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.     

Measurement of tissue oxygen tension: Comparison between two subcutaneous oxygen tonometers

We compared the 95% response time (95% RT) of two tissue oxygen tonometers under two sets of circumstances. We first evaluated the devices during normoxia, hyperoxia, and anoxia in vitro, using a transcutaneous PO₂ electrode (PtcO₂) as the reference. The responses to normoxia and to different grades of hyperoxia were examined in vivo in 8 healthy volunteers to assess the relationship between changes in subcutancous PO₂ and PtcO₂, an estimate of arterial PO₂ (PaO₂). One subcutaneous method (ScA) used a technique based on a polarographic needle electrode in situ connected to an ammeter; the second method (ScB) was based on a blood gas analyzer system first described by Hunt (Lancet 164;2:1370). ScA and PtcO₂ both responded to stepwise changes in ambient oxygen concentration (21–100%) in vitro within 10 seconds; the 95% RT of ScA was 1.39±0.5 to 2.39±0.8 minutes and that of PtcO₂ was 0.32±0.1 to 0.49±0.1 minutes. ScB had a lag of 3 minutes, and the 95% RT was 6.75±0.5 to 8.2±0.8 minutes. In contrast to the results in vitro, the response of ScA to changes in FiO₂ in vivo was delayed compared with the rapid response of PtcO₂, reflecting the physiologic delay of tissue PO₂ in response to increased PaO₂. The time lag and the long 95% RT of ScB were even more evident in vivo. ScA reacted three to four times faster than ScB, both in vitro and in vivo, to changes in the oxygen environment. The in vitro 95% RT of ScA to changes in ambient oxygen varied from 2 to 3.5 minutes. In contrast, the 95% RT of ScB was 8 to 9 minutes. PtcO₂ had the fastest 95% RT, from 0.4 to 0.5 minutes. The results suggest that the subcutaneous needle electrode method (ScA) provides close to real-time assessment of tissue PO₂.Supported by the Paulo Foundation and the Orion Foundation of Research.We thank the local distributor of Radiometer, Oriola Oy, for the loan of TINA.     

Transcutaneous carbon dioxide and oxygen tension in newborn infants: Reliability of a combined monitor of oxygen tension and carbon dioxide tension

We evaluated a new combined sensor for monitoring transcutaneous carbon dioxide tension (PtcCO₂) and oxygen tension (PtcO₂) in 20 critically ill newborn infants. Arterial oxygen tension (PaO₂) ranged from 16 to 126 torr and arterial carbon dioxide tension (PaCO₂) from 14 to 72 torr. Linear correlation analysis (100 paired values) of PtcO₂ versus PaO₂ showed anr value of 0.75 with a regression equation of PtcO₂=8.59+0.905 (PaO₂), while PtcCO₂ versus PaCO₂ revealed a correlation coefficient ofr=0.89 with an equation of PtcCO₂=2.53+1.06 (PaCO₂). The bias between PaO₂ and PtcO₂ was –2.8 with a precision of ±16.0 torr (range, –87 to +48 torr). The bias between PaCO₂ and PtcCO₂ was –5.1 with a precision of ±7.3 torr (range, –34 to +8 torr). The transcutaneous sensor detected 83% of hypoxia (PaO₂ <45 torr), 75% of hyperoxia (PaO₂ >90 torr), 45% of hypocapnia (PaCO₂ <35 torr), and 96% of hypercapnia (PaCO₂ >45 torr). We conclude that the reliability of the combined transcutaneousPo ₂ andPCo ₂ monitor in sick neonates is good for detecting hypercapnia, fair for hypoxia and hyperoxia, but poor for hypocapnia. It is an improvement in that it spares available skin surface and requires less handling, but it appears to be slightly less accurate than the single electrodes.     

Postoperative monitoring of conjunctival oxygen tension and temperature

To define the utility of conjunctival temperature (Tcj) and conjunctival oxygen tension (PcjO₂) monitoring during rewarming in the postoperative period, we measured serial Tcj, PcjO₂ and PcjO₂ index (PcjO₂/PaO₂) values in 10 patients after cardiac surgery. PcjO₂ and PcjO₂ index were markedly depressed at the low conjunctival temperatures recorded during the immediate postoperative period. As the patients' core and conjunctival temperatures increased, there was a concomitant, linear increase in PcjO₂ and PcjO₂ index for Tcj<33.5° C. Two patients showed deviation from this temperature-related rise in PcjO₂ and PcjO₂ index, and both of these patients demonstrated physiologic deterioration associated with cardiac arrest or hypotension. These results indicate that monitoring of PcjO₂ and Tcj can provide a continuous assessment of the adequacy of peripheral perfusion and oxygenation in the postoperative period.     

