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Summary

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References
  8. Supporting Information

Inexperienced rescuers may encounter severe problems in an unconscious patient with opening and maintaining a patent upper airway. Designing a ventilating device that could indicate how to open an upper airway correctly may be beneficial. The heads of 102 volunteers were randomly placed in different head positions by one investigator. A pocket mask was then pressed gently on the volunteer's face followed by measurement of the head position angles. Mean (SD) flexion was − 4° (8°) (95% CI − 5.9 to − 2.9); the mean neutral position was 21° (6°) (95% CI, 19.9 to 22.3); extension was 42° (6°) (95% CI 40.8 to 43.0°) and differed significantly between each position (p < 0.001). The flexion and neutral position angles were significantly greater in men than in women: − 2 (7°) vs. −8 (7°) and 22 (7°) vs 20 (5°); p < 0.001 and p = 0.03, respectively. Maximum extension of the head in both supine men and women was 42°, which could be utilised to optimise assisted ventilation of an unprotected upper airway.

Ventilation during basic life support improves survival in cardiac arrest patients significantly [1]. Unfortunately, this is in contrast to the willingness of potential rescuers to perform mouth-to-mouth ventilation [2]. For example, although healthcare professionals would perform mouth-to-mouth ventilation on a 4-year-old drowned child in > 90% of cases, this likelihood would decrease to ∼ 10% in the case of a young male unconscious patient on a San Francisco public bus [3]. Possibly, lay rescuers would perform assisted ventilation more often if a simple ventilation device were available. However, both the willingness to perform assisted ventilation plus the ability to open and to maintain a patent airway are necessary to ensure efficient ventilation in an unconscious patient with an unprotected upper airway.

Since retention of skills after basic life support classes are notoriously low [4, 5], a resuscitation tool should incorporate self-explanatory features to improve applicability and to provide built-in safety. Thus, an option could be to ensure an open airway by the use of a built-in indicator within a ventilating device to confirm correct head extension. One possible approach may be to determine head positions that make an open airway likely and then extrapolate these angles to a scale that could be integrated into a ventilating device; however, safe head extension needs to be determined first to prevent harm.

The purpose of this study was to determine head position angles reflecting maximal flexion, neutral position, and maximal extension in conscious, supine adult volunteers as a first step towards designing a ventilating device to optimise ventilation of an unprotected upper airway.

Methods

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References
  8. Supporting Information

The protocol of this study was approved by the Local Ethics Committee. Bystanders attending a county fair signed written informed consent prior to participation; only ASA I and II patients were included in the study. Exclusion criteria were cervical spine pathologies, peripheral nerve deficiencies, excessive beard growth and obvious primary or secondary craniofacial abnormalities. Dentures were not removed during assessment. Gender, age, weight and height were recorded. Volunteers had to position themselves in a supine position on a flat stretcher with a hard surface without any cushion to support the head. Head, neck and limbs were aligned to the longitudinal axis of the body. Photos were taken with a digital camera (G2 Powershot, Canon, Tokyo, Japan), from a distance of 3 m, located on a tripod. The axis of the camera view was aligned with the axis of head flexion in the cervical spine. The head of the volunteer was placed in three different positions by one investigator; namely maximal flexion (chin positioned on the chest), neutral position (no apparent flexion, torsion, or extension of the neck) and maximal extension. A face mask (Pocket Mask, Laerdal, Stavanger, Norway) was pressed gently on the volunteer's face according to the manufacturer's recommendations, namely to centre the face mask on the patient's face so the triangle is over the bridge of the patient's nose and the larger portion of the mask is placed between the lower lip and the chin. In addition, chin lift was performed as recommended by resuscitation guidelines [6]. Images were recorded for all three positions. Head position angles were then measured between the longitudinal axis of the hard surface of the stretcher and a line through the longitudinal axis of the face mask (Fig. 1).

image

Figure 1.  Position of the head and pocket mask in extension, neutral position and flexion with the head position angles (α, β, γ) being measured.

