Mixed Venous Blood Gas Analysis Research Articles

Immediate cardiopulmonary responses to consecutive pulmonary embolism: a randomized, controlled, experimental study

BackgroundAcute pulmonary embolism (PE) induces ventilation-perfusion mismatch and hypoxia and increases pulmonary pressure and right ventricular (RV) afterload, entailing potentially fatal RV failure within a short timeframe. Cardiopulmonary factors may respond differently to increased clot burden. We aimed to elucidate immediate cardiopulmonary responses during successive PE episodes in a porcine model.MethodsThis was a randomized, controlled, blinded study of repeated measurements. Twelve pigs were randomly assigned to receive sham procedures or consecutive PEs every 15 min until doubling of mean pulmonary pressure. Cardiopulmonary assessments were conducted at 1, 2, 5, and 13 min after each PE using pressure-volume loops, invasive pressures, and arterial and mixed venous blood gas analyses. ANOVA and mixed-model statistical analyses were applied.ResultsPulmonary pressures increased after the initial PE administration (p < 0.0001), with a higher pulmonary pressure change compared to pressure change observed after the following PEs. Conversely, RV arterial elastance and pulmonary vascular resistance was not increased after the first PE, but after three PEs an increase was observed (p = 0.0103 and p = 0.0015, respectively). RV dilatation occurred following initial PEs, while RV ejection fraction declined after the third PE (p = 0.004). RV coupling exhibited a decreasing trend from the first PE (p = 0.095), despite increased mechanical work (p = 0.003). Ventilatory variables displayed more incremental changes with successive PEs.ConclusionIn an experimental model of consecutive PE, RV afterload elevation and dysfunction manifested after the third PE, in contrast to pulmonary pressure that increased after the first PE. Ventilatory variables exhibited a more direct association with clot burden.

The Impact of Diabetes on Haemodynamic and Cardiometabolic Responses in Heart Failure With Preserved Ejection Fraction

Heart failure with preserved ejection (HFpEF) and diabetes mellitus (DM) commonly co-exist. However, it is unclear if DM modifies the haemodynamic and cardiometabolic phenotype in patients with HFpEF. We aimed to interrogate the haemodynamic and cardiometabolic effects of DM in HFpEF. We compared the haemodynamic and metabolic profiles of non-DM patients and patients with DM-HFpEF at rest and during exercise using right heart catheterisation and mixed venous blood gas analysis. Of 181 patients with HFpEF, 37 (20%) had DM. Patients with DM displayed a more adverse exercise haemodynamic response vs HFpEF alone (mean pulmonary arterial pressure: 47 mmHg [interquartile range {IQR} 42-55] vs 42 [38-47], p<0.001; workload indexed pulmonary capillary wedge pressure indexed: 0.80 mmHg/W [0.44-1.23] vs 0.57 [0.43-1.01], p=0.047). HFpEF-DM patients had a lower mixed venous oxygen saturation at rest (70% [IQR 66-73] vs 72 [69-75], p=0.003) and were unable to enhance O2 extraction to the same extent (Δ-28% [-33 to -15] vs -29 [-36 to -21], p=0.029), this occurred at a 22% lower median workload. Resting mixed venous lactate levels were higher in those with DM (1.5 mmol/L [IQR 1.1-1.9] vs 1 [0.9-1.3], p<0.001), and during exercise indexed to workload (0.09 mmol/L/W [0.06-0.13] vs 0.08 [0.05-0.11], p=0.018). Concurrent diabetes and HFpEF was associated with greater metabolic responses at rest, with enhanced wedge driven pulmonary hypertension and relative lactataemia during exercise without appropriate augmentation of oxygen consumption.

Prospective, observational study of carbon dioxide gaps and free energy change and their association with fluid therapy following cardiac surgery.

Background Venoarterial carbon dioxide pressure (pv-a CO2 ) and content (Cv-a CO2 ) differences, including the ratio to arteriovenous oxygen content difference (Ca-v O2 ), and free energy changes (-∆∆Ga-v ) may reflect tissue hypoperfusion. The associations with changes in cardiac output (CO) or oxygen consumption (VO2 ) following fluid bolus administration were investigated. Methods Single-centre, observational study of 89 adult post-operative cardiac surgical patients admitted to ICU. The pv-a CO2 , Cv-a CO2 and their ratios to Ca-v O2 as well as the -∆∆Ga-v were determined before and after a 250-500mL fluid bolus using arterial, central venous and mixed venous blood gas analyses. Responses associated with changes ≥ or <15% in CO or oxygen consumption (VO2 ) were compared. Results In 234 boluses, the mixed venous to arterial pv-a CO2 and its ratio to Ca-v O2 were independently associated with an increase in CO; odds ratio 1.3 (95% CI 1.1-1.5) and 1.7 (95% CI 1.5-1.9) respectively, P<.001) and VO2 ; odds ratio 2.1 (95% CI 1.3-3.1), P<.001 for Ca-v O2 . No measures of pv-a CO2 , Cv-a CO2 or related ratios to the Ca-v O2 were associated with an increase in CO ≥15% following a single volume bolus. The mixed venous and central venous Cv-a CO2 to Ca-v O2 ratios were different for the first bolus episode only; mean differences 0.81 (95% CI 0.13-1.5), P=.02 and 0.44 (95% CI 0.06-0.82), P=.02, respectively, for increased VO2 ≥15%. The -∆∆Ga-v did not change. Conclusion The venoarterial carbon dioxide gradients and related calculations to assess the adequacy of tissue perfusion before a fluid bolus were not associated with subsequent increases in CO of oxygen consumption. Editorial Comment In some shock conditions, regional tissue hypoperfusion can be obvious and arterio-venous differences for CO2 or O2 may reflect this. This is not always the case; sometimes there are A-V differences or even a high lactate level without any obvious regional tissue hypoperfusion. Fluid therapy is a cornerstone in shock resuscitation treatment, but determining optimal fluid therapy is challenging, particularly as fluid overload may be detrimental. Fluid challenges are used as an "ex juvantebus" method to dose fluid therapy, but it is not clear if a positive response reflects a state of hypoperfusion or the existence of a cardiac reserve. Still, a better understanding on how to target and guide fluid therapy is welcome, and studies digging into the problem are needed. Here, invasively monitored post-operative cardiac surgery patients are assessed as a model to investigate if carbon dioxide gaps and free energy charge may be useful in detecting possible tissue hypoperfusion.

