Impact of pleurotomy, continuous positive airway pressure, and fluid balance during cardiopulmonary bypass on lung mechanics and oxygenation

Pleural effusion post coronary artery bypass surgery: associations and complications

Background

One of the most frequent complications of coronary artery bypass grafting (CABG) is pleural effusion. Limited previous studies have found post-CABG pleural effusion to be associated with increased length-of-stay and greater morbidity post-CABG. Despite this the associations of this common complication are poorly described. This study sought to identify modifiable risk factors for effusion post-CABG.

Methods

A retrospective cohort study of prospectively collected data assessed patients who underwent CABG over two-years. Data was collected for risk factors and sequelae related to pleural effusion requiring drainage.

Results

A total of 409 patients were included. Average age was 64.9±10.2 years, 330 (80.7%) were male. 59 (14.4%) patients underwent drainage of pleural effusion post-CABG. Effusions were drained on average 9.9±8.4 days post-CABG. Earlier removal of drain tubes and removal near time of extubation were associated with development of pleural effusion. Post-CABG pleural effusion was associated with post-operative renal impairment (P<0.01) and pericardial effusion (P<0.01). Patients with pleural effusion were more likely to require readmission to ICU (P<0.01), reintubation (P=0.03) and readmission to hospital (P=0.03).

Conclusions

Pleural effusion is a common complication of cardiac surgery and is associated with significant morbidity and resource utilization. This study identifies several associated complications that should be considered in the presence of pleural effusion. Modifiable associated factors in the management of drains that may contribute to accumulation of pleural effusion include: early removal of chest drains, higher outputs and removal during or close to mechanical ventilation. Further research is required to assess how adjusting these modifiable factors can decrease rates of effusion post-operatively.

Early Open-Lung Ventilation Improves Clinical Outcomes in Patients with Left Cardiac Dysfunction Undergoing Off-Pump Coronary Artery Bypass: a Randomized Controlled Trial

Objective

To compare pulmonary function, functional capacity and clinical outcomes amongst three groups of patients with left ventricular dysfunction following off-pump coronary artery bypass, namely: 1) conventional mechanical ventilation (CMV); 2) late open lung strategy (L-OLS); and 3) early open lung strategy (E-OLS).

Methods

Sixty-one patients were randomized into 3 groups: 1) CMV (n=21); 2) L-OLS (n=20) initiated after intensive care unit arrival; and 3) E-OLS (n=20) initiated after intubation. Spirometry was performed at bedside on preoperative and postoperative days (PODs) 1, 3, and 5. Partial pressure of arterial oxygen (PaO₂) and pulmonary shunt fraction were evaluated preoperatively and on POD1. The 6-minute walk test was applied on the day before the operation and on POD5.

Results

Both the open lung groups demonstrated higher forced vital capacity and forced expiratory volume in 1 second on PODs 1, 3 and 5 when compared to the CMV group (P<0.05). The 6-minute walk test distance was more preserved, shunt fraction was lower, and PaO₂ was higher in both open-lung groups (P<0.05). Open-lung groups had shorter intubation time and hospital stay and also fewer respiratory events (P<0.05). Key measures were significantly more favorable in the E-OLS group compared to the L-OLS group.

Conclusion

Both OLSs (L-OLS and E-OLS) were able to promote higher preservation of pulmonary function, greater recovery of functional capacity and better clinical outcomes following off-pump coronary artery bypass when compared to conventional mechanical ventilation. However, in this group of patients with reduced left ventricular function, initiation of the OLS intra-operatively was found to be more beneficial and optimal when compared to OLS initiation after intensive care unit arrival.

Pulmonary Complications After Cardiac Surgery

Over the past two decades there has been a steady evolution in the practice of adult cardiac surgery with the introduction of “off-pump” surgery. However, respiratory complications remain a leading cause of postcardiac surgical morbidity and can prolong hospital stays and increase costs. The high incidence of pulmonary complications is in part due to the disruption of normal ventilatory function that is inherent to surgery in the thoracic region. Furthermore, patients undergoing such surgery often have underlying illnesses such as intrinsic lung disease (e.g., chronic obstructive pulmonary disease) and pulmonary dysfunction secondary to cardiac disease (e.g., congestive heart failure) that increase their susceptibility to postoperative respiratory problems. Given that many patients undergoing cardiac surgery are thus susceptiple to pulmonary complications, it is remarkable that more patients do not suffer from them during and after cardiac surgery. This is to a large degree because of advances in anesthetic, surgical and critical care that, for example, have reduced the physiological insults of surgery (e.g., better myocardial preservation techniques) and streamlined care in the immediate postoperative period (e.g., early extubation). Moreover, the development of minimally invasive surgery and nonbypass techniques are further evidence of the attempts at reducing the homeostatic disruptions of cardiac surgery. This review examines the available information on the incidences, consequences, and treatments of postcardiac surgery respiratory complications.

Pulmonary pathophysiology and lung mechanics in anesthesiology: a case-based overview

Anesthesia, surgical requirements, and patients' unique pathophysiology all combine to make the accumulated knowledge of respiratory physiology and lung mechanics vital in patient management. This article take a case-based approach to discuss how the complex interactions between anesthesia, surgery, and patient disease affect patient care with respect to pulmonary pathophysiology and clinical decision making. Two disparate scenarios are examined: a patient with chronic obstructive pulmonary disease undergoing a lung resection, and a patient with coronary artery disease undergoing cardiopulmonary bypass. The impacts of important concepts in pulmonary physiology and respiratory mechanics on clinical management decisions are discussed.

