Cardiopulmonary effects of positive end-expiratory pressure during one-lung ventilation in anesthetized dogs with a closed thoracic cavity

OBJECTIVE: To evaluate the effects on oxygen delivery (DO2) of 2.5 and 5 cm H2O of positive end-expiratory pressure (PEEP) applied to the dependent lung during one-lung ventilation (OLV) in anesthetized dogs with a closed thoracic cavity. ANIMALS: 7 clinically normal adult Walker Hound dogs. PROCEDURE: Dogs were anesthetized, and catheters were inserted in a dorsal pedal artery and the pulmonary artery. Dogs were positioned in right lateral recumbency, and data were collected during OLV (baseline), after application of 2.5 cm H2O of PEEP for 15 minutes during OLV, and after application of 5 cm H2O of PEEP for 15 minutes during OLV. Hemodynamic and respiratory variables were analyzed and calculations performed to obtain DO2, and values were compared among the various time points by use of an ANOVA for repeated measures. RESULTS: PEEP induced a significant decrease in shunt fraction that resulted in a significant increase in arterial oxygen saturation. However, it failed to significantly affect arterial oxygen content (CaO2) or cardiac output. Thus, DO2 was not affected in healthy normoxemic dogs as a net result of the application of PEEP. CONCLUSIONS AND CLINICAL RELEVANCE: The use of PEEP during OLV in anesthetized dogs with a closed thoracic cavity did not affect DO2. Use of PEEP during OLV in dogs with a closed thoracic cavity is recommended because it does not affect cardiac output and any gain in CaO2 will be beneficial for DO2 in critically ill patients.     

Hemodynamic and respiratory responses in halothane-anesthetized horses exposed to positive end-expiratory pressure alone and with dobutamine

The influence of positive end-expiratory pressure (PEEP) on the alveolar-arterial O2 tension difference [P(A-a)O2], physiologic right-to-left shunt fraction, physiologic dead space-to-tidal volume ratio, and hemodynamic variables was studied in halothane-anesthetized horses maintained in dorsal recumbency during controlled ventilation. Dobutamine was used to minimize the adverse cardiovascular consequences of PEEP. Six adult horses were anesthetized, using xylazine (2.2 mg/kg of body weight, IM), guaifenesin (50 mg/kg, IV), thiamylal Na (4.4 mg/kg, IV), and halothane (1.5 to 2% inspired) in 100% O2. Mechanical ventilation was controlled to maintain arterial eucapnia for at least 45 minutes during base-line measurements. Hemodynamic and respiratory variables were determined every 15 minutes during equilibration. Each horse was subjected to 4 randomized treatments: 5 cm of H2O PEEP, 10 cm of H2O PEEP, 5 cm of H2O PEEP plus dobutamine (1 microgram/kg/min), and 10 cm of H2O PEEP plus dobutamine (1 microgram/kg/min). Each treatment lasted 15 minutes and immediately followed its predecessor. Although the magnitude of PEEP was randomized with and without dobutamine, PEEP without dobutamine always preceded PEEP with dobutamine. Differences in hemodynamic or respiratory variables among base-line measurements, 5 cm of H2O PEEP, or 10 cm of H2O PEEP were not significant (P greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

The influence of ventilation mode (spontaneous ventilation, IPPV and PEEP) on cardiopulmonary parameters in sevoflurane anaesthetized dogs

