Exploring oxygen reserve index for timely detection of deoxygenation in canine patients recovering from anesthesia.

Pulse oximetry (SpO2) identifies a decrease in the partial pressure of oxygen (PaO2) when it falls below 80 mmHg, while oxygen reserve index (ORi), a dimensionless index ranging from 0 to 1, detects PaO2 changes between 100 and 200 mmHg. This study investigates the usefulness of ORi in detecting impending deoxygenation before traditional SpO2. Fifty-one dogs undergoing anesthesia were mechanically ventilated maintaining a fraction of inspired oxygen of 0.50 and an ORi of 1. Animals were classified according to their body condition score (BCS) as normal-fit (BCS 4-5/9), overweight (BCS 6-7/9), or obese (BCS 8-9/9). At the end of the procedure, dogs were placed in sternal recumbency, and after 10 min disconnected from the ventilator and maintained in apnea. ORi added warning time was determined at various ORi values as the time difference in reaching SpO2 of 95% from ORi of 0.9 and 0.5, compared to the SpO2 warning time from SpO2 of 98%. During apnea, ORi decreased before noticeable SpO2 changes. An ORi of 0.9 anticipated an SpO2 of 95% in normal-fit dogs by 87 (33-212) [median (range)] seconds or in those with a BCS ≥ 6/9 by 49 (7-161) seconds. Regardless of the BCS class, the median time from ORi of 0.5 to SpO2 of 95% was 30-35 s. ORi declined from 0.9 to 0.0 in 68 compared to 33 s between normal-fit and obese dogs (p < 0.05). In dogs, ORi added warning time could facilitate timely intervention, particularly in obese patients.

Successful management of pulmonary edema secondary to accidental electrocution in a young dog.

BACKGROUND: Human records describe pulmonary edema as a life-threatening complication of electric shock. Successful management requires prompt recognition and intensive care. However, in companion animals, electrocutions are rarely reported, even though domestic environments are full of electrical devices and there is always the possibility of accidental injury. Therefore, it is important for veterinarians to know more about this condition in order to achieve successful patient outcomes. CASE PRESENTATION: A 3-month-old male Labrador Retriever was presented with a history of transient loss of consciousness after chewing on a household electrical cord. On admission, the puppy showed an orthopneic position with moderate respiratory distress. Supplemental oxygen via nasal catheter was provided, but the patient showed marked worsening of respiratory status. Point-of-care ultrasound exams suggested neurogenic pulmonary edema due to electrical shock close to the central nervous system and increased B-lines without evidence of cardiac abnormalities. Mechanical ventilation of the patient was initiated using volume-controlled mode with a tidal volume of 9 to 15 ml/kg until reaching an end-tidal carbon dioxide ≤ 40 mm Hg, followed by a stepwise lung-recruitment maneuver in pressure-controlled mode with increases of the peak inspiratory pressure (15 to 20 cm H2O) and positive end-expiratory pressure (3 to 10 cm H2O) for 30 min, and return to volume-controlled mode with a tidal volume of 15 ml/kg until reaching a peripheral oxygen saturation ≥ 96%. Weaning from the ventilator was achieved in six hours, and the patient was discharged two days after admission without neurological or respiratory deficits. CONCLUSIONS: We present a rather unusual case of a neurogenic pulmonary edema subsequent to accidental electrocution in a dog. Timely diagnosis by ultrasound and mechanical ventilation settings are described. Our case highlights that pulmonary edema should be considered a potentially life-threatening complication of electrical shock in small animal emergency and critical care medicine.

Seizures in 3 juvenile dogs after intravenous anesthetic drug withdrawal during weaning from mechanical ventilation suspected to be a sign of iatrogenic withdrawal syndrome.

OBJECTIVE: To describe seizure activity in juvenile dogs successfully weaned from long-term mechanical ventilation. CASE SERIES SUMMARY: Three juvenile dogs (all approximately 3 months old) underwent long-term mechanical ventilation with IV anesthesia for suspected noncardiogenic pulmonary edema. Within 24 hours of extubation and within 10 hours of discontinuing midazolam continuous infusions, all dogs experienced seizures, which is 1 sign of iatrogenic withdrawal syndrome. Each dog was treated with an anticonvulsant protocol, and none experienced seizures after being discharged. NEW OR UNIQUE INFORMATION PROVIDED: Each dog received IV anesthesia, including fentanyl, dexmedetomidine, midazolam, and propofol, during mechanical ventilation and subsequently experienced seizures after successful weaning from mechanical ventilation. Juvenile dogs may be at risk for seizures after weaning from mechanical ventilation and IV anesthesia. Neurological monitoring and further research into an appropriate weaning protocol may prove beneficial in juvenile dogs requiring prolonged anesthesia.

