Esmolol is more effective than sodium nitroprusside in reducing blood loss during orthognathic surgery.

The goal of this study was to compare the efficacy of esmolol and sodium nitroprusside (SNP) as primary drugs for producing controlled hypotension and limiting blood loss during orthognathic surgery. Thirty ASA physical status I and II patients (mean age 22 yr) undergoing LeFort I maxillary osteotomies were randomly assigned to receive either esmolol (n = 15) or SNP (n = 15) as the primary drug to induce hypotension. All patients received a balanced anesthetic technique including isoflurane, with controlled hypotension during the downfracture of the maxilla. Patients assigned to the esmolol treatment group received boluses of 500 micrograms/kg of esmolol, followed by a continuous infusion of 100-300 micrograms.kg-1.min-1, and the SNP treatment group received a continuous infusion of SNP at 0.25-4.00 micrograms.kg-1.min-1; both infusions were titrated to obtain a mean arterial blood pressure within the target range of 55-65 mm Hg. The mean arterial blood pressure during the hypotensive period was 58.7 +/- 0.7 (mean +/- SEM) and 61.8 +/- 0.4 mm Hg for esmolol and SNP, respectively (P less than 0.001). In addition, 40% +/- 4% of the observed values in the esmolol group and 53% +/- 3% in the SNP group were outside the target range for mean arterial blood pressure (difference significant at P less than 0.05), and a greater proportion of the deviations were above 65 mm Hg in the SNP group than in the esmolol group (0.64 vs 0.46, respectively, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Alterations in cerebrospinal fluid uridine, hypoxanthine, and xanthine in head-injured patients.

1. Examination of the cerebrospinal fluid (CSF) of head-injured patients reveals that the concentration of intraventricular xanthine is elevated and that of uridine is decreased relative to those of adult lumbar CSF. 2. No correlations were observed between CSF lactate and CSF hypoxanthine, xanthine, or uridine, suggesting that changes in purine metabolites and the pyrimidine nucleoside do not index similar cellular events as does lactic acid production. 3. Ventricular CSF from hydrocephalic infants had uridine and hypoxanthine concentrations not significantly different from those of normal adult lumbar CSF, but xanthine was significantly elevated. 4. Since uridine has anticonvulsant properties and is a crucial substrate for cerebral metabolism, it may be useful to evaluate this pyrimidine for use in the management of patients with head injury.

Pulse oximetry: evaluation of accuracy during outpatient general anesthesia for oral surgery.

Pulse oximetry has been shown to be accurate under steady state conditions. In this study, the accuracy of four pulse oximeters are evaluated and compared during outpatient general anesthesia for third molar extractions. The oximeters evaluated are the Nellcor N-100, the Ohmeda 3700, the Novametrix model 500, and the Bird 4400 portable pulse oximeter.Ultralight general anesthesia for oral surgery presents a unique challenge for respiratory monitoring in that patients are often not intubated and commonly experience periods of hyper- and hypoventilation. Airway obstruction, apnea, and laryngospasm may occur easily and patients often vocalize and move during surgery. Because hypoxemia is the primary cause of morbidity and mortality during anesthesia, an accurate, continuous, and noninvasive monitor of oxygenation is critical to risk management.Twenty ASA class I and II patients underwent outpatient general anesthesia for third molar removal using nitrous oxide-oxygen, midazolam, fentanyl, and methohexital. Arterial blood samples were obtained at five-minute intervals during anesthesia, as well as any time a desaturation of >5% occurred, for measurement of arterial SaO(2) with an IL282 CO-Oximeter. These values were compared with simultaneously recorded saturations observed for each pulse oximeter. A total of 122 arterial samples were obtained over a range of PaO(2) from 52-323 mm Hg and observed saturations of 70-100%.The Bird 4400 portable pulse oximeter proved to be the most accurate and reliably predicted arterial saturation under these conditions (y = 1.03x - 2.8, r = 0.85). The Novametrix model 500 pulse oximeter also demonstrated a high degree of accuracy by linear regression analysis, but displayed the lowest correlation coefficient (spread of data points) overall (y = 0.97x + 2.8, r = 0.80.) The Nellcor N-100 pulse oximeter also proved to be highly accurate. (y = 1.05x - 4.1, r = 0.84.) In contrast, regression analysis of the observed saturations obtained with the Ohmeda 3700 pulse oximeter revealed that this unit significantly underestimated arterial saturation (y = 1.20x - 19.6, r = 0.83.)This study demonstrates that despite the rigorous conditions imposed by outpatient general anesthesia for oral surgery, three of the pulse oximeters tested were linearly accurate in predicting arterial oxyhemoglobin saturation over the range of 70-100%. The Ohmeda 3700 was found to significantly underestimate arterial saturation.

