nitric oxide gas

Action and Spectrum

Actions and Spectrum: 

Actions 

• Vasodilation: One of the most critical roles of nitric oxide is its function as a vasodilator. It relaxes and widens blood vessels, increasing blood flow and improving oxygen and nutrient delivery to tissues and organs. 
• Neurotransmission: nitric oxide is a signaling molecule in the nervous system. It plays a role in the communication between neurons, contributing to various processes such as learning and memory. 
• Immune response: NO is involved in the body’s immune response, particularly in fighting pathogens and regulating inflammation. 
• Platelet aggregation: nitric oxide helps prevent excessive blood clotting by inhibiting platelet aggregation and adhesion, thus reducing the risk of thrombosis. 
• Erectile function: In the male reproductive system, nitric oxide is essential for penile erection. It relaxes the smooth muscles in the penile blood vessels, allowing increased blood flow and causing an erection. 
• Mitochondrial respiration: NO interacts with the electron transport chain in mitochondria, influencing cellular respiration and energy production. 
• Neuroprotection: nitric oxide protects nerve cells from damage and promotes neural regeneration. 
• Antioxidant activity: At low concentrations, nitric oxide can act as an antioxidant, helping to protect cells from oxidative stress. 

Spectrum: 

nitric oxide gas has both beneficial and harmful effects, depending on its concentration and context: 

• Beneficial effects: As mentioned above, nitric oxide’s vasodilatory and neurotransmitter roles are essential for various physiological processes. It also contributes to the immune response, cell signaling, and other essential bodily functions. 
• Harmful effects: At high concentrations, nitric oxide can become toxic. It can react with superoxide radicals to form peroxynitrite, a highly reactive and damaging species. Peroxynitrite can lead to oxidative stress, cellular damage, and inflammation. Excessive nitric oxide production is associated with various diseases, including septic shock, inflammatory conditions, and neurodegenerative disorders. 
• Environmental impact: In the environment, nitric oxide contributes to air pollution and forms nitrogen oxides (NOx) when reacting with oxygen and other pollutants. NOx is a precursor to harmful secondary pollutants like ozone and particulate matter, which can adversely affect air quality and human health. 

Drug Interaction

Adverse Reaction

Frequency defined 

>10% 

Withdrawal (12%) 

Hypotension (13%) 

1-10% 

Atelectasis (9%) 

Infection (6%) 

Cellulitis (5%) 

Hematuria (8%) 

Hyperglycemia (8%) 

Sepsis (7%) 

Stridor (5%) 

Frequency not defined 

Seizure 

Methemoglobinemia 

Intracranial hemorrhage 

Hematuria 

Acute lung injury 

Pulmonary hemorrhage 

Pulmonary edema 

Black Box Warning

Black Box Warning: 

None 

Contraindication / Caution

Contraindication/Caution: 

Contraindications: 

• Pulmonary hypertension 
• Hypersensitivity 
• Inhaled anesthetics 
• Certain medications 
• Hemodynamic instability 

Cautions: 

• Methemoglobinemia 
• Oxygenation monitoring 
• Lung compliance 
• Nitrogen dioxide production 
• Rebound pulmonary hypertension 
• Pregnancy 
• Lactation 

Pregnancy / Lactation

Pregnancy consideration:  

Limited data is available; risk is increased in pregnant females if nitric oxide is inhaled. 

Breastfeeding warnings:  

nitric oxide and its metabolites are excreted in the breast milk. 

Pregnancy category: 

Category A: well-controlled and satisfactory studies show no risk to the fetus in the first or later trimester. 

Category B: there was no evidence of risk to the fetus in animal studies, and there were not enough studies on pregnant women. 

Category C: there was evidence of risk of adverse effects in animal reproduction studies, and no adequate evidence in human studies must take care of potential risks in pregnant women.    

Category D: adequate data with sufficient evidence of human fetal risk from various platforms, but despite the potential risk, and used only in emergency cases for potential benefits.    

Category X: Drugs listed in this category outweigh the risks over benefits. Hence these categories of drugs need to be avoided by pregnant women.    

Category N: No data is available for the drug under this category. 

