Question 1

A 65-year-old, female (Weight: 70 kg, Height: 160 cm), with a previous medical history of end-stage renal disease (ESRD) on hemodialysis, essential hypertension, diabetes mellitus type 2, peripheral vascular disease admitted to the ICU with acute pulmonary oedema secondary to fluid overload. On day one, she presented with shortness of breath, orthopnoea, and bilateral lower extremity oedema.
Her vitals are as follows-
Blood Pressure: 170/95 mmHg; Heart Rate: 100 bpm; Respiratory Rate: 28 breaths/min; Oxygen Saturation: 88% on room air, which improved to 95% on 5 L/min nasal cannula.
Her laboratory investigations are:
Hemoglobin: 10.5 g/dL
WBC: 11,000 /µL
Platelets: 140,000 /µL
Serum Creatinine: 8.2 mg/dL
Blood Urea Nitrogen (BUN): 90 mg/dL
Potassium: 6.2 mEq/L
BNP: 1500 pg/mL

Arterial Blood Gas (ABG) values are as follows--
pH 7.30, PaCO2 : 50 mmHg, PaO2 : 65 mmHg, HCO3 : 24 mEq/L

A Chest X-ray showed bilateral pulmonary infiltrates consistent with pulmonary edema. Emergency hemodialysis was planned, and a dialysis catheter insertion was scheduled as the patient does not have a functioning arteriovenous fistula.

Wrong Answer: A. Pressure difference before/after catheter (∆P), femoral vein.

Wrong Answer: B. Length of catheter shaft (L), right internal jugular vein

Right Answer:C. Inner radius (r), right internal jugular vein

Explaination:
Calculated AG: 13, Corrected AG: 15.5. Delta Gap: 15.5-12=3.5, Delta HCO3: 24-17=7; Therefore, delta-delta ratio in this case is calculated to be 0.5, which is suggestive of mixed high anion gap metabolic acidosis (HAGMA)+normal anion gap metabolic acidosis (NAGMA). Now let’s dive into the cause of HAGMA+NAGMA, in the options provided.

Explanation:
Let’s examine Hagen-Poiseuille Law, which describes the laminar flow of fluids through intravenous (IV) catheters, allowing for the calculation of flow rate based on the pressure difference, fluid viscosity, and catheter dimensions. (See Figure 1)

Figure 1. The flow (Q) of fluid through the catheter depends on a number of factors: the viscosity (n) of the fluid, the pressure gradient across the catheter(P1-P2), the length (L) and inner radius (r) of a catheter

The inner radius exerts the greatest impact on blood flow. In theory, optimal blood flow can be accomplished by employing a catheter with a short length, a large radius, and blood with low viscosity. Nevertheless, if the catheter is insufficiently long, the tip will not be appropriately situated in a region with a robust blood flow, ideally the superior or inferior cava vein. Hence, the length of the catheter must strike a balance between reducing resistance and guaranteeing the accurate placement of the catheter tip. The right internal jugular vein is the most optimal site for insertion because it offers a shorter and more direct route to the right atrium. If possible, it is best to avoid using the subclavian site for catheter insertion due to its higher complication rate, including pneumothorax, hemothorax, subclavian artery perforation, and brachial plexus injury, compared to other insertion sites. Central venous stenosis occurs in up to 40% of cases at this location, limiting the use of this vein for long-term tunneled dialysis catheter placement (Permacath). The use of the left internal jugular vein for immediate dialysis is not ideal since it takes a long and tortuous path to reach the right atrium. In the case of long-term dialysis, it is recommended to refrain from interfering with the central venous veins in the upper extremities to reduce the likelihood of future constriction to allow for the insertion of a tunneled hemodialysis catheter. The use of the femoral vein offers several possible advantages. Placement is typically more straightforward, especially for operators with limited experience. Although there is a potential risk of femoral artery puncture and retroperitoneal bleeding. Initially, there was a perception that the femoral route had a higher risk of infection. Recent data from the Cathedia Study Group suggests that the rates of infection and the time it takes for the catheter tip to get colonized (14 days) are comparable for both femoral and internal jugular catheters (Dugué, 2012). Hence, the most favorable site for implantation is the right internal jugular vein.

