Early
Human
Development,
29 (1992)
293
293-291
Elsevier Scientific Publishers Ireland Ltd. EHD 01291
Advances in mechanical ventilation: high frequency ventilation Toshio Kawano Department
of Neonatology.
National
Children’s
Hospital,
3-35-31
Taishido,
Setagaya-ku,
Tokyo
(Japan)
Summary High frequency oscillatory ventilation (HFOV) is a technique in which a small tidal volume of airway gas is vibrated by moving a piston at an extremely fast rate (15 Hz). By this technique infants are ventilated in less traumatic ways compared to the conventional mechanical ventilation (CMV). The control study performed in Japan showed the efficacy and safety of HFOV compared to CMV. Key words: high frequency ventilation; conventional mechanical ventilation; preterm infants; broncho-pulmonary dysplasia; intraventricular hemorrhage; pulmonary air leaks
Advances in mechanical ventilation The introduction of mechanical ventilation into neonatal intensive care units improved the outcome of sick newborns especially that of low birth weight infants. Commonly used infant ventilators operate on the same principle. The expiratory valve is closed by a time cycle mechanism for mandatory breaths and constant flow is intermittently forced into the patient. The increased survival of critically ill infants has been accompanied by a high incidence of both acute and chronic complications of mechanical ventilation, such as air leaks and bronchopulmonary dysplasia. To overcome these problems some new technique of mechanical ventilation was developed. Figure 1 shows the chart of advances in mechanical ventilation. As shown here, there are three main directions. One is the improvement of conventional mechanical ventilators. The other directions are high frequency ventilation and ECMO. Correspondence
to: Toshio
Kawano,
Department
Taishido, Setagaya-ku, Tokyo, Japan.
of Neonatology,
National
Children’s
Hospital,
3-3.5-3 I
294
Conventional
Mechanical (CMV)
Ventilation
__---*\ . , .
-. -.
Extracorporial
Menbrane (ECMO)
synchronized pressure
*.
Constant
IMV support
Flow
ventilation
Ventilation
Oxygenation
Fig. 1. Advances in mechanical ventilation. Three main directions of advance are shown; the improvement in conventional mechanical ventilators, the improvement in high frequency ventilation, and in extracorporial membrane oxygenation.
Many new techniques have been developed in adult ventilators. Some of them will be applied to the infant ventilator in the near future. Two of them deserve mention. One method is pressure support ventilation. Pressure support ventilation is a technique in which the patient’s spontaneous inspiration triggers the ventilator to provide a variable flow of gas that increases until airway pressure reaches a preselected level. The other method is SIMV. Synchronous ventilation has been suggested as a method of ventilatory support for neonates which can reduce fighting and the incidence of barotrauma. SIMV is usually triggered by intratracheal pressure change but recently a method utilizing a respiration monitor attached to the abdomen has been investigated. HFV will be given greatest attention in this report. High frequency ventilation -
HIFI study
High frequency ventilation is usually divided into three groups. HFO is a technique in which a small tidal volume of airway gases is vibrated by moving a piston at an extremely fast rate [ 11. The use of HFO was begun to decrease the barotrauma of conventional mechanical ventilation. In North America, a multicenter randomised clinical trial comparing the efficacy and safety of HFO with that of CMV in the treatment of respiratory failure in preterm infant was conducted. The study was called the High Frequency Intervention trial, or HIFI study [2]. The criteria for entry to HIFI trial were as follows. Neonates weighing between 750 and 2000 g and in need of ventilatory support were admitted. They were required to be less than 24 h of age and to have been on CMV for less than 12 h. Some exclusion criteria were also applied, for example babies with meconium aspiration syndrome, hydrops fetalis, etc. were not admitted to the study. The result of the study was published in the New England Journal of Medicine in 1989. Of 673 preterm infants weighing between 750 and 2000 g, 346 were assigned to receive CMV and 327 to receive HFO. Their backgrounds were well matched. The
295
