New formulae for predicting tracheal tube length

Transcription

1 Pediatric Anesthesia : doi: /j x New formulae for predicting tracheal tube length NICKY LAU*, STEPHEN D. PLAYFOR MD, ASRAR MRCPCH AND MUTHU DHANARASS MRCPCH RASHID MRCPCH MRCPCH *University of Manchester Medical School, Manchester, Honorary Clinical Lecturer in Paediatric Intensive Care Medicine, Paediatric Intensive Care Unit, Royal Manchester Children s Hospital, Pendlebury, Manchester and Paediatric Intensive Care Unit, Queens Medical Centre, University Hospital NHS Trust, Nottingham, UK Summary Background: The aim of this study was to determine the accuracy of standard techniques for estimating oral and nasal tracheal tube length in children and to devise more accurate predictive formulae that can be used at the bedside. Methods: Data were collected from 255 children who required tracheal intubation whilst on the Pediatric Intensive Care Unit over a period of 1 year. Age, weight, the final length of the tracheal tube and the internal diameter were documented. Patients with a tracheostomy were excluded from the study. Results: Using linear regression the following formulae best predicted final tracheal tube length. For children over 1 year of age: Insertion depth (cm) for orotracheal intubation ¼ age=2 þ 13 Insertion depth (cm) for nasotracheal intubation ¼ age=2 þ 15 For children below 1 year of age: Insertion depth of orotracheal tube (cm) ¼ weight=2 þ 8 Insertion depth of nasotracheal tube (cm) ¼ weight=2 þ 9 Conclusions: Current Advanced Paediatric Life Support guidelines underestimate the appropriate tracheal tube lengths for orotracheal intubation in children over 1 year of age. Similarly, the novel weightbased formulae for tracheal tube lengths in children below the age of 1 year proved more accurate than standard reference charts. We therefore recommend that these new formulae are prospectively evaluated. Keywords: tracheal tubes; tracheal; intubation; pediatric critical care; pediatrics Correspondence to: Stephen D. Playfor, Consultant Paediatric Intensivist, Honorary Clinical Lecturer in Paediatric Intensive Care Medicine, Paediatric Intensive Care Unit, Royal Manchester Children s Hospital, Hospital Road, Pendlebury, Manchester M27 4HA, UK ( stephen.playfor@cmmc.nhs.uk). Introduction Significant morbidity and mortality is associated with the placement of tracheal tubes of inappropriate length; a tube which is too short may result in 1238 Journal compilation Ó 2006 Blackwell Publishing Ltd

2 PREDICTING TRACHEAL TUBE LENGTH 1239 inadequate ventilation, may be more easily inadvertently removed and may cause trauma to the laryngeal inlet. A tracheal tube which is too long may result in physiologic instability if it sits at the carina, whilst endobronchial intubation may result in overdistension of ventilated segments of lung with collapse of the contralateral lung, impaired gas exchange and increased risk of air leaks. The Advanced Paediatric Life Support (APLS) guidelines (1) recommend calculating tracheal tube insertion depth for children >1 year of age according to the formulae: Insertion depth (cm) for orotracheal intubation ¼ age=2 þ 12 Insertion depth (cm) for nasotracheal intubation ¼ age=2 þ 15 For children younger than 1 year of age standard reference charts are most commonly used to predict the lengths of tracheal tubes, primarily indexed against weight and age, such as the Drug Doses handbook compiled by Shann (2). Other techniques involve relying on depth markers present on the distal end of tracheal tubes and other formulae based on age, weight, height and other parameters including the internal diameter of the selected tracheal tube. Methods Data were retrospectively collected from all children who required tracheal intubation whilst on the Pediatric Intensive Care Unit (PICU) over a period of 1 year. Data collected included; age at admission, weight, route of intubation, final tracheal tube length, and internal diameter of the tracheal tube. Final tracheal tube lengths had all been assessed by chest radiography as being satisfactory. Patients with a tracheostomy were excluded from the study. For each individual patient their actual tracheal tube length was plotted against age, for children over the age of 1 year and compared with the tube length predicted by APLS formulae. Using linear regression, a line of best fit was plotted and evaluated to produce a new formula. For children below the age of 1 year actual tracheal tube lengths were plotted against weight and compared with the tube length recommended by the standard reference chart in the Drug Doses handbook compiled by Shann (2). Using linear regression, a line of best fit was plotted and evaluated to produce a novel weight-based formula for predicting tracheal tube length in this age group. Results A total of 255 sets of case notes were obtained and of these, 29 were excluded from the study; 25 sets of notes were inadequate and four patients had a tracheostomy. Of the 226 sets of case notes included in the study 137 patients were intubated orally and 89 were intubated nasally with an age range from 1 day to 15 years and a weight range of kg (Table 1). Tracheal tube length in children over 1 year of age Oral tracheal tube length. Orotracheal tube length showed a strong correlation with age (Figure 1). Actual tracheal tube lengths were significantly different to those predicted by the APLS formula [insertion depth (cm) for orotracheal intubation ¼ age/2 + 12); P ¼ 0.011, unpaired t-test]. When length of the orotracheal tube is the dependent variable and age is the independent Length of tube (cm) APLS guideline Age (years) Figure 1 Relationship between age and orotracheal tube length in children over 1 year of age.

