Journal of clinical monitoring
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A simple hydraulic hand dynamometer was used to assess the hand grip force before and after general anesthesia. Eight patients received a general anesthetic of nitrous oxide and oxygen and an inhalational agent without relexants (non-relaxant group). Ten patients received a similar anesthetic of nitrous oxide and oxygen and an inhalational agent with non-depolarizing relaxants (relaxant group). ⋯ Patients in the relaxant group had a mean of only 29% of initial hand grip force when they could lift their heads. One hour later, hand grip force increased to 76% of preoperative force in the relaxant group. Hand grip force appears to be a sensitive measurement of residual relaxant effect.
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Comparative Study
Noninvasive monitoring of oxygenation during one-lung ventilation: a comparison of transcutaneous oxygen tension measurement and pulse oximetry.
Oxygenation was monitored concomitantly by measurement of transcutaneous oxygen tension and by pulse oximetry, and the data were compared with arterial blood oxygen tension and saturation values in 10 patients who became hypoxemic when undergoing thoracotomy and one-lung ventilation. A steep decrease in arterial blood oxygen tension was obvious immediately after the institution of one-lung ventilation, reaching the lowest mean value of 63 +/- 2 mm Hg (+/- SEM) at 12 minutes. ⋯ In contrast, the decrease in arterial blood oxygen saturation from 97.9 +/- 0.3% to 92.2 +/- 0.8% as measured by CO-Oximeter was accurately followed by pulse oximetry with almost beat-to-beat response, bringing about a highly significant linear correlation between the two methods (r = 0.93; P less than 0.001). We conclude that pulse oximetry is a simpler and more rapidly responding method than measurement of transcutaneous oxygen tension for detection of hypoxemia during one-lung ventilation in adults.
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Biography Historical Article
History of blood gas analysis. VII. Pulse oximetry.
Pulse oximetry is based on a relatively new concept, using the pulsatile variations in optical density of tissues in the red and infrared wavelengths to compute arterial oxygen saturation without need for calibration. The method was invented in 1972 by Takuo Aoyagi, a bioengineer, while he was working on an ear densitometer for recording dye dilution curves. ⋯ William New and Jack Lloyd recognized the potential importance of pulse oximetry and developed interest among anesthesiologists and others concerned with critical care in the United States. Success brought patent litigation and much competition.
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To determine if end-tidal carbon dioxide tension (PETCO2) is a clinically reliable indicator of arterial carbon dioxide tension (PaCO2) under conditions of heterogeneous tidal volumes and ventilation-perfusion inequality, we examined the expiratory gases of 25 postcardiotomy patients being weaned from ventilator support with intermittent mandatory ventilation. Using a computerized system that automatically sampled airway flow, pressure, and expired carbon dioxide tension, we were able to distinguish spontaneous ventilatory efforts from mechanical ventilatory efforts. The PETCO2 values varied widely from breath to breath, and the arterial to end-tidal carbon dioxide tension gradient was appreciably altered during the course of several hours. ⋯ The most accurate indicator of PaCO2 was the maximal PETCO2 value in each sample period, the correlation coefficient being 0.768 (P less than 0.001) and the arterial to end-tidal gradient being 4.24 +/- 4.42 mm Hg (P less than 0.01 compared with all other measures). When all values from an 8-minute period were averaged, stability was significantly improved without sacrificing accuracy. We conclude that monitoring the maximal PETCO2, independent of breathing pattern, provides a clinically useful indicator of PaCO2 in postcardiotomy patients receiving intermittent mandatory ventilation.