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Biomedical subjects

H R Muñoz

Publications and source records attributed to H R Muñoz.

17 recordsLinked to original sources
PubMed2006

Effect site concentrations of propofol producing hypnosis in children and adults: comparison using the bispectral index.

BACKGROUND: No study has determined the concentration of propofol producing a degree of hypnosis compatible with anaesthesia in children. As a result, concentrations determined in adults are recommended for children. As this can result in an inadequate depth of anaesthesia, we determined the predicted effect site concentration (C(e)) of propofol necessary to obtain a bispectral index (BIS) of 50 in 50% (EC(e50)) of children and adults. METHODS: Twenty adults (aged 33-44 years) and 20 children (aged 3-11 years) undergoing surgery under general anaesthesia were studied. All were monitored with a BIS monitor, and a target controlled infusion of propofol aiming for a constant C(e) value was started. After 10 min, patients were evaluated using a sedation scale, and the last 5 min was used to determine the mean BIS for this C(e) value. The C(e) value of propofol was defined using the up-and-down method of Dixon and Massey. The first patient in each group received C(e)= 6 microg/ml; thereafter, it was modified in 0.5 microg/ml decrements/increments with positive or negative responses, respectively. A positive response was BIS < 50 and a negative response was BIS > or = 50. The EC(e50) value was compared using unpaired Student's t-test. The prediction probability (P(K)) was used to study the association between BIS and the sedation score. RESULTS: The mean EC(e50) (95% confidence interval) values were 3.75 microg/ml (2.97-4.75 microg/ml) in adults and 3.65 microg/ml (3.36-3.96 microg/ml) in children (not significant). All patients with BIS < 50 were unarousable with tactile stimulation. The P(K) value was 0.99 in both groups. CONCLUSIONS: The predicted C(e) value of propofol resulting in BIS = 50 was similar in adults and children aged 3-11 years. The predicted C(e) value of propofol producing hypnosis in adults also seems to be useful in this paediatric population.

Adolescent↗
PubMed2006

[Pharmacodynamics of propofol in children and adults: comparison based on the auditory evoked potentials index].

INTRODUCTION: The clinically useful concentrations of propofol to provide loss of consciousness in children have not been determined. Therefore, target-controlled infusion systems are used with parameters taken from results for adults. As a result, hypnosis can be inadequate in the pediatric population. We studied the dose-response relationship by comparing the predicted effect-site concentration (Ce) and the level of hypnosis measured by a monitor of depth of anesthesia based on auditory evoked potentials. MATERIAL AND METHODS: After injection of a submaximal bolus dose of propofol, the auditory evoked potential index was measured in 25 children (3-11 years old) and 25 adults (35-48 years old). We calculated the predicted Ce of propofol using the plasma effect-site equilibration rate constant (ke0) for each patient and the pharmacodynamic parameters of propofol for adults from the model of Schnider and for children from the models of Kataria and of the Paedfusor system. The relation of Ce to evoked potentials was analyzed with a sigmoid Emax model in the NONMEM program. RESULTS: The mean (SD) propofol doses in adults and children were 1.6 (0.1) mg x kg(-1) and 2.7 (0.3) mg x kg(-1), respectively. The Ce associated with auditory evoked potentials at 50% of the maximum effect (Ce50) for adults was 6.45 (0.59) microg/mL(-1), which was significantly higher than that estimated by either model for children (Kataria, 2.06 [0.24] microg/mL(-1); Paedfusor, 3.56 [0.22] microg/mL; P<0.001 between adults and children for both models). CONCLUSION: Children seem to be more sensitive to propofol than adults, suggesting that the higher dose requirements described for children would be attributable to pharmacokinetic differences between the 2 populations.

Adult↗
PubMed2005

Pre-oxygenation in the obese patient: effects of position on tolerance to apnoea.

BACKGROUND: In obese patients, reduced functional residual capacity exacerbated by supine position might decrease the effectiveness of pre-oxygenation and the tolerance to apnoea. The aim of this study was to compare the effect of body posture during pre-oxygenation, sitting or supine, on its effectiveness in obese patients. METHODS: Forty obese patients (BMI > or =35 kg m(-2)) undergoing surgery with general anaesthesia were randomly assigned to one of two groups: Group 1 (sitting, n=20) or Group 2 (supine, n=20). In the predetermined body position, pre-oxygenation was achieved with eight deep breaths within 60 s and an oxygen flow of 10 litre min(-1). After rapid sequence induction of anaesthesia in decubitus position, the trachea was intubated and the patient was left apneic and disconnected from the anaesthesia circuit until Sp(o2) decreased to 90%. The time taken for desaturation to 90% from the end of induction of anaesthesia was recorded. Arterial blood oxygen tension was measured before (baseline) and after pre-oxygenation. Values were compared with two-way anova and unpaired Student's t-test. RESULTS: Oxygen and carbon dioxide tensions were similar between groups, both at baseline and after pre-oxygenation. However, the mean time to desaturation to 90% was significantly longer in the sitting group compared with the supine group [mean (SD): 214 (28) vs 162 (38) s, P<0.05]. CONCLUSIONS: Pre-oxygenation in sitting position significantly extends the tolerance to apnoea in obese patients when compared with the supine position.

