Use of the Microcuff^® During General Anesthesia for Patients With Scoliosis

Abstract

Scoliosis may often be associated with a variety of cardiovascular and respiratory conditions or diseases, and depending on the severity of the spinal deformity, it may also complicate anesthetic management because of the difficulty of neck extension and tracheal deformity. Therefore, patients with scoliosis may require careful perioperative anesthetic considerations. A 14-year-old girl was scheduled to undergo extractions and restorative treatment for dental caries under general anesthesia. Her medical history was significant for intellectual disability and autism as well as previously undiagnosed scoliosis. After fixation of a 6.0 Portex^® endotracheal tube (ETT), percutaneous oxygen saturation (SpO₂) decreased to 93%, peak airway pressures increased, and unilateral lung ventilation was noted. Inadvertent mainstem bronchial intubation was immediately suspected, prompting removal of the Portex ETT and reintubation with a shorter 6.0 Microcuff^® ETT. The dental treatment was completed successfully without further incident. Assessment of the ETTs used intraoperatively led to the determination that the distance from the glottis to the carina was considerably shorter than normal for this patient. It was speculated that the Microcuff ETT may be optimal for anesthetic management of scoliosis patients because of its shorter lengths compared with other style ETTs, which may reduce the risk of bronchial intubation in such cases.

Scoliosis is characterized by the lateral curvature of the spine in the coronal or frontal plane greater than 10°, as measured by the Cobb angle, that is often accompanied by variable rotation of the vertebrae.^1,2 Underlying causes of scoliosis can be classified as congenital, neuromuscular, or idiopathic, which is the most common. The clinical relevance and severity of this condition are related to several factors, including the degree of spinal curvature, with Cobb angles exceeding 40° being considered severe. Furthermore, patients with more severe scoliosis often suffer from associated cardiopulmonary complications, such as right-sided heart failure and/or restrictive lung disease.^3–5 The anesthetic management for patients with scoliosis may be further complicated by difficulties associated with airway management, particularly tracheal intubation, often caused by compromised neck extension and tracheal deformity.^5,6 Therefore, scoliosis patients require careful anesthesia management.

General anesthesia was administered to a 14-year-old female patient scheduled to undergo dental treatment with severe, previously undiagnosed scoliosis. During treatment, 2 tracheal intubations were performed, the first of which led to an inadvertent mainstem bronchial intubation. After the initial bronchial intubation, the endotracheal tube (ETT) was changed to a shorter pediatric Microcuff^® ETT. This is a case report involving successful nasotracheal intubation using the pediatric Microcuff ETT under general anesthesia. Written consent was obtained from the patient's family for use of all information presented in this report.

CASE PRESENTATION

A 14-year-old girl (height 130 cm, weight 47 kg, body mass index 27.8 kg/m²) with a medical history notable for intellectual disability, autism spectrum disorder, and previously undiagnosed scoliosis (ASA-PS I) was admitted to a medical center for dental treatment under anesthesia. She was unable to cooperate for the indicated treatment in the customary dental clinic setting because of the severity of her intellectual disability and autism. Therefore, it was planned to have the dental treatment performed under general anesthesia. During preoperative examination, it was impossible to perform the routine preanesthetic physical examinations, such as assessing her maximum interincisal distance or Mallampati classification. At this medical center, children and individuals with intellectual disability generally do not routinely undergo preoperative pulmonary function tests, such as spirometry, prior to anesthesia. Accordingly, we did not perform pulmonary function tests for this patient. However, the preanesthetic evaluation for all patients does include blood tests (blood chemistry panel and complete blood count), a chest radiograph, and an electrocardiogram. The preoperative electrocardiogram revealed tachycardia, but otherwise no other abnormal findings were noted, and the blood tests were also normal. Notably, the preoperative chest radiograph showed severe scoliosis with a Cobb angle of 50° and associated curvature of the trachea (Figure 1). A cardiology consult obtained to assist with the preanesthetic assessment found no appreciable cardiac abnormalities. The risk of general anesthesia for this patient was acceptably low, as she had no indications of significant cardiopulmonary dysfunction nor any restrictions on daily activities.