Conjunctival oxygen tension monitoring in experimental septic shock

Continuous non-invasive monitoring of conjunctival oxygen tension (PcjO₂) versus conventional invasive hemodynamic and oxygen transport variables was evaluated in a porcine model of septic shock induced by a continuous i.v. infusion of E.coli endotoxin over 2 hours. Seventeen pigs under ketamine anesthesia and breathing air spontaneously were investigated. PcjO₂, which reflects local oxygen tension at tissue level, correlated significantly at baseline and throughout the septic course with mixed venous oxygen saturation and oxygen utilization coefficient. All these correlations were significant at the 1% level. The corresponding correlations between PcjO₂ and cardiac output were significant at the 5% level. A finding of great importance was that changes in PcjO₂ preceded major changes in the intermittently measured physiological variables such as SvO₂ and cardiac output.We conclude that PcjO₂ monitoring is a valuable non-invasive method and which can provide a continuous assessment of the hemodynamic and oxygenation status in experimental septic shock.     

Arterial oxygen tension and mortality in mechanically ventilated patients

Purpose  

Early hyperoxia may be an independent risk factor for mortality in mechanically ventilated intensive care unit (ICU) patients. We examined the relationship between early arterial oxygen tension (PaO₂) and in-hospital mortality.     

Continuous monitoring of tissue oxygen tension during hyperoxia and hypoxia: relation of subcutaneous, transcutaneous, and conjunctival oxygen tension to hemodynamic variables

Subcutaneous, transcutaneous, and conjunctival oxygen tensions (PscO2, PtcO2, and PcjO2, respectively) were measured in anesthetized dogs subjected sequentially to normoxia, hyperoxia, and hypoxia. Intravascular pressure, hemodynamic and oxygen transport variables were measured simultaneously. PtcO2 and PcjO2 closely paralleled PaO2 during normoxia, hyperoxia, and hypoxia over a wide range of arterial oxygen tensions. PtcO2 was reliable over the widest range of PaO2, with a correlation coefficient of .94. The PcjO2/PaO2 index fell at very low PaO2. The PscO2/PaO2 index decreased at both very low and very high PaO2. Only minor changes were found in hemodynamic and oxygen transport variables during hyperoxia. During hypoxia, however, cardiac output and other central hemodynamic measurements increased, while PscO2, PtcO2, and PcjO2 fell. Oxygen delivery and oxygen consumption were maintained or only slightly changed during hypoxia. All three continuous measurements of oxygen tension are reliable indices of PaO2 over a wide range under normovolemic conditions. The instruments for measuring PscO2 and PcjO2 are unheated and therefore may have advantages for human application.     

Progress in the development of a fluorescent intravascular blood gas system in man

In vitro and in vivo animal studies have shown accurate measurements of arterial blood pH (pHa), carbon dioxide tension (PaCO₂), and oxygen tension (PaO₂) with small intravascular fluorescent probes. Initial human clinical studies showed unexplained intermittent large drops in sensor oxygen tension (PiO₂). Normal volunteers were studied to elucidate this problem. In the first part of this study, the probe and cannula were manipulated and the probe configuration and its position within the cannula were varied. The decreases in PiO₂ were judged to be primarily due to the sensor touching the arterial wall. Retraction of the sensor tip within the cannula eliminated the problem. In the second part of this study, the accuracy of the retracted probe was evaluated in 4 subjects who breathed varying fractions of inspired oxygen and carbon dioxide. The arterial ranges achieved were 7.20 to 7.59 for pH, 22 to 70 mm Hg for PaCO₂, and 46 to 633 mm Hg for PaO₂. Linear regression of 48 paired sensor (i) versus arterial values showed pHi = 0.896 pHa + 0.773 (r = 0.98, SEE = 0.017); PiCO₂ = 1.05 PaCO₂-1.33 (r = 0.98, SEE = 2.4 mm Hg); and PiO₂ = 1.09 PaO₂-20.6 (r = 0.99, SEE = 21.2 mm Hg). Bias (defined as the mean differences between sensor and arterial values) and precision (SD of differences) were, respectively, -0.003 and 0.02 tor pHi, 0.77 and 2.44 mm Hg for PiCO₂, and -2.9 and 25.4 mm Hg for PiO2. The mean in vivo 90% response times for step changes in inspired gas were 2.64, 3.88, and 2.60 minutes, respectively, for pHi, PiCO₂, and PiO₂.     

