1,721,075 research outputs found
Severe Sepsis and Septic Shock
No full textWe would like to address two potentially confusing issues concerning venous oxygen saturation (Svo2) as presented in Table 1 of the review by Angus and van der Poll (Aug. 29 issue).1 First, Table 1 suggests that Svo2 is raised in “sepsis, severe sepsis, and septic shock.” Depending on the timing of patient presentation and the type of sepsis and septic shock, Svo2 may indeed be elevated as a result of microcirculatory shunting or mitochondrial dysfunction. However, in septic shock, Svo2 can be depressed, reflecting an increase in the extraction of oxygen due to a decrease in cardiac output.2-4 Timely treatment to increase low Svo2 values in adults and children may improve outcomes2,3 and has therefore been added to current guidelines for the treatment of sepsis.5 Second, Table 1 indicates that higher Svo2 levels (70 to 80%) are normal in children.
As pediatric intensivists, we wish to point out that the opposite may be true in children with sepsis, since their cardiac output is more often decreased rather than increased.3,4 This effect compromises oxygen delivery and decreases Svo2 levels.
Is muscle StO2 an appropiate variable for investigating early compensatory tissue mechanisms under physiological and pathological conditions ?
No full textBecause StO2 measured during ischemia actually measures oxygen extraction and, therefore, reflects the tissue metabolic rate, the desaturation slope serves only as a comparative measurement. Nevertheless, some authors describe contrasting results on the effects of
desaturation rates measured with various NIRS devices in two forearm muscles in subjects undergoing volemic subtraction. We have mentioned only some reasons why, provided that studies are designed to give a wider range of information, NIRS can offer a useful insight into the early
compensatory tissue mechanisms under various physiological or pathological conditions. Instead of focusing on a single variable, StO2, future clinical studies should aim to investigate several other variables that are highly sensitive and specific and provide more meaningful findings
Assessing Skeletal Muscle Variations in Microvascular Pressure and Unstressed Blood Volume at the Bedside
No full textObjective: Quantitative NIRS measurements for MBV partitioning inside microvessels are of current physiologic and clinical interest. In this study, in healthy subjects, we sought new bedside NIRS variables for noninvasively measuring Vu and Pi changes.
Methods: Fifteen healthy subjects underwent graded venous congestion for MBV measurements with NIRS and the reference technique strain-gauge plethysmography. From DMBV we calcu- lated vascular compliance, blood flow, and new NIRS variables including Vu and Pit and Pcrit.
Results: Extrapolating MBV changes to 0 yielded Pit 4.19 ` 0.5 mmHg corresponding to a Vu of 2.53 ` 0.43 mL/ 100 mL T. The slope for MBV began steeper at values below 18 mmHg (Pcrit). Microvascular compliance measured with NIRS or with strain gauge gave matching results. The change in MBV depended on the oxyhemoglobin increase. No correlation was found between Vu and microvascular compliance or the overall DMBV. Cumulative pressure steps showed higher linearity in DMBV than that induced by discontinuous steps.
Conclusions: The new NIRS variables we report could be a practical bench-to-bedside tool to assess venous driving pressure for systemic perfusion and measure changes in Vu within the microvascular bed
Measurement of esophageal pressure. Possible limits to its clinical application
No full textNo abstract availabl
Lateral or posterior popliteal approach for sciatic nerve block: Difference is related to the anatomy
No full textTo the Editor:
March and colleagues (1) comparing single- and double-injection techniques for blockade of the sciatic nerve block via a posterior popliteal approach, concluded that double-nerve stimulation resulted in similar onset time and overall success rate when compared with that after single-nerve stimulation. In the double-injection group, they located both common peroneal and tibial nerve, whereas in the single-injection group they preferentially elicited foot inversion, interpreting this motor response to reflect needle proximity to both sciatic nerve trunks (2).
Our group has extensive experience providing regional anesthesia for outpatients undergoing foot surgery (3). We recently showed that, when using a lateral popliteal sciatic nerve block, a single injection targeting the tibial nerve is more effective than a single injection targeting the peroneal nerve and is also as effective as a double injection of both branches of the sciatic nerve (4).
We believe that results from March's work lend further support for our results, even when the different drugs and dosages used are taken into account. When a double-injection procedure is employed, the success rates after the lateral or posterior approaches are similar (respectively, 94% vs 87%) whereas a single-injection technique yields similar or even better results only if it is performed via a lateral approach and it is targeted at the tibial branch of the sciatic nerve (success rate: lateral 94% vs posterior 77%).
Considering the anatomy of the sciatic nerve at the popliteal level (5), targeting the tibial nerve via a lateral popliteal approach will likely result in injecting local anesthetic within the adventitia that envelops both branches of the sciatic nerve (4). On the other hand, the same single injection technique performed via a posterior approach will not assure that local anesthetic is injected within the tibial and peroneal common perineural space.
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COMPARISON OF TWO METHODS OF MEASURING FOREARM OXYGEN CONSUMPTION (VO2) BY NEAR INFRARED SPECTROSCOPY
No full textBedside Assessment of the Microvascular Venous Compartment in Cardiac Surgery Patients With Valvular Diseases Undergoing Cardiopulmonary Bypass
No full textOBJECTIVE: Blood volume reserve for venous return and the effects of cardiopulmonary bypass (CPB) on microvascular bed partitioning and blood flow were examined in patients with valvular diseases.
DESIGN: Prospective, consecutive, case-control study.
SETTING: Single university hospital.
PARTICIPANTS: The study comprised 20 adult cardiac surgery patients and 20 healthy volunteers.
INTERVENTIONS: Cardiovascular and microvascular variables were collected soon after the induction of anesthesia, after commencement of CPB, 20 minutes after separation from CPB, and in the intensive care unit.
MEASUREMENTS AND MAIN RESULTS: The unstressed and stressed volumes (Vu, Vs) and pressures therein (Pit, Ps) were measured in the brachioradial muscle with near-infrared spectroscopy, applying incremental venous occlusions. At the first time point, Vs and Pit showed lower and higher values, respectively, than those of control patients, but Vs increased with Vu during the study, whereas Pit remained unchanged. Fluid balance correlated with Pit (r = 0.83, p<0.001) and hemoglobin (r = 0.78, p = 0.004). A nonlinear regression was found between fluid balance and ΔVu (r = 0.90, p<0.001) [y = 1.85+37.43(-0.01×x)]. The Vu/Pit and Vs/Ps ratios were lower than those of the control patients. Blood flow correlated to Vs/Ps (r = 0.75, p<0.001). The time constant was lower than reference (p = 0.005) and increased 10 times after CPB.
CONCLUSIONS: Cardiac surgery patients have a limited blood volume reserve for venous return due to a reduced microvascular bed capacitance. This study demonstrated that during CPB a positive fluid balance induced an extravascular pressure increase and further reduced blood volume reserve
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