter randomized trial of high frequency oscillatory ventilation as compared with conventional mechanical ventilation in preterm infants with respiratory failure

A multicenter randomised trial was conducted in nine neonatal centers in Japan to re-evaluate the safety and the efficacy of high frequency oscillatory ventilation using the piston type oscillator (Hummingbird) in the treatment of respiratory failure in preterm infants weighing between 750 and 2000 g at birth. A total of 92 infants were enrolled in the study. Forty-six infants were allocated to high frequency oscillatory ventilation and 46 infants to conventional mechanical ventilation. There were no differences in sex, birth weight, gestation and Apgar score between groups. The study was begun 2.0 ± 1.6 h (mean ± S.D.) after birth in the high frequency oscillation group and 1.7 ± 1.5 h after birth in the conventional mechanical ventilation group. The absence of intraventricular hemorrhage was confirmed by echography in all cases before beginning ventilation. Mortality was similar in high frequency oscillatory ventilation and conventional mechanical ventilation (0 and 2%). The incidence of intraventricular hemorrhage was also similar in the high frequency and conventional mechanical ventilation groups (15 and 13% overall; 4 and 2% in grades III and IV, respectively). Nine percent of the infants in high frequency oscillatory ventilation and 13% in conventional mechanical ventilation developed bronchopulmonary dysplasia, but the difference was not significant. The frequency of air leaks was also equal in both groups. Periventricular leukomalacia was detected in 9% of infants on conventional mechanical ventilation and 2% on high frequency oscillation, but the difference was not significant. Mean airway pressure was significantly higher in the high frequency oscillatory ventilation group and the infants on high frequency oscillation showed a significantly higher arterial to alveolar oxygen tension ratio after 6 h of treatment. These results suggest that high frequency oscillatory ventilation does not increase the risk of severe complications such as air leaks, intraventricular hemorrhage or periventricular leukomalacia when it is used by experienced neonatologists. Indeed high frequency oscillatory ventilation helps provide better oxygenation with higher mean airway pressure without increasing the risk of bronchopulmonary dysplasia and severe complications such as air leaks and intraventricular hemorrhage.

Effect of artificial ventilation and anaesthesia on surfactant turnover in rats

We have tested the hypothesis that breathing releases pulmonary surfactant via distortion of the alveolar type II cell. Gas exchange was maintained in the anaesthetized rat by applying high frequency (10 Hz) oscillations (HFO) to the chest wall; this resulted in apnoea within two to three breaths. After instrumentation under anaesthesis for 30 min, rats were infused with [ 3H]choline and [ 14C]choline, and we compared the tubular myelin-rich (PLalv-1) and -poor (PLalv-2) alveolar phospholipids and the microsomal and lamellar body phospholipids (PLlb) together with their specific activities after three forms of ventilation for 90 min: HFO (group 1), conventional mechanical ventilation (group 2) and spontaneous breathing (group 3). Group 4 was killed after surgical instrumentation and in group 5 the lungs were removed immediately after induction of anaesthesia. Groups 1–3 did not differ in any measured variable. Groups 1–4, which were anaesthetized for 30–120 min, had a lower PLalv-2 than did group 5. In contrast, PLlb was greater in groups 1–3, which were anaesthetized for 120 min, than in groups 4 and 5. In conclusion, we have successfully maintained normal gas exchange during complete apnoea by applying external HFO in rats for periods up to 90 min. Compared to mechanically ventilated or spontaneously breathing anaesthetized rats, surfactant turnover was unaltered by HFO, despite a markedly tidal volume. However, the barbiturate anaesthetic itself appeared to inhibit surfactant turnover. We suggest that distortion of the type II cell may be the stimulus for surfactant release at tidal volumes above resting values.

A randomized comparison of total extracorporeal CO2 removal with conventional mechanical ventilation in experimental hyaline membrane disease

Apnoeic oxygenation (AO) combined with extracorporeal CO2 removal (ECCO2R), using venovenous perfusion across a membrane area of 0.1 m2 has been shown to be feasible in six healthy anaesthetized rabbits. In a further twelve rabbits, ECCO2R has been randomly compared with conventional mechanical ventilation (CMV) following saline lavage to induce respiratory failure. Blood gases were maintained for up to 6 h within the same range (PaO2 = 8-20 kPa, PaCO2 = 4-6 kPa) in two groups of six by varying airway pressures and the oxygen fraction delivered either to the membrane lung (ECCO2R group) or to the ventilator (CMV group). The influence of single hourly sustained inflations (SI) on oxygenation was studied. ECCO2R subjects remained stable and survived. CMV subjects deteriorated and had 80% mortality. Hyaline membranes were absent from ECCO2R subjects and present in all CMV subjects. The response to SI suggests that a lung volume recruitment is maintained during AO for up to 1 h but is ineffective during CMV.

