Continuous arterial and venous blood gas monitoring during cardiopulmonary bypass

A new monitoring technique, based on optical fluorescence chemistry, allows continuous monitoring of all blood gas variables during cardiopulmonary bypass. To evaluate the clinical performance of this monitor, we drew 220 arterial and 216 venous blood samples from 15 patients, and simultaneous blood gas values displayed by the monitor were compared with standard laboratory measurements. The continuous monitor predicted laboratory values with varying degrees of accuracy. (R2 values by linear regression: arterial oxygen tension 0.86, venous oxygen tension 0.36, arterial carbon dioxide tension 0.58, venous carbon dioxide tension 0.72, arterial pH 0.53, venous pH 0.58; pH 0.53, venous pH 0.58; p less than 0.0001). Monitor values of arterial oxygen tension overestimated laboratory values (bias = + 43.5 mm Hg), but the laboratory reference method likely underestimated true arterial oxygen tension in the high range achieved on bypass. Monitoring of venous oxygen tension was imprecise (precision = +/- 6.51 mmHg), regardless of whether stable conditions existed during the sampling period. Monitoring of carbon dioxide tension and pH showed small bias (carbon dioxide tension within 2 mm Hg, pH within 0.03) and good precision (carbon dioxide tension within 3 mm Hg, pH within 0.03). With the development of unstable conditions on bypass, monitor arterial oxygen tension values showed a changing relationship to corresponding laboratory values. In conclusion, arterial and venous carbon dioxide tension and pH monitoring provide acceptably accurate alternatives to laboratory measurement of these variables during cardiopulmonary bypass. Arterial oxygen tension monitoring accurately indicates changes in oxygen tension in the arterial oxygen tension range typically produced during extracorporeal circulation. Oxygen tension monitoring in the venous oxygen tension range is too imprecise for clinical decision-making purposes.     

Cerebral blood flow autoregulation: effect of hypercapnia on cerebral tissue gas concentrations.

Cerebral tissue oxygen and carbon dioxide tensions were monitored continuously in six rhesus monkeys using a Teflon coated catheter and a medical mass spectrometer. The monkeys were exposed to several ambient gas mixtures in a sealed helmet. Gases included air, 12% oxygen in nitrogen, and 12% oxygen with 5% carbon dioxide in nitrogen. Twelve percent oxygen in nitrogen resulted in a marked decrease in tissue pO₂ to 5.0 ± 2.2 mm Hg from a control of 16.5 ± 2.9. The addition of 5% carbon dioxide to the 12% oxygen provided almost complete amelioration of the decline in tissue pO₂ with a mean value of 15.7 ± 0.5 mm Hg.     

Comparison of a New Miniaturized Extracorporeal Membrane Oxygenation System With Integrated Rotary Blood Pump to a Standard System in a Porcine Model of Acute Lung Injury

Extracorporeal membrane oxygenation (ECMO) is used for severe acute respiratory distress syndrome. However, available ECMO systems are large and not well designed for fast delivery, emergency implantation, and interhospital transfer. Therefore, a new miniaturized oxygenator with integrated rotary blood pump (ILIAS) was developed and compared with a standard ECMO system in a large animal model. Acute lung injury was induced with repeated pulmonary saline lavage in 14 pigs until PaO₂/FiO₂‐ratio was <100 mm Hg with a positive‐end‐expiratory‐pressure of 5 mbar. Pigs were assigned to the following three groups: group 1 (n = 4): control group with conventional ventilation; group 2 (n = 5): standard vv‐ECMO; group 3 (n = 5): vv‐ILIAS. Gas exchange, hemodynamics, hemolysis, and coagulation activation were examined over a period of 8 h. No device failed during the observation period. PaCO₂ decreased from 59.40 ± 4.14 mm Hg to 48.62 ± 4.50 mm Hg after 1 h in the ILIAS group compared with an improvement of PaCO2 from 48.86 ± 7.45 to 40.10 ± 6.02 in the conventional ECMO group (P = not significant [n.s.]). ARDS‐induced respiratory acidosis was controlled promptly with a pH of 7.2 ± 0.1 at baseline increasing to 7.4 ± 0.1 in both study groups after 60 min of ECMO support. Mean carbon dioxide transfer was comparable between the conventional ECMO and ILIAS (211.36 ± 78.39 mL/min vs. 219.99 ± 76.72 mL/min, P = n.s.). PaO₂/FiO₂ increased from 118.4 ± 15.5 mm Hg to 179.1 ± 72.4 mm Hg in the ILIAS group compared with an improvement of oxygenation from 107.1 ± 24.9 mm Hg to 179.0 ± 45.7 mm Hg in the standard ECMO group (P = n.s.). Mean oxygen transfer was calculated with 136.09 ± 30.25 mL/min for the ILIAS and 129.05 ± 36.28 mL/min for the standard ECMO. Hemodynamic instability or significant activation of the plasmatic coagulation was not observed. However, hemolysis was significantly higher in the ILIAS group compared with the conventional ECMO. As the ILIAS prototype provided excellent gas exchange with hemodynamic stability comparable with a standard ECMO system, we believe this study serves as a proof of concept. Further development and design modifications (optimized rotation speed and surface coating of rotor) are already done and another experiment is projected to reduce hemolysis and platelet consumption for clinical application.     

