1.4 Maternal Cardiac and Respiratory Disorders

Hemodynamic Physiology of Pregnancy and High-Risk Windows

Normal pregnancy induces profound, progressive cardiovascular remodeling to satisfy the metabolic demands of the growing uteroplacental unit:

• Total Blood Volume: Increases by 40% to 50% (1,200–1,600 mL), with plasma volume expanding proportionally more than red blood cell mass.
• Cardiac Output (CO): Increases by 30% to 50% above baseline, driven initially by an increase in stroke volume (20–30%) and subsequently by an increase in resting heart rate (15–20 beats per minute).
• Systemic Vascular Resistance (SVR): Decreases by 20% to 30% due to the low-resistance uteroplacental shunt and vasodilatory effects of progesterone, prostacyclin, and nitric oxide.

The Three High-Risk Windows for Cardiac Decompensation

Maternal cardiac decompensation characteristically occurs during three peak hemodynamic stress intervals:

1. 28 to 32 Weeks Gestation: Plasma volume expansion reaches its absolute maximum peak.
2. Labor and Delivery (Second Stage): Every uterine contraction expels 300 to 500 mL of blood from the uteroplacental bed into the central maternal circulation (autotransfusion), increasing venous return and transiently elevating cardiac output by 30% to 50%. Maternal pushing (Valsalva maneuver) further causes dramatic swings in intrathoracic pressure, preload, and arterial blood pressure.
3. Immediate Postpartum (First 24–48 Hours): Following placental delivery, vena caval compression is completely relieved, and dramatic uterine involution autotransfuses up to 500 to 1,000 mL of blood into maternal systemic circulation. Simultaneously, interstitial edema mobilizes rapidly back into the intravascular space, driving cardiac output up to 60% to 80% above baseline—the single highest period of maternal cardiac arrest and pulmonary edema.

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|                                 CARDIAC OUTPUT PROFILE ACROSS PREGNANCY & LABOR                                   |
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  Gestational Phase                   Cardiac Output Change Relative to Baseline Non-Pregnant State
  -----------------                   -------------------------------------------------------------
  Baseline Non-Pregnant               100% (approx. 4.5 - 5.0 L/min)
  Early 1st Trimester (12 wk)         ↑ 10 - 15% (5.5 L/min)
  Peak Antepartum (28 - 32 wk)        ↑ 40 - 50% (6.5 - 7.0 L/min) [Peak Volume Load]
  Labor: Early 1st Stage              ↑ 15 - 20% above antepartum baseline
  Labor: Active 2nd Stage (Contraction) ↑ 45 - 50% above antepartum baseline (8.5 - 9.5 L/min)
  Immediate Postpartum (10 - 60 min)  ↑ 60 - 80% ABOVE BASELINE (Up to 10.0 L/min) [HIGHEST DECOMPENSATION RISK]
  Postpartum Day 2 to 7               Gradual decline toward pre-pregnancy values (normalizes by 6-12 wk)
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Cardiac Risk Stratification: NYHA and Modified WHO Systems

Cardiac disease is currently the leading cause of indirect maternal mortality in the United States. Risk assessment combines the New York Heart Association (NYHA) Functional Classification with the disease-specific Modified World Health Organization (WHO) Pregnancy Cardiac Risk Classification:

NYHA Functional Classification

• Class I: Uncompromised; ordinary physical activity does not cause undue fatigue, palpitations, dyspnea, or anginal pain.
• Class II: Slightly compromised; comfortable at rest, but ordinary physical activity results in fatigue, dyspnea, or angina.
• Class III: Markedly compromised; comfortable at rest, but less than ordinary activity causes fatigue, dyspnea, or palpitations.
• Class IV: Severely compromised; inability to perform any physical activity without discomfort; symptoms of cardiac insufficiency or angina present even at rest.