Cardiorespiratory and conjunctival oxygen tension monitoring during resuscitation from hemorrhage

Placement of an unheated miniaturized oxygen electrode against the palpebral conjunctiva permits noninvasive measurement of tissue oxygen tension. In this study, the relationship between conjunctival oxygen tension (PcjO2) and standard cardiorespiratory variables was examined during a sequential resuscitation protocol after acute hemorrhage. Anesthetized dogs were rapidly bled to a mean arterial pressure of 40 mm Hg and then retransfused with the shed blood in a stepwise fashion. PcjO2 fell to 2% of control values after hemorrhage and did not return to prehemorrhage values until more than 90% of the shed blood had been reinfused. PcjO2 was among the last set of cardiorespiratory variables to return to control values during resuscitation and was the last noninvasive variable to normalize. The ratio of PcjO2 to arterial oxygen tension decreased from a prehemorrhage value of 0.76 +/- 0.05 (SEM) to 0.02 +/- 0.003 after hemorrhage, and did not increase to values greater than 0.50 until resuscitation was more than 90% complete. Conjunctival oxygen monitoring may play an important role in assessing the adequacy of resuscitation after acute hemorrhage.     

Effect of sevoflurane on P50 and on measurement of oxygen tension

Fresh samples of heparinized human blood from 10 healthy nonsmoking volunteers were used to study the effect of the inhaled anesthetic sevoflurane on the oxygen half-saturation pressure of hemoglobin (P₅₀) and on polarographic measurements of oxygen tension at low values. Control samples had a baseline P₅₀ of 26.9±0.2 mm Hg. When the blood samples were exposed to 1.75% (1 minimum alveolar concentration, MAC), 2.75%, and 3.5% (2 MAC) of sevoflurane, the P₅₀ values were 27.0±0.5 mm Hg, 27.1±0.4 mm Hg, and 26.9±0.5 mm Hg, respectively. Our present data show that 1 to 2 MAC sevoflurane has no significant effect on P₅₀ (P>0.05). Our data also show that sevoflurane did not interfere with polarographic measurements of oxygen tension (P>0.05). Other inhaled agents—halothane, enflurane, and isoflurane—do interfere with these measurements, and we cannot explain the difference.Presented at the annual meeting of the American Society of Anesthesiologists, Atlanta, GA, October 1987.     

Effects of anesthetic agents on the drift of a transcutaneous oxygen tension sensor

Both halothane and nitrous oxide can be reduced at the cathode of a polarographic oxygen electrode, causing the electrode current to drift upward and report falsely high oxygen tension. Because transcutaneous oxygen tension is measured by a heated oxygen electrode, there is a potential for significant upward drift of these values. To examine the clinical significance of this drift, the following study was performed. Transcutaneous oxygen tension sensors were calibrated at oxygen tensions of 0 mm Hg and 157 mm Hg (room air) just before clinical use during anesthesia. This calibration was rechecked immediately upon removal of the sensor from the patient at the end of the anesthesia. The predominant anesthetic agent used and the duration of monitoring were noted from the record. Data were collected from 208 patients representing a total of 463.6 hours of anesthesia. The patients were divided into five groups based on anesthetic administered: halothane, enflurane, isoflurane, nitrous oxide-narcotic, and local/regional. The mean zero point recalibration value was 0.4 mm Hg or less for all agents except halothane, for which it was 1.8 ± 3.2 mm Hg. This halothane drift was significantly greater than that for the other agents (P<0.01). Room air recalibration was not significantly different in any of the five groups, varying from 160 ± 4.9 mm Hg for halothane to 157 ± 4.9 mm Hg for enflurane. All these drift values are within the manufacturer’s specifications. We conclude that the drift of the transcutaneous oxygen tension sensor due to anesthetic agents is not clinically significant. However, caution should be exercised when halothane is used during an extremely long period of anesthesia.     

