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doi:10.1111/jpc.12393
ORIGINAL ARTICLE
Quantifying temperature and relative humidity of medical gases used for newborn resuscitation Jennifer A Dawson,1,2,3 Louise S Owen,1,2,3 Robin Middleburgh4 and Peter G Davis1,2,3 1
The Royal Women’s Hospital, 2Murdoch Childrens Research Institute, and 3The University of Melbourne, Melbourne, Victoria, Australia and 4University of Newcastle, Newcastle, England
Aim: The gases used to stabilise infants during resuscitation are usually unconditioned air and oxygen, often described as ‘cold and dry’, in comparison with the heated, humidified gases used for ongoing ventilation in neonatal intensive care units. The aim of this study was to determine exactly how ‘cold and dry’ these unconditioned gases are. Method: Multiple measurements of temperature and relative humidity (RH) of piped gases were recorded at different sites, and at different times of day, across The Royal Women’s Hospital, Melbourne. Ambient temperature and relative humidities were also recorded. Results: Eighty paired air and oxygen measurements of temperature and RH were recorded. Mean temperatures of piped oxygen and air were 23.3 (0.9) and 23.4 (0.9) °C respectively. Mean RH of piped air was 5.4 (0.7) %; piped oxygen was significantly drier, mean RH 2.1 (1.1) %. Conclusion: Piped gases were delivered at room temperature and were extremely dry. This highlights the importance of research assessing the practicality of heating and humidifying resuscitation gases, and assessing the impact of their use on clinically important neonatal outcomes. Key words:
humidification; medical air; oxygen.
What is already known on this topic?
What this paper adds?
1 Most infants are resuscitated with gases described as ‘cold’ and ‘dry’. 2 Gases used for ongoing ventilation are usually heated and humidified. 3 Unconditioned gases can damage respiratory mucosa.
1 Piped gases used for delivery room resuscitation are extremely dry. 2 The temperature of piped gases is similar to ambient temperature. 3 The relative humidity of piped oxygen is significantly drier than piped air.
Background Newborn resuscitation guidelines have undergone significant changes over the past decade. The introduction of saturation targeting, the provision of blended air and oxygen, the use of positive end expiratory pressure and improved measures for thermoregulation have all been introduced1 with the aim of Correspondence: Dr Jennifer Dawson, Neonatal Services, The Royal Women’s Hospital, Corner Grattan Street and Flemington Road, Parkville, Vic. 3052, Australia. Fax: 0308345 3789; email: jennifer.dawson@ thewomens.org.au Conflict of interest: None declared. Author Contributions JAD: Conceived and designed the study, collected, analysed and interpreted data, drafted the manuscript. LSO: Contributed to study design, collected, analysed and interpreted data, drafted the manuscript. RM: Contributed to data collection and editing of manuscript. PGD: Contributed to study design, data interpretation, drafting the manuscript, supervision of all aspects of the study. All authors approved the final version of the manuscript. Accepted for publication 29 May 2013.
24
improving neonatal outcomes. The use of heated, humidified gases in the delivery room may also improve outcomes by reducing hypothermia,2 preserving mucosal function3 and reducing respiratory complications.4 However, the gases used to stabilise infants during resuscitation are usually unconditioned air and oxygen, often described as ‘cold and dry’, in comparison to the heated humidified gases used for ongoing ventilation in neonatal intensive care units (NICU). The aim of this study was to determine exactly how ‘cold and dry’ these unconditioned gases are.
Method This observational study took place at The Royal Women’s Hospital (RWH), Melbourne, Australia. The RWH supplies piped air and oxygen to sites throughout the hospital including delivery rooms, operating theatres and the NICU. Piped gas outlets are fitted with flow meters and blenders (Bird Low Flow Air/O2 MicroBlender, Care Fusion, Dublin, OH, USA). We connected gas tubing and a t-connector to these flow meters and set gas flow to 10 L/min. A calibrated thermohygrometer and probe (Testo 635 and 9769, Testo AG, Lenzkirch, Germany) was inserted into the t-connector, such
Journal of Paediatrics and Child Health 50 (2014) 24–26 © 2013 The Authors Journal of Paediatrics and Child Health © 2013 Paediatrics and Child Health Division (Royal Australasian College of Physicians)
JA Dawson et al.
