Respiratory monitoring: arterial blood gas analysis, pulse oximetry, and end-tidal carbon dioxide analysis

Relationship between Respiratory Rate, Oxygen Saturation, and Blood Test Results in Dogs with Chronic or Acute Respiratory Disease: A Retrospective Study

This study aimed to investigate the association of respiratory rate (RR), oxygen saturation (SpO2), and blood findings with respiratory disease in dogs and to compare the examination findings in the chronic and acute phases. Dogs that visited a veterinary referral hospital with respiratory symptoms were classified into the chronic disease group (GC), and those that visited the emergency veterinary hospital were classified into the acute disease group (GA). In total, 704 and 682 dogs were included in GC and GA, respectively. The RR and SpO2 were significantly higher and lower, respectively, in patients with lung disease compared to other disease sites in both groups. White blood cell counts were significantly increased in patients with lung and pleural diseases in both groups. Respiratory alkalosis and respiratory acidosis were most common in GC and GA, respectively. The C-reactive protein levels were elevated in both groups, primarily in patients with lung disease. Associations between the results of several tests for understanding and diagnosing respiratory conditions and diseases were recognized, and differences in the trends of the chronic and acute phases were clarified. These tools may be used as adjuncts to other tests for the diagnosis and monitoring of treatment responses.

Investigation of the association between oxygen reserve index and arterial partial oxygen pressure in anesthetized dogs

OBJECTIVE

To evaluate the relationship between oxygen reserve index (ORI) and arterial partial pressure of oxygen (PaO2) in anesthetized dogs.

STUDY DESIGN

Prospective experimental study.

ANIMALS

A total of eight healthy adult Beagle dogs with a median age of 38 (range 20-87) months and a median body mass of 8.6 (range 7.0-13.8) kg.

METHODS

After induction of general anesthesia with propofol, dogs were mechanically ventilated and anesthesia maintained with isoflurane carried in oxygen. Arterial blood samples were collected from a catheter placed in the femoral artery. ORI was measured by placing a CO-oximeter sensor on the tongue. Inspired oxygen fraction (FiO2) was increased from 21% to > 95% in increments of 5%. PaO2 and ORI were recorded and compared at different times. The relationship between ORI and PaO2 was investigated using a nonlinear function, the Hill equation, and a linear regression analysis was performed, as appropriate.

RESULTS

A total of 128 pairs of values were compared for all dogs. Applying the Hill equation to the relationship between ORI and PaO2 resulted in R2 = 0.80 (p < 0.001) with a Hill coefficient of 3.7. It was predicted that ORI ranged 0.1-0.9 as PaO2 ranged 127.0-417.9 mmHg and that in the more linear portion of the range, PaO2 of 127.0-289.9 mmHg ORI ranged 0.1-0.7. Linear regression analysis in the more linear portion showed a weak correlation (R2 = 0.29, p = 0.006).

CONCLUSIONS AND CLINICAL RELEVANCE

In the present study, the Hill equation predicted the relationship between PaO2 and ORI for PaO2 ranging 127.0-417.9 mmHg in anesthetized dogs. However, in the linear portion of the PaO2, the coefficient of determination was low, indicating that ORI is not a surrogate for PaO2.

[Pulmonary function testing in the cat - an overview]

This article provides an overview of currently available pulmonary function tests in cats, divided into invasive and non-invasive methods. Invasive techniques comprise arterial blood gas analysis and measurement of pulmonary mechanics. Non-invasive techniques include pulse oximetry and capnography, as well as methods not yet integrated into everyday practice such as tidal breathing airflow-volume loops, whole-body barometric plethysmography and thorax compression. In this article, the background, execution, interpretation, and limitations of each test are discussed. Proper performance and assessment of pulmonary function measurements may aid in understanding the pathophysiology of feline respiratory disease and in increasing objectivity when assessing the existing disease and treatment efficacy.

Blood Biomarker Profile Alterations in Newborn Canines: Effect of the Mother's Weight

This study aims to determine the effect of the weight of bitches on liveborn and stillbirth puppies from eutocic births, and physiological blood alterations during the first minute postpartum. A total of 52 female dogs were evaluated and distributed in four categories: C1 (4.0-8.0 kg, n = 19), C2 (8.1-16.0 kg, n = 16), C3 (16.1-32.0 kg, n = 11), and C4 (32.1-35.8 kg, n = 6). The dams produced 225 liveborn puppies and 47 were classified as stillbirth type II. Blood samples were taken from the umbilical vein to evaluate the concentration of gases, glucose, lactate, calcium, hematocrit levels, and blood pH. The liveborn puppies in C2, C3, and C4 had more evident physiological alterations (hypercapnia, acidosis) than those in C1 (p < 0.05). These signs indicate a process of transitory asphyxiation. The stillborn pups in all four categories had higher weights than their liveborn littermates. C3 and C4 had the highest mean weights (419.86 and 433.79 g, respectively) and mortality rates (C3 = 20.58%, C4 = 24.58%). Results suggest that if the weight of the bitch is >16.1 kg in eutocic births, there is a higher risk of intrapartum physiological alterations and death. The results of this study allowed us to identify that the weight of dams before birth determines the weight of the puppies at birth.

