Changes in circulating blood volume after cardiac surgery measured by a novel method using hydroxyethyl starch

Haemoglobin drift in patients following Whipple's procedure

BACKGROUNDS

This study aims to identify the objective findings of haemoglobin (Hb) drift in patients that had a Whipple's procedure in the last 10 years, their transfusion status intraoperatively and post-operatively, the potential factors affecting Hb drift, and the outcomes following Hb drift.

METHODS

A retrospective study was conducted at Northern Health, Melbourne. All adult patients who were admitted for a Whipple's procedure from 2010 to 2020 were included and information collected retrospectively for demographics, pre-operative, operative and post-operative details.

RESULTS

A total of 103 patients were identified. The median Hb drift calculated from a Hb level at the end of operation was 27.0 g/L (IQR 18.0-34.0), and 21.4% of patients received a packed red blood cell (PRBC) transfusion during the post-operative period. Patients received a large amount of intraoperative fluid with a median of 4500 mL (IQR 3400-5600). Hb drift was statistically associated with intraoperative and post-operative fluid infusion leading to concurrent issues with electrolyte imbalance and diuresis.

CONCLUSION

Hb drift is a phenomenon that does happen in major operations such as a Whipple's procedure, likely secondary to fluid over-resuscitation. Considering the risk of fluid overload and blood transfusion, Hb drift in the setting of fluid over-resuscitation needs to be kept in mind prior to blood transfusion to avoid unnecessary complications and wasting of other precious resources.

Perioperative blood loss: estimation of blood volume loss or haemoglobin mass loss?

BACKGROUND

Perioperative blood loss is an essential parameter in research into Patient Blood Management. However, currently there is no "gold standard" method to quantify it. Direct measurements of blood loss are considered unreliable methods, and the formulae to estimate it have proven to be significantly inaccurate. Given the need for better research tools, this study evaluated an estimation of haemoglobin mass loss as an alternative approach to estimate perioperative blood loss, and compared it to estimations based on blood volume loss.

MATERIAL AND METHODS

We studied one hundred consecutive patients undergoing urological laparoscopic surgery. Both haemoglobin mass loss and blood volume loss were directly measured during surgery, under highly controlled conditions for a reliable direct measurement of blood loss. Three formulae were studied: 1) a haemoglobin mass loss formula, which estimated blood loss in terms of haemoglobin mass loss, 2) the López-Picado's formula and 3) an empirical volume formula that estimated blood loss in terms of blood volume loss. The empirical volume formula was developed within the study with the aim of providing the best possible estimation of blood volume loss in the studied population. The formulae were evaluated and compared by assessing their agreements with their respective direct measurements of blood loss.

RESULTS

The haemoglobin mass loss formula met the predefined agreement criterion of ±71 g, with 95% limits of agreement ranging from 0.6 to 44.1 g and a moderate overestimation of 22.4. In comparison to both blood volume loss formulae, the haemoglobin mass loss formula was superior in every agreement parameter evaluated.

DISCUSSION

In this study, the estimation of haemoglobin mass loss was found to be a more accurate method to estimate perioperative blood loss. This estimation method could be a robust research tool, although more studies are needed to establish its reliability.

Intercompartmental fluid volume shifts during cardiopulmonary bypass measured by A-mode ultrasonography

To investigate the time course of fluid extravasation during cardiopulmonary bypass (CPB), we measured the peripheral tissue thickness (TT) by A-mode ultra-sound in 34 patients undergoing elective cardiac surgery. TT of the forehead was determined by a handheld A-mode ultrasound device and 10 MHz Transducer at nine defined intervals, from the night before surgery until the first postoperative day.

Mean calculated loss of 1700±40 mL (SEM) water during the fasting period resulted in a significant reduction of TT by 0.28±0.03 mm. From induction to start of CPB, rehydration with 1000 mL of fluid was performed and TT increased to baseline. After 60 min of extracorporal circulation, forehead TT increased significantly by 0.75±0.08 mm and remained unchanged until the end of surgery when the measured fluid gain was 1580±138 mL. At discharge from ICU, negative fluid regimen resulted in a balance of -127±146 mL whereas TT declined significantly to + 0.16±0.09 mm compared to baseline.

Dehydration due to fasting and the marked interstitial fluid extravasation during CPB could be detected by the changes of the peripheral TT. We conclude that parts of the fluid load during CPB are shifted from the intravascular compartment to the interstitial space in a time-dependent manner.