The purpose of this study was to investigate the cardiopulmonary influences of sevoflurane in oxygen at two anaesthetic concentrations (1.5 and 2 MAC) during spontaneous and controlled ventilation in dogs. After premedication with fentany-droperidol (5 microg/kg and 0.25 mg/kg intramuscularly) and induction with propofol (6 mg/kg intravenously) six dogs were anaesthetized for 3 h. Three types of ventilation were compared: spontaneous ventilation (SpV), intermittent positive pressure ventilation (IPPV), and positive end expiratory pressure ventilation (PEEP, 5 cm H2O). Heart rate, haemoglobin oxygen saturation, arterial blood pressures, right atrial and pulmonary arterial pressures, pulmonary capillary wedge pressure and cardiac output were measured. End tidal CO2%, inspiratory oxygen fraction, respiration rate and tidal volume were recorded using a multi-gas analyser and a respirometer. Acid-base and blood gas analyses were performed. Cardiac index, stroke volume, stroke index, systemic and pulmonary vascular resistance, left and right ventricular stroke work index were calculated. Increasing the MAC value during sevoflurane anaesthesia with spontaneous ventilation induced a marked cardiopulmonary depression; on the other hand, heart rate increased significantly, but the increases were not clinically relevant. The influences of artificial respiration on cardiopulmonary parameters during 1.5 MAC sevoflurane anaesthesia were minimal. In contrast, PEEP ventilation during 2 MAC concentration had more pronounced negative influences, especially on right cardiac parameters. In conclusion, at 1.5 MAC, a surgical anaesthesia level, sevoflurane can be used safely in healthy dogs during spontaneous and controlled ventilation (IPPV and PEEP of 5 cm H2O).     

Effect of one-lung ventilation on oxygen delivery in anesthetized dogs with an open thoracic cavity

OBJECTIVE: To evaluate effects of one-lung ventilation on oxygen delivery in anesthetized dogs with an open thoracic cavity. ANIMALS: 8 clinically normal adult Walker Hound dogs. PROCEDURE: Each dog was anesthetized and subjected to one-lung ventilation during a period when it had an open thoracic cavity. A Swan-Ganz catheter was used to measure hemodynamic variables and obtain mixed-venous blood samples. A catheter was inserted in the dorsal pedal artery to measure arterial pressure and obtain arterial blood samples. Oxygen delivery index was calculated and used to assess effects of one-lung ventilation on cardiopulmonary function. Effects on hemodynamic and pulmonary variables were analyzed. RESULTS: One-lung ventilation caused significant decreases in PaO2, arterial oxygen saturation (SaO2), mixed-venous oxygen saturation, and arterial oxygen content (CaO2). One-lung ventilation caused significant increases in PaCO2, physiologic dead space, and alveolar-arterial oxygen difference. Changes in SaO2, CaO2, and PaCO2, although significantly different, were not considered to be of clinical importance. One-lung ventilation induced a significant increase in pulmonary arterial wedge pressure, mean pulmonary artery pressure, and shunt fraction. One-lung ventilation did not have a significant effect on cardiac index, systemic vascular resistance index, pulmonary vascular resistance index, and oxygen delivery index. CONCLUSIONS AND CLINICAL RELEVANCE: One-lung ventilation affected gas exchange and hemodynamic function, although oxygen delivery in clinically normal dogs was not affected during a period with an open thoracic cavity. One-lung ventilation can be used safely in healthy dogs with an open thoracic cavity during surgery.     

Effects of isovolemic resuscitation with hemoglobin-based oxygen carrier Hemoglobin glutamer-200 (bovine) on systemic and mesenteric perfusion and oxygenation in a canine model of hemorrhagic shock: a comparison with 6% hetastarch solution and shed blood

OBJECTIVE: To study Hemoglobin glutamer-200 bovine (Hb-200), 6% hetastarch (HES) and shed whole blood (WB) resuscitation in canine hemorrhagic shock. STUDY DESIGN: Prospective laboratory investigation. Animals Twelve adult dogs [29 +/- 1 kg (mean +/- SD)]. METHODS: Anesthetized dogs were instrumented for recording systemic and mesenteric hemodynamic parameters and withdrawal of arterial, mixed and mesenteric venous blood, in which hematological, oxygenation, blood gas and acid-bases variables were determined. Recordings were made before [baseline (BL)], after 1 hour of hypovolemia and immediately and 3 hours post-resuscitation with 30 mL kg(-1) of either Hb-200, HES, or WB. RESULTS: Blood withdrawal (average 34 +/- 2 mL kg(-1)) caused significant hemodynamic changes, metabolic acidosis and hyperlactatemia characteristic for hemorrhagic shock. Only WB transfusion restored all variables. Hemoglobin glutamer-200 bovine infusion returned most hemodynamic parameters including cardiac output and mesenteric arterial blood flow to BL but increased mean arterial pressure above BL (p < 0.05). However, Hb-200 failed to restore total Hb and arterial oxygen content (CaO2), leaving systemic (DO2I) and mesenteric O2 delivery (DO2Im) below BL (p < 0.05). Nevertheless, acid-base variables recovered completely after Hb-200 resuscitation, and met-hemoglobin (Met-Hb) levels increased (p < 0.05). Hetastarch resuscitation returned hemodynamic variables to or above BL but further decreased total Hb and CaO2, preventing recovery of sDO2I and mDO2I (p < 0.05). Thus, systemic and mesenteric O2 extraction stayed above BL (p < 0.05) while acid-base variables recovered to BL, although slower than in Hb-200 and WB groups (p < 0.05). CONCLUSIONS AND CLINICAL RELEVANCE: Resuscitation with Hb-200 seemed to resolve metabolic acidosis and lactatemia more rapidly than HES, but not WB; yet it is not superior to HES in improving DO2I and DO2Im. The hyperoncotic property of solutions like Hb-200 that results in rapid volume expansion with more homogenous microvascular perfusion and the ability to facilitate diffusive O2 transfer accelerating metabolic recovery may be the key mechanisms underlying their beneficial effects as resuscitants.     

