Simultaneous Arterial Blood Gas Research Articles

Retrospective Validation of a Computerized Physiologic Equation to Predict Minute Ventilation Needs in Critically Ill Children.

Mechanical ventilation (MV) is pervasive among critically ill children. We sought to validate a computerized physiologic equation to predict minute ventilation requirements in children and test its performance against clinician actions in an in silico trial. Retrospective, electronic medical record linkage, cohort study. Quaternary PICU. Patients undergoing invasive MV, serial arterial blood gas (ABG) analysis within 1-6 hours, and pharmacologic neuromuscular blockade (NMB). ABG values were filtered to those occurring during periods of NMB. Simultaneous ABG and minute ventilation data were linked to predict serial Pa co2 and pH values using previously published physiologic equations. There were 15,121 included ABGs across 500 encounters among 484 patients, with a median (interquartile range [IQR]) of 20 (10-43) ABGs per encounter at a duration of 3.6 (2.1-4.2) hours. The median (IQR) Pa co2 prediction error was 0.00 (-3.07 to 3.00) mm Hg. In Bland-Altman analysis, the mean error was -0.10 mm Hg (95% CI, -0.21 to 0.01 mm Hg). A nested, in silico trial of ABGs meeting criteria for weaning (respiratory alkalosis) or escalation (respiratory acidosis), compared the performance of recommended ventilator changes versus clinician decisions. There were 1,499 of 15,121 ABGs (9.9%) among 278 of 644 (43.2%) encounters included in the trial. Calculated predictions were favorable to clinician actions in 1124 of 1499 ABGs (75.0%), equivalent to clinician choices in 26 of 1499 ABGs (1.7%), and worse than clinician decisions in 349 of 1499 ABGs (23.3%). Calculated recommendations were favorable to clinician decisions in sensitivity analyses limiting respiratory rate, analyzing only when clinicians made changes, excluding asthma, and excluding acute respiratory distress syndrome. A computerized equation to predict minute ventilation requirements outperformed clinicians' ventilator adjustments in 75% of ABGs from critically ill children in this retrospective analysis. Prospective validation studies are needed.

O009 Are there Differences in SpO2 Recordings from Two Oximeters on the same hand during an Overnight Sleep Study Significant?

Abstract Background Accurate non-invasive oxygen saturation (SpO2) measurement is crucial in healthcare, however is challenged by numerous devices using variable algorithms1. We compared two commonly used oximeter devices worn simultaneously in patients during an overnight polysomnogram. Aim To assess (1) differences between two SpO2 recording devices and (2) SpO2 accuracy against SaO2. Methods SpO2 data of two devices were recorded, downloaded and analysed with corresponding software: device 1 (Rad7 [Masimo, Irvine, CA, USA] set at 2-4sec averaging time) with software 1 (PSG 4 [Compumedics, Melbourne, Australia]) and device 2 (Wrist-Ox2® [Nonin Medical Inc, Plymouth, MN, USA] set at 3 sec averaging time) with software 2 (Noxturnal [Nox Medical Inc, Reykjavik, Iceland]). Responsiveness of each oximeter to changes in the patients’ desaturations associated with apnoeas and hypopnoeas overnight was assessed. In addition, both device SpO2 values were compared with SaO2 from simultaneous arterial blood gas sampling. Preliminary Results 7 patients (age 56.4±7.1 years, BMI 31.6±2.2 kg/m2, 100% male, 87% light skinned) were studied. The mean SpO2 with RAD7 was higher than the Nonin (95.9±1.6 vs 94.2±1.4%, mean difference 1.6±1.0%). Differences in the responsiveness of the oximeters during overnight desaturations were also observed. However, both device SpO2 values were found to be within ±2% of SaO2. Conclusions Discrepancies in SpO2 measurement do occur between devices and may have important clinical implications especially when it comes to the measurement of hypoxemic burden during sleep. 1.Blanchet MA et al. Accuracy of Multiple Pulse Oximeters in Stable Critically Ill Patients. Respir Care. 2023 May;68(5):565-574.

Comparison of mathematically arterialised venous blood gas sampling with arterial, capillary, and venous sampling in adult patients with hypercapnic respiratory failure: a single-centre longitudinal cohort study

BackgroundAccurate arterial blood gas (ABG) analysis is essential in the management of patients with hypercapnic respiratory failure, but repeated sampling requires technical expertise and is painful. Missed sampling is common...

