A Hazard of an Anesthesia Delivery System in a Developing Country

In many hospitals throughout the developing world, reliable sources of compressed medical gas are often not available because of the high cost of production, acute shortages of appropriate gas cylinders, or problems of distribution that result in frequent but unpredictable interruptions in supply [1]. Consequently, in hospitals in these countries, drawover anesthetic equipment using room air is commonly used to provide inhaled anesthesia during surgery because it does not require a source of compressed gas to function properly [2]. The addition of a manual bellows to the drawover system allows the use of controlled ventilation during major surgical procedures. Although barotrauma is a well-recognized complication when compressed gases are used to drive anesthesia machines or mechanical ventilators or to provide supplemental oxygen [3-7], we report a case wherein barotrauma occurred during anesthesia administered with drawover anesthesia equipment. This case report describes a patient who experienced life-threatening barotrauma resulting in subcutaneous emphysema, pneumomediastinum, and cardiac arrest after inadvertent displacement of the magnet from the expiratory valve of an Oxford inflating bellows used in combination with a drawover vaporizer to provide anesthesia to a young man undergoing bladder cystoscopy. Case History A 15 yr-old male weighing 25 kg presented for bladder cystoscopy and examination under anesthesia. He had a 3-mo history of intermittent fever and lower abdominal pain. At the time of admission to Kilimanjaro Christian Medical Centre, the patient was afebrile but appeared pale and wasted. A firm, mobile mass, 10 cm in diameter, was palpable in the hypogastric area. His blood pressure was 110/70 mm Hg, heart rate 76 bpm, respiratory rate 18 breaths/min, and temperature 37.4 degrees C. Hemoglobin concentration was 10 g/dL. In the operating room, before induction of anesthesia, routine monitoring was applied, including a blood pressure cuff and a precordial stethoscope. Anesthesia was induced with intravenous (IV) atropine 0.5 mg, lidocaine 35 mg, diazepam 2.5 mg, and thiopental 75 mg. Succinylcholine 25 mg was administered to facilitate endotracheal intubation. A 6-mm inside diameter cuffed endotracheal tube passed easily into the trachea, and its position was confirmed by auscultation of breath sounds. Anesthesia was continued with halothane (1.0%-2.5%) in room air and oxygen entrained through an Oxford Miniature Vaporizer (OMV) and Epstein Macintosh Oxford (EMO) vaporizer (both Penlon, Arbingdon, UK) connected in series. Ventilation was controlled manually with an Oxford inflating bellows (OIB) (Penlon). Surgery began 7 min after induction of anesthesia. Approximately 5 min later, increased resistance to inspiration with the Oxford inflating bellows was noted. At about the same time, subcutaneous emphysema involving the supraclavicular areas became apparent bilaterally and ascended rapidly to involve the neck and face. Subcutaneous crepitations and bilateral jugular venous distention were also noted. Arterial blood pressure, femoral and carotid pulses, and heart sounds were absent. Halothane was immediately discontinued, and the endotracheal tube was replaced with a new tube of the same size and type and cardiopulmonary resuscitation was started. Adrenaline 1 mg and atropine 0.5 mg were administered through the endotracheal tube, and external cardiac massage was started. At the time the resuscitation began, it was noted that the magnet used to disable the expiratory valve on the OIB had been dislodged. When it was replaced in its correct position, ventilation immediately improved. Approximately 4 min after beginning the resuscitation, pulse and arterial blood pressure were again obtained. The blood pressure remained below preoperative levels for approximately 20 min before returning to normal. The cystoscopy was then completed and the patient transported to the recovery room tracheally intubated and breathing spontaneously. On arrival in the postanesthesia care unit, arterial blood pressure was 100/60 mm Hg, heart rate 80 bpm, and respiratory rate 20 breaths/min. Ten minutes after arriving in the postanesthesia care unit, the patient was fully awake. Examination of the chest revealed normal bilateral breath sounds. His trachea was extubated, and supplemental oxygen was administered via a Venturi face mask. A postoperative radiograph revealed free air in the soft tissues of the neck and mediastinum. No pneumothorax was detected. The patient was admitted to the surgical intensive care unit and received humidified supplemental oxygen for 24 h. Twelve hours after admission to the surgical intensive care unit, he developed hoarseness but had no stridor or difficulty breathing, and his vital signs remained stable. The following day, his blood pressure was 100/60, heart rate 76 bpm, respiratory rate 14 breaths/min, and temperature 37.2 degrees C. The subcutaneous emphysema subsided gradually over the next 72 h, and he was discharged to the pediatric ward for further observation. Two days later, the subcutaneous emphysema had resolved completely and his hoarseness had disappeared. One week postoperatively, his chest radiograph was normal. Discussion The OIB is a manual mechanical ventilator widely used in developing countries during anesthesia in conjunction with a drawover vaporizer and a universal breathing valve attached to the anesthesia face mask or the endotracheal tube Figure 1. Drawover vaporizers are particularly useful in austere situations because they do not require a continuous flow of pressurized oxygen to function. Their low internal resistance allows room air to be drawn through the vaporizing chamber by the patient's own inspiratory efforts. Despite the fluctuations in flow that occur during spontaneous ventilation, the output of a drawover vaporizer remains constant. The OIB