Sex Differences in Heart Failure With Preserved Ejection Fraction Pathophysiology: A Detailed Invasive Hemodynamic and Echocardiographic Analysis

ObjectivesThis study sought to identify sex differences in central and peripheral factors that contribute to the pathophysiology of heart failure with preserved ejection fraction (HFpEF) by using complementary invasive hemodynamic and echocardiographic approaches. BackgroundWomen are overrepresented among patients with HFpEF, and there are established sex differences in myocardial structure and function. Exercise intolerance is a fundamental feature of HFpEF; however, sex differences in the physiological determinants of exercise capacity in HFpEF are yet to be established. MethodsPatients with exertional intolerance with confirmed HFpEF were included in this study. Evaluation of the subjects included resting and exercise hemodynamics, echocardiography, and mixed venous blood gas sampling. ResultsA total of 161 subjects included 114 females (71%). Compared to males, females had a higher pulmonary capillary wedge pressure (PCWP) indexed to peak exercise workload (0.8 [0.5 to 1.2] mm Hg/W vs. 0.6 [0.4 to 1] mm Hg/W, respectively; p = 0.001) and lower systemic (1.1 [0.9 to 1.5] ml/mm Hg vs. 1 [0.7 to 1.2] ml/mm Hg, respectively; p = 0.019) and pulmonary (2.9 [2.2 to 4.2] ml/mm Hg vs. 2.4 [1.9 to 3] ml/mm Hg, respectively; p = 0.032) arterial compliance at exercise. Mixed venous blood gas analysis demonstrated a greater rise in lactate indexed to peak workload (0.05 [0.04 to 0.09] mmol/l/W vs. 0.04 [0.03 to 0.06] mmol/l/W, respectively; p = 0.007) in women compared to men. Women had higher mitral inflow velocity to diastolic mitral annular velocity at early filling (E/e′) ratios at rest and peak exercise, along with a higher ejection fraction and smaller ventricular dimensions. ConclusionsWomen with HFpEF demonstrate poorer diastolic reserve with higher echocardiographic and invasive measurements of left ventricular filling pressures at exercise, accompanied by lower systemic and pulmonary arterial compliance and poorer peripheral oxygen kinetics.

Acute Effects of Inspiratory Muscle Training on Pulmonary Arterial Pressure,Cardiac Output and Pulmonary Arterial Saturation Derived Oxygen Cost of Breathing

Respiration and respiratory maneuvers affect cardiac output. Inspiratory muscle training (IMT) increases the negative thoracic pressure, which could have an impact on intra-thoracic hemodynamics and thereby influence the cardiac output (CO). The objective of our study was to determine changes in pulmonary arterial (PA) hemodynamics and the CO during IMT in patients with suspected pulmonary hypertension. A new method for measuring the oxygen cost of breathing during IMT was also developed. 22 patients were included in this prospective study. They performed IMT during right heart catheterization. Mixed-venous blood gas analysis was performed before and at the end of IMT to calculate the oxygen cost of breathing. The baseline PA pressure was systolic/diastolic/mean (s/d/m) 41 ± 20/13 ± 20/25 ± 11 mmHg. The CO was 5.3 ± 1.5 l/min. The IMT was set to 2.3 ± 0.6 kPa (23.7 ± 5.7 cmH2O). The PA pressure at the end of IMT was s/d/m 44/10/22 mmHg s/d/m. Though there was a trend towards a lower diastolic pressure, this change was not statistically significant (p=0.06). CO (6.2 ± 1.1 l/min) did not change due to IMT. The mixed-venous hemoglobin oxygen saturation was 71.8 ± 2.3% before IMT, with a significant reduction to 65.8 ± 5.9% (p=0.027) at the end of IMT. IMT as performed in our study neither changed the mean PA pressure nor the CO. Measuring the oxygen cost of breathing is feasible by the method described in our paper.

