Oswaldo Rivera

Validation of a noninvasive neonatal optical cerebral oximeter in veno-venous ECMO patients with a cephalad catheter

Introduction:Cerebral Oximetry is an optical technique that allows for noninvasive and continuous monitoring of brain oxygenation by determining tissue oxygen saturation (SctO2). In conjunction with pulse oximetry, cerebral oximetry offers a promising method to estimate cerebral venous oxygen saturation (SvO2).Objective:The aim of this study was to validate the cerebral oximetry measurements with the cerebral oxygen saturation measured from blood drawn in neonates on veno-venous ECMO with existing cephalad catheter with a prototype neonatal cerebral oximeter developed by CAS Medical Systems (Branford, CT, USA).Study design:After obtaining informed consent, neonates undergoing VV-ECMO with cephalad catheterization were monitored by the CAS cerebral oximeter. Cephalad blood samples were periodically obtained to validate the monitors accuracy.Results:Seventeen neonates were studied with 1718 h of cerebral oximetry data collected. Compared to the reference values, the bias±precision for cerebral oximetry SctO2 was 0.4±5.1% and derived SvO2 was 0.6±7.3%Conclusion:We recommend the use of this noninvasive method as an alternative to blood draws for cerebral venous saturation measurements in neonates requiring extracorporeal life support.

Effect of nitric oxide in meconium aspiration syndrome after treatment with surfactant.

OBJECTIVE To test the hypothesis that inhaled nitric oxide may be an effective therapeutic agent in meconium aspiration syndrome and may improve oxygenation after pretreatment with surfactant. DESIGN Prospective, interventional study. SETTING The animal research laboratory at The Childrens National Medical Center. SUBJECTS Eight newborn pigs, 1 to 2 wks of age, 4.1 +/- 0.4 kg, were used for the study. INTERVENTIONS Animals were anesthetized, paralyzed, intubated, and mechanically ventilated. Catheters were placed in the femoral vein and artery, and in the pulmonary artery. After 1 hr of recovery, 10 mL/kg of 20% meconium in normal saline solution was insufflated into the lungs. Animals were ventilated to maintain arterial blood gases in a normal range (i.e., pH of 7.35 to 7.45, Paco2 of 40 to 45 torr [5.3 to 6.0 kPa], and Pao2 of 70 to 90 torr [9.3 to 12.0 kPa]). Ventilatory settings were increased, as needed, until the following maximum settings were reached: FIO2 of 1.0; peak inspiratory pressure of 40 cm H2O; and intermittent mandatory ventilation of 60 breaths/min. After 2 hrs of conventional ventilation or demonstration of clinically important lung disease by failure to maintain desired blood gases on the maximum ventilatory settings, 4 mL/kg of beractant was given intratracheally. After a short period of stabilization following surfactant therapy, inhaled nitric oxide was administered. Concentrations of 40, 20, and 10 parts per million were given. To assure that there was no additive effect of inhaled nitric oxide, each dose was given for 20 mins, followed by a 15-min normalization period at 0 parts per million. MEASUREMENTS AND MAIN RESULTS Physiologic measurements, ventilatory settings, arterial blood gases, and methemoglobin were recorded at each study period. Measurements were taken after each exposure to inhaled nitric oxide and after its discontinuation. Arterial oxygen saturation and Pao2 were significantly lower after meconium aspiration when compared with baseline values. After treatment with surfactant, administration of inhaled nitric oxide improved oxygenation without a significant decrease in pulmonary arterial pressure. CONCLUSIONS In this model of meconium aspiration syndrome, short-term exposure to inhaled nitric oxide after treatment with surfactant improved oxygenation secondary to better distribution of inhaled nitric oxide. The increase in oxygenation may be secondary to an improved ventilation/perfusion mismatch, since the primary etiology of hypoxia in this model may be a combination of parenchymal lung disease and pulmonary hypertension.