Pharmacology

Pharmacology:  

nitric oxide (NO) inhalation is a medical treatment used primarily in the management of certain respiratory conditions, particularly in neonates with persistent pulmonary hypertension (PPHN) and acute respiratory distress syndrome (ARDS) in adults. It works as a potent vasodilator and has a selective effect on the pulmonary circulation, improving oxygenation and reducing pulmonary artery pressure.  

Pharmacodynamics: 

• Vasodilation: Inhaled nitric oxide acts as a potent vasodilator in the pulmonary circulation. When inhaled, NO diffuses into the smooth muscle cells of the pulmonary arteries, activating the enzyme guanylate cyclase. This activation leads to an increase in the production of cyclic guanosine monophosphate (cGMP). Elevated cGMP levels cause relaxation of smooth muscle cells, resulting in vasodilation of the pulmonary vasculature. The vasodilation reduces pulmonary artery pressure, improving blood flow through the lungs and better oxygenation. 
• Selective Pulmonary Vasodilation: One of the unique features of inhaled nitric oxide is its selective effect on pulmonary circulation. Unlike many other vasodilators, NO has a more significant impact on the blood vessels in the lungs than the systemic blood vessels. This selectivity is crucial as it helps to improve pulmonary blood flow and oxygenation without causing widespread systemic hypotension. 
• Oxygenation Improvement: By dilating pulmonary blood vessels, inhaled NO improves blood flow to well-ventilated lung areas, leading to better matching of ventilation and perfusion. This results in enhanced oxygenation of the blood and improved gas exchange in the lungs. 
• Short Duration of Action: Inhaled nitric oxide has a short duration of action, as it is rapidly metabolized and inactivated in the body. This characteristic makes it suitable for use as an acute treatment rather than a chronic therapy. 
• Lack of Systemic Effects: Due to its selective pulmonary vasodilation, inhaled NO has minimal impact on systemic blood pressure. This feature is advantageous, especially in critically ill patients, as it avoids compromising blood flow to vital organs. 
• Tolerance and Rebound Hypertension: Some patients may develop tolerance to inhaled NO with prolonged use, leading to reduced responsiveness. Additionally, upon discontinuing nitric oxide therapy, a rebound increase in pulmonary artery pressure can occur, which requires careful monitoring and management. 
• Methemoglobinemia Risk: Inhaled NO can interact with hemoglobin in the blood, forming methemoglobin. Methemoglobin cannot effectively transport oxygen, potentially resulting in reduced oxygen-carrying capacity. To avoid adverse effects, monitoring methemoglobin levels is essential during nitric oxide therapy. 

Pharmacokinetics: 

Absorption 

Inhaled nitric oxide is rapidly absorbed from the lungs’ alveoli into the bloodstream. As a gas, it quickly diffuses across the alveolar-capillary membrane and enters the pulmonary circulation. The absorption is almost instantaneous upon inhalation.  

Distribution 

Once absorbed into the bloodstream, nitric oxide, including the pulmonary vasculature, is distributed throughout the body. However, due to its high reactivity and short half-life, inhaled NO has a selective effect on pulmonary circulation, causing vasodilation primarily in the lungs.  

Metabolism 

In the body, nitric oxide rapidly reacts with hemoglobin in red blood cells to form nitrite and methemoglobin. nitric oxide can also react with oxygen and superoxide to form reactive nitrogen species. These metabolic processes contribute to the rapid inactivation and elimination of nitric oxide from the circulation.

Elimination and Excretion 

nitric oxide is excreted by exhalation from the lungs. The metabolites are excreted in the urine. 

Adminstartion

Administration: 

nitric oxide is inhaled, typically using a ventilator or mechanical ventilation system. It is mixed with oxygen and delivered to the patient through an endotracheal tube or breathing circuit. The nitric oxide concentration in the inhaled gas mixture is usually measured in parts per million (ppm). 

Patient Information Leaflet

Patient information leaflet 

Generic Name: nitric oxide gas 

Pronounced as: nai-truhk awk-side gas 

Why do we use nitric oxide gas? 

nitric oxide (NO) gas is primarily used for medical purposes due to its vasodilatory properties and selective effect on pulmonary circulation. Inhaled nitric oxide is a potent vasodilator that causes relaxation of the smooth muscles in the pulmonary arteries.

This selective vasodilation primarily affects the blood vessels in the lungs, leading to a decrease in pulmonary artery pressure. As a result, blood flow through the lungs is improved, and oxygenation of the blood is enhanced.