Oxygen Utilization Coefficient Research Articles

Age features of O2 mass transfer regimes in adolescents’ body at rest

The results of complex studies of the quantitative relationship between the stage-by-stage mass transfer of O2 and the efficiency of cardiorespiratory system functioning in relation to its consumption in adolescents’ body under conditions of relative rest are presented.
 The results obtained show that in adolescents, the modes of mass transfer of O2 in the body and the nature of the respiratory and circulatory systems functioning in relation to its consumption have a number of age-related differences compared with adult men. So, in adolescents, the external respiration system at rest functions less economically than in adults. Each liter of O2 consumed by adolescents is extracted from almost 3 liters more than in adults the amount of air ventilated per minute through the lungs. The volumetric indicators of blood circulation are also higher in adolescents, which may indicate the influence of neuro-humoral rearrangements in the body during the pubertal period. The coefficient of oxygen utilization by tissues from arterial blood in adolescents turned out to be significantly higher, which may characterize a higher tension of tissue metabolic processes.

Lungs volume status and oxygen transport in patients with coronary artery disease with various types of comorbidity before and after coronary artery bypass grafting

Aim. Assessment of lung volume status and oxygen transport system in patients with coronary artery disease (CAD) with different clinical types of comorbidity before and after coronary artery bypass grafting (CABG).Material and methods. The observational controlled study included 66 patients with CAD with a median age of 67 years (95% confidence interval [59; 74]), admitted to the Far Eastern Federal University Hospital for elective CABG. Depending on the prevalence of clinical manifestations of comorbidities, CAD patients were ranked into 3 groups of comorbidity: cardiovascular, respiratory and metabolic. The first of them was represented by a combination of CAD and peripheral artery disease, the second — CAD and chronic obstructive pulmonary disease (COPD),the third — CAD and metabolic syndrome. All patients underwent isolated CABG under cardiopulmonary bypass (CPB). Volume and hemodynamic monitoring was carried out by transpulmonary thermodilution using the Pulsion PiCCO Plus (Germany) technology and the following indices: cardiac function index (CFI), extravascular lung water (EVLW), pulmonary vascular permeability index (PVPI). Pulmonary blood volume and oxygen transport indices were determined: oxygen delivery (DO2I) and consumption (VO2I) indices, oxygen-utilization coefficient, and pulmonary shunt fraction (Qs/Qt). The study was carried out in three stages: before the onset of CABG, after its completion and one day after CABG.Results. The analysis of volume and hemodynamic monitoring data demonstrated the heterogeneity of their changes during CABG and one day after with different comorbidity profile. A more noticeable inhibition of the circulatory component of oxygen transport was revealed in patients with COPD, which was illustrated by the lowest CFI (3,2-3,4 ml/min) in relation to other groups of patients. The imbalance of cardio-respiratory interactions in this cohort after withdrawal from cardiopulmonary bypass was manifested by lower DO2I and VO2I and a maximum increase in Qs/Qt, exceeding 1,6 times the comparison groups. The respiratory and metabolic comorbidity of CAD was characterized by a significantly larger volume of extravascular lung water due to the higher permeability of the pulmonary vessels, which was documented by EVLW values, which exceeded the upper reference limit by 1,8-2 times and an increase in PVPI. In patients with cardiovascular comorbidity, lung volume violation was less noticeable.Conclusion. A comprehensive analysis of lung volume status and oxygen transport makes it possible to more accurately assess the functional status of patients with CAD, to increase the effectiveness of risk stratification and to prevent possible complications during CABG and in the early postoperative period.

