Saad Al-Saedi

Subarachnoid fluid collections: A cause of macrocrania in preterm infants

We report the outcome of 12 very low birth weight infants with macrocrania caused by subarachnoid fluid collections. By the age of 15 to 18 months, head growth had stabilized along a curve above and parallel to the 95th percentile. No infant required neurosurgical intervention, nor was cerebral palsy or mental retardation diagnosed in any of the infants.

Spinal cord infarct after arterial switch associated with an umbilical artery catheter

Paraplegia after an open heart operation in a neonate is a rare complication. We report a case of a infant in whom paraplegia developed after a successful arterial switch operation for transposition of the great arteries. The infant was monitored and resuscitated in the preoperative period with umbilical arterial and venous catheter tips located in the midthoracic region. He likely suffered a clinically silent thromboembolic event predisposing him to a localized hemorrhagic infarction during the repair.

In Search of the Respiratory Center: Medullary Pacemaker Cells and Their Response to Neurotransmitters

In Search of the Respiratory Center: Medullary Pacemaker Cells and Their Response to Neurotransmitters

Pacemaker Cells Uniquely Responsive to CO2 in Cultured Cells of the Upper Medulla: Dose Response and Effect of Neuromediators. |[bull]| 1476

We have previously found specific pacemaker cells, highly sensitive to CO2, in the areas of the nucleus ambiguus (NA) and nucleus tractus solitarius (NTS), 2 mm rostral to the obex, in the fetal rat (J. Neurosci. Res., 33:590-597, 1992 & 33:579-589, 1992). We now report on the dose response evaluation of these cells as well as on their responsiveness to neurotransmitters. Twenty days old fetuses of pregnant Dawley rats were block dissected and the cells of the target areas were dissociated as previously described. Neuronal cells were plated in medullary background and placed in the incubator with 10% CO2 for 2 or 3 weeks. Cells were then studied using patch-clamp techniques. Pacemaker cells with single or bursting potentials showed responsiveness to CO2 starting with pulses of 10 msec(n=28 cells; 16 NA and 12 NTS). Irregularly beating or silent cells show either absent or poor responsiveness to CO2 (50 cells; 23 NA, 27 NTS). Pacemaker cells responded to norepinephrine (n=11) with an increase in firing potential, in a dose- response manner; this action was blocked by prazosin. Irregular beating cells (n=5) responded to norepinephrine poorly; silent cells(n=18) did not respond. Pacemaker cells responded to carbachol (n=18) with an increase in activity. Irregular beating cells responded poorly and silent cells did not respond; atropine blocked these effects. There were no differences in response related to the NA or NTS areas of the medulla. The findings suggest: 1) there is a very specific group of pacemaker cells in the most crucial respiratory area of the upper medulla which responds uniquely to CO2 in a dose-dependent manner. This property is not shared by non- pacemaker neurons; and 2) the responses to norepinephrine and carbachol are in agreement with respiratory responses observed in brainstem sectioned fetal lambs. We speculate that these pacemaker cells have been specifically designed for central CO2 chemoreception and may be involved in the generation of breathing.

COMPARISON OF TWO STRATEGIES TO DELIVER OXYGEN IN PRETERM INFANTS. † 1286

With the advent of new technologies, it has become routine to offer supplemental oxygen to neonates via nasal prongs rather than by increasing the ambient oxygen in the incubator. The rationale for use of nasal prongs is that it provides more constant inspired O2 concentration whereas ambient oxygen is subject to fluctuations due to opening of the incubator doors. Nasal prongs, however, have significant disadvantages including i) nasal trauma, ii) increased restlessness, and iii) increased upper airway resistance with increased work of breathing. It remains subject to inspired O2 fluctuation due to prong dislodgement, which is common. Furthermore, we observed substantial clinical improvement in two preterm infants who had fewer apneas and appeared more comfortable after removing the nasal prongs and increasing the ambient O2 concentration. We hypothesized, therefore, that infants would have less apnea, less desaturation and less bradycardia with increased ambient O2 concentration compared with the nasal canulae. To test this hypothesis we studied 8 preterm infants[birthweight 1160±587g (mean ± SE), study weight 1240±534g, gestational age 28±3wk, postnatal age 28 + 4 d] on 9 occasions. Each study consisted of two consecutive 4 hour epochs where FiO2, hypopharyngeal O2, episodes of desaturation 10 s duration were measured while the infant was given O2 by either nasal prongs or into the isolette to maintain saturations at about 95%. Hypopharyngeal FiO2 was measured using a 10F suction catheter inserted via the nares and through which a 60 cc sample of gas was aspirated and its FiO2 measured with a Miniox O2 analyzer. Although hypopharyngeal O2 concentrations were similar (24 ± 4 vs 23 ± 5%, p = 0.55), we observed significantly greater number of apneas 13.2 ± 3 vs 2.8 ± 7 (p < 0.008) and desaturations 14 ± 3 vs 9 ± 3 (p < 0.008) when using nasal prongs. There was no difference in the number of bradycardias. We conclude that administration of O2 into the isolette is associated with fewer apneas and less desaturations and, for this reason, it may be a superior method of O2 administration in preterm infants. Supported by Childrens Hospital Research Foundation & Canadian Lung Association.

COMPARISON OF THE PREVALENCE OF SILENT AND OVERT AIRWAY OBSTRUCTIONS DURING APNEA IN PRETERM AND TERM INFANTS. † 2011

We have previously described a system of infant apnea classification which relies on the presence or absence of a cardiac airflow oscillation during apnea to detect airway obstruction. Obstructive apneas are defined by absence of oscillations during the entire apnea. By noting a patients respiratory efforts in response to obstruction one can further classify obstructive apneas as either overt or silent. Overt obstructions correspond to classically defined obstructive apnea where the patient makes respiratory efforts against the obstruction throughout the apnea. Although the prevalence of such overt obstruction in preterm and term infants is well known, data on silent obstructions are lacking. We therefore decided to examine the prevalence of these types of apneas in 17 preterm infants [BW 1590±150 g(means±SE), SW 2330±260 g, GA 30±0.7 wk, PNA 41±7 d] and 8 term infants [BW 3190±125 g, SW 3590±250 g, GA 40±0.3 wk, PNA 23±4 d] referred to our laboratory for investigation of apnea. A total of 2674 apneas ≥ 3 seconds (preterm 1357, term 1317) were analyzed yielding 68 overt and 108 silent obstructions. There were significantly more overt (60 vs 7, p < 0.001, Chi square) and silent(57 vs 31, p ≤ 0.01) obstructions in preterm infants when compared to term infants. While both apnea types were equally common in preterm infants (57 silent vs 60 overt), silent obstructions were four times more prevalent than overt obstructions in term infants (31 silent vs 7 overt). We conclude that preterm infants have a high prevalence of silent obstructions. We speculate that the lack of apparent deleterious effects with silent obstructions in term infants relates to i) the low prevalence of these events, andii) the greater maturity of the respiratory control system. Supported by Can. Lung Assoc. & Child. Hosp. Res. Found.

LOW DOSE TOLAZOLINE COUNTERACTS VASOSPASM IN PERIPHERAL ARTERIAL CATHETERS IN NEONATES. † 1334

LOW DOSE TOLAZOLINE COUNTERACTS VASOSPASM IN PERIPHERAL ARTERIAL CATHETERS IN NEONATES. † 1334