Across the Lifespan Flashcards
how does pregnancy affect minute ventilation?
Progesterone is a respiratory stimulant. It increases minute ventilation up to 50%
- Vt increased by 40%
- RR increased by 10%
how does pregnancy affect the mother’s arterial blood gas?
Progesterone is a respiratory stimulant. It increases minute ventilation up to 50%. As a consequence, mom’s PaCO2 falls, and she develops respiratory alkalosis. Renal compensation eliminates bicarbonate to normalize blood pH. A small reduction in physiologic shunt explains the mild increase in PaO2. This increases the driving pressure of oxygen across the fetoplacental interface and improves fetal gas exchange.
- Arterial pH= no change
- PaO2 = increased (104-108 mmHg)
- PaCO2= Decreased (28-32 mmHg)
- HCO3= decreased ( 20mmol/L)
How does pregnancy affect the oxyhemoglobin dissociation curve?
Right shift (increase P50)-> facilitates O2 offloading to the fetus
How does pregnancy affect the lung volumes and capacities?
Functional residual capacity is reduced as a function of a decrease in expiratory reserve volume and residual volume (ERV decreases more than RV)
An increased oxygen consumption paired with a decreased FRC hastens the onset of hypoxemia. Failure to reverse hypoxemia results in brain death of the mother and the fetus
how does cardiac output change during pregnancy and delivery
How do blood pressure and systemic vascular resistance change during pregnancy?
Who is at risk for aortocaval compression, and how do you treat it?
In the supine position, the gravid uterus compresses both the vena cava and the aorta. This decreases venous return to the heart as well as arterial flow to the uterus and lower extremities. Decreased CO compromises fetal perfusion and can also cause the mother to lose consciousness.
By displacing the uterus away from the vena cava and aorta, we can reduce its compressive effects. We can accomplish this by elevating the mother’s right torso 15 degrees. It should be used for anyone in their 2nd (14-26 weeks) or 3rd trimester
How does the intravascular fluid volume change during pregnancy?
Intravascular fluid increases 35%
* plasma volume increases 45%
* erythrocyte volume increases 20%
What hematologic changes accompany pregnancy
- Clotting factors 1, 7, 8, 9, 10, 12 increase
- anticoagulants: Proteins S decreases and no change in protein C
- fibrin breakdown increases
- anti-fibrinolytic system: 11 & 13 decrease
How does MAC change during pregnancy?
MAC is decreased by 30-40%. This is probably due to increased progesterone.
How does pregnancy affect gastric pH and volume?
Pregnancy increases gastric volume and decreases gastric pH. This is due to increased gastrin.
How does pregnancy affect gastric emptying?
Before onset of labor = No change
After onset of labor = Slowed
How does pregnancy affect uterine blood flow?
Non-pregnant state = 100mL/min
Pregnancy at term = up to 700mL/min or 10% of the cardiac output (some texts say up to 800 or 900mL/min)
What conditions can reduce uterine blood flow?
uterine blood flow does NOT autoregulate- therefore, it is dependent on MAP, CO, and uterine vascular resistance (UVR).
Causes of reduced uterine blood flow:
* decreased perfusion: Maternal HoTN (sympathectomy, hemorrhage, aortocaval compression)
* increased resistance: Uterine contraction, HTN conditions that increase UVR
Uterine blood flow= (uterine artery pressure- uterine venous pressure)/ Uterine vascular resistance
Discuss the use of phenylephrine and ephedrine in the laboring pt.
Classic teaching states that phenylephrine increases uterine vascular resistance and reduces placental perfusion.
More recent evidence suggest that phenylephrine is as efficacious as ephedrine in maintaining placental perfusion and fetal pH in healthy mothers. In fact, mothers that received phenylephrine had higher fetal pH values (less fetal acidosis)
Which law determines which drugs will pass through the placenta?
The Fick principle determines which drugs can pass across the placenta.
Rate of diffusion (Diffusion coefficient x surface area x concentration gradient (between mom and fetus)/ membrane thickness
Drug characteristics that favor placental transfer:
* Low molecular weight < 500 Daltons (most anesthetic drugs and smaller than 500 Daltons)
* High lipid solubility
* nonionized
* nonpolar
Define the 3 stages of labor.
stage 1: beginning of regular contraction to full cervical dilation (10cm)
Stage 2: full cervical dilation to delivery of the fetus (pain in the perineum begins during stage 2)
Stage 3: Delivery of the placenta
How does uncontrolled labor pain affect the mother and the fetus?
May result in:
* increased maternal catecholamines -> HTN -> reduced uterine blood flow to the fetus
* maternal hyperventilation -> leftward shift of oxyhgb curve-> reduced delivery of O2 to the fetus
Compare and contrast the pain that results from the first and second stages of labor.
First stage:
* pain begins in the lower uterine segment and the cervix
* origin: T10-L1 posterior nerve roots
Second stage:
* Adds in pain impulses from the vagina, peritoneum, and pelvic floor.
* origins: S2-S4 posterior nerve roots
Compare and contrast the regional anesthetic technique that can be used for first and second stage labor pain.
Neuraxial techniques that provide analgesia to T10-L1 during the first stage of labor must be extended to cover S2-S4 during the second stage of labor
compare and contrast bupivicaine and ropivicaine for labor
discuss the use of 2-chloroprocaine for labor
- Useful for emergency C/S when epidural is already in place (very fast onset)
- metabolized by pseudocholinesterase in the plasma- minimal placental transfer
- antagonized opioid receptor (mu & kappa) and reduces the efficacy of epidural morphine
- risk of arachnoiditis when used for spinal anesthesia due to preservatives
- solutions without methylparaben and metabisulfite do not cause neurotoxicity
discuss the consequences of an epidural that is placed in the subdural space.
Although a rare and unpreventable event, It is possible to position the tip of the epidural catheter in the subdural space - between the dura and the arachnoid. Neither catheter aspiration nor a test dose will rule out subdural placement.
Within 10-25 minutes after the epidural is dosed, the patient will experience symptoms of an excessive cephalad spread of local anesthetic. Because the subdural space is a potential space, it holds a very low volume. For this reason, the block height for a given amount of local anesthetic will be much higher than if the same volume was administered in the epidural space.
What is the treatment for a total spinal?
A total spinal may result from:
* an epidural dose injected into the subarachnoid space
* an epidural dose injected into the subdural space
* a single shot spinal after a failed epidural block
Initial tx includes: vasopressors, IVF, left uterine displacement, elevation of the legs, and intubation if LOC