WO2008142650A1

WO2008142650A1 - A cooling system for inducing neuro-protective hypothermia in a newborn infant

Info

Publication number: WO2008142650A1
Application number: PCT/IB2008/051997
Authority: WO
Inventors: Alan Richard Horn
Original assignee: University Of Cape Town
Priority date: 2007-05-21
Filing date: 2008-05-21
Publication date: 2008-11-27
Also published as: ZA200907720B

Abstract

A cooling system (10) for inducing neuro-protective hypothermia in an infant (14) is installed in a warming incubator (12). A temperature probe (32) senses the infant's core temperature. The probe is connected to a temperature controller of the incubator which controls the heating intensity of the incubator heater. The system (10) includes a number of blowers which each comprise a servo-motor and a cooling fan which is positioned at the head of the infant for blowing ambient air onto the infant's head. The system (10) further includes a control unit which is operable to receive inputs from the temperature controller, of the infant's core temperature and to control the speed of rotation of the cooling fans in response to the temperature inputs received, thereby to control the volume of air blown onto the infant (10) so as to maintain the core temperature of the infant within a target temperature range within which neuro-protective hypothermia is induced.

Description

A COOLING SYSTEM FOR INDUCING NEURO-PROTECTIVE HYPOTHERMIA IN A NEWBORN INFANT

FIELD OF INVENTION

This invention relates to a cooling system for inducing neuro-protective hypothermia in a newborn infant.

BACKGROUND TO THE INVENTION

Hypoxia and ischaemia during labour or at the time of birth is the commonest cause of brain injury in term and near term infants. These infants are often described as having suffered from "birth asphyxia". Brain injury which occurs in this way is an evolving process and the clinical manifestation of this injury is termed hypoxic ischaemic encephalopathy (HIE). Infants with moderate and severe HIE are at highest risk of developing permanent brain damage.

Several animal studies have shown that the evolving brain injury in new born animals, following hypoxic ischaemic insults, is potentially amenable to neuro- protective rescue therapy, in the form of hypothermia, which can stop the progression of the brain injury and prevent or decrease the occurrence of permanent brain damage. In particular, focal celebral cooling with mild systemic cooling has achieved neuro-protection with fewer systemic complications. The optimal post-asphyxial brain temperature to achieve neuro-protection with minimal side effects is likely to be between 32 °C and 34 °C.

The newborn infant's response to hypoxia is to decrease metabolic rate and thus body temperature. Newborn infants do not respond to low ambient temperature with the same increase in metabolism as adults. Thus infants who are severely asphyxiated should only require minimum intervention for cooling and simply removing the source of heating has been successful in case reports. However, spontaneous cooling is still dependent on ambient temperature and there is also some evidence that selective head cooling with mild systemic hypothermia is more effective at reducing brain damage than global systemic hypothermia when applied to infants with brain injury.

The active methods of inducing neuro-protective hypothermia in newborn infants described to date, include immersion in running water at 8 ^°C to 14^°C, application of soft gel packs at 10^°C to the head, application of insulated frozen gel packs to the head, application of soft gel packs at 10^°C around the head and body, application of a cooling cap with water circulating at 10^°C around the head, blowing cold air over the body of the infant and application of bags of cold water and blowing room temperature air over the body of the infant. All of these methods were successful at achieving the goal temperature. However, all these methods require extremely close monitoring and repeated adjustments and intervention by medical staff to ensure that over cooling does not occur.

It is an object of the present invention to ameliorate the problems encountered with the abovementioned methods of inducing neuro-protective hypothermia in newborn infants. SUMMARY OF INVENTION

According to a first aspect of the invention there is provided a cooling system for inducing neuro-protective hypothermia in an infant, the cooling system including:

a blower including a cooling fan which can be positioned near the head of the infant to blow ambient air onto the head and body of the infant; and

control means which is operable to receive temperature inputs corresponding to the core body temperature of the infant, the control means being connected to the blower and being operable to control the speed of rotation of the cooling fan in response to temperature inputs received by it, thereby to control the volume of ambient air which is blown onto the infant.

