(Acta Paediatr Jpn 1992; 34: 631
- 635)
High Frequency Oscillation Toshio Kawano, M.D. Department of Neonatology, National ChildrenS Hospital, Tokyo, Japan
The current state of high frequency oscillation (HFO) in Japan is reviewed. The discussion is focused on the following: (i) the repeated application of short duration SI (sustained inflation) is effective in recruiting lung volume and increasing P%,; (ii) HFO can prevent the formation of granulocytes related to lung injury; and (iii) HFO does not increase the risk of severe complications such as air leaks, bronchopulmonary dysplasia or intraventricular hemorrhage. Key Words High frequency ventilation, Sustained inflation, Lung injury
Introduction High frequency oscillation (HFO) is a new technique in which a small tidal volume of airway gases is vibrated by moving a piston at an extremely fast rate. Many neonatal centers in Japan have been using HFO successfully with babies who have severe respiratory failure. This review attempts to focus on the following three points concerning HFO: volume recruitment during HFO, the role of granulocytes during mechanical ventilation and clinical study using HFO.
Volume Recruitment During HFO It is important to maintain sufficient lung volume using sustained inflation (SI) during HFO. Kolton et a1 [ l ] demonstrated that SI during HFO increased both lung volume and Pa,,. They performed SI by maintaining the pressure at 30 mmHg for 15 sec. While this technique was successful with animals, it is dangerous to Received August 14, 1992 Correspondence address: Toshio Kawano, M.D., Department of Neonatology, National Children’s Hospital, 3-35-31 Taishido, Setagaya-ku, Tokyo, Japan.
use such high pressure for long periods with low birthweight infants. Sugiura et a1 [2] investigated the effect of HFO and SI on systemic and intracranial circulation using a rabbit model (Figs 1,2). The magnitude of the suppression and the rebound in arterial blood pressure (ABP) associated with SI was larger when higher pressure and a longer duration of SI were applied. The magnitude of the suppression of ABP caused by SI increased until the SI duration extended to 3 sec, and then plateaued. The magnitude of the rebound in ABP caused by SI tended to increase with SI over 3 sec, and therefore repeated SI with a duration less than 3 sec was applied [2]. Sufficient volume recruitment and Pa,, were obtained with little fluctuation of ABP and central venous pressure when the experiment was performed with repeated application of short duration SI [3]. Short SI makes the lung volume change from the deflation curve to the inflation curve before completely disappearing. As the interval between SI widens, lung volume is maintained with a mean airway pressure of 15 cmHzO until the application of the next SI increases lung volume (Figs. 3,4). In our experiments [3], the repeated applicationofshort durationSIwaseffectiveinrecruiting
632 (54) Kawano et al.
lung volume and increasing Pao2. The influence on the circulatory system was less than that of continuous SI. SI of short duration should be used at first in a clinical situation, SI is considered to be effective if a rise in transcutaneous Po? or SpoZis observed. SI is repeated until the desired value is reached. SI should be extended or the mean airway pressure of HFO raised if the first SI is not effective.
The Role of Granulocytes During Mechanical Ventilation
Fig. 1: Change of the arterial pressure, central venous pressure and intracranial pressure during SI.
HFO was commenced in order to decrease the barotrauma of conventional mechanical ventilation (CMV). Many laboratory experiments have suggested the advantage of HFO compared with CMV. However, the protective mechanism is still unknown. Recent studies have demonstrated that inflammatory cells, especially granulocytes, are largely involved in lung damage. Merrit et a1 [4]
20 Normal lung 10
** 0
I I F :
I
I
I
1 :
I
I
'
I
m I
E
-E
a
$
-10
*
c
m a, 5
R
6
:
Q
-20
L -30 Suppression during
!
Sl
-40
0.5
1 .o
20
30
3
6
10
15
SI duration Isec) . .
Fig. 2: Decrease and rebound in arterial blood pressure (ABP) with various duration and pressure of SI in normal rabbit lungs. The portion below the baseline indicates the magnitude of the decrease in mean arterial pressure during SI. The upper portion indicates the magnitude of ABP rebound following Sf. 10 cmH,O above MAP (*); 15 cmH,O above MAP (a):20 cmH,O above MAP (H).