Successful treatment of a severe 5-hydroxytrytophan intoxication using carbon hemoperfusion, hemodiafiltration, and mechanical ventilation in a dog.

OBJECTIVE: To describe the successful use of carbon hemoperfusion and hemodiafiltration in combination with mechanical ventilation (MV) to treat a severe intoxication of 5-hydroxytryptophan (5-HTP) in a dog. CASE SUMMARY: A dog ingested a minimum of 550 mg/kg of extended-release 5-HTP, resulting in serotonin syndrome that progressed to a comatose state and severe hypoventilation requiring MV. Extracorporeal carbon hemoperfusion coupled with hemodiafiltration was performed to remove 5-HTP from this patient. A carbon hemoperfusion cartridge was placed in series upstream in the extracorporeal circuit from the hemodialyzer. A total of 46.5 L of blood (4.89 L/kg) was processed during a 4.85-hour treatment. Serial plasma samples were obtained at 0, 60, 90, and 150 minutes during the session and 14 hours after the session. These samples were later analyzed for 5-HTP and serotonin concentrations. The extraction ratio of 5-HTP was 93.6%-98.9% through the carbon filter. The dog was weaned from MV within 8 hours after extracorporeal therapy and, after a full recovery, was successfully discharged. NEW OR UNIQUE INFORMATION PROVIDED: Despite an extensive review of the available literature, this appears to be the first reported case of using a carbon hemoperfusion, hemodiafiltration, and MV to treat severe serotonin syndrome secondary to 5-HTP intoxication in a dog. The combination of carbon hemoperfusion and hemodiafiltration can significantly reduce plasma 5-HTP concentrations after acute intoxication and may serve to decrease morbidity and mortality in patients with severe intoxication.

High carbohydrate is preferable to high lipid parenteral nutrition in healthy dogs undergoing prolonged sedation.

Parenteral nutrition (PN) is commonly used in intensive care units (ICUs) and is associated with earlier hospital outcome. However, there is scarcity of information about the metabolic effects of PN caloric distribution for dogs. Considering the high tolerance of dogs to lipids and, also, that hospitalized animals usually present insulin resistance, PN formulation with high fat instead high glucose can provide metabolic benefits in this specie. This study evaluated two PN protocols, based on high lipid or high carbohydrate in 12 healthy dogs under sedation/ventilation during 24 h. For baseline data, blood samples were collected 24 h before the study beginning. After fasting, the dogs were anesthetized and put under mechanical ventilation without energy support for 12 h to obtain: daily energy expenditure (DEE), respiratory quotient (RQ), oxygen consumption (VO2), carbon dioxide production (VCO2), lactate, glucose, cholesterol, and triglycerides concentrations. After, the dogs were allocated into two groups: lipid-based energy group (LEG) and carbohydrate-based energy group (CEG). Both groups received the PN infusions at a rate of 3 mL/kg/h for 12 h. Blood tests were performed 12, 24, and 48 h after infusion's completion. VO2 increased after PN in LEG, increasing energy expenditure compared to CEG. RQ remained close to 1 in CEG, indicating carbohydrate preferential consumption. Triglycerides increased in both groups after propofol infusion, remaining higher in LEG until the end of the evaluation. Glycaemia increased in CEG compared to baseline. In conclusion, both PN protocols can be used in healthy animals undergoing prolonged sedation protocols. However, high lipid PN had higher VO2 and DEE, and resulted in higher triglycerides concentrations and lower glycaemia indexes than carbohydrate, making high carbohydrate PN preferable to high lipid PN. Therefore, for use in critically ill patients, the data obtained in this study should be extrapolated, taking into consideration the specificity of each case.

Comparative study of ventilation techniques with supraglottic airway devices in cats: volume-controlled vs pressure-controlled techniques.

