Thoracic intravascular and extravascular fluid volumes in cardiac surgical patients

Post-cardiopulmonary bypass hypoxaemia in paediatric patients undergoing congenital heart disease surgery: risk factors, features, and postoperative pulmonary complications

Background

Hypoxemia after cardiopulmonary bypass (CPB) is the quantifiable manifestation of pulmonary dysfunction. This retrospective study was designed to investigate the risk factors for post-cardiopulmonary bypass hypoxaemia and the features of hypoxaemia and pulmonary complications in paediatric congenital heart disease surgery involving CPB.

Methods

Data including demographics, preoperative pulmonary or cardiac parameters, and intraoperative interventions were retrospectively collected from 318 paediatric patients who underwent radical surgery with CPB for congenital heart disease. Among them, the factors that were significant by univariate analysis were screened for multivariate Cox regression. The lowest ratio of arterial oxygen tension and the inspiratory oxygen fraction (PaO₂/FiO₂), hypoxaemia (PaO₂/FiO₂ ≤ 300) insult time, duration of hypoxaemia, extubation time, and pulmonary complications were also analysed postoperatively.

Results

The morbidity of post-cardiopulmonary bypass hypoxaemia was 48.4% (154/318). Months (6 < months ≤ 12, 12 < months ≤ 36 and 36 < months compared with 0 ≤ months ≤ 6: HR 0.582, 95% CI 0.388–0.873; HR 0.398, 95% CI 0.251–0.632; HR 0.336, 95% CI 0.197–0.574, respectively; p < 0.01), preoperative intracardiac right-to-left shunting (HR 1.729, 95% CI 1.200–2.493, p = 0.003) and intraoperative pleural cavity entry (HR 1.582, 95% CI 1.128–2.219, p = 0.008) were identified as independent risk factors for the development of post-cardiopulmonary bypass hypoxaemia. Most hypoxaemia cases (83.8%, 129/154) occurred within 2 h, and the rate of moderate hypoxaemia (100 < PaO₂/FiO₂ ≤ 200) was 60.4% (93/154).

Conclusion

The morbidity of post-cardiopulmonary bypass hypoxaemia in paediatric congenital heart disease surgery was considerably high. Most hypoxaemia cases were moderate and occurred in the early period after CPB. Scrupulous management should be employed for younger infants or children with preoperative intracardiac right-to-left shunting or intraoperative pleural cavity entry.

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.

ICU Blood Pressure Variability May Predict Nadir of Respiratory Depression After Coronary Artery Bypass Surgery

Objectives: Surgical stress induces alterations on sympathovagal balance that can be determined through assessment of blood pressure variability. Coronary artery bypass graft surgery (CABG) is associated with postoperative respiratory depression. In this study we aimed at investigating ICU blood pressure variability and other perioperative parameters that could predict the nadir of postoperative respiratory function impairment.

Methods: This prospective observational study evaluated 44 coronary artery disease patients subjected to coronary artery bypass surgery (CABG) with cardiopulmonary bypass (CPB). At the ICU, mean arterial pressure (MAP) was monitored every 30 min for 3 days. MAP variability was evaluated through: standard deviation (SD), coefficient of variation (CV), variation independent of mean (VIM), and average successive variability (ASV). Respiratory function was assessed through maximal inspiratory (MIP) and expiratory (MEP) pressures and peak expiratory flow (PEF) determined 1 day before surgery and on the postoperative days 3rd to 7th. Intraoperative parameters (volume of cardioplegia, CPB duration, aortic cross-clamp time, number of grafts) were also monitored.

Results: Since, we aimed at studying patients without confounding effects of postoperative complications on respiratory function, we had enrolled a cohort of low risk EuroSCORE (European System for Cardiac Operative Risk Evaluation) with < 2. Respiratory parameters MIP, MEP, and PEF were significantly depressed for 4–5 days postoperatively. Of all MAP variability parameters, the ASV had a significant good positive Spearman correlation (rho coefficients ranging from 0.45 to 0.65, p < 0.01) with the 3-day nadir of PEF after cardiac surgery. Also, CV and VIM of MAP were significantly associated with nadir days of MEP and PEF. None of the intraoperative parameters had any correlation with the postoperative respiratory depression.

Conclusions: Variability parameters ASV, CV, and VIM of the MAP monitored at ICU may have predictive value for the depression of respiratory function after cardiac surgery as determined by peak expiratory flow and maximal expiratory pressure.

ClinicalTrials.gov Identifier: NCT02074371.

Comparison of Static End-expiratory and Effective Lung Volumes for Gas Exchange in Healthy and Surfactant-depleted Lungs

Background:

Effective lung volume (ELV) for gas exchange is a new measure that could be used as a real-time guide during controlled mechanical ventilation. The authors established the relationships of ELV to static end-expiratory lung volume (EELV) with varying levels of positive end-expiratory pressure (PEEP) in healthy and surfactant-depleted rabbit lungs.

Methods:

Nine rabbits were anesthetized and ventilated with a modified volume-controlled mode where periods of five consecutive alterations in inspiratory/expiratory ratio (1:2–1.5:1) were imposed to measure ELV from the corresponding carbon dioxide elimination traces. EELV and the lung clearance index were concomitantly determined by helium wash-out technique. Airway and tissue mechanics were assessed by using low-frequency forced oscillations. Measurements were collected at PEEP 0, 3, 6, and 9 cm H2O levels under control condition and after surfactant depletion by whole-lung lavage.

Results:

ELV was greater than EELV at all PEEP levels before lavage, whereas there was no evidence for a difference in the lung volume indices after surfactant depletion at PEEP 6 or 9 cm H2O. Increasing PEEP level caused significant parallel increases in both ELV and EELV levels, decreases in ventilation heterogeneity, and improvement in airway and tissue mechanics under control condition and after surfactant depletion. ELV and EELV exhibited strong and statistically significant correlations before (r = 0.84) and after lavage (r = 0.87).

Conclusions:

The parallel changes in ELV and EELV with PEEP in healthy and surfactant-depleted lungs support the clinical value of ELV measurement as a bedside tool to estimate dynamic changes in EELV in children and infants.

Changes in airway and respiratory tissue mechanics after cardiac surgery

BACKGROUND

Because of the critical importance of the first postoperative week in the development of respiratory complications after cardiac surgery, the mechanical properties of the respiratory system in this period were followed up systematically.

METHODS

The input impedance of the respiratory system (Zrs) was measured during spontaneous breathing in patients (n=35) undergoing cardiac surgery on the day before surgery to establish the baseline, and for six days thereafter. The airway resistance was inferred from the average of the resistive component of Zrs, while the changes in respiratory elastance were assessed from the imaginary part of Zrs by model fitting. An assessment was made of the impact on the postoperative changes of factors characteristic of the patients (gender, age, smoking, and obesity) or the surgery duration and the need or not for a cardiopulmonary bypass.

RESULTS

Airway resistance increased immediately after extubation (peak rise on day 1, evening: 48+/-10%) and subsequently gradually decreased to the initial level, the recovery proving prolonged in obese patients. Postoperative elevation in elastance peaked later (day 2, evening: 83+/-14%), lasted longer, and was affected by both cardiopulmonary bypass (p<0.05) and obesity (p<0.005).

CONCLUSIONS

These findings demonstrate the need for particular attention in the postoperative management of patients after cardiac surgery in order to reduce the immediate airway symptoms, and to take steps to maintain the lungs open during the critical postoperative days 2 and 3, especially in obese patients and (or) if the surgery involves the use of cardiopulmonary bypass.

Comparison of three methods of extravascular lung water volume measurement in patients after cardiac surgery

INTRODUCTION

Measurement of extravascular lung water (EVLW) by using the lithium-thermal (Li-thermal) and single-thermal indicator dilution methods was compared with the indocyanine green-thermal (ICG-thermal) method in humans.

METHODS

Single-center observational study involving patients undergoing cardiac surgery with cardiopulmonary bypass. Paired measurements were taken 1, 2, 4, and 6 hours after surgery. Bland-Altman analysis was used to calculate bias and limits of agreement. Data are presented as mean (SD) or median (IQR).

RESULTS

Seventeen patients were recruited (age, 69 years (54 to 87 years); Parsonnet score 10 (0 to 29)). Sixteen ICG-thermal measurements were excluded after blinded assessment because of poor-quality indicator dilution curves. EVLW volume as measured by the ICG-thermal technique was 4.6 (1.9) ml/kg, compared with 5.3 (1.4) ml/kg for the single-thermal method. Measurements taken with the Li-thermal method were clearly erroneous (-7.6 (7.4) ml/kg). In comparison with simultaneous measurements with the ICG-thermal method, single-thermal measurements had an acceptable degree of bias, but limits of agreement were poor (bias, -0.3 ml/kg (2.3)). Li-thermal measurements compared poorly with the ICG-thermal reference method (bias, 13.2 ml/kg (14.4)).