result of this study is as follows. The incidence of bronchopulmonary dysplasia was similar in two groups. HFO did not reduce mortality. HFO, as compared with CMV, was associated with an increase incidence air leaks, grade 3 and 4 intraventricular hemorrage and periventricular leukomalacia. Their conclusion was ‘Because of the lack of an objective advantage with the use of high frequency ventilation and its potential adverse effect, we suggest that this form of ventilation should be used with caution in preterm infants with respiratory failure.’ Japanese HFV study Since 1985, this piston pump high frequency ventilator has been available in Japan and our group started to use this ventilator to rescue babies. In Japan, clinical experiences suggest that HFO provides better oxygenation with fewer complications, which were compatible with the data from laboratory animal study [3]. The data presented by the NIH were quite disappointing, so we planned to conduct a similar multicenter randomized trial in Japan [4]. A multicenter randomized trial was conducted in 9 neonatal centers in Japan to re-evaluate the safety and the efficacy of HFO using piston type oscillator in the treatment of respiratory failure in preterm infants. In the HIFI trial, very few centers had any experience of HFO and none had any experience with the ‘Humming-bird’ which was the ventilator chosen for the trial. Therefore neonatal centers were chosen which had adequate experience with the HFO machine. Table I outlines the protocol of the Japanese study. One of the problems of the HIFI study was that subjects had already been on CMV for a long time before randomization. The study was begun as soon as possible to decrease the effect of CMV. Mechanical ventilation either with HFO or CMV began within 60 min for the inborn and within 6 h after birth for the outborn infants. Another problem of HIFI study was the incidence of IVH. From their study we could not tell the time when hemorrage occurred. So we tried to exclude the babies who already had intracranial hemorrage. Those who were screened and confirmed for the absence of intraventricular
TABLE I Protocol (Japanese study). Birth weight 750-2000 g With respiratory distress needing ventilatory care Entry for study possible within 60 min after birth for inborn within 6 h after birth for outbom Exclusions: MAS, Hydrops fetalis, etc. Surfactant treatment: recommended in cases of RDS Ventilator settings Goals: to maintain Pao2 between 60 and 100 Torr and P,COZ between 30 and 45 Torr. Frequency (HFO): 15 Hz
296 TABLE II Number and percentage of complications of HIFI study and Japanese study HFOVCMV
HIFI study HFOV
ICH IVH (> III”) PVL Air leaks BPD Mortality
JAPAN CMV
HFOV
CMV
No.
o/o
No.
%I
No.
‘A,
No.
o/
160 84 38 148 130 60
49 26 12 45 40 18
146 63 25 131 141 60
42 18 I 38 41 17
I 2 1 4 4 0
15 4 2 9 9 0
6 I 4 6 6 1
13 2 9 13 13 2
hemorrage by brain echography were randomized. After randomization brain echography was performed every day for a week. The same exclusions were made as in HIFI study. We used artificial surfactant when the diagnosis of RDS was clinically made. Ventilator settings are given in Table I. The results of this study were as follows. Fio2 were the same in both groups. The mean airway pressure was higher in HFO group than in CMV group. Arterial to alveolar oxygen tension ratios in the two groups also showed significant difference. There was only one death in the group of conventional mechanical ventilation. There were no significant differences in the incidence of air leaks, symptomatic PDA, pulmonary hemorrage and pneumonia. Incidence of intraventricular hemorrage was also similar in both groups. For periventricular leukomalacia, infants in the CMV group showed slightly higher incidence compared to HFO, but the difference was not significant. The incidence of bronchopulmonary dysplasia is also slightly higher in the CMV group, but the difference was not significant. Table 2 shows the number of complications of HIFI study and Japanese study. Of course, the number of infants involved in the Japanese study is much smaller than that of HIFI study, but the percentage of complications in the Japanese study is much smaller than that of HIFI study, and also there is no significant difference in the number of complications between HFO group and CMV group in the Japanese study. Conclusions We conclude that high frequency ventilation with piston pump oscillator does not increase the risk of severe complications such as air leaks, BPD, or IVH if used carefully by experienced staff in neonatal centers. References 1 Bohn, D.J., Miyasaka, K., Marchak, B.E., Thompson, W.K., Froese, A.B. awl Bryan, A.C. (1980): Ventilation by high frequency oscillation. J. Appl. Physiol., 48, 710. 2 HIFI study group. (1989): High-frequency oscillatory ventilation in the treatment of respiratory failure in preterm infants. N. Engl. J. Med., 320, 88.
297
3 Hamilton, P.P., Onayemi, A., Smith, J., Cutz, E., Froese, A.B. and Bryan, A.C. (1983): Comparison of conventional and high-frequency ventilation: oxygenation and lung pathology. J. Appl. Physiol., 4
55, 131. Ogawa, Y., Miyasaka,
K., Kawano, T. and Nishida, H. (1991): A multicenter randamized trial of high frequency oscillatory ventilation as compared with conventional ventilation in preterm Infants with respiratory failure. Presented at the 7th conference on High Frequency Ventilation in infants, Snowbird, Utah, April, 1990.
