What are the recommended mechanical ventilation parameters for a 55-year-old woman with hypertension managed by losartan (angiotensin II receptor antagonist) and neuropathic pain managed by pregabalin (anticonvulsant) undergoing a transpedicular C-arm guided biopsy at T9-T10 under general anesthesia?

Mechanical Ventilation Parameters for Transpedicular Biopsy Under General Anesthesia

For this 55-year-old woman on losartan and pregabalin undergoing a short procedural biopsy under general anesthesia, use volume-controlled or pressure-controlled ventilation with a tidal volume of 6-7 mL/kg predicted body weight (approximately 400-480 mL), respiratory rate of 10-12 breaths/minute, PEEP of 5 cmH2O, and FiO2 of 0.4-0.5 to maintain SpO2 92-97%. 1

Initial Ventilator Settings

Tidal Volume and Respiratory Rate

• Set tidal volume at 6-7 mL/kg predicted body weight (approximately 400-480 mL for a 70 kg woman) to prevent ventilator-induced lung injury while maintaining adequate ventilation 1
• Use a respiratory rate of 10-12 breaths/minute for this short procedure in a patient with healthy lungs, which provides adequate minute ventilation without causing respiratory alkalosis 2, 1
• For patients with normal lungs undergoing brief procedures, lower respiratory rates are appropriate compared to critically ill patients 2

Oxygenation Parameters

• Maintain FiO2 at 0.4-0.5 (40-50%) initially, which provides adequate oxygenation for most patients with healthy lungs during general anesthesia 1
• Target SpO2 of 92-97% to avoid both hypoxemia and hyperoxemia 2, 1
• Avoid excessive FiO2 as it provides no additional benefit and may cause absorption atelectasis 2

PEEP Settings

• Apply PEEP of 5 cmH2O to prevent atelectasis and maintain functional residual capacity during general anesthesia 2, 1
• This level of PEEP is standard for patients with healthy lungs undergoing routine procedures 2

Critical Anesthetic Considerations for This Patient

Medication-Specific Ventilatory Concerns

• Pregabalin potentiates respiratory depression when combined with opioids, requiring careful titration of remifentanil or fentanyl if used 3
• Research demonstrates that pregabalin combined with remifentanil increases end-tidal CO2 by 16.4 mmHg compared to 10.1 mmHg with remifentanil alone, indicating significant additive respiratory depression 3
• Monitor end-tidal CO2 continuously as pregabalin reduces anesthetic requirements by 10-20% through calcium channel modulation, potentially leading to relative hypoventilation if standard doses are used 4

Hemodynamic Monitoring During Ventilation

• Avoid excessive positive pressure ventilation as losartan impairs compensatory vasoconstriction, and high intrathoracic pressures will further reduce venous return and cardiac output 2, 4
• Use the lowest effective inspiratory pressures to achieve adequate tidal volumes, particularly important in this patient on an angiotensin II receptor blocker 2
• Monitor blood pressure continuously as positive pressure ventilation combined with losartan can cause exaggerated hypotensive responses 4

Ventilation Targets and Monitoring

Blood Gas Targets

• Target pH of 7.35-7.45 with normocapnia (PaCO2 35-45 mmHg) for this patient with healthy lungs 2, 1
• Maintain PaO2 >80 mmHg or SpO2 92-97% 2
• For short procedures in healthy patients, permissive hypercapnia is unnecessary and normocapnia should be maintained 1

Continuous Monitoring Parameters

• Monitor end-tidal CO2 continuously to assess adequacy of ventilation and detect early hypoventilation from pregabalin-opioid interactions 2, 4
• Measure peak inspiratory pressure and plateau pressure to avoid barotrauma; keep plateau pressure <30 cmH2O 2
• Assess patient-ventilator synchrony if any spontaneous breathing occurs, as dyssynchrony increases work of breathing and can cause hemodynamic instability 2, 1

Procedural-Specific Adjustments

Prone Positioning Considerations

• Verify hemodynamic stability before and after prone positioning, as this position combined with losartan and positive pressure ventilation significantly increases hypotension risk 4
• Consider slightly higher PEEP (6-7 cmH2O) in prone position to counteract increased abdominal pressure on the diaphragm, but monitor blood pressure closely 2
• Ensure adequate chest and pelvic support to allow unrestricted diaphragmatic excursion 2

Anesthetic Agent Selection Impact

• Use total intravenous anesthesia (TIVA) with propofol and short-acting opioids rather than volatile anesthetics, as this provides more stable ventilatory control and avoids potential complications in patients on multiple medications 2, 4
• Reduce propofol induction doses by 20-30% due to losartan-induced exaggerated hypotensive responses 4
• Titrate remifentanil carefully starting at lower effect-site concentrations (0.5-1.0 ng/mL) given pregabalin's potentiation of opioid respiratory depression 3

Common Pitfalls to Avoid

• Do not use excessive tidal volumes (>8 mL/kg) even if airway pressures seem acceptable, as this increases risk of ventilator-induced lung injury 1
• Avoid hyperventilation (respiratory rate >15 breaths/minute for this short procedure) as it causes respiratory alkalosis, decreases cerebral blood flow, and provides no benefit 2
• Do not use high FiO2 (>0.6) unnecessarily as the patient's baseline oxygenation should be normal and excessive oxygen provides no advantage 1
• Never use succinylcholine if neuromuscular blockade is needed, though it should not be required for this procedure; use non-depolarizing agents if necessary 2

Extubation Planning

• Plan for immediate extubation at procedure completion once the patient is responsive and has adequate spontaneous ventilation 2
• Ensure full reversal of neuromuscular blockade if used, with train-of-four ratio >0.9 2
• Provide supplemental oxygen via face mask initially post-extubation, as pregabalin's respiratory depressant effects persist into the recovery period 3
• Monitor for delayed emergence and excessive sedation in the post-anesthesia care unit given pregabalin-opioid interactions 4