The different parts of the human body function as one unit in harmony to maintain life. In this crucial goal, the body’s mechanisms are all functioning toward achieving homeostasis or simply put, balance. Homeostasis can be best defined by explaining its two root words: homeo, which means sameness; and stasis, which means stability (Clark 2005). Using these keywords, homeostasis is described as a stable state of balance, which the human body maintains to achieve despite influences that threaten to disrupt the balanced state (Clancy, Baird, and McVicar 2002; Clark, 2005).
The nervous system and the endocrine system are the two main regulatory mechanisms in the body that maintain homeostatic balance (Clark 2005; Sherwood 2006). In order to maintain homeostasis, the body uses feedback mechanisms to respond to influencing factors that may disrupt homeostasis. These so called feedback mechanisms are categorised into either positive or negative feedback processes (Coad, Dunstall, and McCandlish 2005). This classification does not entail one as being good or bad but rather delineates the direction of change to stabilise or balance reactions.
A positive feedback mechanism acts by synergising a change inside the body causing a bigger response than the initial one (Sherwood 2006). On the other hand, a negative feedback mechanism acts in the direction opposite of the change in such a way that the initial response becomes diminished (Sherwood 2006). These feedback mechanisms are in a loop in which these mechanisms that cause the initial changes to become either greater or lesser stop when the body achieves balance.
An example of the positive feedback mechanism is when a tissue in the body becomes injured; this stimulus will signal the production of platelets for blood clotting (Coad, Dunstall, and McCandlish 2005). In this case, there is a need to increase platelet production thus the initial response will trigger more platelets to be produced to avoid further blood loss. On the other hand, a negative feedback mechanism is seen when the body experiences extreme cold – a state in which the body loses heat. In this case, the body will act in the opposite direction by producing heat through shivering, which is a state of muscle contraction that produces energy and heat for the body (Coad, Dunstall, and McCandlish 2005). Note that the direction of the feedback mechanism is dependent on the direction at which balance could be attained.
In this paper, the concepts on anatomy and physiology will be applied to discuss and explain the body’s responses. A patient will be followed during the perioperative phase. Different body responses to both internal and external influences of the patient will be discussed in terms of physiological changes and body’s attempts to maintain balance.Patient Case
The patient at focus in this paper is a 65 year old, healthy male who was scheduled for endarterectomy of common femoral artery under general anaesthesia. Endarterectomy is a surgery that is performed on individuals who manifest signs and symptoms of limb ischemia due to thickened or clogged arteries (Eskandari et al. 2010; Hands 2007). The surgical procedure is done to remove the fatty deposits or plaque in the arterial lining that occludes the normal blood flow in that area (Hands 2007). In the case of the patient, endarterectomy of common femoral artery will be done – indicating that the occluded artery is that of the common femoral artery.
The pathology of this disease lies in its occlusive nature that disrupts the normal blood flow and oxygen delivery to other parts of the body (Smeltzer et al. 2009). The pathophysiology of the patient’s condition can be likened to a water pipeline. A normal artery looks like a new pipe that allows water to flow freely through it and deliver its contents sufficiently and timely. On the other hand, when dirt and other materials stick to its walls, a blockage is formed similar to that formed by an atheromatous plaque. This impedes smooth water flow thus delivering less water and in time, it may fully block the pipe. When the blockage is removed, the water may flow normally again.
In this case, the patient needs to have the surgical procedure done to remove the cause of the occlusion in the common femoral artery; otherwise, blood flow as well as oxygen delivery will be compromised leading to vascular complications (Smeltzer et al. 2009). A dangerous complication is amputation of the limb because when there is poor blood and oxygen supply to parts especially those below the femoral artery, then the tissues will die in that limb. In the patient’s case, once the atheromatous plaque is removed, the femoral artery will be reopened thus restoring the normal blood flow in that area as well as other parts of the body (Smeltzer et al. 2009).
The benefits of common femoral artery endarterectomy for this patient will save the patient from disability and death. There will be reduced risk for stroke and heart attack because these diseases are usually caused by ischemia or lack of oxygen, which usually results from poor blood circulation from any part of the body (World Health Organization 2003: 47). Also, it provides relief of symptoms and increase rates of saving the limbs from amputation (Hoch, Turnipseed, and Acher 1999).Preliminary Assessment Stage
The patient is generally healthy. Vital signs as well as routine physical assessment and observations were performed and documented; assessment findings were normal. The client’s blood pressure is a very important measure in this pre-operative stage. Blood pressure is the measurement of the force acted upon on the arteries – which is the blood vessel that carries blood away from the heart – as the heart pumps out the blood into the different parts and systems of the body (Singh 2008).
