Brief Report

Percutaneous transtracheal emergency ventilation during respiratory arrest: comparison of the oxygen flow modulator with a hand-triggered emergency jet injector in an animal model^B

Yahya Yildiz MD^c, Niels-Peter Preussler MD^a, Torsten Schreiber MD^a, Lars Hueter MD^a, Elke Gaser MD^a, Harald Schubert VD^b,

Reiner Gottschall MD^a, Konrad Schwarzkopf MD^a,*

^aDepartment of Anesthesiology and Intensive Care Medicine, University of Jena, 07740 Jena, Germany

^bInstitute for Experimental Animals, University of Jena, 07740 Jena, Germany ^cDepartment of Anesthesiology and Reanimation, Siyami Ersek Thoracic and Cardiovascular Surgery Training and Research Hospital, 34840 Istanbul, Turkey

Received 21 July 2005; accepted 16 January 2006

Abstract The oxygen flow modulator is a device for percutaneous transtracheal emergency ventilation. Simulating a respiratory arrest situation, we studied the effects of this device in comparison with a hand- triggered emergency jet injector during pulmonary resuscitation. Nine pigs were anesthetized and mechanically ventilated. After surgical exposure, an emergency transtracheal airway catheter was inserted into the trachea. Ventilation was stopped until SpO₂ was below 70%. Each animal was subsequently randomly ventilated via the transtracheal airway catheter with either the hand-triggered emergency jet injector or the oxygen flow modulator. After 10 minutes, respiratory and hemodynamic parameters were recorded. Ventilation was stopped again until SpO₂ reached 70%, and the animal was ventilated with the second device. With both devices, pulmonary resuscitation was successful. Whereas PaO₂ differed not significantly between the two devices, PaCO₂ was lower during percutaneous transtracheal ventilation with the hand-triggered emergency jet injector.

D 2006

^B The study was presented in part at the 13th Annual Meeting of the European Society of Anaesthesiologists 2005, Vienna.

* Corresponding author. Department of Anesthesiology and Intensive Care Medicine, University Hospital, 07740 Jena, Germany. Tel.: +49 3641 9323279; fax: +49 3641 9323122.

E-mail address: [email protected] (K. Schwarzkopf).

Introduction

The management of the difficult airway especially in the preclinical situation is a demanding task. Percutaneous transtracheal jet ventilation (PTJV) via the Cricothyroid membrane is a way to oxygenate patients in the bcannot intubate, cannot ventilateQ situation [1]. The oxygen flow modulator is a new device for emergency PTJV if intubation

0735-6757/$ – see front matter D 2006 doi:10.1016/j.ajem.2006.01.014

Fig. 1 The Enk oxygen flow modulator (Cook). The openings for adjusting flow are located at the opposite sides of the tube.

and mask ventilation fails [2]. The device consists of a noncompliant tube with a distal Luer lock connector and 5 openings located at opposite sides for adjusting flow (Fig. 1). The oxygen flow modulator can be connected between a transcricothyroidal needle and an oxygen supply–such as the sideport of a transportable emergency respirator or a wall outlet in the ED–capable of delivering oxygen at a flow rate of 15 Ld min^–1. The oxygen flow to the lung can be adjusted depending on how many of the openings are occluded at will by the fingers of the operator placed over the holes of the tube. The openings reduce the risk of barotrauma because a complete exposure to the pressure to which the system is set can only occur if all 5 openings are closed. In an earlier study, the efficacy of the device in Ventilation and oxygenation during PTJV was demonstrated in animals, which were normoventilated at the beginning of PTJV [3]. The aim of the present study is to compare the efficacy of the oxygen flow modulator with a hand-triggered emergency jet injector with regard to oxygenation and ventilation in an open-circuit animal model of hypoxemia simulating pulmonary resuscitation by emergency PTJV after respiratory arrest (Fig. 2).

Methods

The study design was approved by the local Animal Protection Committee as well as by the governmental Animal Care Office (Landesverwaltungsamt Thueringen, Germany). After overnight fasting with free access to water, 9 pigs (31 F 3 kg) were premedicated with ketamine (500 mg, intramus- cular [IM]) and atropine (0.5 mg, IM) to allow placement of an intravenous (IV) line and to initiate continuous electro- cardiogram and Pulse oximetry monitoring. Anesthesia was induced with propofol (2-3 mg/kg, IV); rocuronium (0.9 mg/kg, IV) was used to facilitate endotracheal intubation with a 6.5- to 8.0-mm tracheal tube. pressure-controlled ventilation was started and adjusted to maintain end-tidal