Figure 1.

(A) Perioperative chest radiographs. (B) Chest radiographs after tracheal intubation with a pediatric Microcuff^® ETT (Halyard^® Microcuff^® Pediatric Endotracheal Tube, Oral/Nasal Magill, I.D. 6.0 mm, Halyard Healthcare Inc, Atlanta, Ga), with fixation in the right nostril at 21 cm. The red line indicates the level of the carina. Preoperative chest radiographs (A) showed pronounced scoliosis with a Cobb angle of 50°.

For induction of general anesthesia, the patient was slowly introduced with nitrous oxide (4 L/min) and oxygen (2 L/min), followed by incremental increases of 1% sevoflurane every 2 to 3 breaths until 5% was reached. Immediately after induction, intravascular access was secured using a 22-gauge intravenous cannula in the left forearm. Remifentanil hydrochloride (0.3 μg/kg/min) and rocuronium bromide (40 mg) were then administered to facilitate intubating conditions. There was no difficulty mask ventilating the patient following neuromuscular blockade. Nasotracheal intubation was performed through the right nostril with a standard Portex^® 6.0 ETT (Portex Oral/Nasal Ivory, Smiths Medical, Keene, NH; Figure 2A). An Airway Scope (AWS-S200, Nihon Kohden Corp, Tokyo, Japan) video laryngoscope was used for visualization and to assist with guidance of the ETT. The ETT was advanced until the guide mark passed through the glottis, at which point the depth was noted to be 24.5 cm at the right nostril. Ventilation was confirmed by the presence of appropriate waveforms as noted by capnography, and bilateral lung ventilation was confirmed by auscultation. Percutaneous oxygen saturation (SpO₂) was stable at 99% with the fraction of inspired oxygen at 40%. The ETT was the secured to the right nostril, after which an immediate decrease in SpO₂ to 93% was observed accompanied by an increase in peak airway pressures. There was no drastic increase in end-tidal carbon dioxide tension (ETCO₂), which remained at 43 mm Hg, nor were there any appreciable alterations to the capnography waveforms, ruling out airway obstruction. These findings suggested high potential for bronchial intubation, which was confirmed after auscultation revealed unilateral lung ventilation. The ETT was withdrawn by 0.5 cm, so that the guide mark was located exactly at the height of the glottis, which was verified using the video laryngoscope. However, ventilator symptoms failed to improve. At this point, the decision was made to remove the 6.0 Portex ETT and reintubate with a standard pediatric 6.0 Microcuff ETT (Halyard Microcuff Pediatric Endotracheal Tube, Oral/Nasal Magill, Halyard Healthcare Inc, Atlanta, Ga; Figure 2B). The new ETT was advanced without difficulty until the depth mark was reached in the glottis, which correlated with a depth of 21.0 cm at the right nostril. Bilateral lung ventilation was confirmed with auscultation, and correct ETT positioning additionally confirmed radiographically. Anesthesia was maintained with sevoflurane in oxygen and air during surgery, which progressed smoothly without incident. Dental treatment consisted of composite resin repair of 2 teeth, pulpectomy of 3 teeth, and extraction of 1 tooth. The patient emerged from anesthesia and was extubated without difficulty after confirming full reversal of neuromuscular blockade. The emergence time was approximately 9 min. Total treatment time was 2 hours, 29 minutes, and anesthesia time was 3 hours, 37 minutes. The patient remained in the recovery room for 2 hours without any further complications.

Figure 2.

