The Effect of Rate of Administration on Brain Concentrations of Propofol in Sheep

Anaesthetic-sparing effect of the anxiolytic drug tasipimidine in Beagle dogs

OBJECTIVE

To evaluate the effect of oral tasipimidine on dog handling, ease of catheter placement and propofol and isoflurane requirements for anaesthesia.

STUDY DESIGN

Placebo-controlled, randomized, blinded, experimental trial.

ANIMALS

A group of seven adult Beagle dogs weighing (mean ± standard deviation) 13.1 ± 2.7 kg with a mean age of 18.6 ± 1 months.

METHODS

The dogs underwent four treatments before induction of anaesthesia with propofol. PP: placebo orally (PO) 60 minutes before induction of anaesthesia followed by placebo (NaCl 0.9%) intravenously (IV). TP: tasipimidine 30 μg kg-1 (PO) 60 minutes before induction of anaesthesia followed by placebo (NaCl 0.9%) IV. TMP: tasipimidine 30 μg kg-1 PO 60 minutes before induction of anaesthesia followed by methadone 0.2 mg kg-1 IV. TMPD: tasipimidine 30 μg kg-1 PO 60 minutes before induction of anaesthesia followed by methadone 0.2 mg kg-1 and dexmedetomidine 1 μg kg-1 IV followed by a dexmedetomidine constant rate infusion of 1 μg kg-1 hour-1. Sedation, response to catheter placement, intubation quality, time to loss of consciousness, time to intubation, required dose of propofol and minimum alveolar isoflurane concentration preventing motor movement (MACNM) were determined. A mixed-model analysis or the Friedman and Mann-Whitney test were used; p-value < 0.05.

RESULTS

Response to catheter placement did not differ between treatments. Tasipimidine alone reduced the propofol dose by 30%. Addition of methadone or methadone and dexmedetomidine reduced the propofol dose by 48% and 50%, respectively. Isoflurane MACNM was reduced by 19% in tasipimidine-medicated dogs, whereas in combination with methadone or methadone and dexmedetomidine, isoflurane MACNM was reduced by 35%.

CONCLUSIONS AND CLINICAL RELEVANCE

An anxiolytic dose of tasipimidine induced mild signs of sedation in dogs and reduced propofol and isoflurane requirements to induce and maintain anaesthesia, which needs to be considered in an anaesthetic plan.

Comparison between total intravenous anesthesia with propofol and intermittent bolus of tiletamine-zolazepam in capuchin monkey (Sapajus apella)

ABSTRACT: Dissociative anesthesia results in stressful and long recovery periods in monkeys and use of injectable anesthetics in medical research has to be refined. Propofol has promoted more pleasure wake up from anesthesia. The objectives of this study were to investigate the use of intravenous anesthetic propofol, establishing the required infusion rate to maintain surgical anesthetic level and comparing it to tiletamine-zolazepam anesthesia in Sapajus apella. Eight healthy capuchin monkeys, premedicated with midazolam and meperidine, were anesthetized with propofol (PRO) or tiletamine-zolazepam (TZ) during 60 minutes. Propofol was infused continually and rate was titrated to effect and tiletamine-zolazepam was given at 5mg/kg IV bolus initially and repeated at 2.5mg/kg IV bolus as required. Cardiopulmonary parameters, arterial blood gases, cortisol, lactate and quality and times to recovery were determined. Recovery quality was superior in PRO. Ventral recumbency (PRO = 43.0±21.4 vs TZ = 219.3±139.7 min) and normal ambulation (PRO = 93±27.1 vs TZ = 493.7±47.8 min) were faster in PRO (p<0.05). Cardiopulmonary effects did not have marked differences between groups. Median for induction doses of propofol was 5.9mg/kg, varying from 4.7 to 6.7mg/kg, Mean infusion rate was 0.37±0.11mg/kg/min, varying during the one-hour period. In TZ, two animals required three and five extra doses. Compared to tiletamine-zolazepam, minor post-anesthetic adverse events should be expected with propofol anesthesia due to the faster and superior anesthetic recovery.

