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Biomedical subjects

J M Steven

Publications and source records attributed to J M Steven.

31 records · Page 2Linked to original sources
PubMed1994

The metabolic effects of surface cooling neonates prior to cardiac surgery.

Neonates undergoing cardiac surgery at The Children's Hospital of Philadelphia frequently developed metabolic acidemia as they passively cooled prior to the start of cardiopulmonary bypass. This study was performed in an attempt to identify the mechanism for this acidemia. After receiving an initial dose of fentanyl (10 micrograms/kg) and pancuronium, 22 neonates were randomly assigned to maintain normothermia by active warming (Group I), or to permit passive cooling (Group II) before surgery. Arterial blood samples were obtained prior to, and at 10 and 45 min after entering the operating room for the analysis of pH, gas tensions, lactate, pyruvate, plasma free fatty acids, acetoacetate, beta-hydroxybutyrate, total CO2, and glucose concentrations. In the last 11 patients studied, the observation period was extended to 75 min at which time another arterial blood sample was obtained. There was a steady decrease in heart rate as the Group II patients cooled; however, arterial blood pressure did not change in either group. There were no changes in blood values measured in Group I neonates. In the Group II patients, there was a progressive decline in calculated base excess, total CO2, and an increase in serum lactate as the patients cooled. The metabolic acidemia that develops in neonates represents lactate accumulation as a consequence of surface cooling prior to surgery and the institution of cardiopulmonary bypass. Whether lactate accumulates as a result of anaerobic metabolism in underperfused tissue beds or reduced hepatic clearance could not be distinguished in this study. Since neither clinically significant hemodynamic changes nor differences in outcome were found between the two groups, the authors believe this mild lactic acidemia is inconsequential and does not require therapy.

Acidosis↗
PubMed1993

Near-infrared monitoring of the cerebral circulation.

Near-infrared spectroscopy is a noninvasive bedside technique for monitoring hemoglobin saturation (HbO2%) in brain vasculature. The method linearly relates the optical signal detected from the surface of the head to HbO2%. To do so, the method relies on constant transcranial optical pathlength and light scattering as well as minimal interference by tissues overlying the brain. This study examined these premises. Optical signals from a dual-wavelength, near-infrared spectrometer were correlated with sagittal sinus HbO2% in 7 anesthetized piglets subjected to 7 different physiological conditions: normoxia, moderate and severe hypoxia, hyperoxia, hypocapnia, hypercapnic hyperoxia, and hypotension. These conditions were induced by varying the inspired O2 concentration (7-100%), ventilatory rate (5-35 breaths/min), and blood pressure (phlebotomy 20 ml/kg) to force HbO2% over a wide range (5-93%). To evaluate interference by tissues overlying the brain, correlations were repeated after the scalp and skull were rendered ischemic. Transcranial optical pathlength was measured by phase-modulated spectroscopy. Linear relationships between optical signals and sagittal sinus HbO2% were found with correlation coefficients ranging from -0.89 to -0.99 (p < 0.05) among animals; however, slope and intercept had coefficients of variability of approximately 15 and 333%, respectively. Almost identical linear expressions were observed whether scalp and skull were ischemic or perfused. Transcranial optical pathlength was constant in each animal, but ranged from 10 to 18 cm among animals. The data indicate that the assumptions underlying near infrared spectroscopy are reasonably accurate in a given animal, but that the constants for transcranial optical pathlength and light scattering are not the same in all animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Influence of sensor site location on pulse oximetry kinetics in children.

A pulse oximeter sensor is used to monitor changes in arterial hemoglobin oxygen saturation (SpO2) in anesthetized pediatric patients. The authors compared the kinetics of desaturation and resaturation measured by sensors placed over central (tongue, cheek) and peripheral (finger, toe) vascular beds in children with congenital heart disease. Desaturation time was defined as the time which elapsed between the onset of apnea and a 4% decrease in SpO2 from baseline. The desaturation times averaged 24 +/- 12 s, 56 +/- 34 s, and 58 +/- 28 s for the cheek, finger, and toe, respectively (n = 40; P < 0.0001 for cheek versus finger or toe). Resaturation time was defined as the interval between the resumption of ventilation and a 4% increase in SpO2 above the nadir. Resaturation times averaged 12 +/- 8 s for the cheek, 40 +/- 36 s for the finger, and 47 +/- 25 s for the toe (n = 40; P < 0.0001 for cheek versus finger or toe). A comparison of the kinetics at two central sensor sites, cheek and tongue, respectively, revealed no significant differences in desaturation times (20 +/- 10 s vs 21 +/- 9 s) or resaturation times (10 +/- 6 s vs 7 +/- 3 s) (n = 13). The authors conclude that both desaturation and resaturation are detected earlier by centrally placed sensors.