Comparison of the distal ends of the tracheal tubes (cuff inflated to 20 cm H₂O): (A) Microcuff^® ETT (Halyard^® Microcuff^® Pediatric Endotracheal Tube, Oral/Nasal Magill, I.D. 6.0 mm, Halyard Healthcare Inc, Atlanta, Ga); (B) Portex^® ETT (Portex^® Oral/Nasal Ivory, I.D. 6.0 mm, Smiths Medical, Keene, NH) I.D. 6.0 mm; (C) Portex^® ETT, I.D. 5.5 mm. DM indicates length from the distal edge of the intubation guide/depth mark to distal end of the ETT; DC, length from the distal edge of cuff to the distal end of the ETT; C, length from the distal edge of cuff and proximal edge of cuff; PM, length from the distal edge of intubation guide/depth mark and the proximal edge of cuff; I.D., internal diameter.

DISCUSSION

Although this patient had not been diagnosed with scoliosis before surgery, preoperative CXR revealed severe scoliosis. Generally, scoliosis patients with a Cobb angle of >50° require surgical correction.⁷ Furthermore, her inability to cooperate or understand instructions made detailed physical examination and pulmonary function tests impossible. Depending on the severity of the spinal deformity, scoliosis patients may be prone to pulmonary complications such as restrictive lung disease with reduced chest wall compliance and functional residual capacity and/or cardiovascular complications such as congenital cardiac abnormalities and right-heart failure.^3–5 The negative impact on the cardiopulmonary status of patients with scoliosis is directly correlated with the degree of spinal curvature.⁸ Blood gas analysis has been recommended as part of the preoperative examination for patients with kyphoscoliosis, which some may recommend for scoliosis patients.⁵ In this particular case, the combination of severe scoliosis and intellectual disability precluded thorough assessment of cardiac and pulmonary function in the usual customary fashion by the anesthesia providers. The decision was made to obtain additional medical consultation from a cardiologist because of the increased risk and impact of such potential comorbidities; however, no appreciable cardiac abnormalities were found.⁹ In addition, she had no history or indications of cardiovascular disease nor any noted restrictions on activities of daily living. Based on these findings, the risk with general anesthesia for this patient was deemed acceptably low.

Laryngoscopy and subsequent tracheal intubation may be rendered difficult in scoliosis patients because of restricted neck movement and airway curvature.^5,6 Because laryngoscopy was expected to be difficult, a monitor-integrated video laryngoscope was prepared for use during intubation and a laryngeal mask airway was prepared for use as an emergent supraglottic airway. However, visualization and tracheal intubation were easily performed without difficulty. Once the guide mark had passed through the glottis, the ETT was advanced no further; however, this failed to prevent inadvertent endobronchial intubation. It has been reported that tracheal and neck lengths of scoliosis patients are likely to be normal, so intubation to the same depth as healthy patients is typically necessary to prevent accidental extubation.¹⁰ In healthy persons, the trachea bifurcates into the left and right mainstem bronchi at the level of the fourth to fifth thoracic vertebrae, and the distance from the glottis to the carina averages 12.6 cm for both men and women.^11,12 The length of the trachea stops growing around age 14 for females on average. Therefore, for this 14-year-old female patient with scoliosis, it was anticipated that the distance from the glottis to the carina would be similar to that of most healthy adults.^12,13 The assumption was made that the left and right bronchus diverged level with the fourth thoracic vertebrae, which could not be easily confirmed on the chest radiograph because of its poor quality. However, the length from the distal edge of the intubation guide/depth mark to distal end (DM) of the 6.0 Portex ETT was 8.2 cm. Therefore, it was inferred that the distance from the glottis to the carina was substantially shorter than that in an otherwise, normal healthy person (Figure 2).

As previously stated, most scoliosis patients are likely to have normal tracheal and neck lengths. However, the severity or degree of thoracic deformity can vary greatly between individual scoliosis patients. Estimating the distance from the glottis to the carina using only the positional relationship between the trachea and the anatomy observed on radiographic images can be quite difficult depending on the degree of the thoracic deformity, the spinal deformity, and other associated rib abnormalities present. Because of previous experience with shortened tracheal lengths found in previous scoliosis patients, the anesthesiologists were alert for a higher risk of endobronchial intubation for this patient.