Functional state dynamics in cross-country skiers in the summer and autumn preparatory phase

Background and Study Aim. To study changes in the functional state of professional Russian cross country skiers in the course of the preparatory phase and their effects on their competition ratings.
 Materials and methods. In this study we examined 10 cross-country skiers. The functional state was assessed through a maximal load bicycle ergometer test, coordination and special performance tests. Concentrations of lactate and cortisol were checked in the blood plasma of participants.
 Results. The training effects on general physical preparedness and special physical preparation in September in comparison with June were observed as an increased number of pull-ups on a pull-up bar (by 14%) and decreased time of the roller ski test (by 4%). In autumn higher systolic (by 11%) and diastolic (by 10%) arterial blood pressure levels, higher levels of plasma lactate and cortisol (by 48% and 64%, respectively) were detected (p<0.05). At anaerobic threshold the following increased: total performance capacity (by 13%), oxygen consumption (by 14%), watt pulse (by 5%), respiratory minute volume, oxygen utilization coefficient, and oxygen pulse (by 15%) (p<0.05-0.01) at rest before the ergometer test. In September upon completion of the ergometer test we observed an increase of oxygen pulse (by 7%), watt pulse (by 10%), and oxygen utilization coefficient (by 24%) (p<0.05). In autumn at the 5th minute of recovery after the ergometer test the heart rate recovered 11% faster, blood lactate – 29% faster, and the oxygen utilization rate increased by 15% (p<0.05-0.01). In June no statistically significant correlations were found between the studied indicators. In autumn statistically significant correlations appeared between indicators of the cardiorespiratory system, physical performance, and coordination test time.
 Conclusions. The package program for the summer-autumn training period contributes to the improvement of the functional status of the cross-country skiers and to the development of physical power, endurance, increased strength of the upper limbs, increased speed of movement on roller skis, faster and more complete recovery of physiological and biochemical parameters.

STUDY OF THE RELATIONSHIP BETWEEN HELIOGEOPHYSICAL FACTORS AND THE COURSE OF CERTAIN PHYSIOLOGICAL PROCESSES IN INDIVIDUALS WITH DIFFERENT PSYCHOSOMATIC STATUS AS A COMPONENT OF PSYCHOLOGICAL SUPPORT

Тhe purpose of the study: to establish a correlation between the average annual values of the minute volume of blood flow in hypertensive men with different temperaments and high anxiety and solar activity. There were 848 patients with arterial hypertension and 422 healthy individuals. All of them were determined by temperament and anxiety, and the minute volume of blood flow. To compare the calculated method for determining the minute volume of blood flow with the hardware method, the authors measured the minute volume of blood flow in patients using tetrapolar rheography on a 6-NEG device connected with a computer and compared it with the value of the minute volume of blood flow determined by calculation. Data on the dynamics of solar activity in wolf numbers and radio emission at a wavelength of 10.5 cm were obtained from the West-Siberian Department for Hydrometeorology and Environmental Monitoring. During the period of increased solar activity, the body was affected by a complex of factors, including socio-economic factors, together with ionizing radiation of the environment; contribute to a decrease in the coefficient of oxygen utilization by tissues, which caused the development of an adaptive reaction, part of which was an increase in the minute volume of blood flow. A significant correlation was established between solar activity indicators, meteorological factors, and minute blood flow volume, which indicates the possibility of a combined effect of the studied factors on increasing the functional activity of the cardiovascular system.

КАРДИОРЕСПИРАТОРНАЯ СИСТЕМА ПРИ ВЕЛОЭРГОМЕТРИЧЕСКОМ ТЕСТИРОВАНИИ У ЛЫЖНИКОВ РЕСПУБЛИКИ КОМИ С РАЗНОЙ СТЕПЕНЬЮ ТРЕНИРОВАННОСТИ

