John E. Scharf

Preemptive Ketamine Decreases Postoperative Narcotic Requirements in Patients Undergoing Abdominal Surgery

The aim of this study was to determine if preemptive administration of systemic ketamine decreases postoperative pain when compared with postwound closure administration of ketamine.Patients undergoing abdominal procedures were randomized into a preemptive or postwound closure ketamine administration group. Before surgical incision, patients in the preemptive group (n = 20) were given 0.5 mg/kg ketamine followed by a ketamine infusion of 10 micro g [centered dot] kg-1 [centered dot] min-1, which was discontinued at abdominal closure. The patients in the postwound closure (n = 20) group were given 0.5 mg/kg of ketamine immediately after abdominal closure. Postoperatively, all patients received intravenous (IV) morphine in the postanesthesia care unit (PACU) and were started on IV morphine patient-controlled analgesia after discharge from the PACU. Postoperative pain was assessed by measuring morphine consumption and visual analog scale (0-100 mm) pain scores at rest. Patients in the preemptive group had significantly lower morphine consumption on postoperative Days 1 and 2. No significant intergroup differences were seen in the pain scores throughout the study period. Preemptive ketamine decreased postoperative opioid requirements, which was observed long after the normal expected duration of ketamine. (Anesth Analg 1997;84:1086-90)

A prospective, randomized, double-blind comparison of epidural and intravenous sufentanil infusions.

BackgroundThe site of action (spinal vs. central) of epidurally administered lipid-soluble opioids has been the subject of controversy. We compared the efficacy, plasma concentration and side effects of epidural and intravenously administered sufentanil for postoperative pain relief. MethodsUsing a double-blind, prospective design, 50 patients scheduled for intraabdominal operations during combined epidural-general anesthesia were randomized into one of two groups. Patients in group 1 (n = 24) received a 1-μg/ml sufentanil infusion epidurally at 0.2 μg · kg−1. h−1 and a saline infusion intravenously at the same rate. Patients in group 2 (n = 26) received a 1-μg/ml sufentanil infusion intravenously at 0.2 μg · kg−1. h−1 and a saline infusion epidurally at the same rate. Intravenous morphine sulfate was available in 2-mg increments to all patients in the postanesthesia care unit until visual analogue scale (0–100 mm) pain score was ≤30. Then, a patient-controlled intravenous pump providing morphine on demand (1 mg with a 10-min lockout) was begun. Blood samples were drawn for sufentanil plasma levels and patients were assessed for pain, sedation and nausea for the 48 h after commencement of the infusions. ResultsSimilar visual analogue pain, sedation, and nausea scores were found between the patients in the two groups. No differences were found in supplemental morphine requirements and plasma sufentanil concentrations between the patients in the two groups. A higher incidence of excessive sedation requiring infusion decrease was infusion decrease was found in the intravenous group (six vs. one, P < 0.05). ConclusionsMany clinical similarities were found when epidural and intravenous sufentanil infusions were compared. The higher incidence of excessive sedation in the patients receiving intravenous sufentanil could not be explained on the basis of plasma sufentanil concentrations alone. This study indicates that little clinical difference exists between epidural and intravenous administration of sufentanil.

Pulse oximetry through spectral analysis

Signal processing algorithms for pulse oximetry waveforms are typically completed in the time domain utilizing analog filtering and moving average techniques. This investigation evaluated the use of spectral analysis as an alternative algorithm for the signal processing of pulse oximetry waveforms. Fast Fourier transformation of eight separate red and infrared waveform data segments was accomplished via a custom C-program. Magnitudes of spectral peaks in the cardiac spectrum were utilized to compute an SpO2 value. In this limited trial, spectral analysis derived SpO2 values were at least as accurate as time series SpO2 values. However, further investigation is needed to further define the limits of spectral analysis on pulse oximetry waveforms with unusual respiratory variations, electrical noise, and motion artifact.<<ETX>>

Optimization of portable pulse oximetry through Fourier analysis

Portable pulse oximetry requires new techniques to minimize hardware expense, footprint, and power consumption. To optimize portability, fast Fourier transform (FFT) analysis was used as an alternative method to calculate hemoglobin oxygen saturation (SpO2) values. The following variables were used for FFT optimization: (i) total collection period; (ii) number of discrete data points; (iii) data sampling rate; and (iv) resolution in the spectral analysis output. The objective was to discover the minimum sampling rate and minimum number of discrete data points which would maintain SpO2 accuracy. Preliminary results indicate that a 15 Hz data sampling rate over a 4.3 second collection period maintains acceptable SpO2 accuracy via a 64 point FFT computation.<<ETX>>

