Reduced sensitivity to beta-adrenergic agonists in Basenji-Greyhound dogs

To investigate the inhibitory effects of beta-adrenergic agonists and aminophylline on pulmonary responsiveness, we evaluated the ability of albuterol and aminophylline to attenuate pulmonary responses to aerosol challenge with methacholine and histamine in intact Basenji-Greyhound (BG) and selected mongrel dogs. Pulmonary responses were measured in untreated dogs and in dogs pretreated with albuterol (1 and 2.5 micrograms/kg) or aminophylline. Before aerosol challenge, baseline pulmonary resistance (RL) and dynamic compliance (Cdyn) were not significantly different between the BGs and the mongrels. In the untreated dogs, pulmonary responses to methacholine and histamine aerosols were not different between the BGs and the mongrels. Pretreatment with albuterol (1 microgram/kg) or aminophylline significantly attenuated the pulmonary response to methacholine in the mongrels but was without effect in the BGs. Albuterol (2.5 micrograms/kg) significantly attenuated the pulmonary response to methacholine in the BGs and the mongrels; however, this attenuation was significantly greater (P less than 0.05) in the mongrels than in the BGs. In response to histamine challenge, no differences were seen between the BGs and the mongrels in the control state (no pretreatment) or after pretreatment with albuterol or aminophylline. This study demonstrates that in BGs pulmonary responsiveness to methacholine but not histamine is resistant to inhibition by beta-adrenergic agonists. This may result from a qualitative or quantitative defect in either the cholinergic or beta-adrenergic receptor or to an abnormality distal to the receptors in the signal transduction mechanism at a site where the two signals interact.

Ketamine by continuous infusion for sedation in the pediatric intensive care unit

ICU physicians generally rely on either narcotics or benzodiazepines to provide analgesia and sedation. We describe five patients in whom ketamine administered as a bolus dose of 0.5 to 1.0 mg/kg, followed by a continuous infusion of 10 to 15 micrograms/kg.min, provided effective sedation and analgesia without significantly compromising cardiorespiratory function. Four of these patients previously experienced deleterious cardiorespiratory effects from either benzodiazepines or narcotics. In three patients who were breathing spontaneously, PaCO2 remained less than 44 torr during the ketamine infusion. With ketamine, no reduction in mean arterial pressure from baseline was noted in any patient. As with any form of iv anesthesia, ketamine can have cardiorespiratory side-effects; therefore, the means to manage these effects should be readily available.

Pulmonary reactivity to methacholine during beta-adrenergic blockade: propranolol versus esmolol

Pulmonary reactivity to methacholine after equipotent beta-blocking doses of propranolol and esmolol was compared in seven basenji-greyhound dogs during thiopental-fentanyl anesthesia. Equipotent doses of esmolol and propranolol were determined by both heart rate effects and by isoproterenol response curves. Propranolol (2 mg/kg) was administered intravenously as a bolus dose and esmolol (0.4-0.5 mg.kg-1.min-1) was administered by continuous infusion. Both esmolol and propranolol significantly decreased heart rate and mean arterial pressure (P less than 0.001). Baseline pulmonary resistance and dynamic compliance did not change after the administration of either propranolol or esmolol. However, propranolol significantly shifted the methacholine dose-response curve to the left so that methacholine (0.3 mg/ml) increased pulmonary resistance by 7.9 +/- 0.97 cmH2O.l-1.s-1 (mean +/- SEM of seven dogs) after pretreatment with propranolol but only 4.4 +/- 0.89 cmH2O.l-1.s-1 (P less than 0.05) without propranolol pretreatment (control). Esmolol, however, did not significantly shift the methacholine dose-response curve. Methacholine (0.3 mg/ml) increased resistance 4.0 +/- 0.89 cmH2O.l-1.s-1 during esmolol administration. This study shows that at equipotent beta 1-blocking doses, propranolol, but not esmolol, produces significant increases in pulmonary reactivity to methacholine.

Intrathecal morphine as an adjunct to anesthesia for head and neck surgery

Within the past 15 years, the use of spinal opiates has gained acceptance as a means of achieving postoperative analgesia during various surgical procedures, though little has been reported concerning such use in head and neck surgery. Our experience with intrathecal morphine for eight patients who have had head and neck surgery is reviewed. Mechanisms of pain and possible sites of action of intrathecal morphine as they pertain to these patients are discussed. Adequate postoperative analgesia was achieved in seven of our eight patients. Only one patient required supplemental intravenous narcotics during the initial 24-hour postoperative period. This patient had a history of chronic narcotic use, suggesting that such patients may be tolerant to intrathecal narcotics as they are to narcotics given by other routes.

Intraosseous succinylcholine for orotracheal intubation

Within the past few years, the use of intraosseous infusions has increased as a means of achieving rapid vascular access. Although initially used for fluid administration, the intraosseous administration of several drugs has been shown to be an effective alternative to the intravenous route. We present two cases of the intraosseous administration of succinylcholine (1 mg/kg) for emergency airway management in children. Intraosseous succinylcholine resulted in adequate intubating conditions within 45 seconds.

