Oxygen tensions and oxyhemoglobin saturations in the assessment of pulmonary gas exchange

We studied the theoretical basis for continuous monitoring of pulmonary gas exchange using arterial and mixed venous oximetry by examining the mathematical relationships between the calculated venous admixture (Qsp/Qt) and the ventilation-perfusion index, which is derived from oxyhemoglobin saturations. We compared this relationship with that between Qsp/Qt and its commonly used estimates: inspired oxygen concentration to arterial blood oxygen tension ratio, arterial to alveolar oxygen tension ratio, and alveolar-arterial oxygen tension difference. The relationship between Qsp/Qt and the oxygen tension-based indices is nonlinear and substantially influenced by changes in inspired oxygen concentration and arteriovenous oxygen content difference. Therefore, it is inaccurate within the clinically acceptable range of arterial blood oxygenation. In contrast, calculation of ventilation-perfusion index from arterial and mixed venous blood oxyhemoglobin saturations provides a linear estimate of Qsp/Qt that is minimally affected by alterations in inspired oxygen concentration or oxygen uptake and, therefore, will allow accurate continuous assessment of pulmonary gas exchange.     

Effect of hydralazine on intrapulmonary shunt

We compared the acute effects of bilateral arteriovenous may be related to levels of PvO2. The hydralazine-associated (p less than .05) decrease in resistance. Mixed venous oxygen fistulas to those of hydralazine infusion on hemodynamics and pulmonary gas exchange in dogs with pulmonary edema induced by administration of oleic acid. Oleic acid significantly (p less than .01) increased intrapulmonary shunt (Qsp/Qt) and pulmonary and systemic vascular resistance, and reduced cardiac output. Once the lesion stabilized, both opening the fistula and infusing hydralazine produced a similar and significant (p less than .01) increase in cardiac output, and a significant (p less than .05) decrease in resistance. Mixed venous oxygen tension (PvO2) closely followed the changes in cardiac output; however, PaO2 did not change. Qsp/Qt significantly (p less than .01) increased with the fistulas open and with hydralazine infusion. Closure of the fistulas or bleeding the animal at the end of the experiment reversed the changes in cardiac output and Qsp/Qt. The comparable increases in cardiac output and Qsp/Qt produced by opening the fistulas or infusing hydralazine may be related to levels of PvO2. The hydralazine-associated PvO2 increase indicates that this drug increased oxygen transport to the tissues even as Qsp/Qt became larger.     

预充氧对减少吸痰导致组织缺氧的临床观察

为研究预充氧对吸痰导致组织缺氧的影响,在非预充氧和预充氧条件下,观察１４ 例危重患者吸痰前、吸痰结束时、吸痰后５ 分钟动脉血气和混合静脉血气的变化。结果：与吸痰前相比,非预充氧组吸痰结束时的动脉血氧分压（ＰａＯ２） 、动脉血氧饱和度（ＳａＯ２）、混合静脉血氧分压（ＰｖＯ２）、混合静脉血氧饱和度（ＳｖＯ２） 均显著降低（ Ｐ＜０．０５）,吸痰结束后５ 分钟,ＳｖＯ２ 仍未恢复正常。如给予预充氧,吸痰结束时无低氧血症,组织缺氧较轻,虽然ＰａＯ２ 、ＳａＯ２ 、ＰｖＯ２ 、ＳｖＯ２ 亦低于吸痰前水平,但明显高于非预充氧组吸痰结束时的水平。吸痰结束后５ 分钟,组织缺氧完全纠正。结论：预充氧可以预防吸痰导致的低氧血症和组织缺氧。     

