'Multi-associations': predisposed to misinterpretation of peripheral tissue oxygenation and circulation in neonates

Interpretation of peripheral circulation in ill neonates is crucial but difficult. The aim was to analyse parameters potentially influencing peripheral oxygenation and circulation. In a prospective observational cohort study in 116 cardio-circulatory stable neonates, peripheral muscle near-infrared spectroscopy (NIRS) with venous occlusion was performed. Tissue oxygenation index (TOI), mixed venous oxygenation (SvO(2)), fractional oxygen extraction (FOE), fractional tissue oxygen extraction (FTOE), haemoglobin flow (Hbflow), oxygen delivery (DO(2)), oxygen consumption (VO(2)), and vascular resistance (VR) were assessed. Correlation coefficients between NIRS parameters and demographic parameters (gestational age, birth weight, age, actual weight, diameter of calf, subcutaneous adipose tissue), monitoring parameters (heart rate, arterial oxygen saturation (SaO(2)), mean blood pressure (MAP), core/peripheral temperature, central/peripheral capillary refill time) and laboratory parameters (haemoglobin concentration (Hb-blood), pCO(2)) were calculated. All demographic parameters except for Hbflow and DO(2) correlated with NIRS parameters. Heart rate correlated with TOI, SvO(2), VO(2) and VR. SaO(2) correlated with FOE/FTOE. MAP correlated with Hbflow, DO(2), VO(2) and VR. Core temperature correlated with FTOE. Peripheral temperature correlated with all NIRS parameters except VO(2). Hb-blood correlated with FOE and VR. pCO(2) levels correlated with TOI and SvO(2). The presence of multiple interdependent factors associated with peripheral oxygenation and circulation highlights the difficulty in interpreting NIRS data. Nevertheless, these findings have to be taken into account when analysing peripheral oxygenation and circulation data.     

Near-infrared and nuclear magnetic resonance spectroscopic assessment of tissue energetics in an isolated, perfused canine hind limb model of dysoxia

This controlled laboratory study examined the efficacy of near-infrared spectroscopy (NIRS) and 31P-nuclear magnetic resonance (NMR) spectroscopy in measuring regional tissue oxygenation in a isolated, perfused hind limb model of tissue dysoxia. Isolated hind limb perfusion was carried out in 20 mongrel dogs and oxygen delivery was varied by manipulating either hemoglobin concentration, oxygen saturation, or flow. Hind limbs from anesthetized mongrel dogs (n = 20) were separated and isolated perfusion performed. NIRS probes for recording relative O2 saturation of tissue hemoglobin (HbO2) and cytochrome a,a3 and NMR probes for measuring 31P-high energy phosphates were placed over the limb. Measurements of physiologic parameters, blood gases, lactate, NIRS values for HbO2 and cytochrome a,a3 redox state, and 31P-phosphate levels were recorded at set intervals throughout the experiment. Measures of tissue oxygen consumption (VO2) correlated with tissue oxygenation as measured by HbO2 and cytochrome a,a3 redox state (NIRS), as well as by 31P-high energy phosphate levels (NMR) throughout the experiment. Delivery-dependent tissue oxygenation was detected at a higher DO2 by NIRS than by VO2 or NMR. Tissue oxygenation as measured by NIRS and NMR shows excellent correlation with oxygen delivery in an isolated, perfused model of shock. NIRS may allow early detection of tissue dysoxia using rapid non-invasive techniques.     

Microvascular dysfunction and skeletal muscle oxygenation assessed by phase-modulation near-infrared spectroscopy in patients with septic shock