CONCLUSIONS

The principal finding of this study was that the prototype Li-thermal method did not provide reliable measurements of EVLW volume when compared with the ICG-thermal reference technique. Although minimal bias was associated with the single-thermal method, limits of agreement were approximately 45% of the normal value of EVLW volume. The Li-thermal method performed very poorly because of the overestimation of mean indicator transit time by using an external lithium ion electrode. These findings suggest that the assessment of lung water content by lithium-indicator dilution is not sufficiently reliable for clinical use in individual patients.

Effects of intrapleural analgesia on pulmonary function and postoperative pain in patients with chronic obstructive pulmonary disease undergoing coronary artery bypass graft surgery

OBJECTIVE

Pain after coronary artery bypass graft (CABG) surgery remains a significant problem and may cause serious complications because of restricted breathing and limited early mobilization. The aim of this study was to assess the effects of intrapleural analgesia on the relief of postoperative pain in patients undergoing CABG surgery.

DESIGN

Postoperative pain, pulmonary function tests, and outcomes were compared with a placebo group after CABG surgery in a double-blind randomized clinical trial.

SETTINGS

Cardiovascular surgery clinic.

PARTICIPANTS

One hundred twenty-five patients with decreased lung function were studied.

INTERVENTIONS

Group A (62 patients) received 20 mL of 0.5% bupivacaine bilaterally in the intrapleural spaces every 6 hours for 4 days, and group B (63 placebo patients) received sterile saline solution.

MEASUREMENTS AND MAIN RESULTS

Group A had a significantly shorter extubation time than the placebo group (8 +/- 1 h v 10 +/- 4 hours, p < 0.001). Blood gas analysis showed higher PaO2 and lower PaCO2 levels in group A. The patients receiving bupivicaine had significantly higher FEV1, FCV, VC, MVV, PEF, and FEF 25-75% values postoperatively when compared with the placebo group. Postoperative analgesic requirements and visual analog pain scales were significantly lower in group A. The intensive care unit stay in group A was shorter (1.2 +/- 0.7 v 1.4 +/- 0.6 days, p = 0.04); however, the hospital stay did not differ between groups.

CONCLUSIONS

Improvement in lung function parameters correlating with decreased postoperative pain with intrapleural bupivacaine was observed. Intrapleural analgesia provided a good level of analgesia, improved respiratory performance, and allowed rapid mobilization, which led to a reduction of postoperative respiratory complications.

Early continuous venovenous hemodialysis in dialysis-dependent patients after cardiac surgery: safety and efficacy

OBJECTIVES

The present study assessed the safety and efficacy of continuous venovenous hemodialysis (CVVHD) early after cardiac surgery.

DESIGN

Retrospective database and medical record review.

SETTING

University teaching hospital.

PARTICIPANTS

Forty-five dialysis-dependent patients who underwent cardiac surgery with cardiopulmonary bypass.

INTERVENTIONS

CVVHD was begun postoperatively after confirmation of hemostasis, irrespective of circulatory status. In the last 5 patients, the ratio of extravascular lung water (EVLW) to intrathoracic blood volume (ITBV) was measured using a single-indicator thermodilution catheter and compared with patients of normal renal function undergoing cardiac surgery.

MEASUREMENTS AND MAIN RESULTS

CVVHD was started at 4 hours after ICU admission. The maximum decrease in blood pressure within 60 minutes after initiation of CVVHD was 11 +/- 9 mmHg in the unstable hemodynamics group (defined as patients who required continuous intravenous adrenaline or intra-aortic balloon pump on admission to the ICU [n = 15]) and 7 +/- 8 mmHg in the stable hemodynamics group (n = 30, not significant). Circulatory status and oxygenation improved significantly 12 hours after CVVHD initiation in the unstable hemodynamics group. Blood volume from the chest tube did not increase after CVVHD. Early mortality (2.2%) was lower than that reported previously. The EVLW/ITBV ratio after ICU admission in dialysis-dependent patients was significantly higher than in patients with normal renal function.

CONCLUSIONS

Early CVVHD after cardiac surgery in dialysis-dependent patients was safe and effective. There was no associated increased postoperative bleeding or hemodynamic instability. Fluid removal improved respiratory status, particularly in patients requiring circulatory assistance, and overall early morality rates were lower that those previously published.

Inhaled Nitric Oxide Does Not Prevent Pulmonary Edema After Lung Transplantation Measured By Lung Water Content

STUDY OBJECTIVE

In order to assess the effects of inhaled nitric oxide (iNO) in preventing early-onset lung edema from occurring after lung transplantation, we measured extravascular lung water (EVLW) in a group of lung transplant recipients who were at high risk for developing ischemia-reperfusion-induced lung injury.

DESIGN

Prospective, randomized study.

SETTINGS

Surgical ICU in a teaching hospital.

PATIENTS

Thirty double-lung transplant recipients.

INTERVENTIONS

Patients were randomized to receive or not receive 20 ppm iNO at the time of reperfusion (ie, before any occurrence of lung edema). In the NO group, iNO was then administered for a 12-h period. A double-dilution technique was used for the serial assessment of EVLW, intrathoracic blood volume, and cardiac index. Standard hemodynamic and pulmonary parameters were also recorded during the first 3 postoperative days.

MEASUREMENTS AND RESULTS

Patients who received iNO did not have a different lung water content compared to control subjects (p = 0.61 [by analysis of variance (ANOVA)]). Blood oxygenation (ie, Pao(2)/fraction of inspired oxygen [Fio(2)] ratio) did not differ between the two groups (p = 0.61 [by ANOVA]). In both groups, EVLW and Pao(2)/Fio(2) ratio dropped significantly over time, regardless of the use of iNO (p < 0.01 [by ANOVA]).

CONCLUSIONS

In the population studied, prophylactic iNO that was administered at 20 ppm had no effect on pulmonary edema formation and resolution following lung transplantation.

Intra- and extravascular volume status in patients undergoing mitral valve replacement

BACKGROUND AND OBJECTIVE

Cardiopulmonary bypass is associated with changes of intra- and extravascular volume status often resulting in cardiopulmonary dysfunction. The purpose of this prospective double-blind study was to evaluate the influence of different priming solutions of the extracorporeal circuit on intra- and extravascular volume status and haemodynamics in patients undergoing elective mitral valve replacement.

METHODS

Twenty-two patients with mitral valve insufficiency were randomly allocated into two equal groups. In Group 1 cardiopulmonary bypass was primed with a nearly isooncotic solution consisting of 4% albumin. The second group received a pure crystalloid priming solution. The thermo-dye indicator dilution technique was used for the assessment of cardiac output, central and pulmonary blood volume, right ventricular end-diastolic volume and total blood volume.

RESULTS

Patients in the crystalloid group showed increased intraoperative fluid requirements. Significantly more fluid was accumulated in the extravascular space whereas total blood volume was decreased after surgery. Stroke volume index (SVI) was significantly decreased in the immediate postoperative period when compared to baseline. As indicated by the increase in extravascular fluid content after surgery, both colloid and crystalloid priming volumes were transferred to the extravascular space.

CONCLUSION

The use of colloid priming solutions in patients with mitral valve insufficiency leads to less fluid requirements and significantly reduced fluid shift in the interstitium. However, these changes are not associated with changes in haemodynamic parameters or short term outcome.

Pulmonary abnormalities after cardiac surgery are better explained by atelectasis than by increased permeability oedema

BACKGROUND

Cardiac surgery can be complicated by pulmonary abnormalities, but it is unclear how various manifestations interrelate.

METHODS

A prospective study in the intensive care unit was performed on 26 mechanically ventilated patients without cardiac failure within 3 h after elective cardiac surgery involving cardiopulmonary bypass. Oedema (extravascular lung water, EVLW) was measured by the thermal-dye technique and permeability by a dual radionuclide technique, yielding a pulmonary leak index (PLI). Radiographic, mechanical and gas exchange features were used to calculate the lung injury score (LIS), ranging between 0 and 4. Evidence for left lower lobe atelectasis was obtained from plain radiographs. The plasma colloid osmotic pressure (COP) was measured by an oncometer.