Racial discrepancy in pulse oximeter accuracy in preterm infants.

ObjectivePulse oximetry is commonly used in Neonatology, however recent adult data suggest racial disparity in accuracy, with overestimation of oxygen saturation for Black patients.Study designBlack and White infants <32 weeks gestation underwent simultaneous arterial blood gas and pulse oximetry measurement. Error by race was examined using mean bias, Arms, Bland–Altman, and linear/non-linear analysis.ResultsA total of 294 infants (124 Black, 170 White) were identified with mean GA of 25.8 ± 2.1 weeks and mean BW of 845 ± 265 grams, yielding 4387 SaO2–SpO2 datapoints. SpO2 overestimation, measured by mean bias, was 2.4-fold greater for Black infants and resulted in greater occult hypoxemia (SpO2 > 90% when SaO2 < 85%; 9.2% vs. 7.7% of samples). Sensitivity and specificity for detection of true hypoxemia were similar between groups (39 vs. 38%; 81 vs. 78%).ConclusionThere is a modest but consistent difference in SpO2 error between Black and White infants, with increased incidence of occult hypoxemia in Black infants.

Validation of a Noninvasive Assessment of Pulmonary Gas Exchange During Exercise in Hypoxia

Pulmonary gas exchange efficiency, determined by the alveolar-to-arterial Po2 difference (A-aDo2), progressively worsens during exercise at sea-level; this response is further elevated during exercise in hypoxia. Traditionally, pulmonary gas exchange efficiency is assessed through measurements of ventilation and end-tidal gases paired with direct arterial blood gas (ABG) sampling. Because these measures have a number of caveats, particularly invasive blood sampling, the development of new approaches for the noninvasive assessment of pulmonary gas exchange is needed. Is a noninvasive method of assessing pulmonary gas exchange valid during rest and exercise in acute hypoxia? Twenty-five healthy participants (10 female) completed a staged maximal exercise test on a cycle ergometer in a hypoxic chamber (Fio2= 0.11). Simultaneous ABGs via a radial arterial catheter and noninvasive gas-exchange measurements (AGM100) were obtained in 2-minute intervals. Noninvasive gas exchange, termed the O2 deficit, was calculated from the difference between the end-tidal and the calculated Pao2 (via pulse oximetry and corrected for the Bohr effect by using the end-tidal Pco2). Noninvasive O2 deficit was compared with the traditional alveolar to arterial oxygen difference (A-aDo2), using the traditional Riley analysis. Under conditions of rest at room air, hypoxic rest, and hypoxic exercise, strong correlations between the calculated gPao2 and directly measured Pao2 (R2= 0.97; P< .001; mean bias= 1.70mmHg) were observed. At hypoxic rest and exercise, strong relationships between the estimated and directly measured Pao2 (R2= 0.68; P< .001; mean bias= 1.01mmHg) and O2 deficit with the traditional A-aDo2 (R2= 0.70; P< .001; mean bias= 5.24mmHg) remained. Our findings support the use of a noninvasive measure of gas exchange during acute hypoxic exercise in heathy humans. Further studies are required to determine whether this approach can be used clinically as a tool during normoxic exercise in patients with preexisting impairments in gas exchange efficiency.

Transcutaneous carbon dioxide monitoring as a predictive tool for all-cause 6-month mortality after acute pulmonary embolism

BackgroundPulmonary embolism (PE) frequently remains undiagnosed. The partial pressure of carbon dioxide (PaCO2), a surrogate of dead-space ventilation, is useful in the evaluation of the degree of pulmonary artery occlusion. At present, there is no knowledge about the prognostic role of PaCΟ2 variations during the first hours of an acute PE. Transcutaneous measurement of CO2 (PtcCO2) is a simple, non-invasive method that correlates well with PaCO2 levels, evaluated in this study for the first time in patients with PE. PurposeTo assess the correlation between PtcCO2 and PaCO2 levels in the acute phase of PE and the role of PtcCO2 in predicting 6-months mortality. MethodsThis was a pilot study including 53 patients with acute PE who hospitalized in Respiratory Medicine Department at University Hospital of Larissa in central Greece during 15 months. PtcCO2 was constantly monitored for four hours after PE diagnosis with the TCM40 monitoring system (SmartCal). Simultaneous arterial blood gas measurements were performed. Each patient was prospectively recorded for six months via standard telephone calls. ResultsPaCO2 and PtcCO2 values were well-correlated in the acute phase of PE. Decreased PtcCO2 levels in the first monitoring hour were associated with a higher risk of mortality. In the PE subgroup who died, the lower PtcCO2 level in the first hour of PE was a predictor of shorter survival time independently of gender, age, comorbidities, and smoking status. ConclusionPtcCO2 measurement, especially in the first hour after PE, seemed to be a valid tool in predicting all-cause 6-month mortality.

