Alveolar-arterial Oxygen Partial Pressure Difference Research Articles

Continuous Positive Airway Pressure at 10 cm H2O During Cardiopulmonary Bypass Improves Postoperative Gas Exchange

Postbypass pulmonary dysfunction including atelectasis and increased shunting is a common problem in the intensive care unit. Negative net fluid balance and continuous positive airway pressure (CPAP) have been used to reduce the adverse effects of cardiopulmonary bypass (CPB) on the lung. To determine whether CPAP at 10 cm H2O during CPB results in improved postoperative gas exchange in comparison with deflated lungs during CPB, we examined 14 patients scheduled for elective cardiac surgery. Seven patients received CPAP at 10 cm H2O during CPB, and in the other seven patients, the lungs were open to the atmosphere (control). Measurements were taken before and after CPB, after thoracic closure, and 4 h after CPB in the intensive care unit. CPAP at 10 cm H2O resulted in significantly more perfusion of lung areas with a normal ventilation/perfusion distribution (VA/Q) and significantly less shunt and low VA/Q perfusion 4 h after CPB in comparison with the control group. Consequently, arterial oxygen partial pressure was significantly higher and alveolar-arterial oxygen partial pressure difference was significantly smaller. We conclude that CPAP at 10 cm H2O during CPB is a simple maneuver that improves postoperative gas exchange. Implications Inflation of the lungs at a pressure of 10 cm H2O as compared with leaving the lungs deflated during cardiopulmonary bypass was examined. Lung inflation during bypass resulted in significantly improved postoperative gas exchange.

Dose-Response to Inhaled Aerosolized Prostacyclin for Hypoxemia Due to ARDS

This study was carried out to determine the efficacy of and dose-response relationships to inhaled aerosolized prostacyclin (IAP), when used as a selective pulmonary vasodilator (SPV) in patients with severe hypoxemia due to ARDS. Unblinded, interventional, prospective clinical study. A general ICU in a university-affiliated, tertiary referral center. Nine adult patients with severe ARDS (lung injury score, > or = 2.5). All patients received IAP over the dose range 0 to 50 ng/kg/min. The IAP was delivered via a jet nebulizer placed in the ventilator circuit. Dose increments were 10 ng/kg/min every 30 min. Cardiovascular parameters (cardiac index and mean pulmonary and systemic pressures), indexes of oxygenation (PaO(2)/fraction of inspired oxygen [FIO(2)] ratio and alveolar-arterial oxygen partial pressure difference [P(A-a)O(2)]) and shunt fraction were measured or calculated at each dose interval, as were platelet aggregation and systemic levels of prostacyclin metabolite (6-keto prostaglandin F1(alpha)). A generalized linear regression model was used to determine a dose effect of IAP on these parameters. The Wilcoxon rank sum test for related measures was used to compare the effects of various doses of IAP. IAP acted as an SPV, with a statistically significant dose-related improvement in PaO(2)/FIO(2) ratio (p = 0.003) and P(A-a)O(2) (p = 0.01). Systemic prostacyclin metabolite levels increased significantly in response to delivered IAP (p = 0.001). There was no significant dose effect on systemic or pulmonary arterial pressures, or on platelet function, as determined by platelet aggregation in response to challenge with adenosine diphosphate. IAP is an efficacious SPV, with marked dose-related improvement in oxygenation and with no demonstrable effect on systemic arterial pressures over the dose range 0 to 50 ng/kg/min. Despite significant systemic levels of prostacyclin metabolite, there was no demonstrable platelet function defect.

Cardiac output and pulmonary gas exchange at maximal exercise after atrial redirection for complete transposition.

