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Biomedical subjects

Markus Weiss

Publications and source records attributed to Markus Weiss.

35 records · Page 2Linked to original sources
PubMed2003

Nitrous oxide does not affect automated air tonometry in children.

PURPOSE: To evaluate the effects of nitrous oxide on automated air tonometry in the clinical setting. MATERIAL AND METHODS: With approval of the Hospital Ethical Committee and after obtaining informed parental consent, an 8-F tonometry catheter was inserted orogastrically in ten children aged one to three years scheduled for elective surgery with combined regional and general anesthesia. A standardized general anesthesia technique with tracheal intubation was used in all patients and consisted of sevoflurane in oxygen/nitrous oxide (30%/70%; n = 5 patients) or in oxygen/air (FIO(2) 0.3; n = 5 patients). After obtaining steady state gastric CO(2) values (PrCO(2)), fresh gas mixtures were rapidly changed from oxygen/nitrous oxide to oxygen/air (A) or vice versa (B). In addition, balloon pressures were recorded using a pressure transducer. Measurements were performed at intervals of ten minutes with recording of balloon pressures, end-tidal CO(2) (PETCO(2)) and PrCO(2) values. Pr-ETCO(2)-gap were calculated to eliminate influences of changes in PaCO(2). RESULTS: Changing the fresh gas mixture from N(2)O/O(2) to O(2)/air resulted in a decrease of balloon pressure of -10.4% (113.4 +/- 14.7 mmHg to 101.6 +/- 25.0 mmHg). Changing the fresh gas mixture from O(2)/air to N(2)O/O(2) resulted in an increase of balloon pressures of 6.4% (107.6 +/- 19.3 mmHg to 114.0 +/- 20.3 mmHg). During both fresh gas exchange experiments no significant changes (> 0.2 kPa) in calculated Pr-ETCO(2)-gaps were observed. CONCLUSIONS: Based on our in vivo data, nitrous oxide during general anesthesia can be used with automated air tonometry and does not affect air tonometric PrCO(2) reading in clinical practice.

Anesthesia, General↗
PubMed2003

Arterial fast bolus flush systems used routinely in neonates and infants cause retrograde embolization of flush solution into the central arterial and cerebral circulation.

PURPOSE: To evaluate the risk of retrograde embolization of flush solution in neonates and infants with routinely used electronic syringe pumps and infusion bag pump flush systems. METHODS: With hospital Ethical Committee approval we studied intubated neonates and infants with a 24-GA radial arterial cannula. Fast flush boluses were delivered from the infusion bag pump flush system by opening the flow regulating device for two seconds at bag pump manometre pressures of 100, 200 and 300 mmHg. In the syringe pump flush system, fast flush bolus volumes of 0.5, 1.0, 1.5 and 2.0 mL were programmed on the electronic syringe pump and released by opening the flow regulating device for two seconds. A 12-MHz ultrasonic probe placed in the jugular fossa was used to detect white bubbles indicating retrograde embolization of flush solution into the ipsilateral subclavian and common carotid artery. RESULTS: Sixteen patients, aged from 1-105 days (median 22 days) were studied. In all patients retrograde embolization into the subclavian artery was detected at syringe pump bolus volumes of 0.5-1.5 mL and at 100-200 mmHg bag pump pressure. In nine of the 16 patients a positive signal was detected in the common carotid artery with 1.5-2.0 mL syringe pump bolus volumes and at 200-300 mmHg bag pump pressure. CONCLUSIONS: In neonates and infants, the standard practice of arterial fast bolus flushing using syringe pump and bag pump flush systems causes retrograde embolization of flush solution into the central arterial and even into the cerebral circulation. The mandatory limitation of fast flush bolus volumes and manometre pressures is urgent in order to reduce retrograde embolization of flush solution and the associated risks in these small patients.

Catheters, Indwelling↗
PubMed2003

Video-enhanced visualization of the larynx and intubation with the Bullard laryngoscope--equipment report.

