Ventilatory effects of propofol during induction of anaesthesia. Comparison with thiopentone

Dose requirement and cardiopulmonary effects of diluted and undiluted propofol for induction of anaesthesia in dogs

OBJECTIVE

To compare the dose, cardiopulmonary effects and quality of anaesthetic induction in dogs using propofol (10 mg mL^-1) and diluted propofol (5 mg mL^-1).

STUDY DESIGN

Randomized, blinded, clinical study.

ANIMALS

A total of 28 client-owned dogs (12 males/16 females).

METHODS

Following intramuscular acepromazine (0.02 mg kg^-1) and methadone (0.2 mg kg^-1), propofol (UP, 10 mg mL^-1) or diluted propofol (DP, 5 mg mL^-1) was administered intravenously (0.2 mL kg^-1 minute^-1) by an anaesthetist unaware of the allocated group to achieve tracheal intubation. Sedation, intubation and induction quality were scored from 0 to 3. Pre- and post-induction pulse rate (PR), respiratory rate (f_R) and systolic (SAP), mean (MAP) and diastolic (DAP) arterial blood pressure were compared. Time to first breath and induction dose were recorded. Data were analysed for normality and Mann-Whitney U or Student t tests were performed where appropriate. Significance was set at p < 0.05. Data are presented as mean ± standard deviation or median (range).

RESULTS

The propofol dose administered to achieve induction was lower in the DP group (2.62 ± 0.48 mg kg^-1) than in the UP group (3.48 ± 1.17 mg kg^-1) (p = 0.021). No difference was observed in pre- and post-induction PR, SAP, MAP, DAP and f_R between groups. The differences between post-induction and pre-induction values of these variables were also similar between groups. Time to first breath did not differ between groups. Sedation scores were similar between groups. Quality of tracheal intubation was marginally better with UP 0 (0-1) than with DP 1 (0-2) (p = 0.036), but overall quality of induction was similar between groups [UP 0 (0-1) and DP 0 (0-1), p = 0.549].

CONCLUSION AND CLINICAL RELEVANCE

Diluting propofol reduced the dose to induce anaesthesia without significantly altering the cardiopulmonary variables.

Hypoventilation patterns during bronchoscopic sedation and their clinical relevance based on capnographic and respiratory impedance analysis

Capnography involves the measurement of end-tidal CO₂ (EtCO₂) values to detect hypoventilation in patients undergoing sedation. In a previous study, we reported that initiating a flexible bronchoscopy (FB) examination only after detecting signs of hypoventilation could reduce the risk of hypoxemia without compromising the tolerance of the patient for this type of intervention. We hypothesize that hypoventilation status could be determined with greater precision by combining thoracic impedance-based respiratory signals, RESP, and EtCO₂ signals obtained from a nasal-oral cannula. Retrospective analysis was conducted on RESP and EtCO₂ waveforms obtained from patients during the induction of sedation using propofol for bronchoscopic examination in a previous study. EtCO₂ waveforms associated with hypoventilation were then compared with RESP patterns, patient variables, and sedation outcomes. Signals suitable for analysis were obtained from 44 subjects, 42 of whom presented indications of hypoventilation, as determined by EtCO₂ waveforms. Two subtypes of hypoventilation were identified by RESP: central-predominant (n = 22, flat line RESP pattern) and non-central-predominant (n = 20, RESP pattern indicative of respiratory effort with upper airway collapse). Compared to cases of non-central-predominant hypoventilation, those presenting central-predominant hypoventilation during induction were associated with a lower propofol dose (40.2 ± 18.3 vs. 60.8 ± 26.1 mg, p = 0.009), a lower effect site concentration of propofol (2.02 ± 0.33 vs. 2.38 ± 0.44 µg/ml, p = 0.01), more rapid induction (146.1 ± 105.5 vs. 260.9 ± 156.2 s, p = 0.01), and lower total propofol dosage (96.6 ± 41.7 vs. 130.6 ± 53.4 mg, p = 0.04). Hypoventilation status (as revealed by EtCO₂ levels) could be further classified by RESP into central-predominant or non-central-predominant types. It appears that patients with central-predominant hypoventilation are more sensitive to propofol during the induction of sedation. RESP values could be used to tailor sedation management specifically to individual patients.

Correlation and Linear Regression between Blood Pressure Decreases after a Test Dose Injection of Propofol and that following Anaesthesia Induction

Propofol reduces systemic vascular resistance and suppresses cardiac function when injected rapidly. In this study we investigated whether blood pressure decrease after a minimal dose (test-dose) injection of propofol correlates with that after an induction-dose injection.

Patients were randomly divided into two groups; anaesthesia was induced in group A (n=60) using 1.5 mg/kg propofol and in group B (n=61) using 2.0 mg/kg. Blood pressure reduction after a minimal dose injection (0.4 mg/kg) was examined non-invasively prior to anaesthetic induction. Bispectral Index monitoring was measured and sedation level scored to evaluate anaesthetic depth.

After the minimal dose injection, 18 of 121 patients showed behaviour suggesting minor disinhibition, five patients were sedated and seven were drowsy. Oxygen saturation was not significantly changed after test-dose injection. Reduction in systolic blood pressure (mean±SD) was 17±11 mmHg after the minimal dose injection, 42±20 mmHg after a 1.5 mg/kg induction dose injection, and 42±22 mmHg after a 2.0 mg/kg induction-dose injection. In both groups, blood pressure after induction was significantly lower than the control value (P<0.05). In both groups, a positive correlation was observed between blood pressure reduction after the minimal dose injection and that after the induction-dose injection [P<0.01, R value for systolic blood pressure correlation in group A 0.712 (P<0.01) and in group B 0.758 (P<0.01)].

We concluded there was a positive correlation between blood pressure reduction after a minimal (test-dose) injection and that after an induction-dose injection.

Respiratory rate is an inadequate parameter of ventilation in non-intubated sedation

We compared the respiratory rate (RR) and transcutaneous carbon dioxide pressure ([Formula: see text]) during intravenous sedation (IVS), to determine whether RR is a useful parameter for monitoring ventilation. This was a prospective cohort study. The study sample comprised dental patients who received IVS via propofol or midazolam administration at Nippon Dental University Hospital. We simultaneously measured RR (through capnography), [Formula: see text] (using the [Formula: see text] monitor), and percutaneous oxygen saturation (SpO₂). RR was the predictor and the outcome variable was [Formula: see text]. Data were analyzed by Dunnett's test and Pearson's correlation coefficient. P < 0.05 was considered statistically significant. The study sample consisted of 15 patients. No significant changes were identified in the RR and SpO₂ measurements over time. However, [Formula: see text] values obtained from 20 to 40 min after induction of sedation were significantly higher than baseline values (P < 0.05). A correlation was found between RR and [Formula: see text] (P < 0.05), but the correlation coefficient was low (r = 0.22), indicating a weak correlation between these two factors. The results of this study suggest that RR is an inadequate parameter for monitoring ventilation during IVS; however, [Formula: see text] may be useful for monitoring.

