Original Paper Neonatology 2015;107:277–282 DOI: 10.1159/000369955
Received: March 27, 2014 Accepted after revision: November 17, 2014 Published online: March 3, 2015
Lung Deposition of Nebulized Surfactant in Newborn Piglets Rikard Linner a Valeria Perez-de-Sa b Doris Cunha-Goncalves a Departments of a Cardiothoracic Anesthesia and Intensive Care and b Pediatric Anesthesia and Intensive Care, Lund University, Skåne University Hospital, Lund, Sweden
Abstract Background: It would be advantageous for the treatment of neonatal respiratory distress syndrome if effective amounts of surfactant could be delivered by nebulization. Objective: To investigate lung deposition and distribution of nebulized porcine surfactant using an investigational eFlow® neonatal nebulizer. Methods: While lying on one side, 1-day-old piglets inhaled 200 mg · kg–1 of nebulized surfactant via mask, nasal prongs, or tracheal tube. The surfactant was diluted with normal saline to 40 mg · ml–1 and labeled with 99mtechnetium-labelled nanocolloid. Undiluted surfactant (80 mg · ml–1) was instilled tracheally in a fourth group. Each group had 8 animals. Lung deposition was measured by gamma scintigraphy, and deposition values were presented as a percentage of the nebulized or instilled dose. Results: The median lung deposition of inhaled surfactant was 5% (range 3–16) via mask, 14% (2–40) via prongs, and 45% (25– 56) via tracheal tube (p < 0.05). It was 88% (71–96) with instillation. In all groups, the surfactant preferentially went to the dependent lung. Deposition ratios (upper lung/both lungs)
© 2015 S. Karger AG, Basel 1661–7800/15/1074–0277$39.50/0 E-Mail [email protected] www.karger.com/neo
were 0.32 (0.13–0.58), 0.15 (0.05–0.58), 0.16 (0.11–0.23), and 0.08 (0.03–0.46). Conclusions: Using this nebulizer, the lung depositions of porcine surfactant were 45% via endotracheal tube and 14% via nasal-continuous positive airway pressure (prongs). These figures might be physiologically relevant, but still have to be confirmed in efficacy studies. © 2015 S. Karger AG, Basel
Introduction
Endotracheally instilled exogenous surfactant has proven effect in neonatal respiratory distress syndrome [1]. If sufficient amounts of aerosolized surfactant could be deposited in the lungs, tracheal intubation and instillation would become unnecessary, and the inherent risks of intubation/instillation avoided [2]. During the 1990s, studies of immature newborn animals with surfactant deficiency [3–5], and an uncontrolled study in premature infants [6] indicated that nebulized surfactant improved lung function. Deposition figures were as low as 1% [5] and interest declined after a neutral outcome in a randomized clinical study of surfactant inhalation versus no treatment [7]. In recent years, the interest in surfactant inhalation has increased, but so Rikard Linner, MD, PhD Department of Cardiothoracic Anesthesia and Intensive Care VO Thorax, Plan 8, Hisshall A, Skåne University Hospital SE–221 85 Lund (Sweden) E-Mail Rikard.Linner @ gmail.com
Downloaded by: Yale Medical Library 198.143.38.65 - 7/13/2015 12:26:30 PM
Key Words Nebulization · Neonatal respiratory distress syndrome · Surfactant
far only an open-label pilot study has suggested that it is effective [8]. Surfactant, a viscous foam-forming fluid with low surface tension, is hard to nebulize, and pulmonary deposition in some early studies with older nebulizers was less than 1–2% of the aerosolized dose [5, 9]. Moreover, the surfactant was unevenly distributed, with most of it in regions that were already well ventilated [9, 10]. These problems could be circumvented if an efficient nebulizer delivered so much to the lungs that even relatively inaccessible regions received therapeutic amounts. Aerosolizer technology has advanced during the last decade and a new nebulizer, based on the vibrating mesh principle [11], has been specifically developed for surfactant inhalation with preserved surfactant properties [12]. We used this nebulizer to perform a feasibility study on the deposition of porcine surfactant in the lungs and upper airway. There are many studies of surfactant deposition during inhalation via tracheal tube [13], but relatively few with other interfaces [3, 14–16]. We therefore studied three interfaces: mask, nasal prongs, and tracheal tube. Additionally, because instilled surfactant preferentially goes to the dependent parts of the lungs [17], we examined whether this also held true for inhaled surfactant.
