sign in sign up
<<
Home , Heliox, Oxygen therapy

VENTILATION © 2006 SNL All rights reserved

Heliox and ventilatory support: What does it mean for the future of infant care?

Helium- gas mixtures, commonly known as ‘’, show promise as a future 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 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 , 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 need to be 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 -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 • • Tracheomalacia mechanical ventilation in infants. • • • Tracheal stenosis 3. Conventional weaning strategies need • Epiglottitis • Bronchiectasis • Subglottic stenosis to be reconsidered in the context of • Bacterial tracheitis • • Pneumothorax Heliox ventilation. Trauma and mass effects • 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 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 (ρ) (η) co-efficient Thermal conductivity (cm2/sec) (g/L)7 (micropoises) (µcal.cm.sec.°K)8 Oxygen Nitrogen Helium CO2 O2 Air (‘-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 and laminar flow, which makes it easier to 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 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 disease. dropping from 115mmHg to 29mmHg resistance, resistive and and pH improving from 7.03 to 7.55. mechanical power of breathing when Diffusion of 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 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 VENTILATION gas mixture density, flow and ventilator instinctive practice is to increase the function). oxygen flow or FiO2 as the patient becomes In contrast, Brown et al22 reported the more hypoxic. In contrast, with Heliox effective use of Heliox-driven mechanical therapy one has to ‘balance’ the helium ventilation in a case of respiratory and oxygen delivery. Indeed, instead of insufficiency due to bronchiolitis, with a increasing the percentage of oxygen being dramatic reduction in CO2 and acid-base administered, it is extremely important in balance, immediately after switching from Heliox therapy to maximise, when conventional air/oxygen to Heliox-driven possible, the percentage of helium being ventilation. Nonetheless, it is interesting to given which will make it easier for the note that, despite the short time intervals oxygen to be ‘carried’ down with the of their study, Gross et al reported a helium to the different levels of the lung. significant reduction in intrapulmonary Therefore, the ultimate objective is to use shunting with Heliox ventilation17 – similar the minimum amount of oxygen required 23 to the findings of Schaeffer et al . FIGURE 3 Inspiration ventilator from eVent to maintain the patient’s oxygen satur- 24 Abd-Allah et al showed that Heliox Medical. ations at a satisfactory level. Experience has ventilation could reduce peak inspiratory shown that this is perhaps the most pressures significantly whilst simultan- difficult concept to understand and the eously achieving improvements in arterial greatest change to current nursing practice. pH and CO2 clearance, consistent with the The setup shown in FIGURE 5 is, in the findings of several case series23,25,26 of Heliox authors’ opinion, the optimum circuit ventilation involving children. design for driving mechanical ventilation Much of the above evidence for Heliox using helium-oxygen gas mixtures. Each ventilation was derived while using existing component is selected for its particular ventilators. Conventional ventilators are Heliox-compatibility features. Further- inaccurate in the presence of Heliox, more, it should be noted that the system making patient management difficult. We shown in FIGURE 5 is not just suitable for therefore recommend that Heliox- Heliox ventilation but may be used equally calibrated ventilators should, preferably, be well for conventional mechanical used for this purpose. There are only two ventilation using air-oxygen gas mixtures. such ventilators currently available in the UK (Inspiration LS, eVent Medical and Minimising leaks of Heliox AVEA, Viasys Healthcare) (FIGURES 3 & 4). During mechanical ventilation, it is It is clear from the above evidence that important to ensure a good seal around the Heliox shows promise for the advancement endotracheal tube (ETT). The use of a of respiratory intensive care. However, to FIGURE 4 AVEA ventilator from Viasys. cuffed ETT is recommended if possible – date, no guidelines exist for its use. even for smaller ETT down to size 3.5mm Therefore, outlined below is a set of Nursing and practical internal diameter. The concern regarding principles to guide Heliox ventilation in considerations “breathing through a narrow straw” ceases paediatrics and neonatology, based on the Providing Heliox therapy to an infant has to be valid in the presence of Heliox vent- literature evidence to date and the proven to be a nursing challenge in several ilation as Heliox passes through narrow collective experience of Heliox ventilation ways. Heliox therapy is a relatively new tubes more easily than conventional gases. from a number of institutions across concept in nursing practice, therefore Europe and North America. As more nurse educators will have a key role to play. Positioning of the patient evidence comes to light these guidance Administrating Heliox requires a good Ideally this should be in the baby’s notes will, no doubt, need to be reviewed understanding of the properties of this gas ‘position of comfort’. This would be and updated. and how it works. With the typically at a 30 degree inclination in a

FIGURE 5 Recommended setup for optimum delivery of helium-oxygen mechanical ventilation.

