Hyperosmolar Therapy in Elderly Neurosurgical Patients: Comparison of the Effect of Mannitol (20%) and Hypertonic Saline (3%) on Advanced Cardiovascular Parameters using Transesophageal Echocardiography - A Preliminary Randomized Controlled Trial.

OBJECTIVE: Osmotherapeutic agents increase the intravascular volume by withdrawing water from the brain followed by relative hypovolemia due to diuresis leading to significant changes in systemic hemodynamics which might have adverse consequences in the elderly. We studied the effect of mannitol (20%) and hypertonic saline (3%) on left ventricle outflow tract velocity-time integral (LVOT-VTI) and cardiac output in elderly patients undergoing supratentorial neurosurgical procedures using transesophageal echocardiography. METHODS: We recruited twenty-eight patients aged above 65 years undergoing supratentorial craniotomy who received equiosmolar solutions of 5.35 ml/kg of 3% hypertonic saline (Group HS, n=14) or 5 ml/kg of 20% mannitol (Group M, n=14). LVOT-VTI was recorded at baseline, 15, 30, 45, 60 and 90 minutes post-infusion and cardiac output (CO) was derived. We also recorded heart rate, blood pressure, fluid balance, brain relaxation, vasopressor use, complications and neurological outcome. RESULTS: We found a significant decrease in LVOT-VTI at 45, and 60 mins in Group M as compared to Group HS [mean(SD), 16.76(1.81) v/s 20.78(1.87), P <0.001, 17.4(2.38) v/s 19.16(2), P = 0.044, respectively]. We also found a corresponding significant fall in CO [3863.16(845.87) v/s 4745.59 (1209.33) ml/min, P = 0.034] and systolic blood pressure (P = 0.039), at 45 mins in Group M. Urine output was higher in Group M (P <0.001). All other parameters were comparable. CONCLUSION: Hypertonic saline appears to be associated with better systemic hemodynamics (LVOT-VTI, CO) while providing equivalent brain relaxation as mannitol in elderly patients. A future larger study is required to confirm our preliminary findings.

Derivation of Stroke Volume from Pulmonary Artery Pressures.

INTRODUCTION: Intermittent cardiac output (CO) studies using thermodilution are considered the gold standard. We have developed a stroke volume (SV) calculator from pulmonary pulse pressure (PP) to allow continuous monitoring of SV and CO from PP. METHODS: Hemodynamic data on 169 patients following orthotopic heart transplantation were used to compare our calculator-derived SV (and SV index, or SVi) against thermodilution-derived SV on admission into intensive care unit immediately following heart transplantation (T0) and 6 h after admission (T6). RESULTS: The calculated SV correlated with thermodilution-derived SV T0 (r = 0.920, p < 0.001, coefficient of 0.539 and the constant of 2.06). The median calculator SV, adjusted for coefficient and constant, was 48.4 ml (37.7, 60.7), comparable to the median thermodilution-derived SV 47.9 ml (37.5, 61.0), p = 0.737 with acceptable agreement on Bland-Altman plots. The thermodilution-derived SVi was 28.1 ml (19.7, 38.7) and adjusted calculator-derived SVi 28.9 ml (19.7, 39.9), p = 0.781. At T6, median thermodilution-derived SVi was 27.7 ml (19.5, 35.9) compared to the calculator-derived SVi median of 26.1 ml (17.7, 37.7), p = 0.203. CONCLUSIONS: Changes in PP can be used to track changes in SV using this calculator. Changes in PP may be used to assess response to treatment in the early post-operative period.

Factors influencing ultrasound cardiac output monitor waveform quality in patients admitted to the emergency intensive care unit.

