The relationship between cerebral and somatic oxygenation and superior and inferior vena cava flow, arterial oxygenation and pressure in infants during cardiopulmonary bypass.

We investigated blood flow and regional oxygenation (rSO(2)) during cardiopulmonary bypass (CPB). Twenty infants (mean (SD) age 5 (3) months, weight 5.4 (1.6) kg) were prospectively studied. Total CPB and superior vena cava (SVC) flow were measured using Transonic Bypass Flowmeters, inferior vena cava (IVC) flow derived arithmetically and rSO(2) measured using Near Infra-Red Spectroscopy. Mean SVC flow was 51.3 (14.8) ml.kg(-1).min(-1) and mean IVC flow 62.5 (19.0) ml.kg(-1).min(-1). Mean cerebral rSO(2) was 71 (11)% and somatic rSO(2) 55 (13)%. Cerebral and somatic rSO(2) showed no correlation with SVC and IVC flow. Cerebral rSO(2) showed a positive correlation with P(a)co(2), mean arterial pressure (MAP) and haematocrit (p < 0.0001). Somatic rSO(2) showed a positive correlation with MAP and haematocrit (p = 0.01, p = 0.02). In conclusion, the distribution of blood flow during CPB varies. The most important factor affecting this is P(a)CO(2). Cerebral and somatic oxygenation are unaffected by flow but significantly influenced by MAP, haematocrit and P(a)CO(2).

Decreased exhaled nitric oxide may be a marker of cardiopulmonary bypass-induced injury.

BACKGROUND: Nitric oxide is an endothelium-derived vasodilator. Cardiopulmonary bypass may induce transient pulmonary endothelial dysfunction with decreased nitric oxide release that contributes to postoperative pulmonary hypertension and lung injury. Exhaled nitric oxide levels may reflect, in part, endogenous production from the pulmonary vascular endothelium. METHODS: We measured exhaled nitric oxide levels before and 30 minutes after cardiopulmonary bypass in 30 children with acyanotic congenital heart disease and left-to-right intracardiac shunts undergoing repair. RESULTS: Exhaled nitric oxide levels decreased by 27.6%+/-5.6% from 7+/-0.8 to 4.4+/-0.5 ppb (p < 0.05) 30 minutes after cardiopulmonary bypass despite a reduction in hemoglobin concentration. CONCLUSIONS: The decrease in exhaled nitric oxide levels suggests reduced nitric oxide synthesis as a result of pulmonary vascular endothelial or lung epithelial injury. This may explain the efficacy of inhaled nitric oxide in the treatment of postoperative pulmonary hypertension. Furthermore, strategies aimed at minimizing endothelial dysfunction and augmenting nitric oxide production during cardiopulmonary bypass may decrease the incidence of postoperative pulmonary hypertension. Exhaled nitric oxide levels may be useful to monitor both cardiopulmonary bypass-induced endothelial injury and the effect of strategies aimed at minimizing such injury.

The current state of congenital tracheal stenosis.

Congenital tracheal stenosis (CTS) is an uncommon condition that has challenged pediatric surgeons for decades. Patients with CTS can present with a wide spectrum of symptoms and varying degrees of severity. In addition, a variety of techniques have been devised to repair this malformation. A review of these procedures and our suggestions for clinical standards and practice guidelines will be presented in this paper. A retrospective review of the literature on CTS from 1964 to 31 March, 2006. There is not one standard technique for the repair of CTS, as individualized approach to each patient and airway lesion is necessary to optimize patient management; nevertheless there is a consensus about segmental resection and anastomosis being best for short segment stenosis while slide tracheoplasty is most effective for the long-segment ones. Conservative management is also an option for select group of patients with careful and close follow up. Survival following surgery over the years has improved, but mortality remained high, particularly in a specific subset of patients presenting at the age less than 1 month with associated cardiac malformations. In conclusion, CTS remains a significant challenge for pediatric surgeons. Additional research is required to improve our understanding of the pathogenesis of CTS, and to develop evidence-based treatment protocols for the entire spectrum of presentation including conservative management.

Assessment of the relationship between cerebral and splanchnic oxygen saturations measured by near-infrared spectroscopy and direct measurements of systemic haemodynamic variables and oxygen transport after the Norwood procedure.

