Salbutamol Delivery From a Hydrofluoroalkane Pressurized Metered-Dose Inhaler in Pediatric Ventilator Circuits

Salbutamol Delivery From a Hydrofluoroalkane Pressurized Metered-Dose Inhaler in Pediatric Ventilator Circuits

Delivery From a Hydrofluoroalkane Pressurized Salbutamol Metered-Dose Inhaler in Pediatric Ventilator Circuits* An In Vitro Study H. Wildhaber, MD; ...

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Delivery From a Hydrofluoroalkane Pressurized

Salbutamol

Metered-Dose Inhaler in Pediatric Ventilator Circuits* An In Vitro Study H. Wildhaber, MD; Mark J. Hayden, MD; Nigel D. Dore, MRRS; Johannes Sunalene G. Devadason, PhD; and Peter N. LeSouef, MD

Study objectives: The aim of our study was to determine the in vitro delivery of salbutamol from (pMDI) containing hydrofluoroalkane (HFA) propellant pressurized metered-dose inhaler to four models of a pediatric lung. through various delivery devices Design: To determine the effect of electrostatic charge, delivery of salbutamol was initially assessed with a multistage liquid impinger (MSLI) through an inline nonchamber device (Baxter MDI Adapter) and a small (Aerochamber MV) and a large (Nebuhaler) inline chamber device. to four lung models appropriate for a child of 70 kg, 50 Following this, the delivery was assessed three 15 4 with the same reduced static devices inserted directly into a pediatric and kg, kg, kg, ventilator circuit. Measurements and results: Reduction of electrostatic charge improved small particle delivery through holding chambers to the MSLI by 12 to 14%. In the ventilator model, the mean delivery was between 1.9% and 5.4% for the nonchamber device, between 14.3% and 27.2% for the small and between 7.2% and 25.7% for the large holding chamber. Delivery was the holding chamber, least efficient in the 4-kg model compared to the 70-kg, 50-kg, and 15-kg models. Conclusions: Salbutamol from an HFA pMDI is delivered efficiently through inline holding chambers with reduced static in pediatric ventilator settings. A large holding chamber has no small holding chamber. In addition, salbutamol delivery is more efficient advantage over a chamber than through a nonchamber device. a through holding a

(CHEST 1998; 113:186-91)

Key words: aerosol therapy; electrostatic charge; inhalation devices; mechanical ventilation

Abbreviations: CFC chlorofluorocarbon; HFA=hydrofluoroalkane; MS LI multistage liquid impinger; PIP=peak inspiratory pressure; pMDI=pressurized metered-dose inhaler; SVN=small-volume nebulizer; TT=tracheal tube; Vt.tidal volume =

=

therapy of reversible airoften delivered via inhala¬ obstruction are way tion to the lower respiratory tract in both spontane¬ ously breathing and mechanically ventilated patients. The devices usually used for delivery of aerosols to ventilated patients are small-volume nebulizers (SVNs) and pressurized metered-dose inhalers "D ronchodilators for the

¦*-*

*From the Perth Medical Aerosol Research Group, Departments of Respiratory Medicine (Drs. Wildhaber, Dore, Devadason,

and LeSouef) and Intensive Care (Dr. Hayden), Princess Margeret Hospital for Children, Subiaco, Western, Australia. Manuscript received January 6, 1997; revision accepted June 25, 1997.

Reprint requests: Johannes Wildhaber, MD, Department of Re¬ for Children, spiratory Medicine, Princess Margeret Hospital e-mail: [email protected] Roberts Subiaco Road,

cyllene.uwa. edu. au 186

6008, WA, Australia;

(pMDIs).

