Acta Pædiatrica ISSN 0803-5253
A DIFFERENT VIEW
Nasal ventilation is not continuous positive airway pressure with a rate but mechanical ventilation without a tube Srinivasa Murthy Doreswamy ([email protected])1,2, Prashanth Murthy3 1.Paediatrics, JSS Medical College, Mysore, India 2.Neonatal and Perinatal Medicine, McMaster University Children Hospital, McMaster University, Hamilton, ON, Canada 3.Neonatology, McMaster Children Hospital, Hamilton, ON, Canada
Correspondence Srinivasa Murthy Doreswamy, 1001, Main street west, Apt no 1004 Hamilton, ON L8S 1A9, Canada. Tel: +011 9059212622 | Email: [email protected] Received 9 January 2014; accepted 27 January 2014 DOI:10.1111/apa.12579
BACKGROUND Advancements in neonatal care have led to the survival of extremely premature babies. In the pursuit of gentle ventilation, neonatologists are more inclined to use nasal intermittent positive pressure ventilation (NIPPV). There is currently no evidence to suggest NIPPV is better than conventional mechanical ventilation (CMV), with respect to the outcomes of broncho-pulmonary dysplasia and death. Studies conducted so far have compared nasal continuous positive airway pressure (CPAP) with NIPPV. Both of them differ in terms of gas movement in and out of the lungs, which is the main determinant of lung injury.
MECHANICS OF BREATHING During normal tidal breathing, negative pressure created in the pleural space is the force that drives gas into the lungs. Respiratory centres have control over the respiratory cycles. Herring Breuer reflex prevents over distension or atelectasis of alveoli. In premature babies, lung immaturity and deficiency of surfactant lead to alveolar collapse, decrease in functional residual capacity (FRC) and increased effort to breathe. Continuous positive airway pressure (CPAP) provides continuous airway distending pressure and helps to maintain FRC. Normal mechanisms active during tidal breathing result in gas movement into the lungs more efficiently.
Articles in the series A Different View are edited by William Meadow ([email protected]). We encourage you to offer your own different view either in response to A Different View you do not fully agree with, or on an unrelated topic. Send your article to Dr. Meadow ([email protected]).
480
Positive pressure ventilation (PPV) is an override on tidal ventilation. The driving force for the gas during inspiration is the positive pressure generated by the ventilator. Initiation and termination of inspiration and inspiratory and expiratory time are all controlled by the clinician with different ventilator settings. PPV becomes un-physiological from this mechanical point of view. One study that looked into pulmonary mechanics postintervention showed that the dynamic compliance of the lung was reduced after PPV compared with post-CPAP therapy (1).
GAS MOVEMENT IN CPAP, NIPPV AND CONVENTIONAL MECHANICAL VENTILATION Continuous positive airway pressure (CPAP) delivers a continuous distending, but not driving, pressure to the airway. The mechanism of the movement of gas is similar to normal tidal breathing. In NIPPV and CMV, positive pressure is delivered to the airway, but, unlike CPAP, the driving pressure is the positive pressure generated by the ventilator. Hence, in both NIPPV and CMV, tidal volume is heavily influenced by ventilator settings. The difference between NIPPV and CMV is the interface. Nasal prongs in NIPPV deliver breaths into the nares or nasopharynx, whereas the endotracheal tube in CMV delivers breaths into the trachea. There is a large degree of variability and unpredictability in delivery of positive pressure to the lungs while using NIPPV. Vocal cords are not bypassed, and hence, there is no control over when they either close or open. Therefore, there is no synchronisation between IPPV breaths being delivered and open vocal cords. Some breaths could be completely dampened with closed vocal cords,
ª2014 Foundation Acta Pædiatrica. Published by John Wiley & Sons Ltd 2014 103, pp. 480–482
Noninvasive new born ventilation
Doreswamy and Murthy
whereas others get transmitted into the lungs. Presence of the oesophageal opening will act as a pop off valve and thereby make NIPPV even more unpredictable. As there could be significant leak and dampening of pressure along the course of the gas before reaching the trachea, the settings on the ventilator may need to be modified to achieve successful gas movement into and out of the lungs.