Modified WHO Pregnancy Cardiac Risk Classification

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|                                MODIFIED WHO PREGNANCY CARDIAC RISK CLASSIFICATION                                 |
+-------------------------------------------------------------------------------------------------------------------+
  WHO Risk Class        Maternal Risk Profile     Clinical Conditions Included
  --------------        ---------------------     ----------------------------
  WHO Class I           Extremely Low Risk        - Mild pulmonary stenosis, patent ductus arteriosus (repaired)
                        (<1% morbidity)           - Successfully repaired simple ASD / VSD
  -------------------------------------------------------------------------------------------------------------------
  WHO Class II / III    Low-to-Moderate Risk      - Unoperated ASD / VSD, repaired Tetralography of Fallot
                        (2 - 15% morbidity)       - Mild left ventricular impairment, hypertrophic cardiomyopathy
                                                  - Marfan syndrome without aortic dilation (<40 mm)
  -------------------------------------------------------------------------------------------------------------------
  WHO Class III         High Risk                 - Mechanical heart valves (complex anticoagulation)
                        (19 - 27% morbidity)      - Systemic right ventricle, Fontan circulation
                                                  - Unrepaired cyanotic congenital heart disease
  -------------------------------------------------------------------------------------------------------------------
  WHO Class IV          EXTREMELY HIGH RISK       - Pulmonary Arterial Hypertension of any etiology (Eisenmenger)
                        (30 - 50% MORTALITY)      - Severe systemic ventricular dysfunction (LVEF <30% or NYHA III-IV)
                        [PREGNANCY                - Previous Peripartum Cardiomyopathy with residual LV impairment
                        CONTRAINDICATED]          - Severe symptomatic aortic stenosis or severe mitral stenosis
                                                  - Severe aortic dilation (>45 mm in Marfan syndrome or bicuspid valve)
                                                  - Severe native coarctation of the aorta
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Specific Maternal Cardiac Disorders

1. Mitral Stenosis (Rheumatic Heart Disease)

• Pathophysiology: Fixed mechanical obstruction to left ventricular inflow. The physiologic tachycardia of pregnancy shortens diastolic filling time, causing massive elevation in left atrial pressures, pulmonary venous congestion, and sudden acute pulmonary edema. Atrial fibrillation can trigger catastrophic hemodynamic collapse.
• Management: Maintain maternal heart rate <80 to 90 bpm using beta-1 selective blockers (Metoprolol). Avoid fluid overload.

2. Eisenmenger Syndrome and Pulmonary Arterial Hypertension (PAH)

• Pathophysiology: Severe, irreversible pulmonary hypertension resulting in right-to-left or bidirectional shunting through a congenital cardiac defect (VSD, ASD, PDA). Maternal mortality is 30% to 50%.
• Mechanism of Collapse: Any sudden drop in systemic vascular resistance (e.g., from blood loss, spinal anesthesia, or vasodilation) worsens the right-to-left shunt, inducing intractable cyanosis, hypoxemia, cardiovascular collapse, and sudden death.

3. Peripartum Cardiomyopathy (PPCM)

• Definition: An idiopathic cardiomyopathy presenting with heart failure secondary to left ventricular systolic dysfunction (Left Ventricular Ejection Fraction [LVEF] <45%) developing during the last month of pregnancy or within 5 months postpartum in a woman without prior heart disease.
• Risk Factors: Advanced maternal age, multiparity, African-American ancestry, multiple gestation, chronic hypertension, and preeclampsia.
• Clinical Presentation: Rapidly progressive dyspnea, orthopnea, paroxysmal nocturnal dyspnea, cough, peripheral edema, elevated B-type Natriuretic Peptide (BNP), and cardiomegaly on chest X-ray.
• Medical Management: Standard heart failure regimen tailored for pregnancy (diuretics [furosemide], beta-blockers [carvedilol/metoprolol succinate], hydralazine and nitrates for afterload reduction; ACE inhibitors and ARBs are strictly contraindicated antepartum but are first-line postpartum; Bromocriptine may be considered to block prolactin cleavage products; therapeutic anticoagulation is indicated due to high thromboembolic risk when LVEF <35%).
• Prognosis & Future Pregnancies: If LVEF does not normalize (>50–55%), subsequent pregnancy carries a 30% to 50% risk of recurrence, irreversible heart failure, and death.