Blood pressure readings are expressed in two numbers in which the numerator is the systolic blood pressure and the denominator is the diastolic blood pressure (Dugdale 2010). The systolic blood pressure is the pressure that the blood in the heart exerts during contraction or when the blood is moved forward (Porth and Matfin 2010). This is the highest pressure exerted when the heart beats. On the other hand, diastolic blood pressure is the pressure exerted on the heart during its resting or relaxed state (Porth and Matfin 2010). Conversely, this is the lowest or minimum pressure exerted.
The measure of the blood pressure is an indicator of the sufficiency of blood pumped out by the heart. If the blood pressure is too high, then the heart may be having hard time pushing out the blood into the system (Carter and Lewsen 2004). On the other hand, a very low blood pressure indicates insufficient output thus resulting to inadequate blood and oxygen circulation to other body parts (Carter and Lewsen 2004). These abnormalities can be attributed to different causes or factors that may affect blood pressure.
Factors affecting Blood Pressure
The three main factors that influence blood pressure are cardiac output, blood volume, and peripheral resistance (Carter and Lewsen 2004; Timby 2008). An important concept in understanding these factors is the Frank-Starling law of the heart. Starling’s law states that the amount of blood that fills and stretches the muscle fibres of the heart determines the force of heart contraction (Timby 2008). This means that a greater stretch in the heart’s muscle fibres will yield a more forceful contraction of the heart and vice versa.
Cardiac output is the amount of blood that the heart ejects from the left ventricle to the aorta per minute (Timby 2008). The higher the cardiac output, the higher the blood pressure. Conversely, a lower cardiac output leads to lower blood pressure. An important concept in understanding cardiac output is stroke volume.
Cardiac output is the product of heart rate multiplied by the stroke volume. Stroke volume is the actual amount of blood ejected by the heart every time it beats (Porth and Matfin 2010). Thus, the stroke volume is the amount of blood that is ejected during the systole or when the heart contracts. To measure the stroke volume, the end diastolic volume or the blood in the ventricle during the resting phase is subtracted with the end systolic volume or the blood that remained in the ventricle after the heart contracted (Timby 2008). If the heart contracts more forcefully, then there is a higher stroke volume because there will be more blood ejected per contraction. It also follows that when the heart is beating so fast, there is lower stroke volume because the heart is not given enough time for blood to fill and stretch its muscle fibres before it contracts again – thus less forceful contraction. Nevertheless, if either stroke volume or heart rate is increased, then the cardiac output increases.
The second factor that affects blood pressure is blood volume. This factor’s concept is also based on Starling’s law of the heart which states that the force of heart contraction is determined by the preload (Timby 2008). Preload is the volume of blood that enters the heart’s chamber and stretches its walls during its relaxed state (Timby 2008). The amount of existing blood that enters the heart determines the stretch, which consequently affects the blood pressure.
When there is little amount of blood in the vessels to begin with, then there is also little amount of blood that enters the heart thus the heart’s muscle fibres will not be stretched enough – resulting to low blood pressure. This is seen in patients who have recently lost a lot of blood such as in haemorrhage (Carter and Lewsen 2004). On the other hand, when the blood volume is increased, the blood pressure is also increased because there is a greater amount of blood that fills and stretches the heart’s muscle fibres leading to a more forceful ejection of blood into the system (Carter and Lewsen 2004).
Another factor affecting blood pressure is peripheral resistance. Peripheral resistance is the force that the heart needs to overcome in order for it to push blood into the system (Timby 2008). When there is greater peripheral resistance, the heart works harder to push the blood leading to a higher blood pressure. This occurs in conditions when the artery is either too narrow or obstructed (Timby 2008). On the other hand, a diminished peripheral resistance leads to a lower blood pressure because the heart needs to overcome very little resistance to eject blood into the system (Carter and Lewsen 2004; Timby 2008). This occurs when the blood vessel is dilated.Intraoperative Assessment Stage
When the patient was transferred to the anaesthetic room, he was very nervous and his blood pressure, respiratory rate, and heart rate increased above normal limits. These manifestations are responses of his body to the perceived stress, which is the upcoming surgery. The stress response is the general adaptation responses produced by the body as it perceives stress (Martini 2005).