Cardiac output from carbon dioxide production and arterial and venous oximetry

OBJECTIVE: To determine cardiac output from measurements of CO2 production (VCO2), and arterial (SaO2) and mixed venous (SvO2) oxygen saturations, using a modified Fick equation, in which cardiac output = VCO2/[k (SaO2 - SvO2)], where k represents a constant. DESIGN: A metabolic measurement cart was used to measure VCO2 and oxygen consumption (VO2) at 3-min intervals. SaO2 and SvO2 were measured via a pulse oximeter and a fiberoptic right heart catheter, respectively. The initial value of k for each study was determined from initial simultaneous measurements of thermodilution cardiac output, VCO2, SaO2, and SvO2 via the equation k = VCO2/[cardiac output (SaO2 - SvO2)]. The value of k was assumed to remain constant for the entire study period. Thereafter, cardiac outputs calculated from k and the measurements of VCO2, SaO2, and SvO2 were compared with the simultaneously obtained cardiac outputs determined by thermodilution. Similarly, cardiac outputs calculated from the traditional oxygen Fick equation, where cardiac output = VO2/[13.4 x hemoglobin (SaO2 - SvO2)], were compared with the simultaneously acquired cardiac outputs determined by thermodilution. SETTING: Surgical ICU in a Veterans Affairs Medical Center. PATIENTS: Seven postoperative patients, mechanically ventilated using the intermittent mandatory ventilation mode, were studied over a mean period of 4 hrs. RESULTS: Cardiac output (obtained from VCO2 and oximetry saturations) was closely related to thermodilution cardiac output: with linear regression showing r2 = .96 and standard error of the estimate = 0.59 L/min, n = 21; and, with bias and precision = 0.17 and 0.68 L/min, respectively. The traditional oxygen Fick cardiac output was also closely related to the thermodilution cardiac output (r2 = .81, standard error of the estimate = 1.46 L/min, n = 22; bias and precision = 0.31 and 1.46 L/min, respectively). CONCLUSION: The proposed method for calculating cardiac outputs solely from VCO2 and oximetry saturations yields results that correspond closely to thermodilution determined cardiac outputs. The method is simple and avoids the difficulties in the Fick method associated with accurate VO2 measurement. This approach may be suitable for continuous cardiac output monitoring in critically ill patients.     

Arterial blood gas derived variables as estimates of intrapulmonary shunt in critically ill children

Oxygen transport data, prospectively collected from 52 critically ill children, were analyzed to determine whether any derived variable accurately estimated intrapulmonary shunt (Qsp/Qt). Arterial hemoglobin saturation was more closely correlated with Qsp/Qt than was PaO2, alveolar-arterial oxygen gradient, arterial mixed venous oxygen difference (C[a-v]O2), arterial/alveolar oxygen ratio, and the ratio of PaO2 to inspired oxygen (FIO2) (r = 0.8, p less than .0001). When C(a-v)O2 was normal, hemoglobin saturation became a very accurate (r = 0.96) assessment of Qsp/Qt. We conclude that various arterial blood gas derived variables do not accurately reflect Qsp/Qt in critically ill children. In these patients, a pulmonary artery catheter is needed to accurately assess intrapulmonary shunt.     

Respiratory index/pulmonary shunt relationship: quantification of severity and prognosis in the post-traumatic adult respiratory distress syndrome

The relationship between the respiratory index (RI = alveolar-arterial oxygen gradient [P(A-a)O2] normalized by PaO2) and the pulmonary shunt (Qsp/Qt) has been examined in 929 studies from 240 critically ill post-traumatic patients. Of these, 88 patients (443 studies) were individuals who developed post-traumatic adult respiratory distress syndrome (ARDS) and 152 were patients (486 studies) who did not develop ARDS. This study demonstrates that the RI to Qsp/Qt [RI/(Qsp/Qt)] relationship was significantly (p less than .0001) increased in patients who developed fatal ARDS compared with those who did not develop ARDS, or with those whose ARDS resolved. Because of the increased oxygen consumption (VO2) in ARDS patients in association with their severe limitations in gas exchange (RI) and increased Qsp/Qt, surviving ARDS patients had a significant increase in the cardiac index which resulted in a higher oxygen delivery to VO2 ratio. ARDS patients showed significant (p less than .0001) evidence of increased pulmonary vascular tone, correlated with the increase in the RI/(Qsp/Qt) relationship. In addition, those patients with high RI/(Qsp/Qt) also had increased right ventricular (RVSW) to left ventricular work (LVSW) ratios which were shown to be a direct function of the rise in RI. This increase in both RVSW/LVSW and RI/(Qsp/Qt) ratios was significantly (p less than .0001) correlated with an increased mortality. Thus, the RI/(Qsp/Qt) relationship, which can be obtained from arterial and mixed venous blood gases and saturations only, can be used to predict the severity of the ARDS process as well as important pulmonary vascular and right ventricular overload consequences.     

