Young Eun Moon

Comparison of Respiratory Mechanics in Adult Patients Undergoing Minimally Invasive Repair of the Pectus Excavatum and Removal of a Pectus Bar

OBJECTIVE The objective of this study was to compare the respiratory mechanics and gas exchange in adult patients undergoing minimally invasive repair of the pectus excavatum (MIRPE group) and removal of a pectus bar (bar removal group). DESIGN A prospective observational study. SETTING A tertiary university hospital. PARTICIPANTS Thirty-two patients scheduled for elective MIRPE or removal of a pectus bar. INTERVENTIONS None. MEASUREMENTS AND MAIN RESULTS Spirometry was used to measure the peak inspiratory airway pressure (PIP), static compliance, and respiratory resistance. The measurements were recorded at 1 minute after beginning mechanical ventilation (T0), 15 minutes after beginning sevoflurane inhalation (T1), and after the insertion (or removal) of a pectus bar through the chest wall (T2). Pulmonary gas exchange was assessed by calculating the alveolar arterial oxygen tension difference (AaDO2) before surgical incision and after insertion (or removal) of the pectus bar. In the MIRPE group, static compliance was decreased significantly (p < 0.001), and PIP was increased significantly (p < 0.001) after insertion of the pectus bar (T2) compared with baseline. In contrast, the bar removal group showed the opposite results. There were significant differences in static compliance and PIP at T2 between the groups (p = 0.002 and 0.026, respectively). AaDO2 was increased significantly in the MIRPE group compared with the bar removal group (p = 0.012). CONCLUSIONS Insertion of the pectus bar through the chest wall results in significant changes in respiratory mechanics and gas exchange. Therefore, close attention to pulmonary function is required during and after these surgical procedures.

Venous air embolism during vitrectomy: a rare but potentially fatal complication.

Over 4,000 articles have been published on intraoperative venous air embolism (VAE) since it was first described in the 19th century [1]. Although its pathological mechanisms, preventative measures, and treatment methods have been established, it still appears consistently. VAE occurs when the pressure in an open vein is lower than atmospheric pressure. Thus, it is caused when a wound is at a higher level than the heart. The pathophysiological consequences of VAE depend on the velocity and quantity of air entry. Air bubbles flowing into the venous system lodge in the pulmonary circulation and are then diffused to alveoli to be exhaled during expiration. In most patients, a small quantity of air bubbles is tolerable. However, if the amount of air exceeds the pulmonary clearance capacity, increasing pulmonary artery pressure and, thus, increased right ventricular afterload, which may cause cardiac arrest. In particular, in patients with patent foramen ovale, paradoxical air embolism can result in a stroke or coronary occlusion, which may be fatal. General management of VAE includes notifying the operating surgeon, procedure discontinuance, use of 100% oxygen, aspiration of entrained air through a central venous catheter, aggressive intravascular volume infusion, use of a vasopressor, bilateral jugular vein compression, placing the patient in a headdown position and, if necessary, cardiac pulmonary resuscitation (CPR). It is known that VAE occurs most commonly during sitting craniotomy [1]. However, suitable conditions for it can occur whenever a wound is above the level of the heart. In this issue of the Korean Journal of Anesthesiology, Shin et al. [2] report VAE occurring during vitrectomy with airfluid exchange. One patient who was under mechanical ventilation with an oxygen/air mixture suddenly showed findings of cardiac arrest after starting air-fluid exchange. Although the surgical procedure was stopped quickly and CPR was performed, vital signs did not recover and thus percutaneous cardiopulmonary support was applied. Postoperative transesophageal echocardiogram revealed a patent foramen ovale. VAE can occur during various surgical procedures [1] but it is rare in ophthalmic surgery. The first case report was published by anesthesiologists in 2005 [3] and it was then first introduced in an ophthalmology journal in 2010 [4]. In sitting craniotomy, where the incidence of VAE is among the highest, neurosurgeons are well aware of VAE but ophthalmic operating surgeons tend not to be. Highlighting this, an interesting study was recently conducted by ophthalmologists [5]. Four donor eyes unsuitable for tissue donation were used for simulated vitrectomies. This experiment was performed with 23- or 25-gauge cannulas under several intraocular pressures (30-60 mmHg). They measured air flow against atmospheric pressure to be ~350 ml/min under 40 mmHg infusion pressure through a 25-gauge line. Considering that an air volume of 200 ml (35 ml/kg) may be fatal [1], both ophthalmologists and anesthetists should be aware that ocular air fluid exchange is not completely safe and may even be fatal, especially for patients with patent foramen ovale. Fortunately, not all air bubbles flowing in the venous system during vitrectomy surgery are potentially fatal. However, like the case described in this issue of the Korean Journal of Anesthesiology, complications in patients with other risk factors may be fatal. Thus, continuous preoperative and intraoperative attention by operating surgeons and anesthetists is required to prevent it.

