Bilateral phrenic nerve block to reduce hazardous respiratory drive in a mechanically ventilated patient with COVID-19-A case report.

Key Clinical Message: Forced inspiration during mechanical ventilation risks self-inflicted lung injury. However, controlling it with sedation or paralysis may cause polyneuropathy and myopathy. We tested bilateral phrenic nerve paralysis with local anesthetic in a patient, showing reduced inspiratory force. This offers an alternative to drug-induced muscle paralysis. Abstract: Mechanical ventilation, although a life-saving measure, can also pose a risk of causing lung injury known as "ventilator-induced lung injury" or VILI. Patients undergoing mechanical ventilation sometimes exhibit heightened inspiratory efforts, wherein the negative pressure generated by the respiratory muscles adds to the positive pressure generated by the ventilator. This combination of high pressures can lead to a syndrome similar to VILI, referred to as "patient self-inflicted lung injury" or P-SILI. Prevention of P-SILI requires the administration of deep sedation and muscle paralysis to the patients, but both these measures can have undesired effects on their health. In this case report, we demonstrate the effect of a bilateral phrenic nerve block aiming to reduce excessive inspiratory respiratory efforts in a patient suffering from COVID-19 pneumonitis.

Mechanisms maintaining right ventricular contractility-to-pulmonary arterial elastance ratio in VA ECMO: a retrospective animal data analysis of RV-PA coupling.

BACKGROUND: To optimize right ventricular-pulmonary coupling during veno-arterial (VA) ECMO weaning, inotropes, vasopressors and/or vasodilators are used to change right ventricular (RV) function (contractility) and pulmonary artery (PA) elastance (afterload). RV-PA coupling is the ratio between right ventricular contractility and pulmonary vascular elastance and as such, is a measure of optimized crosstalk between ventricle and vasculature. Little is known about the physiology of RV-PA coupling during VA ECMO. This study describes adaptive mechanisms for maintaining RV-PA coupling resulting from changing pre- and afterload conditions in VA ECMO. METHODS: In 13 pigs, extracorporeal flow was reduced from 4 to 1 L/min at baseline and increased afterload (pulmonary embolism and hypoxic vasoconstriction). Pressure and flow signals estimated right ventricular end-systolic elastance and pulmonary arterial elastance. Linear mixed-effect models estimated the association between conditions and elastance. RESULTS: At no extracorporeal flow, end-systolic elastance increased from 0.83 [0.66 to 1.00] mmHg/mL at baseline by 0.44 [0.29 to 0.59] mmHg/mL with pulmonary embolism and by 1.36 [1.21 to 1.51] mmHg/mL with hypoxic pulmonary vasoconstriction (p < 0.001). Pulmonary arterial elastance increased from 0.39 [0.30 to 0.49] mmHg/mL at baseline by 0.36 [0.27 to 0.44] mmHg/mL with pulmonary embolism and by 0.75 [0.67 to 0.84] mmHg/mL with hypoxic pulmonary vasoconstriction (p < 0.001). Coupling remained unchanged (2.1 [1.8 to 2.3] mmHg/mL at baseline; - 0.1 [- 0.3 to 0.1] mmHg/mL increase with pulmonary embolism; - 0.2 [- 0.4 to 0.0] mmHg/mL with hypoxic pulmonary vasoconstriction, p > 0.05). Extracorporeal flow did not change coupling (0.0 [- 0.0 to 0.1] per change of 1 L/min, p > 0.05). End-diastolic volume increased with decreasing extracorporeal flow (7.2 [6.6 to 7.8] ml change per 1 L/min, p < 0.001). CONCLUSIONS: The right ventricle dilates with increased preload and increases its contractility in response to afterload changes to maintain ventricular-arterial coupling during VA extracorporeal membrane oxygenation.

Modified Thermodilution for Simultaneous Cardiac Output and Recirculation Assessment in Veno-venous Extracorporeal Membrane Oxygenation: A Prospective Diagnostic Accuracy Study.

