Venous Partial Pressure Of Carbon Dioxide Research Articles

Relation Between Multiplication of Venous Carbon Dioxide Partial Pressure (PvCO2) and the Ratio of Gas Flow to Pump Flow (Ve/Q) with Hyperlactatemia During Cardiopulmonary Bypass.

The incidence of hyperlactatemia due to hypoperfusion during cardiopulmonary bypass (CPB) increases morbidity. Carbon dioxide production during CPB is one of the lactate production markers, in addition to other markers such as delivery oxygen (DO2), oxygen consumption (VO2), mixed vein oxygen saturation (SvO2), and oxygen extraction ratio (O2ER). This observational analytic study was conducted on 40 adult cardiac surgery patients using a CPB machine. Initial lactate is taken when entering CPB and final lactate is examined 15 min after coming off bypass. The values of DO2, VO2, SvO2, VCO2, respiratory quotient (RQ), DO2/VCO2, PvCO2 × Ve/Q were calculated from the results of blood and venous gas analysis 1 h after entering CPB in the nadir of core temperature and lowest pump flow. The multivariate test showed that the value of PvCO2 × Ve/Q was more effective than other oxygenation and carbon dioxide parameters in predicting an increase in the percentage of lactate. Each increase of 1 mmHg PvCO2 ×× Ve/Q can predict a final lactate increase of 29% from the initial lactate. The high PvCO2 × Ve/Q value is also the strongest correlation factor for the incidence of hyperlactatemia after CPB (final lactate >3 mmol/L). The cutoff value of this marker is >19.3 mmHg, which has a sensitivity of 100% and a specificity of 55.6% with a strong correlation value. The PvCO2 × Ve/Q value proved to be one of the significant markers in predicting hyperlactatemia during cardiac surgery using CPB.

Clinical effects and adverse effects of intravenous lipid emulsion treatment in dogs and cats with suspected poisoning.

This retrospective study aimed to evaluate the effects on the clinical signs of poisoning and adverse effects of intravenous lipid emulsion treatment in 82 animals (dogs and cats) with suspected poisonings over 18 months. Physical examination parameters and state of consciousness were documented every hour after the intravenous administration of a bolus of 2 ml/kg and 0.25 ml/kg/min over 60 minutes of a 20% intravenous lipid emulsion. The modified Glasgow coma scale and laboratory findings (blood gas analysis, triglyceride, lactate) were evaluated initially and three hours after discontinuing intravenous lipid emulsion administration. A statistical evaluation of the occurrence of adverse effects and the development of laboratory values was performed. A decrease in respiratory rate in the second control (8-12 hours) after ILE was observed. Three hours after completing of the intravenous lipid emulsion, triglyceride concentration increased about 10 times (p <0.001). Venous carbon dioxide partial pressure, bicarbonate, base excess, as well as the electrolytes sodium, potassium and ionized calcium decreased significantly (p <0.001). Patients who experienced a worsening of the modified Glasgow coma scale had a higher increase in triglyceride concentrations (p = 0.041) and plasma lactate (p = 0.034) and a larger decrease in bicarbonate concentrations (p = 0.053) compared to others. About 54% (n = 44) of the patients showed adverse effects which could be attributed to the administration of intravenous lipid emulsion and may be associated with a higher triglyceride increase. All of them were completely reversible within 33 hours. Adverse effects associated with intravenous lipid emulsion therapy were observed in half of the patients and were associated with a higher increase in triglycerides.

