Characterization and biological activity of a rat monoclonal antibody to rat/human corticotropin-releasing factor

To produce a rat monoclonal antibody directed to rat CRF (rCRF), female Wistar rats were actively immunized with a rCRF-bovine thyroglobulin conjugate. Immunization resulted in the formation of CRF antibodies, as indicated by binding of [125I]iodo-rCRF and attenuation of the plasma corticosterone responses to ether stress. Rat spleen cells were fused with mouse myeloma P3 cells, and a hybridoma clone (PFU 83) was selected according to its capacity to bind [125I]iodo-rCRF and inhibit rCRF-induced ACTH release from cultured rat pituitary cells. PFU 83 antibodies (IgG2a subclass) are directed to the extreme C-terminal part (amino acids 38-39) of rCRF and bind with an affinity constant of 21 nM. In vitro, PFU 83 causes a parallel shift to the right of the rCRF dose-ACTH response curve, with an apparent affinity of 10 nM. PFU 83 neither binds nor blocks the ACTH-releasing activity of oCRF. Intravenous administration of PFU 83 ascites (generated in nude mice) to Wistar rats caused a dose-dependent inhibition of ether-induced ACTH secretion. Full blockade of the ACTH response to ether was found at a dose of 10 nmol PFU 83/rat. Based on the dynamics of rCRF binding and its in vitro and in vivo effects, we conclude that the rCRF-blocking bioactivity of PFU 83 is due to binding of PFU 83 to native rCRF and formation of a biologically inactive complex. Finally, we found that PFU 83 did not affect resting or ether-induced alpha MSH secretion, indicating that CRF does not play a major role in the control of alpha MSH secretion.     

Ventilatory sensitivities of peripheral and central chemoreceptors of young piglets to inhalation of CO2 in air.

In 20 piglets aged 2-12 d (mean 6.8 d) and anesthetized with alpha-chloralose-urethane, we investigated the contribution of the peripheral and central chemoreceptors to the ventilatory response to inhalation of CO2 in air. For this purpose we used the dynamic end-tidal forcing technique, applying square-wave changes in end-tidal CO2 tension of 1.5-2.0 kPa at a constant end-tidal O2 tension of 15 kPa. Each response, measured on a breath-to-breath basis, was separated into a fast peripheral and a slow central component by fitting the sum of two exponentials to the measured ventilation. Each component was characterized by a CO2 sensitivity, a time constant, a time delay, and an apneic threshold. The results showed that in 2- to 12-d-old piglets the peripheral chemoreceptors are responsive to CO2 during air breathing. The contribution of the peripheral chemoreceptors in mediating the response to CO2 averaged 30 +/- 10%. Within this age range we could not demonstrate a significant correlation of the parameters characterizing the dynamic ventilatory response to CO2 with postnatal age.     

The correlation of the bispectral index monitor with clinical sedation scores during mechanical ventilation in the pediatric intensive care unit

In patients who are mechanically ventilated in the pediatric intensive care unit (PICU), sedative and/or analgesic medications are routinely provided and titrated to effect based on clinical assessment of the patient. The bispectral index (BIS) monitor uses a modified electroencephalogram to quantify the effects of central nervous system-acting drugs on the level of consciousness. To evaluate the usefulness of the BIS monitor to predict clinical sedation levels in the PICU, we compared BIS values with simultaneously obtained clinical sedation scores in 24 mechanically ventilated pediatric patients aged 5.7 plus minus 6.1 yr. For each sedation scale used, the BIS value correlated with increasing depth of sedation (P < 0.0001) and was independent of the drug(s) used for sedation. To differentiate adequate from inadequate sedation, a BIS value <70 had a sensitivity of 0.87--0.89 and a positive predictive value of 0.68--0.84. To differentiate adequate from excessive sedation, a BIS value <50 had a sensitivity of 0.67--0.75 and a positive predictive value of 0.07--0.52. We conclude that the BIS monitor may be a useful adjunct for the assessment of sedation in PICU patients. IMPLICATIONS: We demonstrate the usefulness of the bispectral index monitor for assessing sedation in pediatric intensive care unit patients. The bispectral index monitor correlated with clinically assessed sedation levels and was useful for differentiating adequate from inadequate sedation, which would be of value when the clinical examination is unavailable.     

