Neurally adjusted ventilatory assist (NAVA) improves patient-ventilator interaction during non-invasive ventilation delivered by face mask.

PURPOSE: To determine if, compared to pressure support (PS), neurally adjusted ventilatory assist (NAVA) reduces patient-ventilator asynchrony in intensive care patients undergoing noninvasive ventilation with an oronasal face mask. METHODS: In this prospective interventional study we compared patient-ventilator synchrony between PS (with ventilator settings determined by the clinician) and NAVA (with the level set so as to obtain the same maximal airway pressure as in PS). Two 20-min recordings of airway pressure, flow and electrical activity of the diaphragm during PS and NAVA were acquired in a randomized order. Trigger delay (T(d)), the patient's neural inspiratory time (T(in)), ventilator pressurization duration (T(iv)), inspiratory time in excess (T(iex)), number of asynchrony events per minute and asynchrony index (AI) were determined. RESULTS: The study included 13 patients, six with COPD, and two with mixed pulmonary disease. T(d) was reduced with NAVA: median 35 ms (IQR 31-53 ms) versus 181 ms (122-208 ms); p = 0.0002. NAVA reduced both premature and delayed cyclings in the majority of patients, but not the median T(iex) value. The total number of asynchrony events tended to be reduced with NAVA: 1.0 events/min (0.5-3.1 events/min) versus 4.4 events/min (0.9-12.1 events/min); p = 0.08. AI was lower with NAVA: 4.9 % (2.5-10.5 %) versus 15.8 % (5.5-49.6 %); p = 0.03. During NAVA, there were no ineffective efforts, or late or premature cyclings. PaO(2) and PaCO(2) were not different between ventilatory modes. CONCLUSION: Compared to PS, NAVA improved patient ventilator synchrony during noninvasive ventilation by reducing T(d) and AI. Moreover, with NAVA, ineffective efforts, and late and premature cyclings were absent.

Performance of an ICU ventilator and two turbin-based ventilators dedicated to non invasive ventilation (NIV) in simulated high inspiratory effort and rate: a NIV-bench-study.

INTRODUCTION. The role of turbine-based NIV ventilators (TBV) versus ICU ventilators with NIV mode activated (ICUV) to deliver NIV in case of severe respiratory failure remains debated. OBJECTIVES. To compare the response time and pressurization capacity of TBV and ICUV during simulated NIV with normal and increased respiratory demand, in condition of normal and obstructive respiratory mechanics. METHODS. In a two-chamber lung model, a ventilator simulated normal (P0.1 = 2 mbar, respiratory rate RR = 15/min) or increased (P0.1 = 6 mbar, RR = 25/min) respiratory demand. NIV was simulated by connecting the lung model (compliance 100 ml/mbar; resistance 5 or 20 l/mbar) to a dummy head equipped with a naso-buccal mask. Connections allowed intentional leaks (29 ± 5 % of insufflated volume). Ventilators to test: Servo-i (Maquet), V60 and Vision (Philips Respironics) were connected via a standard circuit to the mask. Applied pressure support levels (PSL) were 7 mbar for normal and 14 mbar for increased demand. Airway pressure and flow were measured in the ventilator circuit and in the simulated airway. Ventilator performance was assessed by determining trigger delay (Td, ms), pressure time product at 300 ms (PTP300, mbar s) and inspiratory tidal volume (VT, ml) and compared by three-way ANOVA for the effect of inspiratory effort, resistance and the ventilator. Differences between ventilators for each condition were tested by oneway ANOVA and contrast (JMP 8.0.1, p\0.05). RESULTS. Inspiratory demand and resistance had a significant effect throughout all comparisons. Ventilator data figure in Table 1 (normal demand) and 2 (increased demand): (a) different from Servo-i, (b) different from V60.CONCLUSION. In this NIV bench study, with leaks, trigger delay was shorter for TBV with normal respiratory demand. By contrast, it was shorter for ICUV when respiratory demand was high. ICUV afforded better pressurization (PTP 300) with increased demand and PSL, particularly with increased resistance. TBV provided a higher inspiratory VT (i.e., downstream from the leaks) with normal demand, and a significantly (although minimally) lower VT with increased demand and PSL.