Comparing lung mechanics of patients with COVID related respiratory distress syndrome versus non-COVID acute respiratory distress syndrome: a retrospective observational study

Background Most patients admitted to the intensive care unit with coronavirus disease (COVID-19) develop severe respiratory failure. Understanding lung mechanics helps to guide protective mechanical ventilation, improve oxygenation, and reduce the ventilator induce lung injury. This study aims to describe lung mechanics characteristics of patients with COVID -19 related acute respiratory distress syndrome (CARDS) and to compare them with non-COVID-19 associated ARDS. Methods We performed a retrospective observational study of lung mechanics: plateau pressure (Pplat), Driving pressure (DP), Mechanical power (MPw), Elastic (dynamic) power (EdPw), Total ventilatory power (TPw), and oxygenation parameters (ratio of arterial oxygen partial pressure to fractional inspired oxygen (PaO2/FiO2), the ratio of arterial oxygen partial pressure to fractional inspired oxygen multiplied by PEEP [PaO2/(FiO2 x PEEP)], arterial and venous carbon dioxide partial pressure (PaCO2, PvCO2), and Ventilation dead space (VD) were measured and compared between the two groups after initiation of mechanical ventilation. Results 30 CARDS and 10 ARDS patients fulfilled the study requirements. We observed a significant higher MPw in the CARDS group (29.17 ± 8.29 J/min vs 15.78 ± 4.45 J/min, P 0.007), similarly observed with EdPw (256.7 ± 84.06 mJ/min vs 138.1 ± 39.15 mJ/min, P 0.01) and TPw (289.1 ± 84.51 mJ/min vs 161.5 ± 45.51, P 0.007). Inside the CARDS group, we found 2 subgroups, a low shunt subgroup and a higher shunt (Qs/Qt (%): 6.61 ± 2.46 for vs 40.3 ± 20.6, P 0.0009), however, between these two subgroups we didn’t find statistical differences on lung mechanic parameters but only in oxygenation parameters (PaO2/FiO2 and PaO2/FiO2*PEEP). When comparing these two subgroups with ARDS patients, we found more similarity between the low shunt CARDS and the ARDS patients on MP (R2 0.99, P 0.001), EdPw (R2 0.89, P 0.05) and TPw (R2 0.99, P 0.0009). Conclusions: Our study suggests important differences between CARDS and ARDS regarding mechanical parameters that could lead to more complicated management of CARDS patients and a higher prevalence of VILI. However due to the study limitations, a bigger study is necessary to corroborate our findings. Keywords: COVID-19, CARDS, ARDS, lung mechanics, VILI.

PCO2 gap, its ratio to arteriovenous oxygen content, ScvO2 and lactate in high-risk abdominal surgery patients: An observational study

BackgroundThe difference between arterial and central venous carbon dioxide partial pressure (PCO2 gap), a marker of oxygen delivery (DO2) and oxygen consumption (VO2) adequacy, has been evaluated as a promising prognostic tool in intensive care unit (ICU) patients. We therefore sought to study the association between intraoperative PCO2 gap and postoperative complications (POC) in the perioperative setting of elective major abdominal surgery. MethodsWe conducted a single-centre prospective observational study. All adult patients who underwent major planned abdominal surgery were eligible. PCO2 gap was measured every 2 h during surgery, at ICU admission and repeated 12 h and 24 h later. Severe POC within 28 days after surgery were defined as complications graded 3 or more according to Clavien-Dindo classification. Following a univariate analysis, a multivariable analysis using a logistic regression model was performed. ResultsNinety patients were included and divided into two groups according to the occurrence of POC. No significant difference was found between groups regarding baseline characteristics at inclusion. Thirty-nine (43%) patients developed postoperative complications. The median [IQR] intraoperative PCO2 gap was significantly higher in patients who had complications (6.5 [5.5−7.3] mmHg) compared to those who did not (5.0 [3.9–5.8] mmHg; p < 0.001). The area under the receiver operating characteristic curve for occurrence of POC was 0.78 for the PCO2 gap. After multivariable analysis, PCO2 gap was found independently associated with POC (OR: 14.9, 95% CI [4.68–60.1], p < 0.001) with a threshold value of 6.2 mmHg. The duration of surgery (OR: 1.01, 95% CI [1.00; 1.01], p = 0.04) and the need for vasoactive support during surgery (OR: 5.76, 95% CI [1.72; 24.1], p = 0.006) were also independently associated with POC. ConclusionIntraoperative PCO2 gap is a relevant predictive factor of severe postoperative complications in high-risk elective surgery patients. Trial registrationClinicalTrials.gov, NCT03914976.