prongs (Large ArgyleTM CPAP Nasal Cannula; Covidien AB, Solna, Sweden) were modified to fit the larger distance between the nostrils. The mouth was held closed during inhalation. In the tube-neb and tube-instill groups, the trachea was intubated (cuffed endotracheal tube, sizes 2.5 or 3.0) after spraying the larynx with lidocaine. Correct tube placement was confirmed by auscultation. A neurally adjusted ventilatory assist catheter (NAVA, Maquet Critical Care AB, Solna, Sweden) was used to monitor the integrated electrical activity of the diaphragm (Edi), which allowed assessment of the breathing pattern and aided in adjusting sedation. At the end of the study, i.e. after the gamma scintigraphy, the piglets were killed using an excess dose of pentobarbital, fentanyl, and potassium. Surfactant Preparation Each animal received 200 mg · kg–1 of porcine surfactant (Curosurf® 80 mg · ml–1; Chiesi Farmaceutici, Parma, Italy), thoroughly mixed with 200 MBq 99mTc-nanocolloid (Nanocoll®; GE Healthcare AB, Stockholm, Sweden) [18]. In the nebulized groups, the surfactant was diluted with normal saline to 40 mg · ml–1 for optimal nebulizer performance, whereas undiluted surfactant was instilled in the tube-instill group.
Ventilation and Surfactant Administration Spontaneous breathing was maintained during surfactant inhalation or instillation with the aid of a Servo-i ventilator (Maquet Critical Care AB). In the mask and prongs groups, the nasal-continuous positive airway pressure mode was used to deliver continuous positive airway pressure (4 cm H2O). In the tube-neb and tube-instill groups, pressure support with PEEP +4 was used, and inspiratory pressure adjusted to achieve a tidal volume of 6–10 ml · kg–1 · FiO2 was 0.5. In the tube-instill group, a catheter was passed 0.5 cm beyond the tip of the tracheal tube, and surfactant was instilled as a bolus in the lower trachea.
Methods The experiments were approved by the regional committee on animal research ethics. Thirty-two 12- to 36-hour-old full-term piglets were studied. They were randomly divided into four groups of 8 with half of the animals lying on their right side, and half lying on their left side during surfactant administration. The four groups were: (1) mask-neb and (2) prongs-neb, in which nebulized surfactant was inhaled via a mask or nasal prongs, and (3) tube-neb and (4) tube-instill, in which animals were tracheally intubated, and surfactant nebulized or instilled. Preparation and Anesthesia Anesthesia was induced with i.m. ketamine (6 mg), midazolam (0.4 mg), and atropine (0.2 mg). An ear vein was cannulated and continuous anesthesia with i.v. ketamine (1–3 mg · kg–1 · h–1) and dexmedetomidine (1–3 μg · kg–1 · h–1) was started. Intermittent ketamine (1–2 mg–1 · kg–1), propofol (1–3 mg · kg–1), and midazolam (0.2 mg · kg–1) were given intravenously as needed. A femoral artery was cannulated for arterial blood pressure monitoring and blood sampling. In the mask and prongs groups, 0.1 ml of the decongestant oxymetazoline hydrochloride (0.5 mg · ml–1) was given in each nostril. To avoid reflex apnea, lidocaine was sprayed in the nostrils before applying the interface. In the mask-neb group, the mouth was held closed and a silicon facial neonatal mask (Infant Silicone-Mask, No. 00; Laerdal Medical, Stavanger, Norway) was placed with its brim surrounding the nostrils. In the prongs-neb group, neonatal
278
Neonatology 2015;107:277–282 DOI: 10.1159/000369955
The Nebulizer The nebulizer (investigational eFlow® Neonatal Nebulizer system; PARI Pharma, Starnberg, Germany) employs the vibrating membrane principle. The mass median aerodynamic diameter (MMAD) for the generated surfactant droplets was 2.5–3.0 μm with a geometric standard deviation of 1.6 [unpubl. in vitro data from PARI Pharma for normal saline-diluted Curosurf 40 mg · ml–1 using a Next Generation Impactor]. The nebulizer was connected at one end to the Y-piece of the ventilator’s breathing circuit, and at the other end to the mask, prongs, or tracheal tube (fig. 1). A new nebulizer was used for each piglet.
