Keywords unilateral pulmonary interstitial emphysema - prematurity - neonate - selective bronchial
intubation - neurally adjusted ventilatory assist - NAVA
Selective bronchial intubation was impressively successful in the management of 46
neonates with a unilateral air leak, and it was associated with only mild and reversible
complications according to a review by Joseph et al.[1 ] Recently, it was reported that neurally adjusted ventilatory assist (NAVA) mode
of ventilation available in SERVO-i ventilator (Maquet, Solna, Sweden) resulted in
resolution of localized pulmonary interstitial emphysema (PIE) in two neonates.[2 ] To date, there has been no comparison between the two strategies in the management
of unilateral PIE: selective bronchial intubation versus NAVA. We report a case of
a premature neonate with unilateral PIE treated initially by selective bronchial intubation.
Subsequently, intubation was switched to endotracheal intubation with the tip of endotracheal
tube withdrawn above the carina. NAVA mode of ventilation was commenced. Our case
provides an opportunity to gain an understanding of the pros and cons of these two
management strategies.
Case Report
A 23-week-old male neonate with birth weight 865 g was treated by two doses of surfactant
at 1 and 12 hours of life. After surfactant therapy, ventilator setting was weaned
down to peak inspiratory pressure (PIP) of 13 cmH2 O and Fio
2 21% on conventional intermittent positive pressure ventilation. He developed pulmonary
hemorrhage at 35 hours of life. Left-sided PIE then developed ([Fig. 1 ]). At 41 hours of life, ventilation was changed from conventional ventilation to
high-frequency oscillatory ventilation (HFO) (Sensormedics 3100A, Yorba Linda, CA)
in the hope of delivering less barotrauma. Mean airway pressure (MAP) of 7.5 cmH2 O and Fio
2 of 50% were used, in keeping with the low volume strategy of HFO. The amplitude was
20 cmH2 O and rate was 15 Hz. We also put the patient to lie laterally on the left side. Despite
all these efforts, PIE, as revealed by the chest X-ray, worsened ([Fig. 2 ]). The strategy of selective bronchial intubation was applied on day 10. The endotracheal
tube was advanced into the right main bronchus. This was done in the hope that the
left lung could be spared of ventilation and could recover from PIE. After intubation
of the right lung, HFO setting needs to be increased to Fio
2 50%, MAP of 8.5 cmH2 O, and amplitude to 24 cmH2 O. On day 12, there was frequent desaturation, and at times oscillatory vibration
was not observed on his chest. Therefore, we stopped HFO and put the patient back
to conventional intermittent positive pressure ventilation using PIP 16 cmH2 O, positive end-expiratory pressure (PEEP) 5 cmH2 O, inspiratory time 0.4 seconds, and Fio
2 30% while pursuing selective bronchial intubation. We used “SIMV with pressure support”
mode on an SERVO-i ventilator. What happened to the chest X-ray during selective bronchial
intubation was that PIE change became localized in the middle zone of the left lung
with areas of atelectasis in the rest of the lungs ([Fig. 3 ]). During selective ventilation, there was frequent desaturation requiring ambu bagging.
On day 15 there was an episode of desaturation, carbon dioxide retention, and hypotension.
Selective bronchial intubation was thus aborted. We commenced bilateral lung ventilation
with HFO. From day 15 to 19, Fio
2 crept up from 50 to 90%. MAP was increased from 9 to 11 cmH2 O. On day 18, ventilator mode was changed to NAVA. Before changing to NAVA, the patient
was sedated with fentanyl infusion. In preparation for NAVA, which relied on the diaphragmatic
signal, we took off fentanyl infusion and loaded the patient with caffeine citrate.
The initial NAVA setting was Fio
2 35%, PEEP 5 cmH2 O, and NAVA level of 3. Apnea time was set at 5 seconds, which by design recruited
backup pressure control when there was no diaphragmatic signal detected for 5 seconds.
Edi peak was variable ranging from 7 to 12 with average 9 and Edi min ranging from
2 to 5 with average 3 in the first day of NAVA. The patient was more stable on NAVA
regarding oxygen saturation. Over the days FiO2 decreased from 100% to 25%. MAP decreased from 12 cmH2 O to 8 cmH2 O. NAVA level was weaned to 2. Edi peak was down to an average of 4 and Edi min was
down to an average of 1 before extubation. PIE change gradually improved as revealed
by chest X-ray. On day 25 there was complete resolution of PIE change in the chest
X-ray ([Fig. 4 ]). Therefore, the patient was successfully extubated on day 26.
