Endotracheal Intubation Using a Flexible Intubation Endoscope as a Standardized Model for Safe Airway Management in Swine

Summary

The use of pigs in research has increased in recent years. Nevertheless, pigs are characterized by difficult airway anatomy. By demonstrating how to perform endoscopically guided endotracheal intubation, the present protocol aims to further increase laboratory animals' safety to avoid animal suffering and unnecessary death.

Abstract

Endotracheal intubation is often a basic requirement for translational research in porcine models for various interventions that require a secured airway or high ventilation pressures. Endotracheal intubation is a challenging skill, requiring a minimum number of successful endotracheal intubations to achieve a high success rate under optimal conditions, which is often unachievable for non-anaesthesiology researchers. Due to the specific porcine airway anatomy, a difficult airway can usually be assumed. The impossibility of establishing a secure airway can result in injury, adverse events, or death of the laboratory animal. Using a prospective, randomized, controlled evaluation approach, it has been shown that fiberoptic-assisted endotracheal intubation takes longer but has a higher first-pass success rate than conventional intubation without causing clinically relevant drops in oxygen saturation. This model presents a standardized regimen for endoscopically guided endotracheal intubation, providing a secured airway, especially for researchers who are inexperienced in the technique of endotracheal intubation via direct laryngoscopy. This procedure is expected to minimize animal suffering and unnecessary animal losses.

Introduction

Endotracheal intubation is often a basic requirement for translational research in porcine models for various interventions that require a secured airway or high ventilation pressures (such as ventilation during cardiopulmonary resuscitation¹ or acute respiratory distress syndrome²) or require that cerebral blood flow is not compromised through internal compression by supraglottic airway devices³, which are occasionally propagated as alternatives in the context of an anticipated difficult airway in pigs^4,5.

While the lung physiology of pigs shows similar features to that of humans⁶, securing the airway is sometimes significantly more difficult⁷ due to specific differences in the porcine orotracheal anatomy. The snout of a pig has a narrow opening with a very large tongue, the larynx is extremely mobile, and the epiglottis is relatively large, with a free end that extends to the soft palate. Caudally, the larynx forms an obtuse angle with the trachea. The arytenoid cartilages are large⁸. The narrowest part of the airway is at the subglottic level⁹, comparable to the airway anatomy of children¹⁰. Since the larynx in pigs is very mobile, there is a risk that the end of the endotracheal tube will pass through the vocal cords but the larynx will only be displaced caudally by up to several centimeters, which may be mistaken for a correct intubation^8,11. Additionally, esophageal intubation is a common risk when dealing with porcine airway management¹².

The rates of difficult or impossible endotracheal intubations with a corresponding negative impact on the experiment or early mortality have not been systematically recorded, but several case reports have been published^13,14. In humans, there is the possibility of using a flexible intubation endoscope in the context of an unexpectedly difficult conventional intubation¹⁵. Various false intubations often precede this measure. These repeated intubation attempts are associated with adverse events in humans^16,17, especially airway complications¹⁸. Such events are deleterious in test animals since, in the simplest case, they represent a confounder variable in the experiment; in the worst case, they can lead to the unnecessary loss of the animal.

The present study has developed a model based on the guidelines for expected difficult airway management in humans^{15,19,20,21,22,23,24}. Previously, a similar technique has been described for learning fiberoptic intubation in human studies^25,26. The protocol presented in this report aims to provide a standardized and easy-to-adapt intubation model that also allows non-airway specialists to perform successful and safe endotracheal intubation in pigs.

Protocol

The experiments in this protocol were approved by the State and Institutional Animal Care Committee (Landesuntersuchungsamt Rheinland-Pfalz, Koblenz, Germany; approval no. G20-1-135). The experiments were conducted following the ARRIVE guidelines. Overall, 10 anesthetized male pigs (Sus scrofa domestica) with a mean weight of 30 kg ± 2 kg and 12-16 weeks in age were used for the present study.