To assess the determinants of exercise capacity and exercise oxygenation after atrial redirection for complete transposition. At graded bicycle ergometry, including respiratory and arterial blood gas analyses, intra-arterial blood pressure recording, and cardiac output determination (dye-dilution technique), we tested 17 post-Mustard/Senning patients, 8.9-22.0 years old (mean 14.5, SD 4.0). Reference data were obtained by similar methods. At maximal exercise, oxygen uptake (29.6 ml x kg(-1) x min(-1)) and heart rate (167 beats x min(-1)) were low (P<0.001). Right-to-left shunts were detected in five patients. Arterial oxygen partial pressure and saturation fell in all subjects (P<0.0001). In 15/16 (94%) the alveolar-arterial oxygen partial pressure difference was > +2 SD. In 13/15 (87%) stroke volumes fell during exercise. Cardiac output per oxygen uptake was low (P<0.0001), which implies a high arteriovenous oxygen difference and a low mixed venous oxygen content at peak exercise. The low exercise capacity was caused by a combination of low maximally attained heart rate and falling stroke volumes. The impaired arterial oxygenation may be caused by a combination of pulmonary ventilation/perfusion mismatch, a low mixed venous content and atrial shunting in some patients.

Exercise-induced hypoxaemia in master athletes: effects of a polyunsaturated fatty acid diet.

Exercise-induced hypoxaemia (EIH) has been associated with an oxygen diffusion limitation. Because polyunsaturated fatty acids (PUFA) administration can modify cell membrane fluidity, we hypothesized that the importance of EIH could be reduced after a 6-week PUFA diet. Resting pulmonary functions and a maximal cycling test were performed before and after the diet, in eight master athletes -48 (SD 6 years)-. The partial pressure of O2 in arterial blood (PaO2), alveolar ventilation (VA) and ideal alveolar-arterial oxygen partial pressure difference (P(Ai-a) O2) were obtained at each exercise intensity. The extent of EIH at maximal exercise was significantly lower after PUFA [PaO2-17.2 (SEM 1.9) vs -12.9 (SEM 2.2)]. Before PUFA, VA accounted for 50% of the variance in the fall in P (Ai-a) for intensities below 80% maximal oxygen uptake (VO2max) and P(Ai-a)O2 for 60% between 70% and 100% VO2max. After PUFA, the reduction in EIH was highly correlated (r2 = 0.85; P < 0.001) to resulting changes in P(Ai-a)O2 and resting pulmonary diffusing capacity (DLCO)/VA but not with changes in ideal alveolar partial pressure of oxygen. The improvement in EIH following PUFA could be related to an increase in alveolar-arterial oxygen conductance following improved pulmonary diffusion.

LUNG MANAGEMENT DURING CARDIOPULMONARY BYPASS: IS CONTINUOUS POSITIVE AIRWAYS PRESSURE BENEFICIAL?

It is not clear if the use of continuous positive airway pressure (CPAP) during cardiopulmonary bypass (CPB) improves lung function after cardiac surgery. We have measured alveolar-arterial oxygen partial pressure difference (PAO2-PaO2) in 61 patients undergoing elective coronary artery bypass surgery. We studied three groups of patients: in group 1 the lungs were disconnected from the breathing system (no CPAP) during CPB; in group 2, 5 cm H2O CPAP with air was applied to the lungs; in group 3, 5 cm H2O of CPAP was applied with 100% oxygen. (PAO2-PaO2) was measured before CPB and then at 30 min, 4 h and 8 h after CPB. Compared with group 1 (no CPAP), (PAO2-PaO2) was significantly smaller in groups 2 and 3 at 30 min (P = 0.036), but not at 4 h and 8 h after CPB (P = 0.32, P = 0.96). The time to extubation (P = 0.42) and early extubation (P = 0.87) were not affected by the use of CPAP. The results of this study do not support the use of CPAP during CPB as a mechanism of improving lung function after cardiac surgery.