Use of intratracheal pulmonary ventilation versus conventional ventilation in meconium aspiration syndrome in a newborn pig model

OBJECTIVE To determine whether intratracheal pulmonary ventilation (ITPV) allows for effective oxygenation and ventilation at lower mean airway pressures and peak inspiratory pressures than conventional ventilation in a piglet model of meconium aspiration syndrome. DESIGN Prospective, interventional study. SETTING The animal research laboratory at Childrens National Medical Center, Washington, DC. SUBJECTS Twenty newborn piglets, 2 to 7 days of age, weighing 1.8 to 2.8 kg. INTERVENTION Animals were anesthetized, paralyzed, intubated, and ventilated. Femoral arterial and venous catheters were inserted; 5 mL/kg of 20% meconium in normal saline was instilled into the endotracheal tube. Animals were randomized to either ITPV or conventional ventilation, and settings were adjusted to maintain ideal blood gases, i.e., pH 7.35 to 7.45, PCO2 40 to 45 torr (5.3 to 6 kPa), PO2 80 to 100 torr (10.7 to 13.3 kPa), and SaO2 > or = 90%. Ventilatory settings were adjusted as needed to a maximum of: FIO2 1.0, peak inspiratory pressure 40 cm H2O, positive end-expiratory pressure 5 cm H2O, and respiratory rate 80 breaths/min. MEASUREMENTS AND MAIN RESULTS Arterial blood gases were taken every 30 mins for 4 hrs and ventilatory settings were adjusted to maintain optimal blood gases. Heart rate, mean arterial blood pressure, and arterial saturation were monitored continuously. The animals in the ITPV group had significantly lower peak inspiratory pressure at 1, 2, 3, and 4 hrs after meconium instillation (p < .018) and significantly lower mean airway pressure at 2, 3, and 4 hrs after meconium instillation (p < .03). The mean peak inspiratory pressure in the ITPV animals ranged from 17 +/- 2.7 cm H2O at baseline to 16.6 +/- 5.7 cm H2O at 4 hrs compared with 16.5 +/- 2.7 cm H2O at baseline to 31.8 +/- 9.1 cm H2O at 4 hrs in the conventionally ventilated animals (p < .04). The mean airway pressure ranged from 6.3 +/- 1.1 mm Hg at baseline to 6.8 +/- 2.5 mm Hg at 4 hrs in the ITPV group compared with 5.5 +/- 1.2 mm Hg at baseline to 10.7 +/- 3.4 mm Hg at 4 hrs in the conventional ventilation group (p < .03). The lungs of the ITPV animals were less hemorrhagic and had less pathologic evidence of injury than the lungs of the conventionally ventilated animals. CONCLUSIONS These results indicate that ITPV can be used to effectively ventilate and oxygenate piglets with meconium aspiration syndrome at lower mean airway pressures and peak inspiratory pressures than conventional ventilation. This lower pressure causes less injury to the lungs of the animals.

Measurement of tracheal airflow in newborns by a differential flow system.

The differential arrangement of two pneumotachographs in a gas blow-by system, upstream and downstream from the patient connection port, permits accurate measurement of the tracheal air flow without introduction of flowmeter dead-space. The method does not require but will accept a constant background gas flow rate and permits humidification and easy switching of the inhalant gases. The admissible background flow rates limiting measurement errors below 5% in the range of tidal volumes relevant for newborns for two sizes of commercially available pneumotachographs were found to be -3 L/min and 0-12 L/min, respectively. The lack of restrictions imposed on the properties of the background flow source makes the differential system especially suitable for measurement of ventilation and pulmonary mechanics in spontaneously breathing or mechanically ventilated newborn infants.

Improved oxygenation with reduced recirculation during venovenous extracorporeal membrane oxygenation: evaluation of a test catheter.

OBJECTIVE To determine whether modifications of the original design of a double-lumen, venovenous, extracorporeal membrane oxygenation (ECMO) catheter would reduce recirculation and improve oxygenation during venovenous ECMO. DESIGN Prospective, interventional study. SETTING The animal research laboratory at The Childrens National Medical Center. SUBJECTS Six newborn lambs, 1 to 7 days old and weighing 4.7 +/- 0.9 kg. INTERVENTIONS Animals were anesthetized, intubated and ventilated. The ductus arteriosus was ligated. Femoral artery and vein, cephalic jugular vein, and pulmonary artery catheters were placed. After systemic heparinization, the test catheter (with venous drainage holes moved away from the arterial return holes) was placed in the right internal jugular vein and advanced into the right atrium. The animal was placed on ECMO and stabilized, with the ventilator settings decreased to a peak inspiratory pressure of 15 cm H2O, peak positive end-expiratory pressure of 5 cm H2O, respiratory rate of 15 breaths/min, and an FIO2 of 0.21. ECMO flows were increased in 100-mL increments from 200 to 600 mL/min, with measurements taken 15 mins after each change. The test catheter was removed, the double-lumen, venovenous ECMO catheter was placed, and the studies were repeated. MEASUREMENTS AND MAIN RESULTS Heart rate, mean arterial pressure, PaO2, jugular cerebral oxygen saturation, pulmonary artery oxygen saturation, mixed venous oxygen saturation, and postmembrane circuit pressures were measured at each study period. The test catheter improved oxygenation significantly, with higher systemic PaO2, higher pulmonary artery and cerebral oxygen saturations, and lower mixed venous oxygen saturations (indicating less recirculation). With the test catheter, PaO2 levels ranged from 62 +/- 6 torr (8.3 +/- 0.8 kPa) to 112 +/- 12 torr (14.9 +/- 1.6 kPa), compared with 46 +/- 4 torr (6.1 +/- 0.5 kPa) to 59 +/- 2 torr (7.9 +/- 0.3 kPa) for the double-lumen, venovenous ECMO catheter (p < or = .001). These findings indicate that at all flow rates studied, less recirculation occurred with the test catheter than with the double-lumen, venovenous ECMO catheter. CONCLUSIONS These findings indicate that the redesign of the double-lumen, venovenous ECMO catheter, as outlined in this study, resulted in a significant reduction of recirculation, thereby resulting in a significant improvement in oxygenation while on venovenous ECMO. This newly designed catheter makes venovenous ECMO more effective, and represents a design that could be used for pediatric and/or adult ECMO.