Human
Development,
29 (1992)
293
293-291
Elsevier Scientific Publishers Ireland Ltd. EHD 01291
Advances in mechanical ventilation: high frequency ventilation Toshio Kawano Department
of Neonatology.
National
Children’s
Hospital,
3-35-31
Taishido,
Setagaya-ku,
Tokyo
(Japan)
Summary High frequency oscillatory ventilation (HFOV) is a technique in which a small tidal volume of airway gas is vibrated by moving a piston at an extremely fast rate (15 Hz). By this technique infants are ventilated in less traumatic ways compared to the conventional mechanical ventilation (CMV). The control study performed in Japan showed the efficacy and safety of HFOV compared to CMV. Key words: high frequency ventilation; conventional mechanical ventilation; preterm infants; broncho-pulmonary dysplasia; intraventricular hemorrhage; pulmonary air leaks
Advances in mechanical ventilation The introduction of mechanical ventilation into neonatal intensive care units improved the outcome of sick newborns especially that of low birth weight infants. Commonly used infant ventilators operate on the same principle. The expiratory valve is closed by a time cycle mechanism for mandatory breaths and constant flow is intermittently forced into the patient. The increased survival of critically ill infants has been accompanied by a high incidence of both acute and chronic complications of mechanical ventilation, such as air leaks and bronchopulmonary dysplasia. To overcome these problems some new technique of mechanical ventilation was developed. Figure 1 shows the chart of advances in mechanical ventilation. As shown here, there are three main directions. One is the improvement of conventional mechanical ventilators. The other directions are high frequency ventilation and ECMO. Correspondence
to: Toshio
Kawano,
Department
Taishido, Setagaya-ku, Tokyo, Japan.
of Neonatology,
National
Children’s
Hospital,
3-3.5-3 I
294
Conventional
Mechanical (CMV)
Ventilation
__---*\ . , .
-. -.
Extracorporial
Menbrane (ECMO)
synchronized pressure
*.
Constant
IMV support
Flow
ventilation
Ventilation
Oxygenation
Fig. 1. Advances in mechanical ventilation. Three main directions of advance are shown; the improvement in conventional mechanical ventilators, the improvement in high frequency ventilation, and in extracorporial membrane oxygenation.
Many new techniques have been developed in adult ventilators. Some of them will be applied to the infant ventilator in the near future. Two of them deserve mention. One method is pressure support ventilation. Pressure support ventilation is a technique in which the patient’s spontaneous inspiration triggers the ventilator to provide a variable flow of gas that increases until airway pressure reaches a preselected level. The other method is SIMV. Synchronous ventilation has been suggested as a method of ventilatory support for neonates which can reduce fighting and the incidence of barotrauma. SIMV is usually triggered by intratracheal pressure change but recently a method utilizing a respiration monitor attached to the abdomen has been investigated. HFV will be given greatest attention in this report. High frequency ventilation -
HIFI study
High frequency ventilation is usually divided into three groups. HFO is a technique in which a small tidal volume of airway gases is vibrated by moving a piston at an extremely fast rate [ 11. The use of HFO was begun to decrease the barotrauma of conventional mechanical ventilation. In North America, a multicenter randomised clinical trial comparing the efficacy and safety of HFO with that of CMV in the treatment of respiratory failure in preterm infant was conducted. The study was called the High Frequency Intervention trial, or HIFI study [2]. The criteria for entry to HIFI trial were as follows. Neonates weighing between 750 and 2000 g and in need of ventilatory support were admitted. They were required to be less than 24 h of age and to have been on CMV for less than 12 h. Some exclusion criteria were also applied, for example babies with meconium aspiration syndrome, hydrops fetalis, etc. were not admitted to the study. The result of the study was published in the New England Journal of Medicine in 1989. Of 673 preterm infants weighing between 750 and 2000 g, 346 were assigned to receive CMV and 327 to receive HFO. Their backgrounds were well matched. The
295