BACKGROUND: Thermodilution is unreliable in veno-venous extracorporeal membrane oxygenation (VV-ECMO). Systemic oxygenation depends on recirculation fractions and ratios of extracorporeal membrane oxygenation (ECMO) flow to cardiac output. In a prospective in vitro simulation, this study assessed the diagnostic accuracy of a modified thermodilution technique for recirculation and cardiac output. The hypothesis was that this method provided clinically acceptable precision and accuracy for cardiac output and recirculation. METHODS: Two ECMO circuits ran in parallel: one representing a VV-ECMO and the second representing native heart, lung, and circulation. Both circuits shared the right atrium. Extra limbs for recirculation and pulmonary shunt were added. This study simulated ECMO flows from 1 to 2.5 l/min and cardiac outputs from 2.5 to 3.5 l/min with recirculation fractions (0 to 80%) and pulmonary shunts. Thermistors in both ECMO limbs and the pulmonary artery measured the temperature changes induced by cold bolus injections into the arterial ECMO limb. Recirculation fractions were calculated from the ratio of the areas under the temperature curve (AUCs) in the ECMO limbs and from partitioning of the bolus volume (flow based). With known partitioning of bolus volumes between ECMO and pulmonary artery, cardiac output was calculated. High-precision ultrasonic flow probes served as reference for Bland-Altman plots and linear mixed-effect models. RESULTS: Accuracy and precision for both the recirculation fraction based on AUC (bias, -5.4%; limits of agreement, -18.6 to 7.9%) and flow based (bias, -5.9%; limits of agreement, -18.8 to 7.0%) are clinically acceptable. Calculated cardiac output for all recirculation fractions was accurate but imprecise (RecirculationAUC: bias 0.56 l/min; limits of agreement, -2.27 to 3.4 l/min; and RecirculationFLOW: bias 0.48 l/min; limits of agreement, -2.22 to 3.19 l/min). Recirculation fraction increased bias and decreased precision. CONCLUSIONS: Adapted thermodilution for VV-ECMO allows simultaneous measurement of recirculation fraction and cardiac output and may help optimize patient management with severe respiratory failure.

The Role of Intraoperative and Early Postoperative Blood Pressure Variations, Fluid Balance and Inotropics in Fibula Free Flap Head and Neck Reconstruction: A Retrospective Analysis.

BACKGROUND: In head and neck reconstructive surgery, postoperative complications are a well-known concern. METHODS: We examined 46 patients who underwent ablative surgery and received fibula free flap reconstruction. The main focus was to assess the influence of intraoperative blood pressure fluctuations and the administration of inotropic drugs on complications, either related to the flap or systemic, serving as the primary endpoint. RESULTS: Utilizing logistic regression models, we identified that intraoperative mean arterial blood pressure (MAP) drops did not correlate with the occurrence of either flap-related complications (MAP < 70, p = 0.79; MAP < 65, p = 0.865; MAP < 60, p = 0.803; MAP < 55, p = 0.937) or systemic medical complications (MAP < 70, p = 0.559; MAP < 65, p = 0.396; MAP < 60, p = 0.211; MAP < 55, p = 0.936). The occurrence of flap-related complications significantly increased if a higher dosage of dobutamine was administered (median 27.5 (IQR 0-47.5) vs. 62 (38-109) mg, p = 0.019) but not if norepinephrine was administered (p = 0.493). This correlation was especially noticeable given the uptick in complications associated with fluid overload (3692 (3101-4388) vs. 4859 (3555-6216) mL, p = 0.026). CONCLUSION: Intraoperative and immediate postoperative blood pressure fluctuations are common but are not directly associated with flap-related complications; however, dobutamine application as well as fluid overload may impact flap-specific complications.

Interactions between extracorporeal support and the cardiopulmonary system.

This review describes the intricate physiological interactions involved in the application of extracorporeal therapy, with specific focus on cardiopulmonary relationships. Extracorporeal therapy significantly influences cardiovascular and pulmonary physiology, highlighting the necessity for clinicians to understand these interactions for improved patient care. Veno-arterial extracorporeal membrane oxygenation (veno-arterial ECMO) unloads the right ventricle and increases left ventricular (LV) afterload, potentially exacerbating LV failure and pulmonary edema. Veno-venous (VV) ECMO presents different challenges, where optimal device and ventilator settings remain unknown. Influences on right heart function and native gas exchange as well as end-expiratory lung volumes are important concepts that should be incorporated into daily practice. Future studies should not be limited to large clinical trials focused on mortality but rather address physiological questions to advance the understanding of extracorporeal therapies. This includes exploring optimal device and ventilator settings in VV ECMO, standardizing cardiopulmonary function monitoring strategies, and developing better strategies for device management throughout their use. In this regard, small human or animal studies and computational physiological modeling may contribute valuable insights into optimizing the management of extracorporeal therapies.