Improving patient safety during procedural sedation via respiratory volume monitoring: A randomized controlled trial

STUDY OBJECTIVE

Assess the utility of a respiratory volume monitor (RVM) to reduce the incidence of low minute ventilation events in procedural sedation.

DESIGN

Randomized control trial SETTING: Endoscopy suite PATIENTS: Seventy-three total patients (ASA Physical Status 1-3) undergoing upper endoscopies were analyzed.

INTERVENTION

Patients were randomized into two groups using a computer generated randomization table: Control (n=41): anesthesia provider was unable to see the screen of the RVM; RVM (n=32): anesthesia provider had access to RVM data to assist with management of the case.

MEASUREMENTS

Minute ventilation (MV), tidal volume, and respiratory rate were continuously recorded by the RVM. MV is presented as percent of Baseline MV (MV_Baseline), defined during a 30s period of quiet breathing prior to sedation. We defined Low MV as MV<40% MV_Baseline, and calculated the percentage of procedure spent with Low MV. Patients in the RVM group were stratified based on whether the anesthesiologist rated the RVM as "not useful", "somewhat useful", or "very useful" during the case.

MAIN RESULTS

Control patients experienced twice as much Low MV compared to RVM patients (15.3±2.8% vs. 7.1±1.4%, P=0.020). The "not useful" (13.7±3.8%) group showed no improvement over the Control group (p=0.81). However, both the "very useful" (4.7±1.4%) and "somewhat useful" (4.9±1.7%) groups showed significant improvement over the "not useful" group (p<0.05).

CONCLUSIONS

Patients in the Control group spent more than double the amount of time with Low MV compared to the RVM group. This difference became more pronounced when the anesthesiologist found the RVM useful for managing care, lending credibility to the usage of minute ventilation monitoring in procedural sedation.

Postinduction apnoea in dogs premedicated with acepromazine or dexmedetomidine and anaesthetized with alfaxalone or propofol

OBJECTIVE

To compare incidence and duration of postinduction apnoea in dogs after premedication with methadone and acepromazine (MA) or methadone and dexmedetomidine (MD) followed by induction with propofol (P) or alfaxalone (A).

STUDY DESIGN

Prospective, randomized clinical trial.

ANIMALS

A total of 32 American Society of Anesthesiologists class I dogs (15 females, 17 males), aged between 4 months and 4 years, weighing between 3 and 46 kg.

METHODS

Dogs were randomly allocated to be administered MA+P, MA+A, MD+P or MD+A (methadone 0.5 mg kg^-1 and acepromazine 0.05 mg kg^-1 or dexmedetomidine 5 μg kg^-1). Induction agents were administered intravenously via syringe driver (P at 4 mg kg^-1 minute^-1 or A at 2 mg kg^-1 minute^-1) until successful endotracheal intubation and the endotracheal tube connected to a circle system with oxygen flow at 2 L minute^-1. Oxygen saturation of haemoglobin (SpO₂), end tidal partial pressure of carbon dioxide and respiratory rate were monitored continuously. If apnoea (≥ 30 seconds without breathing) occurred, the duration until first spontaneous breath was measured. If SpO₂ decreased below 90% the experiment was stopped and manual ventilation initiated. Data were analysed with general linear models with significance set at p ≤ 0.05.

RESULTS

There was no statistical difference in the incidence (11 of 16 dogs in A groups and 12 of 16 dogs in P groups), or mean ± standard deviation duration (A groups 125 ± 113 seconds, P groups 119 ± 109 seconds) of apnoea. The SpO₂ of one dog in the MD+P group decreased below 90% during the apnoeic period.

CONCLUSIONS AND CLINICAL RELEVANCE

Propofol and alfaxalone both cause postinduction apnoea and the incidence and duration of apnoea is not influenced by the use of acepromazine or dexmedetomidine in premedication. Monitoring of respiration is recommended when using these premedication and induction agent combinations.

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.

The relationship of muscle perfusion and metabolism with cardiovascular variables before and after detomidine injection during propofol-ketamine anaesthesia in horses

OBJECTIVES

To study in horses (1) the relationship between cardiovascular variables and muscle perfusion during propofol-ketamine anaesthesia, (2) the physiological effects of a single intravenous (IV) detomidine injection, (3) the metabolic response of muscle to anaesthesia, and (4) the effects of propofol-ketamine infusion on respiratory function.

STUDY DESIGN

Prospective experimental study.

ANIMALS

Seven standardbred trotters, 5-12 years old, 416-581 kg.

METHODS

Anaesthesia was induced with intravenous (IV) guaifenesin and propofol (2 mg kg^-1) and maintained with a continuous IV infusion of propofol (0.15 mg kg^-1 minute^-1) and ketamine (0.05 mg kg^-1 minute^-1) with horses positioned in left lateral recumbency. After 1 hour, detomidine (0.01 mg kg^-1) was administered IV and 40-50 minutes later anaesthesia was discontinued. Cardiovascular and respiratory variables (heart rate, cardiac output, systemic and pulmonary artery blood pressures, respiratory rate, tidal volume, and inspiratory and expiratory O₂ and CO₂) and muscle temperature were measured at pre-determined times. Peripheral perfusion was measured continuously in the gluteal muscles and skin using laser Doppler flowmetry (LDF). Muscle biopsy samples from the left and right gluteal muscles were analysed for glycogen, creatine phosphate, creatine, adenine nucleotides, inosine monophosphate and lactate. Arterial blood was analysed for PO₂, PCO₂, pH, oxygen saturation and HCO₃. Mixed venous blood was analysed for PO₂, PCO₂, pH, oxygen saturation, HCO₃, cortisol, lactate, uric acid, hypoxanthine, xanthine, creatine kinase, creatinine, aspartate aminotransferase, electrolytes, total protein, haemoglobin, haematocrit and white blood cell count.