Capillary Leakage in Cardiac Surgery with Cardiopulmonary Bypass

Cardiopulmonary bypass causes a systemic inflammatory response, which can lead to capillary leak syndrome. In 15 adults undergoing elective cardiac surgery with cardiopulmonary bypass, we determined the volume and peak time of capillary leakage from the measurements of extracellular fluid volume and circulating blood volume taken preoperatively, at various intervals up to 24 hours after surgery, and on the 7th postoperative day. Extracellular fluid volume rose from 15.5 ± 2.7 Lpreoperatively to a peak 4 hours after surgery of 18.3 ± 3.2 L and remained elevated at 24 hours. Circulating blood volume fell from 4.10 ± 0.68 L preoperatively to 3.20 ± 0.58 L at the end of surgery. Fluid administered intraoperatively did not raise the circulating blood volume. Intraoperative fluid balance was positive at 2.62 ± 0.72 L but negative at all time points postoperatively. There was significant postoperative capillary leakage, increasing from 4.7% ± 2.3% of body weight at the end of surgery to a peak 4 hours later of 5.4% ± 2.0% and falling to 2.8% ± 3.3% at 24 hours. This knowledge of the pattern of change in capillary leakage after cardiac surgery with cardiopulmonary bypass might serve as a valuable guide for postoperative management.

Perioperative Circulating Blood Volume and Cardiac Function in Valve Disease

Circulating blood volume is important in managing fluid balance and cardiac function after surgery under cardiopulmonary bypass. Appropriate management differs among the valve disorders, but perioperative blood volume has not yet been considered. From February 2001 to March 2003, perioperative blood volume, fluid balance, cardiac index, and left ventricular stroke work index were measured in 31 patients: 10 with aortic stenosis, 9 with aortic regurgitation, 3 with mitral stenosis, and 9 with mitral regurgitation. All immediate postoperative blood volume measurements were less than preoperative values, and gradually returned to baseline. At all time points, blood volume in patients with aortic or mitral regurgitation was high, whereas it was low in those with stenosis, especially mitral stenosis. Fluid balance was positive in all patients. Postoperatively, there was a positive correlation between cardiac index and blood volume in all groups. The left ventricular stroke work index in the mitral regurgitation group was significantly higher than other groups, the aortic stenosis group was slightly lower, the mitral stenosis and mitral regurgitation groups were higher than the baseline, and the aortic regurgitation group was essentially unchanged. Thus, it is necessary to consider blood volume perioperatively in different valvular diseases to manage water balance.

Tissue oxygen saturation as an early indicator of delayed lactate clearance after cardiac surgery: a prospective observational study

Background

In this observational study near infrared spectroscopy (NIRS) was evaluated as a non-invasive monitor of impaired tissue oxygenation (StO₂) after cardiac surgery. StO₂, cardiac output, mixed venous oxygen saturation and mean arterial pressure were compared with lactate clearance as established measure for sufficient tissue perfusion and oxygen metabolism.

Methods

Forty patients after cardiac surgery (24 aortocoronary bypass grafting, 5 heart valve, 3 ascending aorta and 8 combined procedures) were monitored until postoperative day 1 with NIRS of the thenar muscle (InSpectra™ StO₂-monitor, Hutchinson Technology), a pulmonary-artery catheter and intermittent blood gas analyses for the assessment of lactate clearance.

Results

StO₂ was reduced 4 h after surgery (75 ± 6 %), but recovered at day 1 (84 ± 5 %), while lactate concentration remained increased. Using uni- and multivariate regression analysis, minimum StO₂ (r = 0.46, p <0.01) and cardiac index (r = 0.40, p <0.05) correlated with lactate clearance at day 1, while minimum mixed venous saturation and mean arterial pressure did not. In a receiver-operating characteristics (ROC) analysis, minimum StO₂ (with a threshold of 75 %) predicted a lactate clearance <10 % at day 1 with an area under the ROC-curve of 0.83, a sensitivity of 78 % and a specificity of 88 %. In the subgroup with StO₂  <75 %, troponin and creatine kinase MB were significantly increased at day 1.

Conclusions

StO₂ below 75 % in the first hours after surgery was a better early indicator of persistent impaired lactate clearance at day 1 than cardiac index, mixed venous oxygen saturation or mean arterial pressure.