Hemodynamics and gas exchange during carbon dioxide insufflation for totally endoscopic coronary artery bypass grafting

BACKGROUND: In addition to single-lung ventilation (SLV), positive-pressure CO2 insufflation is mandatory for totally endoscopic coronary artery bypass grafting. Studies on the effects of unilateral CO2 insufflation on hemodynamics produced controversial results, and bilateral insufflation has not been studied to our knowledge. The present study sought to investigate hemodynamics and gas exchange during unilateral and bilateral CO2 insufflation in patients who underwent totally endoscopic coronary artery bypass grafting. METHODS: Eleven hemodynamic and gas exchange variables were monitored during 22 totally endoscopic coronary artery bypass grafting procedures with unilateral (n = 17) or bilateral (n = 5) CO2 insufflation at a pressure of 10 to 12 mm Hg. Data were obtained at baseline with double-lung ventilation, after institution of SLV, during insufflation, after cardiopulmonary bypass during SLV, and after return to double-lung ventilation. RESULTS: Arterial oxygen tension decreased significantly during SLV, whereas the peak inspiratory pressure increased. In addition, central venous pressure and heart rate increased significantly during insufflation, but mean arterial pressure remained unchanged. Although the end-tidal CO2 pressure did not change, arterial carbon dioxide tension increased progressively to a maximum of 44.6 +/- 5.9 mm Hg during unilateral insufflation, and 55.7 +/- 14.6 mm Hg during bilateral insufflation (p < 0.05 versus baseline and between groups). Mixed venous oxygen saturation declined during SLV regardless of CO2 insufflation and recovered to baseline once double-lung ventilation was restarted. Left and right ventricular ejection fractions remained unaltered. No patient required inotropic or vasopressor support. CONCLUSIONS: Carbon dioxide insufflation for totally endoscopic coronary artery bypass grafting with SLV had no adverse effects on hemodynamics. In contrast to a moderate increase of arterial carbon dioxide tension during unilateral insufflation, markedly elevated arterial carbon dioxide tension levels remain a cause of concern during bilateral insufflation.     

Evaluation of an autoregulatory ECMO system for total respiratory support in an acute ovine model

Extracorporeal membrane oxygenation (ECMO) has become a mainstay of therapy for patients suffering from severe respiratory failure. Ambulatory ECMO systems aim to provide long-term out-of-hospital respiratory support. As a patient’s activity level changes, the required level of ECMO support varies with oxygen consumption and metabolic fluctuations. To compensate for such changes, an autoregulatory ECMO system (AR-ECMO) has been developed and its performance was evaluated as a proof of concept in an acute ovine model. The AR-ECMO system consists of a regular ECMO circuit and an electromechanical control system. A custom fuzzy logic control algorithm was implemented to adjust the blood flow and sweep gas flow of the ECMO circuit to meet the varying respiratory demand by utilizing two noninvasive sensors for venous oxyhemoglobin saturation and the oxygenator exhaust gas CO₂ concentration. Disturbance responses of the AR-ECMO to induced acute respiratory distress were assessed for six hours in four juvenile sheep cannulated with a veno-pulmonary artery ECMO configuration, including acute ventilator shutoff, ventilator step change (off-on-off), and forced desaturation. All sheep survived for the study duration. The AR-ECMO system was able to respond and maintain stable hemodynamics and physiological blood gas contents (SpO₂ = 96.3 % ± 4.29, pH 7.44 ± 0.09, pCO₂ = 38.9 ± 9.9 mm Hg, and pO₂ =237.9 ± 123.6 mm Hg) during simulated respiratory distress. Acceptable correlation between oxygenator exhaust gas CO₂ and oxygenator outlet pCO₂ were observed (R² = 0.84). In summary, the AR-ECMO system successfully maintained physiologic control of peripheral oxygenation and carbon dioxide over the study period, utilizing only measurements taken directly from the ECMO circuit. The range of system response necessitates an adaptable system in the setting of variable metabolic demands. The ability of this system to respond to significant disturbances in ventilator support is encouraging. Future work to evaluate our AR-ECMO system in long-term, awake animal studies is necessary for further refinement.     