Fig. 1 Schematic diagram of equipment; (a) wall gas outlet, (b) gas blender/flow meter, (c) gas tubing, (d) thermo-hygrometer probe, (e) t-connector.
that the sensor of the probe was held in the centre of the gas flow. The distal end of the t-connecter was open to air (Fig. 1). Over a 1-month period multiple, repeated measurements of temperature and relative humidity (RH) of the piped gases were recorded, including samples at different sites, on different floors and at different times of the day. At each site ambient temperature and RH were also recorded.
Results Eighty paired air and oxygen measurements of temperature and RH were recorded from wall outlets across RWH, including the NICU (31), operating theatres (9), birthing rooms (23) and neonatal research laboratory (17). In a subset of twenty recordings, ambient temperatures and RHs were measured (n = 8 NICU, n = 4 theatres, n = 5 birthing rooms, n = 3 neonatal laboratory).
Temperature Mean (standard deviation (SD)) ambient temperature at test sites was 23.0 (0.95) °C. The mean temperatures of piped oxygen and air were 23.3 (0.9) and 23.4 (0.9) °C respectively (P = 0.49). Temperatures of piped air and oxygen were slightly higher, in the afternoon (both by 0.3°C).
Relative humidity Mean (SD) ambient RH at test sites was 41.1 (2.2) %. The mean RH of piped air was 5.4 (0.7) % and of piped oxygen was 2.1 (1.1) % (this was significantly drier than piped air (P < 0.001)). Both gases had slightly lower RH after midday, by an average of 0.7% (oxygen) and 0.4% (air).
Discussion This study describes the temperature and RH of piped hospital gases at the RWH, Melbourne. We demonstrated that values were stable across time and test sites. However, Knobel et al. measured delivery room temperatures and found they ranged
Temperature and humidity of wall gases
from 19 to 31°C.5 Although temperatures were clinically indistinguishable from room temperatures; RH of both air and oxygen were consistently very low and much lower than ambient air. When resuscitating with room air and a selfinflating bag, infants would receive gas at around 23°C at ambient humidity. The piped gases were drier than air used in commercial aeroplane cabins (RH ∼14%)6 and lower than humidity recorded in some of the driest places on earth, for example Mojave Desert, California (RH 10–30%). Humidification of ventilator gases for patients of all ages has been standard care for decades and is particularly important to newborn infants because of their delicate lungs,7 their problems maintaining normal temperature and fluid balance. Animal studies have shown that breathing dry gas slows tracheal mucous velocity to almost zero, dries secretions and causes inflammation of the respiratory tract, which continues even after humidified gases are reintroduced.8 Dry gas has also been shown to decrease functional residual capacity, reduce compliance and decrease oxygenation.9 In adults the use of unconditioned gases has been shown to cause airway obstruction due to increased mucous viscosity and reduced mucociliary clearance, and cause cessation of ciliary beating, within 10 min.10 There is evidence that heated, humidified gases may be beneficial, particularly in low birthweight and preterm neonates, as they have larger surface areas, higher insensible losses and are more likely to receive assisted ventilation in the delivery room. The UK Project 27/28, studying outcomes in infants of 27 and 28 weeks’ gestation, earmarked poor initial thermal care as a major cause of mortality in this age group.7 A recent retrospective review of heated, humidified gas in the delivery room, in infants less than 33 weeks’ gestation, showed less hypothermia at NICU admission than infants stabilised using unconditioned gases.2 An older study, in the pre-surfactant, pre-antenatal steroid era, showed infants
doi:10.1111/jpc.12393
ORIGINAL ARTICLE
Quantifying temperature and relative humidity of medical gases used for newborn resuscitation Jennifer A Dawson,1,2,3 Louise S Owen,1,2,3 Robin Middleburgh4 and Peter G Davis1,2,3 1
The Royal Women’s Hospital, 2Murdoch Childrens Research Institute, and 3The University of Melbourne, Melbourne, Victoria, Australia and 4University of Newcastle, Newcastle, England
