Spontaneous for Suspected Airway Foreign Body Removal

Robert S. Holzman MD, FAAP

I choose a spontaneous breathing technique for theoretical and practical reasons.

Ventilation Theoretical

1. More effective alveolar ventilation: When difficulty with positive pressure ventilation occurs, anesthesiologists typically exert more pressure. For the patient with airway compromise, this results in more turbulence in the upper airways and less effective air exchange downstream because the Fanning equation (turbulent flow) supersedes the Hagen-Poiseuille Equation (laminar flow). To enhance flow, the pressure drop (DP) proximal and distal to the obstruction must be minimized. This is best achieved with spontaneous breathing. 2. Better ventilation/perfusion matching: lungs of equal compliance and resistance increase their volumes equally when mouth pressure is increased. If the compliances of the two lungs are identical but the resistance of one is twice that of the other, the time constant is also twice normal and the affected lung will fill more slowly, although the volume increase in both will be the same IF inflation is prolonged indefinitely. While controlled ventilation does not greatly alter gas exchange (V/Q matching, VD/VT and shunt) in healthy, young patients, this is not true for patients with inequalities in the distribution of ventilation because of asymmetrical resistances between lung units.

Practical

1. Better ventilation during bronchoscopy with window closed: with the proximal opening sealed, gas delivered into the lumen exits at the distal end. A spontaneously breathing patient receives fresh gas through the lumen of the bronchoscope as well as by entrainment around the bronchoscope, and can exhale the same way. 2. Better ventilation during bronchoscopy with window open: controlled ventilation through the side port of a ventilating bronchoscope when the window is open is impossible because gases are exhausted into the room rather than delivered to the patient. Opening the window does not impair spontaneous ventilation. 3. Better ventilation with bronchoscope and telescope in place: Placing a telescope through the eyepiece seals the proximal end and partially occludes the lumen of the ventilating bronchoscope. The spontaneously breathing patient still has entrainment available to augment tidal volume while receiving anesthetic gases; the controlled ventilation patient loses this advantage and in addition (particularly in pediatrics) requires a much higher peak inspiratory pressure against a far greater resistance. Furthermore, the elastic recoil of the chest wall and lung is insufficient to adequately expel gas against this pressure gradient during the usual expiratory time constant. Air trapping and stacking may easily occur, often confirmed by a tracheal "whoosh" as the bronchoscopist removes the telescope and the trapped gas in the overinflated lung escapes. 4. In case the etiology is a foreign body mimic: not every patient believed to have a foreign body, even if stridor is present, actually has one. If there is any doubt, then spontaneous ventilation should be preserved in order to make a diagnosis. 5. Neuromuscular blockade may worsen the situation by converting a patient with a compromised airway to a patient with no airway. The insertion of a diagnostic instrument may dislodge the obstruction into a life-threatening position before it can be successfully retrieved. Airways enlarge during inspiration and are reduced in size during expiration. Check-valve physiology producing air trapping may be the result. A peanut may be particularly bad in this regard because of the mucosal irritation and edema produced by natural oils. 6. If a foreign body is difficult to grasp: placement of a variety of foreign body forceps may be attempted through the open bronchoscope and expired gases will be exhausted to the room rather than delivered to the patient during controlled ventilation, unless the window is constantly replaced. A deeply anesthetized spontaneously breathing patient will continue to breathe spontaneously throughout the endoscopist's manipulations. 7. If a foreign body is lost during attempted removal: it must be relocated immediately! The endoscopist will inspect the pharynx and then want to re-examine the airway. The anesthesiologist will not know whether the patient is completely obstructed if there is no spontaneous breathing!

There are some (potential) disadvantages:

1. Increased CO2: may also occur with controlled ventilation and paralysis because of prolonged pauses for instrumentation, uneven ventilation with accumulating CO2 in the less well-ventilated lung and possible air-trapping. 2. Hard to GUARANTEE no movement: therefore additional airway trauma may occur; expert assessment of anesthetic depth is critical. 3. Prolonged emergence may be a problem since the patient must remain deeply anesthetized until the conclusion of the procedure. 4. Unprotected airway: when the bronchoscope is removed during the procedure, the airway of the deeply anesthetized patient is unprotected. Also true for the patient undergoing controlled ventilation.

Controlled Ventilation for Suspected Airway Foreign Body

Thomas J. Mancuso MD, FAAP

Before discussing the advantages I see for the techniques of controlled ventilation, I will very briefly outline the techniques I have used. After denitrogenation, a RSI is performed with propofol and a rapid acting muscle relaxant and the trachea intubated by the surgeon with the bronchoscope. Anesthesia is maintained with IV propofol +/-remifentanil and muscle relaxation with an infusion or frequent small doses of an intermediate acting muscle relaxant. I prefer a mivacurium infusion. Continue anesthesia and muscle relaxation until the foreign body has been passed through the laryngeal inlet. At the conclusion of the case, an appropriately sized endotracheal tube is placed, the stomach suctioned, anesthesia discontinued and extubation performed using usual criteria.

