Uncuffed endotracheal tubes are routinely used in young children. This study tests a formula for selecting appropriately sized cuffed endotracheal tubes and compares the use of cuffed versus uncuffed endotracheal tubes for patients whose lungs are mechanically ventilated during anesthesia.
Full-term newborns and children (n = 488) through 8 yr of age who required general anesthesia and tracheal intubation were assigned randomly to receive either a cuffed tube sized by a new formula [size(mm internal diameter) = (age/4) + 3], or an uncuffed tube sized by the modified Cole's formula [size(mm internal diameter) = (age/4) + 4]. The number of intubations required to achieve an appropriately sized tube, the need to use more than 21.min-1 fresh gas flow, the concentration of nitrous oxide in the operating room, and the incidence of croup were compared.
Cuffed tubes selected by our formula were appropriate for 99% of patients. Uncuffed tubes selected by Cole's formula were appropriate for 77% of patients (P < 0.001). The lungs of patients with cuffed tubes were adequately ventilated with 2 1.min-1 fresh gas flow, whereas 11% of those with uncuffed tubes needed greater fresh gas flow (P < 0.001). Ambient nitrous oxide concentration exceeded 25 parts per million in 37% of cases with uncuffed tubes and in 0% of cases with cuffed tubes (P < 0.001). Three patients in each group were treated for croup symptoms (1.2% cuffed; 1.3% uncuffed).
Our formula for cuffed tube selection is appropriate for young children. Advantages of cuffed endotracheal tubes include avoidance of repeated laryngoscopy, use of low fresh gas flow, and reduction of the concentration of anesthetics detectable in the operating room. We conclude that cuffed endotracheal tubes may be used routinely during controlled ventilation in full-term newborns and children during anesthesia.
Cuffed endotracheal tubes are recommended for use with children only for specific indications. Most pediatric anesthesiologists traditionally use uncuffed endotracheal tubes for children younger than 8 yr. Frequently cited reasons for this practice are: adding a cuff necessitates a smaller tube, which increases airway resistance and work of breathing; cuffs increase the risk of airway mucosa injury; and cuffs are not necessary, because appropriately sized uncuffed tubes seal well at the cricoid ring where the lumen is narrowest in children. 
In contrast, the use of cuffed endotracheal tubes may have some advantages. Because the fit of a cuffed tube can be adjusted, it may allow fewer laryngoscopies to replace ill-fitted endotracheal tubes. The reliable presence of a soft seal may reduce the risk of aspiration, may improve the reliability of end tidal gas monitoring, and may reduce contamination of the operating room environment with anesthetic gases to meet the recommendation of the National Institute for Occupational Safety and Health (NIOSH).*
There are no controlled studies comparing the use of cuffed and uncuffed tracheal tubes in pediatric patients undergoing tracheal intubation as part of their anesthetic care. Our null hypotheses were that choice of cuffed or uncuffed endotracheal tubes would not affect the number of endotracheal tube changes needed to place the appropriately sized endotracheal tube, the ability to ventilate the patient's lungs adequately, the ability to use low fresh gas flows, the anesthetic gas concentration in the operating room and the incidence of postoperative croup.
Materials and Methods
The hospital clinical research review committee approved the protocol and agreed that an informed consent document was not necessary because use of cuffed and uncuffed endotracheal tubes are within the standard care provided at our institution. Children between the ages of full-term newborn and 8 yr who required tracheal intubation as part of their anesthetic care were enrolled. Children with odd medical record numbers were assigned to the cuffed tube group, and those with even numbers were assigned to the uncuffed tube group. Children with a history or physical evidence of intrinsic or extrinsic airway obstruction or severe pulmonary disease or those who required nasotracheal intubation were excluded from the study. Patient gender, weight, age, history of croup or recent upper respiratory tract infection, and surgical procedure were recorded. This study was not blinded.
Patients in the cuffed endotracheal tube group were tracheally intubated with Mallinkrodt lo-pro (Mallinkrodt, Inc., Glens Fall, NY), oral RAE, or Sheridan low pressure cuffed endotracheal tubes (Sheridan Catheter Corp., Argyle, NY). The endotracheal tube size was selected based on the following formula:Equation 1.
