Arterial blood gases during exercise: Validity of transcutaneous measurements

OBJECTIVE: To investigate the validity of transcutaneous measurements of blood gas tensions for the assessment of partial arterial pressure of oxygen (PaO(2)) and carbon dioxide (PaCO(2)) during treadmill exercise. DESIGN: Experimental, self-controlled against a reference standard. SETTING: Lung function laboratory. PATIENTS: Eighty-one patients with various lung diseases. INTERVENTIONS: At rest and at symptom-limited peak exercise, puncture of the radial artery with concurrent transcutaneous measures of blood gases. MAIN OUTCOME MEASURES: Arterial blood samples were analyzed with a radiometer to measure PaO(2) and PaCO(2). A microgas apparatus was used to measure gas tensions transcutaneously. Values obtained transcutaneously (TcPO(2), TcPCO(2)) were compared with those obtained by blood sample. TcPO(2) was adjusted as close as possible to the PaO(2) obtained in the same conditions, with the correction factor of the apparatus. Values obtained transcutaneously were compared with those obtained by blood sample to establish the sensitivity and specificity of the noninvasive method. RESULTS: Mean differences +/- standard deviation between transcutaneous and arterial tension at peak exercise were 0.4 +/- 7.0mmHg and 2.1 +/- 3.3mmHg for PaO(2) and PaCO(2), respectively. The transcutaneous device enabled us to predict a decrease in PaO(2) (>or=2mmHg) from rest to exercise with a sensitivity of 92.1% and a specificity of 90% and an increase in PaCO(2) with a sensitivity of 88% and a specificity of 58.9%. CONCLUSIONS: Although transcutaneous measurement are sufficiently sensitive and specific to detect patients whose PaO(2) decreases during exercise, its precision is not sufficient for gas exchange calculations.     

动脉血压监测患儿的安全管理

[目的]探讨护理安全管理对减少有创血压监测并发症的影响.[方法]将2012年1月—6月没有开展安全护理模式的50例患儿设为对照组,2012年7月—12月开展安全护理模式的50例患儿设为观察组,比较两组患儿常见并发症的发生率.[结果]观察组并发症发生率明显低于对照组,两组比较差异有统计学意义（P＜0.05）.[结论]对有创血压监测的患儿采取安全管理护理,明显降低了并发症的发生率.     

Relationship between detrended fluctuation analysis and spectral analysis of heart-rate variability

The recently-introduced technique of detrended fluctuation analysis (DFA) for heart-rate variability appears to yield improved prognostic power in cardiovascular disease through calculation of the fractal scaling exponent alpha. However, the physiological meaning of alpha remains unclear. In DFA, the signal is segmented into lengths from 4 to 64 beats. For each segmentation length (n), the individual segments are cumulated, detrended and the sum of the squares (F2) of residuals calculated. Alpha is the slope of log(F) against log(n). We show mathematical equivalence between alpha calculated by DFA and by a novel alternative method using frequency-weighted power spectra. We show F2 (and thus alpha) can be obtained from a frequency-weighted power spectrum without DFA. To do this, we cumulate and detrend the Taylor series of individual Fourier components. F2 is found to depend on the relationship between the signal period and segment length. F2 can therefore be expressed in terms of frequency-weighted power spectra. From this, the alpha coefficient of DFA can then be described in power-spectral terms, which facilitates exploration of its physiological basis. We confirm these findings using samples from 20 healthy volunteers and 40 patients with heart failure.     

探讨监测新生儿低血糖对稳定血糖的临床意义

目的 探讨临床检测新生儿血糖变化,及时发现并纠正低血糖,对稳定血糖的临床意义。 方法 86例低血糖患儿中,经监测发现的44例为观察组,仅出现症状后进行监测的42例为对照组,两组治疗方法相同。 结果 新生儿低血糖稳定纠正平均时间:观察组为10.98±7.03h,对照组为17.84±9.26h,两组比较差异有显著性意义(t=3.89, P＜0.01)。 结论 积极监测血糖的变化有助于早期纠正低血糖,可以减少低血糖带来的损害。     

Application of heart-rate variability in patients undergoing weaning from mechanical ventilation

Introduction

The process of weaning may impose cardiopulmonary stress on ventilated patients. Heart-rate variability (HRV), a noninvasive tool to characterize autonomic function and cardiorespiratory interaction, may be a promising modality to assess patient capability during the weaning process. We aimed to evaluate the association between HRV change and weaning outcomes in critically ill patients.

Methods

This study included 101 consecutive patients recovering from acute respiratory failure. Frequency-domain analysis, including very low frequency, low frequency, high frequency, and total power of HRV was assessed during a 1-hour spontaneous breathing trial (SBT) through a T-piece and after extubation after successful SBT.

Results

Of 101 patients, 24 (24%) had SBT failure, and HRV analysis in these patients showed a significant decrease in total power (P = 0.003); 77 patients passed SBT and were extubated, but 13 (17%) of them required reintubation within 72 hours. In successfully extubated patients, very low frequency and total power from SBT to postextubation significantly increased (P = 0.003 and P = 0.004, respectively). Instead, patients with extubation failure were unable to increase HRV after extubation.

