Acta anaesth. scand. 1977, 21, 534-540

Intubation of Newborns and Infants: A Solution to the Problem of Water Condensation BRYNJOLP PEDERSEN Department of Anaesthetics, Senderborg Hospital, Senderborg, Denmark

Treatment with humidified air in intubated newborns and infants is often complicated by the embarrassing problem of water condensation. This problem is solved by the humidification system described below, in which the tube delivering Iiumidified air is surrounded by an Armaflex"-insulated spiral-wire tube. Through the space between the two tubes, an adjustable air wariner delivers dry air at a temperature and flow rate such that the temperature of the humidified air in the delivery tube is maintained above its dew-point temperature.

Received 5 March, accepted,for publication 8 April 1977

In the treatment of nasally intubated infants, tube if the temperature of the humidified air the problems associated with the humidifi- is lower than tpD. O n thc other hand, water cation of the inspired air have been solved condensation does not occur if the temperasatisfactorily by using a thermostatically con- ture of the humidified air cverywhere in the trolled water bath (hygrotherm) (LOMHOLT tube is higher than tp,,. Accordingly, condensation of water is et al. 1968, BENVENISTE & PEDERSEN 1976). Several authors have devised methods for eliminated if the tube delivering humidified the avoidance of condensed water in part of air is surrounded by an insulated tube, and a the delivery tube (LOMHOLTet al. 1968, current of dry air is blown through the space PEDERSEN 1972). A centralized system was between the two tubes at a temperature and recently described by BENVENISTE & PEDERSEN flow rate sufficiently high to maintain the (1976), who solved the problem of water con- humidified air above its tp,. With this densation by circulating water at 39-40°C arrangement, the delivery tube is surrounded through a fine plastic tube closely wrapped by a hot-air jacket, and at an appropriate temperature and air flow it will also be around the entire delivery tube. The purpose of this paper is to describe a possible to avoid condensed water in the nonsimple method by which the formation of insulated part of the delivery tube. condensed water is eliminated by means of a hot-air jacket. This method is a further development of a previously described tech- COMPONENTS OF THE HUMIDIFICATION SYSTEM nique (PEDERSEN 1972). The system consists of four coniponents:

THEORETICAL CONSIDERATIONS When humidified air containing an amount of water vapour corresponding to 100% saturation at its dew-point temperature (tp,) is conducted through a delivery tube, condensed water will form on the inside of the

1. 2.

Hygrotherxn. Delivery tube widi a spiral-wire tube, a nylon tube, a heat exchanger and a nylon connection piece. 3. Jet nozzle. 4. Air warmer. 1. The hygrotherrn has been described prcviously

(PEDEKSEN 1973).

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535

Fig. 1. The components of the humidification system (without the hygrotherm). (a) Jet nozzle, delivery tube, spiral-wire tube, nylon tube, heat exchanger and nylon connection piece, partly insulated with Armaflex tubing (see text), (b) brass heat exchanger with pocket for the sensor of the Trafag thermostat, (c) heating element, (d) air warmer ready for use. For clarity of presentation, the tubing system has been shortened.

2. The delivery tube consists of silicone tubing (5 x 8

4. The air warmer consists of a brass heat exchanger

mm), about 100 cm in length. Its proximal end is fitted to a nylon connection piece for the outlet tube of the hygrotherm (Fig. la). From the connection piece, the delivery tube is passed through a heat exchanger (angle piece with a side branch), further through a nylon tube with an end branch (internal diameter 10 mm) and through a spiral-wire tube (10 x 14 mm; 75 cm long) connected to the end branch of the nylon tube and ending 5-8 cm distal to the spiral-wire tube (Fig. la). The delivery tube is insulated with Armaflex tubing (thermal conductivity 0.029 Cal/mh°C), with the exception of a section 5-8 cm in length distal to the spiral-wire tube (Fig. l a ) .

(Fig. 1 b) placed in a heating element (Fig. lc). In order to prevent overheatingof the heat exchanger, the device is provided with a thermostat, with a sensor placed in a brass pocket soldered to the heat exchanger (Fig. Ib). The temperature of the heating element is controlled by a variotransformer. The above-mentioned components are built into a stainless steel box which can be fixed to the bedside panel (Fig. Id).

