Ex vivo evaluation of a new neonatal/infant oxygenator: comparison of the Terumo CAPIOX Baby RX with Dideco Lilliput 1 and Polystan Safe Micro in the piglet model

OBJECTIVE: A newly developed neonatal and infant oxygenator with a nonheparin biocompatible polymer coating, low priming volume (43 mL), high oxygen transfer, wide operating range (<1.5 L/min) and low pressure drop represents a promising solution for cardiac surgery in neonates and infants. We compared the new CAPIOX Baby RX, Terumo (BRX) with two commonly used neonatal oxygenators: Dideco Lilliput 1 (DL1) and Polystan Safe Micro (PSM) in a piglet model. METHODS: Fifteen piglets (5.6 +/- 1.3kg) were placed on standardized cardiopulmonary bypass (CPB) for 6 hours using one of the three oxygenators (n = 5 in each group). After 120 min, the system was cooled to 25 degrees C for 60 min and then returned to normothermia. Arterial and venous blood gas data and temperature were recorded continuously by a CDI500 System (Terumo). Pressure drop, FiO2 and gas flow were recorded. Blood samples were taken before CBP, after 10 min, before and after cooling, and at the end. Total blood counts, thrombin-antithrombin complex and plasma-free haemoglobin (PfHb) were measured. RESULTS: All oxygenators showed acceptable performance for the duration of CPB. The BRX had lower mean gas flow (0.33 +/- 0.05 L/min) and FiO2 (0.43 +/- 0.02%) throughout CPB than the DL1 (1.14 +/- 0.25 L/min, p = 0.006 and 0.60 +/- 0.02%, p = 0.009, respectively) or the PSM (1.47 +/- 0.87 L/min and 0.54 +/- 0.08%, p = ns). Pressure drop in the BRX group ranged from 12 to 22 mmHg. This was significantly lower than in the DL1 group (39-65 mmHg, p = 0.005). In the PSM group, values ranged between 24 and 33 mmHg (p = ns). The increase in PfHb at six hours was significantly lower in the BRX (11.3 +/- 4.2 ng/dL) versus the DL1 (42.2 +/- 6.1 ng/dL, p = 0.004) and the PSM (56.7 +/- 15.5 ng/dL, p = 0.045). CONCLUSIONS: The BRX is as safe as the DL1 and the PSM, with superior performance in pressure drop, efficient blood gas management and lower haemolysis. The BRX exhibited the lowest prime, hold-up volume and breakthrough time.     

Evaluation of a preprimed microporous hollow-fiber membrane for rapid response neonatal extracorporeal membrane oxygenation

Delays in initiating extracorporeal membrane oxygenation (ECMO) in the critically ill pediatric patient may lead to adverse outcomes. Maintaining a primed ECMO circuit can considerably reduce the initiation time. The predominant concerns precluding this practice are a decrease in oxygenator efficiency due to the saturation of microporous hollow fibers and compromised sterility when the oxygenator has been primed for 30 days. For institutions using a hollow-fiber oxygenator for ECMO, there are no data reporting pre-primed hollow-fiber oxygenator viability. This study reports the efficiency of oxygen transfer and the sterility of the Carmeda Minimax Plus (Medtronic, Inc, Minneapolis, MN) oxygenator after being crystalloid primed for 30 days. A total of 10 Minimax Plus oxygenators were tested for oxygen transfer in a laboratory setting utilizing fresh whole bovine blood. The control group (n =5) were tested immediately after priming. The test group (n =5) were oxygenators primed for 30 days with crystalloid solution and left stagnant until tested. Prior to testing, all oxygenators were circulated for 5 min and samples drawn to test for circuit sterility. Venous inlet saturations were manipulated to achieve three levels of testing: venous saturation (SvO2) of 55% for an oxygen challenge, SvO2 of 65% to comply with AAMI standards, and SvO2 of 75% to assess oxygen transfer rates and peak PaO2 achievement. Blood flow for all tests was maintained at 2 L/min with 1:1 blood to gas flow ratio and 100% FiO2. Samples were drawn pre- and postoxygenator at 1- and 6-hour time intervals to compute actual oxygen transfer values. All cultures from the test group priming solution produced no microbial growth after 30 days of stagnant prime. Average oxygen transfer values (ml/O2/min) for the control group after 1 hour of continuous use were 130.1+/-15.5 (@ 55% SvO2), 113.7+/-10.4 (@ 65% SvO2), 97.7+/-8.9 (@ 75% SvO2). After 6 hours, the average transfer values increased to 134.2+/-13.2 (@ 55% SvO2), 118.76+/-6.6 (@ 65% SvO2) and 98.9+/-8.3 (@ 75% SvO2). The average oxygen transfer values after 1 hour for oxygenators primed for 30 days were 114.9+/-10.0 (@ 55% SvO2), 112.4+/-8.2 (@ 65% SvO2) and 89.6+/-16.0 (@ 75% SvO2). After 6 hours of use, the average transfer values all decreased to 111.4+/-2.1 (@ 55% SvO2, p <0.05 versus control), 104.0+/-5.6 (@ 65% SvO2, p <0.05 versus control) and 88.4+/-3.2 (@ 75% SvO2, p <0.05 versus control). In conclusion, there was a decrease in the average oxygen transfer values for the test group after 6 hours versus the control. The modest loss of oxygen transfer ability observed can be considered acceptable due to the amount of surface area of the Minimax Plus oxygenator when used on a neonate, making it feasible to adopt the practice of prepriming the Minimax oxygenator for neonatal ECMO.     