Arterial blood gases in extraperitoneal laparoscopic urethrocystopexy

BACKGROUND: The aim of this study was to investigate the effects of extraperitoneal laparoscopy and carbon dioxide insufflation on hemodynamic parameters, arterial blood gases and complications in urethrocystopexy operations. METHODS: Twenty-five female patients who underwent extraperitoneal laparoscopic mesh urethrocystopexy operation for the correction of urinary incontinence were allocated to the study. Hemodynamic parameters were noted and blood gas analyzes were performed before the induction of anesthesia, 10 min after induction, 5 and 10 min after the beginning of carbon dioxide insufflation, at the end of carbon dioxide insufflation and 30 min after exsufflation. RESULTS: There was no significant change in mean arterial pressure, peripheral oxygen saturation, arterial carbon dioxide pressure, and arterial oxygen saturation compared to preinsufflation and preinduction values. End-tidal carbon dioxide pressure did not increase above 45 mm/Hg during carbon dioxide insufflation. Arterial oxygen saturation and partial oxygen pressure did not decrease. Subcutaneous emphysema, pneumothorax, pneumomediastinum and pleural effusion were not noted in any patient. CONCLUSION: We conclude that, extraperitoneal laparoscopic urethrocystopexy is not associated with hemodynamic and respiratory impairment.     

Systemic and Cerebral Haemodynamics During Craniotomy Under Mild Hypothermia in Patients with Acute Subarachnoid Haemorrhage

Summary ? Background. Mild hypothermia provides cerebral protection against ischaemic insults in various animal models. We compared systemic and cerebral oxygenation between mild hypothermic and normothermic management in 60 patients with acute subarachnoid haemorrhage who underwent clipping of cerebral aneurysms.  Method. The temperature in the pulmonary artery was maintained at 36°C in 28 patients and was reduced to 34°C in 32 patients. Parameters in the systemic and cerebral haemodynamics from pulmonary artery and internal jugular vein catheters were compared between the two groups immediately after the induction of anaesthesia (T1), and just before temporary occlusion or aneurysm clipping (T2).  Findings. Cardiac index, oxygen delivery index, oxygen consumption index, and oxygen saturation of the jugular bulb were significantly lower at T2 in hypothermic group (H) (2.9±0.6 L/min/m², 400.8±106.3 ml/min·m², 87.0±14.8 ml/min·m², 55.2±6.6%, respectively) than in normothermic group (N) (3.7±0.6, 521.0±105.5, 109.9±21.7, 60.9±6.6) (p<0.05). The arterial lactate and arteriojugular difference in oxygen content were significantly higher in H (2.3±1.3 mmol/L, 6.5±1.5 ml/dl, respectively) than in N (1.7±1.0, 5.6±1.2) (p<0.05). Arteriojugular differences in carbon dioxide tension and hydrogen ion content were significantly lower at T2 in H (−10.8±2.1 mm Hg, −6.4±1.3 nmol/L, respectively) than in N (−8.9±2.8, −5.3±1.0) (p<0.05).  Interpretation. The balance between oxygen supply and demand systemically and in the brain may worsen during aneurysm surgery for patients with acute subarachnoid haemorrhage under mild hypothermia. Oxygenation of the brain and the whole body should be monitored closely during this surgery, and adequate circulatory assistance is recommended under mild hypothermia.     

