The most lethal direct complication of general anesthesia is asphyxia caused by failure to establish or maintain a patent airway. Whereas endotracheal intubation is conventionally performed when the patient is in the supine position, it may be sometimes required to secure the airway in the lateral position (1,2). Although the acquisition of skill and experience of intubation in the lateral position has been advocated (3), its effect on airway anatomy and management of the airway have not been determined in humans. In a population of patients with low a priori predicted risk of difficult airway control, we sought to (a) determine the effect of lateral positioning on laryngoscopic airway visualization with and without cricoid pressure, (b) investigate the feasibility of endotracheal intubation in this position, and (c) compare intubation with laryngeal mask airway (LMA; Laryngeal Mask Co., Henley-on-Thames, United Kingdom) insertion.
After institutional ethical approval and informed written consent, 70 ASA physical status I patients undergoing elective general anesthesia requiring endotracheal intubation participated in the trial. Exclusion criteria were known or predicted difficult airway, significant medical illness, cervical spine disease, dental abnormalities or prostheses, or relevant drug allergy. After application of noninvasive monitors, administration of oxygen, and the induction of a standardized general anesthetic (Table 1), subjects were randomly allocated to airway maintenance with a LMA or an endotracheal tube. In the supine position, a single pillow was positioned under the occiput of the patient and adjusted as required to achieve a “sniffing” position. After confirmation of neuromuscular blockade using peripheral nerve stimulation and establishment of mask ventilation and before attempted airway insertion, an independent observer who was a senior anesthesiologist performed direct laryngoscopy to grade the degree of laryngeal visualization (4) in the presence and absence of cricoid pressure. The patients were then turned into the left lateral position. In the lateral position, the head was positioned on pillows so that the sagittal axis of the head and neck was parallel to the tabletop and placed in a sniffing position, as when supine. The observer again performed laryngoscopy with and without cricoid pressure. Participating anesthesiologists then attempted to secure the airway using either a standard endotracheal tube or LMA (choice was determined by a randomization schedule) in the presence of cricoid pressure while being timed by an investigator (CMC, MR). Welch-Allyn laryngoscopes (Skaneateles Falls, NY) were used with curved Macintosh blades for intubation (size 3 for women and 4 for men). Endotracheal tube size was 8.5 for men and 7.5 for women. LMA size was 4 for men and 3 for women. The airway was considered secured once a positive capnographic waveform was observed with hand ventilation in conjunction with visible chest movement. To maximize patient safety, securing the airway was deemed to have failed if a capnographic waveform was not seen within 60 s of commencing the airway maneuver or if more than 2 attempts were made. After the study period, or in the event of desaturation (Sao2 < 90%) or hemodynamic instability, the patient was returned to the supine position and the airway secured in standard fashion.
We collected data on patient demographics, duration of airway maneuvers, success or failure of airway placement, and vital signs during the study procedure. Categorical data are presented as numbers and percentages. Continuous variables are presented as mean (sd). Demographic factors and symptoms were compared in the two groups. Continuous variables (demographics and time intervals) were analyzed using Student’s t-test. Categorical data (success rates and changes in laryngoscopic view) were analyzed using Fisher’s exact test and χ2 testing with Yates correction as appropriate. The null hypothesis was discarded for P < 0.05.
Seventy patients (of 74 invited) agreed to participate; one was later excluded because of obesity (Table 1). Data for 69 patients were analyzed. Turning from the supine to the lateral position resulted in a deterioration of laryngoscopic view in 35% of patients and improvement in none (Fig. 1). In the lateral position, failure of airway management occurred in more patients when a standard tracheal tube versus LMA was used (8 of 39 versus 1 of 30; P = 0.03), and the mean time to successful completion of airway management was longer with tracheal intubation compared with the laryngeal mask airway (39 ± 19 s versus 26 ± 12 s; P = 0.002). The application of cricoid pressure improved laryngoscopic view in 26% of patients when supine, in 30% of patients when in the lateral position, and did not worsen the view in any patient. There was no relationship between success or failure of airway management and level of training of the anesthesiologist (Table 1).
The current study used a simulated airway emergency to examine the effect of the practice of turning a patient into the recommended lateral position. Multiple detrimental effects were observed. First, laryngoscopic view deteriorated. Second, there was frequent intubation failure compared with that anticipated for the same patient group in the supine position. Third, the use of an attempted endotracheal intubation took longer and was less successful compared with LMA insertion.