An upward rounding approach was used. A child who passed his or her first birthday is calculated as 2 yr old and received a 3.5-mm internal diameter cuffed tube (Table 1). If there was resistance to passage of the tube into the trachea, a tube one size (0.5 mm) smaller was placed. The cuff was inflated using a Shiley pressure relief adapter, which limits cuff pressure to 25 mmHg. When a leak occurred at an inflation pressure less than 10 cm water, the tube was changed to a tube one size larger.
Patients in the uncuffed tube group were tracheally intubated with uncuffed tubes manufactured by the same companies. Size was based on the commonly used modification of Cole's formula:[4,5]
In children younger than 1 yr, tubes smaller than indicated by this formula were used at the discretion of the attending anesthesiologist (Table 1). If there was resistance to passage of the initial tube into the trachea, or if there was not an audible leak when the lungs were inflated to a pressure of 20–30 cm water, a tube one size (0.5 mm) smaller was placed. If a leak occurred at an inflation pressure less than 10 cm water, the tube was changed to a tube one size larger. Equality of breath sounds was checked to ensure that the endotracheal tubes were in the trachea. The number of attempts needed to arrive at the final endotracheal tube size were recorded in both groups.
All patients received 60–70% nitrous oxide, and their lungs were mechanically ventilated using a semi-closed circle system. Ohmeda anesthesia ventilators (Ohmeda, Columbia, MD) were set to maintain adequate oxygenation and carbon dioxide elimination. Fresh gas flow rates of 2 1 [center dot] min sup -1 were used, if possible, to keep the ventilator bellows up, and were then recorded.
In a subset of patients selected at random using an Ohio Trace Gas Analyzer, nitrous oxide concentrations at 6 and 24 inches away from the patients's mouth were measured 10–15 min after tracheal intubation. All anesthesia machines are equipped with a waste gas scavenging system. Our operating rooms have volumes between 142 m3and 2293and are ventilated with at least 12 air exchanges per hour. All hoses and equipment are routinely maintained and inspected for leaks.
All patients' tracheas were extubated in the operating room after completion of the surgical procedure. The duration of intubation was recorded. Patients were observed for evidence of croup during their hospital stay. The presence of stridor, a persistent barking or brassy cough, sternal or intercostal retractions, and treatment or unplanned admission for croup were recorded. The data were analyzed using a two-tailed Student's t test for continuous parametric variables, Mann-Whitney U test for nonparametric variables, and chi-square analysis with Yates correction for nominal variables.
There were 251 patients in the cuffed tube group and 237 patients in the uncuffed tube group. Age, weight, duration of intubation, and surgical procedure were comparable for the two groups (Table 2and Table 3). The number of patients who required tracheal reintubation to place an appropriately sized tube was significantly greater in the uncuffed tube group than in the cuffed tube group (Table 4). The three patients in the cuffed tube group who required a second tube were 3, 4, and 6 yr of age and required placement of an tracheal tube one size (0.5 mm) larger. In the uncuffed tube group, a larger tube was placed in 13 (5.5%) patients whose average age was 4.5 yr, and a smaller tube was placed in 41 (17%) patients whose average age was 1.9 yr. The rate of reintubation in the uncuffed tube group was 30%(27/89) in children younger than 2 yr and was 18%(27/148) in patients 2 yr or older. These rates were significantly different than rates for patients in the cuffed tube group with those age ranges by chi-square analysis (P < 0.001). More patients in the uncuffed tube group required a fresh gas flow greater than 2 1 [center dot] min sup -1 to maintain inflation of the bellows on the anesthesia ventilator (Table 4).
Nitrous oxide concentrations in the operating room were measured during the care of 39 patients in the cuffed tube group and 40 patients in the uncuffed tube group. This subset of patients was similar to the overall population in terms of age. The distribution of nitrous oxide concentrations at 24 inches from the patient's mouth is shown in Table 5. Nitrous oxide concentrations were greater when uncuffed tracheal tubes were used (P < 0.001 by Mann-Whitney U test). Nitrous oxide concentration at 24 inches, which approximates the anesthesiologist's breathing zone, were compared with the NIOSH limit for time-weighted exposure of 25 parts per million (ppm). Measured concentration exceeded 25 ppm more frequently when uncuffed tracheal tubes are used (15/40, 37%) than when cuffed tracheal tubes are used (0/39, 0%, P < 0.001 by Mann-Whitney U test).