The blower may include an electrical servo-motor which drives the cooling fan and which is connected to the control means, the servo-motor being operable to control the speed of rotation of the cooling fan in response to control signals received from the control means.

The blower may include flow directing means for directing a focused stream of ambient air to the head of an infant.

In a particular embodiment of the invention, the cooling system may include a number of blowers.

In use, the temperature inputs to the control means may be provided by a temperature probe which is inserted at a site which represents core temperature such as deep rectal or mid-oesophageal.

The control means may be operable to control the speed of rotation of the cooling fan thereby to maintain the core temperature of the infant within a target temperature range within which neuro-protective hypothermia is induced in the infant. The control means may be operable to control the speed of rotation of the cooling fan in an arrangement wherein control signals are sent to the servo-motor to reduce the speed of rotation of the cooling fan exponentially in response to a drop in the core temperature of the infant being detected.

The control means may be in the form of a processor and a memory device in which a number of control values corresponding to different core temperatures, can be stored.

The processor may be operable to send a control signal to the servo-motor to operate the cooling fan at a predetermined speed in response to a temperature input being received by the processor which matches a core temperature corresponding to one of said control values.

The memory device may have stored therein a first control value corresponding to a particular first core temperature of the infant and a second control value corresponding to a second core temperature of the infant which is relatively higher than the first core temperature, the processor being operable to:

a) send a control signal to the servo-motor to switch the servo-motor on and to operate the cooling fan at a predetermined first speed in response to a temperature input being received by the processor which matches the first core temperature; and

b) send a control signal to the servo-motor to operate the cooling fan at a predetermined second speed which is relatively higher than the first speed, in response to a temperature input being received by the processor which matches the second core temperature.

The memory device may have stored therein a number of additional control values which each correspond to a different core temperature which is relatively higher than the second core temperature, the processor being operable to send control signals to the servo-motor to operate the cooling fan at speeds which are relatively higher than the second speed, in response to a temperature input being received by the processor which matches a particular core temperature corresponding to one of said additional control values.

The processor may be operable to switch the servo-motor off in response to a temperature input being received by the processor which is below the first core temperature.

The cooling system may include a housing in which the blower is housed, the housing being positionable at the head of the infant when the infant is located on a support platform of the incubator, in use, and including a front side defining an opening through which ambient air can be blown onto the infant's head and a deflector panel which extends outwardly from the front side of the housing so as to form a cover over the infant's head in order to deflect heat emitted by the heater of the incubator, away from the infant's head.

The invention extends to the control means as defined and described hereinabove.

In use, the cooling fan may be positioned near the head of the infant in an arrangement wherein the fan is operable to blow ambient air onto the head of the infant in a direction along the length of the infants' body from head to toe. As such, the cooling air blown by the cooling fan will cool the infants head relatively more than the rest of the infants' body.

According to a second aspect of the invention there is provided an incubator for incubating an infant, the incubator including:

a heating system for heating the infant; and

the cooling system in accordance with the first aspect of the invention.

The heating system may include a heater for heating the infant and heater control means which is operable to receive temperature inputs corresponding to the core body temperature of the infant and to control the intensity of the heat generated by the heater in response to temperature inputs received by it. The control means of the cooling system and the heater control means of the heating system may be operable together to maintain a core body temperature of the infant within a target temperature range within which neuro-protective hypothermia may be induced in the infant, by controlling the speed of rotation of the cooling fan and the intensity of the heat generated by the heater, respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features of the invention are described hereinafter by way of a non-limiting example of the invention, with reference to and as illustrated in the accompanying diagrammatic drawings. In the drawings:

Figure 1 shows a schematic perspective view, showing hidden detail, of an incubator for a newborn infant, having a cooling system in accordance with the invention, installed therein;

Figure 2 shows a top plan view of the incubator of Figure 1 sectioned along section line N-II of Figure 1 , illustrating the positioning of the cooling system at the head of the newborn infant;

Figure 3a shows a perspective view, showing hidden detail, of the cooling system of Figure 1 ;

Figure 3b shows a front view of the cooling system of Figure 1 ;

Figure 3c shows a rear view of the cooling system of Figure 1 ;

Figure 3d shows a top view of the cooling system of figure 1 ;

Figure 3e shows a left side view of the cooling system of Figure 1 ;

Figure 3f shows a right side view of the cooling system of Figure 1 ; Figure 4 shows a block diagram of the cooling system of Figure 1 ; and

Figure 5 shows a graph of rectal temperature versus fan speed illustrating the operation of the cooling system of Figure 1.

