Optimal Sweep Gas to Blood Flow Ratio (V/Q) for Initiation of Cardiopulmonary Bypass in a Pediatric Patient Population: A Retrospective Analysis.

The optimal setting to achieve a suitable PaCO2 value of 35-45 mmHg upon initiating cardiopulmonary bypass (CPB) in the pediatric population is undefined in the literature. Sweep gas is set upon initiating and modified throughout CPB to reduce potential complications related to compensatory metabolic acidosis or metabolic alkalosis and associated cerebral blood flow fluctuations. This study retrospectively examined 1,077 CPB cases for which PaCO2 values were no less than 30 mmHg and no greater than 50 mmHg on the pre-CPB blood gas result. Through an observation of the results, we attempted to determine the optimal sweep gas setting upon initiating CPB to obtain a physiologic PaCO2 value of 35-45 mmHg. The probability of achieving an optimal PaCO2 value was modeled as a function of the average sweep gas to blood flow ratio during the period before the first blood gas on CPB. The median sweep gas to blood flow ratio (V/Q) was .64 (.51; .76), with a median first PaCO2 value on CPB of 42 mmHg (38.8; 45). A .6 V/Q had an odds ratio (OR) of 1.57 of obtaining a PaCO2 value between 35 and 45 mmHg on the first CPB blood gas when compared with a .4 V/Q (Figure 1Figure 1.Bivariate associations between PaCO2 and the V/Q ratio. (A) Spike histogram with loess curve showing the proportion of patients with a first PaCO2 value on CPB between 35 and 45 mmHg according to the V/Q ratio. (B) Scatterplot and loess curve (gray line) for PaCO2 on CPB according to the V/Q ratio. Dashed lines indicate the target range of 35-45 mmHg. (C) Model-based estimate of the predicted probability and 95% CI for PaCO2 on CPB between 35 and 45 mmHg according to the V/Q ratio obtained from logistic regression. (D) Model-based estimate of the predicted PaCO2 on CPB according to the V/Q ratio obtained from ordinal regression. Prop, proportion.). A .9 V/Q had a 1.76 OR when compared with a .4 and a 1.12 OR when compared with .6. Using a .6 V/Q ratio achieved a PaCO2 value within normal physiologic limits with no significant advantage to a higher V/Q ratio overall. However, younger or smaller patients required a higher V/Q to achieve similar probabilities of being within limits and similar PaCO2 values when compared with the older or larger patients.

Higher Flow on Cardiopulmonary Bypass in Pediatrics Is Associated With a Lower Incidence of Acute Kidney Injury.

Adequate perfusion is of paramount concern during cardiopulmonary bypass (CPB) and different methodologies are employed to optimize oxygen delivery. Temperature, hematocrit, and cardiac index (CI) are all modulated during CPB to ensure appropriate support. This study examines 2 different perfusion strategies and their impact on various outcome measures including acute kidney injury (AKI), urine output on CPB, ICU length of stay, time to extubation, and mortality. Predicated upon surgeon preference, the study institution employs 2 different perfusion strategies (PS) during congenital cardiac surgery requiring CPB. One method utilizes a targeted 2.4 L/min/m2 CI and nadir hematocrit of 28% (PS1), the other a 3.0 L/min/m2 CI with a nadir hematocrit of 25% (PS2). This study retrospectively examines CPB cases during which the 2 perfusion strategies were applied to determine potential differences in packed red blood cell administration, urine output during CPB, AKI post-CPB as defined by the KDIGO criteria, and operative survival as defined by the Society of Thoracic Surgeons. Significant differences were found in urine output while on CPB (P < 0.01) and all combined stages of postoperative AKI (P = 0.01) with the PS2 group faring better in both measures. No significant difference was found between the 2 groups for packed red blood cell administration, mortality, time to extubation, or ICU length of stay. Avoiding a nadir hematocrit less than 25% has been well established but maintaining anything greater than that may not be necessary to achieve adequate oxygen delivery on CPB. Our results indicate that higher CI and oxygen delivery on CPB are associated with a lower rate of AKI and this may be achieved with increased flow rather than increasing the hematocrit thus avoiding unnecessary transfusion.

Retrospective analysis of cardiac index and lactate production on cardiopulmonary bypass for a congenital cardiac patient population.

BACKGROUND: Providing adequate metabolic support is the principal concern during cardiopulmonary bypass (CPB) with different strategies utilized to enhance oxygen delivery to the patient. Modifying temperature, hematocrit (Hct) and cardiac index (CI) during CPB are primary techniques which aid in this effort. Based upon surgeon preference, the study institution employs differing perfusion strategies (PS) during congenital cardiac surgery requiring CPB. One method utilizes a 2.4 L/min/m2 CI and nadir Hct of 28% (PS1) and the other a 3.0 L/min/m2 CI with a nadir Hct of 25% (PS2). METHODS: Cardiopulmonary bypass cases during which the PS1 or PS2 strategies were applied were retrospectively examined, finding no significant difference in pre-CPB lactate, maximum lactate on CPB or maximum change in lactate on CPB. RESULTS: While the post-CPB lactate was statistically significantly higher in the PS2 group (p=0.024), the magnitude of difference (0.15 mmol/L) was small. CONCLUSIONS: This study illustrates that, when oxygen delivery or tissue perfusion is suspected as the primary cause of lactate production during CPB, increasing the CI to a 3.0 rather than a 2.4 CI may be more advantageous than packed red blood cell administration.

Clampless cardioplegia: an alternative to conventional cardioplegia administration.