Association between computed tomographic thoracic injury scores and blood gas and acid-base balance in dogs with blunt thoracic trauma.

To determine the association between thoracic injuries evaluated by computed tomography (CT) and arterial blood gas and acid-base status in dogs with blunt thoracic trauma caused by motor vehicle accidents. Prospective observational clinical study. University teaching hospital. Thirty-one client owned traumatized dogs and 15 healthy dogs. All trauma group dogs underwent a CT scan and simultaneous arterial blood gas analysis within 24 hours, but not before 4 hours, after the traumatic incident within a 45-month enrollment period. Thorax injuries were classified as pulmonary, pleural space, or rib cage and each of these components was scored for severity using a CT composite pulmonary, pleural, and rib score. The trauma group arterial blood gas and acid-base status were evaluated for statistical difference from the control group. The pulmonary-arterial oxygen pressure was significantly lower in the trauma group compared to the control group that was supported by significant differences in the calculated variables of arterial blood oxygenation as well. There was also a significant correlation between the composite lung score and pleural score and the variables of arterial oxygen status. The pulmonary-arterial carbon dioxide pressure was not significantly different to any of the thoracic injury variables indicating normal alveolar ventilation. Acid-base imbalances were generally mild, insignificant, and variable. Blunt thoracic trauma causes significant pulmonary and pleural injury and the blood oxygen economy is significantly affected by this. The functional measures of arterial blood oxygenation were well correlated with thoracic CT pathology. Alveolar ventilation was mostly spared but a clinically significant ventilation perfusion mismatch was present.

Accuracy of Pulse Oximetry in the Detection of Hypoxia in Liver Transplant Candidates

Hypoxia is common in patients with chronic liver disease. Screening guidelines for detecting the presence of arterial hypoxemia do not exist. The aim of this study was to investigate the accuracy and utility of pulse oxymetry in the detection of hypoxemia (PaO2<65) in a group of patients with liver cirrhosis who were candidate for liver transplantation. Two hundred and ninety-five transplant candidates enrolled in this study. Arterial oxyhemoglobin saturation was obtained by pulse oxymetry (SpO2) and compared with simultaneous arterial blood gas (ABG) oxyhemoglobin values (SaO2). Bias, the overestimation or underestimation of one method compared with another, is defined as the difference between SpO2 and SaO2. SpO2 overestimated SaO2 in 78.3% (n=231) and underestimated in 18.6% (n=54) cases. The bias was over 4% or less than -4% (Bias4) in 11.6% (n=34) of the cases and significantly different between the patients with SaO2 =94%. PaO2 =65 mmHg (p=0.000) and SpO2 =94% (p=0.003). Also, when we used the cut-off level of A-a O2 gradient =20 and =15, the bias was significantly different between the patients (p=0.000). Pulse oximetry is a useful screening test to detect hypoxemia in patients with liver disease.

The accuracy of pulse oximetry in emergency department patients with severe sepsis and septic shock: a retrospective cohort study

