Preoperative preparation

Apnea of prematurity

Several studies have described an increased incidence of apnea after general anesthesia in premature infants. The combined incidence from all the studies is 25%, with a range from 5% to 49% ( ; ; ). There is significant interinstitution variability that likely is related to the method of measuring the apnea. The studies that used a continuous recording device rather than clinical observation captured more apneic events. The probability of the apnea is inversely related to gestational age (GA) and postconceptual age (PCA). Those neonates with the most profound prematurity have the greatest probability of apnea (see Chapter 27 : Neonatology for Anesthesiologists). In addition, anemia and apnea at home increase the likelihood of postoperative apnea. The risk of apnea declines with increasing age of the infant. Given the risk of postoperative apnea, up to what age should the former premature infant be observed in a monitored setting after surgery? The risk of apnea may not decline to less than 1% until 56 weeks PCA with a GA of 32 weeks or 54 weeks PCA with a GA of 35 weeks ( Fig. 16.3 ) ( ). The criteria to allow same-day surgery in the formerly premature infant are variable at different pediatric centers. Some centers will allow the formerly premature infant at 44 weeks PCA to be discharged on the day of surgery, whereas others require 60 weeks PCA. Full-term infants who are less than 44 weeks PCA should also be admitted after general anesthesia. If the infant is to be admitted overnight for observation, an apnea-bradycardia monitor must be used. In the study by of infants aged 60 weeks PCA or younger scheduled for inguinal herniorrhaphy, the incidence of post operational apnea occurring from 30 minutes to 12 hours postoperatively was the same (2%) for patients who received a spinal anesthetic versus a general anesthetic. The administration of a pure regional technique (spinal) may not confer significant benefit over a general anesthetic, and premature infants receiving a spinal technique may still require observation for 12 to 24 hours.

Bronchopulmonary dysplasia

Bronchopulmonary dysplasia historically occurred secondary to a premature lung being exposed to volutrauma, barotrauma, and high inspired concentrations of oxygen in the absence of surfactant (“old BPD”). Reduced ventilation settings, lower inspired oxygen concentration, prenatal steroids, and surfactant have resulted in a “newer” version of BPD. It is defined as oxygen dependence 28 days after birth, and the pathology is characterized by fewer but larger alveoli, less inflammation, less smooth muscle hypertrophy, and less fibroproliferation ( ). Infants with a history of bronchopulmonary dysplasia may have increased bronchial hyperreactivity at baseline and may be at increased risk for intraoperative bronchospasm. The clinical pathology associated with BPD may extend into adulthood ( ). Patients may be taking beta-2 agonists and steroids. These medications should be continued preoperatively. Rarely, they may be taking a diuretic, and electrolytes should be evaluated in these patients. Desflurane should not be used in patients with bronchial hyperreactivity (BHR) because it increases airway resistance ( ) (see Chapter 47 : Respiratory Disorders).

Subglottic stenosis

Prolonged intubation in the neonatal period may increase the risk of subglottic stenosis. The duration of intubation and mechanical ventilation should be identified in the preoperative history of the premature infant. Patients with trisomy 21 also have a higher incidence of subglottic stenosis. Stridor (biphasic or inspiratory) may be appreciated on exam. The absence of stridor does not rule out subglottic stenosis. If there is a concern for stenosis, a smaller endotracheal tube (ETT) should be available, and an airway exam with a bronchoscope may need to be performed if there is difficulty passing smaller ETTs.

Airway

Identifying patients who are difficult to ventilate or intubate is essential to the preoperative evaluation. A history of a craniofacial abnormality, including craniosynostosis (Apert, Crouzon, Pfeiffer), hypoplasia (Pierre Robin sequence, hemifacial microsomia [Goldenhar]), or clefting (Treacher Collins) will indicate a patient who will likely be difficult to ventilate and/or intubate (see Chapter 35 : Plastic Surgery). Patients with mucopolysaccharidosis will also be difficult to ventilate and intubate. Acquired conditions like an abscess involving the face or the neck or previous surgery involving the cervical spine will potentially make airway management more difficult. As mentioned previously, neonates with a history of prolonged intubation may have subglottic stenosis and require a smaller endotracheal tube. Previous anesthetics are important to evaluate for the airway management. The laryngoscopic view, numbers of attempts, laryngoscope blade used, and size and route of the endotracheal tube will identify problems with future anesthetics. The physical exam features of the pediatric difficult airway are discussed in the Physical Exam section.

