Pre-procedural ultrasound assessment as a step towards the safety of percutaneous dilatational tracheostomy: a comparative study

Introduction and Aim of the work

Tracheostomy is a commonly performed bedside procedure in prolonged ventilated critically ill patients. ¹ Percutaneous dilatational tracheostomy (PDT) has a well-known advantages and it’s favored over surgical tracheostomy (ST), ² however PDT heralds many peri-procedural complications as hemorrhage, pneumothorax, pneumomediastinum, false passage, posterior tracheal wall injury, subcutaneous emphysema, and difficult to place the tube. ³ It is common for patients indicated for PDT to have rather difficult anatomical variations most often due to obesity, chronic musculoskeletal pathology, previous injuries, or surgical procedures. Among the difficulties confronted; difficulty in locating cricothyroid membrane and difficulties with tracheal puncture when the tracheal anatomy is not easily palpable and attempting palpation of the usually used anatomical landmarks seems sometimes to be difficult or even impossible. ^4,5 Many assisting tools have been used to assist guidance during PDT and therefore decreasing the incidence of these peri-procedural problems. ⁶ These include the laryngeal mask airway (LMA), pre procedure ultrasound (US) scanning, light wand for trans-illumination of the neck soft tissues, and flexible fiber optic bronchoscopy. ^7,8 US can be especially useful to assess tracheal midline, pre tracheal soft tissues including type and size of blood vessels in the area of interest, the sternomastoids and infrahyoid muscles, and lastly the jugular veins and carotid arteries prior to PDT. ⁹ Also it may help in accurate selection of size and length of tracheostomy tube, especially in patients with an increased pre tracheal soft tissue thickness. ¹⁰

Aim of the study isto compare fiber optic bronchoscope guided percutaneous dilatational tracheotomy outcomes between those patients with pre-insertion Ultrasound imaging of the neck (USPDT) and those without (PDT). Our primary outcome was time of the technique, while ease of the procedure, failure, and complications as bleeding, transient hypoxemia, tracheal wall injury or false passage were secondary outcomes.

Patients and methods

This prospective randomized comparative study was carried out in Al-Hussain and Sayed Galal university hospitals between July 2016 and December 2018. A total of 49 adults intubated mechanically ventilated patients admitted in intensive care were assessed for eligibility for PDT. Of those, five patients were excluded for surgical conversion, and 44 patients, scheduled to undergo bedside tracheostomy (due to inability to protect airway or difficult weaning from mechanical ventilation), were enrolled in the study.

Approval for this study was obtained from the Institutional committee of ethics and informed consents were obtained from the legal guardian of patients. Patients were randomly divided into two equal groups: PDT group: represented patients subjected to flexible fiber optic bronchoscope guided PDT without US guidance, and USPDT group: represented patients who underwent pre-procedural US neck imaging followed by flexible fiber optic bronchoscope guided PDT. The following conditions were excluded: Age <16, obese patients with Body Mass Index (BMI) ≥ 45 kg/m², severe coagulopathy, and unsuitable anatomy (e.g., previous cervical surgery, cervical trauma, or tumors).

All tracheostomies were done as a bedside procedure in the intensive care unit, and patients monitored by capnography, pulse oximetry and noninvasive blood pressure. Positive end expiratory pressure (PEEP) were decreased to zero, synchronized intermittent mandatory ventilation (SIMV) mode was used and the ventilator set to deliver 6mL/kg tidal volume, respiratory rate 12/minute and fraction inspired oxygen (FiO₂) 50%. For analgesia and sedation, we used intravenous fentanyl 0.5 µg/kg and propofol 3mg/kg/hour infusion plus lidocaine 2% subcutaneous infiltration, no muscle relaxants were used in our study.

