**2. Definition of pulmonary hypertension**

#### **2.1 Hemodynamic parameters used in clinical settings**

There are several hemodynamic parameters used in defining PH (Table **1**) (Gomez & Palazzo, 1998). These definitions have been used in various studies.

#### **2.2 Diagnosis in awake and anesthetized patients**

Pulmonary hypertension is usually diagnosed prior to cardiac surgery in awake patients. The diagnosis is obtained either directly by cardiac catheterization or indirectly by using Doppler signals from transesophageal echocardiography (TEE) and using Bernoulli's equation. In the presence of tricuspid regurgitation, the simplified Bernoulli's equation gives an estimation of the pressure gradient across the tricuspid valve (Fig. **1**) (Denault et al., 2010a). This pressure gradient is equal to the difference in systolic pressure between the right ventricle (RV) and the right atrium. Therefore, with the measurement of right atrial pressure (Pra), the estimation of systolic right ventricular pressure (Prv) is possible. In the absence of right ventricular outflow tract obstruction (RVOTO) and pulmonic valve stenosis, systolic Prv represents a reliable estimation of the systolic pulmonary artery pressure (SPAP).


CI: cardiac index; CO: cardiac output; MAP: mean arterial pressure; PAOP: pulmonary artery occlusion pressure; SVRI: indexed systemic vascular resistance. Adapted from Gomez (Gomez & Palazzo, 1998).

Table 1. Definitions of Pulmonary Hypertension Used in Clinical Settings

CI: cardiac index; CO: cardiac output; MAP: mean arterial pressure; PAOP: pulmonary artery occlusion pressure; SVRI: indexed systemic vascular resistance. Adapted from Gomez (Gomez & Palazzo, 1998).

Table 1. Definitions of Pulmonary Hypertension Used in Clinical Settings

Fig. 1. (**A**) Estimation of right ventricular systolic pressure (systolic Prv or RVSP) using the pressure gradient (PG) obtained from tricuspid regurgitation (TR) and right atrial pressure (Pra). (**B**) Note that the RVSP is higher than the systolic pulmonary artery pressure (Ppa) due to a small gradient across the pulmonic valve. (EKG: electrocardiogram; V: velocity). With permission from Denault *et al*. (Denault et al., 2010a).

#### **2.3 Comparison of absolute and relative values in the assessment of pulmonary hypertension**

Following the induction of general anesthesia, a reduction in both the systemic and the pulmonary artery pressures is observed. Consequently, using absolute values of SPAP in defining PH would underestimate its severity. To address this issue, Robitaille *et al*. studied 1557 patients undergoing cardiac surgery (Robitaille et al., 2006). In the 32 patients with preoperative PH, induction of general anesthesia resulted in a significant reduction in mean arterial pressure (MAP) and mean pulmonary artery pressure (MPAP) but the ratio of MAP/MPAP remained stable (Fig. **2**). The normal value for this ratio is > 4, and lower values can be used to quantify the severity of PH.

The relevance of the MAP/MPAP ratio was demonstrated after comparing its ability to estimate the probability of postoperative complications with the ability of other normally used hemodynamic parameters for this purpose (listed in Table **1**). Values of the ratio obtained after induction of general anesthesia but before cardiopulmonary bypass (CPB) in 1439 patients undergoing cardiac surgery showed similar trend when compared to other

Fig. 2. Changes in mean arterial pressure (MAP), mean pulmonary artery pressure (MPAP), and the MAP/MPAP ratio after the induction of anesthesia in 32 patients with preoperative pulmonary hypertension. No significant change in the MAP/MPAP ratio was observed (\*p < 0.05). (Robitaille et al., 2006)

hemodynamic parameters (Fig. **3**). Furthermore, the ratio turned out to be the best predictor of perioperative complications, defined as death, need for intra-aortic balloon pump, cardiac arrest, or use of vasoactive support for more than 24 hours.

An abnormal MAP/MPAP ratio was also recognized to be significantly correlated with abnormal systolic and/or diastolic cardiac function (Fig. **4**) (Robitaille et al., 2006). The use of relative instead of absolute values to estimate PH is currently used in congenital cardiology (Therrien et al., 2001a; Therrien et al., 2001b).