LUNG INJURY AND VENTILATION When babies are supported on CPAP, the lung is not subjected to excessive pressure, volume or shear forces as in positive pressure ventilation. Positive pressure ventilation has a disadvantage that it inflicts lung injury by virtue of pressure, volume and shear forces that are inherent to this mode of ventilation. Theoretically, the same mechanisms are active whether the gas is delivered at the nasopharynx or into the trachea. In other words, the chances of lung injury may not be different between NIPPV and CMV as both are forms of positive pressure ventilation.
INVASIVE AND NONINVASIVE VENTILATION This terminology can be confusing, because the term ‘invasive’ has been used for PPV via an endotracheal tube and ‘noninvasive’ for any mode of ventilation without an endotracheal tube (2). The usage of the term invasive for intubation and noninvasive for no intubation has led to the belief among many neonatologists that the endotracheal tube is the main cause of lung injury. This is not entirely accurate, because positive pressure ventilation does contribute to lung injury. In fact, one could argue that an advantage of the endotracheal tube is that it bypasses the irregular leaky upper airway conduit and thereby ensures that gas is delivered directly into the dedicated airway. This enables lower ventilator settings to achieve the same gas movement compared with NIPPV.
NIPPV – CURRENT UNDERSTANDING NIPPV for respiratory distress syndrome Klugman (3), Sai Sunil Kishore (4), Ramanathan (5) and Meneses (6) have compared CPAP and NIPPV as primary modes of respiratory support in preventing mechanical ventilation in premature babies with RDS. Three of these studies (3–5) reported a significant reduction in the need for mechanical ventilation. It is important to note here that their primary outcome was to prevent mechanical ventilation, that is, intubation. The outcome the authors chose implies that they too believed intubation to be more harmful than positive pressure ventilation. NIPPV for apnoea of prematurity A Cochrane meta-analysis looked at the advantages of NIPPV over nasal CPAP in decreasing or preventing apnoea of prematurity (7), and one of the studies from this meta-analysis did not find any difference between the two methods. Another study found a significant reduction in the
number of apnoeic spells in the NIPPV group. It is plausible that some of these apnoeic episodes in the NIPPV group could have been masked or treated with positive pressure breaths. NIPPV for extubation failure The studies that have looked into the need for re-intubation following extubation have shown that reintubation was significantly less in the NIPPV group (8,9). Similar to the studies mentioned earlier, these authors compared NIPPV with CPAP. Obviously babies in the NIPPV group continued to receive positive pressure ventilation, and therefore, it is not surprising that they needed less intubation. Broncho-pulmonary dysplasia A recent study by Kripalani et al. (10) compared NIPPV and CPAP with a primary outcome as death or bronchopulmonary dysplasia. This study did not find NIPPV to be superior to CPAP in reducing this outcome. It is interesting to note that nearly 60% of the babies in both the groups failed to respond to noninvasive support and had to be intubated. Given this fact, having similar outcomes in both groups can be expected. NIPPV is more similar to CMV than we think Continuous positive airway pressure (CPAP) is a gentle mode of respiratory support, which improves the FRC and makes efficient use of the baby’s efforts to breathe. When CPAP fails, it indicates a severity of respiratory disease that might be an indication for positive pressure ventilation. In contrast, successful NIPPV drives gas into the lungs in a similar way to conventional mechanical ventilation (CMV). As a result, immature respiratory units are subjected to similar mechanical forces, as seen in CMV, potentially leading to similar injurious effects. An added disadvantage with NIPPV is that it delivers gas into the nasopharynx rather than the mid trachea. This results in inconsistent positive pressure breaths and a failure rate. An NIPPV failure rate as high as about 60% was noted in a recent study (10). The endotracheal tube provides a secure conduit, and hence, conventional mechanical ventilation delivers consistent positive pressure breaths. Persisting with NIPPV, with the sole intention of preventing intubation when the lung disease is severe, may result in frequent atelectasis and increased atelecto-trauma. It is important for clinicians to appreciate that NIPPV is not CPAP with a rate but IPPV without a tube. If we intend to use NIPPV in lieu of invasive positive pressure ventilation, and not in lieu of CPAP, we need to have studies comparing these modes of positive pressure ventilation with respect to important outcomes such as broncho-pulmonary dysplasia, neuro-disability and death. There are currently no studies comparing NIPPV and CMV. We feel that the pendulum has swung too far towards NIPPV, with a presupposition that it is ‘noninvasive’ and thereby less injurious. We also feel that it is time to revisit existing, confusing terminologies. For example, ‘driving
ª2014 Foundation Acta Pædiatrica. Published by John Wiley & Sons Ltd 2014 103, pp. 480–482
481
Noninvasive new born ventilation
Doreswamy and Murthy
pressure support’ and ‘nondriving pressure support’ would be more physiologically apt than the currently used terms of invasive and noninvasive ventilation support.