DESCRIPTION OF PREFERRED EMBODIMENTS

With reference to the drawings, a cooling system in accordance with the invention, is designated generally by the reference numeral 10. The cooling system 10 is adapted to be installed in a warming incubator 12 for a newborn infant 14. The incubator 12 is an open incubator including a wheeled carriage 16 and a stand 18 extending upwardly therefrom. A support platform 20 on which the infant 14 is supported on a mattress 22, extends laterally outwardly from one side of the stand. Fold-down side panels 23 are hingedly connected to sides of the support platform 20. The incubator includes two phototherapy units 24. The incubator is temperature-controlled and as such, includes a heating system including an overhead radiant heater 26 which is elevated above the support platform 20 and a temperature controller 28 which is supported on a shelf 30 of the stand. The temperature controller 28 is connected to the heater 26 for switching the heater on and off. The temperature controller 28 has connection ports for connection to the heater 26 and to a temperature probe 32 which can be inserted deep rectal so as to sense the core body temperature of the infant 14. The temperature controller 28 has a RS 232 data cable 33 which can be connected to external devices such as the cooling system 10. The configuration of the incubator 12 described above, is conventional and is thus not described in any further detail hereinafter.

The cooling system 10 comprises, broadly, three blowers 34 and a control unit designated generally by the reference numeral 36, which is operable to control the operation of the blowers 34 in response to temperature inputs received indirectly via data cable 33, from the temperature controller 28 or directly via an additional temperature probe as will be explained in more detail hereinafter. In use, the cooling system 10 is located on the mattress 22 at the head of the infant 14. Each blower 34 comprises an electrical servo-motor 38 and a cooling fan 40 which is connected to the servo-motor 38. The servo-motors 38 are connected to the control unit 36 and are operable to control the speed of rotation of the cooling fans 40 in response to control signals received from the control unit 36.

The control unit 36 comprises a processor 42 and a memory device 44 in which a number of control values corresponding to different core temperatures of the infant, are stored.

The control unit 36 and the blowers 34 are housed in a box-shaped housing 46 which is divided into an upper compartment 48 and lower compartment 50 by a partitioning wall 51. The control unit 36 is housed in the upper compartment, whereas the blowers 34 are housed in the lower compartment. The servo-motors 38 are mounted to a rear panel 52 of the housing 46, with the corresponding cooling fans 40 being mounted in a row adjacent one another along an inner side of the rear panel 52. The housing 46 has a grille 54 mounted within an opening 56 defined in a front panel 58 of the housing 46, through which airflow from the cooling fans is directed. The grille 54 thus directs a focused stream of air blown by the cooling fans 40 in a direction perpendicular to the plane of the front panel 58 of the housing 46. The housing has four feet 60 which raise the height of the blowers 34 so that the blowers are elevated above the mattress 22.

The housing 46 includes a front cover panel 62 which is hingedly connected to an upper end of the front panel 58 of the housing so as to be displaceable between an extended position wherein the front cover panel 62 extends forwardly as is shown in Figure 3e so as to completely cover the infants head and a folded position wherein the front cover panel is located adjacent the front panel 58. When deployed into its extended position, the front cover panel 62 provides an overhang which is operable to deflect airflow passing through the grille 54 onto the infant's head and to deflect heat from the heater 26 away from the infant's head.

The housing further includes an air intake guard 64 mounted to a lower side of the rear panel 52 of the housing. The air intake guard 64 is dome-shaped and defines a number of air intake slits therein which provide for the intake of air to the cooling fans while protecting the fans from foreign objects being sucked into the fans when in operation.