Rescue sedation with dexmedetomidine for diagnostic imaging: a preliminary report

BACKGROUND: Sedation is frequently required during noninvasive radiological imaging in children. Although commonly used agents such as chloral hydrate and midazolam are generally effective, failures may occur. The authors report their experience with dexmedetomidine for rescue sedation during magnetic resonance imaging. METHODS: A retrospective chart review was undertaken. RESULTS: The cohort included five patients ranging in age from 11 months to 16 years. Following the failure of other agents (chloral hydrate and/or midazolam), dexmedetomidine was administered as a loading dose of 0.3-1.0 microg x kg(-1) x min(-1) over 5-10 min followed by an infusion of 0.5-1.0 microg x kg(-1) x h(-1). The dexmedetomidine loading dose required to induce sedation was 0.78 +/- 0.42 microg x kg(-1) (range 0.3-1.2). The maintenance infusion rate was 0.57 +/- 0.06 microg x kg(-1) x h(-1) (range 0.48-0.69). The imaging procedures were completed without difficulty. No patient required additional bolus administrations or changes in the infusion rate. The duration of the dexmedetomidine infusion ranged from 30 to 50 min. The mean decrease in heart rate was 13.6 +/- 5.1 b x min(-1) (14.3 +/- 5.0% from baseline; P = 0.02), the mean decrease in systolic blood pressure was 26.4 +/- 15.2 mmHg (24.6 +/- 12.4% decrease from baseline; P = 0.004), and the mean decrease in respiratory rate was 1.4 +/- 1.5 min(-1) (7.5 +/- 7.9% decrease from baseline; P = NS). P(E)CO2 exceeded 6.5 kPa (50 mmHg) in one patient [maximum 6.6 kPa (51 mmHg)] with a maximum value of 6.0 +/- 0.4 kPa (46 +/- 3 mmHg). Oxygen saturation decreased from 98 +/- 1 to 95 +/- 1%; P = 0.001. No patient developed hypoxemia (oxygen saturation less than 90%). Mean time to recovery to baseline status was 112.5 +/- 50.6 min and time to discharge was 173.8 +/- 83.8 min. CONCLUSIONS: Our preliminary experience suggests that dexmedetomidine may be an effective agent for procedural sedation during radiological imaging. Its potential application in this setting is discussed and other reports regarding its use in pediatric patients are reviewed.     

Preliminary experience with oral dexmedetomidine for procedural and anesthetic premedication

BACKGROUND: Oral premedication is often required in children to provide anxiolysis and lessen the psychological impact of hospitalization and/or procedures. We present our experience with dexmedetomidine as an oral premedicant prior to procedural sedation or anesthetic induction. METHODS: We undertook a retrospective review of the anesthesia or sedation service records of patients who received oral dexmedetomidine. RESULTS: The cohort for the study included 13 patients ranging in age from 4 to 14 years. Oral dexmedetomidine (mean dose: 2.6 +/- 0.83 microg.kg(-1); range 1.0-4.2 microg.kg(-1)) was used as premedication prior to anesthesia induction in four patients and prior to intravenous (IV) cannula placement for procedural sedation in nine patients with neurobehavioral problems. Effective sedation was achieved in 11 of 13 patients. The one patient in whom anxiolysis was not achieved received the lowest dose of dexmedetomidine (1 microg.kg(-1)) prior to anesthesia induction. In the other three patients, parental separation and acceptance of the mask was achieved at 20-30 min with a dose of 2.5 microg.kg(-1). When used for procedural sedation, placement of an IV cannula was accomplished without difficulty in seven of eight patients with neurobehavioral disorders and with only mild resistance in the other. No complications were noted and parental satisfaction with the sedation experience was high. CONCLUSIONS: These preliminary data suggest that dexmedetomidine may be an effective oral premedicant prior to anesthesia induction or procedural sedation. We found that it was effective even in patients with neurobehavioral disorders in whom previous attempts at sedation had failed.     

