Simplifying Transcutaneous Intratracheal Drug Delivery in the Newborn Preterm Rabbit

Summary

Transcutaneous intratracheal injection allows for effective intrapulmonary drug delivery during spontaneous respiration. Single and multiple injections are well tolerated with no effect on survival. The technique is simple to perform and can examine the effect of substances on lung development and the prevention of lung injury in newborn rabbits.

Abstract

Intratracheal (IT) drug delivery allows the direct delivery of pharmaceutical substances to the lung, maximizing potential pulmonary benefit and minimizing systemic drug exposure. The transcutaneous technique is simple and allows for the IT delivery of substances to the lung of prematurely born rabbits shortly after birth. Newborn pups are anesthetized with inhaled Isoflurane before being placed in a supine position with the neck extended. The larynx is identified and stabilized before transcutaneous placement of a 26-gauge (G) catheter into the trachea. Following catheterization of the trachea, a 30 G blunt needle attached to a Hamilton syringe is introduced into the IT catheter and is used for delivering a precise volume into the trachea during spontaneous respiration. After the IT injection is completed, the needle and catheter are withdrawn, and the pup is allowed to recover from anesthesia. Transcutaneous IT injection delivers a large proportion of the injected substance to the lung, with the majority remaining in the lung 3 hours after the intervention. The injections are well tolerated from the day of birth and can be repeated for multiple consecutive days without influencing survival. This technique can be used to investigate the effect of pharmaceutical agents on lung development and in the prevention of neonatal lung injury in preterm rabbits.

Introduction

Chronic neonatal lung disease (CNLD) following premature birth continues to occur in a significant number of infants¹. Improved modern neonatal care has significantly increased survival and decreased the majority of significant complications following preterm birth. While neurological, gastrointestinal, and ophthalmological complications have decreased, respiratory complications remain largely unchanged over the past 2 decades with nearly one in two infants born before 28-week gestation developing lung disease.

Prematurity, inflammation, oxidative damage, and ventilator-associated injury all play a role in the pathop....

Protocol

For all experiments involving IT injection, permission has been sought from the Animal Ethics Committee of KU Leuven, and all guidelines of animal welfare and care of KU Leuven were adhered to.

1. Preparation

1. Collect all required materials to complete the IT injection (Table 1).
2. Ensure that the exhaust of the anesthetic chamber is open and connected to a scavenger to prevent exposing the researcher to Isoflurane.

2. Delivery of pups

NOTE: Rabbit pups (New Zealand white-Flemish giant hybrid) were delivered via hysterotomy on day 28 gestation (....

Results

Representative results of the technique of single and repeated daily transcutaneous IT injections have been published and demonstrate that survival was not influenced by IT injection (single or multiple injections), nor did IT injection with placebo (saline) alter the lung function or lung structure compared to controls¹⁸.

Additionally, we have validated the technique in a series of experiments that investigated pulmonary delivery of IT delivered normal saline and surfa.......

Discussion

Several critical steps should be followed to successfully perform IT injection. When performed correctly, the transcutaneous IT injection method allows for effective and reliable intrapulmonary drug delivery in the preterm rabbit. Temperature control is important as the newborn pups easily become hypothermic, which can negatively influence survival. Prior to placing the pups in the induction chamber, temperature control should be ensured to maintain normothermic conditions. A heating matt placed under the induction chamb.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Anesthesia
Heating matt to prevent cooling during anesthesia			1
Isoflurane vaporizer with oxygen supply			1
Isoflurane (Iso-Vet; 1000 mg/g)	Dechra Veterinary Products NV, Belgium		2% at 2 liters/minute
Plexiglas induction chamber with exhaust and scavenger	In house built		1
Positioning for injection
Mounting stage	In-house built (made out of styrofoam to allow flexible positioning		1
Nose cone connected to anesthetic circuit			1
Scavenger system			1
Tape to restrain limbs	Any		1 roll
Intratracheal injection
Allis tissue forceps			1
19-mm-long 26-gauge catheter	BD Biosciences	391349	1
Hamilton syringe (10µl with 20 mm blunt 30-gauge needle	Hamilton Company	7638-01	1
Pharmaceutical substance of choice			as per protocol
Saline (0.9% NaCl)			5 µl per animal
Animal housing
Humidity- and temperature-controlled incubator	Okolab Srl. Custom built cage incubator. Alternatively, in-house built cage incubators can be used