consists of a rubber concertina bellows mounted between two one-way valves, an upstream (inspiratory) valve and a downstream (expiratory) valve. When the bellows is manually compressed, the inspiratory valve closes to prevent the "pumping effect" that can occur when a drawover vaporizer is subjected to fluctuating back pressure [9], and the expiratory valve opens to direct the anesthetic gases toward the patient.Figure 1: The Epstein Macintosh Oxford drawover vaporizer, Oxford inflating bellows (OIB), and Ambu E1 universal breathing valve. For the Ambu E1 valve to function properly with the OIB, the expiratory valve on the OIB must be disabled by placing a magnet on it. This holds the disk off the valve seat, making the valve nonfunctional (reproduced with permission from Dobson MB. Anaesthesia at the district hospital. World Health Organization, Geneva, 1988:65.The Ambu E1 valve, located at the patient end of the circuit, is a universal breathing valve that allows flow of gas in one direction only Figure 2[8]. It can be used with controlled or spontaneous ventilation. This type of valve directs the anesthetic gases from the OIB into the patient's lungs during inspiration and prevents rebreathing by venting the patient's exhaled gases to the atmosphere during exhalation. During controlled ventilation with the OIB, the positive pressure created by compression of the bellows opens the Ambu E1 inspiratory port, allowing fresh anesthetic gases to enter the patient's lungs. When the inspiratory port of the Ambu E1 valve moves into the inspiration position, it occludes the expiratory port, preventing the escape of anesthetic gases from the lungs. Normally, the Ambu E1 inspiratory port closes when the pressure in the system drops to zero as the bellows is lifted in preparation for delivering the next breath. This opens the expiratory port and allows the patient's exhaled gases to escape.Figure 2: The Ambu E1 universal breathing valve (reproduced with permission from Dobson MB. Anaesthesia at the district hospital. World Health Organization, Geneva, 1988:24.For the Ambu E1 valve to function properly when used in conjunction with the OIB, the one-way expiratory valve on the OIB must be disabled. This is done by placing a magnet on the valve cover which holds the disk off the valve seat, making it nonfunctional. In the case described here, the magnet was inadvertently dislodged from the expiratory valve after induction of anesthesia, and the valve disk returned to its functional position. Consequently, lifting the OIB created a negative pressure which closed the expiratory valve. Closing the expiratory valve on the OIB prevented the positive pressure that existed in the anesthetic system on the inspiratory side of the Ambu E1 from returning to zero when the bellows was lifted. Therefore, the inspiratory port of the Ambu E1 remained in the open position, occluding the expiratory port and preventing the patient from exhaling. With each successive inspiration, pressure within the breathing system increased, eventually causing barotrauma and cardiac arrest. Replacing the magnet immediately opened the OIB expiratory valve and relieved the positive pressure within the system. This allowed the Ambu E1 inspiratory port to close and the expiratory port to open so that the patient was able to exhale again. Increased intraalveolar pressure due to expiratory obstruction of an anesthetic breathing system is a well-recognized cause of barotrauma. Excessive airway pressure can result in rupture of the alveolar membrane, allowing air to enter the interstitium of the lung and dissect along interlobular septa, producing pulmonary interstitial emphysema. As an increasing volume of air escapes through ruptured alveoli, it accumulates around the pulmonary vessels and within the mediastinum, the pleural space, and the subcutaneous tissues of the thorax, neck, and face [3,4]. At the same time, intrathoracic pressure may increase rapidly, impeding venous return and reducing cardiac output. This can result in cardiac arrest. In the case described here, subcutaneous emphysema, pneumomediastinum, and cardiac arrest occurred without pneumothorax. The design and interaction of the OIB and Ambu E1 valve contributes to the risk of barotrauma when they are used together with this type of anesthetic breathing system. Therefore, it is essential that the expiratory valve on the OIB be disabled, and early recognition of a misplaced magnet is critical if barotrauma is to be avoided. With increasing resistance to ventilation when using an OIB and a universal breathing valve such as the Ambu E1, the patency of the system and the appropriate function of the one-way valves must be confirmed. This complication can be avoided by completely removing the expiratory valve disk. This would eliminate the need for a magnet when using an OIB with a universal breathing valve. However, if the OIB is then used with a relief valve, such as a Heidbrink valve, instead of a universal breathing valve, significant rebreathing will occur because of the absence of the OIB expiratory valve. This case of barotrauma and cardiac arrest resulted from the interaction between the OIB and the Ambu E1 valve when the magnet disabling the OIB expiratory valve was inadvertently displaced. The purpose of this report is to raise the awareness of anesthesiologists and anesthesia officers to a potentially lethal complication that can occur when using this type of equipment. Because the OIB, and a drawover vaporizer are two of the most commonly used anesthesia devices in developing countries, anesthesiologists should be thoroughly familiar with the proper function and interaction of the OIB, the magnet, and the universal breathing valve. We are indebted to Mrs. Nkanga and Monica Gonzalez for their expert secretarial assistance in the preparation of this manuscript and to Dr. Nicholas M. Greene without whose vision this collaboration would not have been possible.