There is still a controversy about which be the optimal system for inhalation therapy in may ventilated patients in ICUs from the point of view of both economic and therapeutic effectiveness.1 Several in vitro and in vivo studies have shown that pMDIs are more efficient in aerosol delivery than SVNs.2-5 In addition, it was also shown that both SVNs and pMDIs can effectively deliver aerosols in a ventilator model and that aerosol delivery can be significantly improved when a proper technique of administration is followed.68 To enhance lung deposition of aerosols from pMDIs, several accessory devices have been devel¬ oped. The accessory devices most commonly used to deliver aerosols from pMDIs into ventilator circuits Laboratory and Animal Investigations

inline nonchamber devices and inline holding chambers. The advantage of a holding chamber inserted in the ventilator circuit is that the actuated aerosol cloud is retained within the chamber and hence impaction of the drug within the ventilator circuit is reduced. Holding chamber devices have been shown to be superior to nonchamber de¬ are

vices.9'10

Until recently, pMDIs contained chlorofluorocarbon (CFC) propellant, which is damaging to the ozone layer.911 These are now being replaced by

pMDIs containing hydrofluoroalkane (HFA) propel¬

lant.12 As the aerosol and delivery characteristics of HFA pMDIs may be different from CFC pMDIs, it is important to test them in in vitro and in vivo studies.13 The aim of our study was to compare the in vitro of salbutamol from an HFA pMDI through delivery an inline nonchamber device and a small and a large inline holding chamber inserted in a pediatric ven¬ tilator circuit under various ventilator settings. Materials

and

Methods

In vitro salbutamol delivery was measured through the follow¬

ing devices using a high-performance multistage liquid impinger (MSLI) (Copley; Nottingham, UK): an inline nonchamber device (Rigid 22mm pMDI Adapter; Baxter; Irvine, Calif); a small inline holding chamber (Aerochamber MV; volume 165 mL; Trudell; Ontario, Canada); and a large holding chamber (Nebuhaler; 750 mL; Astra; Lund, Sweden) modified to function as an inline

device for a ventilator circuit. Modification of the large chamber performed by sealing off air leaks, removing the valve, and inserting the inline nonchamber device in the actuator orifice. The salbutamol HFA pMDI (20 canisters, Lot 96E01K of Airomir; 3M Pharmaceuticals; St. Paul, Minn) was actuated 10 times into the study devices and shaken vigorously between actuations. Air was drawn through the study devices that were attached to the MSLI at a continuous flow of 60 L/min. Aerosol droplets were deposited on the device, the glass throat of the MSLI, or one of four stages. The MSLI was calibrated by the manufacturer so that particles >13, 6.8 to 13, 3.1 to 6.8, and <3.1 ixm were deposited on stage 1, 2, 3, and 4, respectively. To determine the influence of electrostatic charge on drug delivery, salbutamol delivery was measured through new and devices. Electrostatic charge on the surface of detergent-coated the devices was measured prior to the in vitro test using a modified electrometer and was classified as none (negligible charge, 0 to 1.2 ixC/m2), low charge (1.2 to 3.3 fiC/m2), and high charge (3.3 to 6.7 ixC/m2). All devices were then detergent coated to reduce electrostatic charge. To coat the devices with deter¬ gent, they were soaked in diluted (1:250) cationic detergent (Cetrimide 40%; Princess Margaret Hospital Pharmacy; Perth, Australia) for 1 h and drip dried for <24 h.14 In addition, in vitro salbutamol delivery was measured through the three devices, an inline nonchamber device (Rigid 22-mm pMDI Adapter; Baxter), a small inline holding chamber (Aero¬ chamber MV; Trudell), and a large holding chamber (Nebuhaler; Astra) modified as an inline device for a ventilator circuit inserted was

in

a

dry unheated pediatric ventilator circuit (Servo Ventilator

900C; Siemens; Elema, Sweden). Four different models

were

constructed to mimic appropriate ventilator settings for children

weighing (a) 70 kg, (b) 50 kg, (c) 15 kg, and (d) 4 kg. All models used the same ventilator (Servo) and circuit, but tracheal tube (TT) size and the volume/compliance of the test lung were altered to mimic that of children of different sizes (test lung for infants: small volume and low compliance; test lung for older children: large volume and high compliance). Additionally the compliance of the test lung in model b was altered by a constricting "band" to mimic normal and "stiff lungs. In keeping with standard clinical