CO₂ (etCO₂) tension at approximately 31-36 mm Hg. FiO₂ was set at 1.0, positive end-expiratory pressure at 5 cm H₂O. Heart rate and oxygen saturation via pulse oximetry positioned on the animal’s tail were measured (all monitoring by Datex, Helsinki, Finland). Anesthesia was maintained with continuous infusion of propofol (15-30 mgd kg^–1d h^–1), remifentanil (10-20 Agd kg^–1d h^–1), and pancuronium (0.3- 0.5 mgd kg^–1d h^–1). For continuous monitoring of blood pressure and intermittent sampling of arterial blood for blood gas analysis (Radiometer Copenhagen, Copenhagen, Den- mark), a 5 F percutaneous sheath introducer set (Arrow, Reading, USA) was inserted in the left femoral artery. To measure pulmonary artery pressure and cardiac output, we advanced a flow-directed thermodilution catheter (Baxter, Irvine, USA) into the pulmonary artery through an 8.5 F introducer (Arrow), positioned in the right external jugular vein. In addition, a central venous catheter was placed in the Right internal jugular vein. Throughout the experiment, the animals were kept in the supine position. Body temperature was maintained by covering the animals with a Warmtouch blanket and was continuously monitored by the sensor in the tip of the pulmonary artery catheter. The animals received 500 mL of hydroxyethylstarch during the instrumentation period, which was continued with body-warm balanced electrolyte solutions at a rate of 10 mL kg^–1d h^–1 during the study period.

A 15-G, 7.5-cm emergency transtracheal airway catheter (Cook, Bloomington, USA) was inserted into the trachea cau- dad to the tracheal tube after surgical exposure of the trachea.

Fig. 2 The hand-triggered emergency jet injector (Manujet III, VBM Medizintechnik).

The correct intraluminal position of the airway catheter was verified in all animals by fiberoptic bronchoscopy.

Table 2 Hemodynamic parameters at the end of each 10-minute phase of ventilation after respiratory arrest using the hand-triggered emergency jet injector or the oxygen flow modulator

Jet ventilation Oxygen flow P

After preparation, anesthesia was maintained with continuous infusion of propofol (15-30 mgd kg^–1d h^–1) and pancuronium (0.3-0.5 mgd kg^–1d h^–1) without changing the dosage throughout the experiment, whereas infusion of remifentanil was stopped.

	(mean F SD)	modulator (mean F SD)
Heart rate	95 F 12	90 F 17	ns
(beats/min)
Mean arterial	84 F 22	84 F 27	ns
pressure (mm Hg)
Mean pulmonary	25 F 5	27 F 7	ns
arterial pressure
(mm Hg)
Central venous	9 F 2	10 F 3	ns
pressure (mm Hg)
Cardiac output (L min–1)	3.5 F 0.8	3.2 F 0.6	ns

After recording stable cardiorespiratory parameters for at least 30 minutes, the tracheal tube was disconnected from the ventilator simulating a situation, where expiration through the glottic aperture is possible. Apnea was main- tained until SpO₂ reached 70%. An arterial blood gas analysis was obtained to verify the arterial deoxygenation at that time. Then pulmonary resuscitation was started.

Each animal was ventilated in randomized order via the transtracheal airway catheter with the following two methods for 10 minutes each:

• 1. Jet ventilation using a hand-triggered emergency jet injector (Manujet III, VBM Medizintechnik, Sulz a.N., Germany) connected to the hospital piped oxy- gen supply (100% oxygen) with an inspiratory/ expiratory ratio of approximately 1:1 at a respiratory rate of 60/min. The driving pressure was set at 1.5 bar.
  2. Ventilation via the Enk oxygen flow modulator (Cook). The oxygen flow modulator was connected to the hospital oxygen supply (100% oxygen) with an oxygen flow of 15 L min^–1. The operator occluded and deoccluded rhythmically 4 of 5 open- ings of the device at a rate of 60/min, with an inspiratory/expiratory ratio of approximately 1:1.

During an interval of 10 minutes between the two phases of the experiment, we maintained pressure-controlled ventilation adjusted to maintain etCO₂ at 31-36 mm Hg.

After each phase of the experiment, respiratory and hemodynamic parameters were recorded (mean arterial pressure, heart rate, mean Pulmonary arterial pressure, etCO₂, oxygen saturation via pulse oximetry), and arterial blood gas samples were taken.

At the end of the experiment, the pigs were killed with a lethal dose of potassium chloride. Then, a midline sternot- omy was performed, and the heart and pericardium were

Table 1 Postapneic blood gas analysis and pulse oximetry

data collected before the start of ventilation with the oxygen flow modulator or the hand-triggered emergency jet injector

Before jet

ventilation (mean F SD)

Before oxygen

flow modulator (mean F SD)

P

carefully mobilized from the inner thoracic wall. A sternal retractor was placed to achieve exposure of the lungs. Pneumothorax was ruled out by confirming expanded lungs adjacent to the intact pleura parietalis.

Statistical analyses were done with the Statistical Package for the Social Sciences (SPSS, Vs. 12.0, Chicago, Ill). The Wilcoxon Signed Rank Test was used to compare data. A P value b .05 was considered statistically significant.

Results

Postapneic baseline measurements of PaO₂, PaCO₂, pH, SaO₂, and SpO₂ before the start of emergency ventilation did not differ between the groups (Table 1). Blood pressure, central venous pressure, and cardiac performance were stable and comparable after the use of both emergency airway salvage techniques (Table 2). PaO₂ was comparable between the two devices, whereas PaCO₂ was lower during the hand-triggered jet ventilation (Table 3). Hypoxemia was corrected (ie, SpO₂ N 90%) within 3 minutes in all animals without difference between the two devices.

