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Oxygen Therapy

14

 

Surinder K. Jindal and Ashutosh Nath Aggarwal

 

A young female patient presented to the emergency department with history of sore throat, high-grade fever, and cough with minimal hemoptysis for the past 5 days. On examination, she was found to be in respiratory distress. Her chest examination report was normal. The chest skiagram showed bilateral infiltrates and SpO2 was 80%.

Oxygen is the commonest drug used in patients admitted in Intensive Care Unit. There are various methods available for delivering oxygen. Overzealous treatment with oxygen should be avoided due to the risk of oxygen toxicity.

Step 1: Assess the need for oxygen therapy

The need for oxygen therapy in the intensive care unit (ICU) depends on the presence of documented hypoxia and/or inadequate oxygenation.

Presence of nonspecific symptoms and signs suggestive of hypoxia should be evaluated with objective measurements of oxygenation.

Arterial blood gas analysis with measurement of oxygen (PaO2) and carbon dioxide (PaCO2) partial pressures remains the gold standard for hypoxia demonstration.

Pulse oximetry is a noninvasive method, which provides arterial oxygen satura-

tion (SpO2) as a substitute for PaO2 for routine monitoring. The reading of pulse oximetry could be inconsistent (see Chap. 15).

Oxygen is applied if any of the following is present:

• Hypoxia (i.e., PaO2 <60 mmHg) due to any cause.

S.K. Jindal, M.D. (*) • A.N. Aggarwal, M.D., D.M.

Department of Pulmonary Medicine, Postgraduate Institute of Medical Education & Research, Chandigarh, India

e-mail: drskjindal@gmail.com

R. Chawla and S. Todi (eds.), ICU Protocols: A stepwise approach,

107

DOI 10.1007/978-81-322-0535-7_14, © Springer India 2012

 

108

S.K. Jindal and A.N. Aggarwal

 

 

Respiratory failure due to

Acute respiratory distress syndrome

Acute exacerbation of chronic obstructive pulmonary disease (COPD) or asthma

Pneumonia

In emergency situations (e.g., cardiorespiratory arrest, acute cardiogenic pulmonary edema, or stroke), oxygen administration may be initiated empirically, pending detailed clinical and laboratory evaluation. Blood gas analysis should be made available as early as possible.

Normoxemic hypoxia (i.e., normal PaO2) but presence of tissue hypoxia in the following conditions:

Severe anemia

Low cardiac output state

Hypotension

Severe sepsis

Vascular (arterial) occlusion

Failure of tissues to utilize oxygen (e.g., poisoning)—histotoxic hypoxia.

Step 2: Initiate oxygen administration

Before giving oxygen, one needs to ensure patency of the airways. This might require endotracheal intubation or tracheostomy.

It is generally customary to start with a high FiO2—100% for cardiorespiratory arrest and 50–100% for acute hypoxemic respiratory failure.

The FiO2 can be increased or decreased after the assessment of clinical and laboratory response to the initial administration.

Relatively lower concentrations are used in patients with hypercapnic respiratory failure (such as COPD) with the preexisting chronic hypoventilation.

High concentration of oxygen may worsen CO2 retention and cause CO2 narcosis by abolishing the hypoxic respiratory stimulation. However, optimum FiO2 must be ensured since hypoxia is always more deleterious than hypercapnia. Various devices can be used for applying oxygen.

Administration Devices

1.Source: Most well-equipped ICUs have continuous pressurized oxygen and air supply available at each bed. In this fashion, both oxygen and air can be simulta-

neously fed into an oxygen blender to control the output FiO2. Oxygen cylinders and concentrators are required as a backup source in case of failure of central supply.

2.Oxygen delivery: Oxygen is delivered either alone noninvasively or along with assisted respiratory support.

A. Stand-alone oxygen

The ICU patients are sicker with high ventilatory requirements than the general ward patients. Higher concentrations of oxygen are required, which are provided with high-flow systems.

14 Oxygen Therapy

109

 

 

Fig. 14.1 Simple face mask

Nasal cannulation is usually insufficient in severe hypoxemic respiratory failure. The nasal cannula is a low-flow, low-oxygen device and cannot deliver tracheal FiO2 more than 0.4–0.5. High flow rates do not result in high FiO2 and have a drying and irritating effect on nasal mucosa.

Simple face mask is a low-flow delivery system which provides FiO2 from 0.4 to 0.6 at flow rate of 5–8 L/min. This mask does not need tight seal (Fig. 14.1).

Venturi masks are preferred for precise titration of oxygen being administered. FiO2 can be more precisely controlled from 0.24 to 0.5 at high flow rates simply by changing the jet nozzle and adjusting oxygen flow rates. This is particularly helpful in patients with acute exacerbation of COPD where controlled oxygen supplementation is quite critical (Fig. 14.2).

Oxygen delivery is also provided through a mask with a reservoir, which

is a high-oxygen, high-flow device. A high FiO2 of up to 0.6–0.9 can be delivered through these masks (Figs. 14.3 and 14.4).

B.O2 supplementation during noninvasive positive-pressure ventilation (NIPPV)

NIPPV in ICUs is administered either through conventional mechanical ventilation or through a portable system.

Supplemental oxygen is delivered by simply adding it to the mask or the circuit.

Oxygen should be added into the circuit distal to the exhalation port.

The highest concentration is achieved with O2 added to the mask, with the leak port in the circuit, and with the lowest setting of inspiratory and expi-

ratory pressures. Unfortunately, the delivered FiO2 with NIPPV portable systems remains unpredictable.

110

S.K. Jindal and A.N. Aggarwal

 

 

Fig. 14.2 Schematic diagram showing the principle involved in the venturi mask

Fig. 14.3 Schematic diagram showing the principle of partial non-rebreather mask

Fig. 14.4 Schematic diagram showing the principle of non-rebreather face mask

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