Acta Paediatr Jpn
High frequency oscillation ( 5 5 ) 633 HFO (MAP 10 cmH,O)
+ SI (25 cmH,O,
15 sec )
HFO (MAP 10 cmH,O)
+ SI (25 cmH,O,
1 sec ) q 30 sec
Lung volume (ml)
30 sec
U
Fig. 3: Comparison between short duration SI and continuous SI. Lung volume was measured by impedance plethysmograph. Pressure-volume curve
Lung volume change during SI (30 cmH2O for 1 s e c . ) x3
___..__ i___...__-___...____ 15
30
Pressure (cmH20)
Fig. 4 Pressure and volume relationship during repeated short duration SI. Short SI makes lung volume change from the deflation curve to the inflation curve before completely disappearing. As the interval between SIs widens, lung volume can be maintained with a mean airway pressure of 15 cmH,O until the application of next SI increases lung volume.
showed that infants with respiratory distress syndrome (RDS) destined to develop bronchopulmonary dysplasia had a greater number of inflammatory cells in the pulmonary effluent than infants with RDS alone. Hamilton et a1 [5] showed that after repetitive lung lavage was performed in rabbits, HFO maintained excellent gas exchange and did not cause hyaline membrane formation. In contrast, CMV produced poor gas exchange and extensive hyaline membrane formation. We have compared these differences to mechanical barotrauma [6]. There was a large number of granulocytes in the damaged lung. With the depletion of granulocytes in the same rabbit ventilated with CMV, this damage disappeared
Vol. 34 No. 6 December I992
[6]. Therefore it was concluded that granulocytes played an important role in this model. Matsuoka et a1 [7] showed that in the same lavaged model, white blood cell (WBC) counts in the lavaged fluid were greater with CMV than with HFO. Figure 5 shows the experimental protocol. WBC counts in the fluid obtained by lung lavage after CMV increased in number much more than those after HFO (Fig. 6). The function of granulocytes was assessed by chemiluminescence. The granulocytes of the HFO group responded better than those of the CMV group (Fig. 7). The explanation of this result may be that granulocytes in the lavaged fluid after HFO maintain their function or, in other words, are in the activated state. On the other hand, granulocytes obtained from the CMV group have impaired function or are in NAESTHESIA AND PARALYSIS
00% OXYGEN AND BAGGING
i-....f”””.ll 7
STABILIZATION USING HFO REMOVAL LUNG SURFACTANT STABILIZATION USING HFO
4 HR VENTILATION GROUP 4 HR CMV
+ 4 HR HFO COLLECTION OF GRANULOCYTES SACRIFICE
Fig. 5 : Experimental protocol.
634 (56) Kawano et al. NS NS
t -
$‘“1 ?% a
Befare After ( % I < ) (n-9)
NS
T
NS
Before After Before Aller ( n - 7 ) ( n = 7 ) (0-4) ( n - 3 )
CMV ( 2 hr)
HFO (2 hr)
CMV (4 hr)
t ‘
m
Before Aller (n-8) ( n S ) HFO ( 4 hr)
Fig. 6: Total number of cells from lung lavage fluids after ventilation. There was a significant difference between 4 h r CMV and 4 h r HFO. There was no significant difference between 2 hr CMV and 2 hr HFO. * P < 0.05; P < 0.025, NS, not significant.
NS
I
t
C M V (2 hr)
HFO (2 hr)
C M V (4 hr)
HFO (4 hr)
(n-6)
(n-5)
(n-5)
(n-11)
Fig. 7: Granulocyte: luminol-dependent chemilurninescence (CL) response stimulated with N-formylmethionyl-leucyl-phenylalanineof lung lavage fluids at the termination of ventilation. There was significant difference between 4 h r CMV and 4 hr HFO. *P< 0.05; P < 0.025; NS, not significant.
the ‘wasted’ state. This may not be the cause of the lung damage but the result of it. This means that granulocytes damage the lung and emerge into the alveoli in the wasted state after longterm ventilation by CMV. Thus we conclude that HFO can prevent granulocyte-related lung injury.
