Hypoxia: An H&T Reversible Cause of Cardiac Arrest
Regardless if a pulseless patient is in a shockable or non-shockable rhythm, as we run a code we’ll consider possible reversible causes of cardiac arrest. To make things a bit “simpler” to remember than a rote list, the reversible causes are frequently referred to as Hs & Ts. Hypoxia is one of the easiest reversible H&T causes of cardiac arrest to identify and treat, and is today’s Pass ACLS tip topic.
Identifying Hypoxia
Hypoxia is a state of low oxygen levels in the blood. Patients with an O2 sat less than 90% on an accurate pulse ox or a PaO2 less than 80 mm Hg are hypoxic and should be started on Oxygen.
A goal of ACLS is to recognize signs of hypoxia and provide timely treatment to prevent an arrest. In-hospital providers should follow their policy, the treating physician’s orders, or call for assistance from a specialized code or rapid response team. The use of specialized, rapid-response teams has been shown to improve patient outcomes by early identification & treatment of deteriorating patients.
Some things that might lead us to think of hypoxia as a cause of cardiac arrest include: asthma, COPD, CHF, narcotics overdose, or being trapped in a confined space. There are others as well.
A pulse ox is not an effective method for measuring oxygen saturation during a cardiac arrest. This is because pulse oximetry relies on adequate circulation through a peripheral capillary bed and that doesn’t happen during cardiac arrest; even with the best CPR. Arterial blood gasses (ABGs) is a more reliable way to assess oxygenation during CPR.
Hypoxia Treatment Actions
We correct hypoxia by delivering 10 ventilations/min with near 100% oxygen concentration using a BVM attached to supplemental O2 at 10-15 L/min and using a reservoir. Early in the code this is done by giving 2 breaths after every 30 compressions. After an advanced airway is placed, we will give one breath every six seconds without stopping compressions.
If we’re using end tidal CO2 waveform capnography, good CPR should produce a peak wave of at least 10 mm Hg.
Small changes to the ventilation rate, tidal volume, or O2 concentration can have significant effects on a patient’s oxygen, carbon dioxide, and pH. For this reason, we should not ventilate a patient more than 12 times a minute without blood gas testing that confirms hypoxia or hypercarbia. We must be careful to avoid excessive ventilation which can decrease effectiveness of CPR by increasing intrathoracic pressure. Increased pressure can compress the vena cava resulting in decreased return of blood to the heart.
