Oxygenation In Horses Research Articles

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

BackgroundThe 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.ResultsCardiovascular variables, respiratory rate, PO2, PCO2, oxygen saturation, haemoglobin content, CaO2, O2ER, P(a-ET)CO2 and Qs/Qt 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).ConclusionEndotracheal intubation reduces the nasal and tracheal endogenous NO concentration. The influence on pulmonary gas exchange and oxygenation is negligible in horses breathing room air.

Effects of acepromazine premedication on arterial oxygenation and cardiovascular variables in isoflurane-anesthetized horses in dorsal recumbency

Introduction: Acepromazine premedication improved the arterial oxygenation in horses anesthetized with tiletamine-zolazepam in lateral recumbency. This study aimed to investigate the effects of acepromazine in isoflurane-anesthetized horses in dorsal recumbency.

Comparison of single-breath continuous positive airway pressure manoeuvre with inhaled salbutamol to improve oxygenation in horses anaesthetized for laparotomy

ObjectiveTo compare the efficacy of single-breath continuous positive airway pressure manoeuvre (CPAP-M) with inhaled salbutamol, and a combination of both. Study designRandomized, clinical study. AnimalsA total of 62 client-owned horses (American Society of Anesthesiologists status III–V) anaesthetized for laparotomy. MethodsHorses were premedicated with intravenous (IV) xylazine (0.4–0.6 mg kg–1), anaesthesia was induced with midazolam (0.06 mg kg–1 IV) and ketamine (2.2 mg kg–1 IV) and maintained with isoflurane in oxygen using volume-controlled ventilation without positive end-expiratory pressure. If PaO2 was < 100 mmHg (13.3 kPa), either a CPAP-M (50 cmH2O for 45 seconds) or salbutamol (0.002 mg kg–1) was administered. The intervention was considered successful if PaO2 reached 100 mmHg (13.3 kPa). If PaO2 remained < 100 mmHg (13.3 kPa), treatments were switched. PaO2/FiO2 ratio and estimated shunt fraction (F-shunt) were derived from data obtained from arterial blood gas measurements. Dynamic compliance (Cdyn) was calculated from variables recorded at the moment of arterial blood analysis. Fisher’s exact tests compared success rates between treatments, and linear models were performed to test whether the treatment modified the values of the measurements; p < 0.05. ResultsSalbutamol was the first intervention in 28 horses and was effective in 22 horses. CPAP-M was the first intervention in 34 horses and was effective in 26 horses. CPAP-M after salbutamol was performed in six horses, with four responders, and salbutamol after CPAP-M was administered to eight horses, with one responder. Salbutamol, but not CPAP-M, significantly decreased F-shunt. Both salbutamol and CPAP-M significantly increased Cdyn. Conclusions and clinical relevanceSalbutamol and CPAP-M were comparably effective in improving oxygenation and Cdyn in anaesthetized horses with PaO2 < 100 mmHg (13.3 kPa). Whether combining both treatments might be beneficial needs to be confirmed on a larger number of horses.

Measurement of peripheral muscle oxygen saturation in conscious healthy horses using a near-infrared spectroscopy device

ObjectiveMaintaining adequate muscle tissue oxygenation is of paramount importance during equine general anesthesia. The objectives of this study were to assess the feasibility, reliability and repeatability of near-infrared spectroscopy (NIRS) muscle oximetry using the Inspectra m650 in conscious healthy adult horses. Study designProspective, observational study. AnimalsA group of 30 healthy client-owned adult horses admitted to the equine hospital between July 2017 and July 2018. MethodsThe probe of an Inspectra m650 NIRS tissue oximeter was placed on the hairless surface of five muscle sites (omotransversarius, triceps long head, extensor carpi ulnaris, vastus lateralis and lateral digital extensor) on the left side of the body of each standing, unsedated horse. Each site had muscle oxygenation (StO2) recordings measured in triplicate and statistical modeling used to assess the reading reliability and repeatability within and between muscle sites. ResultsThe readings acquired at the vastus lateralis and extensor carpi ulnaris muscle sites had highly repeatable values [mean (90% confidence interval): StO2, 95% (93.8%, 96.5%) and 93% (91.6%, 93.9%), respectively; intraclass correlation coefficients, 0.92 and 0.80, respectively]. These two sites also had high reliability (represented by the percentage of successful readings; 70% and 86%, respectively). Conclusions and clinical relevanceThe use of NIRS muscle oxygenation technology is a clinically feasible means to assess tissue oxygenation in horses. The vastus lateralis and extensor carpi ulnaris muscle sites provided the most reliable and repeatable readings when using the Inspectra m650 machine in horses.