Table 3 Blood gas analysis and pulse oximetry data at the

end of each 10-minute phase

Jet ventilation (mean F SD)

PaO₂ (mm Hg) 229 F 56

PaCO₂ (mm Hg) 26 F 7

pH 7.66 F 0.11

SaO₂ (%) 99.7 F 0.2

SpO₂ (%) 100 F 1

Oxygen flow

modulator (mean F SD)

298 F 112

50 F 14

7.41 F 0.12

99.7 F 0.2

99 F 1

P

ns

b.01 b.01

ns ns

Oxygen flow during the use of the oxygen flow modulator was 15 L

min^–1, and the driving pressure during jet ventilation was 1.5 bar. Respiratory rate was 60/min, and inspiration to expiration ratio was approximately 1:1 for both devices.

PaO2 (mm Hg)	41 F 9	41 F 11	ns
PaCO2 (mm Hg)	60 F 7	59 F 13	ns
pH	7.34 F 0.03	7.35 F 0.07	ns
SaO2 (%)	66 F 7	65 F 10	ns
SpO2 (%)	70 F 1	69 F 2	ns

The inspection of the thoracic organs at the end of the experiment demonstrated no pneumothorax.

Discussion

The most important finding of our pilot study was that respiratory arrest was successfully and quickly treated in all animals with both the oxygen flow modulator and the hand- triggered emergency jet injector.

Although percutaneous transtracheal emergency ventila- tion is not at all a new technique for the management of life- threatening cannot intubate, cannot ventilate scenarios, controversy still exists regarding the most efficacious equipment to use [4].

Several studies and case reports describe self-made equipment for percutaneous transtracheal oxygenation or ventilation [5-7]. In 2003, Preussler et al [3] compared the hand-triggered emergency jet injector with the oxygen flow modulator in animals which were normoventilated at the beginning of the percutaneous transtracheal ventilation. In contrast to many self-made devices, both the oxygen flow modulator and the hand-triggered emergency jet injector provided not only adequate oxygenation but also adequate ventilation during the whole study period [3,8].

In the present study, we could demonstrate that both devices can also be used with success to treat severe hypoxemia and hypercarbia after respiratory arrest.

We found that PaCO₂ was lower during jet ventilation as compared to the oxygen flow modulator, which indicates that hyperventilation occurred with the chosen driving pressure (1.5 bar). We used a driving pressure of 1.5 bar in this study because this pressure is within the manufac- turer’s settings recommended for children and because with this approach, normocarbia was achieved in an earlier study in pigs with a lower body weight (21 F 1 vs 31 F 3 kg in the present study), simulating a situation where some expiration through the glottic aperture was possible [3]. In the present model with an unobstructed endotracheal tube in place, improved expiration might have contributed to the finding of hyperventilation in conjunction with the driving pressure of 1.5 bar. Most likely, hyperventilation could be avoided by adjusting the ventilation strategy with the hand- triggered emergency jet injector (eg, applying a lower respiratory rate or a reduced driving pressure), thereby creat- ing results comparable with the oxygen flow modulator.

The maintaining of an unobstructed endotracheal tube in place did not simulate an upper airway obstruction. This has to be recognized as an important limitation of the study because limited expiration should reduce the effectiveness of jet ventilation and increase barotrauma risk.

A further limitation of our study is the modest body weight of the animals (31 F 3 kg). We cannot extrapolate our results to adult human subjects because different settings regarding driving pressure and respiratory rate may be needed in this population to achieve adequate oxygenation

and ventilation. In addition, the absence of concomitant pulmonary diseases in our animals limits the transfer to clinical scenarios.

We decided to study a ventilation period of 10 minutes with both devices, because within this period, advanced equipment for difficult airway management (eg, bronchos- copy) should be available during an inhospital difficult airway scenario. In our experience, the use of the oxygen flow modulator over such a period is already quite uncomfortable for the operator.

In our study, the inspection of the respiratory system at the end of the experiment did not demonstrate any complications related to the airway catheter placement or the used ventilation techniques. However, the airway catheter was inserted under stable conditions and after surgical exposure of the trachea, a situation significant- ly different from an emergency situation in humans. In addition, as already discussed, the expiration was not limited, reducing the barotrauma risk. During the emergency insertion of these devices in patients, perforation of the posterior wall of the trachea may occur and misplacement of the catheter may cause mediastinal or subcutaneous emphysema, hemoptysis, esophageal perforation, or injury to carotid or jugular vessels [9-11]. It is strongly recom- mended that endotracheal intubation or tracheostomy should be performed in these patients as soon as possible.

In conclusion, in our animal study, the oxygen flow modulator was an Effective airway salvage method after respiratory arrest. Within the limitations of this pilot study, this simple device produced adequate oxygenation and ventilation. According to our study design, we are unable to decide weather the oxygen flow modulator is superior to the hand-triggered emergency jet injector. Further studies should also simulate an upper airway occlusion to rule out the limitations of our experiment.

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