Enhanced Hemocompatibility and In Vivo Analytical Accuracy of Intravascular Potentiometric Carbon Dioxide Sensors via Nitric Oxide Release

In this letter, the innate ability of nitric oxide (NO) to inhibit platelet activation/adhesion/thrombus formation is employed to improve the hemocompatibility and in vivo accuracy of an intravascular (IV) potentiometric PCO₂ (partial pressure of carbon dioxide) sensor. The catheter-type sensor is fabricated by impregnating a segment of dual lumen silicone tubing with a proton ionophore, plasticizer, and lipophilic cation-exchanger. Subsequent filling of bicarbonate and strong buffer solutions and placement of Ag/AgCl reference electrode wires within each lumen, respectively, enables measurement of the membrane potential difference across the inner wall of the tube, with this potential changing as a function of the logarithm of sample PCO₂. The dual lumen device is further encapsulated within a S-nitroso-N-acetyl-DL-penicillamine (SNAP)-doped silicone tube that releases physiological levels of NO. The NO releasing sensor exhibits near-Nernstian sensitivity toward PCO₂ (slope = 59.31 ± 0.78 mV/decade) and low drift rates (<2 mV/24 h after initial equilibration). In vivo evaluation of the NO releasing sensors, performed in the arteries and veins of anesthetized pigs for 20 h, shows enhanced accuracy (vs non-NO releasing sensors) when benchmarked to measurements of discrete blood samples made with a commercial blood gas analyzer. The accurate, continuous monitoring of blood PCO₂ levels achieved with this new IV NO releasing PCO₂ sensor configuration could help better manage hospitalized patients in critical care units.

Evaluation of the reliability of pulse oximetry, at different attachment sites, to detect hypoxaemia in immobilized impala (Aepyceros melampus)

OBJECTIVE

Evaluation of the reliability of pulse oximetry at four different attachment sites compared to haemoglobin oxygen saturation measured by a co-oximeter and calculated by a blood gas analyser in immobilized impala.

STUDY DESIGN

Randomized crossover study.

ANIMALS

A total of 16 female impala.

METHODS

Impala were immobilized with etorphine or thiafentanil alone, or etorphine in combination with a novel drug. Once immobilized, arterial blood samples were collected at 5 minute intervals for 30 minutes. Then oxygen was insufflated (5 L minute^-1) intranasally at 40 minutes and additional samples were collected. A blood gas analyser was used to measure the arterial partial pressure of oxygen and calculate the oxygen haemoglobin saturation (cSaO₂); a co-oximeter was used to measure the oxygen haemoglobin saturation (SaO₂) in arterial blood. Pulse oximeter probes were attached: under the tail, to the pinna (ear) and buccal mucosa (cheek) and inside the rectum. Pulse oximeter readings [peripheral oxygen haemoglobin saturation (SpO₂) and pulse quality] were recorded at each site and compared with SaO₂ and cSaO₂ using Bland-Altman and accuracy of the area root mean squares (A_rms) methods to determine the efficacy. P value < 0.05 was considered significant.

RESULTS

Pulse quality was 'good' at each attachment site. SpO₂ measured under the tail was accurate and precise but only when SaO₂ values were above 90% (bias = 3, precision = 3, A_rms = 4). The ear, cheek and rectal probes failed to give accurate or precise readings (ear: bias = -4, precision = 14, A_rms = 15; cheek: bias = 12, precision = 11, A_rms = 16; and rectum: bias = 5, precision = 12, A_rms = 13).

CONCLUSIONS AND CLINICAL RELEVANCE

In order to obtain accurate and precise pulse oximetry readings in immobilized impala, probes must be placed under the tail and SaO₂ must be above 90%. Since SaO₂ values are usually low in immobilized impala, pulse oximeter readings should be interpreted with caution.

Clinical Application of Pulmonary Function Testing in Small Animals

Pulmonary function tests (PFTs) are important diagnostic tools that have wide clinical applications in human and veterinary medicine. Widespread use of PFTs in measuring lung volumes in veterinary medicine was historically limited by the need for specialized equipment to accurately perform and interpret these tests, and by lack of patient cooperation. However, recent advances and modifications have allowed PFTs to be safely performed in conscious veterinary patients with minimal stress. This article focuses on the most commonly used tests of pulmonary function including tests of pulmonary mechanics and of gas exchange in the lungs.

