Anesthesia for Pediatric Thoracic Surgery




Anesthesia for Pediatric Thoracic Surgery



Cesar Rodriguez-Diaz



Abstract


Pediatric patients undergoing thoracic surgery present special challenges to the anesthesiologist. The anatomic and physiologic differences to adult patients, as well as techniques that have been proven successful in taking care of these population are discussed in this chapter.


Keywords


pediatric thoracic anesthesia; pediatric; children; thoracic; one-lung ventilation; infant; anesthesia



Introduction


Pediatric patients undergoing thoracic surgery can be particularly challenging because of the differences in anatomy, physiology, and behavior in comparison to adult patients. The anesthesiologists must be cognizant of these to successfully manage these patients. The availability of proper pediatric size equipment, such as bronchoscopes and bronchial blockers (BBs), allows the anesthesiologist to achieve optimal operating conditions particularly during minimally invasive procedures. However, oftentimes, because of the small size of some patients, the anesthesiologist is required to modify the standard adult techniques to achieve one-lung ventilation (OLV). In this chapter, we will review the specific anatomic and physiologic characteristics that make pediatric thoracic patients different from adult patients. In addition, we will review techniques that have been proven successful even in the smallest patients.



Pediatric Anatomy and Physiology




Physiology


Pediatric patients have a baseline limited respiratory reserve during normal two-lung ventilation compared with adults because of several reasons listed here2:



In addition to the baseline limited respiratory reserve in two-lung ventilation, the respiratory physiology of pediatric patients is also different from adults in the lateral decubitus OLV. Unlike adults, oxygenation is higher in the nondependent lung rather than the dependent one (healthy lung), especially in neonates and infants. The reason for this is that children have an easily compressible chest wall and FRC becomes equal to the residual volume in the dependent lung, and small airways begin to close even in tidal volume values. Hydrostatic pressure between dependent and nondependent lungs is minimal because of the small size of children. Therefore the advantage of better oxygenation in the nondependent lung is not present in children. As a result, compared with adults, children are at greater risk for developing hypoxemia or airway complications during thoracoscopic surgery or thoracotomy.



Preoperative Evaluation


A standard preoperative evaluation assessing for allergies, comorbidities, and current medication use, is necessary to reduce perioperative complications children undergoing thoracic surgery. Fasting time should be reviewed. Two hours nil per os (NPO) for clear fluids, 4 hours for breast milk, and at least 6 hours for formula milk or a light meal, is recommended per the American Society of Anesthesiology guidelines.3 It is imperative for the anesthesiologist to evaluate for the presence of acute and chronic pulmonary and cardiac pathology. Dyspnea and decreased tolerance to exercise are signs indicating decreased pulmonary reserve.


The presence of a current or recent upper respiratory tract infection must be ascertained because the risk of perioperative complications increases for the following 2 to 4 weeks from the initial illness. Sometimes it might be prudent to delay the surgery for such time to pass. However, on occasions it might be advisable to proceed with surgery if it is deemed that the outcome would supersede the increased risk. The decision to proceed or delay the surgery should be made after a thoughtful discussion between the surgeon, the anesthesiologist, and the parents.


Lung auscultation must be performed to evaluate for the presence of pathologic breath sounds, such as rhonchi or wheezing. Ancillary tests, such as arterial blood gas analysis, radiographies, echocardiograms, or respiratory function tests should be reviewed if present, but not necessarily ordered routinely. Blood gas analysis is not mandatory in children. It is usually sufficient to evaluate peripheral oxygen saturation and venous bicarbonate concentrations, which is always elevated in children with chronic carbon dioxide (CO2) retention.4,5 Radiographic studies may help the anesthesiologist to anticipate for possible problems, such as difficult intubation, potential blood loss if a lesion is adherent to a great vessel, or even cardiovascular collapse from anterior mediastinal mass following induction of anesthesia. Although respiratory function tests are not routinely recommended in asymptomatic patients, they may be useful to determine the progression of disease. Since they require patient’s cooperation it is only feasible from a certain age. It is also necessary for the anesthesiologists to investigate whether the indication for surgery is related to a congenital disease. In adults, the indication is usually limited to infections, and commonly for tumors and lobe resections, whereas in younger children, congenital diseases, such as pulmonary sequestration, congenital diaphragmatic hernia, tracheoesophageal fistulas, congenital lobar emphysema, vascular rings, and tracheal stenosis are most common. In these cases, it is necessary to rule out the presence of a cardiac disease that is often associated with many congenital pathologies.