Targeting two different levels of both arterial carbon dioxide and arterial oxygen after cardiac arrest and resuscitation: a randomised pilot trial

Purpose

We assessed the effects of targeting low-normal or high-normal arterial carbon dioxide tension (PaCO₂) and normoxia or moderate hyperoxia after out-of-hospital cardiac arrest (OHCA) on markers of cerebral and cardiac injury.

Methods

Using a 2³ factorial design, we randomly assigned 123 patients resuscitated from OHCA to low-normal (4.5–4.7 kPa) or high-normal (5.8–6.0 kPa) PaCO₂ and to normoxia (arterial oxygen tension [PaO₂] 10–15 kPa) or moderate hyperoxia (PaO₂ 20–25 kPa) and to low-normal or high-normal mean arterial pressure during the first 36 h in the intensive care unit. Here we report the results of the low-normal vs. high-normal PaCO₂ and normoxia vs. moderate hyperoxia comparisons. The primary endpoint was the serum concentration of neuron-specific enolase (NSE) 48 h after cardiac arrest. Secondary endpoints included S100B protein and cardiac troponin concentrations, continuous electroencephalography (EEG) and near-infrared spectroscopy (NIRS) results and neurologic outcome at 6 months.

Results

In total 120 patients were included in the analyses. There was a clear separation in PaCO₂ (p?<?0.001) and PaO₂ (p?<?0.001) between the groups. The median (interquartile range) NSE concentration at 48 h was 18.8 µg/l (13.9–28.3 µg/l) in the low-normal PaCO₂ group and 22.5 µg/l (14.2–34.9 µg/l) in the high-normal PaCO₂ group, p?=?0.400; and 22.3 µg/l (14.8–27.8 µg/l) in the normoxia group and 20.6 µg/l (14.2–34.9 µg/l) in the moderate hyperoxia group, p?=?0.594). High-normal PaCO₂ and moderate hyperoxia increased NIRS values. There were no differences in other secondary outcomes.

Conclusions

Both high-normal PaCO₂ and moderate hyperoxia increased NIRS values, but the NSE concentration was unaffected.

Registration

ClinicalTrials.gov, NCT02698917. Registered on January 26, 2016.

     

不同氧环境中破骨细胞特异性基因的表达

背景：课题组以往研究证实,氧浓度过低乃至处于低氧时（体积分数2%O2）,破骨前体细胞的增殖及破骨细胞的分化和功能都受到抑制,但体外培养的破骨细胞在不同氧环境下的基因表达未见有相关报道。目的：实验拟观察不同氧环境下破骨细胞各特异性基因的表达规律,探寻氧环境改变影响破骨细胞分化的表达机制。方法：将破骨前体细胞株经质量浓度均为10μg/L的核因子κB受体活化因子配体和巨噬细胞集落刺激因子联合诱导成为成熟的破骨细胞,然后分别置于常氧、组织氧、低氧（体积分数20%,7%,2%）条件下培养,用抗酒石酸酸性磷酸酶染色检测破骨细胞形成的变化,并分别在培养第1-7天收集细胞,通过定量PCR方法检测核因子κB受体活化因子,肿瘤坏死因子受体相关因子6,抗酒石酸酸性磷酸酶,组织蛋白酶K基因mRNA的表达。结果与结论：低氧条件下抗酒石酸酸性磷酸酶阳性的破骨细胞数显著低于组织氧和常氧培养时形成的抗酒石酸酸性磷酸酶阳性细胞数（P〈0.05）。不同氧环境下,破骨细胞中核因子κB受体活化因子mRNA的表达无明显改变,组织氧和常氧培养下肿瘤坏死因子受体相关因子6 mRNA的表达在培养第5天最高（P〈0.05）。随着氧浓度的降低,抗酒石酸酸性磷酸酶和组织蛋白酶K mRNA表达时间延后,组织氧培养条件下此2者的表达可以保持在最高水平。结果证实,与常氧和低氧条件相比,破骨细胞在组织氧培养条件下培养时更易促进其分化,从而维持其活性和功能。     

Noninvasive monitoring of oxygenation during one-lung ventilation: A comparison of transcutaneous oxygen tension measurement and pulse oximetry