OBJECTIVES: To evaluate the clinical utility of near-infrared spectroscopic (NIRS) monitoring of cerebral (ScO2) and splanchnic (SsO2) oxygen saturations for estimation of systemic oxygen transport after the Norwood procedure. METHODS: ScO2 and SsO2 were measured with NIRS cerebral and thoracolumbar probes (in humans). Respiratory mass spectrometry was used to measure systemic oxygen consumption (O2). Arterial (SaO2), superior vena caval (SvO2) and pulmonary venous oxygen saturations were measured at 2 to 4 h intervals to derive pulmonary (Qp) and systemic blood flow (Qs), systemic oxygen delivery (DO2) and oxygen extraction ratio (ERO2). Mixed linear regression was used to test correlations. A study of 7 pigs after cardiopulmonary bypass (study 1) was followed by a study of 11 children after the Norwood procedure (study 2). RESULTS: Study 1. ScO2 moderately correlated with SvO2, mean arterial pressure, Qs, DO2 and ERO2 (slope 0.30, 0.64. 2.30, 0.017 and -32.5, p < 0.0001) but not with SaO2, arterial oxygen pressure (PaO2), haemoglobin and O2. Study 2. ScO2 correlated well with SvO2, SaO2, PaO2 and mean arterial pressure (slope 0.43, 0.61, 0.99 and 0.52, p < 0.0001) but not with haemoglobin (slope 0.24, p > 0.05). ScO2 correlated weakly with O2 (slope -0.07, p = 0.05) and moderately with Qs, DO2 and ERO2 (slope 3.2, 0.03, -33.2, p < 0.0001). SsO2 showed similar but weaker correlations. CONCLUSIONS: ScO2 and SsO2 may reflect the influence of haemodynamic variables and oxygen transport after the Norwood procedure. However, the interpretation of NIRS data, in terms of both absolute values and trends, is difficult to rely on clinically.

Chest wall motion during halothane anaesthesia in infants and young children.

Chest wall motion during anaesthesia may differ from the awake state because of the effect of anaesthetic agents on the muscles of respiration. The purpose of this study was twofold (1) to describe the pattern of chest wall motion in infants and children during halothane anaesthesia (HA) using respiratory inductive plethysmography (RIP) and (2) to calibrate the voltage output of RIP in units of volume. Seven infants (2.3 +/- 1.7 mo, 5.9 +/- 0.7 kg) and five children (2.9 +/- 1.1 yr, 15.5 +/- 1.5 kg) were studied. Since results in both age groups were qualitatively similar they are presented as a single group. Respiratory excursions of the rib cage (RC) and abdomen (ABD) were measured using RIP. Airflow was measured with a pneumotachograph. During spontaneous breathing the analogue signals of airflow, pressure, RC and ABD were recorded. Measurements were taken during (1) halothane anaesthesia and (2) during emergence from anaesthesia. The XY plots of the RC and ABD signals were plotted for each period. In addition the voltage output of the respiratory excursions of the RC and ABD signals was converted to units of volume using the simultaneous solution of equation method. The accuracy of conversion factors was validated by regression analysis of the predicted and measured tidal volume using breaths sampled at random throughout the entire period of study. Regression analysis of this relationship gave a slope between 0.85 and 1.15 (r2 value greater than 0.7) in five of the twelve patients. The pattern of chest wall motion in the XY plots showed synchronous motion between RC and ABD signals during HA in nine of the twelve patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Minute ventilation during mask halothane anaesthesia in infants and children.

The pattern of respiration in infants during anaesthesia is not well documented. In this study, minute ventilation (MV) during elective mask halothane anaesthesia (HA) was measured during spontaneous ventilation in infants (Group I) and children (Group II). Airflow was measured with pneumotachography (#0 Fleisch in Group I and #1 Fleisch in Group II). Analogue signals of pressure and flow were recorded on magnetic tape for off-line playback. The flow signal was mathematically integrated to volume. The surgical procedure was divided into three stages: A, B and C representing HA, surgical stimulation and emergence respectively. The pattern of respiration during spontaneous ventilation was described as tidal volume (VTx), respiratory frequency (fx), mean inspiratory flow (VT/TIx), inspiratory duty cycle (TI/TTotx) where the subscript x denoted the stage. Seven infants (2.7 +/- 0.5 mo, 5.8 +/- 0.5 kg) and five children (3.1 +/- 1.1 yr, 15.8 +/- 1.7 kg) were studied. There was no difference in MV between Groups I and II. Halothane anaesthesia in both groups was characterized by rapid shallow breathing: VTA was lower in Group I (2.90 +/- 0.8 ml.kg-1) than in Group II (3.74 +/- 0.40 ml.kg-1) (P < 0.05). Tidal volume was lower during anaesthesia than emergence in both groups (P < 0.05). There was no difference in VT/TIx between groups. The VT/TIA was lower than VT/TIC in Group I (P < 0.05) but not in Group II. There was no intra or intergroup difference in TI/TTot between stages. We suggest that during HA infants have a greater reduction in VT than children, which may predispose infants to hypercarbia during HA.