3 1240 N. LAU ET AL. ¼ð0:53 Age in yearsþþ12:72 ¼ Age=2 þ 13 Nasal tracheal tube length. Nasotracheal tube length also showed a strong correlation with age (Figure 2). Actual tracheal tube lengths were not significantly different to those predicted by the APLS formula [insertion depth (cm) for nasotracheal intubation ¼ age/2 + 15; P ¼ 0.219, unpaired t-test]. When length of the nasotracheal tube is the dependent variable and age is the independent ¼ð0:62 Age in yearsþþ14:6 ¼ Age=2 þ 15 Tracheal tube length in children below 1 year of age Oral tracheal tube length. Orotracheal tube length showed a strong correlation with weight (Figure 3). Actual tracheal tube lengths were significantly different to those predicted by the standard reference chart (P < 0.01, unpaired t-test) Length of tube (cm) APLS guidelines Age (years) Figure 2 Relationship between age and nasotracheal tube length in children over 1 year of age Weight (kg) When length of the orotracheal tube is the dependent variable and weight is the independent ¼ð0:48 Weight in kgþþ7:8 ¼ Weight=2 þ 8 Nasal tracheal tube length. Nasotracheal tube length showed a strong correlation with weight (Figure 4). Actual tracheal tube lengths were significantly different to those predicted by the standard reference chart (P < 0.01, unpaired t-test). When length of the nasotracheal tube is the dependent variable and weight is the independent ¼ð0:65 Weight in kgþþ8:7 ¼ Weight=2 þ 9 Discussion Guideline Figure 3 Relationship between weight and orotracheal tube length in children below 1 year of age. Successful tracheal intubation depends on a threestage process of: (i) selecting a tracheal tube of appropriate diameter, (ii) inserting it into the trachea

