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Biomedical subjects

N Gravenstein

Publications and source records attributed to N Gravenstein.

71 records · Page 4Linked to original sources
PubMed1985

Clinical relevance of long-latency SEPs and VEPs during coma and emergence from coma.

Follow-up measurements of long-latency visual (VEP) and somatosensory (SEP) evoked potentials were performed on 30 comatose patients. Twenty-seven of the patients had severe head injury, 2 had encephalitis and 1 was in a posthypoxic state. For the SEP study a mechanical vibration stimulus was used, applied 60 times at intervals of 10 sec. The same rate was used for visual stimulation. The late EP components were classified by a signal-to-noise ratio (SNR), whereby an SNR of less than 2.6 is characteristic of a questionable or unmeasurable EP and an SNR greater than 2.6 is evidence of a clearly existing EP; the clinical state was scored using the Glasgow Coma Scale (GCS); the patient outcome was assessed 6 months after the injury using the Glasgow Outcome Scale. The highest correlation (r = 0.72) was found between the clinical state, represented by the GCS, and the SEP. A similar correlation (r = 0.66) was obtained between the GCS and the vertex VEP. The occipital VEP showed no correlation. Emergence from coma and recovery was accompanied by an increase of the SEP and an increasing spread of the VEP over the whole scalp. Most patients with a clear long-latency SEP in coma had a favourable outcome; a missing or a questionable SEP indicated a poor outcome.

Adolescent↗
PubMed1984

Pitfalls with mass spectrometry in clinical anesthesia.

Mass spectrometry of respired gases puts a powerful analytic tool into the hand of the clinician. However, serious misinterpretations may result if the principle of operation and certain weaknesses of spectrometry are not appreciated. The potential pitfalls of clinical mass spectrometry are related to the need to have one unit serve many patients and to the design of the spectrometer and its algorithms.

Anesthesiology↗
PubMed1977

Comparison of central corneal endothelial cell numbers with peripheral areas.

Using a specific fixation device on a group of patients, we compared corneal endothelial cell count areas above, below, and temporally with the central corneal cell counts. Although younger patients, the central cornea mirrored the peripheral cell counts; peripheral counts were similar in each group. Patients with intraocular lenses had fewer cells than patients with uneventful cataract extraction, and the central cornea was representative in the cataract group. Only in the intraocular lens group was there a small difference between central endothelial cell counts and the temporal and inferior cell counts; but even this difference was significantly less than that seen in patients with intracapsular cataract extraction.

Adult↗
PubMed1976

The effect of 10-0 running nylon versus 8-0 silk on the healing of corneal gragts.

A previously reported well standardized tensile strength model in rabbits was sued in order to answer whether or not monofilament nylon does in fact delay corneal wound healing in general, and in particular, in corneal grafts. The tensile strength of penetrating keratoplasty wounds closed with either 10-0 running monofilament nylon or 8-0 interrupted black silk was measured in rabbits. The tensile strength of wounds closed with either suture was comparable in all groups. The advantages of 10-0 nylon in corneal transplantation and cataract extraction was presented. In addition, the assumption that the tensile strength of linear central wounds parallels that of a circular trephine wound was proven to be correct.

Animals↗
PubMed1976

Scanning electron microscopy of postoperative M-K and moist chamber-stored corneas.

In the present study, using the in vivo test situation which all corneal donor material must meet, we performed penetrating keratoplastics utilizing corneal tissue stored for five days in either M-K medium or conventional moist chambers. Cat corneas stored for five days in M-K medium had a higher incidence of postoperative graft clarity along with an intact endothelial cell layer as determined by scanning electron microscopy than corneas stored in a conventional moist chamber. The endothelium of corneas immediately after moist chamber storage revealed minimal surface alteration which contrasted to the more severely stressed endothelium immediately after M-K storage. However, the M-K stored endothelium survived the trauma of penetrating keratoplasty much better than cells stored in moist chambers.

Animals↗
PubMed1975

Aspirin stabilization of the blood-aqueous barrier in the human eye.