Ex Vivo Normothermic Perfusion of Human Upper Limbs.

Ischemia-reperfusion injury remains a primary concern in upper extremity transplantation. Ex vivo normothermic perfusion (EVNP) enables near-physiological organ preservation, avoiding the deleterious effects of hypoxia and cooling. We investigated the effectiveness of human limb EVNP compared with static cold storage (SCS). Twenty human upper extremities were procured. Ten were perfused at 38 °C with an oxygenated red blood cell-based solution, and contralateral limbs served as SCS control (4 °C). EVNP was terminated with systolic arterial pressure ≥115 mm Hg, compartment fullness, or a 20% decline in oxygen saturation. Weight, contractility, compartment pressure, tissue oxygen saturation, and uptake rates were assessed. Perfusate fluid dynamics, gases, electrolytes, and metabolites were measured. Myocyte injury scores and liquid chromatography-mass spectrometry analysis were performed. EVNP duration was 41.6 ± 9.4 h. Vascular resistance averaged 173.0 ± 29.4 mm Hg × min/L. Weight change and compartment pressures were 0.4 ± 12.2% ( P = 0.21) and 21.7 ± 15.58 mm Hg ( P = 0.003), respectively. Arterial and venous carbon dioxide partial pressure, oxygen saturation, and pH were 509.5 ± 91.4 mm Hg, 15.7 ± 30.2 mm Hg, 87.4 ± 11.4%, and 7.3 ± 0.2, respectively. Oxygen uptake rates averaged 5.7 ± 2.8 mL/min/g. Lactate reached 20 mmol/L after 15 (interquartile range = 6) h. Limb contractility was preserved for 30.5 (interquartile range = 15.8) h ( P < 0.001) and negatively correlated with perfusate potassium (ρ = -0.7, P < 0.001). Endpoint myocyte injury scores were 28.9 ± 11.5% (EVNP) and 90.2 ± 11.8% (SCS) ( P < 0.001). A significant increase in taurine ( P = 0.002) and decrease in tryptophan ( P = 0.002) were detected. Infrared thermography and indocyanine green angiography confirmed the presence of peripheral perfusion. EVNP can overcome the limitations of cold preservation by extending preservation times, enabling limb quality assessment, and allowing limb reconditioning before transplantation.

Physiological responses of juvenile Colossoma macropomum after different periods of air exposure

The objective of this work was to evaluate the physiological responses of juvenile Colossoma macropomum exposed to air for different periods of time. Juveniles weighing 74.78 ± 17.39 g were acclimated for 15 days in 30-L tanks in a recirculating aquaculture system (RAS) at a density of 6 animals/tank. The animals were then fasted for 24 h prior to the air exposure test and six juveniles were captured for blood collection to establish basal levels of the parameters. Next, 24 animals were exposed to air for 30 min and the other 24 for 60 min. Blood samples were taken from six animals of each exposure treatment immediately after exposure (IAE), and the other animals returned to their tanks. Subsequent blood samples were taken for six animals (n = 6) per exposure time at 1 h (1hAE), 24 h (24hAE) and 48 h (48hAE) after air exposure. No mortality was recorded. Hematocrit and hemoglobin did not vary according to air exposure time, collection time or the interaction between these two factors. There was an interaction of the factors times of exposure to air and times of collection for glucose where was higher for the 60 min exposure compared to the 30 min exposure at the 1hAE collection, while after 24hAE the levels did not differ from basal. For lactate there was also an interaction between the factors being higher for the 60 min exposure compared to the 30 min exposure at IAE and 1hAE. Blood pH varied among the collections, with a lower value at 1hAE for the 60 min exposure. The parameters PvCO2 (venous carbon dioxide partial pressure) and PvO2 (venous oxygen partial pressure) were inversely proportional; while PvCO2 increased, PvO2 decreased after collection 1hAE. Values of HCO3− (bicarbonate) differed between exposure times and varied among collections. The electrolytes Cl− (Chloride) and K+ (Potassium) varied among collections in relation to basal, however, they did not differ between exposure times. The value for Na+ (Sodium) for the 60 min exposure at IAE was higher than basal, and only 24hAE was different from basal for both exposures. Ca2+ (Calcium) values differed between exposure times (30 and 60 min) in the 24hAE collection, however, values did not differ from basal. Exposure to air caused physiological, biochemical, gasometric and electrolytic in juvenile C. macropomum. These animals can be considered resistant to this stress due to their ability to restore physiological.

