Nasal and tracheobronchial nitric oxide production and its influence on oxygenation in horses undergoing total intravenous anaesthesia

BACKGROUND

The present study aimed to investigate the effect of endotracheal intubation on nasal and tracheal endogenous NO concentrations, gas exchange and oxygenation in horses undergoing general anaesthesia. In many species a major part of physiological nitric oxide (NO) production takes place in the nasopharynx. Inhaled NO acts as a pulmonary vasodilator and regulates lung perfusion and endotracheal intubation bypasses the nasopharynx. Six horses were randomly assigned to either the "intubated" (INT) or the "non-intubated" (nINT) treatment group. Horses were premedicated with dexmedetomidine (5 μg/kg IV). Anaesthesia was induced with 2.5 mg/kg ketamine and 0.05 mg/kg diazepam IV, and it was maintained by administration of a triple-drip (100 mg/kg/h guaifenesin, 4 mg/kg/h ketamine, 7 μg/kg/h dexmedetomidine). The horses were spontaneously breathing room air. Heart rate, cardiac output, arterial blood pressure, pulmonary arterial blood pressures and respiratory rate were recorded during a 100-min anaesthesia period. Arterial, venous and mixed venous blood samples were taken every 10 minutes and analysed for partial pressure of oxygen (PO₂) and carbon dioxide (PCO₂), oxygen saturation and haemoglobin content. Standard oxygenation indices were calculated. Nasal and tracheal endogenous NO concentration was determined by chemiluminescence.

RESULTS

Cardiovascular variables, respiratory rate, PO₂, PCO₂, oxygen saturation, haemoglobin content, CaO₂, O₂ER, P_(a-ET)CO₂ and Q_s/Q_t did not differ significantly between the two treatment groups. The P_(A-a)O₂ was significantly higher in INT (6.1 ± 0.3 kPa) compared to nINT (4.9 ± 0.1 kPa) (p = 0.045), respectively. The nasal (8.0 ± 6.2 ppb) and tracheal (13.0 ± 6.3 ppb) endogenous NO concentration differed significantly in INT (p = 0.036), but not in nINT (nasal: 16.9 ± 9.0 ppb; tracheal: 18.5 ± 9.5 ppb) (p = 0.215).

CONCLUSION

Endotracheal intubation reduces the nasal and tracheal endogenous NO concentration. The influence on pulmonary gas exchange and oxygenation is negligible in horses breathing room air.

Recovery of horses from general anaesthesia: A systematic review (2000-2020) of the influence of anaesthetic protocol on recovery quality

BACKGROUND

The recovery phase after equine general anaesthesia (GA) is a time of considerable risk and therefore has been the subject of extensive research over the last 20 years. Various pharmacological interventions have been developed and studied with the objective of improving recovery quality and reducing anaesthetic-related mortality and morbidity. Nevertheless, some controversy remains regarding the influence of anaesthetic protocol choice on recovery quality from GA and its implications for recovery-related mortality and morbidity. A systematic review of the literature investigating the influence of anaesthetic protocol choice on recovery quality is currently lacking.

OBJECTIVES

To perform a detailed evaluation of the equine veterinary literature investigating the effect of anaesthetic protocol choice on equine recovery quality utilising the GRADE framework.

STUDY DESIGN

A systematic evaluation of the equine veterinary literature was performed using the GRADE framework.

METHODS

A literature search was performed and studies were assessed for eligibility by both authors utilising PRISMA guidelines. Studies meeting inclusion criteria were evaluated by both authors, categorically summarised and the quality of evidence for each sub-topic was assessed using the GRADE framework.

RESULTS

A total of 124 studies were identified which directly assessed the impact of anaesthetic protocol choice on recovery quality after GA in horses. Evaluation of the available evidence indicated that certain partial intravenous anaesthesia (PIVA) agents, cessation of intravenous lidocaine 30 minutes prior to recovery and provision of adequate analgesia improves recovery quality.

MAIN LIMITATIONS

The validity of the results of some studies may have been compromised by missing data and small sample sizes.

