Metabolic acid-base disorders.

Acid-base homeostasis is an important determinant of many physiologic functions. Nowhere is understanding the mechanisms and significance of hydrogen ion (H+) imbalance more important than in critical care management, where patients are threatened with a physiochemical disorder that is often as complex as it is dangerous. Although there may be contentious issues yet unresolved concerning acid-base homeostasis, the incontrovertible fact is that the body at least seems to defend H+ balance as vigorously as it does oxygen transport or perfusion pressure. Equally, there seems to be an important and predictable relation between this balance and other physiochemical variables such as concentrations of other ionic species, carbon dioxide, and plasma proteins. The prudent clinician strives to understand whether or not and how acid-base imbalances are affecting his or her patient and what to do about it.     

Respiratory acid-base disorders.

Respiratory acid-base disorders, although infrequently diagnosed in veterinary medicine, can cause or contribute to adverse clinical outcomes. Recognition of the mechanisms and causes of respiratory acidosis and alkalosis can prompt clinical detection of the acid-base derangement, allowing for appropriate intervention.     

Mixed acid-base disorders

Mixed acid-base disturbances are combinations of two or more primary acid-base disturbances. Mixed acid-base disturbances may be suspected on the basis of findings obtained from the medical history, physical examination, serum electrolytes and chemistries, and anion gap. The history, physical examination, and serum biochemical profile may reveal disease processes commonly associated with acid-base disturbances. Changes in serum total CO2, serum potassium and chloride concentrations, or increased anion gap may provide clues to the existence of acid-base disorders. Blood gas analysis is usually required to confirm mixed acid-base disorders. To identify mixed acid-base disorders, blood gas analysis is used to identify primary acid-base disturbance and determine if an appropriate compensatory response has developed. Inappropriate compensatory responses (inadequate or excessive) are evidence of a mixed respiratory and metabolic disorder. The anion gap is also of value in detecting mixed acid-base disturbances. In high anion gap metabolic acidosis, the change in the anion gap should approximate the change in serum bicarbonate. Absence of this relationship should prompt consideration of a mixed metabolic acid-base disorder. Finding an elevated anion gap, regardless of serum bicarbonate concentration, suggests metabolic acidosis. In some instances, elevated anion gap is the only evidence of metabolic acidosis. In patients with hyperchloremic metabolic acidosis, increases in the serum chloride concentration should approximate the reduction in the serum bicarbonate concentration. Significant alterations from this relationship also indicate that a mixed metabolic disorder may be present. In treatment of mixed acid-base disorders, careful consideration should be given to the potential impact of therapeutically altering one acid-base disorder without correcting others.     

Simple acid-base disorders

The body regulates pH closely to maintain homeostasis. The pH of blood can be represented by the Henderson-Hasselbalch equation: pH = pK + log [HCO3-]/PCO2 Thus, pH is a function of the ratio between bicarbonate ion concentration [HCO3-] and carbon dioxide tension (PCO2). There are four simple acid base disorders: (1) Metabolic acidosis, (2) respiratory acidosis, (3) metabolic alkalosis, and (4) respiratory alkalosis. Metabolic acidosis is the most common disorder encountered in clinical practice. The respiratory contribution to a change in pH can be determined by measuring PCO2 and the metabolic component by measuring the base excess. Unless it is desirable to know the oxygenation status of a patient, venous blood samples will usually be sufficient. Metabolic acidosis can result from an increase of acid in the body or by excess loss of bicarbonate. Measurement of the "anion-gap" [(Na+ + K+) - (Cl- + HCO3-)], may help to diagnose the cause of the metabolic acidosis. Treatment of all acid-base disorders must be aimed at diagnosis and correction of the underlying disease process. Specific treatment may be required when changes in pH are severe (pH less than 7.2 or pH greater than 7.6). Treatment of severe metabolic acidosis requires the use of sodium bicarbonate, but blood pH and gases should be monitored closely to avoid an "overshoot" alkalosis. Changes in pH may be accompanied by alterations in plasma potassium concentrations, and it is recommended that plasma potassium be monitored closely during treatment of acid-base disturbances.     

Analgesia in critical care.

All medical interventions, including the provision of analgesia, are associated with risks and benefits, which, when considered together, comprise that intervention's risk/benefit ratio. All interventions have alternatives (including no intervention), and each alternative possesses its own risk/benefit ratio. Clinical decision making involves comparing and contrasting the risk/benefit ratios of alternative interventions (relative risk/benefit ratio). The most formidable limitations of drug treatment relate to their potential to produce pharmacologic side effects or complications. Careful monitoring and the use of strategies for preventing and managing drug side effects are often all that is required to maintain efficacy.     