OBJECTIVES: This study compared the effectiveness of a new supraglottic airway device (SGAD) in cats undergoing anaesthesia using two types of mechanical ventilation: volume-controlled ventilation (VCV) and pressure-controlled ventilation (PCV). METHODS: A total of 13 healthy cats (five male, eight female; median age 2 years [range 1-3]) were randomly allocated to either VCV or PCV. Five tidal volumes (6, 8, 10, 12 and 14 ml/kg) and five peak inspiratory pressures (4, 5, 6, 7 and 8 cmH2O) were randomly applied with a minute ventilation of 100 ml/kg/min. Various parameters, such as blood pressure, gas leakage, end-tidal CO2 (ETCO2) and work of breathing (WOB), were measured while using VCV or PCV. RESULTS: The occurrence of hypotension (mean arterial blood pressure <60 mmHg) was slightly less frequent with VCV (38 events, 65 ventilating sessions) than with PCV (40 events, 65 ventilating sessions), but this difference did not reach statistical significance (P = 0.429). The number of leakages did not differ between the VCV group (3 events, 65 ventilating sessions) and the PCV group (3 events, 65 ventilating sessions) (P = 1.000). Hypercapnia was identified when using VCV (10 events, 65 ventilating sessions) less frequently than when using PCV (17 events, 65 ventilating sessions), but this difference did not reach statistical significance (P = 0.194). The study found a significantly higher WOB in the PCV group compared with the VCV group (P <0.034). CONCLUSIONS AND RELEVANCE: The present results suggested that both VCV and PCV can be used with an SGAD during anaesthesia, with VCV preferred for prolonged mechanical ventilation due to its lower workload. Adjusting tidal volume or inspiratory pressure corrects hypercapnia.

Isoflurane and Pentobarbital Anesthesia for Pulmonary Studies Requiring Prolonged Mechanical Ventilation in Mice.

Mechanical ventilation can be used in mice to support high-risk anesthesia or to create clinically relevant, intensive care models. However, the choice of anesthetic and inspired oxygen concentration for prolonged procedures may affect basic physiology and lung inflammation. To characterize the effects of anesthetics and oxygen concentration in mice experiencing mechanical ventilation, mice were anesthetized with either isoflurane or pentobarbital for tracheostomy followed by mechanical ventilation with either 100% or 21% oxygen. Body temperature, oxygen saturation, and pulse rate were monitored continuously. After 6 h, mice were euthanized for collection of blood and bronchoalveolar lavage fluid for evaluation of biomarkers of inflammation and lung injury, including cell counts and cytokine levels. Overall, both isoflurane and pentobarbital provided suitable anesthesia for 6 h of mechanical ventilation with either 21% or 100% oxygen. We found no differences in lung inflammation biomarkers attributable to either oxygen concentration or the anesthetic. However, the combination of pentobarbital and 100% oxygen resulted in a significantly higher concentration of a biomarker for lung epithelial cell injury. This study demonstrates that the combination of anesthetic agent, mechanical ventilation, and inspired oxygen concentrations can alter vital signs and lung injury biomarkers during prolonged procedures. Their combined impact may influence model development and the interpretation of research results, warranting the need for preliminary evaluation to establish the baseline effects.

Large animal ventilator-integrated volumetric capnography generates clinically acceptable values of physiologic dead space in anesthetized healthy adult horses.

OBJECTIVE: To evaluate the agreement between the Tafonius large animal ventilator-integrated volumetric capnography (vCap) software and the Respironics NICO noninvasive cardiac output monitor reference system. ANIMALS: Data were collected from 56 healthy adult horses undergoing general anesthesia. METHODS: Animals were placed under general anesthesia and connected to the Tafonius large animal ventilator circle system. A flow partitioning device with CO2 and flow sensors was utilized to couple the endotracheal tube to the NICO monitor. Tafonius CO2 and flow sensors are incorporated into the Y-piece of the breathing circuit. Arterial blood samples were collected to determine the partial pressure of arterial carbon dioxide (PaCO2) immediately before data collection. The PaCO2 was input into the Tafonius and NICO monitor, and dead space ventilation (%Vd), end-tidal CO2 partial pressure (ETco2), mixed-expired CO2 partial pressure (Peco2), and expired tidal volume (Vt) were calculated over a single breath. Multiple measurements were completed for each patient, with a total of 200 paired data points collected for analysis. Data were assessed for normality, and Bland-Altman analysis was performed. Bias and 95% limits of agreement were calculated. RESULTS: The limits of agreement for %Vd of the ventilator-derived measurements fell within ± 10% of the NICO monitor reference method. CLINICAL RELEVANCE: Our results indicate that, when compared to the NICO monitor method, the Tafonius-integrated vCap software provides clinically acceptable values of Peco2, Vt, and %Vd in healthy adult horses.

