David A. Paulus

Pulse oximetry for vascular monitoring in upper extremity replantation surgery

Pulse oximetry as a postoperative monitor for replanted or revascularized digits was evaluated experimentally and clinically. The accuracy of detection of vascular occlusion was 100%, and arterial and venous occlusion could be differentiated by changes in pulse inflow and oxygen saturation. Digits demonstrating O2 saturations above 95% remained viable, those below 85% were associated with venous occlusions, and those with no saturation represented arterial occlusions. This method is simple, noninvasive, continuous, and accurate, and it reliably assesses revascularized digits and replanted parts.

Methylene Blue and Indocyanine Green Artfactually Lower Pulse Oximetry Readings of Oxygen Saturation. Studies in Dogs

The effects of fluorescein, methylene blue, and indocyanine green on hemodynamic variables and on pulse oximetry and co-oximetry measurements of arterial hemoglobin oxygen saturation (SaO2) and oxyhemoglobin percentage (% HbO2) were evaluated in 16 anesthetized dogs in vitro by cooximetry (% HbO2) and in vivo by pulse oximetry (SaO2). The light absorbance (optical density) in plasma (range 500 to 800 nm) was measured by a spectrophotometer. Fluorescein did not affect oximetry measurements, plasma light absorbance in the range measured, or hemodynamic variables. Methylene blue caused dose-dependent decreases in measurements made with both forms of oximetry for up to 30 minutes, the decrease being greater and longer lasting with pulse oximetry (P < 0.05). Hemodynamic measurements in 5 dogs showed that methylene blue (1 to 5 mg/kg) increased arterial pressure transiently, after which cardiac output, stroke index, and left ventricular stroke work index decreased and left ventricular end-diastolic pressure and systemic and pulmonary vascular resistances increased (P < 0.05 with 5 mg/kg). Methemoglobin concentration measured by co-oximetry increased significantly (to 19.9 ± 1.4%, P < 0.05) 1 minute after 5 mg/kg of methylene blue was injected. Methylene blue had a dose- and time-dependent effect on plasma light absorbance, and this effect peaked in the 660- to 670-nm range. The data do not distinguish the relative contributions of physiology (hemodynamic change), chemistry (methemoglobin production), and physics (optical properties) to the decrease in pulse oximetry and co-oximetry measurements that follows injection of methylene blue. Indocyanine green affected neither hemodynamic variables nor co-oximetry readings but decreased pulse oximetry readings for up to 10 minutes dose dependently. With doses of 0.1 to 3.0 mg/kg of indocyanine green plasma light absorbance peaked at 805 nm but increased dose dependently for up to 30 minutes at 660 nm. Methylene blue and indocyanine green (and, by implication, other dyes with plasma light absorbance peaks in the 600- to 1,000-nm range) artifactually alter oximetric detection of arterial hemoglobin oxygen saturation and oxyhemoglobin percentage.

Carcinoid heart disease: A case report and literature review

We report a patient who presented for elective exploratory laparotomy, and resection of a pelvic mass, which was thought to be ovarian carcinoma. Intraoperative transesophageal echocardiography demonstrated right-sided valvular heart lesions, which suggested the diagnosis of carcinoid syndrome before a pathologic confirmation was obtained. This article discusses the classical presentation and anesthetic management of patients with carcinoid syndrome and emphasizes the importance of proper preoperative diagnosis and careful planning if the incidence and severity of the symptoms that this condition can provoke are to be reduced.

Tissue hypoxia distal to a Peñaz finger blood pressure cuff

The Peñaz finger method to measure blood pressure uses a finger cuff in which the pressure level fluctuates in the vicinity of the mean arterial pressure level and thereby interferes with the circulation of blood to and from the fingertip. We measured capillary blood gases and saturation of hemoglobin in the finger during Peñaz finger blood pressure (PFBP) monitoring to assess the degree to which it impairs circulation in the fingertip. Within 2.5 minutes after initiating PFBP monitoring, capillary oxygen tension (Po2) had decreased significantly, from about 71 mm Hg to between 49 and 58 mm Hg for up to 50 minutes. These changes were quite different from those occurring when an occlusive tourniquet was applied around the finger. Within 10 minutes of tourniquet application, acidosis (pH 7.25), hypercapnia (carbon dioxide tension, 59.0 mm Hg), and hypoxemia (Po2, 29 mm Hg) resulted. Within 30 seconds of releasing the PFBP cuff, capillary blood gas values were back to normal. Interspersing 30-second rest periods every 5 minutes during 35 minutes of PFBP monitoring actually decreased capillary oxygen values compared with monitoring without such rest periods. A finger pulse oximeter distal to the PFBP cuff showed desaturation from an average of 97% to 93.7%, with much variability. However, desaturation was statistically significant within 1 minute of application of the PFBP cuff. Within 1 minute the finger volume increased an average of 0.05 ml. After 1 minute the volumes varied widely and, on the average, returned to normal despite continued PFBP monitoring.