Anesthetic Techniques



Bronchoscopy


Flexible bronchoscopy is helpful in the diagnosis of chronic respiratory ailments. It allows the evaluation of the airway for fixed or dynamic changes occurring with ventilation, such as in vascular rings or tracheomalacia, respectively. Maintaining spontaneous ventilation is necessary to diagnose dynamic changes in airway patency. Intravenous sedation along with topicalization is often the preferred choice of anesthetic for older children. Younger children will often require general anesthesia, which can be facilitated with an airway device such as a laryngeal mask airway, but as mentioned previously, spontaneous ventilation must be insured. If the flexible bronchoscopy is being done for other purposes, such as for biopsy samples or performing an alveolar lavage, general endotracheal anesthesia with or without paralysis is often preferred. It is not uncommon to have to upsize the endotracheal tube (ETT) size to accommodate a flexible fiberoptic scope with a working channel.


Rigid bronchoscopy (RB) is another diagnostic and therapeutic modality. It is most commonly used in pediatric patients for the treatment of aspirated foreign bodies to be removed through the rigid bronchoscope lumen. Because of the highly stimulating effects from the rigid bronchoscope, it is performed under general anesthesia. The plan for maintaining either spontaneous ventilation or providing controlled ventilation should be discussed and coordinated with the surgeon. The techniques can vary but can be summarized as: (1) insufflating sevoflurane on the airway of a spontaneously breathing patient; (2) intermittent controlled ventilation via the bronchoscope; or (3) intermittent jet ventilation. Each technique has its benefits and downsides. Insufflating sevoflurane on a spontaneously breathing patient, in theory, should minimize dislodgement of a foreign body but can risk hypoventilation if deeply anesthetized, or unwanted motion, cough, retching, laryngospasm and even bronchospasm if the anesthetic depth is not sufficient.6–8 Another concern is operating room pollution with volatile anesthetic and aerosol particles spread. Intermittent controlled ventilation via the bronchoscope can work for a deeply anesthetized and perhaps paralyzed patient, but has the downside of air leak through the outer part of the rigid bronchoscope leading to suboptimal tidal volumes. In addition, the positive pressure can dislodge a foreign body distally. During positive pressure ventilation, the viewing port must be occluded, interfering with the procedure, to deliver an effective breath through the ventilation port of the rigid bronchoscope.9 Jet ventilation offers the advantages of allowing bronchoscopic interventions to be performed without cessations. Complications include barotrauma, inability to predict fraction of inspired oxygen (FiO2) and monitor end-tidal CO2, foreign body dislocation, and blowing of blood and debris materials to distal airways resulting in inadequate gas exchange. Low-frequency jet ventilation should not be used in patients with tracheobronchial mucosa injury or low respiratory compliance.10 A total intravenous anesthetic should be considered in cases where controlled ventilation is planned, to minimize operating room air pollution with inhaled anesthetic. It is advised to use spontaneous ventilation for the removal of proximally located foreign bodies and positive pressure ventilation for the removal of distally located foreign bodies.11 Regardless of the technique used, adequate depth of anesthesia and airway patency need to be ensured. The key to an uncomplicated procedure is the cooperation of the surgeon and the anesthesiologist.


It should be considered that aspirated foreign body retrieval is usually performed emergently. Foreign bodies can swell, progressively occluding the airway, can cause an inflammatory reaction on the airway, or can cause airway perforation leading to pneumomediastinum or subcutaneous emphysema. Fortunately, most patient do not present with many comorbidities because there is minimal time for optimization. Premedication targeting a decrease in the production of saliva and anxiety is beneficial. Albuterol sulfate and budesonide inhalations are reported to be advantageous in reducing perioperative pulmonary complications.6 The knowledge of the type, place, and aspiration time of the foreign body is important. If it is above the carina, there is a total obstruction risk, which could be precipitated with positive pressure ventilation. Inhalational or intravenous agents or both may be administered. During maintenance, short-acting agents, such as propofol, dexmedetomidine, remifentanil and short-acting muscle relaxants are administered as the procedure is generally quite short. Nitrous oxide is not recommended because many patients undergoing RB have air trapping to some extent.