Clinical characteristics and outcome of patients admitted to a medico- surgical ICU requiring non invasive ventilation (NIV) for hypercapnic respiratory failure

Introduction Because it decreases intubation rate and mortality, NIV has become first-line treatment in case of hypercapnic acute respiratory failure (HARF). Whether this approach is equally successful for all categories of HARF patients is however debated. We assessed if any clinical characteristics of HARF patients were associated with NIV intensity, success, and outcome, in order to identify prognostic factors. Methods Retrospective analysis of the clinical database (clinical information system and MDSi) of patients consecutively admitted to our medico-surgical ICU, presenting with HARF (defined as PaCO2 > 50 mmHg), and receiving NIV between May 2008 and December 2010. Demographic data, medical diagnoses (including documented chronic lung disease), reason for ICU hospitalization, recent surgical interventions, SAPS II and McCabe scores were extracted from the database. Total duration of NIV and the need for tracheal intubation during the 5 days following the first hypercapnia documentation, as well as ICU, hospital and one year mortality were recorded. Results are reported as median [IQR]. Comparisons were carried out with Chi2 or Kruskal-Wallis tests, p<0.05 (*). Results Two hundred and twenty patients were included. NIV successful patients received 16 [9-31] hours of NIV for up to 5 days. Fifty patients (22.7%) were intubated 11 [2-34] hours after HARF occurence, after having receiving 10 [5-21] hours of NIV. Intubation was correlated with increased ICU (18% vs. 6%, p<0.05) and hospital (42% vs. 31%, p>0.05) mortality. SAPS II score was related to increasing ICU (51 [29-74] vs. 23 [12-41]%, p<0.05), hospital (37% [20-59] vs 20% [12-37], p<0.05) and one year mortality (35% vs 20%, p<0.05). Surgical patients were less frequent among hospital fatalities (28.8% vs. 46.3%, p<0.05, RR 0.8 [0-6-0.9]). Nineteen patients (8.6%) died in the ICU, 73 (33.2%) during their hospital stay and 108 (49.1%) were dead one year after HARF. Conclusion The practice to start NIV in all suitable patients suffering from HARF is appropriate. NIV can safely and appropriately be used in patients suffering from HARF from an origin different from COPD exacerbation. Beside usual predictors of severity such as severity score (SAPS II) appear to be associated with increased mortality. Although ICU mortality was low in our patients, hospital and one year mortality were substantial. Surgical patients, although undergoing a similar ICU course, had a better hospital and one year outcome.

Magnetic pill tracking : a novel non-invasive tool for investigation of human digestive motility

