Kai Rehder

Regional intrapulmonary gas distribution in awake and anesthetized-paralyzed man.

Intrapulmonary distribution of ventilation/unit lung volume was studied in 28 volunteers in the sitting, supine, or right lateral decubitus position, either awake or anesthetized-paralyzed and mechanically ventilated. We found significant differences between the awake state and anesthesia-paralysis with mechanical ventilation in 1) intrapulmonary gas distribution, and 2) the vertical gradient of regional functional residual capacities for the subjects in the lateral decubitus position, but not for those in the sitting and supine positions. The effect of increasing the tidal volume on distribution of ventilation was significantly different 1) between the three body positions for a given state, and 2) between the two states for a given body position. The data suggest thoracoabdominal mechanics are different in the three body positions and that anesthesia-paralysis and mechanical ventilation may cause a different pattern of expansion of the respiratory system than spontaneous breathing in the awake state.

Position and motion of the human diaphragm during anesthesia-paralysis

Regional motion of the human diaphragm was determined by high-speed, three-dimensional x-ray computed tomography. Six healthy volunteers were studied first while awake and breathing spontaneously and again while anesthetized-paralyzed and their lungs ventilated mechanically. Tidal volume (VT) and respiratory frequency were similar during both conditions. Three subjects were studied while they were supine and three while they were prone. During spontaneous breathing, movement of dependent diaphragm regions was greater than that of nondependent regions in four of six subjects. In five of the six subjects, dorsal diaphragm movement exceeded ventral movement regardless of body position. The volume displaced by the diaphragm (delta Vdi) was similar to VT in supine subjects but tended to be less than VT in prone subjects. After induction of anesthesia-paralysis, the end-expiratory position of the diaphragm did not change consistently in supine subjects, whereas a consistent cephalad volume shift occurred in prone subjects. During anesthesia-paralysis and mechanical ventilation, delta Vdi was reduced to approximately 50% of VT in both body positions. In the supine position, the pattern of diaphragm motion during mechanical inflation was nearly uniform. By contrast, in the prone position, the motion was nonuniform, with most motion occurring in the dorsal (nondependent) regions. It is concluded that the dominant influence on diaphragm motion may be some anatomical difference between the crural and costal diaphragm regions rather than the abdominal hydrostatic pressure gradient.

Cemented Versus Noncemented Total Hip Arthroplasty—Embolism, Hemodynamics, and Intrapulmonary Shunting

Bone cement implantation syndrome is characterized by hypotension, hypoxemia, cardiac arrhythmias, cardiac arrest, or any combination of these complications. It may result from venous embolization that occurs in conjunction with intramedullary hypertension in the femur during insertion of the prosthesis in patients undergoing cemented total hip arthroplasty (THA). Intramedullary hypertension does not occur in patients undergoing noncemented THA. In this study, we sought to compare embolization between patients undergoing cemented and noncemented THA and to determine whether this state resulted in cardiorespiratory deterioration. In this prospective investigation of 35 patients undergoing elective THA, we used transesophageal echocardiography and invasive hemodynamic monitoring, and in 12 of them, we monitored distribution of pulmonary ventilation and perfusion intraoperatively. Embolization was significantly greater after insertion of the prosthesis in patients undergoing cemented than in those undergoing noncemented THA. Cemented THA was also associated with decreased cardiac output and increased pulmonary artery pressure and pulmonary vascular resistance. Increases in ventilation-perfusion mismatching, however, could not be demonstrated 30 minutes after insertion of the femoral prosthesis. Intraoperative monitoring for embolism may help physicians assess patients in whom cardiorespiratory function deteriorates during THA.

Halothane Biotransformation in Man: A Quantitative Study

The metabolic breakdown of halothane was quantiatively determined in two patients. Trifluoroacetic acid and bromide were found as metabolites in the urine. Both metabolites have a protracted excretion rate. Since the biological half-life of trifluoroacetic acid is unknown, one can calculate only the least amount of halothane that had been metabolized on the basis of the excreted trifluoroacetic acid: 12 per cent in both patients. On the basis of the excreted urinary bromide, 20 per cent and 17 per cent, respectively, of the halothane taken up by the body was calcalated to be metabolized, if one assumes a biological half-life of 12 days for bromide.

Multicenter Study of General Anesthesia. II. Results

A prospective, stratified, randomized clinical trial of the safety and efficacy of four general anesthetic agents (enflurane, fentanyl, halothane, and isoflurane) was conducted in 17,201 patients (study population). Patients were studied before, during, and after anesthesia for up to 7 days. Nineteen patients died (0.11%), and in seven of these (0.04%) the anesthetic may have been a contributing factor. The rates of death, myocardial infarction, and stroke in the study population were so low (less than 0.15%) that no conclusions regarding the relative rates of these outcomes among the four anesthetic agents could be reached. The rates of 16 of 66 types of adverse outcomes in the study population were significantly different among the four study agents. Most of these outcomes were minor. However, severe ventricular arrhythmia (P less than 10(-6)) was more common with halothane, severe hypertension (P less than 10(-6)) and severe bronchospasm (P = 0.028) were more common with fentanyl, and severe tachycardia (P = 0.001) was more common with isoflurane. Recovery from anesthesia during the first 30 min was slowest in those patients who received halothane (P less than or equal to 0.001). In addition, patients who received fentanyl experienced less pain during the first hour in the recovery room (P less than 10(-6)). In conclusion, clinically important differences do exist for some outcomes among the four study agents.

