VENTILATION © 2006 SNL All rights reserved Heliox and ventilatory support: What does it mean for the future of infant care? Helium-oxygen gas mixtures, commonly known as ‘Heliox’, show promise as a future therapy in a wide range of paediatric respiratory diseases. However, use of Heliox ventilation is not yet widespread in infant care. This article outlines principles and provides guidelines for Heliox- driven mechanical ventilation in neonatology and paediatrics. M Mohiul M Chowdhury n the year 2000, respiratory disease cost MBChB Ithe National Health Service over £2.5 Clinical Research Fellow and Specialist billion. Compared to adults, children are Registrar (Hon), Paediatric Respiratory and more likely to suffer from respiratory Critical Care Medicine, Imperial College London and St Mary’s NHS Trust, London illnesses (TABLE 1). Mortality is highest in infancy amongst all paediatric age groups Elisabeth Reus (FIGURE 1), with respiratory disease being BSc MSc one of the top three causes3,4. In the UK in Lead Nurse in Paediatric Heliox Research and Senior Sister (Hon), Paediatric Respiratory 2004, 3,607 infants died, i.e. >1 in 200 and Critical Care Medicine, Imperial College infants5,6. It is clear therefore that new and FIGURE 1 Childhood deaths in the UK (2004). London and St Mary’s NHS Trust, London more effective therapies need to be current trend of evidence continues. In this Melissa K Brown developed to address the growing burden article the background principles behind BSRT RRT-NPS RCP of respiratory disease in infancy. Heliox therapy in intensive care units are Clinical Research Facilitator, Chest Medicine Administration of a helium-oxygen gas reviewed and the use of Heliox-driven & Critical Care, Sharp Memorial Hospital, mixture (commonly termed ‘Heliox’) is mechanical ventilation is discussed, San Diego, California one such therapy that has been tried in a including a proposed guidance for medical Parviz Habibi wide range of paediatric and neonatal management. MB ChB FRCP FRCPH BSc PhD respiratory diseases (TABLE 2), with Reader and Consultant, Paediatric promising results. There have been no Heliox and its effects on respiratory Respiratory Intensive Care Medicine, Imperial College London and St Mary’s NHS documented side effects in the past 35 pathology Trust, London years of paediatric use. Heliox is any gas mixture containing However, knowledge and awareness of helium (He) and oxygen (O2). In the UK Keywords this treatment option is still not wide- this is available as a set preparation: spread, particularly amongst paediatric Heliox; helium; oxygen; respiratory Heliox-21, containing 21% O2 and 79% and neonatal intensive care units, where it failure; mechanical ventilation; air flow; He. Therefore, in terms of oxygen content, humidification may become a life-saving treatment if the it is comparable to air, which contains 21% Key points Population1 Respiratory cases2 Acute respiratory cases per 1,000 population Chowdhury M.M.M., Reus E., Brown M.K., Habibi P. (2006) Heliox and ventilatory Age 0-14 10,890,790 182,874 16.8 support: What does it mean for the future Age 15+ 48,760,732 612,749 12.6 of infant care? Infant 2(5): 194, 96, 98, TABLE 1 Incidence of respiratory disease in the UK, 2004. 200-03. 1. Heliox is a safe treatment. Upper airway disorders Lower airway disorders Other disorders 2. Heliox, as an adjunct, may enhance Infection • Asthma • Tracheomalacia mechanical ventilation in infants. • Croup • Cystic fibrosis • Tracheal stenosis 3. Conventional weaning strategies need • Epiglottitis • Bronchiectasis • Subglottic stenosis to be reconsidered in the context of • Bacterial tracheitis • Bronchiolitis • Pneumothorax Heliox ventilation. Trauma and mass effects • Pneumonia 4. The success or failure of Heliox therapy • Foreign body aspiration • Respiratory distress syndrome relies heavily on optimising nursing care. • Airway tumours • Bronchopulmonary dysplasia 5. Increasing the helium content of the • Subglottic injury •ARDS driving gas mixture is the key to • Post-extubation stridor maximising the benefits of Heliox. TABLE 2 Reported uses of helium-oxygen gas mixtures in the paediatric respiratory literature. 194 VOLUME 2 ISSUE 5 2006 infant VENTILATION Gas Approximate proportions in gas mixture Density (ρ) Viscosity (η) Diffusion co-efficient Thermal conductivity (cm2/sec) (g/L)7 (micropoises) (µcal.cm.sec.