Biomedical subjects

T G Monk

Publications and source records attributed to T G Monk.

43 records · Page 3Linked to original sources

PubMed1993

Electroencephalogram spectral edge frequency, lower esophageal contractility, and autonomic responsiveness during general anesthesia.

Both the electroencephalogram (EEG) spectral edge frequency (SEF) and lower esophageal contractility (LEC) indices have been reported to be useful indicators of anesthetic depth. We designed a prospective study to evaluate the relationship between changes in these two variables and objective measurements of physiologic responsiveness to surgical stress (i.e., changes in hemodynamic variables and plasma levels of norepinephrine, epinephrine, total catecholamines, and vasopressin). Eighty-nine consenting adult males undergoing radical prostatectomy procedures under a standardized general anesthetic technique were studied according to a randomized, single-blinded protocol. General anesthesia was induced with 30 micrograms/kg intravenous (i.v.) alfentanil, 2.5 mg/kg i.v. thiopental, and 0.1 mg/kg i.v. vecuronium, and subsequently maintained with 0.5 microgram/kg/min alfentanil, nitrous oxide (N2O) 67% in oxygen, and 0.8 microgram/kg/min vecuronium. Following retropubic dissection, 81 patients (92%) manifested acute hypertensive responses, with mean arterial pressure increasing from 90 +/- 14 to 122 +/- 14 mm Hg (mean +/- SD). This acute hypertensive response was treated with one of three different treatment modalities (20 to 60 micrograms/kg i.v. alfentanil, 0.5 to 2.0% inspired isoflurane, or 0.05 to 0.15 mg/kg i.v. trimethaphan) to return the mean arterial pressure to within 10% of the preincisional (baseline) value within 5 to 10 minutes. Although the mean arterial pressure, heart rate, and plasma levels of catecholamines and vasopressin significantly increased following the surgical stimulus, and decreased after adjunctive therapy, the EEG-SEF and LEC index (LECI) values did not significantly change during these study intervals. Furthermore, using a logistic regression analysis, we observed that preincision EEG-SEF and LECI values could not predict whether patients would manifest a hypertensive response. Therefore, the EEG-SEF and LECI were unreliable indicators of anesthetic depth.

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PubMed1992

Treatment of stress response during balanced anesthesia. Comparative effects of isoflurane, alfentanil, and trimethaphan.

Acute hypertensive responses during nitrous oxide-opioid-relaxant anesthesia are a common clinical problem. In adult men undergoing radical prostatectomy procedures and anesthetized with a standardized technique, we evaluated the effectiveness of alfentanil, isoflurane, and trimethaphan in treating acute hemodynamic and stress hormone responses to surgical stimulation. Stress hormone concentrations were measured 1 min before skin incision, after the onset of an acute hypertensive response, and after returning the mean arterial pressure to within 10% of the preincision values with one of the three treatment modalities. Pretreatment plasma alfentanil concentrations (151 +/- 47 to 156 +/- 47 ng.ml-1) and end-tidal nitrous oxide concentrations (66 +/- 2 to 68 +/- 2%) were similar in all three groups. Acute hypertensive events were associated with significantly increased concentrations of catecholamines and vasopressin (antidiuretic hormone [ADH]). Whereas intravenous alfentanil returned all hormone concentrations to preincision values, norepinephrine and glucose concentrations were significantly increased after adjunctive isoflurane administration. Although trimethaphan decreased the norepinephrine concentration, the epinephrine, beta-endorphin, cortisol, ADH, and glucose concentrations were significantly increased compared to preincision values. However, the persistent elevation in the posttreatment ADH concentration in the trimethaphan group was the only significant difference between the three groups. Mean (+/- standard deviation) times to awakening (2.8 +/- 3.3 to 3.8 +/- 4.2 min), extubation (8.1 +/- 4.8 to 10.3 +/- 8.5 min), and orientation (19.6 +/- 20.4 to 24.6 +/- 19.1 min) were similar in all three groups. Naloxone was required more frequently in patients in the alfentanil (35%) and isoflurane (24%) groups than in the trimethaphan group (4%).(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMed1992

Total intravenous anesthesia: effects of opioid versus hypnotic supplementation on autonomic responses and recovery.

During radical prostatectomy procedures under total intravenous anesthesia, acute hemodynamic responses to retropubic dissection (30% +/- 8% to 36% +/- 12% [mean +/- SD] increases in mean arterial pressure) were treated with supplemental doses of either an opioid analgesic (alfentanil) or a sedative-hypnotic (propofol) to return the mean arterial pressure to within 10% of the preincision value. Although both drugs were effective, control with propofol required 10.1 +/- 2.5 min compared with 6.3 +/- 2.6 min in the alfentanil group (mean +/- SD; P < 0.01). Plasma stress hormone concentrations increased significantly in response to this surgical stimulus: epinephrine increased from 246% +/- 169% to 283% +/- 330%; norepinephrine increased from 44% +/- 33% to 83% +/- 104%; and antidiuretic hormone increased from 1300% +/- 1591% to 1700% +/- 1328%. Both alfentanil and propofol were equally effective in returning the catecholamine concentrations to their preincision levels. However, antidiuretic hormone levels remained above preincision values in both groups. Despite earlier awakening (3.4 +/- 2.9 vs 9.1 +/- 6.8 min; P < 0.05) in the alfentanil treatment group, there was no difference in time to spontaneous ventilation or tracheal extubation between the groups. In addition, 36% of the alfentanil-treated patients required antihypertensive therapy in the postanesthesia care unit compared with only 9% in the propofol group (P < 0.05). Postanesthesia care unit and hospital discharge times were similar in both treatment groups. We conclude that supplemental doses of alfentanil or propofol were equally effective in controlling acute hemodynamic and hormonal responses to surgical stimuli during total intravenous anesthesia.

