The effects of halothane and isoflurane on cardiovascular function in laterally recumbent horses

Sevoflurane versus isoflurane in shoulder arthroscopy in beach chair position in patients with prior interscalene brachial plexus block: A prospective randomised equivalency-based haemodynamic evaluation trial

Background and Aims:

There is a paucity of literature on comparative effects of different inhalational anaesthetics in beach chair position (BCP) for shoulder arthroscopy. We aimed to investigate and compare the haemodynamic effects, anaesthetic and surgical outcomes between two inhalational agents.

Methods:

In this randomised study, patients of age 18–60 years, were allotted to two groups (29, sevoflurane and 28, isoflurane) and received protocol-based anaesthesia. Intraoperatively, different haemodynamic and other data were recorded.

Results:

All mean of averages of individual subject's vitals were comparable between the groups [P = 0.681, 0.325, 0.803, and 0.051, respectively for systolic blood pressure (SBP), diastolic blood pressure (DBP), mean blood pressure (MBP) and heart rate (HR)]. Higher mean HR was recorded for maximum readings of isoflurane (P = 0.028). Equivalency was observed for SBP, MBP, and DBP (P = 0.000, 002, and 0.027, respectively). Process capability indices indicated that sevoflurane had better values (Pp: 0.55 versus 0.41, Ppk: 0.35 versus 0.22) for SBP as with MBP (Pp: 0.62 versus 0.51, Ppk: 0.36 versus 0.33). For achieving optimal vision, higher pump pressures (PPs) were demanded by surgeon (P = 0.025) and higher differences observed between initial and highest PPs (P = 0.027), in isoflurane subjects. Multivariable analysis revealed that no continuous predictor was able to predict the quality of vision except additional pump flow factor, for both groups.

Conclusion:

Both inhalational agents demonstrated equivalent haemodynamic effects. Increased arthroscopic PP requirements were observed with isoflurane anaesthesia. Sevoflurane may be superior to isoflurane during BCP arthroscopy.

Isoflurane versus sevoflurane with interscalene block for shoulder arthroscopic procedures: Value of process capability indices as an additional tool for data analysis

BACKGROUND AND AIMS

Hypotensive anaesthesia reduces intra-articular bleed and promotes visualisation during arthroscopy. The haemodynamic effects of inhalational agents isoflurane and sevoflurane were studied extensively, and both were found to reduce mean arterial pressures (MBP) to an equivalent magnitude. We investigated the relative ability of isoflurane vis-a-vis sevoflurane to maintain the target systolic blood pressure (SBP) in patients undergoing shoulder arthroscopic procedures.

METHODS

In a prospective randomised study, 59 patients in two groups of 30 and 29 patients each received concomitant general anaesthesia (1.2-1.5 MAC of isoflurane and sevoflurane) and interscalene brachial plexus block. Nitrous oxide was used in both groups. Intraoperatively, serial blood pressure recordings of SBP, diastolic blood pressure (DBP), MBP and heart rates were done at every 3^rd min intervals. The manipulations needed to achieve target SBP (T = 90 mmHg) for optimal arthroscopic visualisation and treat unacceptable hypotensive episodes were noted. Conventional statistical tests and process capability index (PCI) evaluation were both deployed for data analysis.

RESULTS

Lower mean SBP and DBPs were recorded for isoflurane patients as compared to sevoflurane (P < 0.05, for mean, maximum and minimum recordings). Higher mean heart rates were recorded for isoflurane (P < 0.05). PCIs indicated that isoflurane was superior to sevoflurane in the ease of achieving target SBP of 90 mmHg as well as maintaining blood pressures in the range of 80-100 mmHg.

CONCLUSION

Isoflurane provides better intraoperative haemodynamic status vis-a-vis sevoflurane in patients undergoing shoulder arthroscopic surgery with preliminary interscalene blockade. The PCI can be a useful additional medical data analysis tool.

A study of measurement of noninvasive blood pressure with the oscillometric device, Sentinel, in isoflurane-anaesthetized horses

OBJECTIVE

To assess accuracy of noninvasive blood pressure (NIBP) measured by oscillometric device Sentinel compared to invasive blood pressure (IBP) in anaesthetized horses undergoing surgery. To assess if differences between the NIBP measured by the Sentinel and IBP are associated with recumbency, cuff placement, weight of the horse or acepromazine premedication and to describe usefulness of the Sentinel.

STUDY DESIGN

Prospective study examining replicates of simultaneous NIBP and IBP measurements.

ANIMALS

Twenty-nine horses.

METHODS

Invasive blood pressure was measured via a catheter in the facial artery, transverse facial artery or metatarsal artery. NIBP was measured using appropriate size cuffs placed on one of two metacarpal or metatarsal bones or the tail in random order. With both techniques systolic (SAP), mean (MAP), and diastolic (DAP) arterial blood pressures and heart rates (HR) were recorded. A mixed effects model compared the IBP to the NIBP values and assessed potential effects of catheter placement, localisation of the cuffs in combination with recumbency, weight of the horse or acepromazine premedication.