Adult↗
PubMed2005

Target-controlled infusion of remifentanil or fentanyl during extra-corporeal shock-wave lithotripsy.

BACKGROUND AND OBJECTIVE: Target-controlled infusions (TCIs) of remifentanil and fentanyl in conscious sedation regimes for extra-corporeal shock-wave lithotripsy have not been reported. We estimated the effect site concentrations of remifentanil and fentanyl needed to obtain adequate analgesia in 50% of patients (EC50) and compared both drugs in terms of intra- and post-procedure complications. METHODS: Forty-four adult patients were randomly distributed into two groups: Group R received remifentanil and Group F received fentanyl TCI with initial effect site concentrations of 1.5 and 2 ng mL(-1), respectively. Pain was assessed using a 10-point verbal analogue scale and <3 was considered adequate analgesia. Increments or decrements of 0.5 ng mL(-1) were then introduced for subsequent patients according to Dixon's up and down method. During the rest of the procedure, TCI was adjusted to maintain verbal analogue scale <3. RESULTS: Remifentanil and fentanyl EC50 were 2.8 ng mL(-1) (95% confidence interval (CI): 1.8-3.7 ng mL(-1)) and 2.9 ng mL(-1) (95% CI: 1.7-4.1 ng mL(-1)), respectively (n.s.). At EC50, the probability of having a respiratory rate <10 was 4% (95% CI: 0-57%) for remifentanil and 56% (95% CI: 13-92%) for fentanyl. Hypoxaemia, vomiting and sedation were more frequent in Group F during and after the procedure (P < 0.05). CONCLUSIONS: A similar EC50 but more respiratory depression, sedation and PONV were found with fentanyl TCI than with remifentanil TCI.

Adolescent↗
PubMed2002

Effect of timing of morphine administration during remifentanil-based anaesthesia on early recovery from anaesthesia and postoperative pain.

BACKGROUND: Since the time to peak analgesic effect of intravenous morphine can be longer than 40-60 min in volunteers, the goal of this study was to evaluate the effect of the timing of intraoperative morphine administration on early postoperative pain. METHODS: A total of 120 adult patients undergoing laparoscopic cholecystectomy were studied. Anaesthesia was induced with remifentanil and etomidate and maintained with remifentanil and sevoflurane/nitrous oxide. Morphine 150 micrograms kg-1 was given randomly at three different times during surgery, and a fourth group received placebo. Times to eyes opening and extubation were measured, and pain was evaluated in the post-anaesthesia care unit (PACU) using a visual analogue scale (VAS). Morphine 2-3 mg was given when the VAS score was > or = 50 mm. The four groups were, according to the time elapsed from morphine administration to the end of surgery, group 1 (n = 30): placebo; group 2 (n = 33): < 20 min; group 3 (n = 30): 20-40 min; group 4 (n = 27): > 40 min. RESULTS: Recovery from anaesthesia and pain scores were similar in all groups. However, mean (SD) morphine consumption was 5.7 (4.7) mg in group 1, 4.4 (4.2) mg in group 2, 4.7 (4.7) mg in group 3, and 2.2 (4.0) mg in group 4 (P < 0.05, group 1 vs 4). Morphine was required in only 38% of patients in group 4 compared with 83%, 67% and 69% in groups 1, 2, and 3, respectively (P < 0.01, group 1 vs 4). CONCLUSIONS: The timing of intraoperative morphine administration did not affect the early recovery from anaesthesia. However, the reduction in the number of patients requiring morphine in the PACU when morphine had been given more than 40 min before the end of surgery supports this practice, rather than administration closer to the end of surgery.

Adult↗
PubMed2001

No clinical evidence of acute opioid tolerance after remifentanil-based anaesthesia.

We have prospectively assessed whether remifentanil-based anaesthesia is associated with clinically relevant acute opioid tolerance, expressed as greater postoperative pain scores or morphine consumption. Sixty patients undergoing elective gynaecological, non-laparoscopic, surgery were randomly assigned to receive remifentanil (group R, n=30) or sevoflurane (group S, n=30) based anaesthesia. Postoperative analgesia was provided with morphine through a patient-controlled infusion device. Mean (SD) remifentanil infusion rate in group R was 0.23 (0.10) microg kg(-1) min(-1) and mean inspired fraction of sevoflurane in group S was 1.75 (0.70)%. Mean (SD) cumulative morphine consumption during the first 24 postoperative hours was similar between groups: 28.0 (14.2) mg (group R) vs 28.6 (12.4) mg (group S). Pain scores, were also similar between groups during this period. These data do not support the development of acute opioid tolerance after remifentanil-based anaesthesia in this type of surgery.