Fig. 1 Early signs of left-sided pulmonary interstitial emphysema at 41 hours of life occurring
after pulmonary hemorrhage.
Fig. 2 Pulmonary interstitial emphysema worsened on day 10 when selective bronchial intubation
was started.
Fig. 3 Persistent pulmonary interstitial emphysema change in left middle lung field with
atelectasis of rest of the lungs on day 14 when selective bronchial intubation was
already undertaken for 4 days.
Fig. 4 Resolution of pulmonary interstitial emphysema 7 days after neurally adjusted ventilatory
assist was commenced.
Discussion
A review by Joseph et al[1 ] showed that selective bronchial intubation was successful in resolving unilateral
air leak in 46 neonates with few mild complications. After this large review, there
were further publications about the success of selective bronchial intubation in two
premature neonates with a unilateral air leak.[3 ]
[4 ] Contrary to these cases, our case showed that selective bronchial intubation failed
to resolve PIE and there were severe complications during selective bronchial intubation.
Why was our case different?
First, the biggest review showing the success of selective bronchial intubation in
the management of 46 neonatal cases of unilateral air leak had selection bias.[1 ] This review collected case reports or case series published in English literature
spanning the period from 1977 to 2010.[1 ] However, this review[1 ] did not include unsuccessful cases reported in the literature and thus was a review
presenting a biased view toward the safety and efficacy of selective bronchial intubation.
For example, they only included nine successful cases from the case series of Glenski
et al in their review but dropped the four unsuccessful cases from the same case series
of Glenski et al.[5 ] This review did not include a case series about three premature neonates treated
by selective bronchial intubation either[6 ] as none of these neonates had improvement. Lately, there was a recent publication
about nine neonates treated by selective bronchial intubation for a unilateral air
leak, in which two cases were unsuccessful.[7 ] These three case series serve to illustrate that indeed selective bronchial intubation
could be unsuccessful at times.[5 ]
[6 ]
[7 ] Therefore, it was not surprising that we encountered yet another case of failure
of selective bronchial intubation.
Furthermore, we feel obliged to highlight the possibility of serious complications
during selective bronchial intubation, and we strongly issue a word of caution when
selective bronchial intubation is contemplated. Our patient was quite unstable during
the period of selective bronchial intubation having recurrent desaturation, carbon
dioxide retention, and hypotension. In fact, the common occurrence of serious complications
was reported by Glenski et al.[5 ] Glenski et al reported that 15 of 32 cases in the literature and their case series
had serious complications.[5 ] Desaturation and hypoxia were common.[1 ]
[5 ] Collapse/atelectasis frequently occurred.[1 ]
[5 ] Atelectasis could have serious consequence and could lead to fatal outcome. A 29-week-old
neonate after the commencement of selective bronchial intubation developed right upper
lobe collapse and had severe hypoxia.[5 ] Severe intraventricular hemorrhage followed this, and the neonate died 24 hours
later. Another 29-week-old neonate developed pneumonia in the lung made atelectatic
by selective bronchial intubation and died secondary to pulmonary insufficiency.[5 ] On the contrary, neonates were more stable and were free of complications according
to our current case report, and the previous case report of NAVA use.[2 ]
Reviewing the chest X-ray in detail for our patient when right lung was selectively
intubated ([Fig. 3 ]) might throw light to why this strategy might not work. The end of the endotracheal
tube was advanced beyond the carina. However, the bevel of the endotracheal tube was
wedge shaped and could have provided some ventilation to the contralateral lung when
the bevel faced the carina. We also believed that any slight shifting of the position
of the endotracheal tube could have contributed to episodes of bradycardia, carbon
dioxide retention and loss of vibration while on HFO in our case. In theory, the best
position of the end of the endotracheal tube should just pass the carina but is open
to ventilate the three lobar bronchi. In practice, the right upper lobar bronchus,
which is the most proximal lobar bronchus, is often occluded by endotracheal tube
during selective bronchial intubation. Further advancement of the endotracheal tube
results in ventilation of the right lower lobe only with occlusion of the right middle
lobar bronchus. Occlusion of these lobar bronchi might result in loss of ventilation
of the corresponding lobes and lobar collapse. In reality, the slight shifting of
the endotracheal tube is not often preventable as current methods for fixing endotracheal
tube like using NeoBars (Neotech) or taping are not 100% steadfast with room for shifting.
This underscores the difficulty in applying selective unilateral ventilation for micropremies.