Cardiac output affects the response to pulsed inhaled nitric oxide in mechanically ventilated anesthetized ponies determined by CT angiography of the lung.

OBJECTIVE: To measure changes in regional lung perfusion using CT angiography in mechanically ventilated, anesthetized ponies administered pulsed inhaled nitric oxide (PiNO) during hypotension and normotension. ANIMALS: 6 ponies for anesthetic 1 and 5 ponies for anesthetic 2. PROCEDURES: Ponies were anesthetized on 2 separate occasions, mechanically ventilated, and placed in dorsal recumbency within the CT gantry. Pulmonary arterial, right atrial, and facial arterial catheters were placed. During both anesthetics, PiNO was delivered for 60 minutes and then discontinued. Anesthetic 1: hypotension (mean arterial pressure < 70 mmHg) was treated using dobutamine after 30 minutes of PiNO delivery. Following the discontinuation of PiNO, dobutamine administration was discontinued in 3 ponies and was continued in 3 ponies. The lung was imaged at 30, 60, and 105 minutes. Anesthetic 2: hypotension persisted throughout anesthesia. The lung was imaged at 30, 60, and 90 minutes. At all time points, arterial and mixed venous blood samples were analyzed and cardiac output (Q˙t) was measured. Pulmonary perfusion was calculated from CT image analysis. RESULTS: During PiNO delivery, perfusion to well-ventilated lungs increased if ponies were normotensive, leading to increased arterial oxygenation, reduced alveolar dead space, and reduced alveolar to arterial oxygen tension gradient. When PiNO was stopped and dobutamine administration continued, alveolar dead space and venous admixture increased, in contrast to when dobutamine and PiNO were both discontinued. CLINICAL RELEVANCE: If PiNO is administered to mechanically ventilated, anesthetized ponies with concurrent hypotension and low Q˙t, this must be supported to achieve favorable redistribution of pulmonary perfusion to improve pulmonary gas exchange.

Effect of end-inspiratory pause on airway and physiological dead space in anesthetized horses.

OBJECTIVE: To evaluate the impact of a 30% end-inspiratory pause (EIP) on alveolar tidal volume (VTalv), airway (VDaw) and physiological (VDphys) dead spaces in mechanically ventilated horses using volumetric capnography, and to evaluate the effect of EIP on carbon dioxide (CO2) elimination per breath (Vco2br-1), PaCO2, and the ratio of PaO2-to-fractional inspired oxygen (PaO2:FiO2). STUDY DESIGN: Prospective research study. ANIMALS: A group of eight healthy research horses undergoing laparotomy. METHODS: Anesthetized horses were mechanically ventilated as follows: 6 breaths minute-1, tidal volume (VT) 13 mL kg-1, inspiratory-to-expiratory time ratio 1:2, positive end-expiratory pressure 5 cmH2O and EIP 0%. Vco2br-1 and expired tidal volume (VTE) of 10 consecutive breaths were recorded 30 minutes after induction, after adding 30% EIP and upon EIP removal to construct volumetric capnograms. A stabilization period of 15 minutes was allowed between phases. Data were analyzed using a mixed-effect linear model. Significance was set at p < 0.05. RESULTS: The EIP decreased VDaw from 6.6 (6.1-6.7) to 5.5 (5.3-6.1) mL kg-1 (p < 0.001) and increased VTalv from 7.7 ± 0.7 to 8.6 ± 0.6 mL kg-1 (p = 0.002) without changing the VTE. The VDphys to VTE ratio decreased from 51.0% to 45.5% (p < 0.001) with EIP. The EIP also increased PaO2:FiO2 from 393.3 ± 160.7 to 450.5 ± 182.5 mmHg (52.5 ± 21.4 to 60.0 ± 24.3 kPa; p < 0.001) and Vco2br-1 from 0.49 (0.45-0.50) to 0.59 (0.45-0.61) mL kg-1 (p = 0.008) without reducing PaCO2. CONCLUSIONS AND CLINICAL RELEVANCE: The EIP improved oxygenation and reduced VDaw and VDphys, without reductions in PaCO2. Future studies should evaluate the impact of different EIP in healthy and pathological equine populations under anesthesia.