Effect of rate of administration of propofol or alfaxalone on induction dose requirements and occurrence of apnea in dogs

OBJECTIVE

To evaluate the effect of rate of administration of propofol or alfaxalone on induction dose requirements and incidence of postinduction apnea (PIA) in dogs following premedication with methadone and dexmedetomidine.

STUDY DESIGN

Prospective, randomized clinical trial.

ANIMALS

Thirty-two healthy American Society of Anesthesiologists class I client-owned dogs (seven females, 25 males), aged between 5 and 54 months, weighing between 2.0 and 48.2 kg.

METHODS

Dogs were premedicated intramuscularly with 0.5 mg kg^-1 methadone and 5 μg kg^-1 dexmedetomidine. Thirty minutes after premedication, dogs were preoxygenated for 5 minutes before the induction agent was administered intravenously via a syringe driver until orotracheal intubation was achieved. Dogs were randomized to receive alfaxalone 0.5 mg kg^-1 minute^-1 (A-Slow), alfaxalone 2 mg kg^-1 minute^-1 (A-Fast), propofol 1 mg kg^-1 minute^-1 (P-Slow), or propofol 4 mg kg^-1 minute^-1 (P-Fast). Oxygen saturation of hemoglobin (SpO₂), end-tidal carbon dioxide and respiratory rate were monitored. If PIA (≥30 seconds without a breath) occurred, the time to the first spontaneous breath was measured. If SpO₂ decreased below 90%, the experiment was stopped and manual ventilation initiated.

RESULTS

The mean±standard deviation induction doses of alfaxalone and propofol were lower in the A-Slow [A-Slow 0.9±0.3 mg kg^-1, A-Fast 2.2±0.5 mg kg^-1 (p≤0.001)] and P-Slow [P-Slow 1.8±0.6 mg kg^-1, P-Fast 4.1±0.7 mg kg^-1 (p≤0.001)] groups, respectively. The incidence of PIA was 25% for the A-Slow and P-Slow groups and 100% for the A-Fast and P-Fast groups (p = 0.007).

CONCLUSIONS AND CLINICAL RELEVANCE

Both propofol and alfaxalone following methadone and dexmedetomidine premedication caused PIA. Induction dose requirement and incidence of PIA were affected by the rate of administration of both drugs. When possible, propofol and alfaxalone doses should be reduced and administered slowly to reduce PIA.

Determination of the appropriate propofol infusion rate for outpatient upper gastrointestinal endoscopy-a randomized prospective study

Background

Pain and discomfort related to endoscopy sessions can be alleviated by sedation, which minimizes anxiety and allows safe examination. For outpatient endoscopy, reliable short-term sedation without secondary effects is required. This study aimed to assess the effects of intravenous propofol rates on sedation in outpatients undergoing upper gastrointestinal endoscopy.

Methods

This randomized prospective study evaluated 300 outpatients submitted to upper gastrointestinal endoscopy. Patients received propofol at 500, 1000 or 2000 ml/h. The primary outcome assessed was hypoxemia incidence. In addition, time to sedation and incidence of hypotension, deep sedation, extremity motor activity, cough, nausea, hiccough, and awareness were evaluated.

Results

Recovery time and incidence of hypoxemia, hypotension, and deep sedation were significantly increased in individuals treated at 2000 ml/h in comparison with values obtained for 500 and 1000 ml/h groups (P < 0.01). Compared with the 500 ml/h group, motor activity of the extremities, cough, nausea, hiccough, and awareness were significantly decreased and the mean scores for endoscopist’s and patients’ satisfaction were significantly increased in the 1000 and 2000 ml/h groups (P < 0.01).

Conclusion

Propofol infused at 1000 ml/h appeared to be the most suitable infusion rate for outpatient upper gastrointestinal endoscopy.

Trial registration

Registration number: ChiCTR-TRC-14004786; Registration date: 2014-06-04

Rapid injection of propofol reduces vascular pain and facilitates Laryngeal Mask Airway insertion

STUDY OBJECTIVE

To compare the clinical efficacy of a rapid injection of propofol in regard to pain and ability to facilitate Laryngeal Mask Airway (LMA) insertion.