Conclusions

HRV responses differ between patients with different weaning outcomes. Measuring HRV change during the weaning process may help clinicians to predict weaning results and, in the end, to improve patient care and outcome.     

Compliance of a microstructured,soft sampling device for transcutaneous blood gas monitoring

Premature neonates are too small for repeated blood sampling, but still require precise monitoring of blood gas levels. The standard method therefore involves transcutaneous blood gas monitoring (TBM), i.e. analyzing gas that permeates the skin. The method involves skin heating and requires frequent relocation of a rigid sensor that is adhesively mounted to the skin, which makes the monitoring intermittent and can cause tissue damage. To mitigate this, this paper introduces a TBM concept that replaces the sensor with a small, non-adhesive, flexible, polydimethylsiloxane patch, routing the gases through skin-facing microchannels laid out in various configurations, to an external optical emission spectroscopy system (OES). As the OES depends on a constant flow of gas, we have investigated the effects external loads, both vertical and with a transverse component, have on the aerodynamic resistance of the patches. The experiments show that patches with 200 μm wide channels can withstand uniformly distributed forces up to 25 N with a change in aerodynamic resistance of about 0.01 mbar per sccm per newton. In subsequent measurements, the proof of concept (POC) TBM system showed a strong and fast blood gas signal that was unaffected by all likely loads in the intended application. Moreover, the rise time of the signal is shown to be inversely proportional to the aerodynamic resistance, and the signal strength to be proportional to the skin area exposed to the microchannels. With these results, the POC TBM system is a viable first step towards truly continuous blood gas monitoring of prematurely born children.

Replacing rigid transcutaneous blood gas monitoring sensors with microstructured silicone patches, makes the proof of concept system developed and evaluated here a viable first step towards truly continuous measurement on premature neonates.     

Preamputation evaluation of limb perfusion with laser Doppler imaging and transcutaneous gases

We studied 31 subjects with severe leg ischemia and 29 age-matched nonischemic control subjects to compare preamputation assessments of leg ischemia using laser Doppler imaging (LDI), transcutaneous partial pressure of oxygen (TcPO(2)), and transcutaneous partial pressure of carbon dioxide (TcPCO(2)). TcPO(2) and TcPCO(2) were evaluated with Novametrix Medical Systems, Inc, monitors (Wallingford, Connecticut) and perfusion (flux) of skin topically heated to 44 degrees C, and adjacent nonheated areas were evaluated with a Moor Laser Doppler Imager (Moor Instruments, Ltd; Devon, England). LDI flux of heated areas, its ratio to nonheated areas, and TcPO(2) (not TcPCO(2)) were lower in ischemic subjects than in control subjects. LDI flux ratio performed better than TcPO(2) in identifying ischemia, with fewer false positive and false negative results. Moreover, LDI flux of heated skin detected a proximal to a distal gradient of perfusion in ischemic subjects, while TcPO(2) did not. LDI was superior to TcPO(2) in discriminating correctly between ischemic and nonischemic skin. The results suggest that an LDI ratio below 5 indicates nonviable skin.     

Continuous monitoring of blood gases during hypercapnia in a patient with severe acute lung failure

We report about our first experiences with a new device for continuous intra-arterial monitoring of blood gases in a patient with severe acute respiratory failure. This device facilitated continuous monitoring of PaO₂, PaCO₂ and pH while weaning the patient from extracorporeal membrane oxygenation (ECMO). Although sufficient oxygenation at FIO₂ 0.45 could be achieved after disconnection from ECMO, carbon dioxide elimination remained inadequate and resulted in severe respiratory acidosis. Within six hours, PaCO₂ increased to 95 mmHg. Continuous monitoring of pH and PaCO₂ helped to monitor CO₂ retention and assisted the decision making process for reinstitution of ECMO.     

产时母体脐部血糖与新生儿生后48小时血糖监测的相关性研究

目的 探讨产时母体脐部血糖与新生儿48小时血糖动态变化的相关性,为临床早期干预提供依据 方法 选取2017年2月～2017年12月于上海市第一人民医院产科阴道分娩的200例孕妇及其分娩新生儿为对象,孕妇产时母体脐部血糖及新生儿出生后1h、3h、6h、12h、24h和48h这6个时间段的血糖进行监测,研究新生儿血糖48小时的动态变化及与母体脐部血糖的相关性。结果 新生儿出生3小时血糖妊娠糖尿病孕妇组新生儿血糖显著低于正常孕妇组新生儿血糖（P＜0.05） 差异有统计学意义 ;母体脐部血糖与新生儿血糖在新生儿出生1小时、3小时血糖呈正相关（P＜0.05）,差异有统计学意义 结论 1、重视新生儿血糖监测,特别是妊娠糖尿病孕妇分娩新生儿3h的血糖监测,及早发现低血糖情况并及时干预 2、母体脐部血糖对新生儿生后3小时内血糖水平有预测的价值     

Halothane interference with transcutaneous oxygen monitoring: in vivo and in vitro

The effect of halothane on electrodes covered with polypropylene and FEP teflon membranes, used for monitoring transcutaneous oxygen tension, was compared in vitro and in patients anesthetized with halothane. In vitro experiments with halothane showed a false increase in PO2 measured by the electrode covered with polypropylene membrane while there was no increase in PO2 values recorded by an electrode covered with teflon membrane. In 15 patients anesthetized with halothane, no interference with transcutaneous oxygen measurement was seen with electrodes covered with either a polypropylene or FEP teflon membrane.     

