Effects of intravenous anesthesia on VA/Q distribution: a study performed during ventilation with air and with 50% oxygen, supine and in the lateral position.

Distribution of ventilation and perfusion in relation to ventilation-perfusion ratio (VA/Q) were studied in 14 patients, with a mean age of 59 yr, before elective lung surgery, in the supine position when awake, during intravenous anesthesia and mechanical ventilation with air, after increasing the fraction of inspired oxygen (FIO2) to 0.5, and in the lateral position. Before anesthesia, small inert gas shunts and perfusion of low VA/Q regions, indicating some degree of VA/Q mismatch, were observed in several patients. After induction, FIO2 = 0.21, the major changes were a significant decrease in cardiac output and an increase in log SD for perfusion from 0.77 +/- 0.45 (SD) to 1.13 +/- 0.50 (SD), while the shunt remained low at 1% of cardiac output and arterial oxygen tension (PaO2) was unchanged. An increase to FIO2 = 0.5 induced only small changes with a shunt of 2.5% of cardiac output. In the lateral position, the shunt was 4.0% and increases in ventilation to high VA/Q regions were observed. The lack of marked changes in the VA/Q distribution after induction either could be a result of only minor alterations in the distribution of ventilation and perfusion or an effective vascular response to alveolar hypoxia (hypoxic pulmonary vasoconstriction, HPV).

Circulatory effects of pancuronium and alcuronium in patients with coronary artery stenosis.

Heart rate and systemic arterial blood pressure were recorded during induction of anaesthesia up to 9 min after endotracheal intubation in 92 patients scheduled for coronary artery bypass surgery, in order to study to what degree the circulatory response to induction of anaesthesia and intubation was modified by different relaxants. Pancuronium (pancuronium bromide) 0.1 mg X kg b.w.-1 and alcuronium (diallyl-nortoxiferine) 0.25 mg X kg b.w.-1 were randomly studied in 36 patients during induction with high-dose fentanyl and in 36 patients induced with thiopentone, diazepam, fentanyl and nitrous oxide. In patients given high-dose fentanyl anaesthesia, systolic blood pressure before, during and after intubation was significantly lower with alcuronium (P less than 0.01). The same difference between alcuronium and pancuronium was observed in balanced anaesthesia before endotracheal intubation. Induction of anaesthesia and intubation were followed by a moderate increase in heart rate, irrespective of the type of anaesthesia and relaxant. Subsequently, 20 patients (10 with high-dose fentanyl and 10 with balanced anaesthesia) were studied. They received pancuronium 0.05 mg X kg b.w.-1 + alcuronium 0.125 mg X kg b.w.-1. This mixture of relaxants produced an intermediate blood pressure response.

Effects of nitroglycerin on central haemodynamics and VA/Q distribution during ventilation with FIO2 = 1.0 in patients after coronary bypass surgery.

The effects of nitroglycerin (TNG) infusion during ventilation with FIO2 = 1.0 on central haemodynamics and the distribution of ventilation-perfusion (VA/Q) were studied with the multiple inert gas elimination technique in eight patients after coronary bypass surgery. Administration of TNG resulted in a significant decrease in mean arterial pressure, and an increase in heart rate while cardiac output remained unchanged. Mean right atrial, pulmonary arterial and pulmonary wedge pressures all decreased. There was a significant reduction in PaO2 from 50.5 to 32.7 kPa, while Pao2 remained unchanged in a control group of eight patients. This was mainly due to an increase in shunt from 9.3 to 16.5% of cardiac output during TNG-infusion. In the control group there was also an increase in shunt from 9.7 to 12.1% of cardiac output with a simultaneous decrease of the same magnitude in perfusion of regions with low VA/Q (0.005-0.1). This was not evident in the group receiving TNG. Twenty min after termination of TNG-infusion the effects on central haemodynamics and gas exchange were not fully reversed. The mechanism behind the increase in inert gas shunt observed with infusion of TNG during oxygen breathing is probably a selective effect on vessels with remaining high vasomotor tone despite high alveolar oxygen tension.

Effects of oxygen on central haemodynamics and VA/Q distribution after coronary bypass surgery.

Central haemodynamics and ventilation-perfusion (VA/Q) distribution were studied in 16 patients, 21 h after coronary bypass surgery, during ventilation with FIO2 = 0.3 and 1.0. VA/Q distributions were determined by the multiple inert gas elimination technique. In 15 patients with normal preoperative lung function, there was a significant shunt of 7.5% of cardiac output and perfusion of regions with VA/Q between 0.005-0.1 of 2.4% (FIO2 = 0.3). Mean VA/Q for the Q-distribution was 0.89 with log s.d. of 0.92. Ventilation of regions with VA/Q above 100 was 0.22. After 30 min of ventilation with FIO2 = 1.0, there was a slight increase in cardiac output while pulmonary arterial mean pressure and pulmonary vascular resistance showed slight decreases. There was a marked increase of the shunt in three patients but the increase for the whole group was not significant. Perfusion of regions with low VA/Q (0.005-0.1) increased significantly to 8.7% while the distribution of ventilation remained unchanged. The changes in distribution of Q were probably due to a release of hypoxic vasoconstriction in combination with complete or incomplete alveolar collapse. One patient with obstructive lung disease showed only minor changes in perfusion distribution.

Effects of prenalterol on central haemodynamics and VA/Q distribution early after open-heart surgery.

The effects of intravenous injection of prenalterol, a selective beta 1-adrenoceptor agonist, on central haemodynamics and the distribution of ventilation-perfusion (VA/Q) were assessed in eight patients after aortic and/or mitral valve replacement. VA/Q distributions were determined by the multiple inert gas elimination technique. Administration of prenalterol resulted in a significant increase in cardiac output and heart rate with no changes in mean pulmonary arterial pressure and wedge pressure. There was an insignificant fall in arterial oxygen tension from 14.3 to 12.4 kPa, accompanied by a significant increase in the inert gas shunt from 6.4 to 11.3% of cardiac output, while the configuration of the distribution of perfusion and ventilation on VA/Q remained unchanged. The increase in shunt was probably more an effect of the increase in cardiac output than a direct effect of the drug on the pulmonary vascular bed.

Effects of nitroglycerin on central haemodynamics and VA/Q distribution early after coronary bypass surgery.

Central haemodynamics and ventilation-perfusion (VA/Q) distribution were studied in nine patients, 21 h after coronary bypass surgery, before and during nitroglycerin (TNG) infusion. VA/Q distributions were established with the multiple inert gas elimination technique of Wagner and West. Administration of TNG resulted in a decrease in mean arterial pressure, a slight reduction in cardiac output and stroke volume and a significant increase in heart rate, possibly explained by an initial relative hypovolaemia. Pulmonary arterial pressures and filling pressures for the right and left ventricles decreased significantly. There was a significant reduction in PaO2 and an increase in venous admixture (QVA/QT) from 11.3 to 16.5% of cardiac output. This was mainly due to an initial SF6-shunt of 6.4% increasing to 12.8%. Only 3.5% of cardiac output during TNG was due to perfusion of hypoventilated areas. The mean for the control Q-distribution was 0.88 with a mean log s.d. of +/- 1.14, indicating VA/Q-mismatch and did not change significantly. The reduction of pressures in the pulmonary vascular bed was accompanied by increased ventilation of areas with high VA/Q.