Murmurs

Heart murmurs are a common auscultatory finding during preoperative examinations. Identifying heart sounds that suggest significant congenital cardiac pathology (intracardiac shunt, obstruction to flow) is important and may change the perioperative course for the patient. The history is very helpful in determining whether the murmur is benign (innocent or functional). Evidence of robust functional capacity without cyanosis suggests a benign cardiac murmur. Infants with feeding intolerance, failure to thrive, or cyanosis may have an underlying cardiac defect. Older children may have chest pain, syncope, or an inability to keep up with friends in regards to physical activity. A family history of sudden death should also raise concern for possible heart disease. Some pediatric conditions have a high incidence of heart disease even though there may be no murmur present. Patients with a history of Williams, Noonan, trisomy 21, Turner, or Marfan should have a cardiology evaluation prior to presenting to the operating room ( ).

An echocardiogram will help define murmurs if the exam is unclear. Echocardiograms correctly identify the underlying anatomy and pathology ( ). The electrocardiogram (ECG) by itself is rarely helpful ( ). Auscultation by a pediatric cardiologist is sensitive and specific for identifying pathologic murmurs. When pediatricians are compared with pediatric cardiologists, pediatricians correctly identified pathologic murmurs as well as pediatric cardiologists. However, they were not as good at identifying innocent murmurs. Pediatric anesthesiologists, like pediatricians, should ideally be able to identify pathologic murmurs in the preoperative setting. Murmurs with uncertain auscultatory findings should be sent for further evaluation with a pediatric cardiologist. Benign heart sounds are generally quiet systolic murmurs. The precordium should be felt for increased activity or a thrill. Increased activity suggests an atrial septal defect, ventricular septal defect (VSD) or patent ductus arteriosus (PDA) ( ). The brachial artery and the femoral artery should also be compared. A delay in the femoral pulse suggests a coarctation of the aorta. The three most common innocent murmurs include Still’s murmur, pulmonary flow murmur, and venous hum. The most common innocent heart murmur is the Still’s murmur. It is musical and heard best at the left lower sternal border and may radiate to the base (upper borders) ( Fig. 16.4 ). The supine position is the optimal position to hear the murmur, and it diminishes with standing. Clinical features that are predictive of the presence of congenital disease include murmurs that are pansystolic, grade 3 or more in intensity, heard best at the left upper sternal border, harsh in quality, or have an abnormal second heart sound and an early or midsystolic click ( ). In addition, most diastolic murmurs are pathologic.

Subacute bacterial endocarditis

Subacute bacterial endocarditis (SBE) is an infection of the endocardium of the heart. It is typically caused by exposure of abnormal endocardium to bacteria from the mouth. Patients at risk of developing SBE should receive antibiotic prophylaxis to minimize the risk. This risk requires both a patient at risk and a surgical procedure that produces a bacteremia. Typically this involves surgery of the oral cavity. Boxes 16.2 and 16.3 and Table 16.2 ( ) describe patients and procedures that require SBE prophylaxis and the appropriate antibiotic coverage.

Asthma

Asthma is one of the most common respiratory comorbidities, and it is the most common chronic disease of childhood ( ) (see Chapter 47 : Respiratory Disorders). As of 2018 the CDC reported the incidence of asthma in children was 7.5% compared with 7.7% in adults. The greatest incidence appears to be in the 15- to 19-year-old group at 11%. There is a higher incidence in African Americans (13.5%) (CDC.gov). The presence of asthma may increase the risk of intraoperative and postoperative complications, which include bronchospasm and laryngospasm. demonstrated that the overall incidence of laryngospasm and bronchospasm is low (1.7%) in asthmatic patients with no symptoms and appears to reflect a similar incidence in patients without asthma (0.2% to 4.1%) ( ). However, more recent studies suggest these perioperative risks may be higher with active asthma at 10% ( ).

The goal of the preoperative visit is to identify the degree of control and to optimize the patient to reduce the risk of a perioperative respiratory complication. The history will identify the degree of control ( Table 16.3 ). The NIH Expert Panel on Asthma Diagnosis and Management defines the severity and degree of control. Once patients have started long-term therapy, their degree of control can be defined as well controlled, not well controlled, and very poorly controlled ( ). Preoperative patients with well-controlled disease who take minimal to no medications will be at minimal risk and will require no significant intervention. Asthma that is not as well controlled is characterized by weekly symptoms, monthly nighttime symptoms, and weekly use of short-acting beta-agonist (SABA) along with multimodal asthma medication therapy. They are more at risk and will require more preoperative evaluation and intervention. The poorly controlled asthmatic is characterized by daily symptoms with daily use of SABA therapy, weekly nighttime awakening, and multiple episodes of oral steroid therapy for exacerbations throughout the year. Monoclonal antibody therapy (omalizumab) is a novel medication that binds to IgE and is recommended for difficult-to-control moderate-to-severe persistent asthma in children 6 years and older with elevated IgE counts ( ).

