The medical problems of the premature neonate do not end with discharge from the neonatal intensive care unit . Many complications of prematurity must be addressed in the follow-up period and often these require surgical intervention . The situation is further complicated by the fact that almost all affected infants have various degrees of bronchopulmonary dysplasia, predisposing to coughing, laryngospasm, and consequent hypoxic episodes in the perioperative period . It is our impression that symptoms of airway irritability often occur after extubation following general anesthesia with tracheal intubation.
Since the laryngeal mask airway (LMA) does not enter the trachea, it is less irritating to both the upper and lower airways; therefore, it may be advantageous in former premature infants and other children with chronic lung disease . We designed the present study to compare the anesthetic course of former premature infants and children with various degrees of bronchopulmonary dysplasia using an LMA or endotracheal (ET) tube. All previous investigations of the LMA have excluded patients with chronic lung disease and focused on patients with normal pulmonary function and compliance [5-8].
Retinopathy of prematurity, previously referred to as retrolental fibroplasia, is a frequent complication of prematurity which occurs in over 50% of infants born prior to 30 wk gestational age and weighing less than 1500 g . These children often require surgical intervention consisting of a lengthy open-sky vitrectomy followed several weeks later by a shorter examination under anesthesia and suture removal. Although mask anesthesia can be used for the second stage procedure, movement of the anesthesiologists hand while holding the mask, the mask itself, or any head motion may interfere with visualization under the microscope. Former premature infants with a history of bronchopulmonary dysplasia undergoing ophthalmic surgery were selected as a model for the use of the LMA in patients with chronic lung disease. Prior to the use of the LMA at our institution, general anesthesia for these procedures was administered, aided by tracheal intubation.
Twenty-seven ASA physical status II former premature infants and children currently 6 mo-5 yr of age with a history of bronchopulmonary dysplasia, presenting for second stage open-sky vitrectomy were evaluated and randomly assigned to either LMA or ET tube for airway maintenance during general anesthesia. This investigation was approved by our institutional review board and written informed consent was obtained from parents prior to the induction of anesthesia. No patient in either group was oxygen or diuretic dependent but all had radiographic findings consistent with bronchopulmonary dysplasia.
No premedication was administered. Anesthesia was induced with 60% N (2) O:40% O2 and halothane in increasing concentration via mask while routine monitoring, consisting of precordial stethoscope, automated blood pressure cuff, pulse oximeter, axillary temperature probe, and electrocardiogram were applied. After intravenous access was established, the inspired halothane concentration was increased using a total gas flow of 6 L until adequate depth of anesthesia was obtained as determined by constricted upward pupillary gaze, softness of abdominal musculature, and relaxation of the jaw. Either the appropriate size LMA (Intavent Registered Trademark) was inserted without direct visualization of the larynx or the appropriate ET tube was inserted aided by laryngoscopy and total gas flow was decreased to 3 L/min for maintenance anesthesia. Halothane concentrations were adjusted to maintain adequate depth of anesthesia for the duration of the surgical procedure. During the procedure, patients were allowed to breath spontaneously and ventilation was assisted by hand, at the discretion of the attending anesthesiologist, to maintain normocarbia. Exhaled CO2 and anesthetic gas concentrations were continuously measured (Datex Registered Trademark 253 Airway Gas Monitor; Datex, Helsinki, Finland) throughout the surgical procedure including the time of extubation. These gas concentrations were measured at the proximal end of both the LMA and ET tube at the Y-connection of the anesthesia breathing circuit. The airway gas monitor was calibrated for CO2 against a known gas mixture of CO2 4.62%, O2 65.34%, and N2 O 30.04% on a daily basis. A circle system was used in all patients (Intertech Pediatric anesthesia breathing circuit; Sims-Intertech Inc., Fort Myers, FL). No narcotics were administered. All patients were in the supine position throughout and body temperature was maintained at 36-37 degrees C. At the end of the surgical procedure, the anesthetics were discontinued, 100% O2 was administered, and the airway device removed at a relatively deep level of anesthesia.