Oxygenation was monitored concomitantly by measurement of transcutaneous oxygen tension and by pulse oximetry, and the data were compared with arterial blood oxygen tension and saturation values in 10 patients who became hypoxemic when undergoing thoracotomy and one-lung ventilation. A steep decrease in arterial blood oxygen tension was obvious immediately after the institution of one-lung ventilation, reaching the lowest mean value of 63 ± 2 mm Hg (± SEM) at 12 minutes. Despite significant correlation between transcutaneous oxygen tension and arterial blood oxygen tension during one-lung ventilation (r = 0.75;P < 0.001), the delay in the transcutaneous oxygen tension response resulted in underestimation of the severity of hypoxemia at the beginning of one-lung ventilation. In contrast, the decrease in arterial blood oxygen saturation from 97.9 ± 0.3% to 92.2 ± 0.8% as measured by CO-Oximeter was accurately followed by pulse oximetry with almost beat-to-beat response, bringing about a highly significant linear correlation between the two methods (r = 0.93;P < 0.001). We conclude that pulse oximetry is a simpler and more rapidly responding method than measurement of transcutaneous oxygen tension for detection of hypoxemia during one-lung ventilation in adults.     

Evaluation of two oxygen analyzers by computerized data acquisition and processing

Monitoring of inspired oxygen concentration during anesthesia with nitrous oxide is becoming accepted as essential. This type of monitoring demands accurate monitors that respond rapidly. We evaluated two such devices for their response patterns to rapid changes in oxygen concentration, a galvanic or “fuel cell” unit and a polarographic device. Data were stored after analog-to-digital conversion. The response patterns to stepwise changes in nitrous oxide and oxygen mixtures were recorded at flow rates ranging from 2 to 10 L/min. Both units responded accurately to all changes in the absolute oxygen concentration; the polarographic unit was, on average, twice as fast. Responsiveness to nitrous oxide was low (<0.4% at 100% nitrous oxide), and the stability of the signals was good. The 90% response time (T₉₀) was consistent for any stepwise increase or decrease in oxygen concentration between 0, 21, 33, 50, and 100%. After a step change from 0 to 100% oxygen at a gas flow rate of 10 L/min, the T₉₀ was 5.8 seconds in the polarographic device and 11.4 seconds in the galvanic device (p<0.01). After a decrease from 100 to 0% oxygen, the T₉₀ was 0.6 second longer in both monitors. Comparing flow rates of 2 L/min with 10 L/min, the T₉₀ was delayed by 1.1 and 2.3 seconds for an increase, and by 1.4 and 2.9 seconds for a decrease in oxygen concentration. Experimental data suggest that both sensors respond adequately during routine clinical use. The faster response of the polarographic device is probably of limited clinical relevance, but it may aid in calibration.     

The oxygen reserve index (ORI): a new tool to monitor oxygen therapy

Supplemental oxygen is administered in the vast majority of patients in the perioperative setting and in the intensive care unit to prevent the potentially deleterious effects of hypoxia. On the other hand, the administration of high concentrations of oxygen may induce hyperoxia that may also be associated with significant complications. Oxygen therapy should therefore be precisely titrated and accurately monitored. Although pulse oximetry has become an indispensable monitoring technology to detect hypoxemia, its value in assessing the oxygenation status beyond the range of maximal arterial oxygen saturation (SpO₂ ≥97%) is very limited. In this hyperoxic range, we need to rely on blood gas analysis, which is intermittent, invasive and sometimes delayed. The oxygen reserve index (ORI) is a new continuous non-invasive variable that is provided by the new generation of pulse oximeters that use multi-wavelength pulse co-oximetry. The ORI is a dimensionless index that reflects oxygenation in the moderate hyperoxic range (PaO₂ 100–200 mmHg). The ORI may provide an early alarm when oxygenation deteriorates well before any changes in SpO₂ occur, may reflect the response to oxygen administration (e.g., pre-oxygenation), and may facilitate oxygen titration and prevent unintended hyperoxia. In this review we describe this new variable, summarize available data and preliminary experience, and discuss its potential clinical utilities in the perioperative and intensive care settings.     

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.     