Objective: The ultrasonic cardiac output monitor (USCOM), an instrument that monitors the evolution of a patient's hemodynamic status and determines the type of shock, has become an important tool for assessing cardiac pathology and predicting changes in disease, but there are some variations in the instrumental findings for different physical conditions of patients. This article examines whether there are differences in the quality of USCOM waveforms measured in different types of critically ill patients based on clinical characteristics and test parameters. Methods: Baseline data, diagnoses, echocardiograms, ventilation patterns, and USCOM results were retrospectively collected from patients in the emergency intensive care unit. Waveform quality was quantified using the Fremantle score to determine the extent to which age, body mass index (BMI), chronic obstructive pulmonary disease (COPD), respiratory failure, cardiac enlargement, valvular heart disease, and ventilation pattern influenced USCOM waveform quality. Results: Age, body mass index, chronic obstructive pulmonary disease, respiratory failure, right and left heart enlargement, aortic valve disease (excluding aortic stenosis), and ventilation mode did not have a significant effect on USCOM waveform quality in critically ill patients (P > 0.05). Conclusions: Various physical conditions of critically ill patients may have limited effect on the quality of the USCOM waveform, potentially rendering USCOM suitable for early assessment of hemodynamic status during ICU admission.

Cardiac index and heart rate as prognostic indicators for mortality in septic shock: A retrospective cohort study from the MIMIC-IV database.

Background: Septic shock is a life-threatening condition that can lead to organ dysfunction and death. In the ICU, monitoring of cardiac index (CI) and heart rate (HR) is commonly used to guide management and predict outcomes in septic shock patients. However, there is a lack of research on the association between CI and HR and the risk of mortality in this patient population. Therefore, the aim of this study was to investigate the relationship between different levels of CI and HR and mortality in septic shock patients. Methods: Data analysis was obtained from the MIMIC-IV version 2.0 database. Sepsis and septic shock were primarily defined by sepsis-3, the third international consensus on sepsis and septic shock. CI was computed using cardiac output (CO) and body surface area (BSA). To evaluate the incidence of CI with respect to each endpoint (7-, 14-, 21-, and 28-day mortality), a restricted cubic spline curve function (RCS) was used. The optimal cutoff value for predicted mortality was determined using the Youden index. Analyses of KM curves, cox regression, and logistic regression were conducted separately to determine the relationship between various CI and HR and 28-day mortality. Results: This study included 1498 patients with septic shock. A U-shaped relationship between CI levels and risk of mortality in septic shock was found by RCS analysis (p < 0.001). CI levels within the intermediate range of 1.85-2.8 L/min/m2 were associated with a mortality hazard ratio (HR) < 1. In contrast, low CI (HR = 1.87 95% CI: 1.01-3.49) and high CI (HR = 1.93 95% CI: 1.26-2.97) had a significantly increased risk of mortality. The AUC for heart rate prediction of mortality by Youden index analysis was 0.70 95%CI:0.64-0.76 with a cut-off value of 93.63 bpm. According to the characteristics of HR and CI, patients were divided into six subgroups HR↓+CI intermediate group (n = 772), HR↓+CI↓ group (n = 126), HR↓+CI↑ group (n = 294), HR↑+CI intermediate group (n = 132), HR↑+CI↓ group (n = 24), and HR↑+CI↑ group (n = 150). The KM curves, COX regression, and logistic regression analysis showed that the survival rates the of HR↓+CI intermediate group, HR↓+CI↓ group, and HR↓+CI↑ were higher than the other groups. The risk factors of HR↑+CI intermediate group, HR↑+CI↓, and HR↑+CI↑ with ICU 28-day mortality were HR = 2.91 (95% CI: 1.39-5.97), HR = 3.67 (95% CI: 1.39-11.63), and HR = 5.77 (95% CI: 2.98-11.28), respectively. Conclusion: Our retrospective study shows that monitoring cardiac index and heart rate in patients with septic shock may help predict the organismal response and hemodynamic consequences, as well as the prognosis. Thus, healthcare providers should carefully monitor changes in these parameters in septic shock patients transferred to the ICU for treatment.