The aim of the study is to examine the impact of training status on ski racers (Komi Republic) at rest and under bicycle ergometry evaluating their cardiorespiratory system parameters. Materials and Methods. The authors examined male ski racers with different training status: 22 first-rank sportsmen, 22 candidates for Master of Sports and 22 Masters of Sports. Athletes underwent bicycle ergometry loads up to refusal. Oxycon Pro system (Germany) was used. Then authors studied the complex of cardiorespiratory parameters, calculating maximum oxygen consumption and unit physiological cost. Results. At rest and under standard physical load (200 W) Masters of Sports demonstrate significantly increased training status among ski racers in such cardiorespiratory system parameters as heart rate, rate pressure product and oxygen pulse. Under standard physical load (200 W) statistically significant differences between first-rank sportsmen and candidates for Master of Sports are detected by heart rate, rate pressure product, respiration rate, respiratory minute volume and oxygen utilization coefficient. Such deviations indicate differences in training status. Under maximum load, the highest training status is found in Masters of Sports: bicycle ergometry load power and duration; unit pulse, pressor and cardiac cost, bulk and unit values of maximum oxygen consumption. Heart rate values, unit pulse and heart-vent cost indicate a high training status in candidates for Master of Sports under load up to refusal, if compared with first-rank sportsmen. Athletes’ organism under load up to refusal works more efficiently than under moderate load (200 W). The training status in ski racers (Komi Republic) is manifested in the saving cardiorespiratory system functions, both at rest and under standard bicycle ergometry, as well as in parameters of unit physiological cost under loads up to refusal and increased values of maximum oxygen consumption. Keywords: ski racers, Komi Republic, training status, bicycle ergometry loads, cardiorespiratory system, maximum oxygen consumption.

Pathophysiological justification for admission of athletes who underwent community­acquired pneumonia to training loads.

Objective: to study the power supply of veloergometric loading in athletes who underwent community-acquired pneumonia to justify the renewal term of physical activity as well as its volume and intensity. Material and methods: 80 athletes aged from 17 to 26 years who were engaged in cyclic sports with I qualification grade and higherwere examined. They were divided into 2 groups: 43 athletes with community-acquired pneumonia (group I) and 37 healthy athletes (group II). The group I included subgroup IA (n=28) withgenerally accepted standard medical treatment of community-acquired pneumonia and subgroup IB (n=15) with additional complex of therapeutic gymnastics, massage, physiotherapeutic procedures. All participants underwent complex general clinical, radiologic and laboratory examinations and alsosome special tests asspirography and spiroergometry, electrocardiography, veloergometric exercise. Results: Athletes with community-acquired pneumonia at the time of clinical recovery showed significant violations of the functional state of the cardiorespiratory system both after exercise and during the recovery period. However amongthe sportsmen with community-acquiredpneumonia all studiedparameters restored more quickly in the subgroup IB, where remedial gymnastics, massage and physiotherapy were used in complex treatment. It was shown that the most informativeparameters for dynamic monitoring of the functional condition of athletes who underwent community-acquired pneumoniawererespiratory minute volume(RMV), heart rate (HR), oxygen pulse of work (peak O pulse), oxygen-utilization coefficient (OUC). Conclusions: athletes who underwentcommunity-acquired pneumoniacan be admitted to training and competitive loads in terms of not earlier than one month after clinical recovery. Admission to training and competitive loads should be conducted after a comparative analysis of the functional parameters of the external respiration system at rest, veloergometric loading and in the recovery period.

Influence of heliogeophysical factors on the minute blood volume in hypertensive patients with different temperament

Correlation between the annual average values of minute volume of blood flow in healthy men with different psychosomatic status, suffering from arterial hypertension, and Solar activity from 1995 to 2015 was investigated. Variations of γ-background during the study period did not exceed the limits of normal regional values (7-9 µr/h). However, the analysis of solar activity dynamics represented periodic increase and a momentary increase by the 2005-2006. With the increase in solar activity and γ-ray background a significant reduction of oxygen utilization coefficient by tissues of healthy individuals and patients with different temperament was noted. The increase in solar activity was followed by an increase in ambient temperature and atmospheric pressure. The study showed a significant increase in minute volume of blood flow in the groups of healthy individuals and patients in the same years as the increase in solar activity and γ-background environment. There has been established a significant correlation relationship between indicators of solar activity, meteorological factors and minute volume of blood flow that indicates on the possibility of combined effects of the studied environmental factors to affect the course of physiological processes in organism of both healthy and hypertension person. Overall, it was reflected in the increase of functional activity of the cardiovascular system (by minute volume of blood flow).