The effect of hyperoxia on survival following adult cardiac arrest: A systematic review and meta-analysis of observational studies

Objective

Studies have shown the detrimental effect of hyperoxia in animals with return of spontaneous circulation (ROSC) after cardiac arrest. To maximize the value of existing clinical studies, we performed the systemic review and meta-analysis of human observational studies to examine the effect of hyperoxia on outcomes of post-ROSC patients.

Methods

We searched PubMed and Embase from the inception to October 2013. We selected adult observational studies that compared different levels of partial pressure of arterial oxygen (PaO₂) in post-ROSC patients with mortality or neurological status at hospital discharge as outcome. Studies comparing hypoxia with normoxia only were excluded.

Results

Fourteen studies were identified from 2982 references. Odds ratio (OR) was used as effect estimate. OR was reconstructed if not provided in original articles. Hyperoxia was defined as a PaO₂ >300 mmHg. Meta-analysis indicated that hyperoxia appeared to be correlated with increased in-hospital mortality (OR, 1.40; 95% CI, 1.02–1.93; I², 69.27%; 8 studies) but not worsened neurological outcome (OR, 1.62; 95% CI, 0.87–3.02; I², 55.61%; 2 studies). However, the results were inconsistent in subgroup and sensitivity analyses.

Conclusions

Hyperoxia appears to be correlated with increased in-hospital mortality of post-ROSC patients. This result should be interpreted cautiously because of the significant heterogeneity and limited number of studies analyzed. However, because exposure to hyperoxia had no obvious benefits, clinicians should monitor PaO₂ closely and titrate oxygen administration cautiously.     

Retrospective analysis of the hemodynamic consequences of prehospital supplemental oxygen in acute stroke

ObjectiveHyperoxia, the delivery of high levels of supplemental oxygen (sO₂) despite normoxia, may increase cerebral oxygenation to penumbral tissue and improve stroke outcomes. However, it may also alter peripheral hemodynamic profiles with potential negative effects on cerebral blood flow (CBF). This study examines the hemodynamic consequences of prehospital sO₂ in stroke.MethodsA retrospective analysis of adult acute stroke patients (aged ≥18 years) presenting via EMS to an academic Comprehensive Stroke Center between January 1, 2013 and December 31, 2017 was conducted using demographic and clinical characteristics obtained from Get with the Guidelines-Stroke registry and subjects' medical records. Outcomes were compared across three groups based on prehospital oxygen saturation and sO₂ administration. Chi-square, ANOVA, and multivariable linear regression were used to determine if sO₂ was associated with differences in peripheral hemodynamic profiles.ResultsAll subjects had similar initial EMS vitals except for oxygen saturation. However, both univariate and multivariable analysis revealed that hyperoxia subjects had slightly lower average ED mean arterial pressures (MAP) compared to normoxia (Cohen's d = 0.313).ConclusionsPrehospital-initiated hyperoxia for acute stroke is associated with a small, but significant decrease in average ED MAP, without changes in heart rate, compared to normoxia. While limited by the inability to link changes in peripheral hemodynamical profiles directly to changes in CBF, this study suggests that hyperoxia may result in a relative hypotension. Further studies are needed to determine if this small change in peripheral vascular resistance translates into a clinically significant reduced CBF.     

Hypoxic ventilatory response in subjects with normal and high oxygen affinity hemoglobins.

It has still not been shown unequivocally whether a decrement of arterial oxygen content or tension governs the ventilatory response to hypoxia. In an attempt to discriminate between the two possibilities, we have measured the ventilatory response to isocapnic progressive hypoxia in two healthy children with a high oxygen affinity hemoglobin (Hb Andrew-Minneapolis) and in their age- and sex-matched normal siblings. Hypoxic ventilatory response was identical in all subjects, there being no difference in minute ventilation at PAo2 = 40 mm Hg or in k (decrement of PO2 required to increase ventilation by a factor of 2.718). In contrast, at PAo2 = 40 mm Hg, hemoglobin oxygen saturation decreased markedly in controls but only slightly in high affinity subjects. Furthermore the increase in heart rate at PAo2 = 40 mm Hg was significantly less in high affinity subjects, suggesting a concomitant difference in oxygen delivery. Thus, with identical decrements in PAo2 but widely divergent changes in arterial oxygen content and oxygen delivery, controls and high affinity subjects showed virtually identical ventilatory response to hypoxia. We conclude that decrements of oxygen tension are the major stimulus for hypoxic ventilatory response.