The procedure details in the US-guided PDT cohort

Ultrasound examination was done with Sono Site M-Turbo (Fujifilm Sono Site, Inc., Washington, USA) portable ultrasound device. A short linear vascular probe (8-12 MHz) was used, the trachea was imaged in the vertical medial plane and continuous or pulsed Doppler signals over the trachea was activated on the level of the second ring. Aiming to reduce the possibility of non visualization of veins, patients could be temporarily positioned in a head down position to improve venous filling in the scanned area. Care was taken during scanning to keep only minimum pressure with the ultrasound probe to avoid collapse of vessels by the probe pressure. When round, well demarcated structures, suspicious of being vascular in nature were identified anterior to the trachea, numerous maneuvers were useful to examine whether the structures seen were artery or vein. 1^st, compression was applied with the probe to inspect for luminal reduction as a response to variable grades of compression. 2^nd, a Doppler curser was located over the structure to be tested and Doppler flow was displayed by sound or graph to screen for signal of pulsatile flow of arteries. 3^rd, a square region of interest was placed around the structure and color Doppler analysis was performed (Figure: 1).

Figure 1: Doppler US at level of 2^nd tracheal ring for preoperative scanning of vascular structures.

Then the patient was placed in tracheostomy position, the endotracheal tube was withdrawn thereafter till the cuff is just lower to the vocal cord. When the tip of the tube reached the 2^nd tracheal ring, the intensity of the Doppler signal significantly increased due to an increased signal from turbulent air, proving the exact site of endotracheal tube. puncture site was typically chosen between 2nd and 3rd tracheal rings, following a clear ultrasonic confirmation of anatomy of the cricoid and thyroid cartilages and tracheal rings (Figure: 2). Cook Ciaglia Blue Rhino ® G 2 (Cook Medical Inc., Bloomington, USA) kit was used and Bronchoscopy was performed using flexible fiber optic bronchoscopes (Pentax Ltd, U.K.).

Figure 2: Preoperative US assessment of the neck in Intensive Care Unit. TI: Thyroid isthmus, RtCA & LtCA: Right & Left carotid arteries.

Time of technique, failure of the procedure, difficulty, and complications were assessed. Time of technique:defined as time from the start till confirmation of the correct placement (expressed with min). Failure of the procedure: defined as conversion after the onset of PDT procedure to surgical tracheostomy. Difficulty:were assessed as follow: easy, some difficulty, or very difficult, some difficulty considered if there was difficulty to define landmarks, or need to change in puncture site due to bleeding, while very difficult considered if there was inability to define landmarks (but no failure). Complications were classified to minor or major: Minor complications include; transient hypotension (systolic blood pressure below 80% of the start reading) for less than 5 minutes, transient hypoxemia (peripheral oxygen saturation [SpO₂] < 90% for less than 5 minutes), localized minor bleeding, localized subcutaneous emphysema, inadvertent cuff puncture, accidental decannulation, while Major complications include; injury of trachea or esophagus, false passage, pneumo thorax, pneumo mediastinum, persistent hypotension (more than 5 min), persistent hypoxemia (SpO₂ < 90 % for more than 5 min), major bleeding (stomal, intratracheal, or bleeding requiring surgical repair).

Sample size were calculated Using G* Power 3.1.9.2 program, Kiel, Germany; depending on our primary outcome (Time of technique), In a previous study, ¹ time of technique in PDT and USPDT were 16.8±4.3 and 12.1±4.6 min respectively, we planned our study in order to detect 5% significance level (α) at a power of 80% (1-β). The minimum sample size was to study 16 patients in each group (and increase 25% [= 4 patients] for dropout), we investigated 22 patients in each group.

Statistical analysis: The data were collected, tabulated and analyzed with SPSS 21.0 (Statistical Package for Social Science, Inc., Chicago, USA). Quantitative data were presented as either mean±standard deviation or median and percentiles (25^th-75^th) as appropriate. Qualitative data were presented as frequencies and percentages. Kolmogorov-smirnov test was used for normality testing. Normally distributed data were compared using Student t-test, whereas non normally distributed data were compared with Mann-Whitney test. χ2 or Fisher exact tests were used to test the association between qualitative variables. P values <0.05 were considered significant.

Results

Demographic data

There were no statistically significant differences regarding demographic data (Table: 1).

Procedure details

Three patients (13.6%) in US group were excluded pre-procedural and converted for surgical tracheostomy after US examination due to the presence of vessels beneath, but no surgical interference (failure) was needed after the start of the procedure and during the observational period in both groups.

Time of technique was shorter, the procedure was easier with less number of tracheal punctures in USPDT group (Table: 2)

Complications

No major complications were identified in both groups. While number of patients with minor bleeding and transient hypoxemia were significantly higher in PDT patients. In general, total number of patients with minor complications was significantly higher in PDT group (Table: 3).