RESULTS

The EVLW (normal, <7 ml/kg) was elevated in 36% of patients and the PLI (normal, <14.1 x 10(-3)/min) in 44%, but the variables did not interrelate directly. Patients with a supranormal EVLW had a lower COP than patients with normal EVLW. The duration of mechanical ventilation was prolonged in patients (20%) with EVLW > 10 ml/kg. There was no difference in EVLW and PLI in patients with LIS < 1 and LIS > 1 (31% of patients). In patients with radiographic evidence for atelectasis (46%), the positive end-expiratory pressure and inspiratory O2 fraction to maintain oxygenation were higher than in those without.

CONCLUSIONS

After cardiac surgery, mild pulmonary oedema is relatively common, even in the absence of high filling pressures, and is mainly attributable to a low COP, irrespective of increased permeability in about one-half of patients. It may prolong mechanical ventilation at EVLW > 10 ml/kg. However, pulmonary radiographic and ventilatory abnormalities may result, at least in part, from atelectasis rather than increased permeability oedema.

Estimation of errors in determining intrathoracic blood volume using thermal dilution in pigs with acute lung injury and haemorrhage †

BACKGROUND

Global end diastolic volume (GEDV) has a constant and predictable relationship to intrathoracic blood volume (ITBV). The present study assesses the difference between ITBV derived from GEDV and ITBV measured directly in pigs with acute lung injury (ALI) and mild haemorrhage.

METHODS

We caused ALI in 12 anaesthetized pigs by i.v. injection of oleic acid and removed 10% of estimated blood volume. EVLW, GEDV, ITBV (COLD; Pulsion Medical Systems), Pa(o(2))/Fi(o(2)), lung compliance and haemodynamic variables were measured at baseline (time 0) and at 30 and 120 min. All animals were volume-resuscitated, followed by measurements at 180 min. A linear equation estimated from the 44 pairs of ITBV and GEDV values in 11 animals was applied iteratively to the four GEDV measurements in the 12th animal, enabling 48 comparisons between measured (ITBVm) and derived ITBV (ITBVd) to be made.

RESULTS

Increase in extravascular lung water index (EVLWi) was associated with significant pulmonary hypertension, worsening of oxygenation and compliance (repeated measures ANOVA; P<0.05). There was good within-subject correlation and agreement between ITBV(m) and ITBV(d) (r=0.72, mean bias 0.8 ml; sd 32 ml). Mean error in deriving ITBV from GEDV was 4.5%. (sd 4.2%; range 0.05-19%). There were no significant differences in errors in the presence of small (up to 10%) deficits in blood volume (F=1.0; P=0.41).

CONCLUSIONS

ITBV estimated by thermodilution alone is comparable to measurements made by the thermo-dye dilution technique in the presence of pulmonary hypertension and mild deficits in total blood volume.

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.

Changes in respiratory mechanics during cardiac surgery

We investigated the role of cardiopulmonary bypass (CPB) in compromised lung function associated with cardiac surgery. Low-frequency respiratory impedance (Zrs) was measured in patients undergoing cardiac surgery with (n = 30; CPB group) or without (n = 29; off-pump coronary artery bypass [OPCAB] group) CPB. Another group of CPB patients received dopamine (DA) (n = 12; CPB-DA group). Extravascular lung water was determined in five CPB subjects. Zrs was measured before skin incision and after chest closure. Airway resistance and inertance and tissue damping and elastance were determined from Zrs data. Airway resistance increased in the CPB group (74.9% +/- 20.8%; P < 0.05), whereas it did not change in the OPCAB group (11.8% +/- 7.9%; not significant) and even decreased in the CPB-DA patients (-40.6% +/- 9.2%; P < 0.05). Tissue damping increased in the CPB and OPCAB groups, whereas it remained constant in the CPB-DA patients. Significant increases in elastance were observed in all groups. There was no difference in extravascular lung water before and after CPB, suggesting that edema did not develop. These results indicate a significant and heterogeneous airway narrowing during CPB, which was counteracted by the administration of DA. The mild deterioration in tissue mechanics, reflecting partial closure of the airways, may be a consequence of the anesthesia itself.

IMPLICATIONS

We observed that cardiopulmonary bypass deteriorates lung function by inducing a heterogeneous airway constriction, whereas no such effects were observed in patients undergoing cardiac surgery without bypass. The impairment in parenchymal mechanics, which was obtained in both groups, may result from peripheral airway closure and/or be a consequence of mediator release.

Intrapulmonary shunt after cardiopulmonary bypass: the use of vital capacity maneuvers versus off-pump coronary artery bypass grafting

OBJECTIVES

It has been proved in human subjects and animals that atelectasis is a major cause of intrapulmonary shunting and hypoxemia after cardiopulmonary bypass. Animal studies suggest that shunting can be prevented entirely by a total vital capacity maneuver performed before termination of bypass. This study aimed to test this theory in human subjects and to evaluate possible advantages of off-pump coronary artery bypass grafting.

METHODS

Twenty-four patients scheduled for coronary artery bypass grafting were randomly assigned to receive no total vital capacity maneuver (control group, n = 12) or standard total vital capacity maneuvers (TVCM group, n = 12). Additionally, 12 consecutive patients undergoing off-pump coronary artery bypass grafting (off-pump group) were studied. Systemic and central hemodynamics, the pattern of breathing, and ventilatory mechanics were evaluated after induction of anesthesia, after sternotomy, after cardiopulmonary bypass and skin closure, and 4 hours after extubation.

RESULTS

The use of total vital capacity maneuvers reduced (P <.05) intrapulmonary shunting after termination of cardiopulmonary bypass. However, shunting increased (P <.05) in all groups (control group, 8.2% +/- 3.3% vs 25.6% +/- 8.1%; TVCM group, 8.7% +/- 3.4% vs 24.4% +/- 8.5%; and off-pump group, 7.8% +/- 2.8% vs 14.0% +/- 5.3%) after extubation, but the increase was significantly (P <.05) less pronounced in the off-pump group. Furthermore, pulmonary compliance decreased (P <.05) in all groups except the off-pump group after extubation. Duration of hospital and intensive care unit stay was significantly shorter (P <.05) in the off-pump group than in the other groups.

CONCLUSION

The development of intrapulmonary shunting and hypoxemia after coronary artery bypass grafting can be substantially reduced by performance of total vital capacity maneuvers while patients are mechanically ventilated. However, off-pump coronary artery bypass surgery is superior in preventing shunting and hypoxemia after bypass grafting in the immediate and early postoperative periods, probably leading to substantially shorter intensive care unit and hospital stays.

Assessment of cardiac output, intravascular volume status, and extravascular lung water by transpulmonary indicator dilution in critically ill neonates and infants

OBJECTIVE

To assess cardiac output, intrathoracic blood volume, global end-diastolic volume, and extravascular lung water in critically ill neonates and small infants using transpulmonary indicator dilution.

DESIGN

Prospective, observational, clinical study.

SETTING

Pediatric intensive care unit in a university hospital.

PARTICIPANTS

Critically ill neonates and small infants suffering from severe heart failure, respiratory failure, or sepsis (n = 10).

INTERVENTIONS

A total of 194 transpulmonary indicator dilution measurements were done. Global end-diastolic volume, intrathoracic blood volume, and stroke volume were measured and compared with standard hemodynamic parameters during the clinical course and before and after volume loading (16 +/- 3.7 mL/kg of 10% albumin solution) in 8 of 10 patients.

MEASUREMENTS AND MAIN RESULTS

A positive correlation was found for stroke volume index versus global end-diastolic volume (r = 0.76, p < 0.001) and intrathoracic blood volume (r = 0.56, p < 0.001). In contrast, no correlation was observed for stroke volume index versus central venous pressure. Volume loading resulted in significant increases in stroke volume index (p < 0.01), global end-diastolic volume (p < 0.01), and intrathoracic blood volume (p < 0.01); whereas central venous pressure, heart rate, mean arterial pressure, and extravascular lung water remained unchanged.

CONCLUSION

Transpulmonary indicator dilution enables measurement of cardiac output and intravascular volume status in critically ill neonates and infants at the bedside. The effects of volume loading on cardiac preload and effective change in stroke volume can be monitored by this technique, whereas central venous pressure was not indicative of changes in intravascular volume status.

Effects of normothermia versus hypothermia on extravascular lung water and serum cytokines during cardiopulmonary bypass: a randomized, controlled trial

OBJECTIVE

To evaluate the influence of perfusion temperature on the systemic effects of cardiopulmonary bypass (CPB), including extravascular lung water index (EVLWI), and serum cytokines.

DESIGN

Prospective, randomized, controlled study.

SETTING

Cardiothoracic intensive care unit of a university hospital.