Modelling lung and tissue diffusion using a membrane oxygenator circuit

A simple model lung has been designed using a membrane oxygenator circuit comprising two membrane oxygenators primed with one to two litres of equine blood, giving reproducible results over several hours. Normoxia and normocapnia were achieved consistently over the duration of the test with a blood flow of 2.5 l/min, oxygenator ventilation gas flow of 5 l/min air with 0.3 l/min O2 and deoxygenator ventilation gas flow of 5 l/min 5% CO2 in N2 with 0.2 l/min CO2. The measured PaO2 was 81.3 (SD 3.35 mmHg), PvO2 38.3 (SD 1.38 mmHg), PvCO2 60.6 (SD 1.13 mmHg) and PaCO2 36.1 (SD 0.69mmHg). MO2 and MCO2 were 116 ml/min and 169 ml/min, respectively. An increasing linear relationship was observed for FiO2 and the corresponding PaO2 and, similarly, with FiCO2 and PvCO2, providing reference ranges for this model.     

In vitro evaluation of the Mera Silox-S 0.5 and 0.8 m 2 silicone hollow-fibre membrane oxygenator for use in neonatal ECMO

The Mera Silox-S is a silicone hollow-fibre membrane oxygenator made up of thousands of fibres in a clear polycarbonate housing. Being a silicone membrane it does not have the plasma leakage problem associated with conventional microporous hollow fibres when used in a long-term application. This device (Mera Senko Medical Instrument Co., Japan) is made in three sizes: 0.3, 0.5 and 0.8 m 2. The performance of the 0.5 m 2 and 0.8 m 2 Silox-S membrane oxygenators was tested in vitro using filtered ovine blood and a customized test circuit designed to provide a continuous source of de-oxygenated, CO 2-laden blood, according to the AAMI standard for oxygenator performance. The 0.8 m 2 membrane provided excellent oxygenation, with a transfer rate of 13.0-43.5 ml/min for blood flows of 200-800 ml/min. CO 2 transfer over the same range of flows measured 32.3-40.8 ml/min. Flow rates of 100-500 ml/min for the 0.5 m 2 membrane provided an oxygen transfer of 6.8-28.3 ml/min and would probably not be suited for the existing neonatal ECMO population. A matter of concern with both oxygenators was an increased pressure drop for blood flow through the devices. The delta P for the 0.5 m 2 for flows of 100-500 ml/min ranged from 155 +/- 7 mmHg to 516 +/- 6 mmHg. For the 0.8 m 2, delta P was 194 +/- 39 mmHg to 492 +/- 53 mmHg for flows of 200-800 ml/min. Overall, favourable results support further long-term evaluation for potential use in neonatal ECMO.     

Clinical experience with the Sorin Monolyth Oxygenator at high altitude

High altitude combined with low barometric pressure can present unique challenges during cardiopulmonary bypass (CPB), not only for the perfusionist, but also for the oxygenator. Manufacturers of cardiopulmonary devices have responded to the requests from the perfusion community with a variety of oxygenators which balance low priming volumes and low pressure drops against high gas transfer. This paper will feature the first author's clinical studies using the Sorin Monolyth Oxygenator in a selected group of patients at an altitude of approximately 5200 feet and an average barometric pressure of 634 mmHg (sea levels is 760 mmHg). A review of the 47 charts on patients requiring CPB and who met the selection criteria was performed retrospectively. To qualify for this study, the patient needed to weigh more than 91 kg. The data reviewed included type of surgery, age, weight, bypass time, crossclamp time, pump flows (l/min/m2), hematocrits pre- and post-CPB, and pressure drop across the membrane. The PaO2, PaCO2, FiO2 and sweep gas flow at hypothermia and normothermia were recorded. Data concerning oxygen transfer were obtained from the manufacturer's report to the Food and Drug Administration. All patients had adequate blood gases while on CPB. We feel that the design of the Sorin Monolyth Oxygenator met our criteria for an oxygenator: low priming volume, low pressure drop, and sufficient gas transfer to provide safe oxygenation of all patients at high altitude.     