Lateral positioning is a controversial component of some failed intubation drills, and its use with cricoid pressure is widespread in the United Kingdom (2,5–10). Whereas there are recommendations, their incorporation into practice is uncommon, and deviation during emergencies is widespread (7). Existing protocols regarding airway emergencies do not provide evidence-based recommendations for airway management loss in the lateral position (11,12). However, this position may be encountered by anesthesiologists in many circumstances, including trauma, accidental airway loss during surgery, and inadequate regional anesthesia requiring conversion to general anesthesia. These issues are important because the consequences of inadequate airway management may be catastrophic, causing hypoxia, aspiration (7), brain injury, and death (13,14).
There are very limited prospective data on the effect of lateral decubitus positioning on airway anatomy and subsequent management. In a seminal study using manikins, Nathanson et al.(3) found that the lateral position was associated with longer intubation attempts and a more frequent failure rate. The relatively rigid structure of the manikin limits the translatability of these data. There are no comparable clinical studies on the effect of this position on airway anatomy or intubation. More recent prospective clinical trials have examined intubation in the lateral or semilateral position using fiberoptics (15), the intubating laryngeal mask (ILMA™) (16), and lightwand (17), but conventional laryngoscopic intubation was not attempted. In our study, although the laryngoscopic view deteriorated in the lateral position and visualization was adequate in most patients, but this was not matched by successful endotracheal intubation, implying that the lateral position causes dissociation between projected and actual ability to intubate. The mean intubation time in the lateral position seems only moderately prolonged compared with the time for LMA insertion, but this difference is minimized by the exclusion from analysis of the eight patients in whom intubation was deemed unsuccessful because of time constraints.
In our study, LMA insertion was achieved with application of cricoid pressure in 26 seconds and was successful in 96.7% of patients. This is comparable with the results of Komatsu et al.(16) and Dimitriou et al. (17) in which ILMA™ insertion was rapidly achieved (a mean time of 24 and 31 seconds, respectively) with a high degree of success (94% versus 100%, respectively). In the latter study, which compared ILMA™ insertion in the supine and either left or right lateral positions, ILMA™ insertion times were similar in all groups, and no failures occurred in any position (17).
This study examined laryngoscopic visualization and ease of insertion of airway devices, but study design and sample size restricted its ability to address the effects on aspiration risk, airway patency, or the ability to ventilate with a face mask. All patients were adequately anesthetized, paralyzed, and oxygenated, presenting the participating anesthesiologist with each patient pharmacologically optimized for airway insertion. This does not mirror the likely clinical scenario in which it may be required to secure an airway in the lateral position where, in an unplanned emergency, anesthesia may be suboptimal and hypoxemia continuing and progressive. Additionally, all intubation attempts were performed in the left lateral position by right-handed anesthesiologists. Laryngoscopic visualization may be more difficult in the right lateral position because of blade design features. All intubation and LMA insertions were made in the presence of cricoid pressure, but this was not standardized. Whereas cricoid pressure has been shown to impede LMA placement (18), our success was very frequent. Whereas it is possible that backwards-upwards-right-pressure (19,20) was inadvertently applied, it is also possible that cricoid pressure may be less likely to displace the larynx posteriorly in the lateral position, owing to the relatively increased mobility of the head, and may explain the frequent success rate. All patients who entered the study had normal preoperative airway assessments, indicating a low a priori probability of difficult intubation. It is unlikely that the 79.5% intubation success rate would be achieved in patients with more difficult anatomy. Although we describe a frequent success rate of LMA placement in the lateral position, caution is warranted given the small sample size involved, because even a zero failure rate is compatible with a 95% upper confidence interval for failure of approximately 10% (21).
The results of the current study suggest that, in the lateral position, an adequate airway can be rapidly established in most patients with a LMA. However, it also calls into question the logic of placing a patient with an inadequate airway and respiratory depression into the left lateral position, and there are no data to support the practice. Data on the success of LMA use in patients with difficult intubation are emerging. In a study examining airway management in a large series of patients (n = 11,257) at low risk for failed intubation, an algorithm incorporating the use of the ILMA™ (without changing patient position) as an adjunct to the use of a gum elastic bougie in patients with unexpected difficult intubation was associated with frequent success in intubation (22); the frequent success rate was attributed by the authors to the use of devices familiar to care providers in the setting of a simple algorithm. Because, apart from the above study, strategies for airway management where conventional endotracheal intubation has failed have not been reported in large-scale clinical trials, specific interventions in the management of the difficult airway are hard to evaluate. Further trials or audit data may help to clarify these issues.