Table 1: Demographic characteristics of the patients:

Data are expressed as mean±SD, or number (percent). PaO_2: arterial oxygen pressure, CNS:central nervous system, MV: mechanical ventilation.

Table 2: Details of the procedure in the target patients:

Data are expressed as mean±SD, or number (percentage). NA denotes not applicable, * P is significant at <0.05.

Table 3: complications of the procedure:

Values are expressed as number (percentage), * P is significant at <0.05.

Discussion

There is increasing attitude of literature proving the value of ultrasound in intensive care patients including airway managing; encouraged by increasing availability of portable, small, ultrasound machines with high resolution leading to its increase usefulness in intensive care settings. To our best of knowledge, the current study is the first prospective study conducted in Egypt to compare the effectiveness and safety between USPDT and those of bronchoscopy guided PDT without pre-procedural US.

In the present study, 44 patients were recruited for PDT insertion. They were randomly divided into two groups: 22 patients opt to bronchoscopy-guided PDT and 22 in the pre-procedural US group (USPDT group) with a mean age of 56.14±16.85, and 52.68±15.78. Female to Male ratio was 1:1.2 compared to 1:1.75 respectively (P>0.05).

Three patients (13.6%) in USPDT group were excluded pre-procedural and converted for surgical tracheostomy after US examination due to the presence of vessels beneath; reflecting the safety of US examination prior to PDT.

The procedure was easy (P<0.05) in 84.2% of patients opt to US-guided PDT with less time (P<0.001) as compared to PDT group. The puncture site was changed in 31.8% of bronchoscopy guided PDT cohort, while none of the US-guided PDT patients required change of puncture site. A previous study in Brazil ¹¹ included 11 patients retrospectively underwent bronchoscopy-guided PDT and 49 US-guided PDT with a mean age of (49±18.7 and 52±19.8 respectively), males were (46% and 67% respectively); they reported US to be effective, as convert to surgical tracheostomy wasn’t needed and only one case of US-guided PDT cohort required bronchoscopy assistance at the stage of guide wire withdrawal, the procedure easy to perform, 2 punctures were needed more in bronchoscopy guided group (P > 0.05). On the other hand, Gobatto and colleagues studied on 58 patients to bronchoscopy group and 60 patients to ultrasound group, they reported portable ultrasound to be a simple technique for screening of blood vessels and for locating the midline before the procedure, procedure failure was 1.7% of cases with tracheal punctures median 2 in both groups, and the puncture site was changed in 23.3% of the US group ^12. Other investigators reported puncture site change in 18 % of the studied US population. ^11,13 In our study the procedure length was shorter in USPDT cohort (P<0.001), this coincides with previous authors. ^13,14,15

In the present study no major complications were detected in both study groups. Injury to blood vessels was highlighted in a previous studies and they recommended the use of ultrasound to identify them, ^16,17 and interestingly, a research in London collecting data from computerized tomography (CT) angiography  to study neck vasculature; revealed that 187 out of 343 patients (55%) verified a pre-tracheal vessel; vein in 131 and artery in 56. ¹⁸ Three previous randomized controlled trials ^19-21 compared USPDT with landmark or bronchoscopy guided PDT; the total minor complication rates vary between 11.52% to 56.75 %; without difference between both compared groups. Contrarily, the current results showed lower total minor complication rate the bronchoscopy group (P<0.05).

In comparison to previous results reported in a meta analysis comparing surgical tracheostomy with PDT in a total of 1212 patients; enrolled in 17 randomized controlled studies, the overall incidence of bleeding and infection in both techniques were 5.7% and 6.6 % respectively. ²² Other authors recruited 12 patients aged (30-66), females were 66.67 % patients; they performed PDT guided with pre-procedural US without complications. ²³ In the current study, the bronchoscopy-guided group revealed more minor bleeding and transient acute hypoxemia. Complications in previous studies widely varied; probably attributed to discrepancy in sample size, candidate population and different equipment. ^11,13,24

Limitations of our study we did not record or compare late complications e.g. infection and stenosis.

Conclusion

Pre-procedural US guided percutaneous dilatational tracheostomy (USPDT) can be considered as a reliable tool to increase safety and improve outcomes of elective tracheostomy.