Clinical Study In North America, a multicenter randomized clinical trial comparing the efficacy and safety of
HFO with that of CMV in the treatment of respiratory failure in preterm infants was conducted. The High Frequency Intervention trial (HIFI) [8] entry criteria are as follows. Babies have to weigh between 750 and 2,OOOg and require ventilatory support. They have to be aged less than 24 hr and to have been on CMV for less than 12 hr. There were some exclusions, such as for meconium aspiration syndrome, hydrops fetalis etc. The result of this study is as follows. The incidence of bronchopulmonary dysplasia was similar in two groups. HFO did not reduce mortality and, compared with CMV, was associated with an increased incidence of air leaks, grades 3 and 4 intraventricular hemorrhage (IVH), and periventricular leukomalacia [81. The study concluded that: ‘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.’ Since 1985, high frequency oscillatory ventilators have been available in Japan and have been used to rescue babies. In Japan, clinicat experience suggests that HFO provides better oxygenation with fewer complications. The data presented by the National Institutes of Health were quite disappointing, so a multicenter randomized trial was conducted at nine neonatal centers in Japan to re-evaluate the safety and efficacy of HFO using a piston-type oscillator in the treatment of neonatal respiratory failure [9]. Neonatal centers experienced with that HFO machine were chosen. Table 1 depicts a protocol of the Japanese study. One of the problems of the HIFI study
Table 1. Protocol (Japanese study) ~
Birthweight 750-2,000 g Entry for study possible within 60 min after birth for inborn within 6 h r after birth for outborn Exclusions: MAS, hydrops fetalis etc. Surfactant treatment: recommended in cases of RDS. Ventilator set to maintain PrhZbetween 60 and 100 mmHg, and Pa,-o between 30 and 45 mmHg. Frequency (HFO) I5dz.
Acta Paediatr Jpn
Highfiequency oscillation (57) 635 Table 2. Complications of HIFI study and Japanese study HIFI Study HFOfCMV
HFO
CMV
JAPAN HFO
CMV
(%) 160(49) 146(42) 7(l5) 6(13) ICH IVH (> 111') (%) 84 (26) 63 (18) 2 (4) l ( 2 ) (%) 38 (12) 25 (7) PVL l(2) 4(9) (%) 148 (45) 131 (38) 4(9) 6 (13) Airleaks (%) 130(40) 141 (41) 4(9) BPD 6(13) (46) 60(18) 60(17) O(0) 1(2) Mortality ICH, intracoronary hemorrhage; PVL, periventricular leukomalacia; BPD, bronchopulmonary dysplasia.
was that babies studied had already been on CMV long before randomization. Therefore, mechanical ventilation with either HFO or CMV was commenced within 60min for the inborn and within 6 hr after birth for the outborn infants in the Japanese study. Another problem of the HIFI study was the incidence of IVH. From their study we could not tell the time when hemorrhage occurred. So we tried to exclude the babies who already had intracranial hemorrhage. We used artificial surfactant (S-TA) when the diagnosis of RDS was clinically made. The results of this study were as follows. The fractional concentration of inspired oxygen (Fio2) was the same in both groups. The mean airway pressure was higher in the HFO group than in the CMV group. The arterial to alveolar oxygen tension ratios in the two groups also were significantly different. There was only one death in the CMV group. There were no significant differences in the incidence of air leaks, symptomatic patent ductus arteriosis, pulmonary hemorrhage and pneumonia. The incidence of IVH was also similar in both groups. As for periventricular leukomalacia, infants in the CMV group showed a slightly higher incidence compared with HFO, but the difference was not significant. The incidence of bronchopulmonary dysplasia was also slightly higher in the CMV group, but the difference was not significant. Table 2 outlines the number of clinical complications encountered in both the HIFI and Japanese studies [9]. Of course, the number of
Vol. 34 No. 6 December 1992
