Pulmonary Resection in the Patient with Pulmonary Hypertension

Abstract

Pulmonary hypertension is a significant medical condition, with a global prevalence estimated as high as 1%. As such, it is no longer an uncommon occurrence for patients with pulmonary hypertension to present for surgery. Pulmonary resection in the patient with pulmonary hypertension has long been considered high risk and discouraged in early literature. The morbidity and mortality associated with pulmonary hypertension in patients presenting for surgery have been quoted as high as 42% and 18%, respectively. In this chapter, we review the perioperative management of patients with pulmonary hypertension presenting for pulmonary resection. This includes the preoperative assessment, pharmacology as it relates to pulmonary hypertension (both preoperative and intraoperative), anesthetic management (including management intraoperatively, monitoring, and a discussion of ventilation and analgesic strategies), and postoperative care. An example clinical case is presented at the end of the chapter to integrate this information.

Clinical Case Discussion

A 68-year-old woman is scheduled to undergo pulmonary resection for a recently diagnosed lung cancer. She initially presented with a worsening cough and shortness of breath, prompting a chest X-ray by her primary care physician. A right-sided lung lesion was seen, leading to additional investigations. A CT scan and CT-guided biopsy revealed a 3 cm × 5 cm × 3 cm right lower lobe mass, with pathology-confirmed squamous cell carcinoma.

Her past medical history includes 40 pack-year smoking history – she has quit smoking since her diagnosis, a few weeks ago. Her other past medical history includes hypertension, hypercholesterolemia, mild gastroesophageal reflux disease, and osteoarthritis of the hips and knees. She has a long-standing history of NYHA 2–3 dyspnea, preceding her recent cancer diagnosis.

She has been referred to a thoracic surgeon for management and has been offered a right lower lobectomy by video-assisted thoracoscopic surgery, possibly open.

What preoperative investigations should be arranged for this patient?

• 1. Pulmonary function testing:

  • (a) FEV₁ 70% predicted [ppoFEV₁ 50%]

  • (b) FEV₁/FVC < 70%

  • (c) DLCO 65% predicted [ppoDLCO 46%]

• 2. Six-minute walk test: 400 m walked, 80% predicted distance. Noted dyspnea during the testing, with desaturation events to as low as 88% on room air.

• 3. Arterial blood gas (on room air): pH 7.35, pCO₂ 48, pO₂ 70.

• 4. CT thorax: no significant bullous disease but evident diffuse centrilobular emphysema. The right lower lobe lesion in question is also seen.

• 5. Metastatic workup: no evidence of metastases.

• 6. ECG: sinus rhythm.

• 7. TTE: normal left ventricular size and function, with evidence of diastolic dysfunction. Mild right ventricular enlargement with low-normal function. There is mild tricuspid regurgitation with a right ventricular systolic pressure calculated at 55 mmHg. There are no other significant valvulopathy. Her blood pressure during the TTE was 140/92.

• 8. V/Q study: demonstrates preferential perfusion to the left lung (60%) relative to the right lung (40%).

• 9. Right heart catheterization: see below.

The investigations above reveal several key pieces of information. Pulmonary function testing shows abnormal spirometry consistent with moderate COPD. The DLCO is also abnormal, consistent with a diagnosis of COPD. The predicted postoperative values for the proposed procedure remain acceptable to proceed, however. Her 6-min walk test is suggestive of reduced cardiopulmonary reserve and may warrant further investigations to assess this. Her room air arterial blood gas is consistent with her underlying diagnosis of COPD. Her imaging and ECG are within expected parameters.

The decision to request further cardiac testing (an echocardiogram) is reasonable, given her cardiac risk factors (smoking history, hypertension, hyperlipidemia) and limited exercise ability due to dyspnea (with a limited 6-min walk test performance). Noninvasive stress testing is likely appropriate/indicated as well. Her TTE result shows clear evidence of pulmonary hypertension (elevated RVSP) with secondary signs of pulmonary hypertension (RV enlargement and impaired systolic function). Given the absence of any history or testing results suggestive of an alternative diagnosis, the underlying cause of her elevated pulmonary pressures is likely to be COPD.

The decision of whether to pursue further invasive cardiac testing, specifically a right heart catheterization, is debatable. The TTE findings are highly suggestive of pulmonary hypertension, and right heart catheterization may not provide additional information that would influence decision-making. While not as accurate as with right heart catheterization, her pulmonary-to-systemic systolic pressure ratios based on TTE remain less than 0.5, which is also reassuring. Noninvasive stress testing may be a more appropriate direction for further testing at this point, with any abnormalities observed prompting left- and right heart catheterization.

