The use of cuffed tubes (CT) is increasing in children younger than 8 yr of age undergoing routine general anesthesia. This practice is related to the valuable advantages of CT, including fewer laryngoscopies to replace ill-fitting tubes (1,2), less contamination of the operating room environment with anesthetic gases (1–3), reliable capnography monitoring (2,4), decreased risk of gastric contents aspiration (5), adequate ventilation with a low fresh gas flow, and, thus, reduced costs of volatile anesthetics (1–3). Historically, pediatric anesthesiologists have refrained from using CT in children younger than 8 yr of age because of the anatomical particularities of their airway (2) and, thus, the increased risk of postintubation tracheal damage. In addition, the use of CT was thought to be dangerous because it enforces the use of a tube with a smaller internal diameter, leading to high respiratory airway pressure and an increased risk of tube obstruction; a correctly sized uncuffed tube could maintain a secure airway and permit mechanical ventilation without excessive air leakage. However, no difference in short-term postoperative complications or respiratory problems has been demonstrated between children who have CT or uncuffed tubes as part of their anesthetic care (1,3,6).
During general anesthesia with tracheal intubation, nitrous oxide (N2O) is frequently used, even if diffusion of N2O into the cuff of the tracheal tube may result in an increase in cuff pressure (Pcuff) (7). The excess Pcuff causes tracheal mucosal erosion and sore throat, as demonstrated after short-term intubation in adult patients scheduled for surgical procedures lasting only up to a few hours (7). The initial intracuff pressure (iPcuff) and changes during N2O anesthesia in pediatric patients have not yet been investigated. We therefore conducted a clinical study whose main end-points were the measurement of the iPcuff after free air inflation and assessment of the kinetics of the Pcuff increase during N2O general anesthesia in children. We hypothesized that iPcuff would be unpredictable after initial free air inflation and that numerous gas removals would be required to avoid overinflation of the cuff during N2O anesthesia in children.
Over a 4-mo period, children of ASA physical status I or II, aged 0–9 yr, weighing 3–35 kg, and scheduled for routine surgery under general anesthesia with tracheal intubation and an expected mechanical ventilation lasting at least 45 min were prospectively included. No attempt was made to influence the anesthetic management, the size of the tracheal tube, the choice between the use of a CT or an uncuffed tube, or the use of N2O. In our department, it is mandatory, when using a CT, to control the Pcuff throughout the duration of tracheal intubation and to maintain the Pcuff between 20 and 25 cm H2O (7,8).
Children were studied after ethical committee approval. Only patients having a CT were included in this prospective study. Data were recorded according to a protocol already used routinely in our department, and the informed consent of the parents was not required by the Comité Consultatif de Protection des Personnes dans la Recherche Biomédicale because the study protocol did not change routine practice. Inclusion required general anesthesia performed with 50% N2O: the other anesthetics used were left to the anesthesiologist’s choice. Children with prior tracheal sequelae, ventilation without N2O, and difficult airway were excluded. Children were divided into six groups according to the size of the CT: CT 3.5, CT 4, CT 4.5, CT 5, CT 5.5, and CT 6. The CTtot group comprised all the patients included in the study. Routine monitoring was applied, and general anesthesia was established as follows. After denitrogenation, induction was performed with sevoflurane or an IV hypnotic drug and a gas mixture, including 50% N2O. The trachea of the child was then intubated with a CT chosen by the anesthesiologist in charge of the patient, with the Pcuff monitoring device (Mallinckrodt® pressure manometer; Mallinckrodt, Athlone, Ireland) already connected to the pilot balloon; ventilation was controlled artificially. Tracheal intubation was performed with sterile CT ranging from size 3.5 to 6.0 (Hi-lo, low pressure/high volume; Mallinckrodt). After the end of the surgical procedure, the tracheal tube was removed in the OR, and all patients were transferred to the postanesthesia care unit (PACU) for postoperative follow-up.
The Pcuff monitoring device consisted of a 20-cm line fixed to the pilot balloon of the tracheal tube and connected to the pressure manometer by a three-way stopcock. Before the beginning of the study, the zero of each pressure manometer was verified by using a column of mercury. A 5-mL syringe was attached to the stopcock and used to inflate the cuff with room air. The inflation of the cuff was performed as usual at the anesthesiologist’s discretion and was assessed by manual palpation of the pilot balloon without seeing the pressure measured by the manometer. The pressure was recorded and immediately adjusted when necessary: the target iPcuff ranged from 20 to 25 cm H2O. Mechanical ventilation was performed with a tidal volume of 8–10 mL/kg, an age-adapted respiratory rate, a maximum peak airway pressure of 26 cm H2O, and an inspiratory/expiratory time ratio of 1:2 or 1:1.5.