Cardiovascular effects of a proprietary l-methadone/fenpipramide combination (Polamivet) alone and in addition to acepromazine in healthy Beagle dogs

ObjectiveTo determine the cardiovascular effects of a proprietary l-methadone/fenpipramide combination (Polamivet) alone and in addition to acepromazine in dogs. Study designProspective, randomized, experimental crossover study. AnimalsFive adult healthy Beagle dogs (one male and four females, weighing 12.8–16.4 kg). MethodsDogs were instrumented for haemodynamic measurements whilst anaesthetized with isoflurane. Three hours after recovery dogs received 0.025 mg kg−1 acepromazine (AP) or saline (SP) IM followed by 0.5 mg kg−1L-methadone/ 0.025 mg kg−1 fenpipramide IV after 30 minutes. Cardiac output using thermodilution, heart rate, mean arterial pressure (MAP), central venous pressure (CVP), mean pulmonary artery pressure (MPAP), pulmonary artery occlusion pressure (PAOP), haemoglobin concentration, arterial and mixed-venous blood gas analysis were measured and sedation evaluated at baseline (BL), 30 minutes after acepromazine or saline IM (A/S), 5 minutes after L-methadone/fenpipramide IV application (35), every 15 minutes for 1 hour (50, 65, 80, 95 minutes) and every hour until baseline cardiac output was regained. Standard cardiovascular parameters were calculated. Data were analyzed by repeated measures anova and paired t-tests with p < 0.05 considered significant. ResultsBaseline measurements did not differ. Cardiac index decreased after acepromazine administration in treatment AP (p = 0.027), but was not significantly influenced after l-methadone/fenpipramide injection in either treatment. In both treatments heart rate did not change significantly over time. Stroke volume index increased after A/S in both treatments (p = 0.049). Systemic vascular resistance index, MAP, CVP, MPAP, and pulmonary vascular resistance index did not change significantly after either treatment and did not differ between treatments. Dogs were deeply sedated in both treatments with a longer duration in treatment AP. Conclusions and clinical relevanceIn healthy dogs the dose of l-methadone/fenpipramide used in this study alone and in combination with acepromazine induced deep sedation without significant cardiovascular changes.

Effects of environmental hypothermia on hemodynamics and oxygen dynamics in a conscious swine model of hemorrhagic shock.

Hypothermia is associated with poor outcome in trauma patients; however, hemorrhagic shock (HS) model with anesthetized swine was different from that of clinical reality. To identify the effects of environmental hypothermia on HS, we investigated hemodynamics and oxygen dynamics in an unanesthetized swine model of HS under simulating hypothermia environment. Totally 16 Bama pigs were randomly divided into ambient temperature group (group A) and low temperature group (group B), 8 pigs in each group. Venous blood (30 mL/kg) was continuously withdrawn for more than 15 minutes in conscious swine to establish a hemorrhagic shock model. Pulmonary arterial temperature (Tp), heart rate (HR), mean arterial pressure (MAP), pulmonary arterial pressure (PAP), pulmonary arterial wedge pressure (PAWP), central venous pressure (CVP), cardiac output (CO), hemoglobin (Hb), saturation of mixed venous blood (SvO2) and blood gas analysis were recorded at the baseline and different hemorrhagic shock time (HST). The whole body oxygen delivery indices, DO2I and VO2I, and the O2 extraction ratio (O2ER) were calculated. Core body temperature in group A decreased slightly after the hemorrhagic shock model was established, and environmental hypothermia decreased in core body temperature. The mortality rate was significantly higher in group B (50%) than in group A (0%). DO2I and VO2I decreased significantly after hemorrhage. No difference was found in hemodynamics, DO2I and VO2I between group A and group B, but the difference in pH, lactic acid and O2ER was significant between the two groups. Environmental hypothermia aggravated the disorder of oxygen metabolism after hemorrhagic shock, which was associated with poor prognosis.

Effects of environmental hypothermia on hemodynamics and oxygen metabolism in unanesthetized swine model of hemorrhagic shock

Objective To investigate the effects of environmental hypothermia on hemodynamics and oxygen metabolism in unanesthetized swine model of hemorrhagic shock.Methods A total of 16 Bama pigs provided by animal experiment centre of the General Hospital of Shenyang Military Command were randomized into two groups ( n =8,each):ambient temperature (A) and hypothermia ( H ).Venous blood (30 mL/kg) was continously withdrawn over 15 minutes to establish hemorrhagic shock model.Core temperature,heart rate,mean arterial pressure,central venous pressure,cardiac output,saturation of mixed venous blood and blood gas analysis were recorded at the baseline and different hemorrhagic shock time.DO2I and VO2I,and the O2 extraction ratio (O2ER) were calculated.Results Core body temperature in group A decreased slightly after hemorrhagic shock model had established and environmental hypothermia resulted in more reduction in core body temperature.The mortality rate was significantly higher in group H (50％) than in group A (0％) (P ＜0.05).DO2I and VO2I decreased significantly after hemorrhage.No difference was found in hemodynamics,DO2I and VO2I between group A and group H,but the difference of pH,lactic acid and O2ER were significant between the two groups (P ＜ 0.05 ).conclusions Environmental hypothermia aggravated the disorder of oxygen metabolism after hemorrhagic shock,which was associated with poor prognosis. Key words: Hemorrhagic shock; Environmental hypothermia; Hemodynamics; Oxygen metabolism; Anesthesia; Swine; Core temperature; Prognosis