Consensus of the Brazilian association of hematology, hemotherapy and cellular therapy on patient blood management: Anemia tolerance mechanisms.

Understanding the physiological concepts of oxygen delivery is essential to discern the mechanisms that influence its increase, reduction or maintenance in the body. This text explores the different mechanisms that help maintain oxygen delivery even in the face of reduced hemoglobin levels. Adequate oxygen delivery ensures tissue and metabolic balance, which is crucial to avoid harmful consequences such as metabolic acidosis and cellular dysoxia. The complex interaction between variables such as cardiac output, hemoglobin and heart rate (HR) plays a fundamental role in maintaining oxygen delivery, allowing the body to temporarily adjust to situations of anemia or high metabolic demand. It is important to emphasize that blood transfusions should not be based on fixed values, but rather on individual metabolic needs. Strategies to reduce myocardial consumption and monitor macro and micro hemodynamics help in making rational decisions. Individualizing treatment and considering factors such as blood viscosity in relation to the benefits of transfusion are increasingly relevant to optimize therapy and minimize risks, especially in complex clinical scenarios, such as neurocritical patients and trauma victims.

High output cardiac state: evaluating the incidence, plausible etiologies and outcomes.

INTRODUCTION: The high output cardiac state (HOCS) [cardiac index (CI) >4 L/min/m2 ], primarily driven by abnormally low systemic vascular resistance (SVR), is a relatively under-recognized condition. Although, majority of these patients meet criteria for heart failure (HF), their treatment should be aimed at the primary pathology, as the majority of guideline directed HF therapies can reduce SVR further. OBJECTIVES: To characterize patients with HOCS and provide valuable insight into the condition. METHODS: Patients investigated by right heart catheterization (RHC) at the St. Boniface Hospital, Winnipeg, Canada between January 2009 and November 2021 were reviewed. Two groups of patients were included: 1) HOCS [CI >4 L/min/m2], and 2) pre-HOCS [CI between 3.8-4.0 L/min/m2]. Their medical records were reviewed to identify plausible etiologies, relevant investigations, and outcomes. RESULTS: 177/2950 (6 %) patients met criteria for inclusion: 144/177 (81 %) with HOCS [mean age 51 years (range 19 - 82); 67/144 (47 %) female] and 33/177 (19 %) with pre-HOCS [mean age 55 years (range 30 - 83); 6/33 (18 %) female]. The most common plausible etiologies for the HOCS included anemia (36 %), obesity (34 %), cirrhosis (17 %), and lung disease (32 %). Trans-thoracic echocardiography and magnetic resonance imaging findings were non-specific and predominantly described preserved left ventricular ejection fraction, and pulmonary hypertension. The population experienced high rates of hospitalization, and significantly high mortality [36/144 (25 %) of HOCS at a median follow-up of 31.5 months, and 13/33 (39 %) of pre-HOCS at a median follow-up of 17 months]. CONCLUSIONS: HOCS is not an uncommon condition and is associated with high mortality. Current HF guideline should incorporate such evaluation into the diagnostic criteria.

Comparison of Left Ventricular Stroke Volume in 2nd- and 3rd Trimester Fetuses Measured by the Product of VTI and Aortic Annular Area With That Assessed by Simpson's Single-Plane Rule Using the STE Technique.