1. Animal preparation

1. Maintain a normal environment for the animals to minimize stress. Withhold food 6 h before the scheduled experiment to lower the risk of aspiration, but allow access to water.
2. Sedate the pigs with a combined injection of midazolam (0.5 mg/kg) and azaperone (2-3 mg/kg) (see Table of Materials) in the gluteal muscle or neck with a needle (20 G) for intramuscular injection. Leave the animals undisturbed until sedation sets in (15-20 min).
   NOTE: Depending on national regulations, the administration of sedating agents may be subject to scrutiny and may or may not require the supervision of a trained veterinarian. Consult with the local authorities before planning the experiments.
3. Transport the sedated animals from the stables to the laboratory. The transport time must not exceed adequate sedation time (here, 30-60 min). Ensure sufficient heat retention so that the animal does not get hypothermic (i.e., below 38 °C), such as by covering the body with a blanket depending on the outside temperature.
4. Using a sensor (see Table of Materials) clipped to the ear or tail, monitor the peripheral oxygen saturation (SpO₂).
5. Disinfect the skin with a disinfectant (alcoholic) before inserting a peripheral vein cannula (22 G) into an ear vein. Spray the area, wipe once, then spray again, and allow the disinfectant to dry. Secure the ear cannula with a band-aid (See Table of Materials).

2. Anesthesia and mechanical ventilation

1. Administer analgesia through an intravenous injection of 4 µg/kg of fentanyl. Induce anesthesia with an intravenous injection of 3 mg/kg of propofol (see Table of Materials).
   NOTE: Due to the bolus application, the drug quickly floods into the active compartment, providing a fast onset of deep anesthesia.
2. Place the pig on a stretcher in a supine position and fix it with bandages. Apply muscle relaxant through an intravenous injection of 0.5 mg/kg of atracurium (see Table of Materials).
3. Instantaneously start noninvasive ventilation via a dog ventilation mask (see Table of Materials) or similar models. To ensure a tight fit of the mask, place the thenar eminence and the thumbs of both hands on top of the mask while performing jaw thrust with the remaining fingers.
   NOTE: Ventilation parameters: FiO₂ (inspiratory oxygen fraction) = 100%, peak inspiratory pressure = <20 cmH₂0, respiratory rate = 18-20 breaths/min, PEEP (positive end-expiratory pressure) = 5 cmH₂0.
4. Maintain anesthesia through continuous infusion of 0.1-0.2 mg/kg/h of fentanyl and 8-12 mg/kg/h of propofol. Start infusing with 5 mL/kg/h of balanced electrolyte solution (see Table of Materials) continuously. Constantly maintain an adequate depth of anesthesia.
   ​NOTE: Surrogate parameters for this are the absence of movement, the lack of own respiratory efforts after intubation, and the absence of a sudden increase in heart rate. If possible, avoid permanent muscle relaxation to enable motor reactions as a sign of insufficient depth of anesthesia.

3. Endotracheal intubation

1. Have an assistant stand on the left side of the head. Have the assistant's left hand open the mouth and pinch the tongue outward and left with a compress. Ask the assistant to press down on the right upper lip with the right index finger to provide a better mouth opening.
2. Perform direct laryngoscopy. To do this, insert the laryngoscope (see Table of Materials) into the right side of the mouth and push it forward while pushing the tongue to the left. Advance the tip of the laryngoscope until it rests in the epiglottic vallecula.
   NOTE: The epiglottis usually obscures the glottis by sticking to the soft palate.
3. Carefully push the epiglottis aside with a tube guiding wire (see Table of Materials) with a gentle scooping motion from the right piriform recess to the left along the soft palate.
4. Pass the handle of the laryngoscope to the assistant to fix it in the current position.
5. Now, take the flexible intubation endoscope onto which an endotracheal tube has already been mounted and that is connected to a video monitor. Insert the endoscope orally and advance it over the base of the tongue until the glottis is visualized.
   NOTE: To avoid fogging of the camera, the prior application of anti-fogging agents (see Table of Materials) is recommended.
6. Advance the endoscope between the vocal ligaments into the trachea. Confirm the anatomy of the trachea by visually identifying the cartilaginous rings and the pars membranacea. Advance the endoscope until it rests above the carina. Try not to touch the sensitive mucosa with the tip of the endoscope to avoid swelling and bleeding.
7. While maintaining the position of the endoscope, advance the endotracheal tube until it becomes visible in the camera image.
   NOTE: If the endotracheal tube cannot be advanced through the glottic plane, there is a possibility that it has become caught on the arytenoid cartilage. In this case, the endotracheal tube must be withdrawn 1 cm and rotated by 90° before gently advancing again. If necessary, this maneuver can be repeated. Similar calibers of flexible intubation endoscope and endotracheal tube can minimize the risk of this issue occurring. If the endotracheal tube cannot be advanced despite this maneuver, it is likely that the subglottic narrowness-the narrowest part of the porcine larynx-cannot be passed. In this case, a smaller endotracheal tube size needs to be selected. Regular commercially available endotracheal tubes in sizes 6.5 cm or 7.0 cm ID should be able to pass the glottis as long as no anatomic abnormalities are present. Endotracheal tube size requirements vary depending on the piglet size and breed.
8. Withdraw the flexible intubation endoscope while maintaining the position of the endotracheal tube.
9. Using a 10 mL syringe, inflate the cuff with 10 mL of air. Control the cuff pressure with a cuff manager (target value: 30 cmH₂O, see Table of Materials).
10. Confirm the correct placement of the endotracheal tube and adequate ventilation by periodic and regular exhalation of carbon dioxide via capnography²⁴ and double-sided ventilation via auscultation¹⁵.
11. Start mechanical ventilation after connecting the tube with a ventilator (PEEP = 5 cmH₂O, respiratory rate = variable to achieve an end-tidal CO₂ of <6 kPa, usually 30-50 min⁻¹, FiO₂ = 0.4, I:E (inspiration to expiration ratio) = 1:2, tidal volume = 6-8 mL/kg).
12. Expand the monitoring (e.g., the establishment of an intra-arterial blood pressure measurement, the installation of a central venous or pulmonary arterial catheter²⁷) or continue with the intervention.
    NOTE: Depending on the question of the further experiments, define limit values for the vital parameters and intervention options and establish the monitoring accordingly in the study protocol.