After anterior chamber paracentesis, patients responded with an effusion of protein into the anterior chamber. Pretreatment with aspirin significantly decreased this trauma-induced, probably prostaglandin-mediated, disruption of the blood-aqueous barrier. Protein levels in aqueous humor of human eyes were measured in samples taken initially and five minutes after anterior chamber tap. The protein rise of 53% in five minutes in control patients was limited to 7% in patients pretreated with systemically administered aspirin. Prostaglandin mechanisms may be important in human ocular trauma and prostaglandin synthetase inhibitors may control the reaction to surgical trauma.

Aqueous Humor↗
PubMed1975

[The effect of Actihaemyl on epithelial regeneration (author's transl)].

After well-defined chemical and mechanical removal of the corneal epithelium of 40 rabbit eyes 20 eyes were treated with Actihaemyl-Augengel 4 times daily. The epithelial regeneration was compared with the untreated contralateral eye. Under Actihaemyl treatment the healing rate was not accelerated. The well-known healing effect of Actihaemyl on different corneal diseases does not seem to come from improving the epithelial regeneration but is probably the result of a general improvement of corneal metabolism.

Actihaemyl↗
PubMedDate not supplied

Duration of carbon dioxide absorption by soda lime at low rates of fresh gas flow.

STUDY OBJECTIVE: To determine the impact of a low fresh gas flow rate on the duration of carbon dioxide (CO2) absorption by soda lime. DESIGN: Nonclinical, experimental. SETTING: Experimental laboratory. METHODS: In vitro test with Sodasorb and a semiclosed breathing circle ventilating a test lung with a CO2 inflow of 250 ml per minute. Fresh gas flow rates of 0.25, 0.5, 1, 2, and 4 L/min were studied. MEASUREMENTS AND MAIN RESULTS: CO2 was measured at the breathing circuit test lung interface with a mainstream capnometer. Duration of CO2 absorption was determined as the time for the inspired CO2 tension (PICO2) to increase from 0 mm to 7 mm of mercury. The times of this interval were recorded four times for each fresh gas flow rate and compared by analysis of variance; p less than 0.05 was considered significant. Time to soda lime failure was significantly longer at 2 L/min than at 1 L/min fresh gas flow and at 1 L/min than at 0.25 L/min fresh gas flow. CONCLUSION: Because soda lime color indicators are unreliable, when a semiclosed breathing circle is used at a low rate of fresh gas flow without CO2 monitoring, the CO2 absorbent must be replaced more frequently.

Absorption↗
PubMedDate not supplied

In vitro comparison of central venous catheters for aspiration of venous air embolism: effect of catheter type, catheter tip position, and cardiac inclination.

STUDY OBJECTIVE: To test the relative efficiency of balloon-tipped and plain catheters for aspiration of venous air embolism. DESIGN: The following four single-lumen central venous catheters were studied in a silastic model of the right atrium, tricuspid valve, and vena cavae: (1) the 16-gauge single-orifice catheter; (2) the 14-gauge Bunegin-Albin multiorifice catheter; (3) the 7-Fr pulmonary angiography catheter with balloon distal to orifices; (4) the 7-Fr pulmonary angiography catheter with balloon proximal to orifices. A 10% glycerol-water solution was circulated at 3.7 to 4.0 L/min. Catheter tips were positioned at 1 cm increments from -3 to +3 cm around the superior vena cava-right atrial junction with cardiac inclinations of 65 degrees and 80 degrees. Air (10 ml) was infused over 30 seconds; aspiration from the test catheter began 5 seconds later at 40 ml/min for 75 seconds. The balloon catheters were evaluated with the balloons inflated and deflated. SETTING: Experimental laboratory of a university-affiliated hospital. MEASUREMENTS AND MAIN RESULTS: Amounts of air aspirated were compared by analysis of variance and Tukey's multiple comparison, p less than 0.05, for all combinations. The 16-gauge single-orifice catheter tested best at a 65 degrees cardiac inclination with 86% of the venous air embolism recovered, while the 14-gauge Bunegin-Albin multiorifice catheter tested best at an 80 degrees cardiac inclination with 62% of the venous air embolism recovered. Both catheters functioned most efficiently at or above the superior vena cava-right atrial junction. CONCLUSIONS: This study demonstrated that efficacy of air recovery depends on catheter type, catheter tip position, and cardiac inclination. No benefit was derived from positioning the catheter tip inside the atrium or from using balloon-tipped catheters.