BackgroundPulse oximetry is routinely used to continuously and noninvasively monitor arterial oxygen saturation (SaO2) in critically ill patients. Although pulse oximeter oxygen saturation (SpO2) has been studied in several patient populations, including the critically ill, its accuracy has never been studied in emergency department (ED) patients with severe sepsis and septic shock. Sepsis results in characteristic microcirculatory derangements that could theoretically affect pulse oximeter accuracy. The purposes of the present study were twofold: 1) to determine the accuracy of pulse oximetry relative to SaO2 obtained from ABG in ED patients with severe sepsis and septic shock, and 2) to assess the impact of specific physiologic factors on this accuracy.MethodsThis analysis consisted of a retrospective cohort of 88 consecutive ED patients with severe sepsis who had a simultaneous arterial blood gas and an SpO2 value recorded. Adult ICU patients that were admitted from any Calgary Health Region adult ED with a pre-specified, sepsis-related admission diagnosis between October 1, 2005 and September 30, 2006, were identified. Accuracy (SpO2 - SaO2) was analyzed by the method of Bland and Altman. The effects of hypoxemia, acidosis, hyperlactatemia, anemia, and the use of vasoactive drugs on bias were determined.ResultsThe cohort consisted of 88 subjects, with a mean age of 57 years (19 - 89). The mean difference (SpO2 - SaO2) was 2.75% and the standard deviation of the differences was 3.1%. Subgroup analysis demonstrated that hypoxemia (SaO2 < 90) significantly affected pulse oximeter accuracy. The mean difference was 4.9% in hypoxemic patients and 1.89% in non-hypoxemic patients (p < 0.004). In 50% (11/22) of cases in which SpO2 was in the 90-93% range the SaO2 was <90%. Though pulse oximeter accuracy was not affected by acidoisis, hyperlactatementa, anemia or vasoactive drugs, these factors worsened precision.ConclusionsPulse oximetry overestimates ABG-determined SaO2 by a mean of 2.75% in emergency department patients with severe sepsis and septic shock. This overestimation is exacerbated by the presence of hypoxemia. When SaO2 needs to be determined with a high degree of accuracy arterial blood gases are recommended.

Utility of pulse oximetry in the detection of arterial hypoxemia in liver transplant candidates.

Hepatopulmonary syndrome, arterial hypoxemia caused by intrapulmonary vasodilatation, occurs in approximately 10% of patients with cirrhosis. The severity of hypoxemia affects liver transplant candidacy and is associated with increased morbidity and mortality posttransplantation. Screening guidelines for detecting the presence of arterial hypoxemia do not exist. The aim of this study is to investigate the accuracy and utility of pulse oximetry in the detection of hypoxemia (PaO(2) < 70 mm Hg) in patients with cirrhosis. Two hundred prospective liver transplant candidates were compared with 94 controls. Arterial oxyhemoglobin saturation was obtained by pulse oximetry (SpO(2)) and compared with simultaneous arterial blood gas (ABG) oxyhemoglobin values (SaO(2); bias = the difference). PaO(2), carboxyhemoglobin, methemoglobin, and routine clinical and biochemical parameters were investigated to account for the bias. SpO(2) overestimated SaO(2) in 98% of patients with cirrhosis (mean bias, 3.37%; range, -1% to 10%). Forty-four percent of patients with cirrhosis and controls had a bias of 4% or greater. No clinical or biochemical parameters of cirrhosis accounted for the overestimation of pulse oximetry. Twenty-five subjects with cirrhosis were hypoxemic, and an SpO(2) of 97% or less showed a sensitivity of 96% and a positive likelihood ratio of 3.9 for detecting hypoxemia. An SpO(2) of 94% or less detected all subjects with an arterial PaO(2) less than 60 mm Hg. Pulse oximetry significantly overestimates arterial oxygenation, and the inaccuracy is not influenced by liver disease. Nevertheless, pulse oximetry can be a useful screening tool to detect arterial hypoxemia in patients with cirrhosis, but a higher threshold for obtaining an ABG must be used.

Pulse oximetry in sickle cell anemia.

To determine whether pulse oximetry is accurate and if it correlates with arterial blood gas saturation in pediatric patients with sickle cell anemia. Prospective, comparative study using a convenience sample of patients with sickle cell anemia who had simultaneous arterial blood gas sampling and pulse oximetry. Children's Memorial Hospital, a large tertiary care pediatric hospital in Chicago, IL. Patients selected from the emergency department and the pediatric intensive care unit. Twenty-four consecutive patients with sickle cell anemia who had simultaneous arterial blood gas sampling and pulse oximetry. Twenty-four patients had a total of 70 simultaneous pulse oximeter and blood gas pair samples. Each patient's initial pulse oximeter/blood gas pair was used in the statistical analysis. Three patients had venous samples and were excluded from comparison, leaving 21 arterial blood gas/pulse oximeter pairs for analysis. The pulse oximeter correlated well with the cooximeter-measured arterial saturation (r(2) =.74). The pulse oximeter significantly underestimated saturation by a mean of -1.6% (95% confidence interval, -0.3 to -3; p =.03). Pulse oximetry correlates well with cooximeter-measured saturation in patients with sickle cell anemia. Pulse oximetry significantly underestimates true arterial saturation, but the bias is clinically insignificant. Pulse oximetry can be used reliably to estimate the arterial oxygen saturation in patients with sickle cell anemia.