Anesthetic management for the insertion of a self-expandable metallic tracheal stent under venovenous extracorporeal membrane oxygenation

Airway stents can provide prolonged palliation from endoluminal malignant tumors when the complete tumor resection is not possible [1]. General anesthesia is frequently used to facilitate the procedure by establishing a quiet operative field [2]. The present report describes the anesthetic management of tracheal stent insertion by rigid bronchoscopy using venovenous extracorporeal membrane oxygenation (VV ECMO). A 69-year-old man, 175.6 cm in height and 64.9 kg in weight, who had undergone total gastrectomy for gastric cancer 9 years earlier, was scheduled for tracheal stent insertion using a rigid bronchoscope. One year before the procedure, he had developed lymph node metastasis at the upper mediastinum, between the trachea and esophagus. The mass had continued to grow into the trachea and aggravated dyspnea (Fig. 1A). The stenotic segment had a diameter of 3 mm and a length of 2.6 cm, based on the CT scan. A pulmonary function test revealed severe airway obstruction, as indicated by a forced expiratory volume at 1 s/forced vital capacity ratio (FEV1/FVC) of 22%. Fig. 1 (A) Preoperative bronchoscopy reveals a metastatic mass infiltrating the trachea. (B) Postoperative bronchoscopy shows that the tracheal lumen is widened by a covered self-expandable metallic tracheal stent. The procedure was performed in the operating room under general anesthesia. Upon arrival in the operating room, the patient demonstrated a slight retraction of the intercostal muscles, but endured a supine position. With sufficient preoxygenation, anesthesia was carefully induced with propofol and remifentanil using target-controlled infusion. After we confirmed that anesthetic induction had not compromised manual ventilation via a facial mask, tracheal intubation was facilitated with rocuronium. A reinforced endotracheal tube with an inner diameter of 7.0 mm was advanced into the patients trachea and placed with the upper margin of the cuff located just below the patients vocal cords. Manual ventilation led to normal inflation of both chest walls and a normal capnograph. An arterial blood gas analysis (ABGA) showed adequate ventilation and oxygenation. After anesthetic induction, VV ECMO was established. Cannulation was performed with a 24 Fr percutaneous venous cannula at the right femoral vein for outflow and with an 18 Fr percutaneous venous cannula at the left internal jugular vein for inflow. An extracorporeal life support system (Capiox EBS, Terumo Inc., Tokyo, Japan) was primed with 1 L of normal saline. Systemic anticoagulation was attained using intravenous heparin to achieve an activated clotting time between 180-200 s. The perfusion flow rate was gradually increased to 3.0 L/min, causing an abrupt decrease in blood pressure. The patients blood pressure (BP) dropped to 65/40 mmHg, with a heart rate (HR) of 120 beats/min. Ephedrine 10 mg was administered, followed by epinephrine 10 µg. 500 ml of colloid solution was infused over 10 min. After resuscitation, the patients vital signs were stable, and the procedure was performed. A rigid bronchoscope was advanced into the trachea after removing the endotracheal tube. The stent delivery catheter was then inserted into the stenotic segment, and a covered self-expandable metallic tracheal stent, with a length of 6 cm and diameter of 18 mm (Hercules Airway, S&G Biotech Inc., Seongnam, Korea), was deployed. After the delivery catheter was removed, the trachea was re-intubated, and the endotracheal tube was positioned similarly to the first intubation. Throughout the procedure, global oxygenation assessed by serial ABGAs was adequate with ECMO augmented by intermittent positive pressure ventilation via a side port of the rigid bronchoscope. Perfusion flow of the ECMO system was maintained at 3.0-4.0 L/min, with oxygen flow around 4.0 L/min at FiO2 of 1.0. When the procedure was complete, the patient was transferred to the intensive care unit. To wean the patient from ECMO, the oxygen flow of the ECMO system was gradually decreased from 4.0 L/min to 0 L/min. After ensuring that removal of the oxygen flow would not result in hypoxia, the perfusion flow was decreased and stopped, and the cannulas were removed. The tracheal stent relieved the upper airway obstruction on a postoperative pulmonary function test, as indicated by an FEV1/FVC of 61% (Fig. 1B). The potential for critical airway obstruction is an important concern during tracheal stent insertion. Thus, various ventilation modes including maintenance of spontaneous ventilation, intermittent positive pressure ventilation via a side port of a rigid bronchoscope, or low- or high-frequency jet ventilation have been introduced [2]. Neither spontaneous ventilation nor intermittent positive pressure ventilation via the ventilating port was feasible in the present case because the stenosis of the trachea by the metastatic mass was so severe that the passage of a delivering catheter into the stenotic segment could have caused complete airway obstruction. Low-frequency jet ventilation from above the stenotic segment through a rigid bronchoscope was also not possible because the flow would not reach the lower respiratory tract beyond the stenotic segment during stent deployment. A high-frequency jet ventilator was not available in our hospital. Distal tracheal intubation was not possible because the mass was located intrathoracically. Therefore, the decision was made to establish VV ECMO prior to the tracheal stent insertion. There are several considerations when using ECMO for airway management in a patient undergoing airway stent insertion. First, it should be determined preoperatively whether ECMO is to be initiated before or after the administration of anesthesia because anesthetic induction can induce catastrophic airway obstruction. Second, standby ECMO may be a sensible choice in some cases because instituting ECMO is associated with coagulopathy, infection, and cannulation site complications [3]. Catheter insertion without initiating extracorporeal blood flow could reduce the time required to establish ECMO. Third, intermittent positive pressure ventilation via a side port of a rigid bronchoscope may be necessary to maintain oxygenation. In a patient with respiratory failure, a target arterial oxygen saturation achieved by VV ECMO is between 85-95% [4]. Applying ECMO in a patient receiving an airway stent allows the functioning lungs to be used for intermittent positive pressure ventilation, which can optimize oxygenation. VV ECMO is considered a valuable option during tracheal stent insertion that is expected to cause critical airway obstruction. For optimal ventilatory support, a strategy for ventilation and anesthesia should be established prior to the procedure, according to the degree of tracheal obstruction, the nature of the mass, and the method being used.