result of this study is as follows. The incidence of bronchopulmonary dysplasia was similar in two groups. HFO did not reduce mortality. HFO, as compared with CMV, was associated with an increase incidence air leaks, grade 3 and 4 intraventricular hemorrage and periventricular leukomalacia. Their conclusion was ‘Because of the lack of an objective advantage with the use of high frequency ventilation and its potential adverse effect, we suggest that this form of ventilation should be used with caution in preterm infants with respiratory failure.’ Japanese HFV study Since 1985, this piston pump high frequency ventilator has been available in Japan and our group started to use this ventilator to rescue babies. In Japan, clinical experiences suggest that HFO provides better oxygenation with fewer complications, which were compatible with the data from laboratory animal study [3]. The data presented by the NIH were quite disappointing, so we planned to conduct a similar multicenter randomized trial in Japan [4]. A multicenter randomized trial was conducted in 9 neonatal centers in Japan to re-evaluate the safety and the efficacy of HFO using piston type oscillator in the treatment of respiratory failure in preterm infants. In the HIFI trial, very few centers had any experience of HFO and none had any experience with the ‘Humming-bird’ which was the ventilator chosen for the trial. Therefore neonatal centers were chosen which had adequate experience with the HFO machine. Table I outlines the protocol of the Japanese study. One of the problems of the HIFI study was that subjects had already been on CMV for a long time before randomization. The study was begun as soon as possible to decrease the effect of CMV. Mechanical ventilation either with HFO or CMV began within 60 min for the inborn and within 6 h after birth for the outborn infants. Another problem of HIFI study was the incidence of IVH. From their study we could not tell the time when hemorrage occurred. So we tried to exclude the babies who already had intracranial hemorrage. Those who were screened and confirmed for the absence of intraventricular
TABLE I Protocol (Japanese study). Birth weight 750-2000 g With respiratory distress needing ventilatory care Entry for study possible within 60 min after birth for inborn within 6 h after birth for outbom Exclusions: MAS, Hydrops fetalis, etc. Surfactant treatment: recommended in cases of RDS Ventilator settings Goals: to maintain Pao2 between 60 and 100 Torr and P,COZ between 30 and 45 Torr. Frequency (HFO): 15 Hz
296 TABLE II Number and percentage of complications of HIFI study and Japanese study HFOVCMV
HIFI study HFOV
ICH IVH (> III”) PVL Air leaks BPD Mortality
JAPAN CMV
HFOV
CMV
No.
o/o
No.
%I
No.
‘A,
No.
o/
160 84 38 148 130 60
49 26 12 45 40 18
146 63 25 131 141 60
42 18 I 38 41 17
I 2 1 4 4 0
15 4 2 9 9 0
6 I 4 6 6 1
13 2 9 13 13 2
hemorrage by brain echography were randomized. After randomization brain echography was performed every day for a week. The same exclusions were made as in HIFI study. We used artificial surfactant when the diagnosis of RDS was clinically made. Ventilator settings are given in Table I. The results of this study were as follows. Fio2 were the same in both groups. The mean airway pressure was higher in HFO group than in CMV group. Arterial to alveolar oxygen tension ratios in the two groups also showed significant difference. There was only one death in the group of conventional mechanical ventilation. There were no significant differences in the incidence of air leaks, symptomatic PDA, pulmonary hemorrage and pneumonia. Incidence of intraventricular hemorrage was also similar in both groups. For periventricular leukomalacia, infants in the CMV group showed slightly higher incidence compared to HFO, but the difference was not significant. The incidence of bronchopulmonary dysplasia is also slightly higher in the CMV group, but the difference was not significant. Table 2 shows the number of complications of HIFI study and Japanese study. Of course, the number of infants involved in the Japanese study is much smaller than that of HIFI study, but the percentage of complications in the Japanese study is much smaller than that of HIFI study, and also there is no significant difference in the number of complications between HFO group and CMV group in the Japanese study. Conclusions We conclude that high frequency ventilation with piston pump oscillator does not increase the risk of severe complications such as air leaks, BPD, or IVH if used carefully by experienced staff in neonatal centers. References 1 Bohn, D.J., Miyasaka, K., Marchak, B.E., Thompson, W.K., Froese, A.B. awl Bryan, A.C. (1980): Ventilation by high frequency oscillation. J. Appl. Physiol., 48, 710. 2 HIFI study group. (1989): High-frequency oscillatory ventilation in the treatment of respiratory failure in preterm infants. N. Engl. J. Med., 320, 88.
297
3 Hamilton, P.P., Onayemi, A., Smith, J., Cutz, E., Froese, A.B. and Bryan, A.C. (1983): Comparison of conventional and high-frequency ventilation: oxygenation and lung pathology. J. Appl. Physiol., 4
55, 131. Ogawa, Y., Miyasaka,
K., Kawano, T. and Nishida, H. (1991): A multicenter randamized trial of high frequency oscillatory ventilation as compared with conventional ventilation in preterm Infants with respiratory failure. Presented at the 7th conference on High Frequency Ventilation in infants, Snowbird, Utah, April, 1990.