PURPOSE: A simple technical solution is presented to provide video transmission from the tip of a Bullard laryngoscope to a bedside video display, while the operator is still able to look through the viewing ocular of the Bullard laryngoscope during tracheal intubation. EQUIPMENT: This is achieved by insertion of an ultrathin fibreoptic video-endoscopic system into the working channel of the Bullard laryngoscope. Thereby the view from the distal blade tip is transmitted to a bedside monitor, without interfering with the use of the Bullards laryngoscope's original eyepiece. The presented technical solution allows video transmission without considerable additional weight normally associated with attaching video endoscopy cameras, light and camera cables to endoscopic devices. Thus, the Bullard laryngoscope remains lightweight and easy to maneuver. A screw-threaded adapter with a side-port is proposed to prevent displacement of the fibreoptic cable while still allowing application of oxygen. CONCLUSION: Experience and skills with tracheal intubation using the presented video-enhanced Bullard laryngoscope can be achieved in the originally intended way, while the supervisor or attending viewers can follow the tracheal intubation procedure on the video display.

Computer Terminals↗
PubMed2003

Video-optic cable endoscopy forceps.

We present a video-endoscopic technology for foreign body extractions with forceps. This can easily be followed and is recordable on video monitor in excellent quality. Instead of a rigid rod lens telescope, a fiberoptic video endoscope is inserted into the optical channel of a bronchoscopic forceps. This keeps the endoscopic device lightweight and easily maneuverable in different angles. The principle can be applied to other rigid diagnostic and therapeutic endoscopic equipment and represents a potential alternative technology to the use of cameras attached to rigid telescopes.

Endoscopes↗
PubMed2003

Measurement of cerebral oxygenation state in anaesthetized children using the INVOS 5100 cerebral oximeter.

BACKGROUND: Near-infrared spectroscopy is a developing technique for monitoring cerebral oxygenation during anaesthesia. The aim of this study was to evaluate absolute values of cerebral oxygenation during stable anaesthesia conditions in otherwise healthy children using the recently introduced INVOS 5100 cerebral oximeter with a paediatric and adult sensor and to compare them with values obtained from the NIRO 300 oximeter. METHODS: Thirty paediatric surgical patients (aged 0.23-15.97 years) were studied during general anaesthesia with tracheal intubation and controlled ventilation. Comparative measurements of cerebral oxygenation were performed on the forehead with two probes within 10 min under stable cardiorespiratory and anaesthesia conditions. Cerebral oxygenation values (rSO2) obtained from the paediatric and adult INVOS 5100 sensors were compared with the tissue oxygenation index (TOI) obtained from the NIRO 300 cerebral oximeter using 4- and 5-cm emitter-detector separation. RESULTS: Cerebral rSO2 values and the TOI values both showed a large range of cerebral oxygenation in the children studied (rSO2: 59-95%, TOI: 48-85%). Cerebral rSO2 values measured by the INVOS 5100, particularly with the paediatric sensor, were significantly higher than the TOI values obtained from the NIRO 300 (P < 0.0001). Agreement between the INVOS and NIRO oximeter was poor. CONCLUSION: The large range and the poor agreement of cerebral oxygenation values between the two oximeters makes it difficult to define a normal value. Cerebral oxygenation readings by these monitors, based on one single point measurement during anaesthesia, should be viewed with caution. Actually, there may be little indication for routine use of such monitoring during general anaesthesia.

Adolescent↗
PubMed2003

Evaluation of a new combined SpO2/PtcCO2 sensor in anaesthetized paediatric patients.

BACKGROUND: The recently introduced TOSCA monitor (Linde Medical Sensors AG, Basel, Switzerland) combines pulse oximetry (SpO2) and transcutaneous PCO2 (PtcCO2) monitoring in a single ear sensor. The aim of the present study was to evaluate accuracy of the TOSCA monitor to estimate SaO2 and PaCO2 in anaesthetized children. METHODS: With approval of the hospital ethical committee and after obtaining informed parental consent, the TOSCA sensor was attached to one ear lobe of anaesthetized children in whom arterial access was established for cardiac catheterization or invasive blood pressure monitoring. SpO and PtcCO2 as well as SpO and PECO2 values from the anaesthesia monitoring (AS5; Datex-Ohmeda, Helsinki, Finland) were compared with SaO2 and PaCO2 values from arterial blood gas analysis. Corresponding data were compared using Bland Altman bias analysis. RESULTS: A total of 111 blood samples were taken from 60 children (median age: 4.41 years; 0.35-16.13 years). SaO2 values ranged from 63 to 100% (median: 98.7%), PaCO2 ranged from 3.8 to 7.3 kPa (median: 4.6 kPa). Mean difference (+/-2 sd) between PaCO2 and PtcCO2 was -0.035 kPa (+/-0.74 kPa), between PaCO2 and PECO2 0.002 kPa (0.73 kPa), respectively (1 kPa = 7.3 mmHg). Bias and precision between SaO2 and SpO was -0.63% (+/-2.77%) and 0.13% (+/-4.52%) between SaO2 and SpO. CONCLUSIONS: In anaesthetized children, the TOSCA ear sensor allows estimation of SaO2 and PaCO2, comparable in accuracy to endtidal capnometry and finger pulse oximetry. This makes the TOSCA monitor a helpful add-on to respiratory monitoring in anaesthetized children, in situations, in which endtidal capnometry is unreliable or difficult to establish.

