The hemodynamics showed dramatic fluctuation in CABG patients during the anesthesia and surgery, which is probably due to its pathophysiological characteristics and operative factors. In this study, these patients were poorly tolerated in the presence of both anesthesia and surgery. Anesthesiologists should maintain the stability of hemanynamics, so some vasoactive drugs such as phenylephrine, norepinephrine, and other catecholamine drugs are inevitably used.
There are three intrinsic vasopressor systems, ie, sympathetic nervous system, renin- angiotensin system and vasopressin system. Mounting studies have indicated that vasopressin was much more potent in cardiopulmonary resuscitation than catecholamines. But for CABG patients, it was unclear which vasopressor was more potent and with less side effects.
Our study confirmed that the vasopressin is similar to the traditional catecholamines to maintain the stability of hemodynamics, and even superior to the catecholamines in some aspects, such as pulmonary artery pressure, metoprololuse usage. Catecholamine hormones could increase blood pressure, while inevitablely increase pulmonary vascular resistance, thereby leading to increase of pulmonary artery pressure. Pulmonary hypertension, as we know, a very dangerous pathophysiological change, deteriorate hemodynamic and respiratory function, meanwhile induce the failure of the entire surgery.
No evidence showed that using of low doses of vasopressin (0.04 U/min) increased PVR or PAP. On the contrary, Basic study showed that vasopressin could decrease PAP. The results of this study suggested that no pulmonary artery pressure elevation after administration of vasopressin, instead, pulmonary artery pressure is relatively stable in vasopressin group perhaps due to the better-maintained systemic arterial pressure and less norepinephrine usage.
Patients undergoing CABG surgery are needed to maintain a slower heart rate to reduce myocardial oxygen consumption and facilitate the surgical procedure. Although CABG patients will have a slower heart rate during the anesthesia and operation because of pre-operative β-blockers and anesthetic agents, but the heart rate still inevitable increase during the surgery and anesthesiologist need to use the additional beta blockers. In this study, vasopressin group patients need less beta blockers but not in norepinephrine group patients. The reasons may be norepinephrine has positive inotropic and positive frequency effect and pulmonary pressure is relatively unstable.
Vasopressin, also known as antidiuretic hormone can reduce urine output. But this study did not indicate an obvious decreament in the urine output after treatment of vasopressin. Enough arterial pressure and cardiac output can assure enough kidney perfusion and result in maintained urine output. Antidiuretic hormone can enhance the kidney collecting duct re-absorption of H2O, leading to dilutional hyponatremia. Serum sodium and other electrolytes should be monitored during prolonged use of vasopressin.
In addition, it was generally believed that high blood pressure can lead to increased surgical drainage. But in this study vasopressin increased blood pressure without increasing the amount of bleeding volume. Some study demonstrated that the anti-diuretic hormone receptor has three subtypes, V1, V2 and V3 receptors. V2 receptor exciting can increase the concentration of plasma coagulation factor VII and vWF. Consequently, researchers have already proposed: for those patients with reduced plasma level of factor VIII and vWF such as hemophilia A and type I von Willebrand disease, anti-diuretic hormone should be administered during perioperative time.
Vasopressin can also cause a transient elevation in blood glucose and the mechanism is related to the liver glycogen catabolism by V1 receptor. We recommended that patients’ blood glucose should be monitored for prolonged use of vasopressin and those with diabetic mellitus.
In conclusion, vasopressin may be another choice to deal with hypotension during CABG surgeries.