4 PREDICTING TRACHEAL TUBE LENGTH Length of tube (cm) Guidelines Weight (kg) Figure 4 Relationship between weight and nasotracheal tube length in children below 1 year of age. Table 1 Distribution of subjects by age with mean tracheal tube lengths by route Age Number of patients Mean orotracheal tube length (cm) Number of patients Mean nasotracheal tube length (cm) 0 1 month months months months months months months year years years years years years years years years years years N/A 12 years N/A 13 years N/A 14 years N/A 15 years to the correct depth, and (iii) securing it in that position (3). The correct position of tracheal tubes should be confirmed immediately after insertion. The chest should be inspected for equal and bilateral chest expansion and auscultated for equal and bilateral air entry. A chest radiograph should be obtained to confirm midtracheal tracheal tube positioning. In a series described by Orf et al., specialist pediatric hospitals receiving children intubated by nonspecialist teams changed the tracheal tube insertion depth in 33.3% of cases (4). These authors also described that almost all tracheal tubes of an inappropriate length (97%) were too long rather than too short. There are a variety of techniques for predicting the correct insertion depth of tracheal tubes prior to, or at the time of insertion. The most commonly used of these include the use of depth markers present on the distal end of tracheal tubes, the use of formulae and standard reference charts. Other techniques include deliberate endobronchial intubation followed by tracheal tube withdrawal to the correct position and flexible fiberoptic bronchoscopy, which was found to be a convenient and timesaving technique in confirming satisfactory tracheal tube positioning compared with chest radiography (5). During the process of intubation, depth markers at the distal end of tracheal tubes can be placed at the level of the vocal cords. This technique is useful in that it applies equally to nasal and oral routes of intubation, meaning that formulae do not need to be remembered, but is less useful once laryngoscopy is completed and the markings are no longer visible; tracheal tubes often migrate from the initial depth of insertion and this is less easily detected if a reference measurement from lip or nostril is not noted. In a recent study it was also demonstrated that there is a marked lack of consistency in the placement of depth markers on tracheal tubes between manufacturers, which makes them a less reliable tool (6). A number of different formulae are available for predicting tracheal tube insertion depth. Within the UK the APLS formulae described here are in common use. Other formulae include that of de la Sierra et al.: ¼ðWeight=2Þ þ 10:5 This formula applies to children under the age of 4 years (7). Another commonly used formula is dependent on the diameter of the tracheal tube selected for a patient.

5 1242 N. LAU ET AL. ¼ Tracheal tube internal diameter (mm) 3 This formula applies only when a tracheal tube of internal diameter >3.0 mm is used and in a recent study, it was suggested that use of this formula results in 15 25% of tracheal tubes being misplaced (8). Yates et al. modified this formula for nasotracheal intubation as follows: ¼ [Tracheal tube internal diameter (mm) 3Šþ2 This formula applies to children over 3 kg (9). It should be remembered that formulae in which predicted tube length depends on selected tube internal diameter rely on the appropriate tube diameter being selected, and that there is more than one method used for predicting tube internal diameter. An APLS formula may be used [tracheal tube internal diameter (mm) ¼ age/4 + 4] or a system such as the Broselow tape which is dependent on body length (10). Also, many critically ill children will be suffering from conditions leading to narrowing of the airway, such as infection, edema, and local trauma including that arising from previous intubation. In these circumstances, where a smaller tracheal tube is necessary, such formulae will not be accurate. The Broselow system is routinely used in many Emergency Departments, but is less commonly available in the other clinical settings where critical care is often established, such as Operating Departments, general pediatric wards and high dependency units. In these settings weight is a more useful parameter than body length for predicted tracheal tube length in the acute setting as the weight of infants is frequently known or can be quickly estimated. Easily remembered formulae, such as ours ( half the weight plus eight for orotracheal tube length for infants below 1 year of age) provide a significant advantage over reference tables that may not be readily to hand. This is especially relevant as tracheal intubation is often carried out by practitioners who are only infrequently involved in the care of critically ill children; in one series approximately 80% of children transported with tracheal tubes by a specialist pediatric transport service were intubated by district general hospital staff (11). The technique of deliberate endobronchial intubation followed by tracheal tube withdrawal to the correct position has been studied by several authors. Bloch et al. reported success with this technique in achieving appropriate tube positioning (12). Similarly, Kim et al. reported acceptable results using the technique, describing the additional method of using a reduction in peak ventilatory pressures as a marker of satisfactory positioning from a previously endobronchial tube rather than chest auscultation (13). The value of hearing bilateral breath sounds has been questioned; however, in a series of 153 pediatric patients undergoing orotracheal intubation for cardiac catheterization. Verghese et al. found that despite bilateral breath sounds being heard, endobronchial intubation was demonstrated by fluoroscopy in 12% of the patients (14). Failure to diagnose endobronchial intubation by auscultation alone may be related to the use of the Murphy eye tracheal tube, which reduces the reliability of chest auscultation in these circumstances (15). Mariano et al. (16) compared three methods for predicting tracheal tube insertion depth; deliberate endobronchial intubation with subsequent withdrawal of the tracheal tube 2 cm above the carina, use of depth markers present on the distal end of tracheal tubes and use of the formula: Length of orotracheal tube (cm) ¼ Tracheal tube internal diameter (mm) 3. In 60 children studied the endobronchial method was associated with the highest rate of appropriate tube placement (73%) compared with both the marker method (53%) and the formula method (42%). There was no difference in success rate between the marker and formula methods overall, but analysis of age-stratified data demonstrated higher success with the marker method compared with the formula method for patients aged 3 12 months. It should be remembered that ours is a retrospective study and that we have no data for children below 1.5 kg. We would therefore recommend that our new formulae for predicting tracheal tube insertion depth be prospectively evaluated. Our data suggest that the commonly used APLS formula for predicting orotracheal tube length underestimates optimal length by 1 cm. We also suggest that our novel, weight-based formulae for orotracheal and nasotracheal tube length in infants

