Ultrasonographic assessment of diaphragmatic contraction and relaxation properties: correlations of diaphragmatic displacement with oesophageal and transdiaphragmatic pressure.

Transdiaphragmatic (Pdi) and oesophageal pressures (Pes) are useful in understanding the pathophysiology of the respiratory system. They provide insight into respiratory drive, intrinsic positive end-expiratory pressure, diaphragmatic fatigue and weaning failure. BACKGROUND: The use of Pdi and Pes in clinical practice is restricted due to the invasiveness of the technique and the cumbersome equipment needed. On the other hand, diaphragmatic displacement is non-invasively and easily assessed with M-mode ultrasound. PURPOSE: We observed striking similarities in shape and magnitude between M-mode diaphragmatic displacement, Pes and Pdi pressures. The study aimed to evaluate if the information provided by these two pressures could be obtained non-invasively from the diaphragmatic displacement curve. MATERIAL AND METHODS: In 14 consecutive intubated patients undergoing a weaning trial, simultaneous recordings of Pes and Pdi pressures and the diaphragmatic displacement were assessed while breathing spontaneously and during a sniff-like manoeuvre. Moreover, the slope of the diaphragmatic displacement curve during relaxation was compared with the maximal relaxation rate (MRR) obtained from the Pdi curve. RESULTS: More than 200 breaths were analysed in pairs. Diaphragmatic displacement significantly correlated with Pdi (R2=0.33, p<0.001) and Pes (R2=0.44, p<0.001), and this correlation further improved during sniff (R2=0.47, p<0.001) and (R2=0.64, p<0.001), respectively. Additionally, a significant correlation was found between the relaxation slope derived from the diaphragmatic displacement curve and the MRR derived from the Pdi curve, both in normal breathing (R2=0.379, p<0.001) and during the sniff manoeuvre (R2=0.71, p<0.001). CONCLUSIONS: M-mode diaphragmatic displacement parameters correlate well with the ones obtained from oesophageal pressure and Pdi, particularly during sniffing. Diaphragmatic displacement assessment possibly offers an alternative non-invasive solution for understanding and clinically monitoring the diaphragmatic contractile properties and weaning failure due to diaphragmatic fatigue.

Tissue Doppler Imaging of the Diaphragm in Healthy Subjects and Critically Ill Patients.

Rationale: Tissue Doppler imaging (TDI) is an echocardiographic method that measures the velocity of moving tissue.Objectives: We applied this technique to the diaphragm to assess the velocity of diaphragmatic muscle motion during contraction and relaxation.Methods: In 20 healthy volunteers, diaphragmatic TDI was performed to assess the pattern of diaphragmatic motion velocity, measure its normal values, and determine the intra- and interobserver variability of measurements. In 116 consecutive ICU patients, diaphragmatic excursion, thickening, and TDI parameters of peak contraction velocity, peak relaxation velocity, velocity-time integral, and TDI-derived maximal relaxation rate were assessed during weaning. In a subgroup of 18 patients, transdiaphragmatic pressure (Pdi)-derived parameters (peak Pdi, pressure-time product, and diaphragmatic maximal relaxation rate) were recorded simultaneously with TDI.Measurements and Main Results: In terms of reproducibility, the intercorrelation coefficients were >0.89 for all TDI parameters (P < 0.001). Healthy volunteers and weaning success patients exhibited lower values for all TDI parameters compared with weaning failure patients, except for velocity-time integral, as follows: peak contraction velocity, 1.35 ± 0.34 versus 1.50 ± 0.59 versus 2.66 ± 2.14 cm/s (P < 0.001); peak relaxation velocity, 1.19 ± 0.39 versus 1.53 ± 0.73 versus 3.36 ± 2.40 cm/s (P < 0.001); and TDI-maximal relaxation rate, 3.64 ± 2.02 versus 10.25 ± 5.88 versus 29.47 ± 23.95 cm/s2 (P < 0.001), respectively. Peak contraction velocity was strongly correlated with peak transdiaphragmatic pressure and pressure-time product, whereas Pdi-maximal relaxation rate was significantly correlated with TDI-maximal relaxation rate.Conclusions: Diaphragmatic tissue Doppler allows real-time assessment of the diaphragmatic tissue motion velocity. Diaphragmatic TDI-derived parameters differentiate patients who fail a weaning trial from those who succeed and correlate well with Pdi-derived parameters.

Effects of continuous positive airway pressure on diaphragmatic kinetics and breathing pattern in healthy individuals.