Blood volume determination in obese and normal-weight gravidas: the hydroxyethyl starch method

OBJECTIVE

The impact of obesity on maternal blood volume in pregnancy has not been reported. We compared the blood volumes of obese and normal-weight gravidas using a validated hydroxyethyl starch (HES) dilution technique for blood volume estimation.

STUDY DESIGN

Blood volumes were estimated in 30 normal-weight (pregravid body mass index [BMI] <25 kg/m(2)) and 30 obese (pregravid BMI >35 kg/m(2)) gravidas >34 weeks' gestation using a modified HES dilution technique. Blood samples obtained before and 10 minutes after HES injection were analyzed for plasma glucose concentrations after acid hydrolysis of HES. Blood volume was calculated from the difference between glucose concentrations measured in hydrolyzed plasma.

RESULTS

Obese gravidas had higher pregravid and visit BMI (mean [SD]): pregravid (41 [4] vs 22 [2] kg/m(2), P = .001); visit (42 [4] vs 27 [2] kg/m(2), P = .001), but lower weight gain (5 [7] vs 12 [4] kg, P = .001) than normal-weight women. Obese gravidas had similar estimated total blood volume to normal-weight women (8103 ± 2452 vs 6944 ± 2830 mL, P = .1), but lower blood volume per kilogram weight (73 ± 22 vs 95 ± 30 mL/kg, P = .007).

CONCLUSION

Obese gravidas have similar circulating blood volume, but lower blood volume per kilogram body weight, than normal-weight gravidas near term.

Hematological Changes in Patients Undergoing Coronary Artery Bypass Surgery: a Prospective Study

Objectives:

Removal of pro inflammatory stimuli after CABG, wound closure and the regenerative ability of the bone marrow will ensure a gradual recovery of hematological parameters. The aim of this study was to assess the hematological changes after CABG.

Materials and Methods:

A prospective cohort study included 164 consecutive patients undergoing on pump CABG surgery between January 2012 and January 2013. Patients with primary hematologic disease, emergent or urgent CABG and off-pump CABG were not included. A time line protocol was employed.

Results:

All patients survived surgery. Average values of erythrocytes, hemoglobin and hematocrit declined, to reach lower values on day 3 after surgery (-33.6 %, -33.1 %, -32.6 % versus preoperative value, p<0.001) and then gradually increased to reach normal values after one month and the preoperative values after three months. The average values of leukocytes and neutrophils increased rapidly to achieve the highest value on day 2, while the average value of lymphocytes decreased quickly to achieve lower value on day 1 after surgery (+74.7 %, +127.1 %, -52.4 % respectively from the preoperative value, p<0.001). The average platelet count decreased to the lowest value on day 2 after surgery (-26.4 % from the preoperative value, p<0.001), after which gradually increased up to +100.8 % of preoperative value on day 14 (p<0.001) and then gradually decreased to reach normal values on day 21 and preoperative values after three months.

Conclusions:

Average values of the three peripheral blood cells parameters undergo important changes after CABG, but not life threatening, and regain normal and preoperative values after 1-3 months after surgery.

Hospital-acquired anemia: prevalence, outcomes, and healthcare implications

BACKGROUND

Evidence suggests that patients with normal hemoglobin (Hgb) levels on hospital admission who subsequently develop hospital-acquired anemia (HAA) may be at risk for adverse outcomes. Our objectives were to (1) determine the prevalence of HAA and (2) examine whether HAA is associated with increased mortality, length of stay (LOS), and total hospital charges.

METHODS

The population consisted of 417,301 adult hospitalizations from January 1, 2009 to August 31, 2011, in an academic medical center and 9 community hospitals. Patients with anemia on admission, and hospitals in the health system without available laboratory data were excluded; 188,447 hospitalizations were included in the analysis. Demographics, comorbidities, and outcomes were retrieved from administrative data; Hgb values were taken from the electronic medical record. Regression modeling was used to examine the association between demographics, comorbidity, hospitalization type, and HAA variables (mild: Hgb >11 and <12 g/dL for women, and >11 and <13 g/dL for men; moderate: Hgb 9.1 to ≤ 11.0 g/dL; severe: Hgb ≤ 9.0 g/dL) on mortality, LOS, and hospital charges.