RESULTS

Noninvasive blood pressure yielded higher measurements than IBP. Agreement varied with recumbency and cuff position. Estimated mean differences between the two methods decreased from SAP (lateral recumbency: range -5.3 to -56.0 mmHg; dorsal recumbency: range 0.8 to -20.7 mmHg), to MAP (lateral recumbency: range -1.8 to -19.0 mmHg; dorsal recumbency: range 13.9 to -16.4 mmHg) to DAP (lateral recumbency: range 0.5 to -6.6 mmHg; dorsal recumbency: range 21.0 to -15.5 mmHg). NIBP measurement was approximately two times more variable than IBP measurement. No significant difference between IBP and NIBP due to horse's weight or acepromazine premedication was found. In 227 of 1047 (21.7%) measurements the Sentinel did not deliver a result.

CONCLUSION AND CLINICAL RELEVANCE

According to the high variability of NIBP compared to IBP, NIBP measurements as measured by the Sentinel in the manner described here are not considered as an appropriate alternative to IBP to measure blood pressure in anaesthetized horses.

Effect of general anesthesia on plasma cardiac troponin I concentrations in healthy horses

OBJECTIVE

To evaluate the effect of general anesthesia on plasma cTnI concentrations in horses.

ANIMALS, MATERIALS AND METHODS

Thirty-two horses undergoing general anesthesia and either elective surgery or MRI without surgery were prospectively studied. Twenty-nine horses (22 surgical, 7 imaging) completed the study. Plasma cTnI concentrations were determined prior to anesthesia and at 6, 12 and 24 h following discontinuation of the inhalant anesthetic.

RESULTS

All horses had cTnI values within the reference range at all time points. Six horses (21%) developed detectable cTnI 6 or 12 h following anesthesia. Risk factors for detectable cTnI include increasing age and dorsal recumbency. Horses with detectable cTnI had significantly lower mean and diastolic arterial blood pressures than those without detectable cTnI.

CONCLUSION

Uncomplicated general anesthesia with or without surgery does not result in cardiac troponin I elevations above the reference range in the first 24 h postoperatively.

Short-term effects of ketamine and isoflurane on left ventricular ejection fraction in an experimental Swine model

Background. General anesthesia is an essential element of experimental medical procedures. Ketamine and isoflurane are agents commonly used to induce and maintain anesthesia in animals. The cardiovascular effects of these anesthetic agents are diverse, and the response of global myocardial function is unknown. Methods. In a series of 15 swine, echocardiography measurements of left ventricular ejection fraction (LVEF) were obtained before the animals received anesthesia (baseline), after an intramuscular injection of ketamine (postketamine) and after inhaled isoflurane (postisoflurane). Results. The mean LVEF of an unanesthetized swine was 47 ± 3%. There was a significant decrease in the mean LVEF after administration of ketamine to 41 + 6.5% (P = 0.003). The addition of inhaled isoflurane did not result in further decrease in mean LVEF (mean LVEF 38 ± 7.2%, P = 0.22). Eight of the swine had an increase in their LVEF with sympathetic stimulation. Conclusions. In our experimental model the administration of ketamine was associated with decreased LV function. The decrease may be largely secondary to a blunting of sympathetic tone. The addition of isoflurane to ketamine did not significantly change LV function. A significant number of animals had returned to preanesthesia LV function with sympathetic stimulation.

Factors affecting the relationship between arterial and end-tidal carbon dioxide pressures in the anaesthetised horse

OBJECTIVE

To assess the effects of the duration of anaesthesia, position of recumbency, mode of ventilation, anaesthetic drug protocol, patient age and type of surgical procedure on the usefulness of capnometry as a measure of the partial pressure of arterial carbon dioxide (P(a)co(2)) during general anaesthesia in horses.

DESIGN

A prospective study compared the P(a)co(2) values with those of partial pressure of end-tidal carbon dioxide (ETco(2)) in horses anaesthetised for elective or emergency surgical procedures. The difference between P(a)co(2) and ETco(2) (P(a)co(2)- ETco(2)) and the physiological dead space to tidal volume ratio (V(D)/V(T)) were calculated. The effects of the study parameters on these variables was determined.

RESULTS

The agreement between P(a)co(2) and ETco(2) was poor. P(a)co(2)- ETco(2) and V(D)/V(T) during the first 60 min of anaesthesia was significantly less than after 60 min of anaesthesia. Mode of ventilation, position of recumbency, anaesthetic drug protocol, patient age and type of procedure did not have a significant affect on either value.

CONCLUSIONS

P(a)co(2)- ETco(2) in anaesthetised horses can be large, making ETco(2) unreliable as a predictor of P(a)co(2) and for assessment of pulmonary ventilation. For anaesthesia lasting less than 60 min at least one blood gas analysis of an arterial blood sample is required to assess P(a)co(2)- ETco(2). Arterial blood gas analysis should be repeated after 60 min of general anaesthesia.