PATIENTS

Patients undergoing elective coronary artery bypass grafting.

INTERVENTIONS

Twenty-one patients undergoing elective coronary artery bypass grafting were randomly assigned to receive either normothermic bypass (36 degrees C, n = 8) with intermittent antegrade warm blood cardioplegia (IAWBC), or hypothermic (32 degrees C, n = 13) CPB with cold crystalloid cardioplegia.

MEASUREMENTS AND MAIN RESULTS

Mean arterial pressure, heart rate, cardiac output, systemic vascular resistance, mean pulmonary arterial pressure, and pulmonary vascular resistance were determined at baseline, i.e., after induction of anesthesia but before sternal opening (T-1), at arrival in the intensive care unit (T0), and 4 hrs (T4), 8 hrs (T8), and 24 hrs (T24) after surgery. EVLWI, intrathoracic blood volume index (ITBVI), and EVLW/ITBV ratio were obtained by using thermal dye dilution utilizing an arterial thermistor-tipped fiberoptic catheter and were recorded at T-1, T0, T4, T8, and T24. Serial blood samples for cytokine measurements were obtained at each hemodynamic measurement time point. Before, during, and after CPB, there were no differences in the conventional hemodynamic measurements between the groups. There were no changes in EVLWI up to T8 in either group. Furthermore, no change in the ratio EVLW/ITBW was observed between the groups at any time, further indicating the absence of a change in pulmonary permeability. Plasma levels of interleukin-6, tumor necrosis factor-alpha, and interleukin-10 increased during and after CPB, independently of the perfusion temperature.

CONCLUSION

Normothermic CPB is not associated with additional inflammatory and related systemic adverse effects regarding cytokine production and EVLWI as compared with mild hypothermia. The potential temperature-dependent release of cytokines and subsequent inflammation has not been observed and normothermic CPB may be seen as a safe technique regarding this issue.

Changes in cardiac output and intrathoracic blood volume: a mathematical coupling of data?

BACKGROUND

Measurements of intrathoracic blood volume (ITBV) provide volumetric information about cardiac preload and are used to investigate the cause of alterations in cardiac output (CO). On the other hand, CO is required to calculate ITBV. Thus, concerns have been raised with respect to a mathematical coupling of data. The aim of this prospective, clinical study was to investigate whether a variation in CO induced by high-dose beta-blockade influences thermodilution measurements of ITBV in the absence of changes in intravascular volume in patients undergoing minimally invasive coronary artery bypass grafting.

METHODS

Sixteen patients undergoing elective minimally invasive direct coronay artery bypass (MIDCAB) surgery were studied. Transpulmonary thermodilution measurements of ITBV and CO were simultaneously performed before bypass grafting, during beta-blockade induced by high-dose esmolol and at the end of surgery.

RESULTS

During esmolol administration, CO significantly decreased by 33%, whereas ITBV remained unchanged compared to control values (876+/-46 ml m-2 during control versus 860+/-61 ml m-2 during esmolol administration). After the end of esmolol administration, CO significantly increased by 79%. Again, ITBV remained virtually unchanged (860+/-61 ml m-2 during esmolol administration versus 911+/-38 ml m-2 after esmolol administration).

CONCLUSIONS

The results of the present study demonstrate that substantial alterations in CO as a consequence of high-dose esmolol infusion are not associated with changes in ITBV. Because haemodynamic changes were induced by factors other than variation of preload, these findings suggest that changes in cardiac output do not influence thermodilution measurements of ITBV in this setting.

Influence of a vital capacity maneuver on pulmonary gas exchange after cardiopulmonary bypass

OBJECTIVE

To investigate the effect of a single, vital capacity breath (vital capacity maneuver [VCM]), administered at the end of cardiopulmonary bypass (CPB), on pulmonary gas exchange in patients undergoing coronary artery bypass graft surgery.

DESIGN

Prospective, randomized, double-blind study.

SETTING

University-affiliated hospital.

PARTICIPANTS

Forty patients scheduled for elective coronary artery bypass graft surgery and early tracheal extubation.

INTERVENTIONS

Patients were randomized to 1 of 2 groups. VCM patients received a VCM at the conclusion of CPB. Control patients received no VCM.

MEASUREMENTS AND MAIN RESULTS

Intrapulmonary shunt (Q(S)/Q(T)), arterial oxygenation (PaO2), and alveolar-arterial oxygen gradients (P(A-a)O2) were measured after induction of anesthesia, CPB, intensive care unit (ICU) arrival, and extubation. The duration of postoperative intubation was recorded for each group. Q(S)/Q(T) increased significantly 30 minutes after CPB in the control group (15.7 +/- 1.8% to 27.4 +/- 2.6%; p = 0.01). In the VCM group, a small decrease in Q(S)/Q(T) occurred (16.1 +/- 2.0% to 14.9 +/- 2.0%). After ICU arrival and extubation, no significant difference in Q(S)/Q(T) existed between the 2 groups. With the exception of a higher P(A-a)O2 in the control group at induction of anesthesia, no differences in PaO2 or P(A-a)O2 were present between the 2 groups at any measurement interval. Patients who received a VCM were extubated earlier than the control group (6.5 +/- 2.1 hours v 9.4 +/- 4.2 hours; p = 0.01).

CONCLUSION

The use of a VCM prevented an increase in Q(S)/Q(T) from occurring in the operating room. Although a VCM did not influence pulmonary gas exchange in the ICU, its application in the operating room appears to exert a beneficial effect on tracheal extubation times after cardiac surgery.

Methylprednisolone does not benefit patients undergoing coronary artery bypass grafting and early tracheal extubation

OBJECTIVE

We sought to determine whether methylprednisolone, when administered to patients undergoing cardiac surgery, is able to ward off the detrimental hemodynamic and pulmonary alterations associated with cardiopulmonary bypass.

METHODS

After institutional review board approval and informed consent was obtained, 90 patients scheduled for elective cardiac surgery were randomized to 1 of 3 groups. Group 30MP patients received 30 mg/kg intravenous methylprednisolone during sternotomy and 30 mg/kg during initiation of cardiopulmonary bypass, group 15MP patients received 15 mg/kg methylprednisolone at the same 2 times, and group NS patients received similar volumes of isotonic sodium chloride solution at the same 2 times. Perioperative care was standardized, and all caregivers were blinded to treatment group. Various hemodynamic and pulmonary measurements were obtained perioperatively, as well as fluid balance, weight, peak postoperative blood glucose level, and tracheal extubation time.

RESULTS

Demographic and clinical characteristics of patients and intraoperative data were similar among the 3 groups. Patients receiving methylprednisolone (either dose) exhibited significantly increased cardiac index (P =.0006), significantly decreased systemic vascular resistance (P =.0005), and significantly increased shunt flow (P =.0020) during the immediate postoperative period. All 3 groups exhibited significant increases in alveolar-arterial oxygen gradient (P <.0001), significant decreases in dynamic lung compliance (P <.0001), and significant decreases in static lung compliance (P <.0001) during the immediate postoperative period, with no differences between groups. Perioperative fluid balance and weights were similar between groups. A statistically significant difference in peak postoperative blood glucose level existed (P =.016) among group NS (234 +/- 96 mg/dL), group 15MP (292 +/- 93 mg/dL), and group 30MP (311 +/- 90 mg/dL). In patients extubated within 12 hours of intensive care unit arrival, a statistically significant difference in extubation times existed (P =.025) between group NS (5.7 +/- 2.3 hours), group 15MP (5.9 +/- 2.2 hours), and group 30MP (7.5 +/- 2.7 hours).

CONCLUSIONS

Methylprednisolone, as used in this investigation, offers no clinical benefits to patients undergoing elective coronary artery bypass grafting with cardiopulmonary bypass and may in fact be detrimental by initiating postoperative hyperglycemia and possibly hindering early postoperative tracheal extubation for undetermined reasons.

Protective ventilation attenuates postoperative pulmonary dysfunction in patients undergoing cardiopulmonary bypass

OBJECTIVE

To ascertain if protective ventilation can attenuate the damaging postoperative pulmonary effects of cardiopulmonary bypass (increases in airway pressure, decreases in lung compliance, and increases in shunt).

DESIGN

Prospective, randomized clinical trial.

SETTING

Single university hospital.

PARTICIPANTS

Twenty-five patients undergoing elective coronary artery bypass graft procedure and early extubation.