Optimizing bag-valve-mask ventilation with a new mouth-to-bag resuscitator

When ventilating an unintubated patient with a self-inflating bag, high peak inspiratory flow rates may result in high peak airway pressure with subsequent stomach inflation; this may occur frequently when rescuers without daily experience in bag-valve-mask ventilation need to perform advanced airway management. The purpose of this study was to assess the effects of a newly developed self-inflating bag (mouth-to-bag resuscitator; Ambu, Glostrup, Denmark) that limits peak inspiratory flow. A bench model simulating a patient with an unintubated airway was used, consisting of a face mask, manikin head, training lung (lung compliance, 100 ml/0.098 kPa (100 ml/cm H(2)O)); airway resistance, 0.39 kPa/l per second (4 cm H(2)O/l/s), oesophagus (LESP, 1.96 kPa (20 cm H(2)O)) and simulated stomach. Twenty nurses were randomised to ventilate the manikin for 1 min (respiratory rate: 12 per minute) with either a standard self-inflating bag or the mouth-to-bag resuscitator, which requires the rescuer to blow up a single-use balloon inside the self-inflating bag, which in turns displaces air towards the patient. When supplemental oxygen is added, ventilation with up to 100% oxygen may be obtained, since expired air is only used as the driving gas. The mouth-to-bag resuscitator therefore allows two instead of one hand sealing the mask on the patient's face. The volunteers were blinded to the experimental design of the model until completion of the experimental protocol. The mouth-to-bag resuscitator versus standard self-inflating bag resulted in significantly (P<0.05) higher mean+/-S.D. mask tidal volumes (1048+/-161 vs. 785+/-174 ml) and lung tidal volumes (911+/-148 vs. 678+/-157 ml), longer inspiratory times (1.7+/-0.4 vs. 1.4+/-0.4 s), but significantly lower peak inspiratory flow rates (50+/-9 vs. 62+/-13 l/min) and mask leakage (10+/-4 vs. 15+/-9%); peak inspiratory pressure (17+/-2 vs. 17+/-2 cm H(2)O) and stomach tidal volumes (16+/-30 vs. 18+/-35 ml) were comparable. In conclusion, employing the mouth-to-bag resuscitator during simulated ventilation of an unintubated patient in respiratory arrest significantly decreased inspiratory flow rate and improved lung tidal volumes, while decreasing mask leakage.     

Comparison between the Datex-Ohmeda M-COVX metabolic monitor and the Deltatrac II in mechanically ventilated patients

OBJECTIVE: To compare the M-COVX and the Deltatrac II metabolic monitors under clinical conditions. DESIGN: Prospective clinical comparison. SETTING: A general Intensive Care Unit of a university hospital. PATIENTS: Twenty mechanically ventilated critically ill patients. INTERVENTIONS: The monitors were compared at FiO(2) 0.3, 0.5, and 0.7 in each patient where possible. MEASUREMENTS AND RESULTS: Pulmonary gas exchange measurements were recorded using the two monitors sequentially (Deltatrac(before), M-COVX, Deltatrac(after)). Each measurement consisted of five consecutive 1-min readings of VO(2) and VCO(2). We compared the Deltatrac(before) with the Deltatrac(after) and the mean of the Deltatrac with the M-COVX. There was no clinically significant bias between the two monitors for VO(2) or VCO(2) but the limits of agreement (LOA) were wide (bias +/-95% LOA: VCO(2) -13 +/- 30 ml/min, -8 +/- 36 ml/min, 7 +/- 50 ml/min; VO(2) -7 +/- 50 ml/min, -5 +/- 56 ml/min, 6 +/- 64 ml/min, at FiO(2) 0.3, 0.5, and 0.7, respectively). The Deltatrac before and after measurements displayed good agreement for VCO(2) but poorer agreement for VO(2) (bias +/- 95% LOA: VCO(2) 0 +/- 18 ml/min, -6 +/- 16 ml/min, -1 +/- 12 ml/min; VO(2) 2 +/- 12 ml/min, 3 +/- 38 ml/min, 10 +/- 42 ml/min, at FiO(2) 0.3, 0.5, and 0.7, respectively). Using within-patient standard deviation as a measure of reproducibility suggested that for VO(2) the M-COVX performed better than the Deltatrac at high FiO(2), and for VCO(2) Deltatrac was better at lower FiO(2). CONCLUSIONS: The M-COVX is a suitable integrated device for measuring metabolic gas exchange in ventilated patients.     