practice, the ventilator was set on volume control mode for models a, b, and c, and on pressure control mode for model d. Thus models a, b, and c, had a set tidal volume (Vt) and resultant peak inspiratory pressure (PIP), whereas model d had a set PIP and resultant Vt. Positive end-expiratory pressure was set at 4 cm H20 in all models as was inspiratory time (25%) and pause time (10%). On this type of ventilator, inspira¬ tory flow is not set and is dependent on PIP, inspiratory time, pause time, and lung model compliance. The models used were as follows: (a) TT (Portex; Kent, England) internal diameter 9 mm, Vt 750 mL, rate 10 breaths/min, PIP 20 cm H20; (b) TT 7.5 mm, Vt 450 mL, breaths/min 10, PIP 20 cm H20 and 40 cm H20; (c) TT 5 mm, Vt 165 mL, breaths/min 18, PIP 20 cm H20; and (d) TT 4 mm, Vt 40 mL, breaths/min 30, PIP 20 cm H20,

respectively (Fig 1). In addition, in vitro salbutamol delivery through all three devices was measured in a humidified and heated (37°C) circuit with ventilator settings for a 70-kg child (model a). All devices were detergent coated to reduce electro¬ static charge. They were inserted into the ventilator circuit at the

opening of the TT. Salbutamol was collected on an inspiratory filter (Anesthesia Filter, Curity; Kendall; Mansfield, Mass) in¬ serted at the tip of the TT. An identical filter was inserted in the expiratory line. The HFA pMDI was actuated 10 times just prior to initiation of inspiration and shaken vigorously inbetween actuations. Between actuations, a sufficient number of inspiratory and expiratory cycles were allowed, to totally clear the dead space

of the delivery device and the ventilator circuit. Each device, throat, TT, inspiratory and expiratory filters, and each ofthe four stages ofthe MSLI were washed separately with 45 mL of methanol immediately after the tests. Five milliliters of 0.1 mmol/L NaOH was added to each wash and the volume was made up to 50 mL with methanol. The absorbance (wave length 246 nm) of each sample was measured in duplicate on a spectrophotometer (Hitachi U-2000; San Jose, Calif). The con¬ centration of salbutamol in each sample was obtained by using the absorbance of a standard solution containing a known concentration of salbutamol. The total actuated dose (10 puffs) in the MSLI was determined by adding the amount of drug in the device, the glass throat, and the four stages. The total actuated dose (10 puffs) in the ventilator circuit was determined by adding the amount of drug in the device, the filters, and the TT. The standard curve for salbutamol was linear (^=1.00) for concen¬ trations between 0 and 2,100 [ig/mL. Each experiment from actuation ofthe pMDI to the measurements ofthe drug concen¬ tration was repeated four times. Validation of the method, to ensure that no other contents of the pMDI interfere with the spectrophotometric measurement of salbutamol at the same wave length, was done, using a placebo pMDI containing only the propellant HFA but no salbutamol (Airomir placebo, 3M Phar¬ maceuticals). All measurements were undertaken under the following atmospheric conditions: mean temperature was 21.7°C (range, 21 to 24°C) and mean barometric pressure was 760 mm

Hg (758 to 766 mm Hg).

Statistical analysis was carried out using analysis of variance (StatView 512 +; Abacus Concepts Inc; Berkeley, Calif) with a

significance level of 95% (p<0.05).