Objective Sepsis is now considered a disease of the microcirculation. Little is known about the various sepsis-induced changes responsible for microvascular dysfunction. We investigated human microvascular function, regulation, oxygenation, and cellular metabolism during subacute septic shock.Design and setting Prospective case-control study in a nine-bed polyvalent surgical ICU of a university hospital.Patients and participants A prospectively enrolled group of 26 patients (13 with septic shock, 13 nonseptic postsurgical patients) and 15 healthy volunteer controls.Measurements and results The absolute tissue hemoglobin concentrations (oxygenated hemoglobin and deoxyhemoglobin) were measured noninvasively in arterioles, capillaries, and venules by phase-modulation near-infrared spectroscopy in the human brachioradial muscle during a series of venous occlusions and an arterial occlusion (ischemia) induced by applying a pneumatic cuff. These measurements were used to calculate tissue blood volume, postischemic hemoglobin resaturation time, microvascular compliance, and O₂ consumption. Patients with sepsis had significantly higher tissue blood volume values and lower compliance than healthy controls. They also had longer postischemic hemoglobin resaturation times than the other two groups and blunted resaturation curves. O₂ consumption was lower in patients with sepsis than in healthy controls. In patients with septic shock cuff-induced ischemia left O₂ consumption unchanged, whereas in healthy volunteers it reduced O₂ consumption to values almost matching those of patients with septic shock.Conclusions These findings show that septic shock alters microvascular muscle function and regulation. Diminished local VO₂ presumably reflects maldistribution and faulty autoregulation of local blood flow.     

Influence of angular velocity on vastus lateralis and rectus femoris oxygenation dynamics during knee extension exercises

The purpose of this study was to investigate whether changes in angular velocity would alter vastus lateralis (VL) and rectus femoris (RF) oxygenation status during maximal isokinetic knee extension exercises. Eleven recreationally active male participants randomly performed ten maximal knee extensions at 30, 60, 120 and 240° s(-1). Tissue oxygenation index (TOI) and total haemoglobin concentration ([tHb]) were acquired from the VL and RF muscles by means of near-infrared spectroscopy (NIRS). Breath-by-breath pulmonary oxygen consumption (VO(2p)) was recorded throughout the tests. Peak torque and VO(2p) significantly decreased as a function of velocity (P<0·05). Interestingly, RF and VL TOI significantly increased as a function of velocity (P<0·05), whereas [tHb] significantly decreased as a function of velocity (P<0·05). A greater number of muscle fibre recruited at slow velocity, where the torque and VO(2p) were the highest, might explain the lower VL and RF TOI observed herein. Furthermore, the increase in local blood flow (suggested by [tHb] changes) during isokinetic knee extension exercises performed at slow angular velocity might have been induced by a higher intramuscular pressure during the contraction phases as well as a greater microcirculatory vasodilatation during relaxation phases. Implementing slow-velocity isokinetic exercises in rehabilitation or other training programmes could delay the short-term anoxia generated by such exercises and result in muscle metabolism enhancement.     

Dynamic near-infrared spectroscopy measurements in patients with severe sepsis

This study evaluated near-infrared spectroscopy (NIRS)-derived measurements in hemodynamically stable patients with severe sepsis, as compared with similar measurements in healthy age-matched volunteers. Prospective, preliminary, observational study in a surgical intensive care unit and clinical research center at a university health center. We enrolled 10 patients with severe sepsis and 9 healthy age-matched volunteers. For patients with severe sepsis, we obtained pulmonary artery catheter and laboratory values three times daily for 3 days and oxygen consumption values via metabolic cart once daily for 3 days. For healthy volunteers, we obtained all noninvasive measurements during a single session. We found lower values in patients with severe sepsis (versus healthy volunteers), in tissue oxygen saturation (StO2), in the StO2 recovery slope, in the tissue hemoglobin index, and in the total tissue hemoglobin increase on venous occlusion. Patients with severe sepsis had longer StO2 recovery times and lower NIRS-derived local oxygen consumption values versus healthy volunteers. In our preliminary study, NIRS provides a noninvasive continuous method to evaluate peripheral tissue oxygen metabolism in hemodynamically stable patients with severe sepsis. Further research is needed to demonstrate whether these values apply to broader populations of patients with systemic inflammatory response syndrome, sepsis, severe sepsis, and septic shock.     

