Anatomy & Physiology
This organ produces hydrochloric acid and begins the digestion of proteins.
Stomach
Parietal cells produce hydrochloric acid, which creates an acidic environment and activates pepsinogen to pepsin, initiating protein digestion.
This process involves the active expulsion of gastric or proximal intestinal contents, usually accompanied by abdominal contractions.
Vomiting is an active reflex involving coordinated gastrointestinal, respiratory, and abdominal muscle activity.
This section of the gastrointestinal tract is primarily responsible for reclaiming water and electrolytes from material entering from the small intestine and storing feces.
The colon reabsorbs water and electrolytes and stores feces before defecation.
This term describes a reduction in total body water.
Dehydration describes a deficit in total body water. It is related to, but distinct from, hypovolemia, which is a reduction in circulating blood volume.
Name two clinical parameters that should be assessed when evaluating the hydration status of a patient presenting with vomiting or diarrhea.
Hydration assessment should combine multiple findings. Perfusion parameters such as heart rate, pulse quality, CRT, and blood pressure help assess circulatory status but are not direct measures of total body water deficit.
A dog presents with a single episode of vomiting but is bright, alert, responsive, and has normal vital signs.
What additional information should be obtained during the initial assessment?
Obtain a focused history, including the timing and frequency of vomiting, appearance of vomitus, appetite, water intake, activity level, possible dietary indiscretion or toxin exposure, medications, and other clinical signs.
Assess hydration, perfusion, abdominal discomfort, and vital signs.
Teaching point: A single episode of vomiting in an otherwise stable patient does not automatically indicate an emergency. However, possible toxin exposure, foreign body ingestion, abdominal distension, or unproductive retching may substantially change the urgency of assessment.
This section of the gastrointestinal tract is responsible for the majority of nutrient absorption.
Small Intestine
The small intestine is the primary site of nutrient absorption, including carbohydrates, proteins, fats, vitamins, minerals, and much of the water entering the GI tract.
This process involves the passive return of esophageal contents without the abdominal contractions associated with vomiting.
Regurgitation is generally a passive process involving the return of esophageal contents. It may occur without nausea or abdominal contractions.
A dog presents with frequent attempts to defecate, small volumes of loose feces, mucus, and straining.
Is this presentation more consistent with small bowel or large bowel diarrhea?
Frequent defecation, small fecal volumes, mucus, tenesmus, and fresh blood are characteristic of large bowel involvement.
This term describes inadequate blood flow to tissues, resulting in insufficient delivery of oxygen and nutrients.
Hypoperfusion occurs when blood flow is insufficient to meet tissue metabolic requirements.
Why is obtaining an accurate body weight important when assessing and treating a patient with gastrointestinal fluid loss?
Serial body weights can help identify fluid loss or retention. A change of approximately 1 kg can represent a change of approximately 1 liter of body water, assuming the change is primarily fluid.
A dog presents with frequent, small-volume diarrhea containing mucus and fresh blood.
What type of diarrhea does this presentation suggest, and what additional clinical signs should be assessed?
The presentation is consistent with large bowel diarrhea.
Assess hydration, perfusion, abdominal discomfort, frequency of defecation, volume and appearance of feces, and the patient's overall clinical condition.
Teaching point: Fresh blood and mucus can occur with colonic inflammation. However, fecal appearance alone cannot establish the underlying cause or determine patient stability.
These finger-like projections increase the surface area of the small intestine, allowing more efficient nutrient absorption.
Villi
Villi and the microvilli on intestinal epithelial cells greatly increase the surface area available for absorption.
A dog presents with repeated episodes of bringing up undigested food immediately after eating. The owner reports no abdominal contractions or retching.
Is this more consistent with vomiting or diarrhea?
The passive return of undigested food without retching or abdominal contractions is more consistent with regurgitation. The timing and appearance of material can provide additional clues.
A dog presents with large volumes of watery diarrhea, weight loss, and increased fecal frequency without significant straining.
Which section of the gastrointestinal tract is most likely involved?
Large fecal volumes, weight loss, and an absence of significant straining are more consistent with small intestinal disease.
A dog presents with vomiting, diarrhea, tacky mucous membranes, and reduced skin elasticity.
Explain why these clinical signs develop.
Skin elasticity and mucous membrane moisture are useful assessment findings but are not sufficiently reliable in isolation to determine the severity of dehydration.
A dog presents with vomiting and diarrhea. Its mucous membranes are pale, its extremities are cool, and its capillary refill time is prolonged.
What do these findings suggest, and what should the veterinary nurse do?
Pale mucous membranes, prolonged CRT, and cool extremities can indicate peripheral vasoconstriction and reduced perfusion. These findings are not specific to hypovolemia, so other causes of shock must also be considered.
A dog presents with repeated vomiting despite receiving maropitant (Cerenia).
What concerns should the veterinary team consider, and why should continued vomiting not simply be treated with additional antiemetic medication?
Continued vomiting despite maropitant should prompt reassessment of the patient and the underlying cause.
Potential concerns include gastrointestinal obstruction, severe gastrointestinal inflammation, pancreatitis, toxin exposure, metabolic disease, and other conditions requiring additional diagnostics or treatment.
Teaching point: Maropitant blocks neurokinin-1 receptors and inhibits substance P-mediated emetic signaling.
It does not correct the underlying cause of vomiting.
Persistent vomiting may indicate that the underlying disease remains active or that the patient requires further investigation.
Discussion prompt: Why could suppressing vomiting without investigating a suspected obstruction delay appropriate treatment?
This muscular movement propels food through the gastrointestinal tract by coordinated contraction and relaxation.