CHEST/113/1 /JANUARY, 1998

187

charge did not affect delivery dirough the nonchamber device. Delivery of small particles (<3.1 |xm) is increased by 12% from the small holding chamber (Aerochamber MV) and by 14% from the large holding chamberwas(Nebuhaler). Delivery of small particles (<3.1 jmm) significantiy higher from the small holding chamber (Aerochamber MV) device compared to the inline nonchamber device (Raxter MDI Adapter) (p<0.001). However, delivery of small particles (<3.1 [xm) was less from the small holding chamber (Aerochamber MV) compared to the large holding chamber (Nebuhaler) (p<0.001). Drug deposition for the four lung models using the pediatric ventilator circuit is shown in Table 2. Drug deposition on the inspiratory filter as a proportion of to the drug delivery patient was between 1.9% and 5.4% through the inline nonchamber device (Raxter MDI Adapter) and was significantly less than through the two inline holding chambers (Aerochamber MV and Nebuhaler) (p<0.001). Drug deposition on the inspiratory filter was between 14.3% and 26.0% through the small holding chamber (Aerochamber MV) and was significandyhigher than through the large (Nebuhaler) for ventilator settings holding chamber for a child of 50 kg (b), 15 kg (c), and 4 kg appropriate (d) (p<0.001). However, there was no significant dif¬ ference for a child of 70 kg (a). The amount of salbutamol through the small holding chamber (Aero¬ chamber MV) deposited on the inspiratory filter was significantly higher (p<0.001) in ventilator settings a for child of 70 kg (a) and 50 kg (b) than appropriate in ventilator settings for a child of 15 kg (c) and 4 kg (d), whereas drug deposition on the expiratoiy filter was lower (p<0.001). Drug deposition on the significantlyfilter was between 7.2% and 25.6% for the inspiratory inline chamber (Nebuhaler) and de¬ large holding Vts creased with lower from the ventilator setting for a child of 70 kg (a) to the ventilator setting for a child of 4 kg (d) (Fig 2). A change in the compliance ofthe lung model while maintaining the same ventilator setting appropriate for a child of 50 kg (b) did not alter drug delivery through the small holding chamber (Aero¬ chamber MV). However, humidification of die ventila¬ tor circuit for a child of 70 kg resulted in a significant decrease of salbutamol deposition on the (p<0.001) filter inspiratory by 24% for the large and 18% for the small inline holding chambers (Table 2). The mean (range) of total dose (10 puffs) of salbutamol from HFA pMDIs was 1,040 p,g (890 to trostatic

Y-ventilator connector / ^ expiratory filter

pMDI/inline non-chamber device

Y-ventilator connector/

expiratory filter test lung

Y-ventilator connector/ expiratory filter

Figure 1. Illustration ofthe three devices, an inline nonchamber

a small inline holding chamber (center, b), and a (top, a),chamber modified as an inline device for a venti¬ holding large lator circuit (bottom, c) inserted in a pediatric ventilator circuit under different ventilator

device

settings.

Results

Measurements of electrostatic charge and drug The delivery using the MSLI are shown in Table 1. from electrostatic charge on the new devices ranged low to high. Reducing electrostatic charge by coating the devices with cationic detergent significantly in¬ creased the delivery of small particles (<3.1 jmm) from the inline holding chambers (p<0.001). Elec¬ 188

1,180

n.g).

Discussion

Inhalation therapy with bronchodilators to me¬ chanically ventilated patients is usually performed Laboratory and Animal Investigations

Table 1.Measurements of Electrostatic

Charge and Drug Delivery*

(Baxter pMDI Adapter)

(Aerochamber MV)

Small Chamber

Large Chamber

Low 4.2% (2.8) 64.5% (2.3) 0.2% (0.2) 7.8% (0.5) 23.3% (1.9) None 5.4% (1.4) 63.0% (1.6) 0.2% (0.2)

Low 42.0% (0.3) 1.2% (0.1) 2.7% (0.3) 14.2% (0.3) 39.8% (0.5) None 34.5% (1.7) 1.2% (0.2) 4.0% (1.8) 15.8% (0.7) 44.5% (0.8)

38.3% (0.9) 0% 0.8% (0.1) 17.5% (0.4) 43.3% (1.3) None 20.2% (0.5) 2.0% (0.7) 5.9% (0.9) 22.5% (1.9) 49.5% (2.5)

Nonchamber

New static

Spacer

Throat

Stage 1+2 Stage 3 Stage 4

Reduced static

Spacer

Throat

Stage 1+2 Stage 3 Stage 4

7.3% 24.2%

(0.4) (1.2)

(Nebuhaler)

Low-high

*Mean (SD) in vitro delivery of salbutamol from HFA pMDI through different inline devices under static and reduced static conditions measured using an MSLI with cutoffs of particles >13, 6.8 to 13, 3.1 to 6.8, and <3.1 |xm for stage 1, 2, 3,and 4, respectively, expressed as percentage

of the total actuated dose.

