|HOW I DO IT
|Year : 2018 | Volume
| Issue : 2 | Page : 46-49
High-frequency jet ventilation: An invaluable tool for anesthesia in microlaryngoscopy with carbon dioxide laser
Swapna Prasad Naik
Department of Anaesthesiology, Deenanath Mangeshkar Hospital and Research Centre, Pune, Maharashtra, India
|Date of Web Publication||24-Jul-2019|
Dr. Swapna Prasad Naik
Department of Anaesthesiology, Deenanath Mangeshkar Hospital and Research Centre, Pune, Maharashtra
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Airway management in laryngeal surgeries is a challenge for an anesthesiologist due to sharing of airway with a surgeon. The airway is often compromised with potential for perioperative worsening. Use of carbon dioxide (CO2) laser further narrows the choice of airway device as conventional endotracheal tubes are combustible by CO2 laser. High-frequency jet ventilator is an invaluable tool in anesthetic armamentarium. Apart from laser safety, it offers a nearly tubeless field for the surgeon to excise airway lesions. Careful patient selection, total intravenous anesthesia, and judicious use of anesthetic and vasoactive agents to minimize pressor response are the factors contributing to successful outcome.
Keywords: Anesthesia for microlaryngeal surgery, carbon dioxide laser, high-frequency jet ventilator
|How to cite this article:|
Naik SP. High-frequency jet ventilation: An invaluable tool for anesthesia in microlaryngoscopy with carbon dioxide laser. J Laryngol Voice 2018;8:46-9
| Introduction|| |
Anesthesia for laryngeal pathologies has always been challenging as there is sharing of airway between a surgeon and an anesthesiologist. Furthermore, the airway is many a times compromised one. Nowadays, carbon dioxide (CO2) laser is commonly used to excise laryngeal lesions, such as papillomas, benign cysts, polyps, and vocal cord malignancies; the advantages being greater precision, better hemostasis, and least collateral tissue damage. The presence of CO2 laser, however, precludes the use of conventional endotracheal tubes and also exposes a patient to a potential risk of airway fires. The commonly used endotracheal tubes such as red rubber and polyvinyl chloride burn readily when CO2 is used and can cause airway fires.,, Wrapping up the tubes with metallic tapes, apneic oxygenation, spontaneous respiration, high-pressure manual jet ventilation, and apnea and intermittent ventilation are a few modalities of ventilation opted by anesthesiologists, but they come with their own shortcomings.,,,
It was proposed by Norton in 1978 that metal endotracheal tubes are the safest option for securing airway in the presence of CO2 laser for microlaryngeal surgery. Accordingly, many metal tubes such as stainless steel Laser-Flex (Mallinckrodt), Oswal–Hunton laser shield (Medtronic Xomed), and Rusch Kemen (Latex tube with double cuff) were devised and are being used. Although they ensure airway safety in the presence of CO2 laser, they compromise surgical access, especially in posterior lesions and lesions with subglottic extension.
Introduction of high-frequency jet ventilation (HFJV) in 1970 offered a new modality to secure airway in the laryngology procedures. HFJV is characterized by delivery of small tidal volumes (1–2 ml/kg) from a high-pressure jet at supraphysiological frequencies (1–10 Hz) followed by passive expiration. Although initially designed for ventilation in patients with ARDS, it became a popular mode of ventilation in laryngeal surgery after 1980 when CO2 laser became indispensable.
| Equipment|| |
The HFJV machine we use is monsoon-type jet ventilator (Acutronic Medical Systems Limited AG, Switzerland) [Figure 1]. It is an electrically powered, solenoid cycled, automated jet ventilator. It is driven by compressed air and oxygen provided by central pipeline supply at 4 atmospheric pressure. The gas passes through a pressure regulator and reaches electromagnetic solenoid valves, which get activated to give a discrete pulse of jet. The volume of each pulse is determined by settings, such as respiratory frequency, driving pressure (DP), and inspiratory time (IT). The ventilator output is not influenced by patient factors such as airway resistance or lung compliance. The safety feature provided to minimize inadvertent barotrauma is an airway pressure alarm and an automated cut-off when airway pressure exceeds the set limit. The set limit is called pause pressure and is usually set at 20 bars. It represents the mean airway pressure and is measured at the tip of the jet cannula.
The HFJV cannula we use is laser jet (Acutronic Medical Systems AG, Switzerland) made up of nonflammable fluoroplastic laser-resistant material [Figure 2]. It has an external diameter of 3.4 mm and has two lumens. One lumen is for jet delivery which is at the tip of the cannula. The other lumen is for monitoring ventilation delivered by jet displayed on machine and has an opening on the lateral wall of cannula 3 cm proximal to jet tip. A flexible metal stylet is used to facilitate intubation. The cannula is placed in subglottis in such a way that both openings of both lumens are well beyond vocal cords but taking care that it lies in the trachea. As the cannula rests between arytenoids, it offers a nearly tubeless field. Vocal cord movement is minimal due to small tidal volume, whereas high respiratory rate ensures ventilation.,
HFJV is our first choice in all phonosurgeries. These lesions usually do not have significant narrowing of airway, which, if present, would lead to air trapping due to inadequate expiration. Having said so, HFJV has been used to secure airway in cases of laryngeal papillomatosis with airway compromise. It is used in these cases as airway diameter is so narrowed that putting in an endotracheal tube is either impossible or would dislodge papillomas in distal airway. Here, HFJV is used as a stop-gap tool till the surgeon gets an opportunity to widen airway to accommodate endotracheal tube.
