Making sense of blood gas results

The Effect of a Subsequent Dose of Dexmedetomidine or Other Sedatives following an Initial Dose of Dexmedetomidine on Electrolytes, Acid-Base Balance, Creatinine, Glucose, and Cardiac Troponin I in Cats: Part II

The administered dose of dexmedetomidine may occasionally fail to produce the anticipated sedative effects. Therefore, a subsequent dose or administration of another sedative may enhance sedation; however, patient safety may be affected. The safety of seven different drugs administered at the following time point after an insufficient dose of dexmedetomidine was evaluated in a crossover, blind, experimental study that included six healthy adult cats. All cats received an initial dose of dexmedetomidine and a subsequent dose of either dexmedetomidine (Group DD), NS 0.9% (DC), tramadol (DT), butorphanol (DBT), buprenorphine (DBP), ketamine (DK), or midazolam (DM). Animal safety was assessed using repeated blood gas analysis and measurement of electrolytes, glucose, cardiac troponin I, and creatinine to evaluate cardiac, respiratory, and renal function. The median values of creatinine, cardiac troponin I, pH, partial pressure of carbon dioxide, potassium, and sodium did not change significantly throughout the study. Heart rate was significantly decreased in all groups after administration of the drug combinations, except for in the DK group. Respiratory rate decreased significantly after administration of the initial dose of dexmedetomidine and in the DBP and DM groups. The partial pressure of oxygen, although normal, decreased significantly after the administration of dexmedetomidine, whereas the median concentration of glucose increased significantly following the administration of dexmedetomidine. The results of our study suggest that the drug combinations used did not alter the blood parameters above normal limits, while cardiac and renal function were not compromised. Therefore, a safe level of sedation was achieved. However, the administration of dexmedetomidine reduced the partial pressure of oxygen; thus, oxygen supplementation during sedation may be advantageous. Additionally, the increase in glucose concentration indicates that dexmedetomidine should not be used in cats with hyperglycaemia, whereas the decrease in haematocrit suggests that dexmedetomidine is not recommended in anaemic cats.

Ferret Sedation and Anesthesia

Providing safe anesthetic events in ferrets can be achieved if fundamental principles in anesthesia are followed. Each phase of the anesthetic, event including preanesthetic, maintenance, and postanesthetic phase, have certain considerations. The anesthetic supervisor or veterinarian providing management should have a firm understanding of the species-specific anatomy, physiology, and common indications of general anesthesia along with perspective of their own experience with ferrets. Ensuring these guidelines are followed will facilitate safe administration of general anesthesia in this species.

Evaluation of two different etorphine doses combined with azaperone in blesbok (Damaliscus pygargus phillipsi) immobilisation

Chemical immobilisation is essential for veterinarians to perform medical procedures in wild African ungulates. Potent opioids combined with neuroleptic drugs are most often used for this purpose. The present study aimed at comparing the quality of immobilisation and effects on physiological variables between a high (high etorphine-azaperone [HE]: 0.09 mg kg-1) and low etorphine dose (low etorphine-azaperone [LE]: 0.05 mg kg-1), both combined with azaperone (0.35 mg kg-1), in 12 adult female boma-acclimatised blesbok. It was hypothesised that a reduction in etorphine's dose in combination with azaperone would result in less cardiorespiratory impairment but likely worsen the quality of immobilisation. Both treatments resulted in rapid induction and recovery times. Overall inter-treatment differences occurred in pulse rate (HE and LE: 52 ± 15 and 44 ± 11 beats minute-1, p 0.0001), respiratory rate (HE and LE: 15 ± 4 and 17 ± 4 breaths minute-1, p 0.006), partial pressure of exhaled carbon dioxide (HE and LE: 62.0 ± 5.0 and 60.0 ± 5.6 millimetre of mercury [mmHg], p 0.028) and arterial carbon dioxide (HE and LE: 58.0 ± 4.5 and 55.0 ± 3.9 mmHg, p 0.002). Both HE and LE led to bradycardia, hypertension and marked hypoxia to a similar extent. Furthermore, quality of induction, immobilisation and recovery were similar in both treatments. The role of azaperone in the development of cardiorespiratory compromise and gas exchange impairment that occurred when these combinations were used is still unclear. Further studies are recommended to elucidate drug- and dose-specific physiological effects in immobilised antelope.