The evaluation should focus on the history and lung auscultation. Patients with expiratory wheezing (not in the setting of a URI) that easily resolves with a short-acting beta-agonist in the setting of a more benign (well-controlled) history can most likely proceed with the anesthetic. Patients who are not well controlled but have no symptoms (wheezing) on the day of surgery can also likely have their elective surgery but should be treated preoperatively with a SABA. Expiratory wheezing is concerning, and elective surgery may need to be rescheduled until their asthma can be optimized. Patients with very poorly controlled asthma should ideally be seen prior to the day of surgery. They may require the addition of inhaled corticosteroids if not already taking them or even a short course of oral steroids (3 to 5 days) ( Tables 16.4 and 16.5 , and see Table 16.3 ). Preoperative pulmonary function testing is rarely performed for asthmatic patients but may be indicated in the poorly controlled patient to define severity of disease and response to therapy. Patients with not well-controlled or poorly controlled asthma having emergency surgery should be pretreated with a SABA, and they should receive steroids (ideally intravenous). The addition of ipratropium bromide to SABAs for moderate-to-severe exacerbations may improve outcome and should be considered (250 to 500 mcg q 20 minutes × 3 PRN) ( ). Desflurane should not be used.

Vaping

The use of e-cigarettes, commonly known as vaping, has increased significantly among pediatric and adolescent patients. In 2018 the prevalence of nicotinic or flavor vaping in a sample of 8th grade students was reported to be 27% ( ; ).

The e-cigarette mimics combustible cigarette smoking by thermally vaporizing a liquid for inhalation that consists of one of two solvents (propylene glycol, vegetable glycerin) and flavorants (fruit, dessert, mint, tobacco-nicotine, and sometimes THC). The vaporization of the liquid at the heating element followed by a rapid cooling generates the aerosol that is inhaled or vaped. Vaping has been associated with thermal injuries, pulmonary injury, myocardial infarction, and psychosocial effects.

The primary purpose of e-cigarettes is to deliver nicotine. E-cigarettes in the United States deliver significantly more nicotine (>60 mg/mL) than those produced in other countries (<15 to 20 mg/mL). Two other components in e-cigarettes include propylene glycol and glycerin. They are responsible for the production of vapor ( ). Propylene glycol has been associated with upper respiratory infection–like symptoms. It is formed by the hydration of propylene oxide, which is a probable human carcinogen. Vegetable glycerin exposure is associated with irritation of the eyes, lungs, and esophagus. In addition to glycols, other toxicants formed during the vaporization of e-liquid include aldehydes, metals, volatile organic compounds, and polycyclic aromatic hydrocarbons ( ). Flavoring compounds like diacetyl-like diacetin, which is approved for flavoring but not inhalation, has been shown to reduce lung capacity as measured by FEV ₁ .

The more significant pulmonary injury is the e-cigarette/vaping-associated lung injury (EVALI). The majority of the lung injury seen in EVALI appears to be associated with tetrahydrocannabinol (THC) as opposed to the components mentioned above that are found in almost all e-cigarettes. THC requires a vitamin E acetate solution to create the vapor, and this lipid-based solution may explain some of the pathology. Lung biopsies reveal acute lung injury with diffuse alveolar damage and foamy (lipid-laden) macrophages ( ).

The present definition of EVALI is use of e-cigarettes within 90 days of symptoms onset, pulmonary infiltrates on imaging studies, and absence of other causes. The lung imaging most frequently seen with EVALI is a bilateral lower lobe ground glass and consolidated opacities with subpleural sparing (see Fig. 16.5 A and B). Clinical symptoms include shortness of breath, cough, pleuritic chest pain, chills, fever, nausea, and abdominal pain. Bronchoscopic findings include pneumocyte vacuolization with lipid accumulation. The treatment has consisted of supportive care, which may include intubation with mechanical ventilation, bronchodilators, and steroids. Rarely patients may require ECMO support. Presently there are no specific guidelines for the anesthetic managements of patients who vape ( ). It is unclear whether patients who vape should have preoperative pulmonary function tests or chest x-rays. Until evidenced-based guidelines are instituted, the preoperative visit should be viewed as an educational opportunity that focuses on the medical consequences of vaping as well as an opportunity to discuss substance abuse as it relates to smoking, nicotine, and marijuana.