The prognostic value of muscle StO<Subscript>2</Subscript> in septic patients

Objective: To quantify sepsis-induced alterations in changes in muscle tissue oxygenation (StO₂) after an ischemic challenge using near-infrared spectroscopy (NIRS), and to test the hypothesis that these alterations are related to outcome. Design Prospective study. Setting Thirty-one-bed, university hospital Department of Intensive Care. Patients Seventy-two patients with severe sepsis or septic shock, 18 hemodynamically stable, acutely ill patients without infection, and 18 healthy volunteers. Interventions Three-minute occlusion of the brachial artery using a cuff inflated 50 mmHg above systolic arterial pressure. Measurements and main results Thenar eminence StO₂ was measured continuously by NIRS before (StO₂baseline), during, and after the 3-min occlusion. Changes in StO₂ were assessed by the slope of increase in StO₂ during the first 14 s following the ischemic period and by the difference between the maximum StO₂ and StO₂baseline (Δ). The slope was lower in septic patients than in controls and volunteers [2.3 (1.3–3.6), 4.8 (3.5–6.0), and 4.7 (3.2–6.3) %/s, p < 0.001]. Δ was also significantly lower in septic patients than in the other groups. Slopes were lower in septic patients with than without shock [2.0 (1.2–2.9) vs 3.2 (1.8–4.5) %/s, p < 0.05]. In 52 septic patients, in whom the slope was obtained every 24 h for 48 h, slopes were higher in survivors than in non-survivors and tended to increase in survivors but not in non-survivors. Conclusions Altered recovery in StO₂ after an ischemic challenge is frequent in septic patients and more pronounced in the presence of shock. The presence and persistence of these alterations in the first 24 h of sepsis are associated with worse outcome. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The value of venous oximetry

PURPOSE OF REVIEW: Maintenance of adequate tissue oxygenation is an important task in intensive care units. In this context, venous oximetry by obtaining mixed venous oxygen saturation or central venous oxygen saturation has been discussed as useful monitoring parameters. This review discusses the physiology and clinical application of these parameters. RECENT FINDINGS: No study has so far demonstrated that venous oxygen saturation monitoring can reduce mortality in critically ill patients although length of stay has been decreased in cardiac surgery patients. Furthermore, pulmonary artery catheter usage does not affect outcome in critically ill patients. In contrast, early goal directed therapy for patients with severe sepsis or septic shock, which includes treatment goals for mean arterial pressure, central venous pressure, and central venous oxygen saturation, was able to increase survival in these patients. There is also evidence that central venous oxygen saturation measurement is beneficial in other types of shock. SUMMARY: Early goal directed therapy should be implemented in the initial resuscitation of septic patients. Measurement of central venous oxygen saturation can easily be applied in intensive care unit patients and offers a useful indirect indicator for the adequacy of tissue oxygenation.     

Skeletal muscle oxygen saturation does not estimate mixed venous oxygen saturation in patients with severe left heart failure and additional severe sepsis or septic shock

Introduction  

Low cardiac output states such as left heart failure are characterized by preserved oxygen extraction ratio, which is in contrast to severe sepsis. Near infrared spectroscopy (NIRS) allows noninvasive estimation of skeletal muscle tissue oxygenation (StO₂). The aim of the study was to determine the relationship between StO₂ and mixed venous oxygen saturation (SvO₂) in patients with severe left heart failure with or without additional severe sepsis or septic shock.     

Measurement of critical lower limb tissue hypoxia by coupling chemical and optical techniques

It has been a long-term goal to develop non-invasive methods that can detect critical levels of tissue hypoxia to help in the management of chronic lower limb ischaemia. In the present study, skeletal muscle oxygenation was measured using a new Clark-type TCPO2 [transcutaneous PO2 (partial pressure of O2)]/PCO2 (partial pressure of CO2) monitoring system and optical NIRS (near-infrared spectroscopy) at graded levels of hypoxaemia using a rabbit model (n=6). The TCPO2/PCO2 probe was placed on the shaved hindlimb to record SPO2 (skin PO2) and SPCO2 (skin PCO2) continuously. A pair of NIRS probes were placed on the limb to monitor HbO2 (oxyhaemoglobin) and Hb (deoxyhaemoglobin). Graded hypoxaemia was achieved by stepwise reductions of FiO2 (fraction of inspired O2) from 30% to 6%. Animals were allowed to recover after each episode of hypoxia at an FiO2 of 30% as indicated by normalized arterial blood PO2. There was a significant (P<0.05) decrease in SPO2 with all grades of hypoxaemia and no significant changes in SPCO2. There was a significant (P<0.05) increase in muscle Hb with all grades of hypoxaemia and a significant (P<0.05) decrease in HbO2 when FiO2 was below 15%. A significant correlation was found between the SPO2 and HbO2 (r=0.92, P<0.001) and both were significantly correlated with arterial blood PO2 (P<0.001). The new TCPO2/PCO2 system, in addition to its application for the assessment of conditions such as chronic venous insufficiency where alteration in skin oxygenation occurs solely, also has potential in conditions such as peripheral vascular disease where both skin and muscle oxygenation may be affected.     

