Mask versus nasal prong leak and intermittent hypoxia during continuous positive airway pressure in very preterm infants.

BACKGROUND: Nasal continuous positive airway pressure (NCPAP) can be applied via binasal prongs or nasal masks; both may be associated with air leak and intermittent hypoxia. We investigated whether the latter is more frequent with nasal masks or prongs. METHODS: Continuous 24 hours recordings of inspired oxygen fraction (FiO2), pulse rate, respiratory rate, pulse oximeter saturation (SpO2) and CPAP level were made in preterm infants with respiratory insufficiency (n=20) managed on CPAP in the NICU at the Royal Hobart Hospital. As part of routine care, nasal interfaces were alternated 4-hourly between mask and prongs. In each recording, the first two segments containing at least 3 hours of artefact-free signal for each interface were selected. Recordings were analysed for episodes with hypoxaemia (SpO2 <80% for ≥10 s) and bradycardia (pulse rate <80/min for ≥4 s) and for episodes of pressure loss at the nasal interface. Data were compared using Wilcoxon-matched pairs test and are reported as median (IQR). RESULTS: Infants had a gestational age at birth of 26 (25-27) weeks and postnatal age of 17 (14-24) days. There was no difference in %time with interface leak between prong and mask (0.9 (0-8)% vs 1.1 (0-18)%, p=0.82), %time with SpO2 <80% (0.15 (0-1.2)% vs 0.06 (0-0.8)%, p=0.74) or heart rate <80/min (0.03 (0-0.2)% vs 0 (0-0.2)%, p=0.64). Three infants had interface leak for >10% of the time with prongs and 5 with the mask. CONCLUSION: Both interfaces resulted in a similarly stable provision of positive airway pressure, and there was also no difference in the occurrence of intermittent hypoxia.

Delayed antivenom for life-threatening tiger snake bite: Lessons learnt.

An adolescent victim of an urban snakebite developed respiratory failure, rhabdomyolysis and consumption procoagulopathy but recovered with two vials of tiger snake antivenom administered after a delay of 48 hours. The clinical significance of a post-bite collapse was not initially appreciated. Tiger snake (Notechis spp.) venom antigen was measurable in blood before antivenom but not after whereas antivenom was measurable in blood for nine ensuing days. This case adds to growing evidence that further pharmacokinetic research of venom-antivenom interaction is required to establish the correct dose and timing of tiger snake antivenom. Antivenom therapy, even when delayed, facilitates recovery from snake envenomation.

Impact of Minimally Invasive Surfactant Therapy in Preterm Infants at 29-32 Weeks Gestation.

BACKGROUND: Most preterm infants born at 29-32 weeks gestation now avoid intubation in early life, and thus lack the usual conduit through which exogenous surfactant is given if needed. OBJECTIVE: The aim of this work was to examine whether a technique of minimally invasive surfactant therapy used selectively at 29-32 weeks gestation would improve outcomes. METHODS: We studied the impact of selective administration of surfactant (poractant alfa 100-200 mg/kg) by thin catheter in infants with respiratory distress syndrome on continuous positive airway pressure (CPAP). The threshold for consideration of treatment was CPAP ≥7 cm H2O and FiO2 ≥0.35 prior to 24 h of life. In-hospital outcomes were compared before and after introducing minimally invasive surfactant therapy (epochs 1 and 2, respectively). RESULTS: During epoch 2, of 266 infants commencing CPAP, 51 (19%) reached the treatment threshold. Thirty-seven infants received surfactant via thin catheter, and CPAP failure was avoided in 34 of these (92%). For the overall cohort of infants at 29-32 weeks gestation, after the introduction of minimally invasive surfactant therapy, there were reductions in CPAP failure (epoch 1: 14%, epoch 2: 7.2%) and average days of intubation, with equivalent surfactant use and days of respiratory support (intubation + CPAP). Pneumothorax was substantially reduced (from 8.0 to 2.4%). These findings were mirrored within the subgroups reaching the severity threshold in each epoch. The incidence of bronchopulmonary dysplasia was low in both epochs. CONCLUSIONS: Selective use of minimally invasive surfactant therapy at 29-32 weeks gestation permits a primary CPAP strategy to be pursued with a high rate of success, and a low risk of pneumothorax.

Lost without trace: oximetry signal dropout in preterm infants.

