Differences in need for hemodynamic support in horses anesthetized with sevoflurane as compared to isoflurane

Dobutamine use in horses during romifidine and isoflurane anaesthesia

This retrospective study aimed to assess the incidence of hypotension and the subsequent administration of dobutamine in horses anesthetized with isoflurane and romifidine during elective surgery. Time from induction of anaesthesia to administration of dobutamine was registered, as well as the time and dose needed to restore mean arterial pressure (MAP) ≥ 70 mmHg. Additionally, the influence of patient and anaesthesia related parameters on the need for dobutamine supplementation was evaluated. In total, 118 horses were included in this retrospective study. Dobutamine was administered to effect when MAP<70 mmHg. Data registered: patient weight, acepromazine premedication, body position, administration of intraoperative ketamine bolus, locoregional anaesthesia, mechanical ventilation, duration of anaesthesia, dose and duration of dobutamine administration, heart rate, MAP before dobutamine administration, MAP and time required to increase MAP≥70 mmHg. Dobutamine infusion was needed in 54.2% of the horses 30 ± 17 min after isoflurane-romifidine anaesthesia started. Dobutamine 0.55 ± 0.18 μg kg-1 min-1 achieved a MAP≥70 mmHg in 12 ± 8 min. Duration of dobutamine infusion was 56 ± 37 min. An univariable logistic regression showed a significant association between dobutamine and acepromazine administration (p = 0.01; OR = 3.43), anaesthesia time (p = 0.02; OR = 2.41) and dorsal recumbency (p < 0.001; OR = 8.40). In a multivariable logistic regression, only dorsal recumbency significantly increased the need for dobutamine supplementation (p < 0.001; OR = 7.70). There was no significant association between patient weight (p = 0.11; OR = 1), locoregional anaesthesia (p = 0.07; OR = 0.47), administration of a ketamine bolus (p = 0.95; OR = 0.98) or volume controlled ventilation (p = 0.94; OR = 1.04) and dobutamine administration. Low doses of dobutamine were suitable to restore MAP above 70 mmHg within a limited time period. Only dorsal recumbency increased the need of dobutamine administration.

Recovery after General Anaesthesia in Adult Horses: A Structured Summary of the Literature

Simple Summary

Recovery is the most dangerous phase of general anaesthesia in horses. Numerous publications have reported about this phase, but structured reviews that try to reduce the risk of bias of narrative reviews/expert opinions, focussing on the topic are missing. Therefore, the aim of the present article was to publish the first structured review as a summary of the literature focussing on the recovery phase after general anaesthesia in horses. The objective was to summarise the available literature, taking into account the scientific evidence of the individual studies. A structured approach was followed with two experts in the field independently deciding on article inclusion and its level of scientific evidence. A total number of 444 articles, sorted by topics and classified based on their levels of evidence, were finally included into the present summary. The most important findings were summarised and discussed. The present structured review can be used as a compilation of the publications that, to date, focus on the recovery phase after general anaesthesia in adult horses. This type of review tries to minimise the risk of bias inherent to narrative reviews/expert opinions.

Abstract

Recovery remains the most dangerous phase of general anaesthesia in horses. The objective of this publication was to perform a structured literature review including levels of evidence (LoE) of each study with the keywords “recovery anaesthesia horse”, entered at once, in the search browsers PubMed and Web of Science. The two authors independently evaluated each candidate article. A final list with 444 articles was obtained on 5 April 2021, classified as: 41 “narrative reviews/expert opinions”, 16 “retrospective outcome studies”, 5 “surveys”, 59 “premedication/sedation and induction drugs”, 27 “maintenance with inhalant agents”, 55 “maintenance with total intravenous anaesthesia (TIVA)”, 3 “TIVA versus inhalants”, 56 “maintenance with partial intravenous anaesthesia (PIVA)”, 27 “other drugs used during maintenance”, 18 “drugs before/during recovery”, 18 “recovery systems”, 21 “respiratory system in recovery”, 41 “other factors”, 51 “case series/reports” and 6 “systems to score recoveries”. Of them, 167 were LoE 1, 36 LoE 2, 33 LoE 3, 110 LoE 4, 90 LoE 5 and 8 could not be classified based on the available abstract. This review can be used as an up-to-date compilation of the literature about recovery after general anaesthesia in adult horses that tried to minimise the bias inherent to narrative reviews.