Adult↗
PubMed1999

Hemodynamic response to tracheal intubation after vital capacity rapid inhalation induction (VCRII) with different concentrations of sevoflurane.

STUDY OBJECTIVE: To evaluate the blood pressure (BP) and heart rate (HR) response to tracheal intubation after vital capacity rapid inhalation induction (VCRII) with four concentrations of sevoflurane followed by nitrous oxide (N2O) 50% and sevoflurane in concentrations administered by clinical judgment. DESIGN: Prospective, randomized study. SETTING: University teaching hospital. PATIENTS: 60 unpremedicated, ASA physical status I and II adult patients undergoing surgery with general anesthesia. INTERVENTIONS: After fentanyl 3 micrograms/kg, VCRII was accomplished with four concentrations of sevoflurane in O2: Group 1 (n = 15): sevoflurane 3%; Group 2 (n = 15): sevoflurane 4%; Group 3 (n = 15): sevoflurane 5%; and Group 4 (n = 15): sevoflurane 6%. At loss of consciousness, rocuronium 0.6 mg/kg was given, and intubation was performed 90 seconds later. Thereafter, anesthesia continued with N2O 50% and sevoflurane. MEASUREMENTS AND MAIN RESULTS: BP and HR measurements were made at the ward (baseline), at loss of consciousness, and just prior to, and each minute after, tracheal intubation during a 5-minute period. The hemodynamic profile among groups was similar, with a slight hypertensive and tachycardic response to intubation. CONCLUSION: VCRII with sevoflurane 3% to 6% following fentanyl 3 micrograms/kg can be considered for blunting the hemodynamic response to tracheal intubation in healthy patients.

Adult↗
PubMed1999

Interregional differences in the systolic and diastolic response of nonischemic myocardium to remote coronary occlusion.

BACKGROUND: Previous work showed a twofold increase in stiffness of nonischemic myocardium at the base during ischemia of the left anterior wall. Whether the diastolic response of nonischemic myocardium to remote ischemia depends on the localization of the ischemic or the nonischemic area is unknown. METHODS: In dogs with open chests, regional function in ischemic and nonischemic myocardium was assessed (sonomicrometry) before and 5 min after occlusion of the left anterior descending coronary artery (LAD; n = 7) or the left circumflex coronary artery (LCX; n = 7). RESULTS: In nonischemic myocardium at the base, left anterior descending and left circumflex coronary artery occlusion both resulted in a twofold increase in chamber stiffness, whereas contractility and peak lengthening rate remained unchanged. In nonischemic myocardium of the posterior wall, left anterior descending coronary artery occlusion resulted in a significant (P<0.05 vs. control, P<0.05 vs. base) increase (mean+/-SD) in chamber stiffness (25+/-6%), contractility (17+/-5%), and peak lengthening rate (28+/-6%). In nonischemic myocardium at the apex, left circumflex coronary artery occlusion resulted in a significant (P<0.05 vs. control, P<0.05 vs. base) increase in chamber stiffness (15+/-5%), contractility (16+/-4%), and peak lengthening rate (19+/-6%). CONCLUSIONS: Stiffening of remote nonischemic myocardium occurs regardless of the localization of the ischemic and nonischemic area. The systolic and diastolic responses of nonischemic myocardium are not necessarily homogenous but may vary among different regions.

Animals↗
PubMed1997

Cardiac mechanical energy and effects on the arterial tree.

Blood flow pulsatility is the result of the heart's activity as a pump unable to develop steady flow, and its interaction with the arterial tree. Thus, the heart is a cyclic energy generator whose adequate function requires the two phases of this cycle to be normal. Diastolic properties determine the degree of filling of the ventricles and the strength of the following systole. Systole, in turn, must generate enough energy to overcome forces opposing ejection. These can be divided into internal (the mechanical characteristics of the ventricle itself) and external loads (the characteristics of the arterial tree). As a result, hydraulic energy is imparted to blood (external ventricular work) that manifests itself as blood pressure and flow. Given the cyclic nature of cardiac activity, the external ventricular work has steady and pulsatile components. The steady component is energy lost during steady flow because of vascular resistance, and the pulsatile work is that lost in arterial pulsations and mainly depends on the aortic impedance. Thus, the characteristics of the arterial tree will determine the relative contribution of these two components to blood flow and the efficency of the heart. In addition, the arterial tree modifies the different waves (pressure and flow) traveling in the circulation. These modifications have important consequences for cardiac function. The ventricle and the arterial tree constitute a coupled biological system, and its overall performance is a function of the behavior of each unit at any given moment.

