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Biomedical subjects

Steven B Backman

Publications and source records attributed to Steven B Backman.

14 recordsLinked to original sources

Upper airway compromise secondary to edema in Graves' disease.

PURPOSE: We report an unusual case of upper airway compromise in a patient with Graves' disease. We speculate that this complication may be due, in part, to poorly controlled hyperthyroidism. CLINICAL FEATURES: A 26-yr-old female suffering from Graves' disease underwent a total thyroidectomy. Awake fibreoptic intubation was attempted because of a large goiter and orthopnea. Upper airway edema impeded the passage of an armored 7.5 mm endotracheal tube. She was subsequently intubated awake with a regular 7.5 mm endotracheal tube under direct laryngoscopy over an Eschmann bougie. The patient was extubated in the operating room over a tube exchanger. Two hours later she developed stridor and upper airway obstruction. Using direct laryngoscopy, she was reintubated with difficulty because of upper airway edema. At this time, she manifested signs of thyrotoxicosis which were managed medically. On postoperative day three she underwent a tracheostomy after failing a trial of extubation. The upper airway was edematous with minimal vocal cord movement. On postoperative day nine the tracheostomy was downsized and the patient was sent home. The vocal cords were still edematous with minimal movement. Three weeks later, she demonstrated normal right vocal cord movement and weak left vocal cord movement, and the tracheostomy was decannulated. CONCLUSIONS: Uncontrolled hyperthyroid patients with large goiters secondary to Graves' disease may develop edema of the upper airway. A high degree of vigilance for airway obstruction is necessary, with a carefully planned approach at each stage of the patient's hospital course to treat this potentially life-threatening situation.

Adult↗

Cortical processing of complex auditory stimuli during alterations of consciousness with the general anesthetic propofol.

BACKGROUND: The extent to which complex auditory stimuli are processed and differentiated during general anesthesia is unknown. The authors used blood oxygenation level-dependent functional magnetic resonance imaging to examine the processing words (10 per period; compared with scrambled words) and nonspeech human vocal sounds (10 per period; compared with environmental sounds) during propofol anesthesia. METHODS: Seven healthy subjects were tested. Propofol was given by a computer-controlled pump to obtain stable plasma concentrations. Data were acquired during awake baseline, sedation (propofol concentration in arterial plasma: 0.64 +/- 0.13 microg/ml; mean +/- SD), general anesthesia (4.62 +/- 0.57 microg/ml), and recovery. Subjects were asked to memorize the words. RESULTS: During all periods including anesthesia, the sounds conditions combined elicited significantly greater activations than silence bilaterally in primary auditory cortices (Heschl gyrus) and adjacent regions within the planum temporale. During sedation and anesthesia, however, the magnitude of the activations was reduced by 40-50% (P < 0.05). Furthermore, anesthesia abolished voice-specific activations seen bilaterally in the superior temporal sulcus during the other periods as well as word-specific activations bilaterally in the Heschl gyrus, planum temporale, and superior temporal gyrus. However, scrambled words paradoxically elicited significantly more activation than normal words bilaterally in planum temporale during anesthesia. Recognition the next day occurred only for words presented during baseline plus recovery and was correlated (P < 0.01) with activity in right and left planum temporale. CONCLUSIONS: The authors conclude that during anesthesia, the primary and association auditory cortices remain responsive to complex auditory stimuli, but in a nonspecific way such that the ability for higher-level analysis is lost.

Acoustic Stimulation↗

Effect of laparoscopic versus open gastric bypass surgery on postoperative pain and bowel function.

BACKGROUND: This study was designed to assess postoperative pain and bowel function in morbidly obese patients undergoing Roux-en-Y gastric bypass (RYGBP) performed either by open or laparoscopic technique. METHODS: We prospectively studied patients scheduled for RYGBP between July 2002 and June 2003. Patients were assigned to the laparoscopic or open procedure by one surgeon. All patients received patient controlled analgesia (PCA) with intravenous morphine and rectal naproxen 500 mg every 12 hours. Postoperative analgesia was assessed daily using a visual analog scale (VAS) at rest, on walking and coughing. The amount of morphine used during the first 48 hours, the time of return of gastrointestinal motility and the time until first oral food intake were recorded. RESULTS: 53 patients were enrolled and studied (laparoscopic group n=33, open group n=20). Patients undergoing laparoscopic RYGBP requested less morphine (P=0.0001) and showed lower VAS pain scores than patients undergoing open RYGBP. The return of bowel movement in the laparoscopic group occurred 1 day earlier than in the open group (P=0.01). The time to first passage of gas (P=0.01) and oral food intake (P=0.06) was shorter after laparoscopic than after open RYGBP. Patients in the laparoscopic group were discharged 1(1/2) days earlier than patients in the open group (P=0.01). CONCLUSION: The laparoscopic RYGBP operation was associated with less postoperative pain and morphine consumption than the open RYGBP, thereby facilitating an earlier recovery of intestinal motility.