Representative Results

Endotracheal intubation was performed on 10 male pigs (age 12-16 weeks, weight 30 kg ± 3 kg) in a prospective, randomized, controlled study setting. The pigs were randomized into two groups: one was conventionally laryngoscopically intubated (CI group), and the other group was intubated assisted via a flexible intubation endoscope as described in the protocol (FIE group). The group assignment was done by pulling sealed envelopes. The investigator was assigned randomly on a daily basis.

The study was performed by anesthesiological interns with more than 3 years of experience in anesthesia, profound knowledge of airway management in humans, and less than 7 months of experience in endotracheal intubation in pigs, with an anesthesia nurse assisting intubation and assessing the data (n = 2, age: 33 years ± 1 year, endotracheal intubation experience in humans: >1,000, awake fiberoptic intubation in humans: >100).

The FIE group underwent fiberoptic-assisted intubation as described in the protocol above. The CI group was treated identically to the FIE group up to step 3.2 of the protocol. After that, the following change was made. After inserting the laryngoscope into the epiglottic vallecula, the examiner pushed the epiglottis aside with an endotracheal tube, into which a tube guiding wire had been inserted, with a gentle swooping motion from the right piriformis recess to the left along the soft palate. Afterward, this endotracheal tube was advanced between the vocal ligaments into the trachea. The guiding wire was withdrawn by the assistant, the cuff of the endotracheal tube was inflated using a 10mL syringe, and mechanical ventilation was started.

If the saturation dropped below SpO₂ 93% or esophagus malposition occurred, the attempt at intubation was discontinued, and mask ventilation was performed for 3 min. After three failed attempts, the practitioner had to change the procedure. The time was counted for each trial from the start of the laryngoscopy.

The primary endpoint was the success of intubation on the first attempt. The secondary endpoints were the time to intubation, measured as the time between the start of the laryngoscopy and CO₂ detection in the ventilator, the need to change the procedure, and the assessment of the airway using the percentage of glottic opening (POGO) scale.

Statistical analyses were performed using commercially available software (see Table of Materials). Normal distribution was examined using the Kolmogorov-Smirnoff test²⁸. If a normal distribution was determined, group differences were analyzed using t-tests of independent samples²⁹ or the Mann-Whitney U test³⁰ for the non-parametric version. Data are presented as mean (± standard deviation). Correlations of ordinal-scale data were examined using Spearman's correlation coefficient³¹. A significance level of p < 0.05 was assumed. All tests were performed with exploratory intention; therefore p-values are descriptive. Nevertheless, p < 0.05 was accepted as indicative of statistical significance.