Neonatal critical care.

The first few minutes after a neonate's birth may determine the quality of its entire life. Immediate care includes prevention of hypothermia, clearing of nasal and oral passages, stimulation of ventilation and oxygenation, and, in a few cases, advanced life support. Any additional stress during the first weeks of life can also result in neonatal morbidity and mortality. Care of the diseased newborn must focus not only on treatment of the underlying disease but on aggressive supportive care. A safe, warm, clean, proper environment and adequate nutrition are essential.     

Small mammal critical care.

In emergency situations, veterinarians often are presented with critical patients of any species. The principles for critical care in traditional species such as the dog or cat can be applied to other small mammals. Although there are many unique aspects of the anatomy and physiology of different species, emergency care of small mammals can be instituted with the adaptation of products found in many general practices. Careful assessment of the patient, prioritization of the injuries, and rapid intervention can be life saving in any species.     

Nutritional support in critical care patients.

Malnutrition in the form of insufficient nutrient intake to support tissue metabolism undermines appropriate medical or surgical therapeutic management of a case. The major consequences of malnutrition in all patients are decreased immunocompetence, decreased tissue synthesis and repair, and altered intermediary drug metabolism. A practical goal is to begin nutritional support within 24 hours of the injury, illness, or presentation. There are only two methods by which nutrients can be supplied to the body: enteral and parenteral. General guidelines are presented to help establish a foundation.     

Amphibian emergency and critical care.

Amphibians present unique challenges for the clinician in the diagnosis and treatment of life-threatening conditions. Their adaptability to both aquatic and terrestrial lifestyles leaves them vulnerable to dehydration and fluid overload, either of which may accompany serious disease. This article presents the most common emergency conditions in amphibians, the physiologic basis of disease, and a guide to the diagnosis and treatment of amphibian emergencies.     

Emergency and critical care of fish.

Most fish emergencies are the result of inappropriate environmental conditions and primary or secondary infectious disease or trauma. The immediate response should be to increase aeration, provide suitable water, and decrease stressors. A thorough history, evaluation of the fish and their environment, and some rapid diagnostic tests (particularly direct and stained cytology) often provide the information needed to make a diagnosis and render appropriate treatment. When cohorts are at risk and the patient is unlikely to recover, euthanasia and necropsy are recommended to reach a definitive diagnosis. Some common emergencies include ammonia and nitrite toxicity; low dissolved oxygen; copper and chlorine toxicity; gas supersaturation; and certain bacterial, protozoal, and viral diseases.     

Respiratory pharmacotherapy in emergency and critical care medicine.

Successful pharmacologic management of most respiratory diseases is possible. All moderately to severely affected animals benefit from rest and supplemental oxygen. Careful identification of the underlying cause as well as an understanding of the pathophysiology behind various diseases is essential to successful patient outcome.     

Cardiac emergencies and problems of the critical care patient.

Cardiac disease and dysfunction can occur as a primary disorder(ie, with pathology situated in one or more of the cardiac structures) or can be classified as a secondary problem when it occurs in patients with another primary problem that has affected the heart either directly or indirectly. Primary cardiac problems are encountered in horses presented to emergency clinics; however,this occurs much less frequently in equine critical patients than cardiac problems arising secondary to other conditions. Nevertheless,if primary or secondary cardiac problems are not identified and addressed, they certainly contribute to the morbidity and mortality of critical care patients.     

Emergency and critical care of pet birds.

Critically ill birds must be assessed accurately and provided with immediate supportive care. This article reviews the assessment and diagnostics required for evaluating the critical avian patient. The most common emergencies seen in pet birds are discussed. Diagnostics and treatments protocols are provided to help direct the practitioner toward a complete recovery.     