Changes in heart-rate variability of survivors of nasopharyngeal cancer during Tai Chi Qigong practice

[Purpose] To explore the changes in heart-rate variability (HRV) of survivors of nasopharyngeal cancer (NPC) before, during, and after a Tai Chi (TC) Qigong exercise. [Subjects and Methods] Eleven survivors of NPC participated voluntarily in the study. The heart rate of each participant was measured continuously for 1 minute before the TC Qigong intervention, during the 5-minute TC Qigong intervention, and for 1 minute after the intervention, using a Polar heart-rate monitor. Spectral HRV was expressed in terms of normalised low frequency (LF) power, normalised high frequency (HF) power, and the low frequency/high frequency (LF/HF) power ratio. [Results] Both the LF-power and the HF-power components had significant time effects. However, the time effect of the LF/HF power ratio was not significant. Post hoc contrast analysis revealed a significant decrease in LF power and a concomitant increase in HF power during the 4th minute and 5th minute of the TC Qigong exercise. [Conclusion] Five minutes of TC Qigong exercise was found to improve HRV by increasing HF power and decreasing LF power, but these effects were transient. TC Qigong might be an appropriate exercise for improving the ANS function and psychological and cardiac health of survivors of NPC.Key words: Autonomic nervous system, Mind-body exercise, Head-and-neck cancer     

Validation of oxygen saturation monitoring in neonates.

BACKGROUND: Pulse oximetry is commonly used to monitor oxygenation in neonates, but cannot detect variations in hemoglobin. Venous and arterial oxygen saturations are rarely monitored. Few data are available to validate measurements of oxygen saturation in neonates (venous, arterial, or pulse oximetric). Purpose To validate oxygen saturation displayed on clinical monitors against analyses (with correction for fetal hemoglobin) of blood samples from neonates and to present the oxyhemoglobin dissociation curve for neonates. METHOD: Seventy-eight neonates, 25 to 38 weeks' gestational age, had 660 arterial and 111 venous blood samples collected for analysis. RESULTS: The mean difference between oxygen saturation and oxyhemoglobin level was 3% (SD 1.0) in arterial blood and 3% (SD 1.1) in venous blood. The mean difference between arterial oxygen saturation displayed on the monitor and oxyhemoglobin in arterial blood samples was 2% (SD 2.0); between venous oxygen saturation displayed on the monitor and oxyhemoglobin in venous blood samples it was 3% (SD 2.1) and between oxygen saturation as determined by pulse oximetry and oxyhemoglobin in arterial blood samples it was 2.5% (SD 3.1). At a Pao(2) of 50 to 75 mm Hg on the oxyhemoglobin dissociation curve, oxyhemoglobin in arterial blood samples was from 92% to 95%; oxygen saturation was from 95% to 98% in arterial blood samples, from 94% to 97% on the monitor, and from 95% to 97% according to pulse oximetry. CONCLUSIONS: The safety limits for pulse oximeters are higher and narrower in neonates (95%-97%) than in adults, and clinical guidelines for neonates may require modification.     

Continuous conjunctival and transcutaneous oxygen tension monitoring during resuscitation in a patient

Conjunctival (PcjO2) and transcutaneous (PtcO2) oxygen tensions were serially measured in a patient with multiple stab wounds. Even though blood pressure was normal, severe hypovolemia due to hemorrhage was detected in the emergency department by abnormally low PcjO2/PaO2 and PtcO2/PaO2 ratios. The adequacy of resuscitation was established by return of these ratios to normal values. The conjunctival sensor stabilized more rapidly than the transcutaneous sensor and is of greater utility in the emergency setting. It was found that conjunctival and transcutaneous oxygen sensors can play an important role in monitoring clinical state and resuscitation of trauma patients.     

The effect of nonnutritive sucking on transcutaneous oxygen tension in noncrying, preterm neonates.

The relationship between transcutaneous oxygen tension (tcpO_2:) and sucking opportunities in noncrying, preterm neonates was investigated. Twenty-six measurements of nonnutritive sucking and its relationship to tcpO₂ were collected on 11 neonates who were monitored continuously for tcpO₂. Of the 26, 10 sets of measurements were recorded on 6 neonates receiving assisted ventilation, and 16 were recorded on 4 neonates breathing room air. One neonate was measured one time on assisted ventilation and two times breathing room air. The design consisted of three 8-minute time periods: pretreatment, treatment (sucking opportunities). and posttreatment. There was a significant relationship between the pretreatment-treatment and treatment-posttreatment tcpO₂ levels (both at p < .01). These results suggest that sucking facilitates more adequate oxygenation in noncrying, preterm neonates.