RESULTS

Circulatory function was preserved during propofol-ketamine anaesthesia. Detomidine caused profound hypertension and bradycardia and decreased cardiac output and muscle perfusion. Ten minutes after detomidine injection muscle perfusion had recovered to pre-injection levels, although heart rate and cardiac output had not. No difference in indices of muscle metabolism was found between dependent and independent muscles. Anaerobic muscle metabolism, indicated by decreased muscle and creatine phosphate levels was evident after anaesthesia.

CONCLUSION

Muscle perfusion was closely related to cardiac output but not arterial blood pressure. Total intravenous anaesthesia with propofol-ketamine deserves further study despite its respiratory depression effects, as the combination preserves cardiovascular function. Decreases in high-energy phosphate stores during recovery show that muscle is vulnerable after anaesthesia. Continued research is required to clarify the course of muscle metabolic events during recovery.

Variable Findings for Drug-Induced Sleep Endoscopy in Obstructive Sleep Apnea with Propofol versus Dexmedetomidine

OBJECTIVE

To compare VOTE classification findings (velum, oropharyngeal-lateral walls, tongue base, and epiglottis) for drug-induced sleep endoscopy (DISE) among patients with obstructive sleep apnea (OSA) using 2 sedation protocols.

STUDY DESIGN

Case series with chart review.

SETTING

Single tertiary institution.

SUBJECTS

Patients with OSA who underwent DISE.

METHODS

A total of 216 patients underwent DISE between November 23, 2011, and May 1, 2015. DISE findings based on VOTE classification were compared between patients receiving the propofol- and dexmedetomidine-based sedation protocols.

RESULTS

Patients with OSA (N = 216; age, 44.3 ± 11.7 years; body mass index, 27.9 ± 4.8 kg/m(2)) underwent DISE with intravenous administration of propofol (n = 52) or dexmedetomidine (n = 164). There were no statistically significant differences between the 2 groups in baseline apnea-hypopnea index, oxygen desaturation index, Mallampati score, tonsil size, Epworth Sleepiness Scale score, peripheral oxygen saturation nadir, age, sex, or body mass index. Patients in the propofol group had a significantly increased likelihood of demonstrating complete tongue base obstruction (75%, 39 of 52) versus partial or no obstruction (25%, 13 of 52) in the anterior-posterior dimension, as compared with the dexmedetomidine group (complete obstruction: 42.7%, 70 of 164; partial or no obstruction: 57.3%, 94 of 164; odds ratio: 4.0; 95% confidence interval: 2.0-8.1; P = .0001). Obstruction of other airway subsites was not significantly different.

CONCLUSION

Use of propofol versus dexmedetomidine to induce sedation may have a significant effect on the pattern of upper airway obstruction observed during DISE. Randomized prospective studies are indicated to confirm these initial findings.

Optical imaging of propofol-induced central respiratory depression in medulla-spinal cord preparations from newborn rats

1. Propofol (2,6-diisopropylphenol) is an intravenous anaesthetic used for the induction and maintenance of general anaesthesia; it also potently and dose-dependently depresses respiration. The aim of the present study was to analyse propofol-induced changes in spatiotemporal patterns of inspiratory-related neural activity and to investigate the involvement of the GABAA receptor by using an optical imaging technique. 2. The brain stems and spinal cords of 0-1-day-old Wistar rats were isolated and stained using a fluorescent voltage-sensitive dye. Neuronal activity in the preparation was detected using an optical recording apparatus containing a charge-coupled device (CCD)-based camera. 3. Bath-applied propofol (7.5 μmol/L) decreased the C4 burst rate to 45.9% of baseline. Although optical signals corresponding to membrane depolarization during the pre-inspiratory phase in the parafacial region of the ventral medulla decreased to 28.7% of baseline following propofol application, those during the inspiratory phase in the caudal part of the rostral ventrolateral medulla did not. 4. The inhibitory effect of bath-applied propofol was reversed by 2 μmol/L bicuculline. 5. Changes in optical signals corresponding to the population activity of pre-inspiratory neurons were parallel to changes in the C4 burst rate. 6. The results suggest that propofol decreases the inspiratory burst rate by reducing the activity of pre-inspiratory neurons and that GABAA receptor activation plays a role in propofol-induced central respiratory depression. These results are consistent with those of previous electrophysiological studies.

A pilot study of a wearable apnoea detection device

RATIONALE

Current techniques for monitoring patients for apnoea suffer from significant limitations. These include insufficient availability to meet diagnostic needs, cost, accuracy of results in the presence of artefacts and difficulty of use in unsupervised conditions.

OBJECTIVES

We created and clinically tested a novel miniature medical device that targets overcoming these limitations.

METHODS

We studied 20 healthy control participants and 10 patients who had been referred for sleep apnoea diagnosis. The performances of the new system and also of the Food and Drug Administration (FDA) approved SOMNO clinical system, conventionally used for sleep apnoea diagnosis were evaluated under the same conditions. Both systems were tested during a normal night of sleep in controls and patients. Their performances were quantified in terms of detection of apnoea and hypopnoea in individual 10 s epochs, which were compared with scoring of signals by a blinded clinician.

MAIN RESULTS

For spontaneous apnoeas during natural sleep and considering the clinician scorer as the gold standard, the new wearable apnoea detection device had 88.6% sensitivity and 99.6% specificity. In comparison the SOMNO system had 14.3% sensitivity and 99.3% specificity. The novel device had been specifically designed to detect apnoea, but if apnoea and hypopnoea during sleep were both considered in the assessment, the sensitivity and specificity were 77.1% and 99.7%, respectively, versus 54% and 98.5%, respectively, for the SOMNO.

CONCLUSIONS

The performance of the novel device compares very well to the scoring by an experienced clinician even in the presence of breathing artefacts, in this small pilot study. This can potentially make it a real solution for apnoea home monitoring.

Effects of anesthetics, sedatives, and opioids on ventilatory control

This article provides a comprehensive, up to date summary of the effects of volatile, gaseous, and intravenous anesthetics and opioid agonists on ventilatory control. Emphasis is placed on data from human studies. Further mechanistic insights are provided by in vivo and in vitro data from other mammalian species. The focus is on the effects of clinically relevant agonist concentrations and studies using pharmacological, that is, supraclinical agonist concentrations are de-emphasized or excluded.