INTERVENTIONS

Thirteen patients received conventional mechanical ventilation (CV; respiratory rate, 8 breaths/min; tidal volume, 12 mL/kg; fraction of inspired oxygen [FIO2], 1.0; positive end-expiratory pressure [PEEP], +5), and 12 patients received protective mechanical ventilation (PV; respiratory rate, 16 breaths/min; tidal volume, 6 mL/kg; FIO2, 1.0; PEEP, +5). Perioperative anesthetic and surgical management were standardized. Various pulmonary parameters were determined twice perioperatively: 10 minutes after intubation and 60 minutes after arrival in the intensive care unit.

MEASUREMENTS AND MAIN RESULTS

The mean postoperative increase in peak airway pressure in group CV was significantly larger than the mean postoperative increase in peak airway pressure in group PV (7.1 v 2.4 cm H2O; p < 0.001). Group CV experienced significant postoperative increases in plateau airway pressure (p = 0.007), but group PV did not (p = 0.644). The mean postoperative decrease in dynamic lung compliance in group CV was significantly larger than the mean postoperative decrease in dynamic lung compliance in group PV (14.9 v 5.5 mL/cm H2O; p = 0.002). Group CV experienced significant postoperative decreases in static lung compliance (p = 0.014), but group PV did not (p = 0.645). Group CV experienced significant postoperative increases in shunt (15.5% to 21.4%; p = 0.021), but group PV did not (18.4% to 21.2%; p = 0.265).

CONCLUSIONS

Data indicate that protective ventilation decreases pulmonary damage caused by mechanical ventilation in normal and abnormal lungs. The results of this investigation indicate that protective ventilation may also help attenuate the postoperative pulmonary dysfunction (increases in airway pressure, decreases in lung compliance, and increases in shunt) commonly seen in patients after exposure to cardiopulmonary bypass.

Limitations of the transpulmonary indicator dilution method for assessment of preload changes in critically ill patients with reduced left ventricular function

OBJECTIVE

We examined whether intrathoracic blood volume (ITBV) and total end-diastolic volume (TEDV), determined by the transpulmonary indicator dilution technique, adequately reflect preload changes during fluid administration in patients with reduced left ventricular function.

DESIGN

A prospective, controlled, clinical study.

SETTING

Medical intensive care unit in a university hospital.

PATIENTS

A total of 18 sedated, mechanically ventilated, and moderately hypovolemic intensive care unit patients, eight with reduced left ventricular function (ejection fraction area, 24.9+/-8.0%, group A), ten with normal left ventricular function (ejection fraction area, 57.6+/-13.0%, group B).

INTERVENTIONS

Continuous crystalloid infusion over 120 mins at a constant rate of 8 mL/kg/30 mins.

MEASUREMENTS AND MAIN RESULTS

Stroke volume index, central venous pressure, pulmonary artery occlusion pressure (PAOP), TEDV, and ITBV were determined simultaneously at baseline and serially every 30 mins during continuous crystalloid infusion. A similar series of measurements was obtained during control conditions. Performance of various variables during fluid administration was assessed by time correlation analysis. Sensitivity for various variables defined as the ability to detect increasing amounts of administered fluid in individual patients was calculated. All examined variables increased during fluid administration and were unaffected during the control period. Mean time correlation (r2) was significantly higher for pressure monitoring (central venous pressure, r2 = 0.8281; PAOP, r2 = 0.5476) than for volume variables (TEDV, r2 = 0.0256; ITBV, r2 = 0.0729) in group A and was high for all variables in group B (central venous pressure, r2 = 0.7056; PAOP, r2 = 0.6241; TEDV, r2 = 0.49; ITBV, r2 = 0.4225). Sensitivities for central venous pressure, PAOP, TEDV, and ITBV after 120 min were 63%, 75%, 25%, and 25% in group A and 90%, 100%, 60%, and 60% in group B, respectively.

CONCLUSION

This study demonstrates limitations of the transpulmonary indicator dilution technique for monitoring of intravascular volume in patients with reduced left ventricular function.

Intrathoracic fluid volumes and pulmonary function during orthotopic liver transplantation

BACKGROUND

Impaired pulmonary function is a frequent finding in patients undergoing orthotopic liver transplantation (OLT). Experimental data suggest an essential contribution of splanchnic ischemia and reperfusion as a result of intraoperative volume shifts, i.e., the accumulation of extravascular lung water (EVLW). Increases of intrathoracic blood volume (ITBV) and pulmonary blood volume (PBV) might additionally influence pulmonary capillary fluid filtration. The main objective of this study was to determine the intrathoracic volume changes during OLT and to test whether there were any relationships between intra- and extravascular volume shifts and pulmonary function, as determined by the calculation of venous admixture (QS/QT) and alveolar-arterial oxygen gradient (AaDO2).

METHODS

Twenty-five patients undergoing OLT were studied. Using the transpulmonary double indicator dilution method, ITBV, PBV, and EVLW were determined from the mean transit times and exponential decay times of the indocyanine green and the thermal indicator curves recorded simultaneously with a fiberoptic catheter in the descending aorta. Recordings were made after induction of anesthesia, at the end of the anhepatic stage, immediately after reperfusion, and 1 and 4 h postoperatively.

RESULTS

Significant increases in QS/QT related to changes of ITBV were observed after reperfusion. Only a minor impact on AaDO2 was perceived. EVLW remained constant during the study period.

CONCLUSIONS

Postreperfusion increases of ITBV influence pulmonary function, as demonstrated by the increase in QS/QT. However, they need not be associated with greater EVLW levels, and impact on oxygenation is less severe than assumed. Hence, sufficient mechanisms protecting oxygenation and stalling increased EVLW seem to be present during uncomplicated human OLT.

The nitric oxide synthase cofactor tetrahydrobiopterin reduces allograft ischemia-reperfusion injury after lung transplantation

OBJECTIVE

Exogenous nitric oxide reduces ischemia-reperfusion injury after solid organ transplantation. Tetrahydrobiopterin, an essential cofactor for nitric oxide synthases, may restore impaired endothelium-dependent nitric oxide synthesis. We evaluated whether tetrahydrobiopterin administration to the recipient attenuates lung reperfusion injury after transplantation in swine.

METHODS

Unilateral left lung transplantation was performed in 15 weight-matched pigs (24-31 kg). Donor lungs were flushed with 1.5 L cold (1 degrees C) low-potassium-dextran solution and preserved for 20 hours. Group I animals served as controls. Group II and III animals were treated with a bolus of tetrahydrobiopterin (20 mg/kg). In addition, in group III a continuous infusion of tetrahydrobiopterin (10 mg/kg per hour over 5 hours) was given. One hour after reperfusion, the recipient right lung was occluded. Cyclic guanosine monophosphate levels were measured in the pulmonary venous and central venous blood. Extravascular lung water index, hemodynamic variables, lipid peroxidation, and neutrophil migration to the allograft were assessed.

RESULTS

In group III a significant reduction of extravascular lung water was noted in comparison with the controls (P =.0047). Lipid peroxidation in lung allograft tissue was significantly reduced in group II (P =.0021) and group III ( P =. 0077) in comparison with group I. Pulmonary venous levels of cyclic guanosine monophosphate increased up to 23 +/- 1 pmol/mL at 5 hours in group II and up to 40 +/- 1 pmol/mL in group III (group I, 4.1 +/- 0.5 pmol/mL [I vs III]; P <.001), whereas central venous levels of cyclic guanosine monophosphate were unchanged in all groups.

CONCLUSION

Tetrahydrobiopterin administration during lung allograft reperfusion may reduce posttransplantation lung edema and oxygen-derived free radical injury in the graft. This effect is mediated by local enhancement of the nitric oxide/cyclic guanosine monophosphate pathway.

8-Br-cGMP is superior to prostaglandin E1 for lung preservation

BACKGROUND

Substitution of the nitric oxide (NO) pathway reduces ischemia/reperfusion injury after lung transplantation. 8-Br-cGMP is a membrane-permeable analogue of cGMP, the second messenger of NO. In this study, we evaluated the effect of administration of 8-Br-cGMP in the flush solution on early graft function.

METHODS

Unilateral left lung transplantation was performed in 10 weight-matched pairs of outbred pigs (24 to 31 kg). Donor lungs were flushed with 1.5 L cold (1 degree C) low potassium dextrane (LPD) solution and preserved for 20 hours. In group I (n = 5), 8-Br-cGMP (1 mg/kg) was added to the flush solution. In group II (n = 5), 8 microg/kg prostaglandin E1 (PGE1) was injected into the pulmonary artery (PA) before flush. One hour after reperfusion, the recipients' contralateral right PA and bronchus were ligated to assess graft function only. cGMP levels in the PA and pulmonary vein were measured. Extravascular lung water index (EVLWI), pulmonary vascular resistance, mean PA pressure, and gas exchange (PaO2) were assessed during a 5-hour observation period. Lipid peroxidation (thiobarbituric acid-reactive substance) and neutrophil migration to the allograft (myeloperoxidase activity) were measured at the end of the assessment.