Sevoflurane or isoflurane anaesthesia? A prospective, randomised blinded clinical trial in horses undergoing elective surgery

BACKGROUND

Isoflurane is the only volatile anaesthetic agent licensed for equine use in the United Kingdom, but sevoflurane is also commonly used. The two agents have rarely been compared for use in clinical elective surgery.

METHODS

This single centre, prospective, randomised, blinded clinical investigation recruited 101 healthy client owned horses undergoing elective surgery. Anaesthesia was standardised and horses randomly assigned to receive isoflurane (I) or sevoflurane (S) for maintenance of anaesthesia in 100% oxygen. Horses were ventilated to normocapnia and received intravenous fluid therapy and haemodynamic support with dobutamine to maintain mean arterial blood pressure above 60 mm Hg. Recovery was timed and video-recorded to allow offline evaluation by two experienced clinicians unaware of the volatile agent used. No post-anaesthetic sedation was administered.

RESULTS

There was no significant difference between groups in terms of haemodynamic support required during anaesthesia nor in quality or duration of recovery. Inotropic support to maintain MAP above 60 mm Hg was required by 67 of 101 (67%) of horses. Five horses in the I group required additional ketamine or thiopentone to improve the plane of anaesthesia.

CONCLUSIONS

Haemodynamic support needed during anaesthesia as well as the duration and quality of recovery were similar with isoflurane and sevoflurane.

Changes in Arterial Blood Pressure and Oxygen Tension as a Result of Hoisting in Isoflurane Anesthetized Healthy Adult Horses

Background: In anesthetized adult horses, changes in recumbency can influence the cardiovascular system but how arterial blood pressures and oxygen tension change in isoflurane anesthetized animals as a direct result of hoisting has not been investigated. Objective: To evaluate effects of hoisting on hemodynamic function and pulmonary gas exchange in isoflurane-anesthetized horses. Study Design: Prospective, experimental study. Methods: Six adult horses were anesthetized three times using isoflurane in pure oxygen (inspired fraction 0.9-1.0), and allowed breathing spontaneously in lateral recumbency. After 45 min horses were hoisted using a single hoist-hobble system for 5 min and returned into left lateral recumbency. Heart rate (HR), respiratory rate (RR), and systolic (SAP), diastolic (DAP), and mean arterial blood pressures (MAP) were measured every minute starting from 5 min before to 5 min after hoisting. Arterial blood gas samples were collected before, during, and after hoisting. Results: Significant changes in hemodynamic parameters and PaO₂ but not PaCO₂ were found between baseline recordings and measurements obtained during and early after hoisting. The MAP decreased within the 1st min of hoisting from a mean of 74 ± 17 mmHg at baseline to 57 ± 20 mmHg (p < 0.05). Thereafter, it rapidly recovered to baseline before continuing to rise to higher than baseline values and then remaining elevated for 5 min after horses were returned into lateral recumbency. Simultaneously, the HR increased by 6-9 beats per min during the initial 3 min of hoisting before returning close to baseline values (p < 0.05). The PaO₂ decreased significantly from a mean of 324.9 ±137.0 mmHg at baseline to a mean of 141.3 ± 104.2 mmHg during hoisting (p < 0.001) without recovering any more to baseline values. Clinical significance: Hoisting an adult horse during or at the end of isoflurane anesthesia carries the risk of a precipitous, though short-lived (1-2 min), drop in arterial blood pressures and a persistent decrease in arterial oxygenation. While in systemically healthy animals the observed functional impairments were not life-threatening, they may be more severe in systemically compromised horses.Therefore, arterial blood pressures and oxygenation must be carefully monitored when hoisting sick equine patients during or at the end of inhalant anesthesia.