Aim: The gases used to stabilise infants during resuscitation are usually unconditioned air and oxygen, often described as ‘cold and dry’, in comparison with the heated, humidified gases used for ongoing ventilation in neonatal intensive care units. The aim of this study was to determine exactly how ‘cold and dry’ these unconditioned gases are. Method: Multiple measurements of temperature and relative humidity (RH) of piped gases were recorded at different sites, and at different times of day, across The Royal Women’s Hospital, Melbourne. Ambient temperature and relative humidities were also recorded. Results: Eighty paired air and oxygen measurements of temperature and RH were recorded. Mean temperatures of piped oxygen and air were 23.3 (0.9) and 23.4 (0.9) °C respectively. Mean RH of piped air was 5.4 (0.7) %; piped oxygen was significantly drier, mean RH 2.1 (1.1) %. Conclusion: Piped gases were delivered at room temperature and were extremely dry. This highlights the importance of research assessing the practicality of heating and humidifying resuscitation gases, and assessing the impact of their use on clinically important neonatal outcomes. Key words:
humidification; medical air; oxygen.
What is already known on this topic?
What this paper adds?
1 Most infants are resuscitated with gases described as ‘cold’ and ‘dry’. 2 Gases used for ongoing ventilation are usually heated and humidified. 3 Unconditioned gases can damage respiratory mucosa.
1 Piped gases used for delivery room resuscitation are extremely dry. 2 The temperature of piped gases is similar to ambient temperature. 3 The relative humidity of piped oxygen is significantly drier than piped air.
Background Newborn resuscitation guidelines have undergone significant changes over the past decade. The introduction of saturation targeting, the provision of blended air and oxygen, the use of positive end expiratory pressure and improved measures for thermoregulation have all been introduced1 with the aim of Correspondence: Dr Jennifer Dawson, Neonatal Services, The Royal Women’s Hospital, Corner Grattan Street and Flemington Road, Parkville, Vic. 3052, Australia. Fax: 0308345 3789; email: jennifer.dawson@ thewomens.org.au Conflict of interest: None declared. Author Contributions JAD: Conceived and designed the study, collected, analysed and interpreted data, drafted the manuscript. LSO: Contributed to study design, collected, analysed and interpreted data, drafted the manuscript. RM: Contributed to data collection and editing of manuscript. PGD: Contributed to study design, data interpretation, drafting the manuscript, supervision of all aspects of the study. All authors approved the final version of the manuscript. Accepted for publication 29 May 2013.
24
improving neonatal outcomes. The use of heated, humidified gases in the delivery room may also improve outcomes by reducing hypothermia,2 preserving mucosal function3 and reducing respiratory complications.4 However, the gases used to stabilise infants during resuscitation are usually unconditioned air and oxygen, often described as ‘cold and dry’, in comparison to the heated humidified gases used for ongoing ventilation in neonatal intensive care units (NICU). The aim of this study was to determine exactly how ‘cold and dry’ these unconditioned gases are.
Method This observational study took place at The Royal Women’s Hospital (RWH), Melbourne, Australia. The RWH supplies piped air and oxygen to sites throughout the hospital including delivery rooms, operating theatres and the NICU. Piped gas outlets are fitted with flow meters and blenders (Bird Low Flow Air/O2 MicroBlender, Care Fusion, Dublin, OH, USA). We connected gas tubing and a t-connector to these flow meters and set gas flow to 10 L/min. A calibrated thermohygrometer and probe (Testo 635 and 9769, Testo AG, Lenzkirch, Germany) was inserted into the t-connector, such
Journal of Paediatrics and Child Health 50 (2014) 24–26 © 2013 The Authors Journal of Paediatrics and Child Health © 2013 Paediatrics and Child Health Division (Royal Australasian College of Physicians)
JA Dawson et al.