INFLUENCE OF AGE ON ATELECTASIS FORMATION AND GAS EXCHANGE IMPAIRMENT DURING GENERAL ANAESTHESIA

We have studied the effects of anaesthesia on atelectasis formation and gas exchange in 45 patients of both sexes, smokers and nonsmokers, aged 23-69 yr. None of the patients showed clinical signs of pulmonary disease, and preoperative spirometry was normal. In the awake patient, partial pressure of arterial oxygen (PaO2) decreased with increasing age (P less than 0.001) and the alveolar-arterial oxygen partial pressure difference (PAO2-PaO2) increased with age (P less than 0.001). Shunt, assessed by the multiple inert gas elimination technique, was small (mean 0.5%) and uninfluenced by age. However, there was an increasing dispersion (log SD Q) of ventilation/perfusion ratios (VA/Q) and increasing perfusion of regions of low VA/Q (VA/Q less than 0.1) with increasing age (P less than 0.001 and P less than 0.05, respectively). No patient displayed any atelectasis as assessed by computed x-ray tomography of the chest. During inhalation anaesthesia (halothane or enflurane) with mechanical ventilation, 39 of 45 patients developed atelectasis and shunt. There was a strong correlation between the atelectatic area and the magnitude of shunt (r = 0.81, P less than 0.001). Atelectasis and shunt did not increase significantly with age, whereas log SD Q and perfusion of regions with low VA/Q ratios did (r = 0.55, P less than 0.001 and r = 0.35, P less than 0.05, respectively). Awake, the major determinant of PaO2 was perfusion of regions of low VA/Q ratios, which increased with age. During anaesthesia shunt influenced PaO2 most, low VA/Q being a secondary factor which, however, was increasingly important with increasing age, thus explaining the well-known age-dependent deterioration of arterial oxygenation during anaesthesia.

CHANGES IN ALVEOLAR-ARTERIAL OXYGEN PARTIAL PRESSURE DIFFERENCE DURING ORTHOTOPIC LIVER TRANSPLANTATION

Changes in the alveolar-arterial oxygen partial pressure difference (PAO2-PaO2) were measured in 39 patients undergoing orthotopic liver transplantation without veno-arterial or veno-venous bypass. The operation can be divided into an initial dissection phase, an anhepatic phase when the hepatic artery, portal vein and vena cava are clamped, and a post-anhepatic phase after the vascular clamps are released. There was an initial increase in (PAO2-PaO2) during the dissection phase, followed by an immediate decrease when the liver was removed. This decrease continued throughout the anhepatic period, but a further increase in (PAO2-PaO2) occurred after release of all the vascular clamps and during abdominal closure.

Effects of Colloid or Crystalloid Administration on Pulmonary Extravascular Water in the Postoperative Period After Coronary Artery Bypass Grafting

The effect of postoperative fluid management on pulmonary extravascular thermal volume (ETVL) as in index of pulmonary extravascular water after coronary artery bypass grafting was compared, using the thermal-dye technique, among five patients who received 5% albumin (group A), five patients who received 6% hydroxyethyl starch (group H), and five who received lactated Ringer's solution (group C). Intraoperatively, all patients received lactated Ringer's solution intravenously, and the cardiopulmonary bypass (CPB) circuit prime included 5% albumin. No statistically significant changes in ETVL occurred postoperatively in any group, nor did ETVL differ significantly between groups. After CPB, colloid osmotic pressure (COP) significantly decreased and pulmonary artery wedge pressure (WP) and the WP-COP gradient significantly increased in each group, implying an increase in transcapillary fluid flux. Cardiac index changed variably. Pulmonary shunt fraction (Qsp/Qt) did not change in groups A and C but decreased during CPB in group H (from 0.22 +/- 0.03 to 0.16 +/- 0.11). Postoperatively, patients in the three groups received similar volumes of fluids and had similar perioperative weight gains. By the next morning (AM1), COP increased in all groups, returning to levels noted before CPB in group C, and exceeding these levels in groups A and H. Wedge pressure was similar in all three groups on AM1. PaO2 decreased significantly, and alveolar-arterial oxygen partial pressure difference increased significantly in all groups on AM1. In Group H, Qsp/Qt returned to levels observed before CPB by AM1 (0.27 +/- 0.09). We conclude that in patients without postoperative increases in WP, ETVL changes minimally during CPB and is not influenced by the type of fluid administered as the primary volume replacement in the postoperative period.

Pulmonary alveolar proteinosis: prospective clinical experience in 23 patients for 15 years.