The fraction of inspired oxygen does not affect the time to extubation in mechanically ventilated, sevoflurane-anesthetized green sea turtles (Chelonia mydas).

OBJECTIVE: To evaluate the effects of providing 100% O2, compared with the provision of 21% O2 (equivalent to room air), in mechanically ventilated, sevoflurane-anesthetized green sea turtles (Chelonia mydas). ANIMALS: Eleven juvenile green sea turtles. PROCEDURES: In a randomized, blinded, cross-over study (1-week interval between treatments), turtles were anesthetized with propofol (5 mg/kg, IV), orotracheally intubated, mechanically ventilated with 3.5% sevoflurane diluted in 100% O2 or 21% O2 for 90 minutes. Sevoflurane delivery immediately ceased and animals remained under mechanical ventilation with the assigned fraction of inspired oxygen until extubation. Recovery times, cardiorespiratory variables, venous blood gases, and lactate values were evaluated. RESULTS: Cloacal temperature, heart rate, end-tidal partial pressure of carbon dioxide, and blood gases were unremarkable between treatments. The SpO2 was higher with the provision of 100% O2 than 21% O2 during both anesthesia and recovery (P < .01). Time to bite the bite block was longer in 100% O2 (51 [39-58] minutes) than in 21% O2 (44 [31-53] minutes; P = .03), while time to first muscle movement, attempt to extubate, and extubation were comparable between treatments. CLINICAL RELEVANCE: Blood oxygenation appears to be lower during sevoflurane anesthesia in room air than in 100% O2, though both fractions of inspired oxygen were able to supply the aerobic metabolism of turtles based on acid-base profiles. In relation to room air, the provision of 100% O2 did not produce meaningful effects on the time to recovery in mechanically ventilated green turtles submitted to sevoflurane anesthesia.

Arterial blood gas tensions during recovery in horses anesthetized with apneustic anesthesia ventilation compared with conventional mechanical ventilation.

OBJECTIVE: To compare PaO2 and PaCO2 in horses recovering from general anesthesia maintained with either apneustic anesthesia ventilation (AAV) or conventional mechanical ventilation (CMV). STUDY DESIGN: Randomized, crossover design. ANIMALS: A total of 10 healthy adult horses from a university-owned herd. METHODS: Dorsally recumbent horses were anesthetized with isoflurane in oxygen [inspired oxygen fraction = 0.3 initially, with subsequent titration to maintain PaO2 ≥ 85 mmHg (11.3 kPa)] and ventilated with AAV or CMV according to predefined criteria [10 mL kg-1 tidal volume, PaCO2 40-45 mmHg (5.3-6.0 kPa) during CMV and < 60 mmHg (8.0 kPa) during AAV]. Horses were weaned from ventilation using a predefined protocol and transferred to a stall for unassisted recovery. Arterial blood samples were collected and analyzed at predefined time points. Tracheal oxygen insufflation at 15 L minute-1 was provided if PaO2 < 60 mmHg (8.0 kPa) on any analysis. Time to oxygen insufflation, first movement, sternal recumbency and standing were recorded. Data were analyzed using repeated measures anova, paired t tests and Fisher's exact test with significance defined as p < 0.05. RESULTS: Data from 10 horses were analyzed. Between modes, PaO2 was significantly higher immediately after weaning from ventilation and lower at sternal recumbency for AAV than for CMV. No PaCO2 differences were noted between ventilation modes. All horses ventilated with CMV required supplemental oxygen, whereas three horses ventilated with AAV did not. Time to first movement was shorter with AAV. Time to oxygen insufflation was not different between ventilation modes. CONCLUSIONS: Although horses ventilated with AAV entered the recovery period with higher PaO2, this advantage was not sustained during recovery. Whereas fewer horses required supplemental oxygen after AAV, the use of AAV does not preclude the need for routine supplemental oxygen administration in horses recovering from general anesthesia.

Caudal vena cava measurements and fluid responsiveness in hospitalized cats with compromised hemodynamics and tissue hypoperfusion.