involved infants in the Japanese study was much smaller than that of the HIFI study. There was no significant difference in the number of complications between the HFO and CMV groups in the Japanese study. We conclude that HFO does not increase the risk of severe complications such as air leaks, bronchopulmonary dysplasia or IVH if used carefully by experienced staff in neonatal centers. References 1. Kolton M, Cattran CB, Kent G, Volgyesi G, Froese AB, Bryan AC. Oxygenation during high frequency ventilation compared with conventional mecbanical ventilation in two models of lung injury. Anesth Analg 1982; 61; 323. 2. Sugiura M, Kawano T, Miyasaka K. Effect of HFO on intracranial circulation. Presented at the 6th conference on High Frequency Ventilation in Infants, Snowbird, Utah, April 1989. 3. Watanabe H, Kawano T, Miyasaka K. Optimal volume recruitment with sustained inflation (Sl) during high frequency oscillatory ventilation. Presented at the 8th conference on High Frequency Ventilation in Infants, Snowbird, Utah, April 1991. 4. Merrit TA, Cochrane CG, Holcomb K, Bohl B, Hallmann M, Strayer D, Edword DK, Gluck L. Elastase and proteinase inhibitor activity in tracheal aspirates during respiratory distress syndrome. J Clin Invest 1983; 72: 656. 5. Hamilton PP, Onayemi A, Smith J, Cutz E, Froese AB, Bryan AC. Comparison of conventional and high frequency ventilation oxygenation and lung pathology. JApplPhysiol 1983; 5 5 : 131. 6. Kawano T, Mori S, Cybulsky M, Burger A, Ballin E, Cutz E, Bryan AC. Effect of granulocyte depletion in a ventilated surfactant-depleted lung. J Appl Physiol 1987; 67: 27. 7. Matsuoka T, Kawano T, Miyasaka K. Preventive role of HFOV in granulocyte-related pulmonary injury in the lungs of surfactant-treated rabbits. Presented at the 8th conference on High Frequency Ventilation in Infants, Snowbird, Utah, April 199I. 8. HIFI Study Group. High frequency oscillatory ventilation compared with conventional mechanical ventilation in the treatment of respiratory failure in preterm infants. N Eng J Med 1989; 320: 88. 9. Ogawa Y, Miyasaka K, Kawano T, Nishida H. A multicenter randomized trial of high frequency oscillatory ventilation as compared with conventional ventilation in preterm infants with respiratory failure. Presented at the 7th conferenceon High Frequency Ventilation in Infants, Snowbird, Utah, April 1990.
- 635)
High Frequency Oscillation Toshio Kawano, M.D. Department of Neonatology, National ChildrenS Hospital, Tokyo, Japan
The current state of high frequency oscillation (HFO) in Japan is reviewed. The discussion is focused on the following: (i) the repeated application of short duration SI (sustained inflation) is effective in recruiting lung volume and increasing P%,; (ii) HFO can prevent the formation of granulocytes related to lung injury; and (iii) HFO does not increase the risk of severe complications such as air leaks, bronchopulmonary dysplasia or intraventricular hemorrhage. Key Words High frequency ventilation, Sustained inflation, Lung injury
Introduction High frequency oscillation (HFO) is a new technique in which a small tidal volume of airway gases is vibrated by moving a piston at an extremely fast rate. Many neonatal centers in Japan have been using HFO successfully with babies who have severe respiratory failure. This review attempts to focus on the following three points concerning HFO: volume recruitment during HFO, the role of granulocytes during mechanical ventilation and clinical study using HFO.
Volume Recruitment During HFO It is important to maintain sufficient lung volume using sustained inflation (SI) during HFO. Kolton et a1 [ l ] demonstrated that SI during HFO increased both lung volume and Pa,,. They performed SI by maintaining the pressure at 30 mmHg for 15 sec. While this technique was successful with animals, it is dangerous to Received August 14, 1992 Correspondence address: Toshio Kawano, M.D., Department of Neonatology, National Children’s Hospital, 3-35-31 Taishido, Setagaya-ku, Tokyo, Japan.