The effect of body position on intraocular pressure in anesthetized horses

OBJECTIVE

To evaluate the effect of four recumbent body positions on intraocular pressure (IOP) in anesthetized normal horses.

ANIMALS STUDIED

Ten nonglaucomatous adult horses.

PROCEDURES

Intraocular pressure was measured with a rebound tonometer in both eyes of standing sedated horses (baseline), then under general anesthesia during four randomized recumbent body positions, including Trendelenburg (Tr; 15-degree head down), reverse Trendelenburg (RTr; 15-degree head up), dorsal, and lateral; only the superior eye was measured in lateral positions. The mean of 3 IOP readings was taken at each position, allowing a minimum of 2 minutes of acclimatization after each position change before obtaining measurements. Repeated Measures Analysis with Newman-Keuls Multiple Comparison Post hoc was used to compare IOPs in different positions, and linear regression was used to compare IOP with age and weight cofactors.

RESULTS

When compared to baseline, the greatest change in IOP occurred in Tr (increase of 25.63 ± 8.12 mm Hg). When comparing all recumbent positions to baseline, IOP significantly increased in 3 of 4 body positions (P < .001), with no significant difference identified between RTr and baseline. When comparing all body positions to each other, the greatest IOP difference occurred between the Tr and the RTr positions (increase of 26.95 ± 5.41 mm Hg). Age and weight were not correlated with IOP in any position.

CONCLUSIONS

Recumbent body position significantly increases IOP in normal eyes of horses under injectable anesthesia.

Clinical effects of constant rate infusions of medetomidine-propofol combined with sevoflurane anesthesia in Thoroughbred racehorses undergoing arthroscopic surgery

Background

The aim of the present study was to evaluate clinical efficacy of constant rate infusions (CRIs) of medetomidine–propofol combined with sevoflurane anesthesia in Thoroughbred racehorses undergoing arthroscopic surgery. Thirty horses were sedated intravenously (IV) with medetomidine (6.0 μg/kg) and midazolam (0.02 mg/kg) and induced IV with ketamine (1.0 mg/kg) and propofol (1.0 mg/kg). These horses were randomly allocated to three groups and maintained with sevoflurane and CRI of either medetomidine (3.0 μg/kg/h) (Group M; n = 10); or medetomidine (3.0 μg/kg/h) and propofol (3.0 mg/kg/h) (Group MP3; n = 10); or medetomidine (3.0 μg/kg/h) and propofol (6.0 mg/kg/h) (Group MP6; n = 10). End-tidal sevoflurane concentration (ET_SEVO), cardiovascular parameters, plasma propofol concentration, and recovery time and quality were compared among groups. Data were analyzed by using ANOVA with Tukey’s multiple comparison test, considering P < 0.05 significant.

Results

ET_SEVO (%) was 2.4 ± 0.1 in Group M, 1.7 ± 0.2 in Group MP3, and 1.4 ± 0.2 in Group MP6; ET_SEVO declined significantly in a propofol-dose-dependent manner. The rates of dobutamine infusion (μg/kg/min) required to keep the mean arterial blood pressure over 70 mmHg were significantly lower in Group MP3 (0.20 ± 0.10) and Group MP6 (0.15 ± 0.06) than in Group M (0.37 ± 0.18). Recovery time and quality did not differ among groups. All horses in Group MP3 required only one attempt to stand, and recovery quality was excellent. Plasma propofol concentrations were stable throughout maintenance of anesthesia in Group MP3, whereas those in Group MP6 increased significantly with increasing duration of maintenance.

Conclusions

CRIs of medetomidine–propofol reduced the sevoflurane requirement for surgical anesthesia as the propofol dose increased, compared with a CRI of medetomidine alone. Additionally, the two propofol protocols provided good maintenance of cardiovascular function. CRIs of medetomidine (3.0 μg/kg/h) and propofol (3.0 mg/kg/h) resulted in excellent-quality recovery. This protocol could therefore be an especially useful additive to sevoflurane anesthesia in Thoroughbred racehorses undergoing arthroscopic surgery.