After tracheal intubation, the time of intubation and the inspiratory and expiratory volumes, as indicated by the anesthetic ventilator, were recorded. The iPcuff, as measured by the manometer, was recorded by the investigator and then adjusted to 20 cm H2O; the inspiratory and expiratory volumes were again recorded. The air leakage was calculated before and after cuff inflation by the following formula: inspiratory volume − expiratory volume/inspiratory volume. In case of airway leakage of >25%, with a Pcuff of 20 cm H2O and a peak airway pressure of 20 cm H2O, the size of the tracheal tube was deemed to be inappropriate and the tube was changed. Because no attempt was made to influence the anesthetic management, including the choice of the size of the tracheal tube used, the size of the CT used was compared retrospectively with the classic formula: CT size = [(age/4) + 3](1). Pcuff was continuously monitored with the manometer, and 50% N2O was used throughout the duration of mechanical ventilation. When Pcuff increased >25 cm H2O, deflation of the cuff was performed to readjust the Pcuff to 20 cm H2O. In case of underinflation with Pcuff <20 cm H2O, the cuff was reinflated to 20 cm H2O. Each inflation or deflation of the cuff, the time elapsed from the intubation time, and the temperature of the patient at that moment were recorded. Events potentially harmful to the tracheal mucosa, such as traumatic laryngoscopy or prolonged hypotension, were also recorded. The total duration of tracheal intubation and the postoperative follow-up in the PACU and events possibly related to the use of a CT (such as sore throat, dyspnea, dysphonia, cough, or postextubation stridor) were also recorded.
The main end-points of this study were the measurement of the iPcuff and the assessment of the kinetics of the Pcuff increase over time. Accordingly, the duration of tracheal intubation was divided into 30-min time intervals, and the number of cuff deflations was noted for each patient. The mean number of deflations per time interval was calculated for each group, and the percentage of CTs deflated during each 30-min time interval was calculated.
Data are expressed as mean (sd) in case of normal distribution, median (95% confidence interval) in case of nonnormal distribution, or number of cases (percentage of cases). Statistical analysis used the unpaired Student’s t-test in cases of normal distribution and the Mann-Whitney U-test in cases of nonnormal distribution for continuous variables, whereas Fisher’s exact test was used for discrete variables. An analysis of variance was performed to compare the different study groups. The Bonferroni multiple comparison test or the Newman-Keuls multiple comparison test was used where appropriate. All P values were two tailed, and a P value of <0.05 was required to reject the null hypothesis. Statistical analysis was performed with NCSS 6.0 software (BMDP Co., Los Angeles, CA).
One-hundred-seventy-four consecutive patients who had a CT inserted were included in the six study groups; their main characteristics are presented in Table 1. Ten patients (5.6%) had to be reintubated with a CT one size (0.5 mm) smaller, either because there was resistance to passage of the initial CT into the trachea or because there was not an audible leak when the lungs were inflated to a pressure of 20–30 cm H2O before the cuff inflation. Among the 174 patients, airway leakage was 17.0% (14.0%–20.0%) immediately after intubation and before the cuff inflation and was 7.5% (6.0%–9.0%) after the Pcuff adjustment at 20 cm H2O (P = 0.000001). No difference in airway leakage was observed among the different CT size groups. The durations of intubation were similar among the different groups (Table 1).
Examination of the CTtot group data shows that the median value of iPcuff was 22 cm H2O (20–24 cm H2O) and ranged from values as low as 0 up to 120 cm H2O. The distribution of iPcuff values is shown in Table 2. In 80% of the cases, iPcuff values were out of the pressure range defined by the study protocol: 39% were more than 25 cm H2O, and 41% were less than 20 cm H2O.
Pcuff did not change throughout the duration of ventilation in 23 patients (13%), and in 4 children (2%), only 1 reinflation was necessary to maintain Pcuff in the fixed range. Thus, in 147 patients (85%), numerous gas deflations were necessary to keep the Pcuff in the fixed range (Fig. 1).
The median time from initial adjustment of Pcuff at 20 cm H2O to the first gas exchange was 12 min (10–15 min) in the CTtot group. Similar variations were found in the CT subgroups, and no particular relationship could be determined between the size of the tube and the time elapsed before the first gas exchange. In the same way, no specific duration between the first and the second or the second and the third deflation was noted. In the CTtot group, 50% of all the deflations took place during the first 30-min time period, and 90% of all the gas exchanges were performed before the first 105 min after intubation. The mean number of deflations per CT per 30-min time interval is shown in Figure 2. Figure 1 shows that, for all 174 patients, the percentage of CTs deflated during each 30-min time interval gradually decreased throughout the duration of N2O anesthesia. Similar results were revealed by the separated data analysis of the tube-size groups.
