Audio spectrum and sound pressure levels vary between pulse oximeters

PURPOSE: The variable-pitch pulse oximeter is an important intraoperative patient monitor. Our ability to hear its auditory signal depends on its acoustical properties and our hearing. This study quantitatively describes the audio spectrum and sound pressure levels of the monitoring tones produced by five variable-pitch pulse oximeters. METHODS: We compared the Datex-Ohmeda Capnomac Ultima, Hewlett-Packard M1166A, Datex-Engstrom AS/3, Ohmeda Biox 3700, and Datex-Ohmeda 3800 oximeters. Three machines of each of the five models were assessed for sound pressure levels (using a precision sound level meter) and audio spectrum (using a hanning windowed fast Fourier trans-form of three beats at saturations of 99%, 90%, and 85%). RESULTS: The widest range of sound pressure levels was produced by the Hewlett-Packard M1166A (46.5 +/- 1.74 dB to 76.9 +/- 2.77 dB). The loudest model was the Datex-Engstrom AS/3 (89.2 +/- 5.36 dB). Three oximeters, when set to the lower ranges of their volume settings, were indistinguishable from background operating room noise. Each model produced sounds with different audio spectra. Although each model produced a fundamental tone with multiple harmonic overtones, the number of harmonics varied with each model; from three harmonic tones on the Hewlett-Packard M1166A, to 12 on the Ohmeda Biox 3700. There were variations between models, and individual machines of the same model with respect to the fundamental tone associated with a given saturation. CONCLUSION: There is considerable variance in the sound pressure and audio spectrum of commercially-available pulse oximeters. Further studies are warranted in order to establish standards.     

Twenty cases of sympathetic ophthalmia.

We reviewed the charts of 20 patients with sympathetic ophthalmia who were seen in the uveitis clinic at the Eye and Ear Infirmary within an 11-year period. Of these 20 patients 14 maintained 20/50 or better visual acuity in at least one eye. We found early enucleation to be associated with a better visual prognosis, possibly due to earlier diagnosis and faster, more aggressive therapy rather than a reduction in antigenic load. The clinical appearance of Dalen-Fuchs nodules appears to indicate a more severe stage of disease. Chlorambucil was useful in patients with severe disease. To be effective and to lessen its side effects chlorambucil was given in daily dosages that were increased weekly over a short period to achieve bone marrow suppression. After a course of chlorambucil therapy intraocular inflammation could be controlled with topical steroids alone.     

Evaluation of renal transplant dysfunction by duplex Doppler sonography: a prospective study and review of the literature

A disconcertingly wide variation exists in the literature as to the accuracy of duplex Doppler sonography in the detection of acute renal transplant rejection. Sensitivities range from 9% to 76%. In an attempt to explain the disparity of results, we undertook a double-blind prospective study of the accuracy of duplex Doppler ultrasound in the detection of acute rejection in renal transplants. We scanned 49 consecutive patients with a total of 65 biopsies; 46 biopsies in 33 consecutive patients were included in our study. In our population, the prevalence of acute rejection was 61% (28/46). Using a resistive index (RI) cutoff of greater than 0.90 based on the main renal artery flow pattern, the sensitivity of our test was 43%, with a 67% specificity. The positive predictive value was 67%. Our results are contrasted and compared with the published data from other groups in a critical survey of the literature. We conclude that duplex Doppler sonography alone is inadequate to evaluate acute rejection in renal transplants.     

Upper airway involvement in Parkinson’s disease resulting in postoperative respiratory failure

