PEDIATRICS Vol. 110 No. 5 November 2002, pp. 964-967
The Efficacy Of Noncontact Oxygen Delivery Methods
From the Luton and Dunstable NHS Trust, Luton, United Kingdom
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMETHODSRESULTSDISCUSSIONCONCLUSIONREFERENCES |
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Objectives. "Wafting" oxygen is a possible strategy to deliver oxygen to a patient who may not tolerate delivery systems that involve contact on the face. We wished to assess the concentration of oxygen delivered to the patient with various methods of "wafting" oxygen.
Design. Three methods of wafting oxygen were examined: an infant resuscitator bag, a standard pediatric Hudson RCI face mask, and a piece of standard green oxygen tubing. Contour lines for oxygen concentrations of 30% to 70% in 10% intervals were found with a Teledyne oxygen meter, at an oxygen flow rate of 5 L/min and 10 L/min. Experimental conditions simulated an infant in a cot in a pediatric ward.
Results. The resuscitator bag can not be recommended for wafting oxygen delivery, as the flow-back valve may close and result in insignificant levels of oxygen delivery. Oxygen tubing gave a useable area too narrow for use with an active patient, with 30% oxygen concentration being available in an area with width of only 18 cm. This is, however, a suitable method in short-term attended administration, either during feeding, or in the situation of a neonatal resuscitation. The standard pediatric Hudson RCI face mask, at a flow rate of 10 L/min, delivers 30% oxygen to an area 35 cm wide and 32 cm from the top of the mask. At 10 L/min, 40% oxygen is delivered to an area 16 cm wide and 14 cm from the top of the mask. This is an area large enough to be usable in the infant who will not tolerate other methods of oxygen delivery. The contour lines are presented graphically.
Conclusions. Although wafting can never replace conventional methods of oxygen delivery to children, if these have failed, a standard pediatric oxygen mask can give significant oxygen therapy without irritating the patient. Care should be taken to place the mask in the area described (ie, opposite the chest) to give the maximum benefit. Short-term administration can be appropriate with standard oxygen tubing aimed at the airway.
Key Words: oxygen delivery • wafting
Abbreviations: FIO2, fraction of inspired oxygen
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INTRODUCTION |
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Delivery of oxygen to sick children has long been a problem. In a group of patients who are unable or unwilling to rationalize treatment interventions, and therefore resist them, it is often a challenge to encourage a child to tolerate a face mask, headbox, or nasal cannulae. This can be augmented by confusion or agitation seen when a child is unwell and especially when hypoxic or hypercapnic. Even in adults who can more readily understand the need for their oxygen therapy, compliance is a problem: in 1 randomized, controlled trial, comparing overnight nasal cannulae with Venturi face masks, half of the patients studied dislodged their device at least once overnight.1
As a last resort, medical staff have used the term "wafting" to mean aiming a stream of oxygen at the patient to give some benefit. This often enables a child to fall asleep with a general improvement of the patient’s situation. However, the efficacy of this method has never been quantified.
Our study has looked at 3 ways of delivering noncontact oxygen (wafting) and charted the relevant oxygen concentrations achieved by each system.
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METHODS |
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Three systems of delivering oxygen were examined, each at flow rates of 5 and 10 L/min. The nozzle was placed 1 cm above the end of a 1 mm2 sheet of graph paper and set at the relevant flow rate on a standard wall-mounted flow rate meter (Therapy Equipment Ltd, Potters Bar, United Kingdom). Although the proximity of the nozzle to the paper may affect the flow dynamics of the experiment, it was believed that this was more "true to life," where a nozzle would be placed on a bed sheet. The oxygen meter was then used to determine the contour lines of the various concentrations at 10% O2 intervals, and this was marked on the paper. A Teledyne oxygen meter (Teledyne Analytical Instruments, City of Industry, CA) with 1% resolution from the pediatric ward was used, which had recently been checked and calibrated. Each point was found by slowly moving the meter away from the nozzle until the reading was correct, and then waiting for the meter to stabilize before marking the point. Each point was then found again by moving toward the nozzle. These markings were then transferred to a computer and joined using a Microsoft Draw (Office 2000; Microsoft Corp, Redmond, WA) package to smooth the lines out. Ethical approval was not sought as no patients were involved.
We examined 3 systems of noncontact oxygen delivery shown in Table 1.
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RESULTS |
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Figures 1 through 3 demonstrate the contour lines of oxygen concentration found. The dashed lines represent 5 L/min flow and the solid lines 10 L/min flow. All charts are to the same scale. The infant resuscitator bag delivered 30% oxygen to an area measuring maximally 35 cm by 37 cm at 10 L/min flow and 12 cm by 22 cm at 5 L/min flow. The oxygen tubing delivered a maximum area of 30% delivery measuring 14 cm by 34 cm at 10 L/min flow and 18 cm by 28 cm at 5 L/min flow. However, it should be noted that the infant resuscitator bag gave poorly repeatable results, as the "fish mouth" valve which allows oxygen out of the bag may seal shut in some models when the bag is at rest. This obstructs oxygen flow out of the bag, leading to no flow out of the mask. If the "fish mouth" valve is open at rest, then the concentration profile is still small, with a maximal 30% area at 10 L/min of 14 cm by 5 cm.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONCONCLUSIONREFERENCES |
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Many systems for the delivery of oxygen to the infant have been tried. A crossover study2 has shown that the best method of administration is the head box (69% achieved PaO2 >90 mm Hg at 4 L/min), followed by the face mask (57% >90 mm Hg at 4 L/min), and the nasal cannulae (25% >90 mm Hg at 1 L/min). When the flow rates for the head box and the nasal cannulae were equalized, oxygenation was comparable.
