Abstract

We report an unexpected ventilation difficulty with an anesthetic breathing circuit in a pediatric patient receiving left herniorrhaphy. A manufacturing defect in a limb of the anesthetic breathing circuit caused this problem. This defect induced a high-pitched, wheezing-like sound, which was difficult to differentiate from a hyper-reactive airway, commonly seen in pediatric patients with recent upper respiratory tract infection. We recommend that the patency of the anesthetic breathing circuit should routinely be examined before connecting it to the anesthesia machine.

Keywords

bronchial spasm; equipment failure: breathing circuit; respiratory sounds: wheezing;

1. Introduction

Although wheezing is a clinical hallmark of bronchospasm and is usually caused by the exacerbation of reactive airway disease,¹ other causes should also be taken into consideration. Failure to detect the cause of the airway problem may place the patient in a life-threatening situation.² We herein report an instance of partial obstruction of the breathing circuit, which caused a high-pitched wheezing-like sound, rendering difficulty in differentiation from acute exacerbation of asthma.

2. Case report

The patient was a 2-year-old boy, 13 kg in weight and 82 cm in height. He showed a protruding mass in the left inguinal region while he was crying. Under the diagnosis of left inguinal hernia, he was scheduled for left herniorrhaphy. His medical history revealed no specific disorder except for mild symptoms of upper respiratory tract infection (URI), i.e., a slight cough without much sputum. These symptoms occurred 2 weeks before the operation. The patient showed good activity without lethargy or fever, and his breathing sound was clear during the preanesthetic evaluation. After routine preanesthetic preparation, including leak tests for the breathing circuit (Pediatric Anesthesia Breathing Circuit TF2502 1L; AC005; Pacific Hospital Supply Co., Ltd, Taipei, Taiwan) and complete self-testing of anesthesia machine (Cato Draeger; 8602015.02, Medizintechnik GmbH, Luebeck, Germany), general anesthesia was induced with sevoflurane in oxygen through a face mask.

Difficult mask ventilation was noted after induction of anesthesia. Chest wall could not undulate evenly in spite of insertion of an oral airway and adjustment of appropriate mask position for ventilation. Succinylcholine (20 mg) was given intravenously and a 5.0-mm endotracheal tube was inserted in suspicion of laryngospasm. After intubation, high airway resistance was felt upon manual ventilation, with increased peak inspiratory airway pressure (>30 mbar), slightly increased plateau airway pressure, and barely detectable end-tidal carbon dioxide output. Chest auscultation revealed inspiratory and expiratory high-pitched wheezing sounds over the upper and middle lungs, and diminished normal breathing sounds. The oxyhemoglobin saturation by pulse oximeter remained stationary at 98–99% during the event. Severe bronchospasm was then suspected and treated with inhaled ipratropium and terbutaline. In the meantime, the anesthesia machine shut down automatically when switching to the ventilator mode. This situation prompted us to change the anesthesia machine and the pediatric breathing circuit; at this juncture, the patient was ventilated with oxygen via a resuscitation bag connected to the source of oxygen in a portable cylinder. Ventilation improved dramatically, with an adequate tidal volume and a good undulation of the chest wall as well as absence of wheezing. A thorough examination of the problematic pediatric breathing circuit although revealed normal external appearance, there was a transparent plastic membrane in the opening of a limb of the breathing circuit, which caused partial occlusion (Fig. 1). The postoperative course was uneventful, and the patient was discharged after 1-hour postanesthetic recovery care without any morbidity.

Download full-size image

Fig. 1. Inspiratory limb of the anesthetic breathing circuit partially sealed by a transparent plastic membrane.