CONCLUSIONS

There is evidence to indicate that certain PIVA agents, cessation of intravenous lidocaine 30 minutes prior to recovery and provision of adequate analgesia improves recovery quality.

Total Intravenous Anaesthesia with Ketamine, Medetomidine and Midazolam as Part of a Balanced Anaesthesia Technique in Horses Undergoing Castration

To evaluate the use of ketamine-medetomidine-midazolam total intravenous infusion as part of a balanced anaesthetic technique for surgical castration in horses. Five healthy Standardbred cross colts were premedicated with IV acepromazine (0.01–0.02 mg/kg), medetomidine (7 µg/kg) and methadone (0.1 mg/kg) and anaesthesia induced with IV ketamine (2.2 mg/kg) and midazolam (0.06 mg/kg). Horses were anaesthetised for 40 min with an IV infusion of ketamine (3 mg/kg/h), medetomidine (5 µg/kg/h) and midazolam (0.1 mg/kg/h) while routine surgical castration was performed. Cardiorespiratory variables, arterial blood gases, and anaesthetic depth were assessed at 5 to 10 min intervals. Post-anaesthesia recovery times were recorded, and the quality of the recovery period was assessed. The anaesthetic period and surgical conditions were acceptable with good muscle relaxation and no additional anaesthetic required. The median (range) time from cessation of the infusion to endotracheal tube extubation, head lift and sternal recumbency were 17.2 (7–35) min, 25 (18.9–53) min and 28.1 (23–54) min, respectively. The quality of anaesthetic recovery was good, with horses standing 31.9 (28–61) min after the infusion was ceased. During anaesthesia, physiological variables, presented as a range of median values for each time point were: heart rate 37–44 beats/min, mean arterial pressure 107–119 mmHg, respiratory rate 6–13 breaths/min, arterial partial pressure of oxygen 88–126 mmHg, arterial partial pressure of carbon dioxide 52–57 mmHg and pH 7.36–7.39. In conclusion, the co-administration of midazolam, ketamine and medetomidine as in IV infusion, when used as part of a balanced anaesthetic technique, was suitable for short term anaesthesia in horses undergoing castration.

Evaluation of intramuscular anesthetic protocols in healthy domestic horses

OBJECTIVE

To assess anesthetic induction, recovery quality and cardiopulmonary variables after intramuscular (IM) injection of three drug combinations for immobilization of horses.

STUDY DESIGN

Randomized, blinded, three-way crossover prospective design.

ANIMALS

A total of eight healthy adult horses weighing 470-575 kg.

METHODS

Horses were administered three treatments IM separated by ≥1 week. Combinations were tiletamine-zolazepam (1.2 mg kg^-1), ketamine (1 mg kg^-1) and detomidine (0.04 mg kg^-1) (treatment TKD); ketamine (3 mg kg^-1) and detomidine (0.04 mg kg^-1) (treatment KD); and tiletamine-zolazepam (2.4 mg kg^-1) and detomidine (0.04 mg kg^-1) (treatment TD). Parametric data were analyzed using mixed model linear regression. Nonparametric data were compared using Skillings-Mack test. A p value <0.05 was considered statistically significant.

RESULTS

All horses in treatment TD became recumbent. In treatments KD and TKD, one horse remained standing. PaO₂ 15 minutes after recumbency was significantly lower in treatments TD (p < 0.0005) and TKD (p = 0.001) than in treatment KD. Times to first movement (25 ± 15 minutes) and sternal recumbency (55 ± 11 minutes) in treatment KD were faster than in treatments TD (57 ± 17 and 76 ± 19 minutes; p < 0.0005, p = 0.001) and TKD (45 ± 18 and 73 ± 31 minutes; p = 0.005, p = 0.021). There were no differences in induction quality, muscle relaxation score, number of attempts to stand or recovery quality.

CONCLUSIONS AND CLINICAL RELEVANCE

In domestic horses, IM injections of tiletamine-zolazepam-detomidine resulted in more reliable recumbency with a longer duration when compared with ketamine-detomidine and tiletamine-zolazepam-ketamine-detomidine. Recoveries were comparable among protocols.