Contemporary approach to acid-base balance and its disorders in dogs and cats

The issue of the acid-base balance (ABB) parameters and their disorders in pets is rarely raised and analysed, though it affects almost 30% of veterinary clinics patients. Traditionally, ABB is described by the Henderson-Hasselbach equation, where blood pH is the resultant of HCO3- and pCO2 concentrations. Changes in blood pH caused by an original increase or decrease in pCO2 are called respiratory acidosis or alkalosis, respectively. Metabolic acidosis or alkalosis are characterized by an original increase or decrease in HCO3- concentration in the blood. When comparing concentration of main cations with this of main anions in the blood serum, the apparent absence of anions, i.e., anion gap (AG), is observed. The AG value is used in the diagnostics of metabolic acidosis. In 1980s Stewart noted, that the analysis of: pCO2, difference between concentrations of strong cations and anions in serum (SID) and total concentration of nonvolatile weak acids (Atot), provides a reliable insight into the body ABB. The Stewart model analyses relationships between pH change and movement of ions across membranes. Six basic types of ABB disorders are distinguished. Respiratory acidosis and alkalosis, strong ion acidosis, strong ion alkalosis, nonvolatile buffer ion acidosis and nonvolatile buffer ion alkalosis. The Stewart model provides the concept of strong ions gap (SIG), which is an apparent difference between concentrations of all strong cations and all strong anions. Its diagnostic value is greater than AG, because it includes concentration of albumin and phosphate. The therapy of ABB disorders consists, first of all, of diagnosis and treatment of the main disease. However, it is sometimes necessary to administer sodium bicarbonate (NaHCO3) or tromethamine (THAM).     

Effect of metabolic disorders accompanying gastroenteritis on the pancreatic exocrine function in piglets. A. Metabolic disturbances in piglets with gastroenteritis

The study were performed on 90 piglets of both sexes, divided into two groups, i.e. control, consisting of 30 healthy animals, and experimental, including 60 piglets with symptoms of gastroenteritis. Clinical, hematological and biochemical tests were performed in all the animals at the age of 21 and 35 days, and 7 days after weaning. Hematological investigations included the determination of Hb, Ht, Erys, Lkcs, MCHC and MCV. Biochemical analyses allowed to determine the serum activity of ALT, ALP, LDH and its isoenzymes, the serum level of Na+, K+ and Cl-, as well as the serum content of glucose, cholesterol and total protein. Indices of the acid-base equilibrium were determined in whole blood. The results obtained show that anemia and a tendency towards metabolic acidosis observed in healthy piglets may have a negative effect on homeostasis. Hypotonic dehydration, metabolic acidosis and energy deficits found in piglets with gastroenteritis may cause damage of some organs including the liver and pancreas. It was also found that isoenzymatic separation of LDH together with indices of the so called hepatic profile may be helpful to diagnose hepatocellular damage.     

Peritoneal dialysis in emergency and critical care medicine

Peritoneal dialysis is a technique that has been used to treat acute renal failure in humans since 1923. Peritoneal dialysis is used in people to manage acute and chronic renal failure, as well as to remove dialyzable toxins (ethylene glycol, barbiturates, and ethanol), reduce severe metabolic disturbances, and for the treatment of peritonitis, pancreatitis, uroabdomen, hypothermia, and fluid overload. In veterinary medicine, acute renal failure is the prevailing indication for dialysis. This report will discuss the pathophysiology of peritoneal dialysis, indications, and contraindications. Catheter selection and placement will be reviewed. Types of dialysate solution will be discussed and the protocol established for instituting peritoneal dialysis. The report will conclude with a discussion of potential complications and methods to minimize them.     

Coxiella burnetii associated reproductive disorders in domestic animals-a critical review

The bacterium Coxiella burnetii has been detected in the fetal membranes, birth fluids and vaginal mucus, as well as in the milk and other excretions of several domestic mammals. The finding of C. burnetii in association with abortion, parturition and in the postpartum period has led to the hypothesis that C. burnetii causes a range of reproductive diseases. This review critically evaluates the scientific basis for this hypothesis in domestic mammals.The review demonstrates a solid evidence for the association between C. burnetii infection and sporadic cases of abortion, premature delivery, stillbirth and weak offspring in cattle, sheep and goats. C. burnetii induced in-herd epidemics of this complete expression of reproductive failure have been reported for sheep and goats, but not for cattle. The single entities occur only as part of the complex and not as single events such as generally increased stillbirth rate. Studies show that C. burnetii initially infects the placenta and that subsequent spread to the fetus may occur either haematogenous or by the amniotic-oral route. The consequences for the equine, porcine, canine and feline conceptus remains to the elucidated but that infection of the conceptus may occur is documented for most species. There is no solid evidence to support a hypothesis of C. burnetii causing disorders such as subfertility, endometritis/metritis, or retained fetal membranes in any kind of domestic animal species.There is a strong need to validate non-pathology based methods such as polymerase chain reaction for their use in diagnostic and research in relation to establishing C. burnetii as the cause of abortion and to adapt an appropriate study design and include adequate control animals when linking epidemiological findings to C. burnetii or when evaluating effects of vaccination in production herds.