Blood-flow magnetic resonance imaging of the retina

This study describes a novel MRI application to image basal blood flow, physiologically induced blood-flow changes, and the effects of isoflurane concentration on blood flow in the retina. Continuous arterial-spin-labeling technique with a separate neck coil for spin labeling was used to image blood flow of the rat retina at 90 x 90 x 1500-microm resolution. The average blood flow of the whole retina was 6.3+/-1.0 ml/g/min under 1% isoflurane, consistent with the high blood flow in the retina reported using other techniques. Blood flow is relatively constant along the length of the retina, except it dipped slightly around the optic nerve head and dropped significantly at the distal edges where the retina terminates. Hyperoxia (100% O(2)) decreased blood flow 25+/-6% relative to baseline (air) due to vasoconstriction. Hypercapnia (5% CO(2)+21% O(2)) increased blood flow 16+/-6% due to vasodilation. Increasing isoflurane (a potent vasodilator) concentration to 1.5% increased blood flow to 9.3+/-2.7 ml/g/min. Blood-flow signals were confirmed to be genuine by repeating measurements after the animals were sacrificed in the MRI scanner. This study demonstrates a proof of concept that quantitative blood flow of the retina can be measured using MRI without depth limitation. Blood-flow MRI has the potential to provide unique insights into retinal physiology, serve as an early biomarker for some retinal diseases, and could complement optically based imaging techniques.     

A wet-primed extracorporeal membrane oxygenation circuit with hollow-fiber membrane oxygenator maintains adequate function for use during cardiopulmonary resuscitation after 2 weeks on standby

OBJECTIVE: To assess the durability of wet-preprimed extracorporeal membrane oxygenation (ECMO) circuits for potential use in resuscitation after a 2-wk period of storage. DESIGN: Experimental laboratory study. SETTING: Tertiary care pediatric cardiac intensive care unit. SUBJECTS: None. INTERVENTIONS AND MEASUREMENTS: 14 ECMO circuits (polyvinyl chloride and super-Tygon tubing with hollow-fiber oxygenator, Medos Hilite 800LT) were primed with crystalloid under sterile conditions and stored for 0 (control, n = 4), 7 (n = 5) and 14 (n = 5) days and maintained at 8 degrees C on pump at 10 rpm and gas flow at 0.2 L/min. Daily samples were inspected for plasticizers by means of high-performance liquid chromatography and for microorganisms by culture and polymerase chain reaction techniques. After storage, the oxygenators were primed with red blood cells (hemoglobin, 12 g/dL) and tested in vitro with a deoxygenator according to Association for Advancement of Medical Instrumentation standards. Oxygen and CO(2) transfer rates were calculated by standard formulae at maximum blood flow (800 mL/min) and maximum sweep gas flow (1.6 L/min). MAIN RESULTS: Oxygen transfer was linearly related to venous oxygen saturation, increasing by 11 mL/min for each 10% decrease in venous oxygen saturation. Estimated oxygen transfer at venous oxygen saturation of 60% was 45.8 mL/min (95% confidence interval [CI], 43.5-48.1) for controls, 51.0 mL/min (95% CI, 48.9-53.2) for 7-day oxygenators, and 49.0 mL/min (95% CI, 47.8-50.1) for 14-day oxygenators. CO(2) transfer declined to 29.2 mL/min at 14 days of storage, a mean fall of 11.5 mL/min (95% CI, 4.2-18.7) in comparison with 7-day storage. All circuits were free from microbes/microbial DNA. Plasticizer levels fell below the lower limit of detection (0.003 microg/mL) at 7 and 14 days. CONCLUSIONS: A wet-preprimed ECMO circuit with hollow-fiber membrane oxygenator can be stored for up to 2 wks with adequately preserved function if prepared appropriately. These data may improve safe access to rapid-response ECMO support.     

Global and regional cerebral blood flow in neonatal piglets undergoing pulsatile cardiopulmonary bypass with continuous perfusion at 25 degrees C and circulatory arrest at 18 degrees C.

To investigate the influence of hypothermic cardiopulmonary bypass (HCPB) at 25 degrees C and circulatory arrest at 18 degrees C on the global and regional cerebral blood flow (CBF) during pulsatile perfusion, we performed the following studies in a neonatal piglet model. Using a pediatric physiologic pulsatile pump, we subjected six piglets to deep hypothermic circulatory arrest (DHCA) and six other piglets to HCPB. The DHCA group underwent hypothermia for 25 min, DHCA for 60min, cold reperfusion for 10 min, and rewarming for 40 min. The HCPB group underwent 15 min of cooling, followed by 60 min of HCPB, 10min of cold reperfusion, and 30 min of rewarming. The following variables remained constant in both groups: pump flow (150 ml/kg/min), pump rate (150 bpm), and stroke volume (1 ml/kg). During the 60-min aortic crossclamp period, the temperature was kept at 18 degrees C for DHCA and at 25 degrees C for HCPB. The global and regional CBF (ml/100g/min) was assessed with radiolabeled microspheres. The CBF was 48% lower during deep hypothermia at 18degrees C (before DHCA) than during hypothermia at 25 degrees C (55.2 +/- 14.3ml/100g/min vs 106.4 +/- 19.7 ml/100 g/min; p < 0.05). After rewarming, the global CBF was 45% lower in the DHCA group than in the HCPB group 48.3 +/- 18.1 ml/100g/min vs (87 +/- 35.9ml/100g/min; p < 0.05). Fifteen minutes after the termination of CPB, the global CBF was only 25% lower in the DHCA group than in the HCPB group (42.2 +/- 20.7 ml/100 g/min vs 56.4 +/- 25.8ml/100g/min; p = NS). In the right and left hemispheres, cerebellum, basal ganglia, and brain stem, blood flow resembled the global CBF. In conclusion, both HCPB and DHCA significantly decrease the regional and global CBF during CPB. Unlike HCPB, DHCA has a continued negative impact on the CBF after rewarming. However, 15 min after the end of CPB, there are no significant intergroup differences in the CBF.     

