PubMed · 8214688
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C Y Lin, J S Wang. 1993. Supramaximal second gas effect--a nonexistent phenomenon.. https://doi.org/10.1213/00000539-199310000-00051
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OBJECTIVE: To examine the physiologic effects of inhalation anesthesia in aquatic turtles to improve anesthetic techniques and postanesthetic monitoring. DESIGN: Retrospective case series. ANIMALS: 9 Kemp's ridley sea turtles. PROCEDURE: Isoflurane was used as the general anesthetic during 14 minor surgical procedures. Turtles were orotracheally intubated, and a surgical plane of anesthesia was maintained with 2.7 +/- 0.4% (mean +/- SE) isoflurane. The duration of anesthesia was 131 +/- 12 minutes. Pulse rate, blood pressure, blood gases (PaO2 and PaCO2) and pH, blood lactic acid concentration, and capnography were used to evaluate the physiologic responses of sea turtles to isoflurane. RESULTS: An isoflurane concentration of 3.4 +/- 0.3% provided anesthetic induction in 7 +/- 1 minutes. The mean duration of the recovery phase was 241 +/- 31 minutes. The duration of the recovery phase was not affected by the duration of anesthesia, type of carrier gas, method of ventilatory weaning, or use of selected pharmacologic agents. The recovery phase was characterized by hypoxemia, progressive acidemia, hypercapnia, and lactic acidosis. Awakening in the turtles was preceded by a characteristic tachycardia and tachypnea. All sea turtles recovered from isoflurane anesthesia without apparent adverse effects within 24 hours. CLINICAL IMPLICATIONS: Isoflurane appears to be safe and effective in providing surgical anesthesia in turtles that require a timely return to an aquatic environment. This study should assist veterinarians in predicting the physiologic responses of aquatic turtles to inhalation agents.
STUDY OBJECTIVE: To determine if reducing respiratory muscle load or increasing tidal volume (VT) with pressure support (PS) would improve ventilatory efficiency by reducing respiratory rate (RR) and resting PaCO2. DESIGN: Prospective, and patient-controlled, with randomized treatment crossover. SETTING: University cancer center and research institute. PATIENTS: ASA status I and II patients scheduled to undergo inhalation anesthesia for operations in which neuromuscular relaxation is undesirable. INTERVENTIONS: Propofol and succinylcholine were used to induce anesthesia and facilitate tracheal intubation. General anesthesia was maintained with desflurane, nitrous oxide, and oxygen. Patients breathed spontaneously at atmospheric pressure for 15 minutes and then randomly received alternate 15-minute trials of PS adjusted to provide either 5 cmH2O or a level titrated to produce VT of 8 ml/kg body weight. Then patients breathed spontaneously at atmospheric pressure for 15 minutes. MEASUREMENTS AND MAIN RESULTS: In 20 patients aged 52 +/- 11 years and weighing 72 +/- 18 kg, airway gas flow and pressure, esophageal pressure, arterial blood gas tensions and pH, and mean arterial pressure (MAP) were measured. Heart rate (HR), VT, RR, minute ventilation (VE), carbon dioxide production (VCO2), ratio of dead space to VT (VD/VT), and inspiratory work of breathing (WI) were calculated. End-tidal desflurane (6.7 +/- 0.4%), VCO2 (142 +/- 39 ml/min), HR, and MAP were unchanged throughout the study. WI, RR, VE, VD/VT, and PaCO2 were reduced significantly when PS was titrated to produce a VT of 8 ml/kg and spontaneous breathing before and after PS trials (p < 0.05). CONCLUSIONS: PS titrated to produce a near normal VT improves the efficiency of spontaneous breathing by lowering RR and PaCO2 while preserving hemodynamic homeostasis in patients undergoing inhalation anesthesia. Lesser PS levels will unload the respiratory muscles, but have no effect on RR or PaCO2.
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