PULMONARY GAS EXCHANGE DURING INDUCTION OF PULMONARY EDEMA IN ANESTHETIZED DOGS

Mechanisms of hypoxemia

Oxygen is an essential element for life and without oxygen humans can survive for few minutes only. There should be a balance between oxygen demand and delivery in order to maintain homeostasis within the body. The two main organ systems responsible for oxygen delivery in the body and maintaining homeostasis are respiratory and cardiovascular system. Abnormal function of any of these two would lead to the development of hypoxemia and its detrimental consequences. There are various mechanisms of hypoxemia but ventilation/perfusion mismatch is the most common underlying mechanism of hypoxemia. The present review will focus on definition, various causes, mechanisms, and approach of hypoxemia in human.

The risk factors and prognostic implication of acute pulmonary edema in resuscitated cardiac arrest patients

Objective

Pulmonary edema is frequently observed after a successful resuscitation in out-of-hospital cardiac arrest (OHCA) patients. Currently, its risk factors and prognostic implications are mostly unknown.

Methods

Adult OHCA patients with a presumed cardiac etiology who achieved sustained return of spontaneous circulation (ROSC) in emergency department were retrospectively analyzed. The patients were grouped according to the severity of consolidation on their initial chest X-ray (group I, no consolidation; group II, patchy consolidations; group III, consolidation involving an entire lobe; group IV, total white-out of any lung). The primary objective was to identify the risk factors of developing severe pulmonary edema (group III or IV). The secondary objective was to evaluate the association between long-term prognosis and the severity of pulmonary edema.

Results

One hundred and seven patients were included. Total duration of cardiopulmonary resuscitation (CPR) and initial pCO₂ level were both independent predictors of developing severe pulmonary edema with their odds ratio (OR) being 1.02 (95% confidence interval [CI], 1.00 to 1.04; per 1 minute) and 1.04 (95% CI, 1.01 to 1.07; per 1 mmHg), respectively. The long term prognosis was significantly poor in patients with severe pulmonary edema with a OR for good outcome (6-month cerebral performance category 1 or 2) being 0.22 (95% CI, 0.06 to 0.79) in group III and 0.16 (95% CI, 0.04 to 0.63) in group IV compared to group I.

Conclusion

The duration of CPR and initial pCO₂ level were both independent predictors for the development of severe pulmonary edema after resuscitation in emergency department. The severity of the pulmonary edema was significantly associated with long-term outcome.

Pulmonary diffusing capacity in left ventricular dysfunction

The purpose of this study was to determine whether there are any consistent spirometric or Dsb findings in patients with LV dysfunction characterized by a clinical diagnosis of CHF and an EF less than 40 percent. We performed spirometry and Dsb in 34 patients, and found that EF correlated only with Dsb. When we separated the patients into those with rales and those without, Dsb correlated strongly with EF only in those with rales. There was no correlation with other spirometric values. Mean Dsb percent predicted was significantly lower in patients with rales despite similar mean EF. Only two of 23 patients without rales had a reduced Dsb while only one of 11 with rales had a normal Dsb. We conclude that Dsb is a good predictor of clinically evident heart failure. When rales are absent, Dsb should be normal in patients with LV dysfunction; when present, Dsb will be diminished in proportion to the EF.

Net fluid leakage (LN) in experimental pulmonary oedema in the dog

Net fluid leakage (LN) from the intravascular to the extravascular pulmonary space was estimated in anaesthetised dogs after injection of oleic acid (OA) (n = 8), or after hydrostatic pressure elevation by inflation of a left atrial balloon (n = 5). LN was calculated as the sum of: (i) rate of change in extravascular lung water (delta EVLW), (ii) thoracic lymph flow, and (iii) pleural fluid formation per time unit. Pleural fluid formation was measured in five dogs with hydrostatic or OA induced pulmonary oedema and was 1.8 +/- 0.9 ml/kg/h. In OA-induced pulmonary oedema, LN increased to a peak of 9.2 ml/kg/h within 2 h after OA injection. Thereafter LN fell and was 2-4 ml/kg/h during the succeeding 2-4 h. During hydrostatic pulmonary oedema LN was increased to as much as 13 ml/kg/h, but it became negative, -5 to -8 ml/kg/h (reabsorption of extravascular fluid) as soon as pulmonary vascular pressures returned to normal following deflation of the left atrial balloon. We conclude that in both forms of oedema there is an initial rapid leakage. In OA-induced oedema this leakage continues, although at a slower rate, whereas in hydrostatic oedema there is a considerable net fluid absorption from the pulmonary extravascular to the intravascular space as soon as vascular pressures are brought to normal levels.

Respiratory and non-respiratory lung function indices during the development and resolution of O,S,S-trimethyl phosphorodithioate-induced lung damage in the rat. A chemical model of adult respiratory distress syndrome