Correction: Comparison of desflurane and propofol at equipotent doses in combination with constant rate infusion of dexmedetomidine on global and peripheral perfusion and oxygenation in horses

Correction: Comparison of desflurane and propofol at equipotent doses in combination with constant rate infusion of dexmedetomidine on global and peripheral perfusion and oxygenation in horses

Pulsed inhaled nitric oxide improves arterial oxygenation in colic horses undergoing abdominal surgery

ObjectiveTo evaluate the effect of pulsed inhaled nitric oxide (INO) on arterial oxygenation in horses during abdominal surgery. Study designProspective, randomized, clinical trial. AnimalsThirty horses that underwent abdominal surgery at the University Animal Hospital in Uppsala, Sweden. MethodsAnaesthesia was induced according to a standard protocol – romifidine, butorphanol, diazepam and ketamine and maintained with isoflurane in oxygen. Fifteen horses were administered pulsed INO and 15 served as controls. After baseline data collection, pulsed INO delivery commenced. Arterial and venous blood were collected and analysed. Cardiorespiratory parameters were measured, and oxygen content and F-shunt were calculated. ResultsArterial oxygen tension (PaO2) and arterial oxygen saturation (SaO2) increased from 10.9±5.7 kPa (82±43 mmHg) and 93±6% to 17.3±6.9 kPa (134±52 mmHg) (p<0.0001) and 98±2% (p<0.0001), respectively, in horses administered pulsed INO. In the control group, PaO2 and SaO2 decreased from 13.9±9.1 kPa (104±68 mmHg) and 93±7% to 12.1±8.6 kPa (91±65 mmHg) (p=0.0413) and 91±8% (p=0.0256), respectively. At the end of anaesthesia, the oxygen content was significantly higher in horses administered pulsed INO compared to controls (p=0.0126). The calculated F-shunt decreased from 39±10% to 27±6% (p<0.0001) in horses administered pulsed INO, and remained unchanged in controls, 40±12% to 44±12%. Blood lactate concentration decreased (–17±21%) in horses administered pulsed INO (p=0.0119), whereas no difference was measured in controls (2±31%). Conclusions and clinical relevanceThe present study showed that it is possible to effectively reduce the F-shunt and improve arterial oxygenation in horses during abdominal surgery by continuous delivery of pulsed INO.

Controlled mechanical ventilation with constant positive end-expiratory pressure and alveolar recruitment manoeuvres during anaesthesia in laterally or dorsally recumbent horses

ObjectiveTo compare the effects of controlled mechanical ventilation (CMV) and constant positive end-expiratory pressure (PEEP) and interposed recruitment manoeuvres (RMs) with those of CMV without PEEP on gas exchange during general anaesthesia and the early recovery period. Study designProspective, randomized clinical trial. AnimalsA total of 48 Warmblood horses undergoing elective surgery in lateral (Lat) (n = 24) or dorsal (Dors) (n = 24) recumbency. MethodsPremedication (romifidine), induction (diazepam and ketamine) and maintenance (isoflurane in oxygen) were identical in all horses. Groups Lat- CMV and Dors-CMV (each n = 12) were ventilated using CMV. Groups Lat-RM and Dors-RM (each n = 12) were ventilated using CMV with constant PEEP (10 cmH2O) and intermittent RMs (three consecutive breaths with peak inspiratory pressure of 60 cmH2O, 80 cmH2O and 60 cmH2O, respectively). RMs were applied as required to maintain PaO2 at > 400 mmHg (> 53.3 kPa). Dobutamine was given to maintain mean arterial blood pressure at > 60 mmHg. Physiological parameters were recorded every 10 minutes. Arterial blood gases were measured intra- and postoperatively. Statistical analyses were conducted using analyses of variance (anova),t tests and the Mann–Whitney U-test. ResultsHorses in Dors-RM had higher PaO2 values [478 ± 35 mmHg (63.7 ± 4.6 kPa)] than horses in Dors-CMV [324 ± 45 mmHg (43.2 ± 6 kPa)] during anaesthesia and the early recovery period. There were no differences between horses in groups Lat-CMV and Lat-RM. Other measured parameters did not differ between groups. Conclusions and clinical relevanceVentilation with CMV, constant PEEP and interposed RM provided improved arterial oxygenation in horses in dorsal recumbency that lasted into the early recovery period, but had no benefit in horses in lateral recumbency. This mode of ventilation may provide a clinically practicable method of improving oxygenation in anaesthetized horses, especially in dorsal recumbency.