Absence of symptoms with carboxyhemoglobin levels of 16-23%.

It has been generally accepted that carboxyhemoglobin levels between 10-20% produce mild headaches, dizziness and/or nausea. Experimental double blind exposures of 18 healthy, nonsmoking young men at rest to 7,000-24,000 ppm CO, designed to elevate COHb to 15-20% in 3-5 minutes, were followed by exposure to 232 ppm CO designed to maintain COHb level for a total of 130 minutes. Resulting COHb values were 16-23%. These COHb values did not produce significantly more symptoms (as reported in an open-ended questioning) than reported in the control group (n = 23). Subjects were especially queried about headache, dizziness and nausea. The symptoms which were previously reported in clinical studies of CO poisoning may have resulted from CO exposure in combination with (a) exposure to other substances, (b) stress due to the event that precipitated medical attention or (c) higher COHb levels before the first blood sample was taken.

Use of capnography and transcutaneous oxygen monitoring during outpatient general anesthesia for oral surgery.

The combination of the capnograph (respired CO2 monitor) and the transcutaneous oxygen monitor was evaluated as a non-invasive system for monitoring of respiratory function in 10 ASA class I patients undergoing ultralight general anesthesia for removal of third molars. Capnography proved to be a sensitive and accurate method for detecting apnea and airway obstruction using the continuous display of the CO2 waveform. All episodes of apnea or obstruction were immediately detected as the respired CO2 level fell to zero baseline. The end-tidal CO2 (PetCO2) obtained via nasal prong sampling was not significantly different from the PaCO2. PetCO2 values served as useful indicators of hypoventilation. During steady-state conditions of respiration, transcutaneous oxygen tensions (PtcO2) correlated well with simultaneously measured PaO2 (r = 0.93). However, during any period when oxygenation was rapidly changing (step increase in FIO2, step decrease in FIO2, or apnea) the PtcO2 lagged behind changes in PaO2 even after a five-minute equilibration period, thereby not accurately reflecting the true state of oxygenation. Consequently, the transcutaneous oxygen monitor does not appear to be optimal as a respiratory monitor in the setting of ultralight general anesthesia where rapid, critical changes in oxygenation must be detected without delay.

Postoperative pulmonary function in children. Comparison of scoliosis with peripheral surgery.

We measured lung volumes, forced expirograms, and arterial blood gases in 2 groups of elective pediatric surgical patients (mean age, 11.4 +/- SD 2.8; n = 11, 12 operations) the day prior to surgery (control) and between the first and eighth postoperative days. The patients were Group I: peripheral surgery (n = 6) and Group II: reconstructive surgery for scoliosis (n = 5). The preoperative lung volumes and forced expiratory volume in one second were within the predicted normal range in both groups, except for a reduction in total lung capacity (TLC) and vital capacity (VC) in Group II. The postoperative lung volumes in Group I were not significantly different from the preoperative volumes. In group II, on postoperative Days 2 and 3, the lung volumes as a percent of preoperative volumes (mean +/- SEM) were VC, 44 +/- 11; functional residual capacity (FRC), 81 +/- 6; residual volume, 124 +/- 10; TLC, 61 +/- 10. Although the mean FRC returned to the preoperative volume by postoperative Days 5 and 6, the VC and its components remained reduced on postoperative Days 5, 6, and 8. We conclude that postoperative lung volume abnormalities are related to the site and magnitude of surgery and associated phenomena, such as pain, and preoperative respiratory function abnormalities.

In vivo response time of transcutaneous oxygen measurement to changes in inspired oxygen in normal adults.

