Effects of dexmedetomidine on propofol and remifentanil infusion rates during total intravenous anesthesia for spine surgery in adolescents

Introduction: Total intravenous anesthesia with propofol and a synthetic opioid is a frequently chosen anesthetic technique for posterior spinal fusion. Despite its utility, adverse effects may occur with high or prolonged propofol dosing regimens including delayed awakening. The current study investigated the propofol‐sparing effects of the concomitant administration of the α₂‐adrenergic agonist, dexmedetomidine, during spinal fusion surgery in adolescents. Methods: The surgical database of the department of orthopedic surgery was searched and patients (12–21 years of age) were identified who had undergone spinal fusion for either idiopathic or neuromuscular scoliosis during the past 24 months. Patients were assigned to two groups. Group 1 included patients anesthetized with propofol and remifentanil and group 2 included patients anesthetized with dexmedetomidine, propofol, and remifentanil. In the latter group, dexmedetomidine was administered as a continuous infusion of 0.5 μg·kg^?1·h^?1 started after the induction of anesthesia without a loading dose. Propofol was adjusted to maintain the bispectral index (BIS) number at 40–50 and remifentanil was adjusted to maintain the mean arterial pressure (MAP) at 50–65 mmHg. Labetolol or hydralazine was used if the MAP could not be maintained at 50–65 mmHg with remifentanil up to a maximum dose of 0.6 μg/kg/min. Statistical analysis included a nonpaired t‐test for parametric data (age, weight, remifentanil/propofol infusion requirements, and heart rate/blood pressure values). A nonparametric statistical analysis (Dunn) was used to compare BIS numbers. Parametric data are presented as the mean ± sd while nonparametric data are presented as the median and the 95th percentile confidence intervals. Results: Twelve patients received propofol–remifentanil–dexmedetomidine and 24 received propofol–remifentanil. There were no differences in the demographic data, BIS numbers or hemodynamic parameters between the two groups. There was a reduction in the propofol infusion requirements in patients who also received dexmedetomidine (71 ± 11 μg·kg^?1·min^?1) compared with those receiving only propofol–remifentanil (101 ± 33 μg·kg^?1·min^?1, P = 0.0045). No difference was noted in the remifentanil infusion requirements or the use of supplemental agents (hydralazine and labetolol) to maintain controlled hypotension. Conclusion: The concomitant use of dexmedetomidine in patients undergoing spinal fusion reduces propofol infusion requirements when compared with those patients receiving only propofol and remifentanil.     

Leukokinetic Studies. VII. Morphology of the Bone Marrow and Blood of Dogs Given Vinblastine Sulfate

The effect of a single injection of vinblastine sulfate was studied in 50mongrel dogs. Nine of 34 dogs given 0.2 mg./Kg. of VLB died with gastrointestinal toxicity and the mortality rate increased as the dosage of VLB wasincreased. The morphologic pattern of leukocyte suppression and recovery inthe bone marrow and blood was studied in detail in surviving animals.

The cells of the bone marrow were markedly affected by VLB. Within 4hours there was an increase in the number of cells in metaphase and, by day1, virtually all proliferating leukocytes and erythrocytes had disappeared. Anorderly repopulation of the bone marrow followed.

The neutrophils, eosinophils, lymphocytes and monocytes of the blood wereall markedly altered in concentration after VLB. Each type of cell first decreased to abnormally small numbers and then increased to abnormally largenumbers in the blood. The curve of disappearance from and reappearance inthe blood differed for each cell type.

The changes in blood neutrophil number and morphology were correlatedwith changes in the blood neutrophil precursor cells of the marrow. The following conclusions were reached concerning the neutrophils and the assumptions implicit to these conclusions were detailed.

1. In the dog, the marrow contains enough post-mitotic granulocytes toreplace those lost from the blood for at least 3 to 4 days.

2. The release of mature neutrophils from the bone marrow is a functionof the rate at which blood neutrophils are lost and proceeds normally evenwhen the marrow granulocyte reserve is partially depleted.

Submitted on March 27, 1963 Accepted on August 20, 1963     

The Acridine Orange Viability Test Applied to Bone Marrow Cells I. Correlation with Trypan Blue and Eosin Dye Exclusion and Tissue Culture Transformation

Suspensions of murine bone marrow cells were stained with acridine orange(A-O) and observed under fluorescent microscopy after treatment withvarious injurious agents in order to establish the staining characteristics of"live" and "dead" cells. The percentage of viable cells demonstrated by the"A-O viability test" were correlated with eosin and trypan blue dye exclusionand tissue culture transformation viability tests. In general, the A-O testdemonstrated the viability of cells preserved by freezing as effectively as theother in vitro tests. In addition, the A-O test may be more sensitive indetermining the viability of cells where metabolic processes have been injuredby poisons or change in pH.

Submitted on September 4, 1963 Accepted on October 29, 1963     

Acute Promyelocytic Leukemia with Fibrinogen and Factor V Deficiencies

1. Two patients with acute promyelocytic leukemia (APL) are reported.Many of the promyelocytes were atypical. Of the 57 patients with thisdisorder in the literature, only three survived more than 4 months. Ourpatients underwent complete remission on 6-mercaptopurine, and survived8 and 14 months, respectively.

2. Coagulation abnormalities in these two patients were thrombocytopenia;fibrinogen and factor V deficiencies; and, in one, prothrombin deficiency.These defects disappeared with remission, then reappeared terminally. Incontrast to most previous reports, no increased fibrinolytic activity was foundin their blood. Infused fibrinogen disappeared abnormally rapidly from theblood of one patient; this was not affected by simultaneous heparin administration, and no thrombi were seen at autopsy.

3. Fibrinogen, factor V, and prothrombin were assayed in 86 patients withother forms of leukemia before treatment or in relapse. Fibrinogen deficiencywas found in none; prothrombin and/or factor V deficiency in eight. Threeof these had acute myeloblastic, three acute myelomonoblastic, and twochronic myelocytic leukemia.

4. The characteristic cellular morphology, combined with the usual findingof fibrinogen and factor V deficiencies, makes for a distinct differentiation ofAPL from other forms of leukemia.

Submitted on July 16, 1963 Accepted on December 23, 1963     

EXTRADURAL BUPIVACAINE OR LIGNOCAINE ANAESTHESIA FOR ELECTIVE CAESAREAN SECTION: THE ROLE OF MATERNAL POSTURE

Extradural anaesthesia was induced in 64 patients in eitherthe sitting or the lateral position, for elective Caesareansection with either 0.5% plain bupivacaine or 2% lignocainewith adrenaline 1 in 200 000. Onset was significantly shorterand a significantly greater number of patients were ready forsurgery within 35 min following injection of lignocaine in thelateral position. Hypotension (defined as a 25% or greater reductionin arterial pressure) occurred in 36% of patients. Significantlymore patients who had received the first injection of localanaesthetic agent in the sitting position required ephedrineto correct maternal hypotension. Most frequently, hypotensioncoincided with transfer of patients to theatre and thus wasassociated with movement of the patient in the presence of extensivesympathetic block.