The effect of the inspired oxygen fraction on arterial blood oxygenation in spontaneously breathing, isoflurane anaesthetized horses: a retrospective study

ObjectivesTo investigate the influence of two inspired oxygen fractions (FIO2) on the arterial oxygenation in horses anaesthetized with isoflurane. Study DesignRetrospective, case-control clinical study. AnimalsTwo hundred equine patients undergoing non-abdominal surgery (ASA class 1–2), using a standardized anaesthetic protocol and selected from anaesthetic records of a period of three years, based on pre-defined inclusion criteria. MethodsIn group O (n = 100), medical oxygen acted as carrier gas, while in group M (n = 100), a medical mixture of oxygen and air (FIO2 0.60) was used. Demographic data, FIO2, arterial oxygen tension (PaO2) and routinely monitored physiologic data were recorded. The alveolar-arterial oxygen tension difference [P(A-a)O2] and PaO2/FIO2 ratio were calculated. The area under the curve, standardized to the anaesthetic duration, was calculated and statistically compared between groups using t-tests or Mann–Whitney tests as appropriate. Categorical data were compared using Chi-square tests. ResultsNo significant differences in age, body weight, sex, breed, surgical procedure, position, anaesthetic duration or arterial carbon dioxide tension were found. Mean FIO2 was 0.78 in group O and 0.60 in group M. Compared to group O, significantly lower values for PaO2 and for P(A-a)O2 were found in group M. In contrast, the PaO2/FIO2 ratio and the percentage of horses with a PaO2 <100 mmHg (13.33 kPa) were comparable in both groups. ConclusionsAlthough a reduction of the inspired oxygen fraction resulted in a lower PaO2, the P(A-a)O2 was also lower and the number of horses with PaO2 values <100 mmHg was comparable. Clinical relevanceIn healthy isoflurane anaesthetized horses, the use of a mixture of oxygen and air as carrier gas seems acceptable, but further, prospective studies are needed to confirm whether it results in a lower degree of ventilation/perfusion mismatching.

Effect of pressure support ventilation during weaning on ventilation and oxygenation indices in healthy horses recovering from general anesthesia

ObjectiveTo determine if pressure support ventilation (PSV) weaning from general anesthesia affects ventilation or oxygenation in horses. Study designProspective randomized clinical study. AnimalsTwenty client‐owned healthy horses aged 5 ± 2 years, weighing 456 ± 90 kg. MethodsIn the control group (CG; n = 10) weaning was performed by a gradual decrease in respiratory rate (fR) and in the PSV group (PSVG; n = 10) by a gradual decrease in fR with PSV. The effect of weaning was considered suboptimal if PaCO2 > 50 mmHg, arterial pH < 7.35 plus PaCO2 > 50 mmHg or PaO2 < 60 mmHg were observed at any time after disconnection from the ventilator until 30 minutes after the horse stood. Threshold values for each index were established and the predictive power of these values was tested. ResultsPressure support ventilation group (PSVG) had (mean ± SD) pH 7.36 ± 0.02 and PaCO2 41 ± 3 mmHg at weaning and the average lowest PaO2 69 ± 6 mmHg was observed 15 minutes post weaning. The CG had pH 7.32 ± 0.02 and PaCO2 57 ± 6 mmHg at weaning and the average lowest PaO2 48 ± 5 mmHg at 15 minutes post weaning. No accuracy in predicting weaning effect was observed for fR (p = 0.3474), minute volume (p = 0.1153), SaO2 (p = 0.1737) and PaO2/PAO2 (p = 0.1529). A high accuracy in predicting an optimal effect of weaning was observed for VT > 10 L (p = 0.0001), fR/VT ratio ≤ 0.60 breaths minute−1 L−1 (p = 0.0001), VT/bodyweight > 18.5 mL kg−1 (p = 0.0001) and PaO2/FiO2 > 298 (p = 0.0002) at weaning. A high accuracy in predicting a suboptimal effect of weaning was observed for VT < 10 L (p = 0.0001), fR/VT ratio ≥ 0.60 breaths minute−1 L−1 (p = 0.0001) and Pe′CO2 ≥ 38 mmHg (p = 0.0001) at weaning. Conclusions and clinical relevancePressure support ventilation (PSV) weaning had a better respiratory outcome. A higher VT, VT/body weight, PaO2/FiO2 ratio and a lower fR/VT ratio and Pe′CO2 were accurate in predicting the effect of weaning in healthy horses recovering from general anesthesia.