Elevated Arterial-Central Venous Carbon Dioxide Partial Pressure Difference Indicates Poor Prognosis in the Early Postoperative Period of Open Heart Surgery in Infants with Congenital Heart Disease.

Elevated arterial-central venous carbon dioxide partial pressure difference (AVCO2) may be an important marker to predict tissue and organ hypoperfusion in adults. We analyzed the hemodynamic data of infants with congenital heart disease who underwent corrective repair with cardiopulmonary bypass (CPB) to identify whether AVCO2 has clinical significance in early postoperative tissue hypoperfusion, occurrence of complications, and clinical outcomes. Infants with clinical conditions of hypoperfusion, without volume responsiveness and with ineffective initial treatment, within 3h of cardiac surgery were enrolled in this study. A pulse contour cardiac output catheter was used to monitor the cardiac index (CI). Eight measurements of arterial blood gas and central venous blood gas were taken within 42h after surgery. Clinical data of all patients were recorded. A total of 69 children were enrolled in this study. Arteriovenous oxygen difference, AVCO2, lactic acid level, and vasoactive inotropic score in the hypoperfusion group (oxygen supply/oxygen consumption ratio [DO2/VO2] of ≤ 2) were significantly higher than those in the non-hypoperfusion group (DO2/VO2 > 2), while the CI in the hypoperfusion group was significantly lower than that in the non-hypoperfusion group. The cutoff value of AVCO2 to predict DO2/VO2 ≤ 2 was 12.3 within 42h of surgery with area under the curve of 0.84. High AVCO2 is more likely to be associated with some complications and prolonged mechanical ventilation and length of stay in the intensive care unit. Elevated AVCO2 within 42h of CPB in infants is associated with tissue and organ hypoperfusion and incidence of complications. Persistent or repeated increase in AVCO2 indicates poor prognosis.

Trending peripheral venous PCO2 in patients with respiratory failure using mathematically arterialised venous blood gas samples

BackgroundTrending venous blood gases (VBGs) has been suggested as an alternative to arterial blood gases (ABGs) in patients with respiratory failure, but there are limits to its utility. The aim...

P1386Continuous, transcutaneous carbon-dioxide monitoring in complex electrophysiological procedures in conscious sedation - is there a safer way to sleep?