Administration, Rectal↗

Brain imaging in research on anesthetic mechanisms: studies with propofol.

Brain imaging helps to refine our understanding of the anesthetic effect and is providing novel information that result in the formulation of hypotheses. They have shown that anesthetics act on specific structures that have been known to be important for consciousness at large. They have also helped to show that anesthetics act on specific structures regionally, rather than being non-specific, general depressant of the central nervous system (CNS). A constant finding is that the drugs that we use seem to exert their action on specific sites within the CNS. This is true for a wide variety of drugs like midazolam, anesthetic vapors and opiates. The thalamus has consistently shown marked deactivation coincident with the anesthesia-induced loss of consciousness, appearing to be a very important target of anesthetic effect. Additionally, when vibro-tactile or pain stimulation is given, anesthetics significantly effect cortical structures even before loss of consciousness while loss of transmission at the thalamic level seems to coincide with loss of consciousness. Finally, the use of radioligands allow in vivo characterization of anesthetic effects on neurotransmitter systems.

Anesthetics, Intravenous↗

PET quantification of muscarinic cholinergic receptors with [N-11C-methyl]-benztropine and application to studies of propofol-induced unconsciousness in healthy human volunteers.

This work evaluated kinetic analysis methods for estimation of the receptor availability of the muscarinic receptor using dynamic positron emission tomography (PET) studies with [N-(11)C-methyl]-benztropine. The study also investigated the effect of propofol on central muscarinic receptor availability during general anesthesia. Six volunteers were scanned three times, once for baseline while awake, once during unconsciousness, and once after recovery to conscious level. An irreversible two-tissue compartment model was used to estimate the [N-(11)C-methyl]-benztropine specific binding rate constant k(3), a measure of muscarinic receptor availability. Two different estimation methods were used: 1) optimization with positivity constraints on all the parameters; 2) optimization with additional constraints determined from a one-tissue compartment fit to the cerebellum. In regions with low to middle muscarinic receptor density, the k(3) values from method (2) had lower standard errors than that for method (1) and gave a higher correlation with the density of muscarinic receptors measured in human tissue by in vitro studies (r(2) of 0.98 for Method 2 and r(2) of 0.72 for Method 1). But the k(3) values determined by Method 2 had higher errors for regions with high muscarinic receptor density compared to Method 1. For both methods the mean k(3) values during unconsciousness were generally lower than those during awake for most regions evaluated. Therefore, the method with additional constraints derived from the cerebellum (Method 2) was deemed superior for regions with low to middle muscarinic receptor density, while the method with positivity constraint is the better choice in the regions with high muscarinic receptor density. Our results also suggest the existence of propofol-related reductions in muscarinic receptor availability.

Adult↗

Decreased heart rate and blood pressure in a recent cardiac transplant patient after spinal anesthesia.

PURPOSE: To describe the cardiovascular effects of neuraxial blockade in a heart transplant patient. CLINICAL FEATURES: A 69-yr-old 70-kg male underwent orthotopic heart transplant (bicaval anastomosis technique) for ischemic cardiomyopathy. Five months after transplantation, the patient underwent a transurethral bladder tumour resection under spinal anesthesia. Two millilitres of bupivacaine 0.75% (15 mg) were injected intrathecally at L(3-4) and the patient remained seated for approximately 20 sec prior to assuming the lithotomy position. Subsequently, both blood pressure (BP) and heart rate (HR) diminished gradually (BP and HR immediately pre-spinal: 113 mmHg (mean arterial pressure) and 92 beats x min(-1), respectively; nadir BP and HR: 94 mmHg (16.8% decrease) 30 min postspinal and 73 beats x min(-1) (20.7% decrease) 40 min postspinal, respectively). HR and mean BP were highly correlated (r = 0.9410, P < 0.0001, R(2) = 0.8854). The dermatome level of neuraxial anesthesia, determined by sensitivity to pin prick, was T(8) (five minutes) and T(6) (ten minutes) postinjection of spinal anesthetic. Control patients (n = 10) undergoing elective urological procedures with identical anesthesia management demonstrated very similar cardiovascular responses. CONCLUSIONS: Although cardiac transplant patients may tolerate neuraxial anesthesia admirably, a fall in HR may ensue which theoretically could have important physiological consequences. It is argued that the change in HR in the transplanted patient was mediated by mechanisms intrinsic to the transplanted heart and/or by reduced catecholamine secretion from the adrenal medulla. It is emphasized that HR changes observed in cardiac transplant patients do not necessarily imply reinnervation of the transplanted organ.

Aged↗

Dose-dependent effects of propofol on the central processing of thermal pain.

