Anesthesia and analgesia
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Anesthesia and analgesia · Sep 1998
Randomized Controlled Trial Clinical TrialIntrathecal, but not intravenous, clonidine reduces experimental thermal or capsaicin-induced pain and hyperalgesia in normal volunteers.
Clonidine is approved for intraspinal administration in the treatment of neuropathic cancer pain. Some studies have suggested an analgesic effect after systemic clonidine administration. The purpose of this study was to compare the analgesic effects of intrathecal and IV clonidine with acute noxious stimulation and with hyperalgesia from intradermal capsaicin injection in volunteers. Sixteen healthy volunteers received intradermal injections of capsaicin (100 microg) before and after the IV or intrathecal injection of clonidine 50 or 150 microg in a randomized, double-blind manner. Pain and areas of mechanical hyperalgesia and allodynia were determined at specified intervals. In addition, pain to noxious heat stimulation was determined. The capsaicin injection produced pain, followed by hyperalgesia and allodynia. The intrathecal, but not IV, injection of 150 microg of clonidine reduced capsaicin-induced pain and area of hyperalgesia. Intrathecal clonidine (150 microg) reduced pain to heat stimulation, whereas IV clonidine did not. The groups did not differ in hemodynamic or sedative effects from clonidine. These data support the value of intraspinal administration of clonidine for the treatment of acute pain and of pain states associated with hyperalgesia. Similarly, they suggest that analgesia from the systemic administration of this alpha2-adrenergic agonist, if any, is weak in doses that produce sedation and reduce blood pressure. ⋯ To the extent that the experimental pain conditions used in this study reflect those in patients with acute and chronic pain, these data support the spinal rather than IV injection of clonidine for analgesia.
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Anesthesia and analgesia · Sep 1998
Clinical TrialThe effects of body mass on lung volumes, respiratory mechanics, and gas exchange during general anesthesia.
We investigated the effects of body mass index (BMI) on functional residual capacity (FRC), respiratory mechanics (compliance and resistance), gas exchange, and the inspiratory mechanical work done per liter of ventilation during general anesthesia. We used the esophageal balloon technique, together with rapid airway occlusion during constant inspiratory flow, to partition the mechanics of the respiratory system into its pulmonary and chest wall components. FRC was measured by using the helium dilution technique. We studied 24 consecutive and unselected patients during general anesthesia, before surgical intervention, in the supine position (8 normal subjects with a BMI < or = 25 kg/m2, 8 moderately obese patients with a BMI >25 kg/m2 and <40 kg/m2, and 8 morbidly obese patients with a BMI > or = 40 kg/m2). We found that, with increasing BMI: 1. FRC decreased exponentially (r = 0.86; P < 0.01) 2. the compliance of the total respiratory system and of the lung decreased exponentially (r = 0.86; P < 0.01 and r = 0.81; P < 0.01, respectively), whereas the compliance of the chest wall was only minimally affected (r = 0.45; P < 0.05) 3. the resistance of the total respiratory system and of the lung increased (r = 0.81; P < 0.01 and r = 0.84; P < 0.01, respectively), whereas the chest wall resistance was unaffected (r = 0.06; P = not significant) 4. the oxygenation index (PaO2/PAO2) decreased exponentially (r = 0.81; P < 0.01) and was correlated with FRC (r = 0.62; P < 0.01), whereas PaCO2 was unaffected (r = 0.06; P = not significant) 5. the work of breathing of the total respiratory system increased, mainly due to the lung component (r = 0.88; P < 0.01 and r = 0.81; P < 0.01, respectively). In conclusion, BMI is an important determinant of lung volumes, respiratory mechanics, and oxygenation during general anesthesia with patients in the supine position. ⋯ The aim of this study was to investigate the influence of body mass on lung volumes, respiratory mechanics, and gas exchange during general anesthesia.
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Anesthesia and analgesia · Sep 1998
Randomized Controlled Trial Clinical TrialThe effect of fresh gas flow and anesthetic technique on the ability to control acute hemodynamic responses during surgery.
We evaluated the effect of the fresh gas flow (FGF) rate and the anesthetic technique on the ability to control the acute hyperdynamic response to a specific surgical stimulus during surgery in 90 consenting ASA physical status I-III patients undergoing lower abdominal procedures. After the administration of midazolam 2 mg IV, anesthesia was induced in all patients with propofol 1.5 mg/kg IV and fentanyl 1 microg/kg IV and was initially maintained with desflurane or isoflurane, 0.7 minimum alveolar anesthetic concentration, at total FGF rates of either 1 or 3 L/min. In response to the surgical stimulation of skin incision and retropubic dissection, an increase in mean arterial pressure (MAP) >20% above the preincision baseline MAP value provoked a stepwise increase in the inspired concentration of the volatile anesthetic or the IV administration of a variable-rate infusion of esmolol. At both FGF rates, the acute hemodynamic response to surgical stimulation was more efficiently treated by increasing the inspired concentration of desflurane than isoflurane. At 1 L/min, the average time to control the increase in MAP was significantly shorter with desflurane (17+/-12 min) compared with isoflurane (29+/-16 min), with 60% of the patients in the isoflurane group requiring rescue therapy. When an esmolol infusion was used to control the increase in MAP, supplementation with fentanyl was required in 40% and 53% of patients anesthetized with desflurane and isoflurane, respectively. In conclusion, desflurane provided more rapid and reliable control of acute hemodynamic responses to surgical stimulation than isoflurane or esmolol when the volatile anesthetics were administered at low FGF rates. ⋯ At low fresh gas flow rates (1 L/min), desflurane more successfully and rapidly controlled the acute hemodynamic responses to painful surgical stimuli than isoflurane.
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Anesthesia and analgesia · Sep 1998
Randomized Controlled Trial Clinical TrialOral antihistamines reduce the side effects from rapid vancomycin infusion.
Rapid infusion of vancomycin causes histamine-mediated side effects, hypotension, and rash, known as "red man syndrome." In this prospective, randomized, double-blind, placebo-controlled study, we examined the ability of oral antihistamines to attenuate three clinical end points: rash, hypotension, and vancomycin discontinuation, and we compared these findings with those of a similar study using IV antihistamines. Patients (ASA physical status I-III) who required vancomycin prophylaxis for elective arthroplasty received either oral antihistamines (diphenhydramine < or = 1 mg/kg and cimetidine < or = 4 mg/kg, n = 20) or placebo (n = 10) 1 h before rapid vancomycin infusion (1 g over 10 min). The vancomycin infusion was discontinued if the mean arterial blood pressure decreased by > or = 20% or if itching was intolerable for the patient. Clinically significant hypotension developed in no treated patients, compared with five (50%) patients in the placebo group (P = 0.001). Rapid infusion was stopped for one treated patient (5%) and for five (50%) patients in the placebo group (P = 0.004). Incidence (P = 0.011) and severity of rash (P = 0.015) were also reduced in treated patients. Peak histamine levels were increased but were similar for patients in both groups (mean +/- SD, 1.9+/-2.5 vs 1.6+/-2.4 ng/mL; P = 0.75). Oral antihistamines were as effective as IV antihistamines. In conclusion, oral H1 and H2 antihistamine pretreatment is a practical, safe, and inexpensive option to attenuate histamine-mediated side effects associated with rapid vancomycin infusion. ⋯ Clinicians often must administer vancomycin faster than the 1-h recommended time, which can cause "red man syndrome" (rash, itching, hypotension). Our randomized, double-blind, placebo-controlled study showed that oral H1 and H2 antihistamine pretreatment significantly reduced the histamine-related side effects of rapid vancomycin infusion.