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AIRWAY MANAGEMENT PAGE II:

CONTROLLED VENTILATION


Ahmed E. Badr, M.D.



Introduction:

Failure to adequately manage the airway continues to be the most frequent cause of anesthesia related morbidity and mortality. It has been estimated that inability to successfully manage very difficult airways has been responsible for as many as 30% of the deaths totally attributable to anesthesia!


Techniques for Ventilation: Clinicians responsible for the care of seriously ill or injured patients must have a well defined plan for maintaining in each patient a patent airway, and ensuring adequate oxygenation and ventilation. Other techniques for ventilation than endotracheal intubation are:

Mask Ventilation

Oral and Nasopharyngeal Airways

Two Person Mask Ventilation

Esophageal -Tracheal Combitube

Laryngeal Mask Airway

Transtracheal Jet Ventilation

Surgical Airway Access


1. Mask Ventilation (See Fig. 1)


In terms of degree of difficulty, mask ventilation can range from zero to infinite. Zero degree of mask ventilation difficulty means that no external effort and/or internal upper airway device is required to maintain airway patency; that is, mask ventilation is extremely easy and occurs via the natural airway. Next, there are progressive degrees of mask ventilation difficulty. These consist of one person jaw thrust/mask seal, insertion of an oro- or nasopharyngeal airway, one person jaw thrust and insertion of one or both airway(s), and two person jaw thrust/mask seal and both airways. Infinite degree of mask ventilation difficulty means that despite maximal external effort and full use of oro- and nasophryngeal airways, adequate airway patency cannot be maintained; that is, mask ventilation is impossible. In any patient the degree of difficulty with mask ventilation may change with time. It is very important to note that patients with residual respiratory effort should be assisted with mask ventilation rather than controlled until these efforts are naturally or pharmacologically abolished.


2. Esophageal Tracheal Combitube
Description: it is a double - lumen airway which combines the functions of an esophageal obturator airway (EOA) and a conventional endotracheal airway. (see fig. 2)


Theory of use: If the tube passes into the esophagus, the patient can be ventilated through the side holes of the tube and the stomach aspirated through the other tube as needed. If the tube passes into the trachea, the patient can be ventilated through the hole at the end of the tube.


Technique of Insertion: (See Fig. 3) 1. Place the patient in the supine position with the neck in the neutral (not the sniffing) position.

2. With the operator standing to the side of the patient's head (not behind it), the thumb is placed deeply in the patient's mouth; grasp the tongue and the lower jaw between the thumb and index finger and open the mouth fully.

3. Insert the combitube blindly until the printed ring is aligned with the teeth.

4. Inflate line 1 (the pharyngeal balloon, with the blue pilot balloon) with 100 ml of air.

5. Inflate line 2 (the distal balloon, with the white pilot balloon) with 15 ml of air.

6. Ventilate the patient through the longer blue tube. If present, continue ventilating the patient through this tube.

7. If no breath sounds are heard or chest rise seen, ventilate the patient through the shorter clear tube. Listen for breath sounds and chest rise. If present, continue ventilation through this tube.


Applications: The combitube has a wide range of applications and advantages. Those benefitting from its use include physicians working in emergency departments, paramedics, medical staff in the military and physicians in private practice.


Indications: * Limited cervical spine movement (c-spine injuries)

* Patients with massive bleeding or regurgitation.

* Difficult intubation. (See Algorithm)


Contraindications: * Patients under age of 16 years.

* Patients under 150 cms.

* Patients with intact gag reflexes irrespective of their level of consciousness.

* Patients with known esophageal pathology.

* Patients who have ingested caustic substances.


Advantages:

* Blind insertion with relative ease. No extensive skills required. Placement success 100%.

* Effective ventilation in esophageal or tracheal position

* The oropharyngeal balloon effectively prevents aspiration of any oral contents. This balloon, when deflated, allows visualization of the vocal cords if replacement of the tube is required.

* Requires no external fixation as the inflated oropharyngeal balloon anchors it behind the hard palate.

* Suitable for patients with difficult anatomical situations.

* Can suction gastric fluids.


Efficacy and Complications:

All of the studies have shown adequate oxygenation when patients are ventilated with the ETC, and several show significantly higher PaO2 levels in patients in whom the ETC was compared with those who were endotracheally intubated. No complications have been reported; however, use has been limited so far.


3. Laryngeal Mask Airway
History:

The development of the LMA began in 1981, when Dr. Archie Brain, a British Anesthesiologist, suggested that the Goldman Dental mask could be modified so as to be positioned around the laryngeal inlet. Since that time it has undergone several modifications and prototypes until its use was launched in 1988 in Great Britain.


Description:

A ridged tube or shaft that is fused at a 30o angle to a distal elliptical spoon shaped mask with an inflatable rim resembling a miniature face mask.

Sizes: Six sizes available (#1, 2, 2 1/2, 3, 4, and 5) which are scaled-down versions from #5. (see Table)


Technique of Insertion: (See Fig. 4)

* The classical intubating or "sniffing" position is recommended.

