Respiratory effects of lung recruitment maneuvers depend on the recruitment-to-inflation ratio in patients with COVID-19-related acute respiratory distress syndrome.

BACKGROUND: In the context of acute respiratory distress syndrome (ARDS), the response to lung recruitment maneuvers (LRMs) varies considerably from one patient to another and so is difficult to predict. The aim of the study was to determine whether or not the recruitment-to-inflation (R/I) ratio could differentiate between patients according to the change in lung mechanics during the LRM. METHODS: We evaluated the changes in gas exchange and respiratory mechanics induced by a stepwise LRM at a constant driving pressure of 15 cmH2O during pressure-controlled ventilation. We assessed lung recruitability by measuring the R/I ratio. Patients were dichotomized with regard to the median R/I ratio. RESULTS: We included 30 patients with moderate-to-severe ARDS and a median [interquartile range] R/I ratio of 0.62 [0.42-0.83]. After the LRM, patients with high recruitability (R/I ratio ≥ 0.62) presented an improvement in the PaO2/FiO2 ratio, due to significant increase in respiratory system compliance (33 [27-42] vs. 42 [35-60] mL/cmH2O; p < 0.001). In low recruitability patients (R/I < 0.62), the increase in PaO2/FiO2 ratio was associated with a significant decrease in pulse pressure as a surrogate of cardiac output (70 [55-85] vs. 50 [51-67] mmHg; p = 0.01) but not with a significant change in respiratory system compliance (33 [24-47] vs. 35 [25-47] mL/cmH2O; p = 0.74). CONCLUSION: After the LRM, patients with high recruitability presented a significant increase in respiratory system compliance (indicating a gain in ventilated area), while those with low recruitability presented a decrease in pulse pressure suggesting a drop in cardiac output and therefore in intrapulmonary shunt.

Doppler Echocardiographic Indices Are Specific But Not Sensitive to Predict Pulmonary Artery Occlusion Pressure in Critically Ill Patients Under Mechanical Ventilation.

OBJECTIVES: The objective of this study was to prospectively evaluate the ability of transthoracic echocardiography to assess pulmonary artery occlusion pressure in mechanically ventilated critically ill patients. DESIGN: In a prospective observational study. SETTING: Amiens University Hospital Medical ICU. PATIENTS: Fifty-three mechanically ventilated patients in sinus rhythm admitted to our ICU. INTERVENTION: Transthoracic echocardiography was performed simultaneously to pulmonary artery catheter. MEASUREMENTS AND MAIN RESULTS: Transmitral early velocity wave recorded using pulsed wave Doppler (E), late transmitral velocity wave recorded using pulsed wave Doppler (A), and deceleration time of E wave were recorded using pulsed Doppler as well as early mitral annulus velocity wave recorded using tissue Doppler imaging (E'). Pulmonary artery occlusion pressure was measured simultaneously using pulmonary artery catheter. There was a significant correlation between pulmonary artery occlusion pressure and lateral ratio between E wave and E' (E/E' ratio) (r = 0.35; p < 0.01), ratio between E wave and A wave (E/A ratio) (r = 0.41; p < 0.002), and deceleration time of E wave (r = -0.34; p < 0.02). E/E' greater than 15 was predictive of pulmonary artery occlusion pressure greater than or equal to 18 mm Hg with a sensitivity of 25% and a specificity of 95%, whereas E/E' less than 7 was predictive of pulmonary artery occlusion pressure less than 18 mm Hg with a sensitivity of 32% and a specificity of 81%. E/A greater than 1.8 yielded a sensitivity of 44% and a specificity of 95% to predict pulmonary artery occlusion pressure greater than or equal to 18 mm Hg, whereas E/A less than 0.7 was predictive of pulmonary artery occlusion pressure less than 18 mm Hg with a sensitivity of 19% and a specificity of 94%. A similar predictive capacity was observed when the analysis was confined to patients with EF less than 50%. A large proportion of E/E' measurements 32 (60%) were situated between the two cut-off values obtained by the receiver operating characteristic curves: E/E' greater than 15 and E/E' less than 7. CONCLUSIONS: In mechanically ventilated critically ill patients, Doppler transthoracic echocardiography indices are highly specific but not sensitive to estimate pulmonary artery occlusion pressure.

Transthoracic echocardiography: an accurate and precise method for estimating cardiac output in the critically ill patient.