3. Discussion

Although hyper-reactive airway in children with a URI presenting for anesthesia is commonly seen and may result in perioperative respiratory adverse events, such as bronchospasm or laryngospasm,3, 4 other causes as culprit should also be taken into consideration. Early detection and resolution of airway problems are pivotal in pediatric patients undergoing anesthesia due to their limited cardiorespiratory reserve,⁵ and such preoccupation may forestall a multitude of problems, from transient desaturation and bradycardia to brain damage or even death.²

According to Hosking et al,⁶ who proposed an algorithm for the diagnosis and management of perioperative airway obstruction, the first step is to ventilate the patient manually to disprove the ventilator as a source of obstruction. The second step is passing a suction catheter through the endotracheal tube to distinguish the cause of obstruction between the breathing circuit and the endotracheal tube. When passing a suction catheter or direct endotracheal tube ventilation is successful, the circuit comes under suspicion. When the circuit and the endotracheal tube have been eliminated as a cause, patient's innate sources of resistance, such as bronchospasm, must be considered. In addition, according to the 2008 American Society of Anesthesiologists (ASA) Recommendations for Pre-Anesthesia Checkout Procedures,⁷ an automated checkout procedure for anesthesia machine although serves, this does not mean that it can completely function in lieu of manual checkout procedure. An automated checkout procedure can be incomplete, incomprehensible to ordinary minds without adequate training, and misleading.

In this case, the breathing circuit and the anesthesia machine were initially excluded as the culprit of the problem because the anesthesia machine had successfully passed the self-testing preoperatively. Subsequently, wheezing was confirmed by auscultation; therefore, bronchodilator was immediately used suspecting bronchospasm, but in vain. After the anesthesia machine shut down automatically upon switching to the circuit system, we reconsidered the possible sources of the problem and turned our attention to the breathing circuit and anesthesia machine. The following steps were immediately carried out: (1) a back-up anesthesia machine and a new breathing circuit were fetched for replacement; (2) the original anesthesia machine and the breathing circuit were retested again, including self-testing and leakage testing; (3) different components of breathing circuit were inspected and retested piece by piece, such as antimicrobial filter, and the limbs that connected to inspiratory and expiratory outlet of anesthesia machine; (4) discussion on the circuit and the anesthesia machine were carried out with the supplier and the manufacturer. A thorough examination of the breathing circuit revealed that the opening of the limb connected to the inspiratory outlet of the anesthesia machine was partially sealed and obstructed by excessive adhesive glue, forming a transparent plastic membrane once air dried (Fig. 1); this finding prompted the manufacturer to strengthen their quality of control. Another important finding was that the leakage testing performed before each operation could not identify any breathing circuit obstruction; this would have eventually caused the machine to shut down when we switched to the ventilator mode.

Although various case reports have documented obstruction of the expiratory filter,8, 9, 10 partial obstruction of a limb of the anesthetic breathing circuit causing high-pitched wheezing-like sound mimicking acute exacerbation of asthma has not been reported. We believe that acceleration of the gas flow through the narrowed lumen of the partially occluded limb of the breathing circuit, which is randomly connected to the inspiratory outlet of the anesthesia machine, is the possible mechanism leading to the high-pitched wheezing-like sound and is somewhat similar in mechanism to that would occur in a real asthmatic attack.¹¹ Therefore, given the facts that the obstruction caused a syndrome mimicking severe exacerbation of asthma with high-pitched wheezing-like sound, coupled with the patient's medical history of recent URI, it is easy to understand why the anesthesiologist concluded that the difficult ventilation was due to severe bronchospasm and was treated as such with a bronchodilator.

In conclusion, our report presents an unusual case of a manufacturing defect in a limb of the breathing circuit, causing difficult ventilation with high-pitched wheezing-like sound, mimicking bronchospasm. Furthermore, our case highlights the importance of the following: (1) awareness should be maintained that airway obstruction caused by structural defects can still occur with commonly used anesthetic breathing circuits; (2) leakage testing of anesthesia machines could not identify breathing circuit obstruction, and therefore we should not fully rely on the guarantee the machine offers; and (3) a manual resuscitation bag and/or bag valve mask and an oxygen cylinder should always be available during all anesthetic practices. Finally, we recommend that the patency of the breathing circuit is routinely examined by simply and quickly inspecting the openings of the circuit before connecting them to the anesthesia machine, and the complete execution of self-testing rather than leakage testing of anesthesia machine is pivotal before each operation.