Organ perfusion depends on mean arterial pressure.
All are true regarding mean arterial pressure except:

Choice A rationale

In a closed chest-drainage system, the water-seal chamber acts as a one-way valve allowing air to exit the pleural space but not enter. While intermittent bubbling during expiration or coughing is normal as air is expelled from a pneumothorax, constant bubbling is not normal. Constant bubbling indicates that air is continuously entering the system from a source other than the patient's pleural space, suggesting a mechanical failure rather than a normal physiological functioning of the device.

Choice B rationale

If a patient has a pneumothorax, air will escape into the water-seal chamber, causing bubbling. However, this bubbling should only occur when the patient exhales or increases intrathoracic pressure. As the lung re-expands and the pneumothorax resolves, this intermittent bubbling will eventually stop. Constant, non-stop bubbling is rarely just the result of a simple pneumothorax and usually points toward a breach in the integrity of the drainage tubing or the chest tube insertion site itself.

Choice C rationale

An obstruction in the chest tube, such as a kink or a clot, would actually prevent air or fluid from reaching the drainage system. This would result in a lack of tidaling (the normal rise and fall of water with respiration) and an absence of any bubbling. Therefore, constant bubbling is the opposite of what would be observed if the system were obstructed. Obstructions are dangerous because they allow pressure to build up in the pleural space, potentially leading to a tension pneumothorax.

Choice D rationale

Constant bubbling in the water-seal chamber is a classic sign of an air leak within the drainage system. This leak can be located at the insertion site, within the tubing connections, or within the drainage unit itself. The nurse should systematically clamp the tube momentarily starting near the dressing to locate the source. If the bubbling stops when clamped at the chest, the leak is at the exit site or inside the patient; otherwise, it is in the external equipment.

Choice A rationale

Supraventricular tachycardia (SVT) is characterized by a regular, very rapid heart rate that typically exceeds 150 beats per minute. In SVT, the P waves are often buried in the preceding T waves because the rate is so fast that the electrical activity overlaps. While this rhythm involves a rapid rate, it does not match the specific criteria for SVT if the rate is lower or if distinct P waves are clearly visible before every QRS complex.

Choice B rationale

Normal sinus rhythm (NSR) is the standard electrical activity of the heart, originating from the sinoatrial node. It must have a regular rate between 60 and 100 beats per minute in an adult. Each QRS complex must be preceded by a normal P wave with a consistent PR interval. If the rate exceeds 100 beats per minute, it no longer meets the definition of NSR and must be classified as a tachycardia, even if all other waves look normal.

Choice C rationale

Sinus tachycardia is defined as a sinus rhythm with a heart rate greater than 100 beats per minute in an adult, typically ranging from 101 to 180 beats per minute. It maintains a regular rhythm where each QRS complex is preceded by a visible P wave, indicating the sinoatrial node is still the primary pacemaker. This occurs due to increased sympathetic stimulation, exercise, fever, or pain, reflecting a normal physiological response to various stressors on the body.

Choice D rationale

Bigeminy is a specific type of arrhythmia characterized by a repeating pattern where every second beat is a premature contraction, most commonly a premature ventricular contraction (PVC). This results in a "grouped beating" appearance on the EKG strip rather than a continuous, fast, regular rate. Because bigeminy involves an irregular rhythm with alternating beat morphologies, it is distinctly different from a sinus-driven tachycardia where all the QRS complexes appear uniform and regular.