Propofol Increases Pulmonary Vascular Resistance During ??-Adrenoreceptor Activation in Normal and Monocrotaline-Induced Pulmonary Hypertensive Rats

The relaxant effect of propofol on isolated rat intrapulmonary arteries

Propofol is a widely used anesthetic. Many studies have shown that propofol has direct effects on blood vessels, but the precise mechanism is not fully understood. Secondary intrapulmonary artery rings from male rats were prepared and mounted in a Multi Myograph System. The following constrictors were used to induce contractions in isolated artery rings: high K(+) solution (60 mmol/L); U46619 solution (100 nmol/L); 5-hydroxytryptamine (5-HT; 3 µmol/L); or phenylephrine (Phe; 1 µmol/L). The relaxation effects of propofol were tested on high K(+) or U46619 precontracted rings. Propofol also was added to induce relaxation of rings preconstricted by U46619 after pretreatment with the nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME). The effects of propofol on Ca(2+) influx via the L-type Ca(2+) channels were evaluated by examining contraction-dependent responses to CaCl2 in the absence or presence of propofol (10 to 300 µmol/L). High K(+) solution and U46619 induced remarkable contractions of the rings, whereas contractions induced by 5-HT and Phe were weak. Propofol induced dose-dependent relaxation of artery rings precontracted by the high K(+) solution. Propofol also induced relaxation of rings precontracted by U46619 in an endothelium-independent way. Propofol at different concentrations significantly inhibited the Ca(2+)-induced contractions of pulmonary rings exposed to high K(+)-containing and Ca(2+)-free solution in a dose-dependent manner. Propofol relaxed vessels precontracted by the high K(+) solution and U46619 in an endothelium-independent way. The mechanism for this effect may involve inhibition of calcium influx through voltage-operated calcium channels (VOCCs) and receptor-operated calcium channels (ROCCs).

Anesthetic management of the patient with dilated cardiomyopathy undergoing pulmonary resection surgery: a case-based discussion

Interactions between the cardiovascular and respiratory systems are complex and profound. General anesthesia, muscle relaxation, and positive-pressure ventilation all impose physiological effects on cardiovascular function. In patients presenting for pulmonary resection, additional effects resulting from positioning, 1-lung ventilation, surgical procedures, and contraction of the pulmonary vascular bed may impose an additional physiological burden. For most patients with adequate pulmonary and cardiovascular reserve, these effects are well tolerated. However, the cardiothoracic anesthesiologist may be asked to provide anesthetic care for patients with significantly reduced cardiac function who require potentially curative pulmonary resection for lung cancer. These patients present a major perioperative challenge and a thoughtful approach to intraoperative management is required. The authors review a case of a patient with severely impaired biventricular function who presented for elective pulmonary lobectomy in an attempt to effect a curative resection of lung cancer and present a discussion of physiological and pathophysiological considerations for clinical management.

Evaluation of the hypnotic and hemodynamic effects of dexmedetomidine on propofol-sedated swine

This study examined the sedative effect of, and hemodynamic response to dexmedetomidine administration in propofol-sedated swine. Sixteen swine were subjects. After anesthetic induction and preparation, the propofol infusion rate was adjusted to maintain a bispectral index (BIS) value between 55 and 65 (i.e., baseline). With the propofol infusion rate fixed at the baseline rate, dexmedetomidine was infused continuously at a rate of 0.2, 0.4, and 0.7 microg.kg(-1).h(-1) for one hour at each rate. The BIS value and hemodynamic parameters were recorded at each step. Dexmedetomidine decreased the BIS value, mean arterial blood pressure, heart rate, cardiac output, and mixed venous oxygen saturation in a dose-dependent manner. The systemic vascular resistance (SVR) did not change, but the pulmonary vascular resistance (PVR) increased. Oxygen delivery (DO(2)) and oxygen consumption (VO(2)) decreased. A small dose of dexmedetomidine (0.2 microg.kg(-1).h(-1)) greatly enhanced the sedative effects of propofol with only small changes in hemodynamics and systemic oxygen balance, suggesting it may be useful in reducing the propofol dose requirement. However, dexmedetomidine 0.4 microg.kg(-1).h (-1) suppressed cardiac contractility, and 0.7 microg.kg(-1).h(-1) induced hemodynamic instability and further systemic oxygen imbalance while the additional sedative effect was limited. A lower dose of dexmedetomidine may be recommended when using it in combination with propofol.

Anaesthesia and right ventricular failure

Acute right ventricular (RV) failure has until recently received relatively little attention in the cardiology, critical care or anaesthesia literature. However, it is frequently encountered in cardiac surgical cases and is a significant cause of mortality in patients with severe pulmonary hypertension who undergo non-cardiac surgery. RV dysfunction may be primarily due to impaired RV contractility, or volume or pressure overload. In these patients, an increased pulmonary vascular resistance (PVR) or a decreased aortic root pressure may lead to RV ischaemia, resulting in a rapid, downward haemodynamic spiral. The key aspects of 'RV protection' in patients who are at risk of perioperative decompensation are prevention, detection and treatment aimed at reversing the underlying pathophysiology. Minimising PVR and maintaining systemic blood pressure are of central importance in the prevention of RV decompensation, which is characterised by a rising central venous pressure and a falling cardiac output. Although there are no outcome data to support any therapeutic strategy for RV failure when PVR is elevated, the combination of inhaled iloprost or intravenous milrinone with oral sildenafil produces a synergistic reduction in PVR, while sparing systemic vascular resistance. Levosimendan is a promising new inotrope for the treatment of RV failure, although its role in comparison to older agents such as dobutamine, adrenaline and milrinone has yet to be determined. This is also the case for the use of vasopressin as an alternative pressor to noradrenaline. If all else has failed, mechanical support of the RV should be considered in selected cases.