Stress is any stimulus, both positive and negative, that may disrupt the body’s homeostasis (Martini 2005). It may be psychological such as joy of seeing one’s loved one, or physical such as exhaustion from a strenuous exercise. Stress serves as an information or signal to stimulate the hypothalamus, which in turn responds by activating the autonomic nervous system’s sympathetic division.
The activation of the sympathetic division causes the adrenal gland to produce adrenaline and noradrenaline – also known as epinephrine and norepinephrine, respectively –as it works with the sympathetic nervous system (Martini 2005). When these hormones are released into the bloodstream, the sympathetic response is increased and prolonged. These hormones cause the blood pressure, pulse rate, and breathing to increase (Timby 2008). This reaction is the fight or flight response that occurs every time the body is faced with stress, which counteracts the parasympathetic division’s maintenance of the resting state (Martini 2005).
Other effects of these hormones in the body include dilatation of the pupil and inhibition of the salivary glands (Porth and Matfin 2010). Glucose secretion from the liver is also stimulated as well as epinephrine and norepinephrine release from the kidneys – which has been discussed to intensify the sympathetic response (Porth and Matfin 2010). Vasoconstriction occurs in the blood vessels and stimulation of the sweat glands cause perspiration (Porth and Matfin 2010). This peripheral vasoconstriction draws the blood away from the digestive tract thus decreasing or inhibiting digestion (Porth and Matfin 2010).
Effects of Pharmacologic Agents
In the anaesthetic room, the patient was given different medications. The following are the medications given to the patient and their respective effects on the patient’s body.
The patient was given 50 mg of Fentanyl. This drug belongs to a class of opioid analgesics or opioid anaesthetics (Deglin and Vallerand 2008). It is given to the client to supplement the anaesthetic agent that will be administered to decrease pain (Deglin and Vallerand 2008). As a premedication before inducing anaesthesia, fentanyl is usually given intramuscularly at a dosage of 50 to 100 mcg (Deglin and Vallerand 2008). Its mechanism of action is binding to opiate receptors in the central nervous system wherein they increase the action of eukephalins and endorphins by mimicking the effects of these opioid peptides (Deglin and Vallerand 2008). Endorphins are commonly known as the happy hormone because it produces pain relief and feelings of pleasure. Similarly, fentanyl creates a similar effect that results to alteration of feeling and responding to pain (Deglin and Vallerand 2008).
The adverse effects of the drug include bradycardia, depression of the central nervous system, hypotension, and increased intracranial pressure (Deglin and Vallerand 2008). Fatal effects include respiratory depression, laryngospasm, and bronchoconstriction (Deglin and Vallerand 2008). These adverse and fatal effects are related to its main effect on the body, which is depression of the central nervous system. Because of its possible life-threatening effects, special precautions are taken when administering the drug to patients with respiratory diseases and problems with the central nervous system.
Propofol was administered in the patient to achieve anaesthetic induction. Propofol is a short-acting sedative and hypnotic (Deglin and Vallerand 2008). In combination with the effects of fentanyl, this drug allows induction and maintenance of a balanced anaesthesia thus producing an analgesic effect with amnesia. On its own, propofol does not produce any analgesia and requires the supplementation of a narcotic for pain relief (Deglin and Vallerand 2008). Similar with fentanyl, propofol depresses the central nervous system. It decreases the blood pressure as well as intracranial pressure (Finkel et al. 2008).
When the patient is on propofol, one of the most important adverse reactions to watch out for among many others is apnea (Deglin and Vallerand 2008). The occurrence of apnea upon anaesthetic induction by propofol is fatal. This drug can cause significant depression of the respiratory system leading to a period of breathing cessation that can last for several minutes (Finkel et al. 2008). This is life-threatening as it can significantly diminish the oxygen supply of the patient that can lead to hypoxia if no oxygen support is given.
Vecuronium (Muscle Relaxant).
Vecuronium is a muscle relaxant indicated to facilitate endotracheal intubation and to relax the skeletal muscles during surgical operations (De Jong and Karch 2000). It belongs to the drug class non-depolarising neuromuscular blocking agent (De Jong and Karch 2000). Muscle relaxants are usually given after the general anaesthetic agent has been administered. Aside from aiding in anaesthesia, this drug was administered in the client to facilitate his intubation in preparation for surgery and to control ventilation.
This drug acts by blocking the neuromuscular transmission thereby paralysing the body and inhibiting muscle contractions produced by acetylcholine (De Jong and Karch 2000). Once muscle relaxation is achieved, the jaw and the larynx become relaxed that makes it easier to insert the endotracheal tube with the least resistance because the gag reflex has already been suppressed (De Jong and Karch 2000). Aside from this, the total muscle relaxation would allow undisturbed tissue handling during the surgical operation.