RESUME Les améliorations méthodologiques des dernières décennies ont permis une meilleure compréhension de la motilité gastro-intestinale. Il manque toutefois une méthode qui permette de suivre la progression du chyme le long du tube gastro-intestinal. Pour permettre l'étude de la motilité de tout le tractus digestif humain, une nouvelle technique, peu invasive, a été élaborée au Département de Physiologie, en collaboration avec l'EPFL. Appelée "Magnet Tracking", la technique est basée sur la détection du champ magnétique généré par des matériaux ferromagnétiques avalés. A cet usage, une pilule magnétique, une matrice de capteurs et un logiciel ont été développés. L'objet de ce travail est de démontrer la faisabilité d'un examen de la motilité gastro-intestinale chez l'Homme par cette méthode. L'aimant est un cylindre (ø 6x7 mm, 0.2 cm3) protégé par une gaine de silicone. Le système de mesure est constitué d'une matrice de 4x4 capteurs et d'un ordinateur portable. Les capteurs fonctionnent sur l'effet Hall. Grâce à l'interface informatique, l'évolution de la position de l'aimant est suivie en temps réel à travers tout le tractus digestif. Sa position est exprimée en fonction du temps ou reproduite en 3-D sous forme d'une trajectoire. Différents programmes ont été crées pour analyser la dynamique des mouvements de l'aimant et caractériser la motilité digestive. Dix jeunes volontaires en bonne santé ont participé à l'étude. L'aimant a été avalé après une nuit de jeûne et son séjour intra digestif suivi pendant 2 jours consécutifs. Le temps moyen de mesure était de 34 heures. Chaque sujet a été examiné une fois sauf un qui a répété sept fois l'expérience. Les sujets restaient en décubitus dorsal, tranquilles et pouvaient interrompre la mesure s'ils le désiraient. Ils sont restés à jeûne le premier jour. L'évacuation de l'aimant a été contrôlée chez tous les sujets. Tous les sujets ont bien supporté l'examen. Le marqueur a pu être détecté de l'oesophage au rectum. La trajectoire ainsi constituée représente une conformation de l'anatomie digestive : une bonne superposition de celle-ci à l'anatomie est obtenue à partir des images de radiologie conventionnelle (CT-scan, lavement à la gastrografine). Les mouvements de l'aimant ont été caractérisés selon leur périodicité, leur amplitude ou leur vitesse pour chaque segment du tractus digestif. Ces informations physiologiques sont bien corrélées à celles obtenues par des méthodes établies d'étude de la motilité gastro-intestinale. Ce travail démontre la faisabilité d'un examen de la motilité gastro-intestinal chez l'Homme par la méthode de Magnet Tracking. La technique fournit les données anatomiques et permet d'analyser en temps réel la dynamique des mouvements du tube digestif. Cette méthode peu invasive ouvre d'intéressantes perspectives pour l'étude de motilité dans des conditions physiologiques et pathologiques. Des expériences visant à valider cette approche en tant que méthode clinique sont en voie de réalisation dans plusieurs centres en Suisse et à l'étranger. SUMMARY Methodological improvements realised over the last decades have permitted a better understanding of gastrointestinal motility. Nevertheless, a method allowing a continuous following of lumina' contents is still lacking. In order to study the human digestive tract motility, a new minimally invasive technique was developed at the Department of Physiology in collaboration with Swiss Federal Institute of Technology. The method is based on the detection of magnetic field generated by swallowed ferromagnetic materials. The aim of our work was to demonstrate the feasibility of this new approach to study the human gastrointestinal motility. The magnet used was a cylinder (ø6x7mm, 0.2 cm3) coated with silicon. The magnet tracking system consisted of a 4x4 matrix of sensors based on the Hall effect Signals from the sensors were digitised and sent to a laptop computer for processing and storage. Specific software was conceived to analyse in real time the progression of the magnet through the gastrointestinal tube. Ten young and healthy volunteers were enrolled in the study. After a fasting period of 12 hours, they swallowed the magnet. The pill was then tracked for two consecutive days for 34 hours on average. Each subject was studied once except one who was studied seven times. Every subject laid on his back for the entire experiment but could interrupt it at anytime. Evacuation of the magnet was controlled in all subjects. The examination was well tolerated. The pill could be followed from the esophagus to the rectum. The trajectory of the magnet represented a "mould" of the anatomy of the digestive tube: a good superimposition with radiological anatomy (gastrografin contrast and CT) was obtained. Movements of the magnet were characterized by periodicity, velocity, and amplitude of displacements for every segment of the digestive tract. The physiological information corresponded well to data from current methods of studying gastrointestinal motility. This work demonstrates the feasibility of the new approach in studies of human gastrointestinal motility. The technique allows to correlate in real time the dynamics of digestive movements with the anatomical data. This minimally invasive method is ready for studies of human gastrointestinal motility under physiological as well as pathological conditions. Studies aiming at validation of this new approach as a clinically relevant tool are being realised in several centres in Switzerland and abroad. Abstract: A new minimally invasive technique allowing for anatomical mapping and motility studies along the entire human digestive system is presented. The technique is based on continuous tracking of a small magnet progressing through the digestive tract. The coordinates of the magnet are calculated from signals recorded by 16 magnetic field sensors located over the abdomen. The magnet position, orientation and trajectory are displayed in real time. Ten young healthy volunteers were followed during 34 h. The technique was well tolerated and no complication was encountered, The information obtained was 3-D con-figuration of the digestive tract and dynamics of the magnet displacement (velocity, transit time, length estimation, rhythms). In the same individual, repea-ted examination gave very reproducible results. The anatomical and physiological information obtained corresponded well to data from current methods and imaging. This simple, minimally invasive technique permits examination of the entire digestive tract and is suitable for both research and clinical studies. In combination with other methods, it may represent a useful tool for studies of Cl motility with respect to normal and pathological conditions.

