Conjunctival oxygen tension and its relationship to arterial oxygen tension

Using a miniaturized Clark electrode embedded in a polymethylmethacrylate eyepiece, we measured transconjunctival oxygen tension (PcjO₂) in 5 healthy volunteer subjects at multiple levels of steady-state isocapnic hypoxia, normoxia, and hyperoxia. PcjO₂ was linearly related to arterial oxygen tension (PaO₂) as PaO₂ ranged from 28 to 205 mm Hg (PcjO₂=0.59 PaO₂+0.36 mm Hg;r=0.94; standard error of the estimate=7.09 mm Hg). However, the relationships between PcjO₂ and PaO₂ varied significantly among subjects. Whereas the overall mean ratio of PcjO₂ to PaO₂ was 0.59, the mean ratio for subjects ranged from 0.47 to 0.79 and was significantly different among subjects (P<0.0001). The time response of the electrode to a step change in oxygen tension in vitro was exponential, with a 90% response time of 38 seconds after a lag of 3.7 seconds. The time responses to in vivo changes in oxygen tension were also exponential. From hypoxia to normoxia, 90% response time was 45.0 seconds after a lag of 5.1 seconds; from room air to hypoxia, 90% response time was 72.4 seconds after a lag of 30.3 seconds; from room air to hyperoxia, 90% response time was 87.2 seconds after a lag of 6.8 seconds. We conclude that, although PcjO₂ measured by a miniaturized Clark electrode is linearly related to PaO₂ in healthy subjects, variation in the relationship of PcjO₂ to PaO₂ among individuals will prevent precise estimation of PaO₂ for any individual unless subject-specific calibration is performed.     

经双腔鼻导管吸氧时实际吸入氧浓度的影响因素

目的研究实际吸入氧浓度（inspired oxygen concentration,FiO2）的变异大小及各种影响因素对其的影响程度。方法选择健康对照者及中-重度慢性阻塞性肺疾病（chronic obstructive pulmonary disease,COPD）急性加重期稳定后患者各8例,经双腔鼻导管吸氧,均按单纯常规吸氧与连接流量计测量呼吸参数两种情况下进行,随机调节给氧流量为1,2,3,4,5L／min,气体平衡后随机模拟加快吸气速度、减慢吸气速度及平静呼吸等3种呼吸模式,采用旁流顺磁法测量氧浓度。结果单纯常规吸氧时,健康对照组的FiO2影响因素影响程度大小的岭回归分析结果为给氧流量、吸气时间与呼吸周期时间比值（inspiratory time／respiratory cycle time,Ti／Tlot）及呼吸频率（respiratory frequency,RR）对FiO2的影响程度较大。在COPD组,给氧流量及RR的影响程度较大。连接流量计测量呼吸参数后,在健康对照组,给氧流量、潮气量（tidal volume,Vτ）、RR、吸气峰流速（peak inspirator flow,PIF）及平均吸气流速（mesn inspiratory flow,MIF）对FiO2的影响程度较大。COPD组的给氧流量、Vτ、Ti/Tlot及PIF的影响程度较大。结论实际FiO2受多种因素影响,其影响程度大小的分析结果显示,强影响因素：给氧流量;较强影响因素：Vτ中影响因素;RR、PIF及Ti／Ttot;弱影响因素：MIF、吸气时间（inspiratory time,Ti）及吸呼比（inspiratory time／expiratory time,I：E）。     

烧伤患者创伤后应激障碍及其影响因素研究

目的：探讨烧伤患者创伤后应激障碍的发生状况及影响因素。方法统计86例烧伤患者创伤后应激障碍的发生状况,比较发生与未发生创伤后应激障碍患者的一般资料,并对创伤后应激障碍的影响因素进行Logistic回归分析。结果本组86例烧伤患者创伤后应激障碍发生率为45．3％。发生与未发生创伤后应激障碍烧伤患者年龄、病程、文化程度、婚姻状况、烧伤深度、烧伤部位及烧伤面积比较差异有显著性（ P＜0．05或0．01）;回归分析显示,年龄、病程、文化程度、婚姻状况、烧伤深度、烧伤部位及烧伤面积均是烧伤患者发生创伤后应激障碍的影响因素（P＜0．01）。结论烧伤患者创伤后应激障碍发生率较高,其影响因素众多,临床上在治疗烧伤的同时,应关注患者的心身健康状况。     