198 VOLUME 2 ISSUE 5 2006 infant VENTILATION supine or prone position unless there is should have an FiHe display regional collapse of the lung necessitating as well as FiO2 to help guide ‘turning’ of the baby (FIGURE 6). therapy. Vater et al29 showed that there was some benefit Humidification in flow characteristics at Davies et al27 have demonstrated that gases all levels of FiHe but that cool rapidly between the point of release the benefit increases with from the humidification chamber to the increasing FiHe, with the point of entry into the airway. This effect maximal rise in benefit may be greater in the presence of Heliox. noted at an FiHe of between It is therefore important that helium- 0.4 and 0.6, which is also oxygen gas mixtures are well heated and consistent with the authors’ humidified as helium can theoretically experience. carry heat away from surfaces more readily, predisposing to cooling of the patient. This Preservation of ventilation circuit integrity is especially important for neonates and FIGURE 6 A patient on Heliox ventilation. infants. However, as long as the gases are It is important to address this heated and humidified to at least 37°C at for two reasons. Heliox is relatively more modes of ventilation. As there is less the point of entry into the airway, this expensive than oxygen and loss of the gas evidence for the other modes of conven- concern should be satisfactorily addressed. would make the treatment less cost- tional mechanical ventilation, the use of effective. Furthermore, leakage of the gas only ‘CMV’ and ‘SIMV’ is recommended Ventilating simultaneously with Heliox could preferentially cause loss of helium until further evidence becomes available and anaesthetic gases from the , thereby for Heliox ventilation. The ventilators Although compatibility of Heliox and diminishing any potential benefit of Heliox. approved for Heliox delivery, that are volatile anaesthetic gases may be possible28, Thus it is important not to ‘break’ the currently available in the UK, have certain there is currently no ventilator that can ventilation circuit during Heliox ventilation. limitations. It is not possible, with current technically administer both. It is therefore If tracheal toilet is required in-line suction technology, to accurately control tidal not recommended that Heliox ventilation catheters should be used. Nebulisation, if volumes of less than 40mL. In such be utilised if volatile anaesthetic gases need required, may be administered by using an patients, therefore, therapy is directed by to be used (e.g. intra-operatively). in-line piezoelectric nebuliser (note: some pressure-mode and not by volume-mode. piezoelectric nebulisers cannot nebulise A further limitation is that in patients Condensation in the expiratory limbs of steroids). The same ‘in-line’ concepts also under 0.5kg , the tidal volumes Heliox ventilation circuits apply to inhaled nitric oxide administration. become too small to be regulated by Heliox During conventional ventilation the ventilators in either mode. expiratory limb of the ventilation circuit Principles of Heliox-driven The mode of ventilation to be used will, does not contain any healing coil or respiratory support therefore, be determined by the desired insulation to avert cooling of expiratory Heliox-driven respiratory support should tidal volume (VT) which will, in turn, be gases. With Heliox ventilation there may be be considered in the following cases: limited by the weight of the patient. Heliox- considerable condensate in the expiratory I Patients who have obstructive airways driven volume-controlled ventilation is tubing which may potentially affect gas disease, both upper and lower (e.g. respi- currently not recommended in patients calibrations and ventilator function. Thus ratory distress syndrome, asthma, bron- needing VT < 40mL (i.e. approximately the use of insulated and heated expiratory chiolitis, croup). < 6kg). Heliox-driven pressure-controlled tubing for the ventilation circuit is I Patients who have lung atelectasis (e.g. ventilation may be used in patients down to recommended during Heliox-driven pneumonia, acute lung injury). premature neonates with ETT size 2.0mm ventilation as well as heating and I Patients with narrow endotracheal tubes, internal diameter and a weight of at least humidifying the inspired gases. who may also benefit. 500 grams and above30 (TABLE 5). As previously stated it is important to Calibration of flow sensors and Mode of mechanical ventilation maximise the helium content to gain the capnographs The bulk of evidence for Heliox-assisted greatest potential benefit of Heliox mech-

