A Review of the Cardiovascular and R I S Respiratory Systems

A Review of the Cardiovascular and RiRespiratory Systems The Heart

• ..is a four chambered pump that cilirculates bloo d throughout the body • At rest the heart beats about 72 beats per minute (BPM) (men), 80 BPM (women) • Our pulse increases when we are nervous, fearful (tachycardia) • A pulse greater than 100 BPM is considered rapid Pulse Baseline

• The pulse is the only vital sign to change (tachycardia) when a patient experiences an adverse reaction to nitrous oxide, • Unless you have a baseline, you will not know if they have tachycardia, so ... • A patient’ s normal pulse should be part of your examination. Practice Taking a Pulse

• Place the patient’s left palm face up • Firmly but gently place two fingers on wrist blbelow the thhbumb • Count the pulse for 15 seconds • Multiply by 4 hemoglobin

• Our body uses oxygen as fuel and gives off carbon dioxide (co2) as a biproduct • HlbiHemoglobin, a component of red blood cells, carries oxygen to the cells • Oxygen rich hemoglobin is called “oxyhemoglobin” and is “red”. • Oxygen depleted hemoglobin or “reduced hemoglobin” is slightly blue. Blood Flow

• Reduced hemoglobin returns to the right side of the heart via the superior vena cava • It is pumped to the lungs via the pulmonary artery where it is oxygenated (converted to oxyhemoglobin) • Oxyhemoglobin returns to the left side of the heart via the pulmonary vein and is pumped to the body via the aorta Measuring Oxygen

• A pulse oximeter measures blood oxygenation by analyzing the blood color • If the amount of oxyhemoglobin falls too low, (ie, the blood is too blue) an alarm can go off. • Breathing inadequate levels of oxygen, a condition called hypoxia will decrease oxyhemoglobin, • Under certain circumstances, high levels of nitrous oxide can cause hypoxia ASA recommendation

• The American Society of Anesthesiologists recommends that dentists who routinely give nitrous oxide in concentrations 50% or higher use a pulse oximeter! • It’s not the law but if you d’don’t fllfollow the recommendation and you have a legal problem, chances of winning decrease! The Air We Breathe • Room air contains 21% oxygen, 78% nitrogen, .03% carbon dioxide. • Cells use oxygen for fuel, give off carbon dioxide as a biproduct. Plants use carbon dioxide as fuel source and give off oxygen as a biproduct. • Nitrogen is inert –has no known ftifunction • What Makes Us Breath?

• In healthy individuals, carbon dioxide (CO2) sensors in the bibrain didrive ilinvoluntary bhibreathing, so normally we breathe to reduce CO2 in our bodies, • A backup system, the carotid body, measures the amount of oxygen in the blood. • The carotid body drives involuntary respiration in patients with COPD, emphysema, • Why is this important?.. • A healthy runner breathes faster to give off more CO2, • ..But a person with emphysema breathes faster to take in more oxygen! • Remember this when treating emphysema patients, because.. • You are giving them lots of oxygen so their carotid body is happy and may say “you can stop bhbreathing now.” Not a good thing!! Respiration Anatomy

• A breath occurs when the diap hragm contttracts and relaxes, • The lungs enlarge when the diaphragm contracts, pulling air into lungs, • When the diaphragm relaxes, the lungs relax, forcing air out of the lungs. • At rest, an adult takes 14 – 20 breaths per minute (BPM) at rest, a child breathes a little faster • Air moves from trachea, to the bronchus, to the bronchioles, and finally to the alveolar sacs where diffusion takes place.

Alveolar sacs • Alveolar sacs resemble a cluster of grapes, • There are 300 million alveolar sacs in human lungs • Alveolar sacs are surrounded by blood vessels. • Components of air pass through the walls of the alveolar sacs into blood by the process of “diffusion” and are carried throughout body. What is Diffusion?