The housing 46 also houses a mains power supply converter 65 in the upper compartment 48, which is operable to convert the alternating current of the mains AC power supply to a stepped-down DC power supply for the control unit 36 and the blowers 34.

In use, the housing 46 containing the blowers 34 and the control unit 36 and the power supply converter 65, is positioned within the incubator 12 at the head of the infant 14 in an arrangement wherein ambient air blown by the cooling fans 40, is blown onto the head of the infant in a direction along the length of the infant's body from head to toe. The cooling system 10 includes a cable connection panel 66 which is mounted to the rear panel 52 of the housing 46 at the height of the upper compartment 48. The cable connection panel 66 is electrically connected to the control unit 36 and to the mains power supply converter 65. The cable connection panel 66 includes a data socket 68 into which the RS 232 data cable 33 connected to the temperature controller 28, can be connected. The panel 66 further includes a port 70 through which a mains power supply cable 72 passes and which is connected to the power supply converter 65. The panel 66 also has an on/off switch 74 for switching power to the control unit 36 on or off. The panel 66 has a temperature connector 76 to which a second temperature probe 35 for also measuring infant core temperature, can be connected if indirect temperature data acquisition from the incubator is not available via data socket 68. The panel 66 includes a second temperature connector 76.1 for optional additional direct site monitoring, should this be required. In this latter arrangement, the first infant temperature probe 32 is connected to the temperature controller 28 and the second infant temperature probe 35 is connectable directly, from a second core temperature site such as under the infant's back, to the temperature connector 76. The panel 66 further includes data output sockets 78.1 and 78.2 for USB and RS 232 data cables, respectively. The Applicant envisages that the socket 68 may be configured to permit data output. As such, the data output sockets provide for optional additional data output. The housing 46 includes a rear cover panel 79 which extends rearwardly from the upper side of the rear panel thereby providing a protective cover for the cable connection panel 66.

The control unit 36 includes a control panel 80 which is mounted to an upper region of the front panel 58 of the housing 46 and which includes two push buttons 82.1 and 82.2 for inputting a control temperature to the processor 42 at which the blowers 34 are switched off. The control panel 50 also includes a first display 84 for displaying the control temperature at which the blowers are switched off and a second display 86 for displaying the current temperature sensed by the temperature probe 32. The control panel 80 further includes a start button 88.1 and a stop button 88.2 for switching the blowers between "on" and "off" modes, respectively. The control panel 80 also includes a LCD message display window 90 which provides messages on the status of the control unit 36. The control panel 80 also includes a fan activation light 92 which is illuminated to indicate that the cooling fans are on. The control panel 80 also includes an alarm light 94 which is illuminated when temperatures which are detected by the temperature probe 32 which are more than a degree below or above the activation temperature as will be explained hereinafter or when predetermined cables are disconnected.

The processor 42 of the control unit 36 is thus operable to receive temperature inputs indirectly from the temperature controller 28 of the core body temperature of the infant 14 as sensed by the probe 32, via the data cable 33 connected to socket 68 or directly via the second temperature probe 35 connected to temperature connector 76. The processor 42 is further operable to send control signals to the servo-motors 38 to thereby operate the cooling fans 40 at predetermined speeds thereby to control the volume of ambient air which is blown onto the head and body of the infant, in response to temperature inputs received by the processor.

The memory device 26 has a number of control values corresponding to different core temperatures stored therein. In use, the recommended temperature for hypothermic neuro-protection is 33 °C to 34 °C. The memory device 44 has stored therein a first control value which corresponds to a "switch on" core temperature of the infant of 33.4 °C. Accordingly, when a core temperature equal to or greater than 33.4 °C is sensed by the temperature probe, the processor 42 is operable to send a control signal to the servo-motors 38 to switch the cooling fans 40 on.

The memory device 44 has stored therein a second control value corresponding to a core temperature of the infant of 33.6 °C (i.e. an increment of 0.2 °C), a third control value corresponding to a core temperature of the infant of 33.8 °C (i.e. an increment of 0.2 °C) and a fourth control value of 33.9 °C (i.e. an increment of 0.1 ⁰C).