Adolescent↗
PubMed2003

Changes in red blood cell integrity related to infusion pumps: a comparison of three different pump mechanisms.

OBJECTIVE: To study the effects of three different infusion pumps on red blood cell (RBC) integrity. SETTING: Laboratory. INTERVENTIONS: Transfusion of packed RBCs using three different pumps (syringe pump, conventional peristaltic pump, and a new volumetric pump with shuttle mechanism). Flow rate was set at 20 mL/hr and duration was 2.5 hrs, simulating a neonatal transfusion. Experiments were repeated in each pump with eight different units of packed RBCs. MEASUREMENTS AND MAIN RESULTS: Plasma hemoglobin, potassium, lactate dehydrogenase, bilirubin, and osmotic fragility were assessed before and after transfusion. There was a significant degree of hemolysis in the RBC bags before transfusion (mean +/- sd for plasma hemoglobin, 5.9 +/- 3.0 g/L; potassium, 40.0 +/- 11.8 mmol/L; lactate dehydrogenase, 64 +/- 38 units/L; total bilirubin,: 1.5 +/- 0.8 microM/L). Overall increase between samples before and after transfusion was 12% for plasma hemoglobin (p =.01, paired Student's t -test), 2% for potassium (p =.03), 20% for lactate dehydrogenase (p =.0001), and 47% for total bilirubin (p =.04). Plasma hemoglobin and lactate dehydrogenase changes were significantly influenced by the type of infusion pump (p =.006 and.01, multiple regression analysis). Regarding these two variables, the new volumetric pump was less hemolytic than the other two pumps. The degree of the transfusion-related RBC changes was also significantly and independently influenced by the storage time of the blood bags with plasma hemoglobin, bilirubin, and osmotic fragility changing less in old bags. CONCLUSIONS: The new pump's shuttle mechanism seems to be less injurious to RBCs compared with a conventional syringe and a peristaltic infusion pump. However, the clinical significance must be related to the hemolytic changes in the RBC units before they are transfused, which are a major source of the overall hemolytic load.

Bilirubin↗
PubMed2002

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.

Catheterization, Central Venous↗
PubMed2002

Transcutaneously measured near-infrared spectroscopic liver tissue oxygenation does not correlate with hepatic venous oxygenation in children.

PURPOSE: To compare transcutaneous near-infrared spectroscopic (NIRS) measured liver tissue oxygenation with hepatic vein oxygen saturation (SvhO2) in children undergoing cardiac catheterization. METHODS: A NIRS optode (containing an emitter and a receiver of near-infrared light) was placed directly below the right costal arch above the palpable liver in 40 children aged 0.02 to 7.28 yr (median: 1.8 yr). Spatially resolved spectroscopic measured tissue oxygenation index (TOI) was recorded using the NIRO-300. Paired blood samples from the hepatic vein were taken under radiological control for determination of SvhO2 in a co-oxymeter. TOI values were compared with hepatic vein oxygenation, with simultaneously obtained arterial oxygen saturation (SaO2), inferior vena cava SO2 and hemoglobin concentration using simple linear and multi-regression analysis. RESULTS: TOI values ranged from 35% to 73% (58.6 +/- 8.4%); SvhO2 from 32% to 80% (58.4 +/- 14.4%), and arterial SO2 from 54% to 100% (90.0 +/- 11.4%). TOI and hepatic vein oxygen saturation failed to correlate (r = 0.052/P = 0.752). A regression model containing arterial saturation (Delta R2 = 0.177) and the ratio of pulmonary to systemic resistance (Delta R2 = 0.095) explained 27.3% of the observed variance in TOI. In this model, hepatic vein oxygen saturation was no longer significant; explaining only 3.4% of the variance. No other variable retained a significant association. CONCLUSION: Transcutaneously measured NIRS tissue oxygenation with an optode placed over the palpable liver does not correlate with SvhO2. The value is dominated by non-hepatic variables such as arterial saturation and vascular resistances.

Child↗
PubMed2002

The Panomat P-10 micro-volumetric infusion pump is suitable for continuous drug administration at minimal flow rates.

