ELECTRONIC SUPPLEMENTAL MATERIAL

Transesophageal echocardiography in the prone position during severe Acute Respiratory Distress Syndrome

Armand Mekontso Dessap, MD, PhD; Olivier Proost, MD; Florence Boissier, MD; Bruno Louis, PhD; Ferran Roche Campo, MD; Laurent Brochard, MD

DETAILED METHODS

Patients

Patients who met American–European Consensus Conference criteria for ARDS (acute onset, bilateral infiltrates on chest radiography, and absence of clinical evidence of left atrial hypertension) [1] and who underwent TEE while in the PP because of severe hypoxemia (PaO2/FiO2 ratio <100 mmHg supine despite optimization of alveolar recruitment by increasing the PEEP to obtain a plateau pressure of 28-30 cmH2O [2]) were included prospectively between April 2008 and November 2009. Noninclusion criteria were contraindications to TEE and/or PP. Contraindications to TEE included extensive oesophageal or gastric disease, cervical spine instability and severe coagulopathy. Contraindications to PP included major uncontrolled bleeding, pregnancy, pelvic fractures, recent head or neck injury, intracranial hypertension, and major hemodynamic instability (systolic blood pressure <80 mmHg despite catecholamine therapy) that the attending physician has considered capable of being further exacerbated by PP. In addition, one patient with chronic severe cervical disease preventing anyhead rotation in PP wasexcluded (no access to the mouth). The study was approved by our institutional ethics committee (Comité de Protection des Personnes Ile de France IX). Because we routinely use TEE to assess the circulatory status of mechanically ventilated patients with ARDS in our ICU, TEE was considered a component of standard care. Written and oral information about the study was given to the families.

TEE

TEE was performed using an Envisor or iE33 system (Philips Ultrasound, Bothell, WA) equipped with a multiplane 5-MHz TEE transducer (see photo, ESM), following a standard procedure, as previously described [3]. The enteral nutrition was interrupted and the gastric contents were emptied (gastric suction) before the examination. A bite blocker was used to prevent patient’s teeth to damage the TEE probe. The following echocardiographic views (standard views) were examined: long axis M-mode view of the superior vena cava (SVC), four-chamber long-axis view, transgastric approach with short-axis view and long-axis view, and a longitudinal view of the fossa ovalis. The long-axis M-mode view of the SVC was used to assess its collapsibility, i.e. the inspiratory decrease in SVC diameter, as previously described [4]. The four-chamber long-axis view was used to assess the end-diastolic right ventricle/left ventricle (RV/LV) area ratio and filling pressures. Filling pressures were evaluated using early (E) and late (A) peak diastolic velocities measured with Doppler transmitral flow, and tissue Doppler imaging of mitral lateral annulus diastolic velocities (e’ and a’). Filling pressures were deemed low if E/e’ ratio was below 8 and were deemed normal or high if E/e’ ratio was ≥8 [5]. The transgastric approach was used to evaluate LV fractional area contraction and the shape and kinetics of the interventricular septum in the short-axis view of the LV, as well as cardiac output via the long-axis view. Left ventricular end-systolic area (LVESA) and left ventricular end-diastolic area (LVEDA) were measured on a cross-sectional view of the LV at the midpapillary muscle level. LV fractional area contraction was computed as (LVEDA– LVESA)/LVEDA and LV systolic function was considered impaired if the fractional area change was below 35%. Acute cor pulmonale was defined as a dilated right ventricle (end diastolic RV/LV area ratio >0.6) associated with septal dyskinesia on the transgastric short-axis view [6]. Cardiac output was calculated as the product of stroke volume by heart rate. Stroke volume was measured using pulsed-wave Doppler across the LV outflow tract in the transgastric long-axis view and the assessment of the cross-sectional area of the aortic annulus. A longitudinal view of the fossa ovalis was also obtained to evaluate shunting across patent foramen ovale (PFO). PFO was detected by injecting 9.5 mL sterile modified fluid gelatin solution (Plasmion®, Fresenius-Kabi, Sevres, France; or Gelofusine 4%®, B-Braun Medical, Boulogne-Billancourt, France) aerated with 0.5 mL room air via two syringes connected with a three-way stopcock, as previously described [7]. Echocardiographic images were recorded on compact disk, and a computer-assisted evaluation was performed off-line by a single trained investigator. The ventilatory conditions (mode, tidal volume, PEEP, plateau pressure, last blood gas analysis) and hemodynamic variables (heart rate, blood pressure and catecholamine treatment) were recorded at the time of TEE. The head rotation (left or right) was also noted. Probe insertion duration was defined as the time required for moving the TEE probe from incisors to the oesophagus. TEE duration was defined as the time elapsed between the first and last image acquisition (preparation time before TEE start and storage and cleaning up after examination were not taken into account). The SAPS II scores at ICU admission as well as SOFA score on the day of TEE were also collected, as well as the use of muscle paralysis or the presence of an orogastric tube during TEE. None of the patients was monitored with a pulmonary artery catheter. In patients who underwent TEE in both supine and PP during the hospital course, we compared the feasibility, tolerance and therapeutic implications of these two explorations. In addition, the image quality of acquired standard views was also compared between both positions, using a score modified from Cohen et al [8], as follows: each image was graded by ascribing a value of 1 (poor quality), 2 (satisfactory) or 3 (excellent quality).