The FIE group showed a tendency toward a higher success rate on the first attempt than the CI group (100% vs. 60%); overall, fewer attempts to intubate were required in the FIE group (1.0 ± 0 vs. 1.4 ± 0.548, p = 0.310) (Figure 1). In no case did the saturation drop below 93%, so there was no need to change the procedure. A second attempt at intubation was required because the passage of the subglottic narrowing was not possible smoothly (n = 1) and because of esophageal malposition (n = 1).

Overall, successful intubation attempts took significantly longer in the FIE group than in the CI group (71.2 s ± 18.336 s vs. 36.8 s ± 18.472 s, p = 0.018). In general, the glottis was easy to visualize with good visibility (POGO: 77% ± 27.1%), with no group differences (FIE 86% ± 26.077% vs. CI 68% ± 27.749%, p = 0.513). In the conventional intubation group (CI), more attempts at endotracheal intubation were required, but this was not statistically significant (1.0 ± 0 vs. 1.4 ± 0.548, p = 0.310). In the endoscopically guided intubation group (FIE), it took significantly longer for CO₂ to be detected in the ventilator (71.2 s ± 18.336 s vs. 36.8 s ± 18.472 s, p = 0.018) (Figure 2).

Figure 1: Number of intubation attempts in group comparison. For the group that was intubated using a flexible intubation endoscope, every intubation attempt was successful; in the group that was conventionally intubated, it took an average of 1.4 attempts before the endotracheal tube could be placed correctly. Error bars show the standard deviation. n = 5 (for each group). Please click here to view a larger version of this figure.

Figure 2: Time until CO₂ detection in group comparison. For the group that was intubated using a flexible intubation endoscope, it took significantly longer until end-tidal CO₂ could be detected, depicted as mean and standard deviation. n = 5 (for each group). Please click here to view a larger version of this figure.

Discussion

In previous studies, our research group has already described specific details regarding the translational benefits of the porcine model^2,27,32,33. Generally, reducing the stress level of the animal and unnecessary pain should be an integral part of any study protocol and is paramount for generating reliably reproducible data. Therefore, awake endoscopically guided intubation of the pig with an expected difficult airway is not an option.

It must be pointed out that inducing and maintaining anesthesia in large animal models should only be performed by specially trained personnel or under their direct surveillance. Failure to follow this rule when planning and conducting such experiments may result in relevant injury, pain, stress, anxiety, or death to the animal. Correct positioning of the pig is required to ensure sufficient ventilation, adequate laryngoscopy, and successful intubation. The supine position facilitates easy access to the presented airway management protocol and allows subsequent instrumentation, if necessary, without repositioning the animal⁸.

Even though multiple intubation attempts need to be avoided, it is crucial to resume mask ventilation in the event of a failed intubation attempt. Stopping the intubation attempt is recommended when the oxygen saturation decreases below 93%. Preoxygenation via mask ventilation must be performed as described above to provide a sufficient oxygen reserve.

To enable the endotracheal tube to be advanced as gently as possible past the glottic opening, an excessive caliber jump between the endoscope and the tube must be avoided. Otherwise, there is a higher risk of getting caught on the large arytenoid cartilages⁸. Flexible intubation endoscope-assisted endotracheal intubation takes significantly longer but has a higher first-attempt success rate. The authors attribute the lack of statistical significance of the success rate at the first intubation attempt to the small number of cases. According to the authors' experience, false intubations are a common risk, in particular if non-anaesthesiologists perform the intubation in training (e.g. doctoral students). Esophageal intubation, which occurred once in the study collective presented here, was possible because the endotracheal tube completely covered the glottis view under direct laryngoscopy due to the relative narrowness of the airways after insertion into the field of vision. In both initially unsuccessful attempts, the intubator was able to create better intubation conditions by repositioning the laryngoscope.

The increased duration had no clinical significance in this cohort. At no time was the termination criterion-a saturation of less than 93%-reached. This is shown in the results because a procedure change was unnecessary at any time. Prior adequate mask ventilation is a critical step to allow sufficient time for fiberoptic endotracheal tube placement to avoid rapid desaturation³⁴. These results are consistent with previous studies comparing conventional intubation and endoscopically assisted intubations with inexperienced providers³⁵. We attribute the prolonged duration of fiberoptic intubation to the fact that one must first reorient again after insertion, whereas with conventional intubation, one retains a view of the glottis. It is also important to avoid contact with the mucosa with the flexible intubation endoscope during advancement. This requires occasional corrective maneuvers. Last but not least, after successful placement, retraction of the relatively long endoscope is required, which increases the time to CO₂ detection slightly.