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Data were analysed with SPSS 13.0.1 software (SPSS Inc. Chicago, IL). Comparisons between groups were carried out with analysis of variance (anova) and the post-hoc-test, Games Howell. The comparison of angles between males and females was carried out by Student's t-test. A p-value < 0.05 was considered significant; a 95% confidence interval (95% CI) is given when appropriate. A sample size estimation revealed that for p < 0.05, power = 90% and a standard deviation of 8°, about 100 volunteers could show a significant clinical difference for head position angles varying more than 8°.

Results

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References
  8. Supporting Information

In total, 102 adults were enrolled into the study; data are presented as mean values (SD) and 95% confidence interval (CI), if not indicated otherwise. Sixty-one volunteers (60%) were male and 41 (40%) female. The mean age of all volunteers was 40 (11) years (minimum age 19, maximum age 73 years). The mean age was 43 (12) and 37 (10) years for men and women, respectively. Mean height was 179 (5) and 169 (5) cm, and mean weight was 73 (7) and 62 (7) kg, respectively. Body mass index was 23 (2) for men and 22 (3) kg.m−2 for women. Flexion angulation was − 4° (8°) (95% CI − 5.9 to − 2.9°); in the neutral position the angulation was 21° (6°) (95% CI 19.9 to 22.3); and in extension the angle was 42° (6°) (95% CI 40.8 to − 43.0) and differed significantly between each position (p < 0.001) (Figs 2, 3). The flexion and neutral position angles were higher in men than in women: 2° (7°) vs − 8° (7°) and 22° (7°) vs 20° (5°), respectively (p < 0.001 and p = 0.03). The extension angle was ∼ 42° in both men and women (p = 0.65) (Figs 2, 3).

image

Figure 2.  Individual angles measured for all 102 volunteers in extension, neutral position and flexion.

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image

Figure 3.  Resulting box-plot-diagrams displaying median (25th−75th percentile) of head position angles in extension, neutral position and flexion. *p < 0.001 Games-Howell test for comparison of head position angles.

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Discussion

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References
  8. Supporting Information

The flexion, neutral position and extension angles differed significantly between each other. Flexion and neutral position angles were higher in men than in women, whereas the extension angle was 42° in both men and women.

As the likelihood of encountering a patient requiring assisted ventilation is especially low for lay rescuers and even for many professional rescuers, stress levels in an emergency may be high, and performance may suffer considerably. For example, the likelihood of managing a cardiac arrest patient was less than once a month for German emergency medical service physicians, and paramedics and lay bystanders might be expected to encounter a patient requiring immediate airway management even less often [7]. This problem of decreased quality due to a lack of frequent performance on the job was confirmed in an emergency medical service and in an emergency room, when even experienced paramedics used excessive ventilation rates (∼ 35 instead of ∼ 10 per min) with a bag-valve mask device [8,9]. Furthermore, when even third-year anaesthesia residents bag-valve mask ventilated patients during routine induction of anaesthesia with an excessive peak airway pressure, resulting in stomach inflation, it is unlikely that a less experienced rescuer or a lay rescuer will be able to ventilate adequately [10].

There are two basic manoeuvres to keep the upper airway open: hyperextension of the head and jaw thrust as described by Safar et al. [11] and Elam et al. [12] almost 50 years ago. The combination of both manoeuvres seems to be the most effective [11, 12]. Unfortunately, this knowledge is often lacking, especially in lay bystanders, who might be able to save a life quickly if they have adequate basic life support skills. For example, in an attempt to position an unconscious patient in a subjectively comfortable position, lay rescuers were found to place a pillow under the head, thereby inadvertently obstructing the airway even further (unpublished observation). Thus, the well-meant help of a lay rescuer may result in an adverse outcome or even the death of an unconscious patient. As ventilation is a complex psychomotor skill [8, 9], it might be a substantial advantage if the proper head position angle of a supine unconscious person could be indicated to an inexperienced rescuer by the airway device itself. With an open upper airway, an unconscious patient could either breathe spontaneously or could be ventilated.