DESIGN

Randomized, single-blinded, placebo-controlled study.

SETTING

University hospital.

PATIENTS

120 ASA physical status 1 and 2 patients undergoing elective orthopedic surgeries.

INTERVENTIONS

Patients were randomly allocated to one of 4 groups. Group A patients were pretreated with normal saline followed by propofol 2.0 mg/kg at 3.3 mg/sec. Group B patients were pretreated with lidocaine 0.5 mg/kg followed by propofol 2.0 mg/kg at 3.3 mg/sec. In Group C, patients were pretreated with lidocaine 1.0 mg/kg followed by propofol 2.0 mg/kg at 3.3 mg/sec. In Group D, patients were pretreated with normal saline followed by propofol 2.0 mg/kg at 50 mg/sec.

MEASUREMENTS

Pain on injection was measured using a 4-point scale. Scale and success rate of smooth LMA insertion also were recorded.

MAIN RESULTS

Rapid injection was less painful than after pretreatment with lidocaine 0.5 mg/kg, but was similar to slow injection after pretreatment with lidocaine 1.0 mg/kg. Rapid injection facilitated LMA insertion, unlike slow injection with lidocaine 0.5 mg/kg pretreatment, and was similarly successful to slow injection after pretreatment with lidocaine 1.0 mg/kg.

CONCLUSIONS

The rapid administration of propofol reduces pain and facilitates LMA insertion versus slow administration of propofol.

Predictive ability of propofol effect-site concentrations during fast and slow infusion rates

BACKGROUND

The performance of propofol effect-site pharmacokinetic models during target-controlled infusion (TCI) might be affected by propofol administration rate. This study compares the predictive ability of three effect-site pharmacokinetic models during fast and slow infusion rates, utilizing the cerebral state index (CSI) as a monitor of consciousness.

METHODS

Sixteen healthy volunteers, 21-45 years of age, were randomly assigned to receive either a bolus dose of propofol 1.8 mg/kg at a rate of 1200 ml/h or an infusion of 12 mg/kg/h until 3-5 min after loss of consciousness (LOC). After spontaneous recovery of the CSI, the bolus was administered to patients who had first received the infusion and vice versa. The study was completed after spontaneous recovery of CSI following the second dose scheme. LOC was assessed and recorded when it occurred. Adequacies of model predictions during both administration schemes were assessed by comparing the effect-site concentrations estimated at the time of LOC during the bolus dose and during the infusion scheme.

RESULTS

LOC occurred 0.97 +/- 0.29 min after the bolus dose and 6.77 +/- 3.82 min after beginning the infusion scheme (P<0.05). The Ce estimated with Schnider (ke0=0.45/min), Marsh (ke0=1.21/min) and Marsh (ke0=0.26/min) at LOC were 4.40 +/- 1.45, 3.55 +/- 0.64 and 1.28 +/- 0.44 microg/ml during the bolus dose and 2.81 +/- 0.61, 2.50 +/- 0.39 and 1.72 +/- 0.41 microg/ml, during the infusion scheme (P<0.05). The CSI values observed at LOC were 70 +/- 4 during the bolus dose and 71 +/- 2 during the infusion scheme (NS).

CONCLUSION

Speed of infusion, within the ranges allowed by TCI pumps, significantly affects the accuracy of Ce predictions. The CSI monitor was shown to be a useful tool to predict LOC in both rapid and slow infusion schemes.

Effects of propofol administration rates on cardiopulmonary function and anaesthetic depth during anaesthetic induction in rats

OBJECTIVE

To compare the effect of three different administration rates of one dose of propofol on the depth and duration of anaesthesia and cardiopulmonary function during induction of anaesthesia in rats using electroencephalogram (EEG) and clinical signs.

STUDY DESIGN

Prospective, randomized experimental trial. Animals Twenty-one, adult, male Sprague-Dawley rats weighing 341 +/- 26 g (mean +/- SD) (325 to 480 g).