RESULTS

In group I, a significant reduction of EVLWI (group I, 6.7 +/- 1.0 mL/kg vs group II, 10.1 +/- 0.6 ml/kg after 2 hours of reperfusion; p = 0.022), TBARS (group I, 65.6 +/- 10.0 pmol/g vs group II, 120.8 +/- 7.2 pmol/g, p = 0.0039), and MPO activity (group I, 0.8 +/- 0.1 change in optical density, (deltaOD)/mg/min vs group II, 1.7 +/- 0.3 deltaOD/mg/min, p = 0.036) was noted in comparison with group II. PaO2 levels tended to be higher in cGMP-treated animals, but the changes were not significant. Hemodynamic parameters did not differ between groups.

CONCLUSIONS

In this large animal model of lung allograft ischemia/reperfusion injury, 8-Br-cGMP as additive to the flush solution improves posttransplant lung edema, lipid peroxidation, and neutrophil migration to the allograft. This effect is not attributable to improved flush by vasodilation, as we compared 8-Br-cGMP with PGE1 given before flush in control animals.

Time-course of impairment of respiratory mechanics after cardiac surgery and cardiopulmonary bypass

OBJECTIVE

Cardiopulmonary bypass (CPB) is associated with abnormalities of lung function characterized by an increase in static elastance of the respiratory system. We examined the following: a) the effects of CPB on the total inspiratory volume-pressure (V-P) relationship of the respiratory system; b) the relative contribution of the chest wall and lung to the impairment of respiratory system mechanics; and c) the time-course of such impairment.

DESIGN

Prospective, interventional study.

SETTING

Surgical and medical intensive care units in a teaching hospital.

PATIENTS

Eight adult patients scheduled for elective open heart surgery to correct valvular dysfunction.

INTERVENTIONS

V-P curves (interrupter technique) of the respiratory system were partitioned between the chest wall and lung by measurements of esophageal pressure. Measurements were obtained before sternotomy (control), immediately after, 4 hrs after, and 7 hrs after separation from CPB.

MEASUREMENTS AND MAIN RESULTS

Control V-P relationships of the respiratory system and lung showed lower inflection points (Pflex) at pressure values of 5.9+/-2.3 and 4.3+/-2.5 cm H2O, respectively. Immediately after and 4 hrs after separation from CPB, both curves had sigmoid shapes because of lower Pflex and formation of upper inflection (UIP) points. The pressures corresponding to the Pflex increased significantly (p < .001) by 56%+/-3% and 78%+/-4%, whereas the UIP corresponded to a pressure value of 42.34+/-8.5 and 35.6+/-7.8 cm H2O in the respiratory system and lung, respectively. A linear V-P relationship of the chest wall was observed during the control condition and after separation from CPB. Four hours later, no further increases in the pressure values corresponding to Pflex were observed on the inspiratory V-P curves of the respiratory system and lung, whereas the UIP occurred at a pressure of 35.6+/-9.1 and 29.7+/-8.4 cm H2O, respectively. A UIP was present on the V-P curve of the chest wall at a volume of 0.77+/-0.02 L. Seven hours after separation from CPB, the inspiratory V-P curves of the respiratory system, chest wall, and lung returned to normal.

CONCLUSIONS

Sternotomy and CPB produced immediate changes in lung mechanics. Chest wall mechanics were affected only 4 hrs after sternotomy. Seven hours after disconnection from CPB, all mechanics had returned to normal.

Increased intrapulmonary oxygen consumption in mechanically ventilated patients with pneumonia

Pulmonary oxygen consumption (V(O2)pulm) is believed to be increased in patients with lung infection. In the present study, VO2pulm was estimated from the difference between total oxygen consumption measured with indirect calorimetry (V(O2)cal) and oxygen consumption assessed with the reverse Fick method (V(O2)Fick). Seventy-five patients requiring mechanical ventilation were included, and were divided for analysis into two groups according to the existence (n = 41) or absence (n = 34) of pneumonia. V(O2)pulm was correlated with various parameters of impaired lung function. To assess the metabolic function of the lung, the differences in lactate and glucose concentrations at different arterial-mixed venous concentrations were determined and transpulmonary lactate flux as well as glucose flux was calculated. As compared with V(O2)pulm in patients without pneumonia (19.4 +/- 1.2 ml/ min/m2), V(O2)pulm was significantly increased in patients with pneumonia (50.7 +/- 1.7 ml/min/m2 (p < 0.001). For intrapatient measurements of V(O2)pulm, a sufficient reproducibility was achieved. V(O2)pulm increased with the lung injury score, number of afflicted lobes, venous admixture, the transpulmonary lactate flux, and the transpulmonary glucose flux, respectively. We speculate that the increased V(O2)pulm of infected lungs is due to different mechanisms, including increased oxidative metabolism by essentially extrapulmonary structures such as neutrophils and macrophages, as well as by changes in the metabolic function of lung tissue itself.

Donor and recipient treatment with the Lazaroid U-74006F do not improve post-transplant lung function in swine

OBJECTIVE

U-74006F is the only Lazaroid which is currently in clinical use. A number of experimental studies demonstrate that Lazaroids reduce ischemia/reperfusion injury in various organ systems. We evaluated the effect of U-74006F on reperfusion injury in a large animal model of lung allo-transplantation.

METHODS

Two different treatment modalities were evaluated and compared with corresponding control groups. Unilateral left lung transplantation was performed in 21 weight-matched pigs (24-31 kg). Donor lungs were flushed with 1.51 cold (1 degrees C) LPD solution and preserved for 20 h. In group I (n = 5), donor animals were pretreated with U-74006F (10 mg/ kg i.v.) 20 min before harvest. In addition U-74006F was added to the flush solution (10 mg/l). In group III (n = 6), the Lazaroid was given to the donor before flush and to the recipient before reperfusion (3 mg/kg i.v.). Group II and IV (n = 5) served as control. One hour after reperfusion, the recipient contralateral right pulmonary artery and bronchus were ligated to assess graft function only. Extravascular lung water index (EVLWI), mean pulmonary artery pressure, cardiac output, and gas exchange were assessed during a 5 h observation period. Lipid peroxidation (TBARS) and neutrophil migration (MPO activity) were measured at the end of the assessment in lung allograft tissue.

RESULTS

A significant change of TBARS concentration was shown in group III (group III 78.7+/-4.6 pmol/g vs. group IV 120.8+/-7.2 pmol/g (P = 0.0065) normal lung tissue 41.3+/-4.2 pmol/g). MPO activity was reduced in group III 3.74+/-0.25 deltaOD/mg per min vs. group IV 4.97+/-0.26 deltaOD/mg per min (P = 0.027), normal lung tissue 1.04+/-0.27 deltaOD/mg per min). Pulmonary hemodynamics and gas exchange after reperfusion did not differ between groups. In group I and III, a tendency towards a reduced EVLWI was noted.

CONCLUSION

We conclude that combined treatment of donor and recipient with U-74006F reduces free radical mediated injury in the allograft. However, this intervention did not result in a significant reduction of post-transplant lung edema or improvement of pulmonary hemodynamics. Donor pretreatment alone did not improve lung allograft reperfusion injury. These results indicate that the benefit of U-74006F is too small to consider clinical application in lung transplantation.

Assessment of cardiovascular volume status by transoesophageal echocardiography and dye dilution during cardiac surgery

Conventional evaluation of cardiovascular volume status by filling pressures is unreliable in critically ill patients. Measurements of left ventricular end diastolic area index by transoesophageal echocardiography and of intrathoracic blood volume index by dye indicator dilution are new approaches to this problem. In this study, different indices of cardiovascular volume status were analysed to define their relation during the pronounced haemodynamic changes associated with systemic inflammation after cardiopulmonary bypass. Correlations were performed with left ventricular end diastolic area index, intrathoracic blood volume index, central venous pressure (CVP) and pulmonary capillary wedge pressure (PCWP). Data from 15 patients receiving coronary artery bypass grafts were compared after induction of anaesthesia and in the intensive care unit. Spearman's correlation coefficient for perioperative absolute changes in left ventricular end diastolic area index and intrathoracic blood volume index was 0.87 (P < 0.05). However, an increase in intrathoracic blood volume index by 125 mL m-2 was necessary to maintain a baseline left ventricular end diastolic area index. Absolute values of all variables varied widely, with the only significant correlation found between CVP and PCWP. Changes in CVP and PCWP did not correlate with changes in left ventricular end diastolic area index or intrathoracic blood volume index. Provided simultaneous baseline measurements are available and a supranormal intrathoracic blood volume index compensates for the haemodynamic changes in systemic inflammation, left ventricular end diastolic area index and intrathoracic blood volume index may substitute for each other during the evaluation of cardiovascular volume status in patients with stable cardiac function.

