Prospective observational study on tracheal tube cuff pressures in emergency patients– is neglecting the problem the problem?

For emergency patients, tracheal intubation with a cuffed tube remains the gold standard for securing the airway. Compared with other airway tools, only cuffed tracheal tubes are able to prevent aspiration. In addition, for controlled ventilation, air leakage must be minimised. This is especially important during the transfer and relocation of patients. In emergency situations, the risk of over-inflation is high [1‐3]. There is evidence from studies and case reports that over-inflation of the tracheal cuff can cause various complications including rather benign complaints such as sore throat or hoarseness and mild mucosal damage expressed by transient blood-streaked expectorant [4‐6], but also serious complications such as tracheal stenosis or even tracheoesophageal fistula or tracheal rupture [7‐12].

Possible damage from inappropriately high cuff pressures is a well-known hazard in long-term (days) ventilated patients but is a less recognised problem in short-term (hours) intubated patients. Nevertheless, a recent publication demonstrated that mucosal damage also occurs in short-term (1-3 hours) intubated patients [4]. Emergency patients are especially prone to cuff pressures that remain unmeasured for hours [1].

In addition, cardiac output and blood pressure in emergency patients are often compromised, and low capillary pressure has been shown to influence tracheal mucosal perfusion [13, 14] resulting in damage that can occur at lower cuff pressures than in haemodynamically stable patients.

Because situations in emergency and critically ill patients are more complex and team compositions are often not as well-rehearsed as in elective hospital intubation settings, we hypothesised that cuff pressures are frequently too high and depend on the provider’s professional background.

The study was approved by the local Institutional Review Board (Ethikkommission beider Basel) as a quality assurance investigation. Requirement for written informed consent was waived by the Institutional Review Board.

After exclusion based on the specified criteria, data of 101 patients were included in the study (Figure 1). Patient demographics were distributed as follows: 77 (76%) were male; mean age was 54 ± 20.1 years (range, 10-85 years), 95 (94%) were ≥18 years. Tube diameters are shown in Table 1. Regarding mission type, the majority of patients (n = 63) underwent an emergency transfer and 38 patients an ICU transfer.

Median initial cuff pressure measured was 45 (25.0/80.0) cmH₂O (mean 55 ± 34.7 cmH₂O; range, 8-120 cmH₂O). There was no difference in cuff pressures dependent on patient characteristics (i.e. sex, age) or tracheal tube diameter. Values of initial cuff pressure were not different if anaesthesia personnel (nurse or anaesthesiologist) or non-anaesthesia personnel (nurse or physician) had inflated the cuffs (median 30 (24.8/70.0) vs. 50 (28.0/90.0) cmH₂O, mean 46 ± 31.5 vs. 60 ± 35.1 cmH₂O); p = 0.113.

Mission type significantly influenced cuff pressure values: 58 (30.0/100.0) cmH₂O for emergency transfers vs. 30 (20.0/45.8) cmH₂O for ICU transfers (mean 64 ± 36.4 vs. 38 ± 24.5 cmH₂O); p < 0.001.

Duration between tracheal intubation and patient handover was 40 ± 41.1 minutes (range, 0-220 minutes) in emergency transfers and 97 ± 167.4 minutes (range, 0-840 minutes) in ICU transfers. The highest percentage of elevated cuff pressures (defined as ≥30 cmH₂O) was found in patients intubated within one hour of measuring (Table 2). Median cuff pressures in patients intubated <60 minutes (n = 65) and ≥60 minutes (n = 30) before measurement were 45 (26.5/87.5) and 42 (23.0/80.0) cmH₂O (mean 56 ± 35.7 and 51 ± 35.4 cmH₂O), respectively.

Different methods for cuff pressure assessment, if any, were applied by the intubating team: a manometer was applied in 22 cases (22%); a specific volume of air was inflated in 14 cases (14%); the palpatory method was used in 10 cases (10%); and the acoustic method was used in one case. In 46 patients (46%), cuff pressures had not been checked by any method, and in 8 cases the referring person could not provide any information on the type of measurement, if any. ICU transfers showed a higher percentage of “measurement” (20 of 34, 59%) compared with emergency transfers (2 of 59, 3%), for 4 patients in each group the technique was unknown.

Different methods of checking showed different cuff pressure values (Figure 2). If a manometer was used, median cuff pressure was 27 (20.0/30.0) cmH₂O, if not 70 (47.3/102.8) cmH₂O (mean 27 ± 8.7 vs. 65 ± 35.6 cmH₂O); p < 0.001. Apart from one cuff pressure evaluated using the acoustic method, manometer measurement was the only method with a median cuff pressure <30 cmH₂O.