Six patients (2.4%) in the cuffed tube group and seven (2.9%) in the uncuffed tube group had signs or symptoms of croup (Table 6). Of these patients, three patients in each group were treated with racemic epinephrine. For one patient in each group, diagnosis of croup was involved in the decision for hospital admission. None of these patients required tracheal reintubation for croup. One of the two patients admitted for croup was 2 yr old, had multiple medical problems, was small for age, and had a history of croup. This child was tracheally intubated with a 3.5-mm cuffed tube. The other was a 1-yr-old child with a preoperative upper respiratory tract infection undergoing an adenoidectomy, and whose trachea was intubated with a 4.0-mm uncuffed tube. There was no significant difference detected between the groups with regard to incidence of croup.
Sizing of Endotracheal Tubes
Pediatric anesthesiologists routinely change endotracheal tubes to achieve an appropriate fit. [3,6]This is necessary when using uncuffed endotracheal tubes because of the normal variations in laryngeal dimensions and the fixed outer diameter of these tubes. Using the protocol-defined choice of initial tube and reintubation criteria, we demonstrated that use of cuffed endotracheal tubes, which have an adjustable outer dimension and shape, almost eliminates the need to replace the initial tube.
Our formula for the size of the initial cuffed tube was based on the experience in our hospital. A variety of formulae are used to calculate uncuffed endotracheal tube size. Many anesthesiologists use different guidelines for tube size in children younger than 1 or 2 yr. We chose the commonly used modification of the age-based formula proposed by Cole for calculating uncuffed tube size in all patients, except those younger than 1 yr. Our belief that this closely approximates common practice is least certain in children younger than 2 yr. However, our results retain significance when children younger than 2 yr are excluded from the analysis.
Our criteria for replacement of uncuffed tubes used a leak test, which is an imprecise way to calibrate tube size because of significant interobserver variability, but reflects common pediatric anesthesia practice. Our reintubation rate of 23% in this group is consistent with the work of other investigators. Although reintubation rates are not directly reported, several studies suggest that calculated tube sizes are frequently inappropriate. Koka et al. reported that 31% of children of as old as 17 yr had no leaks at 25 cm of water pressure. Mukubo et al. judged the tube to be the wrong size in 35% of children younger than 6 yr. Mostafa found that the final endotracheal tube that was used varied from the calculated size in 28% of children younger than 14 yr.
Operating Room Contamination with Anesthetic Gas
We measured ambient nitrous oxide 24 inches away from the patient's mouth during a steady state of anesthesia. The NIOSH-recommended exposure limit is 25 ppm as a time-weighted average. Wood et al. found (using passive atmospheric samplers) that nitrous oxide exposure to operating room personnel consistently exceeded 25 ppm and could be as great as 500 ppm during pediatric otolaryngology surgery. They concluded that “NIOSH recommendations are currently unattainable in practice.” We did not measure time-weighted averages, and we recognize that gas leaks around the tube during the maintenance phase of anesthesia is only one component of operating room pollution. However, it is a component that makes compliance with NIOSH recommendations difficult. This study demonstrated a reduction in nitrous oxide concentration with the use of cuffed endotracheal tubes compared with uncuffed tubes. It is desirable to reduce the waste gas concentration in the operating room. 
Upper airway symptoms were noted as an indication of laryngotracheal injury, and treatment with racemic epinephrine was noted as a more specific marker for subglottic edema. Our rate of patients treated for croup is similar to that reported by Koka et al. We looked for markers of laryngotracheal injury because it has been suggested that use of cuffed endotracheal tubes may predispose children to airway injury. [3,4]Deakers et al. concluded that cuffed endotracheal tube intubation is not associated with an increased risk of postintubation stridor or significant long-term sequelae in pediatric intensive care patients. Although we did not demonstrate a difference in the incidence of postintubation airway injury related to tube type, it is possible that a difference exists that could not be detected with this sample size. Further study in a larger patient population will be needed to resolve this issue.
In summary, this study demonstrates that use of cuffed endotracheal tubes in children has several advantages relative to use of uncuffed tubes. It virtually eliminates the need for repeat laryngoscopy and intubation. It allows use of low fresh gas flows and reduces operating room pollution with anesthetic gas. Use of cuffed endotracheal tubes selected using our formula is a favorable alternative to use of uncuffed tubes in children during general anesthesia.
*Centers for Disease Control and Prevention, U.S. Dept of Health and Human Services. Controlling exposures to nitrous oxide during anesthetic administration. NIOSH ALERT, April 1994; 1–10.