6 PREDICTING TRACHEAL TUBE LENGTH 1243 below 1 year of age provide an advantage over commonly used reference tables. Acknowledgement Financial support: None. Conflict of interest None References 1 Advanced Life Support Group, Advanced Paediatric Life Support: The Practical Approach, 3rd edn. London, UK: BMJ Books, Shann F. Drug Doses, 12th edn. Collective Pty Ltd, 2003 (ISBN ). 3 Luten R. Accurate endotracheal tube placement in children: depth of insertion is part of a process. Pediatr Crit Care Med 2005; 6: Orf J, Thomas SH, Ahmed W et al. Appropriateness of endotracheal tube size and insertion depth in children undergoing air medical transport. Pediatr Emerg Care 2000; 16: Lee YS, Soong WJ, Jeng MJ et al. Endotracheal tube position in pediatrics and neonates: comparison between flexible fiberoptic bronchoscopy and chest radiograph. Zhonghua Yi Xue Za Zhi (Taipei) 2002; 65: Goel S, Lim SL. The intubation depth marker: the confusion of the black line. Paediatr Anaesth 2003; 13: de la Sierra AM, López-Herce J, Rupérez M et al. Estimation of the length of nasotracheal tube to be introduced in children. J Pediatr 2002; 140: Phipps LM, Thomas NJ, Gilmore RK et al. Prospective assessment of guidelines for determining appropriate depth of endotracheal tube placement in children. Pediatr Crit Care Med 2005; 6: Yates AP, Harries AJ, Hatch DJ. Estimation of nasotracheal tube length in infants and children. Br J Anaesth 1987; 59: Lubitz DS, Seidel JS, Chameides L et al. A rapid method for estimating weight and resuscitation drug dosages from length in the pediatric age group. Ann Emerg Med 1988; 17: Ramnarayan P, Britto J, Tanna A et al. Does the use of a specialised paediatric retrieval service result in the loss of vital stabilisation skills among referring hospital staff? Arch Dis Child 2003; 88: Bloch EC, Ossey K, Ginsberg B. Tracheal intubation in children: a new method for assuring correct depth of tube placement. Anesth Analg 1988; 67: Kim KO, Um WS, Kim CS. Comparative evaluation of methods for ensuring the correct position of the tracheal tube in children undergoing open heart surgery. Anaesthesia 2003; 58: Verghese ST, Hannallah RS, Slack MC et al. Auscultation of bilateral breath sounds does not rule out endobronchial intubation in children. Anesth Analg 2004; 99: Sugiyama K, Yokoyama K, Satoh K et al. Does the Murphy eye reduce the reliability of chest auscultation in detecting endobronchial intubation? Anesth Analg 1999; 88: Mariano ER, Ramamoorthy C, Chu LF et al. A comparison of three methods for estimating appropriate tracheal tube depth in children. Pediatr Anesth 2005; 15: Accepted 21 April 2006