The nasopharyngeal airway

Transcription

1 Anaesthesia, 1993, Volume 48, pages The nasopharyngeal airway Assessment of position by fibreoptic laryngoscopy M. D. STONEHAM Summary Artijicial nasopharyngeal airway position and performance were assessed in I20 anaesthetised adult patients. Using a fibreoptic laryngoscope mean distances from nares to larynx were measured at 209 mm (SD 11) in s and 180 mm (SD 11) in fes; those from nares to epiglottis were 159 mm (SD 12) in s and 140 mm (SD 11) in fes. Nasopharyngeal airways were frequently misplaced, 60% lying beyond the tip of the epiglottis and 13% lodged in the vallecula. Forty-two percent of subjects had clinical evidence of respiratory obstruction. Nasopharyngeal airway compression in the nasopharynx and obstruction by the tongue and soft palate were common causes of respiratory obstruction. Regression analysis revealed that nares-epiglottis length correlated signijican fly with subject height (t = 3.9, p = ), but not with three external measurements made around the head and neck. Head flexion and extension resulted in comparatively little relative movement of the nasopharyngeal airway. Nasopharyngeal airway length and diameter should be standardised to optimise performance. Key words Equipment; airway, nasopharyngeal. The nasopharyngeal airway is used to assist in the maintenance of a clear airway during anaesthesia, in the recovery ward. or in an emergency. It may also be used during induction of anaesthesia in circumstances when the patient might not tolerate an oropharyngeal airway. The nasopharyngeal airway has been used successfully in the past to facilitate access to the trachea for suctioning and fibreoptic bronchoscopy [I], and for nasogastric and nasotracheal intubation [2]. Early nasopharyngeal airways were plain, uncuffed red rubber tubes but these have largely been replaced with latex or polyvinyl chloride tubes. Displacement of the airway into the nasopharynx is prevented by a flange on the proximal end, and the Portex pack now includes a safety pin as a further safeguard [3]. The ability of the nasopharyngeal airway to maintain airway patency is critically dependent on (1) the internal diameter of the airway when correctly positioned and (2) the position of the distal end of the airway relative to anatomical structures, particularly the epiglottis and tongue. Movement of the airway relative to laryngeal structures during flexion or extension of the head and neck may occur, however. Portex nasopharyngeal airways have an internal diameter of 6, 7, 8 or 9 mm, but the lumen may be compressed, sometimes completely, by passage through the nasopharynx. Ideally the length of the tube should be such that, following full insertion up to the flange, the tip protrudes beyond the pharyngeal edge of the soft palate but does not extend past the epiglottis [4]. Nasopharyngeal airways are available in a range of sizes but the suitability of these has not been properly assessed. The length of Portex airways increases as the internal diameter increases, although this is not based on a British Standard specification. There is, however, an American Standard which specifies lengths which are 10 to 20 mm less than the Portex airways [5]. The purposes of this study were to assess the patency and position of Portex nasopharyngeal airways by fibreoptic laryngoscopy and to investigate whether the airways are available in appropriate lengths. In addition, the possibility of a relationship between the length of nasopharyngeal airway required and various external measurements of the face and neck was examined. Lastly, an assessment was made of the extent to which head and neck movements altered the position of the distal tip of the nasopharyngeal airway relative to laryngeal structures. Methods The study was approved by the Hospital Ethics committee. Patients selected for study were men and women, aged M.D. Stoneham, MA, MB, BChir, Registrar, Department of Anaesthesia, Royal Naval Hospital, Stonehouse, Plymouth PLI 3JY. This study was presented in part at the 1992 Winter Meeting of the Society of Anaesthetists of the South Western Region and awarded the President s prize. Accepted 19 January O /93/ The Association of Anaesthetists of Gt Britain and Ireland 575