The accuracy of pulse oximetry in the emergency department

The objective of this retrospective study was to identify factors affecting the accuracy of pulse oximetry in the ED. Over a 3-year period, 664 consecutive emergency department (ED) patients had simultaneous arterial blood gas (ABG) and pulse oximeter readings taken. Pulse oximeter saturations (SpO 2) were compared with ABG CO-oximeter saturations (SaO 2) for accuracy. Multiple variables including age, sex, hemoglobin, bicarbonate, pH, and carboxyhemoglobin (COHb) were analyzed to see if they affected SpO 2 accuracy. ROC curves were used to determine the best pulse oximeter threshold for detecting hypoxia. Using multivariate analysis, COHb was the only statistically significant factor affecting the accuracy of pulse oximetry. In patients with COHb < 2%, SpO 2 overestimated SaO 2 by more than 4% in 8.4% of cases. In patients with COHb ≥ 2%, SpO 2 overestimated SaO 2 by more than 4% in 35% of cases. The best pulse oximetry threshold for detecting hypoxia is 92%. At this threshold, if COHb is <2%, pulse oximetry has a sensitivity of 0.92 and specificity of 0.90. If COHb is ≥2%, sensitivity is 0.74 and specificity is 0.84. For patients likely to have a COHb < 2, pulse oximetry is an effective screening tool for detecting hypoxia. However, more caution must be exercised when using pulse oximetry in patients likely to have a COHb ≥ 2%. (Am J Emerg Med 2000;18:427-431.

Oxygen transport in critically ill infants after congenital heart operations

Background. Oxygen transport variables reflect the balance of oxygen delivery and demand. Because oxygen transport in infants undergoing congenital cardiac operations is not well described, we examined oxygen transport in such patients. Differences in oxygen transport between survivors and nonsurvivors and variables that might be predictive of outcome were sought. Methods. We reviewed hospital records of infants admitted to the pediatric cardiac intensive care unit in our institution from January 1996 through April 1997. Infants in whom simultaneous arterial blood gas and systemic venous oxygen saturation measurements were performed on admission and at 6 and 24 hours after admission were included. Analyses of arterial pH, base excess, arteriovenous oxygen saturation differences, and oxygen extraction ratio were performed, including comparisons of survivors and nonsurvivors and changes over time. Results. Forty-nine infants were included in the study, with 39 survivors. There were no differences in any parameter between survivors and nonsurvivors on admission or at 24 hours. At 6 hours, differences between survivors and nonsurvivors were significant for arterial pH (7.48 versus 7.35, p < 0.001), base excess (2.9 versus −4.3 mmol/L, p < 0.01), arteriovenous oxygen saturation difference (34 versus 43, p < 0.05), and oxygen extraction ratio (0.28 versus 0.53, p < 0.001). The oxygen extraction ratio at 6 hours was at least 0.5 in 6 of 39 survivors and 7 of 10 nonsurvivors ( p = 0.002). Conclusions. Infants who die after cardiac operations have significant derangements of oxygen transport at 6 hours after admission to the intensive care unit. Infants with an oxygen extraction ratio greater than 0.5 at 6 hours are at highest risk.

Blood Anion Gaps and Venoarterial Carbon Dioxide Gradients as Risk Factors in Long-Term Extra corporeal Support

Increases in the blood anion gap (AG) and venoarterial carbon dioxide gradients [p(VA) CO2 ] may indicate changes in intracellular acid concentration not demonstrated by blood gas measurements. This prospective study examines these two physiologic markers to determine their relationship to extracorporeal membrane oxygenation (ECMO) survival and duration in 100 patients. Serum electrolytes were drawn every 6 hours and the AG calculated. Simultaneous arterial blood gases and venous blood gases were drawn every 4 hours and the p(V-A)CO2 calculated. Cumulative averages were then calculated from all the AG and p(V-A)CO2 values during each ECMO treatment. The average AG was 11 mEq/L. The average p(V-A)CO2 was 9 mm of mercury (mmHg). Patients with an AG of 11 mEq/L or less had a 12% mortality and those with a higher AG had a 43% mortality (p=0.0005). Patients with a p(V-A)CO2 of less than 9 mmHg had a 13% mortality and those with a 9 mmHg or higher gradient had a 35% mortality (p=0.0126). Patients with both a low AG and a low p(V-A)CO2 had a 7% mortality and survivors were on ECMO 100 (± 37) hours. Patients with both a high AG and a high p(V-A)CO2 had a 56% mortality and survivors were on ECMO 190 (± 1 05) hours. Both mortality and survivors’ ECMO time increase as one or both risk factors increase. Patients with increases in both risk factors have a mortality rate 8 times greater and survivors remain on ECMO almost twice as long as those without increased risk factors. Patients may benefit from a perfusion strategy that seeks to minimize the AG and p(V-A)CO2.