Effect of CPAP during cardiopulmonary bypass on postoperative lung function. An experimental study

BACKGROUND

Respiratory failure secondary to cardiopulmonary bypass (CPB) remains a major complication after cardiac surgery. We tested the hypothesis that post-CPB lung function impairment can be prevented by continuous positive airway pressure (CPAP) applied during the CPB.

METHODS

In 6 pigs, CPAP with 5 cmH2O pressure was applied during CPB. Six other pigs served as control, i.e. the lungs were open to the atmosphere during CPB. After median sternotomy, the right atrial appendage as well as the ascending aorta were cannulated. The total CPB duration was 90 min with 45 min cardioplegic arrest. Ventilation-perfusion distribution was measured with the multiple inert gas elimination technique and atelectasis by CT-scanning.

RESULTS

Large atelectasis appeared after CPB, corresponding to 14.5% +/- 5.5 (percent of the total lung area) in the CPAP group and 18.7% +/- 5.2 in the controls (P = 0.20). Intrapulmonary shunt increased and PaO2 decreased after the CPB in both groups.

CONCLUSIONS

We conclude that in this pig model post-CPB atelectasis is not effectively prevented by CPAP applied during CPB.

Cardiac output measurement by transpulmonary versus conventional thermodilution technique in intensive care patients after coronary artery bypass grafting

OBJECTIVE

The aim of the present study was to evaluate the correlation, accuracy, and precision of transpulmonary thermodilution cardiac output (CO) measurement. For this purpose, this technique was compared with the clinical gold standard, the CO measurement by pulmonary artery catheter in patients after coronary artery bypass grafting (CABG).

DESIGN

A prospective clinical study.

SETTING

A university medical center.

PARTICIPANTS

Seventy-five patients in an intensive care unit (ICU) after CABG.

INTERVENTIONS

Standard (SCO) and transpulmonary thermodilution CO measurement (TPCO) measurements were simultaneously performed in triplicate by central venous injection of cooled saline solution. All variables were recorded at five different time points of measurement during weaning from mechanical ventilation.

MEASUREMENTS AND MAIN RESULTS

CO measurements yielded 375 data pairs. SCO ranged from 2.0 to 10.2 L/min, and TPCO from 1.3 to 10.6 L/min. During the entire observation period, TPCO measurements tended to yield relatively high values, whereas SCO measurements resulted in lower values. Correlation between TPCO and SCO measurements was significant (r = 0.73; p < 0.05), accompanied by an accuracy with a bias of 0.456 L/min (7.3%) and a precision of 1.156 L/min (18.5%).

CONCLUSION

In most patients, TPCO measurement will not replace the conventional technique by pulmonary artery catheter, but in some patients it offers an attractive, reliable, and safe method to determine CO.

Intrathoracic and pulmonary blood volume during CO2-pneumoperitoneum in humans

BACKGROUND

Induction of CO2-pneumoperitoneum may have significant effects on systemic and pulmonary haemodynamics. We hypothesized that intrathoracic (ITBV) and pulmonary blood volume (PBV) are affected during intra-abdominal CO2-insufflation, which may be pronounced by positional changes of the patient.

METHODS

Sixteen anaesthetized patients were studied before, during and after CO2-pneumoperitoneum for laparoscopic cholecystectomy. A dye indicator technique was used to assess ITBV and PBV. In addition, gas exchange and haemodynamics were recorded.

RESULTS

In the supine position, induction of CO2-pneumoperitoneum had no effects on ITBV, PBV and cardiac output. Mean systemic arterial pressure increased from 10.9 +/- 1.5 kPa (82 +/- 11 mmHg) to 12.7 +/- 1.5 kPa (95 +/- 11 mmHg, P < 0.01). In the reverse Trendelenburg position ITBV decreased from 19.8 +/- 5.1 ml.kg-1 to 16.7 +/- 3.7 ml.kg-1 (P < 0.05) during CO2-insufflation, but increased to control values after 20 min. PBV decreased from 4.2 +/- 1.2 ml.kg-1 to 3.4 +/- 1.1 ml.kg (P < 0.05) and remained decreased during CO2-pneumoperitoneum. Calculated venous admixture was unchanged throughout the study. Deflation of CO2-pneumoperitoneum increased ITBV (22.4 +/- 5.2 ml.kg-1, P < 0.05) and cardiac output above control values.

CONCLUSIONS

In anaesthetized-paralyzed patients in the reverse Trendelenburg position intra-abdominal CO2-insufflation is associated with significant alterations of ITBV and PBV. The release of CO2-pneumoperitoneum is associated with a re-distribution of blood into the thorax.

Pulmonary effects of methylprednisolone in patients undergoing coronary artery bypass grafting and early tracheal extubation

Numerous clinical studies suggest that methylprednisolone may facilitate early tracheal extubation after cardiac surgery, yet no investigation has rigorously examined the use of the drug in this setting. In this prospective, randomized, double-blind, placebo-controlled study, we examined the pulmonary effects of methylprednisolone in patients undergoing coronary artery bypass grafting (CABG) and early tracheal extubation. Sixty patients undergoing elective CABG and early tracheal extubation were randomized into two groups. Group MP patients received i.v. methylprednisolone (30 mg/kg during sternotomy and 30 mg/kg during initiation of cardiopulmonary bypass) and Group NS patients received i.v. placebo at the same two times. Perioperative management was standardized. Alveolar-arterial (A-a) oxygen gradient, lung compliance, shunt, and dead space were determined four times perioperatively. Postoperative tracheal extubation was accomplished at the earliest appropriate time. Both groups exhibited significant postoperative increases in A-a oxygen gradient and shunt (P < 0.000001 for each group) and significant postoperative decreases in dynamic lung compliance (P < 0.000001 for each group). Patients in Group MP exhibited significantly larger increases in postoperative A-a oxygen gradient (P = 0.001) and shunt (P = 0.001) compared with patients in Group NS. Postoperative alterations in dynamic lung compliance, static lung compliance, and dead space were not statistically significant between the groups. The time to postoperative tracheal extubation was prolonged in Group MP patients compared with Group NS patients (769 +/- 294 vs 604 +/- 315 min, respectively; P = 0.05). Methylprednisolone was associated with larger increases in postoperative A-a oxygen gradient and shunt, was unable to prevent postoperative decreases in lung compliance, and prolonged extubation time, which indicate that use of the drug may hinder early tracheal extubation in patients after cardiac surgery.

IMPLICATIONS

Traditionally, methylprednisolone has been administered to patients undergoing cardiac surgery to decrease postoperative pulmonary dysfunction. This study revealed that the drug is associated with larger increases in postoperative alveolar-arterial oxygen gradient and shunt and prolonged tracheal extubation time in patients undergoing coronary artery bypass grafting, which indicate that use of the drug may hinder early tracheal extubation.

Effect of soluble complement receptor type 1 on reperfusion edema and neutrophil migration after lung allotransplantation in swine

OBJECTIVE

Soluble complement receptor type 1 inhibits complement activation by blocking C3 and C5 convertases of the classical and alternative pathways. We evaluated the effect of soluble complement receptor type 1 on lung allograft reperfusion injury.

METHODS

Left lung transplantation was performed in 13 weight-matched pigs (25 to 31 kg) after prolonged preservation (20 hours at 1 degree C). One hour after reperfusion the recipient contralateral right lung was excluded to assess graft function only. Complement activity and C3a levels were measured after reperfusion and at the end of the assessment. Extravascular lung water index, intrathoracic blood volume, and cardiac output were assessed during a 5-hour observation period. Gas exchange and hemodynamics were monitored. At the end of the 5-hour assessment period, myeloperoxidase assay and bronchoalveolar lavage were performed to assess neutrophil migration, and C5b-9 (membrane attack complex) deposits in the allograft were detected by immunohistochemistry. Two groups were studied. In group II (n = 6) recipient animals were treated with soluble complement receptor type 1 (15 mg/kg) 15 minutes before reperfusion. Group I (n = 7) served as the control group.

