Evaluation of pulse co-oximetry to determine haemoglobin saturation with oxygen and haemoglobin concentration in anaesthetized horses: a retrospective study.

OBJECTIVE: This study compared the values of variables measured by pulse co-oximetry (Masimo Radical 7; Masimo Europe Limited, UK) with those measured by a co-oximeter-enabled blood gas analyser (Siemens Rapid-point 500; Siemens Healthcare Limited, UK) in anaesthetized horses. STUDY DESIGN: Retrospective study. ANIMALS: A total of 30 anaesthetized horses. METHODS: In total, 47 heparinized arterial blood samples were collected for blood gas analysis to determine haemoglobin concentration (tHb, g L-1) and percentage of haemoglobin saturation with oxygen (SaO2). Arterial haemoglobin saturation with oxygen was determined noninvasively by pulse co-oximetry (Masimo SpO2). Pulse co-oximetry also provided arterial haemoglobin concentration (SpHb) and arterial oxygen content (SpCaO2). Arterial oxygen content was calculated (CaO2) in 39 samples using SaO2 and the value of Hüfner's constant used by Masimo Radical 7 (1.3 mL g-1). Data were compared using Bland-Altman analysis, correlation tests, accuracy root mean square (ARMS) statistics and total allowable error, where available. RESULTS: Low bias but wide limits of agreement (LoA) were found between Masimo SpO2 and SaO2 (bias = -1.4%, LoA = -4.0 to 1.3%), with an ARMS of 3%. Compared with tHb, SpHb showed low bias (6.2 g L-1) but wide LoA (-39.6 to 52.6 g L-1); its % bias (5.2%) was still within the 7% limits recommended by the Clinical Laboratory Improvement Amendments (CLIA) for humans. When comparing SpCaO2 and CaO2, the bias and LoA were -0.2 mL dL-1 and -6.7 to 6.2 mL dL-1, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: Masimo SpO2 was acceptable for current ARMS standards, and SpHb measurements also met CLIA limits. The wide LoA in this study, however, suggest that the Masimo Radical 7 cannot be recommended as a substitute for direct measurements. As blood gas machines, pulse oximeters and co-oximeters use algorithms based on human haemoglobin, no true gold standard exists for horses.

Local anaesthetics or their combination with morphine and/or magnesium sulphate are toxic for equine chondrocytes and synoviocytes in vitro.

BACKGROUND: Chondrotoxic effects of local anaesthetics are well reported in humans and some animal species but knowledge on their toxic effects on synoviocytes or equine chondrocytes or the effects on cellular production of inflammatory cytokines is limited. The purpose of this study was to evaluate the in vitro effects of local anaesthetics, morphine, magnesium sulphate (MgSO4) or their combinations on cell viability and pro-inflammatory cytokine gene expression of equine synoviocytes and chondrocytes. Equine synoviocytes and cartilage explants harvested from normal joints in a co-culture system were exposed to mepivacaine (4.4 mg/ml), bupivacaine (2.2 mg/ml), morphine (2.85 mg/ml) and MgSO4 (37 mg/ml) alone or each local anaesthetic plus morphine or MgSO4 or both together. Chondrocyte and synoviocyte cell viability was assessed by CellTiter-Glo Luminescent Cell Viability Assay. Synoviocyte gene expression of IL-1ß, IL-6 or TNF-α was measured and compared using the ∆∆CT method. RESULTS: Morphine alone, MgSO4 alone or their combination did not alter cell viability or the expression of IL-1ß, IL-6 or TNF-α. However, local anaesthetics alone or in combination with morphine and/or MgSO4 reduced cell viability and increased the gene expression of IL-1ß, IL-6 or TNF-α. Single short exposure to local anaesthetics is toxic to both chondrocytes and synoviocytes and their combination with morphine and/or MgSO4 enhanced the cytotoxic effects. CONCLUSIONS: This in vitro study gives further evidence of the absence of cytotoxic effects of morphine alone, MgSO4 alone or their combination on normal articular tissues. However, local anaesthetics alone or in combination with morphine and/or MgSO4 have cytotoxic effects on equine articular tissues.

Comparison of the spread of two different volumes of contrast medium when performing ultrasound-guided transversus abdominis plane injection in dog cadavers.

OBJECTIVES: To compare, via CT imaging, the spread of different volumes of diluted iodinated contrast medium in the transversus abdominis muscle plane of dog cadavers. METHODS: Prospective, randomised study. An electro stimulation or a SonoTAP needle was inserted in plane with the ultrasound beam in the fascia between the internal oblique and transversus abdominis muscles. A test dose of 1 ml of diluted contrast (30 mg/mL iohexol) was injected to confirm positioning, followed by 0 · 5 mL/kg (n=14) or 1 mL/kg (n=12) and the distribution of the fluid compared. RESULTS: Contrast medium was identified exclusively in the transversus abdominis plane in 19 of 26 dogs. In one dog, the contrast lay between the external and internal oblique muscles and partially in three dogs. Intraperitoneal contrast was detected in 6 of 26 dogs (23%). No significant differences were found in the dorso-ventral or cranio-caudal spread or area of distribution but a significant difference was found in the transverse spread. There was an association between poor ultrasound visualisation of the tip of the needle and intraperitoneal injection. CLINICAL SIGNIFICANCE: Injection of 1 mL/kg of diluted contrast did not result in wider cranio-caudal spread in the transversus abdominis muscle plane of dog cadavers when compared with 0 · 5 mL/kg. Intraperitoneal injection is a risk and might be reduced with good needle visualisation.