Value of early-stage cerebral oxygen utilization coefficient in predicting delayed encephalopathy after acute carbon monoxide poisoning

Objective: To investigate the dynamic change in cerebral oxygen utilization coefficient (O(2)UCc) in the early stage of acute severe carbon monoxide poisoning (ASCMP) and its value in predicting delayed encephalopathy after acute carbon monoxide poisoning (DEACMP) . Methods: A prospective observational study was conducted for patients with ASCMP who were admitted to our hospital from November 2013 to March 2016, and their baseline features and physiological parameters were recorded. Observation ended at two months after acute poisoning; according to the presence or absence of DEACMP, the patients were divided into DEACMP group with 21 patients and non-DEACMP group with 64 patients. The change in O(2)UCc was monitored on admission and at 6, 24, 48, and 72 hours. Spearman correlation was used to investigate the correlation between O(2)UCc and Acute Physiology and Chronic Health Evaluation II (APACHE II) score, and the receiver operating characteristic (ROC) curve was used to evaluate the accuracy of O(2)UCc in predicting DEACMP. Results: Both groups had a significant increase in O(2)UCc on admission, and the DEACMP group had a significantly greater increase than the non-DEACMP group (52.57%±9.30% vs 41.46±%6.37%, P<0.05) . Then both groups tended to have a reduction in O(2)UCc, and the DEACMP group had a significantly higher O(2)UCc than the non-DEACMP group at 6, 24, and 48 hours (47.40%±7.92%, 39.38%±8.01%, and 32.29%±6.31% vs 34.51%±7.89%, 28.79%±5.4%, and 27.72%±5.46%, P<0.05) . On admission and at 6, 24, and 48 hours, O2UCc was positively correlated with APACHE II score (r=0.304, 0.398, 0.426, and 0.300, P=0.005, 0.000, 0.000, and 0.005) . The ROC curve showed that O(2)UCc had a value in predicting DEACMP on admission and at 6, 24, and 48 hours, and 6-hour O2UCc had the highest predictive value with an area under the ROC curve of 0.870 (95% confidence interval 0.794-0.947, P<0.05) . Conclusion: The dynamic change in O(2)UCc has a reference value in early identification of DEACMP, and O(2)UCc can be used as an important reference index for predicting DEACMP.

INFLUENCE OF THE CHRONIC OBSTRUCTIVE PULMONARY DISEASE ON POST-OPERATION COURSE IN CORONARY HEART DISEASE

Aim. To study the influence of chronic obstructive pulmonary disease (COPD) on post-operation period course in coronary heart disease (CHD) patients after coronary bypass surgery (CBG). Material and methods. Totally, 92 patients included, with CHD. Two groups were formed: 1st — 50 patients with CHD, 2nd — 42 patients with CHD and COPD. We studied the condition of ventilation via bodypletismography method, and registered oxygen consumption at rest and assessed the effectiveness of pulmonary ventilation — oxygen utilization coefficient (OUC2 , mL/L). Via the method of monofactor logistic regression analysis we calculated independent predictors of cardiovascular and respiratory complications during the nearest period of CBG. Results. After CBG the number of in-hospital complications in the 2nd group was higher than in the 1st. In 2nd group there were more prevalent respiratory failure, atrial fibrillation, cerebral function alteration. As predictor for complications after CBG was COPD (OR 2,1; CI 1,7-2,9; p=0,002). Combination of low values of the forced expiration by 1 s (FEV1) — less than 60% from normal with increase of residual volume (RV) more than 130% is significant predictor for the increase of ventilatory support (VS) (OR 2,5; CI 1,9-3,2; p=0,01). At baseline, decrease of OUC2 less than 20 mL/L is also the predictor for RS prolongation (OR 1,9; CI 1,4-2,8; p=0,003). Conclusion. COPD in CHD increases the chances of complicated clinical course of in-hospital period 2,1 times. Such specifics of baseline disorder in ventilation system as decrease FEV1 less than 60% with increase of RV more 130%, and significant decrease of effectiveness of pulmonary ventilation — OUC2 less than 20 mL/L increase chances for RS duration after CBG 2,5 and 1,9 times, respectively.