CONCLUSIONS Nasal intermittent positive pressure ventilation (NIPPV) has similar respiratory mechanics to conventional mechanical ventilation, and its adverse effects could be similar to CMV. As NIPPV is used in lieu of invasive ventilation, studies are needed to show whether NIPPV superiority over invasive ventilation.
FUNDING SOURCE No funding was secured for this study.
FINANCIAL DISCLOSURE None.
CONFLICT OF INTEREST Author has no conflict of interest to disclose.
References 1. Ahlstrom H. Pulmonary mechanics in infants surviving severe neonatal respiratory insufficiency. Acta Paediatr Scand 1975; 64: 69–80. 2. Ramanathan R. Nasal respiratory support through the nares: its time has come. J Perinatol 2010; 30: S67–72.
482
3. Kugelman A, Feferkorn I, Riskin A, Chistyakov I, Kaufman B, Bader D. Nasal intermittent mandatory ventilation versus nasal continuous positive airway pressure for respiratory distress syndrome: a randomized, controlled, prospective study. J Pediatr 2007; 150: 521–6. 4. Sai Sunil Kishore M, Dutta S, Kumar P. Early nasal intermittent positive pressure ventilation versus continuous positive airway pressure for respiratory distress syndrome. Acta Paediatr 2009; 98: 1412–5. 5. Ramanathan R, Sekar KC, Rasmussen M, Bhatia J, Soll RF. Nasal intermittent positive pressure ventilation after surfactant treatment for respiratory distress syndrome in preterm infants
A DIFFERENT VIEW
Nasal ventilation is not continuous positive airway pressure with a rate but mechanical ventilation without a tube Srinivasa Murthy Doreswamy ([email protected])1,2, Prashanth Murthy3 1.Paediatrics, JSS Medical College, Mysore, India 2.Neonatal and Perinatal Medicine, McMaster University Children Hospital, McMaster University, Hamilton, ON, Canada 3.Neonatology, McMaster Children Hospital, Hamilton, ON, Canada
Correspondence Srinivasa Murthy Doreswamy, 1001, Main street west, Apt no 1004 Hamilton, ON L8S 1A9, Canada. Tel: +011 9059212622 | Email: [email protected] Received 9 January 2014; accepted 27 January 2014 DOI:10.1111/apa.12579
BACKGROUND Advancements in neonatal care have led to the survival of extremely premature babies. In the pursuit of gentle ventilation, neonatologists are more inclined to use nasal intermittent positive pressure ventilation (NIPPV). There is currently no evidence to suggest NIPPV is better than conventional mechanical ventilation (CMV), with respect to the outcomes of broncho-pulmonary dysplasia and death. Studies conducted so far have compared nasal continuous positive airway pressure (CPAP) with NIPPV. Both of them differ in terms of gas movement in and out of the lungs, which is the main determinant of lung injury.
MECHANICS OF BREATHING During normal tidal breathing, negative pressure created in the pleural space is the force that drives gas into the lungs. Respiratory centres have control over the respiratory cycles. Herring Breuer reflex prevents over distension or atelectasis of alveoli. In premature babies, lung immaturity and deficiency of surfactant lead to alveolar collapse, decrease in functional residual capacity (FRC) and increased effort to breathe. Continuous positive airway pressure (CPAP) provides continuous airway distending pressure and helps to maintain FRC. Normal mechanisms active during tidal breathing result in gas movement into the lungs more efficiently.
Articles in the series A Different View are edited by William Meadow ([email protected]). We encourage you to offer your own different view either in response to A Different View you do not fully agree with, or on an unrelated topic. Send your article to Dr. Meadow ([email protected]).
