Oxygen-enriched air has a higher FiO2 than 0.21; up to 1.00 which means 100% oxygen. FiO2 is typically maintained below 0.5 even with mechanical ventilation, to avoid oxygen toxicity, but there are applications when up to 100% is routinely used.

If a PaO2 level is lower than 80 mmHg, it means that a person is not getting enough oxygen . A low PaO2 level can point to an underlying health condition, such as: emphysema. chronic obstructive pulmonary disease, or COPD.

pO2: This is measured by a pO2 electrode. It is the partial pressure (tension) of oxygen in a gas phase in equilibrium with blood. High or low values indicate blood hyperoxia or hypoxia, respectively. pO2 in venous blood is lower than arterial blood due to oxygen extraction by peripheral tissues.

The most common cause of decreased PCO2 is an absolute increase in ventilation. Decreased CO2 production without increased ventilation, such as during anesthesia, can also cause respiratory alkalosis. Decreased partial pressure of carbon dioxide will decrease acidity.

*A normal pH of 7.35-7.45 indicates chronic hypercapnic respiratory failure only….Acute Respiratory Failure – All There Is To Know.

The alveolar gas equation is used to calculate alveolar oxygen partial pressure: PAO2 = (Patm – PH2O) FiO2 – PaCO2 / RQ.

At steady state,2 in a normal individual breathing room air, PIO2 is 149 mmHg, and if PACO2 is 40 mmHg, PAO2 can be as high as 109 mmHg. However, in the normal resting state, the measured PAO2 (from end-expiratory air) is 100 mmHg when PACO2 is 40 mmHg. Therefore, there must be other factors that affect PAO2.

How to Calculate FIO2 from Liters. Example: A patient has a pO2 of 85mmHg on ABG while receiving 5 liter/minute of oxygen. 5 L/min = 40% oxygen = FIO2 of 0.40, the P/F ratio = 85 divided by 0.40 = 212.5.

fraction of inspired oxygen

Damages on the central nervous system toxicity may be caused by exposure to high oxygen partial pressures (as in hyperbaric oxygenation) (45), while pulmonary and ocular toxicity may be caused by longer exposure to high oxygen levels at atmospheric pressure conditions (46).

Applying physiologic PEEP of 3-5 cm water is common to prevent decreases in functional residual capacity in those with normal lungs. The reasoning for increasing levels of PEEP in critically ill patients is to provide acceptable oxygenation and to reduce the FiO2 to nontoxic levels (FiO2< 0.5).

Nurses who look after ventilated patients should be aware that high PEEP can lead to barotrauma and a drop in cardiac output- thus protocols should be in place to counter these complications.

Applied (extrinsic) PEEP is usually one of the first ventilator settings chosen when mechanical ventilation is initiated. It is set directly on the ventilator. A small amount of applied PEEP (4 to 5 cmH2O) is used in most mechanically ventilated patients to mitigate end-expiratory alveolar collapse.

Best or optimal PEEP will be defined as the PEEP below which PaO2 /FIO2 falls by at least 20%. If at least 20% PaO2 /FIO2 decrement is not obtained, then PEEP that will result in the highest PaO2 will be selected.

This, in normal conditions, is ~0.5, while in ARDS it can range between 0.2 and 0.8. This underlines the need for measuring the transpulmonary pressure for a safer application of mechanical ventilation.

Second, PEEP increases intrathoracic pressure, particularly when used in focal processes. This decreases venous return and cardiac output with subsequent adverse effects on systemic blood pressure and tissue oxygen delivery.

As a treatment, prone position ventilation results in significantly better oxygenation than mechanical ventilation applied in the supine position in ARDS patients [46].

APPROACH

1. increase FiO2 to improve PAO2.
2. increased PEEP. increase surface area for gas exchange. decrease atelectasis. redistribution of lung water.

There are specific problems for those who are being ventilated. High peak airway pressure suggests an impending pneumothorax. There will be difficulty ventilating the patient during resuscitation. A tension pneumothorax causes progressive difficulty with ventilation, as the normal lung is compressed.

Pneumomediastinum can happen when pressure rises in the lungs and causes the air sacs (alveoli) to rupture. Another possible cause is damage to the lungs or other nearby structures that allow air to leak into the center of the chest.

Treatment. Often, no treatment is required as the air is gradually absorbed from the mediastinum. If pneumomediastinum is accompanied by pneumothorax, a chest tube may be placed. Breathing high concentrations of oxygen may allow the air in the mediastinum to be absorbed more quickly.

How is pneumopericardium treated? Pneumopericardium is often a medical emergency. Your doctor may recommend an emergency procedure known as pericardiocentesis. This involves draining the excess fluid with a needle.