OBJECTIVES: The aim of the study was to compare left ventricle stroke volume in healthy, eutrophic fetuses in the 2nd and 3rd trimesters evaluated using the velocity time integral and aortic annulus area with left ventricular stroke volume measured using Simpson's single-plane rule and to determine the discrepancy equation. METHODS: The study included 354 fetuses. In each fetus, during the same examination, simultaneous assessment of stroke volume was performed by pulsed-wave Doppler using the product of the velocity time integral and aortic annulus area and by the fetalHQ® software using Simpson's single-plane rule. The Mann-Whitney U test was used to compare the "product-derived" stroke volume and stroke volume using fetalHQ® software values in the 2nd and 3rd trimesters separately. The agreement between the two methods were verified using Bland-Altman analysis. A linear regression model was used to obtain the discrepancy equation. RESULTS: In the 2nd trimester, the mean percentage difference between both the techniques showed that the stroke volume values determined using pulsed-wave Doppler were, on average, 88% higher than the stroke volume values determined using fetalHQ®. The upper limit of agreement between the compared techniques was approximately 146% and the lower limit of agreement was equal to 29.6%. In the 3rd trimester, the results indicated that the stroke volume values determined using pulsed-wave Doppler were, on average, 76% higher than the stroke volume values determined using fetalHQ®. The upper limit of agreement between the compared techniques was approximately 129% and the lower limit of agreement was 23%. Based on the results of the linear regression models, discrepancy formulas of the stroke volume values were obtained. The equations to calculate the predicted mean and standard deviations were used to compute the reference intervals for the mean, 5th and 95th centiles. CONCLUSION: The calculation of left ventricular stroke volume using pulsed Doppler has higher result in relation to stroke volume determined using Simpson's rule significantly. The aortic annulus area showed a higher correlation regarding stroke volume than the velocity time integral in both the 2nd and 3rd trimesters. Stroke volume increased with the increase in aortic annulus area, whereas the velocity time integral remained relatively constant. The retrospective analysis of the collected material enabled the determination of the discrepancy equation.

Towards the automatic detection and correction of abnormal arterial pressure waveforms.

Both over and underdamping of the arterial pressure waveform are frequent during continuous invasive radial pressure monitoring. They may influence systolic blood pressure measurements and the accuracy of cardiac output monitoring with pulse wave analysis techniques. It is therefore recommended to regularly perform fast flush tests to unmask abnormal damping. Smart algorithms have recently been developed for the automatic detection of abnormal damping. In case of overdamping, air bubbles, kinking, and partial obstruction of the arterial catheter should be suspected and eliminated. In the case of underdamping, resonance filters may be necessary to normalize the arterial pressure waveform and ensure accurate hemodynamic measurements.

Effects of tasipimidine premedication with and without methadone and dexmedetomidine on cardiovascular variables during propofol-isoflurane anaesthesia in Beagle dogs.

OBJECTIVE: To evaluate cardiovascular effects of oral tasipimidine on propofol-isoflurane anaesthesia with or without methadone and dexmedetomidine at equianaesthetic levels. STUDY DESIGN: Prospective, placebo-controlled, blinded, experimental trial. ANIMALS: A group of seven adult Beagle dogs weighing (mean ± standard deviation) 12.4 ± 2.6 kg and a mean age of 20.6 ± 1 months. METHODS: The dogs underwent four treatments 60 minutes before induction of anaesthesia with propofol. PP: placebo orally and placebo (NaCl 0.9%) intravenously (IV); TP: tasipimidine 30 µg kg-1 orally and placebo IV; TMP: tasipimidine 30 µg kg-1 orally and methadone 0.2 mg kg-1 IV; and TMPD: tasipimidine 30 µg kg-1 orally with methadone 0.2 mg kg-1 and dexmedetomidine 1 µg kg-1 IV followed by 1 µg kg-1 hour-1. Isoflurane in oxygen was maintained for 120 minutes at 1.2 individual minimum alveolar concentration preventing motor movement. Cardiac output (CO), tissue blood flow (tbf), tissue oxygen saturation (stO2) and relative haemoglobin content were determined. Arterial and mixed venous blood gases, arterial and pulmonary artery pressures and heart rate (HR) were measured at baseline; 60 minutes after oral premedication; 5 minutes after IV premedication; 15, 30, 60, 90 and 120 minutes after propofol injection; and 30 minutes after switching the vaporiser off. Data were analysed by two-way anova for repeated measures; p < 0.05. RESULTS: Tasipimidine induced a significant 20-30% reduction in HR and CO with decreases in MAP (10-15%), tbf (40%) and stO2 (43%). Blood pressure and oxygenation variables were mainly influenced by propofol-isoflurane-oxygen anaesthesia, preceded by short-lived alterations related to IV methadone and dexmedetomidine. CONCLUSIONS AND CLINICAL RELEVANCE: Tasipimidine induced mild to moderate cardiovascular depression. It can be incorporated into a common anaesthetic protocol without detrimental effects in healthy dogs, when anaesthetics are administered to effect and cardiorespiratory function is monitored.