Effects of time and temperature on blood gas and electrolytes in equine venous blood

This study aimed to evaluate the viability time of horse venous blood samples kept at laboratory temperature (LT) and in water with ice (WI), to perform blood gas analysis. Eleven blood samples were collected in duplicates from 10 healthy horses. The samples were transported to the laboratory and subjected to one of the 24 h storage method. Each pair of syringes was distinctly kept at LT or submerged in WI. Blood gas tests were performed at times T0h, T1h, T2h, T3h, T4h, T5h, T6h, T8h, T10h, T12h and T24h after collection. Analyses of electrolytes were also performed from the same samples. A difference in blood pH was found between the treatments (P < 0.05). From T4h, pH decreased in samples kept at LT, but in WI, pH did not change. For partial pressure of carbon dioxide (pCO2), a difference between treatments (P < 0.05) was noted starting at T8h. In samples kept at LT, pCO2 increased; no changes occurred in samples stored in WI. There was a decrease in the base concentration beginning at T5h in samples kept at LT (P < 0.05), but no variation in samples kept in WI. These changes can be attributed to the erythrocyte metabolism, still active in vitro, which generates lactic acid from anaerobic glycolysis. The potassium concentration increased in samples kept in WI from T4h, with a gradual increase until T24h. Conservation of equine venous blood samples in WI is efficient in reducing cellular metabolism, thereby increasing the viability of samples for examination and interpretation of results.

Interventionist videothermometry: a new model of cardiac ischemia evaluation

Background

The purpose of the present study was to evaluate, through videothermometry, the temperature variation in the hearts of rabbits, that underwent induced myocardial ischemia and reperfusion.

Results

A total of 20 female rabbits were divided into two groups: a treated group and a sham group, the treatment group underwent 5 min of cardiac arrest and reperfusion, using the inflow occlusion technique. Throughout the experiment, the animals were monitored by videothermometry, observing the thermal variations of the myocardial tissue. During the experiment, at different times, blood gas tests and tests to evaluate the lactate concentrations were performed. At the end of the experiment, each heart was submitted to histopathological evaluation. In the treated group, there was a reduction in temperature of the myocardial tissue during the circulatory arrest compared to the sham group. Additionally, a colder area next to the caudal vena cava ostium and the right atrium was observed. Notably, despite the 5 min of cardiac arrest in the treated group, both the lactate and bicarbonate levels were maintained without significant variation. However, there was an increase in PaCO2 and pH reduction, featuring respiratory acidosis. In relation to the histopathological study, the presence of hydropic degeneration in the myocardium of animals in the treated group was observed.

Conclusions

Based on these results, the videothermometry was efficient in identifying the range of myocardial tissue temperature, suggesting that the first areas to suffer due to cardiac arrest were the caudal vena cava ostium and the right atrium. However, in regard to the angiographic coronary thermography, the study was not feasible due to the small size of the coronary. There was no variation between the groups regarding the presence of myocardial infarction, myocardial congestion, myocardial edema and myocardial hemorrhage.

Acid-Base, Electrolyte and Lactate Abnormalities as Well as Gastric Necrosis and Survival in Dogs With Gastric Dilation-Volvulus Syndrome. A Retrospective Study in 75 Dogs