* With the patients mouth open, and the distal aperture of the LMA facing anteriorly, the tip of the cuff is firmly and continuously applied against the hard palate.

* The tube is then advanced in one smooth movement until a characteristic resistance is felt as the upper esophageal sphincter is engaged.

* Without holding the tube, the cuff is inflated with 10 - 30 ml of air. The longitudinal black line on the shaft of the tube should be in the midline against the upper lip.

* Success rate of insertion is 90% on first attempt rising to 95 - 98% on second attempt.

* Adequate depth of anesthesia is required whether topical in awake patients or GA in anesthetized patients.

* In pediatrics and difficult cases. Insertion may be done with the aperture facing posteriorly and inferiorly. Then the LMA is turned to the side as it passes the base of the tongue to make 180% as it engages the esophageal sphincter. (see fig.)


Role and Uses:

* The difficult airway. Benumof suggests that the low risk benefit ratio associated with the LMA means that it may be a suitable alternative before trans-tracheal jet ventilation is attempted in the "difficult airway management algorithm". However, familiarity with the LMA should be obtained before attempting to use it in difficult situations.

* In emergencies and cardiopulmonary resuscitation, especially when intubation is difficult for anatomical reasons or for fear of moving the cervical spine and causing neurological damage.

* In most of the elective surgical procedures, including pediatrics

* Very valuable for bronchoscopy


Contraindications:

* Patients at risk of regurgitation, as in full stomach or obstetric patients. The LMA, however, may be life saving even in these situations when the "cannot ventilate, cannot intubate" scenario applies.

* Patients requiring surgeries in prone or jack knife position. Although some authors reported using LMA in these cases without problems.


4. Transtracheal Jet Ventilation


History:

The modern technique of TTJV is based upon work done at the beginning of this century that demonstrated animals could be ventilated via pressurized air delivered through an incision in the tracheal wall. Furthermore, both oxygenation and ventilation could be achieved in apneic animals with high pressurized oxygen to produce ventilatory movements.

Requirements and Equipment:

Emergency manual TTJV requires three conditions:

1. A high pressure source of oxygen (50psi).

2. A transtracheal cannula of at least 14 gauge.

3. A method of interrupting the burst of oxygen to the cannula to allow for exhalation.


The equipment should be assembled, packaged, and available on the "crash cart", in the operating rooms, in the ambulance, or with the airway cart in the emergency department.


Technique:

* The cannula is attached to a 5 or 10 ml syringe.

* The cricothyroid membrane is best felt by palpating the sternal notch, and working the examining finger up the midline. The first prominent cartilage felt is the cricoid cartilage. Above this is the cricothyroid membrane.

* The cannula with syringe attached is inserted at about 45o through the membrane while the thumb and index fingers of the dominant hand steady the cricoid cartilage and stretch the skin over the membrane.

* The cannula is then advanced with continuous aspiration on the syringe until the hub or flange lies firmly against the skin.

* The oxygen tubing is then connected. The ventilatory rate should be from 12 to 20 min., insufflation time being about 1 second.


Indications:

* Patients in whom direct visualization of the airway is difficult or impossible

* Patients whose anatomy is distorted due to injury

* Patients with suspected or actual cervical spine injury


Contraindications:


* A relative contraindication is inability to locate the cricothyroid membrane.

* The only absolute contraindication is total obstruction of the airway at or above the cord.


Complications:

* Damage to the cricothyroid cartilage or vocal cords with a misdirected cannula, and later complication, infection.

* Puncture of the posterior tracheal wall or misplacement of the cannula into the soft tissues which would result in life-threatening barotrauma to the mediastinum.

* Subcutaneous emphysema, most commonly results around the puncture site of the cannula.


REFERENCES

1. Caplan RA, Posner KL, Ward RJ, et al: Adverse respiratory events in anesthesia: a closed claims analysis. Anesthesiology 72:828, 1990.


2. Benumof JL. Management of the difficult adult airway. Anesthesiology 75:1087-1110, 1991.


3. Frass M, Rödler S, Frenzer R, Ilias W, Leithner F: Esophageal tracheal combitube, endotracheal airway and mask: comparison of ventilatory pressure curves. Journal of Trauma 29:1476-1479, 1989.


4. Johnson JC and Atherton GL. The esophageal tracheal combitube: an alternate vente to airway management. JEMS May: 29-34, 1991.


5. Asai T and Morris S: The laryngeal mask airway: its features, effects, and role. Can J Anesthesia 41:930-960.


6. Pennant JH, White PF. The laryngeal mask airway: its uses in anesthesiology. Anesthesiology. 71:769-778, 1989.


7. Benumof JL, Shneff PK, Skenman JLT. Trantracheal ventilation. In Benumof JL (ed) Clinical Procedure in Anesthesia and Intensive Care. J.B. Lippincott Co., N.Y. 1992.


8. Benumof JL and Scheller MS. The importance of trastracheal jet ventilation in the management of difficult airway. Anesthesiology. 71:769-778, 1989.



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