The effects of inhalation salbutamol administration on systemic and pulmonary hemodynamic, pulmonary mechanics and oxygen balance during general anaesthesia in the horse

This research aimed to determine the effect of aerosolized salbutamol administration on systemic and pulmonary hemodynamic, pulmonary mechanics and oxygen balance in healthy horses during general anaesthesia. Six healthy Thoroughbreds (body weight range 471&amp;ndash;587 kg) underwent two general anaesthesias in dorsal recumbency with and without aerosolized salbutamol administration in randomized order with a one month washout period. The anaesthesia was induced by 1.1 mg/kg of xylazine, 0.02 mg/kg of diazepam and 2.2 mg/kg of ketamine, maintained with isoflurane in oxygen and air and horses were mechanically ventilated. Measurement of arterial and pulmonary arterial blood pressures, cardiac output and arterial and mixed venous blood gas analysis was carried out. Spirometry was performed using a Horse-lite. After achieving a steady state, baseline (T&lt;sub&gt;0&lt;/sub&gt;) values of cardiac output, systemic and pulmonary arterial blood pressures, heart rate, dynamic compliance, airway resistance and arterial and mixed venous blood gas values and pH were recorded in both groups. In the S-group (salbutamol), 2 &amp;micro;g/kg of aerosolized salbutamol were administered synchronously with inspirium into the tracheal tube. In both groups data were recorded at 15, 30, 45 and 60 min (T&lt;sub&gt;15&lt;/sub&gt;, T&lt;sub&gt;30&lt;/sub&gt;, T&lt;sub&gt;45&lt;/sub&gt;, T&lt;sub&gt;60&lt;/sub&gt;) after the baseline. PaO&lt;sub&gt;2&lt;/sub&gt;/FiO&lt;sub&gt;2&lt;/sub&gt; ratio, oxygen consumption (VO&lt;sub&gt;2&lt;/sub&gt;), oxygen delivery (DO&lt;sub&gt;2&lt;/sub&gt;), pulmonary shunt values were calculated. Data were tested for normality and compared within each group: T&lt;sub&gt;0&lt;/sub&gt; value with T&lt;sub&gt;15&lt;/sub&gt;, T&lt;sub&gt;30&lt;/sub&gt;, T&lt;sub&gt;45&lt;/sub&gt;, T&lt;sub&gt;60&lt;/sub&gt; values using Wilcoxon's test with Bonferoni correction (significance level 0.0125). For each time point, comparisons were made between the S- and C-groups (control) using Wilcoxon's test. In the S-group, there was a significant increase in values (mean &amp;plusmn; SD) of cardiac output (l/min), T&lt;sub&gt;0&lt;/sub&gt; (38 &amp;plusmn; 7), a peak at T&lt;sub&gt;15&lt;/sub&gt; (64 &amp;plusmn; 25.5), significantly higher values persisted throughout the period of anaesthesia; heart rate (beats/min), T&lt;sub&gt;0&lt;/sub&gt; (32 &amp;plusmn; 2), T&lt;sub&gt;15&lt;/sub&gt; (40 &amp;plusmn; 6), T&lt;sub&gt;30&lt;/sub&gt; (38 &amp;plusmn; 5); DO&lt;sub&gt;2&lt;/sub&gt; (l/min), T&lt;sub&gt;0&lt;/sub&gt; (5.8 &amp;plusmn; 0.8), a peak at T&lt;sub&gt;15&lt;/sub&gt; (9.6 &amp;plusmn; 3.2), significantly higher values persisted until the end of anaesthesia and VO&lt;sub&gt;2&lt;/sub&gt; (l/min), T&lt;sub&gt;0&lt;/sub&gt; (1.1 &amp;plusmn; 0.5), T&lt;sub&gt;30&lt;/sub&gt; (1.6 &amp;plusmn; 0.7) and T&lt;sub&gt;45&lt;/sub&gt; (1.8 &amp;plusmn; 0.5). In the C-group, there was a significant decrease in values of PaO&lt;sub&gt;2&lt;/sub&gt;/FiO&lt;sub&gt;2&lt;/sub&gt; ratio from T&lt;sub&gt;0&lt;/sub&gt; (176 &amp;plusmn; 67) to a minimum at T&lt;sub&gt;60&lt;/sub&gt; (114 &amp;plusmn; 36) and in DO&lt;sub&gt;2&lt;/sub&gt; from T&lt;sub&gt;0&lt;/sub&gt; (6 &amp;plusmn; 2.3) to a minimum at T&lt;sub&gt;60&lt;/sub&gt; (4.3 &amp;plusmn; 1.2). A comparison of the S- and C-groups did not reveal any difference in the baseline data. Subsequently, significantly higher values of cardiac output, heart rate, DO&lt;sub&gt;2&lt;/sub&gt;, and the PaO&lt;sub&gt;2&lt;/sub&gt;/FiO&lt;sub&gt;2 &lt;/sub&gt;ratio were found in the S-group compared to the C-group. Pulmonary arterial blood pressure was significantly lower in the S-group. Aerosolized salbutamol administration in healthy horses during general anaesthesia caused hemodynamic changes which resulted in an elevation of oxygen delivery. It can have a positive effect on arterial oxygenation, but the effect varies between individuals.

