Predicting postoperative complications with the respiratory exchange ratio after high-risk noncardiac surgery: A prospective cohort study.

BACKGROUND: The respiratory exchange ratio (RER), defined as the ratio of CO2 production (VCO2) to O2 consumption (VO2), is reported to be a noninvasive marker of anaerobic metabolism. The intubated, ventilated patient's inspired and expired fractions of O2 and CO2 (FiO2, FeO2, FiCO2 and FeCO2) are monitored in the operating room and can be used to calculate RER. OBJECTIVE: To investigating the ability of the RER to predict postoperative complications. DESIGN: An observational, prospective study. SETTING: Two French university hospitals between March 2017 and September 2018. PATIENTS: A total of 110 patients undergoing noncardiac high-risk surgery. MAIN OUTCOME MEASURES: The RER was calculated as (FeCO2 - FiCO2)/(FiO2 - FeO2) at five time points during the operation. The primary endpoint was at the end of the surgery. The secondary endpoints were systemic oxygenation indices (pCO2 gap, pCO2 gap/arteriovenous difference in O2 ratio, central venous oxygen saturation) and the arterial lactate level at the end of the surgery. Complications were classified according to the European Peri-operative Clinical Outcome definitions. RESULTS: Postoperative complications occurred in 35 patients (34%). The median [interquartile range] RER at the end of surgery was significantly greater in the subgroup with complications, 1.06 [0.84 to 1.35] than in the subgroup without complications, 0.81 [0.75 to 0.91], and correlated significantly with the arterial lactate (r = 0.31, P < 0.001) and VO2 (r = -0.23, P = 0.001). Analysis of the area under the receiver operating characteristic curve for the predictive value of RER for postoperative complications revealed a value of 0.77 [95% confidence interval (CI) 0.69 to 0.88, P = 0.001]. The best cut-off for the RER was 0.94, with a sensitivity of 71% (95% CI 54 to 85) and a specificity of 79% (95% CI 68 to 88). CONCLUSION: As a putative noninvasive marker of tissue hypoperfusion and anaerobic metabolism, the RER can be used to predict complications following high-risk surgery. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT03471962.

Central Venous-to-Arterial Carbon Dioxide Partial Pressure Difference in Patients Undergoing Cardiac Surgery is Not Related to Postoperative Outcomes.

OBJECTIVE: The objective of this study was to assess the association between increased central venous-to-arterial carbon dioxide difference (ΔPCO2) following cardiac surgery with cardiopulmonary bypass and postoperative morbidity and mortality. DESIGN: A prospective, observational, non-interventional study. PATIENTS: Three hundred ninety-three patients undergoing cardiac surgery with cardiopulmonary bypass. INTERVENTIONS: The primary endpoint was the occurrence of one or more major postoperative complications. A ΔPCO2 ≥ 6 mmHg was considered to be abnormal. Data were first analyzed globally, and then according to 4 subgroups based on time course of ΔPCO2 during the study period: [(1) persistently normal ΔPCO2; (2) increasing ΔPCO2; (3) decreasing ΔPCO2; and (4) persistently high ΔPCO2]. RESULTS: A total of 238 of the 393 (61%) patients developed complications. The major postoperative complication rate did not differ among the 4 groups: 64% (n = 9) in group 1, 62% (n = 21) in group 2, 53% (n = 32) in group 3, and 62% (n = 176) in group 4 (p = 0.568). Mortality rates did not differ among the 4 groups (p > 0.05). ΔPCO2 was correlated weakly with perfusion parameters. CONCLUSIONS: These results suggested that ΔPCO2 is not predictive of postoperative complications or mortality.

Low-positive pressure ventilation improves non-hypoxaemic apnoea tolerance during ear, nose and throat pan-endoscopy: A randomised controlled trial.

