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A simple device for determining the degree of head up / back up tilt

1. Goneppanavar Umesh

2. Venkateswaran Ramkumar

3. Kaur Jasvinder

4. Philip Ann Frenny

Department of Anaesthesiology
Kasturba Medical College
MANIPAL 576 104
Karnataka State
India

Introduction

A simple device for determining the degree of head up / back up tilt
Preoxygenation, the routine administration of 100% oxygen to a conscious individual before induction of general anaesthesia, has now become an integral component of safe conduct of general anaesthesia. It has come to be described as a new ‘minimum standard of care’ as the benefits incurred by it far outweigh the disadvantages.1

Recent literature evidence suggests that providing varying degrees (20° - 90°) of head up tilt / back up tilt during preoxygenation can significantly prolong the duration of non-hypoxic apnoea as compared to conventional preoxygenation. However the difference in PaO2 is not significantly different between the groups.2-5 Further studies on preoxygenation with head up / back up tilt may help in better understanding of the mechanisms involved. However, the exact technique used to achieve the necessary degree of tilt is not mentioned in the methodology of these studies.

Method

We requested the corresponding authors of several such studies to inform us of the technique they employed for achieving the requisite degree of tilt. Their responses revealed that there are two methods by which they have achieved the goal. One of the methods involves use of electrically controlled tables which can provide accurate degree of tilt. However, these tables are not available universally in all institutions and even when available, may not be in all the theatres. This in itself can become a limiting factor for performing studies involving head up or back up tilt. To overcome this, some have used a goniometer which can, with careful handling, assist in providing appropriate tilt manually.

tilt guide anaesthesia

Fig 1: A prototype of the device in use for obtaining a 20° head up tilt

We devised a simple alternative to these which can be prepared with no expense and made available in all the theatres. A sheet of transparent plastic (25 x 25 cm), a scale and a small compass and a marker pen is all that is needed for the preparation. A long straight line (20 cm) can be drawn at the base of the plastic sheet and different angles from the centre of the baseline can be marked using the compass (Fig 1). This is then held against the operating table such that the centre of the baseline corresponds with the fulcrum at which the head up tilt occurs and then the requisite degree of tilt can be achieved manually.

Conclusion

Prior to this device, simple visual assessment was used to provide the approximate tilt to the table. We requested five anesthesiologists to position the table in an approximately 20° back up tilt by simple visual assessment and we measured the angle with a large compass. We found that the variation in the degree of back up tilt was approximately between 15° to 30°. A small variation in the degree of tilt may not make any significant difference to the outcome of the study. However, we believe that a variation of 15° to 30° is unacceptable as 30 is double that of 15. This prompted us to device this simple equipment

We hope that such an inexpensive device will make it easier for those scientifically inclined but materially limited to perform studies in this interesting area.

References:

1. Bell MD. (2004) Routine pre-oxygenation - a new 'minimum standard' of care? Anaesthesia. 59: 943-5.
2. Altermatt FR, Munoz HR, Delfino AE, Cortinez LI. (2005) Pre-oxygenation in the obese patient: effects of position on tolerance to apnoea. Br J Anaesth. 95: 706-9.
3. Baraka AS, Hanna MT, Jabbour SI, et al. (1992) Preoxygenation of pregnant and nonpregnant women in the head-up versus supine position. Anesth Analg. 75: 757-9.
4. Dixon BJ, Dixon JB, Carden JR, Burn AJ, Schachter LM, Playfair JM, Laurie CP, O’Brien PE. (2005) Preoxygenation is more effective in the 25 degrees head-up position than in the supine position in severely obese patients: a randomized controlled study. Anesthesiology. 102: 1110-5.
5. Lane S, Saunders D, Schofield A, Padmanabhan R, Hildreth A, Laws D. (2005) A prospective, randomised controlled trial comparing the efficacy of pre-oxygenation in the 20 degrees head-up vs supine position. Anaesthesia. 60: 1064-7.

First Published October 2008

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