Conventional or minimized cardiopulmonary bypass support during coronary artery bypass grafting? – An analysis by means of perfusion and body mass index

The use of minimized cardiopulmonary bypass support to reduce the side effects of extracorporeal circulation is still contradictorily discussed. This study compares perfusion operated by conventional (CCPB) and minimized (MCPB) cardiopulmonary bypass support during coronary artery bypass grafting (CABG). This study includes the data of 5164 patients treated at our department between 2004 and 2014. Tissue perfusion during cardiopulmonary bypass support and cardiac arrest was assessed by means of body mass index, hemodilution, blood pressure with corresponding pump flow and venous oxygen saturation, serum lactate, and serum pH. Hemodilution was more pronounced after CCPB: hemoglobin had dropped to 4.47 ± 0.142 g/dL after CCPB and to 2.77 ± 0.148 g/dL after MCPB (P = 0.0022). Despite the higher pump flow in conventional circuits (4.86–4.95 L/min vs. 4.1–4.18 L/min), mean blood pressure was higher during minimized bypass support (53 ± 10 vs. 56 ± 13 mm Hg [aortic clamping], 57 ± 9 vs. 61 ± 12 mm Hg [34°C], 55 ± 9 vs.59 ± 11 mm Hg [aortic clamp removal], P < 0.0001) at all time points. Venous oxygen saturation remained on comparable levels of >70% during both conventional and minimized cardiopulmonary bypass support. The increase in serum lactate was more pronounced after CCPB (8.98 ± 1.28 vs. 3.66 ± 1.25 mg/dL, P = 0.0079), corresponding to a decrease in serum pH to acidotic levels (7.33 ± 0.06 vs. 7.35 ± 0.06, P < 0.0001). These effects were evident in all BMI ranges. Minimized cardiopulmonary bypass support provides efficient perfusion in all BMI ranges and is thus equivalent to conventional circuits.     

Continuous arterial P(O2) and P(CO2) measurements in swine during nitrous oxide and xenon elimination: prevention of diffusion hypoxia

BACKGROUND: During nitrous oxide (N2O) elimination, arterial oxygen tension (PaO2) decreases because of the phenomenon commonly called diffusive hypoxia. The authors questioned whether similar effects occur during xenon elimination. METHODS: Nineteen anesthetized and paralyzed pigs were mechanically ventilated randomly for 30 min using inspiratory gas mixtures of 30% oxygen and either 70% N2O or xenon. The inspiratory gas was replaced by a mixture of 70% nitrogen and 30% oxygen. PaO2 and carbon dioxide tensions were recorded continuously using an indwelling arterial sensor. RESULTS: The PaO2 decreased from 119+/-10 mm Hg to 102+/-12 mm Hg (mean+/-SD) during N2O washout (P<0.01) and from 116+/-9 mm Hg to 110+/-8 mm Hg during xenon elimination (P<0.01), with a significant difference (P<0.01) between baseline and minimum PaO2 values (deltaPaO2, 17+/-6 mm Hg during N2O washout and 6+/-3 mm Hg during xenon washout). The PaCO2 value also decreased (from 39.3+/-6.3 mm Hg to 37.6+/-5.8 mm Hg) during N2O washout (P<0.01) and during xenon elimination (from 35.4+/-1.6 mm Hg to 34.9+/-1.6 mm Hg; P< 0.01). The deltaPaCO2 was 1.7+/-0.9 mm Hg in the N2O group and 0.5+/-0.3 mm Hg in the xenon group (P<0.01). CONCLUSION: Diffusive hypoxia is unlikely to occur during recovery from xenon anesthesia, probably because of the low blood solubility of this gas.     

Avoiding hypoxemia during anesthesia

The incidence of unexpected hypoxaemia during general anaesthesia was studied in 230 healthy patients undergoing a peripheral surgical procedure. Measurements of arterial oxygen and carbon dioxide tension (paO2 and paCO2) were performed under rigorously controlled conditions in regard to the age of the patients, their smoking habits, course and type of the anaesthetic and surgery, body position, inspiratory fraction of oxygen (FiO2), expiratory fraction of carbon dioxide (FECO2), respiratory minute volume and inspiratory to expiratory time ratio. 10% of the patients receiving FiO2 of 0.33 and 3.3% of those receiving 0.40 were found to have a paO2 below 80 mm Hg. 25% respect. 0% of older (greater than 60) and 6.7% respect. 4.4% of younger patients (less than 60 years) receiving FiO2 of 0.33 respect. 0.40 were hypoxemic (paO2 less than 80 mm Hg). These figures were compared with the results of an inquiry of practicing anaesthesiologists (in USA, West Germany and Switzerland) and their opinions about the safe FiO2 and paO2 limits. Most of the respondents use under the described conditions of this study an FiO2 of 0.33. At the same time 96% of them expect a paO2 over 80 mm Hg. On the basis of 10% incidence of hypoxaemic values among the patients studied it was concluded that FiO2 of 0.33 can not be considered as safe: increasing FiO2 to 0.40 helps to decrease the incidence of unexpected hypoxaemia especially in the patients over 40 years old.     