Arterial Blood Gases Arterial blood gases were measured at baseline and at 15 min of nebulization, or 15 min after instillation, and analyzed on an ABL 700 blood gas analyzer (Radiometer, Copenhagen, Denmark). Measurement of Surfactant Deposition Piglets were placed supine in a gamma camera (Philips Skylight; Philips AB, Stockholm, Sweden) with dual heads, simultaneously acquiring one anterior and one posterior image. These were analyzed as 128 × 128 matrices with a pixel size of 3.2 mm. After a 3-min exposure, approximately 25 MBq of 99mTc-labelled macroaggregated albumin (TcMAA; TechneScan LyoMAA; Covidien
Linner/Perez-de-Sa/Cunha-Goncalves
Downloaded by: Yale Medical Library 198.143.38.65 - 7/13/2015 12:26:30 PM
Inspiratory limb Y-piece
Interface
Exhaust Ventilator Activated charcoal
Fig. 1. Breathing circuit setup. A pediatric disposable breathing
circuit with 10-mm internal diameter, with low compliance and low compressible volume was connected to a Servo-i ventilator. The nebulizer is directly interposed between the Y-piece (also low volume) on one side and the interface, i.e. tracheal tube, nasal
Sverige AB) was injected intravenously, and a second exposure was made (fig. 2). The TcMAA is trapped in the lung capillaries, and was used to outline the lungs and to do internal calibration (fig. 3) [19]. Deposition was calculated at various sites from the mean of the anterior and posterior images, and presented as a percentage of the nebulized or instilled surfactant dose. Statistical Analyses Differences between groups were assessed by one-way ANOVA using SigmaPlot 12 (Systat Software Inc., San Jose, Calif., USA). In case of overall significance, Bonferroni’s test was used to assess pair-wise differences between groups. Differences within groups were assessed by a two-sided t test. p < 0.05 was considered significant. Results are presented as medians (range), if not otherwise stated.
Results
Nebulizer
Expiratory limb
prongs, or mask, on the other. The nebulizer adds 8 ml of apparatus dead space and the Y-piece and interface connection another 2 ml. The nebulizer is lead-shielded during nebulization and the expiratory gas is passed through an activated charcoal filtering chamber before being evacuated by the scavenger gas system.
TcMAA injected
Surfactant inhaled Nose and pharynx
19%
Trachea
4%
R 2%
L 12% 12%
Lungs Gut
Fig. 2. Gamma scintigraphy images of a pig after inhalation of ra-
Lung Deposition of Nebulized Surfactant
tively (table 2). A median 2–4% of surfactant was deposited in the trachea or tracheal tube in all groups (table 2). There was marked intersubject variability in the observed lung distribution of surfactant/nanocolloid, and significantly more went to the dependent lung in all groups (p values ranging from 0.047 to
Received: March 27, 2014 Accepted after revision: November 17, 2014 Published online: March 3, 2015
Lung Deposition of Nebulized Surfactant in Newborn Piglets Rikard Linner a Valeria Perez-de-Sa b Doris Cunha-Goncalves a Departments of a Cardiothoracic Anesthesia and Intensive Care and b Pediatric Anesthesia and Intensive Care, Lund University, Skåne University Hospital, Lund, Sweden
Abstract Background: It would be advantageous for the treatment of neonatal respiratory distress syndrome if effective amounts of surfactant could be delivered by nebulization. Objective: To investigate lung deposition and distribution of nebulized porcine surfactant using an investigational eFlow® neonatal nebulizer. Methods: While lying on one side, 1-day-old piglets inhaled 200 mg · kg–1 of nebulized surfactant via mask, nasal prongs, or tracheal tube. The surfactant was diluted with normal saline to 40 mg · ml–1 and labeled with 99mtechnetium-labelled nanocolloid. Undiluted surfactant (80 mg · ml–1) was instilled tracheally in a fourth group. Each group had 8 animals. Lung deposition was measured by gamma scintigraphy, and deposition values were presented as a percentage of the nebulized or instilled dose. Results: The median lung deposition of inhaled surfactant was 5% (range 3–16) via mask, 14% (2–40) via prongs, and 45% (25– 56) via tracheal tube (p < 0.05). It was 88% (71–96) with instillation. In all groups, the surfactant preferentially went to the dependent lung. Deposition ratios (upper lung/both lungs)
© 2015 S. Karger AG, Basel 1661–7800/15/1074–0277$39.50/0 E-Mail [email protected] www.karger.com/neo
