Changes in colloid osmotic pressure as a function of anesthesia and surgery in the presence and absence of isotonic fluid administration in dogs

Objective  To determine how a combination of anesthetic drugs; including pre-medication, induction agents and inhalational agents; affect colloid osmotic pressure (COP) in the presence and absence of isotonic fluid administration. Secondarily, to determine if changes in total plasma protein (TPP) correlate with COP in anesthetized patients.
Study Design  Prospective, randomized clinical study.
Animals  Ten female dogs, 4 months to 4 years of age and >8 kg undergoing elective ovariohysterectomy.
Methods  All dogs were anesthetized in a similar fashion. After induction, five dogs received lactated ringer's solution (LRS) at 10 mL kg⁻¹ hour⁻¹ and five dogs received no fluid therapy during anesthesia. Blood samples were collected prior to pre-medication, prior to induction, immediately post-induction/prior to the inhalational agent, 30 minutes post-induction, at the time of recovery and 45 minutes post-discontinuation of inhalant. TPP and COP were measured from each sample.
Results  Administration of fluids resulted in a decrease in COP and TPP over time that did not return to baseline by 45 minutes after recovery. Anesthesia without the administration of fluids also resulted in a significant decrease in COP over time, that was rebounding by recovery (but still significantly less than baseline). TPP had variable correlation with COP at different time points with or without fluid administration.
Conclusions and clinical relevance  Anesthetic drugs alter COP similarly in the presence and absence of isotonic fluids. These changes in COP did not have a simple relationship to TPP and so the latter could not be used to predict COP in this patient population.     

Evaluation of an indirect oscillometric blood pressure monitor in normotensive and hypotensive anesthetized dogs

Objective – To determine the accuracy and precision of an oscillometric noninvasive blood pressure device as a predictor of invasive direct blood pressure in healthy anesthetized hypotensive and normotensive dogs. Design – Prospective observational study. Setting – University teaching hospital. Animals – Eight crossbred adult dogs. Interventions – Anesthesia was induced with propofol and maintained with isoflurane. A catheter was placed in the dorsal pedal artery to record systolic, mean, and diastolic arterial blood pressures (aSAP, aMAP, and aDAP, respectively). The noninvasive blood pressure device cuff was placed around the contralateral front limb to record noninvasive systolic, mean, and diastolic blood pressure (nSAP, nMAP, and nDAP). Two states of blood pressure (BP) were studied: baseline state was established by keeping end‐tidal isoflurane concentration at 1.2±0.1%. The hypotensive state was achieved by maintaining the same isoflurane concentration while withdrawing approximately 40% of the animal's blood volume until aMAP was stable at approximately 40 mm Hg. At the end of the study, blood was returned to the animal and it was allowed to recover from anesthesia. Measurements and Main Results – Agreement between the direct and indirect BP measurements was determined by the Bland‐Altman method. The SAP and MAP but not DAP bias varied significantly between each BP state. Normotensive absolute biases (mean [SD]) for SAP, MAP, and DAP were ?14.7 mm Hg (15.5 mm Hg), ?16.4 mm Hg (12.1 mm Hg), and ?14.1 mm Hg (15.8 mm Hg), respectively. Absolute biases during the hypotensive state for SAP, MAP, and DAP were ?32 mm Hg (22.6 mm Hg), ?24.2 mm Hg (19.5 mm Hg), and ?16.8 mm Hg (17.2 mm Hg), respectively. Conclusion – The oscillometric device was not reliably predictive of intra‐arterial BP during hypotension associated with acute hemorrhage.     

Evaluation of a new oscillometric blood pressure monitor in isoflurane-anesthetized dogs