FUNCTIONING PRINCIPLE OF THE HUMIDIFICATION SYSTEM

The working principle of the system is shown schema3. The jet nozzle connected to the distal end of the tically in Figure 2. delivery tube has been described previously (BENVENFrom a respirator and/or flowmeter, a n oxygen-air ISTE & PEDEKSEN 1968) (Fig. la). mixture is conducted to the hygrotherm (A). This G

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C

A

Fig. 2. T h e working principle of the humidification system (see text). (A) Hygrotherm, (B) jet nozzle, (C) air warmer, (D) inlet tube, (E)heat exchanger with sensor pocket, (F) AC mains, (G) heating element, (H) outlet tube, (K) thermostat sensor, (L) change-over switch of thermostat, with contacts (1) and (Z), (J) variotransformer, (I) green pilot lamp, (M) red pilot lamp. mixture is warmed and humidified, and then passed on through the delivery tube to the jet nozzle (B). Atmospheric air is conducted at a constant flow rate (12-15 l/min) to the air warmer through its inlet tube (D), warmed by the heat exchanger (E), which is placed in the heating element (G), and passed on to the outlet tube (H). From there, the air is conducted through a length of silicone tubing (5 x 8 mm) into the space between the delivery tube and the spiral-wire tube, where it forms a hot-air jacket around the delivery tube until it escapes from the system 5-8 cm proximal to the jet nozzle. The connection of the heating element to the mains is indicated by a green pilot lamp (I). Stepless regulation of the temperature of the heating element- and hence the air-is achieved by the means of the variotransformer (J),which is supplied from the mains (F). If the temperature around the sensor (K) of the thermostat becomes too high, the change-over switch (L) will change from contact (1) to (Z),thus breaking the current to the heating element and a red pilot lamp (M) will light up.

CLINICAL USE O F THE HUMIDIFICATION SYSTEM From a respirator and/or flowmeter, the desired oxygen-air mixture is conducted to the hygrotherm. This mixture is warmed to the body temperature plus 2-3°C and passed on through the delivery tube. Atmospheric air (never oxygen !) is conducted

to the air wanner at a constantjow rate (12--15 l/min). The air from the air warmer, which in the tubing system forms a hot-air jacket around the delivery tube, should normally be let out a few centimeters proximal to the jet nozzle (Fig. 2), whereas, in incubator treatment, it should be allowed to escape before it reaches the incubator (Fig. 3). When the temperature of the hygrotherm air has become stabilized, the control knob of the airwarmer thermostat is set at 125"C, following which, the variotransfrmer is adjusted so that the temperature of the humidifid air (measured in the non-insulated part of the delivery tube, close to the jet nozzle, by means of a specially designed sensor (Ellab@))is the same as that of the hygrotherm air, i.e. body temperature ptus 2-3°C. Finally, by turning the control knob of'the thermostat, the temperature-read on the same control knob-at which the red pilot lamp lights up is checked. The thermostat is then adjusted so that it will be activated at a temperature 5°C higher. The thermostat will thus function as an alarm device. DISCUSSION If the above instructions for the use of the

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537

Fig. 3. Escape of the air from the hot-air jacket (visualized by smoke) before it reaches the incubator.

humidification system are followed, water condensation will be avoided as the temperature of the air everywhere in the delivery tube will be higher than its tpo. The minimum requirements for sufficient humidification of the inspired air in the trachea (Lee a relative humidity (R.H.) of 72% at body temperature (LOMHOLT et al. 1968)) are satisfied if the following conditions are fulfilled :

1. The tpD of the air in the delivery tube should correspond to the body temperature. 2. Admixture of dry atmospheric air at the

jet nozzle should be less than 30%, as this is the highest admixture of air which renders it possible to satisfy the minimum requirements for sufficient humidification ( PEDERSEN 1974).

1. The temperature of the hygrotherm air should be kept at a level 2-3°C higher than the body temperature, partly because such a fall in the temperature of the air occurs during its passage from the hygrotherm to the heat exchanger, and partly because measurements of the humidity of the hygrotherm air (made by a Psychrometer B 119, Ellab, at

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flow rates varying between 10 and 30 l/min) have shown that the R.H. is between 95 and 90%, lowest at the highest flow rates.

2. During respirator treatment, the admixture of atmospheric air at the jet nozzle will be very slight (BRENDSTRUP et al. 1975), whereas greater admixture may occur in infants on spontaneous respiration. In the latter category-infants weighing up to 15 kg-the admixture of air will be less than 25% if the air flow through the jet nozzle is 6 l/min (BRENDSTRUP et al. 1975). If, during respirator treatment, spontaneous respiration is allowed between the insufflations of the respirator - for example, during weaning from the treatment - the humidity of

the inspired air will be sufficient if 6 1 air per minute are conducted to the hygrotherm in addition to the amount of air supplied to it from the respirator (CPAP + respirator). For reasons of safety, atmospheric air (neuer oxygen!) should be supplied to the air warmer from a flowmeter which can be connected only to the outlet tube for atmospheric air. I n order to withstand the high temperatures, silicone tubing should be used both for the delivery tube and the connecting tube between the outlet tubeofthe air warmer and the side branch of the heat exchanger. Armaflex tubing has proved to be very suitable as insulation material. The needle electrode which records the temperature of the air in the delivery tube is

Fig. 4.The delivery tube fixed to the head of the infant (see text).