A non-invasive assessment of hepatic glycogen kinetics and post-absorptive gluconeogenesis in man.

A novel approach to the study of hepatic glycogen kinetics and fractional gluconeogenesis in vivo is described. Ten healthy female subjects were fed an iso-caloric diet containing 55% carbohydrate energy with a 13C abundance of 1.083 atom percent for a 3-day baseline period; then, a diet of similar composition, but providing carbohydrate with a 13C abundance of 1.093 atom percent was started and continued for 5 days. Resting respiratory gas exchanges, urinary nitrogen excretion, breath 13CO2 and plasma 13C glucose were measured every morning in the fasting state. The enrichment in 13C of hepatic glycogen was calculated from these measured data. 13C glycogen enrichment increased after switching to a 13C enriched carbohydrate diet, and was identical to the 13C enrichment of dietary carbohydrates after 3 days. The time required to renew 50% of hepatic glycogen, as determined from the kinetics of 13C glycogen enrichment, was 18.9 +/- 3.6 h. Fractional gluconeogenesis, as determined from the difference between the enrichments of glucose oxidized originating from hepatic glycogen and plasma glucose 13C was 50.8 +/- 5.3%. This non-invasive method will allow the study of hepatic glycogen metabolism in insulin-resistant patients.

Neurally Adjusted Ventilatory Assist (NAVA) improves the matching of diaphragmatic electrical activity and tidal volume in comparison to pressure support (PS) under non invasive ventilation

INTRODUCTION. Patient-ventilator asynchrony is a frequent issue in non invasivemechanical ventilation (NIV) and leaks at the patient-mask interface play a major role in itspathogenesis. NIV algorithms alleviate the deleterious impact of leaks and improve patient-ventilator interaction. Neurally adusted ventilatory assist (NAVA), a neurally triggered modethat avoids interferences between leaks and the usual pneumatic trigger, could further improvepatient-ventilator interaction in NIV patients.OBJECTIVES. To evaluate the feasibility ofNAVAin patients receiving a prophylactic postextubationNIV and to compare the respective impact ofPSVandNAVAwith and withoutNIValgorithm on patient-ventilator interaction.METHODS. Prospective study conducted in 16 beds adult critical care unit (ICU) in a tertiaryuniversity hospital. Over a 2 months period, were included 17 adult medical ICU patientsextubated for less than 2 h and in whom a prophylactic post-extubation NIV was indicated.Patients were randomly mechanically ventilated for 10 min with: PSV without NIV algorithm(PSV-NIV-), PSV with NIV algorithm (PSV-NIV+),NAVAwithout NIV algorithm (NAVANIV-)and NAVA with NIV algorithm (NAVA-NIV+). Breathing pattern descriptors, diaphragmelectrical activity, leaks volume, inspiratory trigger delay (Tdinsp), inspiratory time inexcess (Tiexcess) and the five main asynchronies were quantified. Asynchrony index (AI) andasynchrony index influenced by leaks (AIleaks) were computed.RESULTS. Peak inspiratory pressure and diaphragm electrical activity were similar in thefour conditions. With both PSV and NAVA, NIV algorithm significantly reduced the level ofleak (p\0.01). Tdinsp was not affected by NIV algorithm but was shorter in NAVA than inPSV (p\0.01). Tiexcess was shorter in NAVA and PSV-NIV+ than in PSV-NIV- (p\0.05).The prevalence of double triggering was significantly lower in PSV-NIV+ than in NAVANIV+.As compared to PSV,NAVAsignificantly reduced the prevalence of premature cyclingand late cycling while NIV algorithm did not influenced premature cycling. AI was not affectedby NIV algorithm but was significantly lower in NAVA than in PSV (p\0.05). AIleaks wasquasi null with NAVA and significantly lower than in PSV (p\0.05).CONCLUSIONS. NAVA is feasible in patients receiving a post-extubation prophylacticNIV. NAVA and NIV improve patient-ventilator synchrony in different manners. NAVANIV+offers the best patient-ventilator interaction. Clinical studies are required to assess thepotential clinical benefit of NAVA in patients receiving NIV.

