ObjectiveHigh-flow nasal cannula (HFNC) therapy is increasingly used in preterm infants despite a paucity of physiological studies. We aimed to investigate the effects of HFNC on respiratory physiology.Study designA prospective randomised crossover study was performed enrolling clinically stable preterm infants receiving either HFNC or nasal continuous positive airway pressure (nCPAP). Infants in three current weight groups were studied: <1000 g, 1000–1500 g and >1500 g. Infants were randomised to either first receive HFNC flows 8–2 L/min and then nCPAP 6 cm H2O or nCPAP first and then HFNC flows 8–2 L/min. Nasopharyngeal end-expiratory airway pressure (pEEP), tidal volume, dead space washout by nasopharyngeal end-expiratory CO2 (pEECO2), oxygen saturation and vital signs were measured.ResultsA total of 44 preterm infants, birth weights 500–1900 g, were studied. Increasing flows from 2 to 8 L/min significantly increased pEEP (mean 2.3–6.1 cm H2O) and reduced pEECO2 (mean 2.3%–0.9%). Tidal volume and transcutaneous CO2 were unchanged. Significant differences were seen between pEEP generated in open and closed mouth states across all HFNC flows (difference 0.6–2.3 cm H2O). Infants weighing <1000 g received higher pEEP at the same HFNC flow than infants weighing >1000 g. Variability of pEEP generated at HFNC flows of 6–8 L/min was greater than nCPAP (2.4–13.5 vs 3.5–9.9 cm H2O).ConclusionsHFNC therapy produces clinically significant pEEP with large variability at higher flow rates. Highest pressures were observed in infants weighing <1000 g. Flow, weight and mouth position are all important determinants of pressures generated. Reductions in pEECO2 support HFNC’s role in dead space washout.

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SummaryThe authors report the case of a 6-year-old girl, presenting with a 4-month history of wheeze associated with barking cough which frequently became wet requiring antibiotics. Her care was transferred to a paediatrician with specialist interest in paediatric respiratory medicine when she had continued symptoms despite bronchodilators and oral steroids for suspected asthma. Spirometry showed a forced expiratory volume 1 of 79% with no evidence of reversibility. The child was investigated for chronic wet cough. Immunoglobulins, sweat test and chest x-ray were all normal. There was no history suggestive of foreign body aspiration (FBA). Tracheomalacia was considered in view of the nature of the cough. The recurrence of an unusual inspiratory noise prompted referral for bronchoscopy. A small piece of plastic tube was removed from the bronchus intermedius. All symptoms resolved. The importance of clinical assessment to ascertain 'wheeze' when acutely unwell is emphasised. Current literature concerning FBA is reviewed.

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The authors report the case of a previously fit and well six-year-old girl who presented to paediatric outpatients with a four month history of wheezing associated with intermittent cough. During her first clinic appointment, she was given a trial of salbutamol via a spacer, which appeared to reduce the wheeze and few crepitations which had been heard prior to administration of the drug. She was diagnosed with asthma and prescribed Beclomethasone and Salbutamol at this time. This apparent initial response to salbutamol was later disputed as spirometry showed no reversibility. Also, she did not report any interval symptoms or increased wheezing with exercise or upper respiratory tract infections. Her mother did not feel that the inhalers had made any difference to her symptoms so her medications were stopped. She developed a number of chest infections and was investigated for possible underlying conditions including cystic fibrosis and structural defects, none of which were found to be present. IgE and RAST for specific allergens were negative and a chest X-ray was completely normal. Full blood count and immunoglobulins were also normal. She was found to have low Hib and tetanus antibodies but these returned to normal after she was re-vaccinated. The doctors treating her began to suspect tracheobronchomalacia was responsible for her symptoms and at this point, the wheeze was noted to be musical in character. At this point, she was referred for a bronchoscopy and a small piece of plastic tubing was found in her airway. It was removed successfully and she has been completely well since, with no further episodes of wheeze or cough. In retrospect she could not remember a choking episode or inhaling a foreign body. This case demonstrates that all that wheezes is not asthma. It is important to re-evaluate and re-consider differential diagnoses when the clinical picture does not completely fit. Airway foreign bodies should be considered even with a long history of cough and no signs of respiratory distress and absence of a history of inhalation of a foreign body does not rule it out, even in older children.

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