Cardiopulmonary interactions-which monitoring tools to use?

Heart-lung interactions occur due to the mechanical influence of intrathoracic pressure and lung volume changes on cardiac and circulatory function. These interactions manifest as respiratory fluctuations in venous, pulmonary, and arterial pressures, potentially affecting stroke volume. In the context of functional hemodynamic monitoring, pulse or stroke volume variation (pulse pressure variation or stroke volume variability) are commonly employed to assess volume or preload responsiveness. However, correct interpretation of these parameters requires a comprehensive understanding of the physiological factors that determine pulse pressure and stroke volume. These factors include pleural pressure, venous return, pulmonary vessel function, lung mechanics, gas exchange, and specific cardiac factors. A comprehensive knowledge of heart-lung physiology is vital to avoid clinical misjudgments, particularly in cases of right ventricular (RV) failure or diastolic dysfunction. Therefore, when selecting monitoring devices or technologies, these factors must be considered. Invasive arterial pressure measurements of variations in breath-to-breath pressure swings are commonly used to monitor heart-lung interactions. Echocardiography or pulmonary artery catheters are valuable tools for differentiating preload responsiveness from right ventricular failure, while changes in diastolic function should be assessed alongside alterations in airway or pleural pressure, which can be approximated by esophageal pressure. In complex clinical scenarios like ARDS, combined forms of shock or right heart failure, additional information on gas exchange and pulmonary mechanics aids in the interpretation of heart-lung interactions. This review aims to describe monitoring techniques that provide clinicians with an integrative understanding of a patient's condition, enabling accurate assessment and patient care.

Gastrointestinal function in critically ill patients.

PURPOSE OF REVIEW: To summarize recent evidence regarding the diagnosis of acute gastrointestinal dysfunction and enteral feeding intolerance, and relationship of these to development of multiple organ dysfunction syndrome, during critical illness. RECENT FINDINGS: Novel gastric feeding tubes that attenuate gastroesophageal regurgitation or facilitate continuous monitoring of gastric motility have been developed. The definition of enteral feeding intolerance remains controversial, which may be resolved using a consensus process. A novel scoring system for gastrointestinal dysfunction (GIDS - GastroIntestinal Dysfunction Score) was recently developed but it is not yet validated or tested to evaluate the effect of any interventions. Studies of biomarkers to identify gastrointestinal dysfunction have yet to yield a suitable biomarker for daily clinical use. SUMMARY: The assessment of gastrointestinal function in critically ill patients continues to rely on complex daily clinical assessment. Scoring systems, consensus definitions and novel technology appear the most promising tools and interventions to improve patient care.

Behaviour and stability of thermodilution signals in a closed extracorporeal circuit: a bench study.

Thermodilution is the gold standard for cardiac output measurement in critically ill patients. Its application in extracorporeal therapy is limited, as a portion of the thermal indicator is drawn into the extracorporeal circuit. The behaviour of thermodilution signals in extracorporeal circuits is unknown. We investigated thermodilution curves within a closed-circuit and assessed the impact of injection volume, flow and distance on the behaviour of the thermodilution signals and catheter constants. We injected 3, 5, 7 and 10 ml of thermal indicator into a heated closed circuit. Thermistors at distances of 40, 60, 80, and 100 cm from the injection port recorded the thermodilution signals (at flow settings of 0.5, 1, 1.5, and 2 L/min). Area under the curve (AUC), rise time, exponential decay and catheter constants were analysed. Linear mixed-effects models were used to evaluate the impact of circuit flow, distance and injection volume. Catheter positioning did not influence AUC (78 injections). Catheter constants were independent of flow, injection volume or distance to the injection port. The distance to the injection port increased peak temperature and rise time and decreased exponential time constant significantly. The distance to the injection port did not influence catheter constants, but the properties of the thermodilution signal itself. This may influence measurements that depend on the exponential decay of the thermodilution signal such as right ventricular ejection fraction.

Current practice of gastric residual volume measurements and related outcomes of critically ill patients: A secondary analysis of the intestinal-specific organ function assessment study.