Myocardial protection is of the utmost importance during cardiac surgery. At times, there are patients who present to the operating room who make the typical use of cardioplegia difficult or impossible. For these patients, a separate protocol and process must be in place. "Clampless cardioplegia" is an option when the ascending aorta cannot be cross-clamped, but the surgeon needs a bloodless field with a quiescent heart. This study reports on the process of developing a policy and protocol for utilizing clampless or systemic cardioplegia. Four case reports of patients who received clampless or systemic cardioplegia and their peri-operative courses are described. These four patients showed no cardiac functional change by post-operative echocardiogram and no peri-operative complications are reported.

The Norwood Stage 1 procedure - conduct of perfusion: 2017 Survey results from NPC-QIC member institutions.

Hypoplastic left heart syndrome (HLHS) is a rare and severe congenital cardiac defect. Approximately 1000 infants are born with HLHS in the United States every year. Healthcare collaboratives over the last decade have focused on sharing patient experiences and techniques in an effort to improve outcomes. In 2010, cardiologists and patient families joined together to improve the care of HLHS patients by forming the National Pediatric Cardiology Quality Improvement Collaborative (NPC-QIC). Sixty-six of the approximately 110 institutions caring for patients with HLHS in the United States and Canada are now members of NPC-QIC. In 2017, cardiovascular perfusionists joined the collaborative as another specialty involved in the care of HLHS patients. Perfusionists and cardiac surgeons developed the collaborative's first conduct of perfusion survey for the Norwood Stage 1 procedure, specifically targeting the provision of cardiopulmonary bypass for patients with HLHS. This manuscript discusses the results of this survey, unveiling a significant variance in the conduct of perfusion for this patient population.

Recent innovations in perfusion and cardiopulmonary bypass for neonatal and infant cardiac surgery.

The development and refinement of cardiopulmonary bypass (CPB) has made the repair of complex congenital heart defects possible in neonates and infants. In the past, the primary goal for these procedures was patient survival. Now that substantial survival rates have been achieved for even the most complex of repairs in these patients, focus has been given to the reduction of morbidity. Although a necessity for these complex neonatal and infant heart defect repairs, CPB can also be an important source of perioperative complications. Recent innovations have been developed to mitigate these risks and is the topic of this review. Specifically, we will discuss improvements in minimizing blood transfusions, CPB circuit design, monitoring, perfusion techniques, temperature management, and myocardial protection, and then conclude with a brief discussion of how further systematic improvements can be made in these areas.

Effect of Normobaric versus Hypobaric Oxygenation on Gaseous Microemboli Removal in a Diffusion Membrane Oxygenator: An In Vitro Comparison.

Gaseous microemboli (GME) are an abnormal physiological occurrence during cardiopulmonary bypass and extracorporeal membrane oxygenation (ECMO). Several studies have correlated negative sequelae with exposure to increased amounts of GME. Hypobaric oxygenation is effective at eliminating GME in hollow-fiber microporous membrane oxygenators. However, hollow-fiber diffusion membrane oxygenators, which are commonly used for ECMO, have yet to be validated. The purpose of this study was to determine if hypobaric oxygenation, compared against normobaric oxygenation, can reduce introduced GME when used on diffusion membrane oxygenators. Comparison of a sealed Quadrox-iD with hypobaric sweep gas (.67 atm) vs. an unmodified Quadrox-iD with normal atmospheric sweep gas (1 atm) in terms of GME transmission during continuous air introduction (50 mL/min) in a recirculating in vitro circuit, over a range of flow rates (3.5, 5 L/min) and crystalloid prime temperatures (37°C, 28°C, and 18°C). GME were measured using three EDAC Doppler probes positioned pre-oxygenator, post-oxygenator, and at the arterial cannula. Hypobaric oxygenation vs. normobaric oxygenation significantly reduced hollow-fiber diffusion membrane oxygenator GME transmission at all combination of pump flows and temperatures. There was further significant reduction in GME count between the oxygenator outlet and at the arterial cannula. Hypobaric oxygenation used on hollow-fiber diffusion membrane oxygenators can further reduce GME compared to normobaric oxygenation. This technique may be a safe approach to eliminate GME during ECMO.

In vitro elimination of gaseous microemboli utilizing hypobaric oxygenation in the Terumo® FX15 oxygenator.

BACKGROUND: This study examines the efficacy of hypobaric oxygenation as it relates to the elimination of gaseous microemboli (GME) at designated flow, pressure and temperature combinations. METHODS: Hypobaric oxygenation was employed for experimental trials (n=60), but not for control trials (n=60), while circuit design, data measurements and testing conditions were maintained for both settings. Hypobaric oxygenation conditions were created by applying 100% oxygen at sub-atmospheric sweep gas pressures of 0.67 atmospheres to the gas phase of an integrated hollow-fiber microporous membrane oxygenator. GME were quantified using an Emboli Detection and Classification system (EDAC), while a continuous air infusion, at a rate of 100 ml/min, was applied to the circuit. Trials were conducted at 37°C, 28°C, and 18°C and at two flow and line pressure combinations of: 3.5 L/min & 150 mmHg and 5 L/min & 200 mmHg. RESULTS: Sub-atmospheric sweep gas pressures allowed adequate oxygenation independent of carbon dioxide removal while significantly reducing the potential entrance of nitrogen into the blood. GME was reduced significantly across all temperatures and flows when compared to control trials; GME counts were reduced by 99.7% post-oxygenator and 99.99% at the arterial cannula. CONCLUSION: Correlation between the use of hypobaric oxygenation and GME counts suggests hypobaric oxygenation could play a significant role in the reduction of GME.