OBJECTIVE: To evaluate the use of the caudal vena cava collapsibility index (CVCCI) and the inspiratory/minimum and expiratory/maximum diameters of the vena cava to predict fluid responsiveness in hospitalized, critically ill cats with hemodynamic and tissue perfusion abnormalities. DESIGN: Diagnostic test study in a prospective cohort of hospitalized cats. SETTING: Private practice referral hospital. ANIMALS: Twenty-four hospitalized cats with spontaneous breathing and compromised hemodynamics and tissue hypoperfusion. INTERVENTIONS: Ultrasonographic examination before and after fluid expansion with 10 ml/kg of lactated Ringer's solution. MEASUREMENTS AND MAIN RESULTS: Fluid responsiveness was evaluated using the velocity-time integral (VTI) of the subaortic blood flow, by measuring it before and after a fluid load of 10 ml/kg of lactated Ringer's solution. The CVCCI was calculated using the following formula: (maximum diameter - minimum diameter / maximum diameter) × 100. Ten cats were fluid responders (42 %) and 14 were nonresponders (58 %). The area under the receiver operating characteristic curve (AUROC) with their 95% confidence interval for the predictors and the best cutoff values were as follows: CVCCI, AUROC = 0.83 (0.66-1.00) and cutoff = 31%; inspiratory/minimum diameter, AUROC = 0.86 (0.70-1.00) and cutoff = 0.24 cm; expiratory/maximum diameter, AUROC = 0.88 (0.74-1.00) and cutoff = 0.22 cm. A significant lineal correlation was observed between the percentage of increase in VTI after expansion and CVCCI (rs  = 0.68, P < 0.001), expiratory/maximum diameter (rs  = -0.72, P < 0.001), and inspiratory/minimum diameter (rs  = -0.71, P < 0.001). The intraobserver and interobserver variability was low for VTI, and the expiratory/maximum diameter and inspiratory/minimum diameter were high for CVCCI. CONCLUSIONS: Caudal vena cava measurements could be useful to predict the response to fluids in hospitalized cats with hemodynamic and tissue perfusion alterations. Additional studies are required to draw definitive conclusions about the role of these variables to guide fluid administration in cats.

Comparison between mainstream (Capnostat 5) and a low-flow sidestream capnometer (Capnostream) in mechanically ventilated, sevoflurane-anesthetized rabbits using a Bain coaxial delivery system.

OBJECTIVE: To evaluate agreement between end-tidal carbon dioxide (Pe'CO2) and PaCO2 with sidestream and mainstream capnometers in mechanically ventilated anesthetized rabbits, with two ventilatory strategies. STUDY DESIGN: Prospective experimental study. ANIMALS: A total of 10 New Zealand White rabbits weighing 3.6 ± 0.3 kg (mean ± standard deviation). METHODS: Rabbits anesthetized with sevoflurane were intubated with an uncuffed endotracheal tube (3.0 mm internal diameter) and adequate seal. For Pe'CO2, the sidestream capnometer sampling adapter or the mainstream capnometer was placed between the endotracheal tube and Bain breathing system (1.5 L minute-1 oxygen). PaCO2 was obtained from arterial blood collected every 5 minutes. A time-cycled ventilator delivered an inspiratory time of 1 second and 12 or 20 breaths minute-1. Peak inspiratory pressure was initially set to achieve Pe'CO2 normocapnia of 35-45 mmHg (4.6-6.0 kPa). A total of five paired Pe'CO2 and PaCO2 measurements were obtained with each ventilation mode for each capnometer. Anesthetic episodes were separated by 7 days. Agreement was assessed using Bland-Altman analysis and linear mixed models; p < 0.05. RESULTS: There were 90 and 83 pairs for the mainstream and sidestream capnometers, respectively. The mainstream capnometer underestimated PaCO2 by 12.6 ± 2.9 mmHg (proportional bias 0.44 ± 0.06 mmHg per 1 mmHg PaCO2 increase). With the sidestream capnometer, ventilation mode had a significant effect on Pe'CO2. At 12 breaths minute-1, Pe'CO2 underestimated PaCO2 by 23.9 ± 8.2 mmHg (proportional bias: 0.81 ± 0.18 mmHg per 1 mmHg PaCO2 increase). At 20 breaths minute-1, Pe'CO2 underestimated PaCO2 by 38.8 ± 5.0 mmHg (proportional bias 1.13 ± 0.10 mmHg per 1 mmHg PaCO2 increase). CONCLUSIONS AND CLINICAL RELEVANCE: Both capnometers underestimated PaCO2. The sidestream capnometer underestimated PaCO2 more than the mainstream capnometer, and was affected by ventilation mode.