Unreliability of oxygen tension-based indices in reflecting intrapulmonary shunting in critically ill patients

Measurement of intrapulmonary shunting (Qsp/Qt), a widely used method for monitoring disturbances of pulmonary oxygen transfer in critically ill patients, involves calculation of arterial and mixed venous oxygen contents. In circumstances where mixed venous blood samples are not readily available, oxygen tension-based indices such as the alveolar to arterial oxygen tension differences (P[A-a]O2), arterial oxygen tension to alveolar oxygen tension ratio (PaO2/PAO2), PaO2 to FIO2 ratio (PaO2/FIO2) and respiratory index (RI) are widely utilized to reflect Qsp/Qt. Oxygen content-based indices such as the estimated shunt are not as widely utilized as the oxygen tension indices. In 75 critically ill patients in whom a pulmonary artery catheter was being utilized to augment clinical care, comparisons were made between Qsp/Qt and P(A-a)O2, PaO2/PAO2, PaO2/FIO2, RI, and estimated shunt to determine which index best reflected Qsp/Qt. Correlations between Qsp/Qt and estimated shunt were good (r = .94) and poor for the P(A-a)O2 (r = .62), PaO2/PAO2 (r = .72), PaO2/FIO2 (r = .71), and RI (r = .74). We conclude that there are no real substitutes for venous oxygen contents in critically ill patients. When pulmonary artery blood is not available for analysis, oxygen tension-based indices are unreliable reflectors of Qsp/Qt while the estimated shunt, an oxygen content-based index, provides a more reliable reflection of Qsp/Qt.     

吸痰对组织氧代谢的影响

研究吸痰对组织氧代谢的影响。方法：观察１４例危重病人吸痰前,吸痰结束时及吸痰后５ｍｉｎ动脉血气和混合静脉血气的变化。结果：与吸痰前相比,吸痰结束时的动脉血氧分压、血氧饱和度,混合静脑海因氧分压,血氧饱和度均显著降低,吸痰结束后５ｍｉｎ,ＳｖＯ３仍未恢复正常。     

Swine model of early adult respiratory distress syndrome induced by intravenous ethchlorvynol

Although ethchlorvynol (ECV) has been used to induce pulmonary damage in animals, changes after injection of this drug have not been studied, nor has the stability of the animal been assessed after injection. Continuously monitored hemodynamic and respiratory changes were followed during and after iv injection of 55 mg/kg ECV in ethanol into anesthetized, paralyzed, and ventilated swine (n = 5) and compared to changes in a control group given ethanol alone (n = 5). Arterial and mixed venous saturations were measured by fiberoptic vascular catheters and oxygen exchange by a gas monitor. Twelve direct and derived variables were monitored every 20 sec using a computer data acquisition system. Arterial oxygen saturation was kept at 90 +/- 2% by adjustment of FIO2. Ethanol produced only transitory changes during infusion. Significant elevations in pulmonary vascular resistance (PVR), shunt (Qsp/Qt) and deadspace (VD/VT) were observed during and after ECV. These were unaccompanied by changes in cardiac output or arterial pressure. PVR increased by 137%, Qsp/Qt by 67%, and VD/VT by 28% over 30 min. These changes were then sustained in the postinfusion period, producing a stable model of early adult respiratory distress syndrome for 3.5 h.     

Reduced venous admixture in hemorrhagic hypovolemia: maintenance of arterial oxygenation by selective pulmonary vascular collapse

In nine anesthetized and ventilated swine, a microcomputer calculated cardiac output, venous admixture (Qsp/Qt) and physiologic deadspace (VD/VT) every 20 sec, utilizing dual oximetry and a gas exchange analyzer. After lung injury with ethchlorvynol (ECV), animals were bled 40% blood volume over 40 min. Mean cardiac output decreased 7.0 to 2.2 L/min (p less than .05) accompanied by a decrease in mean Qsp/Qt from 0.28 to 0.14 (p less than .05) and an increase in mean VD/VT from 0.39 to 0.54 (p less than .05). Arterial Hgb saturation (Sao2) increased from 88 +/- 7% to 90 +/- 6%. On regression of all data points for each variable, Qsp/Qt had a positive correlation with cardiac output (r = .90), mean arterial pressure (MAP, r = .87), mean pulmonary artery pressure (MPAP, r = .86), and mixed venous Hgb saturation (Svo2, r = .89, p less than .001). VD/VT had an inverse correlation with cardiac output (r = -.90), MAP (r = -.82), Qsp/Qt (r = -.83), MPAP (r = -.77), and Svo2 (r = -.92, p less than .001). The decreasing Qsp/Qt and increasing VD/VT, with decreasing pulmonary perfusion pressures, were attributed to selective loss of perfusion to alveoli with low ventilation/perfusion ratios.     