Arterial blood gases and the pulmonary uptake of putrescine and 5-hydroxytryptamine (5-HT) were studied between 6 h and 18 days after the administration to rats of an oral LD50-dose of the pneumotoxin, O,S,S-trimethyl phophorodithioate (OSSMe), a potential impurity in several organophosphorus insecticides. Aortic blood was sampled under pentobarbitone anaesthesia for measurements of arterial pH, and partial pressures of oxygen (PaO2) and carbon dioxide (PaCO2). PaO2 was significantly decreased 4 days after OSSMe administration, i.e. at the time of maximum lethality and increases in wet lung weight. This was accompanied by a significant increase in PaCO2 and acidosis. These results are compatible with an impairment of gas exchange due to diffuse lung damage. For reasons that are unclear, PaCO2 was slightly increased 2, 6 and 12 days after dosing. The uptake of putrescine (1,4-diaminobutane) and of 5-HT was measured by incubating lung slices with several concentrations of [3H]-putrescine and [14C]-5-HT, so as to estimate the apparent kinetic parameters of uptake, Vmax and Km. The Vmax for putrescine-uptake was significantly decreased 1, 2, 4, 6 and 12 days after the administration of OSSMe. The Vmax for 5-HT-uptake was significantly increased 1 day and significantly decreased 4 days after OSSMe administration. The uptake of 5-HT is an endothelial function, and the decrease in 5-HT-uptake at 4 days may reflect injury to the pulmonary vascular endothelium at this time. The uptake of putrescine probably reflects the function of the pulmonary (mainly alveolar) epithelium.(ABSTRACT TRUNCATED AT 250 WORDS)

Severe hypoxemia secondary to pulmonary embolization treated successfully with the use of a CPAP (continuous positive airway pressure) mask

We describe a patient who was admitted with acute onset of dyspnea and pleuritic chest pain. The patient was in acute hypoxic respiratory failure documented by arterial blood gas levels. The severe hypoxemia was refractory to 100 percent O2 administration. The cause of the patient's sudden deterioration was a pulmonary embolus documented by angiography. The patient was managed successfully with heparin therapy. A continuous positive airway pressure (CPAP) mask corrected the severe hypoxemia, which otherwise would have required a more invasive method of respiratory support.

Mechanism of increased tracheo-bronchial response to inhalative acetylcholine aerosol in pulmonary vascular congestion and unilateral pulmonary artery occlusion

The study was carried out in anesthetized, intubated and spontaneously breathing dogs. The aim of this study was to examine the responsiveness of the tracheo-bronchial system to inhalative ACh. It was considered that any change in ACh-sensitivity signifies the involvement of receptors in the lung itself. Increased pressure in the right heart and main pulmonary artery did not affect the ACh-sensitivity. Whereas, the sustained pulmonary vascular congestion produced by blocking the ascending aorta or by glass bead embolism provoked greater ACh-sensitivity. Increased ACh-sensitivity was also observed in unilateral pulmonary artery occlusion. ACh-sensitivity was greater in the later part of occlusion or vascular congestion and persisted even after the occlusion or block was withdrawn. It is concluded that the increased ACh-sensitivities in pulmonary vascular congestion and in unilateral pulmonary artery occlusion are due to the formation of edema and atelectasis respectively. Anyway, the disturbance of the metabolism of the receptor cells around the small vessels of the lung circulation seems to be essential.

The effects of continuous positive pressure ventilation on pulmonary oedema, gas exchange and lung mechanics

The effect of continuous positive pressure ventilation was studied in 23 dogs in whom pulmonary oedema was induced by rapid intravenous infusion of dextran 40. CPPV slowed but did not prevent the formation of oedema. CPPV prevented or reversed the formation of liver-like areas in the dependent lobes, maintaining the oedematous lung compliant and aerated. This led to a reduction of shunt and an increase in PaO2. The use of CPPV decreased cardiac output and body oxygen consumption. Mixed venous oxygen tension was higher in dogs ventilated by CPPV and these dogs tolerated fulminant frothy oedema without distress.

Hypoxemia in pulmonary embolism, a clinical study

The cause of hypoxemia was studied in 21 patients with no previous heart or lung disease shortly after an episode of acute pulmonary embolism. The diagnosis was based on pulmonary angiography demonstrating distinct vascular filling defects or "cutoffs." It was found that virtually all of the hypoxemia in patients with previously normal heart and lungs could be accounted for on the basis of shunt-like effect. The magnitude of the shunting did not correlate with the percent of the pulmonary vascular bed occluded nor with the mean pulmonary artery pressure. The shunts tended to gradually recede over about a month after embolism. Patients without pulmonary infarction were able to inspire 80-111% of their predicted inspiratory capacities, and this maneuver temporarily diminished the observed shunt. Patients with pulmonary infarcts were able to inhale only to 60-69% of predicted inspiratory capacity, and this did not reverse shunting. These data suggest that the cause of right-to-left shunting in patients with pulmonary emboli is predominantly atelectasis. When the elevation of mean pulmonary artery pressure was compared to cardiac index per unit of unoccluded lung, it fell within the range of pulmonary hypertension predicted from published data obtained in patients with exercise in all except one case. This observation suggests that pulmonary vasoconstriction following embolism is not important in humans, although these data are applicable only during the time interval in which our patients were studied and in patients receiving heparin.

Electron microscopic alterations at the alveolar level in pulmonary edema

The electron microscopic alterations of the alveolar septum in advanced hemodynamin and alloxan-induced pulmonary edema were compared. Pulmonary edema was produced in anesthetized dogs by means of increased lefy atrial pressure and hemodilution and by allocan administration. Sections of pulmonary tissue from these dogs and similarly anesthetized controls were processed for and examined by light and electron microscopy. In the hemodynamic form of edema the interstitial fluid collects only in the collagen-containing portions of the septum. The endothelium, epithelium, their respective basement membranes and large portions of the air-blood barrier are unaffected. Alloxaninduced edema, in contrast, is characterized by degeneration of both endothelium and epithelium and by the appearance of fibrin within the alveoli. The hemodynamic type of pulmonary edema appears to result from an accentuation of the normal process of fluid exchange within the lung. Allocan-induced edema, on the other hand, is a pathologic process. The functional implications of these results are discussed.