121 Questions
What is a common cause of acute respiratory acidosis in perioperative medicine?
Increased dead space ventilation
How is acute respiratory acidosis manifested in patients in the recovery room?
Elevated PaCO2
What does slow shallow breathing in a patient signify according to the text?
Impaired respiratory drive
In perioperative medicine, what can lead to respiratory alkalosis?
excessive mechanical ventilation
What should be the expected value of Base Excess (BE) in the context of acute respiratory acidosis?
Zero
During laparoscopy, CO2 insufflation might lead to ?
respiratory acidosis
What is the expected baseline PaCO2 for a patient with a total CO2 of 30 mEq/L?
60 mm Hg
In a patient with a postoperative PaCO2 of 90 mm Hg and total CO2 of 35 mEq/L, what condition is indicated?
acute or chronic respiratory acidosis
What might be a cause of acute respiratory alkalosis?
Hyperventilation due to anxiety
How much does the [HCO3−] fall for every 10 mm Hg fall in PaCO2 in acute respiratory alkalosis?
2 mEq/L
What may result in respiratory acidosis in a patient with abdominal hypertension?
Failure to ventilate due to high intraabdominal pressures
In a patient with lactic acidosis and a lactate level of 10 mEq/L, what should the BE be?
-10
What does the reduction in PCO2 from baseline equate to in acute metabolic acidosis?
Magnitude of the base deficit
What happens to PaCO2 in a multi-trauma patient with massive blood loss and lactic acidosis?
Increases
What is the expected baseline total CO2 for a patient with chronic respiratory failure and PaCO2 of 50 mm Hg?
27 mEq/L (mmol/L)
patient arrive to PACU from OR with respiratory distress, what is the first thing to do for management?
examination of the patient’s breathing pattern
rapid shallow breathing suggests
chest wall or lung pathology
For patient with chronic respiratory failure, for intraoperative management, the etCO2 should be maintained
between 3 and 5 mm Hg of baseline
respiratory acidosis due to patient “won’t breathe” can be due to
neurologic injury
patients with acute metabolic acidosis characterized by?
pH < 7.35 with fall in PaCO2 and (HCO3−)
Which condition results in a negative base excess (BE) in the context of metabolic acidosis?
Diabetic ketoacidosis
What is the primary purpose of using the Anion Gap (AG) in evaluating metabolic acidosis?
To differentiate hyperchloremic acidosis from other causes
What change in PaCO2 is typically observed in patients without COPD or chronic CO2 retention in acute metabolic acidosis?
PaCO2 < 40 mm Hg
What characterizes a metabolic acidosis that is metabolic in origin according to the text?
[HCO3−] below 24 mEq/L
What is the recommended action if plasma lactate does not fall after fluid resuscitation?
Discontinue fluid resuscitation
In lactic acidosis, why is the presence of good overall oxygen delivery and normal consumption not reassuring?
It may mask underlying conditions like bowel ischemia
when should D-lactate levels be measured ?
in post major abdominal surgery
What is a significant risk factor for metformin-associated lactic acidosis?
Renal impairment
What is the mechanism through which metformin may induce lactic acidosis?
impair oxidative metabolism in hepatocyte mitochondria
What is the recommended treatment for patients with metformin-associated lactic acidosis?
Withdraw the drug and provide gentle rehydration
What is the primary cause of lactic acidosis?
Overproduction of lactate
Which isoform of lactate can only be produced by fermentation by bacteria?
D-lactate
What is the main function of lactate in isotonic fluids like lactated Ringer’s solution?
To act as a buffer
Under what conditions does lactate metabolism lead to gluconeogenesis?
In aerobic conditions
Plasma lactate and arterial pH should be measured early in any critically ill patient—it is now a diagnostic component of
Septic shock
In which type of lactic acidosis does global inadequate oxygen delivery play a significant role?
Type 1 (type A)
What is a characteristic feature of type 2 (type B) lactic acidosis?