Balanced anesthesia and ventilation strategies for an alpaca (Lama pacos) with an increased anesthetic-risk

We report the use of a balanced anesthetic technique in a three-year-old, female Huacaya alpaca with an increased anesthetic risk that underwent an extensive dental surgery. Anesthesia was provided with an infusion of midazolam, fentanyl, S-ketamine and low concentrations of isoflurane in oxygen. The mandibular alveolar nerve was desensitized with a lidocaine-bupivacaine combination. The alpaca showed signs of hypoxemia fifteen minutes after anesthesia induction and arterial blood gases confirmed severe venous admixture. Application of positive end expiratory pressure (PEEP) of 6-9 cm H2O improved the arterial oxygenation. Other cardiopulmonary variables remained within the normal range. At the end of surgery, sarmazenil was administered to antagonize the effects of midazolam and emergence from anesthesia was smooth and uneventful. Flunixine meglumine and a transdermal delivery system for fentanyl were administered for post-operative analgesia. This method of balanced anesthesia allowed for an adequate anesthetic plane and a safe recovery, however, special ventilation strategies (PEEP) had to be applied.     

Effects of an alveolar recruitment maneuver on cardiovascular and respiratory parameters during total intravenous anesthesia in ponies

OBJECTIVE: To evaluate pulmonary and cardiovascular effects of a recruitment maneuver (RM) combined with positive end-expiratory pressure (PEEP) during total intravenous anesthesia in ponies. ANIMALS: 6 healthy adult Shetland ponies. PROCEDURE: After premedication with detomidine (10 microg/kg, IV), anesthesia was induced with climazolam (0.06 mg/kg, IV) and ketamine (2.2 mg/kg, IV) and maintained with a constant rate infusion of detomidine (0.024 mg/kg/h), climazolam (0.036 mg/kg/h), and ketamine (2.4 mg/kg/h). The RM was preceded by an incremental PEEP titration and followed by a decremental PEEP titration, both at a constant airway pressure difference (deltaP) of 20 cm H2O. The RM consisted of a stepwise increase in deltaP by 25, 30, and 35 cm H2O obtained by increasing peak inspiratory pressure (PIP) to 45, 50, and 55 cm H2O, while maintaining PEEP at 20 cm H2O. Hemodynamic and pulmonary variables were analyzed at every step of the PEEP titration-RM. RESULTS: During the PEEP titration-RM, there was a significant increase in PaO 2 (+12%), dynamic compliance (+ 62%), and heart rate (+17%) and a decrease in shunt (-19%) and mean arterial blood pressure (-21%) was recorded. Cardiac output remained stable. CONCLUSIONS AND CLINICAL RELEVANCE: Although baseline oxygenation was high, Pa(O2) and dynamic compliance further increased during the RM. Despite the use of high PIP and PEEP and a high tidal volume, limited cardiovascular compromise was detected. A PEEP titration-RM may be used to improve oxygenation in anesthetized ponies. During stable hemodynamic conditions, PEEP titration-RM can be performed with acceptable adverse cardiovascular effects.     