Preoperative video-laryngoscopy and discussion with a surgeon are mandatory. HFJV is relatively contraindicated in patients with pulmonary pathologies, such as chronic obstructive pulmonary disease and interstitial lung disease. Morbid obesity is another condition where HFJV might not be effective for maintaining ventilation, and a laser-safe endotracheal tube might replace it during the procedure to prevent hypoxia.
Preoperative evaluation and premedication
Apart from detailed history and routine hematology, X-ray chest is done for all the patients to rule out other lesions, such as emphysema and tuberculosis. Patients are nebulized preoperatively with lignocaine (topical 4%) and steroid (budesonide).
Anesthetic concerns in microlaryngeal surgeries, where HFJV is being used, include optimal ventilation with the lowest acceptable FiO2 to minimize airway fires and maintenance of unobstructed airway to prevent air trapping. Attenuating pressor response to suspension laryngoscopy and minimizing postoperative edema are other concerns. Inability to monitor end-tidal CO2 (EtCO2) is a limitation, and the anesthesiologist has to rely on clinical signs for effective CO2 washout.
Mainstay of anesthesia in the presence of HFJV is intravenous infusion of propofol (total intravenous anesthesia) as anesthetic gases cannot be delivered through the jet ventilator. Patients are anesthetized with midazolam (0.02-0.04 mg/kg), fentanyl (0.002-0.003 mg/kg), propofol (2-3 mg/kg) as induction agent and atracurium (0.35-0.5 mg/kg) as muscle relaxant. Direct laryngoscopy is done and HFJV cannula is inserted placing the lateral wall aperture beyond vocal cords [Figure 3] and [Figure 4]. Endobronchial placement is ruled out by confirming bilateral equal air entry as there are no markings on HFJV cannula.
|Figure 3: High-frequency jet ventilation in place while carbon dioxide laser being used to excise vocal cord cyst|
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|Figure 4: Suspension microlaryngoscope with high-frequency jet ventilation in place (outside view)|
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Insertion and maintenance of suspension laryngoscope elicit pressor response with hypertension and tachycardia, which is detrimental in patients with compromised cardiac function. Anticipating this, depth of anesthesia is increased by giving boluses of fentanyl (20–30 mcg) and propofol (25–30 mg). Vasoactive agents such as beta-blockers (metoprolol 1 mg, labetalol 2–5 mg) or alpha agonists such as clonidine (0.001-0.0015 mg/kg 15 minutes before induction) are also used to attenuate the pressor response. Sustained pressor response is anticipated in cordectomy as it takes longer duration and an infusion of alpha agonist dexmedetomidine (0.4–0.7 mcg/kg/h) is started preoperatively and is continued throughout as it offers stable hemodynamics.
Jet ventilator is set by adjusting DP at 1.1–1.5 bar, frequency 100–120/min, and IT 40%. FiO2 is set at 1 initially which is reduced to 0.4 when CO2 laser is being used to minimize oxygen-rich environment, a safety precaution against airway fire. Adequacy of ventilation is assessed by delivered tidal volume, minute volume, and airway pressure displayed on HFJV machine. Standard monitoring with pulse oximetry (SPO2), noninvasive blood pressure, and electrocardiography with ST analysis is continued intraoperatively. Possibility of desaturation, either transient or sustained, is always borne in mind and alternative airway device is kept ready. Usually, the lowest acceptable SPO2 is 90% and increasing FiO2 improves saturation. If it does not, HFJV cannula is replaced by Laser-Flex tube and positive pressure ventilation installed.
Safety measures for the prevention of laser fire include covering the patient with wet drapes and minimizing FiO2. Constant vigilance is maintained by the surgical team to keep the airway patent and prevent any combustion. At the end of the surgery, intravenous infusions are discontinued. Vocal cords are sprayed with topical 10% lignocaine to minimize throat irritation. HFJV is stopped and laryngeal mask (LMA) of appropriate size is inserted. This is to wash out CO2 as well as to maintain airway till the patient is reversed with glycopyrrolate 0.02 mg/kg and neostigmine 0.05 mg/kg, given after confirming spontaneous breathing attempts. LMA is removed after the patient regains consciousness and airway reflexes. In the recovery room, patients are nebulized with steroid (budesonide) and adrenaline (1:200,000) to prevent postoperative edema, more likely event after cordectomy and papilloma excision.
Most of the patients tolerate HFJV well with very low incidence of barotrauma (pneumothorax in one patient in 10 years). Desaturation (up to 90%) has been observed in a few patients initially but could be rectified by increasing DP and frequency. Replacing HFJV with another airway device due to persistent low saturation (<90%) had to be done in a small set of patients. At the end of the surgery, when LMA is inserted, EtCO2 readings observed are in the range of 45–50 mmHg in most of the patients which can be reduced to 40 mmHg over 10 min. We have used HFJV in the pediatric age group also keeping low DP (0.6–0.8 bar) without any untoward events.
| Conclusion|| |
HFJV is a ventilating modality in the anesthetic armamentarium which can be safely used in the presence of CO2 laser for microlaryngeal surgery.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]