Maternal and fetal effects of propofol anaesthesia in the pregnant ewe

The objective of this study was to determine the effects of propofol (PRF) on maternal and fetal cardiopulmonary function during the last trimester of pregnancy. Six pregnant 2-3 year-old Ripollesa sheep, each weighing 78+/-8 kg were used in the study and prepared by placing catheters in the maternal jugular vein and carotid artery. A catheter was also placed in the fetal femoral artery. Twenty-four hours later the sheep were anaesthetized with PRF (6 mg/kg intravenous (IV) followed by a continuous infusion at a rate of 0.4 mg/kg/min for 60 min) and cardiopulmonary data collected. Further data were collected for 105 min following termination of the infusion. The maternal mean arterial pressure (MAP) and diastolic arterial pressure (DAP) were significantly decreased (P<0.05) during the first 15 min of the infusion period, while the maternal pH was also significantly decreased. Maternal PaCO(2) and PaO(2) were significantly increased throughout the total infusion period. It was further observed that the fetal pH decreased significantly, throughout the infusion period, whereas the fetal MAP, DAP and PaCO(2) were significantly increased during the first 15 min of the infusion, after which time all parameters returned to control values. No differences in either maternal or fetal parameters were observed between control and recovery times.

Evaluation of different doses of propofol in xylazine pre-medicated horses

OBJECTIVE

To characterize responses to different doses of propofol in horses pre-medicated with xylazine.

ANIMALS

Six adult horses (five females and one male).

METHODS

Each horse was anaesthetized four times with either ketamine or propofol in random order at 1-week intervals. Horses were pre-medicated with xylazine (1.1 mg kg-1 IV over a minute), and 5 minutes later anaesthesia was induced with either ketamine (2.2 mg kg-1 IV) or propofol (1, 2 and 4 mg kg-1 IV; low, medium and high doses, respectively). Data were collected continuously (electrocardiogram) or after xylazine administration and at 5, 10 and 15 minutes after anaesthetic induction (arterial pressure, respiratory rate, pH, PaO2, PaCO2 and O2 saturation). Anaesthetic induction and recovery were qualitatively and quantitatively assessed.

RESULTS

Differences in the quality of anaesthesia were observed; the low dose of propofol resulted in a poorer anaesthetic induction that was insufficient to allow intubation, whereas the high dose produced an excellent quality of induction, free of excitement. Recorded anaesthesia times were similar between propofol at 2 mg kg-1 and ketamine with prolonged and shorter recovery times after the high and low dose of propofol, respectively (p < 0.05; ketamine, 38 +/- 7 minutes; propofol 1 mg kg-1, 29 +/- 4 minutes; propofol 2 mg kg-1, 37 +/- 5 minutes; propofol 4 mg kg-1, 50 +/- 7 minutes). Times to regain sternal and standing position were longest with the highest dose of propofol (32 +/- 5 and 39 +/- 7 minutes, respectively). Both ketamine and propofol reversed bradycardia, sinoatrial, and atrioventricular blocks produced by xylazine. There were no significant alterations in blood pressure but respiratory rate, and PaO2 and O2 saturation were significantly decreased in all groups (p < 0.05).

CONCLUSION

The anaesthetic quality produced by the three propofol doses varied; the most desirable effects, which were comparable to those of ketamine, were produced by 2 mg kg-1 propofol.

Use of sedative and analgesic agents in neurotrauma patients: effects on cerebral physiology

Sedation and analgesia is used primarily in the intensive care unit (ICU) to limit the stress response to critical illness, provide anxiolysis, improve ventilatory support, and facilitate adequate ICU care. However, in the neurotrauma ICU there are many other reasons for the use of these agents. The primary aim is to prevent secondary cerebral damage by maintaining adequate cerebral perfusion pressures. This is accomplished in several different ways. Controlling intracranial pressure (ICP) and maintaining an adequate mean arterial pressure (MAP) is at the cornerstone of this management. Lowering the metabolic demands of the brain is also an important consideration as a treatment strategy. Analgesic and sedative agents are utilized to prevent undesirable increases in ICP and to lower cerebral metabolic demands. Concerns surrounding the use of these agents include time to awakening after discontinuation, effect on the cerebrovasculature, and the effect on patient outcome. There are many different pharmacological agents available, each with their distinct advantages and disadvantages. The purpose of this review is to evaluate the pharmacokinetic and pharmacological effects of each of these agents when used in neurotrauma patients.

Effect of propofol at two injection rates or thiopentone on post-intubation apnoea in the dog

Ventilatory effects at induction of anaesthesia were studied following intubation in 66 dogs anaesthetised using thiopentone (10 mg/kg) or propofol (4 mg/kg, injected rapidly or 4 mg/kg, injected slowly). Acepromazine and morphine preanaesthetic medication was administered, and anaesthesia was maintained with halothane in nitrous oxide and oxygen. The time from connection of the breathing system to the first breath was measured. Apnoea was defined as cessation of spontaneous respiration for 15 seconds or longer. Respiratory rate and minute volume were measured for the first five minutes of anaesthesia. Propofol was associated with a greater incidence of apnoea than thiopentone (59 per cent and 64 per cent compared with 32 per cent), but this difference was not statistically significant. Time to first breath was significantly longer with propofol than thiopentone and longest with the slower injection of propofol (P<0.05) (median of four seconds for thiopentone, 19.5 seconds for the propofol rapid injection, and 28.8 seconds for the propofol slow injection). In conclusion, the induction agent and speed of injection affect the incidence and duration of post-intubation apnoea.

Estudo comparativo da anestesia com propofol ou thionembutal em cães

Os autores compararam o uso de propofol e thionembutal observando as freqüências cardíaca e respiratória e a presença das seguintes intercorrências: apnéia, tremor, bradicardia, taquicardia, taquipnéia e parada cardíaca. Foram randomizados 100 cães para serem anestesiados com propofol ou thionembutal, sendo monitorizados os parâmetros de interesse ao estudo. Foi constatado que existe importância significantemente maior em relação a ocorrência de apnéia e tremor em ambos os grupos, sendo menores com o uso de propofol. O propofol mostrou-se uma droga mais segura para a anestesia em cães do que o thionembutal.

Laryngeal mask insertion using thiopental and low dose atracurium: a comparison with propofol

PURPOSE

To compare the laryngeal mask airway (LMA) insertion conditions produced by propofol and a thiopental - low dose atracurium combination.

METHODS

In a randomized controlled double blind study, 120 premedicated patients were allocated into four groups. After pre-oxygenation, anesthesia was induced as follows: 1 microg x kg(-1) fentanyl, 2.5 mg x kg(-1) propofol (group I); 1 microg x kg(-1) fentanyl, 5 mg x kg(-1) thiopental (group II); 1 microg x kg(-1) fentanyl, 5 mg x kg(-1) thiopental, 0.05 mg x kg(-1) or 0.1 mg x kg(-1) atracurium (groups III and IV respectively). The LMA was inserted by a blinded anesthesiologist who also assessed the following insertion conditions on a three point scale; jaw relaxation, biting, gagging, coughing, presence of laryngospasm, adequacy of airway patency, number of attempts at insertion and overall insertion conditions.