BACKGROUND: Gastric residual volume (GRV) measurement to detect gastrointestinal (GI) dysfunction is a common diagnostic procedures in critical care, albeit still not well standardized being operator-, patient-, and tube-dependent. Our aim was to describe current practice of GRV measurements and its association with clinical outcomes in critically ill patients. METHODS: This was a secondary analysis of an international prospective observational cohort study (intestinal-specific organ function assessment). Eligibility criteria were defined as ≥1 GRV measurement during the 7-day study period. Data collection included GRV measurement practices, tube diameters and volumes, symptoms of GI dysfunction, and clinical outcomes. The primary aim was to describe current practices of GRV measurements, and the secondary aim was to test the association of high (>200 ml) vs. low GRV with symptoms of GI dysfunction and clinical outcomes using generalized linear regression and survival models. RESULTS: Two hundred fifty-eight patients with 2422 GRV measurements on 875 study days were analyzed. GRV was mainly measured via passive drainage twice daily using large diameter tubes. There was no significant association between tube size or measurement technique and high GRV. High GRV occurred in 34% of patients and was associated with other GI symptoms and with increased disease severity but not with 28-day or 90-day mortality, intensive care unit-free and ventilator-free days. CONCLUSION: There was substantial variability of GRV measurement techniques, but this had no impact on the amount of GRV. High GRV was not associated with mortality or ventilator-free days but may serve as a marker of GI dysfunction and disease severity.

Integral assessment of gas exchange during veno-arterial ECMO: accuracy and precision of a modified Fick principle in a porcine model.

Assessment of native cardiac output during extracorporeal circulation is challenging. We assessed a modified Fick principle under conditions such as dead space and shunt in 13 anesthetized swine undergoing centrally cannulated veno-arterial extracorporeal membrane oxygenation (V-A ECMO, 308 measurement periods) therapy. We assumed that the ratio of carbon dioxide elimination (V̇co2) or oxygen uptake (V̇o2) between the membrane and native lung corresponds to the ratio of respective blood flows. Unequal ventilation/perfusion (V̇/Q̇) ratios were corrected towards unity. Pulmonary blood flow was calculated and compared to an ultrasonic flow probe on the pulmonary artery with a bias of 99 mL/min (limits of agreement -542 to 741 mL/min) with blood content V̇o2 and no-shunt, no-dead space conditions, which showed good trending ability (least significant change from 82 to 129 mL). Shunt conditions led to underestimation of native pulmonary blood flow (bias -395, limits of agreement -1,290 to 500 mL/min). Bias and trending further depended on the gas (O2, CO2) and measurement approach (blood content vs. gas phase). Measurements in the gas phase increased the bias (253 [LoA -1,357 to 1,863 mL/min] for expired V̇o2 bias 482 [LoA -760 to 1,724 mL/min] for expired V̇co2) and could be improved by correction of V̇/Q̇ inequalities. Our results show that common assumptions of the Fick principle in two competing circulations give results with adequate accuracy and may offer a clinically applicable tool. Precision depends on specific conditions. This highlights the complexity of gas exchange in membrane lungs and may further deepen the understanding of V-A ECMO.

Impact of intraabdominal hypertension on kidney failure in critically ill patients: A post-hoc database analysis.

PURPOSE: To assess whether intraabdominal hypertension (IAH) may influence kidney failure as well as mortality. METHODS: This post-hoc analysis of two databases (IROI and iSOFA study) tested the independent association between IAH and kidney failure. Mortality was assessed using four prespecified groups (IAH present, kidney failure present, IAH and kidney failure present and no IAH or kidney failure present). RESULTS: Of 825 critically ill patients, 302 (36.6%) developed kidney failure and 192 (23.7%) died during the first 90 days. Only 'Cumulative days with IAH grade II or more' was significantly associated with kidney failure (OR 1.29 (1.08-1.55), p = 0.003) while 'cumulative days with IAH grade I or more' (p = 0.135) or highest daily IAP (p = 0.062) was not. IAH combined with kidney failure was independently associated with 90-day mortality (OR 2.20 (1.20-4.05), p = 0.011), which was confirmed for higher grades of IAH (grade II or more) alone (OR 2.14 (1.07-4.30), p = 0.032) and combined with kidney failure (OR 3.25 (1.72-6.12), p < 0.001). CONCLUSIONS: This study suggest that duration as well as higher grades of IAH are associated with kidney failure and may increase mortality.

Experimental validation of a mean systemic pressure analog against zero-flow measurements in porcine VA-ECMO.