Peristalsis
Coordinated contraction and relaxation of gastrointestinal smooth muscle propel contents through the digestive tract.
A dog with suspected megaesophagus presents with coughing, increased respiratory effort, and fever.
What complication should the veterinary team be concerned about?
Patients with megaesophagus are at increased risk of aspirating regurgitated material into the respiratory tract. Coughing, fever, and increased respiratory effort warrant prompt veterinary assessment.
Explain the difference between osmotic diarrhea and secretory diarrhea.
Osmotic diarrhea may improve when the offending substance is removed. Secretory diarrhea can persist despite fasting, depending on the underlying cause. Both mechanisms may occur together.
A patient with severe gastrointestinal fluid loss develops tachycardia.
Explain why the heart rate increases and how this response helps maintain cardiac output.
Cardiac output equals heart rate multiplied by stroke volume. When circulating blood volume decreases, venous return and ventricular filling may fall, reducing stroke volume. Increasing heart rate can temporarily help maintain cardiac output.
A hospitalized patient receiving IV fluid therapy continues to experience vomiting and diarrhea.
Identify four parameters that should be monitored to evaluate fluid balance and the patient's response to treatment.
Fluid balance assessment requires evaluating both the patient's response to treatment and continued losses. Monitor for signs of inadequate resuscitation and fluid overload.
A dog presents with profuse hemorrhagic diarrhea, vomiting, tachycardia, and signs of dehydration.
The veterinarian suspects acute hemorrhagic diarrhea syndrome (AHDS).
Explain the primary physiological concern and identify the nursing priorities.
AHDS can cause substantial fluid loss into the gastrointestinal tract, producing hypovolemia and potentially hypovolemic shock.
The nursing priorities include immediate assessment of perfusion and hydration, prompt veterinary notification, IV access and prescribed fluid therapy, appropriate diagnostics, monitoring of ongoing losses, and frequent reassessment.
Teaching point: AHDS may produce marked hemoconcentration due to fluid loss. Severe cases require careful assessment of circulating blood volume and tissue perfusion.
The presence of hemorrhagic diarrhea does not automatically establish AHDS; other causes must be considered.
Explain how the small intestine normally absorbs water and electrolytes, and why damage to the intestinal lining can result in diarrhea.
Water follows the absorption of electrolytes and nutrients, particularly sodium. Damage to the intestinal lining can impair absorption and increase fluid secretion, allowing excess water to remain in the intestinal lumen.
Intestinal inflammation can damage absorptive cells, alter permeability, and disrupt normal transport mechanisms. The resulting imbalance between absorption and secretion contributes to diarrhea.
Explain why a patient experiencing repeated vomiting may develop metabolic alkalosis.
Include the role of gastric hydrochloric acid and the kidneys.
Gastric fluid contains hydrogen and chloride ions. Repeated loss of hydrogen ions through vomiting can increase blood bicarbonate relative to hydrogen ions. Concurrent volume depletion, chloride depletion, and potassium abnormalities may promote renal bicarbonate retention and maintain the alkalosis.
A patient has experienced severe diarrhea for 48 hours.
Explain how the loss of bicarbonate-rich intestinal fluid can contribute to metabolic acidosis.
Bicarbonate acts as an important extracellular buffer. When bicarbonate is lost through diarrhea, blood bicarbonate concentration may decrease. Severe dehydration and poor tissue perfusion can also contribute to metabolic acidosis through lactate accumulation.
A patient experiences severe dehydration and a reduction in circulating blood volume.
Explain the relationship between venous return, preload, stroke volume, cardiac output, and tissue perfusion.
Reduced ventricular filling generally lowers end-diastolic volume. Through the Frank-Starling mechanism, this can reduce stroke volume. If compensatory mechanisms cannot maintain cardiac output and vascular tone, tissue oxygen delivery becomes inadequate.
A patient presents with severe vomiting and diarrhea. The veterinarian requests bloodwork, including electrolytes and blood gas analysis.
Explain why sodium, potassium, chloride, bicarbonate, and blood pH are important in assessing this patient.
Gastrointestinal losses may produce different electrolyte and acid-base abnormalities depending on the site and severity of disease. Blood gas and electrolyte results help guide the veterinarian's fluid and electrolyte treatment plan.
A dog presents with a three-day history of vomiting and diarrhea.
On examination:
Explain what is happening physiologically, identify the immediate nursing priorities, and describe the parameters you would monitor to evaluate the patient's response to treatment.
The patient's tachycardia, pale mucous membranes, prolonged CRT, cool extremities, dull mentation, and hypotension indicate significant circulatory compromise.
In the context of severe gastrointestinal fluid loss, hypovolemic shock is a major concern.
Reduced circulating blood volume can decrease venous return and ventricular filling, resulting in reduced preload and stroke volume.
Compensatory tachycardia may initially help maintain cardiac output, but the patient's hypotension and other clinical findings suggest that compensation is inadequate.
Reduced tissue perfusion may impair oxygen delivery and contribute to anaerobic metabolism and lactate accumulation.
Immediate nursing priorities:
Parameters indicating a response to treatment:
Improvement in mentation, pulse quality, mucous membrane color, CRT, extremity temperature, and blood pressure may indicate improving perfusion.
Heart rate may decrease as circulating volume and stroke volume improve.
Serial lactate measurements, when indicated, may provide additional information about changes in tissue perfusion and metabolic status.
Teaching point: Blood pressure is only one component of cardiovascular assessment. A patient can have apparently acceptable blood pressure while still experiencing inadequate tissue perfusion.