Clinical significance of granulation tissue after transoral laser microsurgery for glottic cancer.

BACKGROUND: Granulation tissue after transoral laser microsurgery can make it difficult to distinguish between normal healing and tumour recurrence. MATERIALS AND METHODS: We carried out a retrospective analysis of 316 consecutive glottic carcinomas (Tis-T3). Presence of granulation tissue at one and six months was correlated with demographic and clinical data, tumour and surgical characteristics, and tumour relapse. RESULTS: Granulation tissue appeared in 53.8 per cent of patients at month 1, resolving spontaneously in 41.8 per cent. Revision surgery was performed in 60.1 per cent and was effective in 41.1 per cent. At month 6, 14.9 per cent of patients presented with granulation tissue. In 74.5 per cent the tissue was surgically removed and was positive for malignancy in 62.9 per cent. Tumour relapse presented in 29.4 per cent with granulation tissue at month 1 and in 61.7 per cent at month 6 (p = 0.000). Granulation tissue at month 1 correlated with thyroid cartilage exposure and continued smoking. At month 6, granulation tissue correlated with thyroid cartilage exposure, the affected surgical margins and diabetes. CONCLUSION: Granulation tissue after transoral laser microsurgery is frequent. When it persists at six months, revision surgery is formally recommended.

Clinical and pharmacokinetic effects of regional or general anaesthesia on intravenous regional limb perfusion with amikacin in horses.

REASONS FOR PERFORMING STUDY: Antimicrobial i.v. regional limb perfusion (IV-RLP) is clinically performed on anaesthetised or sedated horses with or without regional anaesthesia. To date, no scientific data are available on the clinical and pharmacokinetic effects of these anaesthetic protocols on antimicrobial IV-RLP, which is believed to result in better tourniquet efficiency due to decreased movement. OBJECTIVE: To determine the effects of regional or general anaesthesia on the clinical and synovial pharmacokinetic parameters of amikacin administered by IV-RLP to horses. STUDY DESIGN: Experimental crossover study. METHODS: Eight healthy horses received 4 treatments of amikacin IV-RLP in a randomised, blinded, crossover design: standing sedation without regional anaesthesia (CNT); standing sedation with i.v. regional anaesthesia; standing sedation with perineural regional anaesthesia (PNA); or general anaesthesia. Synovial fluid amikacin concentrations were measured over 24 h and regional pharmacokinetic parameters calculated. Heart and respiratory rates, visual analogue scale of discomfort, number of times the limb was lifted and number of additional sedations administered were recorded. Analysis of variance crossover analysis was applied with significance level at P < 0.05. RESULTS: Amikacin concentrations and regional pharmacokinetic parameters did not differ significantly among treatments. Visual analogue scores (mean ± s.d.) were significantly lower with PNA (19 ± 15) vs. i.v. regional anaesthesia (69 ± 36) or CNT (81 ± 13; P < 0.001). Significantly less lifting of the limb (mean ± s.d.) occurred with PNA (20 ± 20) vs. CNT (54 ± 22; P < 0.04). CONCLUSIONS: Perineural regional anaesthesia before IV-RLP was most effective in providing comfort to standing, sedated horses without significantly affecting the regional pharmacokinetic parameters of amikacin. High variability of synovial amikacin concentrations was present. The use of general anaesthesia for IV-RLP is not justified based on this study.

Use of near-infrared spectroscopy to identify trends in regional cerebral oxygen saturation in horses.