Bernoulli’s principle states that gas flow in therapy is in the areas of CMV and SIMV anical ventilation. This means that FiO2 a tube is affected by the density of the gas in that tube. Therefore flow sensors and Desired tidal Weight Typical patient Mode of ventilation capnographs are liable to be inaccurate volume (VT) limits unless specifically calibrated for use with < 40mL per breath < 6kg Premature neonate Pressure-controlled low density helium-oxygen gas mixtures. Term neonate ventilation Young infant (< 3 months) (CMV or SIMV) Importance of monitoring ≥ 40mL per breath ≥ 6kg Older infant (≥ 3 months) Volume-controlled Monitoring inspired fractions of oxygen Child ventilation Adolescent (PRVC-CMV or PRVC-SIMV) (FiO2) is as important as helium (FiHe) during Heliox ventilation. Ideally, one TABLE 5 Selecting the most appropriate mode for Heliox-driven mechanical ventilation.

200 VOLUME 2 ISSUE 5 2006 infant VENTILATION

Weight < 6kg ≥ 6kg Mode of ventilation Pressure control modes Volume control modes (e.g. P-SIMV) (e.g. PRVC-SIMV)

Fractional inspired oxygen FiO2 = 0.4 FiO2 = 0.4 Tidal volume (VT) Not applicable (derived from PIP) 10 mL/kg Peak inspiratory pressures Whatever minimum PIP is required to Not applicable (derived from tidal volume)

achieve SpO2 of at least 93%

Positive end-expiratory pressure 5 cmH2O 5 cmH2O Inspiratory time To achieve an I:E ratio of 1:1.5 To achieve an I:E ratio of 1:1.5 Set respiratory rate (RR) 30 breaths per minute (bpm) 30 bpm (infants), 20 bpm (children) Inspiratory rise phase Fast Fast Exhalation sensitivity 40% of peak inspiratory flow 40% of peak inspiratory flow NB. Alarm limits have to be adjusted accordingly.

TABLE 6 Recommended initial settings for Heliox ventilation. should be kept to the minimum required lung recruitment may take time. Resist the generated by air/oxygen mixtures31. for adequate oxygenation, in order to urge to increase FiO2 during this time Therefore when weaning from mechanical optimise FiHe. This necessitates greater period. Accept SpO2 as low as 90%. ventilation, it is recommended that the flexibility and tolerance of oxygen satur- Effect on VT and PIP – In volume- PEEP is reduced down to at least 2cmH2O ations. The aim is to achieve FiHe ≥ 0.6, controlled ventilation, the higher the FiHe before extubation. i.e. FiO2 ≤ 0.4 where possible. If a patient is then the lower will be the PIP generated, Increasing PEEP may lead to gas 26 hypoxic, it is preferable to use volume whilst still achieving the same VT . In trapping in conventional ventilation. recruitment strategies; increase PEEP, VT pressure-controlled ventilation, the higher However, this is less likely with Heliox (or PIP in the case of pressure-controlled the FiHe then the higher will be the VT ventilation as the physical properties of the ventilation) before increasing FiO2. generated, whilst still achieving the same gas reduce the likelihood of gas trapping. PIP. However, alveolar recruitment may Thus increases in Heliox-PEEP should lead Special features of Heliox respiratory take time (up to one hour) to become fully to an increase in alveolar recruitment up to support manifest. a higher “maximum” PEEP before gas Success requires patience – When Effect on PEEP – In terms of volume trapping starts to become a problem. This increasing Heliox ventilation settings (PIP, recruitment (VT) it has been suggested that indicates Heliox may confer advantage

VT or PEEP), wait at least 15-30 minutes 1-2 cmH2O PEEP generated by Heliox may compared to conventional gases when 31 before increasing further, as Heliox-driven be equivalent to up to 5cmH2O PEEP using PEEP levels up to 9cmH2O .