PURPOSE: To evaluate the performance of the Panomat P-10 micro-volumetric infusion pump for its use in drug administration at minimal flow rates (microL x hr(-1); e.g., intrathecal application). METHODS: Fluid delivery at steady state conditions, and after vertical displacement of the syringe pump by -50 cm was determined gravimetrically. The Panomat P-10 infusion pump was evaluated at 4, 10, 20, 50 and 100 microL x hr(-1), and compared to a conventional syringe pump assembly at 100, 200, 500 and 1000 microL x hr(-1). Measurements were repeated twice with two different devices of each syringe pump system, and with two syringes. Data are reported as mean +/- SD. RESULTS: Steady state fluid delivery of the Panomat P-10 infusion pump revealed less than 5% deviation to set flow rate at 10, 20, 50 and 100 microL x hr(-1), and 12% deviation at 4 microL x hr(-1). Mean zero-drug delivery time (ZDDT) after lowering the pump by 50 cm at 4 microL x hr(-1) flow rate was 38.4 +/- 7.3 min. At 100 microL x hr(-1) and with original infusion line ZDDT was almost 20 times shorter when compared to the conventional syringe pump assembly (1.5 +/- 0.5 min vs 28.5 +/- 5.0 min). CONCLUSION: The tested Panomat P-10 micro-volumetric pump shows an acceptable flow accuracy as well as a low susceptibility to vertical displacement, and is therefore suitable for continuous drug administration at minimal flow rates. The technology used in this pump carries potential implications for a new generation of syringe pumps.

Drug Delivery Systems↗
PubMed2002

Tracheal intubation in children with Morquio syndrome using the angulated video-intubation laryngoscope.

PURPOSE: There are a number of syndromes with proven or suspected instability of the cervical spine especially in pediatric patients. It is a challenge for the anesthesiologist to intubate these patients with as little movement of the cervical spine as possible. A new device to facilitate this task is the angulated video-intubation laryngoscope (AVIL). CLINICAL FEATURES: The AVIL is a curved endoscopic intubation laryngoscope with angulated distal tip. The video-view from the distal blade tip improves glottic visualization during difficult direct laryngoscopy. We report three sisters with Morquio syndrome scheduled for otorhinolaryngology surgery the same day. Two of them had radiologically suspected cervical spine instability. Tracheal intubation was planned with careful direct laryngoscopy under manual in-line stabilization of the neck and head by an assistant. Direct visualization of the larynx using a Miller blade No. 2 was impaired in two of the three children in whom the cervical spine was immobilized. They were both successfully intubated under endoscopic control using the AVIL. CONCLUSION: The AVIL may become a helpful device to aid endotracheal intubation in patients when cervical spine immobilization impairs direct laryngoscopy.

Child↗
PubMed2002

Apnoea in a former preterm infant after caudal bupivacaine with clonidine for inguinal herniorrhaphy.

Awake regional anaesthesia for inguinal hernia repair in former preterm infants is suggested to avoid life-threatening respiratory complications known to occur after general anaesthesia. Caudal anaesthesia is becoming a more popular technique for this purpose. To prolong duration of anaesthesia and to reduce postoperative need for analgesics in these infants, caudal clonidine has been considered useful. We report a former preterm infant, who had two awake caudal anaesthetics for herniotomy within 3 weeks. The first was uneventful with bupivacaine 0.25% at 35 weeks postconceptional age. At 38 weeks, the baby suffered form intra- and postoperative apnoeas after inadvertent administration of bupivacaine 0.125% plus clonidine.

Anesthesia, Caudal↗
PubMed2002

Flush volumes delivered from pressurized bag pump flush systems in neonates and small children.