Effect of passive pneumoperitoneum on oesophageal pressure, cardiovascular parameters and blood gas analysis in horses

Standing surgical procedures are being employed to an ever-greater extent in horses. Pneumoperitoneum during abdominal surgery might adversely affect the work of breathing. To determine whether development of pneumoperitoneum during abdominal surgery adversely influences the work of breathing. Eight healthy mature horses were equipped with carotid artery and thoracic vena cava catheters and an intraluminal manometry system. The following measurements were obtained before and at +5, +10, +15 and +30 min following establishment of pneumoperitoneum by paralumbar puncture using an 8 gauge needle: vital signs, oesophageal pressure, gastric pressure, arterial and central venous blood pressures, and arterial and mixed venous blood gas analyses. Significant changes in oesophageal pressure, central venous pressure and results of arterial and mixed venous blood gas analysis were not detected. Arterial diastolic and mean pressures and rectal temperature increased slightly (P ≤ 0.05). Passive pneumoperitoneum did not adversely affect breathing mechanics or haemodynamic variables under experimental conditions. Changes in arterial pressure could have occurred as a response to the passive pneumoperitoneum or be related to handling stress. Subtle variations in rectal temperature were not clinically relevant and likely resulted from stress associated with restraint. It is unlikely that mature horses will develop signs of respiratory difficulty as a result of the development of passive pneumoperitoneum during standing laparoscopy.

The Effect of Thoracic Epidural Anesthesia on Pulmonary Shunt Fraction and Arterial Oxygenation During One-Lung Ventilation

To compare the effect of thoracic epidural local anesthetic, epidural opioid, and intravenous opioid on pulmonary shunt fraction, arterial oxygenation, and hemodynamic changes during one-lung ventilation (OLV) in patients undergoing thoracic surgery. A prospective, randomized, double-blind study. A university hospital. Thirty-nine patients undergoing OLV for pulmonary resection. Patients were randomized into 1 of 3 groups: epidural bupivacaine (TEA-B group, n = 13), epidural sufentanil (TEA-S group, n = 13), or intravenous remifentanil (IV-R group, n = 13) during general anesthesia with propofol. A double-lumen tube was inserted, and mechanical ventilation with 100% oxygen was used in the lateral decubitus position. Hemodynamic variables and arterial and mixed venous blood gas analysis from the radial and pulmonary artery catheter were measured and shunt fraction was calculated during two-lung ventilation (TLV), 15, 30, and 60 minutes after the initiation of OLV, and 15 minutes after the reinstitution of TLV. Although mean arterial pressures 15 and 30 minutes after OLV in the IV-R group were significantly higher than the value in TEA-S group, cardiac output and pulmonary vascular resistance were maintained. Decreases in PaO(2), SaO(2), PvO(2), and SvO(2) and an increase in the shunt fraction after OLV were not different among groups and returned to baseline value after the resumption of TLV. Thoracic epidural bupivacaine, epidural sufentanil, and intravenous remifentanil-combined general intravenous anesthesia have comparable effects on shunt fraction and arterial oxygenation during OLV in patients undergoing thoracic surgery.

Jugular bulb desaturation during off-pump coronary artery bypass surgery

Off-pump coronary artery bypass grafting surgery (OPCAB) frequently results in significant jugular bulb desaturation. Although jugular bulb desaturation during OPCAB may be associated with postoperative cerebral injury, routine jugular bulb oximetry appears to be invasive and expensive. We hypothesized that intraoperative hemodynamic compromise during OPCAB due to cardiac displacement is associated with jugular bulb desaturation which correlates with specific hemodynamic and physiological changes. Hemodynamic and physiological data were measured at the following points: (1) before anastomosis of the coronary artery (baseline); (2) during anastomosis of the left anterior descending artery; (3) during anastomosis of the circumflex branch or posterior descending artery; and (4) after chest closure. Arterial, mixed venous, and jugular venous bulb blood gas analyses were performed serially. Jugular bulb desaturation (<or=50%) frequently occurred during surgical displacement of the heart. Mixed venous oxygen saturation (S(VO2)), partial pressure of carbon dioxide (Pa(CO2)), and central venous pressure (CVP) showed a significant relationship with jugular bulb oxygen saturation (r = 0.45) by multivariate linear regression analysis. Multivariate logistic regression analysis also demonstrated that S(VO2) <or= 70%, Pa(CO2) <or= 40 mmHg, and CVP >or= 8 mmHg were likely predictors of the occurrence of jugular bulb desaturation. Changes in S(VO2) and Pa(CO2) were associated with jugular bulb oxygen saturation, and S(VO2) <or= 70%, Pa(CO2) <or= 40 mmHg, and CVP >or= 8 mmHg had a significant odds ratio for jugular bulb desaturation. We suggest that achieving normal values of S(VO2), Pa(CO2) and CVP may be important to prevent cerebral desaturation during OPCAB.