Respiratory function in patients with coronary heart disease in combination with chronic obstructive pulmonary disease

The objective of the study was to assess the state of respiratory function (RF) in patients with CHD and in patients with CHD combined with COPD. Also evaluated was the efficiency of pulmonary gas exchange, while taking into account the oxygen-utilization coefficient (OUC). RF was investigated in 73 patients with coronary heart disease (CHD) and in 51 patients with CHD combined with COPD by means of a bodyplethysmography approach. In patients with CHD and COPD there was a significant reduction of the efficiency of pulmonary ventilation (OUC decreased by 24% as compared to the normal value) against a background of bronchial conductivity. The patients with CHD without COPD showed a moderate decrease in RF reserves, with the effectiveness of pulmonary ventilation maintained at an optimal level.

호기성 입상화 슬러지를 이용한 SBR 운전의 동력학적 해석 및 설계분석

In the present work, the aerobic particle's characteristics were enhanced. A polymer was used to make aerobic granular sludge in short period of time. And operation parameters were calculated for organic matter removal in domestic wastewater using a sequencing batch reactor (SBR). The experiment for sewage (Influent concentration of 63~72 mg COD/L) by using mature aerobic granular sludge showed the organic matter removal rate k and oxygen utilization coefficient a', b' were 10.161 d and 0.87 mg O2/mg CODr, 0.11 mg O2/mg MLVSS.d respectively. Therefore, it was more effective than K value 5~8 d of conventional activated sludge process. The sludge synthetic value and sludge auto-oxydation value were 0.45 mg VSS/mg CODr and 0.05 mg VSS/mg MLVSS.d respectively. Consequently, mortality rates of microorganisms was lower than conventional activated sludge process.

Oxygen Transport in Pulmonary Oxygenizing Dysfunction in the Early Periods after Extracorporeal Circulation

Objective: to study the specific features of oxygen transport function in patients with various oxygen delivery changes caused by alveolar opening maneuver (mobilization) performed early after extracorporeal circulation. Subjects and methods. Alveolar opening maneuver was made in the presence of relative arterial hypoxemia under the control of dynamic thora-copulmonary compliance. The maximum airway pressure was as high as 31.1±0.3 cm H2O; the positive end-expiratory pressure was 16.0±0.3 cm H2O. According to the changes in oxygen delivery after alveolar opening maneuver, the investigators retrospectively identified the following groups: 1) (n=14) with a lower and 2) (n=15) higher values. The groups did not differ in age (53.6±2.8 and 56.4±1.8 years), extracorporeal circulation duration (106.4±11.2 and 86.8±4 min), and inotropic support intensity (4.7±0.5 and 4.6±0.6 ^g/kh/min for dopamine and/or dobutamine) (p&gt;0.05). The mode of alveolar opening maneuver and its impact on thoracopulmonary compliance and pulmonary oxygenizing function were identical in the groups (p&gt;0.05). Results. 48.3% of the patients with relative arterial hypoxemia show a linear relationship between the oxygen delivery and consumption indices (r=0.73; p=0.003), and there was a close inverse correlation between the oxygen utilization coefficient and intrapulmonary shunting (r=-0.77; p=0.001). After alveolar opening maneuver, the oxygen delivery index decreased in these cases from 440.7±31.7 to 376.9±20.4 ml/min/m2 (p&lt;0.05). The time course °f changes oxygen delivery influenced mixed venous hemoglobin oxygen saturation (r=-0.71; p=0.005), which was related to lactatemia before (r=0.71; p=0.004) and after (r=0.7; p=0.005) alveolar opening maneuver. Conclusion. After extracorporeal circulation, relative arterial hypoxemia may be concurrent with the signs of oxygen transport system tension in patients with impaired pulmonary oxygenizing function. Moreover, regional blood flow impairments in the peripheral tissues and those in the lung are closely related. After alveolar opening maneuver that improves pulmonary oxygenizing function, oxygen delivery decreases, affecting mixed venous hemoglobin oxygen saturation. The findings give grounds to recommend close monitoring and timely correction during alveolar mobilization in the early period after cardiosurgery. The specific features of oxygen transport and utilization during standard interventions into the heart under extracorporeal circulation call for further in-depth studies. Key words: oxygen transport, oxygen delivery and consumption, alveolar opening maneuver (mobilization), arterial hypoxemia in cardiosurgical patients.