Clinical evaluation of constant rate infusion of alfaxalone-medetomidine combined with sevoflurane anesthesia in Thoroughbred racehorses undergoing arthroscopic surgery

Background

Alfaxalone has a number of pharmacological properties which are desirable for constant rate infusion (CRI). Previously, the co-administration of alfaxalone and medetomidine is shown to be suitable for short-term anesthesia in horses. However, the use of alfaxalone–medetomidine CRI with inhalational anesthesia under surgical procedures have not been investigated in clinical cases. The aim of the present study was to evaluate the clinical efficacy of alfaxalone–medetomidine CRI in sevoflurane-anesthetized Thoroughbred racehorses undergoing arthroscopic surgery. Sevoflurane requirement, cardiovascular function, and induction/recovery quality were compared between horses maintained with sevoflurane in combination with medetomidine CRI (3 µg/kg/h) (Group M; n = 25) and those maintained with sevoflurane in combination with alfaxalone–medetomidine CRI (0.5 mg/kg/h and 3 µg/kg/h, respectively) (Group AM; n = 25).

Results

The mean end-tidal sevoflurane concentrations were significantly lower in Group AM (1.8 ± 0.2%) than in Group M (2.4 ± 0.1%). The mean dobutamine infusion rate required for maintaining mean arterial blood pressure within the target values (60–80 mmHg) was significantly lower in Group AM (0.53 ± 0.20 µg/kg/min) than in Group M (0.85 ± 0.32 µg/kg/min). Induction and recovery scores were not significantly different between two groups. However, excitatory response during recovery were observed in five horses in Group AM. The mean plasma alfaxalone concentrations were stable throughout the maintenance period (0.77 ± 0.12 to 0.85 ± 0.13 µg/mL), and decreased significantly immediately after standing (0.32 ± 0.07 µg/mL).

Conclusions

Alfaxalone–medetomidine CRI reduced sevoflurane requirement by approximately 26% with good maintenance of cardiopulmonary function in Thoroughbred racehorses undergoing arthroscopic surgery. Sevoflurane in combination with alfaxalone–medetomidine CRI may be a clinically effective anesthetic technique for Thoroughbred racehorses. However, 20% of horses administered alfaxalone showed remarkable excitatory response during recovery. Greater attention to excitatory response may be advisable if alfaxalone is used for induction or maintenance of anesthesia. A larger study is needed to explore the clinical relevance of these findings.

Anesthetic management with sevoflurane combined with alfaxalone-medetomidine constant rate infusion in a Thoroughbred racehorse undergoing a long-time orthopedic surgery

A three-year old Thoroughbred racehorse was anesthetized with sevoflurane and oxygen inhalation anesthesia combined with constant rate infusion (CRI) of alfaxalone-medetomidine for internal fixation of a third metacarpal bone fracture. After premedication with intravenous (IV) injections of medetomidine (6.0 µg/kg IV), butorphanol (25 µg/kg IV), and midazolam (20 µg/kg IV), anesthesia was induced with 5% guaifenesin (500 ml/head IV) followed immediately by alfaxalone (1.0 mg/kg IV). Anesthesia was maintained with sevoflurane and CRIs of alfaxalone (1.0 mg/kg/hr) and medetomidine (3.0 µg/kg/hr). The total surgical time was 180 min, and the total inhalation anesthesia time was 230 min. The average end-tidal sevoflurane concentration during surgery was 1.8%. The mean arterial blood pressure was maintained above 70 mmHg throughout anesthesia, and the recovery time was 65 min. In conclusion, this anesthetic technique may be clinically applicable for Thoroughbred racehorses undergoing a long-time orthopedic surgery.

Comparison of equi-minimum alveolar concentration of sevoflurane and isoflurane on bispectral index values during both wash in and wash out phases: A prospective randomised study

BACKGROUND AND AIMS

At equal minimum alveolar concentration (MAC), volatile agents may produce different bispectral index (BIS) values especially at low BIS levels when the effect is volatile agent specific. The present study was performed to compare the BIS values produced by sevoflurane and isoflurane at equal MAC and thereby assessing which is a better hypnotic agent.