Effects of phenylephrine on the sublingual microcirculation during cardiopulmonary bypass

The objective of the present study was to investigate sublingual microvascular blood flow and microcirculatory haemoglobin oxygen saturation (Smc(O(2))) during cardiopulmonary bypass (CPB) using constant systemic blood flow but different perfusion pressures achieved by phenylephrine administration. Fifteen patients undergoing coronary artery bypass grafting were enrolled in this pilot study. Systemic haemodynamics, oxygen transport variables, arterial and mixed venous blood gas analysis, and microcirculatory variables were determined after initiation of general anaesthesia, during CPB (systemic blood flow=2.4 litre m(-2)), after increasing perfusion pressure by 20 mm Hg with a continuous infusion of phenylephrine, and after termination of phenylephrine infusion. CPB immediately resulted in a significant (P<0.05) decrease in systemic oxygen transport without alterations in sublingual microcirculatory blood flow and Smc(O(2)). Increasing perfusion pressure from 47 (SD 9) to 68 (7) mm Hg using phenylephrine=1.4 (1.0) microg kg(-1) min(-1) resulted in a significant decrease in sublingual small vessel blood flow (from median 2.5 to 1.8 arbitrary units) representing mostly capillary blood flow, but not in medium-sized vessels (median 3 to 2.8 arbitrary units). Concurrently, global tissue blood flow from 110 (54) to 197 (100) perfusion units and Smc(O(2)) increased from 72 (11)% to 84 (7)%, suggesting significant microcirculatory blood flow shunting in vessels with diameters >25 microm. Our data demonstrate that an increased perfusion pressure produced by phenylephrine at constant CPB flow may decrease microcirculatory blood flow in the sublingual mucosal microcirculation due to microvascular blood flow shunting.

Oxygen availability during orthotopic liver transplantation

Studies have stressed the role of adequate tissue oxygenation in the light of an optimal patient outcome and allograft viability in liver transplantation. The practice of monitoring conventional hemodynamic parameters during liver transplantation could be complemented by parameters assessing real oxygen availability. In the present prospective study, real arterial available oxygen content (CavlO(2)) and its extraction ratio (O(2)ERavl) were calculated. These parameters include the effect of changes in oxyhemoglobin dissociation curve (ODC; expressed by P(50)) on oxygen availability, under the different circumstances occurring during liver transplantation. Sixteen adult cirrhotic patients were studied during orthotopic liver transplantation with the use of venovenous bypass. Classic hemodynamic measurements using a Swan-Ganz thermodilution catheter and arterial and mixed venous blood gas analysis were performed, and P(50), oxygen delivery index (DO(2 ind)), oxygen consumption index (VO(2 ind)), oxygen extraction ratio (O(2)ER), CavlO(2), and O(2)ERavl were calculated. Statistical analysis was performed using ANOVA for repeated measures and Spearman correlation coefficient matrix among the six variables (DO(2 ind), VO(2 ind), O(2)ER, P(50), CavlO(2), and O(2)ERavl) taken two at a time at every phase. Parameter P(50) changed from 25.98 +/- 1.10 to 23.15 +/- 2.24 (at the end of operation). A leftward shift of the ODC was observed. The results showed positive association between P(50) and CavlO(2) after the removal of the native liver, and a weak and inconsistent relation of DO(2 ind) with any of the other study variables. The intraoperative changes in P(50) values, which represent a shift of the ODC to the left, may reflect a more accurate estimation of O(2) release to the tissues, than the hemoglobin, Pao(2) and Sao(2) alone. Besides conventional hemodynamic parameters, P(50), which includes the effect of alterations in ODC on oxygen availability, could be of value in monitoring the systemic oxygenation during liver transplantation.

Pathophysiological responses following phosgene exposure in the anaesthetized pig.

This study aimed to develop a reproducible model of phosgene-induced lung injury in the pig to facilitate the future development of therapeutic strategies. Ten female young adult large white pigs were used. Following induction of anaesthesia using a halothane/oxygen/nitrous oxide mixture, arterial and venous catheters were inserted together with a pulmonary artery thermodilution catheter, and a suprapubic urinary catheter by laparotomy. Anaesthesia was maintained throughout the experiment by intravenous infusion of ketamine, midazolam and alfentanil. On completion of surgery the animals were allowed to equilibrate for 1 h and then were divided into two groups. Group 1 (n = 5) was exposed to phosgene for 10 min (mean Ct = 2443 +/- 35 mg min m(-3)) while spontaneously breathing, whereas control animals (Group 2 n = 5) were exposed to air. At 30 min post-exposure, anaesthesia was deepened in order to allow the initiation of intermittent positive pressure ventilation and the animals were monitored for up to 24 h. Cardiovascular and respiratory parameters were monitored every 30 min and blood samples were taken for arterial and mixed venous blood gas analysis and clinical chemistry. A detailed post-mortem and histopathology was carried out on all animals following death or euthanasia at the end of the 24-h monitoring period. Control animals (Group 2) all survived until the end of the 24-h monitoring period with normal pathophysiological parameters. Histopathology showed only minimal passive congestion of the lung. Following exposure to phosgene (Group 1) there was one survivor to 24 h, with the remainder dying between 16.5 and 23 h (mean = 20 h). Histopathology from these animals showed areas of widespread pulmonary oedema, petechial haemorrhage and bronchial epithelial necrosis. There was also a significant increase in lung wet weight/body weight ratio (P < 0.001). During and immediately following exposure, a transient decrease in oxygen saturation and stroke volume index was observed. From 6 h there were significant decreases in arterial pH (P < 0.01), P(a)O(2) (P < 0.01) and lung compliance (P < 0.01), whereas oxygen delivery and consumption was reduced from 15 h onwards in phosgene-exposed animals. Mean pulmonary artery pressure of phosgene-exposed animals was increased from 15 h post-exposure, with periods of increased pulmonary vascular resistance index being recorded from 9 h onwards. We have developed a reproducible model of phosgene-induced lung injury in the anaesthetized pig. We have followed changes in cardiovascular and pulmonary dynamics for up to 24 h after exposure in order to demonstrate evidence of primary acute lung injury from 16 h post-exposure. Histopathology showed evidence of widespread damage to the lung and there was also a significant increase in lung wet weight/body weight ratio (P < 0.001).