The Microcuff ETT is designed for pediatric use, with a high-volume, low-pressure polyurethane cuff and the shortest length from the distal edge of the cuff to the distal end of the ETT (DC) among comparable ETT models. The 6.0 Microcuff ETT has a DC of 1.2 cm, which is substantially shorter than the 2.6 cm DC of the 6.0 Portex ETT. In addition, the DM of the 6.0 Microcuff ETT measures a substantial 2.7 cm shorter, at 5.5 cm versus 8.2 cm in the 6.0 Portex ETT. In this case, the patient was reintubated with the 6.0 Microcuff ETT, which was advanced until the intubating depth mark was level with the glottis. Radiographic images showed an estimated distance from the distal end of the ETT to the carina of approximately 3 cm. Therefore, when this distance (3 cm) is added to the DM (5.5 cm) for the 6.0 Microcuff ETT, it can be suggested that that the length from glottis to carina was approximately 8.5 cm for this patient.

Neck extension during and immediately after intubation with the Portex ETT likely permitted bilateral lung ventilation while the ETT was in a relatively shallow position. However, once the ETT was fixed and the neck extension was released, the ETT shifted in a caudal direction coincident with neck flexion, resulting in bronchial intubation.¹⁴ Extension of the head and neck is particularly common during many oral and maxillofacial or dental procedures. Potential movement or migration of the ETT and any likely sequelae should be anticipated as a result of positional changes for any intubated patients during such procedures.¹⁵ In fact, approximately 6 mm of caudal migration has been attributed to neck flexion of 20° with the use of a 6.0 ETT.¹⁴ Therefore, there would have been a strong likelihood of recurrent bronchial intubation during flexion of the neck even if the patient would have been reintubated with a smaller 5.5 Portex ETT (Figure 2C) during the reported surgery. Constant monitoring of ventilation volume and airway pressures are necessary precautions during surgery in patients at risk of bronchial intubation.

In addition to the risks of bronchial intubation, use of the most appropriate length and proper positioning of an ETT is key for avoidance of neural damage to the airway and associated structures. An overly long or excessively deep ETT can be especially problematic because it can lead to potentially life-threatening complications such as pneumothorax, hypoxemia, cardiac arrhythmias, and atelectasis during the perioperative period.^16,17 It is generally recommended that the distance from the distal end of the ETT to the carina be 2 to 2.5 cm or more to help avoid these complications.¹² An overly short or excessively shallow ETT can be also be problematic as well, especially if the ETT has a cuff and is positioned too close to the vocal cords. Neuropathy due to cuff pressure tends to occur approximately 6 to 10 mm below the vocal cords. Ideally, the cuff should be positioned at least 1.5 cm from the vocal cords to help reduce risk of neuropathy and/or prevent vocal cord paralysis, which is why it is necessary to avoid securing the tracheal tube at a position shallower than the intubating guide or depth mark.¹⁸ In the present case, tracheal intubation with the 6.0 Microcuff ETT was performed using the depth mark as an index which, ensured the cuff was positioned approximately 2.1 cm from the vocal cords. Use of the Microcuff ETT thus secured a safety margin approximating 2.5 cm or more from the distal end of the ETT to the carina. While use of the shorter Microcuff ETT is likely to be beneficial for reducing the risk of inadvertent bronchial intubation, some may state that this style of ETT could theoretically have an increased risk of intraoperative accidental extubation. However, it has been shown that the possibility of inadvertent extubation is acceptably low for the Microcuff ETT, despite its short DM and DC lengths, when the depth mark is properly located at the level of the glottis.¹³ The depth mark allows the placement of this ETT in the proper position and minimizes the risk of inadvertent extubation.¹³ Given these considerations, the Microcuff ETT is a viable option well suited for anesthesia management of scoliosis patients.

In conclusion, in this case study of a patient with severe scoliosis with associated tracheal deviation, successful nasotracheal intubation was reported using the pediatric Microcuff ETT under general anesthesia. This particular model of ETTs may be considered ideal for anesthetic management of scoliosis patients, mainly because of its short DM and DC length, which help reduce the risk of accidental bronchial intubation.