Reliability of Bioreactance and Pulse-Power Analysis in Measuring Cardiac Index During Open Abdominal Aortic Surgery.

OBJECTIVE: To investigate the accuracy, precision, and trending ability of noninvasive bioreactance-based Starling SV and the mini invasive pulse-power device LiDCOrapid as compared to thermodilution cardiac output (TDCO) as measured by pulmonary artery catheter when assessing cardiac index (CIx) in the setting of elective open abdominal aortic (AA) surgery. DESIGN: A prospective method-comparison study. SETTING: Oulu University Hospital, Finland. PARTICIPANTS: Forty patients undergoing elective open abdominal aortic surgery. INTERVENTIONS: Intraoperative CI measurements were obtained simultaneously with TDCO and the study monitors, resulting in 627 measurement pairs with Starling SV and 497 with LiDCOrapid. MEASUREMENTS AND MAIN RESULTS: The Bland-Altman method was used to investigate the agreement among the devices, and four-quadrant plots with error grids were used to assess trending ability. The agreement between TDCO and Starling SV was associated with a bias of 0.18 L/min/m2 (95% confidence interval [CI] = 0.13 to 0.23), wide limits of agreement (LOA = -1.12 to 1.47 L/min/m2), and a percentage error (PE) of 63.7 (95% CI = 52.4-71.0). The agreement between TDCO and LiDCOrapid was associated with a bias of -0.15 L/min/m2 (95% CI = -0.21 to -0.09), wide LOA (-1.56 to 1.37), and a PE of 68.7 (95% CI = 54.9-79.6). The trending ability of neither device was sufficient. CONCLUSION: The CI measurements achieved with Starling SV and LiDCOrapid were not interchangeable with TDCO, and the ability to track changes in CI was poor. These results do not support the use of either study device in monitoring CI during open AA surgery.

Diagnosis, management and long term cardiovascular outcomes of phenotypic profiles in pulmonary hypertension associated with congenital diaphragmatic hernia.

Congenital diaphragmatic hernia (CDH) is a developmental defect of the diaphragm resulting in herniation of viscera into the chest. This condition is characterized by pulmonary hypoplasia, pulmonary hypertension (PH) and cardiac ventricular dysfunction. PH is a key component of the pathophysiology of CDH in neonates and contributes to morbidity and mortality. Traditionally, PH associated with CDH (CDH-PH) is thought to be secondary to increased pulmonary arterial resistance and vasoreactivity resulting from pulmonary hypoplasia. Additionally, there is increasing recognition of associated left ventricular hypoplasia, dysfunction and elevated end diastolic pressure resulting in pulmonary venous hypertension in infants with CDH. Thus, hemodynamic management of these infants is complex and cautious use of pulmonary vasodilators such as inhaled nitric oxide (iNO) is warranted. We aim to provide an overview of different phenotypic profiles of CDH associated PH and potential management options based on current evidence and pathophysiology.

Leucoglycemic index predicts post-operative vasopressor-inotropic requirement after adult cardiac surgery (LEUCOGLYPTICS): A retrospective single-center study.

