肺泡－动脉血氧分差在急诊肺栓塞筛查中的意义

目的探讨肺泡-动脉血氧分差（P（A—a）O2）改变在早期肺栓塞筛查的意义。方法以53例急性肺栓塞病例作为观察组,作单样本t检验。结果肺栓塞组血气资料pH值（7．423±0．048）在正常值范围。存在低氧血症（62．9±26．72）;PaCO2降低;肺泡-动脉血氧分差（P（A-a）O2增大（37．455±17．226,P〈0．01）。讨论肺泡动脉血氧分差增大,在肺栓塞临床可能性测评表基础上结合D—Dimer等检查可提高急诊早期肺栓塞诊断准确率。     

Compliance, alveolar-arterial oxygen difference, and oxygenation index changes in patients managed with extracorporeal membrane oxygenation

Eighteen patients with meconium aspiration syndrome who failed conventional management were treated with extracorporeal membrane oxygenation (ECMO) for reversible respiratory failure. Dynamic lung compliance measurements were made prior to, during, and after ECMO support. P(A-a)O2 and oxygenation index (OI) measurements were calculated prior to and after ECMO support. Lung compliance decreased significantly comparing before-ECMO to during-ECMO, and increased significantly comparing during- to after-ECMO, but not comparing before- to after-ECMO measurements. P(A-a)O2 and OI decreased significantly from before to after ECMO. The improvement in oxygenation allowing removal from ECMO does not appear to be related to improved pulmonary mechanics, but may rather be secondary to increased effective pulmonary capillary blood flow.     

The components of the alveolar-arterial oxygen tension difference in normal subjects and in patients with pneumonia and obstructive lung disease

The contributions of the pulmonary shunt and total right to left shunt to the alveolar-arterial oxygen tension difference were studied in twenty normal subjects, ten patients with severe pneumonia and eleven patients with chronic obstructive pulmonary disease. The total right to left shunt was measured by the oxygen breathing method, and the pulmonary shunt component of the total shunt was measured by a combined indicator dilution technic with radioactive xenon and indocyanine green dye injected intravenously and sampled from a peripheral artery. The dye curve and the amount of xenon in the collection syringe were used to calculate the pulmonary shunt since only shunted blood would retain dissolved xenon. The difference between the total shunt (oxygen breathing method) and the pulmonary shunt (xenon method) was used to estimate the post-pulmonary shunt. In normal subjects all of the alveolar-arterial oxygen tension difference was due to shunting, most (69 per cent) of which was postpulmonary shunt. In pneumonia there were large pulmonary shunts that caused most of the hypoxemia, although the postpulmonary component became larger in very severe pneumonia. In patients with COPD there is an insignificant increase in the pulmonary shunt and no increase in the postpulmonary shunt. The pulmonary shunt was measured with this combined indicator technic both on air and oxygen; 100 per cent oxygen breathing did not have an important effect on the pulmonary shunt.     

The alveolar-arterial oxygen gradient in patients with documented pulmonary embolism

It has been reported that the finding of a normal PaO2 level on arterial blood gas analysis does not exclude the diagnosis of acute pulmonary embolism. We wished to determine whether a more thorough evaluation of the blood gases would prove more helpful; specifically, whether it is possible for a patient with acute pulmonary embolism to have a normal alveolar-arterial (A-a) oxygen gradient. We studied this question in a patient population in which the diagnosis was definitively made via pulmonary arteriography. Sixty-four patients met all study criteria. In these patients, the A-a gradient ranged from 11.6 to 83.9 mm Hg (mean, 41.8 mm Hg). In three patients, the A-a gradient was normal for age. We conclude that a normal A-a oxygen gradient does not exclude the diagnosis of acute pulmonary embolism, and should not preclude further diagnostic procedures if there is a high index of suspicion.     

Prognostic role of alveolar-arterial oxygen pressure difference in acute pulmonary embolism.

BACKGROUND: This study investigated the utility of the alveolar - arterial oxygen pressure difference (AaDO (2)) in predicting the short-term prognosis of acute pulmonary embolism (PE). METHODS AND RESULTS: This study retrospectively enrolled 114 consecutive patients with acute PE, diagnosed by either spiral computed tomography or high probability ventilation - perfusion lung scans. During the first 24 h of admission, all patients had initial artery blood gas collected under room air. Patient exclusion criteria were chronic lung disease, septic emboli, and moderate and low probability lung scans. Patients were assigned to 2 groups based on either 30-day death or a 30-day composite event. Receiver operating characteristic analyses was used to determine the AaDO(2) cut-off value for predicting primary and composite endpoints. Statistical analysis demonstrated significant differences in AaDO(2) between the 30-day composite endpoint group and the 30-day composite event-free survival group (p=0.012). The AaDO(2) had a strong trend between the 30-day death group and the survival group (p=0.062). The best cut-off value for AaDO(2) was 53 mmHg and using this, the positive predictive value for 30-day death was 25% and the negative predictive value was 92%. For the 30-day composite endpoint, the positive predictive value for AaDO(2) was 35%, and the negative predictive value was 84%. In this study, thrombocytopenia was also an indicator of poor prognosis for patients with acute PE. CONCLUSION: The AaDO(2) measurement is a highly useful and simple measurement for predicting short-term prognosis in patients with acute PE. It has high negative predictive value and moderate positive predictive value for 30-day death and 30-day composite event. Aggressive thrombolytic treatment strategies should be considered for patients with an initial poor prognostic parameter (ie, AaDO(2) >or=53 mmHg).     