Measurement of the liver tissue oxygenation by near-infrared spectroscopy

Objective To study the relation between the liver tissue oxygenation index (TOI), transcutaneously measured with spatially resolved spectroscopy (a new method of near-infrared spectroscopy or NIRS), the mixed venous oxygen saturation and the blood flow in the different parts of the splanchnic circulation in newborn piglets.Design Tissue oxygenation index of the liver was measured in six newborn piglets at 33°C, 35°C, 37°C and after a decrease in arterial carbon dioxide pressure (PaCO₂).Measurements Mixed venous oxygen saturation, blood gas analysis and peripheral oxygen saturation were measured at each step. Gastric, proximal jejunal, midgut, distal ileal, splenic and hepatic arterial blood flow were measured by injection of coloured microspheres into the left atrium. NIRS optodes were attached to the skin over the liver and TOI was calculated.Results No significant changes of TOI of the liver were seen during the increase in temperature or change in PaCO₂. TOI correlated well with mixed venous oxygen saturation (r=0.85), the mid-ileal blood flow (r=0.57) and the distal ileal blood flow (r=0.72).Conclusions Measurement of the TOI of the liver might be a non-invasive way to measure the distal ileal blood flow.     

丙酮酸乙酯对脓毒性休克犬氧代谢及组织灌注指标的影响

目的 探讨丙酮酸乙酯(EP)对脓毒性休克犬组织氧合及灌注指标的影响.方法 健康雄性杂种犬20只,用脂多糖(LPS)静脉注射复制犬脓毒性休克模型,随机分为对照组(n=8)和EP组(n=12).对照组只接受林格液复苏;EP组除给予林格液复苏外加EP,首剂0.05 g/kg,然后以0.05 g·kg-1·h-1的量持续泵入.脓毒性休克模型稳定后记为0 h,此后12 h内每2 h收集组织氧合及灌注指标:氧输送(DO2)、氧消耗(VO2)、血乳酸(Lac)水平、混合静脉血氧饱和度(S vO2)、尿量、胃黏膜pH值(pHi)、胃-动脉二氧化碳分压差(Pg-aCO2).结果 脓毒性休克模型建立后,DO2、VO2、S vO2、尿量明显下降(P均＜0.05),Lac、Pg-aCO2明显上升(P均＜0.05).EP组DO2逐渐回升,8 h后与对照组比较差异仍有统计学意义(P＜0.05);VO2也有增加趋势,但与对照组比较差异无统计学意义(P＞0.05);S vO2逐渐上升,10 h后已显著超过制模前水平,且与对照组比较差异有统计学意义(P＜0.05);Lac水平逐渐下降,8 h后与对照组比较差异有统计学意义(P＜0.05);尿量在8 h后明显增加,10 h后与对照组比较差异有统计学意义(P＜0.05);pHi在6 h后明显上升,且与对照组比较差异有统计学意义(P＜0.05);Pg-aCO2在休克后8 h其升高程度较对照组低(P＜0.05).结论 EP可以改善脓毒性休克犬氧代谢及组织灌注.     

Liver tissue oxygenation as measured by near-infrared spectroscopy in the critically ill child in correlation with central venous oxygen saturation