Upper respiratory tract infections

Another cause for bronchial hyperreactivity (BHR) is the upper respiratory tract infection (URI). A URI is defined as a nasopharyngitis secondary to a viral infection. Patients typically present with rhinitis, nasal congestion, sore throat, cough, malaise, and fever. Although the symptoms would suggest the pathology is isolated to the upper respiratory tract, there is involvement of the lower respiratory tract (see Chapter 47 : Respiratory Disorders, Tables 47.10 and 47.11 and Fig. 47.3 ). Empey demonstrated significant bronchial constriction in healthy volunteers with colds who were exposed to an airway irritant ( ). Several studies have demonstrated an increased risk of perioperative respiratory complications when infants and children are anesthetized either during or following a URI. demonstrated in a retrospective study that respiratory complications were greatest within a 2-week period after a “cold” but not during the cold. Other studies have identified an increased incidence of respiratory complications when pediatric patients are anesthetized during or recently following a URI (up to 4 weeks) ( ; ). These complications include laryngospasm, bronchospasm, oxygen desaturation, and severe coughing. However, not all patients with colds will have these events. Identifying patients most at risk may help minimize cancellations and may identify patients most at risk for respiratory complications. In 2001 Tait identified independent risk factors for perioperative complications ( ). These included intubation in children less than 5 years old, reactive airway disease, paternal smoking, prematurity, airway surgery, and the presence of copious secretions along with nasal congestion. noted that parental report of a URI was predictive of laryngospasm.

Another assessment tool called the COLDS score was designed to predict the likelihood of perioperative respiratory complications related to the presence of a URI ( ). COLDS refers to c urrent signs or symptoms, o nset of symptoms, l ung disease, d evice (airway), and s urgery (minor or major airway) (see Table 16.6 ). The higher the score, the higher the percentage of patients that went on to develop perioperative respiratory events that include laryngospasm, bronchospasm, severe coughing, and oxygen desaturation. Score approaching 18 demonstrated a 50% incidence of a perioperative respiratory adverse event (see Fig. 16.6 ). Scores over 19 typically resulted in cancellation of surgery in the cohort of patients studied.

During the preoperative visit, the presence of an ongoing URI or one within the previous 2 to 4 weeks will be important to identify. Most of the studies investigated patients with mild or moderate colds. Patients with more severe symptoms might be more at risk and should have their surgeries postponed. These include patients with fever, significant purulent discharge, changes in behavior (lethargy), or abnormal lung sounds (wheezing, rhonchi) ( ). The real dilemma is identifying patients at risk when they have milder symptoms. Emergent or urgent surgery will need to proceed as scheduled. The decision to postpone elective surgery is multifactorial. Elective surgery in patients with mild URI symptoms can likely proceed. However, the presence of more significant URI symptoms and/or one or more of the risk factors outlined by Tait may indicate that the surgery should be delayed. The decision will be at the discretion and clinical judgment of the anesthesiologist, and their experience is an important factor. One study indicated that younger anesthesiologists were more likely to proceed, whereas older anesthesiologists were more likely to cancel surgery ( ). A clinical pathway algorithm has been suggested by Tait and colleagues and is shown in Fig. 16.7 ( ). The duration of delay is not clear. Bronchial hyperreactivity appears to last for 4 to 6 weeks. However, delaying surgery for that period of time will potentially increase the likelihood the patient will encounter another URI, and the delay may not be appropriate for some surgical procedures. A delay of 2 weeks for mild URI symptoms has been advocated and may be a safe compromise ( ; ; Ramgalon et al. 2018).

Preoperative preparation for patients who require anesthesia for emergency surgery in the setting of a URI may include preoperative administration of nebulized albuterol. Anesthetics that minimize airway resistance and maximize bronchodilation should be used. These include propofol and sevoflurane. Desflurane increases airway resistance and should be avoided in patients with bronchial hyperreactivity. Empiric administration of glycopyrrolate should not be administered because it has not been shown to reduce airway complications in pediatric patients with URIs. In fact, the relative risk of laryngospasm requiring succinylcholine was higher (RR = 3.7) in patients receiving glycopyrrolate ( ).

Obstructive sleep apnea

Obstructive sleep apnea (OSA) in children has increased in frequency and severity. Unfortunately, it is linked with the growing epidemic of childhood obesity. As many as 10% to 12% of children suffer from OSA, and this may predispose them to cardiovascular and pulmonary dysfunction, as well as neurocognitive and behavioral problems ( ). The pathology of OSA is different in children than adults. The peak incidence is between 2 to 6 years of age, and obesity is not always associated. Tonsillar hypertrophy is a common finding, and adenotonsillectomy corrects the majority of OSA (unlike adults). However, a significant portion of pediatric OSA is not corrected with AT (30%) ( ) (see Chapter 34 : Anesthesia for Pediatric Otorhinolaryngologic Surgery).