°K)8 Oxygen Nitrogen Helium CO2 O2 Air (‘Nitrox-21’) 21% 79% 0% 1.29 170.8 0.160 0.19 58.0 Heliox-21 21% 0% 79% 0.43 189.5 0.560 0.65 Oxygen 100% 0% 0% 1.43 192.6 0.138 58.5 Nitrogen 0% 100% 0% 1.25 167.4 0.139 58.0 Helium 0% 0% 100% 0.18 188.7 0.165 352.0 TABLE 3 The physical properties of different gas mixtures. O2 and 79% nitrogen. However, due to the helium content, Heliox has a number of important properties (TABLE 3). Viscosity FIGURE 2 The effect of Heliox on gas flow pattern in the airway. Heliox has a high kinematic viscosity (ratio pulmonary atresia and severe tracheal reduction in oxygen requirements, a of viscosity to density). This promotes stenosis. This patient had hypercapnoeic reduction in mean airway pressures and laminar flow, which makes it easier to respiratory failure unresponsive to high shorter duration of ventilation. This was breathe (FIGURE 2). The greater the helium pressures and 100% oxygen with the first well designed, prospective, double- content in the helium-oxygen gas mixture, conventional ventilation. Subsequent blind randomised controlled trial of Heliox the greater is the potential benefit. Heliox introduction of Heliox ventilation allowed ventilation in neonates. Elleau’s work is also passes through narrow airways more a gradual reduction in oxygen supported by the earlier findings of easily and may reduce the work of requirements from 100% down to 30%, a Wolfson et al16 who showed that breathing by improving O delivery to, and 2 rise in SpO2 from 80% to 96%, a rise in spontaneously breathing infants with CO2 removal from, the alveoli. Heliox may tidal volume from 66mL to 100mL and an bronchopulmonary dysplasia had a also reduce gas trapping and dynamic improvement in acid-base with PaCO2 significantly decreased pulmonary hyperinflation in obstructive lung disease. dropping from 115mmHg to 29mmHg resistance, resistive work of breathing and and pH improving from 7.03 to 7.55. mechanical power of breathing when Diffusion of carbon dioxide and oxygen Elleau et al15 provided favourable breathing Heliox compared to air. Heliox has high binary diffusion evidence for the use of Heliox ventilation Most authors who have reported a coefficients for carbon dioxide and oxygen. in neonatal respiratory distress syndrome benefit from Heliox ventilation have noted This means that, in the presence of Heliox (RDS), demonstrating a combined the effect after at least one hour of 17 breathing, CO2 and O2 diffuse at a much reduction in incidence of morbidity ventilation. Gross et al presented a small more rapid rate which is important for (bronchopulmonary dysplasia) and case series of Heliox ventilation in infants alveolar gas transfer, i.e. Heliox may mortality from 71% down to 23%, a with bronchiolitis but failed to show any improve arterial oxygenation and removal statistically significant benefit from Heliox of waste gases. Collateral ventilation at the Impact of breathing Heliox on physiology treatment. The authors of this study altered bronchoalveolar level (through Martin’s Cardiovascular effects the helium-oxygen composition every 15 Channels, Canals of Lambert and Pores of I Increased cardiac index minutes. This may not have given Kohn) is dependent on diffusion. Heliox I Decreased right atrial pressure sufficient time to equilibrate the ventilator may therefore enhance collateral I Increased pulse pressure driving gases nor for the benefits of the 9 ventilation and reduce atelectasis . I Decreased pulse pressure variations helium to be manifest. Furthermore, the The effects of Heliox on cardio- I No change in heart rate sample size of only 10 patients is likely to respiratory physiology have been a source I Increased pulmonary blood flow have been too small to detect any of debate for over 70 years. The effects Respiratory effects statistically meaningful differences. Finally, noted in previous studies are summarised 18-21 I Reduced work of breathing a number of studies have demonstrated in TABLE 4 9-13. Most of the evidence is I Reduced peak and mean airway that the Servo 900C (amongst other Grade 4 or 5. Further high quality pressures ventilators) malfunctions with respect to physiological studies are therefore needed. I Reduced intrinsic PEEP tidal volume measurements and FiO2 I Improved oxygenation delivery, in the presence of helium-oxygen A review of Heliox-driven I Improved carbon dioxide clearance gas mixtures. Five out of the 10 patients in mechanical ventilation I Reduced gas trapping and dynamic the Gross study were under three months Heliox-driven mechanical ventilation is not hyperinflation of age. Accurately guiding such small tidal I Reduced atelectasis new in paediatrics and neonatology. In volumes and FiO2 during volume- 1991 Sauder et al14 reported the successful I Reduced inflammatory cell controlled Heliox ventilation is even use of Heliox ventilation to treat infiltration more technically difficult, especially when respiratory failure in a two month old TABLE 4 The cardiorespiratory effects of the helium content is being altered every infant who had Tetralogy of Fallot, Heliox. 15 minutes (with resultant changes in 196 VOLUME 2 ISSUE 5 2006 infant