METHODS

ANIMALS

were randomly divided into three groups to receive 20 mg kg(-1) propofol as a bolus injection over 1, 2 or 3 minutes (groups P1, P2 and P3 respectively) intravenously (IV). The total duration and number of burst suppression (BS) episodes in the EEG, the time to loss of righting reflex, reflex score from electrical stimulation, respiratory rate, mean arterial pressure and pulse rate were measured from the beginning of propofol injection.

RESULTS

While loss of reflex to electrical stimulus and time to loss of righting reflex in group P3 were slower than in other groups, the total duration and number of BS episodes in group P3 were significantly higher than in groups P1 and P2 and cardiopulmonary depression was less prominent in group P3 than in groups P1 and P2 up to 2 minutes after the start of administration.

CONCLUSIONS

Twenty milligram per kg propofol administration IV for 3 minutes increased the duration of anaesthesia and decreased cardiopulmonary depression in rats.

CLINICAL RELEVANCE

Slower infusion of propofol produced surgical anaesthesia with less cardiopulmonary depression in rats.

Comparison of two pre-anaesthetic medetomidine doses in isoflurane anaesthetized sheep

OBJECTIVE

To compare the sedative, anaesthetic-sparing and arterial blood-gas effects of two medetomidine (MED) doses used as pre-anaesthetic medication in sheep undergoing experimental orthopaedic surgery.

STUDY DESIGN

Randomized, prospective, controlled experimental trial.

ANIMALS

Twenty-four adult, non-pregnant, female sheep of various breeds, weighing 53.9 +/- 7.3 kg (mean +/- SD).

METHODS

All animals underwent experimental tibial osteotomy. Group 0 (n = 8) received 0.9% NaCl, group L (low dose) (n = 8) received 5 microg kg(-1) MED and group H (high dose) (n = 8) received 10 microg kg(-1) MED by intramuscular (IM) injection 30 minutes before induction of anaesthesia with intravenous (IV) propofol 1% and maintenance with isoflurane delivered in oxygen. The propofol doses required for induction and endtidal isoflurane concentrations (F(E')ISO) required to maintain anaesthesia were recorded. Heart and respiratory rates and rectal temperature were determined before and 30 minutes after administration of the test substance. The degree of sedation before induction of anaesthesia was assessed using a numerical rating scale. Arterial blood pressure, heart rate, respiratory rate, FE'ISO, end-tidal CO2 (FE'CO2) and inspired O2 (FIO2) concentration were recorded every 10 minutes during anaesthesia. Arterial blood gas values were determined 10 minutes after induction of anaesthesia and every 30 minutes thereafter. Changes over time and differences between groups were examined by analysis of variance (anova) for repeated measures followed by Bonferroni-adjusted t-tests for effects over time.

RESULTS

Both MED doses produced mild sedation. The dose of propofol for induction of anaesthesia decreased in a dose-dependent manner: mean (+/-SE) values for group 0 were 4.7 (+/-0.4) mg kg(-1), for group L, 3.2 (+/-0.4) mg kg(-1) and for group H, 2.3 (+/-0.3) mg kg(-1)). The mean (+/-SE) FE'ISO required to maintain anaesthesia was 30% lower in both MED groups [group L: 0.96 (+/-0.07) %; group H: 1.06 (+/-0.09) %] compared with control group values [(1.54 +/- 0.17) %]. Heart rates were constantly higher in the control group with a tendency towards lower arterial blood pressures when compared with the MED groups. Respiratory rates and PaCO2 were similar in all groups while PaO2 increased during anaesthesia with no significant difference between groups. In group H, one animal developed a transient hypoxaemia: PaO2 was 7.4 kPa (55.7 mmHg) 40 minutes after induction of anaesthesia. Arterial pH values and bicarbonate concentrations were higher in the MED groups at all time points.

CONCLUSION AND CLINICAL RELEVANCE

Intramuscular MED doses of 5 and 10 microg kg(-1) reduced the propofol and isoflurane requirements for induction and maintenance of anaesthesia respectively. Cardiovascular variables and blood gas measurements remained stable over the course of anaesthesia but hypoxaemia developed in one of 16 sheep receiving MED.