Anaesthesia/Wiley Research Grant
Extravascular lung water as an early predictor and marker of the severity of reperfusion lung injury in pulmonary endarterectomy: A prospective cohort study
Dr Vasileios Zochios
Background
Patients undergoing pulmonary endarterectomy (surgical treatment for pulmonary arterial hypertension) are at risk of developing reperfusion lung injury following surgery. This represents a form of high permeability lung oedema occuring in up to 40% of patients. In its severe form, it presents as severe airway bleeding with profound hypoxaemia and it is associated with poor clinical outcomes including significant increases in duration of respiratory support, length of intensive care unit stay and death. Extravascular lung water (EVLW) is the fluid in the lung that is not within the vascular or pleural spaces. EVLW can be measured by transplulmonary thermodilution which is based on injection of cold water through a central vein. An arterial thermister placed in the femoral artery measures the change in blood temperature in the lungs and plots it against time. From these measurements EVLW can be calculated. EVLW indexed to predicted body weight (EVLWi) has been proposed as a predictor of perioperative lung oedema and a marker of disease severity.
Objective
The primary aim of this prospective cohort study is to evaluate EVLW as a predictor of clinically significant lung reperfusion injury in the context of pulmonary endarterectomy surgery. Clinically significant reperfusion injury is defined as: acute pulmonary infiltrates on chest X-ray, low oxygen levels and need for respiratory support.
Our hypothesis is that pulmonary endarterectomy patients with high perioperative EVLWi values are more likely to develop clinically significant reperfusion lung oedema.
Patients undergoing pulmonary endarterectomy constitute a unique patient population at risk of development of pulmonary oedema, and an ideal model for evaluating whether EVLW correlates with severity of lung injury, response to treatment and outcomes.
Methods
After full institutional ethical approval is granted we will study a cohort of 51 patients undergoing pulmonary endarterectomy, estimated to provide 80% (a=0.05) power to detect correlations and differences. Patients requiring perioperative mechanical cardiovascular support will be excluded. All patients will be anaesthetised and monitored according to a standard pulmonary endarterectomy protocol. The value of EVLWi considered as normal will be <7ml/kg of predicted body weight. A cutoff value of 10ml/kg predicted body weight will be considered as the highest limit of the normal range.
Measurements will be obtained at the following time points: first measurement after induction of anaesthesia following insertion of the catheters. Second and third measurements will be obtained immediately before initiation of cardiopulmonary bypass and within 30min of separation from cardiopulmonary bypass, respectively. Additional measurements will be planned 2, 4, 6, 12, 24, 36, 48 hours after the third measurement. Various respiratory parameters and lung injury severity scores will be determined for each patient. Patients will also undergo daily chest radiographs which will be reported by a radiologist blinded to the study intervention.
The relationship of these indices to early diagnosis and severity of reperfusion injury and hospital mortality will be studied using the appropriate statistical tests. Positive and negative likelihood ratios, pre- and post-test odds for diagnosis of reperfusion injury and mortality will be calculated.