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Inpatient Nursing Bundle for Intrapartum Cardiac Care

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|                                 INTRAPARTUM CARDIAC NURSING BUNDLE PROTOCOL                                       |
+-------------------------------------------------------------------------------------------------------------------+
  1. POSITIONING:           - Maintain continuous Left Lateral Decubitus tilt to maximize IVC blood flow and avoid
                              sudden preload swings.
  -------------------------------------------------------------------------------------------------------------------
  2. ANESTHESIA:            - Early continuous lumbar epidural analgesia (slow, fractionated titration) to blunt
                              sympathetic catecholamine surges, tachycardia, and cardiac workload.
  -------------------------------------------------------------------------------------------------------------------
  3. FLUID BALANCE:         - Strict fluid restriction: Total intake limited to 50 - 75 mL/hour (<1,000 mL/24h).
                            - Continuous hourly Foley output monitoring; avoid rapid fluid boluses during epidural placement.
  -------------------------------------------------------------------------------------------------------------------
  4. SECOND STAGE:          - "LABORING DOWN" (Passive Descent): Allow uterine contractions to move fetal head down to perineum.
                            - AVOID prolonged Valsalva pushing.
                            - ELECTIVE OPERATIVE VAGINAL DELIVERY (Low Forceps or Vacuum) to shorten/eliminate 2nd stage.
  -------------------------------------------------------------------------------------------------------------------
  5. POSTPARTUM (STAGE 3):  - Administer slow dilute IV oxytocin infusion (e.g., 20 units in 500 mL crystalloid over 1-2 hr).
                            - AVOID RAPID IV PUSH OXYTOCIN (causes severe hypotension, peripheral vasodilation, & tachycardia).
                            - STRICT CONTRAINDICATIONS: Methylergonovine (Methergine) is contraindicated (causes severe
                              vasoconstriction/hypertension); Carboprost (Hemabate) is contraindicated (causes pulmonary HTN).
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Maternal Respiratory Disorders and Critical Medication Contraindications

Asthma Management in Inpatient Obstetrics

Asthma complicates 4% to 8% of pregnancies. As a clinical rule of thumb, "one-third improve, one-third worsen, and one-third remain unchanged." Maintenance of maternal oxygenation is vital; maternal PaO2 must be maintained >70 mmHg or SpO2 >= 95% to ensure an adequate maternal-to-fetal oxygen diffusion gradient across the placenta.

• Stepwise Pharmacotherapy: Inhaled short-acting beta-agonists (Albuterol) are safe first-line rescue agents; Inhaled Corticosteroids (Budesonide preferred) must be continued without interruption throughout labor; systemic corticosteroids (oral Prednisone or IV Methylprednisolone) are indicated for moderate-to-severe acute exacerbations.
• Critical Obstetric Medication Contraindications in Asthmatics:
  • Carboprost Tromethamine (Hemabate / PGF2-alpha): STRICTLY CONTRAINDICATED. Potent smooth muscle constrictor that induces immediate, life-threatening bronchospasm and arterial desaturation.
  • Methylergonovine (Methergine): Use with extreme caution; can trigger bronchospasm in patients with aspirin-exacerbated respiratory disease (AERD / Samter's triad).
  • Indomethacin (NSAID Tocolytic): Contraindicated in aspirin-sensitive asthmatics due to cyclooxygenase inhibition shunting arachidonic acid into the leukotriene pathway, inducing severe bronchospasm.