Parameter Target Wean only if all the following conditions are met Weaning strategy to wean

1. FiO2 ≤ 0.4 • SpO2 > 90% Reduce FiO2 in steps of 0.05 • Patient has been on the current settings for at least 1. Wait at least 10 minutes between each drop in

10 consecutive minutes FiO2 before weaning further

2. If at any point after a drop in FiO2, the SpO2 < 90% for

5 mins go back up on the FiO2 by 0.05

2. PIP 16cmH2O Stable for at least the past 2 hours on the Reduce the “set PIP” in steps of 1 cmH2O (note that

following settings: even one cmH2O PIP of Heliox is a lot!!)

• Set PIP > 16 cmH2O AND 1. Wait at least 2 hours between each drop in PIP

•FiO2 ≤ 0.4 2. If at any point within this waiting period, the SpO2 < 90% for 5 consecutive minutes go back up on the

PIP by +1 cmH2O. Do NOT increase FiO2 during this waiting period

3. PEEP 2 cmH2O Patient has been on the current settings for at least 2 hours Reduce the PEEP in steps of 1 cmH2O until you reach the

• SpO2 > 90% target of 2 cmH2O

•FiO2 ≤ 0.4 1. Wait at least 2 hours between each drop in PEEP

2. If at any point within this waiting period, the SpO2

< 90% for 5 consecutive minutes increase PEEP by 1 cmH2O 4. RR 5 bpm For at least the past 2 hours: Reduce the backup respiratory rate in steps of 5-10 breaths

• Patient is breathing (i.e. no longer paralysed) per minute (bpm). If the PaCO2 is low, the respiratory rate • There is adequate depth of spontaneous can be weaned more aggressively. • Backup respiratory rate (RR) > 5 breaths per minute 1. Wait at least 2 hours between each drop in backup RR

• PEEP ≤ 5 cmH2O 2. If at any point within this waiting period, the SpO2 < 90%

• Set PIP ≤ 16 cmH2O for 5 consecutive minutes go back up on the backup

•FiO2 ≤ 0.4 respiratory rate by 5-10 bpm

TABLE 7 Weaning patients <6kg in weight from Heliox ventilation. infant VOLUME 2 ISSUE 5 2006 201 VENTILATION

Stepping down – It is suggested that Guidance for the medical choosing a threshold of PaCO2 of less than 6 patients be weaned directly from Heliox- management of Heliox-driven kPa in Heliox ventilation is that it theoreti- driven mechanical ventilation onto either mechanical ventilation cally represents a degree of permissive non-invasive Heliox-driven CPAP or, if hypercapnoea in conventional air/oxygen The following guide is proposed for tolerated, spontaneous inhalation of Heliox. ventilation. starting, maintaining and weaning This is because stepping down from Heliox- mechanical ventilation driven by helium- The following sequence of stepping driven mechanical ventilation into oxygen gas mixtures. down is recommended due to the special conventional gases would mean simul- nature of Heliox ventilation. However, taneously losing the ongoing benefits of Initial settings there should be a ONE HOUR interval Heliox as well as those of mechanical Settings for starting Heliox ventilation are before weaning the next parameter. ventilatory support, thereby risking failure shown in TABLE 6. Note that as a driving There is one generic point to remember of weaning. Even changing from Heliox gas, Heliox has less distending pressure and during the whole weaning sequence. Take ventilation to conventional ventilation could effect on the alveoli than air/oxygen advantage of high SpO2 to reduce FiO2. result in a step back for the patient as there mixtures. Thus a longer inspiratory phase Therefore, if at ANY point in this is such a significant difference between the is required compared to conventional sequence: I two in terms of alveolar recruitment, as mechanical ventilation. SpO2 ≥ 95% consistently for 10 minutes, demonstrated by Nawab et al9. reduce FiO further in 0.05 steps. Wait 10 Maintaining Heliox ventilation 2 Drop in SpO2 – As the FiHe increases minutes between each FiO2 change. If Aim to reach the following target (and FiO2 drops), there may be a transient during this 10 minute period SpO2 < 90% parameters prior to discontinuing Heliox- (10-15 minute) drop in SpO2 (occasionally for at least 5 minutes...go back up by 0.05 driven mechanical ventilation: as low as 85-90%) and a fall in PIP. This FiO2 step. I SPO ≥ 90% may be because it takes time for the higher 2 Consider discontinuing mechanical I FiO ≤ 0.4 FiHe to take effect (by increasing alveolar 2 ventilation if patients meet the following I PIP = 16 cmH O recruitment and oxygen delivery). The 2 criteria (TABLE 7 & 8): I Respiratory rate = five breaths per drop in SpO is followed by a subsequent I There is no hypercapnoea or 2 minute I rise in SpO2 and VT if Heliox ventilation is Minimal PIP needed to ventilate ade- successful. Reducing Heliox ventilation settings quately, i.e. ≤ 16 cmH2O (patients < 6kg Hypocapnoea – Be vigilant for hypocap- Reduce the ventilation support if there is: weight) or noea during Heliox ventilation. Heliox acts I Minimal VT support needed to ventilate Adequate oxygenation (i.e. SpO2 ≥ 90%) quite rapidly, particularly with gas mix- I adequately, i.e. ≤ 5mL/kg (patients ≥ 6kg Adequate CO2 clearance [i.e. PaCO2 < 6 tures that have higher helium content. This kPa (or in the case of chronic lung dis- weight) I Backup respiratory rate (RR) ≤ five is because oxygen and CO2 gas transfers ease, back to baseline PaCO2)]. occur 3.5 times faster in the presence of CO2 clearance is much more rapid in the breaths per minute I Heliox than with conventional air/oxygen presence of Heliox due to the high binary PEEP ≤ 2 cmH2O I gas mixtures as explained earlier. diffusion coefficients. The justification for FiO2 ≤ 0.4