use such high pressure for long periods with low birthweight infants. Sugiura et a1 [2] investigated the effect of HFO and SI on systemic and intracranial circulation using a rabbit model (Figs 1,2). The magnitude of the suppression and the rebound in arterial blood pressure (ABP) associated with SI was larger when higher pressure and a longer duration of SI were applied. The magnitude of the suppression of ABP caused by SI increased until the SI duration extended to 3 sec, and then plateaued. The magnitude of the rebound in ABP caused by SI tended to increase with SI over 3 sec, and therefore repeated SI with a duration less than 3 sec was applied [2]. Sufficient volume recruitment and Pa,, were obtained with little fluctuation of ABP and central venous pressure when the experiment was performed with repeated application of short duration SI [3]. Short SI makes the lung volume change from the deflation curve to the inflation curve before completely disappearing. As the interval between SI widens, lung volume is maintained with a mean airway pressure of 15 cmHzO until the application of the next SI increases lung volume (Figs. 3,4). In our experiments [3], the repeated applicationofshort durationSIwaseffectiveinrecruiting
632 (54) Kawano et al.
lung volume and increasing Pao2. The influence on the circulatory system was less than that of continuous SI. SI of short duration should be used at first in a clinical situation, SI is considered to be effective if a rise in transcutaneous Po? or SpoZis observed. SI is repeated until the desired value is reached. SI should be extended or the mean airway pressure of HFO raised if the first SI is not effective.
The Role of Granulocytes During Mechanical Ventilation
Fig. 1: Change of the arterial pressure, central venous pressure and intracranial pressure during SI.
HFO was commenced in order to decrease the barotrauma of conventional mechanical ventilation (CMV). Many laboratory experiments have suggested the advantage of HFO compared with CMV. However, the protective mechanism is still unknown. Recent studies have demonstrated that inflammatory cells, especially granulocytes, are largely involved in lung damage. Merrit et a1 [4]
20 Normal lung 10
** 0
I I F :
I
I
I
1 :
I
I
'
I
m I
E
-E
a
$
-10
*
c
m a, 5
R
6
:
Q
-20
L -30 Suppression during
!
Sl
-40
0.5
1 .o
20
30
3
6
10
15
SI duration Isec) . .
Fig. 2: Decrease and rebound in arterial blood pressure (ABP) with various duration and pressure of SI in normal rabbit lungs. The portion below the baseline indicates the magnitude of the decrease in mean arterial pressure during SI. The upper portion indicates the magnitude of ABP rebound following Sf. 10 cmH,O above MAP (*); 15 cmH,O above MAP (a):20 cmH,O above MAP (H).
Acta Paediatr Jpn
High frequency oscillation ( 5 5 ) 633 HFO (MAP 10 cmH,O)
+ SI (25 cmH,O,
15 sec )
HFO (MAP 10 cmH,O)
+ SI (25 cmH,O,
1 sec ) q 30 sec
Lung volume (ml)
30 sec
U
Fig. 3: Comparison between short duration SI and continuous SI. Lung volume was measured by impedance plethysmograph. Pressure-volume curve
Lung volume change during SI (30 cmH2O for 1 s e c . ) x3
___..__ i___...__-___...____ 15
30
Pressure (cmH20)
Fig. 4 Pressure and volume relationship during repeated short duration SI. Short SI makes lung volume change from the deflation curve to the inflation curve before completely disappearing. As the interval between SIs widens, lung volume can be maintained with a mean airway pressure of 15 cmH,O until the application of next SI increases lung volume.
showed that infants with respiratory distress syndrome (RDS) destined to develop bronchopulmonary dysplasia had a greater number of inflammatory cells in the pulmonary effluent than infants with RDS alone. Hamilton et a1 [5] showed that after repetitive lung lavage was performed in rabbits, HFO maintained excellent gas exchange and did not cause hyaline membrane formation. In contrast, CMV produced poor gas exchange and extensive hyaline membrane formation. We have compared these differences to mechanical barotrauma [6]. There was a large number of granulocytes in the damaged lung. With the depletion of granulocytes in the same rabbit ventilated with CMV, this damage disappeared
Vol. 34 No. 6 December I992
[6]. Therefore it was concluded that granulocytes played an important role in this model. Matsuoka et a1 [7] showed that in the same lavaged model, white blood cell (WBC) counts in the lavaged fluid were greater with CMV than with HFO. Figure 5 shows the experimental protocol. WBC counts in the fluid obtained by lung lavage after CMV increased in number much more than those after HFO (Fig. 6). The function of granulocytes was assessed by chemiluminescence. The granulocytes of the HFO group responded better than those of the CMV group (Fig. 7). The explanation of this result may be that granulocytes in the lavaged fluid after HFO maintain their function or, in other words, are in the activated state. On the other hand, granulocytes obtained from the CMV group have impaired function or are in NAESTHESIA AND PARALYSIS
00% OXYGEN AND BAGGING
i-....f”””.ll 7
STABILIZATION USING HFO REMOVAL LUNG SURFACTANT STABILIZATION USING HFO
4 HR VENTILATION GROUP 4 HR CMV
+ 4 HR HFO COLLECTION OF GRANULOCYTES SACRIFICE
Fig. 5 : Experimental protocol.
