Determining an optimum propofol infusion rate for induction of anaesthesia in healthy dogs: a randomized clinical trial.

OBJECTIVE: To determine an optimum infusion rate of propofol that permitted rapid tracheal intubation while minimizing the duration of postinduction apnoea. STUDY DESIGN: Prospective, randomized, blinded clinical trial. ANIMALS: A total of 60 client-owned dogs presented for elective neutering and radiography. METHODS: Dogs were randomly allocated to one of five groups (groups A-E) to have propofol at an infusion rate of 0.5, 1, 2, 3, or 4 mg kg-1 minute-1, respectively, following intramuscular premedication with methadone 0.5 mg kg-1 and dexmedetomidine 5 µg kg-1. Propofol administration was stopped when adequate conditions for tracheal intubation were identified. Time to tracheal intubation and duration of apnoea were recorded. If oxygen haemoglobin saturation decreased to < 90%, manual ventilation was initiated. A one-way analysis of covariance was conducted to compare the effect of propofol infusion rate on duration of apnoea and intubation time whilst controlling for covariates, followed by post hoc tests. The significance level was set at p < 0.05. RESULTS: Propofol infusion rate had a significant effect on duration of apnoea (p = 0.004) and intubation time (p < 0.001) after controlling for bodyweight and sedation scores, respectively. The adjusted means (± standard error) of duration of apnoea were significantly shorter in groups A and B (49 ± 39 and 67 ± 37 seconds, respectively) than in groups C, D and E (207 ± 34, 192 ± 36 and 196 ± 34 seconds, respectively). Group B (115 ± 10 seconds) had a significantly shorter intubation time than group A (201 ± 10 seconds, p < 0.001). CONCLUSIONS AND CLINICAL RELEVANCE: An infusion rate of 1.0 mg kg-1 minute-1 (group B) appears to offer the optimal compromise between speed of induction and duration of postinduction apnoea.

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.

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.

The use of alfaxalone for premedication, induction and maintenance of anaesthesia in pigs: a pilot study.

OBJECTIVE: The evaluation of alfaxalone as a premedication agent and intravenous anaesthetic in pigs. STUDY DESIGN: Prospective, clinical trial. ANIMALS: Nine healthy, 6-8-week-old female Landrace pigs weighing 22.2 ± 1.0 kg, undergoing epidural catheter placement. METHODS: All pigs were premedicated with 4 mg kg-1 alfaxalone, 40 µg kg-1 medetomidine and 0.4 mg kg-1 butorphanol administered in the cervical musculature. Sedation was subjectively scored by the same observer from 1 (no sedation) to 10 (profound sedation) prior to induction of anaesthesia with alfaxalone intravenously to effect. All pigs were maintained on alfaxalone infusions with the rate of administration adjusted to maintain appropriate anaesthetic depth. Quality of induction was scored from 1 (poor) to 3 (smooth) and basic cardiorespiratory variables were recorded every 5 minutes during anaesthesia. Results are reported as mean ± standard deviation or median (range) as appropriate. RESULTS: Sedation scores were 9 (7-10). Inductions were smooth in all pigs and cardiovascular variables remained within normal limits for the duration of anaesthesia. The induction dose of alfaxalone was 0.9 (0.0-2.3) mg kg-1. Three pigs did not require additional alfaxalone after premedication to facilitate intubation. CONCLUSIONS AND CLINICAL RELEVANCE: Intramuscular alfaxalone in combination with medetomidine and butorphanol produced moderate to deep sedation in pigs. Alfaxalone produced satisfactory induction and maintenance of anaesthesia with minimal cardiovascular side effects. Appropriate monitoring of pigs premedicated with this protocol is required as some pigs may become anaesthetized after intramuscular administration of this combination of drugs.

Use of Propofol for Induction and Maintenance of Anesthesia in a King Penguin ( Aptenodytes patagonicus ) Undergoing Magnetic Resonance Imaging.

Anesthesia protocols for patients with intracranial lesions need to provide hemodynamic stability, preserve cerebrovascular autoregulation, avoid increases in intracranial pressure, and facilitate a rapid recovery. Propofol total intravenous anesthesia (TIVA) maintains cerebral blood flow autoregulation and is considered superior to inhalant agents as an anesthetic protocol for patients with intracranial lesions. A propofol-based TIVA subsequent to premedication with medetomidine and diazepam was used in a king penguin ( Aptenodytes patagonicus ) undergoing magnetic resonance imaging of the brain after a new onset of seizures. This protocol provided a rapid and smooth induction and calm recovery in the penguin. When ventilation control is possible, propofol TIVA may be a superior choice to inhalant agents for anesthesia of birds with potential intracranial lesions.