The Dynamic Observation of Plasma Concentration of Antimicrobial Agents During Balanced Ultrafiltration In Vitro

Routine perioperative intravenous antimicrobial agents are administered as surgical prophylaxis. However, whether balanced ultrafiltration during extracorporeal circulation has substantial effect on the concentration of antimicrobial agents remains unclear. The concentrations of antimicrobial agents in plasma and ultrafiltrate samples were measured in this pseudo‐extracorporeal circulation model. Extracorporeal circulation consisted of cardiotomy reservoir, membrane oxygenator, and pediatric arterial line filter. A hemoconcentrator was placed between the arterial purge line and oxygenator venous reservoir. Fresh donor human whole blood was added into the circuit and mixed with Ringer's solution to obtain a final hematocrit of 24–28%. Two kinds of antimicrobial agents, cefotiam (320 mg) and cefmetazole (160 mg), were bolus added into the circuit. After 30 min of extracorporeal circulation, zero‐balanced ultrafiltration was initiated and arterial line pressure was maintained at approximately 100 mm Hg with a Hoffman clamp. The rate of ultrafiltration (12 mL/min) was controlled by ultrafiltrate outlet pressure. An identical volume of Plasmalyte A was dripped into the circuit to maintain stable hematocrit during 45 min of experiment. Plasma and ultrafiltrate samples were drawn every 5 min, and concentrations of antimicrobial agents (including cefotiam and cefmetazole) were measured with high performance liquid chromatography. Both antimicrobial agents were detected in ultrafiltrate, demonstrating hemoconcentration may remove antimicrobial agents. The concentrations of plasma antimicrobial agents decreased linearly with the increase of ultrafiltrate volume. At end of balanced ultrafiltration, the concentration of plasma cefotiam was 104.96 ± 44.36 mg/L, which is about 44.38% ± 7.42% of the initial concentration (238.95 ± 101.12 mg/L) (P < 0.001); the concentration of plasma cefmetazole decreased linearly to 25.76 ± 14.78 mg/L, which is about 49.69% ± 10.49% of the initial concentration (51.49 ± 28.03 mg/L) (P < 0.001). The total amount of cefotiam in ultrafiltrate is 27.16% ± 12.17% of the total dose administered, whereas cefmetazole in ultrafiltrate is 7.74% ± 4.17%. Balanced ultrafiltration may remove antimicrobial agents from plasma and has a prominent influence on plasma concentration of antimicrobial agent. The strategy of surgical prophylaxis should consider this unique technique during extracorporeal circulation.     

A capnography and transcutaneous CO2 profile of bariatric patients during early postoperative period after opioid-sparing anesthesia

BackgroundNoninvasive monitoring of partial pressure of carbon dioxide can be accomplished indirectly with capnography (P_ETCO₂) or with transcutaneous carbon dioxide monitoring (P_TCCO₂). The use of capnography has been shown to offer an advantage over pulse oximetry alone in the early detection of adverse respiratory events when supplemental oxygen is administered. Furthermore, capnography allows for the monitoring of various respiratory measures, including end-tidal carbon dioxide, respiratory rate, tidal volume, and changes in breathing patterns. Transcutaneous CO₂ also closely approximates arterial CO₂ values, but is not as easy to monitor for prolonged periods. The purpose of this study was to examine the usefulness of capnography and of transcutaneous carbon dioxide monitoring in patients recovering from obesity surgery at high risk of developing postoperative obstructive sleep apnea.MethodsIn a prospective observational study, 64 bariatric surgery patients at risk of developing obstructive sleep apnea were monitored in the postanesthesia care unit (PACU) with either capnography alone (31 patients) or capnography plus transcutaneous carbon dioxide monitoring (33 additional patients) every 3–5 minutes for the duration of their recovery. Primary endpoints included end-tidal and transcutaneous carbon dioxide, peripheral oxygen saturation, respiratory rate, pain scores, and incidence of adverse respiratory events.ResultsAlthough no adverse pulmonary events were observed, capnography detected several patients who experienced short periods of respiratory apnea while maintaining pulse oximetry readings within normal limits. Transcutaneous values were slow to change and averaged 4.5 ± 5.5 mm Hg (P < .05) higher than corresponding end-tidal measurements.ConclusionsThese results indicate the capabilities of both these noninvasive techniques for postoperative monitoring. Capnography acutely monitors changes in respiration, whereas transcutaneous monitoring more accurately reflects arterial CO₂ levels.     