Effects of acid-base abnormalities on blood capacity of transporting CO(2): adverse effect of metabolic acidosis.

To investigate the effects of some acid-base abnormalities on blood capacity of transporting CO(2). Prospective study. General and Cardiosurgical ICUs of a University hospital. Six groups of ten patients characterized by: metabolic alkalosis; respiratory alkalosis; absence of acid-base abnormalities; metabolic acidosis; uncompensated respiratory acidosis; and compensated respiratory acidosis. The CO(2) dissociation curve, Haldane effect, and the ratio Ra-v between Ca-vCO(2) and Pa-vCO(2) were calculated from arterial and mixed-venous blood gas analyses. The CO(2) dissociation curve was shifted upwards by metabolic alkalosis and compensated respiratory acidosis and downwards by metabolic acidosis. The slope of the curve was unaffected, but CO(2) transport not due to Haldane effect was significantly lower in respiratory acidosis since the slope was less steep at higher PCO(2) values. In comparison with controls, patients affected by metabolic acidosis showed lower Haldane effect values (0.18+/-0.15 vs 0.59+/-0.26 ml of CO(2) per ml of arterial-mixed venous O(2) content difference; P <.05) and Ra-v values (0.43+/-0.10 vs 0.84+/-0.17 ml of CO(2) transported by 100 ml of blood per Torr of arterial-mixed venous PCO(2) gradient; P <.05). Our findings suggest that acid-base abnormalities, particularly metabolic acidosis, markedly affect blood capacity of transporting CO(2) and may worsen tissue hypercarbia associated with hypoperfusion. However, because of possible errors due to small measurements and the assumptions of the method, in the future definitive clarification will require the construction of original CO(2) dissociation curves for each acid-base abnormality.

Effect of breathing a heliox gas mixture on cardiopulmonary function in horses-anesthetized immediately following exercise

The purpose of this study was to determine the cardiopulmonary effects of breathing a heliox (60% He: 40% O2) carrier gas mixture in horses anesthetized immediately following treadmill exercise. Using a randomized crossover design, six healthy, Thoroughbred horses (five males, one female) weighing 517 ± 36.9 kg were instrumented to enable measurement of heart rate (HR), systolic (SAP), mean (MAP) and diastolic (DAP) carotid arterial pressures, mean pulmonary arterial pressure (PAP), central venous pressure (CVP), pulmonary arterial temperature (TEMP), and cardiac output. Horses were warmed up for 3 minutes at 4 m second−1, then exercised to the point of fatigue at 115% VO2max and immediately anesthetized using detomidine (0.04 mg kg−1 IV) followed by tiletamine-zolazepam (1.25 mg kg−1 IV). Anesthesia was maintained using 1.3 MAC isoflurane (ISO) vaporized in either 100% O2 (O), 60% N2 : 40% O2 (N), or 60% He : 40% O2 (H). End-tidal ISO concentration was measured using a RASCAL II anesthetic gas analyzer. Minute ventilation (MV) was measured during ISO anesthesia using a heated, calibrated pneumotachometer and differential pressure transducer. Ventilation during ISO anesthesia was controlled to maintain constant, similar minute ventilation between the O, N and H treatment groups. Cardiovascular data and samples for arterial and mixed venous blood gas analysis were recorded while the horse stood quietly prior to exercise, 30 seconds after the point of fatigue, immediately prior to isoflurane anesthesia and 15, 30, 45 and 60 minutes after initiating isoflurane anesthesia. Data were analyzed using repeated measures anova with posthoc differences between means identified using Bonferroni's method (p < 0.05). Exercise was associated with significant increases in HR, SAP, MAP, DAP, PAP, CVP, TEMP and significant decreases in pH, HCO3– and BE. Anesthesia was associated with a return of HR, SAP, MAP, DAP, PAP and CVP to pre-exercise values. MV measured during ISO was not different between groups. Horses in the O group had significantly higher values for PaO2 (156.7 mm Hg, 20.9 kPa) compared to the N group (93.6 mm Hg, 12.5 kPa) or the H group (90.4 mm Hg, 12.1 kPa). No other differences between treatments were identified. We conclude that use of H as a carrier gas does not improve gas exchange in horses anesthetized immediately following exercise.

Impaired carbon dioxide transport during and after cardiopulmonary bypass.