METHODS

Sixty American Society of Anaesthesiologists I and II patients undergoing elective mastoidectomy were divided into groups receiving either isoflurane or sevoflurane, and at equi-MAC. BIS value was measured during both wash in and wash out phase, keeping other parameters same. Statistical analysis was performed using the Friedman two-way analysis and Mann-Whitney U-test. A P < 0.05 was considered significant.

RESULTS

BIS value was significantly lower with sevoflurane at all MAC values as compared to isoflurane, except in the beginning and at MAC awake. However, both the drugs proved to be cardiostable.

CONCLUSION

At equi-MAC sevoflurane produces lower BIS values during wash in as well as wash out phase as compared to isoflurane, reflecting probably an agent specific effect and a deficiency in BIS algorithm for certain agents and their interplay.

Hemodynamic parameters of low-flow isoflurane and low-flow sevoflurane anesthesia during controlled ventilation with laryngeal mask airway

Background:

Nowadays laryngeal mask airway (LMA) is popular as one of the best choices for airway management. Low-flow anesthesia has some advantages like lower pollution, hemodynamic stability and cost effectiveness. Volatile anesthetics are widely used for anesthesia maintenance during operations. Sevoflurane has more hemodynamic stability compared to isoflurane, but there are few studies comparing the hemodynamic stabilities of these two anesthetics during controlled low flow anesthesia with LMA.

Objectives:

The aim of this study was to compare the effects of low-flow sevoflurane and low-flow isoflurane on hemodynamic parameters of patients through LMA.

Patients and Methods:

Eighty patients, scheduled for elective ophthalmic surgery, were randomly divided into two groups. After induction, an LMA with an appropriate size was inserted in all the patients and they were randomly allocated to two groups of low-flow sevoflurane (n = 40) and low-flow isoflurane (n = 40). Hemodynamic parameters (heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP) and Mean Arterial Pressure (MAP) were recorded at 5, 10, 15, 20, 25 and 30 minutes after the anesthesia induction.

Results:

The mean heart rate values were significantly less in the sevoflurane group (P value < 0.05) at 25 minutes after the surgery. The mean Blood Pressure in the isoflurane group was significantly higher compared with the sevoflurane group in 10, 20 and 30 minutes after the surgery (P values = 0.0131, 0.0373 and 0.0028, respectively). These differences were clinically unimportant because heart rate and mean blood pressure were on normal ranges.

Conclusions:

Seemingly, low-flow sevoflurane with LMA did not have any significant hemodynamic effect on clinical practice. Therefore, low-flow sevoflurane anesthesia with LMA might be considered in patients with short operations who need rapid recovery from anesthesia.

The cardiovascular effects of sevoflurane and isoflurane after premedication of healthy dogs undergoing elective surgery

Sevoflurane and isoflurane are commonly used in veterinary anesthesia. The objective of this prospective, randomized, open-label clinical study was to compare the cardiovascular effects of sevoflurane and isoflurane via direct arterial blood pressure measurements and the lithium dilution cardiac output (LDCO) on premedicated healthy dogs undergoing elective tibial plateau leveling osteotomy (TPLO). Nineteen client-owned dogs were included. All dogs were premedicated with hydromorphone (0.05 mg/kg IV and glycopyrrolate 0.01 mg/kg subcutaneously). Ten dogs were anesthetized with sevoflurane and nine dogs were anesthetized with isoflurane. Eighteen dogs were instrumented with a dorsal pedal arterial catheter, and one dog had a femoral arterial catheter. All dogs had continuous, direct systolic (SAP), diastolic (DAP), and mean arterial (MAP) blood pressure readings as well as heart rate (HR), cardiac output (CO), cardiac index (CI), systemic vascular resistance (SVR), systemic vascular resistance index (SVRI), stroke volume variation (SVV), and pulse pressure variation (PPV) recorded q 5 min during the surgical procedure. There was no significant statistical difference in all parameters between the sevoflurane and isoflurane treatment groups. Both sevoflurane and isoflurane inhalant anesthetics appear to have similar hemodynamic effects when used as part of a multimodal anesthetic protocol in premedicated healthy dogs undergoing an elective surgical procedure.