Aorta↗
PubMed1995

Platelet-activating factor (PAF) does not affect diastolic function in isolated rat hearts.

Platelet-activating factor might be responsible for the alterations of diastolic function observed in different disease states and these potential effects have not been studied. The effect of incremental concentrations of platelet-activating factor (to a maximum of 200 nM) was therefore examined in isolated perfused rat heart. Platelet-activating factor decreased coronary flow rate and contractility in a dose-dependent manner. Although high-dose platelet-activating factor decreased peak -dP/dt compared to baseline, this was not significant when compared to vehicle-administered control. There were no changes in the time constant of left ventricular relaxation and the chamber stiffness constant. These results do not support a major direct role of platelet-activating factor in diastolic dysfunction.

Animals↗
PubMedDate not supplied

Benzodiazepine premedication causes hypoxemia during spinal anesthesia in geriatric patients.

BACKGROUND AND OBJECTIVES: The use of sedatives during regional anesthesia can lead to life-threatening hypoxemia. Older patients particularly are prone to enhanced effects of these drugs. We studies whether oral premedication with benzodiazepines produced hypoxemia during spinal anesthesia in elderly patients. METHODS: In a prospective, double-blind, and randomized study, we evaluated the effect of oral benzodiazepine premedication on the incidence of hypoxemia measured by pulse oximetry (arterial oxygen saturation less than 90% for 30 seconds or longer) during surgery under spinal anesthesia in 80 geriatric patients divided into four equal groups: 1, control, no premedication; 2, 1 mg flunitrazepam; 3, 1 mg lorazepam; and 4, 7.5 mg midazolam. RESULTS: The incidence of hypoxemia in the four groups was: 1, 15%; 2, 45%; 3, 20%; and 4, 60% (p = 0.0078); overall incidence was 42% in premedicated patients versus 15% in unpremedicated controls (p = 0.0304). Seventy-four percent of patients who presented drowsiness and anesthetic level above T7 had desaturation compared to only 7% of those who were awake and had lower level (p less than 0.0005). No association between hypoxemia and other factors (age, weight, ASA physical status, and position during surgery) was found. All the episodes of desaturation were easily corrected with low supplemental oxygen concentrations. CONCLUSIONS: Premedication with oral benzodiazepines may produce hypoxemia during spinal anesthesia in elderly patients. Lorazepam appeared safer than flunitrazepam and midazolam. Monitoring of arterial blood oxygen saturation and/or supplemental oxygen is mandatory in geriatric patients with high spinal anesthetic level and/or drowsiness during surgery.

Administration, Oral↗
PubMedDate not supplied

Preoperative percutaneous ilioinguinal and iliohypogastric nerve block with 0.5% bupivacaine for post-herniorrhaphy pain management in adults.

The safety, effectiveness and duration of a percutaneous ilioinguinal-iliohypogastric nerve block with 10 ml 0.5% bupivacaine, as a method for postoperative analgesia, were studied prospectively in adult patients undergoing unilateral inguinal herniorrhaphy under spinal anesthesia. Group I (n = 20) blocked patients were compared with Group II (n = 25), non-blocked control patients. A blinded observer assessed pain scores and analgesic requirements after surgery. Group I patients had less pain at 3, 6, 24 and 48 hours after surgery and also required less analgesics during the first two postoperative days. This technique appears to be a simple and safe method for providing effective and long-lasting postoperative analgesia following inguinal hernia repair in adults.

Adult↗
PubMedDate not supplied

Direction of catheter insertion and incidence of paresthesias and failure rate in continuous epidural anesthesia: a comparison of cephalad and caudad catheter insertion.

BACKGROUND AND OBJECTIVES: Paresthesias and unblocked segments during continuous epidural anesthesia--sometimes leading to higher doses of local anesthetics--can increase the risk of this technique. A cephalad insertion of the epidural catheter might decrease the incidence of these problems, but this has not been evaluated before in a controlled study. METHODS: In a prospective, double-blind, randomized study, we compared the incidence of paresthesias during catheter insertion and the failure rate of continuous epidural anesthesia in two groups of obstetric patients. In group 1 (n = 52), the Tuohy needle bevel was directed cephalad during catheter insertion. In group 2 (n = 53), it was directed caudad. The catheter was introduced 4-5 cm into the epidural space, and bupivacaine 25 mg plus fentanyl 50 micrograms were administered through it. RESULTS: Twenty percent of the patients in group 1 had paresthesias versus 40% in group 2 (p = 0.0249; 95% confidence interval of the difference 1-40%); intensity of paresthesias was greater in group 2. Pain relief was complete in 75% and 80% of the patients in groups 1 and 2, respectively (NS); three patients in group 1 and one in group 2 had unblocked segments (NS). CONCLUSIONS: Our results support the contention that the catheter should be directed cephalad during insertion for continuous epidural anesthesia.

Adult↗