Central Hemodynamics and Oxygen Transport during Alveolar Mobilization in Early Periods after Extracorporeal Circulation

Objective: to study central hemodynamics, the determinants of coronary blood flow and myocardial oxygen demand, and the parameters of blood oxygen-transport function during alveolar mobilization in early periods after extracorporeal circulation in patients operated on for coronary heart disease. Subjects and methods. Twenty-nine patients were examined after myocardial revascularization. The alveolae were mobilized 63±2 min after extracorporeal circulation. The peak airway pressure was 31±0.3 H2O. Invasive hemodynamic monitoring was provided with Swan-Ganz catheters. Results. After building up the peak airway pressure, there was a 7.5—15 mm Hg blood pressure reduction (p<0.05) and 3.7 mm Hg right atrial and pulmonary artery wedge pressure elevations (p<0.05). Total pulmonary vascular resistance increased by 44% (p<0.05). Cardiac index reduced by 15% (p<0.05) due to decreased stroke volume. Coronary perfusion gradients and myocardial oxygen demand proportionally changed: r=0.62—0.77 (p<0.001). Oxygen transport significantly unchanged due to alveolar mobilization. After the latter, there was a close correlation between oxygen delivery and uptake (r=0.74; p<0.001). After alveolar mobilization, the changes in oxygen utilization coefficient and cardiac index had a significant correlation (r=0.43; p=0.02). After switching to artificial ventilation in the fitted mode, all the study parameters did not differ from the baseline values. Conclusion. The production of the peak airway pressure required for alveolar mobilization is attended by cardiac depression due to the right and left ventricular function determinant changes resulting in reductions in stroke volume and blood pressure. At the same time, there is imbalance between the conditions for coronary blood flow and the myocardial oxygen demand values. After artificial ventilation with the fitted positive end-expiratory pressure is switched, the mean hemodynamic values return to the baseline levels; however, there are signs of tense blood transport function. Key words: alveolar mobilization in cardiosurgical patients, hemodynamic effects of alveolar mobilization, recruitment maneuver.

Effect of PEEP on oxygen utilization coefficient in patients with acute respiratory distress syndrome

Objective To observe the effects of positive end-expiratory pressure(PEEP) on oxygen utiliza-tion coefficient in patients with acute respiratory distress syndrome(ARDS). Methods 28 ARDS patients with me-chanical ventilation were studied. Catheter of central vein was laid. Increment levels of PEEP(0,5, 10, 15 and 20cmH2O) were applied sequentially. Hemodynamics and oxygen metabolism parameters were measured and calcula-tion of O2 UC [O2 UC = (SaO2 -SvO2.)/SaO2] were carried out respectively. O2 UC in 30 normal subject groups were carried out. Results Arterial oxygen tension(PaO2) increased significantly(P 0.05) at PEEP 10cmH2O. At PEEP 15cmH2 O, O2UC and HR increased significantly (P < 0.05), but M BP reduced obviously(P < 0.05). Conclusions Too high PEEP can result in oxygen utilization coefficient of ARDS patient de-acend furthur, can not really correct oxygen difieiency condition in patients' organization cell. The optimal PEEP should be found, and blood capacity should be appropriately increased. Key words: Mechanical ventilation; Acute respiratory distress syndrome ; Oxygen utilization coefficient