Abstract Funding Acknowledgements Karolina Weinmann was supported by the Hertha-Nathorff fellowship from Ulm University Background – Ablation of cardiac arrhythmias by complex electrophysiological procedures is a growing field. A moderate to deep sedation is needed to immobilize the patient to warrant a safe and effective intervention. The administrated medication to obtain an adequate sedation has respiratory depressant side effects and could cause respiratory complications, like hypercapnia and hypoxia. Purpose – Our aim was to investigate the feasibility and accuracy of an additional, continuous transcutaneous carbon-dioxide (tpCO2) measurement during moderate to deep sedation in complex electrophysiological catheter ablations. Methods – Consecutive patients received an electrophysiological intervention with need for deep sedation. Routine hemodynamic monitoring was performed by the measurement of non-invasive blood-pressure, oxygen saturation and half-hourly venous blood gas analysis. Additionally, patients received a tpCO2 sensor on the forehead with an automated, continuous documentation of transcutaneous oxygen saturation and carbon-dioxide. A precise sedation protocol was performed and administrated drugs were registered. Results – We included 110 patients to the analysis. Fifty patients received cryoballoon pulmonary vein isolation, 58 patients 3D-mapping procedure and two patients ventricular tachycardia ablation. The mean procedure time was 135.1 ± 63.5 minutes and the fluoroscopy time was 21.5 ± 10.9 minutes. To achieve an adequate sedation a mean of 5.0 ± 0.8 mg midazolam, 583.8 ± 320.4 mg propofol, 72.0 ± 30.3 µg fentanyl and 0.2 ± 0.1 mg remifentanil were administrated. Hypercapnia (pCO2 &amp;gt; 70 mmHg) was detected in five patient by the tpCO2 monitoring and only in two patients using venous carbon-dioxide partial pressure (vpCO2) analysis. Correlation of tpCO2 and vpCO2 were analyzed half-hourly by Pearsons’ correlation coefficient. There was a good correlation during the investigated 120 minutes of procedure time (baseline: r = 0.65, p &amp;lt; 0.0001; 30 minutes: r = 0.75, p &amp;lt; 0.0001; 60 minutes: r = 0.77, p &amp;lt; 0.0001; 90 minutes: r = 0.78, p &amp;lt; 0.0001; 120 minutes: r = 0.85, p &amp;lt; 0.0001). The detected difference between tpCO2 and vpCO2 was at baseline &amp;lt;5 mmHg in 65% (79/110) and &amp;lt;10 mmHg in 96% (103/110), after 30 minutes the difference was &amp;lt;5 mmHg in 71% (78/110) and &amp;lt;10 mmHg in 96% (105/110), after 60 minutes the difference was &amp;lt;5 mmHg in 77% (60/78) and &amp;lt;10 mmHg in 96% (75/78) and after 90 minutes the difference between the two methods was &amp;lt;5 mmHg in 63% (30/48) and &amp;lt;10 mmHg in 98% (47/48) of the cohort. Conclusion – The continuous tpCO2 monitoring is a feasible and precise method with a good correlation to the venous blood gas carbon-dioxide analysis of the standard monitoring during complex catheter ablations in deep sedation. Randomized trials are required to further analyze if tpCO2 monitoring adds further safety to electrophysiological procedures in deep sedation.

Performance of a capnodynamic method estimating effective pulmonary blood flow during transient and sustained hypercapnia

The capnodynamic method is a minimally invasive method continuously calculating effective pulmonary blood flow (COEPBF), equivalent to cardiac output when intra pulmonary shunt flow is low. The capnodynamic equation joined with a ventilator pattern containing cyclic reoccurring expiratory holds, provides breath to breath hemodynamic monitoring in the anesthetized patient. Its performance however, might be affected by changes in the mixed venous content of carbon dioxide (CvCO2). The aim of the current study was to evaluate COEPBF during rapid measurable changes in mixed venous carbon dioxide partial pressure (PvCO2) following ischemia–reperfusion and during sustained hypercapnia in a porcine model. Sixteen pigs were submitted to either ischemia–reperfusion (n = 8) after the release of an aortic balloon inflated during 30 min or to prolonged hypercapnia (n = 8) induced by adding an instrumental dead space. Reference cardiac output (CO) was measured by an ultrasonic flow probe placed around the pulmonary artery trunk (COTS). Hemodynamic measurements were obtained at baseline, end of ischemia and during the first 5 min of reperfusion as well as during prolonged hypercapnia at high and low CO states. Ischemia–reperfusion resulted in large changes in PvCO2, hemodynamics and lactate. Bias (limits of agreement) was 0.7 (−0.4 to 1.8) L/min with a mean error of 28% at baseline. COEPBF was impaired during reperfusion but agreement was restored within 5 min. During prolonged hypercapnia, agreement remained good during changes in CO. The mean polar angle was −4.19° (−8.8° to 0.42°). Capnodynamic COEPBF is affected but recovers rapidly after transient large changes in PvCO2 and preserves good agreement and trending ability during states of prolonged hypercapnia at different levels of CO.