RESULTS

Serum complement activity was completely inhibited in group II. In contrast to group I, C5b-9 complexes were not detected in group II allograft tissue samples. C3a was reduced to normal levels in group II (p = 0.00005). Extravascular lung water index was higher in group I animals throughout the assessment period (p = 0.035). No significant difference in allograft myeloperoxidase activity (p = 0.10) and polymorphonuclear leukocyte count of the bronchoalveolar lavage fluid (p = 0.057) was detected.

CONCLUSION

Inhibition of the complement system by soluble complement receptor type 1 blocks local complement activation in the allograft and reduces posttransplantation reperfusion edema but does not improve hemodynamic parameters.

Bedside determination of fluid accumulation after cardiac surgery using segmental bioelectrical impedance

OBJECTIVES

Bioelectrical impedance analysis (BIA) is based on the physical property of tissues to conduct electrical currents, impedance being inversely related to tissue fluid content. At high frequency, the electrical current flows across both intracellular and extracellular pathways, making the assessment of fat-free mass possible while a low-frequency current flows through the extracellular space. Similarly, segmental BIA may be used to assess segmental body fluid repartition. The aim of this study was to assess fluid accumulation after cardiac surgery by multiple frequency segmental BIA.

DESIGN

Observational, clinical study.

SETTING

A 17-bed, surgical intensive care unit in a university hospital.

PATIENTS

Twenty-six patients before and after open-heart surgery with cardiopulmonary bypass.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

After surgery, fluid accumulation resulted in a decrease in whole-body and segmental bioelectrical impedance in the arm and in the trunk. There was a good correlation between the fluid accumulation measured by fluid balance and by whole-body or segmental impedance changes. The major part (71%) of fluid accumulation occurred in the trunk. Multiple frequency measurements did not indicate a fluid shift between the intra- and extracellular compartments.

CONCLUSION

Cardiac surgery produced a significant decrease in segmental trunk BIA, reflecting fluid accumulation at the trunk level.

Effect of a short period of warm ischemia after cold preservation on reperfusion injury in lung allotransplantation

OBJECTIVE

A short period of warm ischemia during lung allograft implantation is inevitable. We studied the effect of 2 h of warm ischemia before implantation after 18 h of cold preservation on reperfusion edema and pulmonary hemodynamics in a large animal model.

METHODS

Left lung transplantation was performed in ten weight-matched pigs (25-31 kg). Donor lungs were flushed with 1.5 l cold (1 degree C) LPD solution and preserved for 20 h. In Group I (n = 5) the grafts were preserved for 20 h at 1 degree C and topically cooled with ice slush during implantation until reperfusion. In Group II (n = 5) lungs were stored at 1 degree C for 18 h followed by 2 h preservation at room temperature (20 degrees C). Topical cooling was not used during implantation. At 1 h after reperfusion the recipient contralateral right pulmonary artery and bronchus were ligated to assess graft function only. Extravascular lung water index (EVLWI), intrathoracic blood volume (ITBV), mean pulmonary artery pressure (PAP) and cardiac output (CO) were assessed during a 4 h observation period. Quantitative myeloperoxidase (MPO) activity and thiobarbituric acid-reactive substance (TBARS) levels as an indicator for lipid peroxidation were determined in allograft tissue samples taken 5 h after reperfusion.

RESULTS

In Group II a tendency to improved pulmonary vascular resistance and cardiac output was noted. Surprisingly, lung edema, assessed by EVLWI, did not increase in animals with warm ischemia. Even a tendency to a reduced EVLWI was noted. However, differences between groups did not reach statistical significance. Gas exchange did not differ statistically significant between groups.

CONCLUSION

Our results indicate that a short period of warm ischemia before reperfusion does not lead to increased pulmonary edema. In animals with a short period of warm ischemia before reperfusion, even a tendency to reduced posttransplant lung reperfusion injury was noted. In this model, topical graft cooling during lung implantation did not improve posttransplant graft function.

Changes in intrathoracic fluid volumes during weaning from mechanical ventilation in patients after coronary artery bypass grafting

PURPOSE

Although it is known that weaning from mechanical ventilation is associated with alterations in intrathoracic pressure, lung volume, and venous return, changes in intrathoracic fluid volumes during weaning are not reported. Especially in patients with impaired cardiac function, the development of pulmonary edema during weaning has been described. Thus, we investigated changes in intrathoracic fluid volumes in patients after coronary artery bypass grafting after changing the ventilatory pattern from mechanical to spontaneous ventilation.

MATERIALS AND METHODS

Intrathoracic blood volume index (ITBVI), pulmonary blood volume index (PBVI), and extravascular lung water (EVLW) were calculated during mechanical ventilation (T1), T-piece breathing (T2), and spontaneous breathing after extubation of the trachea (T3) in 72 consecutive patients after coronary artery bypass grafting using a combined dye-thermal dilution method.

RESULTS

Changing from mechanical ventilation to T-piece breathing resulted in an increase in ITBVI from 880 +/- 22 mL/m2 to 970 +/- 22 mL/m2 (P < .01), and in PBVI from 162 +/- 6 mL/m2 to 173 +/- 6 mL/m2 (P < .01). After extubation of the trachea, both parameters decreased again (ITBVI, 879 +/- 20 mL/m2; PBVI, 160 +/- 7 mL/m2). EVLW remained unchanged after transition to T-piece breathing (T1, 5.8 +/- 0.3 mL/kg; T2, 6.0 +/- 0.3 mL/kg), but increased to 6.6 +/- 0.5 mL/kg (P < .01) after extubation of the trachea. However, pathological values of EVLW were not observed.

CONCLUSIONS

In patients after coronary artery bypass grafting, changes in intrathoracic intravascular fluid volumes during weaning are restricted to the period of T-piece breathing and reflect an increased venous return. The maintenance of EVLW in the normal range during weaning indicates that cardiac function was matched to this elevated preload.

Effects of continuous (CPAP) and bi-level positive airway pressure (BiPAP) on extravascular lung water after extubation of the trachea in patients following coronary artery bypass grafting

OBJECTIVE

To evaluate the effects of continuous positive airway pressure (CPAP) and bi-level positive airway pressure (Bi-PAP) on extravascular lung water during weaning from mechanical ventilation in patients following coronary artery bypass grafting.

DESIGN

Prospective, randomized clinical study.

SETTING

Intensive care unit at a university hospital.

PATIENTS

Seventy-five patients following coronary artery bypass grafting.

INTERVENTIONS

After extubation of the trachea, patients were treated for 30 min with CPAP via face mask (n = 25), with nasal BiPAP (n = 25), or with oxygen administration via nasal cannula combined with routine chest physiotherapy (RCP) for 10 min (n = 25).

MEASUREMENTS AND RESULTS

Extravascular lung water (EVLW), pulmonary blood volume index (PBVI) and cardiac index (CI) were obtained during mechanical ventilation (T1), T-piece breathing (T2), interventions (T3), spontaneous breathing 60 min (T4) and 90 min (T5) after extubation of the trachea using a combined dye-thermal dilution method. Changing from mechanical ventilation to T-piece breathing did not show any significant differences in EVLW between the three groups, but a significant increase in PBVI from 155 +/- 5 ml/m2 to 170 +/- 4 ml/m2 could be observed in all groups (p < 0.05). After extubation of the trachea and treatment with BiPAP. PBVI decreased significantly to 134 +/- 6 ml/m2 (p < 0.05). After treatment with CPAP or BiPAP, EVLW did not change significantly in these groups (5.5 +/- 0.3 ml/kg vs 5.0 +/- 0.4 ml/kg and 5.1 +/- 0.4 ml/kg vs 5.7 +/- 0.4 ml/kg). In the RCP-treated group, however, EVLW increased significantly from 5.8 +/- 0.3 ml/kg to 7.1 +/- 0.4 ml/kg (p < 0.05). Sixty and 90 min after extubation, EVLW stayed at a significantly higher level in the RCP-treated group (7.5 +/- 0.5 ml/kg and 7.4 +/- 0.5 ml/kg) than in the CPAP-(5.6 +/- 0.3 ml/kg and 5.9 +/- 0.4 ml/kg) or BiPAP-treated groups (5.2 +/- 0.4 ml/kg and 5.2 +/- 0.4 ml/kg). No significant differences in CI could be observed within the three groups during the time period from mechanical ventilation to 90 min after extubation of the trachea.

CONCLUSIONS

Mask CPAP and nasal BiPAP after extubation of the trachea prevent the increase in extravascular lung water during weaning from mechanical ventilation. This effect is seen for at least 1 h after the discontinuation of CPAP or BiPAP treatment. Further studies have to evaluate the clinical relevance of this phenomenon.