Patients were observed for the presence of coughing, wheezing, and decreased O2 saturation during surgery and in the postanesthesia care unit (PACU). Supplemental O2, 10 L/min delivered by face tent, was administered routinely to all patients in the PACU until awake and responsive with baseline O2 saturation equivalent to preoperative values. In the PACU, all patients were observed by the same recovery nurse who was blinded to the airway used intraoperatively. Patients were discharged when awake and drinking, having scored at least 9 on the Aldrete postanesthesia recovery evaluation. Prior to discharge, the parents were asked to evaluate the presence of hoarseness in their child's voice.
Data are presented as mean +/- SE, except for age and weight which were presented as SD, and were analyzed by t-test and Fisher's exact test. Statistical significance was achieved when P < 0.05.
Twenty-seven ASA physical status II infants and children with bronchopulmonary dysplasia were evaluated. In 13 patients the airway was maintained with the LMA; in 14 the ET tube was used. The average duration of surgery was 32 min in the LMA group and 38 min in the ET tube group. There was no significant difference between the two groups in age (LMA 19.9 +/- 4.2 mo; ET tube 14.3 +/- 2.3 mo), weight (LMA 11.1 +/- 3.3 kg; ET 9.3 +/- 3.1 kg), inspired O2 concentration (LMA 0.45% +/- 0.03%; ET tube 0.47% +/- 0.01%), and mean exhaled halothane concentration measured throughout the procedure (LMA 1.7% +/- 0.13%; ET tube 1.5% +/- 0.1%). End-tidal CO (2) and respiratory rates during the procedure, however, were significantly higher in children with the LMA than in children with the ET tube Table 1, whereas mean intraoperative pulse rate and both systolic and diastolic blood pressures were higher in patients in the ET tube group. There were no episodes of coughing or desaturation in either group during the study period.
No child in either group required supplemental postoperative oxygen for longer than our institution standard of 15 min. A significant difference was noted in the recovery and discharge variables after the discontinuation of halothane in both groups of patients Table 2. Children in the LMA group opened their eyes and were discharged home earlier than children with in the ET tube group. No postoperative complications were noted in patients with the LMA. Of the children in the ET tube group, three developed transient complications; one had a cough associated with inspiratory and expiratory wheezing; another had a cough with oxygen desaturation to less than 95%; and a third child had wheezing and desaturation. The parents of this last child, as well as those of one other, said they noted postoperative hoarseness in the child's voice. There was a significant difference between the two groups as to the incidence of postoperative complications with the ET tube relative to children with LMA (Fisher's exact test, P = 0.04).
Bronchopulmonary dysplasia (BPD) is the most common cause of chronic lung disease in infants . Rather than being a specific disease, it is a symptom complex characterized by airway obstruction, airway hyperactivity, and lung hyperinflation . This results in uneven distribution of ventilation, reduced compliance, increased work of breathing, and compromised gas exchange. The clinical manifestations of this condition are rapid respiration, wheezing, cough, and frequent episodes of fever, desaturation, and bradycardia [2,3]. Instrumentation of the airway is associated with pulmonary, as well as systemic, hypertension . Further respiratory compromise may prove to be disastrous in these patients, and it is well documented that infants with BPD are at increased risk to develop bronchospasm, atelectasis, and pneumonia in the postoperative period [11,12].
Open-sky vitrectomy is not the only surgical procedure that the former premature infant might undergo, but it illustrates the physiologic considerations of these children under general anesthesia. Although airway irritability is undesirable during any surgical procedure, it is especially deleterious during ophthalmologic and neurosurgical procedures, where hypertension, hypoxemia, hypercarbia, and any increase in central venous pressure (as is encountered during coughing, straining, or bucking), will increase intraocular or intracranial pressure. In certain situations a single acute increase in intraocular pressure (IOP) can cause blindness .