BACKGROUND: Anatomic and physiologic data show that multiple regions of the forebrain are activated by pain. However, the effect of anesthetic level on nociceptive input to these regions is not well understood. METHODS: The authors used positron emission tomography to measure the effect of various concentrations of propofol on pain-evoked changes in regional cerebral blood flow. Fifteen volunteers were scanned while warm and painful heat stimuli were presented to the volar forearm using a contact thermode during administration of target propofol concentrations of 0.0 microg/ml (alert control), 0.5 microg/ml (mild sedation), 1.5 microg/ml (moderate sedation), and 3.5 microg/ml (unconsciousness). RESULTS: During the 0.5-microg/ml target propofol concentration (mild sedation), the subjects' pain ratings increased relative to the alert control condition; correspondingly, pain-evoked regional cerebral blood flow increased in the thalamus and the anterior cingulate cortex. In contrast, when subjects lost consciousness (3.5 microg/ml), pain-evoked responses in the thalamus and the anterior cingulate cortex were no longer observed, whereas significant pain-evoked activation remained in the insular cortex. CONCLUSION: These data show that propofol has a dose-dependent effect on thalamocortical transfer of nociceptive information but that some pain-evoked cortical activity remains after loss of consciousness.

Adult↗

Autonomic nervous system response to epidural analgesia in laboring patients by wavelet transform of heart rate and blood pressure variability.

BACKGROUND: Epidurals are effective in relieving labor pain but result in a sympathectomy that may compromise maternal hemodynamic stability and fetal perfusion. Decreases in blood pressure and heart rate can be corrected, but markers of autonomic activity would be useful to predict and prevent such changes. The goal of this study was to find markers describing the changes in autonomic nervous system activity with epidural anesthesia in laboring patients. METHODS: The authors analyzed heart rate variability and blood pressure variability in 13 laboring patients using wavelet transform, a time-frequency analysis that accommodates rapid changes in autonomic activity. Heart rate and blood pressure variability were obtained 5 min before and 10 min after injection of 20 ml bupivacaine, 0.125%, and 50 microg fentanyl in the epidural space. RESULTS: Blood pressure and heart rate were not affected by epidural analgesia. However, high-frequency power of heart rate variability increased after epidural (increase in parasympathetic drive). The ratio of low-frequency:high-frequency power of heart rate variability decreased. High- and low-frequency power of blood pressure variability decreased (decrease in sympathetic outflow). CONCLUSIONS: Indices of parasympathetic and sympathetic activity after neuraxial blockade in laboring patients can be obtained by analysis of both heart rate variability and blood pressure variability. The analysis by wavelet transform can discern changes in autonomic activity when values of blood pressure and heart rate do not vary significantly. Whether this technique could be used to predict and prevent hemodynamic compromise after neuraxial blockade merits further studies.

Adult↗

Effects of the anticholinesterase edrophonium on spectral analysis of heart rate and blood pressure variability in humans.

Edrophonium, an anticholinesterase, exerts a biphasic effect on cardiovascular autonomic drive in humans (lower doses enhance; higher doses reduce). Twenty-five anesthetized, mechanically respired (10 breaths. min(-1), constant tidal volume) patients were given either saline (n = 10) or edrophonium (0.01-1.0 mg. kg(-1), n = 15) following surgery. ECG, radial arterial pressure, and respiratory rate were sampled at 250 Hz to obtain time series for consecutive R-R intervals (RRIs), and systolic (SBP) and diastolic blood pressure (DBP). A Wigner distribution was used for time frequency mapping of spectral powers at high (HFP, 0.15-0.5 Hz) and low (LFP, 0.0-0.05 Hz) frequency. Edrophonium produced a dose-dependent decrease in heart rate [baseline 66.8 +/- 1.9 (S.E.M.) beats per minute; maximum decrease to 55.8 +/- 1.4 beats per minute with 1.0 mg. kg(-1), P < 0.01]. HFP of the RRI increased at low doses (0.2-0.4 mg. kg(-1); maximum increase to 111.0 +/- 58.2% baseline; P < 0.01) but decreased (-49.5 +/- 35.5% baseline; P < 0.01) at higher (1.0 mg. kg(-1)) doses. Edrophonium had no effect on SBP and DBP. HFP of SBP decreased with increasing doses (maximal decrease to -26.2 +/- 7.5% baseline, P < 0.01, 1.0 mg. kg(-1)). LFP of SBP was also decreased (-46.3 +/- 10.9% baseline, P < 0.01, 1.0 mg. kg(-1)). Edrophonium may enhance (lower dose) or reduce (higher dose) cardiovascular autonomic drive in humans, as evidenced by the significant changes it evokes in HFP of the RRI (parasympathetic drive), and in the HFP and LFP of SBP (sympathetic drive). These observations may account for the modest autonomic side effects of edrophonium when this drug is used clinically.

Adult↗