Continuous positive airway pressure is beneficial in treatment of smoke inhalation

This study demonstrates that continuous positive airway pressure (CPAP) improves pulmonary function after smoke inhalation by dogs. Sixteen dogs were anesthetized with iv sodium pentobarbital. Arterial and mixed venous blood gas tensions; carboxyhemoglobin concentration (COHgb); mean systemic arterial (MAP), mean pulmonary arterial (MPAP), and pulmonary arterial wedge (WP) pressures; heart (HR) and respiratory (f) rates; cardiac output (CO); and airway pressure (Paw) were measured. Intrapulmonary physiologic shunt (Qsp/Qt) and pulmonary (PVR) and systemic (SVR) vascular resistances were calculated. The animals then breathed an aerosol of smoke and were divided randomly into 2 groups. The treatment group breathed spontaneously on 8-torr CPAP whereas the control group continued to breathe spontaneously at ambient pressure. After inhalation of smoke, Qsp/Qt, MPAP, PVR, COHgb, HR, and f rose, whereas PaO2 and MAP fell in untreated animals. When CPAP was applied, PaO2 and Qsp/Qt returned nearly to baseline values. Mean f also was significantly lower in the treated animals. We found that the early institution of CPAP improves oxygen exchange in the lungs after the inhalation of smoke.     

Stable and reproducible porcine model of acute lung injury induced by oleic acid

BACKGROUND AND METHODS: Previous studies on acute lung injury induced with oleic acid did not attempt to limit the influence of secondary changes on pulmonary circulation, and cardiopulmonary variable data were only collected and processed intermittently. Our study was designed to continuously monitor the following variables in five swine: systemic and pulmonary pressure; mixed venous oxygen saturation (SVO2) and arterial oxygen saturation (SaO2); minute oxygen consumption and CO2 production before, during, and for 4 hr after the infusion of oleic acid. A personal computer was programmed to produce 20-sec updates of deadspace ratio (VD/VT), venous admixture (Qsp/Qt), pulmonary (PVR) and systemic vascular resistance (SVR), and cardiac output (Qt) from these data. RESULTS: During the oleic acid infusion, there were increases in PVR, SVR, heart rate (HR), mean pulmonary arterial pressure (MPAP), Qsp/Qt, and VD/VT, and a decrease in Qt, SaO2, and SVO2. Thirty minutes after the oleic acid infusion, there was a further increase in HR, Qsp/Qt, and VD/VT, while MPAP, PVR, and SVR gradually decreased to pre-oleic acid infusion levels. No further decrease in SaO2, SVO2, and Qt was observed during that time. After the 30-min period, there was no further change in the cardiopulmonary variables. CONCLUSION: Our method of continuous monitoring was able to demonstrate in swine both the dynamic changes during, and stability after, the oleic acid infusion.     

Venous oxygen measurements in the inferior vena cava in neonates with respiratory failure

BACKGROUND: The present study was undertaken to examine the feasibility of venous oxygen measurements in the inferior vena cava (IVC) via a catheter through the umbilical vein. This may serve as a proxy for mixed venous oxygenation and the complications of right atrial cannulation can be avoided at the same time. It has the added advantage of not being affected by atrial right-left shunting. RESULTS: The study included 22 neonates requiring mechanical ventilation for respiratory insufficiency. The success rate of catheterization of the IVC via the umbilical vein was 81% and there was no catheter-related complications. Fifty paired blood samples were obtained and analyzed while the patients were hemodynamically stable. Linear regression analysis showed a poor correlation between arterial oxygen tension (PaO2) and the arterial-venous oxygen content difference [C(a-v)O2], r = -0.005, and between PaO2 and the fractional oxygen extraction (FOE), r = -0.114. There was also a poor correlation between arterial oxygen saturation (SaO2) and C(a-v)O2, r = -0.057, and between SaO2 and FOE, r =-0.139. The correlations between venous oxygen tension (PvO2) and C(a-v)O2 and between PvO2 and FOE were r = -0.528 and r = 0.592, respectively. There were good correlations between various oxygen saturation (SvO2) and C(a-v)O2, r = -0.634, and between SvO2 FOE, r = -0.712. CONCLUSION: Venous oxygen measurement in the IVC via an umbilical vein catheter is a simple and safe procedure and provides information about the tissue oxygenation status of critically ill neonates.     