480
Positive pressure ventilation (PPV) is an override on tidal ventilation. The driving force for the gas during inspiration is the positive pressure generated by the ventilator. Initiation and termination of inspiration and inspiratory and expiratory time are all controlled by the clinician with different ventilator settings. PPV becomes un-physiological from this mechanical point of view. One study that looked into pulmonary mechanics postintervention showed that the dynamic compliance of the lung was reduced after PPV compared with post-CPAP therapy (1).
GAS MOVEMENT IN CPAP, NIPPV AND CONVENTIONAL MECHANICAL VENTILATION Continuous positive airway pressure (CPAP) delivers a continuous distending, but not driving, pressure to the airway. The mechanism of the movement of gas is similar to normal tidal breathing. In NIPPV and CMV, positive pressure is delivered to the airway, but, unlike CPAP, the driving pressure is the positive pressure generated by the ventilator. Hence, in both NIPPV and CMV, tidal volume is heavily influenced by ventilator settings. The difference between NIPPV and CMV is the interface. Nasal prongs in NIPPV deliver breaths into the nares or nasopharynx, whereas the endotracheal tube in CMV delivers breaths into the trachea. There is a large degree of variability and unpredictability in delivery of positive pressure to the lungs while using NIPPV. Vocal cords are not bypassed, and hence, there is no control over when they either close or open. Therefore, there is no synchronisation between IPPV breaths being delivered and open vocal cords. Some breaths could be completely dampened with closed vocal cords,
ª2014 Foundation Acta Pædiatrica. Published by John Wiley & Sons Ltd 2014 103, pp. 480–482
Noninvasive new born ventilation
Doreswamy and Murthy
whereas others get transmitted into the lungs. Presence of the oesophageal opening will act as a pop off valve and thereby make NIPPV even more unpredictable. As there could be significant leak and dampening of pressure along the course of the gas before reaching the trachea, the settings on the ventilator may need to be modified to achieve successful gas movement into and out of the lungs.
LUNG INJURY AND VENTILATION When babies are supported on CPAP, the lung is not subjected to excessive pressure, volume or shear forces as in positive pressure ventilation. Positive pressure ventilation has a disadvantage that it inflicts lung injury by virtue of pressure, volume and shear forces that are inherent to this mode of ventilation. Theoretically, the same mechanisms are active whether the gas is delivered at the nasopharynx or into the trachea. In other words, the chances of lung injury may not be different between NIPPV and CMV as both are forms of positive pressure ventilation.
INVASIVE AND NONINVASIVE VENTILATION This terminology can be confusing, because the term ‘invasive’ has been used for PPV via an endotracheal tube and ‘noninvasive’ for any mode of ventilation without an endotracheal tube (2). The usage of the term invasive for intubation and noninvasive for no intubation has led to the belief among many neonatologists that the endotracheal tube is the main cause of lung injury. This is not entirely accurate, because positive pressure ventilation does contribute to lung injury. In fact, one could argue that an advantage of the endotracheal tube is that it bypasses the irregular leaky upper airway conduit and thereby ensures that gas is delivered directly into the dedicated airway. This enables lower ventilator settings to achieve the same gas movement compared with NIPPV.