RESULTS

There was no difference in insertion conditions between groups I, III and IV. Group II produced the worst overall conditions (P<0.05). There were no differences in hemodynamic changes and apnea times between all four groups.

CONCLUSION

The combination of fentanyl-thiopental with low dose atracurium (0.05 or 0.1 mg x kg(-1)) provided conditions comparable with those of propofol for LMA insertion.

Propofol or sevoflurane for laryngeal mask airway insertion

PURPOSE

Sevoflurane is a volatile anesthetic agent, which combines rapid, smooth inhalational induction of anesthesia with rapid recovery, making it particularly suitable for day case anesthesia. The laryngeal mask airway is often also used in ambulatory anesthesia, with intravenous propofol being the agent of choice for its insertion. Our objective was to compare the conditions for laryngeal mask airway (LMA) insertion obtained by modified vital capacity breath sevoflurane inhalational induction of anesthesia with propofol intravenous induction.

METHODS

Eighty-eight patients, aged 18-65 yr, ASA I-II, undergoing general anesthesia for elective surgery were randomized into two groups in a prospective, single-blind study. Patients in Group P (n=44) received 2.5 mg x kg(-1) propofol i.v. and in Group S (n=44) received sevoflurane 8% in nitrous oxide 50% and oxygen. Ventilation was not assisted. Laryngeal mask airway insertion was attempted at one minute intervals from loss of both verbal response and eyelash reflex, by an anesthesiologist unaware of the induction technique. Complications, such as coughing and head movement, were also noted at each attempt.

RESULTS

Mean time to successful LMA insertion was 1.3 (1-3) min in P and 2.2 (1-3) min in S, P < 0.05. Eleven patients in Group P, (25%) required additional propofol compared with four (9%) in S, P < 0.05. Incidence of complications was similar in both groups and by 3 min, LMA was successfully inserted in all patients.

CONCLUSION

Modified vital capacity breath inhalational induction with sevoflurane 8% is efficient for LMA insertion in most cases, but takes slightly longer than propofol.

Synergistic interaction between the effects of propofol and midazolam with fentanyl on phrenic nerve activity in rabbits

BACKGROUND

It has been shown that the depressive effects of both propofol and midazolam on consciousness are synergistic with opioids, but the nature of their interactions on other physiological systems, e.g. respiration, has not been fully investigated. The present study examined the effect of propofol and midazolam alone and in combination with fentanyl on phrenic nerve activity (PNA) and whether such interactions are additive or synergistic.

METHODS

PNA was recorded in 27 anaesthetised and artificially ventilated rabbits. In three groups, propofol, fentanyl and midazolam were administered intravenously in incremental doses to construct dose-response curves for the depressant effects of each one on PNA. In another two groups, the effect of pretreatment with either fentanyl 1 microgram.kg-1 i.v. or midazolam 0.05 mg.kg-1 i.v. on the effects of propofol and fentanyl respectively on PNA were studied.

RESULTS

Propofol and fentanyl caused a dose-dependent depression of PNA with complete abolition at the highest total doses of 16 mg.kg-1 i.v. and 32 micrograms.kg-1 i.v., respectively. In contrast, midazolam in incremental doses to a total of 0.8 mg.kg-1 reduced mean PNA by 63%, but approximately 12% of PNA remained at a total dose as high as 6.4 mg.kg-1. The mean ED50s, calculated from dose-response curves, were 5.4 mg.kg-1, 3.9 micrograms.kg-1 and 0.4 mg.kg-1 for propofol, fentanyl and midazolam, respectively. Initial doses of either fentanyl 1 microgram.kg-1 i.v. or midazolam 0.05 mg.kg-1 i.v. acted synergistically with subsequent doses of either propofol or fentanyl to abolish PNA at total doses of 8 mg.kg-1 and 8 micrograms.kg-1, respectively.

CONCLUSION

Fentanyl has a synergistic interaction with both propofol and midazolam on PNA and hence potentially on respiration.

Propofol and fentanyl compared with midazolam and fentanyl during third molar surgery

PURPOSE

The purpose of this study was to measure the safety and efficacy of propofol combined with fentanyl as sedative agents during third molar outpatient surgery.

PATIENTS AND METHODS

A double-blind, prospective, randomized clinical trial involving 57 patients undergoing removal of third molars under intravenous sedation between November 1994 and December 1995 was performed. Patients randomly received either propofol and fentanyl (P + F, th = 24) or midazolam and fentanyl (M + F, M = 33). Patient demographics, Corah anxiety scores, and physiologic parameters were determined preoperatively. All medications were titrated to the same clinical end point for sedation. Intraoperative physiologic parameters, cooperation, alertness, and pain scores were assessed. Postoperative recovery and degree of amnesia also were determined.

RESULTS

There were no significant differences in either patient demographics or surgical characteristics between groups. The P + F group was significantly less cooperative than the M + F group. Pain during injection of propofol was a significant adverse side effect. Both groups experienced a small percentage of apneic episodes, but mechanical ventilation was never required. There were no differences in recovery between groups as measured by the Treiger dot test and psychomotor recovery scores. The degree of anterograde amnesia was greater for the M + F group, although the difference was not statistically significant. Sedation was rated good to excellent by the patient, surgeon, and observer, and there were no statistically significant differences between groups.

CONCLUSION

Propofol appears to be a safe and efficacious drug for use during outpatient oral surgical procedures.

Midazolam versus propofol for long-term sedation in the ICU: a randomized prospective comparison

OBJECTIVE

To compare the efficacy, safety, and cost of midazolam and propofol in prolonged sedation of critically ill patients.

DESIGN

Randomized, prospective study.

SETTING

General intensive care unit (ICU) in a 1100-bed teaching hospital.

PATIENTS

67 critically ill, mechanically ventilated patients.

INTERVENTIONS

Patients were invasively monitored and mechanically ventilated. A loading dose [midazolam 0.11 +/- 0.02 (SEM) mg.kg-1, propofol 1.3 +/- 0.2 mg.kg-1] was administered, followed by continuous infusion, titrated to achieve a predetermined sedation score. Sedation was continued as long as clinically indicated.