Transorally obtained oxygen tension as an indicator of arterial oxygen tension

Transcutaneous oxygen electrodes have been used with success in neonates as indicators of arterial oxygenation, but with less success in adults because of differences in skin thickness and vascularity. In this study a prototype transoral oxygen electrode was evaluated to determine if a heated mucous membrane would yield arterialized values of oxygen tension in adults. Using a miniaturized Clark electrode, we measured transoral oxygen tension (PtoO₂) in 29 subjects at steady-state conditions. Simultaneously a sample was anaerobically obtained from a radial artery for measurement of arterial oxygen tension (PaO₂). Data were analyzed using linear regression analysis, Student'st test, and analysis of variance. There was no statistically significant difference between non-white and white subjects or male and female subjects. There was a highly significant difference (P<0.001) between the pooled, matched values for PtoO₂ versus PaO₂, and the regression between the PtoO₂ and the PaO₂ was linear (slope 0.92, y-intercept ?8.37,r=0.62,P<0.003). The calculated ratio of PtoO₂ to PaO₂ was 0.83±0.03 (standard error). We concluded that the PtoO₂ was linearly related to the PaO₂, although its accuracy in reflecting PaO₂ was low. This finding correlates with previously published data that suggested that the PtoO₂ reflects tissue oxygen tension rather than arterialized oxygen tension. Gender and race appeared not to affect the function of the electrode in our study.     

Exceptionally high arterial oxygen tension in diabetic ketoacidosis.

We recently managed a patient with diabetic ketoacidosis who had an exceptionally high arterial oxygen tension of 144 mm Hg while breathing room air. This was higher than the calculated alveolar oxygen tension and suggested the impossible situation of an uphill diffusion gradient. We were surprised to find this is a relatively common phenomenon (occurring in 25% of a retrospective study of similar patients). There are a number of probable mechanisms responsible for this observation, all of which reflect the severe metabolic aberration occurring in these patients.     

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.     

Time required for partial pressure of arterial oxygen equilibration during mechanical ventilation after a step change in fractional inspired oxygen concentration

OBJECTIVE: To determine the time required for the partial pressure of arterial oxygen (PaO2) to reach equilibrium after a 0.20 increment or decrement in fractional inspired oxygen concentration (FIO2) during mechanical ventilation. SETTING: A multi-disciplinary ICU in a university hospital. PATIENTS AND METHODS: Twenty-five adult, non-COPD patients with stable blood gas values (PaO2/FIO2 > or = 180 on the day of the study) on pressure-controlled ventilation (PCV). Following a baseline PaO2 (PaO2b) measurement at FIO2 = 0.35, the FIO2 was increased to 0.55 for 30 min and then decreased to 0.35 without any other change in ventilatory parameters. Sequential blood gas measurements were performed at 3, 5, 7, 9, 11, 15, 20, 25 and 30 min in both periods. The PaO2 values measured at the 30th min after a step change in FIO2 (FIO2 = 0.55, PaO2[55] and FIO2 = 0.35, PaO2[35]) were accepted as representative of the equilibrium values for PaO2. Each patient's rise and fall in PaO2 over time, PaO2(t), were fitted to the following respective exponential equations: PaO2b + (PaO2[55]-PaO2b)(1-e-kt) and PaO2[55] + (PaO2[35]-PaO2[55])(e-kt) where "t" refers to time, PaO2[55] and PaO2[35] are the final PaO2 values obtained at a new FIO2 of 0.55 and 0.35, after a 0.20 increment and decrement in FIO2, respectively. Time constant "k" was determined by a non-linear fitting curve and 90% oxygenation times were defined as the time required to reach 90% of the final equilibrated PaO2 calculated by using the non-linear fitting curves. RESULTS: Time constant values for the rise and fall periods were 1.01 +/- 0.71 min-1, 0.69 +/- 0.42 min-1, respectively, and 90% oxygenation times for rises and falls in PaO2 periods were 4.2 +/- 4.1 min-1 and 5.5 +/- 4.8 min-1, respectively. There was no significant difference between the rise and fall periods for the two parameters (p > 0.05). CONCLUSION: We conclude that in stable patients ventilated with PCV, after a step change in FIO2 of 0.20, 5-10 min will be adequate for obtaining a blood gas sample to measure a PaO2 that will be representative of the equilibrium PaO2 value.     