In conclusion, the left lateral decubitus position is associated with deterioration in laryngoscopic viewing conditions, dissociation between quality of laryngoscopic view and ease of endotracheal intubation, and an increased incidence of intubation failure. LMA placement in the left lateral position has more frequent success. The use of lateral decubitus positioning as part of a planned response to difficult intubation seems inappropriate.
1. Goldik Z, Mecz Y, Bornstein J. LMA insertion after accidental extubation. Can J Anaesth 1995;42:1065.
2. Tunstall M. Failed intubation drill. Anaesthesia 1976;31:850.
3. Nathanson MH, Gajraj NM, Newson CD. Tracheal intubation in a manikin: comparison of supine and left lateral positions. Br J Anaesth 1994;73:690–1.
4. Cormack RS, Lehane J. Difficult tracheal intubation in obstetrics. Anaesthesia 1984;39:1105–11.
5. Hawthorne L, Wilson R, Lyons G, Dresner M. Failed intubation revisited: 17-yr experience in a teaching maternity unit. Br J Anaesth 1996;76:680–4.
6. McBrien ME. Failed tracheal intubation. Br J Anaesth 1996;77:559–60.
7. Morris J, Cook TM. Rapid sequence induction: a national survey of practice. Anaesthesia 2001;56:1090–7.
8. Thwaites AJ, Rice CP, Smith I. Rapid sequence induction: a questionnaire survey of its routine conduct and continued management during a failed intubation. Anaesthesia 1999;54:376–81.
9. Barnardo PD, Jenkins JG. Failed tracheal intubation in obstetrics: a 6-year review in a UK region. Anaesthesia 2000;55:690–4.
10. Hinchliffe D, Norris A. Management of failed intubation in a septic parturient. Br J Anaesth 2002;89:328–30.
11. Benumof JL. Laryngeal mask airway and the ASA difficult airway algorithm. Anesthesiology 1996;84:686–99.
12. Benumof JL. The unanticipated difficult airway. Can J Anaesth 1999;46:510–1.
13. Arbous MS, Grobbee DE, van Kleef JW, et al. Mortality associated with anaesthesia: a qualitative analysis to identify risk factors. Anaesthesia 2001;56:1141–53.
14. Rosenstock C, Moller J, Hauberg A. Complaints related to respiratory events in anaesthesia and intensive care medicine from 1994 to 1998 in Denmark. Acta Anaesthesiol Scand 2001;45:53–8.
15. Adachi YU, Satomoto M, Higuchi H. Fiberoptic orotracheal intubation in the left semilateral position. Anesth Analg 2002;94:477–8.
16. Komatsu R, Nagata O, Sessler DI, Ozaki M. The intubating laryngeal mask airway facilitates tracheal intubation in the lateral position. Anesth Analg 2004;98:858–61.
17. Dimitriou V, Voyagis GS, Iatrou C, Brimacombe J. Flexible lightwand-guided intubation using the intubating laryngeal mask airway in the supine, right, and left lateral positions in healthy patients by experienced users. Anesth Analg
18. Asai T, Barclay K, Power I, Vaughan RS. Cricoid pressure impedes placement of the laryngeal mask airway and subsequent tracheal intubation through the mask. Br J Anaesth 1994;72:47–51.
19. Knill RL. Difficult laryngoscopy made easy with a “BURP.” Can J Anaesth 1993;40:279–82.
20. Takahata O, Kubota M, Mamiya K, et al. The efficacy of the “BURP” maneuver during a difficult laryngoscopy. Anesth Analg 1997;84:419–21.
21. Hanley JA, Lippman-Hand A. If nothing goes wrong, is everything all right: interpreting zero numerators. JAMA 1983;249:1743–5.
22. Combes X, Le Roux B, Suen P, et al. Unanticipated difficult airway in anesthetized patients: prospective validation of a management algorithm. Anesthesiology 2004;100:1146–50.