BACKGROUND AND OBJECTIVE: In this study, we investigate the changes in diaphragmatic kinetics, breathing pattern and work of breathing induced by 10 cmH2 O of continuous positive airway pressure (CPAP). METHODS: We used sonography to study diaphragmatic kinetics and measured energy expenditure using indirect calorimetry in 50 healthy volunteers at 0 cmH2 O positive end expiratory pressure (ZEEP) and after application of 10 cmH2 O CPAP. In a subgroup of 14 subjects, the changes in thoracic and abdominal volumes and thoraco-abdominal asynchrony were recorded with inductive plethysmography, while accessory respiratory muscle activity was recorded with electromyography. RESULTS: Continuous positive airway pressure breathing induced acute lung hyperinflation of 600 mL above passive functional residual capacity. This hyperinflation induced changes in diaphragmatic kinetics and breathing pattern; diaphragmatic excursion, thickness and thickness ratio, tidal volume (Vt) and oxygen consumption (VO2) increased while respiratory rate decreased. The increase in Vt with CPAP was mainly due to rib cage contribution. Activation of the accessory inspiratory (scalene) and expiratory (transversus abdominis) muscles was recorded. The raised respiratory muscles workload induced an increase in VO2. CONCLUSION: In healthy volunteers, CPAP therapy leads to lung overdistention and recruitment of respiratory muscles. These mechanisms operate at a high energy cost.

Sonographic evaluation of the diaphragm in critically ill patients. Technique and clinical applications.

The use of ultrasonography has become increasingly popular in the everyday management of critically ill patients. It has been demonstrated to be a safe and handy bedside tool that allows rapid hemodynamic assessment and visualization of the thoracic, abdominal and major vessels structures. More recently, M-mode ultrasonography has been used in the assessment of diaphragm kinetics. Ultrasounds provide a simple, non-invasive method of quantifying diaphragmatic movement in a variety of normal and pathological conditions. Ultrasonography can assess the characteristics of diaphragmatic movement such as amplitude, force and velocity of contraction, special patterns of motion and changes in diaphragmatic thickness during inspiration. These sonographic diaphragmatic parameters can provide valuable information in the assessment and follow up of patients with diaphragmatic weakness or paralysis, in terms of patient-ventilator interactions during controlled or assisted modalities of mechanical ventilation, and can potentially help to understand post-operative pulmonary dysfunction or weaning failure from mechanical ventilation. This article reviews the technique and the clinical applications of ultrasonography in the evaluation of diaphragmatic function in ICU patients.

Sonographic assessment of changes in diaphragmatic kinetics induced by inspiratory resistive loading.

BACKGROUND AND OBJECTIVE: Diaphragmatic breathing patterns under resistive loading remain poorly documented. To our knowledge, this is the first study assessing diaphragmatic motion under conditions of inspiratory resistive loading with the use of sonography. METHODS: We assessed diaphragmatic motion during inspiratory resistive loading in 40 healthy volunteers using M-mode sonography. In phase I of the study, sonography was performed during normal quiet breathing without respiratory loading. In phase II, sonography was performed after application of a nose clip and connection of the subjects to a pneumotachograph through a mouth piece. In phase III, the participants were assessed while subjected to inspiratory resistive loading of 50 cm H(2)O/L/s. RESULTS: Compared with baseline, the application of a mouth piece and nose clip induced a significant increase in diaphragmatic excursion (from 1.7 to 2.3 cm, P < 0.001) and a decrease in respiratory rate (from 13.4 to 12.2, P < 0.01). Inspiratory resistive loading induced a further decrease in respiratory rate (from 12.2 to 8.0, P < 0.01) and a decrease in diaphragmatic velocity contraction (from 1.2 to 0.8 cm/s, P < 0.01), and also an increase in tidal volume (from 795 to 904 mL, P < 0.01); diaphragmatic excursion, however, did not change significantly. CONCLUSIONS: Inspiratory resistive loading induced significant changes in diaphragmatic contraction pattern, which mainly consisted of decreased velocity of diaphragmatic displacement with no change in diaphragmatic excursion. Tidal volume, increased significantly; the increase in tidal volume, along with the unchanged diaphragmatic excursion, provides sonographic evidence of increased recruitment of extradiaphragmatic muscles under inspiratory resistive loading.

The role of echocardiography in the early diagnosis of the complications of endovascular repair of blunt aortic injury.