Objective This study was conducted to evaluate the performance of a new veterinary oscillometric noninvasive blood pressure (NIBP) monitor in anesthetized dogs. Study design Assessment was made to determine how closely indirect measurements were associated with direct measurements, and if there were statistically significant differences between the measurements by site. Animals Six mongrel dogs weighing 27.8 ± 2.9 kg. Methods Dogs were anesthetized with thiopental and maintained with isoflurane, which was delivered with controlled ventilation. Direct pressure measurements were obtained via a percutaneously placed arterial catheter. A range of systolic arterial pressures (SAP) were achieved by changing the isoflurane concentrations. Sites of cuff placement for indirect measurements were identified as metacarpus, metatarsus, and anterior tibial. Results At pressures below 80 mm Hg, indirect systolic measurements averaged 4 ± 3 mm Hg, higher than the direct values. At normal and high levels, indirect systolic measurements underestimated direct values by 18 ± 6 and 23 ± 6 mm Hg, respectively. Diastolic and mean pressure measurements followed the same trend, with indirect values being lower than the direct arterial pressures. Systolic, diastolic and mean arterial pressure measurements differed by cuff‐placement site. Conclusions When analyzed by site and level, indirect systolic and mean arterial blood pressures during hypotension were essentially the same as direct pressures. However, at pressures within the normal or high range, indirect measurements underestimated the direct pressures. Clinical relevance Noninvasive blood pressure measurements with a new oscillometric monitor provided an excellent means of detecting arterial hypotension in anesthetized dogs. The metatarsal site for cuff placement was slightly better than the metacarpal or anterior tibial site, considering that the regression line was closest to complete equality between the indirect and direct measurements for SAP.     

Analysis of tidal breathing flow volume loop in dogs with tracheal masses

Objectives To investigate whether there are any changes in the tidal breathing flow volume loop (TBFVL) in calm, non-dyspnoeic dogs with intratracheal masses. Methods We compared 4 dogs with intratracheal masses (group 1) with 10 healthy dogs (group 2). Routine clinical and laboratory examinations of the dogs were unremarkable, except for episodic upper respiratory obstructive signs in the dogs in group 1. Lateral radiography of the neck and thorax showed that group 1 dogs had masses that appeared to protrude into the tracheal lumen. Tracheoscopy and surgery or necropsy was performed to confirm the presence of the mass. Arterial blood gas and TBFVL analysis was carried out in all dogs to assess respiratory status. Results The shape of the TBFVL for dogs in group 1 was narrower and ovoid compared with that for the group 2 dogs. Tidal volume and expiratory and inspiratory times were significantly reduced, whereas the respiratory rate was increased for dogs in group 1 compared with dogs in group 2. Arterial blood gas analysis was unremarkable for all dogs. Conclusions TBFVL is a non-invasive technique that is easy to perform and well tolerated by dogs. In the absence of abnormalities detected by routine diagnostic evaluations and arterial blood gas analysis in dogs with intratracheal masses, the TBFVL contributes to the definition of the physiologic status of the airways at the time of testing, and results suggests that these dogs breathe quite normally when they are calm and non-dyspnoeic.     

Proof-of-concept study: Evaluation of plasma and urinary electrolytes as markers of response to L-asparaginase therapy in dogs with high-grade lymphoma

Response to chemotherapy is one of the most important prognostic factors in dogs with lymphoma. The objective of this feasibility study was to evaluate if clinical responses to a specific cytotoxic agent (L-asparaginase) could be anticipated by measuring analyte concentrations in plasma and urine concentrations of lymphoma-bearing dogs. We hypothesized that potassium and phosphate concentrations in plasma and urine would be higher in dogs that completely responded to therapy. Plasma and urine samples of dogs with lymphoma were obtained before 12 and 24 hours after intramuscular L-asparaginase injections. Peripheral lymph node volumes were evaluated according to the Veterinary Cooperative Oncology Group standardized criteria. Plasma and urine electrolyte, calcium, phosphate, creatinine, urea, total protein, and albumin concentrations were measured, and the fractional excretions of each electrolyte were calculated. Statistical analyses compared complete vs partial responders using a linear regression model. Contrast analyses were also performed to differentiate the mean of each group, with adjustments made with the Benjamini-Hochberg procedure. Fourteen dogs were included, eight with complete responses, and six with partial responses. Plasma phosphate concentrations were significantly higher at 12 hours (P = .0003) and 24 hours (P = .009) after complete responses to therapy. This study demonstrates the potential use of plasma and urine analyte monitoring after chemotherapy induction. Plasma phosphate measurements represent a potential indicator of early responses to L-asparaginase therapy. Larger population studies are warranted to confirm these preliminary results.     

Ability of pulse wave transit time to detect changes in stroke volume and to estimate cardiac output compared to thermodilution technique in isoflurane-anaesthetised dogs

Objective

To evaluate the ability of pulse wave transit time (PWTT) to detect changes in stroke volume (SV) and to estimate cardiac output (CO) compared with the thermodilution technique in isoflurane-anaesthetized dogs.