• “Diffusion” is the movement of gas across a membrane. • Movement occurs from an area of hhhigh pressure to an area of

low pressure until the pressure is OXYGEN equal on both sides. OXYGEN • With respiration, the wall of the alveolar sac is the membrane that oxygen (and nitrous oxide ) crosses. Alveolar Sacs Under A Microscope

Red Blood Cells

Alveolar sacs

Gases we breathe diffuses through the wall of the alveolar sacs. Remember, there are 300 million of these! • During inspp,iration, air (oxygen and nitrogen) enters the alveolar sacs. • Oxygen diffuses into blood and attaches to hemoglobin • Nitrogen diffuses iitnto bloo d but combines with nothing. • During expiration, carbon CO2 dioxide enters the alveolar N sacs and is exhaled. O2 So, what happens to the nitrogen?

• After entering the bloodstream, nitrogen leaves the bloodstream quickly because it is fairly insoluble in blood. • It diffuses into body cavities like sinuses, the middle ear, the intestines, the cranium, etc. • It does so until the pressure of nitrogen in the cavity is the same as in blood. • If I looked in your middle ear right now, I’d find a lot of nitrogen! What happens when we administer N2O ?

• Nitrogen is replaced with N2O, so the nitrogen gas pressure in the lungs decreases, causing.. • Nitrogen to diffuse from the blood into the lungs to be exhaled, causing.. • A drop of nitrogen pressure in the blood, N causing.. N2O • Nitrogen in the body O2 cavities to diffuse back into the blood. • Nitrous oxide is even less soluble in blood than nitrogg,en, therefore..

• N2O enters body spaces faster than nitrogen leaves, • The net result is an increased pressure in the body space! • Patients may feel ear, sinus head pressure, so warn them! It’s only temporary. Respiration Terms To Know

• Tidal volume • Inspiratory reserve volume • Expiratory reserve volume • Residual volume • Total lung capacity Tidal Volume

• ..is the amount of air inhaled and exhaled during normal respirations • For adldults, tiddlal volume is normally 6 –8 liters per minute • For children, tidal volume is 4‐6 liters per minute • Nitrous oxide eqqpuipment (the flowmeter) can measure tidal Flowmeter measures volume in liters per minute. liters per minute of gas flow Inspiratory Reserve Volume

..is the additional amount of air ihldinhaled ddiuring maximum inhalation (like smelling a flower) • The effec t of a maximum inhalation is to increase the concentration of any substance inhaled. • However, a maximum inhalation interrupts normal respiration, and breathing pauses. Take a Deep Breath • Take a deep breath and see if you don’t pause normal breathing for a few seconds • Patients receiving nitrous oxide may take deep breaths to experience more euphoria. • However, after a deep breath, they pause , and nitrous oxide concentrations drop, • The result is an “up and down” effect, like a roller coaster. Roller Coaster Effect • Patients sometimes say nitrous oxide makes them nauseated, • Abnormal breathing patterns may be the problem, • tell your patients to breath normally to avoid the “roller coaster” effect and the resulting consequences! Other Respiratory Terms

Exppyiratory reserve volume: The additional air exhaled during maximum exhalation Residual Volume: air remaining after maximum exhalation Total lung capacity: total amount of air lungs can hold Total Lung Capacity

• Individuals with a large total lung capacity (Athletes, exercise enthusiasts, etc,) receive a higher dose of nitrous oxide per body weight, • CidConsider a lower percentage of nitrous oxide for such patients. Establishing Equilibrium

• When administering nitrous oxide, the gas passes from the lungs to the blood and then to body cavities including the cranium where it produces its effects, • This process continues until the partial pressures of N2O in the lungs, blood and body cavity are the same. • Equal pressure in all three is called “equilibrium” and occurs within one to two minutes. Establishing CORRECT equilibrium

• When administering nitrous oxide, allow equilibrium to be reached before titrating (increasing or decreasing) more nitrous oxide • If you do not allow equilibrium to be reached with each increase in dose, you may exceed the comfort level of the patient. What happens when N2O is terminated? • When nitrous oxide is terminated, the partilial pressure in the lungs drops and N2O rapidly diffuses out of blood, filling the lungs with N2O. • Oxygen content in lungs may be decreased because so much nitrous oxide fills the lungs, • This condition is called “diffusion hypoxia” • The syypmptoms of diffusion hypoxia can be headache, hallucinations, nausea. Diffusion Hypoxia • Research disputes whether diffusion hypoxia can occur with N2O/O2 analgesia, nonetheless.. • To avoid the possibility of diffusion hypoxia, terminate N20 slowly, then post oxygenate for 3 –5 minutes