Target Wean only if the following conditions are met Weaning strategy

1. FiO2 ≤ 0.4 • SpO2 > 90% Reduce FiO2 in steps of 0.05

• Patient has been on the current settings for at least 1. Wait at least 10 minutes between each drop in FiO2 10 consecutive minutes before weaning further

2. If at any point after a drop in FiO2, the SpO2 < 90% for

5 mins go back up on the FiO2 by 0.05

2. VT 5 mL/kg Patient has been on the current settings for at least one hour Reduce the “set VT” in steps of 1 mL/kg until you reach the

• SpO2 > 90% target of 5 mL/kg

•FiO2 ≤ 0.4 1. Wait at least 1 hour between each drop in VT

2. If at any point within this waiting period, the SpO2 < 90% for 5 consecutive minutes increase VT by +1 mL/kg.

Do NOT increase FiO2 during this waiting period.

3. PEEP 2 cmH2O Patient has been on the current settings for at least one hour Reduce the PEEP in steps of 1 cmH2O until you reach the

• SpO2 > 90% target of 2 cmH2O

•FiO2 ≤ 0.4 1. Wait at least 1 hour between each drop in PEEP

2. If at any point within this waiting period, the SpO2 < 90%

for 5 consecutive minutes increase PEEP by 1 cmH2O 4. RR 5 bpm Patient has been on the current settings for at least one hour Reduce the backup respiratory rate in steps of 5-10 breaths

• SpO2 > 90% per minute (bpm)

•FiO2 ≤ 0.4 1. Wait at least 1 hour between each drop in backup RR

2. If at any point within this waiting period, the SpO2 < 90% for 5 consecutive minutes increase the backup respiratory rate by 5-10 bpm (i.e. to the previous setting)

TABLE 8 Weaning patients ≥6kg in weight from Heliox ventilation.