Associated with cyanide poisoning
What is a common association with type 2 lactic acidosis?
Excess circulating catecholamines
Under normal conditions, the ratio of lactate to pyruvate is
less than 20:1
Persistence of lactic acidosis strongly predicts
poor outcomes in acute illness
What are the three types of ketone bodies?
Acetone, acetoacetate, β-hydroxybutyrate
What type of acid-base disorder can be associated with increased acetone levels in the body?
Metabolic acidosis
What is a potential consequence of untreated ketoacidosis in a patient?
Hypokalemia
What role do ketone bodies play in the body during fasting or starvation?
Primary source of energy for the brain and heart
what is the most abundant Ketone bodies
3-β-hydroxybutyrate (βOHB
During ketogenesis, acetoacetate is generated from
acetyl co-enzyme
in which amount the ketones are found normally in blood and urine ?
undetectable
in starvation or low-carbohydrate diets, what is the primary ketones found in blood
3-β-hydroxybutyrate (βOHB)
in starvation or low-carbohydrate diets, what is the primary ketones found in urine
acetoacetate
dramatic increase in circulating ketones occurs. most commonly occur in
insulin deficiency (DM)
The diagnosis of DKA.is confirmed by?
ABG analysis.
What may lead physicians to miss ketoacidosis in patients presenting for emergency surgery?
Elevated lactate levels resulting in search satisficing
What inappropriate therapies may be administered to a patient with unresolved acidosis in ketoacidosis?
Renal replacement therapy and sodium bicarbonate
What is a key treatment requirement for all forms of ketoacidosis, including non-diabetic cases?
insulin administration
In what time frame can ketoacidosis of non-diabetic origin take to resolve?
Hours, and occasionally days
What scenario may cause urinary ketones to increase while whole-body ketone load is falling during the resolution of ketosis?
Acetoacetate metabolism
What is the primary purpose of administering IV dextrose in the management of DKA?
To assist ketone metabolism
In the management of DKA, what is a significant benefit of using Plasmalyte-148 compared to normal saline (NS)?
Improved blood pressure profile
Why is it important to measure blood ketones rather than relying solely on urinary ketone sticks for diagnosing ketoacidosis?
Urinary ketone sticks only detect acetoacetate, not all ketones
What is the effect of insulin on ketone production in the context of DKA?
Suppresses ketone production
How does the majority of ketones exist in the body during a state of ketoacidosis?
As βOHB only
What is a major error often made in DKA management due to misinterpretation?
Mistaking hyperchloremic acidosis for persistent ketoacidosis
What is the primary source of acidosis early in acute kidney injury (AKI)?
Chloride
Which electrolyte accounts for up to 30% of the acidosis associated with AKI?
Phosphate
What percentage of patients with AKI in critical illness have a normal Anion Gap (AG)?
50%
In perioperative medicine, AKI may accompany all of the following EXCEPT:
Liver failure
Which of the following is NOT a symptom associated with metabolic acidosis in AKI?
Hypokalemia
What is key to the diagnosis, severity, and therapeutic strategy in AKI?
Identification of metabolic acidosis
How is renal acidosis usually diagnosed?
By excluding ketones and lactate
What is a key decision step regarding RRT ?
hyperkalemia
How is hyperchloremia typically related to renal acidosis?
It accompanies renal acidosis
What can be a temporary control method for renal acidosis?
Sodium bicarbonate administration
What is the risk associated with delaying Renal Replacement Therapy (RRT) in critical illness?
4.7% increase in mortality at 90 days
Which solution was demonstrated to lead to more acidosis and hyperkalemia in anephric patients undergoing renal transplantation?
normal saline solution
What is one of the major excretory roles of the kidney?
Excreting more chloride than sodium
What is the consequence of renal failure in relation to chloride levels?
Chloride accumulates
What is the approximate amount of chloride excretion per day to maintain electrical neutrality?