were 0.32 (0.13–0.58), 0.15 (0.05–0.58), 0.16 (0.11–0.23), and 0.08 (0.03–0.46). Conclusions: Using this nebulizer, the lung depositions of porcine surfactant were 45% via endotracheal tube and 14% via nasal-continuous positive airway pressure (prongs). These figures might be physiologically relevant, but still have to be confirmed in efficacy studies. © 2015 S. Karger AG, Basel
Introduction
Endotracheally instilled exogenous surfactant has proven effect in neonatal respiratory distress syndrome [1]. If sufficient amounts of aerosolized surfactant could be deposited in the lungs, tracheal intubation and instillation would become unnecessary, and the inherent risks of intubation/instillation avoided [2]. During the 1990s, studies of immature newborn animals with surfactant deficiency [3–5], and an uncontrolled study in premature infants [6] indicated that nebulized surfactant improved lung function. Deposition figures were as low as 1% [5] and interest declined after a neutral outcome in a randomized clinical study of surfactant inhalation versus no treatment [7]. In recent years, the interest in surfactant inhalation has increased, but so Rikard Linner, MD, PhD Department of Cardiothoracic Anesthesia and Intensive Care VO Thorax, Plan 8, Hisshall A, Skåne University Hospital SE–221 85 Lund (Sweden) E-Mail Rikard.Linner @ gmail.com
Downloaded by: Yale Medical Library 198.143.38.65 - 7/13/2015 12:26:30 PM
Key Words Nebulization · Neonatal respiratory distress syndrome · Surfactant
far only an open-label pilot study has suggested that it is effective [8]. Surfactant, a viscous foam-forming fluid with low surface tension, is hard to nebulize, and pulmonary deposition in some early studies with older nebulizers was less than 1–2% of the aerosolized dose [5, 9]. Moreover, the surfactant was unevenly distributed, with most of it in regions that were already well ventilated [9, 10]. These problems could be circumvented if an efficient nebulizer delivered so much to the lungs that even relatively inaccessible regions received therapeutic amounts. Aerosolizer technology has advanced during the last decade and a new nebulizer, based on the vibrating mesh principle [11], has been specifically developed for surfactant inhalation with preserved surfactant properties [12]. We used this nebulizer to perform a feasibility study on the deposition of porcine surfactant in the lungs and upper airway. There are many studies of surfactant deposition during inhalation via tracheal tube [13], but relatively few with other interfaces [3, 14–16]. We therefore studied three interfaces: mask, nasal prongs, and tracheal tube. Additionally, because instilled surfactant preferentially goes to the dependent parts of the lungs [17], we examined whether this also held true for inhaled surfactant.
prongs (Large ArgyleTM CPAP Nasal Cannula; Covidien AB, Solna, Sweden) were modified to fit the larger distance between the nostrils. The mouth was held closed during inhalation. In the tube-neb and tube-instill groups, the trachea was intubated (cuffed endotracheal tube, sizes 2.5 or 3.0) after spraying the larynx with lidocaine. Correct tube placement was confirmed by auscultation. A neurally adjusted ventilatory assist catheter (NAVA, Maquet Critical Care AB, Solna, Sweden) was used to monitor the integrated electrical activity of the diaphragm (Edi), which allowed assessment of the breathing pattern and aided in adjusting sedation. At the end of the study, i.e. after the gamma scintigraphy, the piglets were killed using an excess dose of pentobarbital, fentanyl, and potassium. Surfactant Preparation Each animal received 200 mg · kg–1 of porcine surfactant (Curosurf® 80 mg · ml–1; Chiesi Farmaceutici, Parma, Italy), thoroughly mixed with 200 MBq 99mTc-nanocolloid (Nanocoll®; GE Healthcare AB, Stockholm, Sweden) [18]. In the nebulized groups, the surfactant was diluted with normal saline to 40 mg · ml–1 for optimal nebulizer performance, whereas undiluted surfactant was instilled in the tube-instill group.
Ventilation and Surfactant Administration Spontaneous breathing was maintained during surfactant inhalation or instillation with the aid of a Servo-i ventilator (Maquet Critical Care AB). In the mask and prongs groups, the nasal-continuous positive airway pressure mode was used to deliver continuous positive airway pressure (4 cm H2O). In the tube-neb and tube-instill groups, pressure support with PEEP +4 was used, and inspiratory pressure adjusted to achieve a tidal volume of 6–10 ml · kg–1 · FiO2 was 0.5. In the tube-instill group, a catheter was passed 0.5 cm beyond the tip of the tracheal tube, and surfactant was instilled as a bolus in the lower trachea.