Effect of diltiazem on regional oxygenation of reperfused myocardium

Reperfusion after 2 hr of experimental ischemia results in reduced blood flow to the reperfused region, as well as elevated regional O2 extraction in that region. The aim of the present study was to determine whether diltiazem, administered during reperfusion, can improve regional blood flow and lower O2 extraction in the previously occluded region. In open-chest anesthetized dogs, 2-hr occlusion of the left anterior descending coronary artery was followed by a 4-hr period of reperfusion. In 7 of the 15 animals, diltiazem (0.45 micrograms/kg/min) was infused i.v. during the reperfusion period; this was preceded by a loading dose of 0.18 micrograms/kg 10 min before release. Small artery and vein O2 saturations obtained microspectrophotometrically were combined with regional blood flow measurements using radioactive microspheres to determine regional myocardial O2 consumption. In both groups, coronary occlusion lowered regional flow to a similar level. After a 4-hr reperfusion, flow to the subendocardial region of treated hearts was significantly greater than that to the untreated reperfused myocardium (75.6 +/- 46.4 vs. 40.3 +/- 25.8 ml/min/100 g), and did not differ from the preocclusion level. The subendocardium/subepicardium flow ratio was reversed in occluded and untreated reperfused myocardium (subendocardium flow less than subepicardium flow), but was not reversed in treated reperfused regions. Myocardial oxygen extraction was 11.0 +/- 2.4 ml of O2/100 ml of blood in the untreated reperfused subendocardium, and was significantly decreased to 8.5 +/- 0.9 ml of O2/100 ml in the treated subendocardium. The proportion of individual veins having O2 saturations below 25% was significantly reduced by diltiazem treatment from 45.2 to 22.7%.(ABSTRACT TRUNCATED AT 250 WORDS)     

Haemodilution improves organ function during normothermic cardiopulmonary bypass: investigations in isolated perfused pig kidneys

We investigated the effects of haemodilution on kidney function during normothermic cardiopulmonary bypass (CPB) by performing in vitro haemoperfusion of pig kidneys for 90 min after cold preservation. We compared two groups (n = 14 each) with respect to rheologic and haemodynamic parameters and glomerular and tubular function. Group 1 was perfused at a haematocrit of 0.33 +/- 0.01, group 2 at 0.21 +/- 0.01. Blood flow was adjusted according to blood pressure. Blood viscosity and vascular resistance were reduced in group 2. Comparison of group 1 versus group 2 revealed a metabolic rate of oxygen 3.4 +/- 1.7 versus 4.3 +/- 1.8 ml/min/100 g, sodium transport 1.2 +/- 1.2 versus 1.8 +/- 1.2 mmol/min/100 g, and creatinine clearance 9.9 +/- 9.1 versus 15.6 +/- 11.9 ml/min/100 g, p < 0.05. We conclude that haemodilution leads to an overproportional decrease in blood viscosity and improves the properties of flow and kidney function. In the ongoing discussion about the optimal extent of haemodilution in CPB, the importance of viscosity and blood flow should be further emphasized.     

Acute effects of combined high-frequency oscillation and tracheal gas insufflation in severe acute respiratory distress syndrome

OBJECTIVE: In acute respiratory distress syndrome (ARDS), high-frequency oscillation (HFO) improves oxygenation relative to conventional mechanical ventilation (CMV). Alveolar ventilation is improved by adding tracheal gas insufflation (TGI) to CMV. We hypothesized that combined HFO and TGI (HFO-TGI) might result in improved gas exchange relative to both standard HFO and CMV according to the ARDS Network protocol. DESIGN: Prospective, randomized, crossover study. SETTING: A 30-bed university intensive care unit. PATIENTS: A total of 14 patients with early (<72 hrs in duration), severe (PaO2/FiO2 of <150 mm Hg and prerecruitment oxygenation index of 22.8 +/- 1.9 [mean +/- SEM]), primary ARDS. INTERVENTIONS: Patients were ventilated with HFO without (60 mins) and combined with TGI (6.1 +/- 0.1 L/min, 60 mins) in random order. HFO sessions were repeated in inverse order within 24 hrs. HFO sessions were preceded and followed by ARDS Network CMV. Four recruitment maneuvers were performed during the study period. During HFO sessions, mean airway pressure was set at 1 cm H2O above the point of maximal curvature of the respiratory system expiratory pressure-volume curve. MEASUREMENTS AND MAIN RESULTS: Gas exchange and hemodynamics were determined before, during, and after HFO sessions. HFO-TGI improved PaO2/FiO2 relative to HFO and CMV (174.5 +/- 10.4 vs. 136.0 +/- 10.0 and 105.0 +/- 3.7 mm Hg, respectively, p < .05 for both) and oxygenation index relative to HFO (17.1 +/- 1.3 vs. 22.3 +/- 1.7, respectively p < .05). PaO2/FiO2 returned to baseline within 3 hrs after HFO. During HFO-TGI, shunt fraction and mixed venous oxygen saturation improved relative to CMV (0.36 +/- 0.01 vs. 0.45 +/- 0.01 and 77.8% +/- 1.2% vs. 71.8% +/- 1.3%, respectively, p < .05 for both). PaCO2 and hemodynamics were unaffected by HFO sessions. Respiratory mechanics remained unchanged throughout the study period. CONCLUSIONS: In early onset, primary, severe ARDS, short-term HFO-TGI improves oxygenation relative to standard HFO and ARDS Network CMV.     