202 VOLUME 2 ISSUE 5 2006 infant VENTILATION

Management of hypercapnoea protective and optimal recruitment subjects breathing a helium-oxygen mixture. Hum Physiol 1983; 9(4): 284-88. strategies are employed. Improved CO2 Hypercapnoea, in the context of Heliox 14. Sauder R.A., Rafferty J.F., Bilenki A.L. et al. Helium- clearance in obstructive pulmonary disease ventilation, is defined as: oxygen and conventional mechanical ventilation in I states is the principle advantage of Heliox PaCO2 > 6kPa (and showing a rising the treatment of large airway obstruction and trend) for all paediatric/neonatal ventilation. Optimising the helium content respiratory failure in an infant. South Med J 1991; cases (except infants with chronic of the driving gas mixtures is the key to 84(5): 646-48. maximising the benefits of Heliox 15. Elleau C., Galperine R.I., Guenard H. et al. Helium- lung disease) oxygen mixture in respiratory distress syndrome: A I ventilation. Conventional weaning PaCO2 > 2kPa above their baseline (and double-blind study. J Pediatr 1993; 122(1): 132-36. showing a rising trend) for infants with strategies must, therefore, be reconsidered 16. Wolfson M.R., Bhutani V.K., Shaffer T.H. et al. chronic lung disease in the context of Heliox ventilation. Mechanics and energetics of breathing helium in In patients < 6kg weight ensure optimal infants with bronchopulmonary dysplasia. J Pediatr Acknowledgements 1984; 104(5): 752-57. lung recruitment using Heliox-PEEP The authors would like to thank Mr Jeff 17. Gross M.F., Spear R.M., Peterson B.M. Helium- strategies as described above. Once oxygen mixture does not improve in adequate Heliox-PEEP has been achieved, Henk, eVent Medical, for providing some mechanically ventilated children with bronchiolitis. follow a sequence of increasing RR, of the photographic material for this article Crit Care 2000; 4(3): 188-92. followed by PIP (once maximum RR has and for his technical input; Mr Christian 18. Tassaux D., Jolliet P., Thouret J.M. et al. Calibration of seven ICU ventilators for mechanical ventilation been reached). Saville, Fisher & Paykel, for input regarding humidification; and Dr David Crosby, with helium-oxygen mixtures. Am J Respir Crit Care Med 1999; 160(1): 22-32. Management of hypoxia BOC Medical, for assistance with Heliox- 19. Berkenbosch J.W., Grueber R.E., Dabbagh O. et al. Poor oxygenation that requires related bibliography. Effect of helium-oxygen (heliox) gas mixtures on intervention, in the context of Heliox the function of four pediatric ventilators. Crit Care References Med 2003; 31(7): 2052-58. ventilation, is defined as: 20. Oppenheim-Eden A., Cohen Y., Weissman C. et al. I 1. National Statistics. UK Census Figures, 2001. SpO2 < 90% (and/or PaO2 < 8kPa) The effect of helium on ventilator performance: http://www.statistics.gov.uk (accessed 2006). Study of five ventilators and a bedside Pitot tube AND 2. HES Online. UK Hospital Episode Statistics, 2000- I spirometer. Chest 2001; 120(2): 582-88. FiO2 > 0.4 2001. http://www.hesonline.nhs.uk (accessed 2006). Use lung recruitment strategies before 3. Guyer B., MacDorman M.F., Martin J.A. et al. Annual 21. Rogers M.S., Scott J.R., Malinowski T. Volume accuracy of the Siemens Servo 900C and increasing FiO > 0.4. Ensure optimal lung summary of vital statistics-1997. Pediatrics 1998; 2 Novametrix Ventrak when delivering helium- recruitment using Heliox-PEEP strategies 102(6): 1333-49. 4. Reyes H., Perez-Cuevas R., Salmeron J. et al. Infant oxygen mixtures. (ABS) Respiratory Care 1995; 1206. as described above. Once adequate Heliox- mortality due to acute respiratory infections: The 22. Brown M.K., Duthie S. Heliox as a therapeutic tool PEEP has been achieved, follow a sequence influence of primary care processes. Health Policy in the management of RSV bronchiolitis: A paediatric case report. Respiratory Care 1999; 44: of increasing PIP (or VT), followed by RR Plan 1997; 12(3): 214-23. 