Association between computed tomographic thoracic injury scores and blood gas and acid-base balance in dogs with blunt thoracic trauma

OBJECTIVE

To determine the association between thoracic injuries evaluated by computed tomography (CT) and arterial blood gas and acid-base status in dogs with blunt thoracic trauma caused by motor vehicle accidents.

DESIGN

Prospective observational clinical study.

SETTING

University teaching hospital.

ANIMALS

Thirty-one client owned traumatized dogs and 15 healthy dogs.

PROCEDURES

All trauma group dogs underwent a CT scan and simultaneous arterial blood gas analysis within 24 hours, but not before 4 hours, after the traumatic incident within a 45-month enrollment period.

MEASUREMENTS AND MAIN RESULTS

Thorax injuries were classified as pulmonary, pleural space, or rib cage and each of these components was scored for severity using a CT composite pulmonary, pleural, and rib score. The trauma group arterial blood gas and acid-base status were evaluated for statistical difference from the control group. The pulmonary-arterial oxygen pressure was significantly lower in the trauma group compared to the control group that was supported by significant differences in the calculated variables of arterial blood oxygenation as well. There was also a significant correlation between the composite lung score and pleural score and the variables of arterial oxygen status. The pulmonary-arterial carbon dioxide pressure was not significantly different to any of the thoracic injury variables indicating normal alveolar ventilation. Acid-base imbalances were generally mild, insignificant, and variable.

CONCLUSIONS AND CLINICAL RELEVANCE

Blunt thoracic trauma causes significant pulmonary and pleural injury and the blood oxygen economy is significantly affected by this. The functional measures of arterial blood oxygenation were well correlated with thoracic CT pathology. Alveolar ventilation was mostly spared but a clinically significant ventilation perfusion mismatch was present.

Evaluation of Pulse Oximetry in Healthy Brachycephalic Dogs

Brachycephalic airway syndrome (BAS) is characterized by increased upper airway resistance due to conformational abnormalities occurring in brachycephalic dogs (BD). In this prospective study, we evaluated pulse oximetry (SpO₂) and arterial blood gas values in 18 healthy BD and compared these values with those of 18 healthy mesocephalic and dolichocephalic dogs (MDD). All dogs were assigned a BAS score based on an owner questionnaire. Inclusion criteria included presentation to the hospital for a problem unrelated to the respiratory system and unremarkable blood analyses and physical examination. In awake dogs, SpO₂ values were obtained from a minimum of two sites. Dogs were then sedated, and SpO₂ values were obtained again concurrently with an arterial blood gas sample. The SpO₂ values were significantly lower in BD compared with MDD, but there were no statistically significant differences between BD and MDD for any arterial blood gas parameters. Based on the BAS score, BD who were moderately BAS-affected (n = 5), had significantly lower arterial saturation of hemoglobin with oxygen values on arterial blood gas when compared with MDD (n = 18). Although BD had statistically lower SpO₂ values than MDD, the mean SpO₂ values for both groups were within the normal range.

Comparison of Enterprise Point-of-Care and Nova Biomedical Critical Care Xpress analyzers for determination of arterial pH, blood gas, and electrolyte values in canine and equine blood

BACKGROUND

Point-of-care analyzers can provide a rapid turnaround time for critical blood test results. Agreement between the Enterprise Point-of-Care (EPOC) and bench-top laboratory analyzers is important to determine the clinical reliability of the EPOC.

OBJECTIVES

The aim of the study was (1) to evaluate the precision (repeatability) of blood gas values measured by the EPOC and (2) to determine the level of agreement between the EPOC and Nova Critical Care Express (Nova CCX) for the assessment of arterial pH, blood gases, and electrolyte variables in canine and equine blood.

METHODS

Arterial blood samples from dogs were analyzed on the EPOC and Nova CCX analyzers to determine precision and agreement of pH, PaCO₂ , PaO₂ , and HCT. The same analytes plus Na⁺ , K^- , and Cl^- were analyzed for agreement using equine blood. Statistical analyses included assessment of precision using the coefficient of variation (CV%), and agreement using the Deming regression, Pearson correlation, and Bland-Altman plots.

RESULTS

Both analyzers provided precise results of pH, PaCO₂ , PaO_2, and HCT, meeting CV% quality requirement values. In both species, Deming regression results were acceptable and correlation values were above 0.93 for arterial pH and blood gases, but lower for sodium and chloride. Bland-Altman plots demonstrated varying degrees of bias, but good agreement between the 2 analyzers was seen when arterial blood gases and electrolytes were measured, except for PaCO₂ and Cl^-. CONCLUSION: The EPOC analyzer provides consistent, reliable results for canine arterial blood gas values and for equine arterial blood gas and electrolyte values. Cl^- results could be acceptable with the application of a correction factor, but the PaCO₂ results were more variable.

