Intra-operative heparin release during lung surgery

Heparin has long been thought to be biosynthesized and stored in the granules of mast cells that are most prevalent in the lungs and gastro-intestinal tract. In response to stimuli such inflammation and trauma, mast cells degranulate and consequently release heparin. This prospective study was designed to investigate if operative trauma during lung mobilization could enhance heparin release into both the pulmonary and systemic circulations.

Prospective investigations and data collection were carried out on 34 patients undergoing elective thoracotomies for 19 patients with chronic inflammatory disease and 15 with lung carcinoma. Heparin assay using the high performance liquid chromatography method was carried out on four blood samples from each patient. Sample 1 was taken pre-operatively from the radial artery. Intra-operatively following lung mobilization and prior to excision, sample 2 was taken from the draining pulmonary vein and at the same time, sample 3 from the radial artery. Postoperatively, the next morning, sample 4 was taken from the radial artery.

The mean values for serum heparin levels in pg/ml of samples 1-4 were found to be 205.1 (SD+/-282.1), 366.0 (SD+/-371.7), 337.2 (SD+/-225.3) and 250.8 (SD+/-282.2), respectively. These results show that intraoperative serum heparin levels (samples 2 and 3) are significantly higher (P = 0.0016, P = 0.0014, respectively) than pre-operative values (sample 1). The difference between sample 2 (pulmonary) and sample 3 (systemic circulation) was not significant (P = 0.6508). Although postoperative heparin levels (sample 4) were found to be higher than pre-operative values, yet it was not statistically significant (P = 0.1340). The mean of pre-operative heparin levels in patients with lung carcinoma and inflammatory diseases were 136.2 (SD+/-62.6) and 259.4 (SD+/-368.3), respectively. Intra-operatively, heparin levels increased to 260.9 (SD+/-139.7) and 449 (SD+/-470.7), respectively. These results suggest that the mean heparin level for patients with inflammatory lung diseases was higher than that for carcinoma patients.

Within the context of lung surgery for carcinoma or inflammatory diseases, it appears that operative trauma enhances heparin release into both the pulmonary and systemic circulations, possibly through pulmonary mast cell degranulation. Thus, an episodic auto anti-coagulant effect is established during the course of surgery. Such findings may partly provide an understanding of the excessive bleeding encountered during some thoracotomies and the recognized reduced incidence of thrombo-embolic complications among thoracic surgical patients. Should an unexplained bleeding occur during the course of surgery, an excess of heparin release is recommended to be kept in mind as a possible cause.