In summary, the evaluation and diagnostic of PH in cardiac surgical patients must be done using specific criteria. In awake patients, the absolute values can be used since they correlate well with outcomes. However, in patients under general anesthesia, the ratio of MAP/MPAP allows to screen for PH when systolic blood pressures are lower due to the anesthetic agents.

Fig. 2. Changes in mean arterial pressure (MAP), mean pulmonary artery pressure (MPAP), and the MAP/MPAP ratio after the induction of anesthesia in 32 patients with preoperative pulmonary hypertension. No significant change in the MAP/MPAP ratio was observed (\*p

hemodynamic parameters (Fig. **3**). Furthermore, the ratio turned out to be the best predictor of perioperative complications, defined as death, need for intra-aortic balloon pump, cardiac

An abnormal MAP/MPAP ratio was also recognized to be significantly correlated with abnormal systolic and/or diastolic cardiac function (Fig. **4**) (Robitaille et al., 2006). The use of relative instead of absolute values to estimate PH is currently used in congenital

In summary, the evaluation and diagnostic of PH in cardiac surgical patients must be done using specific criteria. In awake patients, the absolute values can be used since they correlate well with outcomes. However, in patients under general anesthesia, the ratio of MAP/MPAP allows to screen for PH when systolic blood pressures are lower due to the

< 0.05). (Robitaille et al., 2006)

anesthetic agents.

arrest, or use of vasoactive support for more than 24 hours.

cardiology (Therrien et al., 2001a; Therrien et al., 2001b).

Fig. 3. Relationship between the estimated probability of hemodynamic complications and variables used in the evaluation of pulmonary hypertension: (**A**) systolic pulmonary artery pressure (SPAP), (**B**) mean pulmonary artery pressure (MPAP), (**C**) indexed pulmonary vascular resistance (PVRI), (**D**) systemic to pulmonary vascular resistance index ratio (SVRI/PVRI), (**E**) mean systemic to pulmonary pressure ratio (MAP/MPAP), and (**F**) transpulmonary gradient defined as MPAP - Wedge or pulmonary artery occlusion pressure (PAOP). For easier comparison, the scale of the x axis of the SVRI/PVRI and the MAP/MPAP are inverted. (n = number of patients). (Robitaille et al., 2006)

Fig. 4. Hemodynamic and transesophageal echocardiographic evaluation of a 46-year-old woman scheduled for aortic valve surgery. Despite a normal pulmonary artery pressure (Ppa) of 34/16 mmHg and pulmonary vascular resistance index (PVRI**)** at 286 dyn·s·cm-5·m-2, this patient had an abnormal right ventricular diastolic filling pressure waveform characterized by a rapid upstroke (**A**) and reduced systolic (S) to diastolic (D) pulmonary (**B**) and hepatic (**C**) venous flows consistent with left and right ventricular diastolic dysfunction. In addition, a dilated right atrium and ventricle were present without significant tricuspid regurgitation in a mid-esophageal right ventricular view (**D**). The mean systemic to pulmonary pressure ratio (MAP/MPAP) was 65/23 or 2.8. (CI: cardiac index; Pa: arterial pressure; PCWP: pulmonary capillary wedge pressure; Pra: right atrial pressure; Prv: right ventricular pressure; RA: right atrium; RV: right ventricle; SVRI: systemic vascular resistance index). (Robitaille et al., 2006)

Fig. 4. Hemodynamic and transesophageal echocardiographic evaluation of a 46-year-old woman scheduled for aortic valve surgery. Despite a normal pulmonary artery pressure (Ppa) of 34/16 mmHg and pulmonary vascular resistance index (PVRI**)** at 286 dyn·s·cm-5·m-

significant tricuspid regurgitation in a mid-esophageal right ventricular view (**D**). The mean systemic to pulmonary pressure ratio (MAP/MPAP) was 65/23 or 2.8. (CI: cardiac index; Pa: arterial pressure; PCWP: pulmonary capillary wedge pressure; Pra: right atrial pressure; Prv: right ventricular pressure; RA: right atrium; RV: right ventricle; SVRI: systemic vascular

2, this patient had an abnormal right ventricular diastolic filling pressure waveform characterized by a rapid upstroke (**A**) and reduced systolic (S) to diastolic (D) pulmonary (**B**) and hepatic (**C**) venous flows consistent with left and right ventricular diastolic dysfunction. In addition, a dilated right atrium and ventricle were present without

resistance index). (Robitaille et al., 2006)