Relationship of pulse oximetry to arterial oxygen tension in infants

Pulse oximetry is a useful technique for noninvasive oxygen monitoring in sick infants. We simultaneously measured oxygen saturation by pulse oximetry and on arterial blood samples by co-oximetry as well as PaO2 and the relative content of fetal (F) and adult hemoglobin in order to evaluate the reliability of pulse oximetry. Comparisons were made in triplicate in ten infants with acute cardiorespiratory disease less than 7 days of age and in 11 infants with chronic lung disease greater than 28 days of age. Oxygen saturation pulse oximetry and arterial saturation were well correlated over a wide range of saturation values. In infants with chronic lung disease, PO2 derived from pulse oximetry was within 10 torr of measured PaO2 in 73% of comparisons. In contrast, calculated PaO2 was within 10 torr of measured PaO2 in only 50% of comparisons in patients with acute disorders. The chronic infants all had less than 10% hemoglobin F, but in the acute infants, hemoglobin F ranged from 26% to 83%. Nonetheless, correction of oxygen dissociation curves for type of hemoglobin in these acute infants failed to improve the correlation between calculated and measured PaO2. We conclude that pulse oximetry saturations and their derived PaO2 values correlated well with measured arterial saturation and PaO2 obtained from arterial blood samples in neonates with chronic lung disease and prolonged oxygen dependence. In infants with acute cardiorespiratory problems, pulse oximetry unreliably reflects PaO2, but may be useful in detecting clinical deterioration.     

综合医院患者动脉血氧饱和度的研究

目的：了解临床送检动脉血标本的动脉血氧饱和度（ＳａＯ２）计算值和测定值的误差大小，以及用ＳａＯ２计算值指导临床实践是否可靠。方法：用临床各科送检的３１００份动脉血气标本测定值的有关数据，描绘动脉血氧分压（ＰａＯ２）血氧饱和度（ＳａＯ２）关系图及ＰａＯ２血氧含量（Ｏ２ＣＴ）关系图。结果：ＰａＯ２与ＳａＯ２的关系图不是单一的一条曲线，而是一个“Ｓ”形的区域带。当ＰａＯ２＝８．００ｋＰａ（１ｋＰａ＝７．５ｍｍＨｇ）时，ＳａＯ２变化范围为０．７２～０．９８；而当ＳａＯ２＝０．９０时，ＰａＯ２范围为６．００ｋＰａ～１２．２０ｋＰａ，实际半饱和氧分压（Ｐ５０）范围从２．１９ｋＰａ～１０．８８ｋＰａ，而ＰａＯ２与Ｏ２ＣＴ二者几乎无相关性。当ＰａＯ２＝８．００ｋＰａ时，Ｏ２ＣＴ范围为２．５４ｍｍｏｌ／Ｌ～９．１９ｍｍｏｌ／Ｌ，分布范围很大。结论：由ＰａＯ２和标准血红蛋白氧解离曲线推算ＳａＯ２、Ｏ２ＣＴ是不可靠的，ＳａＯ２必须直接测定     

Mechanical ventilation with permissive hypercapnia increases intrapulmonary shunt in septic and nonseptic patients with acute respiratory distress syndrome