Effect of Lung Ventilation With 50% Oxygen in Air or Nitrous Oxide Versus 100% Oxygen on Oxygenation Index After Cardiopulmonary Bypass

OBJECTIVE

This study was designed to assess the use of 100% oxygen or 50% oxygen in air or nitrous oxide after cardiopulmonary bypass (CPB) on atelectasis, as evidenced by the oxygenation index (PaO2/F(I)O2), after coronary artery bypass graft (CABG) surgery.

DESIGN

Prospective, randomized clinical study.

SETTING

University teaching hospital.

PARTICIPANT

Thirty-six adult patients undergoing CABG surgery.

INTERVENTIONS

Patients either received 50% O2 in air (50% O2 group), 50% O2 in N2O (50% N2O group), or 100% O2 (100% O2 group) after CPB.

MEASUREMENTS AND MAIN RESULTS

Apart from demographic and perioperative clinical data, extubation time, mediastinal drainage, and pulmonary complications were also recorded. After CPB, arterial blood gases done at various time points until 3 hours postextubation and oxygenation index were calculated. No significant differences were noted in demographic and perioperative data except preoperative hemoglobin and fluid use. Significant deterioration in arterial oxygenation was noted in the 100% O2 group from the baseline value, whereas significant improvement was seen in the 50% O2 group at 4 time points from baseline value and at all time points from the 100% O2 group. After initial deterioration in oxygenation, no further change was evident in the 50% N2O group. Furthermore, there was a greater increase in the oxygenation index as compared with the 100% O2 group. Time to extubation was also longer in the 100% O2 group than the 50% O2 group.

CONCLUSION

Significant deterioration in arterial oxygenation and an increase in the extubation time occurred with the use of 100% O2 after CPB, whereas better oxygenation was evident with the use of 50% O2 in air.

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.

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.

Acute pleuropulmonary complications detected by computed tomography following myocardial revascularization

INTRODUCTION: Pleuropulmonary changes are common following coronary artery bypass grafting surgery performed with a saphenous vein graft, with or without an internal mammary artery. The presence of atelectasis or pleural effusions reflects the thoracic trauma. PURPOSE: To define the postoperative incidence of changes in the lung and in the pleural space and to evaluate the influence of the trauma. METHODS: Thirty patients underwent elective coronary artery bypass grafting surgery (8 saphenous vein grafts and 22 saphenous vein grafts and internal mammary artery grafts with pleurotomy). Chest tubes in the left pleural space were used in all internal mammary artery patients. On the second (day 2) and seventh (day 7) postoperative day, patients underwent a computed tomography, and pleural effusions were rated as follows: grade 0 = no fluid to grade 4 = fluid in more than 75% of the hemithorax. Atelectasis was rated as follows: laminar = 1, segmental = 3, and lobar = 10 points. RESULTS: All patients had pleural effusion or atelectasis. Between day 2 and day 7, the number of patients with effusions or atelectasis on the right side decreased (P < 0.05). The incidence of effusions on day 2 in the saphenous vein graft group (87.5%) was higher (P < 0.05) than in the internal mammary artery group (52.3%). The incidence of atelectasis in the lower right lobe decreased (P < 0.05) from 86.7% (day 2) to 26.7% (day 7). The degree of atelectasis in both sides did not differ on day 2 (P = 0.42) but did on day 7 (P < 0.0001). There was a decrease in the atelectasis from day 2 to day 7 on the right side (P < 0.001), but not on the left (P = 0.21). On day 2 there was a relationship between atelectasis and effusion on the right (P = 0.04), but not on the left (P = 0.113). CONCLUSION: The present series demonstrates that there is a high incidence of both minimal pleural effusion and atelectasis after coronary artery bypass grafting surgery, which drops on the right side from day 2 to day 7 post surgery. Factors that contribute to the persistence of changes on the left side include the thoracic trauma and the presence of chest tubes and pericardial effusion.

Fenoldopam infusion associated with preserving renal function after aortic cross-clamping for aneurysm repair

BACKGROUND

Cross-clamping of the descending aorta during operative repairs causes sudden, significant reductions in renal function that may persist well beyond arterial clamp release. Commonly used agents, such as dopamine and mannitol, have not consistently affected renal outcome in these high-risk patients. Fenoldopam mesylate is a novel, highly selective dopamine type-1 agonist that preferentially dilates the renal and splanchnic vasculature, but has not been investigated in patients undergoing prolonged aortic clamping for whom adverse renal outcomes should be more likely.

METHODS AND RESULTS

Twenty-two adult patients without significant pre-existing renal dysfunction and presenting for elective repairs of abdominal aortic aneurysms were studied. Fenoldopain mesylate was infused after obtaining baseline values ranging from 0.1 to 1.0 microg/kg/min for the first 24 hours postoperatively to maintain mean arterial pressure +/-25% baseline. Serial renal function indices, including creatinine clearance and electrolyte fractional excretions, were measured at baseline, at aortic clamping and unclamping, and post-clamp release, and were estimated through hospital discharge. Creatinine clearance fell during abdominal exploration and clamping, reaching a nadir with clamp removal. Partial recovery occurred by 2 hours after clamp removal, and returned to baseline values by postoperative day 1 and thereafter. Fractional excretions rose rapidly throughout the operative phase. Total fenoldopam dose was directly related to the baseline creatinine clearance; after clamp removal, creatinine clearance was directly related to the mean arterial pressure at the lowest dose of fenoldopam, and inversely related to the mean arterial pressure at clamp release.

CONCLUSIONS

In elderly patients with severe vascular disease undergoing aneurysmal repairs, the use of a fenoldopam infusion in this open-label, uncontrolled trial was associated with a relatively rapid return of renal function to baseline values, despite profound decreases during aortic cross-clamping. Further studies will be necessary to investigate how fenoldopam infusions compare with traditional therapies.

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.