Wrong Answer: D. Viscosity (η), right subclavian vein

Reference:

[1] Berman, D. J., Schiavi, A., Frank, S. M., Duarte, S., Schwengel, D. A., & Miller, C. R. (2020). Factors that influence flow through intravascular catheters: the clinical relevance of Poiseuille’s law. Transfusion. doi:10.1111/trf.15898

[2] Girardot T, Monard C, Rimmelé T. Dialysis catheters in the ICU: selection, insertion and maintenance. Curr Opin Crit Care. 2018 Dec;24(6):469-475. doi: 10.1097/MCC.0000000000000543. PMID: 30299308.

[3] Dugué AE, Levesque SP, Fischer MO, Souweine B, Mira JP, Megarbane B, Daubin C, du Cheyron D, Parienti JJ; Cathedia Study Group. Vascular access sites for acute renal replacement in intensive care units. Clin J Am Soc Nephrol. 2012 Jan;7(1):70-7. doi: 10.2215/CJN.06570711. Epub 2011 Nov 10. PMID: 22076877; PMCID: PMC3265351.

Clinical Case Scenario 2

A 67-year-old woman with chronic heart failure presents with worsening dyspnea and significant peripheral edema. She is diagnosed with cardiorenal syndrome, and her renal function has declined considerably.

Wrong Answer: A. Fluid restriction and aggressive diuresis are always contraindicated in cardiorenal syndrome. This is incorrect. While fluid management must be carefully balanced, fluid restriction and diuresis are often necessary to manage fluid overload in cardiorenal syndrome. However, these interventions should be closely monitored to avoid worsening kidney function.

Right Answer:B. The use of ultrafiltration can be beneficial in managing fluid overload in cardiorenal syndrome. This is correct. Ultrafiltration is a method used to remove excess fluid in a controlled manner, which can be beneficial for patients with cardiorenal syndrome who suffer from significant fluid overload. It helps in achieving a negative fluid balance without causing hemodynamic instability.

Nephro-critical care pearls:
The pathophysiology of CRS is multifaceted, involving hemodynamic, neurohormonal, and inflammatory pathways. One key mechanism is the activation of the renin-angiotensin-aldosterone system (RAAS), which leads to worsening kidney function as a response to heart failure. In acute CRS (Type 1), reduced cardiac output leads to renal hypoperfusion, causing acute kidney injury (AKI). Conversely, in chronic forms (Type 2 and 4), long-term cardiac dysfunction contributes to chronic kidney disease (CKD) and vice versa. These complex interorgan communications create a vicious cycle of worsening function in both organs (Table 1).

Table 1. Primary dysfunction and key pathophysiological mechanisms in various types of cardio-renal syndrome


The pathophysiology of CRS is multifaceted, involving hemodynamic, neurohormonal, and inflammatory pathways. One key mechanism is the activation of the renin-angiotensin-aldosterone system (RAAS), which leads to worsening kidney function as a response to heart failure. In acute CRS (Type 1), reduced cardiac output leads to renal hypoperfusion, causing acute kidney injury (AKI). Conversely, in chronic forms (Type 2 and 4), long-term cardiac dysfunction contributes to chronic kidney disease (CKD) and vice versa. These complex interorgan communications create a vicious cycle of worsening function in both organs (Table 1).
Table 1. Primary dysfunction and key pathophysiological mechanisms in various types of cardio-renal syndrome

Emerging treatments are being developed to target these interactions, including SGLT-2 inhibitors like empagliflozin, which show promise in enhancing heart and kidney outcomes for patients with chronic kidney disease. Additionally, diuretic strategies and combination therapies are being refined to address the fluid overload typical in CRS.

Wrong Answer: C. ACE inhibitors should be avoided in all patients with cardiorenal syndrome. This is incorrect. ACE inhibitors can be beneficial in certain patients with cardiorenal syndrome, particularly those with heart failure, as they help reduce afterload and potentially improve cardiac output. However, their use must be balanced against the risk of worsening renal function and monitored carefully.

Wrong Answer:D. Renal function typically improves immediately following aggressive fluid removal. This is incorrect. While removing excess fluid can relieve symptoms and potentially improve heart function, renal function does not always improve immediately and can sometimes worsen temporarily due to hemodynamic changes.