Noncardiogenic pulmonary edema after abdominal aortic aneurysm surgery

Pathophysiology of ischaemia reperfusion injury: central role of the neutrophil

Ischaemia is a common clinical event leading to local and remote injury. Evidence indicates that tissue damage is largely caused by activated neutrophils which accumulate when the tissue is reperfused. If the area of ischaemic tissue is large, neutrophils also sequester in the lungs, inducing non-cardiogenic pulmonary oedema. Ischaemia reperfusion injury is initiated by production of reactive oxygen species which initially appear responsible for the generation of chemotactic activity for neutrophils. Later, once adherent to endothelium, neutrophils mediate damage by secretion of additional reactive oxygen species as well as proteolytic enzymes, in particular elastase. Therapeutic options for limiting ischaemia reperfusion injury include inhibition of oxygen radical formation, pharmacological prevention of neutrophil activation and chemotaxis, and also the use of monoclonal antibodies which prevent neutrophil-endothelial adhesion, a prerequisite for injury.

Pulmonary hypertensive response to declamping of the aorta during abdominal aortic reconstructive surgery-role of metabolic derangement and anaphylatoxin in the reaction

Metabolic parameters and anaphylatoxin activities in mixed venous blood were measured in 16 patients undergoing abdominal aortic reconstructive surgery to study the mechanism of pulmonary hypertensive response after aortic declamping. This reaction was confirmed by a rise in ratio between mean pulmonary arterial pressure and mean systemic arterial pressure (Pp/Ps). Aortic declamping was followed by a significant increase in lactate level and lactate-pyruvate ratio (L/P ratio) as compared with pre-declamping level ( P << 0.01). Although anaphylatoxin C3a concentration rose significantly after declamping ( P << 0.01), C5a showed no change at any stage. When the patients were divided into two groups according to the degree of Pp/Ps change by declamping, significant elevation of L/P ratio and C3a level were observed in the group with higher increase (Post-/Pre-declamp value >/=1.25) of Pp/Ps compared to the lower (>>1.25) group. After declamping, in the higher Pp/Ps group, a positive correlation existed not only between Pp/Ps change and aortic clamp time, but also between L/P ratio and C3a level. The present results suggest that muscular metabolic derangement distal to the aortic clamp may play an important role in the development of post-declamping pulmonary hypertensive response through anaphylatoxin C3a.

Pulmonary edema after aneurysm surgery is modified by mannitol

Abdominal aortic aneurysmectomy (AAA) results in thromboxane (Tx)A2 generation, a rise in mean pulmonary artery pressure (MPAP), leukopenia, and noncardiogenic pulmonary edema. This study tests whether mannitol, a hydroxyl radical scavenger, modifies these events. Patients received mannitol 0.2 g/kg (n = 14) or saline (n = 12) intravenously before infrarenal aortic clamping. With saline, 30 minutes after clamping, plasma TxB2 levels rose from 124 to 290 pg/mL (p less than 0.01), and MPAP rose from 19 to 27 mmHg (p less than 0.01). Aortic clamp release led to further increases in plasma TxB2 to 378 pg/mL (p less than 0.01) and MPAP to 34 mmHg (p less than 0.01). The white blood count (WBC) fell from 9800 to 4400/mm3 (p less than 0.01). Four to eight hours after surgery, physiologic shunting (Q[sc]S[xsc]/Q[sc]T[xsc]) rose from 9% to 20% (p less than 0.01) and peak inspiratory pressure (PIP) increased from 22 to 32 cmH2O (p less than 0.01). Chest radiography demonstrated pulmonary edema while the pulmonary wedge pressure was 12 mmHg, excluding left ventricular failure. By 24 hours pulmonary edema resolved and the PIP and PaO2 returned to baseline. Mannitol treatment relative to saline, during and after aortic clamping reduced plasma TxB2 levels to 155 and 198 pg/mL, respectively (p less than 0.01); MPAP to 21 and 26 mmHg (p less than 0.01); minimized the decline in WBC to 5850/mm3 (p less than 0.01), and the postoperative rise in Q[sc]S[xsc]/Q[sc]T[xsc] to 12%, and PIP to 28 cmH2O (both p less than 0.01). Chest radiography showed no pulmonary edema. Finally in vitro studies documented that mannitol 1 to 10(-4)M, but not dextrose, in a dose-dependent manner inhibited Tx synthesis by ADP-activated platelets. These data indicate that mannitol maintains pulmonary function after AAA by limiting ischemia-induced thromboxane synthesis.