Background and Aims: Cardiac surgery often necessitates considerable post-operative vasoactive-inotropic support. Given an encouraging literature on the prognostic potential of leucoglycemic index (LGI) [serum glucose (mg/dl) × total leucocytes count (cells/mm3)/1000], we aimed to evaluate whether intensive care unit (ICU)-admission LGI can predict post-operative vasopressor-inotropic requirements following cardiac surgery on cardio-pulmonary bypass (CPB). Material and Methods: The data of patients undergoing cardiac surgery at our tertiary care center between January 2015 and December 2020 was retrospectively reviewed. The vasopressor-inotropic requirement was estimated using the VIS (vasoactive-inotropic score) values over the first post-operative 72 hrs. Subsequently, VISi (indexed VIS) was computed as maxVIS[0-24hrs] + maxVIS[24-48hrs] +2 × maxVIS[48-72hrs]/10), and the study participants were divided into h-VISi (VISi ≥3) and l-VISi (VISi <3). Results: Out of 2138 patients, 479 (22.40%) patients categorized as h-VISi. On univariate analysis: LGI, age, European System for Cardiac Operative Risk Evaluation score (EuroSCORE II), left-ventricle ejection fraction, prior congestive heart failure (CHF), chronic renal failure, angiotensin-converting enzyme inhibitors, combined surgeries, CPB and aortic cross-clamp (ACC) duration, blood transfusion, and immediate post-operative glucose were significant h-VISi predictors. Subsequent to multi-variate analysis, the predictive performance of LGI (OR: 1.09; 95% CI: 1.03-1.14; P = 0.002) prior CHF (OR: 2.35; 95% CI: 1.44-3.82; P = 0.001), CPB time (OR: 1.08; 95% CI: 1.02-1.14; P = 0.019), ACC time (OR: 1.03; 95% CI: 1.02-1.04; P = 0.008), and EuroSCORE II (OR: 1.14; 95% CI: 1.06-1.21; P < 0.001) remained significant. With 1484.75 emerging as the h-VISi predictive cut-off, patients with LGI ≥ 1484.75 also had a higher incidence of vasoplegia, low-cardiac output syndrome, new-onset atrial fibrillation, acute kidney injury, and mortality. LGI additionally exhibited a significant positive correlation with duration of mechanical ventilation and ICU stay (R = 0.495 and 0.564, P value < 0.001). Conclusion: An elevated LGI of greater than 1484.75 independently predicted a VISindex ≥3 following adult cardiac surgery on CPB.

Continuous Peripheral Electrical Nerve Stimulation Improves Cardiac Function via Autonomic Nerve Regulation in MI Rats.

BACKGROUND: Peripheral electrical nerve stimulation (PENS) reportedly improves cardiac function after myocardial ischemia (MI) by rebalancing the cardiac autonomic nervous system. The dynamic and continuous influence of the PENS on autonomic and cardiac functioning based on cardiac self-repair is not well understood. OBJECTIVE: This study aimed to explore the correlations between autonomic nervous balance and functional cardiac repair after MI and to clarify the optimal acupoint selection and time course for PENS. METHODS: The activity of the superior cervical cardiac sympathetic nerve (SN) and vagus nerve (VN) was recorded to reflect the autonomic tone directly. The Millar pressure-volume loop system was used for LV diastolic and systolic functioning. Noninvasive continuous ECG and echocardiography were performed to analyse HR, HRV, and LV function. The effect of continuous PENS (cPENS) or instant PENS (iPENS) on autonomic and cardiac indications was tested. RESULTS: SN activity and VN activity increased as compensatory self-regulation on days 7 and 14 post-MI, followed by an imbalance of autonomic tone and cardiac dysfunction on day 28. cPENS-PC6 maintained autonomic hyperexcitability, improved myocardial systolic and diastolic abilities, and reduced myocardial fibrosis on day 28 post-MI, whereas cPENS-ST36 had a limited effect. Both iPENS-PC6 and iPENS-ST36 improved the autonomic and cardiac function of rats in the cPENS groups. CONCLUSION: Rats showed autonomic fluctuations and cardiac dysfunction 28 days post-MI. cPENS produced sympathomimetic action to sustain cardiac self-compensation, but with acupoint specificity. Based on cPENS, iPENS evoked autonomic regulation and cardiac benefits without acupoint differentiation.