Cardiovascular assessment in horses sedated with xylazine or amitraz

Cardiovascular effects due to intravenous (IV) xylazine (1.0mg/kg) or amitraz (0.1 or 0.4mg/kg) were evaluated in horses. Left ventricular function indexes, heart rate (HR), and cardiac output (CO) were measured by echocardiography. Second degree atrioventricular (AV) block was detected by electrocardiography. Invasive arterial blood pressure (AP) was also evaluated. All parameters were measured immediately before and during 60 minutes after drug injection. HR, CO, and second degree AV block were different between xylazine and amitraz-0.4mg/kg groups. Xylazine induced initial hypertension 10 minutes after injection, and hypotension was observed 30 minutes after amitraz-0.4mg/kg administration. Except for the second degree AV block which occurred only at five minutes, there was no change in the echocardiographic measurements after administration of amitraz-0.1mg/kg. Thus, amitraz-0.4mg/kg and xylazine (1.0mg/kg) induced similar cardiovascular side effects, but long-lasting action of amitraz-0.4mg/kg in the cardiovascular system was observed.

A clinical comparison of two anaesthetic protocols using lidocaine or medetomidine in horses

OBJECTIVE

To compare the effects of two balanced anaesthetic protocols on end-tidal isoflurane (Fe'ISO), cardiopulmonary performance and quality of recovery in horses.

DESIGN

Prospective blinded randomized clinical study.

ANIMALS

Sixty-nine client-owned horses, American Society of Anesthesiologists category I and II, undergoing elective surgery.

METHODS

The horses were premedicated with acepromazine (0.03 mg kg(-1)) IM 30-60 minutes before induction of anaesthesia and were randomly assigned to one of two treatments: in group L (37 horses) xylazine (1 mg kg(-1)) and in group M (31 horses) medetomidine (7 microg kg(-1)) was administered IV for sedation. Anaesthesia was induced 5 minutes later with ketamine (2.2 mg kg(-1)) and diazepam (0.02 mg kg(-1)) IV and maintained with isoflurane in oxygen/air (initial FIO2 0.40-0.50) and a constant rate infusion (CRI) of either lidocaine (2 mg kg(-1)/15 minutes loading dose followed by 50 microg kg(-1) minute(-1)) (group L) or medetomidine (3.5 microg kg(-1) hour(-1)) (group M). If horses showed movement or nystagmus, additional thiopental or ketamine was administered. Heart rate, mean arterial pressure (MAP), Fe'ISO and arterial blood gases were measured. Cardiac output was measured with the lithium dilution method in 10 (group L) and 11 (group M) horses every 45 minutes. Recovery was scored.

RESULTS

Heart rate and the cardiac index (CI) were significantly higher in group L with changes over time. In group M, MAP was significantly higher during the first 50 minutes. Group L needed more additional ketamine and thiopental to maintain a surgical plane of anaesthesia and Fe'ISO was significantly higher from 70 minutes. Recovery was longer in group M and of better quality. The significance level was set at p < 0.05.

CONCLUSIONS AND CLINICAL RELEVANCE

In group M, maintenance of stable anaesthetic depth was easier and lower Fe'ISO was required to maintain a surgical plane of anaesthesia. Recoveries were longer but of better quality. The CI was higher in group L but cardiovascular function was generally well maintained in both groups.

Comparison of noninvasive cardiac output measured by use of partial carbon dioxide rebreathing or the lithium dilution method in anesthetized foals

OBJECTIVE

To compare cardiac output (CO) measured by use of the partial carbon dioxide rebreathing method (NICO) or lithium dilution method (LiDCO) in anesthetized foals.

SAMPLE POPULATION

Data reported in 2 other studies for 18 neonatal foals that weighed 32 to 61 kg.

PROCEDURES

Foals were anesthetized and instrumented to measure direct blood pressure, heart rate, arterial blood gases, end-tidal isoflurane and carbon dioxide concentrations, and CO. Various COs were achieved by administration of dobutamine, norepinephrine, vasopressin, phenylephrine, and isoflurane to allow comparisons between LiDCO and NICO methods. Measurements were obtained in duplicate or triplicate. We allowed 2 minutes between measurements for LiDCO and 3 minutes for NICO after achieving a stable hemodynamic plane for at least 10 to 15 minutes at each CO.

RESULTS

217 comparisons were made. Correlation (r = 0.77) was good between the 2 methods for all determinations. Mean +/- SD measurements of cardiac index for all comparisons with the LiDCO and NICO methods were 138 +/- 62 mL/kg/min (range, 40 to 381 mL/kg/min) and 154 +/- 55 mL/kg/min (range, 54 to 358 mL/kg/min), respectively. Mean difference (bias) between LiDCO and NICO measurements was -17.3 mL/kg/min with a precision (1.96 x SD) of 114 mL/kg/min (range, -131.3 to 96.7). Mean of the differences of LiDCO and NICO measurements was 4.37 + (0.87 x NICO value).

CONCLUSIONS AND CLINICAL RELEVANCE

The NICO method is a viable, noninvasive method for determination of CO in neonatal foals with normal respiratory function. It compares well with the more invasive LiDCO method.