Biosensing Techniques↗
PubMed1993

Desmopressin does not decrease bleeding after cardiac operation in young children.

Young children undergoing complex cardiac operation lose more blood after cardiopulmonary bypass than do older patients. This study was designed to investigate the effect of desmopressin on blood loss during the first 24 hours after cardiac operation in children undergoing principally complex surgical procedures. The study consisted of a randomized, blinded comparison of 112 pediatric patients who received either desmopressin 0.3 microgram/kg or saline solution placebo after cardiopulmonary bypass. A coagulation profile including bleeding time, quantitation of von Willebrand factor, and qualitative analysis of the factor VII:von Willebrand factor complex was performed before, 30 minutes after, and 3 hours after the operation. Blood loss and blood replacement were recorded for the first 24 hours after the operation. The surgeon classified the technical difficulty of each procedure as simple or complex. Statistical analysis was performed with Student's unpaired t test and chi 2 analysis. Significance was defined as p < 0.05. Results are listed as mean +/- standard deviation. Data collection was completed for 95 patients. The mean age of all patients was 26 +/- 40 months, and the mean weight was 10 +/- 11 kg, with 84% undergoing complex procedures. There were no differences between the desmopressin and placebo groups with respect to age, weight, or surgical complexity. Twenty-four-hour blood loss and replacement between the desmopressin and placebo groups were not different (blood loss: desmopressin 30 +/- 33 ml/kg, placebo 35 +/- 36; blood replacement: desmopressin 65 +/- 43 ml/kg, placebo 64 +/- 46 ml/kg). Coagulation profiles between the desmopressin and placebo groups were not different at any time. We conclude that desmopressin does not reduce blood loss or blood replacement in young children after cardiopulmonary bypass for either simple or complex cardiac surgical procedures.

Adolescent↗
PubMed1992

Carbon dioxide prevents pulmonary overcirculation in hypoplastic left heart syndrome.

Circulatory and metabolic homeostasis in patients with hypoplastic left heart syndrome is dependent on a delicate balance between systemic and pulmonary blood flow. Hypocarbia can result in a marked decrease in pulmonary vascular resistance accompanied by pulmonary overcirculation, systemic hypotension, metabolic acidosis, and death. This report illustrates that early and precise control of the arterial carbon dioxide tension using inspired carbon dioxide can be effective in preventing or treating instability arising during management of a patient with hypoplastic left heart syndrome.

Acidosis, Respiratory↗
PubMed1992

The effect of administering or withholding dextrose in pre-bypass intravenous fluids on intraoperative blood glucose concentrations in infants undergoing hypothermic circulatory arrest.

Thirty-six fasted infants under 1 year of age who were scheduled for elective cardiac surgery using hypothermic bypass with circulatory arrest were randomized to receive a lactated Ringer's (LR) solution (group I) or a LR with 5% dextrose solution (group II) in the pre-bypass period. Marked increases in blood glucose concentrations were found following institution of bypass and circulatory arrest in the children in both groups. There was no correlation between the amount of dextrose infused in the pre-bypass period and the presence of hyperglycemia following institution of bypass. A single patient in group I was hypoglycemic (blood glucose less than 30 mg/dL) on the initial glucose determination and the blood glucose did not increase during the pre-bypass period. Elimination of dextrose from the parenteral fluids given before bypass will not eliminate hyperglycemia following institution of bypass; however, it may expose pediatric patients to the risks of hypoglycemia before bypass.

Blood Glucose↗
PubMed1992

Kinetics of cerebral deoxygenation during deep hypothermic circulatory arrest in neonates.

Brain injury associated with neonatal congenital heart operations performed during deep hypothermia and/or total circulatory arrest is often attributed to cerebral hypoxia. We studied the kinetic changes in cerebrovascular hemoglobin O2 saturation (HbO2%) and total hemoglobin concentration (Hbtotal) in 17 neonates undergoing cardiac surgery as they were cooled to 15 degrees C, underwent total circulatory arrest, and were rewarmed. HbO2% and Hbtotal in brain vasculature were monitored noninvasively by near-infrared spectroscopy. Neonates were cooled over 12 min and rewarmed over 15 min while being perfused using cardiopulmonary bypass (CPB). Total circulatory arrest lasted from 20 to 70 min. We found that HbO2% in brain vasculature increased during the initial 8 min of CPB as nasopharyngeal temperature decreased, and then remained constant until circulatory arrest. After the onset of circulatory arrest, cerebrovascular HbO2% decreased curvilinearly for 40 min; no further hemoglobin desaturation was observed from 40 to 70 min of arrest. The changes in cerebrovascular Hbtotal were quite different from those in HbO2%, as Hbtotal decreased during the initial minute of CPB and circulatory arrest and then remained constant until recirculation. Brain intravascular HbO2% and Hbtotal increased within 3 min after the onset of recirculation to prearrest levels, and during rewarming, HbO2% decreased to normothermic baseline values. The results demonstrate that cerebral oxygenation increased during CPB cooling; O2 was consumed by the neonatal brain during the initial 40 min of deep hypothermic circulatory arrest; and cerebral oxygenation was restored on recirculation. These observations may be important in identifying the etiologies of brain injury during neonatal congenital heart surgery.