Extracorporeal membrane oxygenation in the treatment of neonatal respiratory failure

We report 18 consecutive neonates with severe respiratory failure due to pulmonary hypertension treated with extracorporeal membrane oxygenation. Extracorporeal membrane oxygenation was begun at 52 +/- 36 hours of age with an arterial partial pressure of oxygen (PO2) of 36 +/- 14 mm Hg despite maximal pharmacologic and ventilator support (inspired fraction of oxygen [FiO2], 0.99 +/- 0.03; respiratory rate, 98 +/- 31/min; and positive inspiratory pressure, 54 +/- 11 cm of water). With initial flows of 130 +/- 17 mL/kg per minute, ventilator settings were reduced to the following: FiO2, 0.30; respiratory rates, 15/min; and positive inspiratory pressure, 24 cm of water. Support using extracorporeal membrane oxygenation was gradually reduced to 22% of initial flows and arterial blood samples showed pH 7.48 +/- .05, PO2 of 106 +/- 27 mm Hg, and PCO2 of 36 +/- 5 mm Hg just prior to decannulation. After 107 +/- 45 hours, extracorporeal membrane oxygenation was stopped and infants were extubated 61 +/- 53 hours (median, 46 hours) afterward. There was one death (94.4% survival rate); all survivors were discharged and underwent a follow-up examination at 1 to 27 months of age. Complications included two intracranial hemorrhages (one death and one asymptomatic), one patent ductus arteriosus requiring ligation on extracorporeal membrane oxygenation, and chronic lung disease in one patient. In selected neonates, extracorporeal membrane oxygenation allows for resolution of pulmonary hypertension, results in improved survival, and is associated with a low incidence of chronic lung disease. Extracorporeal membrane oxygenation should be considered in the treatment of severe respiratory failure.     

Use of extracorporeal membrane lung assist device (Novalung) in H1N1 patients

Abstract We present three patients with severe respiratory failure secondary to H1N1 influenza type A pneumonitis, in whom hypercapnia and respiratory acidosis were not controlled by the conventional mechanical lung ventilation or high‐frequency oscillatory ventilation. Use of a pumpless arteriovenous extracorporeal carbon dioxide removal device (Novalung?, Inspiration Healthcare Ltd, Leicester, UK) resulted in reduced carbon dioxide levels, improved pH, and a reduction in inspiratory pressures, allowing for a less‐harmful ventilator strategy. These cases demonstrate that the Novalung is a safe and effective device to use in patients with H1N1 pneumonitis refractory to the conventional therapy and may be an alternative to extracorporeal membrane oxygenation (ECMO) in selected cases. (J Card Surg 2011;26:449‐452)     

Initial evaluation of an intracorporeal oxygenation device

We describe a recently developed intracorporeal gas transfer device, its potential applications and hazards. To date, patients with potentially reversible respiratory failure have been treated with controlled oxygen therapy and positive pressure ventilation, but this treatment may itself contribute to lung parenchymal damage from barotrauma and oxygen toxicity. Total or partial extracorporeal gas exchange can be used to reduce these risks, but this treatment is complex and has significant morbidity and mortality. This gas exchange device has been designed to provide partial gas transfer with simplicity of insertion and use. The oxygenator lies in the vena cava to provide prepulmonary gas exchange. In preliminary studies with three calves we have shown that the device increases both mean mixed venous and arterial oxygen content and reduces mean arterial carbon dioxide tension.     