Non-invasive monitoring of diaphragmatic timing by means of surface contact sensors: an experimental study in dogs

Background: Non-invasive monitoring of respiratory muscle function is an area of increasing research interest, resulting in the appearance of new monitoring devices, one of these being piezoelectric contact sensors. The present study was designed to test whether the use of piezoelectric contact (non-invasive) sensors could be useful in respiratory monitoring, in particular in measuring the timing of diaphragmatic contraction.Methods: Experiments were performed in an animal model: three pentobarbital anesthetized mongrel dogs. The motion of the thoracic cage was acquired by means of a piezoelectric contact sensor placed on the costal wall. This signal is compared with direct measurements of the diaphragmatic muscle length, made by sonomicrometry. Furthermore, to assess the diaphragmatic function other respiratory signals were acquired: respiratory airflow and transdiaphragmatic pressure. Diaphragm contraction time was estimated with these four signals. Using diaphragm length signal as reference, contraction times estimated with the other three signals were compared with the contraction time estimated with diaphragm length signal.Results: The contraction time estimated with the TM signal tends to give a reading 0.06 seconds lower than the measure made with the DL signal (-0.21 and 0.00 for FL and DP signals, respectively), with a standard deviation of 0.05 seconds (0.08 and 0.06 for FL and DP signals, respectively). Correlation coefficients indicated a close link between time contraction estimated with TM signal and contraction time estimated with DL signal (a Pearson correlation coefficient of 0.98, a reliability coefficient of 0.95, a slope of 1.01 and a Spearman's rank-order coefficient of 0.98). In general, correlation coefficients and mean and standard deviation of the difference were better in the inspiratory load respiratory test than in spontaneous ventilation tests.Conclusion: The technique presented in this work provides a non-invasive method to assess the timing of diaphragmatic contraction in canines, using a piezoelectric contact sensor placed on the costal wall.

Clinical characteristics and outcome of patients admitted to a medico-surgical ICU requiring non invasive ventilation (NIV) for hypercapnic respiratory failure

Introduction: Because it decreases intubation rate and mortality, NIV has become first-line treatment in case of hypercapnic respiratory failure (HRF). Whether this approach is equally successful for all categories of HRF patients is however debated. We assessed if any clinical characteristics of HRF patients were associated with NIV intensity, success, and outcome, in order to identify prognostic factors. Methods: Retrospective analysis of the clinical database (clinical information system and MDSi) of patients consecutively admitted to our medico-surgical ICU, presenting with HRF (defined as PaCO2 >50 mm Hg), and receiving NIV between January 2009 and December 2010. Demographic data, medical diagnoses (including documented chronic lung disease), reason for ICU hospitalization, recent surgical interventions, SAPS II and McCabe scores were extracted from the database. Total duration of NIV and the need for tracheal intubation during the 5 days following the first hypercapnia documentation, as well as ICU and hospital mortality were recorded. Results are reported as median [IQR]. Comparisons with Chi2 or Kruskal-Wallis tests, p <0.05 (*). Results: 164 patients were included, 45 (27.4%) of whom were intubated after 10 [2-34] hours, after having received 7 [2-19] hours of NIV. NIV successful patients received 15 [5-22] hours of NIV for up to 5 days. Intubation was correlated with increased ICU (20% vs. 3%, p <0.001) and hospital (46.7% vs. 30.2, p >0.05) mortality. Conclusions: A majority of patients requiring NIV for hypercapnic respiratory failure in our ICU have no diagnosed chronic pulmonary disease. These patients tend to have increased ICUand hospital mortality. The majority of patients were non-surgical, a feature correlated with increased hospital mortality. Beside usual predictors of severity such as age and SAPS II, absence of diagnosed chronic pulmonary disease and non-operative state appear to be associated with increased mortality. Further studies should explore whether these patients are indeed more prone to an adverse outcome and which therapeutic strategies might contribute to alter this course.