Brain↗
PubMed1992

Pulmonary mechanics in infants after cardiac surgery.

OBJECTIVE: To determine pulmonary mechanical characteristics in neonates after cardiac surgery. DESIGN: A prospective study. SETTING: A 23-bed, pediatric ICU in a 280-bed children's hospital. PATIENTS: Twenty-six infants on the first post-operative day after cardiac surgery. METHODS: Pulmonary mechanics measurements were made during spontaneous breathing, using the esophageal balloon technique and a pneumotachometer. The least mean square method of analysis was used to calculate mechanics. Infants who tolerated withdrawal of mechanical ventilation (group 1) were compared with those infants with respiratory failure (group 2). RESULTS: Spontaneous respiratory rate, tidal volume, and minute ventilation were similar in groups 1 and 2. Lung compliance was decreased, with no difference between groups. Total lung resistance (34.3 +/- 21.6 cm H2O/L.sec in group 1 vs. 136.8 +/- 105.8 cm H2O/L.sec in group 2, p = .002) and resistive work of breathing (33.4 +/- 29.9 g.cm/kg in group 1 vs. 212.9 +/- 173.8 g.cm/kg in group 2, p = .001) were significantly higher in group 2. All infants with a total lung resistance greater than 75 cm H2O/L.sec exhibited respiratory failure (resistance greater than 75 cm H2O/L.sec correlated with respiratory failure, r2 = .73, odds ratio of 70 [confidence interval, 4.4 to 3240], p less than .001). CONCLUSIONS: Increased lung resistance identifies neonates with respiratory failure after cardiac surgery. Pulmonary mechanics testing may be useful in timing withdrawal of mechanical ventilation.

Airway Resistance↗
PubMed1989

Evaluation of a user-operated patient-side blood gas and chemistry monitor in children undergoing cardiac surgery.

A study was performed to evaluate a user-operated patient-side blood gas and chemistry monitor (GEM-STAT, Mallinckrodt Sensor Systems, Ann Arbor, MI) for the first time in a group of infants and children with congenital heart disease undergoing cardiac surgery. Paired blood samples from 18 patients were analyzed by the test instrument and by standard clinical laboratory instruments. One failure of the test instrument, malfunction of a cartridge, occurred during the evaluation. The integrated and external quality control functions gave readings within the manufacturer's tolerance. The differences between the measurements obtained using the GEM-STAT and the standard laboratory instruments for five of the six variables are summarized as follows (mean +/- SD, units of measure, number of samples): pH (-0.017 +/- 0.02, 132), PaCO2 (-1.90 +/- 3.3 mm Hg, 130), hematocrit (-1.3 +/- 2.3%, 129), potassium (-0.17 +/- 0.20 mmol, 112) and sodium (-2.0 +/- 3.3 mmol, 112). The mean difference in the measurements of PaO2 in the clinically important range defined by the upper quality control limit for oxygen tension of 172 mm Hg for the GEM-STAT is: (-0.20 +/- 7.26 mm Hg, 51). The mean difference between the measurements for PaO2s below the lowest quality control point (60 mm Hg) was (-2.3 +/- 5.5 mm Hg, 30). The values for all variables obtained from the GEM-STAT during the trial period, with the exception of the PaO2 less than 60 mm Hg, showed good correlation with the laboratory over the clinically useful range.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Chemical Analysis↗
PubMed1983

Chest tube perforation of the lung in premature infants: radiographic recognition.

Newborn infants with severe respiratory distress syndrome have an increased incidence of pulmonary interstitial emphysema, pneumomediastinum, and pneumothorax. A chest tube inserted for treatment of a pneumothorax may inadvertently perforate the lung. Recognition of chest tube perforation can be suggested by the occurrence of: (1) persistent or repeated pneumothoraces despite the presence of a chest tube and (2) atelectasis and/or infiltrate near the end of the chest tube.

Humans↗