Journal of clinical monitoring and computing
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J Clin Monit Comput · Apr 1998
Influence of pulse oximeter settings on the frequency of alarms and detection of hypoxemia: Theoretical effects of artifact rejection, alarm delay, averaging, median filtering or a lower setting of the alarm limit.
The potential benefit of a reduced frequency of false pulse oximeter low oxyhemoglobin saturation (SpO2) alarms is that the attention of personnel is only directed to patients who experience hypoxemia. The present study was undertaken to better understand the effects of different settings of the pulse oximeter on false (artifact) and true (hypoxemia) alarms. ⋯ The data from the present study suggest that in order to effectively suppress false alarms caused by pulse oximeter artifacts, it may be preferable to use a longer filtering epoch of approximately 40 s, rather than to decrease the lower alarm limit.
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J Clin Monit Comput · Apr 1998
Randomized Controlled Trial Clinical TrialClonidine does not attenuate median nerve somatosensory evoked potentials during isoflurane anesthesia.
Clonidine, an alpha2 agonist, reduces the requirements of several anesthetics. However, the effects of clonidine on somatosensory evoked potentials (SEPs) are unclear. These effects on cortical SEPs during isoflurane anesthesia were studied in 20 ASA I-II patients scheduled for elective surgery. Furthermore, the isoflurane concentration required to induce electroencephalogram (EEG) burst-suppression with and without clonidine was studied. METHODS. Anesthesia was maintained with isoflurane at a FiO2 of 0.4. At 1 MAC isoflurane the patients were randomly given either intravenous clonidine 2 microg kg(-1) (ten patients) or saline (ten patients). Finally, the isoflurane concentration was increased to a point at which a burst-suppression pattern appeared in the EEG. SEPs upon median nerve stimulation were recorded (1) before induction of anesthesia, (2) at 1 MAC before clonidine/saline, (3) at 1 MAC after clonidine/saline, (4) at EEG burst-suppression. ⋯ The effect of clonidine in reducing the requirements of anesthetics during general anesthesia is not seen in the cortical SEPs. The isoflurane-induced burst-suppression in the EEG was not affected by clonidine, suggesting that the EEG effects of clonidine and isoflurane were not additive. If SEPs are monitored intraoperatively, clonidine can be used as an adjuvant during isoflurane anesthesia without harmful effects on SEP monitoring.
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J Clin Monit Comput · Apr 1998
Comparative carbon dioxide output through injured and noninjured peritoneum during laparoscopic procedures.
Tension pneumoperitoneum may force gas into a small injured vessel if the opening is kept patent by surrounding tissues. However, the amount of carbon dioxide (CO2) that penetrates through injured or noninjured peritoneum has not been systematically determined. In 25 patients undergoing elective laparoscopic ultrasonography and cholecystectomy, CO2 output (VCO2) and O2 uptake (VO2) were measured at baseline and during anesthesia, pneumoperitoneum, laparoscopic surgical procedure (Surgery), and after hemostasis of the surgical field (Postsurgery). ⋯ Minute volume increased from 2.24 +/- 0.20 in anesthesia to 2.89 +/- 0.25, 4.01 +/- 0.32, and 3.46 +/- 0.28 L x min(-1) x m(-2) during pneumoperitoneum, Surgery, and Postsurgery, respectively, to maintain PaCO2. We conclude that the amount of CO2 absorbed following pneumoperitoneum prior to surgery is lower than that during Surgery or Postsurgery. The amount of CO2 absorbed through the surgical field was 2.3 times higher than that through the nonsurgical field while that from the peritoneum after hemostasis of surgical field was 1.6 times higher.
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J Clin Monit Comput · Apr 1998
Propagation of nitric oxide pools during controlled mechanical ventilation.
Infusing nitric oxide at a constant rate into a breathing circuit with intermittent mainstream flow causes formation of nitric oxide pools between successive breaths. We hypothesized that incomplete mixing of these pools can confound estimates of delivered nitric oxide concentrations. ⋯ Incomplete mixing of nitric oxide confounds estimates of delivered nitric oxide concentrations. When nitric oxide is infused at a constant rate into a breathing circuit, we doubt that any sampling site outside the patient's lungs can reliably predict delivered nitric oxide concentrations. Strategies to ensure complete mixing and representative sampling of nitric oxide should be considered carefully when designing nitric oxide delivery systems.