BACKGROUND: It has been suggested that oxygenation using pressure support ventilation (PSV) before general anaesthesia can reduce the duration of non-hypoxaemic apnoea. OBJECTIVE: The objective was to determine whether or not pre-oxygenation with PSV increases the duration of non-hypoxaemic apnoea in non-obese patients during pan-endoscopy. DESIGN: A randomised, controlled trial. SETTING: Amiens University Hospital, France. PATIENTS: Fifty patients scheduled for ENT pan-endoscopy with a BMI lower than 35  kg  m(-2). INTERVENTION: Patients scheduled for pan-endoscopy were enrolled to receive either 100% oxygen at neutral pressure (the control group) or 100% oxygen with positive-pressure ventilation (a positive inspiratory pressure of 4  cmH2O and a positive end-expiratory pressure of 4  cmH2O; the PSV group) during spontaneous ventilation with a face mask. The goal of pre-oxygenation was to obtain an end-tidal oxygen concentration of more than 90% prior to induction of anaesthesia. MAIN OUTCOME MEASURES: The primary efficacy criterion was the duration of non-hypoxaemic apnoea (i.e. before the peripheral capillary oxygen saturation fell to 90%). Secondary outcomes were duration of pre-oxygenation, pre-oxygenation failure and tolerance. RESULTS: The mean (interquartile range) duration of non-hypoxaemic apnoea was longer in the PSV group [598 (447 to 717) s] than in the control group [310 (217 to 451) s] (P < 0.001). Oxygenation time was shorter in the PSV group [190 (159 to 225) s] than in the control group [245 (151 to 435) s] (P = 0.037). Pre-oxygenation was unsuccessful (i.e. end-tidal oxygen concentration was < 90%) in 20% of the patients in the control group but none in the PSV group. The intergroup difference in the duration of pan-endoscopy was not significant. Tolerance was good or very good in all patients. CONCLUSION: Our results show that pre-oxygenation with PSV is associated with a longer duration of non-hypoxaemic apnoea and a lower frequency of manual reventilation during ENT pan-endoscopy. CLINICALTRIALS. GOV REGISTRATION NUMBER: NCT02167334.

Dynamic arterial elastance predicts mean arterial pressure decrease associated with decreasing norepinephrine dosage in septic shock.

INTRODUCTION: Gradual reduction of the dosage of norepinephrine (NE) in patients with septic shock is usually left to the physician's discretion. No hemodynamic indicator predictive of the possibility of decreasing the NE dosage is currently available at the bedside. The respiratory pulse pressure variation/respiratory stroke volume variation (dynamic arterial elastance (Eadyn)) ratio has been proposed as an indicator of vascular tone. The purpose of this study was to determine whether Eadyn can be used to predict the decrease in arterial pressure when decreasing the NE dosage in resuscitated sepsis patients. METHODS: A prospective study was carried out in a university hospital intensive care unit. All consecutive patients with septic shock monitored by PICCO2 for whom the intensive care physician planned to decrease the NE dosage were enrolled. Measurements of hemodynamic and PICCO2 variables were obtained before/after decreasing the NE dosage. Responders were defined by a >15% decrease in mean arterial pressure (MAP). RESULTS: In total, 35 patients were included. MAP decreased by >15% after decreasing the NE dosage in 37% of patients (n = 13). Clinical characteristics appeared to be similar between responders and nonresponders. Eadyn was lower in responders than in nonresponders (0.75 (0.69 to 0.85) versus 1 (0. 83 to 1.22), P <0.05). Baseline Eadyn was correlated with NE-induced MAP variations (r = 0.47, P = 0.005). An Eadyn less than 0.94 predicted a decrease in arterial pressure, with an area under the receiver-operating characteristic curve of 0.87 (95% confidence interval (95% CI): 0.72 to 0.96; P <0.0001), 100% sensitivity, and 68% specificity. CONCLUSIONS: In sepsis patients treated with NE, Eadyn may predict the decrease in arterial pressure in response to NE dose reduction. Eadyn may constitute an easy-to-use functional approach to arterial-tone assessment, which may be helpful to identify patients likely to benefit from NE dose reduction.

Mini-fluid challenge predicts fluid responsiveness during spontaneous breathing under spinal anaesthesia: An observational study.