One-lung versus two-lung ventilation in the closed-chest anesthetized dog: a comparison of cardiopulmonary parameters

OBJECTIVE: To evaluate cardiopulmonary effects of one-lung ventilation (OLV) versus two-lung ventilation (TLV) in closed-chest anesthetized dogs. STUDY DESIGN: Controlled, randomized experiment. ANIMALS: Fourteen, 2- to 7-year-old adult dogs, weighing 23 +/- 6 kg. METHODS: The dogs were anesthetized with acepromazine, morphine, thiopental, and halothane in oxygen, ventilated, and paralyzed with vecuronium. Tidal volume was 10 mL/kg. Respiratory rate was set to maintain end-tidal CO2 (ETCO2) at 40 +/- 2 mm Hg before instrumentation then not changed. The left bronchus of 7 dogs was obstructed with a Univent bronchial blocker (Fuji Systems Corp, Tokyo, Japan). Blood gas analysis and hemodynamic measurements were taken at predetermined intervals for 1 hour in the TLV group and at baseline and following bronchial obstruction in the OLV group. RESULTS: Shunt fraction was not significantly different between groups, but in OLV shunt increased from baseline at 5 minutes. Arterial oxygen (PaO2) decreased after baseline in OLV compared with TLV. Arterial carbon dioxide (PaCO2) increased with OLV and decreased with TLV. In OLV, systemic vascular resistance was variable and decreased compared with TLV. Cardiac index increased over time in both groups but was not affected by treatment. Heart rate, mean arterial pressure, and diastolic arterial pressure increased with OLV compared with TLV but did not change over time. CONCLUSION: This study shows that OLV statistically decreases oxygen tension and transiently increases shunt fraction, but with 100% O2 it appears to be a feasible procedure with minimal cardiopulmonary side effects in healthy dogs. CLINICAL RELEVANCE: OLV is a feasible procedure in anesthetized dogs to better facilitate thoracic procedures such as bronchopleural fistula repair and thoracoscopy.     

Cardiopulmonary changes induced during one-lung ventilation in anesthetized dogs with a closed thoracic cavity

OBJECTIVE: To evaluate the effects of one-lung ventilation (OLV) on oxygen delivery (DO2) in anesthetized dogs with a closed thoracic cavity. ANIMALS: 7 clinically normal adult Walker Hound dogs. PROCEDURE: Dogs were anesthetized. Catheters were inserted in a dorsal pedal artery and the pulmonary artery. Dogs were positioned in right lateral recumbency. Data were collected at baseline (Paco2 of 35 to 45 mm Hg), during two-lung ventilation, and 15 minutes after creating OLV. Hemodynamic and respiratory variables were analyzed and calculations performed to obtain DO2, and values were compared among the various time points by use of an ANOVA for repeated measures. RESULTS: OLV induced a significant augmentation of shunt fraction that resulted in a significant reduction in Pao2, arterial oxygen saturation, and arterial oxygen content. Cardiac index was not significantly changed. The net result was that DO2 was not significantly affected by OLV. CONCLUSIONS AND CLINICAL RELEVANCE: Use of OLV in healthy dogs does not induce significant changes in DO2, which is the ultimate variable to use when evaluating tissue oxygenation. One-lung ventilation can be initiated safely in dogs before entering the thoracic cavity during surgery. Additional studies are necessary to evaluate OLV in clinically affected patients and variations in age, body position, and type of anesthetic protocol.     

Cardiopulmonary effects of positive end-expiratory pressure in anesthetized horses.

The cardiopulmonary effects of 0, 5, 10, and 15 cm of H2O positive end-expiratory pressures (PEEP) were determined in anesthetized, spontaneously breathing horses, using a 4 by 4 Latin-square design with one repetition. Cardiac output, alveolar-arterial oxygen tension difference, alveolar ventilation, dead space/tidal volume ratio, and carbon dioxide elimination were not significantly altered by the procedure. As PEEP was increased, alveolar and arterial oxygen tensions, respiratory exchange ratio, and pH decreased, whereas arterial carbon dioxide tension and oxygen consumption increased. These results indicate PEEP is contraindicated in laterally recumbent spontaneously ventilating anesthetized horses breathing air, because it causes alveolar hypoventilation and does not improve pulmonary gas exchange.     