Gastric dilation-volvulus (GDV) syndrome in dogs is associated with complex metabolic, acid-base, and electrolyte abnormalities. The aim of this study was to evaluate previously analyzed factors (lactate and BE) in combination with other acid-base parameters (pH, pCO₂, bicarbonate, base excess [BE], anion gap [AG], and strong ion difference) and electrolyte concentrations and to evaluate their association with the incidence of gastric necrosis and outcome in dogs with GDV. A retrospective study in 75 dogs with gastric dilation-volvulus syndrome, University veterinary teaching hospital. Medical records were reviewed including signalment, history, initial plasma lactate, acid-base parameters, and electrolyte concentrations, surgical findings and outcome. The overall mortality was 18.7%. In dogs with gastric necrosis, higher initial plasma lactate (median 5.84 vs. 3.36 mmol/L) and AG (20.7 vs. 16.55 mmol/L) and lower pH (7.29 vs. 7.36), bicarbonate (18.7 vs. 22.9 mmol/L), and BE concentration (-8.1 vs. -1.85 mmol/L) were found compared to dogs without gastric necrosis. Anorganic phosphorus was the only electrolyte investigated for which a significant difference was noted between dogs with and without gastric necrosis (1.93 vs. 1.39 mmol/L). The initial plasma lactate concentration (3.36 mmol/L vs. 9.68 mmol/L) and AG (16.8 vs. 20.95 mmol/L) were lower in survivors than nonsurvivors. Survivors had higher pH (7.35 vs. 7.27), bicarbonate concentrations (22.9 vs. 17.35 mmol/L), and BE (-1.9 vs. -9.55 mmol/L) compared to nonsurvivors. Anorganic phosphorus was ultimately the only electrolyte with a significant difference between survivors and nonsurvivors (1.4 vs. 1.84 mmol/L). A multivariate logistic regression model of combination lactate, pH, bicarbonate, BE, AG, and anorganic phosphorus identified pH ≤7.331 and bicarbonate as factors independently associated with gastric necrosis. Similarly, pH ˃7.331, bicarbonate and anorganic phosphorus were independently associated with outcome. Higher initial plasma lactate, AG and anorganic phosphorus levels, and lower pH, BE and bicarbonate concentrations were found in GDV dogs with gastric necrosis. Similarly, initially higher plasma lactate, AG and anorganic phosphorus concentrations, and lower pH, BE and bicarbonate were found in GDV dogs who required euthanasia or who died after surgery. Of these parameters, pH and bicarbonate were strongly and independently associated with gastric necrosis, and pH, bicarbonate and phosphorus were independently associated with outcome.

Surrogate scale for evaluating respiratory function based on complete blood count parameters

BACKGROUND

In this study, we aimed to identify a simple method for evaluating respiratory function using complete blood count parameters.

METHODS

The complete blood count parameters, including red blood cell (RBC) count, hemoglobin (Hb) level, lymphocyte (Lym) and platelet (Plt) count, and partial pressure of oxygen (PO₂ ) level, were measured using automated analyzers in patients with chronic obstructive pulmonary disease (COPD), aged subjects, and young subjects (control group). The red cell index (RCI) was calculated using the following equation: (RBC × Hb)/(Lym × Plt); in theory, the RCI is inversely proportional to the respiratory function.

RESULTS

We observed a significant relationship between the RCI and PCO₂ values, and between the RCI and FEV1/FVC values (P < .05). The RCI in the COPD, and aged subject groups were all significantly higher than that in the control group (P < .05). The cutoff value for normal respiratory function was 2.3. The positive rates for an abnormal increase in RCI were also considerably higher in each observation group than in the control group (P < .05).

CONCLUSION

The RCI can be considered as a simple and effective tool for evaluating respiratory function.

EVALUATION OF THE EFFECTS OF STERNAL VERSUS LATERAL RECUMBENCY ON TRENDS OF SELECTED PHYSIOLOGIC PARAMETERS DURING ISOFLURANE ANESTHESIA IN ZOO-HOUSED BLACK-TAILED PRAIRIE DOGS (CYNOMYS LUDOVICIANUS)

