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Managing Hypoxia

Introduction || Signs and Symptoms || Causes || Diagnosis || Treatment || Overview || Related Articles || References and Resources || Comment || Search

Introduction





What is hypoxia? Hypoxia is a lack of adequate organ oxygenation. In other words, the body is unable to provide enough oxygen to its various components. This can be complete (ie: the whole body is involved) or focal (ie: only one organ is involved).

There are a whole slew of things that can cause hypoxia. Both lung and cardiovascular pathologies commonly cause hypoxia. In addition, emboli (ie: blood "clots") can lodge in blood vessels and stop blood flow; the result is hypoxia of everything downstream from the blockade.

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Signs and Symptoms

So how do you know if someone is hypoxic? The first method is to examine the patient. Are they feeling fatigued? Having trouble breathing? Are they confused? Do they look cyanotic (ie: blue)? These are all clinical findings that can indicate that someone may be hypoxic.

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Causes

Determining the reason for hypoxia is crucial, because treatment is aimed at the underlying cause. In general, most hypoxia is a result of heart and lung pathology.

In lung pathology the capillaries in the alveoli are unable to absorb oxygen. As a result, blood flows back to the left side of the heart unoxygenated. From there it is pumped out to the rest of the body. If a significant percentage of lung tissue is diseased the body's oxygen demand will outstrip the alveoli's ability to oxygenate the blood stream. The end result? Hypoxia!

There are a couple of standard ancillary tests that should be done if someone is hypoxic. The first is order an arterial blood gas if it hasn't already been done. A chest x-ray is also often ordered to determine if there is lung pathology causing the hypoxia. In addition an ECG can be very helpful in deciding if heart pathology is contributing to the hypoxia.

In addition, basic labs should also be ordered, a complete blood count (CBC) can tell you if anemia is contributing. A basic metabolic panel (BMP, aka: chem-7), can give you information about kidney perfusion and electrolyte status.

Several clinical questions should be posed. How much IV fluid (IVF) has the patient received? Patients who receive too much IVF can go into pulmonary edema. In addition, the amount of pain medication should also be ascertained. Morphine and its derivatives can decrease respiratory rate and lead to hypoxia.

Pulmonary embolism (PE) is a common cause of hypoxia in the hospitalized patient. If the patient is a high risk for thrombo-embolic events (ie: long periods in bed, known coagulopathy, known deep vein thrombus on lower extremity doppler testing, etc.) testing for embolism should be strongly considered, especially when no other pathology accounts for the hypoxia. Testing for PE includes ventilation/perfusion scans and helical CT scans.

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Diagnosis

The easiest way to diagnosis hypoxia is to use a pulse oximeter. This is the little finger or earlobe "thingy". It uses infrared technology to distinguish oxygenated from deoxygenated hemoglobin in the blood. A low pulse oximetry reading (ie: less than 92%) is indicative of hypoxia.

Another method that is often used in conjunction with pulse oximetry is to send an arterial blood gas (ABG). This involves sticking a needle into an artery (usually the radial artery in the wrist) and extracting arterial blood. It is sent to the lab and analyzed for oxygen and carbon dioxide content. In general an arterial blood gas oxygen content (aka: PaO2) of 40, 50, and 60 mmHg corresponds roughly to a pule oximetry reading of 70, 80, and 90%, respectively.

To review: clinical questions should include...

(1) How much IV fluid has the patient received?
(2) How much pain medicine has the patient received?
(3) Does the patient have known pulmonary disease (ie: emphysema)?
(4) Is there any history of thrombus (ie: blood "clots") or embolism?
(5) Any history of aspiration or vomiting?

Ancillary testing should include the following...

(1) Arterial blood gas (ABG)
(2) Chest X-ray
(3) Basic metabolic panel (BMP)
(4) Complete blood count (CBC)
(5) Electrocardiogram (ECG)
(6) Possible pulmonary embolism testing (ie: VQ scan or helical CT scan).

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Treatment

If possible, sit the patient up if they are supine. This alone can have a drastic impact on their breathing.

For patients who are mildly hypoxic (ie: high 80s and low 90s) nasal cannula oxygen is started. Sometimes this will not be enough to increase their pulse oximetry reading and more "aggressive" measures may be necessary.

The next step would be to use various facemask oxygen delivery systems. Venturi masks are connected to an oxygen source and also have valves which allow for mixing with normal air. Non-rebreather masks do not allow mixing with normal air, and therefore much higher percentages of oxgyen can be delivered (ie: FiO2).

If all else fails and the patient continues to deteriorate, intubation and mechanical ventilation become necessary.

To review the sequence for managing hypoxia:

Nasal cannula --> Venturi mask --> Non-rebreather mask --> Intubation (mechanical ventilation)

It is important to note that these steps are not always followed in this order. For example a patient may go directly from nasal cannula to intubation, especially if they are decompensating quickly!

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Overview

Hypoxia is a result of low blood oxygen content. There are numerous causes, most of which relate to heart and/or lung pathologies. Treatment consists of giving the patient oxygen either by nasal cannulae, face mask, or via mechanical ventilation. Diagnosis is based on pulse oximetry and/or arterial blood gas results. Liberal ancillary testing should be done to figure out the underlying cause of the hypoxia.

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Related Articles

- Pulmonary embolism

- Intrapulmonary percussive ventilation

- Mechanical ventilation

- Pneumothorax

- Respiratory acidosis

- Respiratory alkalosis

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References and Resources

(1) Berry CE, Wise RA. Mortality in COPD: causes, risk factors, and prevention. COPD. 2010 Oct;7(5):375-82.

(2) Pawloski DR, Broaddus KD. Pneumothorax: a review. J Am Anim Hosp Assoc. 2010 Nov-Dec;46(6):385-97.

(3) Stein PD, Matta F. Acute pulmonary embolism. Curr Probl Cardiol. 2010 Jul;35(7):314-76.

(4) Lynes D. An introduction to blood gas analysis. Nurs Times. 2003 Mar 18-24;99(11):54-5.

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The complete blood count measures the following values in blood:

(1) White blood cell count (ie: a measure of infection)
(2) Hemoglobin
(3) Hematocrit
(4) Platelets

The results of an arterial blood gas includes the following values:

(1) PaO2 (ie: the amount of oxygen dissolved in the arterial blood).
(2) PaCO2 (ie: the amount of carbon dioxide dissolved in arterial blood).
(3) pH (ie: determines if the blood is acidic or basic).
(4) HCO3 (ie: the bicarbonate level; bicarbonate is an important buffer in blood).

A basic metabolic panel includes the following components:

(1) blood glucose levels
(2) Sodium level (ie: Na)
(3) Potassium level (ie: K)
(4) Chloride (ie: Cl)
(5) Bicarbonate (ie: HCO3)
(6) Calcium (ie: Ca) - not considered part of a "chem-7".
(7) Blood urea nitrogen (ie: BUN)
(8) Creatinine