Dynamical systems applied to dynamic variables of patients from the intensive care unit (ICU): Physical and mathematical mortality predictions on ICU

Methodologies have been developed to evaluate the heart rate (HR) chaotic dynamics, differentiating normality of chronic and acute disease and the evolut ion between these states; other dynamic variables of system on ICU have shown a chaotic behavior. An induction from 8 patients was realized, five discharged alive from ICU and 3 cases of mortality, defining sets and subsets, as well as operations between them that differentiate and predict the dynamics of patients who survive of those with fatal outcome, through the maximum and minimum values of chaotic attractors of 4 dynamic variables: Heart rate (HR), arterial carbon dioxide partial pressure (PACO2), venous carbon dioxide partial pressure (PvCO2), and oxygen venous saturation (SVO2). Finally a blind study was done with 12 patients, calculating sensitivity, specificity, PPV, NPV and accu racy. Also a temporal decrease in the cardiac dynamics evaluation was done, from 21 to 15 hours, through an induction with two cases, one with normal dynamic and one with acute dynamic. The occupation spaces of cardiac chaotic attractors were measured, and then a blind study was realized with 18 patients, calculating sensitivity, specificity and Kappa coefficient. The equation T = [(B2 ∩ C2) U A1 U D3] U [(A2 ∩ B1) U C3 U D1] differentiates and predicts the dynamics of patients who survive of those with fatal outcome in the ICU. The sensitivity, specificity, PPV and NPV were 100%, and accuracy was 1. Acute cardiac dynamic was differentiated of normal dynamic on 15 hours, allowing to reduce the time of the evaluation of this dynamic of 21 to 15 hours, the sensitivity and specificity values were 100% and Kappa coefficient was 1. Dynamical systems in the context of set algebra allow differen tiate patients who are discharged alive from those with an adverse outcome. The evolution to death can be predicted in a physical and mathematical way in the ICU.

Different fasting periods in tiletamine-zolezepam-anethetized cats: Glycemia, recovery, blood-gas and cardiorrespiratory parameters

The effects of different fasting periods on glycemia levels and on cardiorrespiratory parameters in tiletamine-zolazepam-anesthetized cats were evaluated. Twenty one animals were randomly assigned to three groups: 8 hours (G8), 12 hours (G12) or 18 hours (G18) of the preoperative fasting. The tiletamine-zolazepam (2 mg/kg) was administered intravenously. The heart rate (HR), respiratory rate (fR), rectal temperature (T R), glycemia (G), laboratorial glycemia (Glab), venous oxygen partial pressure (PvO2), venous carbon dioxide partial pressure (PvCO2), venous hemoglobin saturation (SvO2), pH, base deficit (BD), bicarbonate concentration (HCO3- ) and haematocrit were evaluated at 90 minutes after the last meal (T0), immediately before anesthesia (T1) and at ten (T2) and thirty (T3) minutes after tiletamine-zolezepam administration. The time between the administration of anesthetic and the cat's trial to elevate head (Th) and the interval between drug administration and aniamal's quadrupedal position (Tqp) were recorded. No differences among groups were recorded for glycemia, HR, PvO2, SvO2, pH, BD, HCO3-, Ht and Tqp. In G12 from T2, glycemia increased and from T1 PvCO2 decreased. At T1, PvO2 increased in all groups. In G8 and G12, from T1, DB and HCO3- decreased. In G12 and G18, from T2, Ht decreased. In G12, the Th mean was higher than G8. In conclusion, in tiletamine-zolazepam-anesthetized cats, the different preoperative fasting did not influence glycemia, blood-gas and cardiorrespiratory parameters. Additionally, there was no relationship between glycemia and anesthesia recovery.