Isoflurane gas anesthesia is often used for immobilization of prairie dogs in field studies, laboratory research, and veterinary clinical purposes. The goals of this prospective study were to evaluate the effects of sternal versus right lateral recumbency on trends of selected physiologic parameters during isoflurane anesthesia in black-tailed prairie dogs ( Cynomys ludovicianus ). Fourteen adult, zoo-housed black-tailed prairie dogs were tested during the study. Animals were anesthetized using isoflurane and randomly placed in either sternal or right lateral recumbency to evaluate changes in trends of physiologic parameters, measured selectively every 30 min throughout a 60-min anesthesia period. Results were analyzed using linear mixed modeling. Right lateral recumbency resulted in a decrease in anion gap of about 4.6 mEq/L (95% confidence interval [95% CI]: 3.1-6.0, P < 0.001), whereas sternal recumbency resulted in a lower decrease of 2.1 mEq/L (95% CI: 0.7-3.6, P = 0.02). However, the absolute values at the beginning and at the end of the anesthesia time were not significantly different between the right lateral and sternal recumbency (all P > 0.57). Body position did not have any effect on any other variables, and most of the observed physiologic changes were due to the duration of anesthesia. Our results indicate no significant effect on trends of selected physiologic parameters between sternal recumbency and right lateral recumbency during 1 hr of isoflurane anesthesia in black-tailed prairie dogs.

Compensation for Acid-Base Disorders

Hydrogen concentration is a critical determinant of many physiologic functions and is tightly regulated. Any alteration in acid-base equilibrium sets into motion a compensatory response by either the lungs or the kidneys. The compensatory response attempts to return the ratio between Pco₂ and [HCO₃^-] to normal and thereby minimize the pH change. A primary increase or decrease in one component is associated with a predictable compensatory change in the same direction in the other component, and the expected compensation can be estimated clinically in dogs and cats.

[Subcutaneous ureteral bypass devices as a treatment option for bilateral ureteral obstruction in a cat with ureterolithiasis]

A 6-year-old female spayed Domestic Shorthair cat was presented with acute lethargy, dehydration, marked azotemia, metabolic acidosis, left-sided renomegaly, and bilateral hydronephrosis. Ureterolithiasis and ureteral obstruction were suspected based on further diagnostics including abdominal sonography. Medical treatment was not successful. Fluoroscopically guided antegrade pyelography confirmed the diagnosis of bilateral ureteral obstruction due to ureterolithiasis. Subcutaneous ureteral bypass (SUB) devices were placed bilaterally, followed by close patient monitoring. Frequent reassessment of patient parameters and blood work served to adjust the fluid needs of the patient and to ensure proper hydration, correction of azotemia at an appropriate rate, and cardiovascular stability. After significant improvement of all patient parameters within 5 days, the patient was discharged from the hospital. Treatment included a dietary change to reduce the risk of stone formation as well as a phosphorus binder. Clinical and clinicopathologic parameters were unchanged at the 1- and 4- and 7-month rechecks (consistent with IRIS CKD stage II-NP-AP0), and both SUB devices continued to provide unobstructed urine flow. Bilateral placement of subcutaneous ureteral bypass devices may be a safe and potentially effective treatment option for acute bilateral ureteral obstruction in cats with ureterolithiasis. Strict patient monitoring and patient-centered postoperative treatment decisions are crucial to successful treatment outcomes.

Blood Gas Analyzers

Acid-base and respiratory disturbances are common in sick and hospitalized veterinary patients; therefore, blood gas analyzers have become integral diagnostic and monitoring tools. This article will discuss uses of blood gas analyzers, types of samples that can be used, sample collection methods, potential sources of error, and potential alternatives to blood gas analyzers and their limitations. It will also discuss the types of analyzers that are available, logistical considerations that should be taken into account when purchasing an analyzer, and the basic principles of how these analyzers work.

Venous blood gas analytes during isoflurane anesthesia in black-tailed prairie dogs (Cynomys ludovicianus)

OBJECTIVE

To describe changes in venous blood gas analytes during isoflurane anesthesia in black-tailed prairie dogs (Cynomys ludovicianus).

DESIGN

Prospective study.

ANIMALS

16 black-tailed prairie dogs.

PROCEDURES

Black-tailed prairie dogs were placed in an anesthesia chamber for induction of general anesthesia, which was maintained with isoflurane in oxygen delivered via mask. Immediately following anesthetic induction, a venous blood sample was obtained from the medial saphenous vein; a second venous blood sample was obtained just prior to anesthetic gas shutoff. An evaluation of venous blood gas analytes was performed on each sample. General linear mixed models with repeated measures were used for data analyses.