SVNs or pMDIs containing CFC propellant. Recent studies have shown that CFC pMDIs are an effective alternative to SVNs for aerosol therapy to

using

the mechanically ventilated patient.24 However, be¬ cause of its harmful effect on the ozone layer, the use of CFC pMDIs will be discontinued. Thus, CFCfree products, such as HFA pMDIs, have been introduced for inhalation therapy. The performance of salbutamol HFA pMDIs in drug delivery is dif¬ ferent from CFC pMDIs in some situations.13 How¬ ever, another study has shown that salbutamol HFA Table

(a: 70 kg)

(Baxter pMDI Adapter)

Dry Humidified

Expiratory filter Inspiratory filter

29.2% (1.5)/30.5% (2.0) 65.0% (3.0)/63.0% (3.4) 0.5% (0.1)/0.5% (0.3) 5.4% (2.1)/6.3% (1.6)

Device TT

27.8% (3.0) 66.1% (3.4)

Device TT

(b: 50 kg)

Expiratory filter Inspiratory filter

(c: 15 kg) Device TT

Expiratory filter Inspiratory filter

(d: 4 kg)

Device TT

Expiratory filter Inspiratoiy filter

model of a pediatric ventilator circuit. Our results with a maximal deposition of 26.0% of salbu¬ tamol from an HFA pMDI on the inspiratory filter are comparable to another study measuring albuterol delivery from a CFC pMDI in an adult ventilator circuit model with a maximal deposition of 25.1%.6 The technique of administration and the devices

vitro

2.Drug Deposition for the Four Lung Models Using the Pediatric Ventilator Circuit* Nonchamber

Ventilator settings

pMDIs did not perform differently from salbutamol CFC pMDIs in drug delivery through spacer de¬ vices.15 We have shown in our study that salbutamol from an HFA pMDI is delivered efficiently in an in

1.4% 4.6%

(1.4) (0.8)

Large Chamber

Small Chamber

(Aerochamber MV) Dry Humidified 12.4%

(1.2)/16.5% (2.2)

(Nebuhaler)

Dry Humidified

58.9% (3.0)/61.8% (2.0) 2.9% (0.6)/0.8% (0.1) 25.9% (1.5)/21.0% (1.5) PIP, 20 cm H2O/40 cm H20 10.2% (2.1)/10.4% (1.7) 60.2% (2.9)/60.3% (4.2) 3.5% (0.7)/3.7% (0.9) 26.0% (2.5)/25.6% (4.6)

6.9% (1.0)/12.8% (1.2) 59.9% (1.9)/60.7% (2.2) 7.5% (0.7)/7.1% (1.2) 25.6% (1.1)/19.6% (1.6)

7.4% 61.1% 11.8% 19.7%

(0.9) (1.2) (2.1) (2.1)

26.0% (3.1) 67.8% (3.2) 2.5% (0.5) 3.7% (0.5)

13.4% 59.3% 7.5% 19.8%

(2.6) (3.5) (1.4) (0.6)

22.1% (3.5) 36.0% (4.7) 25.7% (0.6) 16.2% (0.6)

(3.0) (1.2) (1.1) (0.7)

36.9% 25.8% 23.0% 14.3%

(1.5) (2.7) (3.6) (1.3)

59.8% 25.7% 7.2% 7.2%

31.1% 62.5% 4.4% 1.9%

(1.7) (3.2) (2.1) (2.1)

(SD) in vitro delivery of salbutamol from HFA pMDI through an inline nonchamber device and two inline holding chambers in pediatric ventilator circuit under different ventilator settings appropriate for a child of 70 kg (a), 50 kg (b), 15 kg (c), and 4 kg (d) with and without humidification, expressed as percentage of the total actuated dose.