Catheterization, Central Venous↗
PubMedDate not supplied

Low back pain following epidural blood patch.

A patient underwent outpatient knee arthroscopy with spinal anesthesia administered at the patient's request. The patient was discharged after a 3-hour recovery period. Three days later, the patient returned because of a headache that had begun the evening after surgery and progressively worsened. Treatment with caffeine and hydration for presumed postdural puncture headache resulted in relief for approximately 1 hour. An epidural blood patch was then performed and relieved symptoms for 3 hours until backache began and worsened over the next 7 hours. Computed axial tomography showed epidural air. After symptomatic treatment and observation overnight, the patient was released, and follow-up by telephone was planned. For 2 days, symptoms persisted. Therapy with aspirin 600 mg 4 times daily resulted in acute and significant relief. The backache resolved after 1 week. A review of the literature on backache following epidural blood patch is presented.

Anesthesia, Spinal↗
PubMedDate not supplied

Intraoperative pulse oximetry: frequency and distribution of discrepant data.

STUDY OBJECTIVE: To determine the types of discrepant data during intraoperative pulse oximetry and their frequency and duration. DESIGN: Prospective study. SETTING: University medical center. PATIENTS: 46 consecutive ASA physical status I-III patients undergoing general anesthesia for elective surgical operations. MEASUREMENTS AND MAIN RESULTS: With an integrated computer algorithm on the pulse oximeter and another computer linked to it, data were screened and the frequency and distribution of the following oximeter signals recorded: absent; low quality or interrupted, as detected by the pulse oximeter algorithm; nonphysiologic, identified by the personal computer as a heart rate change greater than 10 beats per minute within 2 consecutive 2-second samples, with no similar abrupt change reported simultaneously on ECG. The number of episodes per hour of discrepant oximeter data and the duration of the episodes were recorded by phase of anesthesia: induction, maintenance, and emergence. Discrepant data occurred most frequently and lasted longest during emergence (p < 0.05); the majority of episodes of discrepant data during emergence lasted less than 12 seconds. Excluding discrepant data that lasted less than 12 seconds decreased the frequency of discrepant data by 63% and excluding those that lasted less than 30 seconds decreased the frequency of discrepant data by 93%. CONCLUSIONS: Pulse oximeters frequently report discrepant data intraoperatively, most frequently during emergence from anesthesia. An alarm delay triggered by discrepant data and lasting 12 to 30 seconds would keep most discrepant data from becoming false alarms and, thus, may reduce distracting sound pollution in the operating room.

Algorithms↗
PubMedDate not supplied

Computer-modulated patient-controlled analgesia. Preliminary evaluation of a prototype.

BACKGROUND AND OBJECTIVES: To provide patients with better postoperative pain relief, the authors developed a prototype computer-controlled infusion pump capable of establishing a steady drug plasma concentration based on patient needs. METHODS: A two-compartment pharmacokinetic model was used to compute the required infusion scheme. Using known pharmacokinetic parameters, the model and the pump's accuracy were studied in four dogs. In the first part of the study, the morphine pharmacokinetic profile of each dog was analyzed and used to develop the parameters of a model tailored to that particular dog. In the second part, this tailored model was implemented to test whether the infusion device was able to achieve the desired concentration profile. RESULTS: The computer-controlled infusion device was able to achieve all the desired plasma concentrations. CONCLUSIONS: These data suggest that it is possible to refine postoperative pain management with adaptive computer algorithms implemented to establish stable plasma analgesic concentrations and to automatically wean the analgesic over time.

Algorithms↗