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Respiratory System And Sepsis

What is Sepsis?

Sepsis is the body’s overwhelming and life-threatening response to infection. It can lead to tissue damage, organ failure, and death. It is a medical emergency that requires rapid diagnosis and treatment. Sepsis can lead to severe sepsis and septic shock.

Symptoms of Sepsis

The main symptoms of sepsis includes abnormal body temperature, some signs of infection, confused state of mind and shortness of breath. Sepsis can be triggered by an infection in any part of the body including the lungs and kidneys.

Systems affected by Sepsis

The common organs that fail during sepsis include the following:

Lungs (Respiratory System)

Heart , blood vessels and arteries (Cardiovascular System)

Kidneys (Renal System)

Brain (Neurologic System)

In this blog, we will discuss the analysis of the respiratory system parameters in relation to sepsis. We are taking hospital dataset for analysis on Tableau. This dataset has a total of 40,336 out of which there are 2,932 sepsis patients and 37,404 non sepsis patients (which includes 2,506 onset sepsis patients).

Lungs (Respiratory System) in relation to Sepsis

Breathing becomes very hard with sepsis. The oxygen levels fall in sepsis patients and they usually need oxygen therapy. Patients with severe sepsis can develop Acute Respiratory Distress Syndrome (ARDS). ARDS patients frequently need more support, such as a mechanical ventilator (breathing machine).

Here are the list of the parameters that we would be discussing in this blog.

1. Oxygen Saturation:

Oxygen saturation is a vital element of patient care. Oxygen is strongly regulated within the body because hypoxemia can lead to numerous acute harmful effects on individual organ systems (brain, heart, and kidneys). Oxygen saturation is a measure of how much hemoglobin (Hb) is currently bound to oxygen compared to amount of unbound hemoglobin. At the molecular level, Hb contains four globular protein subunits. Each subunit is linked with a heme group. Each hemoglobin molecule subsequently has four heme-binding sites quickly available to bind oxygen. Hence, during the oxygen transport in the blood, hemoglobin is capable of carrying up to four molecules of oxygen. Due to the critical nature of tissue oxygen consumption in the body, it is very important to monitor existing oxygen saturation.

Normal levels of Oxygen Saturation

Normal levels of oxygen saturation is between 95 and 100%. A below-normal blood oxygen level is called hypoxemia. The lower the oxygen level, the more severe the hypoxemia. The O2Sat reading below 95 percent is considered low.

Measurement of Oxygen Saturation

Oxygen Saturation is measured by two methods:

1. Non Invasive Method (SpO2)

A simple pulse oximeter can measure the oxygen saturation . It is a noninvasive device placed over patient’s finger. It measures light wavelengths to establish the ratio of the existing levels of oxygenated Hb to deoxygenated Hb.

In the hospital dataset, simple bar graphs were used to analyze the number of sepsis patients and patients developing sepsis in ICU with normal and low oxygen saturation levels. Approximately 33% of sepsis patients and 43% of onset sepsis patients had low oxygen saturation indicating hypoxia during sepsis and immediately prior to development of sepsis.

2. Invasive Method (PaO2)

A PaO2 test measures partial pressure of oxygen —the oxygen pressure in the arterial blood. PaO2 indicates how well oxygen is able to move from the lungs to the blood. The PaO2 is one of the components measured in an Arterial Blood Gas (ABG) analysis. The normal levels are 94-99% and below 90% are considered under-oxygenated and below 70% is usually fatal.

PaO2 was performed on a very few patients as it is an invasive and expensive test in comparison to pulse oximetry. Analysis of hospital dataset showed that 31% of sepsis patients and 37.9% of onset sepsis patients had lower oxygen saturation levels by this method.

2. Fraction of Inspired Oxygen:

Fraction of Inspired Oxygen (FiO2) is the volumetric fraction of oxygen in the inhaled gas. When the oxygen saturation decreases in the patients, they are provided with oxygen-enriched air. The natural air contains 21% oxygen (Fi02 is 0.21). Oxygen-enriched air has FiO2 higher than 0.21 and up to 1.00 (which means

100% oxygen). In sepsis, there is an increase in oxygen demand and therefore oxygen enriched

air is given to some patients depending on their oxygen levels.

Patients were grouped according to their FiO2 levels. Analysis of the hospital dataset showed that 33.8% of sepsis and 42.7% of Onset Sepsis patients required more than 50% oxygen. Majority of the patients required oxygen enriched air with highest in the group of 21-50% FiO2 levels. This implies that in sepsis and patients developing sepsis in the ICU have affected respiratory system that causes hypoxia and thus have need for supplemental oxygen.

3. Ratio of P/F

PaO2/FiO2 ratio is the ratio of arterial oxygen partial pressure (PaO2 in mmHg) to fractional inspired oxygen (FiO2 expressed as a fraction, not a percentage. At sea level, the normal PaO2/FiO2 ratio is ~ 400-500 mmHg . P/F ratio is a widely used clinical indicator of hypoxemia. Research shows that ratio below 300 showed high specificity for mortality in sepsis patients.

Hospital dataset analysis showed that maximum number of sepsis and onset sepsis patients had a ratio below 400 indicating hypoxemia.

4. Respiratory Acidosis and Alkalosis

A crucial property of blood is its degree of acidity or alkalinity. The acidity or alkalinity of blood is indicated on the pH scale.

Normal blood pH: 7.35 – 7.45

pH > 7.45 indicates alkalinity

pH <7.35 indicates acidity

Every organ system of the human body depend on pH balance; however, the renal system and the pulmonary system are the two main modulators. The pulmonary system adjusts pH using carbon dioxide; upon expiration, carbon dioxide is projected into the environment. Due to carbon dioxide forming carbonic acid in the body when combining with water, the amount of carbon dioxide expired can cause pH to increase or decrease.

Respiratory Acidosis and Alkalosis is calculated by measuring the blood pH, Partial pressure of carbon dioxide (PaCO2) and Bicarbonate (HCO3).

Respiratory Regulation of Acid-Base Balance


Respiratory Acidosis

Respiratory acidosis is a condition that occurs when the lungs cannot remove all the carbon dioxide the body produces. This causes the blood to become too acidic and disrupts their body's acid-base balance.


Respiratory Alkalosis

Respiratory Alkalosis is a condition marked by a low level of carbon dioxide in the blood due to breathing excessively.


Analysis of Respiratory Acidosis and Alkalosis from Hospital DataSet

A total of 64 sepsis patients from the entire dataset had acid base disturbance contributed by the lungs. Of these 64 patients, 45 patients had respiratory acidosis and 19 patients had respiratory alkalosis.


In this blog we have discussed the relation between respiratory parameters and sepsis. The lung is an important identified organ to fail in sepsis and is also very common primary site of infection. Hope this blog provides an insight in this area and aids in further research. Thanks for reading!



  2. The lung in sepsis: guilty or innocent? Endocr Metab Immune Disord Drug Targets. 2006 Jun;6(2):213-6. E L V Costa 1, I A L Schettino, G P P Schettino

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