634 (56) Kawano et al. NS NS
t -
$‘“1 ?% a
Befare After ( % I < ) (n-9)
NS
T
NS
Before After Before Aller ( n - 7 ) ( n = 7 ) (0-4) ( n - 3 )
CMV ( 2 hr)
HFO (2 hr)
CMV (4 hr)
t ‘
m
Before Aller (n-8) ( n S ) HFO ( 4 hr)
Fig. 6: Total number of cells from lung lavage fluids after ventilation. There was a significant difference between 4 h r CMV and 4 h r HFO. There was no significant difference between 2 hr CMV and 2 hr HFO. * P < 0.05; P < 0.025, NS, not significant.
NS
I
t
C M V (2 hr)
HFO (2 hr)
C M V (4 hr)
HFO (4 hr)
(n-6)
(n-5)
(n-5)
(n-11)
Fig. 7: Granulocyte: luminol-dependent chemilurninescence (CL) response stimulated with N-formylmethionyl-leucyl-phenylalanineof lung lavage fluids at the termination of ventilation. There was significant difference between 4 h r CMV and 4 hr HFO. *P< 0.05; P < 0.025; NS, not significant.
the ‘wasted’ state. This may not be the cause of the lung damage but the result of it. This means that granulocytes damage the lung and emerge into the alveoli in the wasted state after longterm ventilation by CMV. Thus we conclude that HFO can prevent granulocyte-related lung injury.
Clinical Study In North America, a multicenter randomized clinical trial comparing the efficacy and safety of
HFO with that of CMV in the treatment of respiratory failure in preterm infants was conducted. The High Frequency Intervention trial (HIFI) [8] entry criteria are as follows. Babies have to weigh between 750 and 2,OOOg and require ventilatory support. They have to be aged less than 24 hr and to have been on CMV for less than 12 hr. There were some exclusions, such as for meconium aspiration syndrome, hydrops fetalis etc. The result of this study is as follows. The incidence of bronchopulmonary dysplasia was similar in two groups. HFO did not reduce mortality and, compared with CMV, was associated with an increased incidence of air leaks, grades 3 and 4 intraventricular hemorrhage (IVH), and periventricular leukomalacia [81. The study concluded that: ‘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.’ Since 1985, high frequency oscillatory ventilators have been available in Japan and have been used to rescue babies. In Japan, clinicat experience suggests that HFO provides better oxygenation with fewer complications. The data presented by the National Institutes of Health were quite disappointing, so a multicenter randomized trial was conducted at nine neonatal centers in Japan to re-evaluate the safety and efficacy of HFO using a piston-type oscillator in the treatment of neonatal respiratory failure [9]. Neonatal centers experienced with that HFO machine were chosen. Table 1 depicts a protocol of the Japanese study. One of the problems of the HIFI study
Table 1. Protocol (Japanese study) ~
Birthweight 750-2,000 g Entry for study possible within 60 min after birth for inborn within 6 h r after birth for outborn Exclusions: MAS, hydrops fetalis etc. Surfactant treatment: recommended in cases of RDS. Ventilator set to maintain PrhZbetween 60 and 100 mmHg, and Pa,-o between 30 and 45 mmHg. Frequency (HFO) I5dz.