BACKGROUND: The aim of this study was to measure the volumes of fluid delivered with a fast flush bolus from a flow regulating device. METHODS: In-vitro fast flush bolus volumes, the volumes delivered from a bag pump flush system while opening the flow regulating device for 1, 2 or 5 s, were gravimetrically measured through a 22-G and a 24-G cannula. In-vivo 1- and 2-s fast flush bolus volumes and the volume required to purge the tubing between stopcock and arterial cannula from visible blood after blood sampling were recorded in 12 anaesthetized neonates and infants (mean age 2.17 +/- 1.97 months, range 0.26-5.37 months) with a 24-G radial arterial cannula by continuously weighing the bag pump flush system at manometer pressures of 100, 200 and 300 mmHg. RESULTS: In-vitro fast flush bolus volumes ranged from 0.23 +/- 0.04 ml (1-s, 100 mmHg, 24-G cannula) to 2.95 +/- 0.38 ml (5-s, 300 mmHg, 22-G cannula). Volumes were larger using a 22-G cannula than a 24-G cannula (P < 0.01) and increased with longer flushing periods (P < 0.0001) and higher manometer pressures (P < 0.0001). In-vivo 1- and 2-s fast flush bolus volumes correlated well with driving pressures (infusion pressure minus mean arterial pressure) (r2 = 0.81/0.72). 1-s fast flush bolus volumes delivered (ml) were 0.0025 x mmHg driving pressure and 2-s fast flush bolus volumes delivered (ml) were 0.0043 x mmHg driving pressure. The mean volume delivered to purge blood from the arterial pressure tubing was 0.94 +/- 0.18 ml (range 0.61-1.34 ml). CONCLUSIONS: Fast bolus flushing from pressurized infusion bag systems, using the flow regulating device tested, can be applied during neonatal and paediatric anaesthesia without delivering uncontrolled amounts of fluid.

Analysis of Variance↗
PubMed2002

Eliminating discard volumes in neonatal and pediatric blood sampling from arterial catheters: A comparison of three simple blood-conserving aspiration techniques.

OBJECTIVE: To compare different blood aspiration techniques to eliminate discarding of blood in arterial blood sampling from critically ill neonates and children. DESIGN: Prospective, randomized controlled trial. SETTING: A 19-bed tertiary neonatal and pediatric intensive care unit. PATIENTS: Critically ill neonates and children with existing arterial and central venous access. INTERVENTIONS: Paired blood samples were obtained by using conventional blood discarding techniques and one of the following blood-conserving aspiration techniques: passive extracorporeal arteriovenous backflow, free passive backflow to ambient pressure, and active aspiration backflow to a distance of 10 or 20 cm proximal to the sampling port of the arterial pressure catheter. Repetitive conventional sampling served as a control and as the standard. The order of sampling was randomly allocated. We determined arterial blood gases, electrolytes, blood glucose, and hemoglobin concentration. Measurement and RESULTS: Bland-Altman bias analysis of the variability among the techniques revealed that the passive backflow and the active aspiration backflow technique with a backflow distance of 20 cm yielded identical results to repetitive conventional sampling with a standardized discard volume of 0.6 mL. In contrast, the extracorporal arteriovenous backflow technique carried the risk of overestimating blood glucose levels (mean bias, 0.96 mmol/L.). A backflow distance of 10 cm (active aspiration) proved insufficient to eliminate contamination by the catheters' flushing solution. CONCLUSIONS: At a backflow distance of 20 cm, the passive backflow and the active aspiration backflow techniques produce, with the used monitoring set, reliable and precise results in critically ill newborns and children and eliminate discard volumes.

Journal Article↗
PubMedDate not supplied

Intubation depth markings allow an improved positioning of endotracheal tubes in children.

OBJECTIVES: To evaluate the position of the new Microcuff pediatric tracheal tube, based upon intubation depth markings. METHODS: With Institutional Ethics Committee approval and informed parental consent, we included patients from birth (> or = 3 kg) to 16 yr undergoing interventional cardiac catheterization requiring general anesthesia with orotracheal intubation. The intubation depth mark of the tracheal tube was placed between the vocal cords by direct laryngoscopy. The distance between tube tip and tracheal carina was measured from routinely taken cardiac catheterization posterior-anterior x-ray computer images with the patient supine and the head in a neutral position. Evaluation was performed for 20 tubes size 3.0 mm internal diameter (ID) and for ten tubes of each size from 3.5 to 7.0 mm ID. RESULTS: 100 patients were studied (47 girls; 53 boys). Tracheal tube tip advancement into the trachea ranged from 40.6% to 68.6% (median 51.4%). The shortest distance from tube tip to the tracheal carina was 15.7 mm using a 3.0 mm ID tube. Using a standard formula for tube insertion in children aged > or = two years [12 cm + (age/2)], in one patient the tube tip would have been below the carina and in seven patients the tube cuffs would have been placed within the larynx. CONCLUSIONS: The intubation depth markings of the new Microcuff pediatric tracheal tube allow safe placement of the tracheal tube with a cuff-free laryngeal zone without the risk for endobronchial intubation. Placement using the intubation depth markings was superior to predicted insertion using a standard formula.

Adolescent↗