Twenty-three patients, including three children, with pulmonary alveolar proteinosis (PAP) were studied over a 15 year period. Based on the overall course and outcome they were divided into two groups. Group I (24%) had spontaneous remission and received no treatment. Group II (76%), because of progressive dyspnea and deterioration of pulmonary function tests, underwent lung lavage. Of those who underwent lung lavage and were followed, 76% had a favorable response (Group II-a) and a significant number of them developed a complete remission, while 21% (Group II-b) had no response to lung lavage. Group I had higher arterial PO2 and lower alveolar-arterial oxygen partial pressure difference [P (A-a)O2] than Group II (72±5 and 38±3 vs 57±4 and 51±3,p<0.05). Similarly, the values of arterial PO2 and P(A-a)O2 were better in Group II-a than Group II-b (57±4 and 51±3 vs 40±6 and 65±11). In lavage material of 16 patients studied, macrophages appeared unusually enlarged and their number (% of differential count) was significantly lower (60±4%) than normal (90–95%). In contrast to previous reports, there was no evidence of active infection related to unusual or opportunistic organisms. No death related to PAP was observed. This prospective long term follow-up of large series of patients with PAP documents the overall course, prognosis and management of this illness.

Stability of the arterial/alveolar oxygen partial pressure ratio

The alveolar-arterial oxygen partial pressure difference (AaDO2) and the arterial/alveolar oxygen partial pressure ratio (a/APO2) were compared for stability when inspired oxygen concentration (FIO2) changed. The analysis was based on a three-compartment lung model and experimental results in 10 patients with respiratory failure receiving assisted ventilation. It was found that a/APO2 was more stable than AaDO2 and more useful for: (1) comparing gas exchange in patients receiving different levels of FIO2, (2) following gas exchange in the same patient as FIO2 is changed, and (3) estimating the PaO2 expected at a given level of FIO2 if blood gas data are available at another level. However, areas with low ventilation/perfusion (V/Q) ratios may cause sudden changes in a/PO2 at certain critical values of PAO2. Most stable is a/APO2 and, therefore, most useful at FIO2 levels greater than 0.3, and PaO2 levels less than 100 torr.

The surface tension of upper airway secretions in patients with and without respiratory disease.

The alveolar-arterial oxygen partial pressure (PAaO2) difference and surface tension of upper airway secretions (UASST) were simultaneously measured in 33 intubated patients. Patients without respiratory disease had UASST and PAaO2 gradients significantly lower than those with chronic obstructive lung disease. Patients in respiratory failure had UASST and PAaO2 gradients significantly higher than when they were out of failure. Correlation of UASST with PAaO2 was good (r = 0.81). These findings demonstrate that UASST closely correlate with the severity of pulmonary disease and suggest that their measurement may be a simple, clinically applicable method of assessing alveolar surfactant function.

Nomogram for the determination of arterial oxygen partial pressure of man in relation to high altitude and in dependence from age (author's transl)

If somebody ascends from sea level to higher altitude within a short time, the change of the atmospheric conditions can be a danger for his life. Therefore, a nomogram was constructed which allows to read off the arterial oxygen partial pressures and the corresponding arterial oxygen saturation in relation to altitude. On the basis of the oxygen partial pressure of the atmosphere determined by steps of 500 m from sea level up to an antitude of 10,000 m, we calculated the decrease of the oxygen partial pressure from the inspired air to the arterial blood. When passing our airways, the inspired oxygen partial pressure is dimished by the adaptation to BTPS conditions and by the increasing CO2 partial pressure when approaching the alveolar gas exchanging zone. Another oxygen partial pressure gradient formed by inhomogeneities of ventilation to perfusion, diffusing capacity to perfusion and shunt perfusion is found at the alveolar-arterial barrier. The value of this alveolar-arterial oxygen partial pressure difference is closely correlated to age. With the values of the single steps, the nomogram was constructed. Seven abscissas show the oxygen partial pressure gradients from the inspired air at a distinct altitude to the arterial blood. In relation to a lot of CO2-depending oxygen dissociation curves, it is possible to read off additionally the corresponding arterial oxygen saturation for a person in rest up to an altitude of 10,000 m.