MEASUREMENTS AND RESULTS

Mean duration of sedation was 141 and 99 h (NS) for midazolam and propofol, respectively, at mean hourly doses of 0.070 +/- 0.003 mg.kg-1 midazolam and 1.80 +/- 0.08 mg.kg-1 propofol. Overall, 68% of propofol patients versus 31% of midazolam (p < 0.001) patients had a > 20% decrease in systolic blood pressure after the loading dose, and 26 versus 45% (p < 0.01) showed a 25% decrease in spontaneous minute volume. Propofol required more daily dose adjustments (2.1 +/- 0.1 vs 1.4 +/- 0.1, p < 0.001). Nurse-rated quality of sedation with midazolam was higher (8.2 +/- 0.1 vs 7.3 +/- 0.1 on a 10-cm visual analog scale, p < 0.001). Resumption of spontaneous respiration was equally rapid. Recovery was faster after propofol (p < 0.02), albeit with a higher degree of agitation. Amnesia was evident in all midazolam patients but in only a third of propofol patients. The cost of propofol was 4-5 times higher.

CONCLUSIONS

Both drugs afforded reliable, safe, and controllable long-term sedation in ICU patients and rapid weaning from mechanical ventilation. Midazolam depressed respiration, allowed better maintenance of sedation, and yielded complete amnesia at a lower cost, while propofol caused more cardiovascular depression during induction.

Lignocaine to aid the insertion of the laryngeal mask airway with thiopentone. A comparison between topical and intravenous administration

Conditions for insertion of a laryngeal mask airway in 90 unpremedicated adult were patients were assessed in a randomised, single-blinded trial. Each patient received fentanyl 1 microgram.kg-1 and thiopentone 5 mg.kg-1, and this was preceded either by lignocaine 0.5 mg.kg-1 intravenously (group 1), lignocaine 1.5 mg.kg-1 intravenously (group 2) or 40 mg of topical lignocaine spray to the posterior pharyngeal wall (group 3). Conditions for laryngeal mask airway insertion were recorded. The group receiving topical lignocaine had a lower incidence of laryngospasm (p < 0.05), required fewer attempts for successful insertion of the laryngeal mask (p < 0.05) and coughed or gagged less frequently than either group receiving lignocaine intravenously (p > 0.05). Overall, the conditions for laryngeal mask airway insertion were better in the topical group (p < 0.05). There were no significant differences in haemodynamic response and apnoea between the three groups. Topical lignocaine spray prior to thiopentone provides conditions for insertion of a laryngeal mask that are superior to those provided by lignocaine and thiopentone intravenously.

Topical lignocaine and thiopentone for the insertion of a laryngeal mask airway; a comparison with propofol

We assessed conditions for insertion of a laryngeal mask airway in 90 unpremedicated adult patients who received either thiopentone 5 mg.kg-1 preceded by 40 mg of topical lignocaine spray to the posterior pharyngeal wall or propofol 2.5 mg.kg-1 alone in a randomised, single-blinded trial. All patients received fentanyl 1 microgram.kg-1. Gagging, coughing and laryngospasm following laryngeal mask insertion were graded and haemodynamic data and apnoea times were recorded. There were no significant differences between the two groups with regard to the incidence of gagging, coughing and laryngospasm, but the apnoea time was significantly less in the thiopentone group (p < 0.005). The decrease in systolic and diastolic blood pressure, following induction and the insertion of a laryngeal mask with propofol was significantly greater than following thiopentone (p < 0.05--systolic, p < 0.01--diastolic). We conclude that thiopentone preceded by topical lignocaine spray provides conditions for insertion of a laryngeal mask equal to those of propofol, with more haemodynamic stability and a shorter period of apnoea.

The influence of alfentanil pre-treatment on ventilatory effects of doxapram following induction of anaesthesia with propofol

BACKGROUND

Hypoventilation may occur following induction of anaesthesia with propofol and is potentiated by concurrent use of opioid drugs. This effect is undesirable in patients who will continue to maintain spontaneous respiration during anaesthesia and surgery. The analeptic drug doxapram is known to have selective respiratory stimulatory effects but its action during induction of anaesthesia has been inconsistent.

METHOD

In a double-blind, placebo-controlled study, the influence of alfentanil pre-treatment on the ventilatory effects of doxapram given during induction of anaesthesia with propofol was studied in 40 patients. Four groups of ten patients (two groups pre-treated with 7 micrograms.kg-1 of alfentanil and two groups with saline) were randomly allocated to receive either 0.5 mg.kg-1 doxapram or saline following infusion of propofol to loss of verbal contact.

RESULTS

In the groups that received doxapram, minute volumes were significantly increased and end-tidal carbon dioxide concentrations were significantly reduced compared to control groups, although the duration and extent of these effects were less in the group that received alfentanil. Doxapram also reversed an alfentanil-induced reduction in respiratory rate. No adverse cardiovascular or neurological stimulatory effects of doxapram were evident at any time.

CONCLUSION

We conclude that doxapram 0.5 mg.kg-1 is effective in augmenting ventilation that has been obtunded following induction of anaesthesia with propofol in patients pre-treated with alfentanil.

Evaluation of propofol as a general anesthetic for horses

This study provides baseline information on the potential use of propofol as a general anesthetic for horses. Using a Latin square design, propofol (2, 4, and 8 mg/kg) was administered intravenously on three separate occasions to six mature horses. Information about anesthetic induction, duration, and recovery was recorded along with results of rectal temperature, heart rate, respiratory rate, pHa, PaCO2 and PaO2. Statistical analysis included a mixed model analysis of variance, a general linear model analysis and least square means test for post hoc comparisons. A P < .05 was considered significant. The quality of induction of anesthesia varied from poor to good. Two horses were not recumbent following the lowest dose of propofol. Brief paddling limb movements occurred occasionally and unpredictably after recumbency induced by all three doses. During recovery, horses were uniformly calm and coordinated in their moves to stand. Duration of recumbency (minutes) was dose related; 15.05 +/- 1.58 (mean +/- SD) following 2 mg/kg, 31.06 +/- 5.56 following 4 mg/kg, and 47.85 +/- 13.63 following 8 mg/kg. During recumbency at all doses, heart rate significantly increased from a predrug value of 40 +/- 6 beats per minute. Substantial respiratory depression, characterized by a significant decrease in respiratory rate (from 11.7 +/- 2.9 to 3.7 +/- 1.6 breaths per minute) and increased PaCO2 (from 44.5 +/- 2.5 to 52.7 +/- 8.0 mm Hg) was seen only after 8 mg/kg. A significant decrease in PaO2 was observed throughout the recumbency induced by 8 mg/kg, and also at 3 and 5 minutes following induction of anesthesia with 4 mg/kg propofol.(ABSTRACT TRUNCATED AT 250 WORDS)