Effect of Intralipid-induced lipaemia on the arterial oxygen tension in preterm infants.

10% Intralipid was infused (1 g/kg body wt.) intravenously for 15 min with Razel pumps to each of eight selected newborn preterm infants whose general condition and pulmonary status were stable for at least 24 h before study. Six of the eight infants showed greater than 10 mmHg reduction in oxygen tension of umbilical arterial blood. These reductions were correlated with elevated triglyceride concentrations. The findings suggest that Intralipid-induced lipaemia has the potential to lower the oxygen tension of the blood and hence patients with pre-existing pulmonary insufficiency may be at risk from hypoxaemia.     

大面积烧伤病人应用高氧液体的动脉血氧分压观察

目的 寻求改善烧伤患休克期全身缺氧的有效途径。方法 按患入院次序,将相同程度的烧伤患给预不同处理,输平衡盐油的30例对照组,输高氧液的30例为观察组。结果 大面积烧伤患输注高氧液后动脉氧分压逐渐升高,高于对照组,两组存在明显的差异。结论 静脉输注高氧医用液,有效改善全身缺氧,纠正酸中毒,有利于病人过休克期。     

Continuous fiberoptic arterial oxygen tension measurements in dogs

An experimental study using a new fiberoptic sensor for the continuous intraarterial measurement of oxygen tension is described. This optode sensor uses the phenomenon of fluorescence quenching to determine the oxygen tension of the surrounding medium. To assess the accuracy of this device, we anesthetized 4 dogs and monitored them continuously with arterial catheters and an intraarterial optode probe, and intermittently with arterial blood gas analysis. The inspired oxygen fraction was varied from 1.0 to 0.1, and arterial blood gases were measured for comparison with the optode reading. Two hundred ninety data sets yielded a correlation coefficient of 0.96, with a linear regression slope of 0.98 and intercept of 5.1 mm Hg. In the 72 data sets from the last dog, the bias and precision of the optode arterial oxygen tension values were –10.3 mm Hg and 20.0 mm Hg, respectively. The optode probe was easily inserted through a 20-gauge catheter and did not interfere with continuous arterial pressure measurement or blood sampling. This study suggests that the optode has great potential as a continuous, real-time monitor of arterial oxygen tension.     

颜面部烧伤患者创伤性成长的相关影响因素分析

目的探讨颜面部烧伤患者创伤性成长相关因素及护理对策。方法选取我院收治的112例颜面部烧伤患者,采用创伤后成长评定量表(PTGI)、领悟社会支持量表(PSSS)、简化版大五人格问卷(BFI-44)和特质应对问卷(TCSQ)进行调查,采取单因素和多元线性回归分析影响创伤后成长的因素。结果 112例颜面部烧伤患者平均PTGI得分(59.64±12.58)分,5个维度中单条目得分最高为人生感悟,最低为自我转变;患者性别、不同社会支持方式、应对方式及人格特征的PTGI得分比较差异有统计学意义(P<0.05);多元线性回归分析结果显示,家庭外支持、积极应对、开放性人格是影响颜面部烧伤患者创伤后成长的主要因素(P<0.05)。结论家庭外支持、积极应对以及开放性人格为颜面部烧伤患者PTG的主要影响因素;针对该类患者医务人员应多关注其心理变化,帮助其塑造开放人格、培养积极应对态度以及寻求家庭和社会支持等护理干预,促进患者创伤后成长。     

The effect of arterial oxygen tension on antipyrine half-time in plasma.

Hospital patients with depressed arterial oxygen tensions (PaO2) from pulmonary disease were given antipyrine orally or intravenously. The half-time (t1/2) of disappearance from plasma was measured. Other patients with normal PaO2 measurements were treated similarly. Patients whose PaO2 was 55 or below had longer t1/2 times than those of patients with a PaO2 above 55. This observation parallels that made previously in rats.     