We examined the in vivo response time of transcutaneous oxygen measurement (PtcO2) to a step increase (100 per cent oxygen) or decrease (air) of inspired oxygen in five normal adults (age 27 +/- SD 4.5 years). The PtcO2 electrode was placed on the upper chest (sensor temperature 44 degrees C). The mean +/- SEM 63 and 95 per cent response times of PtcO2 to a step increase in inspired oxygen were 2.9 +/- 0.2 and 6.8 +/- 0.2 and to a step decrease were 2.4 +/- 0.2 and 5.1 +/- 0.3 minutes. The 63 and 95 per cent response times for the pulmonary washin of oxygen were 1.0 and 2.6 minutes and washout were 0.8 and 2.3 minutes. We conclude that the in vivo response time of the PtcO2 is reproducible but substantially longer than that of the pulmonary washin and washout times and inadequate to monitor rapid changes in arterial oxygenation during anaesthesia, perioperative period or sleep in adults.

Vendor questionnaire to evaluate product quality, service, and support.

A questionnaire was developed to obtain verifiable data on the quality of a manufacturer's product, availability and quality of service, qualifications of service personnel, availability of spare parts, availability of inservice training programs for users and clinical engineering staff, history and future support of product, and technical requirements for preventive maintenance and repair. The questionnaire was constructed on the premise that product quality, service, and support throughout the life of the instrument are of equal importance to the function and price in purchase decisions. They play an important role in determining the true cost of patient monitoring equipment and contribute to the quality, safety, and efficiency of patient care.

Regulation of the tidal volume and ventilatory responses to CO2 in normal man and in scoliosis.

The variation of the ventilatory response to CO2 and its pattern among normals and in the presence of pulmonary disease is wide. In normal subjects the relationship between the slopes of the ventilatory (delta V/delta PCO2), tidal volume (delta VT/delta PCO2) and the frequency (delta f/delta PCO2) responses and body size, metabolic rate, resting ventilation and pattern, lung volumes or mechanical properties of the respiratory system have only been demonstrated in a few studies. In idiopathic scoliosis there is a positive correlation between the delta V/delta PCO2 and delta VT/delta PCO2 and body size, resting ventilation and tidal volume, lung volumes and compliance of the respiratory system. Although there were significant correlations between the delta V/delta PCO2 and the delta VT/delta PCO2 and th delta f/delta PCO2 the correlation between the delta VT/delta PCO2 and delta f/delta PCO2 was not significant. Correlations between the delta f/delta PCO2 and lung volumes, compliance or body size were also not significant. Therefore variation in the frequency response to CO2 contribute to the variation between individuals of the delta V/delta PCO2 and this variation is unrelated to respiratory mechanics or body size. We conclude that in human studies any examination of possible relationships between ventilatory response to CO2 and body size, lung volumes and mechanics should examine separately the tidal volume and frequency response to CO2. We postulate that the tidal volume response is the most appropriate variable to normalize for lung volumes, e.g., vital capacity (delta VT/VC/delta/ PCO2).

Respiratory and cardiovascular responses to hypoxemia and the effects of anesthesia.

The normoxic ventilatory drive contributes to the normal level of ventilation, and the hypoxic ventilatory drive contributes to the maintenance of adequate gas exchange in the presence of ventilation/blood flow maldistribution and increased mechanical load to breathing. This respiratory drive arises principally from stimuli at the carotid chemoreceptors. The reflex cardiovascular responses to hypoxia also contribute to the delivery of O2 to vital organs, and their efficacy depends on the integrity of the respiratory response and the autonomic nervous system as well as the function of the vascular system. Prolonged exposure to hypoxemia from altitude, cyanotic congenital heart disease, and chronic pulmonary disease impair the ventilatory response to hypoxia. In addition, the respiratory and cardiovascular responses to hypoxemia are impaired by familial or acquired abnormalities of the autonomic effector system. There is growing evidence that impaired respiratory response to hypoxemia is a major factor in recurrent respiratory failure in obesity, obstructive pulmonary disease, idiopathic or familial "hypoventilation," and contributes to disturbances in oxygenation during sleep [152, 189, 192, 202]. Although the ventilatory response to hypoxemia was traditionally thought to be resistant to the effects of inhalational anesthetics, barbiturates, and narcotics, there is abundant evidence that in fact the ventilatory response to hypoxia is more sensitive to depression by drugs than the ventilatory response to CO2. In addition, the hemodynamic responses to hypoxia are modified by anesthesia and anesthetic techniques. The clinical implications of these observations are wide. The ventilatory and cardiovascular response to hypoxemia will be altered, and usually depressed by age, disease processes, premedicant and anesthetic drugs, and autonomic blocking drugs. The cardiovascular responses will be modified indirectly by altered ventilatory control due to neuromuscular blocking drugs and controlled ventilation. Thus, not only will the responses to hypoxemia be depressed by anesthesia but the early clinical hemodynamic signs will be modified or absent, or indeed the cardiovascular response will further impair oxygen delivery. Furthermore, it is not only anesthetic doses that impair the reflex respiratory responses, but also subanesthetic doses of inhalational anesthetics and premedicant doses of barbiturates and narcotics. Hence the patient in the perioperative period continues to have impaired respiratory response to hypoxemia. As anesthetic and surgical care extends to older patients, patients with systemic disease, and recipients of cardiovascular peripheral and central drugs, the clinical implications of the impairment of ventilatory and cardiovascular responses to hypoxia, and the maintenance of organ and system function, escalate. Only a few hesitant steps have been taken into this vast arena of clinical and experimental research.