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.

Total intravenous anaesthesia with ketamine, medetomidine and guaifenesin compared with ketamine, medetomidine and midazolam in young horses anaesthetised for computerised tomography

BACKGROUND

There is no information directly comparing midazolam with guaifenesin when used in combination with an alpha-2 agonist and ketamine to maintain anaesthesia via i.v. infusion in horses.

OBJECTIVES

To compare ketamine-medetomidine-guaifenesin with ketamine-medetomidine-midazolam for total intravenous anaesthesia (TIVA) in young horses anaesthetised for computerised tomography.

STUDY DESIGN

Prospective, randomised, blinded, crossover trial.

METHODS

Fourteen weanlings received medetomidine 7 μg/kg bwt i.v. and anaesthesia was induced with ketamine 2.2 mg/kg bwt i.v. On two separate occasions horses each received infusions of ketamine 3 mg/kg bwt/h, medetomidine 5 μg/kg bwt/h, guaifenesin 100 mg/kg bwt/h (KMG) or ketamine 3 mg/kg bwt/h, medetomidine 5 μg/kg bwt/h, midazolam 0.1 mg/kg bwt/h (KMM) for 50 min. Cardiorespiratory variables and anaesthetic depth were assessed every 5-10 min. Recovery times after the infusions ceased were recorded and recovery quality was assessed using a composite score system (CSS), simple descriptive scale (SDS) and visual analogue scale (VAS). Multivariable models were used to generate mean recovery scores for each treatment and each recovery score system and provide P-values comparing treatment groups.

RESULTS

Anaesthesia was uneventful with no difference in additional anaesthetic requirements and little clinically relevant differences in cardiopulmonary variables between groups. All horses recovered without incident with no significant difference in recovery times. Quality of the anaesthetic recovery was significantly better for the KMM group compared with the KMG group using the CSS (P<0.001), SDS (P<0.001) and VAS (P<0.001).

MAIN LIMITATIONS

No surgical stimulus was applied and study animals may not represent general horse population.

CONCLUSION

Midazolam is a suitable alternative to guaifenesin when co-infused with ketamine and medetomidine for anaesthesia in young horses undergoing noninvasive procedures. Both infusions produce a clinically comparable quality of anaesthesia; however, recovery from anaesthesia is of a better quality following an infusion of ketamine-medetomidine-midazolam.

Cardiopulmonary effects and recovery characteristics of horses anesthetized with xylazine-ketamine with midazolam or propofol

OBJECTIVE

To evaluate cardiopulmonary and recovery characteristics of horses administered total intravenous anesthesia (TIVA) with xylazine and ketamine combined with midazolam or propofol.

STUDY DESIGN

Randomized crossover study.

ANIMALS

A group of eight adult horses, aged 7-22 years, weighing 493-740 kg.

METHODS

Horses were administered xylazine (1 mg kg^-1) intravenously (IV), and anesthesia was induced with ketamine (2.2 mg kg^-1) IV. Anesthesia was maintained for 45 minutes via IV infusion of xylazine (0.016 mg kg^-1 minute^-1) and ketamine (0.03 mg kg^-1 minute^-1) combined with midazolam at 0.002 mg kg^-1 minute^-1 (MKX), propofol at 0.05 mg kg^-1 minute^-1 (PKX_low) or propofol at 0.1 mg kg^-1 minute^-1 (PKX_high). Additional ketamine was administered if a horse moved spontaneously. Cardiopulmonary variables, blood gases, lactate concentration, packed cell volume and total solids were recorded before sedation (baseline), at 10, 20, 30 and 45 minutes during TIVA and 10 minutes after standing. Recovery variables and quantitative recovery scores were compared. Significance was set at p < 0.05.

