Preventing and managing perioperative pulmonary complications following cardiac surgery.

PURPOSE OF REVIEW: To provide an update of research findings on the mechanisms underlying respiratory complications after cardiac surgery, especially acute respiratory distress syndrome, transfusion-related lung injury and ventilation-associated pneumonia. The article will review some of the preventive and therapeutic measures that can be implemented to reduce these complications, focusing on the use of protective invasive ventilation and postextubation noninvasive ventilation. RECENT FINDINGS: The development of postoperative pulmonary complications is related to various perioperative factors. The most effective preventive measures are a correct preoperative preparation and an uneventful surgery. The implementation of nosocomial pneumonia prevention bundles, or early extubation in a fast-track program, has proven to be effective in reducing the complication rate. The application of protective invasive ventilation, with low tidal volumes, has been found to reduce lung injury and mortality in patients with lung injury or healthy lungs. The use of noninvasive ventilation as a preventive postextubation approach in patients at risk and rescue noninvasive ventilation in those developing respiratory failure remains under debate and is subject to ongoing research. SUMMARY: Postoperative pulmonary complications are common, but severe complications are infrequent. Their reduction requires measures to prevent infection and mechanical ventilation-associated lung injury through the use of low tidal volumes and early extubation. Noninvasive ventilation after extubation can be utilized to avoid reintubation and the associated increased morbidity and mortality. However, noninvasive ventilation should be done under rigorous conditions and by following strict criteria.

Alveolar overdistension as a cause of lung injury: differences among three animal species.

This study analyses characteristics of lung injuries produced by alveolar overdistension in three animal species. Mechanical ventilation at normal tidal volume (10 mL/Kg) and high tidal volume (50 mL/Kg) was applied for 30 min in each species. Data were gathered on wet/dry weight ratio, histological score, and area of alveolar collapse. Five out of six rabbits with high tidal volume developed tension pneumothorax, and the rabbit results were therefore not included in the histological analysis. Lungs from the pigs and rats showed minimal histological lesions. Pigs ventilated with high tidal volume had significantly greater oedema, higher neutrophil infiltration, and higher percentage area of alveolar collapse than rats ventilated with high tidal volume. We conclude that rabbits are not an appropriate species for in vivo studies of alveolar overdistension due to their fragility. Although some histological lesions are observed in pigs and rats, the lesions do not appear to be relevant.

Intermittent alveolar overdistension for 30 or 240 minutes does not produce acute lung injury in normal pig lung.

BACKGROUND: The objective is to study whether alveolar overdistension can induce acute lung injury in pigs as assessed by analysis of respiratory and histological parameters and inflammatory markers. MATERIALS AND METHODS: Experimental study, using mixed-breed pigs. Animals were assigned to one of the following groups: Control Group (CG) (n = 5), applying mechanical ventilation with tidal volume (Vt) of 10 ml/kg, respiratory rate (RR) of 18 bpm, and FiO2 of 1 for 240 min; High Vt for 30 min (HVt-30) Group (n = 5), applying ventilation with Vt of 50 ml/kg and RR of 8 bpm and FiO2 of 1 for 30 min, followed by ventilation as in the CG for a further 210 min; and HVt-240 Group (n = 5), applying ventilation with Vt of 50 ml/kg, RR of 8 bpm, and FiO2 of 1 for 240 min. Hemodynamic parameters, airway pressures, arterial blood gases, extravascular lung water (EVLW), and cytokines (IL-2, IL-4, IL-6, IL-10, TNF-alpha, and ITF-gamma) in plasma and bronchoalveolar lavage (BAL) were determined. Lungs were fixed with 10% formalin for histological analysis. Results are expressed as mean +/- standard deviation. The ANOVA test was used to compare measurements among the three groups. RESULTS: At 30 min, airway pressures and oxygenation of HVt-30 and HVt-240 groups were higher than those of controls [Pplateau: 39.2 +/- 5.6 and 33.0+/- 5.1 versus 12.2 +/- 1.3 (P < 0.01); PaO2/FiO2: 443.8 +/- 55 and 430.6 +/- 34 versus 194.4 +/- 77 (P < 0.01)]. In HVt-240 group, these parameters were also higher than in the other two groups at the subsequent measurement times. There were no differences among the groups in EVLW values. Cytokines were undetected or negligible in plasma and BAL in all of the groups. The histological analysis showed no changes suggestive of acute lung injury. CONCLUSIONS: In this animal model, ventilation for 4 h with large tidal volume did not cause ventilator-induced lung injury.