Pulse oximetry fails to accurately detect low levels of arterial hemoglobin oxygen saturation in dogs.

The accuracy of two commercially available pulse oximeters (the Ohmeda Biox 3700, software version “J,” and the Nellcor N-100) in detecting low levels of arterial hemoglobin oxygen saturation (SaO2) was evaluated in 10 dogs in which hypoxia was induced by stopping the fresh gas flow into the anesthesia machine circle system. Measurements made in vivo with the pulse oximeters, with detectors placed on the tongue, were compared with measurements made in vitro using an IL 282 CO-Oximeter as SaO2 decreased toward zero. Measurements from the two oximeters correlated poorly over the range from 0 to 100% SaO2 (r = 0.69). In this range, the correlation between Nellcor N-100 measurements and those of the CO-Oximeter had an r of 0.82, a regression line slope of 0.82, and a y intercept of 14.8; the correlation between the Ohmeda Biox 3700 and the CO-Oximeter had an r of 0.83, a regression line slope of 0.66, and a y intercept of 32.7. The correlation with the CO-Oximeter was similar for both the Ohmeda and the Nellcor pulse oximeters at an SaO2 of 80% or more. However, when SaO2 was less than 80%, measurements by pulse oximetry correlated less well with CO-Oximeter measurements (r = 0.62, slope = 0.64, and y intercept = 21.0 for Nellcor; r = 0.71, slope = 0.67, and y intercept = 32.4 for Ohmeda). When SaO2 was less than 60%, both oximeters inaccurately indicated the co-oximetry values (r = 0.36 and y intercept = 26.1 for the Nellcor; r = 0.48 and y intercept = 33.2 for the Ohmeda). In this animal model, with pulse oximeter measurements obtained from the tongue and with rapidly decreasing SaO2, measurements of SaO2 by pulse oximetry become inaccurate in comparison with co-oximetry measurements at low levels of SaO2.

Haemodynamic effects of ketamine and thiopentone during anaesthetic induction for Caesarean section

Ketamine (1 mg·kg-1) or thiopentone (4mg·kg-1) was used to induce anaesthesia for Caesarean section in 62 normotensive patients. During induction of anaesthesia and before laryngoscopy, blood pressure did not change in either group (preinduction systolic blood pressure, 131 mmHg, and diastolic blood pressure, 75 mmHg). When laryngoscopy and intubation were performed, mean blood pressures of both patient groups increased 20–30 per cent. With ketamine (n = 30) heart rate was unchanged from the preinduction rate of 85 beats/min before laryngoscopy and increased significantly by 15 per cent during laryngoscopy and intubation. With thiopentone (n = 32), heart rate increased significantly to 20 per cent above the preinduction rate of 87 beats/min during induction and increased further (to 35 per cent above the preinduction rate) during laryngoscopy and intubation. The average maximal rate-pressure product calculated for the thiopentone group was over 18,000, which was significantly higher than the 15,000 calculated for the ketamine group. Neonatal outcome as assessed by Apgar score and umbilical blood gas analysis was good and did not differ significantly between groups.RésuméLa kétamine (1 mg·kg-1) ou le thiopentone (4 mg·kg-1) a été utilisé comme agent d’induction chez 62 patientes normotensives devant subir une césarienne. Lors de l’induction et avant la laryngoscopie, la tension artérielle n’a pas changé dans aucun des deux groupes (la tension artérielle systolique après induction, 131 mmHg, et la pression artérielle diastolique, 75 mmHg). Lors de la laryngoscopie et l’intubation la tension artérielle dans les deux groupes augmenta de 20 à 30 pour cent. Avec la ketamine (n = 30) la fréquence cardiaque qui était de 85 battements/min. avant l’induction n’a pas changée lors que l’induction et avant la laryngoscopie. Cependant on observa une augmentation significative de 15 pour cent lors de la laryngoscopie et l’intubation. Avec le thiopentone (n = 32) la fréquence cardiaque qui était de 87 battements/min. avant l’induction augmenta significa-tivement de 20 pour cent lors de l’induction et avant la laryngoscopie. Cette augmentation de la fréquence cardiaque atteint 35 pour cent lors de la laryngoscopie et l’intubation. Le produit de la fréquence cardiaque par la pression maximale moyenne, calculé pour le groupe thiopentone était supérieur à 18,000, significativement supérieur à celui du groupe kétamine calculé à 15,000. Concernant les nouveaux-nés évalués par les tests d’Apgar et l’analyse des gaz sanguins du cordon ombilical le résultat final était considéré bon et n’a pas différé significativement entre les deux groupes.