RESULTS

Among 188,447 hospitalizations, 139,807 patients (74%) developed HAA: mild, 40,828 (29%); moderate, 57,184 (41%); and severe, 41,795 (30%). Risk-adjusted odds ratios and 95% confidence intervals for in-hospital mortality with HAA were: mild, 1.0 (0.88-1.17; P = 0.8); moderate, 1.51 (1.33-1.71, P < 0.001); and severe, 3.28 (2.90-3.72, P < 0.001). Risk-adjusted relative mean LOS and hospital charges relative to no HAA were higher with HAA: LOS: mild, 1.08 (1.08-1.10, P < 0.001); moderate, 1.28 (1.26-1.29, P < 0.001); severe, 1.88 (1.86-1.89, P < 0.001). Hospital charges: mild, 1.06 (1.06-1.07, P < 0.001); moderate, 1.18 (1.17-1.19, P < 0.001); severe, 1.80 (1.79-1.82, P < 0.001).

CONCLUSIONS

HAA is common and associated with increased mortality and resource utilization. Factors related to its development necessitate further study.

Hemoglobin drift after cardiac surgery

BACKGROUND

Recent literature suggests that a restrictive approach to red blood cell transfusions is associated with improved outcomes in cardiac surgery patients. Even in the absence of bleeding, intravascular fluid shifts cause hemoglobin levels to drift postoperatively, possibly confounding the decision to transfuse. The purpose of this study was to define the natural progression of hemoglobin levels in postoperative cardiac surgery patients.

METHODS

All cardiac surgery patients from October 2010 through March 2011 who did not receive a postoperative transfusion were included. Primary stratification was by intraoperative transfusion status. Change in hemoglobin was evaluated relative to the initial postoperative hemoglobin. Maximal drift was defined as the maximum minus the minimum hemoglobin for a given hospitalization. Final drift was defined as the difference between initial and discharge hemoglobin.

RESULTS

The final cohort included 199 patients: 71 (36%) received an intraoperative transfusion, whereas 128 (64%) did not. The average initial and final hemoglobin levels for all patients were 11.0±1.4 g/dL and 9.9±1.3 g/dL, respectively, giving a final drift of 1.1±1.4 g/dL. The maximal drift was 1.8±1.1 g/dL and was similar regardless of intraoperative transfusion status (p=0.9). Although all patients' hemoglobin initially dropped, 79% of patients reached a nadir and experienced a mean recovery of 0.7±0.7 g/dL by discharge. On multivariable analysis, increasing cardiopulmonary bypass time was significantly associated with total hemoglobin drift (coefficient/hour, 0.3 [0.1-0.5] g/dL; p=0.02).

CONCLUSIONS

In this report of hemoglobin drift after cardiac surgery, although all postoperative patients experienced downward hemoglobin drift, 79% of patients exhibited hemoglobin recovery before discharge. Physicians should consider the eventual upward hemoglobin drift before administering red blood cell transfusions.

Theory and in vitro validation of a new extracorporeal arteriovenous loop approach for hemodynamic assessment in pediatric and neonatal intensive care unit patients

OBJECTIVES

No simple method exists for repeatedly measuring cardiac output in intensive care pediatric and neonatal patients. The purpose of this study is to present the theory and examine the in vitro accuracy of a new ultrasound dilution cardiac output measurement technology in which an extracorporeal arteriovenous tubing loop is inserted between existing arterial and venous catheters.

DESIGN

Laboratory experiments.

SETTING

Research laboratory.

SUBJECTS

None.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

In vitro validations of cardiac output, central blood volume, total end-diastolic volume, and active circulation volume were performed in a model mimicking pediatric (children 2-10 kg) and neonatal (0.5-3 kg) flows and volumes against flows and volumes measured volumetrically. Reusable sensors were clamped onto the arterial and venous limbs of the arteriovenous loop. A peristaltic pump was used to circulate liquid at 6-12 mL/min from the artery to the vein through the arteriovenous loop. Body temperature injections of isotonic saline (0.3-10 mL) were performed. In the pediatric setting, the absolute difference between cardiac output measured by dilution and cardiac output measured volumetrically was 3.97% +/- 2.97% (range 212-1200 mL/min); for central blood volume the difference was 4.59% +/- 3.14% (range 59-315 mL); for total end-diastolic volume the difference was 4.10% +/- 3.08% (range 24-211 mL); and for active circulation volume the difference was 3.30% +/- 3.07% (range 247-645 mL). In the neonatal setting the difference for cardiac output was 4.40% +/- 4.09% (range 106-370 mL/min); for central blood volume the difference was 4.90% +/- 3.69% (range 50-62 mL); and for active circulation volume the difference was 5.39% +/- 4.42% (range 104-247 mL).