Carbon dioxide exhalation temporarily increases during electroconvulsive therapy

Electroconvulsive therapy induces hypermetabolism and elevates oxygen and energy demands, while more carbon dioxide is produced than usual. The purpose of the present study was to determine the elevated carbon dioxide exhalation and the adequate ventilation volume during electroconvulsive threrapy. Carbon dioxide exhalation during an electrically induced seizure was continuously monitored by capnography and spirography in 15 patients with endogenous depression. A laryngeal mask airway was used to measure the airway gas flow. Data were collected during a total of 80 electroconvulsive therapy trials. The carbon dioxide exhalation at 1 min after electrical stimulation was higher than the control value (2.8 ± 0.4 versus 2.3 ± 0.3 ml·min⁻¹·kg⁻¹, mean ± SD; P < 0.05). The ventilation volume was increased for 3 min after the electrical stimulation to maintain the end-tidal carbon dioxide partial pressure at 35–40 mmHg. The results showed that increasing the ventilation volume by approximately 20% may be necessary to compensate for the increased carbon dioxide exhalation during electroconvulsive therapy. Presented in part at the 49th annual meeting of the Japanese Society of Anesthesiologists, kobe, Japan.     

Dialysis Reduces Portal Pressure in Patients With Chronic Hepatitis C

The purpose of this study was to characterize changes in hepatic venous pressures in patients with chronic hepatitis C. The histology and laboratory data from patients with chronic hepatitis C who underwent a transjugular liver biopsy (TJLB) and hepatic venous pressure gradient measurement were analyzed. Portal hypertension was defined as hepatic venous pressure gradient ≥6 mm Hg. A single pathologist masked to hepatic venous pressure gradient scored liver sections for inflammation and fibrosis. The patients with high‐grade inflammation (relative risk [RR] 2.82, P = 0.027, multivariate analysis) and late‐stage fibrosis (RR 2.81, P = 0.022) were more likely to have a hepatic venous pressure gradient ≥6 mm Hg, while the patients on dialysis (RR 0.32, P = 0.01) were less likely to have a hepatic venous pressure gradient ≥6 mm Hg. The patients on dialysis (n = 58) had an elevated serum blood urea nitrogen and creatinine when compared with those who were not (n = 75) (47.6 ± 3.3 and 7.98 ± 0.4 vs. 25.9 ± 2.0 and 1.66 ± 0.22 mg/dL, respectively; P < 0.001). While the hepatic venous pressure gradient increased with the rising levels of liver fibrosis in the latter group (P < 0.01), it did not change in the patients on dialysis (P = 0.41). The median hepatic venous pressure gradient was especially low in late‐stage fibrosis patients on dialysis when compared with the latter group (5 vs. 10 mm Hg, P = 0.017). In patients on dialysis, serum transaminases were low across all levels of fibrosis. Twenty‐three of the 92 patients with early fibrosis had a hepatic venous pressure gradient ≥6 mm Hg. In patients with chronic hepatitis C, concomitant TJLB and hepatic venous pressure gradient measurement identify those who have early fibrosis and portal hypertension. Long‐term hemodialysis may reduce portal pressure in these patients.     

Effects of inhaled nitric oxide 10 ppm in spontaneously breathing horses anaesthetized with halothane

Inhaled nitric oxide, a selective pulmonary vasodilator, is known to improve arterial oxygenation after cardiopulmonary bypass and during acute respiratory distress syndrome in humans. During general anaesthesia with spontaneous ventilation, healthy adult horses develop large alveolar-arterial oxygen tension differences. In this study, we have determined the effects of inhaled nitric oxide (10 parts per million (ppm)) on venous admixture and pulmonary haemodynamics in horses anaesthetized with halothane. Seven adult horses were studied twice in random sequence. After premedication with romifidine 100 micrograms kg-1, anaesthesia was induced with ketamine 2.2 mg kg-1 and maintained with 1.1 MAC (0.95%) of halothane in oxygen. Horses breathed spontaneously. After 65 min, each horse had nitric oxide 10 ppm added to the inspired gas for 20 min (procedure HA + NO) or anaesthesia was continued with halothane in oxygen (procedure HA). Cardiac output, minute ventilation, arterial and mixed venous oxygen and carbon dioxide tensions, and mean pulmonary and carotid arterial pressures were measured for 100 min. Shunt fraction and pulmonary and systemic vascular resistances were calculated. Shunt fraction (SF) and mean pulmonary artery pressure (PPA mean) were not different between the two groups after 65 min of general anaesthesia (HA: SF 0.20 (SD 0.06), PPA mean 45 (8) mm Hg; HA + NO: SF 0.21 (0.04), PPA mean 44 (7) mm Hg) or after 85 min (HA: SF 0.22 (0.07), PPA mean 45 (8) mm Hg; HA + NO: SF 0.20 (0.03), PPA mean 43 (7) mm Hg). There were no significant effects of time or nitric oxide inhalation on any other variable. There was a significant correlation (r = 0.80, P < 0.05) between calculated shunt fraction 65 min after induction of anaesthesia and body weight.      