Venous blood gas and metabolite response to low-intensity muscle contractions with external limb compression

The effect of low-intensity resistance exercise with external limb compression (100 [EC100] and 160 [EC160] mm Hg) on limb blood flow and venous blood gas-metabolite response was investigated and compared with that of high-intensity resistance exercise (no external compression). Unilateral elbow flexion muscle contractions were performed at 20% (75 repetitions, 4 sets, 30-second rest intervals) and 70% of 1-repetition maximum (1-RM; 3 sets, each set was until failure, 3-minute rest intervals). Precontraction brachial arterial blood flow (Doppler ultrasound) was reduced with EC100 or EC160 (56% and 39% of baseline value, respectively) compared with no external compression (control). At 20% 1-RM, brachial arterial blood flow increased after contractions performed with EC160 (190%), but not with the others. Decreases in venous oxygen partial pressure (P vO 2) and venous oxygen saturation (S vO 2) were greater during EC100 and EC160 than control (mean [SE]: P vO 2, 28 [3] vs 26 [2] vs 33 [2] mm Hg; S vO 2, 41% [5%] vs 34% [4%] vs 52% [5%], respectively). Changes in venous pH (pH v), venous carbon dioxide partial pressure (P vCO 2), and venous lactate concentration ([L −] v) were greater with EC160 than EC100 and/or control (pH v, 7.19 [0.01] vs 7.25 [0.01] vs 7.27 [0.02]; P vCO 2, 72 [3] vs 64 [2] vs 60 [3] mm Hg; [L −] v, 5.4 [0.6] vs 3.7 [0.4] vs 3.0 [0.4] mmol/L, respectively). Seventy percent 1-RM contractions resulted in greater changes in pH v (7.14 [0.02]), P vCO 2 (91 [5] mm Hg), and [L −] v (7.0 [0.5] mmol/L) than EC100 and EC160, but P vO 2 (30 [4] mm Hg) and S vO 2 (40% [3%]) were similar. In conclusion, changes in pH v, P vCO 2, and [L −] v, but not in P vO 2 and S vO 2, are sensitive to changes in relative, “internal” intensity of low-intensity muscle contractions caused by reduced blood flow (EC160) or high-intensity muscle contractions. Given the magnitude of the changes in pH v, P vCO 2, and [L −] v, it appears plausible that they may be involved in stimulating the observed increase in muscle activation via group III and IV afferents.

Near-fatal pediatric asthma managed with pumpless arteriovenous carbon dioxide removal*

To describe the use of pumpless arteriovenous carbon dioxide removal in support of four pediatric patients with near-fatal asthma. Report of four cases. Tertiary care university pediatric intensive care unit. Four pediatric patients, ages 4, 10, 12, and 13, were intubated and initially managed with positive pressure ventilation for severe respiratory failure. Despite pharmacologic therapy with inhaled beta-agonists, inhaled anticholinergics, systemic corticosteroids, and intravenous magnesium, marked progressive hypercapnia and acidosis rapidly developed requiring high levels of positive pressure ventilation. Application of pumpless arteriovenous carbon dioxide removal (AVCO2R) via percutaneous femoral cannulation. Arterial or mixed venous carbon dioxide partial pressure (PCO2) and pH were measured before and at intervals following initiation of AVCO2R. Before cannulation, PCO2 was elevated to 100, 108, 90, and 186 mm Hg in the four patients, with corresponding pH of 7.07, 6.96, 7.09, and 6.80, respectively. Pco2 levels were reduced to more acceptable levels (37-57 mm Hg) within 2-4 hrs of initiation of AVCO2R, with corresponding improvements in pH despite reductions in ventilatory frequency and tidal volumes to safe levels. Duration of support ranged from 18 hrs to 5 days during resolution of bronchospasm. No red blood cell or platelet transfusions were required, and no complications resulted from AVCO2R or from mechanical ventilation. All patients were discharged from the hospital without sequelae. Percutaneous cannulation with a simplified pumpless extracorporeal circuit is capable of removing sufficient carbon dioxide to allow application of a protective ventilatory strategy in severe hypercapnic pediatric respiratory failure. The procedure was safely applied without complications in four pediatric patients as young as 4 yrs of age.