15 to 20 mmol
What is the primary component of isotonic saline solution (normal saline, NS)?
Chloride
What is the metabolic load increase for the kidney when administering 1 liter of NaCl 0.9% to a patient?
8 to 10-fold increase
Why is high circulating chloride nephrotoxic according to the text?
reduced renal blood flow
What is the effect of hyperchloremia on mortality in critically ill patients with acid-base disorders, according to the text?
Mortality rates are lowest for hyperchloremic acidosis compared to lactic acidosis and SIG acidosis.
What is a potential outcome difference between intravenous saline and balanced salt solutions (BSS) in surgical patients?
Intravenous saline increases the risk of blood transfusions compared to BSS.
What is a potential consequence of a hyperchloremic state in relation to renal function?
Renal vasoconstriction and hypoperfusion.
What was the outcome of a before-and-after cohort study comparing chloride-rich fluids to balanced salt solutions (BSS) in an Australian ICU?
Chloride-rich fluids were associated with a 3.7% absolute increase in the risk for RRT relative to BSS.
What is a common cause of metabolic alkalosis in perioperative patients?
Loss of chloride-rich fluids from the GI tract
Why are isotonic fluids usually administered in perioperative fluid therapy?
To prevent cerebral edema
What is a challenge associated with acquired hypernatremia in perioperative patients?
Difficult to treat and linked to adverse outcomes
Why are balanced salt solutions (BSSs) considered safer than normal saline (NS) for resuscitation?
They are less likely to cause hypernatremia
What is the primary cause of metabolic alkalosis in patients with over ventilation-induced acute metabolic alkalosis?
Increased SID due to sodium gain
How is chloride-sensitive alkalosis, induced by sodium gain, best treated?
Administration of potassium chloride
Which ion is responsible for 'chloride-sensitive' alkalosis ?
Sodium
How does the administration of large volumes of BSSs contribute to metabolic alkalosis?
ATOT dilution
Which condition may result from ineffective treatment of chloride-sensitive alkalosis?
Respiratory acidosis
What is the primary adverse effect of not correcting chloride-sensitive alkalosis in patients during perioperative care?
'CO2 narcosis'
What is the most common single disturbance in acid-base in critically ill patients?
Hypoalbuminemia
Which acid-base disturbance may be masked by hypoalbuminemia in critically ill patients?
Lactic acidosis
What additional metabolic alkalosis may be induced by prolonged respiratory failure in critically ill patients?
Alkalosis due to chloride loss in urine
What might be a significant consequence of late polyuric renal failure in critically ill patients?
Contraction alkalosis
In critically ill patients, what is vulnerable to significant changes and may indicate fluid shifts?
Strong Ion Difference (SID)
What may be associated with hypercarbia-induced metabolic alkalosis in the context of respiratory failure?
Chloride loss
What electrolyte imbalance may be provoked by loop diuretics like furosemide in critically ill patients?
contraction alkalosis
Which therapy may lead to a metabolic acidosis similar to that caused by ethylene glycol ingestion due to its dilution in propylene glycol?
Lorazepam
What effect might continuous renal replacement therapy (CRRT) have on a metabolic alkalosis in the presence of hypoalbuminemia?
unmask a metabolic alkalosis
What electrolyte disturbance is commonly associated with the administration of isotonic saline solution (normal saline, NS) in neurosurgical patients?
Hyperchloremic acidosis
Which electrolyte abnormality may be treated with carbonic anhydrase inhibitors like acetazolamide?
Hypochloremia
How does surgery with drains placed in tissue beds contribute to electrolyte disturbances?
By increasing sodium levels through drainage fluid
What is the primary treatment for diabetic ketoacidosis according to the text?
Insulin, IV fluid, and glucose
How is hyperchloremic acidosis commonly managed based on the text?
Sodium bicarbonate (NaHCO3-) administration
What is the main treatment approach for acute kidney injury (AKI) according to the text?