Diagnostic de la maladie coronarienne stable par FFR non invasive, mythe ou réalité [Diagnosis of stable coronary artery disease with non-invasive FFR: myth or reality?].

Decision to revascularize a patient with stable coronary artery disease should be based on the detection of myocardial ischemia. If this decision can be straightforward with significant stenosis or in non-significant stenosis, the decision with intermediate stenosis is far more difficult and require invasive measures of functional impact of coronary stenosis on maximal blood (flow fractional flow reserve=FFR). A recent computer based method has been developed and is able to measure FFR with data acquired during a standard coronary CT-scan (FFRcT). Two recent clinical studies (DeFACTO and DISCOVER-FLOW) show that diagnostic performance of FFRcT was associated with improved diagnostic accuracy versus standard coronary CT-scan for the detection of myocardial ischemia although FFRcT need further development.

IRM cardiaque: imagerie de référence dans le diagnostic de la myocardite aiguë [Cardiac magnetic resonance in acute myocarditis: a new non-invasive diagnostic gold standard?].

Acute myocarditis was until recently one of the most difficult diagnoses in cardiology. The spectrum of signs and symptoms is very wide, the usual non-invasive tests lack specificity and the myocardial biopsy is only performed in a minority of cases to confirm the diagnosis. Due to its unique ability to directly image myocardial necrosis, fibrosis and oedema, cardiac magnetic resonance (CMR) is now considered the primary tool for noninvasive assessment of patients with suspected myocarditis. CMR is also useful for monitoring disease activity under treatment. Myocarditis has been associated with the development of dilated cardiomyopathy; CMR could play a role in the follow-up of such cases to detect the progression toward a dilatative phenotype. Precise mapping of myocardial lesions with cardiac MRI is invaluable to guide myocardial biopsy and increase its diagnostic yield by improving sensitivity.

Self-paced Movement Intention Detection from Human Brain Signals: Invasive and Non-invasive EEG

Neural signatures of humans' movement intention can be exploited by future neuroprosthesis. We propose a method for detecting self-paced upper limb movement intention from brain signals acquired with both invasive and noninvasive methods. In the first study with scalp electroencephalograph (EEG) signals from healthy controls, we report single trial detection of movement intention using movement related potentials (MRPs) in a frequency range between 0.1 to 1 Hz. Movement intention can be detected above chance level (p<0.05) on average 460 ms before the movement onset with low detection rate during the on-movement intention period. Using intracranial EEG (iEEG) from one epileptic subject, we detect movement intention as early as 1500 ms before movement onset with accuracy above 90% using electrodes implanted in the bilateral supplementary motor area (SMA). The coherent results obtained with non-invasive and invasive method and its generalization capabilities across different days of recording, strengthened the theory that self-paced movement intention can be detected before movement initiation for the advancement in robot-assisted neurorehabilitation.

Non-invasive quantification of brain glycogen absolute concentration.

The only currently available method to measure brain glycogen in vivo is 13C NMR spectroscopy. Incorporation of 13C-labeled glucose (Glc) is necessary to allow glycogen measurement, but might be affected by turnover changes. Our aim was to measure glycogen absolute concentration in the rat brain by eliminating label turnover as variable. The approach is based on establishing an increased, constant 13C isotopic enrichment (IE). 13C-Glc infusion is then performed at the IE of brain glycogen. As glycogen IE cannot be assessed in vivo, we validated that it can be inferred from that of N-acetyl-aspartate IE in vivo: After [1-13C]-Glc ingestion, glycogen IE was 2.2 +/- 0.1 fold that of N-acetyl-aspartate (n = 11, R(2) = 0.77). After subsequent Glc infusion, glycogen IE equaled brain Glc IE (n = 6, paired t-test, p = 0.37), implying isotopic steady-state achievement and complete turnover of the glycogen molecule. Glycogen concentration measured in vivo by 13C NMR (mean +/- SD: 5.8 +/- 0.7 micromol/g) was in excellent agreement with that in vitro (6.4 +/- 0.6 micromol/g, n = 5). When insulin was administered, the stability of glycogen concentration was analogous to previous biochemical measurements implying that glycogen turnover is activated by insulin. We conclude that the entire glycogen molecule is turned over and that insulin activates glycogen turnover.