The effect of oxygenator mechanical characteristics on energy transfer during clinical cardiopulmonary bypass

The hollow-fibre oxygenator is a key component of any extracorporeal circuit used to provide cardiopulmonary bypass (CPB) during open-heart surgery. Since the oxygenator is placed downstream of the pump, the energy losses over it have a direct impact on the quality of pulsatile pressure and flow waveforms. The objective of this study was to describe the effects of hydrodynamic characteristics of the oxygenator on energy transfer during pulsatile, normothermic CPB. Twenty-three adult patients scheduled for coronary bypass surgery were divided randomly into two groups, using either an oxygenator (Group 1) with a relatively high-resistance and low-compliance (2079 ± 148 dyn.s.cm(-5) and 0.00348 ± 0.00071 ml.mmHg(-1), respectively) or an oxygenator (Group 2) with a relatively low-resistance and high-compliance (884 ± 464 dyn.s.cm(-5) and 0.01325 ± 0.00161 ml.mmHg(-1), respectively). During perfusion, pre- and post-oxygenator pressures, radial artery pressure, and blood flow were recorded simultaneously. A 32% decline of mean pressure was observed in Group 1 and a 16% decline in Group 2 (p<0.0001). Another decrease by approximately 73% in mean pressure in the rest of the perfusion system was noted in both groups. The mean radial artery pressure did not differ between the groups (74 ± 6 mmHg in Group 1 and 73 ± 6 mmHg in Group 2, p=0.608). Although lower total energy transfer indices were noticed through the low-resistance oxygenator (Group 2), both oxygenators showed a decrease of the generated pump oscillatory energy of approximately 50%. Despite the differences in resistance and compliance of the hollow-fibre oxygenators used, both oxygenators cause a comparable loss of generated oscillatory energy. Exclusion of the oxygenator downstream of the pulsatile pump would improve energy transfer during CPB.     

Albumin in the cardiopulmonary bypass prime: how little is enough?

Previous studies have demonstrated high transoxygenator pressures with noncoated hollow-fiber membrane oxygenators. These reports have been associated with dramatic platelet count drops during cardiopulmonary bypass (CPB). It has also been shown that adding human albumin to the prime of the bypass circuit reduces, if not eliminates, these problems. This study was conducted to determine what is the smallest amount of albumin added to the prime that will still display its protective effects. Eighty patients undergoing nonemergency open-heart surgery were randomly divided into four groups. Groups I and II received the Sarns Turbo 440 oxygenator with 0.0375 g of albumin/100 ml of prime and 0.125 g of albumin/100 ml of prime, respectively, added to the pump prime. Groups III and IV received the Medtronic Maxima-PRF oxygenator with 0.0375 g of albumin/100 ml of prime and 0.125 g of albumin/100 ml of prime, respectively, added to the pump prime. Pre-CPB, on CPB (15-20 min after the initiation of bypass) and warming hemoglobin, hematocrit and platelet counts were drawn on all patients. Net platelet count drop, which accounted for hemodilutional effects, was calculated for all specimens and compared to previous results obtained from the test oxygenators without albumin in the prime. The net platelet count drops for the study groups were as follows: Sarns oxygenator with no albumin in the prime = 11.8+/-12.5%; Sarns oxygenator with 0.0375 g of albumin/100 ml prime = -3.7+/-10.8%; Sarns oxygenator with 0.125 g of albumin/100 ml prime = -2.0+/-12.6%; Medtronic oxygenator with no albumin in the prime = 20.1+/-14.5%; Medtronic oxygenator with 0.0375 g albumin/100 ml prime = -6.9+/-8.7%; and Medtronic oxygenator with 0.125 g albumin/100 ml prime = -14.0+/-12.4%. Our results illustrate that adding as little as 0.0375 g albumin/100 ml prime (3 ml of 25% solution/2000 ml of prime) to the pump prime illicits the beneficial effects of surface coating on platelet loss during CPB.     