A simple method for the maintenance of oxygen saturation following intravenous induction of anaesthesia with propofol

One hundred unpremedicated fit adult patients having elective minor day-stay surgery and general anaesthesia were randomly allocated to one of two groups. During 30 s of intravenous propofol administration (2.5 mg.kg-1), study group patients (n = 50) were instructed to take three vital capacity breaths of room air, whilst control group patients (n = 50) were given no specific instructions. Pulse oximetry was continuously recorded over the next 5 min and the lowest oxygen saturation was noted. Pre-induction oxygen saturation was the same for both groups, but the lowest median oxygen saturation in the study group patients was 94% versus 88% in the control group patients (p < 0.001). Oxygen saturation returned to the pre-induction value significantly earlier in the study group patients compared with controls (97 s vs 135 s, p < 0.01). These results demonstrate that significant desaturation occurs in patients following intravenous induction of anaesthesia with propofol. This desaturation may be attenuated by asking patients to take three vital capacity breaths of room air during induction of anaesthesia.

Intravenous Anesthetic Agents

Intravenous (IV) anesthetics are used in the operating room setting for the induction and maintenance of general anesthesia. These agents are used in combination with many other therapeutic agents including inhalational anesthetics, anticholinergics, neuromuscular blockers, local anesthetics, and antihistamines. Currently available intravenous anesthetics include barbiturates (eg, thiopental and methohexital), benzodiazepines (eg, diazepam and midazolam), etomidate, ketamine, propofol, and opioids (eg, morphine, meperidine, fentanyl, alfentanil, and sufentanil). The barbiturates are the most frequently used agents for induction today. The benzodiazepines are used primarily for preoperative sedation intraoperatively; however, they may also be used for induction in certain clinical situations. Etomidate offers the advantage of minimal cardiovascular side effects, while ketamine is distinguished by stimulant cardiovascular effects. Propofol has a short recovery time and a low incidence of nausea and vomiting when compared with that of barbiturates and opioids. The opioids are used most often for the production of analgesia, although they may also be used as primary anesthetic agents in select patient populations. In this article, the pharmacokinetics of these agents will be reviewed as well as factors affecting their pharmacokinetic profile. These factors include age, hemodynamic changes, renal or hepatic dysfunction, and interaction with concomitant medications.

[Diprivan: drug interactions]

Concerning the pharmacokinetic or pharmacodynamic interactions, the following is recommended: Use smaller doses of alfentanil when the latter is combined with propofol, because of a higher risk of ventilatory depression. Decrease doses of each agent whenever propofol is combined with thiopentone or midazolam to induce anaesthesia. The prophylactic or therapeutic use of atropine is indicated when propofol is associated with agents reducing heart rate. Prefer propofol to induce anaesthesia for eye surgery, if suxamethonium is required. In the absence of sufficient data, propofol should be administered with care in patients taking cardiovascular medication (risk of hypotension) or cyclosporine (enhanced toxicity).

Cardiovascular effects of a continuous two-hour propofol infusion in dogs. Comparison with isoflurane anesthesia

The cardiovascular effects during 2 hours of anesthesia with either a continuous propofol infusion or isoflurane were compared in the same six healthy dogs. Dogs were randomly assigned to be anesthesized with either propofol (5 mg/kg, i.v. administered over 30 seconds, immediately followed by a propofol infusion beginning at 0.4 mg/kg/min), or isoflurane (2.0% end-tidal concentration). The propofol infusion was adjusted to maintain a light plane of anesthesia. Dogs anesthetized with propofol had higher values for systemic arterial pressure due to higher systemic vascular resistance. Dogs anesthetized with isoflurane had higher values for heart rate and mean pulmonary artery pressure. Cardiac index was not different between the two groups. Apnea and cyanosis were observed during induction of anesthesia with propofol. At the end of anesthesia the mean time to extubation for dogs anesthetized with either propofol or isoflurane was 13.5 min and 12.7 min, respectively. A continuous infusion of propofol (0.44 mg/kg/min) provided a light plane of anesthesia. Ventilatory support during continuous propofol infusion is recommended.

Patient response to laryngeal mask insertion after induction of anaesthesia with propofol or thiopentone

The response to insertion of the laryngeal mask airway (LMA) following either propofol 2.5 mg.kg-1 or thiopentone 5 mg.kg-1 was assessed in two groups of patients. The purpose of the study was to ascertain which of these two induction agents provided the better conditions for insertion of the LMA. Anaesthesia was induced by propofol in 35 patients and by thiopentone in 37. Following induction, ventilation was assisted for two minutes using 50% oxygen and nitrous oxide and 2% isoflurane, before insertion of the LMA. The presence of gagging, coughing, laryngospasm and movement was noted and graded. Thiopentone was associated with an adverse response in 76% of patients, compared with propofol in 26% (P < 0.01). Gagging, laryngospasm and head movement were more common using thiopentone (P < 0.01, P < 0.05 and P < 0.05 respectively) and in 11% (P < 0.05) of the thiopentone group insertion of the LMA was impossible due to inadequate relaxation. We conclude that, using these doses, propofol is superior to thiopentone as an induction agent for insertion of the laryngeal mask airway.

Intermittent thiopentone for teaching fibreoptic nasotracheal intubation

A technique for teaching fibreoptic nasotracheal intubation is described. Fifty patients presenting for elective dental surgery received thiopentone by intermittent injection for induction and maintenance of anaesthesia whilst a trainee anaesthetist attempted to visualise the vocal cords using an intubating fibrescope. During endoscopy patients spontaneously breathed oxygen-enriched air and passage of the tracheal tube was facilitated by suxamethonium. Arterial blood pressure, heart rate and arterial oxygen saturation were monitored continuously. Time from loss of eyelash reflex to successful intubation was 113 (90) (35-480) s (mean (SD) (range)). Changes in arterial blood pressure and heart rate were similar to those described in previous studies of tracheal intubation. Haemoglobin oxygen saturation remained above 95% in 43 patients, and above 93% in 46 patients; the lowest saturation recorded was 91%. Intermittent thiopentone provides good conditions for teaching fibreoptic nasotracheal intubation whilst maintaining arterial blood pressure and oxygen saturation.