Severe complications can occur during RB,12 which are closely related to the patient’s condition, the severity of the pathology, the experience of the surgeon and the anesthesiologist. Failure to retrieve the foreign body might necessitate an emergent thoracotomy or tracheostomy.



Sternotomy


In children, sternotomy is generally performed for the biopsy or removal of the mediastinal tumors. A detailed history and physical examination are extremely important. Anesthesiologists should focus on the respiratory system symptoms, such as difficulty in breathing, cyanosis, or stridor aggravated by motion, cough, or straining. Wheezing unresponsive to the bronchodilators, recurrent pneumonia, persistent atelectasis, pericardial invasion, arrhythmias, pulsus paradoxus, or signs of the superior vena cava syndrome are the warning pathologies for a complicated perioperative period. Echocardiographic examination is mandatory in children with mediastinal tumors to determine a possible mass effect from compression of the surrounding structures. The riskiest period is the induction of anesthesia especially in previously symptomatic children. Decrease in the sympathetic tonus, loss of the spontaneous ventilation and physiologic changes related to patient position diminish compensatory mechanisms. Children with mediastinal mass are at increased risk of severe airway obstruction and hemodynamic instability on induction. The pediatric surgeon must be ready to perform emergent RB during the anesthesia induction of children with a mediastinal mass in cases of total obstruction as a result of a mass effect. During induction of anesthesia, preservation of the spontaneous ventilation to secure the airway continuity (and to never burn your bridges), is recommended. If airway obstruction occurred during induction of anesthesia, turning the child to the lateral position will move the obstructing mass away from the trachea and help to open the airways. In cases of superior vena cava obstruction symptoms, induction must be performed in the sitting position and intravenous lines must be inserted into the lower limb veins. If possible, biopsy must be taken under local anesthesia. Chemotherapy or radiotherapy must be done to shrink tumors before surgery. A cardiopulmonary bypass circuit on standby should be considered for extremely high-risk cases.



Two-Lung Ventilation With Manual Retraction


Several thoracic procedures, for example, patent ductus arteriosus ligation, vascular ring resection, and tracheoesophageal fistula repair, can be performed with a single lumen tube positioned in the trachea providing ventilation to both lungs, with the surgeon gently retracting the lungs as necessary. This is typically done for short procedures in small infants where the surgeon is operating in the chest cavity but not directly on the lungs. This technique is especially helpful in the management of emergencies, such as acute hemorrhagic conditions or tension pneumothorax. Lung injury is a concern, and thus retraction should be kept to the minimum necessary. It is also possible for the surgeon to insufflate CO2 into the pleural space to displace the lung if a thoracoscopy is being performed. That may influence the delivered tidal volume, displace the lung isolation device, and cause hypercarbia and hypotension.



Lung Isolation and One-Lung Ventilation


OLV is a ventilation strategy that facilitates surgical exposure and provides still lung in thoracoscopy or thoracotomy.13 Unlike adult patients, OLV presents a challenge in children, especially in neonates and infants because of equipment limitations. Nevertheless, technology is advancing daily and equipment available to help anesthesiologists in performing OLV has been developed. OLV has other advantages other than surgical exposure, they include:




Providing Lung Separation in the Pediatric Patients (Table 23.1)



Table 23.1































Approach to One-Lung Ventilation by Age
Age Endotracheal Tube Feasible One-Lung Ventilation Technique Fiberoptic Size
Newborn to 2 years 3.0–4.5 mm Endobronchial intubation/5 Fr parallel bronchial blocker (BB) <2.2 mm
2–8 years 4.5–6.0 mm 5 Fr BB coaxial/endobronchial intubation 2.2–2.8 mm
8–10 years 6.0–7.0 mm 5 Fr BB coaxial/4.0 Univent tube 2.8–4.0 mm
>10 years 7.0 mm plus 7 Fr BB coaxial/≥26 double lumen tube/≥4.0 Univent tube 2.8–4.0 mm

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Oct 6, 2021 | Posted by in ANESTHESIA | Comments Off on Anesthesia for Pediatric Thoracic Surgery
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