The effect of oxygenator membranes on blood: a comparison of two oxygenators in open-heart surgery

Open-heart surgery (OHS) requires cardiopulmonary bypass (CPB) in most patients. Membrane oxygenators are a critical component of the CPB system. Despite advancements in CPB technology, injury to blood components during CPB still occurs and may result in complications after surgery. The purpose of the present study was to evaluate the performance of the Medtronic Affinity NT with Trillium coating and the Cobe Optima XP oxygenators and compare their influence on blood components. Two hundred and fifty-six male and female patients scheduled for urgent or elective cardiac surgery with CPB were randomly assigned to either the Affinity NT or the Optima XP oxygenators. Outcomes included platelets, hemoglobin, leukocyte counts, and O2 transfer, measured preoperatively and at 15, 45 and 75 min of CPB time. Blood loss was measured at six and 12 hours postoperatively. A modified intention-to-treat analysis was conducted. The two groups were similar for age, sex, height, weight, body surface area, and blood components at baseline. There were no differences between the Affinity NT and Optima XP for any outcome measure, although a significant change with time was seen in platelets, hemoglobin, hematocrit and leukocytes, as well as O2 transfer for both groups (p < 0.001). The Affinity NT oxygenator had a significantly lower difference in pressure across the membrane (p < 0.001) compared with the Optima XP. In conclusion, the two oxygenators performed similarly with respect to their impact on blood components, O2 transfer, and blood loss postoperatively during OHS with CPB. The Affinity NT had the smaller transmembrane pressure drop of the two.     

Clinical validation of a new metabolic monitor suitable for use in critically ill patients

This report documents the validity of clinical measurements of oxygen consumption (VO2) and carbon dioxide production (VCO2) made with a new metabolic gas monitor (MGM) suitable for use in critically ill patients receiving mechanical ventilatory support. Paired samples of inspired and expired gases were obtained, and exhaled minute volume was measured in 12 patients receiving supplemental oxygen, intermittent mandatory ventilation, and PEEP. Gas volume was measured with a calibrated spirometer and oxygen and CO2 fractions were measured by mass spectrometry. Measured and derived values were compared to those obtained from the MGM connected in series with the ventilator circuit. There were no statistically significant differences between values obtained from the mass spectrometer/spirometer vs. the MGM in exhaled volume (8.60 +/- 3.81 vs. 8.58 +/- 3.72 [SD] L/min), fraction of inspired oxygen (0.451 +/- 0.011 vs. 0.452 +/- 0.010), fraction of expired oxygen (0.413 +/- 0.013 vs. 0.415 +/- 0.012), VO2 (290 +/- 113 vs. 275 +/- 88 ml/min), VCO2 (245 +/- 95 vs. 247 +/- 96 ml/min), or respiratory quotient (0.85 +/- 0.14 vs. 0.88 +/- 0.08). The fraction of expired CO2 measured by the MGM was significantly greater (0.034 +/- 0.006 vs. 0.035 +/- 0.006; p less than .001) than that measured by mass spectrometer/spirometer. Twelve additional patients were studied to compare metabolic measurements made on 45% oxygen with those made at other fraction of inspired oxygen values. There was no significant difference between values measured on 45% oxygen and those measured on 30% to 50% oxygen.(ABSTRACT TRUNCATED AT 250 WORDS)     

Decreased supply-dependent oxygen consumption in the skeletal muscle of the spontaneously hypertensive rat during acute hypoxia

The purpose of this study was to correlate microvascular oxygen delivery (DO2) and consumption (VO2) in the skeletal muscle of spontaneously hypertensive rats (SHRs) and Wistar Kyoto rats (WKY) with hemodynamics during acute hypoxia. We expected greater abnormalities in central and microvascular hemodynamics during hypoxic induced shock in the SHR compared with the WKY due to microvascular rarefaction. The inspired oxygen fraction (FiO2) was lowered from 0.21 to 0.15, 0.1, 0.08, and 0.05 in anesthetized, mechanically ventilated rats. Lactate and base deficit values were similar for both groups at 0.21 and 0.15 FiO2, but higher in SHR at lower FiO2. Baseline aortic blood flow (SHR, 56.2+/-4.0 mL min; WKY, 61.8+/-5.3 mL min) and systemic DO2 (SHR, 9.02+/-0.82 mL min; WKY, 9.32+/-0.54 mL min) increased similarly when FiO2 was lowered to 0.15. Further reductions in FiO2 caused lower aortic flow and systemic DO2 in the SHR than WKY at 0.08 and 0.05 FiO2. Spinotrapezius blood flow increased from baseline (SHR, 24.8+/-1.8 nL s; WKY, 22.7+/-2.1 nL s) in both groups when FiO2 was reduced to 0.15; further reductions in FiO2 decreased blood flow in both groups, with lower values in the SHR group at 0.1 and 0.08 FiO2. The SHR group demonstrated higher venous oxygen saturation at low values of FiO2 compared with WKY. This reduced oxygen extraction in SHR resulted in a lower supply-dependent VO2 at low values of spinotrapezius DO2, perhaps attributed to arteriolar thickening and rarefaction seen in chronic hypertension.     