Oxygen saturation (SpO2) signal dropout leaves caregivers without a reliable measure to guide oxygen therapy. We studied SpO2 dropout in preterm infants on continuous positive airway pressure, noting the SpO2 values at signal loss and recovery and thus the resultant change in SpO2, and the factors influencing this parameter. In 32 infants of median gestation 26 weeks, a total of 3932 SpO2 dropout episodes were identified (1.1 episodes/h). In the episodes overall, SpO2 decreased by 1.1%, with the SpO2 change influenced by starting SpO2 (negative correlation), but not dropout duration. For episodes starting in hypoxia (SpO2 <85%), SpO2 recovered at a median of 3.2% higher than at SpO2 dropout, with a downward trajectory in a quarter of cases. We conclude that after signal dropout SpO2 generally recovers in a relative normoxic range. Blind FiO2 adjustments are thus unlikely to be of benefit during most SpO2 dropout episodes.

Oxygen saturation targeting in preterm infants receiving continuous positive airway pressure.

OBJECTIVE: The precision of oxygen saturation (SpO2) targeting in preterm infants on continuous positive airway pressure (CPAP) is incompletely characterized. We therefore evaluated SpO2 targeting in infants solely receiving CPAP, aiming to describe their SpO2 profile, to document the frequency of prolonged hyperoxia and hypoxia episodes and of fraction of inspired oxygen (FiO2) adjustments, and to explore the relationships with neonatal intensive care unit operational factors. STUDY DESIGN: Preterm infants <37 weeks' gestation in 2 neonatal intensive care units were studied if they were receiving CPAP and in supplemental oxygen at the beginning of each 24-hour recording. SpO2, heart rate, and FiO2 were recorded (sampling interval 1-2 seconds). We measured the proportion of time spent in predefined SpO2 ranges, the frequency of prolonged episodes (≥30 seconds) of SpO2 deviation, and the effect of operational factors including nurse-patient ratio. RESULTS: A total of 4034 usable hours of data were recorded from 45 infants of gestation 30 (27-32) weeks (median [IQR]). When requiring supplemental oxygen, infants were in the target SpO2 range (88%-92%) for only 31% (19%-39%) of total recording time, with 48 (6.9-90) episodes per 24 hours of severe hyperoxia (SpO2 ≥98%), and 9.0 (1.6-21) episodes per 24 hours of hypoxia (SpO2 <80%). An increased frequency of prolonged hyperoxia in supplemental oxygen was noted when nurses were each caring for more patients. Adjustments to FiO2 were made 25 (16-41) times per day. CONCLUSION: SpO2 targeting is challenging in preterm infants receiving CPAP support, with a high proportion of time spent outside the target range and frequent prolonged hypoxic and hyperoxic episodes.

Exercise training in dilated cardiomyopathy improves rest and stress cardiac function without changes in cardiac high energy phosphate metabolism.

OBJECTIVE: To determine the effects of short-term exercise training on cardiac function and metabolism during rest and physical exercise in patients with heart failure from dilated cardiomyopathy (DCM). DESIGN: Patients with DCM (n=15, age 58±2 years, NYHA class I-III) were studied before and after 8 weeks of cycle exercise for 20 min, five times per week. MAIN OUTCOME MEASURES: Cardiac volumes, function and high energy phosphate metabolism were measured using cardiac magnetic resonance during rest and 7 min of acute physical exercise (leg-raising). RESULTS: At baseline, average left ventricular ejection fraction (LVEF) was 38±3%, which did not alter during 7 min of exercise. After 8 weeks of home exercise training, there was a 16% improvement in resting LVEF to 44±3% (p<0.01). Training caused a further 20% improvement in LVEF (p<0.05) during acute physical exercise. There was a negative correlation between subjects' baseline level of exercise and change in LVEF (r=-0.67, p<0.05), with sedentary patients having the greatest improvement. Cardiac phosphocreatine (PCr) to ATP ratio did not change during acute physical exercise or after exercise training. CONCLUSIONS: Short-term exercise training improves resting LVEF and LVEF with acute physical exercise with sedentary patients having the greatest improvement. There were no changes in cardiac PCr to ATP, before or after exercise training, suggesting that the improved cardiac function was not caused by improved energetics. Therefore, peripheral factors likely underlie the improved cardiac function in patients with heart failure after short-term exercise.