Non invasive assessment of the oropharyngeal tract in healthy volunteers

We used the two-microphone acoustic reflection method [9] to assess the duct cross section of the oropharyngeal tract in 10 healthy adult volunteers in three consecutive positions: supine, PP with head rotation to the right, and PP with head rotation to the left. Briefly, this method is based on pressure measured at two distinct sites in a wave tube connected to the airway opening and allows the estimation of the cross sectional area along the oropharyngeal and laryngeal cavities, and pulmonary airway as a function of the axial position [9, 10]. The minimal area of the oropharyngeal cavity (from incisors to the glottis) was calculated for all subjects in each position.

RESULTS

Characteristics of patients undergoing TEE in PP

A total of 34 consecutive patients (all orally intubated) were included (Table 1). Continuous sedation (midazolam, Sanofi-Aventis, France), analgesia (fentanyl, Mylan, France) and neuromuscular blockade (atracurium, GlaxoSmithKline, France) were used in all patients. In 26 of the 34 patients (77%), TEE was performed during the first PP session. Vital signs did not change significantly during probe insertion for TEE in PP (Table 2), and there was no modification of the ventilatory settings or hemodynamic support.

Feasibility, tolerance and therapeutic implications of TEE in PP

The TEE probe was inserted blindly through the midline, after placement of a bite blocker. Probe insertion was successful in all but one patient with severe kyphoscoliosis, with a median insertion time of 30 [10-60] sec. Direct laryngoscopy was never used. Dislodgment of orogastric tube, vomiting or significant gastrointestinal bleeding were never observed. During TEE in PP, patient's head was rotated to the right in 19 (61%) cases. The median duration of TEE in PP was 19 [15-30] minutes. In the 33 patients with successful probe insertion, all standard views and measures could be obtained except for cardiac output in four patients. Patent foramen ovale was not checked in one patient (already checked the day before while supine). The main findings of TEE in PP are summarized in Table 3. When performed, the examination was always conclusive and led to a proposal of therapeutic change in 23 (70%) patients. Proposals for therapeutic changes included start or intensification of fluid loading (8 cases), stopping fluid administration or starting depletion (5 cases), introduction or increase in dose of inotropes (8 cases), introduction or increase in vasopressor dose (4 cases),increase in airway pressures (1 case), decrease in airway pressures (6 cases), initiation of nitric oxide inhalation (2 cases).


REFERENCES

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