Blood Gas, Hemoglobin, and Growth of Tibetan Chicken Embryos Incubated at High Altitude

Metabolism and hatchability are impaired when chicken eggs laid at sea level are incubated at high altitude. The Tibetan chicken is an excellent local poultry breed that inhabits altitudes of 2,900 m and has a hatchability of approximately 75% at that altitude. To understand how Tibetan chicken embryos develop successfully at high altitude, we compared blood gas, pH, hemoglobin concentrations and embryo mass for Tibetan chicken embryos (T) and for embryos from a dwarf breed (D) that normally is reared at sea level. The 2 breeds (T and D) and 2 incubation altitudes (2,900 m = high, H; and 100 m = low, L) were compared at 9, 12, 15, and 18 d of incubation. Embryo weights were lower for the high altitude groups (TH, DH) than for the low altitude groups at all stages of incubation. The embryo mass of TH appeared to increase more quickly than that of DH. Compared with DH, TH embryos had lower arterialized oxygen partial pressure on d 18, higher venous carbon dioxide partial pressure from d 12 to 18, and higher hemoglobin concentration and lower venous blood pH values on d 12 and 15. These findings indicate that the ability of the Tibetan chicken embryos to adapt to the high altitude may be due to the increase in hemoglobin concentration, which augments the blood oxygen-carrying capacity. In addition, the higher venous carbon dioxide partial pressure and lower venous blood pH promote unloading of oxygen from hemoglobin.

A new method of using gas exchange measurements for the noninvasive determination of cardiac output: clinical experiences in adults following cardiac surgery.

New mathematical algorithms have been applied to a computer controlled closed breathing circuit system for non-invasive measurement of cardiac output (COniv). This system has been described in an animal study. Forty patients were studied 5 and 18 hours after cardiac surgery using the thermodilution technique as the reference (COtd). The variables entered into the algorithms for COniv were oxygen uptake, carbon dioxide elimination, end-tidal carbon dioxide partial pressure, tidal volume and arterial oxygen saturation. Mixed venous carbon dioxide partial pressure was obtained from an automatically implemented short rebreathing manoeuvre. Pulmonary perfusion was calculated by a modified Fick equation for carbon dioxide and the shunt flow added to obtain COniv. During mechanical ventilation, there was a good agreement between COtd and COniv (r = 0.8). The bias was -0.14 l/min and the precision was 0.77 l/min. The reproducibility of COniv was 0.03 l/min and for COtd -0.03 l/min with a standard deviation of the difference being 0.35 l/min for COniv and 0.31 l/min for COtd. In awake, but sedated extubated patients, the method proved unsatisfactory on account for uneven tidal volumes and difficulties with leakage around the mouth piece. We conclude that this new technique provides reliable and reproducible measures of cardiac output in sedated, ventilated patients.

Utility of capnography in predicting venous carbon dioxide partial pressure in sedated patients during outpatient oral surgery

Twelve ASA class I patients scheduled for removal of third molars under intravenous sedation were included in the study. Samples for venous blood gas analysis were drawn every 5 minutes and the venous partial pressure of carbon dioxide was compared to the end-tidal CO 2 recorded from a modified nasal cannula at the same time the samples were drawn. Correlation analysis was performed using the Pearson correlation coefficient. The overall correlation between end-tidal CO 2 and P vco 2 was .54 ( P = .0001). The results of the investigation indicate that through simple modifications of the end-tidal CO 2 monitoring device, the correlation between end-tidal CO 2 and serum P co 2 in a nonintubated patient can be improved.

Discussion: Utility of Capnography in Predicting Venous Carbon Dioxide Partial Pressure in Sedated Patients During Outpatient Oral Surgery

Discussion: Utility of Capnography in Predicting Venous Carbon Dioxide Partial Pressure in Sedated Patients During Outpatient Oral Surgery