*Mean

CHEST/113/1 /JANUARY, 1S

189

¦ Baxter pMDI Adapter ?Aerochamber WI.V. H Nebuhaler

Figure 2. Mean (SD) drug deposition on the inspiratory filter of salbutamol from HFA pMDI through an inline nonchamber device and two inline holding chambers in pediatric ventilator circuit under different ventilator settings appropriate for a child of 70 kg, 50 kg, 15 kg, and 4 kg, respectively, expressed as percentage of the total actuated dose.

used for administration of CFC pMDIs play a major role in the efficacy of aerosol delivery.6 We have shown in the present study the importance of the choice of devicefor HFA pMDI administration. We showed in a previous study that electrostatic charge on the surface of a plastic spacer device is the most important factor influencing salbutamol delivery from a CFC pMDI.16 We also found in that study that the shape and the volume of the spacer device role in delivery of salbutamol CFC play a major In the present study, we have shown that pMDI.16 the delivery of salbutamol from an HFA pMDI is also dependent holding chamberand through a plastic surface on electrostatic hence, is in¬ charge, creased when the holding chambers are coated with ionic detergent to reduce static. In the MSLI model, salbutamol delivery from the HFA pMDI was higher through the large-volume chamber than the small. One might there¬ holding fore expect that a large holding chamber may be superior to a small holding chamber in delivery of salbutamol from an HFA pMDI in a pediatric ventilator circuit. However, we have shown that a large chamber has no advantage over a small cham¬ ber in this setting. This might be explained by the low Vts used in pediatric ventilator settings and the clearance of a holding chamber, inserted between the Y-ventilator connector and the TT in a ventilator circuit, in both the inspiratory and expiratory phase. Thus, a large inline chamber might not be totally cleared in inspiration but will be cleared in both inspiration and expiration, hence, wasting drug dur¬ ing the expiratory phase. We have shown that inline are only efficiently cleared in holding chambers when the Vt exceeds the volume of the inspiration inline holding chamber. This problem may be over¬ 190

by inserting the spacer in the inspiratory limb of the ventilator circuit. We have also shown that a small chamber is more efficient in pediatric ventila¬ tor settings where low Vts are used. A change in the while maintaining the compliance of the lung model same ventilator settings did not alter drug delivery. In addition, we found that salbutamol delivery is less efficient through a nonchamber device than through a holding chamber. A change in the compliance of the lung model did not alter salbutamol delivery. However, salbutamol chambers was reduced through the holding delivery small chamber 24% 18% the by through chamber in a heated and by the and humidi¬ large through fied ventilator circuit compared to a dry ventilator circuit. Humidification may lead to hygroscopic of the aerosols and increased impaction of growth aerosols on the chamber surface, and hence, de¬ creased delivery of salbutamol to the inspiratory filter.17 Our in vitro study with measurements of drug on a filter gives only an idea about the deposited dose most likely reaching the lungs in a clinical setting. The distribution of the aerosol and the clinical response remain unknown. However, the importance of the in vitro assessment of different devices, under different conditions, proceeding in vivo studies, is shown by the results of three previous studies. One study, using a suboptimal delivery device (pMDI adapter), did not show a clinical response of bronchodilators administered by CFC pMDI,18 whereas the other two studies, using a device (inline holding chamber), shown in delivery vitro to be optimal, found a significant clinical come

response.1920

In conclusion, we have shown that salbutamol from an HFA pMDI is efficiently delivered through inline holding chambers with reduced static in pedi¬ atric ventilator circuits and that a large holding chamber has no advantage over a small holding chamber. However, delivery through a nonchamber device was distinctly inefficient.

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