Anaphylactoid response to Optison(R) and its effects on pulmonary function in two dogs

Two of 26 anesthetized dogs given the cardiac echo-enhancing agent Optison showed anaphylactoid responses (AR) related to the human albumin component of this agent. The episodes of AR were self-limited, and could be reproduced by human albumin injection alone. Gas exchange was maintained by mechanical ventilation and 5 cm H(2)O PEEP, and dispersion of ventilation remained normal during AR despite severe hypotension. We suggest that: (1) pre-screening by measuring blood pressure response to intravenous injection of small doses of Optison, and (2) availability of access to the airway in addition to emergency agents may be prudent preventive measures when Optison is used in animals to enhance echocardiographic imaging.     

Cardiopulmonary effects of thoracoscopy in anesthetized normal dogs

Objective To evaluate the effect of an open‐chest condition on oxygen delivery in anesthetized dogs. Study design Prospective, controlled experimental study. Animals Eight clinically normal adult Walker Hound dogs weighing 25.6–29.2 kg. Methods Eight anesthetized dogs underwent an open‐chest operation after the insertion of thoracoscopy cannulae in the lateral chest walls . A Swan Ganz catheter was used to both measure hemodynamic parameters and obtain mixed venous blood samples for blood gas analysis. A dorsal pedal catheter was placed to both measure arterial blood pressure and obtain blood samples for blood gas analysis. Oxygen delivery index and oxygen extraction ratio were calculated. A randomized block anova for repeated measures was used to evaluate the effect of the treatment on hemodynamic and pulmonary parameters. Results Creation of an open chest did not significantly affect oxygen delivery index (DO₂I; p = 0.545). It induced a significant decrease in arterial oxygen partial pressure (PaO₂; p = 0.018) and arterial oxygen content (CaO₂; p = 0.025). It induced a significant increase in shunt fraction (p = 0.023), physiologic dead space (p = 0.015), and alveolar‐arterial oxygen difference (p = 0.019). Arterial partial pressure of carbon dioxide (PaCO₂; p = 0.766) and arterial hemoglobin oxygen saturation (SaO₂; p = 0.178) were not significantly affected. Diastolic (DPAP; p = 0.050) and mean (MPAP; p = 0.033) pulmonary arterial pressures were significantly increased by opening the chest. Other hemodynamic parameters were not significantly affected. Conclusions Opening the thoracic cavity is not detrimental to hemodynamic function and oxygen delivery in normal dogs, although impaired gas exchange does occur. Clinical relevance Close monitoring of patients is recommended during open‐chest thoracoscopy as adverse effects on gas exchange can contribute to hypoxemia.     

The cardiopulmonary effects of dobutamine and norepinephrine in isoflurane-anesthetized foals

OBJECTIVE: To evaluate the cardiovascular effects of norepinephrine (NE) and dobutamine (DB) in isoflurane-anesthetized foals. STUDY DESIGN: Prospective laboratory study. METHODS: Norepinephrine (0.05, 0.10, 0.20, and 0.40 microg kg(-1) minute(-1)) and dobutamine (2.5, 5.0, and 10 microg kg(-1) minute(-1)) were alternately administered to seven healthy, 1- to 2-week-old isoflurane-anesthetized foals. Arterial and pulmonary arterial blood pressure, right atrial pressure, pulmonary artery occlusion pressure, heart rate, body temperature, cardiac output, arterial and mixed venous blood pH, partial pressure of carbon dioxide, partial pressure of oxygen [arterial partial pressure of oxygen (PaO(2)) and mixed venous partial pressure of oxygen (PvO(2))], and packed cell volume were measured. Standard base excess, bicarbonate concentration, systemic and pulmonary vascular resistance, cardiac index (CI), stroke volume, left and right stroke work indices, oxygen delivery (DO(2)), consumption, and extraction were calculated. Results Norepinephrine infusion resulted in significant increases in arterial and pulmonary arterial pressure, systemic and pulmonary vascular resistance indices, and PaO(2); heart rate was decreased. Dobutamine infusion resulted in significant increases in heart rate, stroke volume index, CI, and arterial and pulmonary arterial blood pressure. Systemic and pulmonary vascular resistance indices were decreased while the ventricular stroke work indices increased. The PaO(2) decreased while DO(2) and oxygen consumption increased. Oxygen extraction decreased and PvO(2) increased. CONCLUSIONS AND CLINICAL RELEVANCE: Norepinephrine primarily augments arterial blood pressure while decreasing CI. Dobutamine primarily augments CI with only modest increases in arterial blood pressure. Both NE and DB could be useful in the hemodynamic management of anesthetized foals.     