Fentanyl-induced muscle rigidity in a dog during weaning from mechanical ventilation after emergency abdominal surgery: A case report.

A 22.5-kg, 8.4-year-old female mixed breed dog was presented for an emergency ovariohysterectomy for pyometra. No neurological abnormalities were observed on preoperative physical examination. Surgery was completed uneventfully under fentanyl- and sevoflurane-based anaesthesia. Cardiorespiratory indices remained stable under mechanical ventilation throughout the procedure. Approximately 23 min after the discontinuation of fentanyl infusion, the investigator noticed jaw closure and stiffness and thoraco-abdominal muscle rigidity. To rule out fentanyl-induced muscle rigidity, naloxone was administered. Following administration of naloxone, there was a return of spontaneous respiratory effort, indicated by capnogram and visible chest wall excursion. Based on the clinical signs and response to naloxone administration, the dog was diagnosed with suspected fentanyl-induced muscle rigidity. Six minutes after the return of spontaneous respiration, the dog was extubated uneventfully without additional naloxone administration. During 4 days of postoperative hospitalization, no recurrent muscle rigidity was observed, and the patient was discharged safely. The total dose of fentanyl administered was 0.61 mg (27 µg kg-1 ).

Some cardiopulmonary effects of capnoperitoneum in anesthetized guinea pigs (Cavia porcellus): spontaneous ventilation versus intubation and mechanical ventilation.

OBJECTIVE: To compare cardiopulmonary variables and blood gas analytes in guinea pigs (Cavia porcellus) during anesthesia with and without abdominal carbon dioxide (CO2) insufflation at intra-abdominal pressures (IAPs) 4 and 6 mmHg, with and without endotracheal intubation. STUDY DESIGN: Prospective experimental trial. ANIMALS: A total of six intact female Hartley guinea pigs. METHODS: A crossover study with sequence randomization for IAP and intubation status was used. The animals were sedated with intramuscular midazolam (1.5 mg kg-1) and buprenorphine (0.2 mg kg-1) and anesthetized with isoflurane, and an abdominal catheter was inserted for CO2 insufflation. Animals with endotracheal intubation were mechanically ventilated and animals maintained using a facemask breathed spontaneously. After 15 minutes of insufflation, the following variables were obtained at each IAP: pulse rate, respiratory rate, rectal temperature, oxygen saturation, end-tidal CO2 (intubated only), peak inspiratory pressure (intubated only), noninvasive blood pressure and blood gas and electrolyte values, with a rest period of 5 minutes between consecutive IAPs. After 4 weeks, the procedure was repeated with the guinea pigs assigned the opposite intubation status. RESULTS: Intubated guinea pigs had significantly higher pH and lower partial pressure of CO2 in cranial vena cava blood (PvCO2) than nonintubated guinea pigs. An IAP of 6 mmHg resulted in a significantly higher PvCO2 (65.9 ± 19.0 mmHg; 8.8 ± 2.5 kPa) than at 0 (53.2 ± 17.2 mmHg; 7.1 ± 2.3 kPa) and 4 mmHg (52.6 ± 10.8 mmHg; 7.01 ± 1.4 kPa), mean ± standard deviation, with intubated and nonintubated animals combined. CONCLUSIONS AND CLINICAL RELEVANCE: Although the oral anatomy of guinea pigs makes endotracheal intubation difficult, capnoperitoneum during anesthesia induces marked hypercapnia in the absence of mechanical ventilation. An IAP of 4 mmHg should be further evaluated for laparoscopic procedures in guinea pigs because hypercapnia may be less severe than with 6 mmHg.

Predicting the effect of fresh gas flow on tidal volume in volume-controlled mechanically ventilated dogs.