The other problem reported in the literature concerning the use of selective bronchial
intubation is a recurrence of PIE. Following resolution of unilateral PIE, selective
bronchial intubation is converted to endotracheal intubation. Then unilateral PIE
might recur, and this has been described before.[7 ]
[8 ]
[9 ] In contrast, unilateral PIE did not recur with the use of NAVA in our case and the
previous case report of NAVA use.[2 ]
We find from the literature that selective bronchial intubation might yield more drastic
improvement when overdistended lung with air leak herniated and compressed on the
contralateral lung causing respiratory embarrassment. It was because under these circumstances
selective bronchial intubation might provide rapid decompression of the overinflated
lung. In fact, some of the success cases of selective bronchial intubation happened
when unilateral air leak was said to be life-threatening,[10 ] caused rapid deterioration[8 ] or resulted in the requirement of high ventilator settings.[11 ] In our case, despite the development of unilateral PIE, the patient was easily ventilated
with low ventilator setting at first. Therefore, there could not be any “drastic”
clinical improvement to see. In the previous report of two patients managed with NAVA[2 ] and in our case, we observed that improvement on NAVA was gradual and it took eight
to ten days for the unilateral PIE to resolve completely.
There was a report of 10 neonates with congenital diaphragmatic hernia (CDH) crossed
over from pressure support ventilation (PSV) to NAVA after a hernia was surgically
repaired.[12 ] NAVA showed superiority over PSV in terms of improved oxygen-linked index, lower
pCO2 and lower peak inspiratory pressure. In these cases of CDH, the lungs on two sides
had different compliance: a relatively normal lung on one side and a hypoplastic lung
on the other side. These cases were similar to our case of unilateral PIE with the
presence of lungs of different compliance on two sides. The author[12 ] came up with the following postulation for the usefulness of NAVA in the ventilation
of two lungs with different compliance. The optimization of ventilatory support is
a crucial issue in the management of CDH, in which the objective of weaning and the
return to spontaneous breathing should be pursued trying to balance the two lungs
and using ventilatory strategies to prevent pulmonary damage in the hypoplasic lung,
without over-inflating the non-CDH lung. This discrepancy can be overcome with more
difficulty during PSV, which could lead to excessive volume delivery and over-distention
since expiration is not neurally detected, whereas during NAVA cycling-off occurs
when the diaphragm activity is turned off by the respiratory centers and hence should
provide a more physiologic termination of assist.
Also, the success in the resolution of unilateral PIE on NAVA could be understood
given the built-in design of NAVA. Neurally generated diaphragmatic signal generates
each ventilator breath. This ventilator breath is terminated once the appropriate
tidal volume is reached due to the Herring–Breuer reflex. This way the most appropriate
tidal volume and thus PIP is delivered disallowing the production of excessive volume
and excessive pressure obviating volutrauma and barotrauma. With the elimination of
volutrauma and barotrauma, PIE gradually improves. This theory has support from that
switch-over studies[13 ]
[14 ]
[15 ] in which conventional ventilation is switched to NAVA. PIP measured becomes smaller
after switch over.[13 ]
[14 ]
[15 ] Our case is the third case of successful resolution of unilateral PIE on NAVA ventilation
reported in the literature. In the previous report of the two neonates with localized
PIE resolving on NAVA,[2 ] PIP measured did diminish once NAVA mode was commenced. In our case, we observed
MAP was described on switching ventilation from HFO to NAVA.
Based on our case and review of the literature, we draw up a table comparing the use
of selective bronchial intubation and NAVA in the management of unilateral PIE ([Table 1 ]). In conclusion, we caution that selective bronchial intubation is not without risk
and serious complications could occur. NAVA might provide a gentler option of ventilation
achieving resolution of unilateral PIE.
Table 1
Comparison of two ventilatory strategies
Selective bronchial intubation
NAVA
Chance of success in resolution
May not always be successful
Successful in all the 3 cases so far reported
Requirement for sedation
Yes
No
Intricacy of placement of endotracheal tube
Change of direction of bevel of endotracheal tube might undermine the desired effects;
Slight shifting of endotracheal tube could occlude upper and middle lobar bronchi
Easy placement of endotracheal tube
Complications
Collapse/atelectasis
Desaturation
Common
Could be frequent in some patients
Probably rare
Infrequent
Recurrence of unilateral PIE after cessation of treatment
Possible in some cases
Probably unlikely
Indication proposed (and expected course)
May have a role in case of life-threatening over-distension of ipsilateral lung compressing
contralateral lung (drastic improvement might ensue)
For most other cases of PIE NAVA provides a gentler approach (NAVA usually resolves
PIE gradually within 10 d)
Abbreviations: NAVA, neurally adjusted ventilator assist; PIE, pulmonary interstitial
emphysema.