The Jena Method: Perfusionist Independent, Standby Wet-Primed Extracorporeal Membrane Oxygenation (ECMO) Circuit for Immediate Catheterization Laboratory and/or Hybrid Operating Room Deployment.

Background: The timely initiation of extracorporeal membrane oxygenation (ECMO) is crucial for providing life support. However, delays can occur when perfusionists are not readily available. The Jena Method aims to address this issue by offering a wet-primed ECMO system that can be rapidly established without the perfusionist's presence. Methods: The goal was to ensure prompt ECMO initiation while maintaining patient safety. The method focuses on meeting hygienic standards, safe primed storage of the circuit, staff training, and providing clear step-by-step instructions for the ECMO unit. Results: Since implementing the Jena Method in 2015, 306 patients received VA-ECMO treatment. Bacterial tests confirmed the sterility of the primed ECMO circuits during a 14-day period. The functionality of all the components of the primed ECMO circuit after 14 days, especially the pump and oxygenator, were thoroughly checked and no malfunction was found to this day. To train staff for independent ECMO initiation, a step-by-step system involves safely bringing the ECMO unit to the intervention site and establishing all connections. This includes powering up, managing recirculation, de-airing the system, and preparing it for cannula connection. A self-developed picture-based guide assists in this process. New staff members learn from colleagues and receive quarterly training sessions by perfusionists. After ECMO deployment, the perfusionist provides a new primed system for a potential next patient. Conclusions: Establishing a permanently wet-primed on-demand extracorporeal life support circuit without direct perfusionist support is feasible and safe. The Jena Method enables rapid ECMO deployment and has the potential to be adopted in emergency departments as well.

Overdot and overline annotation must be understood to accurately interpret V.O2MAX physiology with the Fick formula.

Few formulas have been used in exercise physiology as extensively as the Fick formula, which calculates the rate of oxygen consumption (i.e., V.O2) as the product of cardiac output (Q.) and the difference in oxygen content in arterial and mixed venous blood (Δav¯O2). Unfortunately, the physiology of maximum V.O2 (V.O2MAX) is often misinterpreted due to a lack of appreciation for the limitations represented by the oft-ignored superscript annotations in the Fick formula. The purpose of this perspective is to explain the meaning of the superscript annotations and highlight how such annotations influence proper interpretation of V.O2MAX physiology with the Fick formula. First, we explain the significance of the overdots above V.O2 and Q., which indicate a measure per unit of time. As we will show, the presence of an overdot above Q. and lack of one above Δav¯O2 denotes they are different types of ratios and should be interpreted in the context of one another-not in contrast to each other as is commonplace. Second, we discuss the significance of the overline above the "v¯" in Δav¯O2, which indicates the venous sample is an average of blood that comes from mixed sources. The mixed nature of the venous sample has major implications for interpreting the influence of oxygen diffusion and blood flow heterogeneity on V.O2MAX. Ultimately, we give recommendations and insights for using the Fick formula to calculate V.O2 and interpret V.O2MAX physiology.

Carotid Blood Flow as a Surrogate for Pulse Contour Analysis in Assessment of Fluid Responsiveness: A Prospective, Observational, Single-Centre Study (Contour Study).