The Comparison of Histopathology of Cats Received Conventional Mechanical Ventilation and High Frequency Oscillation Ventilation

The tracheobronchial histopathologic findings in 7 healthy cats used with high frequency oscillation ventilation (HFOV) were compared with those in 6 cats used with conventional mechanical ventilation (CMV). 4-point, 9-variable scoring system was used to evaluate the injury in the trachea, right & left main bronchi and parenchyme. The following results were obtained ; 1) The tracheobronchial tree received HFOV had no significant damage compared with CMV (P>0.05). 2) Intraepithelial mucus loss and emphysema were s lightly more prominent in CMV groups. As above results ; the tracheobronchial histopathologic difference was not prominent between CMV and HFOV groups received with relatively short period, however, the cellular function and barotrauma may be more prominent in CMV groups. From now on, as causes of tracheobronchial injury in HFV, interaction between humidification and mechanical trauma considers further study.

Traumatic respiratory insufficiency

Eleven patients suffering severe traumatic respiratory insufficiency were mechanically ventilated using a new system which combined high-frequency positive-pressure ventilation (HFPPV) with low-rate conventional mechanical ventilation (LRCMV). Ten similar patients were ventilated by conventional mechanical ventilation (CMV) with PEEP. HFPPV patients were fully conscious and cooperative during ventilation and did not need sedatives or muscle relaxants. Arterial oxygenation was significantly (p less than .005) better in HFPPV than CMV patients (89.91 +/- 10.24 vs. 78.43 +/- 11.13 torr, respectively), and pulmonary shunt was also better in the HFPPV group (13.1 +/- 4.7% vs. 20.4 +/- 6.4%, p less than .01). Moreover, inspired oxygen concentrations were lower (PaO2/FIO2 197.8 +/- 51.3 in the HFPPV group vs. 130 +/- 46.6 in the CMV group, p less than .005) and the time required for mechanical ventilation was shorter (4.2 +/- 0.91 vs. 6.1 +/- 0.8 days, p less than .1). All HFPPV patients immediately began breathing spontaneously when they were disconnected from the ventilator. We suggest this method as a better ventilatory mode for patients suffering traumatic respiratory insufficiency.

What can we learn from Sweden?

<h3>Background</h3> Preterm birth followed by prolonged mechanical ventilation often results in chronic lung disease (CLD) of prematurity. Associated with lung injury is brain injury. The molecular pathways that are affected in the brain of preterm neonates during the evolution of CLD are unclear. On the other hand, animal models of intrauterine growth retardation have shown that apoptosis is greater in the brain of postnatal rat pups with intrauterine growth retardation compared to controls (Ke et al, AJP 2004). A marker of apoptosis is expression of downstream targets of p53, such as caspase-3. <h3>Hypothesis</h3> Apoptosis of neuronal cells in the brain is enhanced during the evolution of CLD. <h3>Methods</h3> Preterm lambs (≈132 d gestation) were managed by conventional mechanical ventilation (CV) or nasal continuous positive airway pressure (nCPAP) for 72 h (<i>n</i> = 4/group). We used nCPAP as the positive control (gold standard) for lung outcome in chronically ventilated preterm lambs (Albertine et al, Pediatr Res 2004). Brain tissue was analyzed for caspase-3 protein abundance (immunoblot analysis) and topographic distribution (immunohistochemistry). <h3>Results</h3> Immunoblot analysis showed that caspase-3 protein abundance in brain tissue homogenates from preterm lambs was greater in the CV group compared to the nCPAP group, at 72 h. Immunohistochemistry showed that caspase-3 protein was localized in more Purkinje cells in the cerebellum in the CV group compared to the nCPAP group at 72 h. <h3>Conclusion</h3> Our results show that markers of apoptosis (caspase-3 protein abundance and immunolocalization) are more prevalent in the brains of preterm lambs that are managed by CV compared to nCPAP. We conclude that CV contributes to attrition of neurons during the first few days of life support with a ventilator. Supported by CHRC, HL62875, HL56401, T35 HL07744.