Methods The experiments were approved by the regional committee on animal research ethics. Thirty-two 12- to 36-hour-old full-term piglets were studied. They were randomly divided into four groups of 8 with half of the animals lying on their right side, and half lying on their left side during surfactant administration. The four groups were: (1) mask-neb and (2) prongs-neb, in which nebulized surfactant was inhaled via a mask or nasal prongs, and (3) tube-neb and (4) tube-instill, in which animals were tracheally intubated, and surfactant nebulized or instilled. Preparation and Anesthesia Anesthesia was induced with i.m. ketamine (6 mg), midazolam (0.4 mg), and atropine (0.2 mg). An ear vein was cannulated and continuous anesthesia with i.v. ketamine (1–3 mg · kg–1 · h–1) and dexmedetomidine (1–3 μg · kg–1 · h–1) was started. Intermittent ketamine (1–2 mg–1 · kg–1), propofol (1–3 mg · kg–1), and midazolam (0.2 mg · kg–1) were given intravenously as needed. A femoral artery was cannulated for arterial blood pressure monitoring and blood sampling. In the mask and prongs groups, 0.1 ml of the decongestant oxymetazoline hydrochloride (0.5 mg · ml–1) was given in each nostril. To avoid reflex apnea, lidocaine was sprayed in the nostrils before applying the interface. In the mask-neb group, the mouth was held closed and a silicon facial neonatal mask (Infant Silicone-Mask, No. 00; Laerdal Medical, Stavanger, Norway) was placed with its brim surrounding the nostrils. In the prongs-neb group, neonatal
278
Neonatology 2015;107:277–282 DOI: 10.1159/000369955
The Nebulizer The nebulizer (investigational eFlow® Neonatal Nebulizer system; PARI Pharma, Starnberg, Germany) employs the vibrating membrane principle. The mass median aerodynamic diameter (MMAD) for the generated surfactant droplets was 2.5–3.0 μm with a geometric standard deviation of 1.6 [unpubl. in vitro data from PARI Pharma for normal saline-diluted Curosurf 40 mg · ml–1 using a Next Generation Impactor]. The nebulizer was connected at one end to the Y-piece of the ventilator’s breathing circuit, and at the other end to the mask, prongs, or tracheal tube (fig. 1). A new nebulizer was used for each piglet.
Arterial Blood Gases Arterial blood gases were measured at baseline and at 15 min of nebulization, or 15 min after instillation, and analyzed on an ABL 700 blood gas analyzer (Radiometer, Copenhagen, Denmark). Measurement of Surfactant Deposition Piglets were placed supine in a gamma camera (Philips Skylight; Philips AB, Stockholm, Sweden) with dual heads, simultaneously acquiring one anterior and one posterior image. These were analyzed as 128 × 128 matrices with a pixel size of 3.2 mm. After a 3-min exposure, approximately 25 MBq of 99mTc-labelled macroaggregated albumin (TcMAA; TechneScan LyoMAA; Covidien
Linner/Perez-de-Sa/Cunha-Goncalves
Downloaded by: Yale Medical Library 198.143.38.65 - 7/13/2015 12:26:30 PM
Inspiratory limb Y-piece
Interface
Exhaust Ventilator Activated charcoal
Fig. 1. Breathing circuit setup. A pediatric disposable breathing
circuit with 10-mm internal diameter, with low compliance and low compressible volume was connected to a Servo-i ventilator. The nebulizer is directly interposed between the Y-piece (also low volume) on one side and the interface, i.e. tracheal tube, nasal
Sverige AB) was injected intravenously, and a second exposure was made (fig. 2). The TcMAA is trapped in the lung capillaries, and was used to outline the lungs and to do internal calibration (fig. 3) [19]. Deposition was calculated at various sites from the mean of the anterior and posterior images, and presented as a percentage of the nebulized or instilled surfactant dose. Statistical Analyses Differences between groups were assessed by one-way ANOVA using SigmaPlot 12 (Systat Software Inc., San Jose, Calif., USA). In case of overall significance, Bonferroni’s test was used to assess pair-wise differences between groups. Differences within groups were assessed by a two-sided t test. p < 0.05 was considered significant. Results are presented as medians (range), if not otherwise stated.
Results
Nebulizer
Expiratory limb
prongs, or mask, on the other. The nebulizer adds 8 ml of apparatus dead space and the Y-piece and interface connection another 2 ml. The nebulizer is lead-shielded during nebulization and the expiratory gas is passed through an activated charcoal filtering chamber before being evacuated by the scavenger gas system.
TcMAA injected
Surfactant inhaled Nose and pharynx
19%
Trachea
4%
R 2%
L 12% 12%
Lungs Gut
Fig. 2. Gamma scintigraphy images of a pig after inhalation of ra-
Lung Deposition of Nebulized Surfactant
tively (table 2). A median 2–4% of surfactant was deposited in the trachea or tracheal tube in all groups (table 2). There was marked intersubject variability in the observed lung distribution of surfactant/nanocolloid, and significantly more went to the dependent lung in all groups (p values ranging from 0.047 to