REASONS FOR PERFORMING STUDY: Alterations in cerebral haemodynamics may contribute to perianaesthetic complications in horses. Near-infrared spectroscopy (NIRS) is frequently used intraoperatively in man to provide information regarding cerebral perfusion. OBJECTIVES: To determine whether NIRS can identify trends in regional cerebral oxygen saturation (rSO2) in horses and whether there is a correlation between rSO2 and venous oxygen tensions. METHODS: A cerebral oximeter sensor recorded rSO2 from the dorsal sagittal sinus of 6 healthy horses. Values for rSO2, arterial and venous oxygen and carbon dioxide tensions (PaO2, PvO2, PaCO2 and PvCO2 respectively), along with arteriovenous oxygen saturations (SavO2) were recorded in unsedated (recording period [RP] 1), sedated (RP2) and anaesthetised horses (RP3-5) and during recovery (RP6-8). During anaesthesia, horses were ventilated to achieve states of normo- (RP3), hyper- (RP4) and hypocapnoea (RP5). Data were evaluated descriptively and analysed using linear mixed-effects models and Pearson's correlation coefficient. RESULTS: Overall mean ± s.d. values for rSO2, PaO2, PvO2, PaCO2, SavO2 and mean arterial pressure varied significantly by RP (P<0.001). Significant decreases in rSO2 were identified between RP1 and the post anaesthetic periods (P<0.001). No significant differences in rSO2 values were identified between RP1 and the intra-anaesthesia periods or between RP3, RP4 and RP5. Significant correlations were identified between rSO2 and PaO2 (r = 0.448, P<0.001), rSO2 and PvO2 (r = 0.512, P<0.001) and rSO2 and SavO2 (r = 0.469, P<0.001). CONCLUSIONS: This is the first study to identify trends in rSO2 in horses using NIRS. A positive correlation was identified between rSO2 and PvO2, suggesting that alterations in cerebral oxygenation may be reflected in PvO2 . POTENTIAL RELEVANCE: Near-infrared spectroscopy may be used to monitor trends in rSO2 during equine anaesthesia. Decreasing rSO2 values may act as an early warning signal, alerting clinicians to potential cerebral desaturation events and indicating a need for intervention.

Comparison of cardiovascular function and quality of recovery in isoflurane-anaesthetised horses administered a constant rate infusion of lidocaine or lidocaine and medetomidine during elective surgery.

REASONS FOR PERFORMING STUDY: The effects of lidocaine combined with medetomidine or lidocaine alone on cardiovascular function during anaesthesia and their effects on recovery have not been thoroughly investigated in isoflurane-anaesthetised horses. OBJECTIVES: To determine the effects of an intraoperative i.v. constant rate infusion of lidocaine combined with medetomidine (Group 1) or lidocaine (Group 2) alone on cardiovascular function and on the quality of recovery in 12 isoflurane-anaesthetised horses undergoing arthroscopy. HYPOTHESIS: The combination would depress cardiovascular function but improve the quality of recovery when compared to lidocaine alone in isoflurane-anaesthetised horses. METHODS: Lidocaine (2 mg/kg bwt i.v. bolus followed by 50 microg/kg bwt/min i.v.) or lidocaine (same dose) and medetomidine (5 microg/kg bwt/h i.v.) was started 30 min after induction of anaesthesia. Lidocaine administration was discontinued 30 min before the end of surgery in both groups, whereas medetomidine administration was continued until the end of surgery. Cardiovascular function and quality of recovery were assessed. RESULTS: Horses in Group 1 had longer recoveries, which were of better quality due to better strength and overall attitude during the recovery phase than those in Group 2. Arterial blood pressure was significantly higher in Group 1 than in Group 2 and this effect was associated with medetomidine. No significant differences in cardiac output, arterial blood gases, electrolytes and acid-base status were detected between the 2 groups. CONCLUSIONS AND POTENTIAL RELEVANCE: The combination of an intraoperative constant rate infusion of lidocaine and medetomidine did not adversely affect cardiovascular function in isoflurane-anaesthetised horses and improved the quality of recovery when compared to an intraoperative infusion of lidocaine alone.

Cardiorespiratory and minimum alveolar concentration sparing effects of a continuous intravenous infusion of dexmedetomidine in halothane or isoflurane-anaesthetized rats.

Dexmedetomidine (DEX) is a highly selective alpha(2)-adrenoceptor agonist in both the central and peripheral nervous systems. Its cardiorespiratory effects have been described; however, these effects have not been reported when it is used in combination with volatile anaesthetics in rats. The cardiovascular and respiratory actions of a continuous intravenous infusion of 0.25 microg/kg/min of DEX administered to rats anaesthetized at 1 minimum alveolar concentration (MAC) of either halothane (HAL) or isoflurane (ISO) were studied. Twenty-eight rats were grouped into four treatment groups: HAL alone, ISO alone, DEX + HAL and DEX + ISO. The MAC(HAL) or MAC(ISO) was determined in each rat from alveolar gas samples at the time of tail clamping. Control MAC values, expressed as mean +/- standard deviation, were 1.31 +/- 0.1% for HAL and 1.46 +/- 0.05% for ISO. DEX reduced HAL MAC from 1.31 +/- 0.1% to 0.36 +/- 0.22% (72 +/- 17% MAC reduction) and ISO MAC from 1.46 +/- 0.05% to 0.83 +/- 0.2% (43 +/- 14% MAC reduction). Heart rate (HR) was decreased in both DEX groups at 1 MAC, with no differences between HAL and ISO. The mean arterial pressure was significantly depressed in the DEX + ISO group compared with the ISO only group. This difference in mean arterial blood pressure (MABP) was not seen between the DEX + HAL and HAL only groups. Respiratory depression was minor at 1 MAC with both inhalant anaesthetics. DEX reduced the MAC of HAL to a degree greater than it decreased the MAC of ISO. The effects of DEX on HR and ventilation were similar in rats anaesthetized with HAL or ISO at 1 MAC; however, hypotension was more pronounced when DEX was combined with ISO at 1 MAC.