A ventilation-perfusion study was done to assess differential lung perfusion and is useful to determine tolerance of one-lung ventilation intraoperatively. The preferential perfusion of the left lung in this case is reassuring, as the risk for hypoxia and rising pulmonary pressures intraoperatively is likely lower despite the expected need to perform one-lung ventilation of the left lung. This is not an absolute predictor, however.

How do you rationalize the information provided by the investigations above? Do you proceed with the case?

This patient presents with a lung malignancy for resection. Her preoperative testing is suggestive of moderate COPD and reduced exertional tolerance and cardiopulmonary reserve. Additionally, her echocardiogram shows clear evidence of pulmonary hypertension, likely related to her long-standing COPD. All of these findings are suggestive of an above-average risk for morbidity and mortality, based on the evidence in the literature concerning perioperative management of pulmonary hypertension patients [4,5,6,7].

However, recent evidence has shown that pulmonary resection in the setting of pulmonary hypertension (by TTE-based diagnosis) is not an absolute contraindication to surgery [14]. Given the presence of a single-lung lesion with no metastases, surgery presents a curative option for this patient. Additionally, the remainder of her workup would be considered acceptable for proceeding with surgery in the absence of pulmonary hypertension.

As such, proceeding with the proposed resection with caution is acceptable. A clear plan and discussion involving the patient and surgeon should be had prior to presenting to the operating room to discuss the elevated risk and the need for specialized intraoperative and postoperative monitoring. There should be a low threshold to abort the procedure should issues with pulmonary hypertension arise intraoperatively despite the adequate precautions and management.

What intraoperative monitoring should be available for this procedure?

Routine noninvasive monitors, including 5-lead ECG, pulse oximetry, capnography, temperature, and invasive and noninvasive blood pressure monitoring, are required for any pulmonary resection procedure. Invasive blood pressure monitoring is of critical importance in the patient with pulmonary hypertension, as it allows for accurate beat-to-beat blood pressure monitoring and facilitates arterial blood gas sampling for assessment of oxygenation and ventilation. Central venous access is recommended for this procedure, as management of hemodynamics with vasoactive substances will likely be required.

Pulmonary artery pressures should be monitored during this procedure, given the need to promptly address any acute rises in pulmonary pressures. The most common options for assessment of pulmonary pressures (and right heart function) are a pulmonary artery catheter or TEE. The decision of which option to employ, if not both, should be based on availability as well as potential risks and benefits as they pertain to this patient.

Typically, PACs are readily available and allow for continuous measurement of pulmonary pressures. In conjunction with invasive blood pressure monitoring, the pulmonary-to-systemic pressure ratio can be easily determined and optimally maintained. This patient has no contraindications to a PAC. However, interpretation of PAC data can be challenging. Furthermore, PACs do not provide direct monitoring of right ventricular functioning. Increases in PA pressures are undesirable but may be tolerated by a well-compensated right ventricle. Conversely, reductions in PA pressures may represent improvement in pulmonary vascular resistance or impending right ventricular failure and need to be interepreted in conjunction with other available parameters such as CVP and systemic blood pressure.

The availability of intraoperative TEE is increasing, but remains a significant barrier to its usage in non-cardiac surgery. TEE allows for monitoring of right ventricular function intraoperatively, which would be beneficial in this scenario, as preexisting right ventricular enlargement and impairment are present. Furthermore, TEE allows for assessment of global cardiac function. Potential limitations of TEE in this scenario, in addition to availability, include limited ability to assess pulmonary pressures directly, as RVSPs can be calculated, but not on a continuous basis. Furthermore, assessment of right ventricular function requires multiple TEE views, again making timely continuous monitoring difficult. Additionally, assessment of TEE views in the lateral position (as required for a thoracotomy or VATS) may be technically challenging.

Should an epidural be placed in this patient?

Given that the proposed pulmonary resection is planned as a VATS procedure, an epidural would typically not be offered to this patient. However, consideration may be given to an epidural (or paravertebral catheter) given the above-average risk for complications postoperatively associated with this patient. Epidurals provide superior analgesia compared to intravenous PCA and have been associated with reduced pulmonary complications and mortality [84, 85]. While this patient has acceptable predicted postoperative FEV₁ and DLCO, optimization of her pulmonary mechanics remains necessary given her pulmonary hypertension. The potential benefits related to an epidural need to be weighed against the potential for complications related to an epidural, as well as the potential for hypotension and possible cardiac dysfunction secondary to neuraxial blockade.