With reference to Figure 5 of the drawings, the processor 42 is operable to send a control signal to the servo-motors 38 to operate the cooling fans 40 at 10% of maximum fan speed in response to a temperature input being received by the processor, which matches the first control value (i.e. 33.4 °C) referred to hereinafter as "fan set point". The processor is further operable to send a control signal to the servo-motors 38 to operate the fans 40 at rotational speeds of 30% of the maximum fan speed in response to a temperature input being received by the processor which matches the second control value (i.e. 33.6 °C). The processor is yet further operable to send a control signal to the servo-motors to operate the fans 40 at rotational speeds of 60% of the maximum fan speed in response to a temperature input being received by the processor which matches the third control value (i.e. 33.8 °C) and at maximum fan speeds in response to a temperature input which matches the fourth control value (i.e. 33.9 °C) and any higher temperature values.

The processor 42 is further operable to send a control signal to the servo-motors 38 to switch the servo-motors off in response to a core temperature of the infant lower than the first control value, being received by the processor. The processor 42 of the cooling system 10 is operable to act in tandem with the temperature controller 28 to maintain the core body temperature of the infant within the target range while the cooling fans 42 induce and maintain cooling in the infant. The temperature controller 28 of the incubator is operable to control the output intensity of the heater 26 in response to core body temperature inputs received from the temperature probe 32. In normal non-hypothermic use, the heater 26 is set by the thermal controller 28 to maintain the surface body temperature of the infant at 36.5°C, but during cooling, they should be set to 33.5°C. In this setting, the heater 26 will decrease output sequentially if the temperature rises above 33.5 °C and will have zero output at temperatures above 34 °C. The temperature controller 28 is operable to control heater output such that it will increase sequentially if the surface body temperature of the infant drops below 33.5 °C, reaching maximum power when the infant temperature is at or below 33 °C. It will be appreciated that the heater cannot induce cooling, but rather it can only maintain the eventual temperature achieved by the cooling system 10 and prevent over-cooling. Thus, while the infant's temperature starts falling below 34 °C in response to the cooling effect of the cooling fans, the temperature controller 28 is operable to control the heating intensity of the heater 26 to ensure that over-cooling does not occur.

The processor 42 of the control unit 36 is operable to control the speed of rotation of the cooling fans 40 and consequently the cooling effect induced thereby, by using an exponential-type decay response pattern. This is shown most clearly in the early period of cooling in Figure 5 where the fan speed rapidly decreases as the infant's core temperature drops. This response is important as it prevents over- cooling in the infant, which would otherwise occur if the fans did not rapidly slow down. It furthermore allows cooling to continue gradually, which would not occur if the fans abruptly switched off. If the fans switched off abruptly, the infant would be exposed to the full heating effect of the heater 26 and the infant's core temperature would rebound upwards.

At the end of a period of induced neuro-protective hypothermia, the infant is rewarmed by switching off the cooling fans and using the heater 26, gradually raising the core temperature of the infant.

The specific ability of the cooling system 10 to automatically act in tandem with the incubator results in more accurate cooling than is possible with other cooling devices for inducing hypothermia in infants. The cooling device disclosed in US 6,986,786 was subjected to a study by Gunn AJ et al in the Paediatrics journal 1998;102:885-893. The study reported that 32% of the infants monitored exhibited problematic temperature control defined as rectal temperatures 2°C above target or > 1 °C below target. A similar cooling device was used by Thorensen M and Whitelaw A and described in the Paediatrics journal 2000;106:92-99. In a study conducted on the cooling device and reported in the abovementioned article, a cooling overshoot of up to 1 °C beyond 33 °C was described. In contrast thereto, in tests conducted by the Applicant on the cooling system 10 in which the cooling

® system was connected to a Servocrib warming incubator, no significant cooling overshoot resulted. The maximum cooling overshoot detected in the tests conducted by the Applicant was 0.1 °C.