Cardiovascular effects of dobutamine and phenylephrine infusion in sevoflurane-anesthetized Thoroughbred horses

To determine dose-dependent cardiovascular effects of dobutamine and phenylephrine during anesthesia in horses, increasing doses of dobutamine and phenylephrine were infused to 6 healthy Thoroughbred horses. Anesthesia was induced with xylazine, guaifenesin and thiopental and maintained with sevoflurane at 2.8% of end-tidal concentration in all horses. The horses were positioned in right lateral recumbency and infused 3 increasing doses of dobutamine (0.5, 1.0 and 2.0 µg/kg/min) for 15 min each dose. Following to 30 min of reversal period, 3 increasing doses of phenylephrine (0.25, 0.5 and 1.0 µg/kg/min) were infused. Cardiovascular parameters were measured before and at the end of each 15-min infusion period for each drug. Blood samples were collected every 5 min during phenylephrine infusion period. There were no significant changes in heart rate throughout the infusion period. Both dobutamine and phenylephrine reversed sevoflurane-induced hypotension. Dobutamine increased both mean arterial blood pressure (MAP) and cardiac output (CO) as the result of the increase in stroke volume, whereas phenylephrine increased MAP but decreased CO as the result of the increase in systemic vascular resistance. Plasma phenylephrine concentration increased dose-dependently, and these values at 15, 30 and 45 min were 6.2 ± 1.2, 17.0 ± 4.8 and 37.9 ± 7.3 ng/ml, respectively.

Pulmonary gas exchange in anaesthetised horses mechanically ventilated with oxygen or a helium/oxygen mixture

REASON FOR PERFORMING STUDY

It is unknown whether administration of gas-mixtures high in inspired fraction of oxygen (FiO2) under general anaesthesia may increase formation of pulmonary atelectasis and impair gas exchange.

OBJECTIVE

To evaluate the effects of different FiO2 on pulmonary gas exchange in isoflurane-anaesthetised horses breathing a helium/oxygen (He/O2) mixture.

METHODS

Thirty healthy mature horses were sedated with i.v. acepromazine (0.02 mg/kg bwt), detomidine (0.002 mg/kg bwt) and xylazine (02-0.4 mg/kg bwt). General anaesthesia was induced with i.v. 5% guaifenesin to effect, diazepam (0.1 mg/kg bwt) and ketamine (2 mg/kg bwt), and maintained with isoflurane. Fifteen horses (Group HX) were ventilated mechanically with gas mixtures of successively increasing FiO2 (0.25-030, 0.50-0.55, > 0.90), obtained by blending 02 with Heliox (70% He/30% O2). The other 15 horses (Group O) were ventilated immediately with 100% O2 (FiO2 > 0.90). After 20 min of ventilation at the different FiO2 levels in Group HX and after 60 min in Group O, PaO2 and PaCO2 were measured and the alveolar to arterial PO2 gradient (P(A-a)O2) was calculated. Data analysis included robust categorical regression with clustering on horse (P < 0.05).

RESULTS

Inhalation of a He/O2 mixture with FiO2 as low as 0.25-030 ensured adequate arterial oxygenation and was associated with a smaller P(A-a)O2 gradient than inhalation of pure O2 (P < 0.05). In Group HX, PaO2 increased with each rise in FiO2 and so did P(A-a)O2 (P < 0.05). The PaO2 was significantly lower and the P(A-a)O2 higher in Group O compared to Group HX at a FiOz >0.90 (P < 0.05).

CONCLUSIONS AND POTENTIAL RELEVANCE

Administration of a He/O2 gas mixture low in FiO2 can better preserve lung function than ventilation with pure oxygen. A step-wise increase of FiO2 using a He/O2 gas mixture might offer advantages with respect to pulmonary gas exchange over an immediate exposure to 100% 2O2.