RESULTS

Additional ketamine was required for 50% of MKX horses. Systolic arterial pressure was elevated in MKX at 20 minutes compared with baseline (p = 0.043), at 10 and 20 minutes compared with PKX_high (p = 0.007, p = 0.024) and at 20 and 30 minutes compared with PKX_low (p = 0.009, p = 0.02). MKX horses (5/8) were hypertensive compared with PKX_low (1/8; p = 0.017). All horses became hypoxemic (PaO₂ ≤80 mmHg; 10.7 kPa) during TIVA. Recovery variables did not differ among treatments.

CONCLUSIONS AND CLINICAL RELEVANCE

PKX_low and PKX_high had similar cardiopulmonary and recovery performance compared with MKX. PKX combinations provided superior quality of anesthesia to that of MKX. A combination of propofol, ketamine and xylazine administered as TIVA can be used in horses to provide anesthesia for short procedures. Supplemental oxygen is recommended.

Partial intravenous anaesthesia in the horse: a review of intravenous agents used to supplement equine inhalation anaesthesia. Part 1: lidocaine and ketamine

OBJECTIVE

To review the literature with regard to the use of different intravenous agents as supplements to inhalational anaesthesia in horses. These drugs include lidocaine, ketamine, opioids and α2 -agonists. The Part 1 of this review will focus in the use of lidocaine and ketamine.

DATABASES USED

Pubmed & Web of Science. Search terms: horse, inhalant anaesthesia, balanced anaesthesia, partial intravenous anaesthesia, lidocaine, ketamine.

CONCLUSIONS

Different drugs and their combinations can be administered systemically in anaesthetized horses, with the aim of reducing the amount of the volatile agent whilst improving the recovery qualities and providing a multimodal analgesic approach. However, full studies as to whether these techniques improve cardiopulmonary status are not always available and potential disadvantages should also be considered.

Effects of dexmedetomidine and xylazine on cardiovascular function during total intravenous anaesthesia with midazolam and ketamine and recovery quality and duration in horses

OBJECTIVES

To compare cardiovascular effects and recovery quality and duration of total intravenous anaesthesia (TIVA) with xylazine-ketamine-midazolam or dexmedetomidine-ketamine-midazolam.

STUDY DESIGN

Prospective, randomized experimental cross-over trial.

ANIMALS

Eight adult warmblood horses.

METHODS

After sedation with acepromazine and either xylazine [0.5 mg kg(-1) , intravenously (IV)] or dexmedetomidine (3.5 μg kg(-1) IV) anaesthesia was induced with ketamine and midazolam and maintained with a constant rate infusion (CRI) of xylazine (1 mg kg(-1)  hour(-1) ) [XKM] or dexmedetomidine (7 μg kg(-1)  hour(-1) ) [DKM] in combination with midazolam (0.1 mg kg(-1)  hour(-1) ), and ketamine infusion (initially 3 mg kg(-1)  hour(-1) ) for 120 minutes. Ketamine infusion rate was increased in response to positive reactions to electrical nociceptive stimulation performed every 30 minutes. Heart rate (HR), mean arterial blood pressure (MAP) and cardiac output (Q˙t) were measured before treatment (baseline), after sedation (not Q˙t), and during anaesthesia. Xylazine, dexmedetomidine, midazolam and ketamine kinetics were calculated, from plasma drug concentrations. Twenty minutes after end of TIVA, flumazenil (0.01 mg kg(-1) IV) was administered. Recovery quality and duration were assessed. Two-way analysis of variance with repeated measurements or Wilcoxon signed rank test as relevant were used to analyse data with an alpha of 5%.

RESULTS

Compared to baseline, MAP did not change, while similar, but limited, decreases in HR and Q˙t were observed in both TIVA's. Mean ketamine doses of 3.7 mg kg(-1)  hour(-1) were required with both treatments. Plasma concentrations of dexmedetomidine and xylazine showed high intra- and inter-individual changes with elimination half-lifes of 46 ± 7 minutes and 64 ± 13 minutes, respectively. Recovery quality was good to excellent with mean duration of 37 ± 16 and 46 ± 21 minutes after stopping TIVA with XKM and DKM, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

Both drug combinations are suitable to maintain anaesthesia for two hours, with good cardiovascular and good to excellent recovery conditions.