OBJECTIVE: To evaluate the clinical usefulness of near-infrared spatially resolved spectroscopic quantitative assessment of liver tissue oxygenation for simple, non-invasive estimation of global tissue oxygenation in critically ill neonates and children. DESIGN: Prospective observational clinical study. SETTING: A tertiary multidisciplinary neonatal and paediatric intensive care unit (23 beds). PATIENTS: One hundred neonates and children consecutively admitted to the paediatric intensive care unit. MEASUREMENTS AND RESULTS: Near-infrared spectroscopic single-point assessment of liver tissue oxygenation index (TOI(Liver)) was compared with global tissue oxygenation as measured by central venous oxygen saturation (SvO(2)) and derived haemodynamic parameters. Data were compared using linear and multiple regression analysis. Overall correlation between TOI(Liver)and SvO(2) was good ( r=0.72, p<0.0001). Multivariable regression revealed that SvO(2) alone explained 51% of the observed variance of TOI(Liver). However, our data demonstrated large inter-individual differences between SvO(2) and TOI(Liver) values. CONCLUSION: Near-infrared spatially resolved spectroscopic quantitative measurement of liver tissue oxygenation correlates well with SvO(2) in critically ill neonates and children. Large inter-individual SvO(2) to TOI(Liver) differences may prevent its use for non-invasive single-point estimation of global tissue oxygenation. Further clinical studies are required to validate the method with other regional and global haemodynamic parameters and to evaluate its clinical use for continuous non-invasive haemodynamic monitoring.     

Prefrontal cortex oxygenation during incremental exercise in chronic fatigue syndrome

This study examined the effects of maximal incremental exercise on cerebral oxygenation in chronic fatigue syndrome (CFS) subjects. Furthermore, we tested the hypothesis that CFS subjects have a reduced oxygen delivery to the brain during exercise. Six female CFS and eight control (CON) subjects (similar in height, weight, body mass index and physical activity level) performed an incremental cycle ergometer test to exhaustion, while changes in cerebral oxy-haemoglobin (HbO2), deoxy-haemoglobin (HHb), total blood volume (tHb = HbO2 + HHb) and O2 saturation [tissue oxygenation index (TOI), %)] was monitored in the left prefrontal lobe using a near-infrared spectrophotometer. Heart rate (HR) and rating of perceived exertion (RPE) were recorded at each workload throughout the test. Predicted VO2peak in CFS (1331 +/- 377 ml) subjects was significantly (P < or = 0.05) lower than the CON group (1990 +/- 332 ml), and CFS subjects achieved volitional exhaustion significantly faster (CFS: 351 +/- 224 s; CON: 715 +/- 176 s) at a lower power output (CFS: 100 +/- 39 W; CON: 163 +/- 34 W). CFS subjects also exhibited a significantly lower maximum HR (CFS: 154 +/- 13 bpm; CON: 186 +/- 11 bpm) and consistently reported a higher RPE at the same absolute workload when compared with CON subjects. Prefrontal cortex HbO2, HHb and tHb were significantly lower at maximal exercise in CFS versus CON, as was TOI during exercise and recovery. The CFS subjects exhibited significant exercise intolerance and reduced prefrontal oxygenation and tHb response when compared with CON subjects. These data suggest that the altered cerebral oxygenation and blood volume may contribute to the reduced exercise load in CFS, and supports the contention that CFS, in part, is mediated centrally.     

Cerebral oxygenation monitor during head-up and -down tilt using near-infrared spatially resolved spectroscopy

Reflectance near-infrared spectroscopy (NIRS) has become a suitable and easily manageable method to monitor cerebral oxygenation changes in presyncopal and syncopal symptoms caused by postural changing or standing. A new clinical tissue oxygenation monitor has been recently developed which measures absolute tissue haemoglobin saturation (Tissue Oxygenation Index, TOI) utilizing spatially resolved spectroscopy (SRS). The present study examined the effects of postural changes on cerebral oxygenation as reflected in SRS-NIRS findings. Cerebral oxyhaemoglobin (O2Hb), deoxyhaemoglobin (HHb), and the TOI were recorded from both sides of the forehead in five healthy male subjects (age range, 28-40 years) during 90 degrees head-up tilt (HUT) and -6 degrees head-down tilt (HDT). Three series of measurements were carried out on separate days. O2Hb was decreased during HUT. TOI was significantly lower in HUT than in the supine position (SUP). There was no significant change in TOI during HDT. A significant session effect was observed in the left forehead TOI during SUP, but not in the right. SRS-NIRS measurements confirmed sub-clinical alterations of cortical oxygenation during HUT. NIRS data from the left side of the forehead, which may vary with cognitive or emotional activation, were more variable than those from the right side.     

