Synthesis of prostaglandins, TXA2 and PGI2, during one lung anesthesia

Cyclooxygenase-2 inhibition and thromboxane A(2) receptor antagonism attenuate hypoxic pulmonary vasoconstriction in a porcine model

AIM

Hypoxic pulmonary vasoconstriction (HPV) causes pulmonary hypertension that may lead to right heart failure. We hypothesized that the COX-2 inhibitor nimesulide and the thromboxane A(2) receptor antagonist daltroban would attenuate HPV.

METHODS

Haemodynamic measurements and blood sampling were performed in 18 anaesthetized, mechanically ventilated pigs, with mean ± SEM weights of 31.3 ± 0.6 kg, in normoxia (F(i)O(2)~0.21) and hypoxia (F(i)O(2)~0.10), before and 5, 15 and 45 min after initiation of right atrial infusion of nimesulide (n = 6) or daltroban (n = 6), respectively, and in six control pigs.

RESULTS

Compared with normoxia, hypoxia (n = 18) increased mean pulmonary artery pressure by 15.8 ± 0.8 mmHg (P < 0.001), pulmonary vascular resistance (PVR) by 2.7 ± 0.3 WU (P < 0.05) and mean right atrial pressure by 2.3 ± 0.3 mmHg (P < 0.001). In the control pigs, mean pulmonary artery pressure, PVR and mean right atrial pressure remained stable (P = ns) throughout 45 min hypoxia, compared with hypoxia baseline. Nimesulide decreased mean pulmonary artery pressure by 3.7 ± 1.3 mmHg after 45 min (P < 0.013), as well as PVR by 0.8 ± 0.2 WU (P < 0.05), levelling off after 15 min. Daltroban transiently increased (P < 0.001) mean pulmonary artery pressure and mean right atrial pressure by 7.2 ± 1.2 and 2.7 ± 0.4 mmHg, respectively, but they returned to hypoxia baseline (P = ns) within 5 min. Daltroban then decreased mean pulmonary artery pressure to after 45 min be 4.2 ± 1.6 mmHg lower (P < 0.005) than at hypoxia baseline.

CONCLUSION

COX-2 inhibition and thromboxane A(2) receptor antagonism attenuate HPV by decreasing mean pulmonary artery pressure by approximately 10-11%, as measured 45 min after initiation of nimesulide or daltroban infusion respectively.

Approaches to hypoxemia during single-lung ventilation

Modern techniques to isolate the lungs, coupled with accurate continuous non-invasive monitoring, have made single-lung ventilation safe and easy to perform. Most patients maintain an adequate arterial oxygen tension during single-lung ventilation. In order to maximize oxygenation, efforts are directed towards optimizing perfusion and ventilation to the ventilated lung or increasing the oxygen content of blood returning from the collapsed lung.

Clinical review: Independent lung ventilation in critical care

Independent lung ventilation (ILV) can be classified into anatomical and physiological lung separation. It requires either endobronchial blockade or double-lumen endotracheal tube intubation. Endobronchial blockade or selective double-lumen tube ventilation may necessitate temporary one lung ventilation. Anatomical lung separation isolates a diseased lung from contaminating the non-diseased lung. Physiological lung separation ventilates each lung as an independent unit. There are some clear indications for ILV as a primary intervention and as a rescue ventilator strategy in both anatomical and physiological lung separation. Potential pitfalls are related to establishing and maintaining lung isolation. Nevertheless, ILV can be used in the intensive care setting safely with a good understanding of its limitations and potential complications.

Acute lung injury and acute respiratory distress syndrome after pulmonary resection

The occurrence of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) after thoracic surgery are perplexing and persistent problems. Variously described as postpneumonectomy pulmonary edema, noncardiogenic pulmonary edema, and postlung resection pulmonary edema, ALI and ARDS may be considered a single entity, with ALI being the less severe form of ARDS. It is characterized by the acute onset of hypoxemia with radiographic infiltrates consistent with pulmonary edema, without elevations in the pulmonary capillary wedge pressure. Although this syndrome does not occur frequently and is usually without identifiable cause, the mortality is high. However, the phenomenon has not been rigorously studied owing to the low incidence, with primarily retrospective case series reported. Thus, the nomenclature, risks, and pathogenesis are not well defined. Interest in this syndrome has recently been renewed as the rate of other perioperative complications has declined. ALI/ARDS is reviewed with a focus on potential etiologies and the spectrum of available interventions.

Improvement of arterial oxygenation by selective infusion of prostaglandin E1 to ventilated lung during one-lung ventilation

BACKGROUND

One-lung anesthesia provides a better surgical field for thoracic procedures but also impairs the arterial oxygenation and venous admixture. During one-lung ventilation, pulmonary vasoconstriction is assumed to be present within both ventilated and collapsed lungs. We propose that arterial oxygenation could be optimized by offsetting the vasoconstriction within the microcirculation of ventilated lung.

METHOD

In an anesthetized dog model, incremental doses of prostaglandin E1 (PGE1) were selectively infused into the main trunk of the pulmonary artery of the ventilated lung after one-lung ventilation for 60 min (PGE1 group, n = 9). Arterial oxygenation and calculated venous admixture (Qs/Qt) was also assessed in a time-course control group (Control group, n = 5). During two-lung ventilation (FIO2: 0.66), arterial PO2 and venous admixture was 44.2 +/- 3.5 kPa and 10.7 +/- 2.3%, respectively. One-lung ventilation (FIO2: 0.66) with left lung collapsed reduced arterial PO2 to 11.6 +/- 1.7 kPa and increased venous admixture to 40.7 +/- 5.8% (P<0.001). Venous O2 tension also decreased from 6.3 +/- 0.7 kPa to 5.0 +/- 0.6 kPa with a slight increase in mean pulmonary artery pressure and pulmonary vascular resistance (P<0.05).

RESULTS

During selective infusion of PGE1 at a dose of 0.04 to 0.2 mu g kg-1 min-1, there was a dose-dependent improvement in arterial PO2 with a parallel reduction of venous admixture during one-lung ventilation. Arterial PO2 increased to a maximum of 23.0 +/- 4.3 kPa, and the venous admixture decreased significantly to a minimum of 27.4 +/- 4.2% by PGE1 at a dose of 0.04-0.4 mu g kg-1 min-1 (P<0.01). PGE1 resulted in a small increase in cardiac output and decreases of pulmonary pressure and pulmonary vascular resistance at a relatively high dose of 0.4 mu g kg-1 min-1 during selective infusion (P<0.05).

CONCLUSIONS

These results suggest that a selective pulmonary artery infusion of PGE1 to the ventilated lung within the dose range of 0.04-0.4 mu g kg-1 min-1 is practical and effective to improve arterial oxygenation and reduce venous admixture during one-lung ventilation.

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.