Cardiopulmonary effects of positive end-expiratory pressure in anesthetized, mechanically ventilated ponies

To investigate the cardiopulmonary effects of positive end-expiratory pressure (PEEP), values of 10, 20, and 30 cm of H2O, were applied to anesthetized, dorsally recumbent, ventilated ponies. After IV induction of general anesthesia, PEEP was superimposed on controlled ventilation with 100% oxygen, and changes in gas exchange and cardiac function were measured. Increasing values of PEEP in these ponies caused a linear increase in the mean (+/- SEM) functional residual capacity, from a control value (zero end-expiratory pressure) of 1.7 +/- 0.24 L to 2.2 +/- 0.31, 2.9 +/- 0.32 and 3.4 +/- 0.3 L at PEEP of 10, 20, and 30 cm of H2O, respectively (P less than 0.05). Paralleling these changes, intrapulmonary shunt fraction decreased significantly (P less than 0.05) from a control value of 12.9 +/- 0.5%, to 7.5 +/- 1.1 and 2.1 +/- 0.6%, at PEEP of 20 and 30 cm of H2O, respectively. Cardiac output was decreased by increasing values of PEEP, from control value of 11.7 +/- 1.56 L/min to 9.9 +/- 1.51, 8.8 +/- 1.33 and 5.62 +/- 0.56 L/min at PEEP of 10, 20, and 30 cm of H2O, respectively. Related to decreasing cardiac output, tissue oxygen delivery also decreased as PEEP was increased, from control value of 2.0 +/- 0.09 L/min to 1.8 +/- 0.07, 1.6 +/- 0.06, and 1.03 +/- 0.04 L/min at PEEP of 10, 20, and 30 cm of H2O, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

High-frequency jet ventilation during pneumothorax in dogs

Pneumothorax (45 ml of N/kg of body weight insufflated into the pleural space) in anesthetized dogs ventilated with air caused a significant (P less than 0.05) increase in pleural pressure, central venous pressure, capillary wedge pressure, and venous admixture. Cardiac index (CI) and arterial O2 tensions were decreased. Ventilation with 100% O2 increased arterial O2 tensions, but did not affect calculated intrapulmonary shunting of blood or CI. Application of 10 cm of H2O-positive end-expiratory pressure in the presence of pneumothorax during positive-pressure ventilation and high-frequency jet ventilation reduced intrapulmonary shunting of blood, which remained higher than control values, and caused a further decrease in CI. Cardiopulmonary function during pneumothorax in anesthetized dogs was more profoundly affected by the application of positive end-expiratory pressure than by the form of mechanical ventilation.     

Cardiopulmonary effects of sufentanil long acting on sevoflurane anaesthesia in dogs