2 576 M. D. Stoneham m, Vallecula Epiglottis Vocal cords \ \- \,\R\ \ \ - Fig. 1. Measurement of nares-larynx (NL) distance with nasopharyngeal airway in siiu. Fig. 2. \ \ / M easurement of nares-epiglottis (NE) distance with nasopharyngeal airway in siru years, presenting for routine surgery under general anaesthesia. Patients having emergency surgery or requiring a rapid sequence induction or those with known nasal abnormalities, vasomotor rhinitis or bleeding diatheses were not studied. Patients to be included in the third part of the study were examined pre-operatively to ensure that they had a full range of neck movements. Written informed consent from each unpremedicated patient was obtained before inclusion in the study. Age, sex, height and weight of all patients were recorded. Three additional measurements were made on each subject in an attempt to relate required nasopharyngeal airway length to various external measurements of the face and neck: (1) distance from tip of nose to angle of mandible (NM); (2) distance from nose to tragus of the ear (NT); (3) cjistance from thyroid prominence to tip of chin with the neck fully extended-the thyro-mental distance (TM). Induction of anaesthesia was carried out in the standard anaesthetic position with one or two pillows behind the head and neck. After induction with thiopentone or propofol, anaesthesia was maintained using 1-2% isoflurane or enflurane in 66% nitrous oxide in oxygen. When a surgical plane of anaesthesia had been achieved, a well-lubricated Portex nasopharyngeal airway with attached safety pin through the flange was inserted into the most suitable nostril as assessed by the sniff test preoperatively. Men and women patients initially received 8 mm or 7 mm airways respectively. No topical vasoconstrictor was used. If gentle insertion was unsuccessful, insertion in the other side was attempted. If this was unsuccessful, a smaller size was inserted. Insertion of the airways was performed by the same anaesthetist (M.D.S.) in all cases. The patency of the nasopharyngeal airway was assessed clinically whilst the patient was breathing spontaneously with no other aid to maintain airway patency and with the other nostril occluded. Features indicating respiratory obstruction such as see-sawing of the chest and abdomen, rib recession and tracheal tug were sought and the degree of obstruction was recorded on a 0-2 scale (0 = no obstruction, 1 = partial obstruction, 2 = total obstruction). An Obympus LF-I fibreoptic intubating laryngoscope was inserted through the nasopharyngeal airway and guided down to the vocal cords. When the tip of the fibrescope was exactly between the vocal cords, a piece of tape was put on the fibrescope at the nares (TI) as a reference point for later measurement (Fig. I). The fibrescope was withdrawn to the tip of the epiglottis, and a second piece of tape placed (T2) similarly (Fig. 2). If the Fibrescope could not be passed (external diameter 4 mm) due to compression of the nasopharyngeal airway in the nasopharynx, or if the larynx could not be seen, for example because the tip of the airway was lodged in the vallecula, then the fibrescope was passed down the other nostril and the measurements made as before. The nitsopharyngeal airway was removed and measured in millimetres from the tip of the bevel to the flange. It was inspected for blood streaking, and obvious bleeding into the oropharynx was noted. Bleeding was scored on a 0-3 scale (0 = none, 1 = streaking, 2 = moderate, 3 = severe, requiring suctioning). Following these observations the patients were transferred to the operating theatre for surgery. The distances from the tip of fibrescope to the points TI and T2 Isorrespond to the distance from the nares to the rima glottidis of the larynx (nares-larynx distance, NL), and to the distance from the nares to the tip of the epiglotti:; (nares-epiglottis distance, NE), respectively. The distance from the distal tip of the nasopharyngeal airway to the vocal cords was calculated by subtracting the measured length of the airway from the nares epiglottis distance. In 23 patients, two additional measurements were made (Fig. 3). With the nasopharyngeal airway in place and the tip of the fibreoptic laryngoscope lying between the vocal cords, the neck was gently flexed by an assistant until the chin was resting on the chest. The new NL distance (NL2) was then measured in the same way as before. The pillows were removed and the patient s neck was fully extended