The limitation of the presented results is that the participants conducting the study were anesthesiologists with a high level of airway expertise. For the representative results, we chose this study collective as investigators to prevent confounding variables through learning effects³⁶. More than 50 successful endotracheal intubations are required in humans to achieve a success rate of over 90%³⁷. These numbers are regularly impossible to accomplish for non-anaesthesiologists.

Compared to humans, pigs are likely to have a difficult airway^7,8,9. An even higher failure rate than in these results could be expected for non-anaesthesiologists. Compared to the learning curve for endotracheal intubation in humans, the learnability for flexible endoscopic intubation in pigs seems more accessible³⁵. It also has the advantage, compared to conventional laryngoscopy, that a supervisor can immediately recognize the failure of intubation as long as a video monitor is used. Therefore, it is recommended to use a high-resolution monitor connected to the flexible intubation endoscope, especially when using this technique for the first time. This makes supervision much easier and increases the learning effect for the person carrying it out since the supervisor can moderate the technique without taking over the task themselves. In the case of esophageal intubation, the most common complication¹², the problem often only becomes apparent after ventilation of the stomach via a missing capnography curve because auscultation can be falsely positive³⁸. A bloated stomach, in turn, has the disadvantage in humans that the functional residual capacity is reduced as a result, and subsequent intubation attempts can lead to a faster drop in saturation³⁹.

In the authors' experience, adequate mask ventilation is easily feasible in pigs. However, the rate of adverse events increases significantly after multiple failed attempts¹⁶, and also the endotracheal intubation itself becomes increasingly difficult after several attempts⁴⁰. Unlike in humans, alternative airway management using extraglottic airway devices or reverting to spontaneous breathing¹⁵ is not reasonable depending on the study design. Therefore, the lowest number of endotracheal intubation attempts to secure the airway should always be aimed for.

In contrast to the rather difficult learnability considering conventional endotracheal intubation, endotracheal intubation using a flexible intubation endoscope is wrongly regarded as difficult to learn⁴¹. To the best of the authors' knowledge, the learning curve for endotracheal intubation using a flexible intubation endoscope with the assistance of a laryngoscope in anesthetized patients has never been systematically investigated. Johnson et al.⁴² showed in systematic research that 10 awake endoscopically guided endotracheal intubations are sufficient to perform a safe, satisfactory intubation endoscopy in humans. However, this applies to awake patients breathing spontaneously, who bring their own levels of difficulty (adequate sedation, the pronounced urge to cough, tumorous changes in the upper respiratory tract, etc.). Cook et al.³⁶ came to a similar conclusion. In the absence of these aggravating circumstances, an even steeper learning curve is anticipated in anesthetized pigs without other relevant airway pathologies. The learning curve in humans flattens out noticeably from the fifth intubation (Cook et al.³⁶, Johnson et al.⁴²). This is a much steeper learning curve than with conventional intubation.

Ruemmler et al.³⁵ were able to show that endoscopically assisted endotracheal intubation is a procedure that is relatively easy to perform for guided beginners after a short introduction. The novices were even faster at endoscopically guided endotracheal intubations than the anesthesiologists in the study presented here. The novices managed to secure the airway independently in all cases, whereas they needed help in 13% of the cases with conventional endotracheal intubation. The flexible endoscope-assisted endotracheal intubation thus represents a safe alternative to conventional endotracheal intubation that is significantly less invasive than, for example, transcutaneous tracheotomy with spontaneous breathing, which was presented in previous studies⁴³. Since the possibilities of adequate oxygen application under spontaneous breathing are low due to limited compliance in pigs, the authors of this report believe that endoscopically assisted endotracheal intubation is the safest variant of alternative airway management in pigs if an endotracheal tube is required. While not every research group might have access to flexible intubation endoscopes or the ability to use them, those that do could provide more animal safety. The economic challenges of acquiring single-use flexible intubation endoscopes, for example, are usually outweighed by the prevention of animal losses during an ongoing trial and the potential to reuse them during multiple trials.

This experimental protocol provides a standardized procedure for endoscopically assisted endotracheal intubation in pigs. This setting enables safe airway management for various experiments that require endotracheal intubation. This can help to reduce animal suffering and the likelihood of unnecessary losses.