Dialysis and ultrafiltration
How does sodium bicarbonate (NaHCO3-) impact respiratory acidosis based on the text?
Exacerbates respiratory acidosis despite increased strong ion difference (SID)
Which of the following scenarios can lead to increased intracellular acidosis according to the text?
Usage of sodium bicarbonate (NaHCO3-)
Why is NaHCO3- commonly used to treat hyperchloremic acidosis according to the text?
To widen the strong ion difference (SID)
What is a potential benefit of NaHCO3− therapy as discussed in the text?
Improved kidney blood flow
How is contraction alkalosis typically treated according to the text?
Correcting free water deficit
What is a possible speculation for the reduction in need for renal replacement therapy with NaHCO3− therapy?
Delayed decision to start RRT
How is respiratory alkalosis typically managed in the perioperative period?
Treating the underlying cause
What is a common cause of metabolic alkalosis in critically ill patients according to the text?
Hypoalbuminemia
How is hypercarbic acidosis typically reversed according to the text?
Increasing tidal volume
What is a potential consequence of a hyperchloremic state on renal function as discussed in the text?
Decreased glomerular filtration rate
What is a recommended treatment for hypochloremic alkalosis as per the text?
Correcting chloride deficit using IV solutions
What is an appropriate approach to managing hypercarbic acidosis associated with ARDS according to the text?
Tolerating hypercarbia ('permissive hypercarbia')
Study Notes
Respiratory Acidosis and Alkalosis
- Acute respiratory acidosis results from hypoventilation or increased dead space ventilation.
- Causes of respiratory acidosis: • Excessive sedation (particularly opioids) • Partial neuromuscular blockade • Intraoperative hypoventilation • Pneumothorax • CO2 insufflation during laparoscopy
- Blood gas analysis of acute respiratory acidosis: • pH falls dramatically • PaCO2 elevates • HCO3- rises by 1 mEq/L (mmol/L) for every 10 mm Hg (1.3 kPa) rise in PaCO2 • BE is zero
Patients with Chronic Respiratory Failure
- Calculate baseline PaCO2 from total CO2 on blood chemistry panel
- Total CO2 (HCO3-) rises by 3 mEq/L (mmol/L) for every 10 mm Hg (1.3 kPa) rise in PaCO2
- For intraoperative management, maintain etCO2 between 3 and 5 mm Hg (0.5 –1 kPa) of baseline
Acute Respiratory Alkalosis
- Caused by hyperventilation, either due to: • Anxiety or pain • Central respiratory stimulation (e.g., early in salicylate poisoning) • Excessive artificial ventilation
- Blood gas analysis of acute respiratory alkalosis: • pH is above 7.45 • PaCO2 is below 40 mm Hg (5.3 kPa) • HCO3- falls by 2 mEq/L (mmol/L) for every 10 mm Hg (1.3 kPa) fall in PaCO2 • No change in BE
Metabolic Acidosis and Alkalosis
Metabolic Acidosis
- Acute metabolic acidosis caused by: • Alteration in SID or ATOT • Alteration in the relative quantity of strong anions to strong cations
- Characteristics of acute metabolic acidosis: • pH < 7.35 • Fall in both PaCO2 and HCO3- below the patient's baseline • Negative BE (base deficit) whose magnitude represents the net strong anion gain
- Tools to investigate metabolic acidosis: • Anion gap (AG) • Osmolar gap • Serum creatinine • Direct measurement of anions (e.g., lactate, ketones, phosphate, albumin)
Lactic Acidosis
- Lactic acidosis is a marker of acute critical illness
- Lactic acidosis occurs when the production of lactate is greater than the liver's capacity to clear it
- Causes of lactic acidosis: • Type 1 (type A): hypovolemic/hemorrhagic shock • Type 2 (type B): despite normal global oxygen delivery and tissue perfusion
- Lactic acidosis may develop in situations with significant regional hypoperfusion
- Lactic acidosis is a sensitive marker of disease severity
- Persistence of lactic acidosis strongly predicts poor outcomes in acute illness
Ketoacidosis
