Breath-dependent pressure fluctuations in various constant- and variable-flow neonatal CPAP devices.

OBJECTIVE: In continuous positive airway pressure (CPAP) devices, pressure can be generated by two different mechanisms: either via an expiratory valve or by one or more jets. Valved CPAP devices are referred to as constant-flow devices, and jet devices are called variable-flow devices. Constant-flow CPAP devices are said to reduce the imposed work of breathing due to lower breath-dependent pressure fluctuations. The present study investigates the performance of various constant- and variable-flow CPAP devices in relation to breath-dependent pressure fluctuations. DESIGN: Experimental study comparing the pressure fluctuations incurred by seven neonatal CPAP devices attached to an active neonatal lung model. METHODOLOGY: Spontaneous breathing was simulated using a tidal volume of 6 ml at pressure levels of 5, 7, and 9 mbar. The main outcomes were respiratory pressure fluctuations, tidal volume, and end-expiratory pressure. RESULTS: All CPAP devices tested showed respiratory pressure fluctuations, varying from 0.631 to 3.466 mbar. The generated tidal volume correlated significantly with the pressure fluctuations (r = -0.947; p = 0.001) and varied between 5.550 and 6.316 ml. CPAP devices with jets showed no advantage over CPAP devices with expiratory valves. End-expiratory pressure in the nose deviated from the set pressure between -1.305 and 0.644 mbar and varied depending on whether the pressure was measured in the device or in the tube extending to the nose. CONCLUSION: During standard spontaneous breathing, breath-dependent pressure fluctuations in constant- and variable-flow devices are comparable. Pressure measurements taken in the tubing system can lead to a considerable deviation of the applied pressure.

When synchronized isn't synchronous- an experimental benchmarking study on the efficiency of SIMV in very-low-birth weight premature infants.

BACKGROUND: Synchronized ventilation promotes a patient's ability to breathe spontaneously by providing intermittent, mechanical-controlled respiration that is synchronized with the patient's own efforts. In "synchronized-intermittent-mandatory-ventilation" SIMV, assisted ventilation is regulated by frequency settings which dictate the interval at which the ventilator becomes sensitive to respiratory efforts and responds with an assisted breath. SIMV has become one of the most widely used modes of ventilation in neonates. Using a neonatal-active-lung-model (NALM), this in-vitro benchmark study investigated how well synchronization works in SIMV with several ventilators. METHODS: The competence of eight ventilators was tested using a NALM simulator representing a preterm infant weighing approximately 1500 grams. Two conditions were explored: first, the ventilators were set to a constant ventilation rate, while the NALM was adjusted to frequencies equal to and below this ventilation rate. The second condition varied the ventilators' rates while the NALM frequency was held constant. Correctly triggered breaths were counted and displayed as a percentage (%) of the total potential triggerable breaths. RESULTS: Performance among devices significantly differed, ranging from a low 38.9% competency to a max of 71.7% under the first condition, and 70.7% to 100% under the second condition. CONCLUSIONS: At high SIMV frequencies, synchronization between the patient and ventilator becomes increasingly limited. Despite their identical ventilator functions, SIMV algorithms of the various manufacturers and models tested, deliver ventilation rates with significantly different degrees of synchronization; not only in comparison to each other, but also in their own ability to continuously and effectively synchronize breaths under variable conditions, typical of preterm lungs.

Early postoperative arterial lactate concentrations to stratify risk of post-hepatectomy liver failure.

BACKGROUND: Post-hepatectomy liver failure (PHLF) represents the major determinant for death after liver resection. Early recognition is essential. Perioperative lactate dynamics for risk assessment of PHLF and associated morbidity were evaluated. METHODS: This was a multicentre observational study of patients undergoing hepatectomy with validation in international high-volume units. Receiver operating characteristics analysis and cut-off calculation for the predictive value of lactate for clinically relevant International Study Group of Liver Surgery grade B/C PHLF (clinically relevant PHLF (CR-PHLF)) were performed. Lactate and other perioperative factors were assessed in a multivariable CR-PHLF regression model. RESULTS: The exploratory cohort comprised 509 patients. CR-PHLF, death, overall morbidity and severe morbidity occurred in 7.7, 3.3, 40.9 and 29.3 per cent of patients respectively. The areas under the curve (AUCs) regarding CR-PHLF were 0.829 (95 per cent c.i. 0.770 to 0.888) for maximum lactate within 24 h (Lactate_Max) and 0.870 (95 per cent c.i. 0.818 to 0.922) for postoperative day 1 levels (Lactate_POD1). The respective AUCs in the validation cohort (482 patients) were 0.812 and 0.751 and optimal Lactate_Max cut-offs were identical in both cohorts. Exploration cohort patients with Lactate_Max 50 mg/dl or greater more often developed CR-PHLF (50.0 per cent) than those with Lactate_Max between 20 and 49.9 mg/dl (7.4 per cent) or less than 20 mg/dl (0.5 per cent; P < 0.001). This also applied to death (18.4, 2.7 and 1.4 per cent), severe morbidity (71.1, 35.7 and 14.1 per cent) and associated complications such as acute kidney injury (26.3, 3.1 and 2.3 per cent) and haemorrhage (15.8, 3.1 and 1.4 per cent). These results were confirmed in the validation group. Combining Lactate_Max with Lactate_POD1 further increased AUC (ΔAUC = 0.053) utilizing lactate dynamics for risk assessment. Lactate_Max, major resections, age, cirrhosis and chronic kidney disease were independent risk factors for CR-PHLF. A freely available calculator facilitates clinical risk stratification (www.liver-calculator.com). CONCLUSION: Early postoperative lactate values are powerful, readily available markers for CR-PHLF and associated complications after hepatectomy with potential for guiding postoperative care.Presented in part as an oral video abstract at the 2020 online Congress of the European Society for Surgical Research and the 2021 Congress of the Austrian Surgical Society.

Liver failure represents a major complication after liver resection and determines the risk of postoperative death, therefore early anticipation and risk stratification are highly relevant. This study, of 991 patients in three international centres, shows that the maximum lactate blood level within 24 h after surgery is a very strong factor predicting the further course after liver operations. Lactate could potentially aid in clinical decision making such as prophylactic treatment, intensified observation or early discharge of patients.