Tracheal tube cuff pressures in patients intubated prior to aeromedical transport are generally too high. This finding is independent of patient characteristics, tube diameter and time since intubation. In particular, professional background of those who performed intubation had no influence. Contrary to expectation, anaesthesia personnel did not reliably control the appropriateness of the cuff inflation. Cuff pressures were much higher in emergency transfers than in ICU transfers. Elevated cuff pressures in tracheally intubated patients prior to emergency transfer have been demonstrated in the prehospital and the emergency department setting [1‐3, 15, 16]. Correlation between high cuff pressure and tracheal injury has been known for decades [13, 17, 18]. This may be especially harmful for intubated patients scheduled for airborne transportation. During helicopter transfer of tracheally intubated patients, cuff pressures have been shown to dangerously increase in spite of cuff control prior to ascent [19, 20]. Similar results have been reported for fixed-wing air-medical retrieval [15, 20] and in an in vitro study simulating flight-level changes in an altitude chamber [21]. If not controlled prior to or monitored during air transfer, high pre-existing pressures will reach extreme values.

Tracheal mucosal blood flow has been shown to be impaired at cuff pressures ≥30 cmH₂O [13]. Animal data suggest ischaemic injury to the tracheal mucosa when cuff-to-tracheal wall pressures ≥20 mmHg persist for 15 minutes [22]. As many emergency transfers of patients involve haemodynamically unstable patients with significant hypotension, blood flow in the tracheal mucosa may be compromised at even lower inflation pressures. In a canine model, capillary mucosal perfusion was already significantly reduced at 22 mmHg mucosal contact pressure during hypotension (defined as a mean arterial pressure (MAP) of 50 mmHg during a period of 15 minutes) [14]. In a rabbit model, tracheal mucosal blood flow was diminished according to the ratio of cuff / MAP: if cuff pressure was 20 to 30% of MAP (which at a MAP of 75 mmHg, corresponds to cuff pressures of 15–22.5 mmHg), there already was a marked reduction of microvascular tracheal mucosal blood flow over the cartilages. To safely avoid total ischaemia, cuff pressure must not have exceeded 40% of MAP [20].

A recent multicentre study recorded cuff pressures in an operating room setting and showed much higher than optimal values if pressure was estimated by clinical judgement alone [4]. In addition, the same study demonstrated by clinical evaluation and fibreoptic control that sore throat, hoarseness and blood-streaked expectoration 24 hours after extubation and, respectively, mucosal injury observed by fibreoptic bronchoscopy immediately after removal of the tube were significantly higher in the non-pressure controlled group. These complications already occurred in procedures as short as 1-3 hours.

For brief procedures lasting only a few hours, most anaesthesiologists pay little attention to tube cuff inflation pressure [4]. Several methods to prevent non-physiological tracheal tissue compression have been suggested and even new simple-to-use devices such as a pressure-sensing syringe have been proposed [23‐25]. For the most common method of pressure control, the pilot balloon palpation, studies have shown a prevailing inability of clinical staff members to accurately determine the pressure [23, 26]. In a more recent investigation, the tendency to overinflate tube cuffs was still dominating, and even more disturbing, this problem was more common in the group of highly experienced anaesthesiologists [27].

In our study, cuff pressures were not controlled at all in nearly half of the cases. In “controlled” cases, the most frequent technique for assessment was measuring using a manometer, followed by insufflating a “specific volume of air”, “palpatory” and “acoustic” methods, whereupon measurements had been performed prior to almost all ICU transfers. Techniques other than direct measurement are unreliable in the prehospital setting.

Acceptable cuff pressures are best achieved by using a manometer.

Tracheal tube cuff pressures in patients intubated prior to aeromedical transport are too high. In our study, cuff pressures were not controlled at all in nearly half of cases. Awareness about this circumstance seems to be absent from daily practice in emergency situations; this seems to apply to anaesthesia personnel, too. We, therefore, recommend the mandatory routine use of a cuff pressure manometer to avoid inappropriately high cuff pressures. Use of a 5 ml syringe may be a perferable pragmatic alternative to the traditional 10 ml syringe. Acknowledging the dangerous increase of cuff pressures during subsequent airborne transport, medical teams responsible for transfer of intubated patients must monitor tracheal tube cuff pressures and adjust the pressures appropriately.