Direct digital capture of pulse oximetry waveforms

Pulse oximetry sensor photodiodes typically generate a current proportional to the intensity of the pulse oximetry waveforms. This method of waveform capture is prone to electrical noise and requires analog-to-digital conversion downstream for further digital signal processing. This investigation evaluated the use of a light-to-frequency photodiode as an alternative sensor for capturing pulse oximetry waveforms. Red and infrared pulse oximetry waveforms were captured with a Texas Instruments TSL220 light-to-frequency converter. The fidelity of the captured waveforms was excellent. The compact TSL220 combination of photodiode, amplifier, and current-to-frequency converter can potentially replace the light-to-current photodiode, current-to-voltage converter, and analog-to-digital converter now used in typical pulse oximetry applications.<<ETX>>

Reducing surgical patient costs through use of an artificial neural network to predict transfusion requirements

Abstract Transfusion and blood bank services have long been identified as a source of potential cost savings. The implementation and use of maximum surgical blood ordering schedules (MSBOS) and type and screen practices have already succeeded in reducing overall waste and costs associated with transfusion services, but further reductions in waste and cost are still realizable. An artificial neural network (ANN) is trained to predict the quantity of transfusion units that are required by surgical patients for a specific operation. The ANNs produce a significant reduction in the quantity of blood ordered and a subsequent reduction in costs to the hospital and patients. ANNs offer a means to reduce patient costs while maintaining a high level of patient care.

Malignant hyperthermia involving the administration of desflurane

PurposeThis report describes an episode of malignant hyperthermia (MH) in a ten year old boy receiving desflurane anaesthesia.Clinical featuresFollowing induction of general endotracheal anaesthesia with thiopentone and succinylcholine, desflurane was administered for maintenance of anaesthesia. Ten minutes after commencing desflurane administration, heart rate andPetCO2 increased to 165 bpm and 50 mmHg, respectively. Initially, the tachycardia was attributed to a sympathetic response secondary to desflurane. Desflurane was discontinued and isoflurane was started. Minute ventilation was increased to decreasePetCO2-Over the next five minutes, temperature increased to 38.4°C as thePetCO2 increased to above 60 mmHg. Venous and arterial blood gases were drawn which showed acidosis and hypercapnia. Temperature andPetCO2 continued to increase, reaching peak values of 41°C and 77 mmHg, respectively. Efforts to cool the patient were made. A total of 220 mg dantrolene sodium was administered iv. Following dantrolene, the temperature increase and acidosis subsided. Heart rate andPetCO2 decreased to 130 bpm and 36 mmHg, respectively. The surgical procedure was expeditiously performed. Postoperatively, in the Paediatric Intensive Care Unit, a dantrolene infusion of 20 mg · hr−1 was administered for 12 hr. The trachea was extubated the following morning. Several days later, the patient underwent another surgical procedure without complications using MH-safe anaesthetics.ConclusionOnset of tachycardia in a patient receiving desflurane may initially be attributed to desflurane-induced sympathetic hyperactivity. This poses a clinical challenge in the diagnosis of MH during desflurane anaesthesia.RésuméObjectifCommuniquer le compte rendu d’un épisode d’hyperthermie (HM) survenu chez un enfant de dix ans anesthésié au desflurane.Caractéristiques cliniquesAprès l’induction d’une anesthésie générale endotrachéale avec du thiopentone et de la succinylcholine, du desflurane a été administré pour l’entretien de l’anesthésie. Deux minutes après le début de l’administration de cet agent, la fréquence cardiaque et lePetCO2 ont respectivement augmenté à 165 bpm et 50 mmHg. Initialement, la tachycardie a été attribuée à une réaction sympathique provoquée par le desflurane. Pendant les cinq minutes suivantes, la température a augmenté à 38,4°C et laPetCO2 a dépassé 60 mmHg. Des échantillons de sang artériel et veineux ont révélé la présence d’acidose et d’hypercapnie. La température et laPetCO2 ont continué d’augmenter à des valeurs maximales respectives de 41 °C et 77 mmHg. Des manoeuvres de refroidissement ont été entreprises. Une dose totale de 220 mg de dantrolène sodique a été administrée par la voie veineuse. La température et l’acidose se sont stabilisées. La fréquence cardiaque et laPetCO2 ont baissé respectivement à 130 bpm et 36 mmHg. L’intervention a été terminée rapidement. En postopératoire, à l’unité des soins intensifs pédiatriques, une perfusion de dantrolène 20 mg · h−1 a été administrée pendant 12 h. La trachée a été extubée le lendemain matin. Quelques jours plus tard, le patient a subi une autre intervention chirurgicale sous anesthésie ne comportant pas d’agents déclenchants de l’HM.ConclusionSous desflurane, il est possible d’attribuer un accès de tachycardie à l’hyperactivité sympathique. Ceci peut compliquer le diagnostic de l’HM.