The presence of OSA increases the risk of perioperative respiratory complications. This is particularly true for the pediatric patient presenting for adenotonsillectomy (AT). The presence of OSA increases the risk of hypoxia, pulmonary edema, airway obstruction, and respiratory failure ( ). Pediatric patients with chronic hypoxia appear to have an elevation in the population of mu opioid receptors. Animal data suggest that chronic hypoxemia results in an activation of mu opioid receptors in the brain and increases the sensitivity to opioids. Identifying the presence and the severity of OSA during the preoperative visit is important but challenging. Polysomnography (PSG) and overnight oximetry are both very effective at identifying the severity of OSA, but they are not often performed prior to surgery. The severity of OSA on PSG and overnight oximetry is shown in Table 16.7 . Anesthesiologists are often left with the history and physical exam findings alone to identify the presence and severity of OSA. Unfortunately, the history and physical are not necessarily sensitive or specific for OSA ( ). Asking about the presence of snoring is sensitive but not specific for OSA. Questionnaires such as STOP-BANG have been developed in adult practice to identify patients at risk of OSA. In pediatric practice the STBUR (Sleep Trouble Breathing and Unrefreshed) questionnaire was developed to identify children at risk of adverse respiratory events related to sleep-disordered breathing ( ; ). Patients with three or more positive questions were significantly more likely to develop an adverse respiratory event as those with fewer than three positive questions ( ). A more recent study suggests that although the STBUR screening tool was found to be sensitive at identifying patients at low risk of adverse events related to sleep-disordered breathing, it did not demonstrate use in identifying patients at high risk for poor outcomes. Box 16.4 outlines the STBUR questions. Some families make a video- or audiorecording of the snoring and pausing, and this can be instructive. A history of congenital abnormalities, including craniofacial anomalies, may increase the likelihood of OSA. Patients with syndromic craniofacial anomalies, including craniosynostosis (Apert, Pfeiffer, Crouzon), clefting (Treacher Collins), and hypoplasia (Pierre Robin sequence, hemifacial microsomia [Goldenhar]), universally have some degree of OSA. Features of concern on physical exam include a small mandible, midface hypoplasia, presence of a craniofacial syndrome, high palate, and large tonsils. These features not only predict OSA but also may predict difficult mask ventilation and/or intubation. The exam should also include an evaluation of the muscle tone. Hypotonia may increase the risk of respiratory complications and may require a planned escalation in postoperative care (intensive care unit) for invasive or noninvasive ventilator support.

Patients with severe OSA are at risk for systemic hypertension and pulmonary hypertension (PAH). Children with severe OSA by PSG, oxygen desaturations less than 80%, or systemic hypertension may also require a preoperative echocardiogram to evaluate for pulmonary hypertension. Suspicion of PAH on physical exam includes a loud single second heart sound.

The perioperative management for patients with OSA includes minimizing the contribution of opioids for analgesia, maximizing nonopioid analgesia (including regional anesthesia), and planning for appropriate postoperative recovery and monitoring. Patients with moderate-to-severe OSA may not be appropriate candidates for outpatient surgery if the surgery involves the airway (AT) or if the patient is very young (≤3 years old). The surgical and anesthesia team should prospectively plan the appropriateness of outpatient surgery in patients suspected of having OSA. Ideally, a protocol is developed and in place to guide the perioperative plan ( ). Patients with known severe OSA who use Bilevel Positive Airway Pressure (BiPAP) or Continuous Positive Airway Pressure (CPAP) should have these modalities available to them in recovery and on the hospital ward. Preoperative initiation of CPAP or BiPAP may reduce pulmonary hypertension and postoperative complications in adults and is being employed in some pediatric centers ( ; ).

Patients with OSA may receive midazolam preoperatively. investigated perioperative complications related to the preoperative administration of 0.5 mg/kg of oral midazolam. One out of 70 children had airway obstruction after the premedication, and this child likely had severe OSA based on a preoperative oximetry desaturation to less than 70%. It appears that oral midazolam may increase the risk of perioperative respiratory complications in patients with mild-to-moderate OSA. Von Ungern-Sternberg also found an association between premedication with midazolam and perioperative respiratory adverse event ( ). If patients that have severe OSA require midazolam, a reduced dose should be considered or an alternative medication with minimal respiratory side effects should be used (alpha-2 agonist like clonidine or dexmedetomidine).