Continuous Blood Gas Monitoring Using an In-Dwelling Optode Method: Comparison to Intermittent Arterial Blood Gas Sampling in ECMO Patients

INTRODUCTION: The ability to measure postmembrane arterial blood gases is essential in the management of critically ill neonates treated with extracorporeal membrane oxygenation (ECMO). A new technology using, the Paratrend 7 system (Diametrics Medical, High Wycombe,UK) allows for continuous measurement of pH, PCO2 and PO2, and calculates oxygen saturation, bicarbonate, and base excess.OBJECTIVE: To evaluate and compare the results of continuous blood gas measurement using the Paratrend 7 system with a standard system of blood gas analysis in our intensive care unit.DESIGN: Prospective, controlled, interventional study.SETTING: The neonatal intensive care unit of a tertiary referral center.PATIENTS: Neonates who required extracorporeal life support and were expected to have frequent postmembrane arterial blood sampling during the testing period.RESEARCH DESIGN AND METHOD: To enable Paratrend 7 sensor access to the ECMO circuit, the postmembrane access port extension set that is routinely used for blood drawn for blood gas analysis was used. The study began with the insertion of the Paratrend 7 sensor. Subjects remained on the study until the ECMO was discontinued and/or frequent blood gases were no longer needed. The blood gas results from the Paratrend 7 system were not used in clinical management of the patient.BLOOD GAS MEASUREMENT: During the study period, with each blood sample drawn for laboratory analysis, a printout from the Paratrend 7 monitor was recorded for comparison.RESULTS: A total of 242 pairs of blood gas samples were collected from 10 neonates. The mean bias/precision for pH was −0.02/0.04; for PO2 68.35/93.44 mm Hg; and for PCO2 1.75/4.23 mm Hg. The correlation (r value) between the sensor reading and the blood gases were 0.89 for pH, 0.96 for PO2, and 0.73 for PCO2 (Table 1).CONCLUSION: The blood gases compared in the two methods had a strong correlation for pH, PCO2 and PO2.Results of this study indicate that this technology provides an accurate means of monitoring continuous blood gas parameters in neonatal ECMO patients. Use of the Paratrend 7 should allow reduced health-care provider exposure to blood and decreased patient iatrogenic blood loss.

Continuous Blood Gas Monitoring Using an In-Dwelling Optode Method: Clinical Evaluation of the Neotrend Sensor Using a Luer Stub Adaptor to Access the Umbilical Artery Catheter