OBJECTIVE: To compare the effects of conventional mechanical ventilation with low-volume, pressure-limited ventilation (LVPLV) and permissive hypercapnia on ventilation-perfusion (V/Q) distributions in patients with acute respiratory distress syndrome. We hypothesized that the advantageous cardiopulmonary effects of LVPLV would be greater in patients with sepsis than in those without sepsis. PATIENTS AND INTERVENTIONS: Twenty-two patients with acute respiratory distress syndrome were studied (group 1: 12 patients with hyperdynamic sepsis; group 2: 10 nonseptic patients). Intrapulmonary shunt (Qsp/Qt) (percentage of cardiac output), perfusion of "low" V/Q areas (percentage of cardiac output), ventilation of "high" V/Q areas (percentage of total ventilation [VE]), and deadspace ventilation (percentage of VE) were calculated from the retention/excretion data of six inert gases. Data were obtained during conventional mechanical ventilation and during LVPLV. MEASUREMENTS AND MAIN RESULTS: In group 1, LVPLV increased PaCO(0)rom 38 +/- 6 torr (5.1 +/- 0.8 kPa) to 61 +/- 12 torr (8.1 +/- 1.6 kPa). Qsp/Qt increased from 28 +/- 16% to 36 +/- 17%, whereas Pao2 (84 +/- 15 torr [11.1 +/- 2.0 kPa] vs. 86 +/- 21 torr [11.5 +/- 2.8 kPa]) and Qt (10.6 +/- 2.3 vs. 11.5 +/- 2.5 L x -1) remained unchanged and PVO(2) (40 +/- 4 [5.3 +/- 0.5 kPa] vs. 49 +/- 6 torr [6.5 +/- 0.3]) increased. In group 2, LVPLV increased PaCO(2) from 38 +/- 6 torr (5.1 +/- 0.8 kPa) to 63 +/- 11 torr (8.4 +/- 1.5 kPa). For Qsp/Qt (24 +/- 9% to 34 +/- 16%), the increase was not significant, whereas Qt (7.4 +/- 1.8 vs. 10.2 +/- 2.2 L x -1), PVO(2)(38 +/- 4 torr [5.1 +/- 0.5 kPa] vs. 50 +/- 6 mm Hg [6.7 +/- 0.8 kPa]), and PaO(2) (89 +/- 16 torr [11.9 +/- 2.1 kPa] vs. 98 +/- 19 torr [13.1 +/- 2.5 kPa]) increased. In both groups, the scatter of perfusion distribution (log SDQ) was greater than expected for normal subjects but was not different between the groups or altered by the treatments. CONCLUSIONS: In patients with acute respiratory distress syndrome, LVPLV with permissive hypercapnia, tended to increase Qsp/Qt, without a concomitant decrease of PaO(2). This occurs because, although atelectasis and increased shunt result from the low ventilatory volume, the effects on PaO(2) are offset by increased PVO(2) resulting from the hypercapnic stimulation of cardiac output. This result was independent of the presence or absence of sepsis.     

Effect of dopamine on intrapulmonary shunt fraction and oxygen transport in severe sepsis with circulatory and respiratory failure.

The hemodynamic response to a dopamine HCl infusion (10 microgram/kg per min) was measured in 25 adult patients with severe sepsis: there were 6 patients with circulatory hyperdynamic states, 9 patients with myocardial failure, and 10 with hypovolemia. Each patient also had acute respiratory failure. Changes of intrapulmonary shunt fraction (Qs/Qt), arterial and mixed venous oxygen tension (PaO2 and PvO2), oxygen transport, and oxygen consumption (VO2) were evaluated before and after dopamine infusion. Dopamine infusion produced clinical improvement and increased cardiac output. The hemodynamic response seemed to differ slightly according to the pattern of circulatory failure: chronotropic effect appeared to be predominant in hyperdynamic states, whereas inotropic effect appeared to be predominant in myocardial failure or hypovolemia. Moreover, in hypovolemic patients we noted a rise in pulmonary capillary wedge pressure suggesting an additional increase in venous return. During this treatment, we also noted a worsening of the Qs/Qt despite the increase in pulmonary blood flow; this worsening did not prevent significant improvements in VO2, but the improvement in PVO2 was offset by increased Qs/Qt and PaO2 remained unchanged.     

Titrating positive end-expiratory pressure therapy in patients with early, moderate arterial hypoxemia