Delivery of oxygen to the lungs may not be strictly associated with the oxygen concentration at a given point in a dynamic system. End-tidal oxygraphy has been used in adults to measure true oxygen delivery3; however, this is not feasible in the pediatric population. We have therefore used point oxygen concentration as our comparison measure. It is likely that in vivo airway oxygen concentration is lower than that measured, but this applies to all oxygen delivery systems apart from intubation. Fraction of inspired oxygen (FIO2) is also a variable of ventilation rate when a tight-fitting face mask is used4; however, as the delivery of oxygen in our systems is constant at 5 L/min or 10 L/min, this should be equalized in the in vivo patient. Furthermore, in a tight-fitting closed system the patient will also be at risk of rebreathing carbon dioxide at low gas flow rates.
Of the methods used at present, that which allows most quantifiable measurement is the head box, where the child’s head is inserted into a box with an oxygen source and an oxygen meter to show the percentage attained. However, some children get distressed by the isolation this entails, and there are inherent problems with delivery while feeding and washing, and also with attachment and bonding to parents. This is especially so when used with neonates.
Oxygen masks are restrictive, and the elastic band holding them in place can irritate the child. They are well tolerated in the older child, but in infants it is difficult to encourage the child to permit the mask to be kept in place. Those that deliver humidified oxygen also create noise, which can frighten or distress the infant. It is sometimes difficult to secure a mask in place in an active infant.
Nasal cannulae are probably tolerated better but are also difficult to secure. They are often found in the mouth, or blowing oxygen onto the cheek having slipped around the face. Another problem, which may decrease acceptability of this method to an infant, is that nasal cannulae may result in drying of the airway and consequent discomfort. Technically, difficulties have been found in stabilizing the flow and oxygen concentration through nasal cannulae.5 However, comparisons with a nasopharyngeal catheter have shown better efficacy6 and decreased nursing effort required for nasal cannulae.7 Also, in developing countries, nasal cannulae have been shown to be effective and safe in delivering oxygen.8
Self-inflating resuscitation bags are only used in the resuscitation situation, but have been shown to give good oxygen delivery. Without a reservoir bag, FIO2 has been shown to be between 50% and 60% at flow rates of over 7 L/min, and with a reservoir bag over 80% at 10 L/min.9 They are not designed to be independently attached to an infant’s face without manual ventilation.
Noncontact oxygen delivery methods can never replace properly administered oxygen. However, there are 3 situations where noncontact (wafting) oxygen may be beneficial: 1) for the child who does not tolerate any of the above methods; 2) for short-term administration of oxygen during feeding, cuddling, or washing an infant who is on oxygen therapy by another means, and 3) as an interim measure in the resuscitation of the newborn.
Of the 3 systems tested, the least reliable was the infant resuscitator bag. This unpredictability means it cannot be recommended as a delivery mechanism. If there are no other options, then the valve should be checked to ensure it is open, or the bag gently rhythmically squeezed to ensure oxygen flow. However, oxygen delivery is poor even in optimal conditions.
The green oxygen tubing has a narrow contour profile that would make it difficult to ensure delivery to the patient’s face in the nonattended infant. Interestingly, the contours for 5 L/min and for 10 L/min are similar, probably because of the Venturi effect of gas flow leaving the nozzle at high speed. The maximal width of the 30% area was only 18 cm at 10 L/min, which is too narrow for reliable delivery unless the medical practitioner was in attendance ensuring the stream of oxygen was continuously aimed at the patient’s airway. If wafted oxygen is required in the case of resuscitation of the newborn, it is more efficacious to pull the oxygen tubing from the resuscitator bag to give wafted oxygen, instead of using the resuscitator bag itself.
The Hudson RCI oxygen face mask has a very large area of significant oxygen delivery. It must be borne in mind that the contour profile is not directed perpendicular to the edge of the mask, but up toward the nasal end of the mask. Placement of the mask opposite the face, at the level of the mouth, would not deliver significant oxygen concentrations. However, if the mask is placed correctly, ie, opposite the sternum, there is a large area wherein >30% oxygen can be achieved, allowing the patient to be active and minimizing distress. This would be the system of choice for the nonattended infant.
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CONCLUSION |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONCONCLUSIONREFERENCES |
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Although noncontact oxygen delivery systems can never replace conventional means, there are certain situations where they may be needed. We recommend 2 different methods: 1) for the short-term, attended patient who is undergoing either resuscitation or being washed or fed, directing standard oxygen tubing at his/her airway will give benefit; and 2) for the patient who will not tolerate medium-term oxygen therapy, the standard pediatric face mask can be used to good effect, if placed in the correct position opposite the sternum.
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FOOTNOTES |
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Received for publication Feb 6, 2002; Accepted Jul 18, 2002.
Reprint requests to (P.D.) Department of Paediatrics, Luton and Dunstable Hospital, Lewsey Rd, Luton LU4 0DZ, United Kingdom. E-mail: daviespatrick{at}hotmail.com
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PEDIATRICS (ISSN 1098-4275). ©2002 by the American Academy of Pediatrics
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