Initial experience with personal digital assistant-based reflectance photoplethysmograph for free tissue transfer monitoring.

Improved microsurgical technique has resulted in a high percentage of successful free tissue transfers. When a tissue transfer fails in the head and neck, however, the results are orocutaneous fistulas, carotid artery exposure, and deformity that adds morbidity, expense, and may delay adjuvant therapy. Postoperative monitoring of tissue perfusion can detect early problems in free tissue transfer that may allow for early intervention and salvage. The authors have demonstrated that reflectance photoplethysmography can detect perfusion changes in free tissue transfer within 5 minutes of a pedicle “insult” intraoperatively. Normative data for viable flaps from various donor sites have been established. The authors now report their initial experience with a newly developed reflectance photoplethysmograph based on a hand-held computer for routine clinical use. Their results are compared with a conventional surveillance protocol that included observation, bleeding to pin prick, and bedside duplex scanning of the vascular pedicle. In a series of 30 free tissue transfers (29 patients), there was one ischemic event (skin paddle loss only), which was detected by the monitor. The monitor was able to predict correctly (one flap) survival of a free tissue transfer even when duplex ultrasonic data were indicative of an absence of perfusion. Personal digital assistant-based photoplethysmography appears to be a promising device for bedside diagnosis of free tissue transfer viability or ischemia.

Transfusion Cost Containment for Abdominal Surgery with Neural Networks

Typing and crossmatching blood is a significant cost for most hospitals, regardless of whether the blood is actually transfused. Many hospitals have implemented a Maximum Surgical Blood Order Schedule, MSBOS, to control over-ordering of blood units for surgery. The research presented in this article examines the use of neural networks for predicting the quantity of blood required by individual patients undergoing abdominal surgery (e.g. splenectomy). A comparison is made between the neural network predictions at a particular hospital versus the current MSBOS methodology for ordering surgical blood, by using the crossmatch to transfusion ratio. Results from the neural network transfusion predictions for the abdominal aortic aneurysm (AAA) surgery imply that neural networks can significantly improve the transfusion efficiency of hospitals. However, further examination of neural network capabilities for predicting the transfusion needs of patients undergoing other types of abdominal surgeries indicates that for operations other than the AAA, neural networks tend to under-predict the transfusion requirements of ten percent of the patients. Even if not used to limit over-ordering of blood for surgical transfusions, neural networks may be used as an intelligent decision support system to evaluate the current efficiency of hospital transfusion practices and to indicate beneficial changes to current MSBOS values.

Dermal absorption of a dilute aqueous solution of malathion

Malathion is an organophosphate pesticide commonly used on field crops, fruit trees, livestock, agriculture, and for mosquito and medfly control. Aerial applications can result in solubilized malathion in swimming pools and other recreational waters that may come into contact with human skin. To evaluate the human skin absorption of malathion for the assessment of risk associated with human exposures to aqueous solutions, human volunteers were selected and exposed to aqueous solutions of malathion. Participants submerged their arms and hands in twenty liters of dilute malathion solution in either a stagnant or stirred state. The “disappearance method” was applied by measuring malathion concentrations in the water before and after human exposure for various periods of time. No measurable skin absorption was detected in 42% of the participants; the remaining 58% of participants measured minimal absorbed doses of malathion. Analyzing these results through the Hazard Index model for recreational swimmer and bather exposure levels typically measured in contaminated swimming pools and surface waters after bait application indicated that these exposures are an order of magnitude less than a minimal dose known to result in a measurable change in acetylcholinesterase activity. It is concluded that exposure to aqueous malathion in recreational waters following aerial bait applications is not appreciably absorbed, does not result in an effective dose, and therefore is not a public health hazard.