Attenuation of histamine-induced airway constriction by albuterol during halothane anesthesia

The effect of albuterol (a beta 2 specific adrenergic agonist) on airway reactivity to histamine aerosol challenge was evaluated during halothane anesthesia and thiopental-fentanyl anesthesia in five Basenji Greyhound dogs. Responses to histamine aerosol challenges (0.01, 0.03, 0.1, 0.3, 1.0, and 3.0 mg/ml) were measured during thiopental-fentanyl anesthesia and during halothane anesthesia in the presence and absence of iv albuterol (2.5 micrograms/kg). Prior to aerosol challenges, baseline pulmonary resistance (RL) and dynamic compliance (Cdyn) did not differ in the four conditions. Albuterol significantly attenuated the pulmonary response to histamine during thiopental-fentanyl anesthesia. Although halothane itself significantly attenuated the pulmonary response to histamine, this response was further attenuated by the addition of albuterol. This study suggests that albuterol is effective in attenuating bronchoconstriction during both thiopental-fentanyl and halothane anesthesia. As the effects of albuterol and halothane on the airways are additive, beta-adrenergic agonists such as albuterol are the agents of choice to treat bronchospasm in patients anesthetized with inhalational anesthetics.

Postoperative analgesia. Use of intrathecal morphine in children

The identification of opiate receptors in the spinal cord gave rise to the suggestion that the use of intrathecal and epidural narcotics may provide effective and safe postoperative analgesia. The authors retrospectively reviewed the records of ten children who received intrathecal morphine as part of their anesthetic care over the last 2 years. Preservative-free morphine (Duramorph) in a dose of 0.02 mg/kg was administered to all patients in the lumbar intrathecal space before the start of the surgical procedure. Adequate postoperative analgesia was achieved in the ten children. No patient required supplemental analgesic agents for the initial 15-hour postoperative period. Surgical procedures included exploratory laparotomy, laryngotracheoplasty, and craniofacial reconstruction. As with narcotics administered by any route, intrathecal morphine can cause respiratory depression, and such depression may be delayed for up to 24 hours after the dose. Therefore, the postoperative respiratory status of these children should be monitored for 24 hours after the dose, preferably in an intensive care unit. With this caveat, the use of intrathecal morphine provides safe and effective postoperative analgesia in children undergoing major surgery.

Aminophylline does not attenuate histamine-induced airway constriction during halothane anesthesia

The effects of aminophylline on the release of endogenous catecholamines and on airway reactivity to aerosol histamine challenge were evaluated during halothane and thiopental/fentanyl anesthesia in basenji-greyhound dogs. Responses to histamine aerosol challenge (0.01, 0.03, 0.1, 0.3, 1.0, and 3.0 mg/ml) were measured during six conditions: 1) thiopental/fentanyl anesthesia (control), 2) thiopental/fentanyl with aminophylline infusion, 3) halothane anesthesia (1.5 MAC), 4) halothane anesthesia with aminophylline infusion, 5) thiopental/fentanyl anesthesia after pretreatment with iv propranolol, and 6) thiopental/fentanyl anesthesia with aminophylline infusion after pretreatment with iv propranolol. Prior to aerosol challenge baseline pulmonary resistance (RL) did not differ in the six groups. Aminophylline significantly attenuated the pulmonary response to histamine and increased catecholamine concentrations during thiopental/fentanyl anesthesia. Although halothane itself significantly attenuated the pulmonary response to histamine, the administration of aminophylline during halothane anesthesia produced no additional protective effect and no increases in catecholamines were noted. Moreover, no protective effect was seen after aminophylline administration during thiopental/fentanyl anesthesia in the same dogs pretreated with propranolol. These data suggest that the protective effect of aminophylline on histamine reactivity results from release of endogenous catecholamines and that the use of aminophylline during halothane anesthesia, which blocks this release, is not warranted.

The significance of calcified regional lymph nodes at the time of diagnosis of osteosarcoma

The presence of lymph node metastases from osteosarcoma was rare at diagnosis, occurring in only four of 176 patients (2.3%) at St. Jude Children's Research Hospital. An additional patient presented with calcified lymph nodes, which were demonstrated to contain no evidence of metastatic osteosarcoma. These patients did not differ in race, sex or age at diagnosis from other osteosarcoma patients. Each of the four patients with lymph node metastases of osteosarcoma had tumors composed predominantly of the osteoblastic type. Regional nodal metastases, whether alone or in conjunction with other metastatic disease were a poor prognostic factor. Despite aggressive therapy, median survival was 8 1/2 months from diagnosis, which did not differ significantly from the survival achieved by other osteosarcoma patients who had other hematogenous metastases.