INTRODUCTION: Arterial blood gases are essential in the management of critically ill neonates. A new technology using the Neotrend system (Diametrics Medical) allows for continuous measurement of pH, PaCO2, and PaO2, and calculates oxygen saturation, bicarbonate, and base excess.OBJECTIVE: To evaluate and compare the results of continuous blood gas measurement using the Neotrend system with a standard system of blood gas analysis in our intensive care unit.DESIGN: Prospective, controlled, interventional study.SETTING: The neonatal intensive care unit of a tertiary referral center.PATIENTS: Neonates with respiratory distress who required respiratory support and frequent arterial blood gas sampling and had a UAC.RESEARCH DESIGN AND METHOD: To enable Neotrend sensor access to an existing Argyle umbilical artery catheter (UAC) the catheter was cut at the 25-cm mark and connected to an 18-gauge blunt needle luer stub adaptor (Vygon 95440). The study began with the insertion of the Neotrend sensor. Subjects remained on the study until the UAC was discontinued and/or frequent blood gases were no longer needed. The blood gas results from the Neotrend system were not used in clinical management of the patient.BLOOD GAS MEASUREMENT: During the study period, with each blood sample drawn for laboratory analysis, a printout from the Neotrend monitor was recorded for comparison.RESULTS: A total of 217 pairs of blood gas samples were collected from seven neonates. The mean bias/precision for pH was 0.01/0.04; for PaO2 0.72/18.5 mm Hg; and for PaCO2 3.96/2.63 mm Hg. The correlation (r value) between the sensor reading and the blood gases were 0.85 for pH, 0.96 for PaO2, and 0.92 for PaCO2.CONCLUSION: The blood gases compared in the two methods had a strong correlation for pH, PaCO2, PaO2, and oxygen saturation. Although the bicarbonate and base excess values showed suboptimal statistical correlation, the difference was not clinically relevant. Results of this study indicate that this technology provides an accurate means of monitoring continuous blood gas parameters in neonatal patients. It also allows reduced healthcare provider exposure to blood and decreased patient iatrogenic blood loss.

Use of the rebreathing method in the differential diagnosis of congenital heart disease and persistent fetal circulation

The differential diagnosis of congenital heart disease from persistent fetal circulation is clinically difficult and cardiac catheterization is often needed. The development of a safe, new technique for use of the rebreathing method has allowed the determination of effective pulmonary blood flow, lung tissue volume, lung diffusion capacity and functional residual capacity in 7 critically ill, ventilator-dependent infants at the bedside. Analysis of the data revealed highly significant differences for lung tissue volume and diffusion capacity, a minimally significant difference for effective pulmonary blood flow and no difference for functional residual capacity between the groups. Use of this method allows not only attainment of clinically useful information but also permits better insight into the pathophysiology of the disease state.

Evaluation of the new generation dual-lumen catheter for neonatal ECMO

Objectives: The purpose of this study was to compare the newly designed dual-lumen venovenous catheter (VR13, OriGen Biomedical, Austin, TX) with the current dual-lumen catheter (VV12, OriGen Biomedical). Methods: Five newborn lambs, 1 to 5 days old and weighing 4.2 ± 0.5 kg, were cannulated with the VV13 OriGen catheter and placed on extracorporeal membrane oxygenation (ECMO). ECMO flows were increased from 200 to 600 ml/min, with measurements taken after the changes. The experiment was then repeated using the VV12 catheter. Results: Recirculation values were equal for both catheters. The pressure drop at the reinfusion port was equal for both catheters at 200 ml/min, increasing to 275 mmHg at 500 ml/min for the VR13 vs. 240 mmHg for the VV12 catheter. Conclusion: These findings indicate that the VR13 catheter resulted in levels of recirculation equal to the VV12. Based on resistance measurements, we do not recommend the use of this new catheter beyond 400 ml/min until minor design changes are made.

In vitro evaluation of the Mera Silox-S 0.5 and 0.8 m2 silicone hollow-fibre membrane oxygenator for use in neonatal ECMO

The Mera Silox-S is a silicone hollow-fibre membrane oxygenator made up of thousands of fibres in a clear polycarbonate housing. Being a silicone membrane it does not have the plasma leakage problem associated with conventional microporous hollow fibres when used in a long-term application. This device (Mera Senko Medical Instrument Co., Japan) is made in three sizes: 0.3, 0.5 and 0.8 m2. The performance of the 0.5 m2 and 0.8 m2 Silox-S membrane oxygenators was tested in vitro using filtered ovine blood and a customized test circuit designed to provide a continuous source of de-oxygenated, CO2-laden blood, according to the AAMI standard for oxygenator performance. The 0.8 m2 membrane provided excellent oxygenation, with a transfer rate of 13.0-43.5 ml/min for blood flows of 200-800 ml/min. CO2 transfer over the same range of flows measured 32.3-40.8 ml/min. Flow rates of 100-500 ml/min for the 0.5 m2 membrane provided an oxygen transfer of 6.8-28.3 ml/min and would probably not be suited for the existing neonatal ECMO population. A matter of concern with both oxygenators was an increased pressure drop for blood flow through the devices. The ΔPfor the 0.5 m2 for flows of 100-500 ml/min ranged from 155 ± 7 mmHg to 516 ± 6 mmHg. For the 0.8 m2, ΔP was 194 ± 39 mmHg to 492 ± 53 mmHg for flows of 200-800 ml/min. Overall, favourable results support further long-term evaluation for potential use in neonatal ECMO.