Respiratory failure and sleep in neuromuscular disease.

Sleep hypoxaemia in non-rapid eye movement (non-REM) and rapid eye movement (REM) sleep was examined in 20 patients with various neuromuscular disorders with reference to the relation between oxygen desaturation during sleep and daytime lung and respiratory muscle function. All the patients had all night sleep studies performed and maximum inspiratory and expiratory mouth pressures (PI and Pemax), lung volumes, single breath transfer coefficient for carbon monoxide (KCO), and daytime arterial oxygen (PaO2) and carbon dioxide tensions (PaCO2) determined. Vital capacity in the erect and supine posture was measured in 14 patients. Mean (SD) PI max at RV was low at 33 (19) cm H2O (32% predicted). Mean PE max at TLC was also low at 53 (24) cm H2O (28% predicted). Mean daytime PaO2 was 67 (16) mm Hg and PaCO2 52 (13) mm Hg (8.9 (2.1) and 6.9 (1.7) kPa). The mean lowest arterial oxygen saturation (SaO2) was 83% (12%) during non-REM and 60% (23%) during REM sleep. Detailed electromyographic evidence in one patient with poliomyelitis showed that SaO2% during non-REM sleep was maintained by accessory respiratory muscle activity. There was a direct relation between the lowest SaO2 value during REM sleep and vital capacity, daytime PaO2, PaCO2, and percentage fall in vital capacity from the erect to the supine position (an index of diaphragm weakness). The simple measurement of vital capacity in the erect and supine positions and arterial blood gas tensions when the patient is awake provide a useful initial guide to the degree of respiratory failure occurring during sleep in patients with neuromuscular disorders. A sleep study is required to assess the extent of sleep induced respiratory failure accurately.     

Carbon dioxide output in laparoscopic cholecystectomy

In pneumoperitoneum, carbon dioxide eliminated in expired gas (carbon dioxide output) contains both metabolic and absorbed carbon dioxide from the peritoneal cavity. When elimination of carbon dioxide is much higher than carbon dioxide output, storage of tissue carbon dioxide and arterial carbon dioxide concentrations change. Finally, the rate of carbon dioxide eliminated in expired gas is not a match for the real rate of metabolic production and absorbed carbon dioxide from the peritoneal cavity. During and after insufflation of carbon dioxide, changes in carbon dioxide output were elucidated under constant arterial carbon dioxide pressure (PaCO2), the same as the preinduction level. We studied patients undergoing elective laparoscopic cholecystectomy. Carbon dioxide output, oxygen uptake, respiratory exchange ratio (RER), expired minute ventilation (VE), deadspace to tidal volume ratio (VD/VT ratio) and arterial to end-tidal carbon dioxide partial pressure difference (PaCO2-PE'CO2) were determined before induction, and during anaesthesia, pneumoperitoneum and recovery. By controlling ventilatory frequency (f) every 1 min, PaCO2 was adjusted to concentrations before induction. Constant monitoring of end-tidal carbon dioxide partial pressure (PE'CO2) and intermittent measurement of (PaCO2-PE'CO2) (15-min intervals) were conducted to predict PaCO2). Carbon dioxide output and oxygen uptake decreased significantly from mean values of 83.5 (SEM 5.2), 101.6 (5.1) to 68.5 (4.2), 81.1 (4.6) ml min-1 m-2 (ATPS, P < 0.05) with sevoflurane anaesthesia, and RER did not change. During carbon dioxide pneumoperitoneum (intra-abdominal pressure 8 mm Hg), carbon dioxide output increased by 49% (102.4 (5.0) ml min-1 m-2) (P < 0.05) while oxygen uptake remained stable and RER increased from 0.84 (0.02) to 1.16 (0.03) (P < 0.05). It was necessary to increase VE during pneumoperitoneum by 1.54 times that during anaesthesia to maintain individual PaCO2 values constant. After removal of carbon dioxide from the abdominal cavity, the regression equation of excess carbon dioxide output/BSA best fitted a two-compartment model. The time constants of the rapid and slow compartments were 8.2 and 990 min, respectively. Excess carbon dioxide output/BSA was still 5.5 ml min-1 m-2, 30 min after pneumoperitoneum.