As the cooling system 10 provides for an automated exponential decay response pattern of the cooling fans, it does not require any humidification or other conditioning of the air. The cooling system 10 also functions seamlessly with the radiant heaters of the incubator.

It will be appreciated that the exact configuration of the cooling system in accordance with the invention may vary greatly while still incorporating the essential features defined and described hereinabove. It will also be appreciated that the control values and the fan speeds associated therewith may also vary according to further data which may be gathered as the cooling system 10 is used in clinical practice. In particular, in another embodiment, the cooling system may be incorporated into a closed warming incubator.

The invention extends to an incubator incorporating the cooling system 10 as a built-in sub-system thereof.

Claims

CLAIMS:

1. A cooling system for inducing neuro-protective hypothermia in an infant, the cooling system including:

2. The cooling system as claimed in claim 1 , wherein the blower includes an electrical servo-motor which drives the cooling fan and which is connected to the control means, the servo-motor being operable to control the speed of rotation of the cooling fan in response to control signals received from the control means.

3. The cooling system as claimed in claim 1 or claim 2, wherein the blower includes flow directing means for directing a focused stream of ambient air to the head of an infant.

4. The cooling system as claimed in claim 3, which includes a number of blowers.

5. The cooling system as claimed in any one of claims 2 to 4, wherein the control means is operable to control the speed of rotation of the cooling fan thereby to maintain the core temperature of the infant within a target temperature range within which neuro-protective hypothermia is induced in the infant.

6. The cooling system as claimed in claim 5, wherein the control means is operable to control the speed of rotation of the cooling fan in an arrangement wherein control signals are sent to the servo-motor to reduce the speed of rotation of the cooling fan exponentially in response to a drop in the core temperature of the infant being detected.

7. The cooling system as claimed in any one of claims 2 to 6, wherein the control means is in the form of a processor and a memory device in which a number of control values corresponding to different core temperatures, can be stored.

8. The cooling system as claimed in claim 7, wherein the processor is operable to send a control signal to the servo-motor to operate the cooling fan at a predetermined speed in response to a temperature input being received by the processor which matches a core temperature corresponding to one of said control values.

9. The cooling system as claimed in claim 8, wherein the memory device has stored therein a first control value corresponding to a particular first core temperature of the infant and a second control value corresponding to a second core temperature of the infant which is relatively higher than the first core temperature, the processor being operable to:

10. The cooling system as claimed in claim 9, wherein the memory device has stored therein a number of additional control values which each correspond to a different core temperature which is relatively higher than the second core temperature, the processor being operable to send control signals to the servo-motor to operate the cooling fan at speeds which are relatively higher than the second speed, in response to a temperature input being received by the processor which matches a particular core temperature corresponding to one of said additional control values.

1 1. The cooling system as claimed in claim 10, wherein the processor is operable to switch the servo-motor off in response to a temperature input being received by the processor which is below the first core temperature.

12. The cooling system as claimed in any one of claims 1 to 1 1 , which includes a housing in which the blower is housed, the housing being positionable at the head of the infant when the infant is located on a support platform of the incubator, in use, and including a front side defining an opening through which ambient air can be blown onto the infant's head and a deflector panel which extends outwardly from the front side of the housing so as to form a cover over the infant's head in order to deflect heat emitted by the heater of the incubator, away from the infant's head.

13. An incubator for incubating an infant, the incubator including:

a heating system for heating the infant; and

the cooling system as claimed in any one of claims 1 to 12.

14. The incubator as claimed in claim 13, wherein the heating system includes a heater for heating the infant and heater control means which is operable to receive temperature inputs corresponding to the core body temperature of the infant and to control the intensity of the heat generated by the heater in response to temperature inputs received by it.

15. The incubator as claimed in claim 14, wherein the control means of the cooling system and the heater control means of the heating system are operable together to maintain a core body temperature of the infant within a target temperature range within which neuro-protective hypothermia is induced in the infant, by controlling the speed of rotation of the cooling fan and the intensity of the heat generated by the heater, respectively.