Use of ultrasound to evaluate internal jugular vein anatomy and to facilitate central venous cannulation in paediatric patients.

Percutaneous cannulation of the internal jugular vein in paediatric patients may be technically difficult and is prone to complications. To investigate the possibility that anatomical factors contribute to these difficulties, we used a two-dimensional ultrasound scanner to examine venous anatomy in children aged up to 6 yr. We found that 18% of our children had anomalous venous anatomy that may account for some of the difficulties reported previously. The diameter of the internal jugular vein was predicted poorly by the patient's age (r2 = 0.259) or weight (r2 = 0.155). We also evaluated the use of this ultrasound scanner during percutaneous central venous cannulation in neonates and infants. Determining the course of the internal jugular vein with the scanner and then marking it on the overlying skin reduced both the time and number of needle insertions required to aspirate jugular venous blood and increased the chance of a complication-free cannulation.

Early tracheal extubation after paediatric cardiac surgery: the use of propofol to supplement low-dose opioid anaesthesia.

BACKGROUND: After institutional approval and parental consent, 103 children, aged 6 months to 18 years, who were undergoing repair of simple and complex congenital heart lesions using cardiopulmonary bypass (CPB) were studied and compared with a group of 135 children who had undergone similar surgery in our institution in the year before. METHODS: Anaesthesia for study patients included fentanyl (< 20 microg.kg-1) and isoflurane. Infusions of propofol (median infusion rate 70 microg.kg-1.min-1) and morphine (median infusion rate 20 microg.kg-1.h-1) were started after weaning from CPB and continued postoperatively. Preestablished criteria were used in the intensive care unit (ICU) to assess readiness for tracheal extubation. RESULTS: Median time from admission to ICU to tracheal extubation was 5 h. Fifty-six children were extubated within 6 h and 73 within 9 h of ICU admission. Mean ICU stay for study patients was 1.7 days [95% confidence interval (CI) 1.2-2.2] and 2.6 days (95% CI 2.3-2.9) in the comparison group (P<0.005). CONCLUSIONS: We found the propofol regimen to be satisfactory with a shorted ICU stay for these patients.

Cerebral hyperthermia in children after cardiopulmonary bypass.

BACKGROUND: Cerebral hyperthermia after hypothermic cardiopulmonary bypass has been poorly documented for adults and never in children. This study was designed to monitor brain temperature during and up to 6 h after cardiopulmonary bypass in infants and children. METHODS: Fifteen infants and children, between 3 months and 6 yr of age, were studied. A right retrograde jugular bulb catheter was used to measure the jugular venous bulb temperature (JVBT) during the procedure and the first 6 h in the critical care unit. The temperature of the blood from the bypass machine was measured at the aorta through the cannula using an indwelling temperature probe. All data were acquired every minute. RESULTS: The age of the patients ranged from 3 to 71 months (median, 15 months). The mean weight was 11.5 +/- 8.4 kg. The mean JVBT recorded at the end of cardiopulmonary bypass was 36.9 +/- 1.4 degrees C but reached 39.6 +/- 0.8 degrees C after six h (P < 0.01). The kinetics of brain rewarming was determined by the slope of the mean JVBT and corresponded to y +/- 0.006x + 37.21 (r2 = 0.97). The JVBT differed from the tympanic temperature after 200 min (P < 0.01) and the lower esophageal (P < 0.05) and rectal (P < 0.001) temperatures after 300 min. After 6 h, the tympanic, rectal, and lower esophageal temperatures were 37.8 +/- 0.9, 37.7 +/- 0.6, and 38.4 +/- 0.7 degrees C, respectively, whereas the JVBT was 39.6 +/- 0.8 degrees C (P < 0.001). However, the correlation coefficients between the JVBT and the tympanic, rectal, and esophageal temperatures were 0.98, 0. 85, and 0.97, respectively. No complications were recorded with placement of the jugular bulb catheter. CONCLUSIONS: Mean JVBT was significantly increased over the mean core temperature at all times from rewarming by cardiopulmonary bypass onward. Although the lower esophageal, rectal, and tympanic temperatures correlated well with JVBT, all three failed to reflect JVBT during recovery. This observation might help to elucidate factors involved in the functional and structural neurologic injury known to occur in pediatric patients.