OBJECTIVE: To evaluate the cardiopulmonary effects of sufentanil long acting (SLA) in sevoflurane-anaesthetized dogs. STUDY DESIGN: Randomized prospective study. Animals Forty female dogs (beagles) aged 1-2 years, weighing 11.97 +/- 1.40 kg. MATERIALS AND METHODS: The dogs were divided into five groups of eight. Two control groups were used: group A received intramuscular (IM), SLA (50 microg kg(-1)) alone, while group B received the SLA vehicle followed by sevoflurane anaesthesia for 90 minutes. In the other groups, SLA (50 microg kg(-1) IM) was given immediately before (group C(0)), 15 minutes before (group D(15)) or 30 minutes (group E(30)) before induction [with intravenous (IV) thiopental] of sevoflurane anaesthesia lasting for 90 minutes. Heart rate, arterial blood pressure, respiratory rate (f(r)), arterial oxygen haemoglobin saturation and end-tidal sevoflurane concentration (Fe'SEVO) were measured every 10 minutes during anaesthesia and at 2, 4 and 24 hours after induction (not Fe'SEVO). Acid-base and blood gas analyses were performed. RESULTS: Sufentanil LA reduced heart rate and increased arterial CO(2) tensions during anaesthesia. Respiratory depression was least in group E(30) compared with groups C(0) and D(15). Bradycardia was present for at least 24 hours. Respiratory rate was least in group B although arterial O(2) and CO(2) tension values were acceptable up to 24 hours after anaesthesia. CONCLUSIONS: Pre-anaesthetic medication with SLA moderately aggravated the cardiopulmonary effects of sevoflurane. CLINICAL RELEVANCE: In spite of a moderate depressant effect on cardiorespiratory parameters, SLA may be of use as pre-anaesthetic medication before sevoflurane anaesthesia in dogs. Intermittent positive pressure ventilation may occasionally be necessary.     

Inadequacy of low-volume resuscitation with hemoglobin-based oxygen carrier hemoglobin glutamer-200 (bovine) in canine hypovolemia

Stroma-free hemoglobin-based oxygen carriers (HBOC) have been developed to overcome problems associated with transfusion of allogeneic blood. We have studied the efficacy of the first licensed veterinary blood substitute, hemoglobin glutamer-200 bovine (Oxyglobin; Biopure, Cambridge, MA, USA, Hb-200), in a canine model of acute hypovolemia and examined whether clinically commonly used criteria are adequate to guide fluid resuscitation with this product. Twelve anesthetized dogs were instrumented for measurements of physiological variables including hemodynamic, oxygenation, and blood gas and acid-base parameters. Dogs were bled to a mean arterial pressure (MAP) of 50 mmHg for 1 h followed by resuscitation with either shed blood (controls) or Hb-200 until heart rate (HR), MAP and central venous pressure (CVP) returned to baseline. Recordings were repeated immediately and 3 h after termination of fluid resuscitation. Hemorrhage (average 32 mL/kg) caused significant decreases in total hemoglobin (Hb), mean pulmonary arterial pressure (PAP), cardiac output (CO) and oxygen delivery (DO2I), increases in HR and systemic vascular resistance (SVRI), and lactic acidosis. In controls, only re-transfusion of all shed blood returned HR, MAP and CVP to prehemorrhage values, whereas in other dogs this endpoint was reached with infusion of 10 mL/kg Hb-200. Unlike blood transfusion, Hb-200 infusion failed to return CI and DO2I to baseline and to increase arterial oxygen content (CaO2) and total Hb; SVRI further increased. Thus, commonly used criteria (HR, MAP, CVP) to guide transfusion therapy in patients posthemorrhage prove insufficient when HBOCs with pronounced vasoconstrictive action are used and lead to inadequate volume repletion.     

Acute hemodynamic effects of hydralazine in dogs with chronic mitral regurgitation

The hemodynamic response to hydralazine administration was evaluated in 6 conscious small dogs with chronic mitral regurgitation. All dogs underwent invasive and noninvasive hemodynamic monitoring before and after hydralazine administration. Cardiac output and pulmonary capillary wedge pressure were measured with a Swan-Ganz thermodilution catheter. Systemic arterial blood pressure (AP) was measured directly by inserting a needle into the femoral artery. Standard M-mode echocardiograms and thoracic radiographs were obtained. Other hemodynamic variables were calculated. Base-line hemodynamic variables were altered severely in all dogs. Hydralazine decreased mean arterial blood pressure from 104 +/- 18 (mean +/- SD) to 78 +/- 12 mm of Hg (P less than 0.005), total systemic resistance index from 2,946 +/- 625 to 1,261 +/- 420 dynes-s-cm-5m2 (P less than 0.005), and pulmonary capillary wedge pressure from 40 +/- 5 to 26 +/- 3 mm of Hg, (P less than 0.005). Cardiac index increased from 2.92 +/- 0.72 to 5.36 +/- 1.67 L/min/m2 of body surface area (P less than 0.005). Mixed venous oxygen tension (PvO2) increased from 28.4 +/- 4.3 to 41.2 +/- 5.2 mm of Hg (P less than 0.001). Pulmonary edema resolved, as determined on thoracic radiographs. Mixed venous oxygen tension correlated well with the cardiac index (r = 0.92; P less than 0.001). It was concluded that hydralazine administration caused a small decrease in end diastolic diameter (4.8 +/- 0.9 to 4.5 +/- 0.8 cm, P less than 0.05) and end systolic diameter (2.6 +/- 0.8 to 2.3 +/- 0.7 cm, P less than 0.05). Fractional shortening and heart rate did not change.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison between facemask and laryngeal mask airway in rabbits during isoflurane anesthesia