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PubMed1991

Comparison of alfentanil and ketamine infusions in combination with midazolam for outpatient lithotripsy.

Sixty unpremedicated outpatients undergoing elective extracorporeal shock wave lithotripsy using an unmodified Dornier HM-3 lithotriptor were randomly assigned to receive an intravenous infusion of either alfentanil or ketamine as an adjuvant to midazolam for sedation and analgesia. Although both drug regimens allowed the maximal number of shock waves and energy level, the alfentanil group had significantly better calculi fragmentation (78% vs. 50% of patients with fragments less than 2 mm). Ketamine infusion provided superior intraoperative cardiorespiratory stability; however, it was associated with more disruptive movements (22 vs. 5) and dreaming (35% vs. 5%) during the procedure (P less than 0.05). Postoperatively, confusion also occurred more frequently in the ketamine-treated patients (31% vs. 5%, P less than 0.05). Alfentanil infusion was associated with more episodes of hemoglobin oxygen desaturation to less than 90% (12 vs. 2, P less than 0.05), itching (23% vs. 4%, P less than 0.05), and ability to recall intraoperative events (45% vs. 12%, P less than 0.05). The incidence of postoperative nausea was decreased (not significantly) in the alfentanil group (32% vs. 54%). The mean anesthesia time was similar in both groups; however, discharge times (means +/- standard deviations) were shorter in the alfentanil group (142 +/- 42 min vs. 161 +/- 31 min, P = 0.05). These data suggest that although both techniques proved effective for anesthesia in outpatients undergoing immersion lithotripsy, alfentanil is superior to ketamine as part of a sedative-analgesic technique because of the improved recovery profile and calculi fragmentation.

Adult↗

PubMed1991

Comparison of intravenous sedative-analgesic techniques for outpatient immersion lithotripsy.

Fifty-three unpremedicated outpatients undergoing elective extracorporeal shock wave lithotripsy using an unmodified Dornier HM-3 lithotriptor received one of two different intravenous sedation-analgesia techniques. Both intravenous midazolam-alfentanil and fentanyl-propofol techniques produced conditions comparable to those achieved with epidural anesthesia during immersion lithotripsy. Of the two sedative-analgesic techniques, midazolam-alfentanil was associated with greater intraoperative amnesia (81% vs 38%), whereas fentanyl-propofol produced less cardiorespiratory depression and fewer postoperative side effects (e.g., pruritus). Compared with a standard epidural anesthesia technique, the mean anesthesia and recovery times were significantly shorter with the two intravenous sedation-analgesia techniques (57-62 min vs 105 min and 143-147 min vs 199 min, respectively). These data suggest that combinations of either midazolam and alfentanil or fentanyl and propofol are viable alternatives to epidural anesthesia for outpatient immersion lithotripsy.

Adult↗

PubMedDate not supplied

Acute hemodynamic effects of indigo carmine in the presence of compromised cardiac function.

This report describes the acute hemodynamic effects of indigo carmine in a surgical patient with compromised cardiac function. A 68-year-old woman with stable but severe cardiac dysfunction and renal artery stenosis was scheduled for an elective aortorenal bypass procedure. No hemodynamic instability occurred during the operation until the patient was administered intravenous (IV) indigo carmine 5 ml. At that time, the patient experienced an acute increase in afterload, which resulted in acute left ventricular failure documented by a decrease in cardiac output (CO) and an increase in pulmonary artery pressure (PAP). Until further studies defining the mechanism for its hypertensive side effect are performed, indigo carmine should be used with caution in patients with severe cardiac dysfunction.

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PubMedDate not supplied

Functional MR imaging of the porcine kidney: physiologic changes of prolonged pneumoperitoneum.

BACKGROUND: Increased intraabdominal pressure (IPA) during laparoscopy has been associated with decreased urine output. The purpose of this study was to use a noninvasive MRI technique to measure renal vessel flow velocity and change in differential renal medulla and cortex perfusion during pneumoperitoneum. STUDY DESIGN: Six female farm pigs underwent general endotracheal anesthesia and dynamic imaging following left ventricular (LV) injection of Gd-DTPA, utilizing a dual echo gradient echo sequence. MRI was repeated after three hours of continuous 15 mm Hg pneumoperitoneum in three study pigs and after three hours of monitored general anesthesia without pneumoperitoneum in three control pigs. Renal artery and renal vein flow velocities were calculated using cine phase-contrast technique. Renal perfusion was independently measured by LV injection of radiolabelled microspheres. RESULTS: There was a decrease in mean renal vein flow velocity in the pneumoperitoneum group as compared to the control group. During pneumoperitoneum there was a similar percentage reduction in the perfusion of the cortex (-28%) and medulla (-31%); this corresponded with a decreased urine output. In addition, radiolabelled microspheres corroborated the similar decrease in both cortical and medullary perfusion rates during pneumoperitoneum. CONCLUSIONS: Prolonged IAP is associated with a decrease in renal vein flow velocity and urine output. There is a similar decrease in the renal medulla and cortex perfusion rates during pneumoperitoneum of 15 mm Hg.

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