1287. (once maximum PIP or VT has been 5. Office for National Statistics. Mortality Statistics - 23. Schaeffer E.M., Pohlman A., Morgan S. et al. reached). Childhood, infant and Perinatal. Review of the Registrar General on deaths in England and Wales, Oxygenation in status asthmaticus improves during ventilation with helium-oxygen. Crit Care Med 1999; Recommended maximum settings 2004. http://www.statistics.gov.uk (accessed 2006). 6. Eurostat: Statistical Office for the European 27(12): 2666-70. The recommended maximum settings for Communities. Younger age profile population 24. Abd-Allah S.A., Rogers M.S., Terry M. et al. Helium- each of the ventilation parameters are: variant - 1st January population (2004). oxygen therapy for pediatric acute severe asthma 1. Maximum PEEP = 9cmH O http://epp.eurostat.ec.europa.eu (accessed 2006). requiring mechanical ventilation. Pediatr Crit Care 2 Med 2003; 4(3): 353-57. 2. Maximum RR = 40 breaths per minute 7. Winters J.W., Willing M.A., Sanfilippo D. Heliox improves ventilation during high-frequency 25. Michael J., Bocklage T., Tobias J. Helium (for infants) or 30 breaths per minute oscillatory ventilation in pediatric patients. Pediatr administration during mechanical ventilation in (children) Crit Care Med 2000; 1(1): 33-37. children with respiratory failure. J Intensive Care Med 8. Gupta V.K., Cheifetz I.M. Heliox administration in 1999; 14: 140-47. 3. Maximum PIP = 30cmH2O for infants, the pediatric intensive care unit: An evidence-based 26. Gluck E.H., Onorato D.J., Castriotta R. Helium- 40cmH2O for children review. Pediatr Crit Care Med 2005; 6(2):204-11. oxygen mixtures in intubated patients with status 4. Maximum VT = 10 mL/kg 9. Nawab U.S., Touch S.M., Irwin-Sherman T. et al. asthmaticus and respiratory acidosis. Chest 1990; If all the above maximum recommended Heliox attenuates lung inflammation and structural 98(3): 693-98. settings have been reached, increase FiO2 as alterations in acute lung injury. Pediatr Pulmonol 27. Davies M.W., Dunster K.R., Cartwright D.W. Inspired 2005; 40(6): 524-32. gas in ventilated neonates. Pediatr required in 0.05 steps. Once FiO2 = 0.6 has 10. Enneper S., Pruter E., Jenke A. et al. Cardio- Pulmonol 2004; 38(1): 50-54. been reached, if SpO2 is still < 90% (PaO2 respiratory effects of heliox using a model of upper 28. Carvalho B., Sanders D. The output of two < 8kPa), start considering alternative airway obstruction. Biomed Tech (Berl) 2005; 50(5): sevoflurane vaporizers in the presence of helium. Br modes of respiratory support in addition 126-31. J Anaesth 2002; 88(5): 711-13. to Heliox. In the meantime, FiO2 can still 11. Lee D.L., Lee H., Chang H.W. et al. Heliox improves 29. Vater M., Hurt P.G., Aitkenhead A.R. Quantitative be increased up to a maximum of 0.9. hemodynamics in mechanically ventilated patients effects of respired helium and oxygen mixtures on with chronic obstructive pulmonary disease with gas flow using conventional oxygen masks. CONCLUSIONS systolic pressure variations. Crit Care Med 2005; Anaesthesia 1983; 38(9): 879-82. 33(5): 968-73. 30. Henk J. Personal Communication: Technical limits The special physical properties of Heliox 12. Tassaux D., Jolliet P., Roeseler J. et al. Effects of for heliox ventilation using the Inspiration LS. 2006. have been utilised in the management of helium-oxygen on intrinsic positive end-expiratory 31. Chowdhury M., Akhter R., Dixon P.D., Habibi P. obstructive pulmonary disease conditions. pressure in intubated and mechanically ventilated Heliox-driven CPAP may be more effective than patients with severe chronic obstructive pulmonary These same properties also hold promise conventional CPAP in reducing work of breathing disease. Crit Care Med 2000; 28(8): 2721-28. and improving tidal volumes in infant respiratory when Heliox is used as the driving gas in 13. Kostylev E.G., Eropkina A.G. State of the pulmonary distress. Proceedings of CHEST Conference. 2006. mechanical ventilation where lung blood flow and central hemodynamics in normal In press. infant VOLUME 2 ISSUE 5 2006 203