Management of Ventilation in Emergency – By Dr. Gnana Sankaralingam
Major function of respiratory system is gas exchange during which air is taken into the body (inspiration) and travels through airway passages to the lungs. Oxygen in the lungs replace carbon dioxide in the blood, which is expelled by the body (expiration). When an interruption in the respiratory function takes place, the entire body becomes compromised. Damage to the brain occurs in three minutes if deprived of oxygen. Thus maintaining a patent airway and restoring breathing is vital. Air passage is divided into upper respiratory tract (nose, mouth, pharynx and larynx) and lower respiratory tract (trachea, right and left bronchi, bronchioles and alveoli where gas exchange occur). These airways can be blocked by inflammation, foreign bodies, tumours or injury.
Opening the Airway – First step in management of airway is proper positioning of the patient, preferably supine but on left lateral side if vomiting. Most common cause of obstruction is the tongue falling back followed by vomitus, swelling of airway, food, secretion or dentures. When a person is unresponsive muscle tone decreases, which increases the chance of tongue or epiglottis to block the pharynx. Look for visible foreign objects and check for chest movements. Suprasternal retraction, intercostal recession, wheezing or cyanosis signifies airway obstruction. Open the airway using either head tilt – chin lift or jaw thrust manouvre to relieve upper airway obstruction caused by tongue or epiglottis. Remove foreign objects in the mouth by finger sweeps or by forceps or suction. Sub-diaphragmatic abdominal thrusts are done to expel foreign objects stuck deeper. If the patient is breathing spontaneously, administer supplemental oxygen through a nasal catheter or a face mask, but if not breathing initiate rescue breaths till an invasive airway can be inserted.
Airway Devices – They are used in unconscious patients as their insertion stimulate gag reflex with risk of aspiration. If they are necessary in conscious patients, sedation is given before insertion. Simple of them is the oral airway inserted into the mouth to connect the outside with the pharynx. Next common ones are naso-pharyngeal airway and endo-tracheal tube (ETT). Others used are oesophageal-tracheal combitube (ETC), laryngeal mask airway (LMA), pharyngo-tracheal lumen airway (PTLA) and trans-tracheal catheter. If these techniques are unsuccessful, crico-thyroidotomy (tracheostomy) may be necessary. Oral airway, curved tubular device made of firm plastic to prevent occlusion by teeth is inserted between tongue and back wall of pharynx to lift the base of the tongue off hypopharynx and establish an open airway. It is inserted upside down into the mouth and when it reaches middle of tongue, it is turned 180 degrees and pushed back to position, so that the flange rests on the lips and other end between base of tongue and back of throat. It is used during bag and mask ventillation to minimise gastric distention and to prevent occlusion of ETT tube by biting with the teeth. Naso-pharyngeal airway, a soft rubber uncuffed tube is inserted through the nostril into oropharynx. It is tolerated fairly well by semi-conscious patients and conscious ones with gag reflex. It is useful in patients with fits, trismus (muscle spasm) or neck vertebral injuries.
Endotracheal airway involves the intubation of a tube through the nostrils or mouth into the trachea to maintain a patent airway. It is the gold standard of invasive airway control in the unconscious patient. It prevents aspiration of bowel contents into the lungs and allows ventillation of the patient. If the patient is conscious or has an intact gag reflex, pharmacological agent has to be used to ease insertion. This should be performed by persons trained in the procedure, each attempt not lasting more than 30 seconds, and in between failed attempts, patient must be oxygenated using bag-valve mask. ET tubes come in different sizes with inflatable cuffs. For children under 8, cuffless tubes are used to prevent compression. Prior to insertion patient is hyperventillated using bag-valve mask with 100% oxygen. Laryngoscope is used to visualise the vocal cord to help the insertion. It has a handle with batteries inside and a blade which may be straight or curved with a bulb at the end to light up the passage for clear vision. Lubricated tube is inserted through the vocal cords and checked for placement by listening to the lungs (both sides must be aerated equally), and when confirmed as correct, tube is secured by inflating the cuffs. Oesophageal – Tracheal double lumen airway, a plastic tube with occlusion ballon at the distal end, where one act as ET tube and the other as oesophageal tube, may be inserted blindly, usually in cardiac arrest situation even by one not trained to intubate or in cases of failed intubation. It facilitates decompression of stomach contents.
Supplemental Oxygen administration – In a respiratory emergency, administration of supplemental oxygen reduces ventilatory effort of the patient and in a cardiac emergency, it helps to counter the increased myocardial workload as the heart attempts to compensate for hypoxaemia (low oxygen level in blood). It is particularly important for a patient with compromised myocardium as in the cases of infarction or arrythmia. Supplemental administration devices include nasal canula, simple mask, non-rebreather mask and Venturi mask. Nasal canula is the most frequently used low flow oxygen delivery system for spontaneous breathing patient not needing precise concentrations. It is comfortable and easy to use, composed of flexible plastic tubing with two prongs and adjustable elastic strap. It provides 24% to 44% humidified oxygen concentration with 1 to 6 litres / minute flow rate for patients with no or minimal respiratory distress. Every increase of 1 litre / minute equals to an increase of 4% oxygen concentration. Simple or basic face mask is a low flow system which allows oxygen to enter through a bottom port and gets air exhaled through holes in the side of the mask. It is capable of delivering 40% to 60% humidified oxygen concentrations to patients with spontaneous breathing for short period of time. It comes in various standard sizes for faces of adults and children. Non-rebreather face mask with attached oxygen reservoir, provides oxygen concentrations of 60% to 90% to spontaneous breathing patient with intact gag reflex. On inhalation, it directs oxygen from the reservoir bag into the mask through a one way inspiratory valve and on exhalation, gas exits the mask through a one way expiratory valve into the atmosphere. Venturi face mask is designed to mix room air with oxygen, allowing administration of oxygen at a constant concentration of 24% to 50% regardless of the respiratory rate of the patient. It increases the spontaneous breathing efficiency of patient with chronic lung disease without drying mucous membranes. Mask is attached by wide bore flexible tube to the adaptors which can change the size of the orifice to vary oxygen flow, which lets inhaled oxygen and air to mix, and has a perforated cuff to allow exhaled air out.
Ventilation devices – There are number of devices and techniques used to ventilate and help deliver oxygen, which include bag-valve device, barrier devices and automatic ventilators. When in place these are used to either deliver supplemental oxygen or room air. Bag-valve device is an inflatable resuscitation bag with a reservoir that can be directly attached to a face mask, ET tube or tracheostomy tube. It is used to deliver ventillation manually of room air or supplemental oxygen by positive pressure to those with inadequate breathing. Barrier devices are face shield preventing contact with the patient, and pocket face mask which allows to deliver breaths through a one-way valve and directs the exhaled gas away. It delivers 16% oxygen concentration, but for higher levels, an oxygen source need to be connected. For those needing long term breathing support, automatic ventilators are used to deliver oxygen through ET tube or tracheostomy which could be time cycled, volume cycled or pressure cycled, or by non-invasive method through mask using CPAP (continuous positive airway pressure) or BiPAP (biphasic positive airway pressure) machines.