Response Characteristics of a Dual Transcutaneous Oxygen/Carbon Dioxide Monitoring System

We tested the response characteristics of a dual transcutaneous (tc) PO2/PCO2 monitoring system in healthy subjects who breathed various gas mixtures, and we compared steady-state tc readings to simultaneous arterial blood gas analysis in 20 stable respiratory outpatients. The electrodes were simple to apply, required very little skin preparation, and had trivial signal drift. In healthy subjects, tcPCO2 lag time during CO2 rebreathing was 16.8 seconds, with a 90 percent response time of 77.9 seconds after CO2 breathing was discontinued. The 90 percent response times of the O2 electrode when subjects breathed a hypoxic mixture was 257 seconds after a lag of 31 seconds. When inhaled gas mixtures were changed from hypoxia to room air, the lag time was shorter (12.5 seconds), but 90 percent response time exceeded 5 minutes. In stable patients with respiratory disease, tcPCO2 and tcPO2 were linearly related to PaCO2 (range, 19 to 53 mm Hg) and PaO2 (range, 45 to 99 mm Hg), respectively (tcPCO2 = 1.4 PaCO2-9.44, with r = 0.90 and SEE = 5.35 mm Hg; tcPO2 = 0.56 PaO2 + 20.4, with r = 0.53 and SEE = 11.7 mm Hg). We conclude that the response of the dual transcutaneous monitoring system is more rapid for the CO2 than the O2 electrode and may be rapid enough to be useful in some clinical settings; however, the O2 system fails to offer the response characteristics and accuracy that would allow it to be substituted for arterial gas tensions in unstable clinical situations.

Respiratory Illness and Hypophosphatemia

We retrospectively reviewed the charts of 308 admissions to a pulmonary disease ward and 100 admissions to the general medical service over one year to find the prevalence, sequelae, and etiology of hypophosphatemia. The overall prevalence of low serum phosphate levels (less than 2.4 mg/dl) occurring at least once during hospitalization in chest patients was 17 percent, but was higher in patients with respiratory infections (28 percent). Moreover, the prevalence of hypophosphatemia on admission (before institution of intravenous fluid or drug therapy) was ten times higher in patients with respiratory infections than in patients with noninfectious respiratory illness or general medical patients (21 vs 2 percent, p less than 0.001). Serum phosphate less than 2.0 mg/dl occurred in 4 percent of patients. Twenty-seven percent of the patients (including two with ventilatory failure) with abnormally low serum phosphate levels had symptoms or signs of uncertain etiology later explicable by the presence of hypophosphatemia. The most common additional laboratory finding associated with hypophosphatemia was elevation of muscle enzymes. Although mortality was no higher in hypophosphatemic patients, hospital stay was twice as long as that of patients with normal levels of serum phosphate. No correlation was found between simultaneous arterial blood gases and serum phosphate levels. Two patients given antacids had severe hypophosphatemia and worsened ventilatory function; phosphate-binding antacids should be used judiciously in patients with severe respiratory disease, since they may lead to the development or worsening of hypophosphatemia and diminished ventilatory function.

Light and electron microscopic examinations of experimentally produced heart muscle necroses following normobaric hyperoxia.

Heart muscle necroses following normobaric hyperoxia as examined under a light microscope occur after 40 hours exposure in the rabbit and increase in intensity with prolongation of the exposition time. Simultaneous arterial blood gas analysis excludes a hypoxemis as the cause, In addition electron microscopic examination of the necroses demonstrate the primary changes in the myofibrils but not in the mitochondria. The ultramorphological picture is however, quite similar to the myocardial necroses after epinephrine application in the rabbit. A pathogenetic relationship between heart muscle necroses after normobaric hyperoxia and after epinephrine should be considered.