Use of a remifentanil-propofol mixture for pediatric flexible fiberoptic bronchoscopy sedation

BACKGROUND: Flexible fiberoptic bronchoscopy is an important diagnostic tool for pediatric pulmonologists. Because of its favorable respiratory profile, ketamine has become a popular sedative for this procedure, but may be associated with unpleasant emergence reactions in the older child. Remifentanil is a newer, ultra-short acting opioid that has been shown to provide effective sedation and cough suppression for fiberoptic bronchoscopy when combined with intermittent propofol boluses. However, delivery of these agents as a combined, single infusion has not been described. METHODS: Children > or =2 years of age undergoing fiberoptic bronchoscopy were enrolled. Remifentanil was mixed in a single syringe with undiluted propofol giving final drug concentrations of 10 mg x ml(-1) of propofol and 15-20 microg x ml(-1) of remifentanil. Sedation was induced with a bolus of approximately 0.1 ml x kg(-1) of this mixture and maintained by titrating the drip throughout the procedure. Vital signs, sedative effectiveness, recovery patterns, and complications were prospectively recorded. RESULTS: Fifteen patients aged 9.0 +/- 5.3 years were sedated. Sedation was induced with 1.2 +/- 0.4 mg x kg(-1) propofol (2.4 +/- 0.8 microg x kg(-1) remifentanil) and maintained with 4.1 +/- 1.8 mg x kg(-1) x h(-1) propofol (0.13 +/- 0.06 microg x kg(-1) x min(-1) remifentanil). Five patients received low-dose ketamine to augment sedation. The maximal decrease in respiratory rate was 6.1 +/- 5.3 b x min(-1) (27.6 +/- 21%) and no patient became hypoxemic. All procedures were completed easily without significant complication. Patients recovered to baseline 13.3 +/- 8.5 min following infusion discontinuation. CONCLUSIONS: A remifentanil/propofol mixture provided effective sedation and rapid recovery in pediatric patients undergoing fiberoptic bronchoscopy.     

Safety and efficacy of ketamine sedation for infant flexible fiberoptic bronchoscopy

OBJECTIVE: To describe our experience with ketamine sedation during infant flexible fiberoptic bronchoscopy. DESIGN: Retrospective chart review. Infants were sedated with midazolam and ketamine with or without fentanyl. The sedation regimen, final procedure performed, procedure duration, and complications were recorded. Complication rates between infants 6 months of age and between infants with upper vs lower airway symptoms were compared by chi(2) test with a contingency table. RESULTS: Fifty-nine procedures were performed in 55 patients aged 6.1 +/- 3.1 months (mean +/- SD). Sedation was achieved with ketamine and midazolam (n = 30) or ketamine, midazolam, and fentanyl (n = 29). Bronchoscopy with BAL was performed in 44 patients and bronchoscopy alone in 3 patients. In 11 patients, severe upper airway obstruction and/or anomalies prevented subglottic passage of the bronchoscope. One patient could not be adequately sedated. There were no major complications. Minor complications occurred in 14 patients (23.7%), most commonly mild hypoxemia (n = 9). Brief central apnea developed in three patients. Complication rates were unaffected by age or indication for bronchoscopy. CONCLUSIONS: Infant flexible fiberoptic bronchoscopy can be safely and effectively performed using ketamine sedation. Complications, especially mild hypoxemia, appear more common in infants, likely due to smaller airway diameter. Regardless of the sedative(s) used, additional vigilance is required when performing bronchoscopy in this population.     

Influence of Acute Pain Induced by Activation of Cutaneous Nociceptors on Ventilatory Control

Background: Although many studies show that pain increases breathing, they give little information on the mechanism by which pain interacts with ventilatory control. The authors quantified the effect of experimentally induced acute pain from activation of cutaneous nociceptors on the ventilatory control system.

Methods: In eight volunteers, the influence of pain on various stimuli was assessed: room air breathing, normoxia (end-tidal pressure of carbon dioxide (PETCO2) clamped, normoxic and hyperoxic hypercapnia, acute hypoxia, and sustained hypoxia (duration, 15-18 min; end-tidal pressure of oxygen, approximately 53 mmHg). Noxious stimulation was administered in the form of a 1-Hz electric current applied to the skin over the tibial bone.

Results: While volunteers breathed room air, pain increased ventilation (V with dotI) from 10.9 +/- 1.7 to 12.9 +/- 2.5 l/min sup -1 (P < 0.05) and reduced PETCO2 from 38.3 +/- 2.3 to 36.0 +/- 2.3 mmHg (P < 0.05). The increase in V with dotI due to pain did not differ among the different stimuli. This resulted in a parallel leftward-shift of the V with dotI -carbon dioxide response curve in normoxia and hyperoxia, and in a parallel shift to higher V with dotI levels in acute and sustained hypoxia.