Fig. 1 Schematic diagram of equipment; (a) wall gas outlet, (b) gas blender/flow meter, (c) gas tubing, (d) thermo-hygrometer probe, (e) t-connector.
that the sensor of the probe was held in the centre of the gas flow. The distal end of the t-connecter was open to air (Fig. 1). Over a 1-month period multiple, repeated measurements of temperature and relative humidity (RH) of the piped gases were recorded, including samples at different sites, on different floors and at different times of the day. At each site ambient temperature and RH were also recorded.
Results Eighty paired air and oxygen measurements of temperature and RH were recorded from wall outlets across RWH, including the NICU (31), operating theatres (9), birthing rooms (23) and neonatal research laboratory (17). In a subset of twenty recordings, ambient temperatures and RHs were measured (n = 8 NICU, n = 4 theatres, n = 5 birthing rooms, n = 3 neonatal laboratory).
Temperature Mean (standard deviation (SD)) ambient temperature at test sites was 23.0 (0.95) °C. The mean temperatures of piped oxygen and air were 23.3 (0.9) and 23.4 (0.9) °C respectively (P = 0.49). Temperatures of piped air and oxygen were slightly higher, in the afternoon (both by 0.3°C).
Relative humidity Mean (SD) ambient RH at test sites was 41.1 (2.2) %. The mean RH of piped air was 5.4 (0.7) % and of piped oxygen was 2.1 (1.1) % (this was significantly drier than piped air (P < 0.001)). Both gases had slightly lower RH after midday, by an average of 0.7% (oxygen) and 0.4% (air).
Discussion This study describes the temperature and RH of piped hospital gases at the RWH, Melbourne. We demonstrated that values were stable across time and test sites. However, Knobel et al. measured delivery room temperatures and found they ranged
Temperature and humidity of wall gases
from 19 to 31°C.5 Although temperatures were clinically indistinguishable from room temperatures; RH of both air and oxygen were consistently very low and much lower than ambient air. When resuscitating with room air and a selfinflating bag, infants would receive gas at around 23°C at ambient humidity. The piped gases were drier than air used in commercial aeroplane cabins (RH ∼14%)6 and lower than humidity recorded in some of the driest places on earth, for example Mojave Desert, California (RH 10–30%). Humidification of ventilator gases for patients of all ages has been standard care for decades and is particularly important to newborn infants because of their delicate lungs,7 their problems maintaining normal temperature and fluid balance. Animal studies have shown that breathing dry gas slows tracheal mucous velocity to almost zero, dries secretions and causes inflammation of the respiratory tract, which continues even after humidified gases are reintroduced.8 Dry gas has also been shown to decrease functional residual capacity, reduce compliance and decrease oxygenation.9 In adults the use of unconditioned gases has been shown to cause airway obstruction due to increased mucous viscosity and reduced mucociliary clearance, and cause cessation of ciliary beating, within 10 min.10 There is evidence that heated, humidified gases may be beneficial, particularly in low birthweight and preterm neonates, as they have larger surface areas, higher insensible losses and are more likely to receive assisted ventilation in the delivery room. The UK Project 27/28, studying outcomes in infants of 27 and 28 weeks’ gestation, earmarked poor initial thermal care as a major cause of mortality in this age group.7 A recent retrospective review of heated, humidified gas in the delivery room, in infants less than 33 weeks’ gestation, showed less hypothermia at NICU admission than infants stabilised using unconditioned gases.2 An older study, in the pre-surfactant, pre-antenatal steroid era, showed infants