A prospective randomized study to compare two physiologic end-points for titrating positive end-expiratory pressure (PEEP) was performed in patients with early, moderate arterial hypoxemia after surgery or trauma. All patients initially received 5 cm H2O of PEEP. In group 1 patients, PEEP was increased only if PaO2 decreased below 65 torr on an inspired oxygen fraction (FIO2) of 0.45. PEEP was then added in 2- to 3-cm H2O increments until PaO2 again was above 65 torr. Group 2 patients were treated with incremental PEEP until the PaO2/FIO2 ratio was greater than 300 or physiologic shunt (Qsp/Qt) was less than 0.20. All therapy other than PEEP was similar in the two groups. There were no statistically significant differences in entry PaO2 (mean 85 +/- 11 [SD] and 87 +/- 11 torr in groups 1 and 2, respectively), and Qsp/Qt was 0.22 in each group. Five (28%) of 18 patients in group 1 and 19 (95%) of 20 patients in group 2 received more than 5 cm H2O of PEEP. Between groups 1 and 2 there were no statistically significant differences in days intubated (3.4 +/- 3 vs. 5.3 +/- 5, respectively), ICU days (5.3 +/- 3 vs. 6.6 +/- 5), hospitalization days (26 +/- 24 vs. 28 +/- 24), incidence of pulmonary barotrauma (0/18 vs. 1/20), ICU mortality (22% vs. 20%), or overall mortality (33% vs. 25%). The number of blood gas analyses and cardiac output measurements, and the total hospital charges were also similar in both groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

七氟醚复合异丙酚麻醉对单肺通气肺内分流和血气的影响

目的观察七氟醚复合异丙酚麻醉在胸外科手术行单肺通气期间对肺内分流和血气的影响。方法 30例ASAⅠ～Ⅱ级的患者,用芬太尼4～5μg/kg,咪唑安定0.05 mg/kg,异丙酚1.5～2 mg/kg,维库溴铵0.1 mg/kg作静脉快速诱导,插入双腔气管导管。用丙泊酚每千克体重6～8 mg/h泵注,吸入1.3～2.5 MAC的七氟醚,间断静脉滴注维库溴铵和芬太尼维持麻醉。分别在单肺通气前1 min(T1)、单肺通气15 min(T2)、30 min(T3)及单肺通气结束前1 min(T4)各时刻抽取动脉血和混合静脉血行血气分析,并根据血气分析结果计算肺内分流率(Qs/Qt)。结果 T2、T3、T4时刻,肺内分流率较T1时刻显著增加,动脉血氧分压较T1时刻显著下降,T4时刻的动脉血氧分压较T3时刻有所回升。结论单肺通气时七氟醚复合异丙酚静吸麻醉虽然对肺内分流有影响,但不影响其在临床中安全应用。     

Cardiovascular adjustments and gas exchange during extreme hemodilution in humans

OBJECTIVE: To examine the cardiovascular adjustments and pattern of gas exchange that occur during hemodilution. DESIGN: Nonrandomized prospective study. SETTING: Operating room in a university hospital. PATIENTS: Seven patients undergoing elective aortocoronary artery bypass surgery. INTERVENTIONS: Before initiating cardiopulmonary bypass, the patients' hematocrit levels were decreased to approximately 15%. This hemodilution was done by removing a sufficient amount of autologous blood from the aortic cannula and replacing it with a sufficient amount of crystalloid solution. After the discontinuation of cardiopulmonary bypass, measurements were made at a hematocrit of approximately 15%. Then, after autologous blood infusion, measurements were made at a hematocrit of 20%, followed by more blood infusion to approximately 25% with repeat measurements. MEASUREMENTS AND MAIN RESULTS: The following measurements were made before hemodilution and then at all three levels of hemodilution: heart rate, mean arterial pressure (MAP), right atrial pressure, mean pulmonary artery pressure, pulmonary artery occlusion pressure, and cardiac output. From these measurements, the following derived variables were calculated: cardiac index, systemic vascular resistance, and pulmonary vascular resistance. From measurements of arterial oxygen content, mixed venous oxygen content, and cardiac output, intrapulmonary shunt (Qsp/Qt), oxygen uptake (VO2), oxygen extraction ratio, and oxygen delivery (DO2) were derived. The MAP was lowest (57 +/- 3 [SD] vs. 92 +/- 3 mm Hg) at the lowest hematocrit. The cardiac index was highest (4.0 +/- 0.3 vs. 2.3 +/- 0.6 L/min.m2) at the lowest hematocrit. DO2 was lowest at the lowest hematocrit but VO2 remained constant at all levels of hematocrit. The oxygen extraction ratio increased as hematocrit decreased. With progressive increases in hematocrit, DO2 increased and Qsp/Qt decreased. CONCLUSIONS: The data suggest that, during hemodilution, tissue autoregulation of VO2 and utilization are not impaired, but gas exchange function (Qsp/Qt) is impaired.