RESULTS

Median anesthetic time was 90 minutes (range, 60 to 111 minutes). A significant increase from immediately after induction to completion of anesthesia was observed in Pco2 and mean blood chloride ion, BUN, and creatinine concentrations. A decrease in Po2, mean blood pH, and anion gap was observed from induction of anesthesia to completion. No significant differences during anesthesia were observed in mean base excess or blood bicarbonate, sodium, potassium, calcium, magnesium, blood glucose, lactate, and total CO2 concentrations. No complications occurred during or after anesthesia for any animal.

CONCLUSIONS AND CLINICAL RELEVANCE

Examination of prairie dogs often requires general anesthesia, with isoflurane currently the inhalation agent of choice. Results suggested respiratory acidosis and relative azotemia may occur during isoflurane anesthesia of prairie dogs. Given the increased risk associated with anesthesia in small mammals and the propensity for respiratory disease in prairie dogs, insight into physiologic changes associated with isoflurane anesthesia in healthy prairie dogs can aid in perioperative evaluation and anesthetic monitoring in this rodent species.

[Blood gas analysis in dogs in veterinary practice. A review]

Blood gas analysis is useful to obtain information about acid-base state and gas exchange of the lung. Interpretation is based on the Henderson-Hasselbalch equation. This approach has its limitations especially in interpretation of complex disturbances of acid-base status and has been complemented by base excess and anion gap. Peter Stewart described a model of quantitative approach to the acid-base disturbances which has been further developed and is known as the strong ion approach. This model differs from the traditional approach in the assessment of metabolic disorders of acid base status. Both models complement each other but also have their advantages and disadvantages. For simple disorders of the acid-base state the Henderson-Hasselbalch approach can be used, however in complex disturbances of acid-base balance, especially with abnormalities of serum albumin and phosphate concentrations, the strong ion approach is recommended. With the understanding of both models and of the clinical presentation of blood gas abnormalities, optimal case management and therapy can be provided.

Practical acid-base in veterinary patients

Acid-base abnormalities are common in critically ill veterinary patients. Rapid recognition of disturbances can be helpful in identifying the underlying cause of the patient's clinical signs, directing diagnostics, and monitoring response to therapy. If acid-base disturbances are left unidentified and untreated, severe physiologic consequences can result, including cardiovascular and neurologic dysfunction, protein and enzyme dysfunction, and electrolyte derangements. Treatment of acid-base disorders is aimed at correcting the underlying disease process.

Point-of-care blood gas and electrolyte analysis in rabbits

This article outlines a practical approach for the use of blood-gas analysis in pet rabbits using the I-STAT analyzer. Sampling techniques and a theoretic approach to diagnosis are described. The following 95% RI were obtained from venous samples of 45 healthy rabbits: pH (7.245-7.533), PCO(2) (28.9-52.9 mm Hg), HCO(3) (17.0-32.5 mmol/L), total CO(2) (18-34 mmol/L), BE(ecf) (-10-8 mmol/L), AnGap (11-26 mmol/L), Na (136-147 mmol/L), K (3.4-5.7 mmol/L), Cl (93-113 mmol/L), Glu (93-245 mg/dL), BUN (9-33 mg/dL). Results from 20 arterial samples were pH (7.358-7.502), PCO(2) (29.1-36.8 mm Hg), HCO(3) (17.5-27.6 mmol/L), BE(ecf) (-7-5 mmol/L), PO(2) (75-101 mm Hg), iCa (1.67-1.85). The article also includes some conclusions obtained comparing results from healthy and ill rabbits over an 18-month period.

Acid-base status in the avian patient using a portable point-of-care analyzer

The i-STAT PCA can be used as a blood analyzer in critical avian patients, although single values must be interpreted carefully. The study of the acid-base status in companion birds is still in its infancy. Further research is needed to establish normal reference values in arterial blood gases, compare them with venous blood gas, and to determine if the formulas that deviate from small animal medicine are or are not applicable.