The decision to offer an epidural should also take into consideration the risks and benefits discussed above, as well as the risk for conversion to a thoracotomy (requiring a discussion with the surgeon), and patient preferences.

What strategies should be employed to prevent or manage rises in pulmonary artery pressures intraoperatively?

Rises in pulmonary artery pressures should be identified and dealt with immediately. Optimization of ventilation parameters, hemodynamics, and pharmacologic interventions should all be considered for this patient.

Transition from ventilation with two lungs to one-lung ventilation is a period associated with many potential triggers for worsening pulmonary artery pressures, specifically hypoxia and hypercarbia. For this patient, a lung-protective strategy employing higher F_iO₂ should be used to optimize ventilation of the left lung. To minimize the risk of hypoxia and avoid significant hypercarbia, the F_iO₂ should be maintained at 1.0 when initiating OLV. A tidal volume of 4–6 mL/kg should be maintained, with the respiratory rate adjusted to target a P_aCO₂ < 30–40 mmHg. Normocapnia (or slight hypocapnia) is ideal; however, aggressive ventilation (higher tidal volumes or higher respiratory rates) can produce higher peak airway pressures leading to worsening pulmonary vascular resistance. The P_aCO₂ can be set to maintain a pH of greater than 7.2, provided there is no significant coexisting metabolic acidosis. The use of PEEP should be titrated carefully (0–10 cmH₂O), to maintain peak airway pressures below 30–35 cmH₂O, and may not be necessary in this patient, as obstructive lung disease tends to create intrinsic PEEP.

Maintenance of the pulmonary-to-systemic systolic pressure ratio at its baseline is also important intraoperatively, and higher ratios are associated with worse outcomes [6]. This can be achieved through augmentation of the systemic systolic pressure or by reducing pulmonary vascular resistance. Norepinephrine and vasopressin are the ideal vasopressors of choice to increase systemic vascular resistance and maintain right ventricular perfusion and cardiac output. Either agent should be started early should systemic pressure begin to drop with initiation of OLV. The use of pulmonary vasodilators should also be considered if pulmonary pressures increase significantly during the case. Consideration should be given to initiating iNO or epoprostenol IV to address this. iNO may be preferred, as its pulmonary selectivity means it can be initiated before OLV has started, and is unlikely to produce systemic vasodilation. iNO should be titrated to a maximum dose of 40 ppm before a second agent (such as epoprostenol IV) is added.

The threshold of concern for the absolute PA pressure, or pulmonary-to-systemic pressure ratio, is not well-defined in the literature but should take into account the patient’s baseline ratio, in this case less than 0.5, and the right ventricular response to increased PA pressures. Continuous PA pressure monitoring using a PAC allows for the former, while TEE is more advantageous to assess the latter. For this patient, two scenarios should prompt discussion regarding aborting the case. First, a continually rising pulmonary-to-systemic ratio beyond 0.5 despite the use of systemic vasopressors and pulmonary vasodilators is highly concerning, given her preoperative baseline. Second, any PA pressure producing signs of RV dysfunction (based on TEE imaging or reduced PA pressures, rising CVP, and hypotension) that does not respond to vasopressors or pulmonary vasodilation is also a cause for alarm. At this point, two-lung ventilation should be restored (if possible), and a discussion about whether to proceed should occur.

The impact of surgical approach for the proposed pulmonary resection should also be considered. There is no evidence in the literature examining outcomes of VATS vs thoracotomy in pulmonary hypertension patients; however, both have been done successfully. A VATS approach is advantageous, since it produces less postoperative pain and, however, is more dependent on effective OLV and may be associated with longer operative time. A thoracotomy for this patient would necessitate a well-functioning epidural for postoperative pain but may allow for better surgical exposure and shorter periods of OLV. Improved surgical exposure through a thoracotomy also allows for advanced ventilation techniques (selective lobar ventilation, application of CPAP) that may be helpful for ventilation. For this patient, a discussion with the surgeon regarding surgical approach should occur preoperatively. It may be reasonable to attempt the procedure with VATS initially while having a low threshold to convert to an open thoracotomy should the surgeon believe this would expedite the surgery.

Where should this patient be admitted to postoperatively?

This patient requires admission to a unit with increased monitoring postoperatively, irrespective of intraoperative course. This should be a step-down unit at the very least; however, the need for intraoperative vasopressor or pulmonary vasodilator use should prompt admission to an intensive care unit.