BACKGROUND: Cardiac output (CO) monitoring is a valuable tool for the diagnosis and management of critically ill patients. In the critical care setting, few studies have evaluated the level of agreement between CO estimated by transthoracic echocardiography (CO-TTE) and that measured by the reference method, pulmonary artery catheter (CO-PAC). The objective of the present study was to evaluate the precision and accuracy of CO-TTE relative to CO-PAC and the ability of transthoracic echocardiography to track variations in CO, in critically ill mechanically ventilated patients. METHODS: Thirty-eight mechanically ventilated patients fitted with a PAC were included in a prospective observational study performed in a 16-bed university hospital ICU. CO-PAC was measured via intermittent thermodilution. Simultaneously, a second investigator used standard-view TTE to estimate CO-TTE as the product of stroke volume and the heart rate obtained during the measurement of the subaortic velocity time integral. RESULTS: Sixty-four pairs of CO-PAC and CO-TTE measurements were compared. The two measurements were significantly correlated (r = 0.95; p < 0.0001). The median bias was 0.2 L/min, the limits of agreement (LOAs) were -1.3 and 1.8 L/min, and the percentage error was 25%. The precision was 8% for CO-PAC and 9% for CO-TTE. Twenty-six pairs of ΔCO measurements were compared. There was a significant correlation between ΔCO-PAC and ΔCO-TTE (r = 0.92; p < 0.0001). The median bias was -0.1 L/min and the LOAs were -1.3 and +1.2 L/min. With a 15% exclusion zone, the four-quadrant plot had a concordance rate of 94%. With a 0.5 L/min exclusion zone, the polar plot had a mean polar angle of 1.0° and a percentage error LOAs of -26.8 to 28.8°. The concordance rate was 100% between 30 and -30°. When using CO-TTE to detect an increase in ΔCO-PAC of more than 10%, the area under the receiving operating characteristic curve (95% CI) was 0.82 (0.62-0.94) (p < 0.001). A ΔCO-TTE of more than 8% yielded a sensitivity of 88% and specificity of 66% for detecting a ΔCO-PAC of more than 10%. CONCLUSION: In critically ill mechanically ventilated patients, CO-TTE is an accurate and precise method for estimating CO. Furthermore, CO-TTE can accurately track variations in CO.

Residents learning ultrasound-guided catheterization are not sufficiently skilled to use landmarks.

INTRODUCTION: Ultrasound-guided (UG) technique is the recommended procedure for central venous catheterization (CVC). However, as ultrasound may not be available in emergency situations, guidelines also propose that physicians remain skilled in landmark (LM) placement. We conducted this prospective observational study to determine the learning curve of the LM technique in residents only learning the UG technique. METHODS: During the first three months of their rotation in our ICU, residents inexperienced in CVC used only the real-time UG technique. During the following three months, residents were allowed to place CVC by means of the LM technique when authorized by the attending physician. RESULTS: A total of 172 procedures (84 UG and 88 LM) were performed by the inexperienced residents during the study. The success rate was lower (72% versus 84%; P = 0.05) and the complication rate was higher (22% versus 10%; P = 0.04) for LM compared to UG procedures. Comparison between the five last UG procedures and the first five LM procedures performed demonstrated that the transition between the two techniques was associated with a marked decrease of the success rate (65% versus 93%; P = 0.01) and an increase of the complication rate (33% versus 8%; P = 0.01). After 10 LM procedures, residents achieved a success rate and a complication rate of 81% and 6%, respectively. CONCLUSIONS: Residents who only learn the UG technique will not be immediately able to perform the LM technique, but require specific training based on at least 10 LM procedures. The question of whether or not the LM technique should still be taught when an ultrasound device is not available must therefore be addressed.

Ultrasound evaluation of central veinsin the intensive care unit:effects of dynamic manoeuvres.

OBJECTIVE: To determine: (1) the proportion of small (<5 mm) or thrombosed internal jugular veins (IJV) and femoral veins (FV) in which catheter placement would be difficult without ultrasound guidance; (2) which position increases central vein sizes and may facilitate cannulation of these vessels. DESIGN: Prospective study. SETTING: Twelve-bed adult medical intensive care unit. PATIENTS AND PARTICIPANTS: Sixty patients (62 +/- 19 years, SAPS II score 36 +/- 17). INTERVENTIONS: Ultrasound examinations of the IJV and FV in supine, Trendelenburg (T) and reverse Trendelenburg (Ti) positions. MEASUREMENTS AND RESULTS: Maximum diameter and cross-sectional area (CSA) were measured. Venous catheter placement would have been difficult (diameter < 5 mm) or even impossible (thrombosis) for 22% of right IJV, 13% of left IJV, 2% of left and 2% of right FV. In the T position, the CSA of the IJV increased (right IJV: 1.7 +/- 1.4 to 2.01 +/- 1.34 cm2, left IJV: 1.18 +/- 0.81 to 1.34 +/- 0.85 cm2; p < 0.05) and theCSA of the FV decreased (right FV: 1.42 +/- 0.61 to 1.22 +/- 0.58 cm2, left FV: 1.51 +/- 0.62 to 1.26 +/- 0.58 cm2; p < 0.05). In the Ti position, the CSA of the IJV decreased (right IJV: 1.7 +/- 1.4 to 1.35 +/- 1.35 cm2, left IJV: 1.18 +/- 0.81 to 0.87 +/- 0.62 cm2; p < 0.05) and the CSA of the FV increased (right FV: 1.42 +/- 0.61 to 1.66 +/- 0.65 cm2, left FV: 1.51 +/- 0.62 to 1.65 +/- 0.68 cm2; p < 0.05). In two-thirds of patients, the right IJV was significantly larger than the left IJV. CONCLUSIONS: Ultrasonography should be performed before at least central venous catheter placement to detect the presence of deep vein thrombosis or vessels less than 5 mm in diameter. Some positions increase veins' diameter at least internally, T position increasing IJV size and Ti position increasing FV size.