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|                         OBSTETRIC DRUG SAFETY & CONTRAINDICATIONS IN CARDIOPULMONARY DISEASE                      |
+-------------------------------------------------------------------------------------------------------------------+
  Drug Name (Brand)         Obstetric Indication       Cardiopulmonary Safety / Contraindications
  -----------------         --------------------       ------------------------------------------
  Carboprost (Hemabate)     Postpartum Hemorrhage      ★ STRICTLY CONTRAINDICATED IN ASTHMA (Induces severe bronchospasm)
                                                       ★ CAUTION IN CARDIAC DISEASE (Increases pulmonary vascular resistance)
  -------------------------------------------------------------------------------------------------------------------
  Methylergonovine          Postpartum Hemorrhage      ★ STRICTLY CONTRAINDICATED IN HYPERTENSION / PREECLAMPSIA
  (Methergine)                                         ★ CONTRAINDICATED IN CORONARY DISEASE (Severe vasoconstriction)
  -------------------------------------------------------------------------------------------------------------------
  Terbutaline (Brethine)    Tocolysis / Tachysystole   ★ CONTRAINDICATED IN MATERNAL CARDIAC DISEASE (Severe tachycardia)
                                                       ★ Black box warning: Do not use for prolonged tocolysis (>48-72h)
  -------------------------------------------------------------------------------------------------------------------
  Oxytocin (Pitocin)        Labor Induction / PPH      ★ AVOID RAPID IV BOLUS (Causes hypotension, flushing, and tachycardia)
                                                       ★ Administer as slow, controlled dilute IV infusion only
+-------------------------------------------------------------------------------------------------------------------+

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Anticoagulation Timing and Neuraxial Anesthesia Protocols

Pregnancy increases the risk of venous thromboembolism (VTE) 4- to 5-fold due to hypercoagulability, venous stasis, and vascular injury. Deep vein thrombosis (DVT) develops predominantly in the left lower extremity (80% of cases) due to compression of the left common iliac vein by the right common iliac artery and the gravid uterus.

Low Molecular Weight Heparin (LMWH, e.g., Enoxaparin) is the anticoagulant of choice during pregnancy because it does not cross the placenta and has a lower risk of heparin-induced thrombocytopenia (HIT) and osteoporosis than Unfractionated Heparin (UFH). However, to prevent spinal/epidural hematoma—which can cause permanent paraplegia—strict timing intervals must be maintained before placing or removing neuraxial needles/catheters:

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|                        NEURAXIAL ANESTHESIA & ANTICOAGULATION TIMING GUIDELINES (ASRA / ACOG)                     |
+-------------------------------------------------------------------------------------------------------------------+
  Anticoagulant Regimen     Dose Classification        Mandatory Hold Time Before Neuraxial Placement
  ---------------------     -------------------        ----------------------------------------------
  LMWH (Enoxaparin)         Prophylactic Dose          HOLD FOR AT LEAST 12 HOURS
                            (e.g., 40 mg SC daily)     (Do not place needle/catheter until 12 hr elapsed)
  -------------------------------------------------------------------------------------------------------------------
  LMWH (Enoxaparin)         Therapeutic Dose           HOLD FOR AT LEAST 24 HOURS
                            (e.g., 1 mg/kg SC q12h)    (Do not place needle/catheter until 24 hr elapsed)
  -------------------------------------------------------------------------------------------------------------------
  Unfractionated Heparin    Intravenous Therapeutic    HOLD FOR 4 TO 6 HOURS
  (UFH)                     Continuous Infusion        (Confirm normal aPTT before neuraxial needle placement)
  -------------------------------------------------------------------------------------------------------------------
  Unfractionated Heparin    High-Dose Prophylactic     HOLD FOR 12 HOURS
  (UFH)                     (>10,000 units SC/dose)    (or check aPTT)
+-------------------------------------------------------------------------------------------------------------------+
| Catheter Removal & Resumption Protocols:                                                                          |
| - Restart Prophylactic LMWH: Wait at least 4 hours AFTER epidural catheter removal.                               |
| - Restart Therapeutic LMWH: Wait at least 24 hours AFTER catheter removal and at least 24 hours post-cesarean.    |
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