The effects of callander modification of laryngoscopic blade on hemodynamic changes according to the degree of difficult airway

BACKGROUND Laryngoscopy and tracheal intubation are known to have profound cardiovascular effects. The Callander modification of Macintosh blade is associated with greater field of laryngoscopic view and decreased risk of dental contact. The purpose of this study was to compare the hemodynamic responses to laryngoscopy and tracheal intubation according to the degree of difficult airway, and to evaluate the usefulness of Callander modification of Macintosh blade for attenuating the hemodynamic responses. METHODS One hundred, forty-eight patients scheduled for elective surgery were divided into Easy group and Difficult group by Wilsons risk sum score. Laryngoscopy was performed using either an ordinary Macintosh No. 3 blade or the modified Macintosh blade. The modification consisted of reducing the height of the flange by partial removal, as described by Callander et al. Hemodynamic variables (systolic, diastolic, mean blood pressure, heart rate and rate pressure product) were noted before induction (baseline) and immediately after intubation. RESULTS The hemodynamic changes after tracheal intubation in Difficult group were significantly greater than those in Easy group (P < 0.05). When using the modified blade, systolic, diastolic and mean blood pressure after tracheal intubation were lower than those using the conventional blade regardless of Wilsons risk sum score, but no statistical significances could be found. CONCLUSIONS The hemodynamic changes after tracheal intubation increased as the degree of airway difficulty increased. Laryngoscopy with the Callanders modified blade did not reduce the degree of hemodynamic stimulation compared with the conventional Macintosh blade.