The mean systemic pressure analog (Pmsa), calculated from running hemodynamic data, estimates mean systemic filling pressure (MSFP). This post hoc study used data from a porcine veno-arterial extracorporeal membrane oxygenation (ECMO) model [n = 9; Sus scrofa domesticus; ES breed (Schweizer Edelschwein)] with eight experimental conditions; Euvolemia [a volume state where ECMO flow produced normal mixed venous saturation (SVO2) without vascular collapse]; three levels of increasing norepinephrine infusion (Vasoconstriction 1-3); status after stopping norepinephrine (Post Vasoconstriction); and three steps of volume expansion (10 mL/kg crystalloid bolus) (Volume Expansion 1-3). In each condition, Pmsa and a "reduced-pump-speed-Pmsa" (Pmsared) were calculated from baseline and briefly reduced pump speeds, respectively. We calculated agreement for absolute values (per condition) and changes (between consecutive conditions) of Pmsa and Pmsared, against MSFP at zero ECMO flow. Euvolemia venous return driving pressure was 5.1 ± 2.0 mmHg. Bland-Altman analysis for Pmsa vs. MSFP (all conditions; 72 data pairs) showed bias (confidence interval) 0.5 (0.1-0.9) mmHg; limits of agreement (LoA) -2.7 to 3.8 mmHg. Bias for ΔPmsa vs. ΔMSFP (63 data pairs): 0.2 (-0.2 to 0.6) mmHg, LoA -3.2 to 3.6 mmHg. Bias for Pmsared vs. MSFP (72 data pairs): 0.0 (-0.3 to -0.3) mmHg; LoA -2.3 to 2.4 mmHg. Bias for ΔPmsared vs. ΔMSFP (63 data pairs) was 0.2 (-0.1 to 0.4) mmHg; LoA -1.8 to 2.1 mmHg. In conclusion, during veno-arterial ECMO, under clinically relevant levels of vasoconstriction and volume expansion, Pmsa accurately estimated absolute and changing values of MSFP, with low between-method precision. The within-method precision of Pmsa was excellent, with a least significant change of 0.15 mmHg.NEW & NOTEWORTHY This is the first study ever to validate the mean systemic pressure analog (Pmsa) against the reference mean systemic filling pressure (MSFP) determined at full arterio-venous pressure equilibrium. Using a porcine ECMO model with clinically relevant levels of vasoconstriction and volume expansion, we showed that Pmsa accurately estimated absolute and changing values of MSFP, with a poor between-method precision. The within-method precision of Pmsa was excellent.

Assessment of Right Heart Function during Extracorporeal Therapy by Modified Thermodilution in a Porcine Model.

BACKGROUND: Veno-arterial extracorporeal membrane oxygenation therapy is a growing treatment modality for acute cardiorespiratory failure. Cardiac output monitoring during veno-arterial extracorporeal membrane oxygenation therapy remains challenging. This study aims to validate a new thermodilution technique during veno-arterial extracorporeal membrane oxygenation therapy using a pig model. METHODS: Sixteen healthy pigs were centrally cannulated for veno-arterial extracorporeal membrane oxygenation, and precision flow probes for blood flow assessment were placed on the pulmonary artery. After chest closure, cold boluses of 0.9% saline solution were injected into the extracorporeal membrane oxygenation circuit, right atrium, and right ventricle at different extracorporeal membrane oxygenation flows (4, 3, 2, 1 l/min). Rapid response thermistors in the extracorporeal membrane oxygenation circuit and pulmonary artery recorded the temperature change. After calculating catheter constants, the distributions of injection volumes passing each circuit were assessed and enabled calculation of pulmonary blood flow. Analysis of the exponential temperature decay allowed assessment of right ventricular function. RESULTS: Calculated blood flow correlated well with measured blood flow (r2 = 0.74, P < 0.001). Bias was -6 ml/min [95% CI ± 48 ml/min] with clinically acceptable limits of agreement (668 ml/min [95% CI ± 166 ml/min]). Percentage error varied with extracorporeal membrane oxygenation blood flow reductions, yielding an overall percentage error of 32.1% and a percentage error of 24.3% at low extracorporeal membrane oxygenation blood flows. Right ventricular ejection fraction was 17 [14 to 20.0]%. Extracorporeal membrane oxygenation flow reductions increased end-diastolic and end-systolic volumes with reductions in pulmonary vascular resistance. Central venous pressure and right ventricular ejection fractions remained unchanged. End-diastolic and end-systolic volumes correlated highly (r2 = 0.98, P < 0.001). CONCLUSIONS: Adapted thermodilution allows reliable assessment of cardiac output and right ventricular behavior. During veno-arterial extracorporeal membrane oxygenation weaning, the right ventricle dilates even with stable function, possibly because of increased venous return.