Materials

Name	Company	Catalog Number	Comments
Ambu aScope Regular	Ambu GmbH, Medizinprodukte, Bad Nauheim, Germany		Disposable fiber optic outer diameter 5 mm
Ambu aView Monitor	Ambu GmbH, Medizinprodukte, Bad Nauheim, Germany		monitor
Atracurium Hikma 50 mg/5mL	Hikma Pharma GmbH, Martinsried		atracurium
Azaperone (Stresnil) 40mg/mL	Lilly Deutschland GmbH, Bad Homburg, Germany		azaperone
BD Discardit II Spritze 2, 5, 10, 20 mL	Becton Dickinson S.A. Carretera, Mequinenza Fraga, Spain		syringe
BD Luer Connecta	Becton Dickinson Infusion Therapy, AB Helsingborg, Schweden		3-way-stopcock
BD Microlance 3 20 G	Becton Dickinson S.A. Carretera, Mequinenza Fraga, Spain		cannula
Curafix i.v. classics	Lohmann & Rauscher International GmbH & Co. KG, Rengsdorf, Germany		Cannula retention dressing
Engström Carestation	GE Heathcare, Madison USA		ventilator
Fentanyl-Janssen 0.05 mg/mL	Janssen-Cilag GmbH, Neuss		fentanyl
Führungsstab, Durchmesser 4.3	Rüsch		endotracheal tube introducer
IBM SPSS Statistics for Windows, Version 20	IBM SPSS Statistics for Windows, Version 20.0. Armonk, NY: IBM Corp.)		Statistical software
Incetomat-line 150 cm	Fresenius, Kabi Deutschland, GmbH		perfusor line
Intrafix Primeline	B. Braun Melsungen AG, Melsungen, Germany		Infusion line
JOZA Einmal Nitril Untersuchungshandschuhe	JOZA, München, Germany		disposable gloves
Laryngoscope, 45.48.50, KL 2000	Medicon		Laryngoscope handle
Littmann Classic III Stethoscope	3M Deutschland GmbH, Neuss, Germany		stethoscope
Luer Lock	B.Braun Melsungen AG, Germany
Maimed Vlieskompresse	Maimed GmbH, Neuenkirchen, Germany		Fleece compress to fix the tongue
Masimo LNCS Adtx SpO2 sensor	Masimo Corporation Irvine, Ca 92618 USA		saturation clip for the tail
Masimo LNCS TC-I SpO2 ear clip sensor	Masimo Corporation Irvine, Ca 92618 USA		Saturation clip for the ear
Masimo Radical 7	Masimo Corporation Irvine, Ca 92618 USA		periphereal oxygen saturation
Midazolam 15 mg/3 mL	Hameln Pharma GmbH, Hameln, Germany		midazolam
Midmark Canine Mask Small Plastic with Diaphragm FRSCM-0005	Midmark Corp., Dayton, Ohio, USA		dog ventilation mask
Octeniderm farblos	Schülke & Mayr GmbH, Nordenstedt, Germany		Alcoholic disinfectant
Original Perfusor syringe 50 mL	B.Braun Melsungen AG, Germany		perfusor syringe
Perfusor FM Braun	B.Braun Melsungen AG, Germany		syringe pump
Propofol 2% 20 mg/mL (50 mL flasks)	Fresenius, Kabi Deutschland, GmbH		propofol
RÜSCH Führungsstab für Endotrachealtubus (ID 5.6 mm)	Teleflex Medical Sdn. Bhd, Malaysia		PVC coated tube guiding wire
Rüschelit Super Safety Clear >ID 6/6.5 /7.0 mm	Teleflex Medical Sdn. Bhd, Malaysia		endotracheal tube
Stainless Macintosh Größe 4	Welch Allyn69604		blade for laryngoscope
Sterofundin	B.Braun Melsungen AG, Melsungen, Germany		Balanced electrolyte solution
Ultrastop Antibeschlagmittel bottle with dropper 25 mL	Sigmapharm Arzneimittel GmbH, Wien, Austria		Antifog agent
Vasofix Safety 22 G-16 G	B.Braun Melsungen AG, Germany		venous catheter
VBM Cuff Manometer	VBM Medizintechnik GmbH, Sulz a.N., Germany		cuff pressure gauge
Zelette	Lohmann & Rauscher International GmbH & Co. KG, Rengsdorf, Germany		Tissue swab