Respiratory complications were recorded in five children (3%). One child in the CT 4 group presented with a hoarse cough, and one case of moderate dysphonia was recorded in the CT 5 group; these complications resolved spontaneously before discharge from the PACU. In the CT 4.5 group, one patient required corticoid nebulization because of postextubation stridor, and 2 cases of traumatic laryngoscopy required 24-h corticotherapy in the CT 3.5 and CT 4.5 groups. No postoperative reintubation was recorded.
Free inflation of the cuff, controlled only by the palpation of the pilot balloon, is not reliable and results in extremely variable iPcuffs, ranging from 0 to 120 cm H2O. During 50% N2O anesthesia in children, Pcuff increases occurred mainly during the first 105 minutes of mechanical ventilation. Nevertheless, the data regarding the delays between the numerous cuff deflations necessary to maintain Pcuff within the limits of 20—25 cmH2O show that a precise inflation rate could not be determined, whatever the size of tube used.
A large percentage of iPcuffs obtained after inflation by either anesthesiologists or residents in anesthesia with more than four months of training in pediatric anesthesia were out of the pressure range fixed by the study protocol. These are the pressure values recommended in adults and, therefore, suggested in children. Attention to the cuff inflation by measuring the iPcuff after intubation for general 50% N2O anesthesia therefore is of major importance. This measurement may be performed using the Mallinckrodt pressure manometer, which is an easy-to-use and reliable monitor (7–9).
Neither the inflating rate nor inflating particularities related to the tube size could be outlined in this pediatric study; the same problems have been observed in adults (10). One could have expected that iPcuff and inflation rate would have been more important in the small tubes, but the age-dependent tracheal smoothness probably explains the variability of the counterpressure exerted on the tube balloon. This may account for the absence of difference among the tube-size groups.
Liquid filling of the CTs cannot be recommended in routine clinical practice, because the cuffs are not designed for such a technique. In a similar way, cuff inflation with the anesthetic gas mixture does not prevent an initial cuff overpressure (7,11–13).
Some of the proposed advantages of using CTs were noted in this study. Ill-fitting tube replacement occurred in only 5.6% of the patients, which is a smaller percentage than often reported (18%–30%) in patients who had an uncuffed tube inserted (1). Airway leakage after cuff inflation was reduced from 17% (14.0%–20.0%) to 7.5% (6.0%–9.0%) and thus was small enough to suggest that capnography could be considered reliable and OR pollution significantly reduced during anesthesia with low fresh gas flow (1–3).
Postoperative respiratory complications, though they occurred in only 3% of the patients, could not be eliminated by continuous Pcuff monitoring. Although pediatric anesthesia publications have reported postextubation respiratory complications mainly after prolonged intensive care unit intubation (14,15), there have been recent reports of problems after short-duration intubation for anesthesia (16). Several risk factors possibly leading to tracheal mucosal lesions have been suggested, including traumatic intubation, emergency intubation, anesthesia protocol, an oversized tube, and a long duration of intubation (15,17–20). In adult patients, the occurrence of tracheal lesions after short-term intubation has been clearly demonstrated (8,21). Considering the overall pediatric and adult data, the risk of tracheal lesions after a few hours of tracheal intubation in children appears real. Pcuff control using a pressure-monitoring device reduces the incidence of sore throat (7,22,23), and this clinical symptom seems to be directly related to tracheal mucosal erosion in adults (7). Mechanical ventilation tolerating a moderate airway leakage may not be sufficient to prevent postoperative respiratory complications in children, because this technique does not eliminate the pressure that a CT could exert on the tracheal mucosa (20,24,25). Thus, Pcuff monitoring in children could reduce the incidence of mucosal erosions, as in adult patients, and limit postintubation sequelae (9,26). The pressure range fitting children’s tracheas is not yet precisely known, and cuff overpressure consequences on the tracheal mucosa have to be studied.
However, in our study we assessed only short-term postoperative respiratory complications, and the study protocol did not enable us to exclude long-term postoperative respiratory complications after tracheal intubation with a CT. However, since the end of the study, we have not been made aware of the occurrence of such long-term complications in our study population. Therefore, further studies are needed to compare the effect of tracheal intubation with either a CT or uncuffed tracheal tube on long-term postoperative respiratory complications.
In conclusion, the results of this study have shown that iPcuff is unpredictable after free air inflation and that numerous gas removals are required to maintain endotracheal Pcuff less than 25 cm H2O during N2O anesthesia in children.
The authors would like to thank Dr DJ Baker, M Phil DM FRCA, SAMU de Paris, CHU Necker-Enfants Malades, for kindly reviewing the manuscript.
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