The effects of localized hypoventilation on ventilation/perfusion (V/Q) ratios and gas exchange in the dog lung

Detection of endobronchial intubation by monitoring the CO2 level above the endotracheal cuff

Early detection of accidental endobronchial intubation (EBI) is still an unsolved problem in anesthesia and critical care daily practice. The aim of this study was to evaluate the ability of monitoring above cuff CO2 to detect EBI (the working hypothesis was that the origin of CO2 is from the unventilated, but still perfused, lung). Six goats were intubated under general anesthesia and the ETT positioning was verified by a flexible bronchoscope. The AnapnoGuard system, already successfully used to detect air leak around the ETT cuff, was used for continuous monitoring of above-the-cuff CO2 level. When the ETT distal tip was located in the trachea, with an average cuff pressure of 15 mmHg, absence of CO2 above the cuff was observed. The ETT was then deliberately advanced into one of the main bronchi under flexible bronchoscopic vision. In all six cases the immediate presence of CO2 above the cuff was identified. Further automatic inflation of the cuff, up to a level of 27 mmHg, did not affect the above-the-cuff measured CO2 level. Withdrawal of the ETT and repositioning of its distal tip in mid-trachea caused the disappearance of CO2 above the cuff in a maximum of 3 min, confirming the absence of air leak and the correct positioning of the ETT. Our results suggest that measurement of the above-the-cuff CO2 level could offer a reliable, on-line solution for early identification of accidental EBI. Further studies are planned to validate the efficacy of the method in a clinical setup.

Alveolar recruitment prevents rapid-reperfusion-induced injury of lung transplants

BACKGROUND

Physical factors play an important role in ischemia-reperfusion-induced injury of lung transplants. For example, rapid restoration of reperfusion resulted in severe pulmonary edema and deterioration of pulmonary function of lung explants in an ex vivo reperfusion system. This type of injury can be prevented by a stepwise increase in the perfusion flow rate, or by adding prostaglandin E1 (PGE1) to the blood perfusate during the first 10 minutes. However, the mechanisms of these protective effects are unknown. We noted a dramatic decrease in airway pressure rather than pulmonary arterial pressure in these studies, suggesting that lung recruitment may be an important factor in minimizing injury.

METHODS

In the present study, we examined the importance of alveolar recruitment in preventing rapid-reperfusion-induced lung injury. Rat lungs were flushed preserved with low potassium dextran solution for 12 hours at 4 degrees C. Lung explants were randomly divided into three groups: 1) untreated control; 2) lungs inflated to total lung capacity for 2 minutes; and 3) lungs ventilated for 10 minutes prior to reperfusion. Postpreservation lung function was assessed in an isolated rat lung reperfusion model.

RESULTS

Rapid initiation of reperfusion led to severe pulmonary edema and significant pulmonary dysfunction. In inflation or ventilation groups, the injury was significantly attenuated. The PaO2 and shunt fractions in these lungs were comparable to normal lungs. A significant drop in airway pressure was observed in these two groups and the lung compliance in the inflation group was significantly better than other two groups.

CONCLUSIONS

These results suggest that overcoming alveolar collapse with inflation or ventilation, may protect the lung from mechanical-stress-induced injury during reperfusion.

Gas exchange and hemodynamics in experimental pleural effusion

OBJECTIVE

To investigate the cardiorespiratory effects of graded bilateral pleural effusions in the anesthetized pig.

DESIGN

Prospective, randomized, controlled, laboratory study.

SETTING

Animal laboratory.

SUBJECTS

Eleven male Yorkshire pigs.

INTERVENTIONS

Animals were anesthetized using inhaled isoflurane. Orotracheal intubation was followed by mechanical ventilation. Bilateral chest tubes were inserted, and graded increasing pleural effusions were created using saline of 0, 20, 40, and 80 mL/kg, divided equally between each side. At each pleural volume, intravascular volume was randomly altered (by phlebotomy or transfusion of colloid) to normal (unchanged), low (decreased by 10 mL/kg), or high (increased by 10 mL/kg).

MEASUREMENTS AND MAIN RESULTS

Hemodynamic parameters, intrapleural pressures, hemoglobin, and blood gases were measured. At the lowest volume of pleural fluid, PaO2 was reduced by approximately 50% vs. baseline, whereas systemic hemodynamics were unchanged. PaO2 was reduced in a dose-dependent fashion as pleural volume increased but was not affected by alterations in intravascular volume. Intrapulmonary shunt was increased both by intrapleural volume in a dose-dependent fashion and by increases in intravascular volume at high levels of pleural volume. Cardiac output and systemic mean arterial pressure increased with elevated intravascular volume but were not influenced by lower levels of intrapleural volume. Mean pulmonary arterial pressure, central venous pressure, and pulmonary artery occlusion pressure were increased by elevations in both intrapleural volume and intravascular volume. Intrapleural pressure and pulmonary vascular resistance were related to intrapleural volume only.

CONCLUSIONS

Hypoxemia occurs as an early event in acute bilateral pleural effusions and precedes hemodynamic decompensation. Oxygenation is independent of intravascular filling pressures, but hemodynamics are preserved with elevated filling pressures. Clinical studies should be undertaken to examine the risks/benefits of careful removal of pleural fluid in patients with pleural effusions, when oxygenation is impaired during mechanical ventilation.

Action of almitrine bismesylate on ventilation-perfusion matching in cats and dogs with part of the lung hypoventilated

Ventilation to one lobe of lung was reduced in anaesthetized open-chest cats and dogs to simulate the ventilation/perfusion (V/Q) mismatching of chronic lung disease. Blood flow to this lobe fell less than ventilation; thus lobar V/Q diminished. In seven cats almitrine (0.5 mg/kg + 10 micrograms/kg per min, i.v.) caused a rise in pulmonary artery pressure (PPA), increased flow through the hypoventilated lobe in six out of seven cats and both increased or decreased lobar vascular resistance (PVR); the lobar V/Q ratio therefore fell. Arterial and lobar venous oxygen tension (PO2) fell. In five dogs almitrine caused a rise in PPA and PVR but lobar flow changes were variable. Arterial and lobar venous PO2 fell. With fixed ventilation, almitrine failed to improve V/Q matching; there was no improvement in gas exchange in the hypoventilated lobe. In eight dogs the hypoventilated lobe was perfused at constant flow with right atrial blood (i.e. while V/Q was held constant). Almitrine caused a rise in perfusion pressure, vasoconstriction, followed, in five out of eight dogs, by vasodilatation. In six similar cat preparations, vasoconstriction but not vasodilatation was clearly shown. In two cats dilatation after almitrine was demonstrated during ventilation with Nitrogen. In all experiments there was no significant effect of the solvent. Thus the dual action of almitrine seen in other species was seen in a proportion of cats and dogs. Results do not support the view that improved arterial gas tensions in patients after almitrine are attributable to diversion of blood flow away from hypoxic lung. Alternative mechanisms are discussed.