Changes in the CO2 carrying power of blood were evaluated during and after cardiopulmonary bypass (CPB) by calculating the equation of the whole blood CO2 dissociation curve and the ratio between the arterial-venous differences of CO2 content and CO2 tension (Ra-v). Sixteen patients undergoing normothermic CPB for coronary revascularization were studied; arterial and mixed venous blood gas analyses were performed prior to CPB, at the end of first cardioplegia infusion, 25 and 45 min after CPB commencement and 10 min after the termination of CPB. After CPB commencement, the whole blood CO2 dissociation curve became flatter and did not further change during or after CPB. Ra-v decreased from 1.06 +/- 0.16 to 0.72 +/- 0.12 ml/mmHg after the start of CPB and did not change significantly during CPB; it was still 0.73 +/- 0.13 ml/mmHg after CPB. The data indicate that during CPB the amount of CO2 removed from tissues by 1 litre of blood decreases by about 30% and that impairment in CO2 transport persists after the restoration of physiological circulation. Impairment in CO2 transport is mainly caused by haemodilution, but it could be worsened by acidosis.

Sequence of cardiovascular changes leading to pulmonary edema in swine fed culture material containing fumonisin

Abstract Objectives To determine the sequence of cardiovascular and blood gas changes induced by ingestion of fumonisin-containing culture material in swine and to examine the temporal relationship of these changes to plasma sphinganine and sphingosine concentrations. Animals 12 healthy castrated pigs (38 to 50 kg). Procedure Pigs were instrumented to permit cardiovascular monitoring and collection of blood samples. Baseline values were obtained, and pigs were randomly assigned to 1 of 2 groups. Control pigs (n = 6) were fed a standard grower diet, whereas culture material that contained 20 mg of fumonisin B1/kg of body weight was added to the feed of treated pigs (n = 6) each day. Hemodynamic data, results of arterial and mixed venous blood gas analyses, and plasma sphinganine and sphingosine concentrations were recorded every 12 hours until treated pigs were euthanatized because of impending death from pulmonary edema. Results Sphinganine and sphingosine concentrations were increased in plasma of treated pigs within 24 hours of initial fumonisin exposure and continued to increase dramatically until euthanasia. Fumonisin-treated pigs had increased respiratory rate, mean pulmonary artery pressure, and pulmonary artery wedge pressure, along with decreased heart rate and cardiac output in the 12-hour period before euthanasia. Fumonisin-treated pigs also had systemic arterial hypotension, arterial and mixed venous hypoxemia, metabolic acidosis, decreased oxygen delivery, and increased oxygen consumption immediately before euthanasia. Conclusions and Clinical Relevance Fumonisin-induced pulmonary edema in swine is probably caused by acute left-sided heart failure. Onset of hemodynamic changes was associated with plasma sphinganine concentration ≥ 2.2 μM/L and plasma sphingosine concentration ≥ 1 µM/L (Am J Vet Res 1999;60:1292–1300)

THE EFFECTS OF ABDOMINAL RETRACTION ON RESPIRATORY GAS EXCHANGE IN MORBIDLY OBESE PATIENTS

S531 Decrease in arterial oxygen tension (PaO2) occurs in anesthetized paralyzed mechanically ventilated morbidly obese patients in the supine position [1]. Decrease in PaO2 is attributed to the decrease in functional residual capacity (FRC) due to the cephalad shift of the diaphragm. Although abdominal traction and intra-abdominal packing may further aggravate oxygenation [2], previous studies were inconsistent regarding the change in PaO2 due to abdominal retraction [1]. Recently, a Bookwalter multi-blade retractor became commonly used in laparotomies, and the necessity of intra-abdominal gauze packing lessened. In this study, we evaluated the effects of placement of this retractor on respiratory gas exchange in morbidly obese patients. Methods: With informed consent and IRB approval, 10 morbidly obese patients (age 39 +/- 11, body weight 140 +/- 39(kg), body mass index 47.7 +/- 13.3) undergoing gastric bypass surgery were studied. Anesthesia was standardized with thiopental, desflurane, fentanyl and atracurium. Inspired oxygen fraction was maintained approximately 0.6. A radial artery canula, pulmonary artery catheter and respiratory gas mixing chamber [3] were placed Arterial and mixed venous blood gas analyses, mixed expired gas analyses, and hemodynamic and mechanical ventilatory data were obtained at two stages: before placement of the retractor (stage I: baseline); 15 min after placement of the retractor (stage II). Arterial PCO2 (PaCO2) values were corrected to pulmonary artery temperature. We calculated dynamic lung compliance (CLung), dead space-tidal volume ratio (VD/VT), and venous admixture (Qs/Qt). Statistical analyses of the data were performed by paired t-test and changes were considered statistically significant at P<0.05. Results: Results are shown in Table 1. Hypoxemia (PaO2 less than 100 mmHg) occurred in 4 of 10 patients after induction of anesthesia. There were no significant differences in PaO2, VD/VT and Qs/Qt between stage I and II. In 7 of 10 patients, CLung even increased after placement of the retractor.Table 1Conclusion and Discussion: Respiratory gas exchange was not aggravated by placement of a Bookwalter multi-blade retractor during laparotomies in morbidly obese patients. Improvement in CLung observed in some patients suggested that placement of the retractor might have relieved high intra-abdominal pressure placed on the diaphragm; thus further decrease in FRC was avoided.