3 ~ Nasopharyngeal airway position 577 Table 1. Mean (95% confidence intervals) values for patient characteristics. Age Height Weight n years (cm) (kg) Men ( ) ( ) ( ) Women Total ( ) ( ) ( ) ( ) ( ) ( ) Fig. 3. Measurement of effect of head flexion and extension on nasolaryngeal length (a) normal position-measurement of NL; (b) flexed position-measurement of NL2; (c) extended position-measurement of NL3. and again the NL distance was measured (NL3). The relative movements due to flexion and extension of the head and neck were then calculated by subtracting NL2 and NL3 from NL respectively. Statistical analysis Male and fe data were analysed separately and compared by unpaired Student s t-testing. Multiple variable backward stepwise linear regression analysis [6] of the data was performed using the Statgraphics computer software package [7] to attempt to find a relation between nares-epiglottis or nares-larynx distances and height, weight, naso-mandibular, naso-tragus, and thyro-mental distances. The flexion/extension data were analysed by paired Student s t-testing. A p level of less than 0.05 was taken as statistically significant. Results One hundred and twenty patients were studied (Table 1). Details of the nasopharyngeal airway sizes and positions are shown in Table 2. Fifty patients (42%) had clinical evidence of upper airway obstruction. In 72 patients (60%) the tip of the nasopharyngeal airway was found to be placed at or beyond the epiglottis tip, and of these the tips of 16 (13%) were lodged in the vallecula anterior to the epiglottis. Two patients experienced complete obstruction (grade 2) with the tip of the airway seen to be lodged in the vallecula. Passage through the nasopharynx caused compression of many of the airways and was sufficient to cause airway obstruction in 19 cases (six women and 13 men). These were patients in whom it was impossible to pass the fibrescope through the nasopharyngeal airway due to narrowing and so the other nostril had had to be used. Upper respiratory obstruction occurred in a further three subjects in whom the distal end of the nasopharyngeal airway lay rostra1 to the soft palate behind the tongue. This occurred when insertion of a larger nasopharyngeal airway was unsuccessful and where a smaller (and therefore shorter) airway had had to be used. One man had complete respiratory obstruction with a size 6.0 airway for this reason. The cause of respiratory obstruction was identified in 38 of the 50 patients including three patients with complete obstruction. The cause of airway obstruction in the other 12 patients was unclear but may have been a combination of the above factors. None of the airways was obstructed by blood, although two patients required suctioning (Table 3). Table 4 presents the airway measurement data. The distributions of nares-larynx and nares-epiglottis distances in men and women are shown as cumulative relative frequency histograms in Figures 4 and 5 respectively. Multivariate backward stepwise linear regression analysis revealed a significant correlation between nares-epiglottis distance and height (t = 3.90, p = ), but no significant correlation between nares-epiglottis distance and Table 2. Sizes and positions of nasopharyngeal airways. ~ Nasopharyngeal airway internal diameter; mm Total Length (range); mm Number used Beyond epiglottis In vallecula Respiratory obstruction -= not used fe all fe all fe all fe a I

4 518 M. D. Stoneham Table 3. Number (YO) of patients in whom introduction of the nasopharyngeal airways caused bleeding. (n = 120). Nasopharyngeal airway internal diameter All (mm) Grade 0 (none) 5 (4) 42 (35) 35 (29) 82 (68) Grade I (streaking) 4 (3) 16(13) 9 (8) 29 (24) Grade 2 (moderate) 1 (1) 3 (3) 3 (3) 7 (6) Grade 3 (severe) 2 (2) 0 (0) 0 (0) 2 (2) weight (t = -0.70, p = 0.49), naso-mandibular (t = , p = 0.27), naso-tragus (t = 1.79, p = 0.08) or thyro-mental (t = -1.03, p = 0.30) distances. The relationship between nares-epiglottis distance and height is shown in Figure 6 and is represented by: NE(mm) = x HEIGHT(cm) (r = p = ). 95% confidence intervals for the intercept were to 49.7 and for the slope of the line were to Twenty-three patients entered the last part of the study (Table 5).