Capnography and the bain circuit I: A computer model

The Mapleson D anesthesia breathing system has no valves and allows rcbreathing ot carbon dioxide. Its coaxial version is known as the Bain system. The interpretation of capnograms obtained during its use requires an understanding of the interrelationships of patient and system variables. Toward that end, a systematic description of mechanical ventilation with the Bain circuit was undertaken based on the physical laws of gas transport. The mathematical formulation ot the model contains the relations between pressure, flow, and volume in the tube, alveolar space, and ventilator. The flows, calculated from these relations, are used to determine the CO2 concentrations in the different parts of the model. Two sets of data are used—patient and system. The patient data, used to solve the equations numerically, are lung-thorax compliance, CO2 inflow into alveolar space (CO2 production), functional residual capacity, dead space volume, airway resistance, and respiratory quotient. The ventilation system data comprise the dimensions and volumes of the Bain circuit, ventilator, connectors, and tubes; spill valve pressure; resistances to flow in the individual tube parts; ventilator settings; and fresh-gas flow rates.After incorporation of a volunteer’s respiratory variables into the model, capnograms obtained from the model compared well with those obtained from the volunteer.The structure of the model is such that it permits easy introduction or changes of patient and system variables to obtain individual results or model specific circumstances. This flexibility makes it a useful tool for understanding the properties of the Bain circuit under a variety of clinical circumstances. The results may be displayed in a number ot different ways.

Computerized Pre-Anesthetic Evaluation Results in Additional Abstracted Comorbidity Diagnoses

ObjectiveTo study the impact of information from a physician-entry computerized preanesthetic evaluation system on the coding of International Classification of Diseases (ICD-9-CM) diagnoses and on hospital reimbursement due to alterations in diagnosis-related group (DRG) codes.MethodsNonrandomized, unblinded trial conducted at a 570-bed university tertiary care hospital. First without and then with reference to information contained on computer-based preanesthetic evaluation reports, medical charts were coded by the study institutions usual professional coders for ICD-9-CM discharge diagnoses and DRG assignment.ResultsFor 22 of 180 charts studied (12%, 95% confidence limits 7.4% to 16.7%), at least one ICD-9-CM diagnosis was added. Three of 84 DRG-based reimbursements were altered, increasing hospital reimbursement by 1.5%.ConclusionsSupplemental information from a physician-entered, problem-oriented, computerized preanesthetic evaluation system improved discovery of diagnoses in the population studied.

Incidence of oxygen desaturation during oral surgery outpatient procedures

The frequency, severity, and duration of oxygen desaturation during oral surgical procedures in outpatients was measured. Sixty patients divided into six groups received either lidocaine; lidocaine, diazepam, and meperidine; lidocaine, diazepam, meperidine, and headphone music; lidocaine, diazepam, meperidine, and nitrous oxide; lidocaine, diazepam, meperidine, methohexital, and nitrous oxide; or lidocaine and nitrous oxide. Forty-three percent of the 30 patients who did not receive supplemental oxygen experienced clinically significant oxygen desaturation (greater than 5%) with a mean duration of 4.6 minutes. Only 13% of the patients who received supplemental oxygen had significant desaturation ranging from ten seconds to 12.3 minutes with a mean duration of 1.4 minutes. An unexpected finding was hypoxia in patients receiving only lidocaine anesthesia.

Comparison between oscillometric and invasive blood pressure monitoring during cardiac surgery

We compared values of invasive blood pressure measured intra-arterially with those measured noninvasively with an automated oscillometric monitor. Twenty-eight patients undergoing cardiac surgical procedures under general anesthesia were studied and 552 determinations were made. The two methods of measuring blood pressure correlated within the expected bounds of experimental accuracy and physiological variation. However, the correlation between invasive and noninvasive methods varied, apparently arbitrarily, with time. These disparities could not be explained by a linear combination of physiological variables recorded. Systolic determinations correlated the best and diastolic the least between the invasive and noninvasive methods. In general, the correlation was better for adults than for children, except with diastolic blood pressure.