Specialised Techniques In Advanced Life Support

Advanced Airway Management

Advanced airway management requires specialised equipment and skills and should be used in an apnoeic patient receiving basic life support.

Oral and nasopharyngeal airways are easy to insert with minimal experience. The commonest forms are the Guedel oropharyngeal airway and the more easily tolerated nasopharyngeal airway.

An oropharyngeal airway is sized by matching the distance between the corner of the mouth and the angle of the jaw. The nasopharyngeal airway is matched approximately to the diameter of the patients little finger and should be well lubricated before insertion. Do not use a nasopharyngeal airway if there is any suspicion of a basal skull fracture.

Tracheal intubation is the best way of providing a secure and reliable airway. However, the technique requires special skills and equipment and attempts at intubation may cause further complications and delay if performed incorrectly. Confirmation of the tube's position is most reliably achieved by seeing it pass between the cords during intubation, auscultation of the chest and, if available, end-tidal carbon dioxide measurement. Various simple oesophageal detector devices are also available ( Oesophageal Detector Devices, Update in Anaesthesia 1997;7:6).

Application of cricoid pressure should be considered if there is a major risk of gastric contents contaminating the airway. It should be applied until the airway is secured with a cuffed endotracheal tube. However it may make intubation more difficult for the inexperienced operator, particularly if it is not done completely correctly ( Anaesthesia for the Patient with a Full Stomach, Update in Anaesthesia 1994;4:2).

Other oropharyngeal airway devices

Although it has been part of routine anaesthetic practice for around ten years in the UK, the laryngeal mask airway (LMA) has also been used for failed intubation and, more recently in resuscitation.

The insertion technique is easily taught and it provides a similarly efficiency of ventilation as a bag and mask technique. However in a few cases LMA's are difficult to position correctly, ventilation of poorly compliant lungs is uncertain, and they do not reliably protect the airway from gastric contents. The double lumen Combitube® has also been used during resuscitation. It is inserted blindly into the oesophagus and then used to inflate the lungs via the second lumen. See  Prediction and Management of Difficult Tracheal Intubation, Update in Anaesthesia 1998;9:9 for more details of the LMA and the Combitube.

Surgical airway techniques are required when life-threatening airway obstruction is present and other means of establishing an airway have failed. Emergency access to the airway is via the relatively avascular cricothyroid membrane. This membrane is identified by locating the midline depression between the easily identifiable cricoid cartilage and the lower edge of the thyroid cartilage. Cricothyroid emergency airway. A 12 or 14 gauge cannula with a syringe attached is introduced through the cricothyroid membrane until air can be aspirated. The cannula is then advanced off the needle down the trachea. The hub of the cannula is connected to an oxygen source at 15 litres/minute and the patient ventilated for one second and then allowed to exhale for 4 seconds. In the absence of an oxygen supply, short-term improvised connections can be made by: The cricothyroid cannula is connected to a 10ml syringe with the plunger removed. An 8.0mm endotracheal tube is inserted into the barrel, the cuff inflated and a self-inflating bag connected and ventilation attempted. A 3.5mm endotracheal tube connector will usually fit directly into the cricothyroid cannula and allow connection to a self inflating bag. Although the patient may be oxygenated in this way, ventilation to remove CO2 cannot be achieved and respiratory acidosis will ensue. Spontaneous respiration is impossible through a needle cricothyrotomy and careful observation is required to prevent barotrauma. A clear expiratory pathway is required to allow the oxygen to escape as an intravenous cannula is not adequate by itself.

A needle cricothyrotomy will ensure a supply of oxygen for a maximum of 10-20 minutes and it should be converted to a surgical cricothyrotomy to allow adequate ventilation. A horizontal incision is made through the membrane and a small (size 5.0-6.5) endotracheal or tracheostomy tube is inserted and connected to a self inflating bag, providing highly efficient ventilation and airway security. Although a simple concept, the equipment may take time to assemble and there is a significant complication and failure rate. Therefore in theatre, or accident/emergency, the equipment should be prepared and ready for use.

Blind, single-stage cricothyrotomy techniques Several kits are commercially available (Portex, Cook Critical Care, Rusch) which are designed to pass a tube through the cricothyroid membrane in a single manoeuvre. They use either a guidewire, introducer or dilational technique and all provide a 22mm connection to standard ventilation equipment.

Defibrillation

The majority of adult cardiac arrests involve ventricular fibrillation that may be reversed by electrical defibrillation. The likelihood of successful defibrillation decreases with the duration of cardiac arrest (an estimated 2 - 7% for every minute of the arrest) and, although BLS measures will slow the deterioration, asystole will inevitably ensue.

Defibrillation delivers an electrical current through the heart simultaneously depolarising a critical mass of the myocardium and introducing a co-ordinated absolute refractory period. This results in a period during which another action potential cannot be triggered by a stimulus of any magnitude and, if successful will stop the chaotic electrical activity of ventricular fibrillation momentarily. The pacemaker cells of the sino-atrial (SA) node have the opportunity to re-establish sinus rhythm as they are the earliest myocardial cells to depolarise spontaneously.

All defibrillators consist of a power source, an energy selector, an AC/DC converter, a capacitor and a set of electrode paddles (Figure 5). Modern machines allow ECG monitoring via the paddles or via leads attached to the machine. The power output is expressed in terms of delivered energy (in Joules), which is the energy delivered through the paddles to the chest wall.