Hemodynamics and Gas Exchange in Hemorrhagic Shock and Hyperbaric Oxygenation (Experimental Study)

Objective: to study the specific features of correction of hemodynamic and oxygen homeostasis in anemic animals exposed to hyperbaric oxygenation (HBO). Materials and methods. Experiments were made on 30 mongrel dogs in 2 series of experiments: 1) 15 animals under hemorrhagic shock (a control group); 2) 15 anemic animals exposed to HBO (pO=300 kPa; 60-min session). Cardiac index (CI), left ventricular stroke output index (LVSOI), myocardial tension index (MTI), heart rate, and blood pressure (BP) were determined in all the animals at the baseline, in 30- and 90-minute shock and after oxygenation. The Astrup micromethod was used to estimate oxygen tension (PaO2, PvO2) and content (CaO2, CvO2) in arterial and venous blood, arteriovenous (AV) oxygen difference, and tissue oxygen-utilization coefficient (TOUC). Results. In the untreated anemic animals, the reduction in central hemodynamic parameters (CI, LVSOI) was attended by the increase in MTI, suggesting significant impairments of metabolic processes in the myocardium and its diminished contractility. Oxygen homeostatic disorder was characterized by a noticeable increase in AV oxygen difference and TOUC with decreases in PvO2 and CvO2. After oxygenation (minute 5) there were positive changes in oxygen homeostatic parameters with the hemodynamic parameters being normalized, which contributed to the recovery of myocardial functional activity and to the diminution of manifestations of tissue hypoxia. Conclusion. HBO used in anemic animals promotes the recovery of hemodynamic homeostasis due to the activation of oxygen-dependent myocardial metabolic processes and the reduction of tissue hypoxic manifestations.

Energy metabolism and thermoregulation in reindeer during early postnatal development

The interrelations of body weight, energy metabolism, and physiological parameters in the early postnatal development of reindeer are analyzed. It is shown that the dependence of energy expenditure at rest and oxygen utilization coefficient on body weight is described by a parabolic equation of the second order. At high ambient temperatures during the summer season, energy metabolism in the young decreases, heat emission by respiration increases, and the temperature homeostasis is disturbed.

Elevated arterial base deficit in trauma patients: a marker of impaired oxygen utilization

Background: In trauma patients, the admission value of arterial base deficit stratifies injury severity, predicts complications, and is correlated with arterial lactate concentration. In theory, elevated base deficit and lactate concentrations after shock are related to oxygen transport imbalance at the cellular level. The purpose of this study was to test the hypothesis that an elevated base deficit in trauma patients is indicative of impaired systemic oxygen utilization and portends poor outcomes. Methods: This study was a retrospective analysis of a prospectively collected database. The study population included all patients admitted to the trauma intensive care unit at a Level 1 trauma center during a 12-month period who were monitored with a pulmonary artery catheter and serial measurements of lactate and base deficit, and who achieved a normal arterial lactate concentration (< 2.2 mmol/L) with resuscitation. The patients were divided into those who maintained a persistently high base deficit (≥ 4 mmol/L) and those who achieved a low base deficit (< 4 mmol/L) during resuscitation. Results: One-hundred patients (mortality 20%) were monitored with a pulmonary artery catheter and achieved a normal arterial lactate concentration. The mean age ± SD (SEM) of the group was 37 ± 17 years and the Injury Severity Score was 25 ± 11. Subgroup analysis revealed that patients with a persistently high base deficit (n = 26) had higher rates of multiple organ failure (35% versus 5%, p < 0.001) and death (50% versus 9%, p < 0.00001) compared with patients who achieved a low base deficit. Patients with a persistently high base deficit also had lower oxygen consumption (126 ± 40 mL/m 2 versus 156 ± 30 mL/m 2, p = 0.01 at 48 hours) and a lower oxygen utilization coefficient (0.20 ± 0.05 versus 0.24 ± 0.03, p = 0.01 at 48 hours) compared with patients with a low base deficit. At 48 hours, both oxygen consumption (r = −0.44, [r, correlation coefficient] p = 0.002) and oxygen utilization (r = −0.46, p = 0.001) had a significant negative correlation with base deficit. Conclusions: In trauma patients, a persistently high arterial base deficit is associated with altered oxygen utilization and an increased risk of multiple organ failure and mortality. Serial monitoring of base deficit may be useful in assessing the adequacy of oxygen transport and resuscitation.