OBJECTIVE: To determine whether a laryngeal mask airway (LMA) provides a better airway than a facemask in spontaneously breathing anesthetized rabbits, and to test if it can be used for mechanically controlled ventilation. STUDY DESIGN: Randomized prospective experimental trial. ANIMALS: Sixteen young, healthy, specific pathogen-free Giant Flemish cross Chinchilla rabbits (10 females and 6 males) weighing 4.1 +/- 0.8 kg. METHODS: Rabbits were assigned randomly to one of three treatment groups: facemask with spontaneous ventilation (FM-SV; n = 5), LMA with spontaneous ventilation (LMA-SV; n = 5), and LMA with controlled ventilation (LMA-CV; n = 6). In dorsal recumbency, and at 2.3% end-tidal isoflurane concentration, Fé isoflurane, Fi isoflurane, partial pressure of expired isoflurane (PECO(2)), partial pressure of inspired carbon dioxide (PiCO(2)), heart rate, respiratory rate, minute volume, arterial oxygen tensions (PaO(2)), arterial carbon dioxide tensions (PaCO(2)), arterial pH (pH(a)), arterial standard base excess (SBE(a)) values were measured for 120 minutes. Results Two individuals in the FM-SV group had PaCO(2) > 100 mm Hg. One rabbit in the FM-SV had PaO(2) < 80 mm Hg. All FM-SV rabbits showed signs of airway obstruction, and two were withdrawn from the study at 45 and 90 minutes, respectively, because cyanosis was observed. No signs of airway obstruction were observed in either LMA group. Four rabbits in the LMA-CV group developed gastric tympanism, one of which refluxed gastric contents after 110 minutes. There were no differences between FM-SV and LMA-SV in any variable tested. PaCO(2) and PECO(2) were decreased, while PaO(2) and minute volume were increased in the LMA-CV group compared to the LMA-SV group. CONCLUSIONS: An LMA provided a better airway than a facemask during spontaneous breathing in rabbits, as the use of a facemask was associated with hypercapnia and low partial pressures of oxygen. Although an LMA can be used for intermittent positive pressure ventilation (IPPV), gastric tympanism may develop, especially at a peak inspiratory pressure of 14 cm H(2)O. CLINICAL RELEVANCE: The LMA can be used in rabbits but further work is needed before it is applied routinely.     

Effect of 5 cm of Water Positive End-Expiratory Pressure on Arterial Oxygen Tension in Dogs During and After Thoracotomy

Thoracotomy in dogs often is associated with lower than expected arterial oxygen tensions (PaO₂). Pulmonary collapse from opening the thoracic cavity is likely to be responsible for decreased PaO₂ during thoracotomy. To examine whether positive end-expiratory pressure (PEEP) is beneficial to dogs undergoing thoracotomy, PaO₂ and hemoglobin saturation (SaO₂) were measured in dogs randomly assigned to receive 5 cm of H₂O PEEP (n = 7) or no PEEP (n = 9). During surgery in both groups of dogs, PaO₂ progressively decreased ( P < .001), but the decrease in PaO₂ was significantly less in the PEEP group ( P = .027). In both groups, PaO₂ did not decrease enough to have a substantial effect on SaO₂. Furthermore, application of PEEP during thoracotomy did not prevent moderate hypoxemia after surgery and discontinuation of PEEP. Application of 5 cm of H₂O PEEP seems to attenuate the decrease in PaO₂ observed in dogs undergoing thoracotomy, but routine application of PEEP does not seem justified. ©