The advantages of controlled ventilation for this procedure are the following:

1. A RSI type induction allows more rapid control of the airway, lessening the chance of aspiration of gastric contents. 2. Patient immobility. Particularly important while the rigid bronchoscope is in the child's airway and when the bronchoscopist is removing the foreign body from the airway. 3. The possibility of more rapid emergence since NMB can be monitored throughout the procedure, allowing administration of lower doses of IV anesthetic agents than would be need in the absence of NMB.

Important considerations in controlling ventilation

1. Adequate time is needed for exhalation through the relatively high resistance bronchoscopist in order to prevent air trapping and the associated barotrauma. 2. Ventilation must be done in concert with the bronchoscopist. Ventilation when the bronchoscope is open will "ventilate" the room, primarily the bronchoscopist. Ventilation while the telescope is within the bronchoscope will require higher inflating pressures and longer exhalation times (see #1 above) since the lumen of the bronchoscope is compromised by the presence the instrument.

Littman, in Anesthesia and Analgesia, reviewed the anesthetic management of 94 cases of suspected airway foreign bodies with regard to the mode of ventilation. He reported that in 47, controlled ventilation was used while in 44 spontaneous or assisted ventilation was used. In 3 cases the anesthesia record had insufficient information to determine the mode of ventilation. In 16 of the cases the mode of ventilation was changed, all to controlled ventilation from either assisted or spontaneous. The following perioperative adverse events: hypoxia, hypercarbia, bradycardia and 02 requirement in the PACU were found with equal frequency in the different groups. Hypotension was noted in one child who was receiving controlled ventilation. This may have resulted from air trapping, a problem that may occur when inadequate exhalation time is allowed during controlled ventilation as mentioned above.

References From Dr. Mancuso

1. Littman RS, Pnnuri J, Trogan I. Anesthesia for pediatric foreign body removal. Anesth & Analg 2000;91:1389-1391 2. Metrangelo S, Monetti C, Zadra N et al. Eight years experience with foreign body aspiration in children. Journal of Pediatric Surgery 34:8:1229-1231

References From Dr. Holzman

1. Holzman R: Advances in pediatric anesthesia: implications for otolaryngology. Ear Nose Throat J 71:99, 1992

2. Holzman R: Aspiration of a Foreign Body, Crisis Management in Anesthesiology. Edited by Gaba D, Fish K, Hoard S. New York, Churchill Livingstone, 1994, pp 267-9

3. Holzman R: Prevention and treatment of life-threatening pediatric emergencies requiring anesthesia. Seminars in Anesthesia, Perioperative Medicine and Pain 1998; 17: 154-63

4. Holzman R: Anesthesia in the Child and Adolescent, Pediatric Otolaryngology: Principles and Practice Pathways. Edited by Wetmore R, Muntz H, McGill T. New York, Thieme, 2000, pp 31-47

5. Nunn J: Applied Respiratory Physiology, 3rd Edition. London, Butterworths, 1987

6. Woods A: Pediatric Bronchoscopy, Bronchography and Laryngoscopy, Anesthetic Management of Difficult and Routine Pediatric Patients. Edited by Berry F. New York, Churchill Livingstone, 1986, pp 189-250

Commentary Thomas J. Mancuso, MD, FAAP

In this point-counterpoint on the anesthetic management of a toddler with a suspected airway foreign body, I will be both moderator as well as a discussant. My counterpart, Dr. Robert Holzman and I were recently on a panel at one of the local anesthesia review courses and were assigned this very topic as a point-counterpoint discussion. Since the presentation was well received (no vegetables were thrown our way), I thought it worth presenting it to the readership of this newsletter.

During my training, both as a rotating resident at Children's Hospital in Boston and as a fellow in pediatric anesthesia and critical care medicine at the Children's Hospital of Philadelphia, I used the technique of spontaneous ventilation that Dr. Holzman elegantly describes. I became familiar with and then an advocate of controlled ventilation during my 10 years at Egleston Children's Hospital in Atlanta. My Chief there, Dr. James Bland, had trained at The Hospital for Sick Children in Toronto and had learned there the technique of controlled ventilation for airway foreign body removal and made it the standard practice at Egleston. I, as a new staff member, followed suit and found it an excellent technique.

My conclusion, following the discussion with Dr. Holzman and supported by my clinical experience, is that either technique can be used successfully or unsuccessfully. It is important to be aware of both the advantages and especially the pitfalls of the two techniques. One last comment: In cases where the airway is shared, not only is communication between the surgeon and anesthesiologist during the case exquisitely important, but agreement beforehand on the details of management is critical.