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INTUBATION AND WATER CONDENSATION

of a special design with the sensitive area on the middle of the needle which is to be inserted obliquely through both walls of the silicone tube. This special electrode eliminates the inaccuracy associated with the use of a standard electrode, the tip of which it is impossible to place centrally in the air stream. From the working principle of the air warmer (Fig. 2)) it appears that the apparatus can also be used as a thermostatically controlled air warmer. A current of 85-105 V is required for the heating element of the air warmer in order to obtain a sufficiently high temperature of the air at the outlet tube of the apparatus (7090°C). This temperature is obtained within about 30min. The delivery tube can easily be fixed to the head of the infant by means of a head dressing (or a tight-fitting cap) to which the tube is tied (Fig. 4). The apparatus is easy to operate. If its components are carefully arranged and the temperature is correctly adjusted, few subsequent adjustments are required. One of the greatest advantages obtained is that, because of the avoidance of water condensation in the tubing system during the treatment, uncontrollable amounts of condensed water are not carried into the lungs of the infants. In fluid therapy of such patients, it must be taken into account that the perspiration from the lungs (15 m1/100 Ca1/24 h at 37°C (WINTERS 1973)) is reduced, and the administration of fluid must therefore be reduced accordingly. I n fluid therapy in which no perspiration from the lungs occurs (during respirator treatment), the administration of fluid should thus be reduced by 15 m1/100 Call24 h. During the last 4 years, the humidification system described has been used with 30 infants and has shown completely satisfactory function. Only in two caseb did plugging of the nasal tube occur, but in both cases the instructions for its use were not closely followed.

Alternative method As an alternative, a hygrotherm (with a thermostatically controlled water temperature of 85-90°C) may be used as the air warmer. If the hygrotherm is provided with two copper heat exchangers (22 x 75 mm), it is changed into a thermostatically controlled air warmer (aerotherm, Figs 5 and 6) (PEDERSEN 1972). The heat exchangers are connected to each other and to the inlet and outlet tubes of the hygrotherm by means of silicone tubes. The air warmer may be supplied with air or oxygen from a flowmeter. At Jlow rates uarying between 10 and 25 llmin, the temperature of the air deliuered by the air warmer will be constant at about 80°C. A sufficiently high temperature of the air in the hotair jacket can then be obtained by regulating the flow rate within the range of 10-15 I/min. An electronically controlled air warmer has also been developed which keeps constant the temperature of the air delivered in spite of varying flow rates. Its function is perfect, but as it is not superior to other air warmers, this solution must be regarded as too costly.

“c

i

l

1 Fig. 5. Working principle of the air warmer (see text). The arrows show the passage of air from the inlet tube of the hygrotherm, through the copper heat exchangers (shown in longitudinal section), and out through the outlet tube.

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B. PEDERSEN

Fig. 6. Coppcr heat cxrhangers, connected to each other with a silicone tube (5 x 8 mm), rcady for immersion iri the hygrotherm.

ACKNOWLEDGEMENTS The author wishes to express his thanks and appreciation to Gunnar Hounsgaard and Bernhard Swienty, Senderborg Technical Institute, for their advice and guidance; to Bent Serensen and Allan Pedersen, Senderborg Hospital, for valuable technical assistance in the construction of the apparatus; and to Flrmrning Clausen and Jergen Walbjern, Clinical Photographic Section, Senderborg Hospital. The study was supported by a grant from the Danish Foundation for Medical Research.

REFERENCES BENVENISTE, D. & PEDERSEN, J. E. POUL (1968) A valve substitute with no moving parts for artificial ventilation in newborn and small infants. Brit. 3. Anaesth. 40, 464. BENVENISTE, D. & PEDEKSEN, J. E. Pour. (1976) Centralked systrm of humification for rcspiratory treatment. Anaesthesia 31, 42 1.

BKENDSTRUP,A., BENVENISTE, L). & PKDERSEN, J. E. POUL(1975) The magnitude of air mixture with a jet device in paediatric anaesthesia. Brit. J . Ailaesth. 47, 1335. LOMHOLT, N., COOKE,K. & LUNDING, M. (1968) A method for humidification in ventilator treatment of neonates. Brit. .j’. .4tiaesth. 40, 335. PEDERSEN, B. (1972) Respirator treatment of neonates. A new principle with optimum humidification of the inspired air. Acta nnaesth. scand. 16, 38. PEDERSEN, B. (1973) Ny hygroterrn med sikring mod overophedning. Ugeskr. Laeg. 135, 2262. PEDEKSEN, B. (1974) E’ugtning af inspirationslufien 110s nasalt intuberede og trakeostomerede patienter. Ugeskr. Laeg. 136, 2238. WINTERS,R. W. (1973) The Body Fluids in Pediatric>. Little, Brown & Company, B O S ~ Opp. I ~ , I 1 5-124. Address : B. Pedersen, M.D Department or Anacstlietirs Sonderborg Hospital Sonderborg, Denmark

Intubation of newborns and infants: a solution to the problem of water condensation.

Acta anaesth. scand. 1977, 21, 534-540 Intubation of Newborns and Infants: A Solution to the Problem of Water Condensation BRYNJOLP PEDERSEN Departme...
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