[Severe lactic acidosis requiring continuos haemodiafiltration in a young patient with unrecognized metabolic abnormality. Case report].

BACKGROUND: Lactic acidosis (LA) is the most common form of metabolic acidosis, defined by lactate values greater than 5 mmol/L and pH<7.34. The pathogenesis of LA involves hypoxic causes (type A) and non-hypoxic (type B), often coexisting. Identification and removal of the trigger are mandatory in the therapeutic management of LA. The case: A 38 years-old male patient entered the Emergency Ward for dyspnea, fever, vomiting and hyporexia. An important respiratory distress with hyperventilation due to severe LA was found, together with severe hypoglicemia, without renal impairment. Past medical history unremarkable, except for reported episodic hypoglicemia in the childhood, with fructose "intolerance", without any other data. No evidence of intoxications, septic shock or significant cytolysis. No drugs causing LA. The patient underwent orotracheal intubation, glucose infusion, and continuous haemodiafiltration for 36-hrs. A rapid general improvement was obtained with stabilization of acid-base balance. A diagnosis of fructose-1,6-diphosphatase deficiency was made. It is an autosomical recessive gluconeogenesis abnormality, with recurrent episodes of hypoglicemia and lactic acidosis after fasting, potentially lethal. The therapy is based on avoiding prolonged fasts, glucose infusion, and a specific diet, rich in glucose without fructose intake. CONCLUSIONS: The presence of not-otherwise-explained lactic acidosis in young patients has to place the suspect of an underlying and unknown metabolic derangement; in these cases, the involvement of the nephrologist appears to be pivotal for the differential diagnosis of the abnormalities of the acid-base balance, and for setting the best treatment.

Effect of external PEEP in patients under controlled mechanical ventilation with an auto-PEEP of 5 cmH2O or higher.

BACKGROUND: In some patients with auto-positive end-expiratory pressure (auto-PEEP), application of PEEP lower than auto-PEEP maintains a constant total PEEP, therefore reducing the inspiratory threshold load without detrimental cardiovascular or respiratory effects. We refer to these patients as "complete PEEP-absorbers." Conversely, adverse effects of PEEP application could occur in patients with auto-PEEP when the total PEEP rises as a consequence. From a pathophysiological perspective, all subjects with flow limitation are expected to be "complete PEEP-absorbers," whereas PEEP should increase total PEEP in all other patients. This study aimed to empirically assess the extent to which flow limitation alone explains a "complete PEEP-absorber" behavior (i.e., absence of further hyperinflation with PEEP), and to identify other factors associated with it. METHODS: One hundred patients with auto-PEEP of at least 5 cmH2O at zero end-expiratory pressure (ZEEP) during controlled mechanical ventilation were enrolled. Total PEEP (i.e., end-expiratory plateau pressure) was measured both at ZEEP and after applied PEEP equal to 80 % of auto-PEEP measured at ZEEP. All measurements were repeated three times, and the average value was used for analysis. RESULTS: Forty-seven percent of the patients suffered from chronic pulmonary disease and 52 % from acute pulmonary disease; 61 % showed flow limitation at ZEEP, assessed by manual compression of the abdomen. The mean total PEEP was 7 ± 2 cmH2O at ZEEP and 9 ± 2 cmH2O after the application of PEEP (p < 0.001). Thirty-three percent of the patients were "complete PEEP-absorbers." Multiple logistic regression was used to predict the behavior of "complete PEEP-absorber." The best model included a respiratory rate lower than 20 breaths/min and the presence of flow limitation. The predictive ability of the model was excellent, with an overoptimism-corrected area under the receiver operating characteristics curve of 0.89 (95 % CI 0.80-0.97). CONCLUSIONS: Expiratory flow limitation was associated with both high and complete "PEEP-absorber" behavior, but setting a relatively high respiratory rate on the ventilator can prevent from observing complete "PEEP-absorption." Therefore, the effect of PEEP application in patients with auto-PEEP can be accurately predicted at the bedside by measuring the respiratory rate and observing the flow-volume loop during manual compression of the abdomen.

Assessment of Factors Related to Auto-PEEP.

BACKGROUND: Previous physiological studies have identified factors that are involved in auto-PEEP generation. In our study, we examined how much auto-PEEP is generated from factors that are involved in its development. METHODS: One hundred eighty-six subjects undergoing controlled mechanical ventilation with persistent expiratory flow at the beginning of each inspiration were enrolled in the study. Volume-controlled continuous mandatory ventilation with PEEP of 0 cm H2O was applied while maintaining the ventilator setting as chosen by the attending physician. End-expiratory and end-inspiratory airway occlusion maneuvers were performed to calculate respiratory mechanics, and tidal flow limitation was assessed by a maneuver of manual compression of the abdomen. RESULTS: The variable with the strongest effect on auto-PEEP was flow limitation, which was associated with an increase of 2.4 cm H2O in auto-PEEP values. Moreover, auto-PEEP values were directly related to resistance of the respiratory system and body mass index and inversely related to expiratory time/time constant. Variables that were associated with the breathing pattern (tidal volume, frequency minute ventilation, and expiratory time) did not show any relationship with auto-PEEP values. The risk of auto-PEEP ≥5 cm H2O was increased by flow limitation (adjusted odds ratio 17; 95% CI: 6-56.2), expiratory time/time constant ratio <1.85 (12.6; 4.7-39.6), respiratory system resistance >15 cm H2O/L s (3; 1.3-6.9), age >65 y (2.8; 1.2-6.5), and body mass index >26 kg/m(2) (2.6; 1.1-6.1). CONCLUSIONS: Flow limitation, expiratory time/time constant, resistance of the respiratory system, and obesity are the most important variables that affect auto-PEEP values. Frequency expiratory time, tidal volume, and minute ventilation were not independently associated with auto-PEEP. Therapeutic strategies aimed at reducing auto-PEEP and its adverse effects should be primarily oriented to the variables that mainly affect auto-PEEP values.