The Function of Each Lung of Anesthetized and Paralyzed Man during Mechanical Ventilation

Intrapulmonary gas distribution of individual lungs was studied in five healthy anesthetized, paralyzed, and mechanically ventilated adult volunteers in the supine and both lateral decubitus positions. Comparison of the results with previous findings in conscious and spontaneously-breathing man indicated that the distribution of inspired gas during mechanical ventilation in anesthetized subjects is different. Inspired gas was more uniformly distributed within the individual lungs of mechanically ventilated anesthetized subjects in the supine position. There was a preferential distribution of tidal volume to the nondependent lung, in contrast to the preferential ventilation of the dependent lung in conscious, spontaneously-breathing man in the lateral position. Although relative end-expiratory lung volumes (that is, functional residual capacity) of individual lungs in persons ventilated mechanically in both positions were similar to those reported for the conscious, spontaneously-breathing subject, preferential ventilation of the nondependent lung and lesser ventilation of the dependent lung resulted in similar nitrogen clearances from the two lungs when the subjects were in the lateral position. This finding is in contrast to the significant differences between nitrogen clearances of the two lungs in spontaneously-breathing man in the lateral position.

Evaluation of intraoperative transesophageal two-dimensional echocardiography

Transesophageal two-dimensional echocardiography (TEE) was evaluated in 11 patients who underwent myocardial revascularization. The TEE transducer was positioned to view the left ventricular (LV) short-axis at the level of the papillary muscles (midcavity). Good quality echocardiographic images were obtainable in ten of 11 patients. Global LV function was assessed by measuring LV end-diastolic and end-systolic area and computing the fractional area change (FAC). Measurements of LV areas and FAC had excellent intraobserver reproducibility. Regional LV function was analyzed in two ways after dividing the short-axis view of the LV into four or five anatomic segments. Systolic wall thickening (SWT) of the myocardium was measured in each of four segments by digitization of the endocardial and epicardial borders of the LV and determining the fractional wall thickening. Measurements of SWT were not reproducible, primarily because of a difficulty in delineating the epicardial border of the LV accurately. In the second method, regional wall motion (RWM) in each of five segments was graded according to a previously developed scoring system. RWM analysis proved to be a measurement with excellent interobserver and intraobserver reproducibility. TEE was performed without complication and found to be a reproducible method for assessing global and regional LV function. Quantitative analysis is tedious and, therefore, currently not available on-line in the operating room.

Effects of Isoflurane Anesthesia and Muscle Paralysis on Respiratory Mechanics in Normal Man

In five healthy adult male volunteers in the supine position, respiratory mechanics and functional residual capacity (FRC) were studied in the awake state (control) and with muscle paralysis and mechanical ventilation during isoflurane anesthesia (inspired concentrations, 1 and 2 per cent). In eight of nine instances, FRC was less during isoflurane anesthesia compared with control. Static compliance of the total respiratory system (Crs) decreased consistently during anesthesia and that of the lung (Ct) decreased in eight of nine instances; static compliance of the chest wall (Cπ) did not change. Average pulmonary resistance (Rl) was significantly higher during anesthesia. The decrease in FRC and increase in Rl appear to be somewhat less than those reported for other anesthetics. Increasing the inspired isoflurane concentration to 2 per cent had no further significant effect on FRC, Crs C19 Cl and Rl Arterial blood pressure was decreased significantly and heart rate remained unchanged during anesthesia with I per cent isoflurane; with 2 per cent isoflurane, blood pressure was further significantly decreased and heart rate did not change significantly.

Physiologic approach to mechanical ventilation.

An understanding of ventilator management must be predicated on physiologic principles. There is a considerable array of equipment, permitting an almost limitless number of permutations in ventilator therapy, to support patients with respiratory failure. The physician who understands patient-ventilator interactions and their effects on cardiopulmonary function will be best equipped to individualize therapy. We believe that further refinements in supportive equipment probably will not improve outcome significantly. Thus, more emphasis should be placed on elucidating the underlying disease process and its effects on respiratory structure and function.

Actions of enflurane, isoflurane, vecuronium, atracurium, and pancuronium on pulmonary resistance in dogs.

The effects of enflurane, isoflurane, vecuronium, atracurium, and pancuronium on pulmonary resistance and heart rate were studied in 30 vagotomized dogs lying supine and anesthetized with chloralose-urethane. None of the five drugs affected pulmonary resistance when the airway was unstimulated. Enflurane and isoflurane significantly attenuated the increase in pulmonary resistance induced by electrical stimulation of the vagus nerves. This effect was dosedependent and similar for both anesthetics at equivalent multiples of their minimum alveolar concentration. Atracurium significantly (P < 0.05) enhanced the increase in pulmonary resistance induced by vagus nerve stimulation; vecuronium had no significant effect. Pancuronium, up to a cumulative dose of 0.14 mg/kg, also significantly (P < 0.05) enhanced the increase in pulmonary resistance induced by vagus nerve stimulation; but this effect was reversed by further increasing the dose. Pancuronium also attenuated the cardiodecelerator response to vagus nerve stimulation in a dose-depen-dent fashion. The underlying mechanisms for the attenuation of responses to vagus nerve stimulation by enflurane or isoflurane or for the increase in response with atracurium are unknown. Pancuronium at lower doses increases the response most likely by blocking prejunctional muscarinic receptors (M2) that physiologically inhibit vagally mediated increases in pulmonary resistance.