OBJECTIVES: To determine if the tidal volume (VT) delivered (VTDEL) to canine patients being mechanically ventilated by a volume-controlled ventilator differed from the volume set on the ventilator (VTSET) at three fresh gas flow (FGF) rates. To determine if VTDEL could be accurately predicted by an FGF-based mathematical model. STUDY DESIGN: Prospective proof-of-concept study. ANIMALS: A total of 23 adult client-owned dogs undergoing elective orthopedic surgery. METHODS: Dogs were anesthetized and ventilated with a volume-controlled mechanical ventilator with constant respiratory rate (fR) of 10 breaths minute-1, inspiratory-to-expiratory ratio of 1:2 [fraction of inspiratory time (TI) in one respiratory cycle (Ttot) 1:3], and VTSET as body weight (kg) × 15 (mL kg-1). VTDEL was measured in 20 dogs at three FGF (500, 1000 and 4000 mL minute-1). A mathematical model was used to calculate predicted volume (VTPRED) for each animal at each FGF: VTSET + {FGF × [(TI/Ttot)/fR]}. Linear repeated measures models were fit comparing VTDEL to VTSET and to VTPRED by FGF. RESULTS: VTDEL was significantly higher than VTSET at every FGF (p < 0.05), and differences were larger at higher FGF (p < 0.001). There were no statistically significant differences between VTDEL and VTPRED at FGF rates of 500 and 4000 mL minute-1 and, although the mean VTDEL was statistically significantly higher than VTPRED at FGF 1000 mL minute-1 (p = 0.017), the mean difference of 9 mL was not clinically significant. CONCLUSIONS AND CLINICAL RELEVANCE: Dogs on volume-controlled ventilators may be ventilated at a higher VTDEL than intended depending on the FGF settings. Ventilation of small animals at high FGF could inadvertently induce pulmonary damage. A mathematical equation can be used to achieve a desired VTDEL by adjusting VTSET values based on FGF, fR and TI/Ttot.

Retrospective evaluation of transportation and outcome of dogs on a mechanical ventilator: 9 cases.

OBJECTIVE: To describe the transportation and clinical outcome of 9 dogs transported to a referral hospital on mechanical ventilation (MV). DESIGN: Retrospective case series (2015-2020). SETTING: University teaching hospital. ANIMALS: Nine dogs transported to a referral center on MV. INTERVENTIONS: All dogs underwent MV during vehicular transport. MEASUREMENT AND MAIN RESULTS: The medical records of 9 dogs transported on a MV to a university teaching hospital were reviewed. Data collected included signalment, reason for MV, ventilator settings, sedation protocol, monitoring in transit, distance traveled, complications, clinical outcome, and cost. All dogs transported survived transport to the referral hospital and 8 of 9 were successfully weaned from the ventilator and discharged home. CONCLUSIONS: MV during transport in this setting was practical and safe. Dogs in this study had a high survival rate compared to previous studies of dogs undergoing MV, likely due to selection of cases assessed to have a correctable underlying disease.

Echocardiographic indicators of fluid responsiveness in hospitalized dogs with compromised hemodynamics and tissue hypoperfusion.

OBJECTIVE: To evaluate the accuracy of selected echocardiographic variables used to predict fluid responsiveness in hospitalized dogs with compromised hemodynamics and tissue hypoperfusion. DESIGN: Diagnostic test study in a prospective cohort of hospitalized dogs. SETTING: Veterinary referral clinics. ANIMALS: Forty-four hospitalized dogs with compromised hemodynamics and tissue hypoperfusion were utilized in this study. INTERVENTIONS: Echocardiographic examination before and after fluid replacement with 30 ml/kg of lactated Ringer's solution. MEASUREMENTS AND MAIN RESULTS: Pre-fluid replacement measurements of velocity of transmitral E wave (E-peak), the left ventricular end-diastolic internal diameter normalized to body weight (LVIDdN), and the left ventricular end-systolic internal diameter normalized to body weight (LVIDsN) were significantly lower in fluid-responsive patients compared with nonresponders (P < 0.001). The area under the receiver operating characteristic curve (AUROC) with its 95% confidence interval (CI) for each significant predictor was as follows: E-peak 0.907 (0.776-1.000, P < 0.001) and LVIDdN 0.919 (0.801-1.000, P < 0.001). The predictive capacity of LVIDsN was not significantly better than chance (AUROC, 0.753; 95% CI, 0.472-1.000, P = 0.078). A significant negative linear correlation was observed between the percentage of increase in velocity-time integral after expansion and the echocardiographic variables LVIDdN (rs  = -0.452, P = 0.023) and E-peak (rs  = -0.396, P = 0.008) pre-fluid replacement. The intraobserver and interobserver variability was very low (<5 %) for all measurements. CONCLUSIONS: In this study using critically ill dogs with compromised hemodynamics and tissue hypoperfusion, pre-fluid replacement measurements of LVIDdN and E-peak adequately predict fluid responsiveness. Because a small number of fluid nonresponders were involved in the present study (11.4%), further studies that include larger numbers of fluid-nonresponsive animals are required.