PURPOSE: Endovascular repair of traumatic aortic injury has been associated with severe procedural complications, including endoleaks, coverage of the left subclavian artery, stent collapse, access complications, and questionable durability. Echocardiography has proven to be a valuable tool in the intraoperative detection of these complications. In the current study, we report on the use of echocardiography as an early postoperative diagnostic technique for the evaluation of endovascular stent graft positioning in the intensive care setting. METHODS: From January 2005 to January 2009, 14 patients who underwent endovascular repair of a blunt aortic injury were admitted in our intensive care unit. Transesophageal and/or transthoracic echocardiography were used as first-line diagnostic tools in the assessment of the endovascular graft position. RESULTS: Twenty-eight percent of patients (4 of 14) developed a pressure gradient between upper and lower limbs (greater than 50 mm Hg), which presented with persistent hypertension, requiring antihypertensive therapy in high doses and difficult weaning. In all 4 patients, stent graft malposition was identified using echocardiography. The diagnosis was verified by computed tomography and aortography. CONCLUSION: Noninvasive echocardiographic monitoring proved to be a valuable tool in the early diagnosis of postoperative stent graft malalignment. To our knowledge, this is the first time that echocardiography is described in the relevant literature as an early diagnostic technique in this setting.

Respiratory, metabolic and hemodynamic effects of clonidine in ventilated patients presenting with withdrawal syndrome.

OBJECTIVE: To investigate the respiratory, metabolic and hemodynamic effects of clonidine in ventilated patients presenting with withdrawal syndrome after sedation interruption. DESIGN: Prospective, interventional, single-center study in 30 ventilated ICU patients. INTERVENTIONS: Metabolic [oxygen consumption (VO(2)), CO(2) production (VCO(2)), resting energy expenditure (REE)], respiratory [minute ventilation (V (E)), tidal volume (V (T)), respiratory rate (RR)] and hemodynamic (HR, SAP, MAP) parameters were measured in 30 ventilated ICU patients. Measurements were performed first under sedation with remifentanil-propofol, then after sedation interruption, and finally after clonidine administration (0.9-1.8 mg of clonidine in two doses of 10 min interval). RESULTS: Sedation interruption produced significant increases in the hemodynamic parameters (SAP and MAP by 33%, HR by 37%), and metabolic rate (increase in VO(2) by 70%, VCO(2) by 88% and REE by 74%), leading to high respiratory demands (increase in V (E) from 9 to 15 l/min). The V (E) was increased due to a twofold increase in the RR; V (T) remained constant. In 25 out of 30 patients, clonidine administration decreased the hemodynamic (SAP, MAP and HR), metabolic (VO(2), VCO(2), REE) and respiratory parameters to values close to those observed with sedation. Clonidine induced mild sedation and patients became more cooperative with the ventilator. All patients responding to clonidine were weaned from the ventilator in 2 days (median, range 1-18 days). CONCLUSION: Patients with withdrawal syndrome had significantly elevated hemodynamic, metabolic and respiratory demands. Clonidine significantly decreased these demands, induced mild sedation and facilitated patient cooperation with the ventilator, enabling ventilator weaning.

Weaning failure from mechanical ventilation due to hypertrophic obstructive cardiomyopathy.

OBJECTIVE: To report the importance of hypertrophic obstructive cardiomyopathy as a potential substrate for difficult weaning from mechanical ventilation. DESIGN AND SETTING: Case report in an adult intensive care unit of a tertiary care hospital. PATIENTS: Two patients who developed intractable pulmonary edema with subsequent difficult weaning from mechanical ventilation in the early postoperative period despite medical treatment for heart failure based on pulmonary artery catheter data. INTERVENTIONS: Mechanical ventilation, medical treatment. MEASUREMENTS AND RESULTS: Pulmonary artery catheter data in these two elderly patients under mechanical ventilation were compatible with congestive heart failure, and the initial therapy was diuretics, vasodilators, and inotropes. Despite this reasonable medical treatment no hemodynamic improvement and thereby failure of weaning from mechanical ventilation was observed. Transesophageal echocardiography demonstrated hypertrophic obstructive cardiomyopathy in both cases, and therapy based on negative inotropes was instituted. This treatment change induced hemodynamic improvement and successful weaning from mechanical ventilation. CONCLUSIONS: In mechanically ventilated patients because of congestive heart failure who have difficult weaning, despite appropriate therapy, intensivists should always suspect causes other than the obvious systolic heart failure. In this clinical setting echocardiography is warranted and produces excellent diagnostic yield for clarifying complex cardiac disturbances.