CONCLUSIONS

In vitro validation confirmed the ability of the ultrasound dilution technology to accurately measure small flows and volumes required for hemodynamic assessments in small pediatric and neonatal patients. Clinical studies are in progress to assess the reliability of this technology under different clinical situations.

Post-operative myocardial dysfunction does not affect the physiological response to early mobilization after coronary artery bypass grafting

BACKGROUND

An acute increase in oxygen demand can be compensated for either by increased cardiac index (CI) or increased oxygen extraction, resulting in reduced mixed venous oxygen saturation (SvO2). We tested the hypothesis that post-operative cardiac dysfunction may explain why oxygen extraction alone is increased during early mobilization after cardiac surgery.

METHODS

Twenty patients with a pre-operative ejection fraction > 50% were included in an open prospective observational study comparing the changes in SvO2 and hemodynamics during mobilizations immediately prior to surgery and on the first post-operative morning.

RESULTS

Mobilization induced an absolute reduction in SvO2 of 17.7 +/- 7.4% pre- and 19.0 +/- 5.5% post-operatively (NS). ANOVA for a series of measurements throughout the mobilization sequence identified no different effect on SvO2 between pre- and post-operative mobilizations (P = 0.567). The SvO2 level was reduced post-operatively resulting in a SvO2 during standing exercise of 55% before and 49% after the surgery (P < 0.01). Mobilization increased the heart rate (HR) and decreased the stroke volume index (SVI), leaving CI unchanged. This response was similar pre- and post-operatively (NS). Compared with pre-operative measurements, CI and HR increased post-operatively while SVI remained unchanged despite elevated cardiac filling pressures and reduced systemic vascular resistance. The left ventricular stroke work index was reduced, indicating reduced myocardial performance.

CONCLUSION

Myocardial function was reduced on the first morning after coronary artery bypass grafting (CABG), but during post-operative mobilization this reduction did not significantly influence the changes in CI or SvO2.

Perioperative monitoring of circulating and central blood volume in cardiac surgery by pulse dye densitometry

OBJECTIVE

To determine perioperative changes in circulating (BVI) and central blood volume (CBVI) by a new dye dilution technique using pulse dye densitometry.

DESIGN AND SETTING

Prospective observational study in the cardiac anesthesia and intensive care unit of a university hospital.

PATIENTS

Sixty-six patients undergoing coronary artery bypass surgery.

MEASUREMENTS AND RESULTS

Hemodynamic measurements by the dye dilution method using pulse dye densitometry were performed prior to skin incision and 3.3+/-1.4 h and 17+/-2.7 h after surgery. Based on conventional monitoring the therapeutic goals of hemodynamic therapy were achieved in all of the patients of this study. Despite a marked positive fluid balance which developed during surgery mean BVI decreased significantly after surgery while CBVI remained unchanged. Postoperative BVI deficits vs. preoperative values were observed in 78% of patients; these BVI deficits were profound in 29% of the cases. In contrast, 65% of the individual patients showed no or only minor postoperative changes in CBVI vs. preoperative values.

CONCLUSIONS

Changes in the intravascular volume compartments affected BVI to a greater extent than CBVI. Therefore measuring circulating in addition to central blood volume may be useful to ensure a normal circulating blood volume that can compensate for any change in the central vascular compartment.

Metabolic changes after cardiac surgery

The metabolic changes that occur after cardiac surgery result from a complex interaction between the effects of surgery and extracorporeal circulation per se, the inflammatory response to surgical trauma and extracorporeal circulation, perioperative use of hypothermia, the cardiovascular and neuroendocrine responses characteristic to cardiac surgery, and the drugs and blood products used to support circulation during and after operation. These changes include among others increased oxygen consumption and energy expenditure and increased secretion of insulin, growth hormone, adrenocorticotrophic hormone, cortisol, epinephrine and norepinephrine. Other changes include decreased total-Trijodthyronine levels, hyperglycemia, hyperlactatemia, increased glutamate, aspartate and free fatty acid concentrations, hypokalemia, an increased production of inflammatory cytokines and increased consumption of complement and adhesion molecules. There is evidence that better control of metabolic abnormalities improves the patients' outcome.