Only a relatively small proportion of the energy is delivered to the heart and variations in transthoracic impedance (resistance to current flow caused by chest tissues) will occur. The energy requirement for defibrillation (defibrillation threshold) will tend to increase with the duration of the arrest. Empirical energy levels of 200 Joules (J) for the first two shocks and 360J subsequently have been decided upon for adult resuscitation. DC shocks should be delivered with the correct paddle position and good contact using conductive pads or a coupling medium. Although the polarity of the paddles is not crucial, the cardiac complexes are upright on the screen if the paddles labelled "sternum" and "apex" are placed correctly. The sternal paddle is placed high on the right side of the anterior chest wall, lateral to the upper part of the sternum and below the clavicle; the apex paddle is placed just lateral to the position of the normal apex beat (figure 6), avoiding breast tissue in females. Other positions, such as apex-posterior may be tried if the conventional paddle position is not successful.

In recent years, semi and fully automatic defibrillators have been developed. When connected to the patient these are able to interpret cardiac rhythms and deliver shocks when appropriate. Some are also able to measure the transthoracic impedance of the patient and attempt to match the energy delivery to the required current flow. The very latest generation of machines use bi- and tri-phasic energy wave forms to achieve successful defibrillation at lower energy levels.

Regardless of the type of defibrillator available, it is essential that the staff using it are familiar with its operation, and are trained regularly in its use.

Cardiac Arrest: Defibrillation Technique

It is assumed that the rhythm has been confirmed as suitable for defibrillation. The first three shocks of the ALS algorithm should be completed within 90 seconds. Unless the rhythm changes on the ECG trace, there is no need to check the pulse between cycles of defibrillation.

Drug Therapy

Adrenaline (epinephrine)is the main drug used during resuscitation from cardiac arrest. A 1mg dose should be given at least every three minutes during the arrest. Intravenous adrenaline enhances cerebral and myocardial blood flow by increasing peripheral vascular resistance and raising aortic diastolic pressure. These peripheral vascular actions are primarily alpha1 (a1), and alpha2 (a2), receptor-mediated. Beta1(b1) and Beta2 (b2) receptor actions also occur though a beta effect has not been shown to be beneficial in restoring spontaneous circulation in VF, asystole or EMD. Indeed, b1 effects may increase myocardial oxygen demand and increase the risk of arrhythmias in a beating heart. Recently, high dose adrenaline (5mg) has been tried during resuscitation in an attempt to improve the survival of cardiac arrest but there was no improvement in outcome.

The ALS algorithm suggests the use of antiarrhythmics, buffers, atropine and pacing. Antiarrhythmic drugs are considered in figure 7.

Atropine as a single dose of 3mg is sufficient to block vagal tone completely and should be used once in cases of asystole. It is also indicated for symptomatic bradycardia in a dose of 0.5mg - 1mg.

Sodium bicarbonate In prolonged arrests, the effects of acidosis become significant. The use of sodium bicarbonate as a buffer has been controversial; it is associated with hyperosmolarity and carbon dioxide production, and may worsen intra-cellular acidosis. Carbon dioxide-consuming buffers, such as Carbicarb and THAM have been developed, but no buffer has been shown to improve outcome. Nevertheless, sodium bicarbonate continues to be recommended (50mls of 8.4% solution) after 15 minutes of cardiac arrest or when the arterial pH is less than 7.1, or the base deficit is more negative than -10. It should be used early in arrests caused by acidosis, hyperkalaemia or tricyclic overdosage, but must not be given by the tracheal route or mixed with calcium or adrenaline solutions.

Drug Delivery

The optimal route of administration for these drugs is via a central venous cannula. However, they are usually given through a peripheral cannula and in this situation, drug administration should be followed by a 20-50ml 0.9% saline flush and elevation of the limb to assist entry to the central circulation.

CPR should not be interrupted for more than 10 seconds to permit intravenous cannulation and consideration should be given to the tracheal route if no intravenous access exists. Although a second-line choice, endotracheal tube placement will often precede intravenous access and adrenaline, atropine and lignocaine can all be given intra-tracheal in doses 2 times the normal intravenous dose, diluted up to 10mls in 0.9% saline. When gaining iv access during a cardiac arrest, choose the most proximal large vein that can be easily cannulated: the external jugular vein is often suitable. Central venous cannulation should only be attempted by those experienced in the technique.

The unpredictable drug delivery and risk of damage to the left anterior descending coronary artery make direct intra-cardiac injection impractical and unsafe.

Advanced Life Support Algorithm The algorithm (figure 7) guides the response to cardiac arrest. If the arrest is witnessed, a precordial thump should be considered. This is delivered with a heel of a clenched fist from a height of around 8 inches from the chest. This generates a few joules of electrical current within the heart which, in the early phase of a cardiac arrest, may be enough to return sinus rhythm. A precordial thump should not be administered by people who have not been trained in the technique, or if the arrest has not been witnessed. Perform a pulse check after delivering a precordial thump. The priority in advanced life support is to determine the underlying rhythm causing the cardiac arrest and whether any underlying treatable cause can be found. The algorithm details the management according to whether the underlying rhythm falls into the category of Ventricular Fibrillation (VF) / Pulseless Ventricular Tachycardia (VT) or, Asystole / Pulseless Electrical Activity (in the figure = Non VF /VT).

(Continued ...)

---

© World Federation of Societies of Anaesthesiologists WWW implementation by the NDA Web Team, Oxford

---