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Clinical use of the Empey index in the emergency department
  1. J E France,
  2. M J C Thomas
  1. Emergency Department, Royal United Hospital, Bath, UK
  1. Correspondence to:
 Dr J E France
 Emergency Department, Royal United Hospital, Combe Park, Bath BA1 3NG, UK; jfrancebtopenworld.com

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Percutaneous tracheostomies (PCT) performed in the intensive care unit (ICU) are becoming a routine procedure in the care of the patient who is likely to require ventilatory support for seven days or more. As the frequency of this procedure increases so will the numbers of complications, such as tracheal stenosis. We discuss the diagnosis of tracheal stenosis in the emergency setting and the use of the Empey index.

CASE HISTORY

A 26 year old woman presented to the emergency department (ED) complaining of shortness of breath and difficulty clearing secretions. She had been discharged from hospital two weeks previously after a four week stay, including 20 days in the ICU. On that occasion she presented with increasing shortness of breath and stridor attributable to bacterial tracheitis. While in the ICU she developed pneumonia and severe sepsis. On day four of her ICU stay she underwent PCT in the ICU with a Blue Rhino tracheostomy set, which remained in situ for 16 days. Before her ICU stay she had been fit and well.

On presentation to the ED she was anxious but looked well with Sao2 100% on oxygen, respiratory rate 20, blood pressure 110/70, pulse 98. Examination of her chest showed a prolonged inspiratory phase and transmitted upper airways noises, presumed to be from secretions but no stridor. Besides a well healed tracheostomy scar and appearing to be undernourished the rest of the examination was normal.

A chest radiograph and lateral soft tissue neck were normal, as were the arterial blood gas pressures. In view of the recent ICU admission bedside spirometry (Micro Medical) was performed and showed a forced expiratory volume in one second (FEV1) of 0.87 litres and a peak expiratory flow rate (PEFR) of 70 litres per minute; giving an Empey index of 12.4. The patient underwent endoscopic examination of the airway (above the cords) while in the ED and this was normal. On day 2 of the patient’s admission she underwent computed tomography, which showed significant tracheal stenosis (see fig 1). She subsequently underwent endoscopic stenting and made a good postoperative recovery.

Figure 1

 CT scan showing tracheal stenosis (arrow) with a minimum diameter of 0.5 cm by 0.8 cm at the level of the 3rd/4th tracheal ring.

DISCUSSION

The Empey index1,2 is a way of predicting if a patient has upper airways obstruction and can be performed simply at the bedside. It is the calculation of the ratio of FEV1 (ml):PEFR (l/min); a normal person will have a ratio of less than 10 while a person with upper airways obstruction will have a ratio greater than 10, the higher the index the more severe the obstruction. The index has been well validated on a variety of patients with upper airways obstruction but also in patients with other forms of lung disease including asthma and emphysema.

At near total lung volumes flow (expiration) is dependent on effort and the pressure within the alveoli; the addition of an upper airways obstruction increases the resistance in the upper respiratory tract and reduces the flow at high lung volumes. At the lower lung volumes the collapse of bronchioles during expiration is much more of a determining factor in flow generation. From figure 2 it can be seen that the FEV1 is very similar in both subjects—that is, FEV1 is little affected by the presence of upper airways obstruction. FEV1 is measured over one second—that is, over a range of diminishing lung volumes, it is less dependent on effort and upper airways resistance. PEFR is measured in the first two milliseconds of a maximal expiration—that is, at high lung volumes. Hence in upper airways obstruction PEFR is much more affected then the FEV1. In asthma and chronic obstructive pulmonary disease both FEV1 and PEFR are affected, and in emphysema the peak flow is relatively less reduced compared with the FEV1.

Figure 2

 Maximal expiratory and inspiratory flow volume curves (continuous lines) for (A) a patient with upper airways obstruction, and (B) a patient with asthma. The interrupted lines show the flow volume curve for a normal subject. (Reproduced with permission BMJ Publishing Group (see reference 1).

Learning points

The diagnosis of tracheal stenosis should be suspected in any patient presenting with respiratory symptoms after an intensive care unit (ICU) stay. The Empey index is a reliable bedside test that can aid the diagnosis of tracheal stenosis in the ED.

Diagnosis of tracheal stenosis may also be aided by chest radiography and lateral soft tissue neck, which may show alteration of the air column. Magnetic resonance imaging and computed tomography are also helpful.3,4 Flow volume loops may also be helpful in long term follow up and monitoring for re-stenosis.

It is important to consider tracheal stenosis in any patient who has undergone a prolonged stay in ICU. Tracheal trauma is the most common cause of stenosis in children and adults. About 90% of all acquired chronic subglottic stenosis results from endotracheal intubation, reported rates vary from 0.9% to 8.3%.5 Intubation causes injury at multiple levels; pressure on the arytenoid cartilage, pressure or motion of the tip of the tube against the subglottic cartilage causing ischaemia and necrosis. Factors important in the development of stenosis include length of time of intubation6 and size of tube. Clearly in a patient who already has an inflamed trachea and is septic then these additional risk factors are likely to predispose to subglottic stenosis.

Tracheostomy allows for easier weaning of ventilated patients, requiring less sedation and reducing both dead space and airway resistance. In addition it has many advantages for the patient including facilitating oral communication and speech, permitting more mobility and comfort. Nursing care is also facilitated with improved oral, nasal, and facial hygiene, easing airway care and suctioning.

PCT is thought to reduce the incidence of laryngeal and subglottic stenosis, the rate of which has been quoted as 1.9%7 but the incidence varies greatly between series and is dependent on the technique used. One long term follow up of 340 critical care survivors of PCT found that 31% of patients had a tracheal stenosis of more than 10% and symptomatic stenosis present in 6% of patients.4 Most stenoses are asymptomatic and can involve between 10%–40% of the diameter, above 75% symptoms are usual. Most cases are diagnosed within one year and most present within 2–12 weeks.8 Presenting features include dyspnoea, stridor, hoarseness, cough, and recurrent pneumonitis.

Factors that minimise the risk of stenosis include using properly sized tracheostomy tubes with high volume low pressure cuffs, flexible ventilator connectors, and placing the tube between 1st and 2nd or 2nd and 3rd tracheal rings (to lower risk of cricoid injury). Operative correction is only rarely required and may include procedures such as tracheopexy with muscle-fascia repair and resection of stenotic segment with end to end repair.

CONCLUSION

The diagnosis of tracheal stenosis should be suspected in any patient presenting with respiratory symptoms after an ICU stay. The absence of stridor, as in our case, does not exclude the presence of significant tracheal stenosis.

The Empey index is a reliable bedside test that can aid the diagnosis of tracheal stenosis in the ED.

REFERENCES

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