* The mean measured alteration in position of the nasopharyngeal airway tip from the anaesthetic position with two pillows supporting the head and neck relative to the flexed position was +5.7 mm (p < 0.001). The mean measured alteration in position from anaesthetic to the extended position was mm (p > 0.2). The change in position of the airway when the head was moved from fully flexed to fully extended was -4.4 mm (p < 0.05). Although two of these show significant changes in position the movement is very small and unlikely to be important clinically. Discussion The incidence of upper airway obstruction through the nasopharyngeal airway was high in this study, although it must be emphasised that this was enhanced by occlusion of the other nostril and mouth. In practice, upper airway obstruction is probably less common because of alternate routes of ventilation through the nose and mouth. There are several potential problems associated with a nasopharyngeal airway which is in the wrong position or is too long. Upper airway obstruction was caused in 13% of patients by the tip of the airway lying in the vallecula in a similar fashion to that described for the Guedel oropharyngeal airway where up to 20% have been reported as similarly malplaced [8]. A nasopharyngeal airway which is too long may enter the oesophagus, with the associated problems of hypoxia and gastric distension. Accidental introduction of the nasopharyngeal airway to the larynx Table 5. Relative movements of the nasopharyngeal airway towards (+) and away from (-) the larynx during flexion and extension of the head and neck. Values are expressed as mean (95Y0 confidence intervals) (n = 23). Relative movement neutral + flexed neutral + ex.tended mm +5.7 ( ) +1.3 ( ) *A positive value indicates that there is an increase in nares-laryngeal length when the head is moved from the neutral position to flexed or extended; a negative value represents the converse. may stimulate laryngeal reflexes leading to coughing or laryngospasm particularly during light planes of anaesthesia or during recovery, when nasopharyngeal airways are commonly used. This was not seen in this study as the patients were all anaesthetised to a plane of surgical anaesthesia during insertion and measurement. In addition to this there were the other causes of upper airway obstruction. Compression of the airway in the nose is a feature of patient anatomy rather than tube design, but obstruction by the tongue and soft palate should be avoidable if nasopharyngeal airway length is more independent of internal diameter. There is a requirement for a longer, narrow nasopharyngeal airway for patients in whom for anatomical reasons, it is impossible to pass the larger diameter.airways. These problems can be avoided if the tip of the airway lies rostra.1 to the epiglottis as described by Gallagher and colleagues [4]. Several groups have attempted to optimise the position of the distal end of the airway using a cuffed version [9,10]. This type of preformed nasal tube is inflated in the hypopharynx in a similar fashion to the laryngeal mask airway. In patients with patent airways, an average length of 14 cm from narcs to the tip of the airway was found, but no data were reported concerning the position of the distal end of the airway in relation to laryngeal structures. It was disappointing that in the study reported here no relation was found between the required length of artificial nasopharyneal airway and simple anthropometric measurements. The relation to height is not unexpected. In the only previous study attempting to correlate length of the patient s nasopharyngeal airway with external measurements of the face [I I], a nasotracheal tube was used to measure the nares+epiglottis distance. The assessments unfortunately, were made by direct laryngoscopy, and were, therefore, subject to distortion. Correlation was only found between height and nares+epiglottis distance. Movernent of tracheal tubes in relation to the carina with flexion and extension of the neck is a well-recognised problem particularly in neonates with their shorter Table 4. Mean (%YO confidence intervals) anatomical distances (mm) measured as described. p values refer to /fe differences. Nares-larynx Nares-epiglottis Airway-lar ynx Naso-mandi bular Naso-tragus Thyremental Men 209 (n = 87) ( ) Women (n = 33) 180 (I ) Total 20 I (n = 120) ( ) P c ( ) 140 (I ) I54 (I ) < ( ) 40 ( ) 47 ( ) c ( ) I38 ( ) 145 ( ) < ( ) 145 ( ) 152 ( ) c ( ) 75 ( ) 17 ( ) c 0.2

5 Nasopharyngeal airway position 579 " Nares-larynx distance (mm) Fig. 4. Cumulative relative frequency (CRF) histogram of nares-larynx distance in s (W. n = 87) and fes (I& n = 33) Nares-epiglottis distance (mm) Fig. 5. Cumulative relative frequency (CRF) histogram of nares-epiglottis distance in s (W, n = 87) and fes (El, n = 33) '"t 150 / ;+ ++ *++ t f + t / + t I I I I I I I I I I Nares-epiglottis distance (mm) Fig. 6. Relation between nares-epiglottis distance (NE) and height. NE = x height (r = 0.478; p = ).