Background and objectives The quest for an accurate and reliable non-invasive method of assessing cardiac output in critically ill patients is still ongoing. Carotid artery Doppler is a promising non-invasive, reproducible, and feasible bedside monitor. So we compared the change in cardiac output derived from arterial pressure waveforms (pulse contour analysis) with that from carotid artery Doppler-derived measurements, in post-major elective abdominal surgery patients. Materials and methods We conducted a prospective observational study in 30 adult post-major elective abdominal surgery patients admitted to the Gastroenterology and Liver Transplant intensive care unit postoperatively on mechanical ventilator support, who were found to be fluid responsive clinically on passive leg raise (PLR) test. Demographics and vasopressor support were recorded. Hemodynamic parameters including heart rate, systolic blood pressure (SBP), diastolic blood pressure (DBP), cardiac output (CO) using arterial pulse contour analysis (Vigileo monitor/FloTrac® sensor; Edwards Lifesciences, Irvine, California, United States), and carotid blood flow (CBF) were recorded on the baseline, pre- and post- PLR, and post fluid bolus administration. Balanced salt solution at the rate of 6ml/kg over 20 minutes was given as a fluid bolus. Results Of the 30 patients who were included in the study, 16 patients (53.3%) were on vasopressor support, mean (± SD) age of the patients was 52.93 (± 8.13) years. There was a significant increase in the SBP (mmHg) pre- to post-PLR, that is, 112.2±15.57 and 118.7±14.96, respectively (p-value = 0.001). Also from pre-PLR to post-fluid bolus administration, the increase in SBP was significant, 112.2±15.57 and 121.93±13.96, respectively (p-value = 0.001). The change in cardiac output measured using Vigileo and CBF from pre- to post-PLR (7.66±1.45 to 9.14±1.76, p< 0.001 for Vigileo and 8.10±1.66 to 9.72±1.99, p<0.001 for CBF) and pre-PLR to post fluid administration (7.66±1.45 to 9.39±1.77, p< 0.001 for Vigileo and 8.10±1.66 to 10.31±2.26, p< 0.001 for CBF) were significant. There was a positive correlation between the change in cardiac output as measured from arterial pulse contour analysis technique (Vigileo) and that measured from CBF (r=0.884) pre- and post-PLR. There was a significant correlation between cardiac output measurements derived from two techniques, before PLR, after PLR, and after fluid expansion (p< 0.001 for each variable). The change in cardiac output before PLR and after fluid expansion was also correlated by both the techniques (correlation coefficient being, r=0.781). Conclusion There was a significant positive correlation of the CO (absolute and change) measurements pre- and post-interventions (that is, PLR and fluid bolus administration) as made by pulse contour analysis (Vigileo) and by CBF in post-surgical patients. Pulse wave Doppler of CBF could be used as a surrogate for invasive measures of CO measurement for prediction of fluid responsiveness in this subgroup. Further larger studies can be performed to validate the same.

Body Positions Alter Hemodynamics and Respiration in Healthy Adults: A Systematic Review and Meta-Analysis.

Objective Different body positions can exert both positive and negative physiological effects on hemodynamics and respiration. This study aims to conduct a literature review and examine hemodynamic and respiratory alterations to different body positions.Methods The study protocol was registered with the International Prospective Registry of Systematic Reviews (register no. CRD42021291464). Two independent reviewers evaluated the methodological quality of all included studies using the Down and Black checklist, while the quality of evidence was evaluated using the Grading of Recommendations, Assessment, Development, and Evaluations approach. The overall effects of different body positions were reported from random effects meta-analysis.Results Three studies with low risk of bias and ten with high risk of bias met the eligibility criteria. The supine resulted in the highest cardiac output compared to the 70 deg head-up tilt, sitting, and standing positions (very low- to moderate-quality evidences) and the lowest systemic vascular resistance compared to the 70 deg head-up tilt and standing positions (moderate-quality evidence). Additionally, the supine was associated with the highest total respiratory resistance compared to the 70 deg head-up tilt, left lateral, and standing positions (very low-to moderate-quality evidence) and higher alveolar ventilation than the prone (low-quality evidence).Conclusions The supine position has the most positive association with hemodynamic variables, resulting in the highest cardiac output and the lowest systemic vascular resistance. The upright positions (70 deg head-up tilt and standing positions) has the most positive association with the respiratory variables, resulting in the lowest total respiratory resistance.