Role of isoflurane on hemodynamic properties and disposition of nicardipine

Nicardipine properties (30 micrograms/kg i.v.) were studied in a group of eight dogs awake and anesthetized with isoflurane 1.6% end-tidal. Awake, nicardipine produced a decrease in mean arterial pressure (-12 +/- 2 mm Hg) associated with an increase in cardiac output (1.63 +/- 0.2 liters/min), heart rate (75 +/- 9 beats/min), dP/dt (741 +/- 202 mm Hg/sec) and carotid (41 +/- 11 ml/min) and coronary blood flows (39 +/- 6 ml/min). During isoflurane, responses to nicardipine injections were less pronounced except for mean arterial pressure (-19 +/- 2 mm Hg) and reversed for dP/dt (-290 +/- 63 mm Hg/sec). In a second group of six conscious dogs, nicardipine (30 micrograms/kg i.v.) injected after ganglionic blockade (chlorisondamine, 2 mg/kg i.v.) elicited changes similar to those recorded during isoflurane anesthesia, data that demonstrated the importance of isoflurane-induced baroreflex blockade as a mechanism of the pharmacodynamic interactions between nicardipine and isoflurane. Isoflurane reduced nicardipine initial volume of distribution (11.6 +/- 1.2 vs. 8.9 +/- 0.8 liters), total clearance (28.5 +/- 2.9 vs. 19.2 +/- 2.1 liters/hr) and volume of distribution at steady state (50.0 +/- 11.3 vs. 29.2 +/- 3.7 liters, P less than .05). Nicardipine-induced hemodynamic changes were linearly correlated with the drug concentrations in plasma. In the presence of isoflurane, the slopes of these relationships were reduced for all hemodynamic variables except for mean arterial pressure, for which the slope was more pronounced, and dP/dt, for which the slope was reversed. In conclusion, isoflurane alters the drug plasma concentration-effect relationship of nicardipine as a result of both pharmacokinetic and pharmacodynamic interactions.     

Enhancing liver blood flow after cardiopulmonary bypass: the effects of dopamine and dopexamine

Liver blood flow is reduced after cardiopulmonary bypass (CPB) and both dopamine and dopexamine are used to overcome this. This study compares the effects of these agents on liver blood flow. Thirty patients undergoing elective coronary artery bypass graft surgery were randomized into three groups (n = 10 per group). Six hours after surgery baseline liver blood flow was determined by the percentage disappearance rate of indocyanine green measured by dichromatic auricular densitometery. Patients then received infusions of either: (1) placebo (dextrose 5%); (2) dopamine (4 micrograms/kg/min); (3) dopexamine (1 microgram/kg/min increasing to 2 micrograms/kg/min). One hour after infusion, liver blood flow measurements were repeated. In the dopexamine group the infusion was increased and the measurements repeated another hour later. We found that patient-specific variables and operative details were similar for all groups. Postoperative cardiac index and heart rate were increased significantly by dopamine (cardiac index 2.82 +/- 0.46 l/m/m2 vs 3.28 +/- 0.67 l/m/m2: p < 0.001 and heart rate 87.5 +/- 13.2 vs 96 +/- 16: p < 0.05) and dopexamine at 2 micrograms/kg/min (cardiac index 2.71 +/- 0.53 l/m/m2 vs 3.45 +/- 0.67 l/m/m2: p < 0.05 and heart rate 89.0 +/- 18.9 vs 107.4 +/- 13.6: p < 0.001) compared to placebo (cardiac index 2.97 +/- 0.8 l/m/m2 vs 3.18 +/- 0.9 l/m/m2: p > 0.05 and heart rate 77.2 +/- 7.4 vs 77.3 +/- 8: p > 0.05) despite similar atrial and systemic arterial pressures. The disappearance rate of indocyanine green was not altered during infusion of placebo group (9.0 +/- 3.2%/min vs 7.9 +/- 3.0%/min: p > 0.05) or dopexamine at 1 microgram/kg/min (9.7 +/- 3.1%/min vs 11.2 +/- 4.1%/min: p > 0.05). The disappearance rate was increased with dopamine (6.7 +/- 3.7%/min vs 11.8 +/- 3.0%/min: p < 0.05) and dopexamine 2 micrograms/kg/min (9.7 +/- 3.1%/min vs 13.5 +/- 3.2%/min: p < 0.05). This indicates a 76% increase in liver blood flow with dopamine and a 38% increase with dopexamine. We conclude that dopamine 4 micrograms/kg/min and dopexamine 2 micrograms/kg/min increase liver blood flow, although this may, in part, be related to an increase in cardiac output. Dopexamine shows no advantage over dopamine in enhancing liver blood flow after CPB.