One could suppose that significantly different head position angles between females and males for the flexion and neutral position may depend on gender-specific morphology, such as thicker adipose tissue at the chin in males [13]. This might hinder men in flexing their head forward in the same way as women. However, the grade of flexion does not seem to depend on body mass index, because this was similar between men and women (23 (2) vs 22 (3) kg.m−2) in our study. Flexion occludes the upper airway and is therefore of no clinical importance for opening the upper airway, as long as it is prevented [14]. Although the neutral position is more apt to open the airway, it is probably not the best position [11, 12]. Interestingly, the extension angle (∼ 42°) did not vary between men and women. This is a useful finding, as the same head position angle could possibly be applied to all adults irrespective of gender. When extrapolating our data by applying a ∼ 40° extension to the head of a supine unconscious person, a rescuer could extend the head optimally, and therefore open the airway, most likely, safely [15]. The next step should be to design a ventilating device which, by incorporating an electronic liquid level, indicates to an inexperienced rescuer the proper head position in a traffic light pattern (red for flexion; yellow for neutral position; and green for extension) to keep the upper airway in an unconscious supine patient open.

Our study has some limitations. Firstly, the study cohort consisted of conscious volunteers only; results in unconscious persons with functional paralysis may therefore be different. It is possible that head angles differ between these two groups, as muscles are hypotonic in unconscious persons. Therefore, the same experiment should be repeated in a cohort of unconscious healthy patients who do not suffer from any cervical spine pathology. Secondly, the mean age of the study volunteers was substantially lower than the mean age of cardiac arrest patients [16]. Older patients are much more likely to have restricted cervical spine movement with progressively reduced maximal extension; therefore, head position angles in cardiac arrest patients could be different. Thirdly, the study was limited to adults only; accordingly, we can not make any statements for infants or even neonates. Finally, we analysed the head positions externally only and are unable to determine whether our results represent the best position for a patent upper airway. Further investigations, such as magnetic resonance imaging or computer tomography studies, may have to be performed in unconscious patients to validate our data.

In conclusion, maximum extension of the head in both supine men and women was 42°, which could be utilised to optimise assisted ventilation of an unprotected upper airway.

Acknowledgements

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References
  8. Supporting Information

We wish to thank Martha and Werner Beikircher, and our colleagues of the Mountain Rescue Service provided by the South Tyrolean Alpine Association in Bruneck, Italy, for their enthusiastic support for this study.

Supported, in part, by the Austrian National Bank grant 11448, Vienna, Austria.

References

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References
  8. Supporting Information
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    Handley AJ, Koster R, Monsieurs K, et al. European Resuscitation Council Guidelines for Resuscitation 2005 Section 2. Adult basic life support and use of automated external defibrillators. Resuscitation 2005; 67 (Suppl. 1): S7S23.
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    Milander MM, Hiscok PS, Sanders AB, et al. Chest compression and ventilation rates during cardiopulmonary resusCitation. the effects of audible tone guidance. Academic Emergency Medicine 1995; 2: 70813.
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    Wagner-Berger HG, Wenzel V, Voelckel WG, et al. A pilot study to evaluate the SMART BAG: a new pressure-responsive, gas-flow limiting bag-valve-mask device. Anesthesia and Analgesia 2003; 97: 16869.
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    Wilson SL, Thach BT, Brouillette RT, Abu-Osba YK. Upper airway patency in the human infant. influence of airway pressure and posture. Journal of Applied Physiology 1980; 48: 5004.
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    Fuchs G, Schwarz G, Baumgartner A, et al. Fiberoptic intubation in 327 neurosurgical patients with lesions of the cervical spine. Journal of Neurosurgical Anesthesiology 1999; 11: 116.
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    Hallstrom AP, Ornato JP, Weisfeldt M, et al. Public-access defibrillation and survival after out-of-hospital cardiac arrest. New England Journal of Medicine 2004; 351: 63746.

Supporting Information

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References
  8. Supporting Information

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