NIPPV – CURRENT UNDERSTANDING NIPPV for respiratory distress syndrome Klugman (3), Sai Sunil Kishore (4), Ramanathan (5) and Meneses (6) have compared CPAP and NIPPV as primary modes of respiratory support in preventing mechanical ventilation in premature babies with RDS. Three of these studies (3–5) reported a significant reduction in the need for mechanical ventilation. It is important to note here that their primary outcome was to prevent mechanical ventilation, that is, intubation. The outcome the authors chose implies that they too believed intubation to be more harmful than positive pressure ventilation. NIPPV for apnoea of prematurity A Cochrane meta-analysis looked at the advantages of NIPPV over nasal CPAP in decreasing or preventing apnoea of prematurity (7), and one of the studies from this meta-analysis did not find any difference between the two methods. Another study found a significant reduction in the
number of apnoeic spells in the NIPPV group. It is plausible that some of these apnoeic episodes in the NIPPV group could have been masked or treated with positive pressure breaths. NIPPV for extubation failure The studies that have looked into the need for re-intubation following extubation have shown that reintubation was significantly less in the NIPPV group (8,9). Similar to the studies mentioned earlier, these authors compared NIPPV with CPAP. Obviously babies in the NIPPV group continued to receive positive pressure ventilation, and therefore, it is not surprising that they needed less intubation. Broncho-pulmonary dysplasia A recent study by Kripalani et al. (10) compared NIPPV and CPAP with a primary outcome as death or bronchopulmonary dysplasia. This study did not find NIPPV to be superior to CPAP in reducing this outcome. It is interesting to note that nearly 60% of the babies in both the groups failed to respond to noninvasive support and had to be intubated. Given this fact, having similar outcomes in both groups can be expected. NIPPV is more similar to CMV than we think Continuous positive airway pressure (CPAP) is a gentle mode of respiratory support, which improves the FRC and makes efficient use of the baby’s efforts to breathe. When CPAP fails, it indicates a severity of respiratory disease that might be an indication for positive pressure ventilation. In contrast, successful NIPPV drives gas into the lungs in a similar way to conventional mechanical ventilation (CMV). As a result, immature respiratory units are subjected to similar mechanical forces, as seen in CMV, potentially leading to similar injurious effects. An added disadvantage with NIPPV is that it delivers gas into the nasopharynx rather than the mid trachea. This results in inconsistent positive pressure breaths and a failure rate. An NIPPV failure rate as high as about 60% was noted in a recent study (10). The endotracheal tube provides a secure conduit, and hence, conventional mechanical ventilation delivers consistent positive pressure breaths. Persisting with NIPPV, with the sole intention of preventing intubation when the lung disease is severe, may result in frequent atelectasis and increased atelecto-trauma. It is important for clinicians to appreciate that NIPPV is not CPAP with a rate but IPPV without a tube. If we intend to use NIPPV in lieu of invasive positive pressure ventilation, and not in lieu of CPAP, we need to have studies comparing these modes of positive pressure ventilation with respect to important outcomes such as broncho-pulmonary dysplasia, neuro-disability and death. There are currently no studies comparing NIPPV and CMV. We feel that the pendulum has swung too far towards NIPPV, with a presupposition that it is ‘noninvasive’ and thereby less injurious. We also feel that it is time to revisit existing, confusing terminologies. For example, ‘driving
ª2014 Foundation Acta Pædiatrica. Published by John Wiley & Sons Ltd 2014 103, pp. 480–482
481
Noninvasive new born ventilation
Doreswamy and Murthy
pressure support’ and ‘nondriving pressure support’ would be more physiologically apt than the currently used terms of invasive and noninvasive ventilation support.
CONCLUSIONS Nasal intermittent positive pressure ventilation (NIPPV) has similar respiratory mechanics to conventional mechanical ventilation, and its adverse effects could be similar to CMV. As NIPPV is used in lieu of invasive ventilation, studies are needed to show whether NIPPV superiority over invasive ventilation.
FUNDING SOURCE No funding was secured for this study.
FINANCIAL DISCLOSURE None.
CONFLICT OF INTEREST Author has no conflict of interest to disclose.
References 1. Ahlstrom H. Pulmonary mechanics in infants surviving severe neonatal respiratory insufficiency. Acta Paediatr Scand 1975; 64: 69–80. 2. Ramanathan R. Nasal respiratory support through the nares: its time has come. J Perinatol 2010; 30: S67–72.
482
3. Kugelman A, Feferkorn I, Riskin A, Chistyakov I, Kaufman B, Bader D. Nasal intermittent mandatory ventilation versus nasal continuous positive airway pressure for respiratory distress syndrome: a randomized, controlled, prospective study. J Pediatr 2007; 150: 521–6. 4. Sai Sunil Kishore M, Dutta S, Kumar P. Early nasal intermittent positive pressure ventilation versus continuous positive airway pressure for respiratory distress syndrome. Acta Paediatr 2009; 98: 1412–5. 5. Ramanathan R, Sekar KC, Rasmussen M, Bhatia J, Soll RF. Nasal intermittent positive pressure ventilation after surfactant treatment for respiratory distress syndrome in preterm infants