Reproducibility of data on steady-state gas exchange and indices of maldistribution of ventilation and blood flow.

The reproducibility of data on steady-state gas exchange and arterial blood gas levels was examined in 45 patients with similar pathophysiologic abnormalities (idiopathic scoliosis) by comparing the data obtained during two sequential periods breathing air. Comparison in all patients of 12 variables by paired t-test demonstrated statistically significant differences in the following three variables: the ratio of physiologic dead space to tidal volume (Vd/TV), the alveolar-arterial oxygen pressure difference (P[A-a]O2), and the arterial oxygen tension. By excluding four patients whose respiratory quotient was greater than two standard deviations from the mean value and one patient with a marked change in the pattern of ventilation, only the Vd/TV was significantly different (P less than 0.05). The range of the coefficients of variation was wide. The highest, which was for P(A-a)O2, was 18.8 percent; the majority were in range of 6 to 13 percent (minute ventilation, TV, frequency, oxygen consumption and carbon dioxide production, respiratory quotient, Vd/TV, dead space, and alveolar ventilation), and the coefficients of variation of partial pressure of oxygen and carbon dioxide in the arterial blood were, respectively, 3.6 and 3.4 percent.

Improved oxygenation during thoractomy with selective PEEP to the dependent lung.

In 22 patients during thoracotomy in the lateral position, the effects of selective positive end-expiratory pressure (PEEP) to the dependent lung while simultaneously ventilating the non-dependent lung at zero end-expiratory pressure (ZEEP) on (1) inspired O2 concentration required to maintain adequate Pao2 during thoractomy and 2) alveolar-arterial oxygen difference (AaO2D) while breathing 100 percent O2 at the end of thoractomy were examined and compared to ventilation of both lungs at ZEEP, Selective PEEP to the dependent lung resulted in adequate PaO2 with a lower inspired O2 concentration (44 +/- SD 6% versus 70 +/- SD 21%), and a smaller AsO2D while breathing 100 percent O2 189 +/- SD 31 versus 342 +/- SD 69 torr) at the end of thoracotomy.

The effects of anesthetic drugs and disease on the chemical regulation of ventilation.

The anesthesiologist uses a wide spectrum of drugs, including inhalational general anesthetics, barbiturates, benzodiazepines, narcotics analgesics and their antagonists, and neuromuscular blocking drugs. All of these drugs in sufficient dose impair the ventilatory response to chemical stimuli, and may cause inadequate gas exchange. The effect of depression of ventilatory control depends on the magnitude of depression and the coexistence of functional abnormalities in the respiratory system. The functional abnormalities are the result of preexistent pulmonary disease or other disease processes that impair respiratory function, the anticipated effects of major surgery (e.g., pulmonary resection), and the complications of anesthesia and surgery. From a functional viewpoint, the mechanisms of the effects of these disease processes on ventilatory control are: (1) interference with the neurophysiological control of automatic ventilation; (2) impairment of peripheral or central chemoreceptor function; (3) impairment of respiratory muscle function; (4) increase in the mechanical load to breathing as a result of increased resistance or decreased compliance of the respiratory system; and (5) increase in the ventilatory requirements as a result of ventilation/blood flow maldistribution, metabolic acidosis, or increased metabolic rate. As a result of current trends in the use of multiple drugs and controlled ventilation during anesthesia, the patient is at greatest risk during the early postoperative period in the recovery room. In addition to the functional abnormalities described above, the probability of impaired gas exchange and respiratory failure is increased as a result of impaired metabolism and elimination of drugs as a result of hepatic and renal insufficiency, and acute changes in acidbase status, which alter the ionization and distribution of drugs.

