Non invasive nasal high frequency ventilation in the course of respiratory syncytial virus bronchiolitis

Introduction

Respiratory syncytial virus (RSV) infection is common in the first 2 years of life, and it is one of the major causes of hospitalization in the first 6 months of life. Respiratory support strategy is still controversial although the non invasive approaches are becoming more popular [3, 6]. On the other hand, the use of non invasive ventilation (NIV) is increasing at any age, and also high frequency NIV has been proposed [4]. Recent in vitro studies [1, 2, 5], showed that High frequency oscillatory ventilation through nasal prongs (nHFOV) has a theoretical rationale and may be feasible in neonates with respiratory distress. We describe the use of nHFOV in an infant with severe bronchiolitis and deep hypercapnia.

Case report

An 11-day-old female infant, born at term from an uncomplicated pregnancy (gestational age 38 weeks, birth weight 3122 g) was discharged from the nursery on day 4 of life. She was admitted to our unit with clinical signs of bronchiolitis (moderate dyspnoea, prolonged expiratory time, rales, oxygen dependency), and a chest X-ray showing an upper right lobe consolidation (Figure 1, panel A). Both nasal and pharyngeal swabs were respiratory syncytial virus (RSV) positive.

Figure 1

Chest X-ray appearance at admission (panel A) and at initiation of nHFOV (panel B).

On admission, the patient was connected to a high flow circuit (NeO₂-Blend, Fisher and Paykel Healthcare Ltd., Auckland, New Zealand), through nasal prongs with a gas flow of 3.5 L/min and a FiO₂ 0.25. In the following 4 h respiratory distress worsened and oxygen requirement increased (up to 0.8) and therefore nasal CPAP (6 cmH₂ O) was started without significant improvement. At 14 h after admission the patient was connected to a SIPAP device (Infant Flow SIPAP, Viasys Respiratory Care, Palm Springs CA, USA), with CPAP 6 and FiO₂ 0.80 reduced then to 0.75. In spite of the respiratory support both clinical signs and blood gas worsened and after 17 h the blood gas showed severe hypercapnia with hypoxia (pH 6.97, pCO₂ 148 mm Hg, A-aDO₂ 374 mm Hg). There was hyperinflation at the lung base as well as consolidation on the left apex noted at chest X-ray (Figure 1, panel B). A nasal HFOV was initiated with a High Frequency Oscillatory Ventilator (Leoni Plus, Heine and Lowenstein, Bad Ems, Germany) through nasal prongs (RAM Cannula, Neotech Products Inc., Valencia CA, USA, Newborn size). The ventilatory settings were set as follows: P_aw 12 cmH₂ O, ΔP 38 cmH₂ O, FR 10 Hz, Ti 33%, FiO₂ 0.95. The level of ΔP was based on the perception of vibration of the chest wall, a frequency of 10 Hz was initially chosen to increase the delivered tidal volume. The pCO₂ dropped to 130 mm Hg after 1 h and progressively to 90 mm Hg in the next 6 h and then to 65 mm Hg. The FR was increased to 15 Hz after 33 h of nHFOV due to hypocapnia (pCO₂ 25 mm Hg). nHFOV was stopped after 65 h, nasal CPAP was supplied for 2 days more and high flow cannula for further 5 days (on oxygen initially and then on room air). The patient was discharged on day 17 of hospitalization free of respiratory symptoms.

Discussion

The issue of the type of respiratory support in cases of bronchiolitis remain unsolved. Conventional mechanical ventilation may be a risk due to the fact that bronchiolitis is an obstructive lung disease implying the use of high tidal and minute volumes and peak pressure with the possibility of air leak. High frequency oscillatory ventilation has been proposed as an alternative to conventional ventilation in case of hypercapnia, though this seems to be contraindicated in case of obstructive lung diseases [6]. On the other hand, the non invasive approach has shown reduction of the ventilatory induced lung injury linked to mechanical ventilation, and infectious complications related to intubation [6].

The usual policy in our unit is to avoid mechanical ventilation as much is possible in case of brochiolitis unless a severe hypercapnia occurs. Since it became available, the use of a RAM cannula has become common in our unit either for CPAP or NIV in preterm or term infants. Our unit has in its charge infants with respiratory problems up to 6 months of age and the RAM cannula is used also in the respiratory support of this of infants with bronchiolitis. Based on the literature data and on our experience in the use of RAM cannulas we applied to the patient nHFOV aiming to avoid intubation. nHFOV was successful, reducing the PCO₂ in a reasonable time and maintaining a sufficient oxygenation.

The larger (Infant) RAM cannula size was used, and care was taken to reduce the leak around the nostrils optimising the transmission of P_aw and ΔP. Initially a 10 Hz frequency was set due to the severe initial hypercapnia to improve ventilation increasing the delivered tidal volume. Our patient confirms with her ventilation improvement what De Luca and Mukerji [1, 2, 5] showed in experimental models, that ΔP is efficiently transmitted to the distal airway by nasal administration of HFOV. We suppose that the particular shape of the nasal device used and its low compliance due to the stiffness of the tubing may have enhanced the transmission. A careful balance between changes in frequency and ΔP, the latter being more efficient [1, 2], is probably crucial to optimize carbon dioxide removal.

We speculated that nHFOV should be carefully evaluated by clinical studies as alternative respiratory support in case of severe bronchiolitis.