6 580 M. D. Stoneham larynx-carina distance and can lead to extubation, or intubation of the right main bronchus. In previous adult studies [ 121 in which distances were measured from cadavers and chest radiographs, movements of up to 5 cm were recorded on flexion and extension of the head and neck. The relative movement of a nasopharyngeal airway has not been investigated previously, but might be expected to be less than that seen with a tracheal tube, due to the shorter length. The alterations in position seen in this study were statistically, but not clinically, significant and occurred in both directions. The incidence of bleeding found in this study was comparable to that found by others [4,10] with fresh bleeding occurring in 5 to 10% of patients and streaking in UP to 30%. It is recognised that there were some limitations with this study, Firstly, the distribution of patients was biased towards young, fit s. Secondly, the relationship between laryngeal structures and anaesthetic airways is obviously influenced by head position. It would have been desirable to have standardised the head positioning more precisely than was done, although the third part of the study suggested that this was not as important as previously thought. Thirdly, it would have been desirable to have used a more accurate assessment of airway obstruction through the nasopharyngeal airway than the three point clinical scale which was used. Despite these limitations, there are clear conclusions which may be drawn. The ideal position for the distal tip of the nasopharyngeal airway is within 1 cm of the epiglottis tip as this will then avoid most of the complications mentioned previously. From Figure 5 it is apparent that lengths of nasopharyngeal airways of 150 mm for s and 130 mm for fes are appropriate for most patients. However, the variation in nares-epiglottis distance is such that one size will not be appropriate for all patients. One solution would be to manufacture all airways to the same length, for example 160 mm, with a range of diameters, and alter the length of airway to be inserted by means of the safety pin. The external surface of the airways should be marked in centimetres in a similar fashion to tracheal tubes, so that the length of nasopharyngeal airway that has been inserted is immediately apparent. This study has shown that the position of the distal end of nasopharyngeal airways relative to structures in the hypopharynx is unpredicable and that this may detract from their ability to maintain a patent airway. This means that there should be a greater awareness of the risk of respiratory obstruction even with the airway in place. Acknowledgments The author thanks Dr M.E. Wilson, PhD, FFARCS for his helpful advice during the planning of the project. The cooperation of the Operating Department Assistants of the Royal Naval Hospital, Plymouth is gratefully acknowledged. References WANNER A, ZIGHELBOIM A, SACKNER MA. Nasopharyngeal airway: a facilitated access to the trachea. Annals of lnternal Medicine 1971; LEWIS JD. Facilitation of nasogastric and nasotracheal intubation with a nasopharyngeal airway. American Journal of Emergency Medicine 1986; SMITH BL. Retained nasopharyngeal airway. Anaesthesia 1990; GALLAGHER WJ, PEARCE AC, POWER SJ. Assessment of a new nasopharyngeal airway. British Journal of Anaesthesia 1988; 60: 1 li.-5. American National Standard ANSI American National Standards Institute ALTMAN DG. Practical statistics for medical research. London: Chapman and Hall Medical, 1991: Statistical Graphics Corporation. Statgraphics Statistical Graphics System version 2.6. USA: STSC Inc MARSH AM, NUNN JF, TAYLOR SJ. CHARLESWORTH CH. Airway obstruction associated with the Guedel airway. Brilish Journal of Anaesthesia 1991; 67: BOHEIMER NO, FELDMAN SA, SONI N. A self-retaining nasopharyngeal airway. Anaesthesia 1990; FELDMAN SA, FAWEL NJ, 001 R. The cuffed pharyngeal airway. European Journal of Anaesthesiology I99 I ; 8: HWANCL, Luu KC, Wu TJ, JAING CJ, LIN YS, LUCIANA S, CHAO CC. Estimation of the length of nasopharyngeal airway in Chinese adults. Ma Tsui Hsueh Tsa Chi 1990; 28: CONRARDY PA. GOODMAN LR, LAINGE F, SINGER MM. Alteration of endotracheal tube position. Critical Care Medicine 1976;