Prior to the availability of the LMA, children presenting for ophthalmologic and other surgery involving the head and neck often required tracheal intubation to allow surgical access to the face. General anesthesia could be administered by face mask, but there was always the risk that either the mask itself or the anesthesiologist's hand might interfere with successful completion of surgery. In addition, pressure on the globe from both the mask or hand has been implicated in increase of IOP. Most of the procedures requiring a dissecting microscope (ophthalmic, otolaryngologic, reconstructive, etc.) are very delicate and any movement by a hand or the face mask will be magnified at the field of surgery. This can be avoided by eliminating the mask or hand from the child's face which has been traditionally accomplished by the use of an ET tube. The disadvantages of laryngoscopy and tracheal intubation, such as marked increases in IOP, systemic pressure, and pulmonary vascular resistance can be avoided by the use of the LMA [5-8,13,14].
In this study we noticed significant differences in respiratory variables between the two patient groups. We realize that although assisted spontaneous ventilation was acceptable for the relatively short second stage of open-sky vitrectomy, controlled ventilation is appropriate for longer surgical procedures. We noted that exhaled CO2 concentration and respiratory rate were higher in children with the LMA than in those with the ET tube. Increased respiratory rate in children ventilated with the LMA seems to be a common feature, and a previous investigation also reported higher respiratory rates in pediatric patients when the LMA was used . A decreased depth of anesthesia in patients managed with the LMA has been demonstrated in adults . Since the LMA does not stimulate the sensitive tissue of the larynx and trachea of pediatric patients, it is possible that in the absence of laryngeal stimulation they too may be maintained at a lighter plane of general anesthesia for minor surgical procedures. The increases in respiratory rate and exhaled CO2 may not be directly attributable to the LMA itself, but rather the depth of anesthesia required to tolerate it. If a lower blood concentration of halothane were present in the LMA group due to decreased depth of anesthesia this might account for the significant difference in discharge times observed in the two groups. This was not measured, however, and since our study was not designed to examine differences in time to awakening and discharge, these were incidental findings to be explained in retrospect. In contrast, the pulse rate and both systolic and diastolic pressures were lower in patients managed with the LMA implying decreased cardiovascular stimulation with LMA insertion in children. Minimal cardiovascular response during insertion of the LMA and decreased anesthetic requirement have been reported to date only in adult patients [17,18].
The immediate postoperative respiratory complications noted in the affected children showed the same trend as in adults during ophthalmologic surgery . The incidence of coughing, straining movements, breath holding, and sore throat were much higher when the ET tube was used compared to when the LMA was used. We also observed that awakening and home discharge were faster with the LMA as compared to patients having undergone ET intubation for the same surgical procedure. These were incidental findings in our patients, and further studies to examine awakening and discharge data are needed to verify this.
Earlier studies suggest that the general consensus among anesthesiologists is that respiratory complications are fewer with the LMA [6,7]. No earlier study has shown this conclusively. To date, the LMA has been used in children during radiation therapy, outpatient dental extractions, minor otologic surgery, ophthalmic examination, and measurement of IOP in healthy children [4,5,19-22]. The LMA is most valuable in procedures where the anesthesiologists must be stationed away from the surgical field, and a better choice than the face mask/oral airway combination in the patient whose face needs to be turned to one side or another . In most previous studies, the LMA was used in essentially healthy children, where the respiratory status is not a major issue. In our study, we found the device to be particularly useful in patients afflicted with a chronic respiratory disease. Based on many observations of this study, it is our practice today to use the LMA for second stage vitrectomy as well as other ophthalmic procedures in children with BPD, unless there is a specific contraindication to the use of the LMA, such as gastroesophageal reflux. The advantages of the LMA are not denied to our young patients because of altered pulmonary function or mild to moderate chronic lung disease.
The authors are indebted to Dr. T. Hirose for his cooperation in studying his patients, Dr. A. Zaslavsky for his assistance in statistical analysis, and Deanna Davis for manuscript preparation.
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