Acta Paediatr Jpn
Highfiequency oscillation (57) 635 Table 2. Complications of HIFI study and Japanese study HIFI Study HFOfCMV
HFO
CMV
JAPAN HFO
CMV
(%) 160(49) 146(42) 7(l5) 6(13) ICH IVH (> 111') (%) 84 (26) 63 (18) 2 (4) l ( 2 ) (%) 38 (12) 25 (7) PVL l(2) 4(9) (%) 148 (45) 131 (38) 4(9) 6 (13) Airleaks (%) 130(40) 141 (41) 4(9) BPD 6(13) (46) 60(18) 60(17) O(0) 1(2) Mortality ICH, intracoronary hemorrhage; PVL, periventricular leukomalacia; BPD, bronchopulmonary dysplasia.
was that babies studied had already been on CMV long before randomization. Therefore, mechanical ventilation with either HFO or CMV was commenced within 60min for the inborn and within 6 hr after birth for the outborn infants in the Japanese study. Another problem of the HIFI study was the incidence of IVH. From their study we could not tell the time when hemorrhage occurred. So we tried to exclude the babies who already had intracranial hemorrhage. We used artificial surfactant (S-TA) when the diagnosis of RDS was clinically made. The results of this study were as follows. The fractional concentration of inspired oxygen (Fio2) was the same in both groups. The mean airway pressure was higher in the HFO group than in the CMV group. The arterial to alveolar oxygen tension ratios in the two groups also were significantly different. There was only one death in the CMV group. There were no significant differences in the incidence of air leaks, symptomatic patent ductus arteriosis, pulmonary hemorrhage and pneumonia. The incidence of IVH was also similar in both groups. As for periventricular leukomalacia, infants in the CMV group showed a slightly higher incidence compared with HFO, but the difference was not significant. The incidence of bronchopulmonary dysplasia was also slightly higher in the CMV group, but the difference was not significant. Table 2 outlines the number of clinical complications encountered in both the HIFI and Japanese studies [9]. Of course, the number of
Vol. 34 No. 6 December 1992
involved infants in the Japanese study was much smaller than that of the HIFI study. There was no significant difference in the number of complications between the HFO and CMV groups in the Japanese study. We conclude that HFO does not increase the risk of severe complications such as air leaks, bronchopulmonary dysplasia or IVH if used carefully by experienced staff in neonatal centers. References 1. Kolton M, Cattran CB, Kent G, Volgyesi G, Froese AB, Bryan AC. Oxygenation during high frequency ventilation compared with conventional mecbanical ventilation in two models of lung injury. Anesth Analg 1982; 61; 323. 2. Sugiura M, Kawano T, Miyasaka K. Effect of HFO on intracranial circulation. Presented at the 6th conference on High Frequency Ventilation in Infants, Snowbird, Utah, April 1989. 3. Watanabe H, Kawano T, Miyasaka K. Optimal volume recruitment with sustained inflation (Sl) during high frequency oscillatory ventilation. Presented at the 8th conference on High Frequency Ventilation in Infants, Snowbird, Utah, April 1991. 4. Merrit TA, Cochrane CG, Holcomb K, Bohl B, Hallmann M, Strayer D, Edword DK, Gluck L. Elastase and proteinase inhibitor activity in tracheal aspirates during respiratory distress syndrome. J Clin Invest 1983; 72: 656. 5. Hamilton PP, Onayemi A, Smith J, Cutz E, Froese AB, Bryan AC. Comparison of conventional and high frequency ventilation oxygenation and lung pathology. JApplPhysiol 1983; 5 5 : 131. 6. Kawano T, Mori S, Cybulsky M, Burger A, Ballin E, Cutz E, Bryan AC. Effect of granulocyte depletion in a ventilated surfactant-depleted lung. J Appl Physiol 1987; 67: 27. 7. Matsuoka T, Kawano T, Miyasaka K. Preventive role of HFOV in granulocyte-related pulmonary injury in the lungs of surfactant-treated rabbits. Presented at the 8th conference on High Frequency Ventilation in Infants, Snowbird, Utah, April 199I. 8. HIFI Study Group. High frequency oscillatory ventilation compared with conventional mechanical ventilation in the treatment of respiratory failure in preterm infants. N Eng J Med 1989; 320: 88. 9. Ogawa Y, Miyasaka K, Kawano T, Nishida H. A multicenter randomized trial of high frequency oscillatory ventilation as compared with conventional ventilation in preterm infants with respiratory failure. Presented at the 7th conferenceon High Frequency Ventilation in Infants, Snowbird, Utah, April 1990.
