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.

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.

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 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.

Rare Case of Transcutaneous Oxygen Desaturation in a Cancer Patient: A Case Report and Diagnostic Approach for a Recurrent Problem.

We present a case of a 73-year-old cancer patient with low transcutaneous oxygen saturation who was transferred to the intensive care unit after deployment of the rapid response team. Differential diagnosis remained broad until methemoglobinemia (MetHb) was detected.MetHb was induced by administration of rasburicase, which was given to prevent tumor lysis syndrome. In a follow-up examination, glucose-6-phosphate dehydrogenase deficiency was found to be the cause of MetHb after rasburicase exposure.Diagnosis was made by either measuring arterial MetHb or CO oximeter. Treatment options involve transfusion and methylene blue, if glucose-6-phosphate dehydrogenase deficiency is not present.