- Ketoacidosis is caused by: • Inadequate insulin • Increased glucagon • Increased cortisol • Increased catecholamines
- Management of DKA: • Insulin administration • Resuscitation with isotonic crystalloid • Administration of IV dextrose when blood glucose falls within a "controlled" range
- Two major mistakes in the management of DKA: • Administration of 0.9% NaCl results in hyperchloremic acidosis • Measuring urinary ketones instead of blood ketones
Renal Acidosis
- Renal acidosis is caused by: • AKI • Hyperchloremia • Hyperphosphatemia • UMA
- Characteristics of renal acidosis: • Widened AG • Base deficit gap • SIG • Exclusion of ketones and lactate
- Key decision step regarding RRT: • Uncontrolled hyperkalemia
- Renal acidosis can be temporarily controlled by: • Administration of sodium bicarbonate • Increasing the SID### Hyperchloremic Acidosis
- The extracellular space contains approximately 58 g of Na+ and 65 g of Cl- for a 70 kg male.
- The body needs to excrete 30% more Cl- than Na+ to maintain the normal ratio of Na+ to Cl- (1.4:1), which is one of the major excretory roles of the kidney.
- In renal failure, Cl- accumulates, leading to early metabolic acidosis associated with AKI.
Metabolic Alkalosis
- Perioperative fluid therapy is highly controversial, and the administration of isotonic fluids can result in large amounts of solute, including sodium and chloride, accumulating in the extravascular space.
- Acquired hypernatremia is associated with adverse clinical outcomes and is difficult to treat.
- Metabolic alkalosis is often of iatrogenic origin, particularly in perioperative patients, and can be caused by over-ventilation, sodium gain, and loss of Cl- rich fluids from the GI tract.
Acid-Base Disturbances in Critical Illness
- Critically ill patients may have multiple confounding acid-base disturbances that are not evident when only a single quantitative measure, such as base deficit, is employed.
- The most common single disturbance in acid-base in critically ill patients is hypoalbuminemia, which causes a metabolic alkalosis of unpredictable magnitude.
- Kidney injury is associated with accumulation of metabolic byproducts, leading to metabolic acidosis.
Treating Acid-Base Disturbances
- Acid-base disturbances are clinical indicators of disease processes that are more harmful than hydrogen ion abnormalities themselves.
- Correcting the pH is usually unlikely to resolve the problem, except in certain circumstances, such as hyperkalemia in AKI, where acidosis is the major cause of the problem.
- Treatment of acid-base abnormalities is determined by whether the acids are organic or mineral acids.
- Sodium bicarbonate (NaHCO3-) has been used to “correct” acidosis, but its benefits are unclear, and it may have drawbacks such as sodium and volume overload, metabolic alkalosis, hypertension, and hypocalcemia.
Specific Treatment Strategies
- Hyperchloremic acidosis can be treated with IV sodium bicarbonate, which corrects the base deficit, but the benefit is unclear.
- Metabolic alkalosis can be treated by correcting the chloride deficit using NS or LR, or by correcting the free water deficit using a specific formula.
- Respiratory alkalosis can be treated by reducing minute ventilation, and hypochloremic alkalosis can be treated by correcting the chloride deficit using NS or LR.
- Hypercarbic acidosis can be treated by increasing minute ventilation, but in ARDS, permissive hypercarbia may be necessary to avoid ventilator-induced lung injury.
Explore the concepts of respiratory acid-base abnormalities in the context of perioperative medicine, focusing on complications related to prolonged spontaneous breathing under anesthesia and inadequate or excessive mechanical ventilation. Learn about acute respiratory acidosis from hypoventilation and increased dead space ventilation.
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