Idiopathic scoliosis. Gas exchange and the age dependence of arterial blood gases.

The aims were to examine the gas exchange and arterial blood gas abnormalities among patients with scoliosis, and the correlation of these abnormalities with age and severity of deformity. Means among 51 patients were as follows: age 25.4 +/- 17.5 yr, angle of scoliosis 80.2 +/- 29.9 (SD), vital capacity 1.94 +/- 0.91 (SD) (i.e. 60.6 +/- 19.2% of predicted), PaO2 85.8 +/- 12.0 (SD), PaCO2 42.4 +/- 8.0, physiological dead space to tidal volume ratio 0.438 +/- 0.074 (SD), and alveolar-arterial oxygen difference breathing air 14.9 +/- 8.9 (SD). Statistically significant correlations were as follows: the PaCO2 and physiological dead space to tidal volume ratio increased with age, and the PaO2 and alveolar ventilation decreased with age. The PaO2, alveolar ventilation, and tidal volume were inversely related to the angle of scoliosis and directly related to the vital capacity, precent predicted vital capacity, and the compliance of the respiratory system. The physiological dead space to tidal volume ratio and the alveolar-arterial oxygen difference were inversely related to the vital capacity, percent predicted vital capacity, and the compliance of the respiratory system. PaCO2 was directly related to the elastance of the respiratory system. We conclude that ventilation-blood flow maldistribution as a result of deformity of the rib cage was the primary abnormality in gas exchange, and that with age there was progressive deterioration in gas exchange. The age-dependent increase in PaCO2 and decrease in alveolar ventilation were due to the increasing physiological dead space to tidal volume ratio and failure of a compensatory increase in ventilation.

Idiopathic scoliosis. Mechanical properties of the respiratory system and the ventilatory response to carbon dioxide.

The aims were to examine the effects of scoliosis (angle), and age on lung volumes, elastic properties of the respiratory system, and the ventilatory response to CO2. The mean age of the 55 patients was 25.4 plus or minus SEM 2.5 yr, and the mean angle was 80 plus or minus SEM 4.2. The mean plus or minus SEM percent predicted lung volumes were vital capacity (VC), 60.5 plus or minus 2.7; total lung capacity (TLC), 70,2 plus or minus 2.6; functional residual capacity (frc), 79.3 plus or minus 3.2; and residual volume (RV), 99.7 plus or minus 5.2. The correlation coefficients between the angle of scoliosis and each of the following were significant: TLC (-0.548), percent predicted TLC (-0.547), VC (-0.485), percent predicted VC (-0.523), FRC (-0.533), percent predicted FRC (-0.338), RV (-0.438), and percent predicted RV (-0.318). The mean compliance of the total respiratory system (Crs) was 0.049 litter/cm H2O plus or minus SEM 0.004, and the mean compliance of the chest wall (Ccw) was 0.080 liter/cm H2O plus or minus SEM 0.012. The Crs and Ccw were inversely proportional to the angle (r-0.620 and -0.721) and directly proportional to the height and the weight. The mean deltaV/deltaPco2 was 1.32 liter/min per mm Hg (SEM 0.171), and the mean deltaVt/deltaPco2 was 28.9 ml/mm Hg (SEM 3.64). The correlation coefficients between deltaV/deltaPco2 and the following were height, 0.499; VC, 0.792; TLC, 0.632; AND Crs, 0.520; and between the deltaTt/deltaPco2 and the following were height, 0.500; VC, 0.878; TLC, 0.802; and Crs, 0.590. We conclude that body size and the deformity were the determinants of the lung volumes and the mechanical properties of the respiratory system, and that these variables were the major factors in both the magnitude and pattern of the ventilatory response to CO2. The correlations between age and the mechanical properties of the respiratory sytem, deltaV/deltaPco2, and deltaVt/deltaPco2, were not significant, but the correlation coefficients between age and several of the derivatives of deltaV/deltaPco2 and deltaVt/deltaPco2 were significant.