Impact of intraoperative hypotension on early postoperative acute kidney injury in cystectomy patients - A retrospective cohort analysis.

STUDY OBJECTIVE: To assess the risk for postoperative acute kidney injury (AKI) after major urologic surgery for different intraoperative hypotension thresholds in form of time below a fixed threshold. We hypothesize that the duration of hypotension below a certain hypotension threshold is a risk factor for AKI also in major urologic procedures. DESIGN: Retrospective observational cohort series. SETTING: Single tertiary high caseload center. PATIENTS: 416 consecutive patients undergoing open radical cystectomy, pelvic lymph node dissection and urinary diversion between 2013 and 2019. INTERVENTIONS: None. MEASUREMENTS: We analyzed intraoperative data and their correlation to postoperative AKI judged according to the Acute Kidney Injury Network criteria. Patients were divided into groups falling below MAP <65 mmHg, MAP <60 mmHg and MAP <55 mmHg. The probability of developing postoperative AKI using all risk variables as well as the hypotension threshold variables (minutes under a certain threshold) was calculated using logistic regression methods. MAIN RESULTS: Postoperative AKI was diagnosed in 128/416 patients (30.8%). Multiple logistic regression analysis showed that minutes below a threshold of 65 mmHg (OR 1.010 [1.005-1.015], P < 0.001) and 60 mmHg (OR 1.012 [1.001-1.023], P = 0.02) are associated with an increased risk of AKI. On average, 26.5% (MAP <65 mmHg), 50.0% (MAP <60 mmHg) and 76.5% (MAP <55 mmHg) of minutes below a certain threshold occurred between induction of anesthesia and start of surgery and are thus fully attributable to anesthesiological management. CONCLUSIONS: Our results suggest that avoiding intraoperative MAP lower than 65 mmHg and especially lower than 60 mmHg will protect postoperative renal function in cystectomy patients. The time between induction of anesthesia and surgical incision warrants special attention as a relevant share of hypotension occur in this period.

Gas exchange calculation may estimate changes in pulmonary blood flow during veno-arterial extracorporeal membrane oxygenation in a porcine model.

Veno-arterial extracorporeal membrane oxygenation (V-A ECMO) is used as rescue therapy for severe cardiopulmonary failure. We tested whether the ratio of CO2 elimination at the lung and the V-A ECMO (V˙co2ECMO/V˙co2Lung) would reflect the ratio of respective blood flows and could be used to estimate changes in pulmonary blood flow (Q˙Lung), i.e., native cardiac output. Four healthy pigs were centrally cannulated for V-A ECMO. We measured blood flows with an ultrasonic flow probe. V˙co2ECMO and V˙co2Lung were calculated from sidestream capnographs under constant pulmonary ventilation during V-A ECMO weaning with changing sweep gas and/or V-A ECMO blood flow. If ventilation-to-perfusion ratio (V˙/Q˙) of V-A ECMO was not 1, the V˙co2ECMO was normalized to V˙/Q˙ = 1 (V˙co2ECMONorm). Changes in pulmonary blood flow were calculated using the relationship between changes in CO2 elimination and V-A ECMO blood flow (Q˙ECMO). Q˙ECMO correlated strongly with V˙co2ECMONorm (r2 0.95-0.99). Q˙Lung correlated well with V˙co2Lung (r2 0.65-0.89, P < = 0.002). Absolute Q˙Lung could not be calculated in a nonsteady state. Calculated pulmonary blood flow changes had a bias of 76 (-266 to 418) mL/min and correlated with measured Q˙Lung (r2 0.974-1.000, P = 0.1 to 0.006) for cumulative ECMO flow reductions. In conclusion, V˙co2 of the lung correlated strongly with pulmonary blood flow. Our model could predict pulmonary blood flow changes within clinically acceptable margins of error. The prediction is made possible with normalization to a V˙/Q˙ of 1 for ECMO. This approach depends on measurements readily available and may allow immediate assessment of the cardiac output response.