Effects of low-dose propofol administration on central respiratory drive, gas exchanges and respiratory pattern

The effects of sedative-hypnotic doses of propofol on respiratory drive and pattern have not yet been extensively described. Repeated small boluses of propofol (0.6-0.3 mg.kg-1) were administered to ten ASA I patients undergoing carpal tunnel release using regional anaesthesia. Airway pressure, capnography and pneumotachography were continuously recorded. With respect to basal values, no significant variations of respiratory rate, minute volume, tidal volume, inspiratory and expiratory time, total expiratory cycle, Ti/Ttot, TV/Ti, P0.1, EtCO2 and blood gas analysis were observed. Low doses of propofol, to maintain conscious sedation of light sleep, have not been shown to cause respiratory depression.

Comparison of propofol and thiopentone for laryngeal mask insertion

Conditions for insertion of the laryngeal mask were assessed following induction of anaesthesia with either propofol 2.5 mg/kg or thiopentone 4.0 mg/kg in 80 patients premedicated with diazepam 10 mg. Insertion following induction with thiopentone resulted in a greater incidence of gagging (p less than 0.01). The use of additional induction agent, where necessary, resulted in no ultimate significant difference between the groups for the provision of satisfactory conditions.

Propofol for long-term sedation in the intensive care unit. A comparison with papaveretum and midazolam

Thirty-seven patients with a wide range of illnesses were studied during mechanical ventilation of the lungs in an intensive care unit. Fifteen were sedated with a continuous propofol infusion, with analgesia provided by bolus doses of papaveretum. Twelve received a continuous infusion of papaveretum, supplemented by bolus doses of midazolam. The level of sedation was assessed every four hours and measurements were made of haemodynamic and respiratory variables. Levels of sedation were generally satisfactory in both groups. Six patients who received propofol required the use of muscle relaxants, because of their strong respiratory drives, to achieve synchronisation with the ventilator. There was no significant difference in respiratory or haemodynamic variables between the groups, but several patients required inotropic support because of their disease. There was no evidence of inhibition of adrenal steroidogenesis in the propofol group. Propofol can be a useful sedative agent in the intensive care unit, but sedative regimens should be tailored to individual patient requirements.

Clinical pharmacology of propofol: an intravenous anesthetic agent

Propofol is a 2,6-diisopropylphenol with sedative-hypnotic properties. Because of its slight solubility in water, the drug is formulated as an emulsion for clinical use. It is highly lipophilic and distributes extensively in the body. The blood concentration-time profile of propofol after an iv bolus injection follows a three-compartment model with half-lives of 2-4 min, 30-45 min, and 3-63 h, respectively. Propofol is extensively metabolized by the liver prior to its elimination by the kidney. Following an iv dose of 2-2.5 mg/kg, loss of consciousness occurs in less than one minute and lasts for approximately five minutes. Hypnosis can be maintained by propofol blood concentrations of 1.5-6 micrograms/mL in the presence of N2O/O2 (60:40 ratio) or other anesthetic agents. During induction, propofol decreases the systolic and diastolic blood pressure by approximately 20-30 percent with minimal change in heart rate; apnea is also common. The cardiovascular and respiratory effects of propofol, however, should not cause major concern in otherwise healthy patients. By virtue of its pharmacokinetic profile, the drug lends itself to continuous infusion for maintenance of anesthesia. When used as the main anesthetic agent, it produces satisfactory anesthesia with rapid recovery and without major adverse effects in healthy individuals. In continuous infusion propofol can be used as an alternative to inhalation anesthetics.

Anaesthesia for computerised tomography of the brain in children: a comparison of propofol and thiopentone

Propofol (2,6-di-isopropylphenol) 1.5-2.0 mg/kg i.v. was compared with thiopentone 3.0-4.0 mg/kg i.v. as an induction agent in anaesthesia for computerised tomography (CT) of the brain in children. Both induction agents were combined with diazepam 0.2 mg/kg i.v. Thirty children (ASA physical status I-II) aged 3 to 10 years and scheduled for elective examination were included in the randomized study. The haemodynamic response to propofol and thiopentone did not differ between the groups. Spontaneous respiration was retained in all patients and no ventilatory support was required during anaesthesia. The incidence of side-effects did not differ between the groups. Pain on injection with propofol was rare (n = 1) after mixing 1 ml lignocaine (1%) with propofol prior to induction. The recovery times were significantly shorter in the propofol than in the thiopentone group. Propofol appears to be a promising alternative for use in short day-case anaesthesia for CT scanning in children.

The pharmacology of propofol

A review of the pharmacology of propofol, a new IV anesthetic agent, is presented. Solubilized in a soybean emulsion, propofol is one of a series of sterically hindered phenols that exhibit anesthetic activity. Induction of anesthesia with propofol may be associated with pain on injection, apnea, and a reduction in arterial blood pressure (BP) and cardiac output. Caution should be ascribed to its use in patients with coronary artery disease, where these effects may have the potential for producing myocardial ischemia. The hemodynamic responses to laryngoscopy and intubation are attenuated. The pharmacokinetic profile suggests suitability as an infusion for either maintenance of anesthesia or sedation. Use of propofol as an infusion during surgery may result in a further reduction in cardiac output, particularly with the concomitant administration of adjuvant increments of fentanyl. The ventilatory response to CO2 is depressed during such an infusion. The high clearance of propofol suggests that even after a prolonged infusion, recovery should be rapid. This finding has been confirmed in a series of studies establishing propofol as an ideal agent for use in a total IV anesthetic technique. Both the quality and speed of recovery, together with the absence of emetic sequelae, support the use of propofol in an outpatient setting. Propofol appears to have no long-term effect on adrenocortical function and appears safe for use in patients with acute intermittent porphyria and susceptibility to malignant hyperpyrexia.

Induction characteristics of propofol in children: comparison with thiopentone

The induction characteristics of propofol were studied and compared with thiopentone in children aged 3-14 years who received either no premedication or pethidine-atropine or trimeprazine. Anaesthesia was maintained with nitrous oxide in oxygen, and isoflurane. The induction doses of propofol and thiopentone were 2.9 mg/kg and 6.5-7.1 mg/kg respectively; premedication had no significant effect on the induction doses of either agent. Spontaneous movement and hypertonus occurred in about 20% of children with both agents. The use of propofol was associated with a high incidence of pain on injection (injections were mostly in veins on the dorsum of the hand), but this was reduced by mixing lignocaine with propofol. Cardiovascular effects were not clinically significant with either agent. Apnoea occurred in 35% of patients given propofol and in 50% of those given thiopentone. Children anaesthetised with propofol awoke significantly earlier after cessation of all anaesthesia. It is concluded that the use of propofol is safe in children and may have advantages where early recovery from anaesthesia is desirable, but offers no advantage over thiopentone for routine induction of anaesthesia.