BACKGROUND: The ability to predict fluid responsiveness in spontaneously breathing patients under spinal anaesthesia is desirable. OBJECTIVE: The objective of this study was to test whether variations in stroke volume (SV) in response to a fixed mini-fluid challenge (ΔSV100) measured by thoracic impedance cardiography (ICG) can predict fluid responsiveness in spontaneously breathing patients under spinal anaesthesia. DESIGN: A prospective observational study. SETTING: Anaesthesiology department in a university hospital. PARTICIPANTS: Seventy-three patients monitored by ICG during surgery under spinal anaesthesia. INTERVENTIONS: Patients received a 100 ml fluid challenge followed by volume expansion with 500 ml of crystalloid. MAIN OUTCOMES MEASURES: Haemodynamic variables and bioimpedance indices [blood pressure, SV, cardiac output (CO)] were measured before and after fluid challenge and before and after volume expansion. Responders were defined as those with >15% increase in SV after volume expansion. RESULTS: SV increased by at least 15% in 27 (37%) of the 73 patients. ΔSV100 predicted fluid responsiveness with an area under the receiver operating characteristic (AUC) curve of 0.93 [95% confidence interval (95% CI) 0.8 to 0.97, P < 0.001]. The cut-off was 7% and a grey zone ranging between 3 and 8% was observed in up to 14% of patients. SV baseline was a poor predictor of fluid responsiveness [AUC of 0.69 (95% CI 0.57 to 0.79, P = 0.002)]. CONCLUSION: ΔSV100 greater than 7% accurately predicted fluid responsiveness during surgery with a grey zone ranging between 3 and 8%.

Doppler-based renal resistive index can assess progression of acute kidney injury in patients undergoing cardiac surgery.

OBJECTIVES: The objective of this study was to test whether assessment of renal resistive index measured after cardiac surgery (RRI(T0)) can diagnose persistent acute kidney injury (AKI). The predictive value was evaluated using a gray-zone approach. DESIGN: A prospective observational study. SETTING: A teaching university hospital. PARTICIPANTS: Eighty-two patients following cardiac surgery with cardiopulmonary bypass. INTERVENTIONS: Measurements of hemodynamic parameters and RRI were obtained before surgery, on admission to the intensive care unit, 6 hours after admission, and on the first postoperative day. AKI was defined according to the renal risk, injury, failure, loss of kidney function, end-stage of kidney disease (RIFLE) classification during the first postoperative week. Persistent AKI was defined as AKI lasting >3 days. MEASUREMENTS AND MAIN RESULTS: Out of the 82 patients, 15 (18%) developed persistent AKI, and 6 (7%) developed transient AKI. The median value and time-course of RRI were significantly different between patients with transient AKI and persistent AKI. Doppler-based RRI(T0) predicted persistent AKI with an area under the receiver-operating characteristic curve of 0.93 (95% confidence interval: 0.85-0.98, p<0.0001). The optimal cut-off of RRI was 0.73 (95% confidence interval: 0.73-0.75). The gray-zone approach identified a range of RRI values between 0.72 and 0.75 in 14% of patients. CONCLUSIONS: Doppler-based RRI can be helpful for noninvasive assessment of renal function recovery after cardiac surgery by using RRI(T0) to predict persistent AKI. The optimal cut-off was 0.73 with a gray zone ranging between 0.72 and 0.75.

Passive leg raising can predict fluid responsiveness in patients placed on venovenous extracorporeal membrane oxygenation.

INTRODUCTION: In ICUs, fluid administration is frequently used to treat hypovolaemia. Because volume expansion (VE) can worsen acute respiratory distress syndrome (ARDS) and volume overload must be avoided, predictive indicators of fluid responsiveness are needed. The purpose of this study was to determine whether passive leg raising (PLR) can be used to predict fluid responsiveness in patients with ARDS treated with venovenous extracorporeal membrane oxygenation (ECMO). METHODS: We carried out a prospective study in a university hospital surgical ICU. All patients with ARDS treated with venovenous ECMO and exhibiting clinical and laboratory signs of hypovolaemia were enrolled. We measured PLR-induced changes in stroke volume (ΔPLRSV) and cardiac output (ΔPLRCO) using transthoracic echocardiography. We also assessed PLR-induced changes in ECMO pump flow (ΔPLRPO) and PLR-induced changes in ECMO pulse pressure (ΔPLRPP) as predictors of fluid responsiveness. Responders were defined by an increase in stroke volume (SV) > 15% after VE. RESULTS: Twenty-five measurements were obtained from seventeen patients. In 52% of the measurements (n = 13), SV increased by > 15% after VE (responders). The patients' clinical characteristics appeared to be similar between responders and nonresponders. In the responder group, PLR significantly increased SV, cardiac output and pump flow (P < 0.001). ΔPLRSV values were correlated with VE-induced SV variations (r² = 0.72, P = 0.0001). A 10% increased ΔPLRSV predicted fluid responsiveness with an area under the receiver operating characteristic curve (AUC) of 0.88 ± 0.07 (95% confidence interval (CI95): 0.69 to 0.97; P < 0.0001), 62% sensitivity and 92% specificity. On the basis of AUCs of 0.62 ± 0.11 (CI95: 0.4 to 0.8; P = 0.31) and 0.53 ± 0.12 (CI95: 0.32 to 0.73, P = 0.79), respectively, ΔPLRPP and ΔPLRPO did not predict fluid responsiveness. CONCLUSIONS: In patients treated with venovenous ECMO, a > 10% ΔPLRSV may predict fluid responsiveness. ΔPLRPP and ΔPLRPO cannot predict fluid responsiveness.