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.

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.

Changes in respiratory function in Pembroke Welsh Corgi dogs with degenerative myelopathy

Canine degenerative myelopathy (DM) is characterized by progressive degeneration of the spinal cord. Although atrophic changes in the intercostal muscles were previously reported in the late stage of DM in Pembroke Welsh Corgis (PWCs), changes in respiratory function have not yet been examined. In the present study, we performed an arterial blood gas analysis and measured respiratory movements over progressive disease stages to document changes in respiratory function in DM-affected PWCs. We found that respiratory dysfunction progressed during the later stages of DM and correlated with a change in respiratory movement to the abdominal breathing pattern. These results suggested that hypoventilation occurred due to dysfunctional changes in the intercostal muscles and resulted in hypoxemia in the later stages of DM.

Pulse oximetry and capnometry

Respiratory dysfunction is common in veterinary patients and various techniques have been developed to rapidly and accurately monitor pulmonary gas exchange. Pulse oximetry and capnometry are tools that allow for continuous evaluation of pulmonary function. Methodology, indications, and limitations of pulse oximetry and capnometry are discussed in this article. Both techniques are useful for monitoring critically ill or anesthetized patients; however, limitations to their use exist which underscore the need for intermittent arterial blood gas analysis.

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.

The measure of treatment agreement between portable and laboratory blood gas measurements in guiding protocol-driven ventilator management

BACKGROUND

Portable blood gas analyzer and monitor devices are increasingly being used to direct ventilator therapy. The purpose of this study was to evaluate the "measure of treatment agreement" between portable and laboratory blood gas measurements used in guiding protocol-driven ventilator management.

MATERIALS AND METHODS

Using National Institutes of Health Acute Respiratory Distress Syndrome network ventilator management guidelines to manage patient care, measurements taken from the Nonin 8500 M pulse oximeter (SpO2), the Novametrix-610 end-tidal CO2 (ETCO2) detector, and the i-STAT 1 (SaO2, PO2, pH, PCO2) were compared with the recommended treatment from paired laboratory ABL-725 (SaCO2, PO2, pH, PCO2) measurements.

RESULTS

Four hundred forty-six intubated adult intensive care unit patients were studied prospectively. Except for the ETCO2 (R2 = 0.460), correlation coefficients between portable and laboratory measurements were high (R2 > or = 0.755). Testing for equivalence, the Nonin-SpO2, iSTAT-PO2, iSTAT-pH, and iSTAT-PCO2 were deemed "equivalent" surrogates to paired ABL measurements. Testing for the limits of agreement found only the iSTAT-PCO2 to be an acceptable surrogate measurement. The measure of treatment agreement between the portable and paired laboratory blood gas measurements were Nonin-SpO2 (68%), iSTAT-SaO2 (73%), iSTAT-PO2 (97%), iSTAT-pH (88%), iSTAT-PCO2 (95%), and Novametrix-ETCO2 (60%). Only the iSTAT-PO2 and the iSTAT-PCO2 achieved the > or =95% treatment agreement threshold to be considered as acceptable surrogates to laboratory measurements.

CONCLUSIONS

: The iSTAT-PO2 and -PCO2 were portable device measurements acceptable as surrogates to standard clinical laboratory blood gas measurements in guiding protocol-directed ventilator management. The "measure of treatment agreement," based on standardized decisions and measurement thresholds of a protocol, provides a simple method for assessing clinical validity of surrogate measurements.

Triage and approach to the acute abdomen

The presentation of a patient with acute abdominal pain often is both a diagnostic and therapeutic challenge for the veterinary practitioner. Rapid physical examination and assessment of the patient's cardiovascular status are critical to initiating appropriate and often aggressive medical management as diagnostic tests are being performed. A number of diagnostic tests can be performed, including complete blood count, serum biochemistry profile, serum amylase and lipase, abdominal radiographs, abdominal ultrasound, abdominal paracentesis or diagnostic peritoneal lavage, cytology, and fluid analysis. In some cases, surgical exploration may be indicated, depending on each patient's clinical signs and response to therapy. Of the most important aspects of medical management of the patient with acute abdominal pain is to maintain oxygen delivery to tissues and to treat aggressively for pain or discomfort. The initial triage and approach to the patient with acute abdomen are discussed.

Pulse oximetry and end tidal carbon dioxide monitoring

Noninvasive monitoring of cardiopulmonary function through pulse oximetry and capnography provides immediate and important information for the clinician. These monitors are not a replacement for vigilant attention to the patient, however; they should be used in conjunction with arterial blood gas analysis and serial physical examinations to ensure that the continuous readings are accurate and make clinical sense.