Nitrous Oxide and Isoflurane.
Blood pressure was monitored by means of an arterial line inserted into the patient’s radial artery. This provides constant and accurate measurements of his systolic, diastolic and mean arterial pressure. Anaesthesia was maintained using a combination of oxygen nitrous oxide and isoflurane.
Isoflurane is an inhalational anaesthetic agent that is used for maintenance of a balanced anaesthesia (Aschenbrenner and Venable 2008). This drug is commonly administered with nitrous oxide and has a rapid onset of action within 7 to 10 minutes (Aschenbrenner and Venable 2008). Because of its bad odour, administration of the inhalant anaesthetic is slow to prevent coughing and holding of breath.
Isoflurane depresses the respiratory system thus respiratory depression is one of its adverse and fatal effects. Increase in dosage administration of this drug causes the tidal volume and respiratory rate to decrease (Finkel et al. 2008). Moreover, isoflurane relaxes the muscles and produces peripheral vasodilation, which causes increased blood flow to the coronary vessels (Finkel et al. 2008).
Nitrous oxide is an inhalation anaesthetic as well. However, it differs from isoflurane in such a way that it does not produce muscle relaxation thus providing incomplete anaesthesia (Finkel et al. 2008). Nevertheless, it is a good analgesic and has a similarly rapid onset of action and recovery. Nitrous oxide decreases the required concentration of isoflurane that need to be inhaled to produce a preferred level of anaesthesia (Finkel et al. 2008). The combination of these two gases aids in the maintenance of a balanced anaesthesia in the patient’s surgery.
During the procedure, the observations remained stable with some exceptions; when the femoral artery was clamped, the cardiac output, blood pressure, and heart rate increased. In addition, there were some changes in the tissues below the clamp due to lack of blood supply and oxygen. These changes can be attributed to the altered blood flow and oxygen delivery.
First, the hemodynamic status of the client changed because blood flow was impeded at the level of the femoral artery and below. When the artery is blocked, the peripheral resistance increases because there is a greater load systemically. As previously discussed in the earlier sections on factors affecting blood pressure, a stronger peripheral resistance will lead to an increased blood pressure because there is a greater resistance that the heart needs to overcome to pump out the blood systemically (Timby 2008).
Also, the presence of a clamped femoral artery will trigger the activation of the sympathetic nervous system as it is under stress. When the sympathetic division is activated, the heart beats faster leading to an increased heart rate (Porth and Matfin 2010), which is seen in the patient. Similarly, cardiac output increases because it is directly related to the measure of heart rate. Since cardiac output is the product of heart rate and stroke volume, when either of the two factors increase, cardiac output also increases.
Second, tissue changes were noted below the clamp because of the poor oxygen supply to this area. When the femoral artery was clamped, the flow of blood below that area also stops because arteries are the blood vessels that carry oxygen-filled blood away from the heart into other parts of the body (Porth and Matfin 2010). Since there is no blood supply below the clamp, there will also be no oxygen supply because blood transports oxygen. When there is no oxygen, the tissue will die and the earliest signs of compromised oxygenation that could lead to tissue death include discoloration of the area (Porth and Matfin 2010).
About 1000 mL of blood was lost by the patient during the surgery that required blood transfusion. Blood transfusions are performed to people who had massive blood loss similar to the case of the patient. Also, blood transfusions are indicated for patients who undergo major operations because they would really lose a lot of blood because their skin and tissues will be injured during the operation (Ashalata 2006). During blood transfusion, lost blood is re-infused to the patient thus providing an active means to support and maintain homeostatic fluid balance in the patient’s body. Normally, the total blood volume of an adult person is 5600 mL (Ashalatha 2006). In the patient’s case, he lost approximately 18% of his blood. To restore the blood volume to the normal level, blood transfusion is done because the body on its own cannot cope with this big loss.Conclusion
The concepts of anatomy and physiology are very important in understanding the changes in the body and its attempts to maintain homeostasis. When there is a change in the body that threatens to disrupt the balance, the body responds in a way to bring back the body to its normal state. In the case of the patient, disruption of homeostasis started with an atheromatous plaque in the artery that occludes normal blood flow. Since the body can no longer restore the artery to its normal state, endarterectomy of the common femoral artery was done to resolve this. Before, during, and after the operation, the body experienced many changes both from internal and external influences. In these changes, the body was in an active state of action toward maintaining homeostasis.List of References
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