Long-term oxygen therapy stops the natural decline of endurance in COPD patients with reversible hypercapnia

BACKGROUND: Respiratory muscle weakness is one of the most important causes of hypercapnia in patients with COPD. There is evidence that stable hypercapnic patients will benefit from long-term oxygen therapy (LTOT). OBJECTIVES: The prognostic role of reversible hypercapnia in COPD is still unclear. Early implementation of LTOT in these patients may influence endurance time and mortality. METHODS: In this pilot study, we investigated 28 patients (26 males, 49-74 years) with COPD, advanced airflow limitation [forced expiratory volume in 1 s (percentage of predicted value) 40.8 +/- 10.2] and mild hypoxaemia (pO(2) 66.5 +/- 6.3 mm Hg). All patients had developed a moderate reversible hypercapnia during an acute exacerbation or during exercise testing (peak pCO(2) 48.0 +/- 2.5 mm Hg). Patients were allocated randomly to a control group (n = 14) or an LTOT group (n = 14). The two groups were well matched in terms of physiological data. Lung function, endurance time (cycle ergometer), dyspnoea score, blood gases and LTOT compliance were measured at baseline and every 6 months over a period of 3 years. RESULTS: Endurance time increased from 6.4 +/- 2.7 min at baseline to 7.1 +/- 2.7 min after 1 year in the LTOT group and decreased from 6.1 +/- 3.0 to 4.9 +/- 3.8 min in the controls (p < 0.05). After 1 year, the end-exercise dyspnoea score was significantly lower in the LTOT group (4.5 +/- 1.5) than in the controls (5.7 +/- 1.9). CONCLUSION: COPD patients with reversible hypercapnia and mild hypoxaemia benefit from LTOT in terms of endurance time and a reduction of exertional dyspnoea after 1 year.     

Arterial blood gas analysis and alveolar-arterial oxygen gradient in diagnosis and prognosis of elderly patients with suspected pulmonary embolism

BACKGROUND: Arterial blood gas analysis (BGA) remains a first-step diagnostic approach in patients with suspected pulmonary embolism (PE). The aim of this study was to evaluate BGA parameters in elderly patients with suspected pulmonary embolism for diagnosis and 14-day prognosis. METHODS: We performed a retrospective cohort observational study of 6 years (1994-1999) in a 60-bed acute geriatric ward of University Hospital in Siena, Italy. Room air arterial oxygen partial pressure (pO2), arterial carbon dioxide partial pressure (pCO2), pH, arterial oxyhemoglobin saturation (SO2), and alveolar-arterial oxygen gradient [D(A-a)O2] were performed on hospital admission of 75 patients with confirmed PE (CPE) and were compared with data from 43 patients with unconfirmed PE (UCPE). The same parameters of 54 CPE surviving patients were compared with 21 CPE nonsurviving patients. RESULTS: Significantly lower PO2 and SO2, and higher DA-aO2 were found in CPE patients. Respiratory alkalosis was found in one third of the patients in both groups (no significant difference). In the CPE group, there was a significantly lower SO2 in nonsurviving patients, without significant differences for the other parameters. Metabolic acidosis was significantly more frequent in nonsurviving patients. CONCLUSION: More severe hypoxemia, oxyhemoglobin hyposaturation, and higher D(A-a)O2 are associated with the diagnosis of PE in elderly patients. Respiratory alkalosis is less frequent than in younger patients, and metabolic disorders are negative prognostic indicators.     

肺心病急性发作期患者的组织氧合状态及机械通气对其影响

目的观察慢性阻塞性肺疾病（ＣＯＰＤ）所致肺心病急性发作期合并Ｉ型呼吸衰竭患者机体组织细胞的氧合状态及机械通气对其影响。方法利用胃粘膜组织内ｐＨ（ｐＨｉ）技术测定１９例ＣＯＰＤ所致肺心病急性发作期合并Ｉ型呼吸衰竭患者机械通气前后及脱机前后ｐＨｉ的变化。结果发现机械通气前ｐＨｉ的三次结果分别为７．１８±０．０６,７．１９±０．０４,７．１８±０．０６,均明显低于７．３２;行机械通气后ｐＨｉ逐渐上升,４天后＞７．３２;脱机前及脱机后ｐＨｉ变化不明显。相关分析显示ｐＨｉ与动脉血ｐＨ（ｐＨａ）、硅胶囊内二氧化碳分压（ＰｇＣＯ２）与动脉血二氧化碳分压（ＰａＣＯ２）无相关性（ｒ＝０．３５２和０．４２１,Ｐ均＞０．０５）,提示ｐＨｉ的测定不受合并高碳酸血症的影响。结论肺心病急性发作期合并Ｉ型呼吸衰竭时存在组织氧合不良。ｐＨｉ的测定对指导临床治疗具有十分重要的意义,并有可能作为指导撤机的一项指标。     

阻塞性睡眠呼吸暂停低通气综合征患者的日间高碳酸血症

部分阻塞性睡眠呼吸暂停低通气综合征患者伴有日间高碳酸血症,甚至出现Ⅱ型呼吸衰竭,病死率明显高于不伴有日间高碳酸血症者.本文综述了阻塞性睡眠呼吸暂停低通气综合征患者日间高碳酸血症的发生情况、机制、影响因素及治疗策略.     

无创正压通气治疗慢性阻塞性肺疾病高碳酸血症的疗效观察

目的探讨无创正压通气治疗慢性阻塞性肺疾病（COPD）高碳酸血症的价值.方法58例COPD二氧化碳潴留患者随机分入治疗组及对照组,对照组仅行常规药物治疗,治疗组在常规药物治疗的基础上加用无创正压通气治疗.比较治疗开始2小时、24小时、7天两组同期血气、血压、心率、呼吸频率等改善情况.结果治疗组同期血气、血压、心率、呼吸频率等较对照组明显改善（P均＜0.05）.结论应用无创通气可明显改善COPD患者症状,提高PO2降低PCO2,对COPD高碳酸血症患者有确切疗效.