Association Between End-Tidal Carbon Dioxide Pressure and Cardiac Output During Fluid Expansion in Operative Patients Depend on the Change of Oxygen Extraction.

In a model of hemorrhagic shock, end-tidal carbon dioxide tension (EtCO2) has been shown to reflect the dependence of oxygen delivery (DO2) and oxygen consumption (VO2) at the onset of shock. The objectives of the present study were to determine whether variations in EtCO2 during volume expansion (VE) are correlated with changes in oxygen extraction (O2ER) and whether EtCO2 has predictive value in this respect.All patients undergoing cardiac surgery admitted to intensive care unit in whom the physician decided to perform VE were included. EtCO2, cardiac output (CO), blood gas levels, and mean arterial pressure (MAP) were measured before and after VE with 500 mL of lactated Ringer solution. DO2, VO2, and O2ER were calculated from the central arterial and venous blood gas parameters. EtCO2 responders were defined as patients with more than a 4% increase in EtCO2 after VE. A receiver-operating characteristic curve was established for EtCO2, with a view to predicting a variation of more than 10% in O2ER.Twenty-two (43%) of the 51 included patients were EtCO2 responders. In EtCO2 nonresponders, VE increased MAP and CO. In EtCO2 responders, VE increased MAP, CO, EtCO2, and decreased O2ER. Changes in EtCO2 were correlated with changes in CO and O2ER during VE (P < 0.05). The variation of EtCO2 during VE predicted a decrease of over 10% in O2ER (area under the curve [95% confidence interval]: 0.88 [0.77-0.96]; P < 0.0001).During VE, an increase in EtCO2 did not systematically reflect an increase in CO. Only patients with a high O2ER (i.e., low ScvO2 values) display an increase in EtCO2. EtCO2 changes during fluid challenge predict changes in O2ER.

Mini-fluid challenge can predict arterial pressure response to volume expansion in spontaneously breathing patients under spinal anaesthesia.

INTRODUCTION: The objective of this study was to test whether stroke volume (SV) variations in response to a fixed mini-fluid challenge (ΔSV100) measured by impedance cardiography (ICG) could predict an increase in arterial pressure with volume expansion in spontaneously breathing patients under spinal anaesthesia. METHODS: Thirty-four patients, monitored by ICG who required intravenous fluid to expand their circulating volume during surgery under spinal anaesthesia, were studied. Haemodynamic variables and bioimpedance indices (blood pressure, SV, cardiac output [CO]) were measured before and after fluid challenge with 100mL of crystalloid, and before/after volume expansion. Responders were defined by ≥15% increase in systolic arterial pressure (SAP) after infusion of 500 mL of crystalloid solution. RESULTS: SAP increased by ≥15% in 20 (59%) of the 34 patients. SAP, SV, and CO increased and HR decreased only in responders. SV variations in response to mini-fluid challenge and volume expansion differed between patients who showed arterial responsiveness and those in whom SAP did not increase with volume expansion (11.6% [9.1-19.3] versus 2.5% [1.3-7], P<0.001, and 22.4% [11.7-36.6] versus 0.9 [0-5.5], P<0.001, respectively). ΔSV100 predicted an increase of arterial pressure with an area under the receiver operating characteristic (AUC) curve of 0.89 (CI95%: 0.73-0.97, P<0.001). The cut-off was 5%. Baseline SAP and HR were not predictive of arterial responsiveness (P>0.05). CONCLUSION: A ΔSV100 over 5% accurately predicted arterial pressure response to volume expansion during surgery.