Imagerie cardiaque non invasive: apport spécifique en clinique des nouvelles modalités (II). Evaluation fonctionnelle [Cardiac imaging: specific clinical role of newly developed non invasive techniques. Part II: functional evaluation].

The non-invasive evaluation of myocardial ischemia is a priority in cardiology. The preferred initial non-invasive test is exercise ECG, because of its high accessibility and its low cost. Stress radionuclide myocardial perfusion imaging or stress echocardiography are now routinely performed, and new non-invasive techniques such as perfusion-MRI, dobutamine stress-MRI or 82rubidium perfusion PET have recently gained acceptance in clinical practice. In the same time, an increasing attention has been accorded to the concept of myocardial viability in the decisional processes in case of ischemic heart failure. In this indication, MRI with late enhancement after intravenous injection of gadolinium and 18F-FDG PET showed an excellent diagnostic accuracy. This article will present these new imaging modalities and their accepted indications.

Non invasive transcutaneous blood carboxyhemoglobine level: reliability in victims of carbon monoxide poisoning

Introduction: Carbon monoxide (CO) poisoning is one of the mostcommon causes of fatal poisoning. Symptoms of CO poisoning arenonspecific and the documentation of elevated carboxyhemoglobin(HbCO) levels in arterial blood sample is the only standard ofconfirming suspected exposure. The treatment of CO poisoning requiresnormobaric or hyperbaric oxygen therapy, according to the symptomsand HbCO levels. A new device, the Rad-57 pulse CO-oximeter allowsnoninvasive transcutaneous measurement of blood carboxyhemoglobinlevel (SpCO) by measurement of light wavelength absorptions.Methods: Prospective cohort study with a sample of patients, admittedbetween October 2008 - March 2009 and October 2009 - March 2010,in the emergency services (ES) of a Swiss regional hospital and aSwiss university hospital (Burn Center). In case of suspected COpoisoning, three successive noninvasive measurements wereperformed, simultaneously with one arterial blood HbCO test. A controlgroup includes patients admitted in the ES for other complaints (cardiacinsufficiency, respiratory distress, acute renal failure), but necessitatingarterial blood testing. Informed consent was obtained from all patients.The primary endpoint was to assess the agreement of themeasurements made by the Rad-57 (SpCO) and the blood levels(HbCO).Results: 50 patients were enrolled, among whom 32 were admittedfor suspected CO poisoning. Baseline demographic and clinicalcharacteristics of patients are presented in table 1. The median age was37.7 ans ± 11.8, 56% being male. Median laboratory carboxyhemoglobinlevels (HbCO) were 4.25% (95% IC 0.6-28.5) for intoxicated patientsand 1.8% (95% IC 1.0-5.3) for control patients. Only five patientspresented with HbCO levels >= 15%. The results disclose relatively faircorrelations between the SpCO levels obtained by the Rad-57 and thestandard HbCO, without any false negative results. However, theRad-57 tend to under-estimate the value of SpCO for patientsintoxicated HbCO levels >10% (fig. 1).Conclusion: Noninvasive transcutaneous measurement of bloodcarboxyhemoglobin level is easy to use. The correlation seems to becorrect for low to moderate levels (<15%). For higher values, weobserve a trend of the Rad-57 to under-estimate the HbCO levels. Apartfrom this potential limitation and a few cases of false-negative resultsdescribed in the literature, the Rad-57 may be useful for initial triageand diagnosis of CO.