Changes in cerebral oxygenation and haemodynamics during postural blood pressure changes in patients with autonomic failure

Patients with autonomic failure suffer severe postural hypotension that may be associated with symptoms of cerebral hypoperfusion. This study utilized near-infrared spectroscopy (NIRS) to measure changes in cerebral oxygenation and haemodynamics during the head-up tilt table test in 18 patients with autonomic failure and 10 healthy age-matched volunteers. Heart rate, blood pressure (MAP), oxygen saturation, cerebral tissue oxygen index (TOI) and total cerebral haemoglobin concentration [HbT] were measured continuously. In patients with autonomic failure there was a mean (SD) reduction in MAP of 46.7 (26.5) mmHg (p < 0.005) associated with a reduction in TOI of 8.6 (6.2)% (p < 0.005) during the head-up tilt table test. In healthy volunteers mean (SD) MAP rose by 12.3 (8.0) mmHg (p < 0.005) and TOI fell by 2.6 (3.2)% (p < 0.05). There was a mean (SD) reduction in [HbT] of 3.09 (2.82) micromol l(-1) (p < 0.005) in patients, equivalent to a decrease in cerebral blood volume of 0.2 (0.18) ml/100 g. There were no changes in [HbT] in the healthy volunteers. Postural hypotension in patients with autonomic failure is associated with a substantial decrease in absolute cerebral oxygenation measured by NIRS and this might reflect a critical reduction in cerebral oxygen delivery.     

Venous oxygen saturation and lactate gradient from superior vena cava to pulmonary artery in patients with septic shock

Monitoring of central venous oxygen saturation (ScvO2) is considered comparable with mixed venous oxygen saturation (SvO2) in the initial resuscitation phase of septic shock. Our aim was to assess their agreement in septic shock in the intensive care unit setting and the effect of a potential difference in a computed parameter, namely, oxygen consumption (VO2). In addition, we sought for a central venous to pulmonary artery (PA) lactate gradient. We enrolled 37 patients with septic shock who were receiving noradrenaline infusions, and their attending physicians had placed a PA catheter for fluid management. Blood samples were drawn in succession from the superior vena cava, right atrium (RA), right ventricle, and PA. Hemodynamic and treatment parameters were monitored, and data were compared by correlation and Bland-Altman analysis. Mixed venous oxygen saturation was lower than ScvO2 (70.2% +/- 11.4% vs. 78.6% +/- 10.2%; P < 0.001), with a bias of -8.45% and 95% limits of agreement ranging from -20.23% to 3.33%. This difference correlated significantly to the noradrenaline infusion rate and the oxygen consumption and extraction ratio. These lower SvO2 values resulted in computed VO2v higher than the VO2cv (P < 0.001), with a bias of 104.97 mL min(-1) and 95% limits of agreement from -4.12 to 214.07 mL min(-1). Finally, lactate concentration was higher in the superior vena cava and RA than in the PA (2.42 +/- 3.15 and 2.35 +/- 3.16 vs. 2.17 +/- 3.19 mM; P < 0.01 for both comparisons). Thus, our data suggest that ScvO2 and SvO2 are not equivalent in intensive care unit patients with septic shock. Additionally, the substitution of ScvO2 for SvO2 in the calculation of VO2 produces unacceptably large errors. Finally, the decrease in lactate between RA and PA may support the hypothesis that the mixing of RA and coronary sinus blood is at least partially responsible for the difference between ScvO2 and SvO2.     

Evaluation of oxygen consumption and resting energy expenditure in critically ill patients with systemic inflammatory response syndrome.