An expert system based on causal knowledge: validation on post-cardiosurgical patients.

A new expert system for the analysis of post-cardiosurgical patients in Intensive Care Units is described, and a preliminary validation performed. The inference engine employs a hybrid reasoning method which integrates quantitative and qualitative simulation techniques in an original manner. The long-term knowledge consists of a causal network which reproduces the main relationships between physiological quantities involved in the course after cardiac surgery. Emphasis has been given to respiratory and metabolic, as well as cardiovascular quantities both in the systemic and pulmonary circulations. Preliminary system validation has been performed on a set of 40 cardiosurgical patients, previously classified either at normal-risk (17 patients) or at high-risk (23 patients) by means of statistical classification techniques. In most cases, predictions of the expert system substantially agree with those provided by the more traditional statistical method. The system, however, is also able to furnish detailed explanations on the possible physiological causes responsible for the patient status. In particular, simulation results indicate that a reduction in the cardiac index (19 cases) and an increase in the oxygen utilization coefficient (19 cases) are the most critical alterations in the high-risk patients. The system imputes the reduced cardiac index to a rise in total systemic resistance (15 high-risk patients), a decrease in cardiac strength (2 high-risk patients) or an insufficient filling volume of the systemic circulation (4 high-risk patients). Furthermore, in 6 high-risk patients the depressed cardiac outflow occurs with a reduction in the arterial oxygen content, mainly imputable to an insufficiency of blood hemoglobin content. Finally, two examples of the complete expert system explanatory capabilities are shown with reference to a pair of high-risk patients and discussed.

Continuous Dual Oximetry in Surgical Critical Care

Continuous dual oximetry combines pulse and venous oximetry to provide real-time information about oxygen utilization and pulmonary function. The authors undertook this study to examine the accuracy, utility, and limitations of the technique in surgical critical care. Twelve critically ill patients underwent placement of a modified pulmonary artery catheter and a pulse oximeter, both connected to an on-line computer. Paired blood gas and oximeter measurements were recorded every 4 to 6 hours, with a minimum of six sets per patient. Blood-gas-derived shunt fraction correlated well with oximeter-derived ventilation-perfusion index (r = 0.78, p less than 0.01). Further, the continuous oxygen extraction ratio (O2EI) and mixed venous oxygen saturation (SpvO2) correlated with the oxygen utilization coefficient (O2EI:r = 0.6, p less than 0.01; SpvO2, r = 0.76, p less than 0.01). Computer modeling of ventilation-perfusion index found limitations in accuracy that occur at high arterial oxygen saturations and when pulse oximetry errors are present. The authors conclude that (1) Continuous dual oximetry offers a significant advantage over routine blood gas analysis for monitoring cardiopulmonary parameters in critically ill patients because of its real-time display; (2) Oximeter-derived determinations parallel traditional parameters; and (3) The most significant technical limitations occur primarily at high arterial saturations and with pulse oximetry errors.

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.