A 71-yr-old man with a six-year history of Parkinson’s disease (PD), Type II diabetes mellitus, myocardial infarction, and remote 20 pack-year smoking history, underwent an anterior resection of the rectum for carcinoma. Sixty hours later, the patient suffered a respiratory arrest; his antiparkinsonian medications had not been resumed. Preoperative flow-volume loops showed the characteristic saw-tooth pattern of PD indicating dysfunction of the striated muscle of the upper airway. Although postoperative respiratory distress was managed as lower airway obstruction, at the time of intubation there were no signs of lower airway pathology. Upper airway dysfunction and obstruction secondary to PD is thought to have been a contributing factor to the postoperative respiratory distress and failure. This case is presented to draw attention to the risk of upper airway dysfunction in Parkinson’s Disease, especially with the withdrawal of antiparkinsonian medications. Un homme de 71 ans souffrant d’une maladie de Parkinson depuis six ans, de diabète type II, d’un infarctus du myocarde avec une histoire de tabagisme de 20 années-paquet, subit une résection antérieure du rectum pour un cancer. Soixante heures plus tard, il fait un arrêt respiratoire avant d’avoir recommencé sa médication antiparkinsonnienne. Les courbes débits-volumes préopératoires montraient un tracé en dents de scie caractéristique du dysfonctionnement des muscles striés des voies aériennes supérieures consécutif au parkinsonnisme. Bien que cette détresse postopératoire ait été traitée comme une obstruction des voies aériennes inférieures, on n’a pas observé de signes de cette pathologie à l’intubation. On emit que le dysfonctionnement de voies aériennes supérieures a surtout contribué à la détresse et à l’insuffisance respiratoires postopératoires. Cette observation est présentée dans le but d’attirer l’attention sur le risque de dysfonctionnement des voies respiratoires causé par la maladie de Parkinson, particulièrement après l’arrêt de la médication spécifique.     

Acute ventilatory complications during laparoscopic upper abdominal surgery

Purpose

This article examines and summarizes the published reports dealing with subcutaneous emphysema, pneumothorax and carbon dioxide (CO₂) embolism during laparoscopic upper abdominal surgery. The purpose is to describe the expected clinical picture, the differential diagnosis and the management of these complications.

Source

The information was obtained from a Medline literature search and the annual meeting supplements of Anesthesiology, Anesth Analg, Br J Anaesth and Can J Anaesth.

Principal findings

An abrupt increase in PetCO₂ is the first sign of subcutaneous emphysema and of pneumothorax. Desaturation and increased airway pressure occur with pneumothorax, but not with subcutaneous emphysema alone. Desaturation and increased airway pressure also occur with bronchial intubation. The preliminary diagnosis is made by verifying the position of the tube, examination of the patient for swelling and crepitus and auscultation for air entry. Chest radiography and paracentesis confirm the diagnosis of pneumothorax, which frequently occurs with subcutaneous emphysema but is rarely of the tension type. Pulmonary embolism due to CO₂ during WAS has not been reported, but the available data suggest that small, haemodynamically inconsequential CO₂ embolism occurs without change in PetCO₂. Massive embolism is possible and will markedly decrease PetCO₂, arterial O₂ saturation (SpO₂) and blood pressure.

Conclusion

The immediate recognition of the three complications requires continuous monitoring of PetCO₂, arterial saturation, airway pressure, and an index of pulmonary compliance.     

Grafts and functional recuperation

Plasticity of undamaged projections (axonal sprouting) in the adult and neonatal mammalian spinal cord has been documented many times. It has been associated, in some paradigms, with recovery of specific functions and motor behavior. This mutually occurring recovery of function appears to be enhanced by transplants of fetal tissue.     

Patient-controlled analgesia (PCA) using fentanyl in a parturient with a platelet function abnormality

A term parturient with documented platelet dysfunction presented to the case room for induction of labour. Since this bleeding abnormality contraindicated the use of lumbar epidural analgesia (LEA), we elected to use an iv fentanyl patientcontrolled analgesia (PCA) technique for pain relief during labour. The patient received a 50 μg fentanyl loading dose after which 20 μg boluses of fentanyl were self-administered every three minutes as required. The patient received a total of 400 μg of fentanyl over the 3 1/2 hr of active labour. Mother and neonate tolerated the fentanyl without sequelae. If facilities to monitor the neonate and mother are present, this method of analgesia is useful in those patients where LEA is contraindicated. Au terme d’une grossesse, une patiente porteuse d’une dysfonction plaquettaire devait avoir une induction de travail au bloc obstétrical. Ecartant l’usage d’une epidurale à cause des risques de saignement, nous avons employé du fentanyl en autoanalgésie (PCA) pour soulager les douleurs du travail. Après une dose initiate de50 μg, la patiente s’injectait des doses de 20 μg de fentanyl iv aux 3 minutes prn. Elle utilisa un total de 400 μg de fentanyl au cours des 3,5 heures que dura le travail. La mère et le nouveau-né tolérèrent fort bien ce mode d’analgésie. L’autoanalgésie offre done une alternative au bloc épidural lorsque ce dernier est contre-indiqué toutefois, nous recommandons de monitorer la mére et le nouveau-né pendant quelques heures.