Unlike the Volume-Cycled Ventilation, patient efforts above the fixed rate are unassisted in the synchronized intermittent mandatory ventilation (SIMV). Pressure-cycled ventilation
The pressure-cycled ventilation includes pressure control ventilation and pressure support ventilation. Both methods offer a set inspiratory pressure. The tidal volume varies depending on the resistance and elastance of the respiratory system. Pressure-cycled ventilation can help alleviate symptoms in patients with acute respiratory distress syndrome by limiting the distending pressure of the lungs. The pressure control ventilation is specifically a pressure-cycled form of assist-control ventilators. Assist-control ventilators describe a mode of ventilation that maintains a minimum respiratory rate regardless of whether or not the patient initiates a spontaneous breath. Each inspiratory effort that is beyond the sensitivity threshold delivers full pressures support for a fixed inspiratory time. There is maintenance of a minimum respiratory rate. In the pressure support ventilation, the minimum rate is not set. Instead, all breaths are triggered by the patient. The way that the pressure support ventilation works is by assisting the patient with a constant pressure until the patients inspiratory flow falls below a threshold. The longer, deeper inspiratory flows by the patient will result in a larger tidal volume. This method of mechanical ventilation will help patients assume more work of breathing. Noninvasive positive pressure ventilation (NIPPV)
Noninvasive positive pressure ventilation is the delivery of positive pressure ventilation through a tight-fitting mask that covers the nose and mouth. It assists patients who can spontaneously breathe. Noninvasive positive pressure ventilation delivers end-expiratory pressure with a volume control setting.
There have also been reports of diabetes insipidus complicating this condition.Many laboratory abnormalities are seen in acute fatty liver of pregnancy. Liver enzymes are elevated, with the AST and ALT enzymes ranging from minimal elevation to 1000 IU/L, but usually staying in the 300-500 range. Bilirubin is almost universally elevated. Alkaline phosphatase is often elevated in pregnancy due to production from the placenta, but may be additionally elevated. Other abnormalities may include an elevated white blood cell count, hypoglycemia, elevated coagulation parameters, including the international normalized ratio, and decreased fibrinogen. Frank disseminated intravascular coagulation, or DIC, may occur in as many as 70% of people.Abdominal ultrasound may show fat deposition in the liver, but, as the hallmark of this condition is microvesicular steatosis (see pathology below), this is not seen on ultrasound. Rarely, the condition can be complicated by rupture or necrosis of the liver, which may be identified by ultrasound. Pathophysiology
The understanding of the causes of acute fatty liver of pregnancy
has been improved by advances in mitochondrial biochemistry. Deficiency of LCHAD (3-hydroxyacyl-CoA dehydrogenase) leads to an accumulation of medium and long chain fatty acids. When this occurs in the foetus, the unmetabolized fatty acids will re-enter the maternal circulation through the placenta, and overwhelm the beta-oxidation enzymes of the mother. The gene responsible for LCHAD has been isolated, and the most common mutation found in acute fatty liver of pregnancy is the E474Q missense mutation. LCHAD deficiency is autosomal recessive in inheritance and mothers are often found to be heterozygous for the affected mutation.