OBJECTIVE: To determine whether oxygen consumption VO2), CO2 production, and resting energy expenditure (REE) in critically ill patients differ in varying grades of systemic inflammatory response syndrome (SIRS). DESIGN: Prospective, clinical study. SETTING: Intensive care unit at a university hospital. PATIENTS: Twenty-six critically ill patients requiring mechanical ventilation. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: A total of 100 metabolic measurements were performed. The grade of SIRS and the Acute Physiology and Chronic Health Evaluation II score were evaluated at the time of the metabolic cart study. VO2 and REE differed among the groups inadequate for SIRS (non-SIRS), with SIRS without infection (nonseptic SIRS), and with SIRS with infection (septic SIRS) (125 +/- 37 mL/min/m2 and 855 +/- 204 kcal/day/m2, 135 +/- 33 mL/min/m2 and 948 +/- 214 kcal/day/m2, and 166 +/- 55 mL/min/m2 and 1149 +/- 339 kcal/day/m2, respectively; p < .005). Patients with septic SIRS had higher VO2 and REE than patients with non-SIRS and nonseptic SIRS. CONCLUSION: VO2 and REE differ among groups of patients with non-SIRS, nonseptic SIRS, and septic SIRS. Patients with septic SIRS have higher VO2 and REE than patients with non-SIRS or nonseptic SIRS. The present study shows that classifying patients into three grades (non-SIRS, nonseptic SIRS, and septic SIRS) is a valid predictor of metabolic stress in critically ill patients.     

Experience with phenylephrine as a component of the pharmacologic support of septic shock

OBJECTIVE: To evaluate the use of the selective alpha 1-adrenergic receptor agonist phenylephrine in the hemodynamic support of patients with septic shock. DESIGN: Retrospective analysis of clinical use of phenylephrine. SETTING: Surgical ICU in a university hospital. PATIENTS: Thirteen patients with septic shock (diagnosed by defined criteria) requiring pharmacologic support for the treatment of hypotension. INTERVENTIONS AND MAIN RESULTS: All patients underwent invasive hemodynamic monitoring followed by volume resuscitation and inotropic support to reverse flow-dependent oxygen consumption and lactic acidosis. Patients with persistent hypotension (mean arterial pressure [MAP] less than 65 mm Hg) and vasodilation (systemic vascular resistance index [SVRI] less than 1500 dyne.sec/cm5.m2 received phenylephrine at iv infusion rates of 0.5 to 9 micrograms/kg.min to maintain MAP greater than 70 mm Hg. MAP, SVRI, left ventricular stroke work index, and stroke volume index were significantly (p less than .05) increased after phenylephrine administration and at the time of highest oxygen consumption (VO2). Cardiac index was unchanged initially but increased at the time of highest VO2 (p less than .05). Pulmonary artery occlusion pressure and heart rate were unchanged. Average baseline VO2 increased from 145 to 200 mL/min.m2 and oxygen delivery (DO2) increased from 447 to 597 mL/min.m2 during phenylephrine treatment (p less than .05). Blood lactate concentrations decreased and urine output increased significantly (p less than .05), while serum creatinine concentrations remained unchanged during phenylephrine therapy. CONCLUSIONS: Treatment with phenylephrine was associated with beneficial hemodynamic effects when used to maintain perfusion, while increasing DO2 and VO2 in patients with septic shock.     

Comparison of systemic oxygen delivery and uptake with NIR spectroscopy of brain during normovolemic hemodilution in the rabbit.

Incremental hyperoxic normovolemic hemodilution was utilized to progressively decrease oxygen delivery (DO2) in anesthetized rabbits. At decreasing DO2, we compared systemic responses related to the adequacy of DO2, i.e. mixed venous oxygen saturation (SvO2), oxygen consumption (VO2), and arterial lactate concentrations, to near infrared spectroscopy (NIRS) of the brain, a regional measure of intracellular oxygen availability. We sought concomitantly to define critical SvO2 and DO2, beyond which whole body VO2 begins to decline and arterial lactate concentrations increase. NIR Spectroscopy provided the means to test the hypothesis that systemic indicators of inadequate DO2 would not accurately reflect the oxygenation of a critical organ such as the brain. In thirteen rabbits anesthetized with fentanyl, paralyzed and artificially ventilated at an FIO2 of 0.60, hemodilution produced an early decrease in mixed venous oxygen saturation. When mixed venous oxygen saturation decreased below approximately 50%, arterial lactate concentrations began to increase significantly. Further decreases in oxygen delivery precipitated a decline in systemic VO2. Finally, NIRS revealed an increase in the reduction level of brain cytochrome a,a3 after systemic parameters of oxygen delivery had been altered. Analysis of the data indicated that falling SvO2 predicted inadequate DO2 to tissue during early hemodilution under narcotic/relaxant anesthesia and that the brain showed evidence of intracellular hypoxia only after systemic parameters such as SvO2 were affected markedly.