维持性血液透析患者血红蛋白浓度影响因素分析

目的：探讨影响维持性血液透析患者血液血红蛋白（ HB）浓度因素。方法对89例尿毒症患者进行日饮食总量、饮食结构及重组人红细胞生成素（ EPO）用量统计,分析患者血液HB浓度。结果摄入荤菜占饮食总量＞60％,30％～60％,＜30％患者,血液HB浓度分别为（103．2±30．36）,（96．96±25．24）,（103．76±16．49）g/L,差异无统计学意义（F＝2．269,P＞0．05）;日饮食总量＞1500,800～1500,＜800 g患者HB浓度分别为（118．36±22．82）,（99．96±18．28）,（83．03±14．22）g/L,差异有统计学意义（F＝11．986,P＜0．01）,两两比较差异均有统计学意义（P＜0．01）;不同饮食总量患者EPO用量差异无统计学意义（P＞0．05）。结论患者摄入饮食量对血液HB浓度影响大,荤菜与素菜对HB浓度影响相似。只有饮食治疗与使用EPO结合血液透析患者的贫血状况才能改善。     

Prediction of changing cerebral blood flow by use of the conjunctival oxygen tension/arterial oxygen tension index

Current methods of assessing cerebral blood flow (CBF) are limited in their ability to provide data at the bedside in a timely, inexpensive, and continuous fashion. Since the palpebral conjunctiva is perfused by branches of the internal carotid artery, perfusion of this tissue may reflect global CBF. Conjunctival oxygen tension (PcjO2), PaO2, PaCO2, and pH were measured in ten healthy subjects during normal ventilation and active hyperventilation. CBF was measured simultaneously using positron emission tomography. CBF decreased from an average of 64.3 +/- 15.1 ml x 100 g-1 x min-1 during baseline measurements to 33.2 +/- 8.4 ml x 100 g-1 x min-1 during hyperventilation. The ratio of PcjO2 to PaO2 (the PcjO2/PaO2 index) decreased from 0.53 +/- 0.07 to 0.35 +/- 0.09 in the same time period. The PcjO2/PaO2 index was significantly correlated with CBF (r = .78, p less than .001). We conclude that the PcjO2/PaO2 index may reflect the reduction in CBF induced by hyperventilation in normal humans, and should be investigated further as a method of assessing CBF in other settings which can result in globally reduced cerebral perfusion.     

Noninvasive arterial hemoglobin oxygen saturation versus transcutaneous oxygen tension monitoring in the preterm infant

We found that results from a transcutaneous arterial hemoglobin oxygen-saturation monitor correlated well with those from a co-oximeter. The monitor was not disturbed by differing hematocrit levels, the presence of fetal hemoglobin, or hypotension. We also found that the results of simultaneous transcutaneous arterial hemoglobin oxygen saturation (StcaO2) and transcutaneous oxygen tension (PtcO2) monitoring were predictably correlated over a wide range of hemoglobin saturations in preterm infants. When StcaO2 was between 80% and 95%, PtcO2 was at a safe level of 40 to 80 torr in 94% of the patients studied. StcaO2 monitoring as an index of arterial oxygenation has several advantages for the preterm infant.     

The impact of arterial oxygen tension on venous oxygen saturation in circulatory failure

Central and mixed venous oxygen saturations have been used to guide resuscitation in circulatory failure, but the impact of arterial oxygen tension on venous oxygen saturation has not been thoroughly evaluated. This observational study investigated the impact of arterial oxygen tension on venous oxygen saturation in circulatory failure. Twenty critically ill patients with circulatory failure requiring mechanical ventilation and a pulmonary artery catheter in an intensive care unit in a tertiary hospital in Western Australia were recruited. Samples of arterial blood, central venous blood, and mixed venous blood were simultaneously and slowly drawn from the arterial, central venous, and pulmonary artery catheter, respectively, at baseline and after the patient was ventilated with 100% inspired oxygen for 5 min. The blood samples were redrawn after a significant change in cardiac index (>or =10%) from the baseline, occurring within 24 h of study enrollment while the patient was ventilated with the same baseline inspired oxygen concentration, was detected. An increase in inspired oxygen concentration significantly increased the arterial oxygen tension from 12.5 to 38.4 kPa (93.8-288 mmHg) (mean difference, 25.9 kPa; 95% confidence interval [CI], 7.5-31.9 kPa; P < 0.001) and the venous oxygen saturation from 69.9% to 76.5% (mean difference, 6.6%; 95% CI, 5.3% - 7.9%; P < 0.001). The effect of arterial oxygen tension on venous oxygen saturation was more significant than the effect associated with changes in cardiac index (mean difference, 2.8%; 95% CI, -0.2% to 5.8%; P = 0.063). In conclusion, arterial oxygen tension has a significant effect on venous oxygen saturation, and this effect is more significant and consistent than the effect associated with changes in cardiac index.